# GenetixBay Knowledge Base: full text > Every article in the GenetixBay Knowledge Base as clean Markdown, with sources. 191 articles, generated 2026-11-01. Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/); attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)". Index: https://genetixbay.com/llms.txt --- # Autoflower first grow, week by week > A feminised autoflower runs about 9–14 weeks from seed to harvest on a fixed countdown from germination, so plant it straight into its final 11–19 L (3–5 gal) pot on day 1, never transplant, run 18/6 to 20/4 (24/0 also works) for the whole grow, and train with low-stress bending, not topping. Any setback costs time the plant can't get back. - Canonical: https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Flower, Harvest · Systems: Soil, Coco - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should I plant an autoflower straight into its final pot?** Yes. Plant an autoflower seed straight into its final 11–19 L (3–5 gal) pot on day 1. Autos run on a fixed countdown from germination, and the GenetixBay house position is that transplanting is almost a no-no: the taproot reacts badly to disturbance, growth stalls for days, and an auto has no veg time to recover. Start in a small wet ring of mix around the seed and water outwards as the roots grow. **Can I top an autoflower?** You can, but the GenetixBay position is that topping an autoflower never produces what proper low-stress training does. Topping costs an auto several days of recovery on a clock it can't stop, and a late top can stunt it. Bend and tie the main stem from about day 14–21 instead, keep the canopy flat, and tuck leaves rather than pluck them. LST gives the same multi-cola shape without the setback. **What light schedule is best for autoflowers?** Autoflowers flower by age, not night length, so run one schedule from seed to harvest: 18/6 or 20/4 is standard, and 24/0 also works because cannabis doesn't need a sleep period. Keep PPFD around 200–300 µmol/m²/s for seedlings, 400–600 in early veg and 600–900 in flower. Never switch an auto to 12/12; it only shortens the day and costs yield. **How long does an autoflower take from seed to harvest?** Most feminised autoflowers take about 9–14 weeks from germination to harvest: roughly 2 weeks of seedling, 2–3 weeks of fast veg, pre-flowers around weeks 3–5 and 6–9 weeks of flowering. Breeder times are averages; your plant is ready when trichome heads show a few clear, mostly cloudy and some amber. Add 7–14 days of drying and at least 2–4 weeks of curing. **Are autoflowers good for beginners?** Autoflowers suit beginners in that they are fast, stay small and need no light-schedule change, but they are not easy. Any stress, overwatering, transplant shock or late training cuts yield, because the plant can't extend its veg to recover. An auto shows quickly who has a green thumb. Grow one with simple, steady conditions: final pot from day 1, light feeding, LST only and one change at a time. **When should I start training an autoflower?** Start low-stress training on an autoflower at about day 14–21, once it has 3–4 nodes and the stem is flexible. Bend the main stem over gently and tie it so the side shoots rise to the same height, then adjust ties every 2–3 days. Finish the main bending by about day 35, as flowers start stretching, because hard bending once stems stiffen risks snapping and stress. **How much should I feed an autoflower?** Feed autoflowers lighter than photoperiods: plain water or a feed at about EC 0.4–0.6 mS/cm for the first 2 weeks, 0.8–1.2 in weeks 3–4, and 1.2–1.8 in flower, starting at a quarter to half the label rate. In quality bagged soil, often water only for the first 2–3 weeks. Feed through to harvest; don't flush. Watch leaf tips: dark, burnt tips mean too strong. **Short answer.** A feminised [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) runs about **9–14 weeks from seed to harvest** on a fixed countdown that starts at germination. Plant it **straight into its final 11–19 L (3–5 gal) pot on day 1**, never transplant, run **18/6 to 20/4** (24/0 also works) for the whole grow, and train with [low-stress training](https://genetixbay.com/knowledge/guides/training-basics.md), not topping. Every setback costs days the plant can't get back. > **House position: autos are a countdown.** An autoflower flowers by age, not by night length, so any stress (a transplant, a drowned root zone, a heavy top) eats into a schedule it cannot extend. The founder's rulings: plant in the final pot (transplanting is almost a no-no, because of how the [taproot](https://genetixbay.com/knowledge/glossary/taproot.md) reacts), and topping will never produce what proper LST does. "Good for beginners" is true, but not because autos are easy. They show who has a green thumb. This guide is the auto track of the [first grow master guide](https://genetixbay.com/knowledge/guides/first-grow-start-to-finish.md). The genetics behind "flowers by age" are in [photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md). ## What do you need for an autoflower grow? An autoflower grow needs the same basic kit as any first grow, minus the second light schedule and the small starter pots. Check the [legal check](https://genetixbay.com/knowledge/guides/legal-check-before-you-grow.md) first. - [ ] A [tent](https://genetixbay.com/knowledge/glossary/tent.md): 60 x 60 cm (2 x 2 ft) for 1–2 autos, 80 x 80 cm (2.7 x 2.7 ft) for 2–3, 120 x 120 cm (4 x 4 ft) for 4–6 - [ ] One dimmable full-spectrum [LED](https://genetixbay.com/knowledge/glossary/led.md) able to reach 600–900 µmol/m²/s over the footprint ([lights for beginners](https://genetixbay.com/knowledge/guides/lights-for-beginners.md)) - [ ] An exhaust fan with a [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md), and a small clip fan - [ ] One final pot per plant: 11–19 L (3–5 gal) [fabric pot](https://genetixbay.com/knowledge/glossary/fabric-pot.md) or plastic pot with drainage holes, plus saucers - [ ] Light, airy medium: quality bagged potting mix with 20–30 % added [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), or buffered [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) with 30 % perlite - [ ] A timer, a [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) with pH 4 and 7 buffers, and an [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) - [ ] A thermo-hygrometer with min/max memory - [ ] Soft [plant ties](https://genetixbay.com/knowledge/glossary/plant-ties.md) or plastic-coated wire, and a few low hooks or pot-rim clips to tie to - [ ] A 60x loupe, a measuring syringe, a watering jug and a [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) - [ ] Feminised autoflower seeds from a line with real journals ([reading a seed listing](https://genetixbay.com/knowledge/guides/reading-a-seed-listing.md)) ## What does an autoflower grow look like, week by week? An autoflower grow follows age, so the weeks below count from the day the seed cracked. Fast lines finish near week 9–10; long lines near week 13–14. The light schedule never changes. | Week from germination | Stage | PPFD (µmol/m²/s) | Watering | Feed EC (coco; soil often water only) | Your job | |---|---|---|---|---|---| | 1 | Sprout, cotyledons | 150–250 | 50–100 mL ring around the stem every 1–2 days | 0–0.4 mS/cm | Keep warm 24–27 °C (75–81 °F), 65–75 % RH | | 2 | First 2–3 true-leaf sets | 200–300 | 100–250 mL, widening the wet ring | 0.4–0.6 | Don't overwater; no training yet | | 3 | Fast veg, 3–5 nodes | 300–450 | 0.3–0.7 L when the pot feels light | 0.6–1.0 | Start LST (day 14–21) | | 4 | Fast veg, pre-flowers appear | 400–600 | 0.5–1.5 L | 0.8–1.2 | Adjust ties every 2–3 days | | 5 | Stretch begins, pistils at the top | 500–700 | 1–2 L | 1.0–1.4 | Finish main bends by about day 35 | | 6–7 | Early flower, stretch | 600–900 | 1.5–3 L, 10–20 % runoff in coco | 1.2–1.6 | Tuck leaves; lower RH to 50–55 % | | 8–10 | Mid flower, bulking | 600–900 | 2–3 L | 1.4–1.8 | Daily check; pest check weekly | | 10–14 | Ripening | 600–900 | As needed | 1.4–1.8; taper N only if mixing salts | Watch trichomes; 40–50 % RH | Water volumes assume an 11–15 L (3–4 gal) pot; scale up for 19 L (5 gal). See [watering](https://genetixbay.com/knowledge/guides/watering-how-much-how-often.md) for the pot-lift method. ## How do you grow an autoflower, step by step? Grow an autoflower in eleven steps, and protect the countdown at every one of them. 1. **Set up and test the room for 48 hours.** Run the light on its final schedule (18/6 or 20/4) and log temperature and RH day and night. Aim for 22–28 °C (72–82 °F) lights on. 2. **Fill the final pot.** Fill an 11–19 L (3–5 gal) pot with light mix. Water the whole pot once to about 10 % runoff, then let it drain for a day so it's moist, not wet. 3. **Plant the seed in the final pot.** Make a hole 0.5–1 cm (¼–½ in) deep in the centre. Plant either a dry seed directly or a seed whose root has just cracked (root down). See [germinating seeds](https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.md). 4. **Water only a small ring for the first 10–14 days.** Give 50–100 mL around the stem every 1–2 days so the top few centimetres stay moist while the rest of the pot dries. This pulls the taproot down instead of drowning it. 5. **Light gently, then raise it.** Start at 150–250 µmol/m²/s and step up about 50–100 µmol/m²/s every 3–4 days if leaves stay flat and green. See [lights for beginners](https://genetixbay.com/knowledge/guides/lights-for-beginners.md). 6. **Start feeding lightly at week 2–3.** In coco, feed every watering from the first true leaves at EC 0.4–0.6 mS/cm. In quality bagged soil, often water only until week 3. Start at a quarter to half the label rate. See [feeding basics](https://genetixbay.com/knowledge/guides/feeding-basics.md). 7. **Start LST at day 14–21.** When the plant has 3–4 nodes, bend the main stem gently towards the pot rim and tie it. Side shoots will turn upward; tie them out so all tips sit at the same height. See [training basics](https://genetixbay.com/knowledge/guides/training-basics.md) and [LST](https://genetixbay.com/knowledge/training/lst.md). 8. **Keep training through week 5, then stop bending hard.** Adjust ties every 2–3 days. Once stems stiffen in the stretch (about day 35–45), only tuck leaves aside to expose bud sites. Tuck, don't pluck. 9. **Lower humidity as buds form.** Move from 55–70 % RH in veg to 45–55 % in flower and 40–50 % in the last 2–3 weeks. See [climate basics](https://genetixbay.com/knowledge/guides/climate-basics-vpd-cheat-sheet.md). 10. **Feed through to harvest.** Keep feeding at stage strength until the chop. Don't flush: it starves the plant while it packs on its final weight and resin (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). 11. **Harvest by trichomes.** From about week 9, check trichome heads on the buds with a 60x loupe every 2–3 days. Cut at a few clear, mostly cloudy, some amber. See [when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md), then [drying](https://genetixbay.com/knowledge/guides/drying-step-by-step.md) and [curing](https://genetixbay.com/knowledge/guides/curing-step-by-step.md). ## Why shouldn't you transplant or top an autoflower? Don't transplant or top an autoflower because both cost recovery days on a clock that keeps running. A photoperiod plant can stay in veg until it recovers; an auto starts flowering at its age whether it has recovered or not. **Transplanting.** The GenetixBay house position is that transplanting autos is almost a no-no. The founder's observation, compared with photoperiods, is that the auto taproot reacts badly to disturbance and growth stalls. Root volume matters too: across 65 studies, doubling pot size raised plant biomass by about 43 % on average [4], so a stunted root system in a small cup is a real loss. Extension guidance treats transplant shock as a normal setback for any seedling [6]; an auto simply has no time to absorb it. See [transplanting](https://genetixbay.com/knowledge/germination/transplanting.md). **Topping.** Topping removes the main tip and makes the plant spend 5–10 days rebuilding two new leaders ([topping](https://genetixbay.com/knowledge/training/topping.md)). On an auto that time comes straight out of veg. LST gets the same flat, multi-cola canopy without cutting anything; in a controlled study on large photoperiod plants, opening up the canopy improved chemical uniformity between top and lower buds [5]. The house view: topping never produces what proper LST does on an auto. ## What light schedule should an autoflower run? An autoflower should run one schedule from seed to harvest: **18/6 or 20/4**, and **24/0** also works. Autoflowering is day-neutral, inherited as a recessive gene (*Autoflower1*), so these plants flower by age even under long days [1][2]. More hours means more daily light, and yield rose with light in the best indoor trial [3]. | Schedule | DLI at 600 µmol/m²/s | Notes | |---|---|---| | 18/6 | 38.9 mol/m²/day | Standard; cooler, cheaper | | 20/4 | 43.2 mol/m²/day | Common auto choice | | 24/0 | 51.8 mol/m²/day | Endorsed; cannabis needs no sleep period in veg. Watch heat | | 12/12 | 25.9 mol/m²/day | Don't: it only cuts light and yield | DLI = PPFD x hours x 0.0036. Keep the flower DLI near 35–45 mol/m²/day for a beginner; more needs CO₂ and experience. See [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md). ## How will you know it's working? You'll know an autoflower grow is working when it hits its age milestones without pauses. Compare your journal with these marks: - **Day 3–7:** cotyledons open, stem short and upright, not stretched. - **Day 10–14:** two to three sets of true leaves, deep green, held flat. - **Day 14–28:** a new node every 2–3 days; the pot goes from heavy to light in 1–3 days. - **Day 21–35:** white pistils at the main tip and branch tips (the auto's own "flip"). - **Weeks 5–7:** stretch of 50–100 %; tied shoots all reach the same height. - **Weeks 7–10:** buds swell week on week; smell increases. - **Final 2–3 weeks:** lower fan leaves fade slowly (normal); trichome heads turn mostly cloudy. A plant that "sits" for 4–7 days with no new growth has had a setback: find the cause in your log before it happens again. ## What mistakes do beginners make with autoflowers? Beginners lose most auto yield to stress early in the grow, when the plant is building the frame it will flower on. - **Starting in a solo cup and transplanting.** Plant in the final pot from day 1. - **Flooding the whole pot in week 1.** A seedling in 15 L of wet mix sits in airless soil. Water a small ring and widen it. - **Topping, or topping late.** Train with LST instead. - **Hard bending after day 40.** Stems stiffen in the stretch; bend gently or just tuck leaves. - **Overfeeding.** Autos are usually smaller; start at a quarter to half label strength and judge by leaf tips. - **Switching to 12/12 "to help it flower".** An auto doesn't need it and loses light. - **Pots that are too small.** Below about 11 L (3 gal), you need very frequent watering and feeding to keep up; pot size is a trade-off against feeding frequency. - **Harvesting by the breeder's week count** instead of by trichomes. - **Flushing in the last two weeks.** It costs yield and resin and gains nothing [7]. - **Changing several things at once** when something looks off. One change, logged, then wait 3–5 days. ## Evidence - Autoflowering as a single recessive locus (*Autoflower1*): *Supported* by genetic mapping [1] and gene-dosage work [2]. - Yield rising with light: *Supported* [3]. Longer photoperiods for autos are *Grower practice*; 24/0 is house-endorsed. - Bigger root volume, bigger plants: *Established* across crops [4]; the auto taproot response to transplanting is the founder's observation (*Grower practice*, house position). - Canopy shape and uniformity: *Supported* [5]. LST over topping for autos: *Grower practice*, house position. - Pre-harvest flushing: *Myth* [7]. ## Sources 1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 2. Kurtz LE, Brand MH, Lubell-Brand JD. 2023. Gene dosage at the autoflowering locus effects flowering timing and plant height in triploid cannabis. Journal of the American Society for Horticultural Science 148(2):83-88. https://doi.org/10.21273/JASHS05293-23 3. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 4. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 5. Danziger N, Bernstein N. 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 6. University of Minnesota Extension. Starting seeds indoors (transplanting seedlings, hardening). https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors 7. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 --- # Choosing your setup: tent, space and budget tiers > Choose the space first, then size everything to it. A 60 x 60 cm (2 x 2 ft) tent suits one or two plants and a 100–200 W LED; 80 x 80 to 90 x 90 cm (about 3 x 3 ft) suits two or three plants and 200–320 W; 120 x 120 cm (4 x 4 ft) suits two to four plants and 400–650 W. Size the exhaust fan to change the tent's air about once a minute, plus 25–50 % for the carbon filter and ducting. - Canonical: https://genetixbay.com/knowledge/guides/choosing-your-setup.html - Category: Start here · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Soil, Coco, DWC - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What size grow tent should a beginner buy?** A beginner should usually buy a 60 x 60 cm (2 x 2 ft) to 90 x 90 cm (3 x 3 ft) tent, about 140–180 cm (4.6–6 ft) tall. It holds one to three plants, needs a modest 100–320 W LED and a small exhaust fan, and is easy to keep cool and dark. A 120 x 120 cm (4 x 4 ft) tent yields more but costs more to light, cool and run. **How many plants fit in a grow tent?** A 60 x 60 cm (2 x 2 ft) tent fits one or two plants in 11 L (3 gal) pots; an 80–90 cm (3 x 3 ft) tent fits two or three in 11–19 L (3–5 gal) pots; a 120 x 120 cm (4 x 4 ft) tent fits two to four in 19 L (5 gal) pots, or more small plants. Fewer, well-trained plants fill a canopy as well as many, and stay within legal plant limits. **How big an exhaust fan do I need for my tent?** Size the exhaust fan to replace the tent's air about once a minute. Multiply length x width x height in feet to get cubic feet, then add 25 % for a carbon filter and 10–20 % for each bend in the ducting. A 4 x 4 x 6.5 ft tent (104 ft³) needs roughly 130–160 CFM of real airflow; a 100 mm (4 in) inline fan with speed control covers 2 x 2 and 3 x 3 tents. **How many watts of LED do I need per square foot?** For flower, plan on roughly 25–40 W of efficient LED per square foot (about 270–430 W/m²) at 2.5–3.0 µmol/J, which gives an average of about 600–900 µmol/m²/s. That is 100–150 W for a 2 x 2 ft tent, 225–320 W for 3 x 3 ft and 400–650 W for 4 x 4 ft. Judge by the fixture's measured PPFD map, not by its 'equivalent' wattage. **Can I grow without a tent?** Yes, a closet, cupboard or spare room can work if you can make it light-tight, keep it at 20–28 °C (68–82 °F), exhaust its air and clean it. A tent is easier for a first grow because its reflective walls, sealed zips and duct ports solve light leaks, smell control and airflow in one box, and it protects floors and walls from water. **How much does a beginner grow setup cost?** A basic 60 x 60 cm (2 x 2 ft) setup with tent, LED, fan and filter, pots, medium and meters typically costs a few hundred dollars; a mid-range 90 x 90 cm (3 x 3 ft) setup with a better light, a logging sensor and a controller-ready fan costs more; a 120 x 120 cm (4 x 4 ft) setup with high-efficacy light and climate control costs the most. Spend first on the light, fan and meters. **Short answer.** Pick the space first and size everything to it. A **60 x 60 cm (2 x 2 ft)** tent suits one or two plants and a **100–150 W** efficient LED; an **80–90 cm (about 3 x 3 ft)** tent suits two or three plants and **200–320 W**; a **120 x 120 cm (4 x 4 ft)** tent suits two to four plants and **400–650 W**. Size the exhaust fan to change the tent's air about **once a minute**, plus 25–50 % for the carbon filter and ducting. Spend on the light, fan and meters before anything else. **Legal first.** Plant-count limits decide how many plants you may grow, which decides the tent. Do the [legal check](https://genetixbay.com/knowledge/guides/legal-check-before-you-grow.md) before you buy. ## What do you need to choose a setup? To choose a setup you need measurements and a short list of generic equipment classes, not a shopping spree. Before buying: - [ ] A tape measure: floor space, ceiling height, distance to a power outlet and to a window or vent for exhaust - [ ] The room's normal temperature range in summer and winter (a cheap thermometer for a week) - [ ] Your legal plant limit and any rules on locks or visibility - [ ] A budget split: roughly 40–50 % light, 15–20 % fan and filter, 15 % tent, the rest pots, medium, meters and nutrients The kit itself (every tier): - [ ] Grow [tent](https://genetixbay.com/knowledge/glossary/tent.md) with light-tight zips and duct ports - [ ] Dimmable full-spectrum [LED](https://genetixbay.com/knowledge/glossary/led.md) with a published PPFD map ([lights for beginners](https://genetixbay.com/knowledge/guides/lights-for-beginners.md)) - [ ] Inline [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) with speed control, ducting and a [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) ([smell control](https://genetixbay.com/knowledge/guides/smell-control-basics.md)) - [ ] One clip-on or [oscillating fan](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) for canopy air - [ ] Pots with drainage ([fabric pots](https://genetixbay.com/knowledge/glossary/fabric-pot.md) or plastic), saucers or a tray - [ ] Medium: potting mix, buffered coco, or a DWC bucket ([choosing a system](https://genetixbay.com/knowledge/systems/choosing-a-system.md)) - [ ] pH and EC meters, calibration buffers ([pH made simple](https://genetixbay.com/knowledge/guides/ph-made-simple.md)) - [ ] Thermo-hygrometer with min/max memory; a timer - [ ] RCD/GFCI-protected power ([electrical and water safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md)) ## Which tent size is right for a beginner? The right first tent is usually 60 x 60 cm (2 x 2 ft) to 90 x 90 cm (3 x 3 ft), because a small tent is cheaper to light, easier to cool and forgives one plant's mistakes. Height matters as much as footprint: allow pot height + plant + 30–45 cm (12–18 in) light gap + the fixture and its hangers. | Tent footprint | Area | Plants (pot size) | Efficient LED for flower | Exhaust fan (real airflow) | |---|---|---|---|---| | 60 x 60 cm (2 x 2 ft) | 0.36 m² (4 ft²) | 1–2 (11 L / 3 gal) | 100–150 W | 100 mm (4 in), 50–100 CFM | | 80 x 80 to 90 x 90 cm (~3 x 3 ft) | 0.64–0.81 m² (9 ft²) | 2–3 (11–19 L / 3–5 gal) | 225–320 W | 100–125 mm (4–5 in), 100–150 CFM | | 120 x 60 cm (4 x 2 ft) | 0.72 m² (8 ft²) | 2 (19 L / 5 gal) | 200–300 W | 100–125 mm (4–5 in), 100–150 CFM | | 120 x 120 cm (4 x 4 ft) | 1.44 m² (16 ft²) | 2–4 (19 L / 5 gal) | 400–650 W | 150 mm (6 in), 150–250 CFM | | 150 x 150 cm (5 x 5 ft) | 2.25 m² (25 ft²) | 4–6 (19–25 L / 5–7 gal) | 650–1,000 W | 150–200 mm (6–8 in), 250–400 CFM | LED wattages assume a fixture of about 2.5–3.0 µmol/J, which delivers an average of about 600–900 µmol/m²/s across the footprint in flower [1][2]. Plant counts are *Grower practice*; your legal limit wins. **Pot size is a trade-off, not a fixed rule.** Bigger pots give bigger plants within reason and hold water longer, which forgives a missed day [5]. Small pots can still produce big plants if you water and feed often (the founder has grown 4 oz+ from a 16 oz cup with high-frequency fertigation). For a first grow, 11–19 L (3–5 gal) is the forgiving choice. ## How do you choose a setup, step by step? Choose a setup in this order; each step depends on the one before. 1. **Measure the space.** Note floor area, ceiling height and the nearest outlet. Leave 30 cm (12 in) around the tent to reach zips and ducting. 2. **Pick the footprint** from the table, within your plant limit. When in doubt, go one size smaller for a first grow. 3. **Pick the height.** 140–160 cm (4.6–5.3 ft) for autoflowers and short, trained plants; 180–200 cm (6–6.6 ft) for photoperiods that stretch 50–150 % after the flip. 4. **Size the light to the footprint.** Choose a dimmable LED whose published PPFD map shows 600–900 µmol/m²/s average over your footprint at 30–45 cm (12–18 in), with edges no lower than about 60–70 % of the centre. 5. **Size the exhaust fan.** Tent volume in cubic feet (L x W x H) ≈ the CFM for one air change a minute. Add 25 % for the carbon filter and 10–20 % per duct bend, and buy a fan with speed control so you can run it at 50–70 % [3]. 6. **Match the carbon filter** to the fan: same duct diameter and a rated airflow at least equal to the fan's. 7. **Add canopy airflow.** One clip fan per 0.4–0.8 m² (4–9 ft²), gently moving leaves, never blasting them. 8. **Check the power budget.** Add up the watts (light + fans + heater or dehumidifier) and keep the circuit under 80 % of its rating (see [electrical safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md)). 9. **Choose the medium.** Soil for the most forgiveness, coco for faster growth and daily attention, DWC for speed with the most risk ([choosing a system](https://genetixbay.com/knowledge/systems/choosing-a-system.md)). 10. **Run the empty tent for 48 h** with light and fans on their timer. Log temperature and RH lights-on and lights-off before any seed goes in. ## What are the budget tiers? A beginner setup comes in three tiers, defined by equipment class rather than brand. Cost ranges are rough and vary by country. | Tier | Footprint | Light class | Air | Meters and control | Typical total (rough) | |---|---|---|---|---|---| | **Starter** | 60 x 60 cm (2 x 2 ft) | 100–150 W LED board, ~2.3–2.6 µmol/J, dimmable | 100 mm (4 in) inline fan, basic speed dial, matching filter, one clip fan | pH pen, EC pen, min/max thermo-hygrometer, mechanical timer | A few hundred USD/CAD | | **Solid** | 80–90 cm (~3 x 3 ft) | 225–320 W LED bar or board, ~2.6–2.9 µmol/J, published PPFD map | 100–125 mm (4–5 in) EC (electronically commutated) fan with thermostat/humidistat speed control | Logging temperature/RH sensor, calibrated pH and EC meters, digital timer | Roughly 1.5–2.5x Starter | | **Serious** | 120 x 120 cm (4 x 4 ft) | 400–650 W multi-bar LED, ~2.8–3.0+ µmol/J, dimmable from a controller | 150 mm (6 in) EC fan with controller, filter, two clip fans, small dehumidifier | Logging sensors (air, leaf temperature, root zone), PAR/quantum meter, controller with alerts | Roughly 3–5x Starter | Where to spend first: light efficacy and a published PPFD map, then a speed-controlled fan, then meters. Cheap fixtures with inflated "equivalent watts" claims, and fans without speed control, are where beginner money is most often wasted [2]. ## How will you know it's working? You'll know the setup is right when the empty-tent test and the first weeks of growth are boring: - **Temperature:** lights-on 22–28 °C (72–82 °F) with the fan at 50–70 % speed, not 100 %. If the fan is flat out and the tent is still above 30 °C (86 °F), the light is too big for the space or the room is too hot. - **RH:** within 5–10 points of the stage target ([climate basics](https://genetixbay.com/knowledge/guides/climate-basics-vpd-cheat-sheet.md)). - **Negative pressure:** the tent walls pull in slightly when zipped ([negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md)), and there's no smell outside the tent in flower. - **Light:** a PPFD reading at canopy height near the target, edges within about 30 % of the centre. - **Darkness:** stand inside the zipped tent with the lights off in a lit room for two minutes; you should see no pinpricks of light ([light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)). - **Plants:** an even canopy with no plant shaded by its neighbours. ## What mistakes do beginners make when choosing a setup? Beginners mostly buy too big, too cheap or in the wrong order: - **Buying the biggest tent that fits.** A 4 x 4 needs four times the light, a bigger fan and more cooling than a 2 x 2. Start small. - **Buying the light by "equivalent watts".** Only measured PPFD over the footprint and µmol/J efficacy count [2]. - **A fan with no speed control.** It's either too loud and too dry, or too weak. - **Forgetting the filter's resistance.** A carbon filter and two bends can cut real airflow by a third or more. - **No room above the plants.** Photoperiods commonly double in height after the flip. - **Too many plants.** Two well-trained plants fill a 3 x 3 as well as six cramped ones, with better airflow and less mould risk [6]. - **Daisy-chained power strips** and no RCD/GFCI near water ([electrical safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md)). - **Skipping the 48 h empty test.** ## Evidence - Yield scaling with light intensity indoors: *Supported* by cannabis trials [1]; light and planting density were among the main yield factors in a meta-analysis [4]. - LED efficacy as the main driver of light cost: *Established* [2]. - Air movement improving canopy gas exchange: *Supported* in non-cannabis research [3]; mould risk in humid, stagnant canopies: *Established* [6]. - Pot size and plant growth: *Established* in a cross-species meta-analysis [5]; the pot-size trade-off against feeding frequency is the house position. - Tent, plant-count and fan sizing figures: *Grower practice*. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 3. Kitaya Y, Tsuruyama J, Shibuya T, Yoshida M, Kiyota M, 2003. Effects of air current speed on gas exchange in plant leaves and plant canopies. Advances in Space Research 31(1):177–182. https://www.science.gov/topicpages/a/air+current+speed 4. Backer R, Schwinghamer T, Rosenbaum P, et al., 2019. Closing the yield gap for cannabis: a meta-analysis of factors determining cannabis yield. Frontiers in Plant Science 10:495. https://doi.org/10.3389/fpls.2019.00495 5. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 6. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Climate basics: temperature, RH and a VPD cheat sheet > Run a grow room at about 24–27 °C (75–81 °F) and 65–75 % RH for seedlings, 22–28 °C (72–82 °F) and 55–70 % in veg, 20–26 °C (68–79 °F) and 45–55 % in flower, and 40–50 % RH in late flower, with nights 3–6 °C cooler. Those pairs land on a leaf VPD of roughly 0.4–0.8, 0.8–1.2 and 1.0–1.5 kPa. Use the cheat-sheet table below: read your air temperature and RH, find the leaf VPD, and adjust RH first. - Canonical: https://genetixbay.com/knowledge/guides/climate-basics-vpd-cheat-sheet.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What temperature should my grow tent be?** A cannabis grow tent should run about 24–27 °C (75–81 °F) for seedlings, 22–28 °C (72–82 °F) in veg and 20–26 °C (68–79 °F) in flower, cooling to 20–24 °C (68–75 °F) in late flower, with lights-off 3–6 °C (5–10 °F) cooler. Above about 30 °C (86 °F) photosynthesis falls in cannabis unless light and CO2 are high. **What humidity should I run in each stage?** Run about 65–75 % RH for seedlings and clones, 55–70 % in veg, 45–55 % in early and mid flower and 40–50 % in the last two to three weeks. High humidity in flower raises the risk of bud rot and powdery mildew, and a 2025 cannabis study found high RH delayed flowering and lowered cannabinoids. **What is a good VPD for cannabis?** A good leaf VPD for cannabis is about 0.4–0.8 kPa for seedlings and clones, 0.8–1.2 kPa in veg and 1.0–1.5 kPa in flower. Calculate it from leaf temperature, which under most lights is 1–2 °C below air temperature. At 26 °C air and a 24 °C leaf, 60 % RH gives about 0.97 kPa and 50 % RH about 1.30 kPa. **Do I need a VPD chart as a beginner?** A beginner needs only a rough VPD chart: one table of air temperature against RH, read once a day. Get temperature and RH into the stage ranges first; VPD then tells you which way to nudge humidity. Don't chase decimals. A steady 1.1 kPa beats a wobbling 0.9–1.4 kPa, and most VPD bands come from greenhouse and grower practice, not cannabis trials. **Do cold nights make buds purple or more terpy?** Cold nights can bring out purple colour, because anthocyanin pigments build up when temperature drops in cultivars that carry the genes for them. That part is real. Claims that cold nights add terpenes, flavour or resin are a myth unless peer-reviewed data shows otherwise. Keep night drops to 3–6 °C (5–10 °F); bigger drops mostly invite condensation and bud rot. **Should I fix temperature or humidity first?** Fix temperature first, because it sets how much water the air can hold, then adjust humidity to land the VPD. Exhaust and room temperature control heat; a humidifier raises RH and a dehumidifier lowers it. In a small tent, exhaust fan speed changes both, so change one setting at a time and wait 24 hours before judging the result. **Short answer.** Keep the grow room at about **24–27 °C (75–81 °F) and 65–75 % RH for seedlings**, **22–28 °C (72–82 °F) and 55–70 % in veg**, **20–26 °C (68–79 °F) and 45–55 % in flower**, and **40–50 % RH in the last 2–3 weeks**, with nights 3–6 °C (5–10 °F) cooler. Those pairs give a leaf [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) of roughly **0.4–0.8, 0.8–1.2 and 1.0–1.5 kPa**. Read your air temperature and RH, look up the VPD in the cheat sheet below, and nudge humidity first. Climate is the boring backbone of every grow. Plants forgive a lot, but not a week at 32 °C or a flower room stuck at 70 % RH. This guide gives the targets, a one-table cheat sheet and the routine; the physics is in [VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md). ## What do you need to control the climate? You need a way to measure, a way to move air and one device for whichever way your room drifts. Generic classes, no brands: - [ ] A digital thermo-hygrometer with min/max memory, placed at canopy height in the shade of a leaf (not in the light beam) - [ ] Ideally a second sensor or a logging one, so you see the night as well as the day - [ ] An inline [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) with a speed controller, venting through a [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) ([smell control basics](https://genetixbay.com/knowledge/guides/smell-control-basics.md)) - [ ] One or two clip or [oscillating fans](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) moving air gently over and under the canopy ([airflow](https://genetixbay.com/knowledge/environment/airflow.md)) - [ ] A [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) if your room runs humid, or a [humidifier](https://genetixbay.com/knowledge/glossary/humidifier.md) if it runs dry (most rooms need one or the other, rarely both) - [ ] Optional: an [IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md) to read [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) directly - [ ] Optional: a small heater with a thermostat and tip-over cut-off for cold rooms (see [electrical and water safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md)) ## What temperature and humidity should you run at each stage? Run warm and humid for young plants and progressively cooler and drier as flowers form. The table is *Grower practice* anchored to cannabis photosynthesis data [3] and disease research [4][5]. | Stage | Air temp, lights on | Lights off | RH | Leaf VPD target | |---|---|---|---|---| | Seedling and clone | 24–27 °C (75–81 °F) | 20–24 °C (68–75 °F) | 65–75 % | 0.4–0.8 kPa | | Veg | 22–28 °C (72–82 °F) | 18–24 °C (64–75 °F) | 55–70 % | 0.8–1.2 kPa | | Early and mid flower | 20–26 °C (68–79 °F) | 18–22 °C (64–72 °F) | 45–55 % | 1.0–1.5 kPa | | Late flower (last 2–3 weeks) | 20–24 °C (68–75 °F) | 17–21 °C (63–70 °F) | 40–50 % | 1.2–1.5 kPa | | Drying room | 15–21 °C (60–70 °F) | Same, dark | 55–62 % | Not used; see [drying](https://genetixbay.com/knowledge/guides/drying-step-by-step.md) | Net photosynthesis in cannabis peaked at about 25–30 °C and fell above that at ambient CO₂ [3], so **30 °C (86 °F) is the practical ceiling** for a normal tent. Keep the root zone and any hydro reservoir at 18–22 °C (64–72 °F) ([temperature by stage](https://genetixbay.com/knowledge/environment/temperature-by-stage.md)). ## What is VPD, in one paragraph? [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) (vapour pressure deficit) is how hard the air pulls water out of the leaf, measured in kilopascals (kPa). It combines temperature and [relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) into one number that tracks [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md). Low VPD (below about 0.4 kPa) means the leaf barely transpires, so the plant moves little water and calcium and mould thrives; high VPD (above about 1.6 kPa) makes plants close their [stomata](https://genetixbay.com/knowledge/glossary/stomata.md) to save water. Calculate it from the leaf, not the air: [leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md) uses leaf temperature, which under most indoor lights runs about 1–2 °C below air temperature [2]. ## What does the VPD cheat sheet say? The cheat sheet gives leaf VPD in kPa for your **air temperature** and **RH**, assuming the leaf is **2 °C cooler than the air**. It uses the standard Tetens equation for saturation vapour pressure, es(T) = 0.6108 × exp(17.27 T / (T + 237.3)) kPa [1], with leaf VPD = es(leaf) − es(air) × RH/100. | Air temp | 40 % | 45 % | 50 % | 55 % | 60 % | 65 % | 70 % | 75 % | |---|---|---|---|---|---|---|---|---| | 20 °C (68 °F) | 1.13 | 1.01 | 0.89 | 0.78 | 0.66 | 0.54 | 0.43 | 0.31 | | 22 °C (72 °F) | 1.28 | 1.15 | 1.02 | 0.88 | 0.75 | 0.62 | 0.49 | 0.36 | | 24 °C (75 °F) | 1.45 | 1.30 | 1.15 | 1.00 | 0.85 | 0.70 | 0.56 | 0.41 | | 26 °C (79 °F) | 1.64 | 1.47 | 1.30 | 1.14 | 0.97 | 0.80 | 0.63 | 0.46 | | 28 °C (82 °F) | 1.85 | 1.66 | 1.47 | 1.28 | 1.09 | 0.90 | 0.72 | 0.53 | | 30 °C (86 °F) | 2.08 | 1.87 | 1.66 | 1.45 | 1.23 | 1.02 | 0.81 | 0.60 | How to read it: seedlings want the 0.4–0.8 band (bottom-right cells), veg 0.8–1.2 (the middle), flower 1.0–1.5 (left-centre). Example: 26 °C at 60 % RH is 0.97 kPa, fine for veg; drop RH to 50 % and it becomes 1.30 kPa, right for flower. Two cautions. Under strong LEDs with good airflow the leaf can sit close to air temperature, which makes real VPD about 0.2–0.3 kPa **higher** than the table [2]; measure leaf temperature with an IR thermometer if you want precision. And many VPD bands are greenhouse and grower practice: cannabis-specific VPD trials are still scarce ([VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md)). ## How do you set up and run your climate, step by step? 1. **Run the empty room for 48 hours** with the light and fans on their normal schedule. Log lights-on and lights-off temperature and RH every few hours, or use the min/max memory. 2. **Place the sensor correctly**: at canopy height, shaded, not touching the tent wall, not in the exhaust stream. Move it up as the plants grow. 3. **Fix temperature first.** Too hot: raise exhaust speed, cool the room the tent pulls from, or dim the light 10–20 %. Too cold: slow the exhaust and warm the surrounding room; avoid a heater blowing on plants. 4. **Then set RH for the stage.** Too humid: more exhaust, then a dehumidifier in the room (or tent). Too dry: slow exhaust, then a humidifier. 5. **Check VPD on the cheat sheet** once both numbers are in range. Nudge RH by about 5 points to move VPD by roughly 0.1–0.2 kPa. 6. **Keep the lights-off drop to 3–6 °C (5–10 °F).** The dark period is when RH spikes; if night RH climbs above about 60 % in flower, run the dehumidifier or exhaust at night too. 7. **Move air under and over the canopy** so leaves flutter gently, about 0.3–1.0 m/s at leaf level. No dead corners, no leaves whipped flat ([airflow](https://genetixbay.com/knowledge/environment/airflow.md)). 8. **Step the targets down at the flip** and again for the last 2–3 weeks of flower, when dense buds are most at risk of [bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md). 9. **Change one setting at a time and wait 24 hours** before judging. Log every change in your [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md). 10. **Recheck after every big change**: a new light height, a pot-up, a dense canopy and a new season all move the numbers. ## Do cold nights improve colour or flavour? Cold nights can bring out colour; they don't add terpenes. Anthocyanins, the pigments behind purple, build up with low temperature and other stresses in plants that carry the genes for them [7], so a cultivar with purple genetics may colour up with cooler nights. That part is real. The GenetixBay house position: claims that cold nights add **terpenes, flavour or resin** are a *Myth* unless peer-reviewed data shows otherwise. Purple is bag appeal, not proof of quality. Large night drops (more than about 8–10 °C) also push RH up in the dark and set up condensation inside buds, which is how botrytis starts [5][6]. A 3–6 °C drop is plenty. See [purple stems and leaves](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) for when purple means something else. ## How will you know the climate is working? You'll know the climate is right when the logs are boring and the leaves look relaxed: - Temperature stays within about 2–3 °C (4–5 °F) of target, lights-on, day after day. - RH stays within about 5 points of target, including the first hour after lights-off. - Leaves sit flat or slightly raised and flutter gently in the fan breeze; no upward [taco or canoe](https://genetixbay.com/knowledge/diagnosis/taco-canoeing-leaves.md), no droop. - The pot dries from heavy to light in 2–4 days in veg; a pot that stays wet for a week often means VPD is too low or the plant is too small for the pot. - No condensation on tent walls in the morning, and no grey fuzz or white powder in flower. - Top leaves are not bleached or crispy; if they are, see [heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md). ## What mistakes do beginners make with climate? - **Measuring in the wrong place**: a sensor in the light beam reads 3–5 °C hot; one on the floor reads cold. - **Only checking during the day.** Lights-off RH spikes are where mould starts. - **Chasing VPD decimals** while temperature swings 8 °C between day and night. - **Running flower at veg humidity**, 60–70 % RH in weeks 6–9, the classic route to bud rot [4][6]. - **Sealing the tent too tight** with no exhaust, so heat and humidity build up and CO₂ runs low. - **Big cold-night drops "for purple"**: colour maybe, terpenes no, condensation yes. - **Blowing a fan straight at one plant** hard enough to cause windburn and clawed leaves. - **Changing exhaust, humidifier and light height on the same day**, then not knowing which one helped. ## Evidence - Saturation vapour pressure and VPD maths: *Established* [1]. - Leaf temperature below air under indoor lights, and closer to air under LEDs: *Established* [2]. - Cannabis photosynthesis peak around 25–30 °C at ambient CO₂: *Supported* [3]. - High RH delaying flowering and lowering cannabinoids: *Supported* (one 2025 cannabis study) [4]. - High RH raising bud rot and mildew: *Established* [5][6]. - Stage VPD bands: *Grower practice*. - Cold nights and anthocyanin colour: *Supported* in plants generally [7]; cold nights adding terpenes or resin: *Myth* (house position, no supporting cannabis data). ## Sources 1. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 3. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 4. Corredor-Perilla IC, Kwon H, Park J, 2025. High relative humidity in cannabis cultivation (effects on flowering, biomass and cannabinoids). Frontiers in Plant Science 16:1678142. https://doi.org/10.3389/fpls.2025.1678142 5. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 6. Utah State University Extension. Hemp bud rot (IPM fact sheet). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot.php 7. Landi M, Tattini M, Gould KS, 2015. Multiple functional roles of anthocyanins in plant-environment interactions. Environmental and Experimental Botany 119:4–17. https://doi.org/10.1016/j.envexpbot.2015.05.012 --- # Coco first grow, week by week > Coco is hydroponics that looks like soil: use buffered coco mixed about 70:30 with perlite, feed a complete mineral nutrient at every watering from day one at pH 5.8–6.2, and water to 10–20 % runoff before the pot dries out. Feed EC climbs from about 0.6–0.8 mS/cm for seedlings to 1.2–1.8 in veg and 1.6–2.2 in flower, fed right to harvest. Never let coco dry out completely. - Canonical: https://genetixbay.com/knowledge/guides/coco-first-grow-week-by-week.html - Category: Start here · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Transition, Flower, Ripening, Harvest · Systems: Coco - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Do I need to feed coco every time I water?** Yes. Coco coir has almost no nutrients of its own, so feed a complete mineral nutrient at every watering from the first day: about EC 0.6–0.8 mS/cm for seedlings, 1.2–1.8 in veg and 1.6–2.2 in flower, at pH 5.8–6.2. Plain-water waterings in coco starve the plant and swing root-zone EC. Water to 10–20 % runoff so salts don't build up. **What is the best coco to perlite ratio?** A coco-to-perlite ratio of about 70:30 by volume is the common beginner choice: airy enough to forgive a heavy hand with water, while still holding plenty. Fine, dense coco benefits from more perlite, up to 50:50 for small pots watered often; chunky coco with coarse chips can run at 80:20 or even straight. Mix the perlite into pre-moistened, buffered coco. **Why do I need to buffer coco?** Raw coco coir holds potassium and sodium on its exchange sites and grabs calcium and magnesium from your feed in exchange, so seedlings can show Ca/Mg deficiency in the first 2–3 weeks. Buffering soaks washed coco in a calcium and magnesium solution (EC about 1.2–2.0 mS/cm, pH 5.8) for 8–24 hours so those sites fill first. Pre-buffered bags can skip it; test runoff anyway. **How much runoff should I get in coco?** Aim for about 10–20 % runoff per day in coco: for every 1 L you pour in, 100–200 mL should drain out. Runoff carries away excess salts so the root zone stays near your feed EC. If runoff EC rises more than about 0.5–1.0 mS/cm above input, increase the volume or frequency of watering rather than cutting the feed strength. **How often should I water coco?** Water coco when the pot has lost about 30–50 % of its available water, before it dries out: usually once a day in veg in an 11 L (3 gal) pot, and two to four times a day in flower for big plants in small pots. Coco that dries out completely turns water-repellent and roots suffer. Lift the pot; it should never feel fully light. **What pH and EC should runoff be in coco?** Coco runoff should usually read pH 5.8–6.5 and an EC within about 0.3–0.5 mS/cm of what you fed in veg, up to about 1.0 above in flower. Runoff EC climbing week on week means salts are building up: water more volume. Runoff pH falling below 5.5 or rising above 6.8 means adjust your input pH by 0.1–0.2 and check your water. **Short answer.** Coco is hydroponics that looks like soil. Use **buffered coco mixed about 70:30 with perlite**, feed a **complete mineral nutrient at every watering from day one** at **pH 5.8–6.2**, and water to **10–20 % runoff** before the pot dries out. Feed EC climbs from about **0.6–0.8 mS/cm** for seedlings to **1.2–1.8 in veg** and **1.6–2.2 in flower**, fed right to harvest. Never let coco dry out completely. Coco grows faster than soil because roots get more air, but it forgives less: there's no starter charge and little buffer. This guide follows one feminised photoperiod plant; for autos, sow straight into the final pot and follow the [autoflower guide](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md) for timing. The why is in [coco as a growing system](https://genetixbay.com/knowledge/systems/coco.md). ## What do you need for a coco grow? A coco grow needs the basic tent kit ([choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md)) plus: - [ ] Washed and buffered [coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), loose or as a compressed block (a 5 kg block makes roughly 60–70 L) - [ ] Coarse [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), about 30 % of the final volume - [ ] A calcium/magnesium product or calcium nitrate plus magnesium sulfate for buffering (if the coco isn't pre-buffered) ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)) - [ ] A complete mineral nutrient made for coco or hydro, usually a two-part [A+B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) - [ ] 7–19 L (2–5 gal) pots with good drainage, raised on a tray or saucer you can empty - [ ] pH meter, buffers, pH up and down ([pH made simple](https://genetixbay.com/knowledge/guides/ph-made-simple.md)) - [ ] EC meter and 1.413 mS/cm calibration solution ([meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)) - [ ] A 10–20 L (3–5 gal) mixing bucket with a lid, measuring syringes and a stirring stick - [ ] A measuring jug and a small cup to catch runoff for testing - [ ] Optional: a pump-and-dripper kit and a timer for automatic watering later ## How much runoff and EC does coco need, week by week? Coco needs feed at every watering, with EC rising steadily and runoff checked a few times a week. Weeks count from the seedling breaking the surface; EC is the total of your water plus nutrients, in mS/cm (ppm500 = EC x 500). | Week | Stage | Light (µmol/m²/s, hours) | Feed EC | pH | Waterings | Runoff target | Key jobs | |---|---|---|---|---|---|---|---| | 1 | Seedling | 150–250, 18/6 | 0.6–0.8 | 5.8–6.0 | Small ring, 50–150 mL, every 1–2 days | Little or none | Keep coco moist, never soaking | | 2 | Seedling | 200–300 | 0.8–1.0 | 5.8–6.0 | 150–300 mL daily | A few drips | Watch for rust spots (Ca/Mg) | | 3 | Early veg | 300–400 | 1.0–1.2 | 5.8–6.2 | 0.3–0.6 L daily | 10–20 % | Pot up from a cup if used | | 4–5 | Veg | 400–550 | 1.2–1.5 | 5.8–6.2 | 0.5–1.5 L, once a day | 10–20 % | Start [LST](https://genetixbay.com/knowledge/guides/training-basics.md) | | 6–7 | Late veg | 500–600 | 1.4–1.8 | 5.8–6.2 | 1–2 L, 1–2 times a day | 10–20 % | Flip at half the final height you can fit | | 8–9 | **Transition** (days 1–14 after the flip) | 600–750, 12/12 | 1.6–1.8 | 5.8–6.2 | 1.5–3 L, 1–3 times a day | 10–20 % | Stretch; tie down; sex check | | 10–12 | Early flower | 700–900 | 1.6–2.0 | 5.8–6.2 | 2–4 L split over 2–3 waterings | 10–20 % | RH 45–55 %; tuck, don't pluck | | 13–15 | Mid flower | 700–900 | 1.8–2.2 | 5.8–6.2 | 2–5 L split over 2–4 waterings | 15–20 % | Runoff EC check twice a week | | 16–18 | Late flower, ripening | 700–900 | 1.6–2.0; taper only N if you mix salts | 5.8–6.2 | Same | 15–20 % | RH 40–50 %; trichome checks | | 17–20 | Harvest | | Feed to the end; **no flush** | | | | Harvest by trichomes | These are *Grower practice* steps that sit inside the published coco range of about EC 1.2–2.4 mS/cm with 10–20 % runoff ([coco](https://genetixbay.com/knowledge/systems/coco.md)). The 10–14 day transition after the flip means "day 1 of flower" lands around week 9–10 here; see the [grow calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md). ## How do you run a coco grow, step by step? Run a coco grow in these steps: 1. **Hydrate and rinse.** Break up the block in a tub with warm water. Rinse with fresh water until runoff EC is below about 0.5 mS/cm, unless the bag says washed and a runoff test agrees [2]. 2. **Buffer, unless pre-buffered.** Soak the coco 8–24 hours in a calcium and magnesium solution at EC about 1.2–2.0 mS/cm and pH 5.8, mixing once or twice, then drain and rinse. Without this, raw coco pulls Ca and Mg out of your feed and releases potassium and sodium for the first few weeks [1][5] ([buffering coco](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md)). 3. **Mix in perlite.** About 70 % coco to 30 % coarse perlite by volume. Use more perlite (up to 50:50) for fine, dusty coco or small pots watered often; less for chunky coco. 4. **Fill and pre-wet with feed,** not plain water: seedling-strength solution at EC 0.6–0.8 and pH 5.8–6.0 until it drips. Coco has no starter charge, so the seedling needs nutrients from day one [3]. 5. **Plant.** Sow root-down 0.5–1 cm (¼–½ in) deep ([germinating seeds](https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.md)). Water a small ring around the stem. 6. **Mix every feed the same way.** Fill the bucket with water, add part A, stir, then part B, stir (never mix concentrates together), add any Cal-Mag, measure EC, then adjust pH last. 7. **Water to runoff before it dries.** When the pot has lost about 30–50 % of its water (it feels noticeably lighter, the top 1–2 cm is dry), water slowly until 10–20 % drains out. Never let coco dry right out: it turns water-repellent ([watering](https://genetixbay.com/knowledge/guides/watering-how-much-how-often.md)). 8. **Empty the saucer** within 30 minutes. Coco sitting in its own runoff wicks salts back up. 9. **Test runoff two or three times a week.** Catch the first 50–100 mL of runoff and read EC and pH ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). If runoff EC is more than 0.5–1.0 mS/cm above input, water more volume or more often rather than lowering the feed. 10. **Water more often as roots fill the pot.** By mid flower, a big plant in an 11 L (3 gal) pot may need two to four smaller waterings a day. That is normal coco behaviour and part of why coco can grow big plants in small pots ([high-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md)). 11. **Raise EC by stage, not by guesswork.** Step up about 0.2 mS/cm at a time when leaves are deep green with no burnt tips. Higher nutrient strength didn't raise yield or cannabinoids in a controlled trial [6] ([feeding basics](https://genetixbay.com/knowledge/guides/feeding-basics.md)). 12. **Flip, then feed through to harvest.** If you mix single salts, taper only nitrogen over the last 2–3 weeks while keeping the rest fed [7]. Do not flush. 13. **Harvest by trichomes** ([when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md)), then [dry](https://genetixbay.com/knowledge/guides/drying-step-by-step.md) and [cure](https://genetixbay.com/knowledge/guides/curing-step-by-step.md). ## Should you flush coco before harvest? No. Pre-harvest flushing is a *Myth*, and in coco it is especially harsh: with no nutrient reserve in the medium, plain water starves the plant within days, in the weeks when it is packing on most of its final weight and resin. A controlled study found no quality gain from flushing [8]; see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). The valid use is a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) for [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), at any stage: water 2–3 pot volumes of a light feed (EC about 0.4–0.8 mS/cm with Ca and Mg, pH 5.8–6.0), not plain water, then return to the normal feed. ## How will you know it's working? You'll know a coco grow is working when plants grow fast and evenly and the runoff numbers stay close to the input: - **Weeks 1–3:** no rust spots or pale interveinal patches on new-ish leaves (the classic sign of unbuffered coco pulling Ca and Mg) ([rust spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md)). - **Veg:** a new node every 2–3 days, faster than soil, with mid to deep green leaves held flat. - **Pots:** go from heavy to noticeably lighter within a day in veg; never bone dry. - **Runoff:** pH 5.8–6.5, EC within 0.3–0.5 mS/cm of input in veg and within about 1.0 in flower, stable week on week. - **Flower:** steady bud swell; oldest fan leaves fade slowly only in the last 2–3 weeks. ## What mistakes do beginners make with coco? Coco beginners usually treat it like soil: - **Plain-water waterings.** Every watering carries feed in coco. - **Unbuffered coco** and early Ca/Mg deficiency in weeks 1–3. - **Letting it dry out** between waterings. Coco forgives overwatering better than soil but punishes drying. - **No runoff.** Salts build up and the plant shows burnt tips and clawing while runoff EC climbs. - **Fixing high runoff EC by cutting feed strength** instead of watering more volume. - **Too little perlite** in fine coco: soggy pots, slow growth, fungus gnats. - **Mixing nutrient concentrates together** or adjusting pH before adding nutrients. - **Flushing at the end.** ## Evidence - Coir chemistry: variable, often high exchange capacity loaded with K and Na: *Established* [1]. Buffering protocols: *Grower and industry practice* [2]. - Ca and K interactions in cannabis nutrition: *Supported* [5]. - Feeding from early on in coir-based media: *Supported* [3]. Higher nutrient strength not increasing yield: *Supported* [6]. - Air-filled porosity and perlite in container media: *Established* [4]. - Nitrogen trade-off: *Supported* [7]. Pre-harvest flushing: *Myth* [8]. - Weekly EC, volumes and the 70:30 ratio: *Grower practice*. ## Sources 1. Abad M, Noguera P, Puchades R, Maquieira A, Noguera V, 2002. Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology 82(3):241–245. https://doi.org/10.1016/S0960-8524(01)00189-4 2. Greenhouse Grower, 2023. Washed, low-EC, or buffered? How to specify coco substrate for your crop. https://www.greenhousegrower.com/?p=180860 3. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17 4. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 5. Saloner A, Sacks MM, Bernstein N. 2019. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 6. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 7. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 8. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 --- # Curing step by step: a slow moisture decline, no humidity packs > Curing is a slow, steady decline in the bud's moisture, not a constant hold. Jar dried buds ¾ full at about aw 0.62–0.65, keep them dark at 15–21 °C (60–70 °F), burp daily for the first week, then every few days, then weekly, and let them settle towards aw 0.55–0.58 over 2–8 weeks. Judge the bud by an equilibrated jar reading, not the room. Skip humidity packs; if a jar is too dry, add a fresh bud. - Canonical: https://genetixbay.com/knowledge/guides/curing-step-by-step.html - Category: Start here · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Cure · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I cure cannabis step by step?** Put properly dried buds, small stems snapping, loosely into airtight glass jars about ¾ full with a small hygrometer. Seal and keep them dark at 15–21 °C (60–70 °F). Burp for 10–15 minutes once or twice a day in week 1, every 2–3 days in weeks 2–3, then weekly. Let the equilibrated jar reading fall slowly from about 62–65 % towards 55–58 % over 2–8 weeks. **What humidity should my curing jars be?** Curing jars should read about 62–65 % RH at the start of the cure and decline slowly towards 55–58 %, but only a reading from a jar sealed for 12–24 hours counts, because only then does jar RH equal the bud's water activity (aw ≈ RH / 100). Above 65–68 %, take the buds out and dry them more. Below about 55 % early on, the dry went too far. **Should I use humidity packs in my jars?** No. GenetixBay's house position is that two-way humidity packs are a marketing gimmick that rob terpenes, and they hold moisture constant when a good cure is a slow decline. Dry properly, burp on schedule and watch an equilibrated hygrometer instead. If a jar is too dry, put in a fresh, slightly moister bud from another jar and let it share its moisture. **How long should I cure cannabis?** Cure cannabis for at least 2 weeks, and 4–8 weeks for the smoothest, roundest result most growers report. Long cures help within reason, then plateau; after about 8 weeks you are really in storage. Curing is a slow moisture decline, so the timeline depends on how the bud started. Note that a cure will never fix a bad dry. **Can curing fix weed that smells like hay?** No. In the GenetixBay house position, a cure will never fix a bad dry. A hay smell means bacteria, over-drying or drying too fast, and it never truly comes out, even after months in the jar. It may fade a little. Prevent it next time with a slow 7–14 day dry at 15–21 °C and 55–62 % RH. **What is burping a jar?** Burping means opening a curing jar for 10–15 minutes to let moist air and gases out and fresh air in, then resealing it. Burp once or twice a day in the first week, every 2–3 days in weeks 2–3 and weekly after that. Sniff each time: an ammonia or musty smell means the buds were jarred too wet and need to come out to dry. **What is water curing?** Water curing soaks buds in water for days to leach out compounds before drying. It is Contested: there is little controlled evidence on quality, and it loses aroma along with whatever it removes. GenetixBay does not recommend it. A slow dry followed by a jar cure with a gradual moisture decline is the proven route for home growers. **Short answer.** Curing is a **slow, steady decline in the bud's moisture**, not a constant hold. Jar properly dried buds **¾ full** at about **aw 0.62–0.65**, keep them **dark at 15–21 °C (60–70 °F)**, **burp** daily in week 1, every 2–3 days in weeks 2–3, then weekly, and let them settle towards **aw 0.55–0.58** over **2–8 weeks**. Judge the bud with an equilibrated jar reading. **Skip humidity packs**: if a jar is too dry, add a fresh bud. ## What do you need to cure cannabis? You need airtight jars, a way to read the bud's moisture, and a dark, cool shelf. - [ ] Airtight glass jars with good seals, enough to fill each about ¾ full (roughly 1 L holds 100–140 g of dry bud, depending on density) - [ ] One small hygrometer per jar, checked first with a salt test (a damp salt slurry in a sealed bag reads 75 % RH) - [ ] A dark cupboard or box at 15–21 °C (60–70 °F), away from heaters and sunlight - [ ] Labels or a marker: cultivar, harvest date, jar date - [ ] A kitchen scale in grams - [ ] Your [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) - [ ] Optional: a water activity meter, the gold standard ([water activity test](https://genetixbay.com/knowledge/glossary/water-activity-test.md)) ## What is curing, exactly? Curing is slowly reducing the bud's moisture content over time, under control, after drying. The GenetixBay house position is explicit: a steady slow decline gives the best product, not a jar held at one number. Moisture still moving from the stem and core to the surface is spread out and released a little at a time by [burping](https://genetixbay.com/knowledge/glossary/burping.md). Smoother smoke and rounder aroma are widely reported, but the chemistry of curing is barely studied, so treat the details as *Grower practice* ([curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md)). ## Why judge the bud, not the jar's air? Judge the bud because what matters is its [moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md) and [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), not the jar's RH as such. A jar's RH reflects the bud's water activity **only once the sealed jar has equilibrated**, usually 12–24 h after sealing: then aw ≈ [equilibrium RH](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md) / 100 [1]. A reading taken right after a burp tells you about room air. ASTM D8197 sets **aw 0.55–0.65** as the acceptable range for dry flower [1]; cured flower measured by water-specific methods typically sits around 5–9 % moisture at aw 0.45–0.60, and oven methods read higher [5]. | Stage of cure | Target aw (equilibrated jar RH) | What to do if off | |---|---|---| | Jarring day | 0.62–0.65 (62–65 %) | Above 0.65–0.68: out of the jar, dry 12–24 h more [2] | | Week 1 | 0.60–0.64, falling slowly | Burp 1–2 times a day, 10–15 min | | Weeks 2–3 | 0.58–0.62 | Burp every 2–3 days | | Weeks 4–8 | 0.55–0.58 | Burp weekly; then store sealed | | Any time below ~0.55 | Getting dry and brittle | Add a fresh bud; never a humidity pack | ## How do you cure cannabis, step by step? Cure in this order, starting the day small stems snap at the end of the dry ([drying step by step](https://genetixbay.com/knowledge/guides/drying-step-by-step.md)). 1. **Check the dry is finished.** Small stems snap; buds are dry outside with slight give inside. 2. **Weigh and trim** if you chose to dry trim. Log the dry weight. 3. **Fill jars loosely to about ¾.** Don't pack buds down; air space lets moisture even out. 4. **Put a hygrometer in each jar, seal, and label it** (cultivar, harvest date, jar date). 5. **Leave sealed 12–24 h, then read.** 62–65 % is right. Above 65–68 %: take the buds out on a tray or back on the line for 12–24 h and repeat. Below 55 %: see step 10. 6. **Week 1: burp once or twice a day** for 10–15 minutes. Sniff every time. Fresh and sharp is good; ammonia, must or wet grass means too wet: take them out and dry more. 7. **Gently roll or shake the jar** at each burp so buds don't sit pressed together. 8. **Weeks 2–3: burp every 2–3 days.** Read the hygrometer just before opening, when the jar has equilibrated. You want a slow downward drift. 9. **Weeks 4–8: burp weekly.** The reading should be settling at about 55–58 %. 10. **If a jar falls too dry early,** put one fresh, slightly moister bud from another jar into it and reseal for 24 h. That moves moisture back without adding anything foreign. 11. **After the cure, store** sealed jars full, dark and cool ([long-term storage](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md)). Log the final reading and your tasting notes. ## Why no humidity packs? GenetixBay's house position is that two-way [humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md) are a **marketing gimmick that rob terpenes**. They are built to hold one RH, which works against the slow decline a good cure needs, and they hide a bad dry instead of fixing it. If you need to add moisture, put a fresh bud in the jar. ASTM notes that salt-based sachets are a means of holding aw below 0.68 [2]; that is a storage convenience, not a curing method. This is house position on *Grower practice* evidence; GenetixBay members can test it in side-by-side [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md). ## Can a cure fix a bad dry? No. A cure will never fix a bad dry: that is a firm house position. A [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) means bacteria, over-drying or drying too fast, and it never truly comes out. Volatile monoterpenes lost in a fast, warm dry are gone [3][4]. A long cure may soften harshness slightly, but the time to win flavour is the 7–14 day dry. ## What about water curing? [Water curing](https://genetixbay.com/knowledge/glossary/water-curing.md) is *Contested* and GenetixBay doesn't recommend it. Soaking buds for days before drying removes water-soluble compounds along with aroma, and there's little controlled evidence that it improves anything a good dry and cure don't. ## How long should you cure, and then store? Cure at least 2 weeks and ideally 4–8. Long cures help within reason and then plateau. After that you are storing, and storage is about protection: light is the largest single cause of cannabinoid loss, and oxidation slowly turns THC into CBN, faster when warm [6]. Store full, airtight, opaque or in the dark, at 15–21 °C or cooler, with the bud at aw 0.55–0.65 [1]. ## How will you know it's working? You'll know your cure is working when: - Equilibrated jar readings drift down slowly, a point or two a week, without jumping up after sealing. - The smell on opening gets louder and more distinct over weeks 1–3, with no ammonia or must. - Buds feel dry and springy, not crunchy or spongy; small stems snap. - Smoke or vapour gets smoother between week 1 and week 4, as most growers report. ## What mistakes do beginners make when curing? Beginners mostly jar too wet or try to fix a dry in the jar. - **Jarring too wet** (stems bend): ammonia smell, mould risk. - **Reading the hygrometer right after a burp** instead of after 12–24 h sealed. - **Packing jars to the lid,** so buds compress and can't breathe. - **Using humidity packs** to hold a fixed RH. - **Spraying water or adding fruit peel** to rehydrate. Use a fresh bud. - **Forgetting to burp in week 1.** - **Curing in a warm or bright spot,** which speeds terpene and THC loss. - **Expecting the cure to save a hay-smelling, fast-dried harvest.** ## Evidence - aw 0.55–0.65 as the safe range; equilibrium RH as its measure: *Established* standard [1][2]. - Terpene loss on drying and storage: *Supported* [3][4]. - Moisture content figures for cured flower: *Supported* (method validation) [5]. - THC to CBN by oxidation and light in storage: *Established* [6]. - Burping schedule, cure length, smoother smoke: *Grower practice*. - Slow decline over constant hold; no humidity packs; a cure never fixes a bad dry: house positions on *Grower practice* evidence. - Water curing: *Contested*. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (salt-based humidity control sachets for aw below 0.68). https://sn.astm.org/node/2445/printable/print 3. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa (monoterpene loss on drying and storage). Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 4. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp (terpenes affected by drying, cannabinoids by storage). https://openscholar.uga.edu/record/27813 5. Modern Canna Laboratories. 2025. Validation of moisture content and water activity methods in cannabis flower (method-validation white paper; cured flower typically 5-9 % moisture by water-specific methods at aw 0.45-0.60; 103 °C oven loss-on-drying overstates moisture). https://moderncanna.com/wp-content/uploads/2026/04/Method_Validation_Study_Moisture_Content_and_Water-Activity_in_Cannabis_Flower.pdf 6. Fairbairn JW, Liebmann JA, Rowan MG, 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1–7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x --- # Drying step by step: the bud's water activity, and dry trim vs wet trim > Dry slowly, in the dark, at 15–21 °C (60–70 °F) and 55–62 % RH with gentle air that moves around the buds but never blows on them, for 7–14 days. The bud is done when small stems snap and its water activity is about 0.60–0.65, ready for jars. Wet trim or dry trim is grower preference. A fast, warm dry gives a hay smell that never cures out. - Canonical: https://genetixbay.com/knowledge/guides/drying-step-by-step.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Harvest, Cure · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How long should cannabis dry before jarring?** Cannabis usually needs 7–14 days of drying at 15–21 °C (60–70 °F) and 55–62 % RH. It is ready for jars when small stems snap rather than bend, the outside of the bud feels dry but the inside still has a little give, and the bud's water activity is about 0.60–0.65. Under 5 days is usually too fast; over 14 risks mould if RH is high. **What temperature and humidity should a drying room be?** A cannabis drying room should run 15–21 °C (60–70 °F) and 55–62 % RH, in the dark, with gentle air circulation that moves the room's air without blowing directly on the buds. The popular 60/60 target, 60 °F and 60 % RH, sits inside that window. Warmer or drier air dries faster and loses volatile terpenes; wetter, still air invites mould. **Is dry trimming better than wet trimming?** Wet or dry trimming is grower preference. Wet trimming at harvest is quicker on sticky leaves and suits a humid drying room, because less leaf slows the dry less. Dry trimming after hanging protects the bud's outer layer and slows drying, which suits a dry room. The GenetixBay founder has trimmed hundreds of pounds and prefers brushing dry buds, accepting slight trichome loss. **What is the stem snap test?** The stem snap test checks whether drying cannabis is ready for jars: bend a small stem, about matchstick thick. If it snaps cleanly with a crack, the buds are close to jar-ready; if it bends and folds, keep drying. Big main stems stay bendy longer and are not a fair test. Confirm with an equilibrated jar reading of about 60–65 % RH after 12–24 h sealed. **Why does my dried weed smell like hay?** A hay or cut-grass smell after drying usually means the buds dried too fast or too warm, were over-dried, or had bacterial activity in a stuffy room. Chlorophyll and sugars don't break down evenly and volatile terpenes escape. Per the GenetixBay house position, a cure will never fully fix a bad dry: hay smell rarely, if ever, truly comes out. Prevent it with a slow 7–14 day dry. **Should I freeze dry my cannabis?** Freeze drying is Contested and GenetixBay does not recommend it. It dries buds very fast at low temperature, and some growers report good terpene retention, but there is little controlled evidence on taste and cure, and the founder isn't sold on it. For a home grow, a slow air dry at 15–21 °C and 55–62 % RH is proven and cheap. **Short answer.** Dry slowly and in the dark at **15–21 °C (60–70 °F) and 55–62 % RH** for **7–14 days**, with gentle air moving around the buds but never blowing on them. The bud is ready for jars when **small stems snap** and its [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) is about **0.60–0.65**. Wet trim or dry trim is **grower preference**. Drying is where most quality is won or lost: a rushed, warm dry gives a hay smell that a cure won't fix. ## What do you need to dry cannabis? You need a dark space you can hold steady for two weeks, and a way to hang or rack the harvest. - [ ] A dark room, cupboard or spare tent with space for the whole harvest (an empty grow tent works well) - [ ] A thermo-hygrometer with min/max memory, ideally a second one to cross-check - [ ] A small fan to move room air, aimed at a wall or the floor, never at the buds - [ ] A small dehumidifier or humidifier if your room sits outside 55–62 % RH ([dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md), [humidifier](https://genetixbay.com/knowledge/glossary/humidifier.md)) - [ ] Line, hangers or a mesh drying rack - [ ] Sharp snips, trimming scissors, gloves and a tray - [ ] Airtight glass jars and a small salt-tested hygrometer for each, for the end of the dry ([curing step by step](https://genetixbay.com/knowledge/guides/curing-step-by-step.md)) - [ ] A kitchen scale in grams for weight-loss tracking ## What conditions should a drying room have? A drying room should hold 15–21 °C (60–70 °F), 55–62 % RH, darkness and gentle air movement for 7–14 days. Those are *Grower practice* targets; a grower benchmark survey found an average near 18 °C (65 °F) and 53 % RH [4]. The goal is the bud, not the room: ASTM D8197 sets **aw 0.55–0.65** as the range for dry cannabis flower that protects against mould without making it brittle [1]. | Parameter | Target | Why | |---|---|---| | Air temperature | 15–21 °C (60–70 °F) | Warmer drives off volatile monoterpenes faster [3][5] | | RH | 55–62 % | Below ~50 % dries too fast; above ~65 % for days risks mould [6] | | Light | Dark | Light degrades cannabinoids | | Air | Gentle room circulation; buds must not sway | Still air grows mould; direct air case-hardens buds | | Time | 7–14 days | Under 5 days usually too fast | | End point (bud) | Small stems snap; aw ≈ 0.60–0.65; jar reads 60–65 % after 12–24 h sealed | Ready for the cure [1] | | Weight | Roughly 70–80 % of wet weight lost (cultivar and trim dependent) | A cross-check, not a target | See [humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) and [the deep drying article](https://genetixbay.com/knowledge/harvest-cure/drying.md). ## Should you wet trim or dry trim? Wet or dry trimming is **grower preference**, and both make excellent flower when the dry itself is right. That is the GenetixBay house position. - **Wet trim** (at harvest, before hanging): fan and sugar leaves are easier to cut while turgid; less leaf means a faster dry, which suits a humid room. It's stickier work and the bud dries more exposed. - **Dry trim** (after drying, before jarring): leaves left on act as a wrapper, slowing the dry, which suits a dry room. Dry sugar leaf brushes or snips off cleanly, and handling is less sticky. You lose a few trichomes as dust. > **The founder's preference.** They have trimmed hundreds of pounds and would rather brush a dry bud than scissor a wet one, even at the cost of a little trichome loss: it all gets used anyway. Choose to suit your room, then log what you did. | Your room | Lean towards | |---|---| | Humid (above ~62 % without help) | Wet trim, or at least strip all fan leaves at the chop | | Dry (below ~50 % without help) | Dry trim, leave sugar leaf on, hang whole plants | | Steady 55–62 % | Either; pick by convenience | ## How do you dry cannabis, step by step? Dry in this order, from harvest day to the jar. 1. **Set the room 24 h before harvest** to 15–21 °C and 55–62 % RH, in the dark. Confirm with your hygrometer at the height the buds will hang. 2. **Harvest at the end of a normal light period.** No darkness ritual and no flush beforehand ([when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md)). 3. **Weigh the wet harvest** in grams and log it. 4. **Remove the fan leaves** at the chop. Decide now on wet or dry trim for the sugar leaves. 5. **Hang whole plants or long branches upside down,** spaced so buds don't touch. [Whole-plant hangs](https://genetixbay.com/knowledge/glossary/whole-plant-hang.md) dry slowest and evenest; small buds on a rack dry fastest and need watching. 6. **Run gentle circulation** with a fan pointed away from the buds. Branches should not sway. 7. **Check twice a day.** Read temperature and RH, sniff for anything musty, and look into dense colas for grey fuzz or brown patches. Remove any mouldy bud with a margin and bag it out of the room ([botrytis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)). 8. **Days 4–7: start the stem snap test** on small, matchstick-thick stems. Bending means keep drying. 9. **When small stems snap** (usually days 7–14), dry-trim if you chose to, then **load a test jar ¾ full**, seal it and leave it 12–24 h. 10. **Read the jar hygrometer.** 60–65 % equilibrated RH (aw ≈ 0.60–0.65) means start the cure. Above 65–68 %: take the buds out and keep drying for 12–24 h. Below about 55 %: you've gone a little far; jar it anyway and see [curing](https://genetixbay.com/knowledge/guides/curing-step-by-step.md) for adding a fresh bud. 11. **Log the end weight,** days dried, room averages and the trim method. ## How do you judge the bud rather than the room? Judge the bud by three checks together: the [stem snap test](https://genetixbay.com/knowledge/glossary/stem-snap-test.md), an equilibrated jar reading, and weight loss. A room reading of 60 % RH tells you the air, not the inside of a dense cola. A sealed jar's RH only reflects the bud's water activity after the jar has equilibrated for 12–24 h, so aw ≈ jar RH / 100 at that point [1][2]. A dedicated water activity meter is the gold standard but optional for a home grow ([water activity test](https://genetixbay.com/knowledge/glossary/water-activity-test.md)). ## Why does a fast dry ruin buds? A fast dry ruins buds because volatile terpenes evaporate first and fastest, and the outside dries before the inside can move its water out. Monoterpenes fell sharply on air drying in early chemistry work [3], and warm drying cost terpenes in hemp trials [5]. Too fast also gives [case hardening](https://genetixbay.com/knowledge/glossary/case-hardening.md): crisp outside, wet core, which rewets the jar later. The house position: **a cure will never fix a bad dry.** A [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) means bacteria, [over-drying](https://genetixbay.com/knowledge/glossary/over-drying.md) or drying too fast, and it never truly comes out. ## What about freeze drying? Freeze drying is *Contested* and GenetixBay does not recommend it. It removes water very fast at low temperature, and some growers report good aroma, but controlled evidence on taste and curing is thin and the founder isn't sold on it ([freeze drying](https://genetixbay.com/knowledge/glossary/freeze-drying.md)). For a home grow, a slow air dry is cheaper and proven. ## How will you know it's working? You'll know your dry is working when: - The room logs stay within about 2 °C and 3–5 RH points of target, day and night. - Small stems start snapping around day 7–14, not day 3. - The room smells of the cultivar, sharper by the day, never of cut grass or must. - A sealed test jar settles at 60–65 % RH after 12–24 h and stays there. - Buds feel dry on the outside with a slight springiness inside. ## What mistakes do beginners make when drying? Beginners mostly dry too fast and too warm. - **Drying in a warm, dry room** in 3–4 days: hay smell, harsh smoke, lost terpenes. - **Pointing a fan at the buds.** Crisp outside, wet inside. - **Drying in a humid, still cupboard.** Mould in dense colas within days. - **Judging by the room's RH** instead of the bud. - **Jarring when the stems still bend,** then getting a jar at 70 %+ RH. - **Using a humidity pack** to "fix" a dry. They're a marketing gimmick that robs terpenes; see [curing](https://genetixbay.com/knowledge/guides/curing-step-by-step.md). - **Leaving the light on** in the drying space. - **Not weighing** wet and dry, so the next run has nothing to compare. ## Evidence - aw 0.55–0.65 as the safe range for dry flower: *Established* as a standard [1][2]. - Terpene losses with fast or warm drying: *Supported* [3][5]. - 15–21 °C, 55–62 % RH, 7–14 days: *Grower practice*, consistent with industry benchmarks [4]. - Mould risk in humid, still air: *Established* [6]. - Wet vs dry trim: *Grower practice*; house position is preference. - A cure never fixes a bad dry; hay smell stays: *Grower practice*, house position. - Freeze drying: *Contested*. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (D8196 water activity measurement; D8197 range). https://sn.astm.org/node/2445/printable/print 3. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 4. Cannabis Business Times. Special report: cannabis post-harvest benchmarks (grower survey; average drying ~53 % RH, ~65 °F). https://www.cannabisbusinesstimes.com/business-issues-benchmarks/cannabis-post-harvest-operations/article/15689633/post-harvest-benchmarks-with-room-to-experiment 5. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 6. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # DWC first grow, week by week > In DWC the roots hang in an aerated nutrient solution, so two things decide success: dissolved oxygen above about 6 mg/L (air running 24/7) and solution at 18–22 °C (64–72 °F). Run pH 5.6–6.0 with drift inside 5.5–6.2 allowed, EC from about 0.6–0.8 mS/cm for seedlings to 1.0–1.6 in veg and 1.4–2.0 in flower, top off as plants drink and change the solution every 7–14 days. A beneficial-microbe reservoir is the house preference; a sterile one is valid only if you commit to it. - Canonical: https://genetixbay.com/knowledge/guides/dwc-first-grow-week-by-week.html - Category: Start here · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Transition, Flower, Ripening, Harvest · Systems: DWC - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is DWC good for a first grow?** DWC can work for a first grow and grows fast, but it is the least forgiving common system: if the air pump stops or the water warms above about 24 °C (75 °F), roots can start to fail within hours. Choose it only if you can check the bucket daily, keep the solution at 18–22 °C (64–72 °F), and run a backup air pump on a safe, RCD/GFCI-protected outlet. **What temperature should a DWC reservoir be?** A DWC reservoir should be 18–22 °C (64–72 °F), with 24 °C (75 °F) as the alarm point. Warm water holds less oxygen, about 9 mg/L at 20 °C versus 8 mg/L at 25 °C, and warm, poorly aerated solution is how Pythium root rot starts. Keep the bucket off warm floors, away from the light, and use a chiller or a cooler room in summer. **How often should I change my DWC water?** Change DWC solution every 7–14 days, sooner for small buckets or big thirsty plants. Between changes, top off with plain pH-adjusted water when EC is rising, or with quarter- to half-strength nutrient when EC is falling. Each change, scrub off any slime, check roots, and refill at the stage's EC and pH 5.6–6.0, at the same temperature as the old solution. **Why does pH rise in my DWC bucket?** pH usually rises in a healthy DWC bucket because plants take up nitrate and release hydroxide or bicarbonate to stay balanced, and bubbling drives off CO₂. A steady rise of a few tenths a day is normal. Let pH ride within about 5.5–6.2 and nudge it back only when it leaves that band. A fast unexplained fall, or a rise with brown roots, points to root trouble. **Should my DWC reservoir be sterile or full of beneficial microbes?** GenetixBay prefers a beneficial-microbe reservoir, because bacteria will turn up in any reservoir whatever you do, so you may as well have the good ones. A sterile reservoir is valid only if you commit fully: continuous oxidiser or UV, clean top-ups, no organics. Never mix the two: adding hydrogen peroxide on top of beneficial microbes kills the microbes and leaves the roots unprotected. **How much air does a DWC bucket need?** A DWC bucket needs roughly 1–2 litres per minute of air per 10 litres of solution, a grower rule of thumb, delivered through an air stone on the bucket floor and running 24 hours a day. The aim is dissolved oxygen above about 6 mg/L and ideally 7–9 mg/L. Size the air pump for all your buckets plus a margin, and keep a spare pump ready. **Short answer.** In deep water culture (DWC) the roots hang in an aerated nutrient solution, so two things decide success: **dissolved oxygen above about 6 mg/L** (air running 24/7) and solution at **18–22 °C (64–72 °F)**. Run **pH 5.6–6.0**, letting it drift within 5.5–6.2. EC climbs from about **0.6–0.8 mS/cm** for seedlings to **1.0–1.6 in veg** and **1.4–2.0 in flower**. Top off as plants drink and **change the solution every 7–14 days**. If the air stops, roots can be in trouble within hours. DWC grows fast and is cheap to build, but it's the least forgiving of the common first-grow systems ([choosing a system](https://genetixbay.com/knowledge/systems/choosing-a-system.md)). The deep detail is in [DWC as a system](https://genetixbay.com/knowledge/systems/dwc.md). This guide follows one feminised photoperiod plant in one bucket. ## What do you need for a DWC grow? A DWC grow needs the basic tent kit ([choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md)) plus: - [ ] One opaque 19–25 L (5–6.5 gal) bucket per plant, with a light-tight lid that holds a 15–20 cm (6–8 in) [net pot](https://genetixbay.com/knowledge/glossary/net-pot.md) - [ ] [Clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md), rinsed until the water runs clear; a rockwool or foam starter plug - [ ] An air pump sized at roughly 1–2 L/min per 10 L of solution for every bucket plus a margin, with a check valve, airline and an [air stone](https://genetixbay.com/knowledge/glossary/air-stone.md) on the bucket floor - [ ] A **spare air pump**, and a battery-powered one if your power cuts out - [ ] A complete hydroponic nutrient (two-part [A+B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md)) and a calcium/magnesium supplement if you use [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) - [ ] pH meter, buffers, pH up and down; EC meter and calibration solution ([meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)) - [ ] A waterproof thermometer for the solution; a [chiller](https://genetixbay.com/knowledge/glossary/chiller.md) or a cool room in summer - [ ] Either a beneficial-microbe root inoculant, or a sterile-reservoir kit you'll commit to (see below) - [ ] A spare bucket for solution changes, a siphon or small pump, a scrub brush - [ ] An RCD/GFCI-protected outlet and drip loops on every cable ([electrical and water safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md)) ## What do EC, pH and water level look like, week by week? A DWC grow raises EC gently, keeps pH in a band and lowers the water as roots grow, so roots get both water and air. Weeks count from the seedling breaking the surface of the plug. | Week | Stage | Light (µmol/m²/s, hours) | EC (mS/cm) | pH band | Water level | Key jobs | |---|---|---|---|---|---|---| | 1 | Seedling in plug | 150–250, 18/6 | 0.4–0.6 | 5.8–6.0 | Touching the bottom of the net pot | Hand-water the top of the plug lightly until roots reach the water | | 2 | Seedling, roots into water | 200–300 | 0.6–0.8 | 5.6–6.0 | Same | Air on 24/7; solution 18–22 °C | | 3 | Early veg | 300–400 | 0.8–1.0 | 5.6–6.0 | Lower to 2–3 cm (1 in) below the net pot | First full solution change | | 4–5 | Veg | 400–550 | 1.0–1.4 | 5.6–6.0 | 3–5 cm (1–2 in) air gap | Start [LST](https://genetixbay.com/knowledge/guides/training-basics.md); roots check weekly | | 6 | Late veg | 500–600 | 1.2–1.6 | 5.6–6.0 | 3–5 cm gap | Flip at half the final height you can fit; DWC plants grow fast | | 7–8 | **Transition** (days 1–14 after the flip) | 600–750, 12/12 | 1.4–1.6 | 5.6–6.0 | Same | Stretch; top off daily; sex check | | 9–11 | Early flower | 700–900 | 1.4–1.8 | 5.6–6.0 | Same | RH 45–55 %; solution change every 7–10 days | | 12–14 | Mid flower | 700–900 | 1.6–2.0 | 5.6–6.0 | Same | Plants can drink 2–4 L a day | | 15–17 | Late flower, ripening | 700–900 | 1.4–1.8, taper only N if you mix salts | 5.6–6.0 | Same | RH 40–50 %; trichome checks | | 16–19 | Harvest | | Feed to the end; **no flush** | | | Harvest by trichomes | DWC plants often veg a week faster than soil, so flip earlier rather than later. The 10–14 day transition still applies: count days since flip and days of flower ([grow calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md)). ## How do you run a DWC grow, step by step? Run a DWC grow in these steps: 1. **Set up and test the bucket empty.** Fill with plain water, run the air pump for 24 h, and check for leaks, light leaks through the lid and solution temperature. It should stay 18–22 °C (64–72 °F) [1]. 2. **Mix the first solution.** Fill with water, add part A, stir, add part B, stir, add Cal-Mag if using RO, then check EC (0.4–0.6 mS/cm for a seedling) and adjust pH to 5.8–6.0 last. 3. **Plant.** Germinate into a rockwool or foam plug ([germinating seeds](https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.md)), seat it in the net pot surrounded by clay pebbles, and set the water so it just touches the bottom of the net pot. 4. **Hand-water the plug** with a few millilitres of solution once or twice a day until roots reach the water, usually 5–10 days. 5. **Run air 24 hours a day.** The air pump is life support: warm or still water favours *Pythium*, which turns roots brown and slimy [2][4]. Extension data from other hydroponic crops show growth inhibition below about 4 mg/L dissolved oxygen and failure below about 3 mg/L [3]. 6. **Lower the water as roots grow.** Once a thick mat of roots hangs in the solution, drop the level to leave a 3–5 cm (1–2 in) air gap under the net pot; the roots in that gap get extra oxygen. 7. **Check every day:** solution temperature, the air pump running, water level, pH and EC. Write them down ([grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md)). 8. **Top off between changes.** If EC is rising as the level drops, the plant is drinking more than eating: top off with plain pH-adjusted water. If EC is falling, it's eating more: top off with quarter- to half-strength solution [7]. 9. **Let pH drift within the band.** A rise of a few tenths a day is normal in a healthy bucket [6] ([pH drift](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md)). Adjust only when it leaves 5.5–6.2, by small additions. 10. **Change the solution every 7–14 days.** Siphon it out, wipe any film off the walls, inspect the roots, refill at the stage EC and pH, and match the new solution's temperature to the old one. 11. **Look at the roots weekly.** White and fuzzy is healthy; light tan from nutrients is normal; brown, slimy and smelling of swamp is root rot ([root browning](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)). Cool the water, raise aeration and act the same day ([root rot](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md)). 12. **Feed through to harvest.** If you mix single salts, taper only nitrogen over the last 2–3 weeks; otherwise keep the stage feed. Don't flush (below). 13. **Harvest by trichomes** ([when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md)), then [dry](https://genetixbay.com/knowledge/guides/drying-step-by-step.md) and [cure](https://genetixbay.com/knowledge/guides/curing-step-by-step.md). ## Should the reservoir be sterile or living? GenetixBay prefers a **beneficial-microbe reservoir** for DWC. Bacteria will turn up in any reservoir whatever you do, so you may as well have the good ones: add a beneficial root inoculant at each solution change, keep the water cool and aerated, and avoid oxidisers. A **sterile reservoir** is a valid choice, but only if you commit to it fully: a continuous oxidiser or UV treatment, clean top-up water and no organic additives. It's a personal choice; the half-way house is what fails, for example adding hydrogen peroxide on top of beneficial microbes, which kills the microbes and leaves the roots unprotected. Extension guidance on Pythium in hydroponics stresses temperature, sanitation and oxygen in both approaches [1][5]. ## Do you flush a DWC plant before harvest? No. Pre-harvest flushing is a *Myth*, and in DWC plain water starves the plant almost immediately, in the weeks when it is building most of its final weight and resin. A controlled study found no quality benefit from flushing [8]; see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). A full solution change replaces old solution in hydro; that's maintenance, not a flush. ## How will you know it's working? You'll know a DWC grow is working when roots are white and the bucket's numbers move slowly and predictably: - **Roots:** white or cream, fuzzy with root hairs, growing visibly every few days; no slime, no smell. - **Temperature:** solution 18–22 °C (64–72 °F) every day, including the warmest afternoon. - **pH:** rises slowly, a few tenths a day, and stays inside 5.5–6.2 with small corrections. - **EC:** changes by no more than about 0.2–0.3 mS/cm a day between top-offs. - **Plant:** very fast veg, often a node every 1–2 days; leaves held flat and green; no wilting while the water is full. - **Water use:** rising steadily week on week; a sudden drop in drinking is an early warning of root trouble. ## What mistakes do beginners make in DWC? DWC beginners mostly lose plants to warm water and stopped air: - **Warm reservoir in summer.** Above 24 °C (75 °F) is an alarm, not a target. - **One air pump and no spare.** A failure overnight can brown roots by morning. - **Light getting into the bucket**: algae, green roots and microbe blooms. - **Chasing pH 5.8 exactly** several times a day instead of letting it drift within band. - **Mixing sterile and living methods**: peroxide on top of beneficial microbes. - **Leaving the water too high** once roots are established, so the root crown never gets air. - **Skipping solution changes** and topping off with full-strength feed regardless of EC. - **Water and mains power together without RCD/GFCI** protection or drip loops. - **Flushing at the end.** ## Evidence - Cool solution and high dissolved oxygen protecting hydroponic roots from Pythium: *Established* in extension literature for other crops [1][2][3][5]; Pythium and Fusarium confirmed on hydroponic cannabis roots [4]. - pH drift from nitrate uptake and top-off rules by EC: *Established* hydroponic practice [6][7]. - Cannabis-specific DO and temperature targets and the 1–2 L/min per 10 L air rule: *Grower practice*. - Beneficial-microbe reservoir preference: house position; sterile is valid when fully committed. - Pre-harvest flushing: *Myth* [8]. ## Sources 1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems (68–72 °F). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 2. e-GRO Alert (Cornell / collaborators). Pythium root rot on hydroponically grown basil and spinach (cool solution 68–72 °F; DO near 8 ppm). https://www.hortidaily.com/article/6040777/pythium-root-rot-on-hydroponically-grown-basil-and-spinach 3. Cornell CEA, 2016. Leafy greens (GPN): DO ~7–8 ppm, failure below 3 ppm. https://cea.cals.cornell.edu/files/2019/06/GPNOctober2016_LeafyGreens.pdf 4. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 5. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic leafy greens and its management (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 6. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 7. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 8. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 --- # Electrical and water safety for home grows > Run every grow device from an RCD/GFCI-protected outlet (30 mA or less), add up the watts and keep continuous load under 80 % of the circuit rating (about 1,440 W on a 15 A, 120 V circuit; about 2,900 W on a 16 A, 230 V circuit), give every cable a drip loop, keep plugs above the highest water level, never daisy-chain power strips, and fit a working smoke alarm near the grow. Wear gloves and eye protection when handling pH acids and concentrates. - Canonical: https://genetixbay.com/knowledge/guides/electrical-and-water-safety.html - Category: Start here · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Do I need a GFCI or RCD for my grow tent?** Yes. Any grow with water, pumps or wet floors should run from an outlet protected by a GFCI (North America) or RCD (UK, Europe, Australia) that trips at 30 mA or less. It cuts power within a fraction of a second if current leaks to ground, through water or a person. Test it with its button monthly; a plug-in GFCI/RCD adapter works where wall outlets lack one. **How many watts can I run on one circuit?** On a 120 V circuit, a 15 A breaker supplies 1,800 W and a 20 A breaker 2,400 W, but continuous loads such as grow lights should stay under 80 %: about 1,440 W and 1,920 W. On a 230 V, 16 A circuit that is about 2,900 W continuous. Divide watts by volts to get amps, and count everything else on that circuit, not just the grow. **Is it safe to use power strips in a grow room?** A single quality power strip with its own overload protection, rated for the load and mounted off the floor, is acceptable. Never plug power strips or extension cords into each other (daisy-chaining), never run a heater or dehumidifier through a thin extension cord, and replace any strip or plug that feels warm, smells hot or shows discolouration. Heat at a plug is a fire warning. **What is a drip loop and why do I need one?** A drip loop is a downward U in a cable just before it reaches an outlet or device, so any water running along the cable drips off at the bottom of the loop instead of running into the plug. Give every cable in a grow a drip loop, and keep plugs and power strips above the highest possible water level, off the floor and away from reservoirs and saucers. **Can a grow light start a fire?** A grow light can contribute to a fire if it is overloaded on a circuit, run through damaged or undersized cords, hung with flammable material against a hot driver, or allowed to fall into water. LEDs run cooler than older lamps but their drivers still get hot. Hang lights on rated hangers, keep drivers ventilated, use the supplied cords, and fit a working smoke alarm near the grow. **What safety gear do I need for pH down and nutrients?** Wear chemical-resistant gloves and safety glasses when handling pH down (usually phosphoric or nitric acid), pH up (potassium hydroxide or carbonate), nutrient concentrates and hydrogen peroxide. Add acid to water, never water to acid. Store chemicals in their original labelled containers, away from children and pets, and rinse any splash on skin or eyes with running water for 15 minutes. **Is CO2 in a grow room dangerous?** Added CO2 can be dangerous in an enclosed room. Workplace limits are 5,000 ppm averaged over 8 hours, and NIOSH lists 30,000 ppm as a 15-minute short-term limit and 40,000 ppm as immediately dangerous. Beginners don't need CO2 enrichment at all. If you use it, fit a CO2 monitor with an alarm, ventilate before entering, and never sleep in or next to an enriched room. **Short answer.** Run every grow device from an **RCD/GFCI-protected outlet** (30 mA or less). Add up the watts and keep **continuous load under 80 %** of the circuit rating: about **1,440 W on a 15 A, 120 V** circuit and about **2,900 W on a 16 A, 230 V** circuit. Give every cable a **drip loop**, keep plugs **above the highest water level**, **never daisy-chain** power strips, and fit a **working smoke alarm** near the grow. Wear **gloves and eye protection** with pH acids and concentrates. A grow tent puts mains electricity, water, heat and fabric in one small box, often running unattended overnight. None of this is difficult, and all of it matters. Where electrical work is needed (a new circuit or outlet), use a licensed electrician; this guide covers what a grower can do safely with plug-in equipment. ## What do you need for a safe grow? A safe grow needs a short list of generic safety equipment: - [ ] An RCD/GFCI-protected outlet, or a plug-in RCD/GFCI adapter rated 30 mA or less - [ ] One quality power strip with built-in overload protection and a switch, rated for the load, mounted off the floor - [ ] Cable ties or hooks to make drip loops and keep cables off the floor - [ ] Rated rope or ratchet hangers for the light, and a tent frame that can carry its weight - [ ] A smoke alarm in or next to the grow room, tested monthly; ideally one linked to the rest of the home - [ ] A small fire extinguisher suitable for electrical fires (a class that covers energised equipment in your country) within reach of the door - [ ] A plug-in energy meter (watts and amps) to check your real load - [ ] Chemical-resistant gloves and safety glasses - [ ] Trays under pots and reservoirs, and an absorbent mat or towel for spills - [ ] A water-leak alarm on the floor (cheap insurance for hydro) - [ ] A CO₂ monitor with alarm, only if you add CO₂ ## How do you work out your electrical load? Work out your load by adding up the watts of everything on the circuit and dividing by the voltage to get amps: **amps = watts ÷ volts**. Then keep continuous loads, which run for 3 hours or more, under 80 % of the breaker or fuse rating. The 80 % rule comes from the North American electrical code for continuous loads [3] and is good practice everywhere. | Circuit | Full capacity | 80 % continuous limit | |---|---|---| | 120 V, 15 A (common in the US and Canada) | 1,800 W | **1,440 W** (12 A) | | 120 V, 20 A | 2,400 W | **1,920 W** (16 A) | | 230 V, 10 A | 2,300 W | **1,840 W** (8 A) | | 230 V, 13 A plug (UK, fused) | ~3,000 W | **~2,400 W** (10.4 A) | | 230 V, 16 A | 3,680 W | **~2,900 W** (12.8 A) | **Worked example.** A 3 x 3 ft tent with a 320 W LED, a 40 W inline fan, a 10 W clip fan, a 300 W dehumidifier and a 10 W air pump draws about **680 W**. That's 5.7 A at 120 V or 3.0 A at 230 V: comfortably inside one circuit, **as long as nothing big shares it**. Add a 1,500 W space heater on the same 15 A, 120 V circuit and you're at about 2,180 W, well over the limit. Check what else is on that circuit (other rooms' outlets often are) by switching off the breaker and seeing what goes dead. Use real numbers: a plug-in energy meter shows the actual draw, which for LEDs is usually close to the label and for heaters, dehumidifiers and air conditioners can spike at start-up. ## How do you set up a grow safely, step by step? Set up the electrics and water in this order, before any plant goes in: 1. **Find the circuit.** Identify which breaker or fuse feeds the outlet and list everything else on it. 2. **Add up the load** with the table above. If the grow plus everything else exceeds 80 %, move devices to another circuit or have an electrician add one. 3. **Get RCD/GFCI protection.** Use a protected outlet or a plug-in RCD/GFCI adapter (30 mA or less). Press its test button: the power must cut. Test monthly [1][2]. 4. **Use one power strip, not a chain.** Plug one overload-protected strip directly into the wall. Never plug strips or extension cords into each other, and never run heaters or dehumidifiers through extension cords [4][5]. 5. **Mount electrics high and dry.** Fix the strip and any controllers to the tent frame or wall, above the highest possible water level and away from reservoirs, saucers and spray. 6. **Make a drip loop on every cable.** Let each cable dip into a U below the outlet or device before rising to it, so water drips off the bottom instead of running into the plug. 7. **Hang the light properly.** Use hangers rated for at least the fixture's weight, check the tent frame isn't bowing, and keep the LED driver ventilated with nothing resting on it. 8. **Keep water low and contained.** Trays under every pot, reservoirs on the floor below any electrics, lids on buckets, and a leak alarm on the floor for hydro. 9. **Fit and test a smoke alarm** in or right outside the grow room, plus an extinguisher by the door [4]. 10. **Run the empty tent for 48 h.** After a few hours at full load, feel every plug, strip and cord: warm is a warning, hot is a fault. Replace anything discoloured or smelling of hot plastic. 11. **Unplug before you reach in with wet hands** to move a pump, fill a reservoir or touch a fixture. 12. **Check monthly:** RCD/GFCI test, cords for nicks and crushing (tent zips and pot rims damage cables), plugs for heat, smoke alarm test. ## How do you handle pH chemicals and nutrients safely? Handle pH chemicals and concentrates with gloves and safety glasses, because pH down is usually phosphoric or nitric acid and pH up is usually potassium hydroxide or carbonate, both able to burn skin and eyes [8]. The habits that matter: - **Add acid to water, never water to acid.** Dilute into the full volume of water, not the other way round. - **Keep chemicals in their original labelled containers**, capped, upright, in a tray, away from children, pets and food. - **Never mix pH up and pH down** concentrates, or nutrient part A with part B, undiluted. - **Hydrogen peroxide** above household strength and sanitisers such as bleach also need gloves and ventilation; never mix bleach with acids or ammonia-containing products, which releases toxic gas. - **Splash on skin or in eyes:** rinse with running water for at least 15 minutes and seek medical help for eyes or persistent burning. Keep the product label handy for the poison centre. See [sanitation and prevention](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) for which cleaners to use where. ## What about heat, CO₂ and fire risk? Heat, CO₂ and fire are the other three hazards in a home grow. **Heat:** a tent that runs above 30 °C (86 °F) is bad for plants and a sign the room or circuit is overworked; fix airflow or reduce light power rather than adding a cooling unit on the same circuit. **CO₂:** a beginner doesn't need CO₂ enrichment. If you add it, the 8-hour workplace limit is 5,000 ppm [6], NIOSH lists 30,000 ppm as a 15-minute limit and 40,000 ppm as immediately dangerous [7]; fit an alarmed monitor, ventilate before entering, and never sleep in or next to an enriched room ([CO₂ enrichment](https://genetixbay.com/knowledge/environment/co2-enrichment.md)). **Fire:** most home electrical fires start at overloaded outlets, damaged cords and misused extension leads [4]; the steps above address all three. ## How will you know it's working? You'll know the setup is safe when it's cool, dry, quiet and boring: - The RCD/GFCI trips when you press its test button, every month. - Measured load is under 80 % of the circuit rating, including everything else on that circuit. - No plug, strip or cord feels more than barely warm after hours at full load. - Every cable has a drip loop; nothing electrical sits on the floor or under a reservoir. - The smoke alarm sounds when tested; the leak alarm (if hydro) sounds when its probe is wetted. - Chemicals are capped, labelled and stored out of reach. ## What mistakes do beginners make with grow safety? Beginners mostly create risk by improvising: - **Daisy-chaining power strips** or running everything off one thin extension cord. - **Ignoring other loads** on the same circuit, especially space heaters and air conditioners. - **Plugs and strips on the floor** next to saucers and reservoirs. - **No RCD/GFCI** with pumps, reservoirs and wet hands in the same space. - **Reaching into a reservoir** with the pump still plugged in. - **Hanging lights from tent bars that weren't made for the weight**, or with string. - **Covering LED drivers** with reflective film or fabric. - **Removing smoke alarms** because the grow smells or is "private". - **Handling acids bare-handed** and without eye protection. - **Running CO₂ without a monitor.** ## Evidence - RCD/GFCI protection against shock in wet locations: *Established* in safety regulation and guidance [1][2][3]. - The 80 % continuous-load rule: *Established* code practice in North America [3]; good practice elsewhere. - Overloaded outlets, cords and extension leads as fire causes; smoke alarms: *Established* [4][5]. - CO₂ exposure limits: *Established* [6][7]. Chemical PPE and first aid: *Established* [8]. - Drip loops, mounting heights and grow-specific setup order: *Grower practice* built on the above. ## Sources 1. US Occupational Safety and Health Administration. Electrical safety: hazards and controls. https://www.osha.gov/electrical 2. UK Health and Safety Executive. Electrical safety and you: RCDs, overloading and inspection. https://www.hse.gov.uk/electricity/ 3. National Fire Protection Association. NFPA 70, National Electrical Code (continuous loads at 80 % of branch-circuit rating; GFCI requirements). https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70 4. US Fire Administration. Electrical fire safety (overloaded outlets, extension cords, smoke alarms). https://www.usfa.fema.gov/prevention/home-fires/prevent-fires/electrical/ 5. Electrical Safety Foundation International. Home electrical safety resources (GFCI testing, power strips, extension cords). https://www.esfi.org/ 6. OSHA. Carbon dioxide, chemical data (PEL 5,000 ppm TWA). https://www.osha.gov/chemicaldata/183 7. NIOSH Pocket Guide to Chemical Hazards: Carbon dioxide (REL 5,000 ppm TWA; ST 30,000 ppm; IDLH 40,000 ppm). https://www.cdc.gov/niosh/npg/npgd0103.html 8. NIOSH Pocket Guide to Chemical Hazards (acids, bases and oxidisers: PPE and first aid). https://www.cdc.gov/niosh/npg/ --- # Feeding basics: EC, the nitrogen taper, and why you don't flush > Feed by EC, not by the label: start at a quarter to half the label rate, about EC 0.4–0.8 mS/cm for seedlings, 1.0–1.8 in veg and 1.6–2.2 in flower in coco and hydro (lower in soil), and raise it only while leaf tips stay clean. Feed right through to harvest. Don't flush: it starves the plant while it packs on its final weight and resin. In late flower, taper only nitrogen and keep P, K, Ca, Mg, S and the micros fed. - Canonical: https://genetixbay.com/knowledge/guides/feeding-basics.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Transition, Flower, Ripening · Systems: Soil, Coco, DWC - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How strong should I feed my cannabis plants?** Measure feed strength as EC in mS/cm. Typical targets in coco and hydro are about 0.4–0.8 mS/cm for seedlings, 1.0–1.8 in veg and 1.6–2.2 in flower; in soil feed lower, around 0.8–1.6, because the mix already holds nutrients. Start at a quarter to half the label rate and raise it in steps of about 0.2 mS/cm only while leaf tips stay clean and green. **Should I flush before harvest?** No. Pre-harvest flushing is a myth, and an actively harmful one. Starving the plant for its last 1–2 weeks takes food away while it is packing on most of its final weight, trichomes and resin. Controlled studies found no gain in quality, taste or cannabinoids, and longer withdrawal tended to cut yield. Cannabis stores what it takes up in its tissue; plain water at the end doesn't wash it out. **What is a nitrogen taper?** A nitrogen taper cuts nitrogen back over the last few weeks of flower, towards zero near the finish, while keeping phosphorus, potassium, calcium, magnesium, sulfur and the micronutrients fed. It is the GenetixBay approach instead of flushing. Lower nitrogen late can raise cannabinoid and terpene percentage while lowering total yield, a trade-off. It needs single salts or per-element dosing; a bottled 2-part can't drop nitrogen alone. **When should I start feeding seedlings?** Start feeding seedlings once the first two or three sets of true leaves have formed, at about EC 0.4–0.8 mS/cm in coco or hydro. Coco and hydro need a light feed from the start because the medium carries almost no nutrients. Most quality bagged potting soils carry enough for 2–4 weeks, so give plain pH-adjusted water first and begin feeding when the lower leaves start to pale. **Do I need Cal-Mag under LED lights?** No. The idea that LED lights create a Cal-Mag need is a myth. Calcium and magnesium demand is driven mainly by the cultivar, your water source (RO or very soft water), the medium (coco's cation exchange grabs Ca and Mg) and root-zone pH. Add Cal-Mag when your water and base nutrient together supply too little, such as RO water or unbuffered coco, not because of the light. **Do bloom boosters increase yield?** No. High-phosphorus bloom boosters don't increase cannabis yield past a moderate level. Controlled trials found yield plateaus at moderate phosphorus, around 30–60 mg/L in solution, and extra P mainly ends up in the runoff. A complete base feed at the right EC for flower is all a beginner needs. Spend the money on a good pH pen and EC meter instead. **When is a flush actually useful?** The only valid flush is a root-zone flush, which washes accumulated salts out of the medium at any stage when there is a real problem: runoff EC about 1.0 mS/cm or more above input, salt crust, or spreading burnt tips and lockout. Run 2–3 times the pot volume through slowly, using plain pH-adjusted water in soil or a light EC 0.4–0.8 feed in coco, then resume normal feeding. **Short answer.** Feed by **EC**, not by the label. Start at **a quarter to half the label rate**: about **EC 0.4–0.8 mS/cm** for seedlings, **1.0–1.8** in veg and **1.6–2.2** in flower in coco and hydro, lower in soil. Raise it only while leaf tips stay clean. **Feed right through to harvest.** Don't flush: it starves the plant while it packs on its final weight and resin. In late flower, **taper only nitrogen** and keep P, K, Ca, Mg, S and the micros fed. > **House position: taper nitrogen, don't flush.** Pre-harvest flushing is a *Myth*, and an actively harmful one. Cannabis is a bioaccumulator: what it takes up is stored in tissue, and plain water in the final days doesn't "flush it out". Flushing is for toilets. Starving the plant in its most critical phase, when it is packing on most of its final weight, trichomes and resin, does far more harm than good. The GenetixBay approach is to cut nitrogen back in late flower while keeping everything else fed. The one valid flush treats the medium, not the plant: a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) for salt build-up, at any stage. Full evidence: [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## What do you need to feed properly? Feeding properly needs a complete base nutrient and two meters. Everything else is optional. - [ ] An [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) reading in mS/cm, and a 1.413 mS/cm calibration solution ([meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)) - [ ] A [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) with pH 4 and 7 buffers, plus pH up and down ([pH made simple](https://genetixbay.com/knowledge/guides/ph-made-simple.md)) - [ ] A complete base nutrient made for your medium: a [one-part](https://genetixbay.com/knowledge/glossary/one-part-nutrient.md) or [A+B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) mineral feed for coco and hydro, or a soil feed (mineral or organic) - [ ] Cal-Mag only if your water is RO or very soft, or your coco is unbuffered ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)) - [ ] Measuring syringes (1, 5 and 10 mL) and a jug or bucket marked in litres - [ ] A cup to catch [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) for EC checks ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)) - [ ] Your [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) for input EC, runoff EC and what you saw - [ ] Gloves and eye protection for concentrated nutrients and pH adjusters You don't need a cabinet of additives, and you don't need a [bloom booster](https://genetixbay.com/knowledge/glossary/bloom-booster.md). ## How do you mix and feed, step by step? Mix and feed in nine steps. The order matters: nutrients first, pH last. 1. **Start with your water.** Measure its EC. Tap water is often 0.2–0.8 mS/cm; RO is near 0. Note it; your target is the final EC of the mix. 2. **Add the base nutrient at a quarter to half the label rate.** Add each part to the water separately and stir between parts. Never mix concentrates together undiluted (A and B parts react). 3. **Add Cal-Mag first, if you need it.** On RO water or unbuffered coco, add Cal-Mag before the base so the water carries about 0.3–0.4 mS/cm of it. 4. **Measure the EC.** Compare with the stage target (table below). Add nutrient or water to adjust. 5. **Adjust pH last.** Soil 6.2–6.8; coco 5.8–6.2; hydro 5.6–6.0. Nutrients shift pH, so always adjust after mixing. 6. **Feed.** Coco and hydro: every watering. Soil: feed every second or third watering, or every watering at a lower EC, once the mix's starter charge runs out (usually after 2–4 weeks). 7. **Check runoff EC weekly.** Use the pour-through method [9]. If runoff is more than about 1.0 mS/cm above input, salts are building up. If it is far below input, the plant is hungry. 8. **Change one thing at a time.** Raise or lower EC in steps of about 0.2 mS/cm, then wait 3–5 days and judge on new growth. 9. **Feed through to harvest.** Keep the stage strength until the chop. If you mix single salts or use per-element dosing, start the nitrogen taper about 2–3 weeks before your expected harvest (below). ## What EC should you feed at each stage? Feed EC depends on the stage and the medium. These are starting ranges for a mineral feed; soil and organic feeds run lower because the mix holds nutrients. Cannabis research shows no benefit from pushing overall strength higher [3][4]. | Stage | Coco / hydro EC (mS/cm) | Soil EC (mS/cm) | ppm500 (coco) | Notes | |---|---|---|---|---| | Seedling (first true leaves) | 0.4–0.8 | Water only | 200–400 | Most bagged soils need nothing yet | | Early veg | 0.8–1.2 | 0.6–1.0 | 400–600 | Start at ¼–½ label | | Late veg | 1.2–1.8 | 0.8–1.4 | 600–900 | | | Transition / stretch | 1.4–1.8 | 1.0–1.4 | 700–900 | Hungry phase; watch new growth | | Mid flower | 1.6–2.2 | 1.2–1.6 | 800–1,100 | Peak demand | | Late flower (last 2–3 weeks) | 1.6–2.2, N tapering | 1.2–1.6 | 800–1,100 | Feed through; no flush | | Runoff EC | Within ~0.5 of input | Within ~0.5 of input | | +1.0 or more = salt build-up | Convert carefully: 1.0 mS/cm reads 500 ppm on a 500-scale meter and 700 on a 700-scale meter ([EC and ppm scales](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md)). Always talk in EC. In organic coir veg, a cannabis trial found an optimal fertiliser rate rather than "more is better" [7]. ## What is the nitrogen taper, and how do you do it? The [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) cuts nitrogen back over the last 2–3 weeks of flower, towards zero near the finish, while keeping phosphorus, potassium, calcium, magnesium, sulfur and the micronutrients fed. It is what GenetixBay does instead of flushing. Why it works: in a controlled study, lower nitrogen raised cannabinoid and terpene concentration while higher nitrogen raised total inflorescence yield [1]. It is a trade-off you set on purpose, not a reason to starve the plant. Late-flower N demand is lower anyway; the optimum N in flower was moderate in soilless trials [2]. How to do it: 1. **About 3 weeks before expected harvest**, reduce nitrogen by roughly a third. 2. **About 2 weeks out**, reduce it to about a third of normal. 3. **The last 5–7 days**, nitrogen near zero; P, K, Ca, Mg, S and micros unchanged, so EC drops only a little. A bottled 2-part can't drop nitrogen without dropping everything else. That is why the taper needs single salts or [per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md), the reason Jardin doses per element. **On bottled nutrients, simply feed the flower formula at stage strength right to the end.** Don't swap to plain water. Lower fan leaves yellowing slowly in the last 2–3 weeks is normal. ## Why don't you flush before harvest? Don't flush before harvest because it costs yield and resin and gives nothing back. Controlled trials found that pre-harvest nutrient withdrawal didn't improve flower quality, and longer withdrawal tended to cut dry mass and cannabinoid yield [5][6]. Taste and clean ash come from a healthy plant, a slow 7–14 day dry and a proper cure, not from starving it. See [drying](https://genetixbay.com/knowledge/guides/drying-step-by-step.md) and [curing](https://genetixbay.com/knowledge/guides/curing-step-by-step.md). **The one valid flush** is a root-zone flush for salt build-up, at any stage: runoff EC about 1.0 mS/cm or more above input, salt crust, or spreading burnt tips. Run 2–3 times the pot volume through slowly, using plain pH-adjusted water (pH 6.3–6.8) in soil or a light EC 0.4–0.8 feed with Ca and Mg at pH 5.8–6.0 in coco, then go straight back to normal feeding. Steps are in [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## What about Cal-Mag and bloom boosters? **Cal-Mag under LEDs is a *Myth*.** LEDs don't create a Cal-Mag need. Calcium and magnesium demand is driven mainly by the cultivar, the water source (RO vs tap), the medium (coco's [cation exchange](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md) grabs Ca and Mg) and root-zone pH [8]. Add Cal-Mag for RO or very soft water and unbuffered coco, not for the light ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)). **Bloom boosters hit a plateau.** Past moderate phosphorus, more P didn't raise yield or cannabinoids in controlled trials; it mostly ended up in the runoff [3][4]. See [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md). ## How will you know it's working? You'll know your feeding is right when the plant looks evenly green and your EC numbers stay stable: - **Leaf colour:** mid to deep green, not pale (hungry) and not glossy dark with clawing tips (too much nitrogen). - **Leaf tips:** clean. A few millimetres of tan tip on a few leaves means you're at the ceiling; back off 0.2 mS/cm. - **New growth:** even and steady, a new node every 2–4 days in veg. - **Runoff EC:** within about 0.5 mS/cm of input, week after week. - **Late flower:** lower fan leaves fade slowly from the bottom over the last 2–3 weeks, while sugar leaves and upper fans stay green. - **Reservoir (hydro):** EC falls slightly and steadily day to day, meaning the plant is drinking and eating. Deficiency pictures are in [mobile vs immobile nutrients](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md); check pH and the root zone before blaming a nutrient ([how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md)). ## What mistakes do beginners make with feeding? Beginners mostly overfeed, and then flush. - **Full label strength from week one.** Labels are often written for the maximum. - **Feeding seedlings in hot soil**, which already carries enough nutrients. - **Mixing by ppm without knowing the scale**, which is ambiguous by 40 % ([EC and ppm](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md)). - **Adjusting pH before adding nutrients.** - **Treating every yellow leaf with more food** instead of checking pH and watering first. - **Adding Cal-Mag "because LED"** on hard tap water with a complete base feed. - **Stacking bloom boosters and additives** past the P plateau. - **Flushing for the last 1–2 weeks.** It starves the plant in its most critical phase. - **Reading fading fan leaves as proof a flush "worked"** or as a reason to feed more in the last week. - **Doing a root-zone flush with plain water in coco**, which strips Ca and Mg. ## Evidence - Nitrogen trade-off between yield and cannabinoid concentration: *Supported* [1][2]. - No yield gain from high P or high overall strength: *Supported* by controlled trials [3][4]. - Pre-harvest flushing: *Myth* [5][6]; house position, stated strongly. - Optimal organic rate in coir veg: *Supported* [7]. - Cal-Mag under LED: *Myth*; Ca/Mg disorders by cultivar, water and medium: *Supported* [8]. - Runoff EC monitoring: *Established* extension method [9]. Start-low feeding and EC steps: *Grower practice*. ## Sources 1. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 2. Bevan L, Jones M, Zheng Y. 2021. Optimisation of nitrogen, phosphorus, and potassium for soilless production of Cannabis sativa in the flowering stage. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 3. Westmoreland FM, Bugbee B. 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 4. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 5. Stemeroff J. 2017. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 6. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 7. Caplan D, Dixon M, Zheng Y. 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307-1312. https://doi.org/10.21273/HORTSCI12401-17 8. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 9. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download --- # Germinating seeds step by step > Cannabis seeds germinate in 1–5 days when kept at 22–27 °C (72–81 °F) with steady moisture and air. Soak for no more than 12–24 h, then either plant directly 0.5–1 cm (¼–½ in) deep in moist mix or wait in a damp paper towel until the root is 0.5–2 cm long and plant it root down. Expect 80–95 % from fresh seed; old seed is slower and lower. - Canonical: https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the best way to germinate cannabis seeds?** The simplest reliable way is to soak seeds in room-temperature water for 12–24 hours, then plant them 0.5–1 cm (¼–½ in) deep in moist, light seedling mix at 22–27 °C (72–81 °F). Direct sowing avoids handling the delicate root. A damp paper towel in a closed dish works too if you want to see the root first; plant once the root is 0.5–2 cm long. **How long does it take for cannabis seeds to germinate?** Fresh cannabis seed usually shows a root in 1–5 days at 22–27 °C (72–81 °F), and the seedling breaks the surface 2–5 days after planting. Old or poorly stored seed can take up to 10 days. Below about 18 °C (64 °F) germination slows sharply. If a seed shows nothing after 10 days in good conditions, it is unlikely to sprout. **How deep should I plant a cannabis seed?** Plant a cannabis seed 0.5–1 cm (¼–½ in) deep, or a sprouted seed with its root pointing down in a hole of the same depth, then cover lightly without pressing the mix hard. Planting deeper than about 1.5 cm makes the seedling spend energy reaching light and raises the risk of rot before it emerges. **Should I soak seeds before planting?** A short soak helps: 12–24 hours in room-temperature water hydrates the seed and can speed germination. Don't soak longer than about 24–36 hours, because a seed sitting underwater runs short of oxygen. Seeds that sink are hydrated, but floaters can still be viable, so plant them anyway after 24 hours. **Do cannabis seeds need light to germinate?** No. Cannabis seeds germinate in the dark; they need warmth, moisture and air, not light. Turn on gentle light, about 150–250 µmol/m²/s for 18 hours a day, as soon as the seedling's hook breaks the surface. A seedling left without enough light for even a day or two stretches into a tall, weak stem. **What germination rate should I expect?** Fresh, well-stored seed from a good producer typically germinates at about 80–95 %. Seed stored cold and dry keeps viability for years, but seed kept warm or humid loses it within months to a few years. If you have old seed, test 5–10 seeds in paper towel first and plant the rest only if most of them sprout. **Short answer.** Cannabis seeds germinate in **1–5 days** at **22–27 °C (72–81 °F)** with steady moisture and air. Soak for **12–24 h at most**, then either plant directly **0.5–1 cm (¼–½ in) deep** in moist mix, or wait in a damp paper towel until the root is **0.5–2 cm** long and plant it root down. Fresh seed usually gives 80–95 %; old seed is slower and lower. No light is needed until the seedling breaks the surface. [Germination](https://genetixbay.com/knowledge/glossary/germination.md) is the step most beginners overthink. Fresh seed wants three things: warmth, water and air. This guide gives the steps; the method comparison and evidence are in [germination methods](https://genetixbay.com/knowledge/germination/germination-methods.md). ## What do you need to germinate seeds? Germination needs a warm spot and clean, simple materials. You probably own most of this already. - [ ] Seeds, stored cold and dry until the day you start ([seed viability and storage](https://genetixbay.com/knowledge/germination/seed-viability-storage.md)) - [ ] A clean glass or cup of room-temperature water (dechlorinated or RO is fine; tap left out overnight is fine) - [ ] For the [paper towel method](https://genetixbay.com/knowledge/glossary/paper-towel-method.md): plain unscented paper towels and two clean plates or a lidded food tub - [ ] Small pots (0.5–1 L) or the final pot for [autoflowers](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md), or seedling plugs or [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) cubes for hydro - [ ] Fresh, light seedling mix or potting mix with 20–30 % [perlite](https://genetixbay.com/knowledge/glossary/perlite.md); never reused or garden soil - [ ] A warm place at 22–27 °C (72–81 °F): a heat mat with a thermostat, or a warm shelf away from drafts - [ ] A thermometer to check the actual temperature at the seed - [ ] A spray bottle, clean tweezers, and labels with the cultivar and date - [ ] Optional: 3 % hydrogen peroxide (diluted to 1 % or less) for old seed, with gloves and eye protection ## How do you germinate cannabis seeds, step by step? Germinate seeds in nine steps. Steps 3 and 4 are the two methods; pick one. 1. **Prepare the pots first.** Fill small pots or the final pot with moist mix: it should hold together when squeezed but not drip. Make a hole 0.5–1 cm (¼–½ in) deep in the centre and label it. 2. **Soak the seeds for 12–24 hours.** Drop them in room-temperature water (20–25 °C / 68–77 °F) in a dark, warm place. Don't go past 24–36 hours: seeds underwater run out of oxygen. 3. **Method A, direct sow (simplest).** Plant each soaked seed in its hole, cover lightly with mix and mist the surface. Go to step 5. 4. **Method B, paper towel (if you want to see the root).** Fold a damp, not dripping, paper towel around the seeds, place it between two plates or in a lidded tub, and keep it dark at 22–27 °C. Check once or twice a day and re-dampen if it dries. Plant each seed when its root (the [radicle](https://genetixbay.com/knowledge/glossary/radicle.md)) is 0.5–2 cm long, root pointing down, handling it by the shell with tweezers. 5. **Keep it warm and moist, not wet.** Hold the mix at 22–27 °C (72–81 °F). Mist the surface if it dries; don't water the whole pot. Below about 18 °C (64 °F) germination slows sharply [1][2]. 6. **Wait in the dark, or under very low light.** Light isn't needed until emergence. Expect the seedling hook to break the surface 2–5 days after planting. 7. **Turn on gentle light as soon as it emerges.** Give about 150–250 µmol/m²/s for 18 hours a day; a DLI of about 10–14 mol/m²/day grows better roots than very low light [6]. See [lights for beginners](https://genetixbay.com/knowledge/guides/lights-for-beginners.md). 8. **Let the seedling shed its shell.** If the seed coat stays stuck on the [cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) for more than a day, mist it and wait another few hours; if still stuck, ease it off very gently with clean tweezers. 9. **Hand over to seedling care.** Water a small ring around the stem, keep RH at 65–75 %, and don't feed most bagged soils yet. See [seedling care](https://genetixbay.com/knowledge/germination/seedling-care.md) and [watering](https://genetixbay.com/knowledge/guides/watering-how-much-how-often.md). ## What numbers matter for germination? Temperature and moisture matter most; the rest is detail. The hemp optimum was about 19–30 °C, with a calculated optimum near 29.6 °C [1]; most growers aim a little lower to avoid drying the medium. | Parameter | Target | Notes | |---|---|---| | Temperature at the seed | 22–27 °C (72–81 °F) | Slow below 18 °C (64 °F); stressed above 32 °C (90 °F) | | Soak time | 12–24 h | Never more than 24–36 h | | Root length to plant (paper towel) | 0.5–2 cm (¼–¾ in) | Longer roots break and twist | | Planting depth | 0.5–1 cm (¼–½ in) | Max ~1.5 cm | | Medium moisture | Squeezes together, doesn't drip | Wet mix means rot and damping-off | | Time to root | 1–5 days (fresh), up to 10 days (old) | | | Time to emergence after planting | 2–5 days | | | Light after emergence | 150–250 µmol/m²/s, 18/6 | DLI ~10–14 mol/m²/day | | RH after emergence | 65–75 % | A vented dome helps | ## What about old or stubborn seed? Old or hard-shelled seed often benefits from a lab-style boost, but fresh seed doesn't need one. In a published protocol, germinating seeds in 1 % [hydrogen peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) gave faster, higher germination than water, with no contamination, and helped very old seed [3]. Another study found hot-water soaking worked best and peroxide or scarification largely did nothing [4], so results conflict. A safe home approach for old seed: 1. Test 5–10 seeds in paper towel first, so you know the batch's real germination rate. 2. Dampen the towel with 1 % hydrogen peroxide (one part 3 % peroxide to two parts water) instead of water. 3. Keep it at 25–27 °C (77–81 °F) and give it up to 10 days. **Safety:** peroxide above 3 % irritates skin and eyes. Wear gloves and eye protection if you dilute a stronger stock, and store it out of reach of children. ## How will you know it's working? You'll know germination is working when the root and then the seedling appear on schedule and the seedling looks short and sturdy: - **Day 1–5:** a white root tip pokes out of the seam of the seed (paper towel), or nothing visible yet (direct sow). - **Day 3–8:** a pale hook breaks the soil surface and straightens. - **Within 24 h of emergence:** two round, smooth cotyledons open and turn green. - **Day 7–10:** the first pair of serrated [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) opens. - **Stem:** short and upright, no more than about 3–5 cm (1–2 in) to the cotyledons. A tall, leaning, pale stem means too little light. - **Germination rate:** 8–9 out of 10 fresh seeds. Log it: it's useful data on the seed listing ([reading a seed listing](https://genetixbay.com/knowledge/guides/reading-a-seed-listing.md)). ## What mistakes do beginners make when germinating seeds? Most failed germinations are too wet, too cold or too deep, not bad seed. - **Soaking for days** instead of 12–24 hours. - **Sopping paper towels** that drown the seed, or dry towels that kill a sprouting root. - **Leaving paper-towel seeds too long**, so the root grows 5 cm, twists and snaps at planting. - **Planting too deep**, or pressing the mix down hard on top. - **Cold windowsills** and drafty floors below 18 °C (64 °F). - **Watering the whole pot** after planting, which starves young roots of air and invites [damping-off](https://genetixbay.com/knowledge/germination/damping-off.md) [5]. - **Reusing old mix** or garden soil, which carries the fungi that cause damping-off [5]. - **No light, or weak light, after emergence**, which gives a stretched, floppy stem. - **Touching the root** with fingers instead of handling the seed by its shell. - **Germinating more seeds than you can legally grow** ([the legal check](https://genetixbay.com/knowledge/guides/legal-check-before-you-grow.md)). ## Evidence - Germination temperature limits: *Supported* by hemp studies [1][2]. - Peroxide protocol benefits: *Supported* in a lab protocol [3] but *Contested* across studies [4]. - Damping-off prevention by sanitation and moisture control: *Established* in extension guidance [5]. - Seedling light needs (DLI ~10–14 for strong plugs): *Supported* in general horticulture [6]; cannabis targets are *Grower practice*. - Soak times, planting depth and paper-towel handling: *Grower practice*. ## Sources 1. Geneve RL, et al., 2022. Temperature limits for seed germination in industrial hemp (Cannabis sativa L.). Crops 2(4):415–427. https://doi.org/10.3390/crops2040029 2. Lisson SN, Mendham NJ, Cornish PS, 2000. Development of a hemp (Cannabis sativa L.) simulation model 1: general introduction and the effect of temperature on the pre-emergent development of hemp. Australian Journal of Experimental Agriculture 40:405–411. https://www.publish.csiro.au/AN/EA99058 3. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 4. Physical and chemical pretreatments on germination efficiency and seedling growth of Cannabis sativa. Nativa (UFMT). https://periodicoscientificos.ufmt.br/ojs/index.php/nativa/article/view/20226 5. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 6. Runkle E. The benefits of lighted plugs. Michigan State University Extension. https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs --- # Grow journal 101: what to log and why > A grow journal is a dated record of what you did and what the plant did: daily climate and watering, weekly photos, pH, EC and height, and every event (germination, transplant, topping, flip, first pistils, problems, harvest weights). Log both days since flip and days of flower. On GenetixBay, a journal tied to a GB-ID links your harvest back to the seed pack, and herm reports and results feed the open record other growers rely on. - Canonical: https://genetixbay.com/knowledge/guides/grow-journal-101.html - Category: Start here · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What should I write in a grow journal?** A grow journal should log, every day, the date, lights-on and lights-off temperature and RH, and any watering or feeding with volume, pH and EC; every week, photos from the same angle, plant height and runoff readings; and every event: germination, transplant, training, the flip, first pistils, any problem and fix, harvest, wet and dry weight, and cure notes. Always write down the seed source and batch. **Why should I keep a grow journal?** Keep a grow journal because it is the only way to learn from a grow: when a problem shows up, the log tells you what changed three to five days earlier. It also lets you repeat what worked, predict harvest dates for a cultivar, and prove what a line did. On GenetixBay, journals link harvests to seed packs and turn individual grows into open, shared evidence. **Why log both days since flip and days of flower?** Log both because the flip isn't day 1 of flower. After switching to 12/12 there is a transition of about 10–14 days before the first pistil clusters appear, and breeder flowering times usually count from those pistils. Logging the flip date and the first-pistil date shows your cultivar's real transition and makes harvest dates predictable. **How often should I take grow photos?** Take photos at least once a week from the same angle, distance and light, and also at every event: before and after training, at the flip, at first pistils, whenever something looks wrong and at harvest. Switch coloured grow lights to white or off for photos so leaf colour is true. Close-ups of a problem should show both old and new growth. **What is a GB-ID in a grow journal?** A GB-ID is GenetixBay's permanent identifier for a line, seed batch, plant, grow or harvest. Tying a journal to the GB-ID of the seed batch links the harvest, photos, problems and any herm report back to the exact seed pack, so the record never gets lost or renamed and other growers can see how that batch really performed. **Should I report a hermaphrodite in my journal?** Yes. Log any intersex flower with the date, days since flip, where on the plant it appeared, how many flowers, and the conditions that week (light leaks, heat). On GenetixBay these herm reports count towards the herm threshold: a line showing more than 2 % intersex plants in tester grows cannot join Bay Lines, the Seed Club or be featured. **Short answer.** A [grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md) is a dated record of what you did and what the plant did. Log **daily** climate and any watering or feeding (volume, pH, EC), **weekly** photos, height and runoff, and **every event**: germination, transplant, training, the flip, first pistils, problems, harvest weights and cure notes. Log both **days since flip** and **days of flower**. On GenetixBay a journal tied to a [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) links your harvest back to the seed pack. ## Why keep a grow journal at all? Keep a journal because it is the only reliable way to learn from a grow. Plants answer slowly: a change in watering or feed shows on new growth 3–5 days later, and memory blurs in that time. A dated log turns "something went wrong in week 6" into "I raised the EC on day 38 and the tips burned on day 41". It is also the base of a clean diagnosis: the [diagnosis order](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) starts with what changed. A journal is also evidence. Strain names alone are unreliable guides to what is in the pack, and genetic studies have found plants sold under one name that don't match each other [4]. A record of what a seed batch actually did, by many growers, is worth more than any description. ## What do you need to keep a journal? You need a place to write and a few instruments you already own for the grow. - [ ] A notebook, a spreadsheet or a GenetixBay journal (pick one and stick to it) - [ ] A phone or camera for photos, and a plain white or neutral light for true colour - [ ] A thermo-hygrometer with min/max memory (a logging sensor is even better) - [ ] Your pH and EC meters, calibrated ([pH made simple](https://genetixbay.com/knowledge/guides/ph-made-simple.md)) - [ ] A measuring jug and a tape measure - [ ] A kitchen scale in grams for pot weight and harvest weight - [ ] Plant labels with a short ID per plant (P1, P2…) and the seed batch ## What should you log, and how often? Log a small, fixed set of readings on a fixed rhythm. Consistency beats volume: the same five numbers every day are worth more than a long note once a fortnight. | When | What to log | Example | |---|---|---| | **Once, at the start** | Seed source, cultivar name as sold, batch or GB-ID, seed type (feminised, regular, auto), number sown, medium, pot size, light model class and wattage, tent size | "Batch GB-…; feminised photo; 3 sown; 15 L fabric pots; coco/perlite 70/30; 240 W LED; 80 x 80 cm" | | **Daily** | Date, day count (from germination; from flip after the flip), lights-on and lights-off temperature and RH (or min/max), anything you did | "Day 23. 26.1 / 21.4 °C, 62 / 70 %. Watered 1.2 L, pH 6.0, EC 1.2, runoff 15 %" | | **Each watering or feed** | Volume in, pH in, EC in, runoff %, runoff pH and EC if measured, pot weight before | "1.5 L in, pH 6.1, EC 1.4; runoff 200 mL, EC 1.9" | | **Weekly** | Photos from the same angle, height in cm, node count or canopy notes, PPFD at canopy if you can measure it, pest check result | "Week 5: 38 cm, 7 nodes, no pests on 10 leaves" | | **Events** | Germination, transplant, topping, LST start, defoliation or tucking, light changes, the flip, first pistil clusters, sex confirmed, any intersex flower, problems and the fix, harvest | "Flip: day 42. First pistils: day 12 since flip" | | **Harvest** | Date, days since flip and days of flower, trichome mix, wet weight per plant, dry weight, drying days and room averages | "Day 67 since flip / day 55 of flower; 1 clear / 7 cloudy / 2 amber; 412 g wet, 96 g dry, 11 days at 18 °C / 58 %" | | **Cure** | Jar date, equilibrated jar readings, burp schedule, smell and smoke notes at 2, 4 and 8 weeks | "Week 2: 60 %, sweet and sharp" | ## How do you start a journal, step by step? Set the journal up before the seeds go in, so day 0 is recorded too. 1. **Pick one format:** a paper notebook, a spreadsheet with the columns above, or a GenetixBay journal. 2. **Record the setup:** tent size, light and its height, fan, pot size, medium and nutrient. 3. **Record the genetics:** where the seed came from, the name as sold, the batch or GB-ID, the seed type and how many you sow. Photograph the pack. 4. **Run the empty room for 48 h** and log day and night temperature and RH. That's your baseline ([climate basics](https://genetixbay.com/knowledge/guides/climate-basics-vpd-cheat-sheet.md)). 5. **Label every plant** (P1, P2…) and keep the label with the plant all the way to the jar. 6. **Log daily** in under two minutes: climate, what you did, one line on how the plants look. The [daily five-minute check](https://genetixbay.com/knowledge/guides/daily-five-minute-check.md) is a good moment. 7. **Photograph weekly** from the same spot, under white light. 8. **At the flip, start a second day counter.** Then note the date of the first pistil clusters at the tops: that's day 1 of flower. 9. **Log every problem** as symptom, location (old or new growth), date, suspected cause, the one change you made, and the result 3–5 days later. 10. **Close the journal** with harvest, dry and cure data and a short verdict: would you grow this batch again, and what will you change? ## Why log days since flip and days of flower? Log both because the flip isn't day 1 of flower. In controlled studies the first real flowering at the top of the plant came about 8–14 days after short days began, around 13–14 days on average and up to three weeks in slow cultivars [2]. Breeder flowering times usually count from those first pistils. That's the GenetixBay house position, and journals and Jardin track both counters. Over a few runs your journal will show your cultivar's real transition and make harvest predictable ([the flip-to-flower transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md), [photoperiod grow calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md)). ## How do GenetixBay journals use your records? GenetixBay journals turn single grows into shared, open evidence. Three things matter for a beginner: - **GB-ID links the harvest to the seed pack.** Tie the journal to the seed batch's GB-ID and your photos, problems and results stay attached to that exact batch, so names and renames can't lose the record [1]. See [documenting lineage evidence](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md). - **Herm reports feed the herm threshold.** Log any intersex flower with date, days since flip, location and conditions. Hermaphroditism has real consequences for seed and progeny [3], and GenetixBay holds lines to a [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md) of 2 % in tester grows for Bay Lines, the Seed Club and featuring. See [telling sex and spotting herms](https://genetixbay.com/knowledge/guides/telling-sex-and-spotting-herms.md). - **Side-by-side records feed open research.** [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) are member-run controlled comparisons that settle grow myths with data. A clean journal with one variable changed between two plants is the seed of a trial. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## How will you know it's working? You'll know your journal is working when: - You can answer "what changed three days before this problem?" in under a minute. - Your second run of a cultivar hits harvest within a few days of the date your first run predicted. - Weekly photos show a clear story when scrolled in order. - You stop repeating the same mistake twice. ## What mistakes do beginners make with journals? Beginners mostly stop logging when things go well, or log too much and burn out. - **Logging only when there's a problem,** so there's no baseline to compare against. - **No seed source or batch recorded,** so the result can't be traced to the pack. - **Counting the flip as day 1 of flower.** - **Photos under purple light** or from a different angle each time. - **Changing several things at once** and logging them as one event. - **Writing "fed" instead of volume, pH and EC.** - **Not recording harvest weights and drying conditions,** the data that links method to result. - **Renaming a cultivar** in your notes; keep the name as sold plus the batch ID ([record-keeping and naming ethics](https://genetixbay.com/knowledge/breeding/record-keeping-naming-ethics.md)). ## Evidence - Strain names are unreliable without records: *Supported* by genetic studies [4]. - Naming and record conventions for cultivated plants: *Established* code [5]. - The 10–14 day transition after the flip: *Supported* [2]; house position. - Hermaphroditism affects seed and progeny: *Supported* [3]; GenetixBay's 2 % herm threshold is house policy. - GB-ID provenance model: GenetixBay documentation [1]. - What and how often to log: *Grower practice*. ## Sources 1. GenetixBay. GB-ID provenance model, 2026. https://genetixbay.com/how-it-works 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 3. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 4. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 5. Brickell CD, et al. (eds). 2016. International Code of Nomenclature for Cultivated Plants, 9th edition. Scripta Horticulturae 18. ISHS. https://www.ishs.org/scripta-horticulturae/international-code-nomenclature-cultivated-plants-ninth-edition --- # Legal check before you grow > Before buying anything, confirm from official sources that home cultivation is legal where you live, then check the plant limit and how it is counted, possession limits for the harvest, where plants may be kept (indoors, out of sight, locked), tenancy and building rules, rules around minors, the ban on selling, and the rules for buying and importing seed. Laws differ by country, state, province and city and change often. This guide is a dated checklist and pointer list, not legal advice. - Canonical: https://genetixbay.com/knowledge/guides/legal-check-before-you-grow.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I check if I can legally grow cannabis at home?** Check the official government source for every level that applies to you: national law, then state or province, then city or municipality, and your lease or building rules. Confirm that home cultivation is allowed, the plant limit and whether it is per person or per household, possession limits, location and security rules, and seed purchase rules. Check again before each grow, because rules change. **How many cannabis plants can I grow at home in Canada?** Under the federal Cannabis Act, adults may grow up to four cannabis plants per residence, not per person, from legal seeds or plants. Provinces can add rules, and Quebec and Manitoba prohibit home cultivation; the Supreme Court of Canada upheld Quebec's ban in 2023. Minimum age is set by province. Check the Health Canada page and your provincial rules for the current position. **Is it legal to grow cannabis at home in the United States?** Under US federal law, cannabis (marijuana) remains a controlled substance, so home cultivation is not legal federally. Many states have legalised home growing for adults or medical patients, each with its own plant limits, age, location and security rules, while some legal-sale states still ban home grows. Check your state's official cannabis regulator and city rules; federal land and federally subsidised housing have their own restrictions. **Can my landlord stop me growing cannabis?** Often, yes. Even where home growing is legal, a lease, condominium or strata bylaw, or housing-authority rule can prohibit cultivation, smoking or the alterations a grow needs, and breaking it can end a tenancy. Read your lease and building rules and ask in writing before you start. Smell, humidity and electrical load are the issues landlords usually raise. **Can I sell or give away cannabis I grow at home?** In nearly every jurisdiction that allows home growing, selling homegrown cannabis is illegal without a commercial licence, and giving it away is limited or banned. Some places allow sharing small amounts between adults with no payment; others don't. Home-grow permission is for personal use only. Check your local rules before sharing anything, and never sell. **Is it legal to buy cannabis seeds online?** Buying cannabis seeds can be legal locally while ordering them across a border is illegal, and some countries ban seed sales or possession of seed intended for growing. In Canada, for example, seeds must come from a legal source, and bringing cannabis, including seeds, across the border without authorisation is illegal. Check national, local and customs rules before ordering. **What happens if home growing is not legal where I live?** Then don't grow. GenetixBay never advises breaking the law. You can still learn: read the guides, follow member journals, and take part in GenetixBay research that doesn't involve growing, while you follow or support lawful reform. Penalties for unlicensed cultivation can be serious, and rules on seeds and equipment vary too, so check before buying anything. **Short answer.** Before you buy a tent or a seed, confirm from **official sources** that home cultivation is legal where you live. Then check **the plant limit and how it's counted**, **possession limits** for the harvest, **where plants may be kept**, **tenancy and building rules**, **rules around minors**, the **ban on selling**, and the rules for **buying and importing seed**. Laws differ by country, state, province and city and change often. This is a dated checklist and pointer list, **not legal advice**. If home growing isn't legal where you live, don't grow. > **Dated: as of 2026-10.** Every jurisdiction note below is a pointer to check, not a ruling. Always confirm with the official source before you start, and again before each new grow. ## What do you need for a legal check? You need an hour, the official sources, and your paperwork. - [ ] Your national government's official page on cannabis law - [ ] Your state, province or territory's official cannabis page or regulator - [ ] Your city or municipality's bylaws (some add zoning, smell or outdoor rules) - [ ] Your lease, tenancy agreement, or condominium, strata or homeowners' association rules - [ ] Your home insurance policy wording (some exclude grow-related claims) - [ ] A note of the date you checked and the pages you used, kept in your [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) ## What should a legal check cover? A legal check covers ten questions. Answer every one from an official source. | # | Question | Why it matters | |---|---|---| | 1 | Is [home cultivation](https://genetixbay.com/knowledge/glossary/home-grow.md) legal here, for adult use or only for registered medical patients? | Some places allow buying but not growing; some only medical ([medical vs adult-use](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md)) | | 2 | What is the [plant limit](https://genetixbay.com/knowledge/glossary/plant-count-limit.md), and is it per person or per residence? | Per-residence limits don't double for two adults ([personal cultivation limit](https://genetixbay.com/knowledge/glossary/personal-cultivation-limit.md)) | | 3 | Do seedlings, clones or vegetative plants count? | Some laws count only flowering plants; many count every plant | | 4 | What is the [possession limit](https://genetixbay.com/knowledge/glossary/possession-limit.md) at home and in public? | A legal harvest can exceed a possession limit | | 5 | Where may plants be: indoors only, out of public view, locked, a minimum distance from schools? | Visibility and security rules are common | | 6 | What is the minimum age, and are there rules about minors in the home? | Many laws require plants to be inaccessible to minors | | 7 | Can a landlord, condo or strata board prohibit growing? | Usually yes; breaking it can end a tenancy | | 8 | Is selling or giving away homegrown cannabis prohibited? | Almost always: selling needs a licence ([licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md)) | | 9 | Where may you legally buy seeds or clones, and may they be imported or mailed? | Cross-border seed shipments are often illegal even where growing is legal | | 10 | Are there extra rules on smell, extraction, electrical work or outdoor grows? | Solvent extraction is banned in many places; smell bylaws exist ([smell control](https://genetixbay.com/knowledge/guides/smell-control-basics.md)) | ## How do you do the legal check, step by step? Work from the top level of law down, and write each answer down with its source. 1. **Find your national law** on the official government site, not a seed seller's summary. 2. **Find your state, province or territory rules.** They can be stricter than national law, including an outright ban. 3. **Check your city or municipality.** Look for zoning, smell, outdoor-growing and building-permit rules. 4. **Read your lease or building rules** and, if you rent, ask the landlord in writing. 5. **Check your insurance policy** for exclusions; electrical and water damage are the usual issues ([electrical and water safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md)). 6. **Confirm how plants are counted** (per person or per residence; seedlings and clones in or out) and plan a plant count inside it. 7. **Confirm the seed route:** where seed may legally be bought, and whether ordering across a border is allowed ([reading a seed listing](https://genetixbay.com/knowledge/guides/reading-a-seed-listing.md)). 8. **Plan security:** a lockable tent or room, plants out of public view, and no access for minors. 9. **Record the date and sources** in your journal. 10. **Recheck before every grow.** Laws, limits and regulator guidance change. ## What are the rules in Canada? In Canada, the federal Cannabis Act lets adults grow up to **four plants per residence**, not per person, from seed or plants obtained legally [1][2]. Provinces and territories set the minimum age and can add rules on location and security. **Quebec and Manitoba prohibit home cultivation**; the Supreme Court of Canada upheld Quebec's ban in 2023 [3]. Bringing cannabis, including seeds, across the border without authorisation is illegal. As of 2026-10; check the Health Canada page and your province's official site to verify the current position. ## What are the rules in the United States? In the United States, cannabis (marijuana) remains a controlled substance under federal law, so home cultivation is not legal federally [4]. Federal scheduling has been under review; check the current federal status, and note that a change of schedule would not by itself make home growing legal. Many states allow adults or registered medical patients to grow at home, each with its own plant limits, age, location and security rules, and some states with legal sales still ban home grows for adult use. Use your state's official cannabis regulator or statute, then your city. Federal land, and federally subsidised housing, have their own restrictions. As of 2026-10; check official sources. ## What about other countries? Rules elsewhere vary from full prohibition to licensed home growing. These are pointers to check, as of 2026-10, not rulings: - **United Kingdom:** cultivating cannabis is an offence under the Misuse of Drugs Act 1971 without a Home Office licence [5]. Don't grow. - **Germany:** since April 2024, adults may grow a small number of plants at their residence under the KCanG, with security and youth-protection duties [6]. Check the current text. - **Australia:** the Australian Capital Territory allows limited personal cultivation by adults under territory law; other states and territories do not, and Commonwealth law still applies [7]. Check ACT and federal guidance. - **Elsewhere:** a few countries allow registered or limited home cultivation; many treat it as a criminal offence, and some have [decriminalised](https://genetixbay.com/knowledge/glossary/decriminalisation.md) possession without legalising growing. Decriminalised is not legal. Check your official national source. International drug-control treaties, such as the [1961 Single Convention](https://genetixbay.com/knowledge/glossary/single-convention-1961.md), shape national laws but don't decide what you may do at home: your national and local law does. ## How will you know you're covered? You'll know your legal check is done when: - Every one of the ten questions has a written answer and an official source. - Your planned plant count is inside the limit as it's actually counted. - Your lease or building rules, and your landlord if you rent, allow it. - Your grow space is out of public view, lockable and inaccessible to minors. - Your seed source is legal for where you live, including how it reaches you. - The check is dated in your journal, and you've set a reminder to recheck before the next grow. ## What mistakes do beginners make with the law? Beginners mostly trust a summary instead of the source. - **Relying on a seed seller, forum or video** for what's legal. - **Assuming a per-person limit** when the law sets a per-residence limit. - **Forgetting that seedlings and clones may count.** - **Assuming legal sales mean legal home growing.** Some places allow one, not the other. - **Ignoring lease, condo or strata rules.** - **Ordering seeds across a border** where import isn't allowed. - **Sharing or selling the harvest.** - **Not rechecking** after a law change. - **Treating decriminalisation as legalisation.** ## Evidence This guide summarises primary legal sources; the evidence ladder applies to facts about the law, not to horticulture. - Canada's four-plants-per-residence limit and provincial powers: primary legislation and government guidance [1][2]; Quebec ban upheld [3]. - US federal controlled-substance status: primary statute [4]; state rules vary. - UK cultivation offence: primary statute [5]. Germany's home-grow allowance: primary statute [6]. ACT cultivation: territory government guidance [7]. - All jurisdiction notes are dated 2026-10 and must be checked against the official source before acting. ## Sources 1. Government of Canada. Cannabis Act (S.C. 2018, c. 16). Justice Laws Website. https://laws-lois.justice.gc.ca/eng/acts/c-24.5/ 2. Health Canada. Cannabis laws and regulations. https://www.canada.ca/en/health-canada/services/drugs-medication/cannabis/laws-regulations.html 3. Supreme Court of Canada. Murray-Hall v. Quebec (Attorney General), 2023 SCC 10 (provincial ban on home cultivation upheld). 4. United States Code. 21 U.S.C. § 812, Schedules of controlled substances. Legal Information Institute, Cornell Law School. https://www.law.cornell.edu/uscode/text/21/812 5. United Kingdom. Misuse of Drugs Act 1971, section 6 (restriction of cultivation of cannabis plant). https://www.legislation.gov.uk/ukpga/1971/38/section/6 6. Germany. Gesetz zum Umgang mit Konsumcannabis (Konsumcannabisgesetz, KCanG), 2024. https://www.gesetze-im-internet.de/kcang/ 7. ACT Government (Australia). Cannabis: personal use and cultivation in the ACT. https://www.act.gov.au/cannabis --- # Lights for beginners: how much light, PPFD and DLI made simple > PPFD is how much usable light lands on the canopy each second (µmol/m²/s); DLI is the day's total (mol/m²/day = PPFD x hours x 0.0036). Aim for about 150–300 µmol/m²/s for seedlings (DLI 10–20), 300–600 in veg (DLI 20–40) and 600–900 in flower at 12/12 (DLI 26–39). Set height and dimming by measuring PPFD at the canopy and watching the top leaves, not by a fixed distance. - Canonical: https://genetixbay.com/knowledge/guides/lights-for-beginners.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the difference between PPFD and DLI?** PPFD (photosynthetic photon flux density) is the number of usable photons hitting a square metre of canopy each second, in µmol/m²/s. DLI (daily light integral) is the total for the whole day, in mol/m²/day. DLI = PPFD x hours of light x 0.0036. So 400 µmol/m²/s for 18 hours is a DLI of about 26, the same as about 600 for 12 hours. **How much light does a cannabis seedling need?** A cannabis seedling needs about 150–300 µmol/m²/s PPFD for 18 hours, a DLI of roughly 10–20 mol/m²/day. That is often an LED dimmed to 25–40 % at 45–60 cm (18–24 in). Too little light makes a long, leaning stem; too much makes small, pale, upward-cupped leaves. Raise the light gradually as true leaves appear. **How much light does cannabis need in flower?** In flower a beginner should aim for about 600–900 µmol/m²/s at the canopy for 12 hours, a DLI of about 26–39 mol/m²/day. Cannabis yield rose roughly linearly with light up to about 1,800 µmol/m²/s in a controlled trial, but above about 900–1,000 without added CO₂ the risk of light stress and the electricity cost climb faster than a beginner's returns. **How far should my LED be from my plants?** There is no single right distance: hang the LED where the canopy reads your target PPFD, usually 30–45 cm (12–18 in) for a mid-power LED in veg and flower and 45–60 cm (18–24 in) or dimmed for seedlings. Check the fixture's PPFD map, measure at the top leaves, and back off 10–20 % if top leaves bleach, cup upward or feel hot. **Can I use a phone app to measure PPFD?** A phone app gives only a rough PPFD estimate. Phone cameras and lux sensors are built for human vision, and converting lux to PPFD depends on the spectrum, so readings can be off by 20–40 % or more. Use one to compare spots and track changes in your own tent, not as an absolute number. A quantum (PAR) meter is the proper tool. **Should I run my lights 24 hours a day in veg?** You can. GenetixBay endorses 24/0 in veg: cannabis does not need a dark period while vegetating. 18/6 is the common default and saves 25 % of the power. If you run 24/0, lower the PPFD so the DLI stays sensible: 400 µmol/m²/s for 24 hours is already about 35 mol/m²/day. Photoperiods need 12/12 or 13/11 with a truly dark night to flower. **Why do my top leaves look bleached under my LED?** Bleached, yellow-white top leaves or bracts under an LED are usually light stress: too much PPFD for that plant, often with high leaf temperature. Raise or dim the light by 10–20 %, check leaf temperature is under about 30 °C (86 °F), and make sure roots are taking up water. Lower leaves stay green because they get less light. **Short answer.** **PPFD** is how much usable light lands on the canopy each second, in µmol/m²/s. **DLI** is the day's total, in mol/m²/day: **DLI = PPFD x hours x 0.0036**. Aim for about **150–300 µmol/m²/s for seedlings** (DLI 10–20), **300–600 in veg** (DLI 20–40) and **600–900 in flower at 12/12** (DLI 26–39). Set the height and dimmer by measuring at the canopy and watching the top leaves, not by a fixed distance. ## What do you need to set up your light? Setting up a grow light needs only a few generic tools: - [ ] A dimmable full-spectrum [LED](https://genetixbay.com/knowledge/glossary/led.md) with a published PPFD map ([choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md)) - [ ] Adjustable rope or ratchet hangers rated for the fixture's weight - [ ] A timer (mechanical or digital) or a controller - [ ] A quantum (PAR) meter, or at least a phone light app used only for comparisons - [ ] An [IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md) to check [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) - [ ] A tape measure and a notebook or [journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) - [ ] Eye protection: sunglasses rated for bright light, or simply don't look straight into the diodes ## What are PPFD and DLI, in plain words? PPFD is the light "speed" at the canopy and DLI is the "distance" the plant travels in a day. [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) counts photons from 400–700 nm ([PAR](https://genetixbay.com/knowledge/glossary/par.md)) landing on one square metre per second. [DLI](https://genetixbay.com/knowledge/glossary/dli.md) adds them up over the whole photoperiod. A plant cares about both: PPFD sets how hard leaves photosynthesise at any moment, and DLI sets how much sugar the day builds. The conversion is fixed: **DLI = PPFD x hours x 3,600 ÷ 1,000,000**, or simply PPFD x hours x 0.0036. | PPFD (µmol/m²/s) | Hours | DLI (mol/m²/day) | Where it fits | |---|---|---|---| | 200 | 18 | 13 | Seedling | | 300 | 18 | 19 | Seedling to early veg | | 450 | 18 | 29 | Veg | | 400 | 24 | 35 | Veg on 24/0 | | 600 | 12 | 26 | Early flower, gentle | | 800 | 12 | 35 | Flower | | 900 | 13 | 42 | Flower on 13/11 | | 1,000 | 12 | 43 | Strong flower, experienced growers | Watts are not light. Lux and foot-candles are weighted for human eyes, not plants ([lux](https://genetixbay.com/knowledge/glossary/lux.md), [foot-candle](https://genetixbay.com/knowledge/glossary/foot-candle.md)). Only PPFD and DLI describe what the plant gets. ## How much light does each stage need? Each stage needs more light than the last, roughly doubling from seedling to veg and again into flower. These targets are for a beginner at ambient CO₂ (~420 ppm): | Stage | PPFD (µmol/m²/s) | Photoperiod | DLI (mol/m²/day) | Typical LED setting | |---|---|---|---|---| | Seedling, clones | 150–300 | 18/6 | 10–20 | 25–40 % power, 45–60 cm (18–24 in) | | Veg | 300–600 | 18/6 to 24/0 | 20–40 | 50–75 %, 30–45 cm (12–18 in) | | Flower | 600–900 | 12/12 or 13/11 | 26–42 | 75–100 %, 30–45 cm (12–18 in) | | With CO₂ and experience | up to ~1,200 | 12/12 | up to ~52 | See [CO₂ enrichment](https://genetixbay.com/knowledge/environment/co2-enrichment.md) | The research ceiling is higher than this. In the best indoor trial, flower yield rose linearly from 120 to about 1,800 µmol/m²/s at ambient CO₂, with no change in cannabinoid concentration [1][2]. That doesn't mean a beginner should run 1,500: the plant must also have the water, nutrients, temperature and CO₂ to use it, and each extra µmol costs electricity [5]. Young plants tolerated high light well in a vegetative study [7], but seedlings and fresh transplants still do better gently. DLI for young plants follows extension guidance for other crops [4]. **Photoperiod notes (house positions).** 24/0 in veg is endorsed: cannabis needs no sleep in veg. Flower doesn't have to be exactly 12/12: 13/11 is endorsed, and some cultivars flower with 14–15 h, usually as about 12 h of full intensity plus [sunrise and sunset ramps](https://genetixbay.com/knowledge/glossary/sunrise-sunset-ramp.md). Test your cultivar. The dark period must be truly dark ([light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)). ## How do you set your light, step by step? Set the light by measurement and by the plant, in this order: 1. **Read the fixture's PPFD map.** Note the PPFD at the centre and edges at 30, 45 and 60 cm (12, 18, 24 in). Ignore "equivalent watts". 2. **Hang the light level** over the centre of the canopy, at 45–60 cm (18–24 in) for seedlings. 3. **Set the timer.** 18/6 for seedlings and veg (or 24/0); 12/12 or 13/11 for photoperiod flower; 18/6 or 20/4 for autoflowers throughout. 4. **Dim to the stage target.** Start seedlings at 25–40 % power. Measure PPFD at the top leaves at the centre, the four corners and halfway out. 5. **Work out your DLI.** Multiply the average PPFD by hours by 0.0036 and compare with the table. 6. **Raise intensity in steps.** Increase power by about 10 % every 2–3 days as the plant grows, or lower the light by 5 cm (2 in) at a time. Never jump from seedling to flower settings in one go. 7. **Check leaf temperature.** With an IR thermometer, the top leaves should read about 24–28 °C (75–82 °F) under LED; above about 30 °C (86 °F), dim or cool first [3]. 8. **Watch the top leaves for 48 h** after every change. Leaves praying slightly upward and a deep green are fine; bleached, yellow-white or upward-cupped tops mean back off 10–20 % ([heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md)). 9. **Keep the gap as plants grow.** Re-measure weekly, and daily in the 2–3 week stretch after the flip, when plants can grow 2–5 cm (1–2 in) a day. 10. **Log every change**: height, power %, PPFD and DLI. ## Does the inverse square law apply to grow lights? Only roughly. The [inverse square law](https://genetixbay.com/knowledge/glossary/inverse-square-law.md) says light from a small point source falls to a quarter when you double the distance. A large LED board or multi-bar fixture is not a point source: at 30–60 cm (12–24 in) its intensity falls more gently, and reflective tent walls return some of the light. So moving a big LED from 30 to 60 cm might cut centre PPFD by about a third to a half, not by three-quarters. The rule is still useful as a warning: small changes in height matter most when the light is close. Measure rather than calculate. ## Can you trust a phone light meter? A phone light meter is good for comparisons, not for absolute numbers. Phone sensors measure lux weighted for human vision, and the lux-to-PPFD conversion depends on the spectrum: roughly 1 µmol/m²/s per 54 lux in sunlight, but different for white LEDs and different again for red-heavy fixtures. Readings can be off by 20–40 % or more. Use a phone app to find hot and dim spots, and to check that today matches last week. Use a quantum meter (or the fixture's PPFD map) for the actual targets. ## Does spectrum matter for a beginner? Spectrum matters much less than the amount of light and the fixture's efficacy. A cannabis trial found that less blue light slightly increased yield, but that efficacy (µmol per joule) mattered more for cost [6]. UV has repeatedly failed to raise cannabinoids in controlled trials [2]. Any reputable white full-spectrum LED is fine; see [light spectrum](https://genetixbay.com/knowledge/environment/light-spectrum.md). ## How will you know it's working? You'll know the light is right when growth is compact and even, and the top leaves look healthy: - **Seedlings:** short, sturdy stems; the first node sits close to the soil; no leaning toward the light. - **Veg:** internodes of 2–5 cm (1–2 in), leaves held flat or slightly up, mid to deep green. - **Flower:** tight, even colas across the tent; no bleached tops; lower buds not much smaller than upper. - **Readings:** canopy PPFD within about 10–15 % of target at the centre and within 30 % at the edges; leaf temperature under 30 °C (86 °F). ## What mistakes do beginners make with lights? Beginners usually have too much light on seedlings and too little in flower: - **Full power on seedlings.** Dim to 25–40 % or raise the light. - **Setting height by a generic chart** instead of the fixture's map and the plant. - **Buying by watts or "equivalent".** Compare µmol/J and the PPFD map [5]. - **Ignoring the corners.** Edge plants can get half the centre's light. - **Forgetting the stretch.** Tops can hit the light within two weeks of the flip. - **Big jumps.** Raise intensity 10 % at a time. - **Light leaks in flower.** Even dim light at night can delay flowering in sensitive cultivars and reveal herm-prone genetics. - **Trusting phone-app numbers** as if they were a quantum meter. ## Evidence - Yield rising linearly with PPFD up to ~1,800 µmol/m²/s with no potency change: *Supported* by cannabis trials [1][2]. - Photosynthesis response to light and temperature: *Supported* [3]. High light tolerated in veg: *Supported*, preprint [7]. - DLI targets for young plants: *Supported*, extrapolated from other crops [4]. - Efficacy over spectrum for cost: *Supported* [5][6]. - Stage PPFD bands, LED settings, phone-meter error ranges: *Grower practice*. - 24/0 in veg and 13/11 in flower: house positions; see [photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) for the evidence. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 3. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 4. Runkle E. The benefits of lighted plugs (DLI for young plants). Michigan State University Extension. https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs 5. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 6. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://pmc.ncbi.nlm.nih.gov/articles/PMC7987162/ 7. Moher M, Llewellyn D, Jones M, Zheng Y, 2021. High light intensities can be used to grow healthy and robust cannabis plants during the vegetative stage of indoor production. Preprints 2021040417 (not peer reviewed). https://doi.org/10.20944/preprints202104.0417.v1 --- # Pest prevention for beginners: keep them out, find them early > Most indoor pest problems arrive on clones, plants, soil, pets or clothes, and are caught too late. Prevent them in this order: quarantine anything new for 10–14 days, start with clean media and a clean room, hang sticky traps and scout under leaves with a loupe every week, release predatory mites before you have a problem, and act at the first find rather than at the first damage. Don't spray buds in flower. Clones can also carry hop latent viroid, so buy seed or test cuts. - Canonical: https://genetixbay.com/knowledge/guides/pest-prevention-for-beginners.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I stop pests getting into my grow tent?** Stop pests at the door. Most arrive on clones and plants from other growers or shops, on outdoor soil, pets and clothes. Quarantine every new plant for 10–14 days in a separate space, use fresh bagged media, keep the tent zipped, don't visit your grow straight after a garden or someone else's grow, and keep houseplants out of the grow room. **How do I check my plants for pests?** Scout once a week, plant by plant: turn over 5–10 leaves from the bottom, middle and top and look at the undersides with a 30–60x loupe for stippling, webbing, eggs, moving dots and silvery scars. Check yellow sticky traps at pot and canopy level and count what is on them. Log the counts, so you see whether numbers are rising. **Should I release predatory mites before I see pests?** Yes, preventive releases of predatory mites are the most reliable biological approach for a home grow, because predators work best before pests explode. Generalist predators such as Neoseiulus californicus or Amblyseius swirskii can be released every 2–4 weeks in veg, and soil-dwelling Stratiolaelaps scimitus once per pot against fungus gnat larvae and thrips pupae. Don't combine them with broad-spectrum sprays. **Can I spray pesticide on my buds in flower?** No. Don't spray buds once flowers have formed, roughly from week 2–3 after the flip. Residues stay in the resin and in what you smoke, and wet sprays into dense buds invite bud rot. Do any soap or oil treatments in veg only, and rely on predatory mites, sticky traps, climate and removing infested leaves during flower. **Are clones a pest risk?** Yes, clones are the main way pests and diseases enter a home grow. They can carry spider mites, broad and russet mites, thrips, root aphids, powdery mildew and hop latent viroid, which has no cure and spreads on tools. Grow from seed when you can, quarantine any clone for 10–14 days, inspect it with a loupe and ask for, or pay for, an HLVd test. **How many pests is too many?** For a home grow, one confirmed spider mite colony, broad-mite damage, or root aphid is enough to act on, because these breed in days. A few fungus gnats on a trap or a single thrips is a warning to correct watering and add predators, not to spray. Act on a rising count: numbers on traps that double week on week mean the population is establishing. **Short answer.** Most indoor pests arrive on **clones, plants, outdoor soil, pets or clothes**, and are found too late. Prevent them in this order: **quarantine** anything new for **10–14 days**, start with clean media and a clean room, hang **sticky traps** and **scout under leaves with a loupe weekly**, release **predatory mites before you need them**, and act at the **first find**, not the first damage. **Don't spray buds in flower.** Clones can also carry [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), so grow from seed or test the cut. Prevention is the whole game for a beginner. Once spider mites or broad mites are established in a flowering tent, there are few good options left. This guide is the routine; the deep articles cover each pest. The approach is [IPM](https://genetixbay.com/knowledge/glossary/ipm.md): prevention, monitoring and the least-harmful control that works [4]. ## What do you need for pest prevention? Pest prevention needs cheap, generic kit used consistently: - [ ] Yellow [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) (and a blue one if you suspect thrips), 1–2 per tent at pot level and canopy level - [ ] A 30–60x [jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) or phone macro lens - [ ] A separate quarantine space: a second small tent, a spare room or a shelf far from the grow - [ ] Fresh bagged potting mix or coco (never garden soil indoors) - [ ] A spray bottle, mild detergent and a diluted disinfectant for cleaning between runs ([sanitation](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md)) - [ ] Dedicated grow clothes or an apron, and disposable gloves - [ ] Intake filter material (a fine mesh or pre-filter) on any passive or active intake - [ ] Optional: sachets or loose predatory mites from a biological supplier ([biological control](https://genetixbay.com/knowledge/glossary/biological-control.md)) ## How do you prevent pests, step by step? 1. **Clean before you start.** Empty the tent, wash walls and floor with detergent, then disinfect and let it dry. Wash pots and trays. Throw out old, used media. 2. **Start from seed if you can.** Seeds carry far fewer pests and pathogens than clones. If you take a clone, follow step 3 without exception. 3. **Quarantine every new plant for 10–14 days.** Keep it in a separate space, inspect it every 2–3 days with the loupe, under every leaf layer, and hang a sticky trap next to it. Many pests need one or two life cycles to show; spider mites can complete one in about a week in warm rooms [1]. 4. **Ask about, or pay for, an HLVd test on any clone.** [Hop latent viroid](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) has no cure, can hide without symptoms and spreads on tools and hands [8][9]. 5. **Close the doors pests use.** Keep the tent zipped. Filter intakes. Keep houseplants, cut flowers and pets out of the grow room. Don't go from the garden, or a friend's grow, straight into yours; change clothes first. 6. **Hang traps on day one.** One at pot level for fungus gnats and shore flies, one at canopy level for thrips, whiteflies and winged aphids. Replace them monthly or when 30–50 % covered [2][4]. 7. **Scout weekly, plant by plant.** Turn over 5–10 leaves from the bottom, middle and top. Look for pale stippling, webbing, eggs, moving dots, silvery scars with black specks, curled or bronzed new growth. Count insects on the traps and log the counts. 8. **Release predators preventively.** In veg, a generalist predatory mite such as [Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md), [Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md) or [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md) every 2–4 weeks, and [Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md) once per pot for fungus gnat larvae and thrips pupae [5][6][7]. Predators keep working into flower, where sprays can't. 9. **Keep the climate out of the pest zone.** Spider mites breed fastest in hot, dry rooms; keep temperature under about 28 °C (82 °F) and RH in range ([climate basics](https://genetixbay.com/knowledge/guides/climate-basics-vpd-cheat-sheet.md)) [1]. Fungus gnats need constantly wet media; let the top 2–3 cm (1 in) dry between waterings [3]. 10. **Act at the first find.** Identify the pest (see the table), remove the worst leaves into a sealed bag, add or increase predators, and in veg only, use a soap or oil treatment on the undersides of leaves if needed. Log what you did and re-scout in 3–4 days. 11. **No sprays on buds.** From about week 2–3 after the flip, nothing wet goes on flowers. Residues stay in the resin, and wet buds rot. 12. **Clean out completely between runs**, before the next plants arrive. ## Which pests should a beginner know, and how do you spot them? Learn these eight; between them they cover nearly every indoor home-grow problem. | Pest | Telltale sign | Where to look | First response | Deep article | |---|---|---|---|---| | [Spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) | Pale pin-prick stippling on leaf tops, fine webbing | Leaf undersides, mid-canopy | Predatory mites, cool and raise RH, remove leaves | [Spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md) | | [Broad and russet mites](https://genetixbay.com/knowledge/glossary/broad-mite.md) | Twisted, glossy, bronzed new growth; mites invisible without high magnification | Growing tips | Act at once; often from clones | [Broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) | | [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md) | Silvery scars with black specks | Leaf tops and undersides, traps | Cucumeris or swirskii, blue traps | [Thrips](https://genetixbay.com/knowledge/pests/thrips.md) | | [Fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) | Small dark flies over wet medium | Pot surface, low traps | Let the medium dry, Bti, S. feltiae, soil mites | [Fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md) | | [Root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md) | Slow, yellowing plants; white waxy specks on roots | Root ball, drainage holes | Isolate; often from soil or clones | [Root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md) | | [Aphids](https://genetixbay.com/knowledge/glossary/aphid.md) | Clusters on stems and new growth, sticky honeydew | New growth | Wipe, beneficials, soap in veg | [Aphids](https://genetixbay.com/knowledge/pests/aphids.md) | | [Whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) | Tiny white moths flying up when disturbed | Leaf undersides, traps | Yellow traps, predators | [Whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md) | | [Caterpillars](https://genetixbay.com/knowledge/glossary/caterpillar.md) | Chewed leaves, droppings, rotting buds | Inside buds (mainly outdoors) | Hand pick; Bt in veg | [Caterpillars](https://genetixbay.com/knowledge/pests/caterpillars.md) | ## When should you act? Act on the first confirmed find for pests that breed in days, and on a rising trend for nuisance pests. Commercial greenhouse [action thresholds](https://genetixbay.com/knowledge/glossary/action-threshold.md) are set for big crops [4]; a home tent with one to four plants has no margin, so the GenetixBay home thresholds are strict: | Find | Action threshold (home grow) | |---|---| | Spider mites, broad or russet mites, root aphids | One confirmed colony or one damaged growing tip: act today | | Thrips, whiteflies, aphids | Any on a plant, or trap counts rising week on week: add predators, remove infested leaves | | Fungus gnats | More than about 5–10 a week on a pot-level trap: dry the medium out, add Bti or nematodes | | Anything in flower | No sprays on buds; predators, traps, climate and leaf removal only | ## How will you know prevention is working? You'll know prevention is working when your weekly scouting is dull: - Sticky trap counts stay at zero to a handful per week, with no rising trend. - Leaf undersides are clean under the loupe: no stippling, eggs or webbing. - New growth is flat and normally coloured, not twisted or glossy. - Predatory mites, if released, are visible as fast-moving tan or pear-shaped mites on leaf undersides. - Quarantined plants come out clean after 10–14 days, and nothing appears in the main tent 2–3 weeks after they join it. - You reach harvest without having sprayed anything in flower. ## What mistakes do beginners make with pests? - **Bringing in an untested clone** straight into the main tent. Quarantine, inspect, test for HLVd. - **Using garden soil or reused, untreated media** indoors. - **Spraying in flower.** It damages trichomes, leaves residue and invites bud rot. - **Waiting for damage** before scouting. By the time leaves look speckled from a step back, the colony is large. - **Constantly wet pots**, which breed fungus gnats. - **Hot, dry tents**, which breed spider mites. - **Mixing predators with broad-spectrum sprays**, which kills the predators first. - **Going from the garden or a friend's grow into your tent** in the same clothes. - **One-off treatments.** Most pests need follow-ups timed to their life cycle, usually every 3–7 days for 2–3 rounds. ## Evidence - Quarantine, sanitation and scouting as the foundation of IPM: *Established* extension practice [4][9]. - Spider mite life cycle speeding up in hot, dry conditions: *Established* [1]. - Predatory mites for spider mites, thrips and fungus gnats: *Established* in greenhouse crops [5][6][7]. - Fungus gnats breeding in wet media: *Established* [3]. - HLVd spread on clones and tools: *Established* [8][9]. Russet mites arriving on plant material: *Supported* [10]. - Home-grow action thresholds: *Grower practice* (house). ## Sources 1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 2. UC IPM. Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html 3. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf 4. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects 5. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf 6. UConn IPM. Biological Control of Western Flower Thrips. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-western-flower-thrips/ 7. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ 8. Punja ZK et al., 2025. Hop latent viroid transmission, spread and longevity in cannabis; meristem tip culture. Plants 14(5):830. https://www.mdpi.com/2223-7747/14/5/830 9. Oregon State University Extension. Hop latent viroid in hemp (EM 9570). https://extension.oregonstate.edu/catalog/em-9570-hop-latent-viroid-hemp 10. Colorado State University. Hemp russet mite, Aculops cannabicola. https://agsci.colostate.edu/agbio/ipm-pests/29895-2/ --- # pH made simple > Keep the water you feed at pH 6.2–6.8 for soil, 5.8–6.2 for coco and 5.6–6.0 for hydro; the accepted wider ranges are about 6.0–7.0 for soil and 5.5–6.5 for soilless, and drift within them is normal. Calibrate your pH pen with pH 7 and pH 4 buffers at least weekly, add nutrients before you adjust, change pH in small drops, and check runoff weekly. Wear gloves and eye protection with acids. - Canonical: https://genetixbay.com/knowledge/guides/ph-made-simple.html - Category: Start here · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Soil, Coco, DWC, Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What pH should I water cannabis at?** Water cannabis at about pH 6.2–6.8 in soil, 5.8–6.2 in coco and 5.6–6.0 in hydroponics such as DWC. These sweet spots sit inside the broadly agreed ranges of about 6.0–7.0 for soil and 5.5–6.5 for soilless and hydro. Drifting a few tenths within the range is normal and fine; there's no need to chase a single exact number. **How do I adjust pH for my plants?** To adjust pH, mix your nutrients into the water first, stir, and measure. Then add pH down (usually phosphoric or nitric acid) or pH up (usually potassium hydroxide or carbonate) a few drops at a time, about 0.5–1 mL per 10 L, stirring for 30 seconds and re-measuring after each addition. Stop once you are inside the target range. Always wear gloves and eye protection. **How often should I calibrate my pH meter?** Calibrate a pH meter at least once a week, and before any session where decisions matter, using two fresh buffers that bracket your readings: pH 7 first, then pH 4. Store the glass probe wet in storage solution or pH 4 buffer, never in RO water or dry. If the meter can no longer be adjusted to the buffers, replace the probe; most last one to two years. **Why does my pH keep rising?** A pH that rises steadily, by a few tenths a day in hydro or over weeks in soil and coco, is usually normal: plants take up nitrate and release hydroxide or bicarbonate. Alkaline tap water adds to it, because bicarbonate alkalinity keeps pushing root-zone pH up. Let pH ride within the range, acidify alkaline water, and only worry about a fast unexplained fall or a rise with brown roots. **Is pH or alkalinity more important in tap water?** Alkalinity matters more than the water's pH. Tap water at pH 8 with little alkalinity is easy to correct, but water with more than about 100–150 mg/L alkalinity as CaCO3 keeps pushing the root zone's pH up for weeks after you adjust it. Get a water report from your supplier; if alkalinity is high, use more acid, blend with RO water, or use RO. **What happens if my pH is wrong?** If root-zone pH is out of range, nutrients become less available even when they are in the pot. High pH starves plants of iron, manganese, zinc, boron and phosphorus, often showing as pale new growth. Low pH reduces calcium, magnesium and molybdenum and can make iron and manganese overly available. Always check input and runoff pH before blaming a nutrient deficiency. **Short answer.** Feed water at **pH 6.2–6.8 for soil**, **5.8–6.2 for coco** and **5.6–6.0 for hydro**. The accepted wider ranges are about **6.0–7.0 for soil** and **5.5–6.5 for soilless and hydro**, and drift within them is normal. Calibrate your pH pen with **pH 7 then pH 4** buffers at least weekly, add nutrients **before** you adjust, change pH in small drops, and check runoff weekly. Wear gloves and eye protection with acids. [pH](https://genetixbay.com/knowledge/glossary/ph.md) is a measure of how acidic or alkaline a solution is, on a 0–14 [scale](https://genetixbay.com/knowledge/glossary/ph-scale.md) where 7 is neutral and each whole step is ten times stronger. For a grower it matters for one reason: root-zone pH controls how available each nutrient is [3]. These ranges are broadly agreed, so this guide doesn't hedge: get into the range, then stop fiddling. ## What do you need to manage pH? Managing pH needs a meter you trust and a way to move the number. That's it. - [ ] A digital [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) or pen with a replaceable glass probe, reading to 0.1 or 0.01 - [ ] Fresh pH 7.0 and pH 4.0 [calibration buffers](https://genetixbay.com/knowledge/glossary/calibration-solution.md) (pH 10 only if you work above 7) - [ ] Probe storage solution (or pH 4 buffer) for the cap - [ ] [pH down](https://genetixbay.com/knowledge/glossary/ph-down.md): a dilute grower's acid, usually phosphoric or nitric - [ ] [pH up](https://genetixbay.com/knowledge/glossary/ph-up.md): usually potassium hydroxide or potassium carbonate - [ ] A dropper or 1 mL syringe, a stirring rod, and a measuring jug or bucket marked in litres - [ ] Nitrile gloves and safety glasses - [ ] A small cup to catch [runoff](https://genetixbay.com/knowledge/glossary/runoff.md), and your [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) - [ ] Optional: your water supplier's water report, for alkalinity ([water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md)) ## What pH should you aim for in each medium? Aim for the sweet spot of your medium and accept anything inside the wider range. Soil buffers pH strongly, so it tolerates a higher, wider band; coco and hydro have little buffer, so they run lower and need closer checks [1][2]. | Medium | Sweet spot (feed water) | Accepted range | Check runoff | Notes | |---|---|---|---|---| | Soil / potting mix | 6.2–6.8 | 6.0–7.0 | Weekly | Organic soils self-buffer; adjust gently | | Living soil | Often unadjusted water | 6.0–7.0 | Every 2 weeks | The soil does the work ([living soil](https://genetixbay.com/knowledge/systems/living-soil.md)) | | Coco coir | 5.8–6.2 | 5.5–6.5 | Weekly | Buffer new coco ([buffering coco](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md)) | | Rockwool | 5.8–6.2 | 5.5–6.5 | Weekly | Pre-soak at pH ~5.5 | | DWC / hydro | 5.6–6.0 | 5.5–6.5 | Reservoir daily | Let it ride 5.5–6.2 ([pH drift](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md)) | ## How do you calibrate a pH meter, step by step? Calibrate a pH meter in seven steps, at least weekly and before any session where a decision depends on the number [4]. 1. **Rinse the probe** with distilled or RO water and blot gently with tissue. Don't wipe the glass bulb. 2. **Pour a little fresh buffer into a clean cup.** Never put the probe into the buffer bottle, and never pour used buffer back. 3. **Calibrate at pH 7 first.** Put the probe in, wait until the reading is steady (usually 30–60 seconds) and press calibrate. 4. **Rinse again, then calibrate at pH 4.** This [two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md) sets the slope for the acidic range you work in. 5. **Check it.** Put the probe back in pH 7: it should read 6.9–7.1. If not, repeat. 6. **Store it wet.** Cap the probe with storage solution or pH 4 buffer. Never store it dry or in RO water, which ruins the glass. 7. **Log the date.** If the meter won't adjust to the buffers or drifts during a reading, the probe is worn; most glass probes last one to two years ([meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)). ## How do you adjust pH, step by step? Adjust pH in eight steps. The rule that saves most beginners: nutrients first, pH last. 1. **Fill the jug or reservoir with water** at room temperature. 2. **Add all nutrients and supplements first**, stirring well between each. Nutrients themselves change pH, often lowering it. 3. **Measure the pH** after 30 seconds of stirring. 4. **Put on gloves and glasses** before opening the acid or base. 5. **Add pH down or up a few drops at a time.** A typical start is about 0.5–1 mL per 10 L (2.6 gal) of concentrated grower's acid; dilute products need more. Add acid to water, never water to acid. 6. **Stir for 30 seconds and re-measure.** Repeat in small steps. Overshooting and correcting back adds salts and wastes time. 7. **Stop inside the target range.** pH 6.3 in soil or 5.9 in coco is perfect; there's no prize for 6.00. 8. **Log the result**, along with the EC ([feeding basics](https://genetixbay.com/knowledge/guides/feeding-basics.md)). Next time you'll know roughly how much to add. **Safety.** Concentrated phosphoric and nitric acids and potassium hydroxide burn skin and eyes. Wear nitrile gloves and safety glasses, work over a sink, keep them in labelled, closed containers out of reach of children and pets, and never mix acids with bleach or other cleaners. If you get any in your eye, rinse with running water for 15 minutes and seek medical help. ## Why does pH drift, and when should you worry? pH drifts because plants and water change it, and a slow drift within the range is normal. When plants take up nitrate, they release hydroxide or bicarbonate to stay electrically balanced, so reservoir and root-zone pH usually rises a few tenths a day in a healthy hydro system [5]. Let it ride within 5.5–6.2 rather than chasing one number. **Alkalinity, not water pH, is what pushes the root zone up over time.** Bicarbonate in tap water acts as a buffer: water above about 100–150 mg/L alkalinity as CaCO3 keeps raising root-zone pH for weeks after you adjust the feed [1]. A tap water at pH 8 with low alkalinity is easy to fix; a pH 7.5 water with high alkalinity is not. Get your water report and see [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md). **Worry when:** - pH falls fast with no explanation, or rises with brown, slimy roots (root trouble; see [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)). - Runoff pH sits outside the accepted range for two weeks running. - New growth turns pale or yellow while the feed is complete, a classic sign of high-pH iron or manganese lockout ([yellow new growth](https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.md)). ## How do you check runoff pH? Check runoff pH weekly in soil and coco with the pour-through method, because what drains out is closer to what the roots sit in than what you poured in [6]. Water normally, wait 30 minutes to 2 hours, pour about 0.3–0.5 L of pH-adjusted water on top, catch the first 50 mL that drains, and measure. Runoff within about 0.5 of your input pH is fine; a steady trend away from it over 2–3 weeks means you need to change the feed pH or the water ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). ## How will you know it's working? You'll know your pH management is working when the readings stay boring and the new growth stays green: - **Meter:** reads 6.9–7.1 in pH 7 buffer after a week. - **Input pH:** inside your target band every time, with similar acid doses from week to week. - **Runoff pH:** within about 0.5 of input, with no trend over several weeks. - **Reservoir (hydro):** drifts up a few tenths a day and you correct it once a day or less. - **Plant:** new growth evenly green; no interveinal yellowing on top leaves; no rust spots appearing across many leaves. ## What mistakes do beginners make with pH? Beginners make pH harder than it is, mostly by trusting a meter that isn't calibrated. - **Never calibrating**, or calibrating with old, contaminated buffer. - **Storing the probe dry or in RO water.** - **Adjusting pH before adding nutrients**, then finding it has moved. - **Chasing a single exact number** and adjusting the reservoir several times a day. - **Adding too much acid at once**, overshooting, then adding base, and building up salts. - **Blaming nutrients first.** Check pH and the root zone before buying a supplement ([how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md)). - **Ignoring alkalinity** in hard tap water. - **Using test drops or strips for decisions.** They're only good to 0.5 units. - **Handling acids without gloves and glasses.** ## Evidence - Accepted pH ranges for soil and soilless media: *Established* in extension and horticultural texts [1][2][3]; house position: broadly agreed. - pH effects on nutrient availability: *Established* [3]; cannabis-specific nutrient uptake data is *Supported* [7]. - Two-point calibration and wet probe storage: *Established* [4]. - Nitrate uptake raising hydro pH; letting it drift in range: *Established* [5]. - Alkalinity as the driver of rising root-zone pH: *Established* [1]. - Pour-through runoff checks: *Established* [6]. ## Sources 1. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 2. Michigan State University Extension. pHix it! Getting substrate pH just right. https://www.canr.msu.edu/news/phix-it-getting-substrate-ph-just-right 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 4. US Geological Survey. National Field Manual for the Collection of Water-Quality Data, Chapter A6.4: pH. https://www.usgs.gov/mission-areas/water-resources/science/national-field-manual-collection-water-quality-data-nfm 5. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 6. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download 7. Velechovsky J, Malik M, Senkyrik JB, Tlustos P. 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 --- # Photoperiod grow calendar: veg, flip, the 10–14 day transition, flower > Plan a photoperiod grow in five blocks: 2 weeks of seedling, 3–6 weeks of veg at 18/6 (24/0 also works), the flip to 12/12 (13/11 also works), a 10–14 day transition before flowering really starts, then the breeder's flowering time counted from that point. So a breeder's '8 weeks' usually means harvest about 9.5–10 weeks after the flip. Log both days since flip and days of flower. - Canonical: https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Transition, Flower, Ripening, Harvest · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is the day I flip to 12/12 day 1 of flower?** No. The flip to 12/12 starts floral induction, not flowering. In controlled studies the first real pistil clusters at the top of the plant appeared about 8–14 days after short days began, around 13–14 days on average across 27 hemp cultivars. The GenetixBay house position is to count a 10–14 day transition after the flip, and log both days since flip and days of flower. **Why does my plant take longer than the breeder's flowering time?** Most runs go longer than the breeder's stated flowering time because breeders often count from the first visible pistils, or flower set, rather than from the flip. The transition after switching to 12/12 takes about 10–14 days, so a breeder's 8 weeks usually means harvest about 9.5–10 weeks after the flip. Count from the flip, add the transition, then confirm ripeness with trichomes. **How do I calculate my harvest date for a photoperiod plant?** To estimate a photoperiod harvest date, take the flip date, add 10–14 days of transition, then add the breeder's flowering time. For an 8-week cultivar flipped on 22 February, flower starts about 4–8 March and harvest falls around 26 April to 10 May. Start checking trichomes about a week before the earliest date and harvest on a mix of mostly cloudy with some amber. **How long should I veg a photoperiod plant?** Veg a photoperiod plant for about 3–6 weeks after the seedling stage on a first indoor grow, then flip when it reaches about half the final height you can fit, because plants commonly stretch 50–150 % in the 2–3 weeks after the flip. In a 120 x 120 cm (4 x 4 ft) tent with two to four plants, 4 weeks of veg is a sensible start. **Can I use 13/11 or 24/0 instead of 12/12 and 18/6?** Yes. The GenetixBay house position endorses 24/0 in veg, because cannabis doesn't need a sleep period, and 13/11 in flower: flower doesn't have to be exactly 12/12. Some cultivars flower at 14–15 h, usually as about 12 h at high intensity with sunrise and sunset ramps. One study found 13 h delayed flowering onset by about 1.5 days in one cultivar. Test your cultivar. **What happens in the first two weeks after the flip?** In the first two weeks after the flip to 12/12, the shoot tips rebuild into flower-making tissue and the plant stretches, often adding 50–150 % in height over 2–3 weeks. Visible pistil clusters at the top usually appear around day 8–14. Keep the dark period completely dark, finish training, check every plant for male flowers and keep feeding at veg-to-flower strength. **What should I track in my grow journal for flowering time?** Track two counters from the flip: days since flip (from the first 12-hour night) and days of flower (from the day you see at least three pairs of pistils at the top of the main shoot). Also note light hours, PPFD and the date trichomes reach your harvest mix. Over several grows this tells you a cultivar's true transition and flowering time. **Short answer.** Plan a photoperiod grow in five blocks: about **2 weeks of seedling**, **3–6 weeks of veg** at 18/6 (24/0 also works), the **flip** to 12/12 (13/11 also works), a **10–14 day transition** before flowering really starts, and then the breeder's flowering time counted from that point. A breeder's **"8 weeks" usually means harvest about 9.5–10 weeks after the flip.** Log both counters: days since flip and days of flower. > **House position: the flip isn't day 1 of flower.** The founder's ruling: after the switch to 12/12 there is a transition of about 10–14 days before flowering really begins, and most growers don't account for it. Breeder flowering times often count from the first visible pistils or "flower set", not from the flip, which is why runs go "longer" by about the same amount. Count from the flip and add the transition. GenetixBay journals and Jardin track both "days since flip" and "days of flower". The evidence is in [the flip-to-flower transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md). ## What do you need to run a photoperiod calendar? A photoperiod calendar needs a reliable timer, a truly dark tent and a way to log dates. The rest of the kit is in [the master guide](https://genetixbay.com/knowledge/guides/first-grow-start-to-finish.md). - [ ] A timer you trust: a digital timer or controller with a battery backup, or a mechanical timer you check weekly - [ ] A light-tight [tent](https://genetixbay.com/knowledge/glossary/tent.md) with no [light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) (check from inside, lights off, after 5 minutes for your eyes to adjust) - [ ] A dim green or low-lumen headlamp for any unavoidable dark-period checks, used for seconds, not minutes - [ ] A wall or phone calendar, plus a [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) with two columns: days since flip and days of flower - [ ] Plant ties or a trellis net, set up before the flip ([training basics](https://genetixbay.com/knowledge/guides/training-basics.md)) - [ ] A 60x loupe for trichome checks from about week 7 of flower ([when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md)) - [ ] The breeder's stated flowering time, written down with a note of how they count it if they say ## What does a photoperiod grow look like on a calendar? A photoperiod grow takes about 16–20 weeks from seed to harvest, plus drying and curing. The worked example below germinates on Monday 11 January 2027, vegs 4 weeks, flips on Monday 22 February and uses a cultivar the breeder lists as "8 weeks". Swap in your own dates. | Date (example) | Days since flip | Days of flower | Stage | Light | What to do | |---|---|---|---|---|---| | 4–10 Jan | – | – | Setup | Test run | Run the empty room 48 h; log temp and RH | | 11 Jan | – | – | Germinate | 18/6 | Seeds in, 22–26 °C (72–79 °F) | | 11–25 Jan | – | – | Seedling (2 weeks) | 18/6, 150–300 µmol/m²/s | Small waterings, gentle light | | 25 Jan–22 Feb | – | – | Veg (4 weeks) | 18/6 or 24/0, 300–600 | Pot up, start LST, top if you want | | **22 Feb** | **0** | – | **Flip** | **12/12 or 13/11** | First long night tonight. Log it | | 23 Feb–8 Mar | 1–14 | – | Transition and stretch | 12/12, ramp to 600–900 | Finish training, check sex, keep dark dark | | **≈ 6 Mar** (range 4–8 Mar) | **≈ 12** (10–14) | **1** | **Flower set** | 12/12 | ≥ 3 pistil pairs at the main top. Start the second counter | | ≈ 15 Mar | 21 | ≈ 9 | Stretch ends | 12/12 | Last tucking; RH to 45–55 % | | 15 Mar–26 Apr | 21–63 | ≈ 9–51 | Bulking flower | 12/12, 600–900 | Feed through; daily 5-minute check | | 26 Apr | 63 | ≈ 51 | Start trichome checks | 12/12 | Loupe every 2–3 days; RH 40–50 % | | **≈ 1 May** (window 26 Apr–10 May) | **≈ 68** (63–77) | **≈ 56** | **Harvest window** | 12/12 | Cut at a few clear, mostly cloudy, some amber | | ≈ 1–13 May | – | – | Dry 7–14 days | Dark | 15–21 °C (60–70 °F), 55–62 % RH | | ≈ 13 May–10 Jun+ | – | – | Cure 2–8 weeks | Dark | Slow moisture decline in jars | The "8 weeks" here became **68 days, about 9.7 weeks, after the flip**: 12 days of transition plus 56 days of flower. Slow cultivars, especially some long-flowering tropical lines, can take three weeks or more to show flower set [2]. ## How do you plan a photoperiod grow, step by step? Plan a photoperiod grow by fixing the flip date first and counting outwards from it. 1. **Pick your germination date.** Count back from when you want to harvest: seed to harvest is roughly 2 (seedling) + 3–6 (veg) + 1.5–2 (transition) + breeder weeks. 2. **Run seedlings for about 2 weeks** at 18/6 and 150–300 µmol/m²/s, until 3–4 sets of true leaves. See [germinating seeds](https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.md). 3. **Veg for 3–6 weeks** at 18/6, or 24/0 (house-endorsed: cannabis doesn't need a sleep period in veg), at 300–600 µmol/m²/s. Pot up and start training. See [training basics](https://genetixbay.com/knowledge/guides/training-basics.md). 4. **Choose the flip by height, not by date.** Flip when plants are about half the final height you can fit between pot rim and the light's safe distance, because plants commonly stretch 50–150 % in the 2–3 weeks after the flip ([stretching](https://genetixbay.com/knowledge/diagnosis/stretching.md)). In a SCROG, flip at 70–80 % net fill ([SCROG](https://genetixbay.com/knowledge/training/scrog.md)). 5. **Flip to 12/12 or 13/11 and log day 0.** The first long, unbroken night is day 0 of "days since flip". Some cultivars flower at 14–15 h of light, usually as about 12 h at high intensity plus [sunrise and sunset ramps](https://genetixbay.com/knowledge/glossary/sunrise-sunset-ramp.md); test your cultivar. 6. **Keep the dark period completely dark.** Light leaks can delay or weaken flowering in sensitive cultivars and reveal herm-prone genetics [6]. See [photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md). 7. **Watch for flower set, days 8–14.** When you can see at least three pairs of pistils at the top of the main shoot [1], log day 1 of "days of flower". 8. **Check sex during the transition.** Any male flowers or herm sacs show in this window. See [telling sex and spotting herms](https://genetixbay.com/knowledge/guides/telling-sex-and-spotting-herms.md). 9. **Calculate the harvest window.** Harvest estimate = flip date + transition (your logged days, or 10–14) + breeder flowering time. Start loupe checks a week before the earliest date. 10. **Harvest by trichomes, not the calendar.** The calendar tells you when to start looking. The plant decides. See [when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md). 11. **Record the real numbers.** Write down your actual transition days and days of flower. Next run with the same cultivar, plan with your numbers, not the breeder's. ## How do you calculate a harvest date from the breeder's flowering time? Calculate a photoperiod harvest date as **flip date + 10–14 days of transition + breeder flowering time**, then confirm with trichomes. This works because breeder times usually count from flower set, and controlled studies put flower set about 8–14 days after short days begin, averaging 13–14 days across 27 hemp cultivars [1][2]. | Breeder says | Transition | Days after flip | Weeks after flip | |---|---|---|---| | 7 weeks (49 d) | 10–14 d | 59–63 | 8.4–9.0 | | 8 weeks (56 d) | 10–14 d | 66–70 | 9.4–10.0 | | 9 weeks (63 d) | 10–14 d | 73–77 | 10.4–11.0 | | 10 weeks (70 d) | 10–14 d | 80–84 | 11.4–12.0 | | 12 weeks (84 d) | 14–21 d | 98–105 | 14.0–15.0 | If a breeder clearly states they count from the flip, skip the transition and use their figure as is. ## Does 13/11 or a longer day change the calendar? A 13/11 schedule changes the calendar very little for most cultivars and can add light. In a controlled study of two THC-dominant cultivars, 13 h days delayed flowering onset by about 1.5 days in one and not at all in the other, and the longer day raised yield [4]. Another study found that some lines yield more under 14 h, with a possible cost in THC concentration [5]. The house position: flower doesn't have to be exactly 12/12. Test your cultivar, one change at a time, and log it. ## How will you know it's working? You'll know the calendar is working when the plant hits each milestone close to plan and your two counters line up with what you see: - **Days 1–7 after the flip:** stems lengthen faster; internodes stretch; new growth looks lighter green. - **Days 8–14:** white pistil clusters form at the top of the main shoot and branch tips. This is day 1 of flower. - **Days 14–21 (stretch ending):** height gain slows; the canopy is set. The PP30,434 plant description is a good picture of a typical post-flip stretch [7]. - **Flower weeks 2–6:** buds swell week on week; leaves stay green. - **Final 2–3 weeks:** pistils darken and recede, lower leaves fade slowly, trichomes go cloudy. - **Logs:** dark period always 11–12 h (or your chosen night) with no breaks, and the timer never skipped. Inflorescence onset needs at least three consecutive short days, and interrupting short days pulls the developing flower apart [3]. If flower set is late past day 21, check the dark period first. ## What mistakes do beginners make with the photoperiod calendar? Beginners mostly lose time by counting the wrong day 1 or by breaking the night. - **Counting the flip as day 1 of flower** and harvesting 10–14 days early, with mostly clear trichomes. - **Flipping too late** in a small tent, then fighting the light with plants that doubled in height. - **Light leaks** from zips, a power LED on a fan controller, or opening the tent "just for a second". - **Timer failures**: a power cut on a cheap digital timer that resets, or a mechanical timer with a pin out. - **Switching back and forth** between 18/6 and 12/12. Returning to long days pulls the inflorescence apart and can trigger re-veg [3]. - **Trusting pistil colour** as the harvest signal instead of trichomes. - **Not writing down the real transition** for your cultivar, so every run is a guess. ## Evidence - Flower set about 8–14 days after short days, averaging 13–14 days: *Supported* by controlled studies [1][2]. - At least three consecutive short days needed; returning to long days disrupts the inflorescence: *Supported* [3]. - 13 h days with small delay and higher yield: *Supported* by one cannabis trial [4]; cultivar-dependent responses to 14 h: *Supported* [5]. - Night light delaying flowering: *Supported* (conference data) [6]. - Breeder counting from flower set, and counting a 10–14 day transition: *Grower practice*, house position. - 24/0 in veg and 13/11 in flower: house-endorsed, with the supporting data above. ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 3. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 4. Ahrens A, Llewellyn D, Zheng Y. 2024. Longer photoperiod substantially increases indoor-grown cannabis' yield and quality. Plants 13(3):433. https://doi.org/10.3390/plants13030433 5. Peterswald TJ, Mieog JC, Azman Halimi R, et al. 2023. Moving away from 12:12; the effect of different photoperiods on biomass yield and cannabinoids in medicinal cannabis. Plants 12(5):1061. https://doi.org/10.3390/plants12051061 6. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis 7. US Plant Patent PP30,434 (cannabis plant 'LW-BB1'), botanical description of post-induction stretch. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/PP30434 --- # Reading a seed listing and buying seeds wisely > Read a seed listing for what can be checked: seed type (feminised, regular or autoflower), parents and generation (F1, IBL, S1), flowering time and how it is counted, real grow journals, herm reports and lineage evidence. Distrust flower potency claims above about 35 % total cannabinoids, 'indica for sleep, sativa for energy' promises and famous names with no records. Buy small, from sellers with documented lines, and check that buying and importing seed is legal where you live. - Canonical: https://genetixbay.com/knowledge/guides/reading-a-seed-listing.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I choose seeds for my first grow?** For a first grow, choose feminised seed of a well-documented line: one with several independent grow journals, a stated parentage and generation, an honest flowering-time range, and no pattern of herm reports. Pick photoperiod for control or autoflower for speed. Ignore headline THC numbers and effect promises. Buy a small pack first, and check seed purchase and import rules where you live. **Can seeds really produce 35–40 % THC flower?** No. GenetixBay's position is that flower labelled above about 35 % total cannabinoids is not credible. Cannabinoids are made only in trichome heads and most of a bud is bract, stem and leaf; a first-principles bound gives about 30–32 % total THC at most. In 215,285 Washington lab tests the 99th percentile was 27–32 % depending on the lab. Marketing that promises 40 %+ describes a concentrate or a bad test. **Do indica and sativa labels tell me the effect?** No. Indica and sativa labels are nearly meaningless as a guide to effects or ancestry: almost everything sold today is a hybrid of one species, Cannabis sativa L. Genetic studies found the labels don't match genetic structure, and chemistry studies found they don't predict cannabinoid or terpene profiles. At most, the words describe plant shape: leaflet width, structure and flowering time. **What does flowering time on a seed listing mean?** A listed flowering time, such as 8–9 weeks, usually counts from the first visible pistil clusters, not from the flip to 12/12. The transition after the flip takes about 10–14 days, so expect harvest roughly 9.5–11 weeks after the flip. For autoflowers the listing usually gives seed-to-harvest days. Real journals from other growers are a better guide than the listing. **Should I buy feminised, regular or autoflower seeds?** Buy feminised photoperiod seeds for a first grow if you want control and the option to train and veg longer; autoflowers if you want speed in a small space and accept they punish any setback; regular seeds if you want to breed, because they give males. Feminised and auto seeds give nearly all females; regulars give about half males. **How do I spot an unreliable seed listing?** Warning signs on a seed listing are potency above 30–35 % total cannabinoids, effect promises, a famous name with no parent or generation stated, no independent grow journals, a flowering time given with no range, and 'naturally occurring bananas are normal' language. Good signs are stated parents, generation and selection, honest ranges, lab certificates from more than one lab, and herm reports published openly. **Is it legal to buy cannabis seeds online?** It depends on where you live and where the seed ships from. Buying seed can be legal locally while importing it across a border is not, and many countries ban seed sales outright. Check your national and local rules and customs rules before ordering, and see the GenetixBay legal check guide. GenetixBay never advises breaking the law. **Short answer.** Read a seed listing for what you can check: the **seed type** (feminised, regular or autoflower), the **parents and generation**, the **flowering time and how it's counted**, and evidence from **real grow journals, herm reports and documented lineage**. Distrust **flower potency above about 35 % total cannabinoids**, effect promises built on "indica" and "sativa", and famous names with no records. Buy a small pack from a seller with documented lines, and check that **buying and importing seed is legal where you live**. > **Buyer beware.** Seeds don't come with a THC number; plants grown from them do, and only after a grow and a lab test. "Our seeds hit 42 %" is a promise the plant can't keep. See [buyer beware: potency labels and other claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## What do you need before you shop? You need a few decisions made and a way to check claims. - [ ] Your [legal check](https://genetixbay.com/knowledge/guides/legal-check-before-you-grow.md) done: home growing, plant limit, and seed purchase and import rules - [ ] Your space and timeline: photoperiod (more control) or autoflower (faster) ([autoflower first grow](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md), [photoperiod calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md)) - [ ] A plant count within your legal limit; for a first run, one to four - [ ] A short list of 2–3 candidate lines, each with independent journals you have read - [ ] A place to store seeds cool, dark and dry: an airtight container in the fridge at about 5 °C (41 °F) ([seed viability and storage](https://genetixbay.com/knowledge/germination/seed-viability-storage.md)) - [ ] A [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) ready to record the pack, batch and GB-ID ## What does each part of a seed listing tell you? Each part of a listing is either checkable or marketing. Weight what you can check. | Listing field | What it really tells you | What to look for | |---|---|---| | **Seed type** | Feminised: nearly all female. Regular: about half males. Autoflower: flowers by age | Matches your plan ([seed types](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md)) | | **Parents** | The cross, if honest | Both parents named; selection or cut named; not just a famous name | | **Generation** | [F1](https://genetixbay.com/knowledge/glossary/f1.md), F2, [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md), backcross | Stated plainly; S1 on S1 is a warning sign for herm risk | | **Flowering time** | Usually counted from first pistils, not the flip | A range (e.g. 8–10 weeks), and add 10–14 days from the flip | | **Height, yield** | Grown in the breeder's room, not yours | Ranges, with conditions; treat as rough | | **THC / "potency"** | A test of one sample, if any | A range from more than one lab; nothing above ~30 % THC or ~35 % total cannabinoids | | **Terpene or flavour notes** | Descriptions | Pleasant to read; not checkable until you grow it | | **"Indica / sativa", effect claims** | Almost nothing | Treat as plant shape at most | | **Journals and reports** | How it really grew for others | Several independent grows, including problems and herm reports | | **Lineage evidence** | How well the parentage is documented | GenetixBay [L0–L4](https://genetixbay.com/knowledge/glossary/evidence-levels-l0-l4.md) and a [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) | ## Why are potency claims above 35 % not credible? Flower labelled above about 35 % total cannabinoids is not credible, and that is a GenetixBay house position. The founder credits Dr. Dedi Meiri with stating this limit at a seminar, with publication pending [3]. It holds from first principles: cannabinoids are made only in [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) [4], and most of a bud's dry mass is bract, stem and leaf. A generous estimate gives roughly 30–32 % total THC at most. A 42 % label would need about 48 % THCA in dry bud (42 / 0.877), a "bud" that is mostly loose resin heads. The data agree. Across 215,285 Washington tests, the 99th percentile was 27.0–31.8 % depending on the lab, and results varied systematically between labs [1]. Retail flower labels often overstate THC when retested [2]. Most flower people believe is mid-20s to 30s really tests mid-teens to low 20s. Growing even 30 % is a real feat. See [label inflation](https://genetixbay.com/knowledge/glossary/label-inflation.md) and [lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md). ## Do "indica" and "sativa" mean anything on a listing? As a guide to effect or species, no. That is a house position backed by evidence: nearly everything sold is a hybrid within one species, *Cannabis sativa* L. Genetic analysis found the labels don't track genetic structure [5], and commercial chemistry clusters into a few groups that the labels don't predict [6]. At most, "indica" and "sativa" describe plant shape: broad or narrow leaflets, structure and flowering time. See [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md). ## Why does the same name not mean the same plant? The same name often doesn't mean the same genetics, because names are copied, reused and attached to different cuts. Genetic testing found samples sold under one strain name that were not closely related [7]. And many "new" names are the same cut renamed, which narrows what's actually on offer ([same cut, a thousand names](https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.md)). Buy the documented line, not the name. ## How do you choose and buy seeds, step by step? Choose and buy in this order. 1. **Do the legal check** for growing, plant numbers, buying and importing seed. 2. **Decide photoperiod or autoflower** from your space and time, and **feminised or regular** from your goal (flower or breeding). 3. **Shortlist 2–3 lines** with stated parents and generation. 4. **Read at least three independent journals** for each. Note real flowering time from the flip, height, problems and any intersex flowers. 5. **Check for herm reports.** An occasional outlier happens; a pattern is poor breeding. Avoid lines with repeated reports ([telling sex and spotting herms](https://genetixbay.com/knowledge/guides/telling-sex-and-spotting-herms.md)). 6. **Check the potency claim.** Discard anything promising more than ~30 % THC or ~35 % total cannabinoids, or "guaranteed" effects. 7. **Check how flowering time is counted.** Add 10–14 days from the flip if it counts from pistils [8]. 8. **Prefer documented lineage:** a GB-ID and an evidence level of L2 or higher, published ranges and lab names ([documenting lineage evidence](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md)). 9. **Buy a small pack first,** for example 3–5 seeds, and grow it before buying more. 10. **Store unused seed** airtight, dark and cold, and log the pack, batch and purchase date. ## What separates a breeder from a pollen chucker? A breeder selects, tests and documents; a [pollen chucker](https://genetixbay.com/knowledge/glossary/pollen-chucker.md) crosses two popular plants and sells the seed untested. The difference shows on a listing: parents, generation, selection work, tester grows and published herm results versus a hype name and a headline number. Hermaphroditism has real consequences for seed and progeny [9], and the GenetixBay position is that herm-prone lines are mainly the product of bad breeding. Late-flower "bananas" are not normal: they are herms. See [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md). ## How will you know you bought well? You'll know you bought well when: - Germination is high, 80–100 % for fresh seed ([germinating seeds](https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.md)). - Plants from one pack look broadly similar in structure and timing, as the listing's generation suggests. - Flowering lands within the stated range plus the 10–14 day transition. - No intersex flowers appear under a clean, leak-free environment. - Your results match the independent journals you read before buying. ## What mistakes do beginners make buying seeds? Beginners mostly buy the headline instead of the evidence. - **Buying the highest THC number** on the page. - **Choosing by "indica for sleep, sativa for energy".** - **Buying a famous name** with no parents, generation or journals. - **Expecting harvest at the stated weeks from the flip.** - **Buying regular seed by accident** for a flower-only grow, or feminised seed when you want to breed. - **Buying large packs of an untested line.** - **Ignoring seed import rules.** - **Storing seed warm** in a drawer for years. ## Evidence - Lab-to-lab variation and the high end of real flower data: *Established* [1]. - Retail labels overstating THC: *Supported* [2]. - The ~35 % ceiling: house position (Meiri, seminar remarks; publication pending) [3], consistent with [1][2][4]. - Indica/sativa labels don't track genetics or chemistry: *Supported* [5][6]. - Strain names unreliable: *Supported* [7]. - Flowering time counted from pistils; 10–14 day transition: *Supported* [8]; house position. - Herms mainly from bad breeding: house position, interpreting [9]. ## Sources 1. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 3. Meiri D. Seminar remarks (personal attendance by the GenetixBay founder); publication pending. 4. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1). https://doi.org/10.1111/tpj.14516 5. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 6. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 7. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 8. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 9. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 --- # Smell control and odour basics: negative pressure and carbon filters > Control grow smell by keeping the tent under negative pressure (the exhaust pulls out more air than comes in, so the walls suck in slightly) and sending every bit of exhaust through an activated-carbon filter rated at or above the fan's airflow. Size the fan for about one tent air exchange per minute plus 25–50 % for filter and duct losses. Replace the carbon every 12–18 months or when smell gets through, keep RH in range, and never use an ozone generator in an occupied home. - Canonical: https://genetixbay.com/knowledge/guides/smell-control-basics.html - Category: Start here · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Veg, Flower, Ripening, Harvest, Cure · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I stop my grow tent from smelling?** Keep the tent under negative pressure and send all exhaust air through an activated-carbon filter. An inline fan pulls air from the tent through the filter and out, so the tent walls draw in slightly and any leak lets fresh air in rather than smell out. Seal unused ports, size the filter at or above the fan's airflow, and keep it running 24 hours a day in flower. **What size carbon filter and fan do I need?** Size the fan for about one full tent air exchange per minute, then add 25–50 % for the filter and ducting. A 120 x 120 x 200 cm (4 x 4 x 6.5 ft) tent holds about 2.9 m³ (102 ft³), so a fan of roughly 150–200 CFM suits it. Choose a carbon filter rated at or above the fan's CFM, so air passes slowly enough for the carbon to catch odour. **What is negative pressure in a grow tent?** Negative pressure means the exhaust removes air faster than it can come back in, so the air pressure inside the tent is slightly lower than the room. You can see it: the tent walls bow gently inwards. It means every gap, zip and port leaks clean room air in, not smelly air out, which makes the carbon filter the only exit. **How long does a carbon filter last?** A carbon filter for a home grow usually lasts about 12–18 months of continuous use, less in humid rooms or with heavy-smelling cultivars, and longer if used only in flower. Replace it when you can smell the exhaust outlet with the plants in flower. A washable pre-filter sleeve, cleaned monthly, keeps dust from clogging the carbon and extends its life. **Are ozone generators safe for smell control?** No, not in a home. Ozone is a lung irritant, and public health agencies warn that ozone generators sold as air cleaners can reach harmful levels indoors without removing odour effectively. Never run one in an occupied room, in the grow tent with plants, or where people and pets breathe the air. Use an activated-carbon filter on the exhaust instead. **Why does my house smell when I harvest and dry?** Drying releases the most smell of the whole grow, because wet buds lose water and volatile compounds fast and the drying space often has no filter. Dry inside the tent or a filtered space with the carbon filter running, at low fan speed to keep the slow 60/60-style dry. Trim and jar in that space too, and keep cured jars sealed. **Short answer.** Keep the tent under [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md), so the [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) pulls out more air than comes in and the walls bow slightly inwards, and send **all** exhaust through an activated [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) rated **at or above the fan's airflow**. Size the fan for about **one tent air exchange per minute plus 25–50 %** for filter and duct losses. Replace the carbon every **12–18 months** or when smell gets through. **Never use an ozone generator** in an occupied home [1]. Smell control is part of being a good neighbour, and in many places part of the law: some jurisdictions with legal home growing require that plants not be detectable from outside the home. Check yours in [the legal check](https://genetixbay.com/knowledge/guides/legal-check-before-you-grow.md). Flowering cannabis is loud for a reason: besides terpenes, it makes potent volatile sulphur compounds that the nose detects at tiny concentrations [2]. ## What do you need for smell control? Smell control needs one airflow path and a few generic parts: - [ ] An inline [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md), ideally with a speed controller, rated in [CFM](https://genetixbay.com/knowledge/glossary/cfm.md) or m³/h - [ ] An activated-carbon filter with a rated airflow at or above the fan's - [ ] A washable pre-filter sleeve for the carbon filter - [ ] Ducting the same diameter as the fan and filter, kept as short and straight as you can - [ ] Duct clamps or foil tape for airtight joints - [ ] Passive intake vents (the tent's low ports), screened against pests - [ ] A small oscillating fan inside for air movement (this does not replace the exhaust) - [ ] Optional: a duct silencer, and a backdraft damper on the outlet - [ ] Airtight glass jars for cured flower ## How do you size the fan and filter? Size by tent volume, then add for losses. Fans are rated at free air; a carbon filter and ducting cut real airflow by about a quarter to a half, so oversize and turn the speed down. | Tent size | Volume | 1 exchange/min | Suggested fan (with filter) | Filter rating | |---|---|---|---|---| | 60 x 60 x 160 cm (2 x 2 x 5.3 ft) | 0.58 m³ (20 ft³) | ~20 CFM | 100 mm (4 in) fan, ~100 CFM | ≥ fan CFM | | 80 x 80 x 180 cm (2.7 x 2.7 x 6 ft) | 1.15 m³ (41 ft³) | ~41 CFM | 100–125 mm (4–5 in), 100–200 CFM | ≥ fan CFM | | 120 x 120 x 200 cm (4 x 4 x 6.5 ft) | 2.88 m³ (102 ft³) | ~102 CFM | 150 mm (6 in), 150–250 CFM | ≥ fan CFM | | 150 x 150 x 200 cm (5 x 5 x 6.5 ft) | 4.5 m³ (159 ft³) | ~159 CFM | 150–200 mm (6–8 in), 250–400 CFM | ≥ fan CFM | Volume (ft³) = width × depth × height in feet; 1 m³ ≈ 35.3 ft³. A lit tent typically needs one full exchange every 1–3 minutes to remove heat and humidity ([airflow](https://genetixbay.com/knowledge/environment/airflow.md)); for smell, one per minute with a properly sized filter is the usual target. Hot LED or HPS setups need the top of that range. **Why the filter must be rated at or above the fan:** activated carbon catches odour molecules only while air is in contact with it. Push air through a too-small filter too fast and it doesn't stay long enough, and smell slips through. A filter rated above the fan, with the fan turned down, gives more contact time (*Grower practice*; consistent with how carbon adsorption works). ## How do you set up odour control, step by step? 1. **Hang the carbon filter high in the tent**, where the warmest, smelliest air collects, with the pre-filter sleeve on. 2. **Connect filter → duct → fan → duct → outlet**, in that order, so the fan pulls through the filter (the tent stays under negative pressure). Seal every joint with clamps or tape. 3. **Vent the exhaust outside the room** if you can, or at least away from doors, windows and shared air paths. 4. **Open only the low passive intakes**, sized about 1.5–2 times the exhaust duct area, and close every other port and zip. 5. **Turn the fan on and check the walls.** They should bow gently inwards. If they suck in hard and flap, open another low intake; if they're flat or bulge out, increase fan speed or close leaks. 6. **Run the exhaust 24 hours a day from about week 2 of flower**, when smell starts to build, through harvest and drying. In veg, it can follow the light. 7. **Keep RH in range** ([climate basics](https://genetixbay.com/knowledge/guides/climate-basics-vpd-cheat-sheet.md)). Above about 60–70 %, water vapour competes with odour for the carbon and shortens filter life (*Grower practice*). 8. **Wash the pre-filter monthly** with plain water and let it dry before refitting. 9. **Sniff-test the outlet weekly in flower.** If you can smell plants at the outlet, the filter is saturated or undersized. 10. **Replace the carbon** every 12–18 months of continuous use, or when the sniff test fails. 11. **Plan the dry and the trim** (see below), because harvest is when smell peaks. ## Sealed room or vented tent? A vented tent is the beginner choice: an exhaust fan and carbon filter pull air through the tent and replace it with room air. A sealed room recirculates air through air conditioning, a dehumidifier and an internal carbon "scrubber", with almost no exchange outside; it controls smell and allows CO₂ enrichment ([CO₂](https://genetixbay.com/knowledge/environment/co2-enrichment.md)), but it costs more and needs reliable cooling and dehumidification, because nothing removes heat or moisture otherwise. In a vented setup, an extra scrubber (a fan and carbon filter recirculating inside the room) can catch smell from opening the tent. ## How do you control smell at harvest, drying and curing? Harvest and drying release the most smell of the whole grow, because the plant is cut, handled and losing water and volatiles fast [3]. Plan for it: - **Dry in the tent or another filtered space**, with the carbon filter running and the fan low enough to keep the slow dry: about 15–21 °C (60–70 °F) and 55–62 % RH for 7–14 days, with no fan blowing on the buds ([drying](https://genetixbay.com/knowledge/guides/drying-step-by-step.md)). - **Trim inside the filtered space** or straight after with the door shut and the filter running. - **Jar promptly once dry.** Buds at aw 0.55–0.65 [5] in sealed glass jars release almost nothing between burps ([curing](https://genetixbay.com/knowledge/guides/curing-step-by-step.md)). - **Burp jars inside the filtered space.** - **Store sealed, cool and dark** ([long-term storage](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md)). Don't speed up drying with heat or strong fans to shorten the smelly period. A fast dry loses terpenes and gives the hay smell that never cures out. ## Are ozone generators, sprays or gels a good idea? No ozone in an occupied home. Public health guidance warns that ozone at levels that might remove odour can harm the lungs, and that ozone generators sold as air cleaners often don't remove odour well anyway [1]. Ozone also damages plants and rubber and plastic parts. Masking sprays and odour gels don't remove smell; they add a second smell on top, and they can taint buds. Used outside the grow, a neutralising gel near a door is a courtesy at best. The carbon filter is the tool that works. ## How will you know smell control is working? You'll know smell control works when nobody can tell: - Tent walls bow gently inwards with the fan running. - You can't smell flowering plants at the exhaust outlet, or outside the grow room door, in late flower. - Temperature and RH stay in range with the fan at a moderate speed, not flat out. - The pre-filter comes out grey but not clogged at its monthly wash. - Opening the tent for your [daily check](https://genetixbay.com/knowledge/guides/daily-five-minute-check.md) produces a brief whiff that fades within minutes. ## What mistakes do beginners make with smell? - **Pushing air through the filter** with the fan before it, which can leak smell out of every joint upstream. Pull through. - **A filter smaller than the fan**, run flat out. Air moves too fast to be cleaned. - **Leaving top ports open**, so smelly warm air escapes without passing the filter. - **Turning the fan off at night in flower** "to keep it warm". Smell builds and RH spikes. - **Drying in an open room** with no filter. - **Using an ozone generator** in the home. - **Never changing the carbon**, then blaming the plants. - **Masking with sprays or incense** instead of fixing the airflow. ## Evidence - Health risks of ozone generators indoors: *Established* [1]. - Volatile sulphur compounds behind strong cannabis smell: *Supported* [2]. - Volatile loss during drying: *Supported* [3]; drying and storage aw: *Established* as a standard [5]. - Humid, stagnant air raising mould risk: *Established* [4]. - Negative pressure, filter sizing, contact time and filter life: *Grower practice*. ## Sources 1. US Environmental Protection Agency. Ozone generators that are sold as air cleaners. https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners 2. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196 3. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 4. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 5. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html --- # Soil first grow, week by week > A soil first grow is the most forgiving: a quality bagged potting mix with 20–35 % perlite in an 11–19 L (3–5 gal) pot, water at pH 6.2–6.8 when the pot feels light, plain water for the first 2–4 weeks while the mix's starter charge lasts, then a dilute feed at EC 0.8–1.6 mS/cm rising through flower. A photoperiod plant runs about 17–20 weeks seed to harvest: 3 weeks seedling, 3–5 weeks veg, a 10–14 day transition and 7–10 weeks of flower. - Canonical: https://genetixbay.com/knowledge/guides/soil-first-grow-week-by-week.html - Category: Start here · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Transition, Flower, Ripening, Harvest · Systems: Soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What soil should I use for a first cannabis grow?** Use a quality bagged potting mix (peat or coco with compost) and add 20–35 % perlite or pumice for air, not garden soil, which compacts and carries pathogens. A light 'seedling' or lightly amended mix is safer than a 'hot' heavily fertilised one for young plants. Fill 11–19 L (3–5 gal) pots with drainage holes and pre-moisten the mix before planting. **When should I start feeding plants in soil?** In most bagged potting mixes, start feeding at about week 3–5 from sprout, when the mix's starter fertiliser runs out and the lower leaves begin to lighten. Begin at a quarter to half label strength, around EC 0.8–1.0 mS/cm, every second or third watering, and raise it as the plant grows. Heavily amended organic mixes may need water only for 4–6 weeks or longer. **How often do I water cannabis in soil?** Water cannabis in soil when the pot feels light and the top 2–3 cm (1 in) is dry, typically every 2–4 days in veg and every 1–3 days in late flower in an 11–19 L (3–5 gal) pot. Water slowly until about 10 % runs out of the bottom, then empty the saucer. Never water on a fixed schedule; lift the pot instead. **What pH should water be for soil?** Water and feed for soil-grown cannabis should be at about pH 6.2–6.8, within the broadly agreed soil range of 6.0–7.0. Peat-based mixes buffer pH, so a reading drifting by a few tenths within that range is normal. Check runoff pH every week or two; if runoff sits below 5.8 or above 7.2, adjust your input pH by 0.2–0.3 for the next few waterings. **Should I flush my soil plants before harvest?** No. Pre-harvest flushing is a myth that starves the plant while it packs on its final weight and resin. Keep feeding soil plants at the strength the stage needs right up to harvest. If you see salt build-up (runoff EC well above input, burnt tips), a root-zone flush to clean the medium is valid at any stage; it treats the soil, not the plant. **How long does a soil grow take week by week?** A soil photoperiod grow takes about 17–20 weeks from seed to harvest: about 3 weeks of seedling, 3–5 weeks of veg, a 10–14 day transition after the flip to 12/12, then 7–10 weeks of flower counted from the first pistil clusters. Add 1–2 weeks of drying and 2–8 weeks of curing. An autoflower in soil finishes in about 9–14 weeks from seed. **Short answer.** Soil is the most forgiving first grow. Use a quality **bagged potting mix with 20–35 % perlite** in an **11–19 L (3–5 gal)** pot. Water at **pH 6.2–6.8** when the pot feels light, to about 10 % runoff. Give **plain water for the first 2–4 weeks** while the mix's starter charge lasts, then a dilute feed at **EC 0.8–1.6 mS/cm**, rising through flower and fed right to harvest. A photoperiod plant takes about **17–20 weeks** from seed to harvest. This guide follows one feminised photoperiod plant. For autoflowers in soil, follow the [autoflower guide](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md); the mix and watering are the same, but there is no flip and no transplant. The why behind each step is in [soil as a growing system](https://genetixbay.com/knowledge/systems/soil.md). ## What do you need for a soil grow? A soil grow needs the basic tent kit ([choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md)) plus: - [ ] Quality bagged [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), lightly amended (not a "hot" mix for seedlings), about 15–20 L (4–5 gal) per plant - [ ] [Perlite](https://genetixbay.com/knowledge/glossary/perlite.md) or pumice, 20–35 % by volume if the mix isn't already airy - [ ] One 11–19 L (3–5 gal) final pot per plant with drainage, plus a 0.5–1 L (pint–quart) starter pot or cup if you are not sowing straight into the final pot - [ ] Saucers or a tray to catch runoff - [ ] A soil-suitable base nutrient (bottled mineral or organic, one-part or two-part) - [ ] pH pen with pH 4 and 7 buffers, pH up and down ([pH made simple](https://genetixbay.com/knowledge/guides/ph-made-simple.md)) - [ ] EC meter ([EC and ppm scales](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md)) - [ ] A watering can or jug with volume marks, and a measuring syringe - [ ] A kitchen or luggage scale for weighing pots (optional but excellent) - [ ] Yellow [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) for [fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ## What does a soil grow look like, week by week? A soil grow moves from plain water to a gently rising feed, with watering volume growing as roots fill the pot. Weeks count from the seedling breaking the surface. | Week | Stage | Light (µmol/m²/s, hours) | Water per 11–19 L pot | Feed EC (mS/cm) | Key jobs | |---|---|---|---|---|---| | 1 | Seedling | 150–250, 18/6 | 50–100 mL ring around the stem every 1–3 days | Water only, pH 6.2–6.8 | Keep the top moist, not wet | | 2 | Seedling | 200–300, 18/6 | 100–250 mL | Water only | Second and third sets of true leaves | | 3 | Early veg | 300–400, 18/6 | 0.25–0.5 L | Water only in most mixes | Pot up from a cup into the final pot if needed | | 4 | Veg | 350–450 | 0.5–1 L | 0.8–1.0 if lower leaves pale | Start [LST](https://genetixbay.com/knowledge/guides/training-basics.md) | | 5 | Veg | 400–500 | 1–2 L | 1.0–1.2 | Top once if you want (photoperiods only) | | 6–7 | Late veg | 450–600 | 1.5–3 L | 1.2–1.4 | Fill the canopy; flip at half the final height you can fit | | 8–9 | **Transition** (days 1–14 after the flip) | 600–700, 12/12 | 2–3 L | 1.2–1.4 | Stretch; tie down; check for male flowers | | 10–12 | Early flower | 700–900, 12/12 | 2–4 L | 1.4–1.6 | Lower RH to 45–55 %; tuck leaves, don't strip | | 13–15 | Mid flower | 700–900 | 3–5 L, may need water every 1–2 days | 1.4–1.8 | Weekly pest check; support colas | | 16–18 | Late flower and ripening | 700–900 | 3–5 L | 1.2–1.6, taper only N if you mix salts | RH 40–50 %; check trichomes from week 15 | | 17–20 | Harvest | | | Feed to the end; **no flush** | Harvest by trichomes, then dry | Water volumes assume an LED tent at the climate targets; heat and big plants drink more. The 10–14 day transition after the flip is real: the first pistil clusters appeared about 13–14 days after short days on average in a 27-cultivar study [5]. Count both days since flip and days of flower ([grow calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md)). ## How do you run a soil grow, step by step? Run a soil grow in these steps; each one has a sibling guide for detail. 1. **Mix and fill.** Blend the potting mix with 20–35 % perlite if it feels dense. Fill the pot to 2–3 cm (1 in) below the rim. Never use garden soil in pots: it compacts and carries damping-off pathogens [1][3]. 2. **Pre-moisten.** Water the filled pot with pH 6.2–6.8 water until it drips, then let it drain for a day. Weigh it: that's your "wet" weight. 3. **Plant.** Sow a cracked seed root-down 0.5–1 cm (¼–½ in) deep ([germinating seeds](https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.md)), either straight into the final pot or into a 0.5–1 L cup. 4. **Water the seedling in a ring.** 50–100 mL around the stem, every 1–3 days, only when the top 1 cm (½ in) is drying. In a big pot of wet mix, the seedling may need no water for several days. 5. **Pot up (photoperiods only, if you started in a cup).** At 2–3 weeks, when roots reach the cup's sides, move the intact root ball into the pre-moistened final pot at the same depth ([transplanting](https://genetixbay.com/knowledge/germination/transplanting.md)). Autoflowers should start in the final pot. 6. **Water by weight from week 3.** Lift the pot. When it feels clearly lighter than wet (often about 40–50 % of the water gone), water slowly until about 10 % drains out, then empty the saucer within 30 minutes ([watering](https://genetixbay.com/knowledge/guides/watering-how-much-how-often.md)). 7. **Start feeding when the mix runs out.** Usually week 3–5: the lowest leaves lighten evenly. Begin at a quarter to half label strength (EC about 0.8–1.0 mS/cm including your water), every second or third watering at first [2]. 8. **Raise the feed gradually.** Increase by about 0.2 mS/cm a week if the plant stays deep green with no burnt tips. More is not better: pushing nutrient strength higher gave no yield or cannabinoid benefit in a controlled study [8] ([feeding basics](https://genetixbay.com/knowledge/guides/feeding-basics.md)). 9. **Train in veg.** Bend and tie the main stem from week 4; tuck leaves to open bud sites rather than pluck them ([training basics](https://genetixbay.com/knowledge/guides/training-basics.md)). 10. **Flip to 12/12.** When plants are about half the final height you can fit (often week 6–7), switch the timer and log the date. Expect the stretch and the 10–14 day transition. 11. **Check runoff every 1–2 weeks.** Collect runoff and read pH and EC ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). Runoff EC much higher than input means salt build-up; much lower means the plant is hungry. 12. **Feed through to harvest.** Keep stage-strength feeding. If you mix single salts, taper only nitrogen over the last 2–3 weeks while keeping P, K, Ca, Mg, S and micros fed [6]. Do not flush (below). 13. **Harvest by trichomes** ([when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md)), then [dry](https://genetixbay.com/knowledge/guides/drying-step-by-step.md) and [cure](https://genetixbay.com/knowledge/guides/curing-step-by-step.md). ## Do you need to flush soil plants before harvest? No. Pre-harvest flushing is a *Myth*, and in soil it is actively harmful: it starves the plant in its last weeks, when it is packing on most of its final weight, trichomes and resin. A controlled study of flushing found no quality benefit [7]; see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). Lower nitrogen late can raise cannabinoid percentage while lowering total yield, a trade-off made through the feed, not by withholding everything [6]. The one valid flush is a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) to wash [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) out of the mix: water with about 2–3 times the pot volume of pH-adjusted water, then resume a normal feed at the next watering. It treats the soil, not the plant, and can be done at any stage. ## Is bigger always better for soil pots? Bigger pots give bigger plants within reason and hold water for longer, so 11–19 L (3–5 gal) forgives a missed day [4]. Small pots can still produce big plants if you water and feed often, which suits experienced growers rather than a first run. Pot size is a trade-off against watering and feeding frequency, not a fixed rule. ## How will you know it's working? You'll know a soil grow is working when the pot cycles from heavy to light in 2–4 days and the plant stays a steady green: - **Seedling:** sturdy stem, new true leaves every 3–5 days, no wilting despite the top drying. - **Veg:** a new node every 2–4 days, leaves mid to deep green with no clawing ([clawing leaves](https://genetixbay.com/knowledge/diagnosis/clawing-leaves.md)) and no burnt tips ([brown tips](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md)). - **Water:** plants perk up within an hour of watering and droop only when the pot is light. - **Runoff:** pH 6.0–7.0 and EC within about 0.5 mS/cm of input. - **Flower:** buds swell weekly; the oldest fan leaves yellow slowly in the last 2–3 weeks, which is normal senescence, not a reason to flush. ## What mistakes do beginners make in soil? Soil beginners mostly drown their plants and overfeed them: - **Overwatering**, especially seedlings in big pots. A heavy pot with droopy, firm leaves is drowning ([drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md)). - **Feeding a "hot" mix** from day one. Let the starter charge run out first. - **Full label strength.** Start at a quarter to half. - **Garden soil in pots.** It compacts and carries pathogens [3]. - **Letting pots sit in runoff.** Empty saucers within 30 minutes. - **Chasing pH.** A soil reading of 6.3 one day and 6.6 the next is normal drift. - **Flushing at the end.** It costs yield and resin. - **Ignoring fungus gnats.** Constantly wet tops breed them; let the top dry ([pest prevention](https://genetixbay.com/knowledge/guides/pest-prevention-for-beginners.md)). ## Evidence - Container media need air-filled porosity; dense mixes waterlog: *Established* [1]. - Organic fertiliser rates in coir-based veg: *Supported* [2]. Higher nutrient strength not raising yield or cannabinoids: *Supported* [8]. - Avoiding garden soil and wet media to prevent damping-off: *Established* [3]. - Pot size and growth: *Established* across species [4]; the trade-off with feeding frequency is the house position. - The 10–14 day transition: *Supported* [5]. Nitrogen trade-off: *Supported* [6]. Pre-harvest flushing: *Myth* [7]. - Week-by-week volumes and EC steps: *Grower practice*. ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 2. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17 3. University of Minnesota Extension. How to prevent seedling damping off (sanitation; avoid garden soil in containers). https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 4. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 5. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 6. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 7. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 8. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 --- # Spotting problems early: a daily five-minute check > Spend five minutes a day, at the same time, on one fixed routine: minute 1 the climate log, minute 2 the root zone (pot weight, reservoir or runoff), minute 3 the whole plant from a step back, minute 4 close-up under leaves with a loupe, minute 5 write it down. Most problems caught on day one are cheap to fix. When something looks wrong, check root zone and pH before blaming a nutrient, and change one thing at a time. - Canonical: https://genetixbay.com/knowledge/guides/daily-five-minute-check.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Transition, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How often should I check my cannabis plants?** Check cannabis plants once a day for about five minutes, at the same time each day, ideally an hour or two after lights-on when leaves have perked up. Add a slower weekly check with a loupe under every leaf layer for pests. Daily checks catch drooping, heat stress, light leaks and pests while they are cheap to fix; problems found a week late usually cost yield. **What should I look at every day in my grow?** Every day, look at five things: the climate log (min/max temperature and RH since yesterday), the root zone (pot weight, reservoir level and temperature in hydro), the whole plant from a step back (posture, colour, new growth), the undersides of a few leaves with a loupe, and your journal entry. Same order every day, so nothing gets skipped. **My plant looks sick: what do I check first?** Check the cheapest, most likely causes first: is the pot waterlogged or bone dry, what are the input and runoff pH and EC, and what did the climate do overnight? Root-zone and pH problems cause most leaf symptoms that look like deficiencies. Only once root zone, pH, environment, light and pests are ruled out should you blame a nutrient. **How do I tell a real problem from normal leaf yellowing?** A real problem spreads or appears on new growth; normal ageing does not. A few lower leaves yellowing slowly in the last 2–3 weeks of flower is normal senescence. Yellowing that climbs the plant week by week, appears on new growth, follows a pattern of spots or edges, or affects one plant and not its neighbours is a problem to diagnose. **Why should I change only one thing at a time?** Change one thing at a time so you can tell what worked. Plants answer slowly: new growth needs 3–5 days to show whether a fix helped, and damaged leaves never turn green again. If you change pH, feed and light height on the same day and the plant recovers, or gets worse, you've learned nothing for next time. **When is the best time to check plants each day?** The best time is about one to two hours after lights-on, when leaves have recovered from the night and any drooping is real. Check again briefly just before lights-off in flower, when RH tends to spike. Never open the tent during the dark period of a flowering photoperiod plant, because light interruptions can delay flowering or reveal herm-prone genetics. **Short answer.** Spend **five minutes a day**, at the same time, on one fixed routine: **minute 1** the climate log, **minute 2** the root zone, **minute 3** the whole plant from a step back, **minute 4** close-up under leaves with a loupe, **minute 5** write it down. Most problems caught on day one cost nothing to fix. When something looks wrong, check **root zone and pH before nutrients**, and **change one thing at a time**. Growers don't lose crops to rare diseases. They lose them to a dead fan, a waterlogged pot or a mite colony that was visible two weeks earlier. A daily habit beats expert knowledge applied late. ## What do you need for the daily check? The daily check needs a few small tools kept by the tent: - [ ] A thermo-hygrometer with min/max memory, or a logging sensor ([climate basics](https://genetixbay.com/knowledge/guides/climate-basics-vpd-cheat-sheet.md)) - [ ] A 30–60x [jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) or a clip-on phone macro lens - [ ] A small torch or headlamp (green light only if you must look during a flowering dark period, and better not at all) - [ ] A [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) and [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md), calibrated weekly ([meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)) - [ ] A water thermometer for hydro reservoirs - [ ] Yellow [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) at canopy and pot level ([pest prevention](https://genetixbay.com/knowledge/guides/pest-prevention-for-beginners.md)) - [ ] Your phone for one photo a day from the same spot - [ ] A [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) ## What do you do in each of the five minutes, step by step? 1. **Minute 1: read the climate.** Note lights-on temperature and RH now, and the min/max since yesterday. Reset the memory. Flags: above 30 °C (86 °F), below 18 °C (64 °F) lights-on, flower RH above 60 %, or a night drop over 8 °C. Check that every fan is running and the light came on at the right time. 2. **Minute 2: check the root zone.** Lift or tip each pot: heavy, medium or light? Compare with yesterday. In hydro, check reservoir level, water temperature (18–22 °C / 64–72 °F), that the air stones are bubbling and that roots are white. On watering days, read input and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) pH and EC ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). 3. **Minute 3: step back and look at the whole plant.** Posture (praying up, flat, drooping or clawing?), colour (even mid-green, pale, dark, yellow, purple?), where any change is (top or bottom, old or new growth, one plant or all?) and whether the new growth since yesterday looks normal. Take the daily photo from the same spot. 4. **Minute 4: get close.** Turn over 3–5 leaves from different heights and look at the undersides with the loupe: stippling, webbing, moving dots, eggs, black specks, silvery scars. Glance at the sticky traps. In flower, look into the densest buds for grey fuzz or a brown, dead leaf poking out ([bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)), and at nodes for male flowers ([sex and herms](https://genetixbay.com/knowledge/guides/telling-sex-and-spotting-herms.md)). 5. **Minute 5: write it down.** Date, day count (days since sprout, days since flip), climate readings, water or feed given with volume, pH and EC, and one line on what you saw. If something looks off, write the symptom and where it started, then decide on **one** action, or decide to wait 24 hours. ## What daily signs should you act on, and how fast? Act fast on root-zone and climate failures; give slow leaf symptoms a day or two and a proper diagnosis. The table ranks common daily signs. | You see | Most likely | Act within | First check | |---|---|---|---| | Whole plant drooping, pot heavy | Overwatering, low root oxygen | Today | Stop watering; see [drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) | | Whole plant drooping, pot light | Underwatering | Within hours | Water slowly to light runoff | | Hydro roots brown, slimy, smelly | Root rot (Pythium) | Today | Water temp, aeration ([root browning](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)) | | Top leaves bleached, tacoing upward | Heat or light stress | Today | Leaf temp, light height ([heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md)) | | Pale stippling on leaf tops, webs | [Spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md) | Within 1–2 days | Loupe under leaves | | Small flies on traps, wet medium | [Fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md) | Within days | Let the top layer dry | | Lower leaves yellowing upwards, weeks 1–6 of flower | Nitrogen shortage or root-zone problem | 2–3 days | Runoff pH and EC ([yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md)) | | New growth yellow or pale | pH lockout, iron or sulphur | 2–3 days | Root-zone pH ([yellow new growth](https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.md)) | | Brown, burnt leaf tips | Feed too strong or salt build-up | 2–3 days | Runoff EC ([brown tips](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md)) | | Dark, glossy, clawed leaves | Too much nitrogen | Within a week | Feed EC ([clawing](https://genetixbay.com/knowledge/diagnosis/clawing-leaves.md)) | | Grey fuzz or a dead leaf inside a bud | Botrytis | Today | Remove the bud, lower RH | | White powder on leaves | [Powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) | Today | RH, airflow | | Banana-shaped anthers in flower | Hermaphrodite | Today | Isolate or cull ([herms](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md)) | ## What order do you check things in when something looks wrong? Diagnose like a clinician: cheapest and most likely first, nutrients last. The fixed order from [how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md): 1. **Is it real?** Old leaves yellowing slowly late in flower is normal senescence. A single damaged leaf is not a trend. 2. **Where did it start?** Old (lower) leaves point to mobile nutrients or the root zone; new growth points to pH, immobile nutrients or light and heat; one plant only points to that plant's roots or genetics [1][2]. 3. **Root zone and pH.** Pot weight, runoff pH and EC, root colour in hydro. Most "deficiencies" are a root zone short of oxygen or a pH out of range [1][4]. 4. **Environment and light.** Overnight min/max, leaf temperature, light distance and PPFD [7]. 5. **Pests and disease.** Loupe under leaves, traps, roots, buds [3][5][6]. 6. **Only then a nutrient.** Match the symptom to the element and fix it through the feed or pH, not with a pile of additives. Then **change one thing**, write it down, and judge the result on **new growth after 3–5 days**. Damaged leaves don't turn green again. ## How will you know your daily check is working? You'll know the routine works when surprises get smaller: - You spot problems while they affect one or two leaves, not half the plant. - Your journal shows every reading for every day, and you can point to the day a problem started. - Pot weights follow a predictable rhythm, so you water before drooping, not after. - Sticky traps show zero to a handful of insects per week, with no week-on-week rise. - Fixes work first time more often, because you changed one thing and saw the result. - Harvests become comparable run to run, because the logs let you repeat what worked. ## What mistakes do beginners make with daily checks? - **Looking only at the tops.** Mites and early mould start underneath and inside. - **Checking at random times**, so drooping before lights-on gets mistaken for a problem. - **Opening the tent in the dark period** of a flowering photoperiod plant ([light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)). - **Reaching for a bottle first.** A new additive is rarely the answer; pH and watering usually are. - **Changing three things at once**, then not knowing what helped. - **Judging a fix on old leaves.** Look at the newest growth after 3–5 days. - **Not writing it down.** Memory says "about a week ago"; the journal says the exact day. - **Ignoring one odd plant.** A single plant that differs from its neighbours is telling you about its roots or its genetics. ## Evidence - Symptom location (old vs new growth) as a diagnostic key: *Established* in cannabis nutrient-disorder studies [1][2]. - Root-zone oxygen and Pythium in hydro: *Established* [4]. - Early scouting and sticky traps as the basis of pest control: *Established* extension practice [5][6]. - Mould risk in dense, humid buds: *Established* [3]. - Leaf temperature vs air under indoor lights: *Established* [7]. - The five-minute routine itself: *Grower practice*. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 4. University of Kentucky, Hydroponic root health / Pythium in nutrient solutions (E706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 5. UC IPM Pest Notes: Spider Mites (Pest Note 7405). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 6. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects 7. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # Telling sex and spotting herms: males, females and hermaphrodites > Sex a cannabis plant by its first solitary flowers at the nodes, usually visible about 4–6 weeks from seed under long days: a female shows a teardrop bract with two white stigmas, a male a small round ball on a stalk with no hairs. A hermaphrodite grows both, or sprouts banana-shaped anthers in the buds. GenetixBay's position: herms are mainly breeder error that stress reveals, late-flower 'bananas' are not normal, and herm plants are culled, never bred from. Good males are valued. - Canonical: https://genetixbay.com/knowledge/guides/telling-sex-and-spotting-herms.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Veg, Transition, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I tell if my cannabis plant is male or female?** Look at the first solitary flowers in the nodes where leaf stems meet the main stalk, usually visible 4–6 weeks from seed under long days, with a 30–60x loupe. A female shows a small teardrop-shaped bract with two white, wispy stigmas. A male shows a round ball on a short stalk, with no hairs, that later opens into pollen sacs. Don't mistake the leafy stipules at each node for flowers. **When can I see the sex of my plant?** Most photoperiod plants show their sex about 4–6 weeks from seed under 18/6, once they are mature enough; it depends on age, not the light schedule. If you can't wait, take a cutting and flower it on 12/12 for 1–2 weeks, or use a DNA sex test from the first true leaves. Every plant from regular seed needs checking; feminised seed should be nearly all female. **What does a hermaphrodite cannabis plant look like?** A hermaphrodite is a female plant that also forms male parts: either clusters of round male flower balls at the nodes, like a male, or single yellow-green banana-shaped anthers ('nanners') poking out of the buds, often in late flower. Both can shed pollen and seed the crop. Check with a loupe under bright white light, not under coloured grow lights. **Are bananas in late flower normal?** No. GenetixBay's firm position is that late-flower bananas are not normal: a banana is a herm, and a sign of poor genetics from bad breeding or pollen-chucking. Even if it's the best-smelling plant you've ever grown, it is unwanted. Don't keep it as a mother, don't breed from it, and report it in your journal so other growers of that line know. **Do herms come from stress or genetics?** Mainly genetics. Cannabis has been dioecious and stable for thousands of years, and GenetixBay holds that herm-prone lines mostly come from bad breeding: repeated selfing, careless feminising and untested seed. Stresses such as light leaks, heat or damage can trigger intersex flowers, but they reveal a susceptible plant rather than cause herms in sound genetics. Fix the stress and cull the plant. **What should I do with a male or herm plant?** Remove a male from the flower room before its flower balls open, usually within 1–2 weeks of the flip, unless you're breeding on purpose. Pluck a single banana only if it's a one-off you'll watch closely; cull a herm that keeps throwing male flowers or sheds pollen. Bag it before moving it, so pollen doesn't drift. Never breed from a herm; good males are worth keeping. **Are male cannabis plants useless?** No. Males are essential: every seed has a father, and GenetixBay encourages and rewards good males through the Stud Book, its showcase of documented males with selection journals and sire credits. If you're growing for flower, remove males from the flower room before they open. If you want to breed, keep the best male in a separate space and collect pollen deliberately. **Short answer.** Sex a cannabis plant by its first solitary flowers at the [nodes](https://genetixbay.com/knowledge/glossary/node.md), usually visible **about 4–6 weeks from seed** under long days. A **female** shows a teardrop-shaped [bract](https://genetixbay.com/knowledge/glossary/bract.md) with **two white stigmas**; a **male** shows a **small round ball on a short stalk, with no hairs**. A [hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) grows both, or pushes banana-shaped anthers ([nanners](https://genetixbay.com/knowledge/glossary/nanners.md)) out of its buds. Check with a 30–60x loupe under white light. > **House position: herms are mainly breeder error.** Cannabis is [dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md) and has kept separate sexes stably for thousands of years [2][5][6]. Herm-prone lines mostly come from bad breeding: repeated selfing, careless feminising and [pollen chuckers](https://genetixbay.com/knowledge/glossary/pollen-chucker.md) spreading untested seed. Stress can trigger intersex flowers, but that is stress *revealing* susceptible genetics, not normal behaviour. **Late-flower bananas are not normal.** A banana is a herm, however good the plant smells. Cull it; never breed from it. ## What do you need to sex your plants? Sexing needs good eyes more than gear: - [ ] A 30–60x [jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) or phone macro lens - [ ] A white torch or headlamp (grow-light colours hide detail), used only during lights-on - [ ] Plant labels or tags, and your [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) - [ ] Clean scissors and a bin bag for removing males and herms - [ ] Optional: a small separate space if you want to keep a male for breeding - [ ] Optional: a DNA sex-test kit (leaf punch) for regular seed ## What do male and female flowers look like? The first flowers form singly in the leaf axils at the nodes, driven by plant age and internal signals, not the light schedule [1]. That's why they appear in veg. | Feature | Female | Male | Hermaphrodite | |---|---|---|---| | First flowers at the nodes | Teardrop bract with 2 stigmas (white hairs) | Round ball on a short stalk, no hairs | Both kinds on one plant | | When visible | ~4–6 weeks from seed under long days | Same, often a few days earlier | Usually after the flip, sometimes late flower | | After the flip | Clusters of white pistils at branch tips | Grape-like clusters of balls that open into pollen sacs in ~2–3 weeks | Pistil clusters plus male balls, or single bananas in buds | | Risk | None | Sheds pollen and seeds the room | Sheds pollen; seeds carry the herm tendency | Don't confuse stipules, the small pointed leafy spurs either side of each node, with flowers. Stipules are thin and green with no bract or stigma. ## How do you sex and check your plants, step by step? 1. **Know your seed type.** Regular seed gives roughly half males; feminised seed should be nearly all female; clones are the sex of their mother ([seed types](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md)). 2. **Start checking at week 4 from seed.** Every 2–3 days, look at the top 3–4 nodes of the main stem with a loupe, during lights-on. 3. **Wait for a clear flower.** One ambiguous bump isn't enough. Wait until you see two stigmas (female) or a definite stalked ball (male). 4. **Tag every plant** with its sex and the date you confirmed it. Log it. 5. **Remove males from the flower room** before their balls open. Male flower clusters usually open about 2–3 weeks after they form; in practice, decide within 1–2 weeks of the flip. Bag the plant before moving it. 6. **Keep checking after the flip.** Days 1–21 after the flip are the main window for herm flowers at the nodes. Look at the lower and inner nodes as well as the tops. 7. **Scan buds weekly from week 4 of flower to harvest** for bananas: single, yellow-green, curved anthers poking out between the calyxes. 8. **If you find one or two bananas**, check for a cause: a [light leak](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md), heat above 30 °C, a damaged branch, a missed feed. Fix it, pluck the bananas with tweezers, and check again every day. 9. **If bananas keep coming, or any open pollen sacs**, cull the plant or harvest it early, bagging it first. Wipe surfaces and change clothes before touching other plants. 10. **Never keep a herm as a mother and never breed from it.** Herm tendency passes straight on: seed from a female's own male flowers is almost all female and inherits the weakness [3]. 11. **Report it** in your journal and on the line's GenetixBay record, with photos and the week. That is how herm-prone lines get exposed. ## Do herms come from stress or bad genetics? Herms come mainly from genetics, and stress is what reveals them. The GenetixBay breeder position: drug-type cannabis has been recorded as dioecious throughout history [5][6], it carries an XY sex-determination system [2], and herm-prone populations mostly come from repeated selfing ([S1 on S1](https://genetixbay.com/knowledge/breeding/s1-selfing.md)), careless [feminising](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) and untested pollen-chucker releases ([breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md)). Research supports the observation that intersex flowers do occur in commercial crops: Punja and Holmes documented them and showed seeds from them were mostly female [3]. GenetixBay interprets those numbers as a sign of poor genetics, not normal cannabis: 5–10 % herms in a commercial room means bad stock. Female plants can also be made to grow male flowers on purpose with silver thiosulfate sprays [7], which is how feminised seed is made, and why careless feminising spreads the trait. The founder has grown thousands of cultivars and doesn't see herms in older lineages, only in the recent wave of low-quality releases. ## What is GenetixBay's herm standard? GenetixBay holds lines to a measured herm standard. To be featured, a line needs a 10-plant screening grow with zero herms; to be Verified as a Bay Line or for the Seed Club, it needs about 150 or more community-grown tester plants with a confirmed herm rate **under 2 %** ([herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md)). Your journal entry, herm or no herm, counts towards that record. ## Are males worth keeping? Yes. Males are a necessity, not waste: every seed has a father, and half of a line's quality comes from him. GenetixBay encourages and rewards good males through the [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md), its showcase of documented males with selection journals and sire credits. If you're growing for flower, move males out before they open. If you want to breed, keep your best male in a separate space and collect pollen deliberately ([pollen collection](https://genetixbay.com/knowledge/breeding/pollen-collection-storage.md), [male selection](https://genetixbay.com/knowledge/glossary/male-selection.md)). ## How will you know you've got it right? You'll know your sexing works when your flower room stays seedless: - Every plant is tagged with its sex and confirmation date before day 14 after the flip. - Female nodes show paired white stigmas; pistil clusters form at the tips about 10–14 days after the flip. - No male flower balls appear at nodes during the first three weeks of flower. - Weekly bud scans from week 4 find no bananas. - At harvest and trim, you find no seeds, or only an odd one. - Your journal records any herm with the week, the trigger you checked, and what you did. ## What mistakes do beginners make with sex and herms? - **Calling sex from stipules** or a single ambiguous bump. - **Looking under coloured grow lights**, which hide pistils and anthers. - **Keeping a male "to see what happens"** in the flower room. One opened cluster can seed every plant. - **Calling bananas normal** because a forum said so. They are a herm. - **Breeding from a herm** or keeping it as a mother because it smells great. - **Ignoring light leaks** in the dark period; they expose susceptible plants. - **Moving a male or herm unbagged**, spreading pollen through the room. - **Not reporting it.** A herm record helps every grower who buys that line next. ## Evidence - Solitary flowers form by age, not photoperiod: *Established* [1]. - XY sex determination and dioecy: *Established* [2]. Validated DNA sex markers: *Established* [4]. - Intersex flowers occur in commercial drug-type crops and produce mostly female seed: *Supported* [3]; GenetixBay interprets high rates as poor genetics. - Herms mainly from breeding practice, stress revealing susceptibility: house position, supported by historical dioecy [5][6] and induced-maleness research [7]. - Late-flower bananas not normal: house position. ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 3. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 4. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 5. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 6. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 7. Lubell JD, Brand MH. 2018. Foliar sprays of silver thiosulfate produce male flowers on female hemp plants. HortTechnology 28(6):743-747. https://doi.org/10.21273/HORTTECH04188-18 --- # Training basics: LST, topping and tuck-don't-pluck > Training spreads a plant into a flat, even canopy so more bud sites sit in strong light. For a first grow, start low-stress training (bending and tying) in early veg, top photoperiods once at 4–6 nodes and allow 5–10 days of recovery, and tuck leaves out of the way rather than plucking them: leaves are the solar farm that feeds the buds. Autoflowers get LST only, not topping. Stop hard bending by mid-stretch. - Canonical: https://genetixbay.com/knowledge/guides/training-basics.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Veg, Transition · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the easiest training method for beginners?** Low-stress training (LST) is the easiest and safest method for a beginner. You bend the main stem and branches outward and down and tie them in place with soft ties, so the plant grows flat and wide and the side shoots catch up with the top. Nothing is cut, so there is no recovery time. Start in early veg and adjust ties every 2–3 days. **When should I top my cannabis plant?** Top a healthy photoperiod plant once it has 4–6 nodes, usually 3–5 weeks from sprouting, by cutting the main tip just above the 3rd to 5th node. Allow 5–10 days of recovery before you top again or flip to 12/12. Don't top a stressed, sick or freshly transplanted plant, and don't top autoflowers. **Should I top an autoflower?** No. GenetixBay's position is that topping an autoflower will never produce what proper LST or training does. Autos run on a fixed countdown from germination, so the recovery days after a cut are lost from veg, and any setback costs yield. Use low-stress training from about week 2–3: bend the main stem over and tie it down so side shoots rise to an even canopy. **Should I remove fan leaves?** Tuck, don't pluck. Fan leaves are the plant's solar farm: they make the sugars that build buds, so tuck them under branches or out of the way of bud sites rather than stripping them. Removing a few leaves within reason doesn't seem to hurt yield in research, and responses vary by cultivar, but in the founder's experience tucking helps more. It is an open GenetixBay trial. **When should I stop training my plant?** Stop hard bending and topping by about the end of the first week after the flip, and stop tying-down by mid-stretch, about 2–3 weeks after the flip, once stems turn woody. After that, only tuck leaves and support heavy colas. Training late in flower stresses the plant when it should be building buds, and woody stems snap rather than bend. **Is supercropping safe for beginners?** Supercropping, pinching a green stem until the inside softens and then bending it over, is safe once you have done some LST. GenetixBay endorses it as grower practice: the founder snaps stems all the time and finds it gives better buds, though no controlled study has measured that yet. Do it in late veg or early stretch, support the bend, and expect a firm knuckle within 3–7 days. **Does training increase yield?** Training mainly increases yield by putting more bud sites into strong, even light, since yield rises with light reaching the canopy. In a controlled study on large plants, pruning twice (at transplant and at the flip) gave the highest flower and cannabinoid yield per plant, and a flatter architecture made potency more uniform between top and lower buds. Beginners gain most from a simple, even canopy. **Short answer.** Training turns a tall, single-cola plant into a flat, even [canopy](https://genetixbay.com/knowledge/glossary/canopy.md) so more bud sites sit in strong light. For a first grow: start [low-stress training](https://genetixbay.com/knowledge/glossary/lst.md) (bending and tying) in early veg; [top](https://genetixbay.com/knowledge/glossary/topping.md) photoperiod plants once at **4–6 nodes** and allow **5–10 days** of recovery; **tuck leaves, don't pluck them**. Autoflowers get LST only, never topping. Stop hard bending by mid-stretch, about 2–3 weeks after the flip. > **House position: tuck, don't pluck.** Leaves are a solar farm for the buds. GenetixBay prefers tucking and training over stripping, to keep the most leaf surface working. Responses vary by cultivar: some lose most of their leaves with no harm, others suffer. Stripping within reason doesn't seem to hurt yield in research [1], but in the founder's experience tucking helps more. Whether tucking beats stripping is an open GenetixBay trial. ## Why train a cannabis plant at all? Training exists because light falls off fast with distance and shade. An untrained photoperiod plant grows one dominant top cola (that's [apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md)) with smaller, shaded buds below. Yield in cannabis rose roughly linearly with the light reaching the canopy in the best indoor trial [2], so lifting lower shoots into the light is the cheapest yield gain there is. In a controlled study on large plants, a flatter architecture also made cannabinoid content more uniform between top and lower buds [1]. ## What do you need for training? Training needs cheap, soft tools; nothing that cuts into stems. - [ ] Soft [plant ties](https://genetixbay.com/knowledge/glossary/plant-ties.md): rubber-coated garden wire, soft tie tape or strips of cloth - [ ] Anchor points: holes punched in the pot rim, a fabric pot's handles, or pegs pushed into the medium - [ ] Clean, sharp small scissors or snips (for topping), wiped with alcohol before use - [ ] Optional: a [trellis](https://genetixbay.com/knowledge/glossary/trellis.md) net 20–40 cm (8–16 in) above the pots for [SCROG](https://genetixbay.com/knowledge/training/scrog.md) - [ ] Optional: stakes or yo-yo supports for heavy colas in late flower - [ ] Your [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) to log the date and node count of every cut ## Which training method should a beginner use? Use LST on everything, add one topping on photoperiods, and tuck leaves throughout. The table compares the beginner options. | Method | What it is | When | Recovery | Autoflowers? | Evidence | |---|---|---|---|---|---| | [LST](https://genetixbay.com/knowledge/training/lst.md) | Bend and tie stems outward and down | Early veg to mid-stretch | None | Yes: the main method | *Grower practice* | | [Topping](https://genetixbay.com/knowledge/training/topping.md) | Cut the main tip above a node: two tops | 4–6 nodes, once or twice | 5–10 days | No | *Supported* [1] | | [FIM](https://genetixbay.com/knowledge/training/fim.md) | Pinch off ~70–80 % of the tip: 2–5 shoots | 4–6 nodes | 5–10 days | No | *Grower practice* | | Tucking | Move leaves under branches to uncover bud sites | Any time | None | Yes | *Grower practice*, house-endorsed | | [Supercropping](https://genetixbay.com/knowledge/training/hst-supercropping.md) | Pinch and bend a green stem | Late veg, early stretch | 3–7 days | Gently, early only | *Grower practice*, house-endorsed | | [Defoliation / lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) | Strip lower growth and shading leaves | Around the flip and day 21 | Some | Light only | *Supported* [1] (no yield change) | | [Mainlining](https://genetixbay.com/knowledge/training/mainlining-manifolding.md) | Build an 8- or 16-cola manifold | Veg, +2–4 weeks | Long | No | *Grower practice* | ## How do you train a first plant, step by step? 1. **Wait for 3–4 nodes and healthy growth** (about 2–3 weeks from sprouting). Never train a wilting, yellowing or freshly transplanted plant. 2. **Start LST.** Gently bend the main stem sideways until the top is level with the next-highest shoots, about 45–90°. Tie it to the pot rim. Bend slowly near the base where the stem is flexible; if it creaks, stop. 3. **Re-adjust every 2–3 days.** The tip turns back up towards the light within a day. Move ties outward so the plant spreads into a star or wheel shape, with each shoot about 5–10 cm (2–4 in) from its neighbours. 4. **Top photoperiods once at 4–6 nodes.** With clean snips, cut the main stem 3–5 mm above the 3rd to 5th node. The two shoots at that node become your new main tops. Log the date. 5. **Let it recover 5–10 days.** You'll see the two new tops grow away. Don't top again, transplant or flip in that window. 6. **Optionally top each new top once more** after recovery, for four main colas. Stop there on a first grow. 7. **Keep tucking.** When a big fan leaf covers a bud site, slide it under a branch or bend it aside instead of cutting it. Leaves are working panels. 8. **Even the canopy before the flip.** Aim for all main tops within about 5–10 cm (2–4 in) of the same height, filling about 70–80 % of the space, because plants commonly stretch 50–150 % after the flip ([stretching](https://genetixbay.com/knowledge/diagnosis/stretching.md)). 9. **Clean the lower third at or just before the flip (optional).** Remove only small, shaded shoots that will never reach the light (lollipopping), plus any leaves lying on the medium. Keep it light; leave healthy fan leaves. 10. **Supercrop runaway shoots in early stretch** (days 1–14 after the flip): pinch the stem between finger and thumb until it softens, bend it over, support it. A firm knuckle forms in 3–7 days. 11. **Stop bending by mid-stretch** (about 2–3 weeks after the flip). From then on, only tuck leaves and stake heavy colas. ## How do you train an autoflower? Train an autoflower with LST only. The GenetixBay house position is that topping will never produce what proper LST or training does on an auto: autos run on a fixed countdown from germination, so every recovery day is taken out of veg, and any setback costs yield. Start bending at about week 2–3 (3–4 nodes), keep adjusting every 2 days, and stop by about week 5–6 when flowering takes off. Tuck rather than strip. See [the autoflower week-by-week guide](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md). ## Why tuck rather than pluck leaves? Tuck because leaves feed the buds. A fan leaf is the plant's solar panel, and the house view is to keep as much leaf surface working as possible, like a solar farm for the colas. Research is mixed rather than against stripping: in a controlled study, defoliation three weeks before harvest did not change flower or cannabinoid yield per plant and made cannabinoids more uniform [1], and a hemp study found the timing of leaf loss mattered [4]. Responses vary widely by cultivar. Stripping within reason doesn't hurt yield, but tucking helped more in the founder's long experience, and it can't backfire. GenetixBay members are testing it in side-by-side trials. Do remove dead, yellow or diseased leaves and anything touching wet medium, which helps airflow and hygiene [6]. ## What about supercropping and other high-stress training? Supercropping is house-endorsed. The founder snaps stems all the time and finds it gives better buds; that's *Grower practice*, and no controlled study has measured a potency gain yet. Every cultivar responds differently. On a first grow, use it to tame one or two shoots that outgrow the canopy in early stretch, not as a routine on every branch. Mild late drought is a separate, house-endorsed stress with some research behind it [5]; leave it for a second grow. Details: [HST and supercropping](https://genetixbay.com/knowledge/training/hst-supercropping.md). ## How will you know training is working? You'll know training worked when the canopy looks like a flat table of tops: - Within 24 hours of a bend, the tip has turned back up towards the light. - After topping, two new shoots are visibly growing within 3–5 days, and both are about equal by day 7–10. - Side shoots catch up with the main tops; by the flip, 4–12 main tops sit within 5–10 cm (2–4 in) of each other. - PPFD across the canopy is even: readings at different tops differ by less than about 20 %. - After the stretch, colas fill the space without any one top burning near the light. - Supercropped stems show a firm, swollen knuckle within a week and stay upright. ## What mistakes do beginners make with training? - **Topping an autoflower.** Use LST. - **Topping a stressed or just-transplanted plant**, which stalls it for two weeks. - **Topping and flipping on the same day.** Give 5–10 days. - **Bending too hard, too high up** on a woody stem, and splitting it. Bend low, slowly, and use tape to splint a crack. - **Ties that cut in.** Check ties weekly as stems thicken; use soft, wide ties. - **Stripping every fan leaf** "to let light in". Tuck first. - **Training late in flower**, after mid-stretch, when the plant should be building buds. - **Not filling the space before the flip**, or overfilling it and running into the light after the stretch. - **Doing everything at once**: topping, defoliation and a pot-up in one day. One stress at a time. ## Evidence - Light at the canopy drives yield: *Supported* [2]. - Pruning twice raised flower and cannabinoid yield per plant; defoliation didn't change yield and improved uniformity: *Supported* (one controlled study) [1]. - Planting density and uniformity trade-offs: *Supported* [3]. - Tuck, don't pluck: *Grower practice*, house-endorsed; an open GenetixBay trial. - Supercropping for better buds: *Grower practice*, house-endorsed. Mild late drought: *Supported* [5]. - LST and topping schedules: *Grower practice*. ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 3. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 4. Sandoval SM et al., 2024. Defoliation timing effects on phytocannabinoids in hemp (simulated hail). Industrial Crops and Products; MSc thesis version, Colorado State University. https://mountainscholar.org/bitstreams/a8421af5-2146-4d67-8751-397a58816f1b/download 5. Caplan D, Dixon M, Zheng Y, 2019. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience 54(5):964–969. https://doi.org/10.21273/HORTSCI13510-18 6. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Watering: how much, how often, by medium and pot size > Water cannabis by pot weight, not by the calendar: lift the pot, and water when it feels about half as heavy as just after watering. In soil that is usually every 2–4 days, giving about 20–30 % of the pot's volume to light runoff; in coco it is daily or more, to 10–20 % runoff. Seedlings get a small ring of 50–250 mL. Overwatering, not thirst, is the most common first-grow killer. - Canonical: https://genetixbay.com/knowledge/guides/watering-how-much-how-often.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Flower · Systems: Soil, Coco, Living soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How often should I water my cannabis plants?** Water cannabis when the pot is light, not on a schedule. Lift the pot after watering and again each day: water when it feels about half as heavy. In soil that usually means every 2–4 days in veg and every 1–3 days in late flower; in coco it means once a day or more, because coco is fed like hydroponics and should never dry out fully. **How much water does a cannabis plant need per watering?** Give about 20–30 % of the pot's volume per watering once roots fill the pot: roughly 2–3 L for an 11 L (3 gal) pot, 3–4 L for 15 L (4 gal) and 4–6 L for 19 L (5 gal), stopping at 10–20 % runoff in coco and a little runoff in soil. Seedlings need far less: 50–250 mL in a ring around the stem every 1–2 days. **How do I know if I'm overwatering?** You are overwatering if the pot still feels heavy when you water again, the leaves droop while firm and swollen-looking, the surface stays dark and wet for days, or fungus gnats appear. Roots need air as much as water. Let the pot dry to about half its wet weight between waterings, check drainage, and remember that drowned roots look like hunger, which tempts more feeding. **Should I water to runoff?** In coco, yes: water to about 10–20 % runoff at each irrigation to keep salts from building up and the root zone even. In soil, a little runoff (about 5–10 %) every watering, or a full runoff once a week, is enough; the potting mix holds nutrients and buffers pH. Throw runoff away rather than letting the pot sit in it for more than 30 minutes. **Does pot size affect how often I water?** Yes. Small pots dry out faster and need watering more often; big pots hold water for days and are easier to overwater when the plant is small. Bigger pots give bigger yields within reason, but pot size is a trade-off against feeding frequency: with frequent watering and feeding, small pots can grow big plants. For a first grow, 11–19 L (3–5 gal) is the forgiving choice. **What is dryback and why does it matter?** Dryback is how much the pot dries between waterings, usually judged by weight. A dryback to roughly half the just-watered weight pulls fresh air into the root zone and keeps roots growing. Too little dryback (watering a still-heavy pot) suffocates roots; too much (bone dry and wilting) stresses them. Experienced growers use deliberate dryback to steer growth, but beginners should simply avoid both extremes. **Short answer.** Water by **pot weight**, not by the calendar. Lift the pot just after watering and again each day; water when it feels about **half as heavy**. In soil that is usually **every 2–4 days**, giving about **20–30 % of the pot's volume** to light runoff. In coco it is **daily or more**, to **10–20 % runoff**. Seedlings get a small ring of **50–250 mL**. Overwatering, not thirst, is the most common first-grow killer. Roots need air as much as water. A container mix that never dries fills its pores with water, the roots run short of oxygen, and the plant droops and yellows as if it were hungry [1]. Every watering rule below is about giving roots both. ## What do you need to water well? Watering well needs a way to measure volume and judge weight. A kitchen scale makes it exact. - [ ] A watering jug or can marked in litres (or a measuring jug) - [ ] A kitchen or luggage scale, if pots are too heavy to judge by hand - [ ] Pots with drainage holes ([fabric pots](https://genetixbay.com/knowledge/glossary/fabric-pot.md) drain and dry fastest) and saucers you can empty - [ ] A free-draining medium: potting mix with 20–30 % [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), or coco with 30 % perlite - [ ] A [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) and [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) for the water going in and the [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) coming out ([pH made simple](https://genetixbay.com/knowledge/guides/ph-made-simple.md)) - [ ] Water at room temperature, 18–22 °C (64–72 °F); a bucket left out overnight works - [ ] A turkey baster or old syringe to empty saucers - [ ] Your [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md), to log volume, runoff and the dry weight ## How do you water by pot weight, step by step? Water by pot weight in eight steps. Do this every time for the first few weeks and it becomes second nature. 1. **Weigh or lift the pot dry.** Before planting, note the weight of the pot filled with dry mix. 2. **Water to saturation once and wait.** Water slowly until 10–20 % drains out, wait 30 minutes, empty the saucer and lift or weigh again. That is the "full" weight, near [field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md). 3. **Lift it every day at the same time.** Most growers check just after lights-on. 4. **Water when it is about half the full weight.** The exact point is a feel you learn; roughly halfway between full and dry. The top 2–3 cm (1 in) of soil will also be dry to the touch. 5. **Water slowly and evenly.** Pour around the whole surface, not just at the stem, in two or three passes a minute apart, so water soaks in rather than running down the sides. 6. **Stop at the right runoff.** In coco, stop at 10–20 % runoff (100–200 mL out for every litre in). In soil, stop at the first trickle, or about 5–10 %. 7. **Empty the saucer within 30 minutes.** A pot standing in runoff wicks the salts back up and stays waterlogged. 8. **Log it.** Write down the volume, runoff, and (weekly) runoff pH and EC. If the pot now dries much faster, the plant has grown and the next watering needs more volume. See [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md). **Seedlings are the exception.** For the first 10–14 days, water only a small ring of 50–250 mL around the stem every 1–2 days, widening it as roots grow. A seedling in a big wet pot sits in airless mix, the classic setup for [damping-off](https://genetixbay.com/knowledge/germination/damping-off.md) [6]. ## How much and how often, by medium and pot size? Water volume and frequency depend on the medium, the pot size and the plant's size. The table gives starting points for a healthy plant that fills its pot under 600–900 µmol/m²/s; check against your own pot weights. | Pot | Soil: volume per watering | Soil: how often | Coco: volume per watering | Coco: how often | |---|---|---|---|---| | Seedling (any pot) | 50–250 mL ring | Every 1–2 days | 50–250 mL ring | Daily | | 1 L (¼ gal) | 0.2–0.3 L | Every 1–2 days | 0.25–0.35 L | 1–2x daily | | 3.8 L (1 gal) | 0.8–1.2 L | Every 2–3 days | 0.9–1.3 L | Daily | | 11 L (3 gal) | 2–3 L | Every 2–4 days | 2–3 L | 1–2x daily in flower | | 15 L (4 gal) | 3–4 L | Every 3–4 days | 3–4.5 L | Daily to 2x daily | | 19 L (5 gal) | 4–6 L | Every 3–5 days | 4–6 L | Daily to 2x daily | | 26 L (7 gal) | 5–8 L | Every 4–6 days | 5–8 L | Daily | A large flowering plant can move 1.5–2 L of water a day through its leaves, so frequency rises sharply from mid veg to mid flower. Coco should never dry out fully: it is fed like hydroponics, with nutrients in every watering ([coco week by week](https://genetixbay.com/knowledge/guides/coco-first-grow-week-by-week.md)). Soil can dry more between waterings ([soil week by week](https://genetixbay.com/knowledge/guides/soil-first-grow-week-by-week.md)). ## Does pot size matter? Pot size matters, but it is a trade-off, not a fixed rule. Across 65 studies, doubling rooting volume raised plant biomass by about 43 % on average [2], and the GenetixBay house position is that bigger pots give bigger yields within reason. Root volume isn't the whole story, though: the founder has grown a 4 oz+ (QP+) plant from a 16 oz cup by watering and feeding very often, which is the logic behind [high-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md). Small pots need more frequent care; big pots forgive a missed day but are easy to overwater while the plant is small. | Pot size | Best for | Watch out | |---|---|---| | Under 7.5 L (2 gal) | Small plants, SOG, high-frequency feeding | Dries in hours in flower | | 11–19 L (3–5 gal) | First grows, most tents | Overwatering seedlings | | 26 L+ (7 gal+) | Long veg, big plants, living soil | Very slow dryback when small | ## What about dryback and drought stress? [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md) is how much the pot dries between waterings, and a moderate dryback is healthy because it pulls fresh air into the root zone. A controlled study found that a mild, controlled drought in late flower increased inflorescence dry weight and cannabinoid content [4], and the founder uses it: some cultivars thrive when allowed to go a bit dry late. Every cultivar responds differently, and the line between "a bit dry" and wilting is narrow. On a first grow, avoid both extremes; deliberate steering is in [drain-to-waste and crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md). ## How will you know it's working? You'll know your watering is right when the plant and the pot follow a steady, repeating rhythm: - **Pot weight:** swings from heavy to about half that weight in 2–4 days (soil) or about 1 day (coco), and the cycle shortens as the plant grows. - **Leaves:** held flat or slightly up in the light, perking up within an hour of lights-on, never limp and never swollen-droopy. - **Surface:** the top 2–3 cm dries between waterings in soil; no green algae or constant dark wet patch. - **Runoff:** clear, at the target %, with runoff EC close to (within about 0.5 mS/cm of) what you put in. - **No fungus gnats.** These breed in constantly wet media [5]. - **Roots** (if you peek at the drain holes): white, branching, with fine hairs. ## What mistakes do beginners make with watering? Nearly all watering mistakes are too much, too often. - **Watering on a schedule** ("every second day") instead of by weight. - **Flooding a seedling's whole pot.** Water a small ring. - **Leaving pots standing in runoff.** - **Treating coco like soil**: plain-water days and letting it dry out fully. - **Watering only at the stem**, so half the pot stays dry and roots don't fill it. - **Cold water** straight from the tap in winter, below about 15 °C (59 °F). - **Mistaking overwatering for hunger** and adding nutrients to a waterlogged pot. Lift the pot first ([drooping: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md)). - **Ignoring drainage**: a pot without holes, or a dense, peaty mix with no perlite [1]. - **Wilting the plant on purpose** on a first grow after hearing about drought stress. Root rot and wilts love a wet, airless, warm root zone [7]; good drainage and dryback are prevention. ## Evidence - Container media physics and air-filled porosity: *Established* in horticultural texts [1]. - Bigger pots, bigger plants: *Established* across crops [2]; pot size as a trade-off against feeding frequency is the house position, backed by the founder's grower data. - Pour-through runoff checks: *Established* extension method [3]. - Mild late drought raising dry weight and cannabinoids: *Supported* by one cannabis study [4]; house-endorsed, cultivar-dependent. - Wet media and gnats, damping-off and root disease: *Established* [5][6][7]. - Water volumes and frequencies in the table: *Grower practice*. ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 2. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 3. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download 4. Caplan D, Dixon M, Zheng Y. 2019. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience 54(5):964-969. https://doi.org/10.21273/HORTSCI13510-18 5. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ 6. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 7. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 --- # When to harvest: talk to her, and read the trichome mix > Harvest when a 60x loupe shows the trichome heads on the buds as a mix of a few clear, mostly cloudy and some amber. That mix is a matter of preference, not a hard rule. Count from the flip and add the 10–14 day transition before you trust a breeder's week count, keep feeding to the end (no flush), and skip the 24–72 h of darkness: both are myths. - Canonical: https://genetixbay.com/knowledge/guides/when-to-harvest.html - Category: Start here · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Ripening, Harvest · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I know when my cannabis is ready to harvest?** Cannabis is ready when a 60x loupe shows the trichome heads on the buds as a mix: a few clear, mostly cloudy (milky) and some amber. Check three or more bud sites, top and lower canopy, on the calyxes rather than the sugar leaves. The exact mix is preference. Pistil colour and the breeder's week count are rough guides only. **Should I look at trichomes on the leaves or the buds?** Look at trichomes on the buds themselves: the calyxes and bracts of the flower. Trichomes on sugar leaves usually turn cloudy and amber earlier than those on the bud, so judging by the leaves leads to harvesting too early. Check the top cola and at least two lower buds, because the top of the plant usually ripens first. **Do amber trichomes make the effect more sleepy?** The popular claim that amber trichomes mean high CBN and a heavier, sedative effect is a myth. Research shows browning marks gland senescence, and CBN forms mainly by oxidation of THC after harvest, during storage. Some growers report preferring a later, more amber harvest; that is taste. No controlled study shows a predictable effect from the amber share. **Should I put my plants in darkness for 48 hours before harvest?** No. Darkness before harvest (24–72 h) is a myth: it cuts photosynthesis in the most important part of the life cycle and no robust study shows a benefit. For more than 20 years the GenetixBay founder has offered a 50-pack of seeds to anyone who finds a peer-reviewed, unbiased, multi-plant study showing one. Nobody has claimed it. Harvest at the end of a normal light period. **Why is my plant taking longer than the breeder's flowering time?** Breeder flowering times often count from the first visible pistil clusters, not from the flip to 12/12. The transition after the flip usually takes 10–14 days, so a stated 8 weeks often means harvest about 9.5–10 weeks after the flip. Log both days since flip and days of flower, and let the trichomes make the final call. **Should I flush before I harvest?** No. Pre-harvest flushing is a myth that actively costs yield and resin: it starves the plant while it is finishing most of its final weight and trichomes, and controlled studies found no quality gain. Feed at stage strength right to harvest. If you mix single salts, taper only nitrogen in the last weeks while keeping the other nutrients fed. **Can I harvest the top and bottom of the plant at different times?** Yes. A staggered harvest is optional and works: cut the ripe top colas first, then give the lower, shaded buds another 5–10 days to catch up. It suits plants with an uneven canopy. The cost is a second harvest session, and lower buds stay smaller than tops whatever you do. **Short answer.** Harvest when a 60x loupe shows the [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) on the buds as **a few clear, mostly cloudy and some amber**. That mix is a matter of preference: earlier and cloudier for a brighter finish, later with more amber if you like it heavier. Count from the flip and add the **10–14 day transition** before trusting a breeder's week count. Keep feeding to the end, and skip the pre-harvest flush and the 24–72 h of darkness: both are *Myths*. > **The founder, on knowing when she's ready:** "Talk to her." She tells you more than you bargained for: swelling calyxes, pistils pulling in, the smell turning, the heads going milky. Look every other day in the last three weeks and you'll see it happen. ## What do you need to judge harvest time? You need a way to magnify trichomes and a record of dates; nothing else is essential. - [ ] A 60x [jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md), or a clip-on phone macro lens or a small digital microscope (60–100x) - [ ] A small torch or a white-light lamp (switch any coloured grow light to white or turn it off while looking) - [ ] Your [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md) with the **flip date** and the date of **first pistil clusters** - [ ] Clean, sharp pruning snips and gloves for harvest day - [ ] A drying space ready at 15–21 °C (60–70 °F) and 55–62 % RH before you cut ([drying step by step](https://genetixbay.com/knowledge/guides/drying-step-by-step.md)) ## When should you start checking trichomes? Start checking trichomes about two weeks before the earliest date your calendar suggests, then every two days. The calendar date is days since flip = breeder's flowering time + 10–14 days, because breeder times usually count from the first visible pistils, not from the switch to 12/12. In controlled studies first flowering came 8–14 days after short days began, and up to three weeks in slow cultivars [5]. See [the photoperiod grow calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md) and [the flip-to-flower transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md). Autoflowers have no flip. Count days from germination and start checking at the earliest finish the listing gives, usually around day 63–70 ([autoflower first grow](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md)). ## How do you check trichomes, step by step? Check trichomes the same way every time so the readings compare. 1. **Pick three sites:** the top cola, a mid-canopy bud and a lower bud. The top usually ripens first. 2. **Light it with white light.** Switch off a purple-tinted LED or use a torch. 3. **Look at the calyxes and bracts,** not the [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md). Leaf trichomes turn cloudy and amber earlier and fool you. 4. **Focus on the heads** of the [capitate-stalked trichomes](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md), the mushroom-shaped ones. 5. **Estimate the mix** in tenths: how many clear, cloudy and amber out of ten heads. Do it on two or three spots per bud. 6. **Write it down** with the date and days since flip, for example "Day 68 since flip: 2 clear / 7 cloudy / 1 amber, top cola". 7. **Repeat every two days.** The change from mostly clear to mostly cloudy usually takes 1–2 weeks; amber builds slowly after that. 8. **Cut when your target mix shows on the buds you care most about.** If the lower buds lag by a week, you may harvest the tops first. ## What trichome mix should you aim for? Aim for a mix of a few clear, mostly cloudy and some amber; within that, it's your preference. That is the GenetixBay house position, and it matches the research: trichome heads go from clear to cloudy to amber or brown as they mature, browning marks gland senescence, and heads on one bract mature unevenly and at rates that differ by genotype [1][2]. Cannabinoid concentration typically rises to a plateau and then falls as the plant senesces [3]. | Mix on the buds | What it means | Typical choice | |---|---|---| | Mostly clear, few cloudy | Immature; cannabinoids still rising | Too early; wait | | ~1–2 clear / 7–8 cloudy / 0–1 amber | Near the plateau | Earliest sensible harvest | | ~1 clear / 7 cloudy / 2 amber | The classic mix | The default target | | ~0 clear / 5–6 cloudy / 4–5 amber | Late; heads senescing | For growers who prefer it heavier | | Mostly amber or brown, heads collapsing | Over-ripe | Losing quality; harvest now | Treat this table as *Grower practice*. Genotype changes the pace, so log your cultivar's mix and date each run; that is how you learn its window ([trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md)). ## Do amber trichomes mean a sleepier effect? No, not in any proven way. The idea that amber heads mean high [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) and couch-lock is a *Myth*: CBN forms mainly by oxidation of THC after harvest, during storage [4], not on the living plant in any useful amount. Some growers report that later harvests feel heavier to them; that is a reported preference, and no controlled study shows a predictable effect from the amber share. Pick the mix you like and record it. ## What other signs tell you she's nearly done? Other signs back up the loupe but never replace it. Expect most of these in the last 2–3 weeks: - Calyxes swell and stack; buds stop getting longer and get denser. - Most [pistils](https://genetixbay.com/knowledge/glossary/pistil.md) darken and curl in. Pistil colour varies by cultivar and stress, so it's only a hint. - Lower fan leaves yellow slowly as the plant moves nitrogen to the flowers: normal [senescence](https://genetixbay.com/knowledge/glossary/senescence.md), not a reason to stop feeding. - Water use drops a little; the smell gets stronger and changes. ## Should you flush or use darkness before harvest? No to both. Pre-harvest flushing is a *Myth* and actively harmful: it starves the plant in the weeks when it is packing on most of its final weight, trichomes and resin, and controlled studies found no quality gain [7]. Feed at stage strength to the end; if you mix single salts, taper only nitrogen. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) and [feeding basics](https://genetixbay.com/knowledge/guides/feeding-basics.md). Darkness before harvest (24–72 h) is a *Myth* too, in the founder's words "complete and utter nonsense": why cut photosynthesis at the most critical part of the life cycle? Photosynthesis drives yield right to the end [6]. > **Greenleaf's standing challenge.** For more than 20 years the founder has offered a 50-pack of seeds, no questions asked, to anyone who finds a peer-reviewed study (not a single-plant study, not biased or skewed) showing a benefit from darkness before harvest. Nobody has claimed it. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## How will you know it's working? You'll know your harvest timing is working when the logs line up run to run: - Your loupe readings move from mostly clear to mostly cloudy over 1–2 weeks, then amber appears. - The harvest date lands about 10–14 days past the breeder's stated time, counted from the flip, and you saw it coming. - Dried buds are dense, smell strong and taste clean after the cure. - Next run of the same cultivar, you can predict the window within a few days from your journal. ## What mistakes do beginners make at harvest? Beginners mostly harvest too early, or ruin a good harvest with a ritual. - **Harvesting by the breeder's week count** from the flip, forgetting the 10–14 day transition. - **Reading sugar-leaf trichomes,** which amber early. - **Judging by pistil colour alone.** - **Flushing the last 1–2 weeks,** which costs yield and resin. - **48–72 h of darkness,** which costs photosynthesis and gains nothing. - **Checking only the top cola** when the lower buds are a week behind. - **Ignoring bud rot** in dense colas in the final weeks: squeeze-check big colas and look for grey or brown inside ([botrytis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)). - **Cutting with no drying space ready.** ## Evidence - Trichome maturation clear → cloudy → amber, uneven and genotype-dependent: *Supported* [1][2]. - Cannabinoids rise to a plateau then decline: *Supported* [3]. - Amber = CBN = couch-lock: *Myth*; CBN forms mainly post-harvest [4]. - The 10–14 day transition after the flip: *Supported* [5]; house position. - Darkness before harvest: *Myth* (house; no supporting study found) [6]. - Pre-harvest flushing: *Myth* [7]. - The trichome mix target: *Grower practice*, house position (preference). ## Sources 1. Punja ZK, Sutton DB, Kim T, 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 2. Livingston SJ, Quilichini TD, Booth JK, et al., 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37–56. https://doi.org/10.1111/tpj.14516 3. Aizpurua-Olaizola O, Soydaner U, Öztürk E, et al., 2016. Evolution of the cannabinoid and terpene content during the growth of Cannabis sativa plants from different chemotypes. Journal of Natural Products 79(2):324–331. https://pubmed.ncbi.nlm.nih.gov/26836472/ 4. Fairbairn JW, Liebmann JA, Rowan MG, 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1–7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x 5. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 6. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 7. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 --- # Your first grow, start to finish: the master guide > A first indoor grow takes about 3–5 months from seed to jar: 1 week to set up and test the room, 1–2 weeks of germination and seedling, 3–6 weeks of veg (photoperiods), a 10–14 day transition after the flip, 7–10 weeks of flower, 7–14 days of drying and at least 2–4 weeks of curing. Use one to four feminised plants, a tent, one good LED, a fan and carbon filter, 11–19 L pots, a pH pen and an EC meter, and keep a journal. - Canonical: https://genetixbay.com/knowledge/guides/first-grow-start-to-finish.html - Category: Start here · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Soil, Coco, DWC - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How long does a first cannabis grow take from seed to harvest?** A first indoor photoperiod grow takes about 14–20 weeks from seed to harvest: 1–2 weeks of germination and seedling, 3–6 weeks of veg, a 10–14 day transition after the flip to 12/12, then 7–10 weeks of flower. Add 1–2 weeks of drying and 2–4+ weeks of curing. A feminised autoflower is quicker, usually 9–14 weeks from seed to harvest, with no flip. **What is the step-by-step order of a first grow?** The order of a first cannabis grow is: check the law, set up and test the room for 48 hours, germinate, raise seedlings under gentle light, veg (photoperiods only, 3–6 weeks), flip to 12/12 and allow a 10–14 day transition, flower for 7–10 weeks while feeding through to the end, harvest by trichomes, dry slowly for 7–14 days, then cure in jars for 2–8 weeks. **How many plants should I grow the first time?** Grow one to four plants on a first run, within your local legal limit. In a 60 x 60 cm (2 x 2 ft) tent, one or two plants is plenty; in a 120 x 120 cm (4 x 4 ft) tent, two to four. Fewer plants means fewer pots to water and lift, more attention per plant and less damage from any one mistake. **What is the biggest mistake on a first grow?** Overwatering is the biggest single mistake on a first cannabis grow, followed by overfeeding and fiddling. Water when the pot feels light, not on a schedule; feed below the label rate; change one thing at a time and wait three to five days to see the result on new growth. A dated journal turns those mistakes into lessons for the next run. **Should I flush my plants before harvest on a first grow?** No. Pre-harvest flushing is a myth, and it actively costs yield and resin: it starves the plant in its last weeks, when it is packing on most of its final weight and trichomes. Controlled studies found no quality gain. Keep feeding at stage strength through to harvest; if you mix single salts, taper only nitrogen late in flower. Taste comes from a healthy plant, a slow dry and a proper cure. **How do I know when my first grow is ready to harvest?** Harvest when a 60x loupe shows the trichome heads on the buds (not the sugar leaves) as a mix: a few clear, mostly cloudy, some amber. That is a matter of taste: more cloudy for a brighter finish, more amber if you prefer it heavier. Pistil colour and breeder week counts are only rough guides; count from the flip and add the 10–14 day transition. **What equipment is essential for a first indoor grow?** The essential first-grow kit is a grow tent, one dimmable full-spectrum LED, an exhaust fan with a carbon filter, a small clip fan, 11–19 L (3–5 gal) fabric or plastic pots, quality potting mix or coco, a pH pen and pH up/down, an EC meter, a thermo-hygrometer, a timer, a 60x loupe and a journal. Everything else is optional on a first run. **Short answer.** A first indoor grow takes about **3–5 months from seed to jar**. Set up and test the room for a week, germinate, run gentle light for 1–2 weeks of seedling, veg photoperiods for 3–6 weeks, flip to 12/12 and allow a **10–14 day transition** before flower really starts, flower for 7–10 weeks while feeding through to the end, then dry slowly for 7–14 days and cure for at least 2–4 weeks. Grow one to four feminised plants. Write everything down. **Legal first.** Home growing is legal only in some places, with plant limits and rules about visibility and security. Do the [legal check before you grow](https://genetixbay.com/knowledge/guides/legal-check-before-you-grow.md) before you buy anything. This guide is the spine of the "Start here" series. Each phase links to the step-by-step guide for it, and from there to the deep article with the evidence. ## What do you need for a first grow? A first indoor grow needs a small set of generic equipment, nothing branded and nothing exotic. Buy for the space you have; see [choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md) for budget tiers. - [ ] A grow [tent](https://genetixbay.com/knowledge/glossary/tent.md) sized to your space: 60 x 60 cm (2 x 2 ft) for one or two plants, 120 x 120 cm (4 x 4 ft) for two to four - [ ] One dimmable full-spectrum [LED](https://genetixbay.com/knowledge/glossary/led.md) that can deliver about 600–900 µmol/m²/s over the tent footprint ([lights for beginners](https://genetixbay.com/knowledge/guides/lights-for-beginners.md)) - [ ] An inline [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) with a [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md), plus one small clip or [oscillating fan](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) - [ ] 11–19 L (3–5 gal) pots, fabric or plastic with drainage, and saucers - [ ] Quality bagged potting mix, or buffered coco plus perlite ([soil](https://genetixbay.com/knowledge/guides/soil-first-grow-week-by-week.md) or [coco](https://genetixbay.com/knowledge/guides/coco-first-grow-week-by-week.md)) - [ ] A [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) or pen, pH 4 and 7 calibration buffers, and pH up and down - [ ] An [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) (needed for coco and hydro; very useful in soil) - [ ] A thermo-hygrometer with min/max memory, ideally one that logs - [ ] A mechanical or digital timer for the light - [ ] A 60x [jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) or clip-on phone macro lens - [ ] A base nutrient for your medium, a measuring syringe and a jug - [ ] Soft plant ties or garden wire for training - [ ] A [grow journal](https://genetixbay.com/knowledge/guides/grow-journal-101.md): paper, a spreadsheet or a GenetixBay journal - [ ] Seeds of a well-documented feminised line ([reading a seed listing](https://genetixbay.com/knowledge/guides/reading-a-seed-listing.md)) ## What does the whole grow look like, week by week? The whole grow runs about 18–24 weeks for a photoperiod plant and 13–20 weeks for an autoflower, counting setup, drying and curing. The table is the timeline; treat the weeks as typical, not fixed, because cultivars differ. | Week | Photoperiod plant | Autoflower plant | Light | Main job | |---|---|---|---|---| | 0 | Set up, run the room empty 48 h | Same | Test run | Log day and night temp and RH; fix the climate first | | 1 | Germinate, plant out | Germinate straight into the final pot | 18/6, 150–300 µmol/m²/s | Keep the medium moist, not wet | | 2–3 | Seedling | Seedling | 18/6, 200–400 | Tiny waterings; no feed in most bagged soils | | 4–6 | Veg; pot up into the final pot | Early veg; start LST about week 3 | 18/6 (up to 24/0), 300–600 | Water by weight; start training | | 7–8 | Late veg; flip at half the final height you can fit | Pre-flower and stretch | Photo: 12/12 from the flip; auto: 18/6 or 20/4 | Fill the canopy evenly | | 9–10 | **Transition: days 1–14 after the flip**, stretch | Flower | Photo 12/12, 600–900 | Count days since flip; check for male flowers | | 11–16 | Flower (day 1 of flower is about day 10–14 after the flip) | Flower and ripening; most finish weeks 10–14 | 600–900 | Lower RH; weekly pest check; feed through | | 17–19 | Ripening; harvest by trichomes | (Already in the jar) | Keep the dark period dark | No flush; taper only N if you mix salts | | +1–2 | Dry 7–14 days | Dry 7–14 days | Dark room | 15–21 °C, 55–62 % RH | | +2–8 | Cure in jars | Cure in jars | Dark | Slow moisture decline | The flip is not day 1 of flower. In controlled studies the first real pistil clusters at the top of the plant appeared about 8–14 days after short days began, around 13–14 days on average across 27 hemp cultivars and up to three weeks in slow ones [2][3]. That's why runs go "longer" than a breeder's stated flowering time: see [the photoperiod grow calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md) and [the flip-to-flower transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md). ## How do you run a first grow, step by step? Run a first grow as twelve plain steps. Each step names its guide; follow that guide for the detail. 1. **Check the law.** Confirm home cultivation is legal where you live, the plant limit, and any rules on visibility, locks and smell. See [the legal check](https://genetixbay.com/knowledge/guides/legal-check-before-you-grow.md). 2. **Choose your space and kit.** Pick the tent size first, then size the light and fan to it. See [choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md) and [electrical and water safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md). 3. **Choose your plant type and medium.** For a first grow, a feminised photoperiod in soil is the most forgiving; an [autoflower](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md) is faster but punishes setbacks. Compare [soil](https://genetixbay.com/knowledge/guides/soil-first-grow-week-by-week.md), [coco](https://genetixbay.com/knowledge/guides/coco-first-grow-week-by-week.md) and [DWC](https://genetixbay.com/knowledge/guides/dwc-first-grow-week-by-week.md). 4. **Run the empty room for 48 hours.** Log temperature and RH with lights on and off. Aim for 22–28 °C (72–82 °F) lights-on and no more than 6 °C (10 °F) cooler at night. See [climate basics](https://genetixbay.com/knowledge/guides/climate-basics-vpd-cheat-sheet.md). 5. **Germinate.** Keep seeds at 22–26 °C (72–79 °F), moist and dark; plant a cracked seed root-down 0.5–1 cm (¼–½ in) deep. See [germinating seeds](https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.md). 6. **Raise the seedling (weeks 1–3).** Light at 150–300 µmol/m²/s for 18 h, RH 65–75 %, and only a small ring of water around the stem. Most seedling deaths are overwatering. See [watering](https://genetixbay.com/knowledge/guides/watering-how-much-how-often.md). 7. **Veg (photoperiods, 3–6 weeks).** Raise light to 300–600 µmol/m²/s, pot up into the final pot when roots fill the small one, start feeding lightly, and begin [training](https://genetixbay.com/knowledge/guides/training-basics.md): bend and tie, tuck rather than pluck. 8. **Flip to 12/12.** Do it when plants are about half the final height you can fit, because they commonly double in the stretch. Keep the dark period completely dark. Log the flip date. See [the grow calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md). 9. **Watch the transition and confirm sex.** Days 1–14 after the flip are stretch and transition. Check every plant for male flowers or [herms](https://genetixbay.com/knowledge/guides/telling-sex-and-spotting-herms.md) and remove any that will shed pollen. 10. **Flower (7–10 weeks of flower).** Light at 600–900 µmol/m²/s, RH 45–55 % falling to 40–50 % late, and a [daily five-minute check](https://genetixbay.com/knowledge/guides/daily-five-minute-check.md). Feed at stage strength right to the end. Do not flush (see below). 11. **Harvest by trichomes.** Look at the heads on the buds with a 60x loupe and cut at a mix of a few clear, mostly cloudy, some amber. See [when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md). 12. **Dry, then cure.** Dry whole branches in the dark at 15–21 °C (60–70 °F) and 55–62 % RH for 7–14 days until small stems snap, then cure in jars, letting the buds' moisture fall slowly over 2–8 weeks. See [drying](https://genetixbay.com/knowledge/guides/drying-step-by-step.md) and [curing](https://genetixbay.com/knowledge/guides/curing-step-by-step.md). ## What numbers should a beginner aim for? A beginner should aim for the middle of each range below and keep it steady; stability matters more than hitting an exact number. These are *Grower practice* ranges anchored to the cited studies; your cultivar may differ. | Parameter | Seedling | Veg | Flower | Late flower | |---|---|---|---|---| | PPFD (µmol/m²/s) | 150–300 | 300–600 | 600–900 | 600–900 | | Photoperiod | 18/6 | 18/6 to 24/0 | 12/12 or 13/11 (photos) | Same | | Air temperature, lights on | 24–27 °C (75–81 °F) | 22–28 °C (72–82 °F) | 20–26 °C (68–79 °F) | 20–24 °C (68–75 °F) | | RH | 65–75 % | 55–70 % | 45–55 % | 40–50 % | | VPD (kPa, leaf) | 0.4–0.8 | 0.8–1.2 | 1.0–1.5 | 1.2–1.5 | | pH, soil / coco and hydro | 6.2–6.8 / 5.8–6.2 | Same | Same | Same | | Feed EC (mS/cm, coco) | 0.4–0.8 | 1.0–1.8 | 1.6–2.2 | 1.6–2.2 (taper N only) | Yield rose roughly linearly with light up to about 1,800 µmol/m²/s in the best indoor trial [1], but a beginner gains more from steady, moderate light than from chasing the ceiling. ## Should you flush before harvest? No. Pre-harvest flushing is a *Myth* in the GenetixBay evidence ladder, and a harmful one. Cutting off nutrients in the last 1–2 weeks starves the plant while it is packing on most of its final weight, trichomes and resin. Controlled trials found no improvement in quality from pre-harvest nutrient withdrawal [6][9]. Cannabis stores what it takes up in its tissue, and plain water at the end does not wash it out. What to do instead: keep feeding at the strength the stage calls for until harvest. If you mix single salts, taper only nitrogen over the last few weeks while keeping P, K, Ca, Mg, S and the micronutrients fed; lower N can raise cannabinoid percentage while lowering total yield, a trade-off rather than a reason to flush [5]. The one valid flush is a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) to clear salt build-up, at any stage. The full evidence is in [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) and [feeding basics](https://genetixbay.com/knowledge/guides/feeding-basics.md). ## How will you know it's working? You'll know a first grow is working when the plant shows steady, even growth and your logs stay boring. Check these signs weekly: - **Seedling:** the stem stays short and sturdy (not leaning or stretched), cotyledons stay green, and a new set of true leaves appears every 3–5 days. - **Veg:** a new node every 2–4 days, leaves a mid to deep green held flat or slightly up, and the pot drying from heavy to light in 2–4 days. - **Transition:** stretch of 50–150 % over 2–3 weeks, then white pistil clusters at the tips about 10–14 days after the flip. - **Flower:** buds swell week on week, lower fan leaves yellow slowly in the last 2–3 weeks (normal), and the smell grows. - **Ripening:** trichome heads turn from clear to mostly cloudy with some amber. - **Dry:** small stems snap rather than bend after 7–14 days. - **Logs:** temperature within about 3 °C (5 °F) of target and RH within about 5 points, day after day. ## What mistakes do beginners make on a first grow? Beginners mostly fail from too much care, not too little. The common ones: - **Watering on a schedule** instead of by pot weight. Drowned roots look like hunger, which tempts more feeding. - **Feeding full label strength from week one.** Start at a quarter to half strength and work up by EC and plant response. - **Lights too close or too strong** for a seedling, especially strong LEDs: bleached tops, upward-cupped leaves. - **Counting the flip as day 1 of flower** and harvesting 10–14 days early. - **Flushing for the last 1–2 weeks** "for taste". It costs yield and resin and gains nothing. - **Harvesting by pistil colour** or by the calendar instead of by trichomes. - **Drying fast and warm.** A hay smell from a rushed dry never cures out. - **Transplanting an autoflower.** Plant autos straight into the final pot. - **Changing three things at once** when something looks wrong. Change one, log it, wait 3–5 days and judge on new growth ([how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md)). - **Skipping the journal.** Without dates and readings, the next grow repeats this one's mistakes. ## Evidence - Light and yield indoors: *Supported* by a cannabis-specific trial [1]. - The 10–14 day transition after the flip: *Supported* by controlled flowering studies [2][3]; the house position counts both days since flip and days of flower. - Organic feed rates in coir veg: *Supported* [4]. - Nitrogen trade-off: *Supported* [5]. Pre-harvest flushing: *Myth* [6][9]. - Drying to aw 0.55–0.65: *Established* as a standard [7]; the drying climate is *Grower practice*. - Mould and hygiene risks in humid flower rooms: *Established* [8]. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 3. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 4. Caplan D, Dixon M, Zheng Y. 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307-1312. https://doi.org/10.21273/HORTSCI12401-17 5. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 6. Stemeroff J. 2017. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 7. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 8. Punja ZK. 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857-3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 9. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 --- # Buyer beware: potency labels, strain names and other claims that don't hold up > Flower labelled above about 35% total cannabinoids is not credible: cannabinoids are made only in trichome heads, and bud is mostly bract, stem and leaf, so numbers like that belong to concentrates or to inflated testing. Studies show potency results vary systematically between labs, and retail flower labels often overstate THC. Be equally sceptical of strain names that promise effects, terpene totals far above the ~2% average, and 'indica for the couch, sativa for energy'. - Canonical: https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.html - Category: Basics · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is 40% THC flower real?** No. Cannabis flower labelled at 40% THC is not credible, because cannabinoids are made only in trichome heads and most of a bud's dry weight is bract, stem and leaf that makes almost none. Numbers like that belong to concentrates such as sieved resin or extracts, where plant tissue has been removed, or to lab shopping and inflated testing. Above 30% is already very rare in large lab datasets. **Is most dispensary weed really 30% THC?** No. Most dispensary flower is not really 30% THC. Independent retests keep finding retail flower in the mid-teens to low 20s, often well below its label; in one Colorado study about 70% of samples tested more than 15% under the label. Reaching 30% total cannabinoids honestly takes elite genetics, a dialled-in environment and a careful dry, so it is a rare, real feat. **What THC does retail flower really test at?** Retail cannabis flower really tests at roughly the mid-teens to low 20s percent THC. One Colorado retest averaged about 15% THC, a larger 2025 Colorado study averaged about 21%, and across 215,285 Washington State results the median for THC-dominant flower ran 17.6-23.1% depending on the lab. Results above 30% total THC were very rare in that dataset. **Have regulators caught inflated THC labels?** Yes. In 2026 the Massachusetts regulator bought 63 flower products off shelves and retested them; 13, about one in five, fell outside the accepted range of their label, and producers had to recall and relabel, retest or destroy the product. California's regulator proposed standardised cannabinoid test methods in 2022, explicitly to tackle potency inflation and lab shopping, and later adopted them. **What is the highest THC cannabis flower can have?** Cannabis flower realistically tops out around 30-32% total THC, and anything labelled above about 35% total cannabinoids is not credible. A generous first-principles estimate, with gland heads at 40% of dry mass and 80% cannabinoids in those heads, gives about 32% cannabinoids and 27% total THC. Across 215,285 Washington tests, the 99th percentile was 27.0-31.8% depending on the lab. **Are cannabis THC labels accurate?** Cannabis THC labels are often not accurate, and they usually err high. A 2025 Colorado study found about 44% of flower labelled inaccurately, mostly overstating THC, while concentrate labels were far more accurate. Another retest found three flower samples with half their labelled maximum. Treat a single label number as a claim, and ask for the full certificate of analysis, lab name and test date. **What is lab shopping?** Lab shopping is when a cannabis producer sends samples to whichever testing lab reports the highest potency. Because the producer chooses and pays the lab, and higher THC sells for more, there is an economic incentive to do it. Related ways numbers creep up include sending the frostiest top bud for testing and reporting results on an over-dried sample. California standardised its test methods partly to stop it. **Why does the same strain test differently at different labs?** The same cannabis strain tests differently at different labs partly because labs differ systematically in sample preparation, extraction and calibration. In 215,285 Washington State results, median THC for THC-dominant flower ran from about 17.6% at the lowest-reporting lab to 23.1% at the highest. The same name can also hide different genotypes, and samples vary in moisture and in which bud was sent. **Is a high terpene percentage on the label believable?** A total terpene label much above about 2% deserves scepticism. A large survey of US commercial flower found total terpenes averaged about 2% of flower weight, and terpenes are volatile, so some are lost in drying and storage. A flower label claiming 6-10% total terpenes is well outside what flower normally tests at, so ask for the certificate of analysis and its test date. **Do indica strains make you sleepy and sativas energetic?** No. Research does not support 'indica for the couch, sativa for energy'. A large US survey found indica, hybrid and sativa labels did not reliably distinguish samples by chemical content, and its authors called the sedating-versus-energising marketing 'specious'. Cannabis is one species, nearly everything sold is a hybrid, and effects vary with the person and dose. As an effects guide, GenetixBay treats the labels as a myth. **Does a strain name guarantee the effect?** No. A cannabis strain name is a claim about genetics, not a guarantee of any effect. Genetic studies of retail cannabis show the same name often hides different genotypes, and effects vary with the person and the dose. On GenetixBay, a name is only backed by a GB-ID with a stated evidence level, and reported effects are treated as reports, never as promises. **Can seeds really hit 42% THC?** No. Seeds marketed to 'hit 42% THC' promise something the cannabis plant cannot make. A 42% total THC label needs about 48% THCA in the dry bud, which would require trichome heads to make up 60-80% of its mass, a lump of kief rather than flower. Ask the breeder for certificates from more than one lab, with test dates and batch numbers; an honest range such as 20-28% means more. **How is total THC calculated?** Total THC on a cannabis label is calculated as THC + 0.877 × THCA. The 0.877 factor is the mass ratio of THC to THCA (about 314.5 / 358.5 g/mol): heating removes a carbon dioxide molecule from each THCA molecule, so 1 g of THCA becomes 0.877 g of THC. A bud with 30% THCA therefore has about 26% total THC. **Does frosty weed mean high THC?** No. Frosty cannabis does not reliably mean high THC. Frost shows how many trichome heads you can see, not how full or mature they are. In a two-year hemp field study, nitrogen raised gland density without significantly raising THC, and in high-THC genotypes gland heads ranged from 40 to 110 µm across. A bud of small or immature heads can test lower than a less sparkly one. **Is purple weed stronger?** No. Purple cannabis is not stronger. The colour comes from anthocyanin pigments, mainly cyanidin-3-rutinoside, which genetics allow and cold brings out. In a 2025 study, anthocyanins peaked at a constant 8 and 15 °C (46 and 59 °F), while cannabidiol content and flower weight rose with temperature instead. Colour and cannabinoids run on separate pathways, so cold nights can give purple but not potency. **Can you judge cannabis quality by looks?** No. You cannot reliably judge cannabis potency or quality by looks. Frost, colour and dense buds reflect visible trichomes, anthocyanins and cultivar structure, not THC. Research shows consumers' potency ratings did not correlate with measured THC, and in a blinded study of 276 volunteers, pleasant aroma tracked liking better than THC did. A named-lab certificate, a smell test and a clean dry and cure tell you more. **What is bag appeal?** Bag appeal is the visual and sensory appeal of cannabis buds: heavy frost, purple or red colour, and tight, dense nugs. It sells product, and it hints at how a plant was grown and handled, but it is not a potency test. GenetixBay's position is that bag appeal does not equal quality; even the founder admits they are 'a sucker for any red strain', which is a fine reason to grow one. **Short answer.** If a jar of flower says more than about **35 % total cannabinoids**, don't believe it. Cannabis flower can't make that much: cannabinoids are made only in the trichome heads, and most of a bud's weight is bract, stem and leaf. Numbers like that come from concentrates, or from lab shopping and inflated testing. Large studies show potency results differ systematically between labs [1], and retail flower labels often overstate THC [2][3]. Treat strain names, sky-high terpene numbers and "indica = couch, sativa = energy" with the same suspicion. > **Buyer beware.** > - **Flower above ~35 % total cannabinoids: not credible.** Above ~30 % total THC is already very rare in large lab datasets [1]. > - **Same strain, different lab, different number.** Some labs report systematically higher THC than others [1]. > - **Labels run high.** In one Colorado retest, about 70 % of flower samples were more than 15 % below their label [2]. > - **Strain names don't guarantee anything** (see [why strain names are unreliable](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md)). > - **Total terpenes average ~2 % of flower weight** [5]. Much higher claims need proof. > - **"Indica = couch, sativa = energy" isn't supported** by the chemistry [5][6]. > > Ask for the full certificate of analysis, the lab's name and the test date. A range of results across batches tells you more than one big number. ## Why flower has a ceiling Cannabinoids are made and stored in **glandular trichomes**. Their acid forms (THCA, CBDA) are produced by the secretory disc cells of each gland and collect in the resin head; the large stalked glands on bracts are the richest source [7]. The tissue the glands sit on (bract and sugar-leaf tissue, pistils, the stem inside the bud) makes almost none, yet it is most of the bud's dry weight. So the potency of flower is limited by two things: 1. **How densely the bracts are covered in glands.** This is genetic, and it has a physical limit: there's only so much bract surface. 2. **How full each gland head is.** Again genetic, and limited by the gland's size. Even the most resinous cultivars still carry all that non-resin plant tissue. That's why separated trichome heads (sieved resin, hash) and extracts test far higher than the flower they came from: removing the plant tissue concentrates the cannabinoids. A label above ~35 % on flower is a number that belongs to a concentrate. The limit itself comes from **Dr. Dedi Meiri** of the **Technion – Israel Institute of Technology** (Laboratory of Cancer Biology and Cannabinoid Research), who stated it at a seminar attended by the GenetixBay founder and said the research behind it was forthcoming [8]. Until that's published, the case rests on the first-principles numbers below and the large lab datasets. Meiri's group is a serious source on cannabis chemistry: it built an LC/MS method that identified 94 phytocannabinoids and profiled 36 of the cultivars most prescribed to patients in Israel [4]. ### Total THC vs THC Labels usually give **total THC** = THC + 0.877 × THCA. The 0.877 factor is the mass ratio of THC to THCA (≈ 314.5 / 358.5 g/mol): heating knocks a CO₂ off each THCA molecule, so 1 g of THCA becomes 0.877 g of THC. A bud with 30 % THCA has about 26 % total THC, and "35 % total cannabinoids" already counts THC, CBD, CBG and the rest together. ## Working it out from first principles You can bound flower potency with four numbers. Every cannabinoid in a bud sits in a gland head, so: **cannabinoids in dry flower ≈ (share of flower dry mass that is gland heads) × (cannabinoid share of gland-head mass)** The first term is the product of how densely the bracts are covered (trichome head density) and how big and full each capitate-stalked head is (resin per gland). Then convert to what the label says: **total THC on the label ≈ cannabinoids × (THCA share of the cannabinoids) × 0.877 × (dry share of the sample as tested)** | Input | Value used | Basis | |---|---|---| | Gland heads as share of flower dry mass (H) | 0.40 (generous) | No direct published measurement; the bud also has to contain bract, pistil, sugar-leaf and stem tissue. | | Cannabinoid share of gland-head mass (C) | 0.80 (generous) | Mechanically separated trichome fractions reached 57–61 % cannabinoids from flower that tested 11.8–29.6 % [9]. Pure heads score higher than kief because kief carries plant debris, but each head also contains cells and membranes, plus the flower's terpenes (about 2 % of flower mass [5]), so it can't be all cannabinoid | | THCA share of the cannabinoids | 0.95 | THC-dominant chemotypes are overwhelmingly THCA [1][5] | | THC per THCA | 0.877 | Molecular-weight ratio (above) | | Dry share as tested | 0.88–1.0 | Cured flower holds roughly 8–12 % water at aw 0.55–0.65 | **Honest upper bound.** 0.40 × 0.80 = **32 % cannabinoids by dry mass**. Even pushing gland heads to 45 % of the bud gives 36 %. Converted: 32 % × 0.95 × 0.877 ≈ **27 % total THC** on a dry basis, or about 24 % as sold at 10 % moisture. Push both generous inputs harder and you reach roughly 30–32 % total THC. That's where the real data top out: the 99th percentile across 215,285 Washington tests was 27.0–31.8 % depending on the lab [1]. **Why 40 %+ isn't credible.** For a label of 42 % total THC, the flower needs 42 / 0.877 ≈ **48 % THCA by dry weight**, before you count any other cannabinoid. At C = 0.80, gland heads would have to be **60 % of the bud's dry mass**. At the 0.60 measured for the best separated trichome fractions [9], they'd be **80 %**. A "bud" that is 60–80 % loose resin heads is a lump of kief, not flower. The number belongs to a concentrate or to a bad test. > **Buyer beware: "our seeds will hit 42 %".** Seed and clone marketing that promises 38, 40 or 42 % THC flower is promising something the plant can't make. Ask the breeder for full certificates of analysis from more than one lab, with test dates and batch numbers, across several grows. A breeder who quotes an honest range (say 20–28 %) is telling you more than one who quotes a headline number. GenetixBay breeders publish ranges and lab names; see [record-keeping and naming ethics](https://genetixbay.com/knowledge/breeding/record-keeping-naming-ethics.md). ## What large datasets show | Study | What they tested | Key finding | |---|---|---| | Jikomes & Zoorob 2018 [1] | 215,285 Washington State test results (after the 2020 correction) from state-certified labs | Labs differed systematically: median THC for THC-dominant flower ranged from about 17.6 % at the lowest-reporting lab to 23.1 % at the highest. Flower "approaching or exceeding 30 %" total THC was very rare; 99th percentile was 27.0 % at the lowest-reporting lab and 31.8 % at the highest | | Schwabe et al. 2023 [2] | 23 flower samples from 10 Colorado dispensaries, retested by one third-party lab | Average measured THC 14.98 ± 2.23 %; ~70 % of samples were more than 15 % below their label; three had half the labelled maximum. Labels ranged 12.8–33.0 % | | Giordano et al. 2025 [3] | 277 products from 52 Colorado dispensaries (178 flower, 99 concentrates) | About 44 % of flower was labelled inaccurately, most overstating THC; flower averaged ~21 % THC; concentrates averaged ~71 % and were labelled far more accurately | Jikomes and Zoorob concluded that many flower products labelled above 30 % total THC "may be inaccurate", and that the differences between labs are likely caused by systematic differences in testing methods [1]. ## What retail flower really tests at Most flower that people believe is in the mid-20s to the 30s really tests in the **mid-teens to low 20s** at best. That isn't a guess; it's what independent retests keep finding: | Data | What it found | |---|---| | Schwabe et al. 2023 [2] | Average measured THC about **15 %**; roughly 70 % of samples more than 15 % below their label | | Giordano et al. 2025 [3] | Flower averaged about **21 %** THC; about 44 % labelled inaccurately, mostly overstated | | Jikomes & Zoorob 2018 [1] | Median THC for THC-dominant flower **17.6–23.1 %** depending on the lab; above 30 % very rare | | Massachusetts shelf audit, 2026 [10] | The regulator retested 63 flower products off the shelf; **13 (about 1 in 5)** fell outside the accepted range of their label | **Reaching 30 % total cannabinoids is a real feat.** It takes elite genetics, a dialled-in environment, a perfect finish and a careful dry. A grower who gets there honestly has done something rare. Yet paid labs hand out numbers like that far too often, and that cheapens the real thing. GenetixBay calls the practice out: on the Bay, a potency number is a claim until it is backed by a named-lab certificate, a test date and, ideally, more than one batch. ## Lab shopping and inflated labels Higher THC sells for more, and the lab is chosen and paid by the producer. That creates an incentive to send samples to whichever lab reports the highest numbers: **lab shopping**. Jikomes and Zoorob noted that price tracking potency may give producers "an economic incentive" to seek higher results [1]. Other ways numbers creep up: - **Unrepresentative samples:** the frostiest top bud goes to the lab; the jar is filled from the whole plant. - **Moisture:** results reported on an over-dried sample read higher per gram than the moist flower you buy. - **Method differences:** sample prep, extraction and calibration standards vary between labs [1]. - **Loose tolerances:** labels are allowed some deviation from the measured value, and many samples still fell outside it [2][3]. **Regulators have acted.** These are public regulator actions, described by the practice rather than by business: - **Massachusetts (2026):** the Cannabis Control Commission bought flower off shelves and retested it; about one product in five fell outside the accepted range of its label, and affected producers had to recall and relabel, retest or destroy the product [10]. - **California (2022–2023):** the Department of Cannabis Control proposed and then adopted standardised cannabinoid test methods, explicitly to address potency inflation and lab shopping [11], and warned labs in 2023 that inaccurate reporting could cost them their licence. - **Other states:** regulators in several states have suspended lab licences or ordered recalls over potency results they judged unreliable. None of this means every high label is fraud. It means a single high number on flower is a claim, not a fact. We criticise the practice; we don't name or accuse a lab, dispensary or breeder unless a regulator has made a public finding. ## The other red flags ### "This strain will do X" A strain name is a claim about genetics, not a guarantee. Genetic studies of retail cannabis show the same name often hides different genotypes, and effects vary with the person and dose. See [why strain names are unreliable](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md). On GenetixBay, a GB-ID with an evidence level is what backs a name. Reported effects are reports, never promises. ### Terpene numbers that are too good In a large survey of US commercial flower, total terpene content averaged about **2 % by weight** [5]. Terpenes are volatile and are lost in drying and storage. A flower label claiming 6–10 % total terpenes is well outside what flower normally tests at; ask for the certificate of analysis and the test date. ### "Indica = couch, sativa = energy" It's one species, *Cannabis sativa*, showing different phenotypes, and nearly everything sold is a hybrid. The labels don't track chemistry. In the same US survey, the Indica/Hybrid/Sativa labels "did not reliably distinguish samples based on their chemical content", and the authors called marketing indicas as sedating and sativas as energising "specious" [5]. Labels track a few terpene-synthase genes at best, not genome-wide ancestry [6]. See [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md). ### "Keep it fresh with a humidity pack" Two-way humidity packs are sold as essential for storage. They're a **marketing gimmick** (house position): a properly dried and cured bud in a full, airtight, dark jar holds its water activity on its own. The only data that says packs improve flower comes from a pack maker's own commissioned test, not from independent research. If a jar has gone too dry, add a fresh bud for a day. See [curing](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md). ## Bag appeal is not quality Frost, purple, red, tight dense nugs: that's **bag appeal**, and it sells. It also tells you less than you'd think. Looks are a clue about how a plant was grown and handled. They aren't a potency test. **Frost is what you can see, not what's in it.** "Frosty" means lots of visible trichome heads. But potency depends on how full and how mature those heads are as well as how many there are, and on how much bract and leaf they sit on. - In a two-year field study of two hemp varieties, nitrogen feeding raised gland density without significantly raising THC, and the authors concluded that gland density "obviously is not a suitable means for the prediction of the THC content" [12]. That's hemp, but the point carries: count isn't content. - In two high-THC genotypes, trichome numbers, stalk length and maturation differed with genotype and plant age, and heads on the same bract were at different stages; the authors note that this variability "can potentially lead to variation in total cannabinoid levels" [13]. Gland heads ranged from 40 to 110 µm across [13]. A frosty bud of small or immature heads can test lower than a less sparkly one with big, full heads. - Visible frost also depends on handling. Rough trimming and drying change trichome morphology [13], and a sample sent to the lab is often the frostiest top bud (see lab shopping above). **People can't judge potency by looking or sniffing.** When untrained consumers rated strains, their potency ratings tracked aroma clusters (citrus-sweet-pungent samples were rated more potent and worth more than earthy-woody ones), but "in neither case was perceived potency correlated with measured THC" [14]. In a blinded study of 276 volunteers, pleasant aroma, not THC potency or dose, was what tracked how much people liked a sample and the effects they reported [15]. If your nose and eyes can't read THC, a label photo certainly can't. **Purple and red are anthocyanins, not potency.** The colour comes from anthocyanin pigments; in cannabis the main one is cyanidin-3-rutinoside, found in purple leaf, stem and flower tissue [16]. Whether a plant can make them is genetic; cold brings them out in plants that carry the trait. In a purple, day-neutral cannabis line grown at 0.5–22 °C, anthocyanins peaked at a constant 8 and 15 °C, while CBD and flower dry weight rose with temperature and tracked plant maturity instead. The authors concluded that anthocyanin regulation is separate from cannabinoid production and yield [17]. Colour and cannabinoids run on different pathways. Cold nights can give you purple; they don't give you potency (see [temperature by stage](https://genetixbay.com/knowledge/environment/temperature-by-stage.md)). Purple leaves in mid-veg can also mean a nutrient or root-zone problem, not genetics: see [purple stems and leaves](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md). > **Founder's aside.** The founder admits they're "a sucker for any red strain". Nothing wrong with that: colour is a perfectly good reason to grow a plant. Just buy it, or keep it, because you love the colour and the smoke, not because the colour promises a number. | What you see | What it tells you | What it doesn't | |---|---|---| | Heavy frost | Lots of visible trichome heads; probably careful handling | How full or ripe the heads are, or the THC % [12][13] | | Purple or red | Anthocyanins: genetics, often brought out by cold [16][17] | Potency, terpenes, quality | | Loud aroma | Plenty of volatiles; a fresh, well-cured sample | THC % [14][15]; but aroma is what tracks enjoyment [15] | | Dense, tight buds | Cultivar structure, good light | Potency | What does tell you something: a full certificate of analysis from a named lab, a smell test, and a proper dry and cure (no hay smell). See [trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md). ## How to buy (or breed) with your eyes open 1. **Read the certificate of analysis:** lab name, test date, batch number, total THC, total cannabinoids, terpenes, moisture or water activity. 2. **Distrust any flower over ~35 % total cannabinoids**, and be cautious above ~30 % total THC. 3. **Compare batches.** A cultivar that tests 20–24 % across several batches and labs is more believable than one 34 % result. 4. **Judge by the plant:** aroma, resin coverage, a proper dry and cure (see [trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md)). 5. **Breeders:** publish ranges and lab names, not just your best number (see [chemotype inheritance](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md)). ## Common mistakes - Buying on the THC number alone. - Comparing results from different labs as if they were the same scale. - Treating a strain name or "indica/sativa" as a promise of effect. - Believing terpene totals that would make the flower sticky with oil. - Buying on frost or colour as if it were a potency test. ## Evidence - Inter-lab differences in reported cannabinoids: *Established* in a large state dataset [1]. - Retail flower labels overstating THC: *Supported* by independent retests [2][3] and a regulator shelf audit [10]. - Most retail flower really testing mid-teens to low 20s: *Supported* [1][2][3]. - Flower above ~35 % total cannabinoids is not credible: **house position**, stated by Meiri at a seminar (publication pending) [8], consistent with large datasets where > 30 % total THC is very rare [1], with cannabinoids being made only in trichomes [7], and with the first-principles bound above [9]. The gland-head share of flower mass is an estimate, not a measured constant. - Indica/sativa labels not predicting chemistry or effects: *Supported* [5][6]; as an effects guide, *Myth* (house position). - Frost (gland density) not predicting THC: *Supported* in hemp [12], consistent with genotype and maturity effects on trichomes [13]; no large drug-type study of density vs THC found. - Consumers unable to judge potency by sensory cues: *Supported* [14][15]. - Purple/red colour being anthocyanins controlled by genetics and temperature, separate from cannabinoids: *Supported* [16][17]. - "Frost and purple mean potency": *Myth*. ## Sources 1. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 (Author correction: Scientific Reports 2020;10:14406. https://doi.org/10.1038/s41598-020-69680-x) 2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 3. Giordano G, et al. 2025. Label accuracy of retail cannabis flower and concentrates in Colorado. Scientific Reports. https://www.nature.com/articles/s41598-025-03854-3 (summary: University of Colorado Boulder, https://www.colorado.edu/today/2025/07/03/can-weed-labels-be-trusted-study-shows-it-depends-what-youre-buying) 4. Berman P, Futoran K, Lewitus GM, Mukha D, Benami M, Shlomi T, Meiri D. 2018. A new ESI-LC/MS approach for comprehensive metabolic profiling of phytocannabinoids in Cannabis. Scientific Reports 8:14280. https://doi.org/10.1038/s41598-018-32651-4 5. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 6. Watts S, McElroy M, Migicovsky Z, et al. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y 7. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1). https://doi.org/10.1111/tpj.14516 8. Meiri D. Seminar remarks (personal attendance by the GenetixBay founder); publication pending. 9. Russo EB, Plumb J, Whiteley VL. 2021. Novel solventless extraction technique to preserve cannabinoid and terpenoid profiles of fresh cannabis inflorescence. Molecules 26(18):5496. https://doi.org/10.3390/molecules26185496 10. Massachusetts Cannabis Control Commission. 2026. Flower shelf potency audit: notices of audit results (63 flower products retested; 13 outside the accepted range of the labelled THC). https://masscannabiscontrol.com/document/potency-audit-results-mederi-inc-august-14-2026/ 11. California Department of Cannabis Control. 2022. California looks to standardize cannabis testing statewide (standard methods proposed to address potency inflation and lab shopping). https://cannabis.ca.gov/2022/07/california-looks-to-standardize-cannabis-testing-statewide 12. Menge-Hartmann U, Höppner F. 1996. Trichomes of pistillate bracts and their relation to the cannabinoid content of two fibre hemp varieties (Brakteentrichome und ihre Beziehung zum Cannabinoidgehalt zweier Faserhanfsorten). Landbauforschung Völkenrode 46(2):49-54. https://agris.fao.org/search/en/records/67a0bb1fb19f43b046c0a3fa 13. Punja ZK, Sutton DB, Kim T. 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 14. Gilbert AN, DiVerdi JA. 2018. Consumer perceptions of strain differences in Cannabis aroma. PLOS ONE 13(2):e0192247. https://doi.org/10.1371/journal.pone.0192247 15. Plumb J, Demirel S, Sackett J, Russo EB, Wilson-Poe AR. 2022. The nose knows: aroma, but not THC mediates the subjective effects of smoked and vaporized cannabis flower. Psychoactives 1(2):70-86. https://doi.org/10.3390/psychoactives1020008 16. Bassolino L, Fulvio F, Pastore C, et al. 2023. When Cannabis sativa L. turns purple: biosynthesis and accumulation of anthocyanins. Antioxidants 12(7):1393. https://doi.org/10.3390/antiox12071393 17. Kim SR, Basnet P, Kovaleski AP, Ellison SL. 2025. Anthocyanin accumulation, inflorescence dry weight and total cannabidiol content have different temperature optima in Cannabis sativa. Journal of Cannabis Research 7:51. https://doi.org/10.1186/s42238-025-00311-w --- # Cannabis growing and breeding glossary > Plain-language definitions of the growing, botany and breeding terms used across GenetixBay, with notes where the popular meaning differs from the scientific one. - Canonical: https://genetixbay.com/knowledge/basics/glossary.html - Category: Basics · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What does F1 mean in cannabis?** F1 in cannabis means the first filial generation: the offspring of crossing two parents, written female first (female x male). F1s of unrelated parents typically show the strongest hybrid vigour, outperforming the parents' average. Crossing F1 siblings gives the F2, where allele pairs segregate and create much more variation. In cannabis, 'F2' usually means sibling-crossed F1s, not selfed plants. **What is a phenotype vs a genotype?** A genotype is a cannabis plant's genetic make-up; a phenotype is what you actually observe, which is the genotype plus the environment plus their interaction. Two clones share a genotype but can look different in different rooms. Growers also use 'pheno' loosely to mean one individual plant from a seed lot, as in 'the #4 pheno', which is really one distinct genotype among siblings. **What is an IBL?** An IBL (inbred line) is a cannabis population inbred over several generations until it breeds fairly true, so seedlings come out much more alike than in a hybrid. No fixed number of generations defines an IBL, so treat the label as a breeder's claim and check the line's documentation. Close inbreeding can also cause inbreeding depression, as hidden harmful recessives become homozygous. **What does S1 mean?** S1 means seed from a cannabis plant pollinated by itself (selfed), usually by reversing one branch or a clone of the same plant so it makes pollen. Because that pollen comes from a female, S1 seed is nearly all female. GenetixBay treats repeated selfing, such as S1 on S1, as a main source of herm-prone lines, so an S1 label deserves a close look at the breeder's grow-out data. **What is a clone-only?** A clone-only, or 'cut', is a selected individual cannabis plant kept only as clones, so the name refers to one specific genotype rather than a seed line. Every rooted cutting is genetically identical to its source, barring rare mutations, and the cut is maintained by keeping mother plants vegetative. Because no seed version exists, the genotype survives only as long as someone keeps it alive. **What is a chemotype or chemovar?** A chemotype or chemovar is a cannabis plant classified by its chemistry rather than its name or looks. The standard scheme has five types: chemotype I is THC dominant, II mixes THC and CBD, III is CBD dominant, IV is CBG dominant and V is near cannabinoid-free. The THC and CBD synthase alleles behave close to codominant, so a plant carrying one of each tends toward the mixed type II. **What does BX mean?** BX means backcross: offspring crossed back to one of its own parents. The generations are numbered BX1, BX2 and so on, also written BC1 and BC2. Breeders use backcrosses to steer a line back toward one parent's traits. The convention for writing any cannabis cross lists the female first (female x male), so the pedigree shows which way each backcross was made. **Short answer.** This is the shared vocabulary for GenetixBay articles and courses. Where growers use a word differently from botanists, both meanings are given. Terms are grouped, then alphabetical within each group. ## Plant and botany | Term | Meaning | |---|---| | **Achene** | The botanical name for a cannabis "seed": one seed inside a hard fruit wall. | | **Bract** | The leafy sheath around each female flower; most glandular trichomes sit here. Growers often call it the **calyx** (botanically, the calyx is a much reduced structure underneath). | | **Cola** | A terminal flower cluster on a main stem or branch. | | **Dioecious** | Separate male and female plants. The natural, long-stable state of cannabis, and of essentially all drug-type cannabis. | | **Monoecious** | Male and female flowers on one plant, bred in on purpose in some modern hemp cultivars. Not the norm for cannabis, and not the same as a stressed hermaphrodite. | | **Hermaphrodite (hermie, intersex)** | A genetic female that also makes pollen sacs or bare anthers ("bananas", "nanners"). An unwanted outlier in a dioecious crop, mainly the result of poor breeding (repeated selfing, careless feminising); stress reveals it. Cull, don't breed from it. See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). | | **Node / internode** | Node: where leaves and branches attach. Internode: stem between nodes. | | **Pistil / stigma** | Growers say "pistils" or "hairs"; strictly, the visible hairs are stigmas. | | **Pre-flower** | Solitary flowers at the nodes before full flowering; used to sex plants. | | **Trichome** | A hair-like outgrowth. Glandular capitate-stalked trichomes make cannabinoids and terpenes. | ## Life cycle and cultivation | Term | Meaning | |---|---| | **Autoflower (day-neutral)** | Flowers by age, not night length. | | **Clone (cutting)** | A rooted piece of one plant; genetically identical to the source, barring rare mutations. | | **Mother** | A plant kept vegetative as a source of clones. | | **Photoperiod** | Flowers in response to long nights. | | **Re-veg** | Returning a flowering plant to vegetative growth by restoring long days. | | **Sinsemilla** | "Without seed": unpollinated female flower. | | **Stretch** | Rapid elongation in the first 2-3 weeks of flower. | ## Genetics | Term | Meaning | |---|---| | **Allele** | One version of a gene. A diploid plant carries two alleles per gene. | | **Dominant / recessive** | A dominant allele shows its effect with one copy; a recessive one needs two. | | **Codominant** | Both alleles show; the heterozygote is a blend of both effects. THC/CBD synthase alleles behave close to this [3]. | | **Genotype** | The genetic make-up. | | **Phenotype** | What you observe: genotype plus environment plus their interaction. Growers say "pheno" to mean one individual plant from a seed lot ("the #4 pheno"). | | **Chemotype / chemovar** | Plant classified by chemistry. Chemotype I (THC dominant), II (THC and CBD mixed), III (CBD dominant), IV (CBG dominant), V (near cannabinoid-free) [3]. | | **Heterozygous / homozygous** | Two different alleles / two identical alleles at a gene. | | **Heritability** | The share of observed variation in a trait that is due to genetic differences, in a given population and environment [1]. | | **Hybrid vigour (heterosis)** | Offspring outperforming the parents' average, typically strongest in F1s of unrelated parents. | | **Inbreeding depression** | Loss of vigour and fertility after close inbreeding, as hidden harmful recessives become homozygous. | | **Locus (plural loci)** | A position on a chromosome; usually a gene. | | **Segregation** | Separation of allele pairs into gametes, which creates variation in F2 and later generations [2]. | ## Breeding notation | Term | Meaning | |---|---| | **P1, P2** | Parents of a cross. Convention: female listed first (female x male). | | **F1** | First filial generation: offspring of two parents. | | **F2, F3...** | Offspring of F1 x F1 (or sibling crosses), and so on. In cannabis "F2" usually means sibling-crossed F1s, not selfed. | | **BX1, BX2 (BC1, BC2)** | Backcross generations: offspring crossed back to one parent. | | **S1** | Seed from a plant pollinated by itself (selfed), usually by reversing one branch or a clone. | | **IBL** | Inbred line: a population inbred over several generations until it breeds fairly true. No fixed generation count defines it; treat the label as a claim. | | **Polyhybrid** | A line with many ancestors from different gene pools, typical of modern "strains". | | **Landrace** | A locally adapted, farmer-maintained population with a distinct identity and history in a region [5]. | | **Clone-only (cut)** | A selected individual kept only as clones; the name refers to one genotype. | | **Tester / test grow** | Seed sent to growers to report how a line performs. | | **Feminised seed** | Seed made with pollen from a sex-reversed female; nearly all progeny female. | | **Regular seed** | Seed from a true male x female; about half males. | ## Naming and records | Term | Meaning | |---|---| | **Cultivar** | A plant population selected for distinct, uniform and stable traits, formally named under the ICNCP [4]. Most cannabis "strains" are not formal cultivars. | | **Strain** | The popular word for a named cannabis line. Not a botanical rank; the same name can hide different genetics. | | **Accession** | A sample entered in a collection (seed bank, genebank) with an ID. | | **GB-ID** | GenetixBay's permanent identifier for lines, batches, plants and documents. See [documenting lineage evidence](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md). | | **Evidence levels L0-L4** | How well a lineage claim is supported: unverified, community reported, breeder reported, documented, lab-confirmed. | ## Evidence ladder used in GenetixBay articles *Established* (multiple studies or extension consensus), *Supported* (some research or strong grower consensus), *Grower practice* (widely used, little research), *Contested*, *Myth*. ## Sources 1. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 2. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 3. Hillig KW, Mahlberg PG. 2004. A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae). American Journal of Botany 91(6):966-975. https://doi.org/10.3732/ajb.91.6.966 4. Brickell CD, et al. (eds). 2016. International Code of Nomenclature for Cultivated Plants, 9th edition. Scripta Horticulturae 18. ISHS. https://www.ishs.org/scripta-horticulturae/international-code-nomenclature-cultivated-plants-ninth-edition 5. Villa TCC, Maxted N, Scholten M, Ford-Lloyd B. 2005. Defining and identifying crop landraces. Plant Genetic Resources 3(3):373-384. https://doi.org/10.1079/PGR200591 --- # Cannabis plant biology: the parts and what they do > Cannabis sativa is a fast-growing annual herb in the hemp family. Most plants are either male or female, it flowers in response to long nights (unless it carries autoflower genetics), and the cannabinoids and terpenes growers want are made in glandular trichomes concentrated on the female flower heads. - Canonical: https://genetixbay.com/knowledge/basics/cannabis-plant-biology.html - Category: Basics · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What are the parts of a cannabis plant?** A cannabis plant is made up of a taproot and fibrous roots, a stem with nodes where leaves and branches arise, fan leaves with usually 5-9 serrated leaflets, small resin-coated sugar leaves, and either female flower clusters (bracts with stigmas) or male flowers with anthers. Glandular trichomes on the flowers make the resin, and a fertilised female flower forms a single seed in a hard shell. **Where are THC and terpenes made in the plant?** THC and terpenes are made in glandular trichomes, mainly the capitate-stalked 'mushroom' glands densest on the bracts of unpollinated female flowers. The plant actually makes THCA, the acid form, in the trichome's secretory cells and stores it in the gland head. It becomes neutral THC mainly through heat (decarboxylation), not on the living plant. This trichome localisation is established science. **What is a trichome?** A trichome is a tiny hair-like outgrowth on the plant surface. On cannabis, the glandular types, large capitate-stalked 'mushroom' glands plus smaller sessile and bulbous ones, are resin factories: secretory cells make cannabinoid acids and terpenes and store them in the gland head. They are densest on female bracts and sugar leaves, which is why sugar leaves are so resin-coated. **Is cannabis a male and female plant?** Yes, cannabis is dioecious: individual plants are normally either male or female, with sex set by X and Y chromosomes (XX female, XY male). That separation has been stable for millennia. Intersex or 'hermie' plants are unwanted outliers, which GenetixBay attributes mainly to poor breeding. Growers usually keep only females, because unpollinated female flowers produce the seedless, resin-rich buds called sinsemilla. **What is the difference between a calyx, a bract and a pistil?** On a female cannabis flower, the bract is the small leafy sheath wrapping the single ovary; growers usually call it the 'calyx', though botanically it is a bract. The 'pistils' or 'hairs' growers talk about are really the two stigmas that stick out to catch pollen. Bracts carry most of the glandular trichomes, so they matter far more for resin than the stigmas do. **How many chromosomes does cannabis have?** Cannabis is diploid with 2n = 20 chromosomes: nine pairs of autosomes plus one pair of sex chromosomes, XX in females and XY in males. Cytogenetic research established this XY system. The genes that decide THC versus CBD sit in large, repeat-rich, low-recombination regions of the genome, which is why chemotype tends to be inherited as a single block. **Short answer.** Cannabis (*Cannabis sativa* L., family Cannabaceae, which it shares with hops) is an annual, wind-pollinated herb. Plants are either male or female (dioecious), with sex set by X and Y chromosomes; that separation has been stable for millennia, and intersex ("hermie") plants are unwanted outliers, mostly from poor breeding (see [male, female and hermaphrodite plants](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md)). The resin that growers value (cannabinoids such as THCA and CBDA, plus terpenes) is made in glandular trichomes, which are densest on the bracts of unpollinated female flower heads. ## What's happening Cannabis grows fast in long days, then switches to flowering when nights get long (photoperiod types) or after a fixed age (autoflowering types). The flowering switch is less "turning on flowers" than a change in shoot architecture: the growing tips stop making long internodes and start building the compact, branched flower clusters we call colas [2]. The genome is diploid with 2n = 20 chromosomes: nine pairs of autosomes plus the sex chromosomes (XX female, XY male) [3]. The genes that decide THC versus CBD sit in large, repeat-rich, low-recombination regions, which is why chemotype tends to be inherited as a block (see [chemotype inheritance](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md)) [4]. Taxonomy is argued over. Most botanists today treat cannabis as one species, *Cannabis sativa*, with subspecies and varieties; the familiar "sativa / indica / ruderalis" labels are a separate, popular vocabulary that does not map cleanly onto genetics (*Contested*; see [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md)) [1][5]. ## The parts | Part | What it is | Why a grower cares | |---|---|---| | Taproot and fibrous roots | Primary root plus a dense lateral mass | Root-zone health limits everything above it | | Stem and nodes | Hollow-ish stem; leaves and branches arise at nodes | Node spacing (internode length) shows light and genetics | | Fan leaves | Palmately compound leaves, usually 5-9 serrated leaflets (1-3 on seedlings and late flower) | Main photosynthetic surface; first place deficiencies show | | Sugar leaves | Small, resin-coated leaves inside flower clusters | Trimmed at harvest; trichome-rich | | Stipules and pre-flowers | Small structures at nodes; the first solitary flowers form here | First visual sign of sex [2] | | Female flower | A single ovary wrapped in a **bract** (often called "calyx" by growers) with two **stigmas** ("pistils", "hairs") | Bracts carry most glandular trichomes; stigmas catch pollen | | Male flower | Five tepals and five anthers hanging on short stalks | Sheds pollen about 1-3 weeks after opening; one plant can seed a room | | Glandular trichomes | Capitate-stalked "mushroom" glands, plus smaller sessile and bulbous types | Where cannabinoids and terpenes are made and stored | | Seed (achene) | Single seed in a hard shell, mottled or plain | Carries half its genes from each parent | ## Where the resin is made Cannabinoids are made as acids (THCA, CBDA, CBGA) inside the secretory cells of glandular trichomes and pushed into the head's storage cavity. They become neutral THC or CBD mainly by heat (decarboxylation), not on the living plant (*Established*) [1]. Unpollinated female flowers keep building bracts and resin for longer, which is why drug-type crops are grown seedless (sinsemilla). ## Numbers that matter | Parameter | Typical value | Notes | |---|---|---| | Chromosome number | 2n = 20 (18 autosomes + XX or XY) | [3] | | Haploid genome size | ~818 Mb (female) / ~843 Mb (male) | Flow cytometry estimates | | Leaflets per fan leaf | 5-9 mature | 1-3 on first true leaves and at the top in flower | | Height outdoors | 1-5 m (3-16 ft) | Strongly genotype and season dependent | | Life cycle | 3-9 months seed to harvest | See [life cycle](https://genetixbay.com/knowledge/basics/life-cycle.md) | ## Common mistakes - Calling the stigma the "pistil" and assuming its colour tells you ripeness. Stigma browning is a rough cue; trichome maturity is the better one. - Assuming "sativa" and "indica" describe genetic ancestry. In modern hybrids they mostly describe shape and expected effect (*Contested*). - Thinking male plants contain no cannabinoids. Males make resin too, just far less flower mass. ## Evidence - Dioecy with XY sex determination and 2n = 20: *Established* [3]. - Trichome localisation of cannabinoid synthesis: *Established* [1]. - Photoperiod response mainly reshapes the shoot apex rather than starting flowers from zero: *Supported* (one detailed study on three medical cultivars) [2]. - Single-species treatment: *Supported* but debated [1][5]. ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 2. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 3. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 4. Laverty KU, Stout JM, Sullivan MJ, et al. 2019. A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci. Genome Research 29(1):146-156. https://doi.org/10.1101/gr.242594.118 5. McPartland JM. 2018. Cannabis systematics at the levels of family, genus, and species. Cannabis and Cannabinoid Research 3(1):203-212. https://doi.org/10.1089/can.2018.0039 --- # Male, female and hermaphrodite cannabis: how sex works > Cannabis is dioecious: females are XX and males XY, and the species has kept separate sexes stably for millennia. Hermaphrodite (intersex) plants are unwanted outliers, mostly the result of bad breeding such as repeated selfing, careless feminising and untested seed; stress reveals the weakness in susceptible plants. Cull herm-prone plants and never breed from them. Seed from a female's own male flowers is almost all female, which is how feminised seed works and why herm tendency passes straight on. - Canonical: https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.html - Category: Basics · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I tell a male from a female cannabis plant?** Look at the first solitary flowers at the nodes, usually visible about 4-6 weeks from seed under long days, with a 30-60x loupe. A female shows a teardrop-shaped bract with two white or coloured stigmas (hairs). A male shows a small round ball on a short stalk with no hairs, which later opens into pollen sacs. Don't mistake stipules, the small leafy spurs at each node, for pre-flowers. **What is a hermaphrodite cannabis plant?** A hermaphrodite (intersex) cannabis plant is a genetic female that also makes male flowers or anthers. It can grow pollen sacs among its buds, often lower down or early in flower, or bare yellow anthers called 'bananas' or 'nanners' inside mature buds. A herm can self-pollinate, seed neighbouring plants and pass the tendency to its seed, so it is unwanted in any sinsemilla or breeding grow. **Are hermaphrodites natural in cannabis?** No. Hermaphrodites are not a natural tendency of cannabis, according to the GenetixBay breeder position. The species is dioecious, with an old, degenerated Y chromosome showing a long, stable history of separate sexes. Herm-prone lines come mainly from bad breeding: repeated selfing (S1 on S1), careless feminising and untested 'pollen chucker' releases. A 5-10% intersex rate in one commercial facility signals poor genetics, not normal cannabis. **What are bananas or nanners on my bud?** Bananas or nanners are bare yellow male anthers poking out of female cannabis buds, usually in late flower. They are a form of hermaphroditism and often appear after a light leak, heat, an irregular dark period or a very late harvest. The stress is the trigger, but the readiness to respond is genetic, so they are not normal. Remove them with tweezers, fix the trigger and never keep that plant as a mother. **Does stress cause hermaphrodites?** Stress does not turn a genetically stable cannabis plant hermaphrodite; it reveals plants that are already susceptible. Light leaks, heat or irregular dark periods can trigger intersex flowers, but a stable plant in the same room stays female. Research supports this, and GenetixBay treats it as a firm breeder position. Blaming only the light leak and keeping the plant is a mistake: cull it from breeding plans. **Can I test seedling sex early?** Yes. A PCR or PACE DNA test can identify male cannabis plants from the first true leaves with high accuracy, using validated Y-linked markers. Cheaper options are watching pre-flowers about 4-6 weeks from seed, or flowering a cutting on 12/12, which gives an answer in roughly 1-2 weeks. A DNA test cannot predict whether a genetic female will later turn hermaphrodite; only growing it out shows that. **Are seeds from a hermie plant all female?** Yes, seeds from a hermaphrodite cannabis plant's own pollen are nearly all female, because that pollen carries only X chromosomes. A controlled study by Punja and Holmes in 2020 found seed from hermaphroditic flowers produced only female plants, while cross-fertilised seed gave about 1:1. The catch is that the herm tendency passes straight on, so GenetixBay advises never saving or breeding from that seed. **Short answer.** Females (XX) make seed-bearing flowers with white or coloured stigmas; males (XY) make pollen sacs that hang like small bunches of grapes. Cannabis is dioecious, and has kept separate sexes stably for millennia [1][2]. A "hermaphrodite" (intersex) plant is a genetic female that also makes male flowers or anthers. It is an unwanted outlier, and herm-prone plants are **mainly the product of bad breeding**, not a natural tendency of the species. Pollen from a herm carries only X chromosomes, so its seed is nearly all female [3]: the tendency passes straight on. Cull those plants; don't breed from them. > **Breeder's standard.** A sound cannabis line stays dioecious: females stay female under normal room conditions. Mothers and pollen donors must run clean for at least two cycles before use. Plants that herm are culled with their clones, never selfed or reversed, and the herm rate of every line is recorded and disclosed. See [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) and [record-keeping and naming ethics](https://genetixbay.com/knowledge/breeding/record-keeping-naming-ethics.md). ## What's happening Cannabis has an XY system with 2n = 20 [1]. Its sex chromosomes are old and the Y is strongly degenerated, with hundreds of sex-linked genes identified [2]. That is the signature of a long, stable history of separate sexes. In a regular (non-feminised) seed lot, expect roughly 1:1 males to females. Real lots often skew one way; that is normal sampling noise, not proof of anything. Sex expression is also controlled by hormones. Ethylene promotes female flowering; blocking ethylene action with silver ions (silver thiosulfate) makes genetic females grow fertile male flowers. That is the controlled, deliberate basis of feminised seed [6]; see [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md). The fact that sex *can* be forced with chemicals doesn't mean plants should switch on their own. The GenetixBay position, from long breeder experience: herm-prone lines come mostly from **repeated selfing (S1 on S1)**, **careless feminising** with unproven donors or stress-herm pollen, and **"pollen chuckers"** who release untested crosses. Stress such as light leaks, heat or irregular dark periods **reveals** susceptible genetics; a stable plant in the same room stays female. ## How to recognise each sex | Sign | Female | Male | Hermaphrodite / intersex | |---|---|---|---| | First solitary flowers at nodes (often visible weeks 4-6 from seed under long days) [5] | Teardrop bract with 2 stigmas | Round ball on a short stalk, no hairs | Both types on one plant | | In flower | Dense clusters of bracts and stigmas | Clusters of pollen sacs that open into 5 tepals | Pollen sacs among buds, or bare yellow anthers ("bananas", "nanners") inside buds | | Timing | Shows a little later | Often shows first, opens sooner | Commonly appears in flower, often after a stress the rest of the room tolerated | | Risk | None | Seeds the whole room once sacs open | Self-pollinates, seeds neighbours, and passes the tendency on | ## Two kinds of "hermie" 1. **Pollen sacs (staminate flowers)** forming among female flowers, often lower on the plant or early in flower. A clear genetic defect: cull. 2. **Exposed anthers ("nanners")** poking out of mature buds, often in late flower, typically after a light leak, heat, an irregular dark period or a very late harvest. The stress is the trigger; the readiness to respond is genetic. Treat it as a warning about that plant, not as normal behaviour. Punja and Holmes (2020) found anthers and pollen in hermaphroditic inflorescences looked like those of normal males, and seed from them produced only female plants, while cross-fertilised seed gave about 1:1 [3]. They saw intersex flowers on about 5–10% of plants in one commercial facility [3]. GenetixBay reads that rate as evidence of poor genetics in those cultivars, not as normal cannabis: the founder, who has grown thousands of cultivars, doesn't see it in older lineages, only in the recent wave of low-quality releases. Drug-type cannabis has been recorded as dioecious throughout its history: growers and writers have always distinguished male from female plants, and ancient Chinese texts already used separate names for male and female hemp. Monoecious hemp, with both sexes on one plant, exists only because 20th-century fibre breeders selected for it on purpose; it is not the norm and says nothing about how drug-type cannabis behaves. Selfing, too, was historically an emergency measure, used to save a line when no male was left, not a trait anyone wanted. ## Sexing early | Method | When | Accuracy | Cost | |---|---|---|---| | Watch pre-flowers | ~4-6 weeks from seed in long days | Good with a loupe (30-60x) | Free | | Take a cutting and flower it on 12/12 | Any time | Good; result in ~1-2 weeks | Space and time | | PCR or PACE DNA sex test | From the first true leaves | High, with validated markers [4] | Lab fee | DNA tests detect male-specific (Y-linked) sequence. They tell you a plant is genetically male; they do **not** tell you whether a genetic female will turn hermaphrodite later. Only growing it out tells you that. ## What to do 1. Not making seed? Remove males before the sacs open. Pollen travels on air and clothing. 2. Find a few nanners in late flower? Remove them with tweezers, fix the trigger, check daily, consider harvesting a little early, and don't keep that plant as a mother. 3. Find a plant with pollen sacs? Remove it from a sinsemilla grow and cull it from any breeding plan. 4. Log it in your journal with photos and the week. Hermaphroditism data is what makes a GenetixBay line record trustworthy. ## Common mistakes - Mistaking stipules (small leafy spurs at each node) for pre-flowers. - Accepting hermies as "just cannabis". A well-bred line doesn't do it. - Blaming only the light leak and keeping the plant. The leak exposed the weakness. - Believing feminised seed can never make a male. Rare true males and intersex plants still occur, more so from careless feminising. ## Evidence - XY system and sex-linked genes, dioecious species: *Established* [1][2]. - Silver ions induce male flowers on genetic females: *Established* [6]. - Hermaphrodite-derived seed is female: *Established* (one controlled study confirms the long-held grower observation) [3]. - Stress reveals susceptible plants; it doesn't make sound ones herm: *Supported* [3] and breeder experience. - Herm-prone lines mainly from breeding practice; cull and don't breed from them: GenetixBay house position (breeder experience). Controlled cannabis heritability data are limited. ## Sources 1. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 2. Prentout D, Razumova O, Rhone B, et al. 2020. An efficient RNA-seq-based segregation analysis identifies the sex chromosomes of Cannabis sativa. Genome Research 30(2):164-172. https://doi.org/10.1101/gr.251207.119 3. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 4. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 5. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 6. Lubell JD, Brand MH. 2018. Foliar sprays of silver thiosulfate produce male flowers on female hemp plants. HortTechnology 28(6):743-747. https://doi.org/10.21273/HORTTECH04188-18 --- # Photoperiod vs autoflower, and how autoflowering is inherited > Photoperiod cannabis flowers when nights get long; autoflowering (day-neutral) cannabis flowers by age, even under 18-24 h light. In the populations studied so far, autoflowering behaves as a single recessive gene (Autoflower1, on chromosome 1): a photoperiod x auto F1 is all photoperiod, and about 1 in 4 of its F2 plants are autos. - Canonical: https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.html - Category: Basics · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the difference between autoflower and photoperiod?** Photoperiod cannabis flowers only when nights get long enough, usually 12 hours of darkness indoors, so the grower decides how long it vegetates. Autoflowering cannabis is day-neutral and starts flowering at a fixed age, usually 3-5 weeks from sprouting, whatever the light schedule. Photoperiods can be cloned and kept as mothers; autos finish seed to harvest in about 9-14 weeks but are impractical to clone. **Is the autoflower gene dominant or recessive?** The autoflower trait is recessive in every population mapped so far. Research by Toth and colleagues in 2022 located a major locus, Autoflower1, on chromosome 1, and a plant needs two copies of the auto allele to autoflower. Heterozygous plants still behave as photoperiods, though in field trials they flowered about two weeks earlier. Whether all commercial autos share this locus is still contested. **If I cross an auto with a photoperiod, what do I get?** Crossing an autoflower with a photoperiod gives an F1 that is 100% photoperiod, because the auto trait is recessive and every F1 plant carries just one copy. Crossing those F1 plants together gives an F2 where about 1 in 4 plants autoflower. Backcrossing the F1 to the auto parent gives roughly half autos, so recovering autos from such a cross takes at least two generations. **Can I grow autos on 12/12?** Yes, autoflowers will still flower on 12/12, because they flower by age rather than night length. But it wastes their potential: an auto on 12/12 gets much less daily light than on its usual 18-20 hours, which gives about 1.5-1.7 times the daily light at the same intensity. With a fixed countdown, the plant cannot make up the lost growth later. **What light schedule for autoflowers?** Autoflowers are usually grown on 18/6 to 20/4 from seed to harvest, with no switch to 12/12 needed. Some growers use 24/0, though that is debated. At the same intensity, 18-20 hours gives an auto about 1.5-1.7 times the daily light of a 12/12 photoperiod, which also means using that much more lighting power per day. Per kilowatt-hour, autos are a closer race. **Why did my autoflower not flower?** An 'autoflower' that never flowers under long days is almost always a photoperiod plant in disguise. Autoflowering is recessive, so a seed must carry two copies of the auto allele, and poorly stabilised lines throw photoperiod plants. That is a quality-control failure by the breeder, not bad luck. A true auto normally starts flowering about 3-5 weeks from sprouting, whatever the light schedule. **Are autos better than photoperiods?** Whether autos are better than photoperiods depends on what 'better' means. Autoflowers are very hard to beat on yield per square foot per year, because they finish in about 9-14 weeks. Photoperiods give more yield per plant, are more forgiving, can be cloned and kept as mothers, and usually test slightly higher. A dialled-in sea of green or SCROG with a dedicated nursery can out-yield autos per area. **Do autos yield more per year?** Autoflowers usually yield more per square foot per year than photoperiods vegged in the same space. A 12-week auto cycle fits about 4.3 harvests a year versus about 3.7 for a 14-week photo cycle, so an auto needs only about 86% of the photo's per-run yield to match it. Against a sea of green with a dedicated nursery, about 5.2 cycles a year, the auto must out-yield by about 20%. **Are autoflowers less potent?** Autoflowers usually test slightly below their photoperiod sisters, in the experience of the GenetixBay founder, but the best elite autos match them; they have had one lab-test at 30%, a rare feat for any flower. No controlled head-to-head study of matched auto and photoperiod lines has been found, so treat this as experienced grower observation rather than research. Breeding has steadily narrowed the gap. **Are autoflowers good for beginners?** Autoflowers are good for beginners, but not because they are easy. They are short, quick and need no light-schedule change, so a beginner gets a harvest in about 9-14 weeks. Yet autos run on a strict countdown and punish overwatering, transplanting, topping and hunger with smaller yields. GenetixBay labels 'autos are easy' a myth: they quickly show who has a green thumb. **Short answer.** A photoperiod plant waits for long nights (12 h dark indoors) to flower; you choose how long it vegetates. An autoflower starts flowering at a fixed age, usually 3-5 weeks from sprouting, whatever the light schedule. In mapped populations, autoflowering is a **single recessive trait**: a plant must carry two copies of the auto allele to autoflower [1]. ## What's happening Photoperiod cannabis measures night length. Day-neutral (autoflowering) plants lack that brake: their flowering switch runs on age. Autoflowering germplasm is usually traced to northern or Central Asian populations popularly called "ruderalis" (*Supported* as a history claim; the taxonomy itself is contested) [4]. ## How autoflowering is inherited Toth et al. (2022) mapped a major locus, **Autoflower1**, to chromosome 1 using bulked segregant analysis. Segregating populations fit a single recessive gene: about 25% of F2 plants flowered under long days (observed 31.8% and 27.3%, not significantly different from 25%) [1]. Call the photoperiod allele **A** and the auto allele **a**: | Cross | Offspring genotypes | What you see | |---|---|---| | Photo (AA) x Auto (aa) | all Aa | 100% photoperiod (F1) | | F1 (Aa) x F1 (Aa) | 1 AA : 2 Aa : 1 aa | ~75% photo, ~25% auto (F2) | | F1 (Aa) x Auto (aa) (backcross) | 1 Aa : 1 aa | ~50% photo, ~50% auto | | Auto (aa) x Auto (aa) | all aa | 100% auto | Two useful details from the same study [1]: - **Heterozygotes are not identical to pure photoperiods.** In the field, Aa plants flowered about two weeks earlier than AA plants and were intermediate in height and biomass, but they still did not flower under continuous light. So "recessive" describes autoflowering itself, not every effect of the gene. - **Not every auto source has been shown to share this locus.** Some day-neutral hemp cultivars did not match the markers, and a complementation cross was inconclusive. The authors say it is not clear the mechanism is the same in all cultivars (*Contested* for the whole gene pool). A 2023 preprint mapping day-neutral flowering in an F2 of 318 plants also found clean two-class segregation with no intermediate plants (*Supported*, not yet peer reviewed) [5]. An industry claim names a pseudo-response regulator (PRR37-like) gene as the candidate; treat that as unconfirmed until peer-reviewed. ## Numbers that matter | Parameter | Photoperiod | Autoflower | |---|---|---| | Flowering trigger | Night length past a critical value (often ~10-11 h dark; cultivar specific) [2] | Plant age | | Indoor veg schedule | 18/6 typical | Not needed | | Indoor flower schedule | 12/12 | 18/6 to 20/4 common; 24/0 used, debated | | Seed to harvest | ~3-5 months indoors | ~9-14 weeks | | Clone and re-veg | Yes, keep a mother indefinitely | Clones flower on the parent's clock; impractical | | Recovery from stress | Can veg longer to recover | Little time to recover; avoid heavy stress early | > **House position: autoflowers.** An auto runs on a strict countdown from germination, so any setback costs it time it can't get back. **Plant it straight into its final pot**: transplanting is almost a no-no, because of how the auto's taproot reacts (the founder's observation, compared with photoperiods). **Train with LST, don't top**: topping will never produce what proper low-stress training does on an auto. *Grower practice*, house-endorsed. ## Are autos better? Better how? Ask "are autos better?" and the honest answer is: how long is a piece of string? Better at what? **Per square foot per year: very hard to beat.** An auto goes from seed to jar in about 9–14 weeks with no veg in the flower space, so you fit more harvests into a year. The only photoperiod setup that reliably beats it on space is a dialled-in sea of green or SCROG fed by a dedicated nursery, where the flowering space only ever holds flowering plants (see [SOG](https://genetixbay.com/knowledge/training/sog.md) and [SCROG](https://genetixbay.com/knowledge/training/scrog.md)). **The arithmetic.** Yield per square foot (or m²) per year = yield per cycle × cycles per year. The cycles are where autos win: | Setup | Weeks the space is tied up per cycle | Cycles a year | Per-cycle yield an auto needs to tie | |---|---|---|---| | Photoperiod, vegged in the same space (4 wk veg + 9 wk flower + 1 wk reset) | 14 | ~3.7 | ~86 % of the photo's | | Photoperiod SOG/SCROG with a dedicated nursery (9 wk flower + 1 wk reset) | 10 | ~5.2 | ~120 % of the photo's | | Autoflower sown in its final pot (11 wk seed to harvest + 1 wk reset) | 12 | ~4.3 | — | Divide 52 weeks by the weeks per cycle; the last column is photo cycles ÷ auto cycles. The week counts are typical, not fixed: a 9-week auto or a 12-week photo moves the numbers, so plug in your own. What the table shows is the shape of the argument. Against a photo that vegs in the flowering space, an auto only has to yield about 86 % as much per run to match it per year, and a good auto does. Against a dialled-in sea of green with its own nursery, the auto would need to out-yield the photo by about a fifth per run, which is a big ask. (The nursery's own space and power aren't counted in that row, which flatters it.) For scale, one controlled study of a photoperiod cultivar flowered for 81 days at 12/12 measured 116 g/m² of dry flower at the lowest light level and 519 g/m² at the highest (1,800 µmol/m²/s at the canopy), rising in a straight line in between [6]. We haven't found a comparable peer-reviewed g/m² figure for autoflowers. One more honest note: autos usually run 18–20 h of light, so at the same intensity they get 1.5–1.7 times the daily light (and use that much more lighting power per day) as a 12/12 photo. Per square foot they're hard to beat; per kilowatt-hour it's a closer race. **Cannabinoids: usually a little behind, sometimes level.** In the founder's experience, autos usually test slightly under their photoperiod sisters, but the best of them give photos a real run. We haven't found a controlled head-to-head study of matched auto and photo lines, so treat this as experienced grower observation. [Breeding autoflowers](https://genetixbay.com/knowledge/breeding/breeding-autoflowers.md) explains why autos lagged and how breeders closed the gap. > **Founder's records.** The founder has had an elite autoflower lab-test at **30 %** and has pulled **3/4 lb (about 340 g) in under 80 days**. That's one grower's results with one elite line, not a typical number: 30 % is a rare feat for any flower (see [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md)). It shows what the ceiling looks like when everything goes right. **Finicky: any stress costs yield.** An auto can't be vegged longer to recover. Overwater it, transplant it, top it, let it get root-bound or hungry in week 3, and the clock keeps running: it flowers on schedule, smaller. That's why the house rules above are so strict. **"Good for beginners": true, but not because they're easy.** Autos are short, quick and need no light-schedule change, so a beginner gets a harvest fast. But they're the opposite of forgiving. They show very quickly who has a green thumb and who doesn't. An elite auto grower naturally makes an even better photoperiod grower, because a photo forgives what an auto punishes. It doesn't work the other way round. | Better how? | Autoflower | Photoperiod | |---|---|---| | Yield per area per year | Very hard to beat | Beats autos with a dialled-in SOG/SCROG and dedicated nursery | | Yield per plant | Lower | Higher; veg as long as you like | | Cannabinoids | Usually slightly under photo sisters; the best match them | The benchmark | | Forgiveness | Very little: stress costs yield | Can veg longer to recover | | Light power per day | 18–20 h | 12 h in flower | | Clones, mothers, selection | Impractical | Yes | | Learning curve | Quick feedback, harsh lessons | More forgiving | ## Decision guide 1. Want the shortest first grow, the most harvests per square foot without a nursery, or outdoor crops at high latitude? Autoflower, and be strict with it. 2. Want to keep a mother, clone, select and breed? Photoperiod. 3. Breeding autos? Read [breeding autoflowers](https://genetixbay.com/knowledge/breeding/breeding-autoflowers.md) first: it takes at least two generations to recover autos from a photo cross. ## Common mistakes - Expecting F1 "auto x photo" seed to autoflower. It won't if the trait is recessive. - Transplanting autos at all, or topping them. They don't pause the clock while recovering: sow into the final pot and use [LST](https://genetixbay.com/knowledge/training/lst.md). - Treating autos as the easy option. They punish mistakes harder than photos do. - Assuming every seed in an "auto" pack is homozygous. Poorly stabilised lines throw photoperiod plants; this is a quality-control failure, not bad luck. ## Evidence - Day-length control of photoperiod flowering and cultivar-specific thresholds: *Established* [2][3]. - Single recessive locus Autoflower1 in the mapped populations: *Supported* (peer reviewed, limited germplasm) [1]. - That all commercial autos share the same locus: *Contested* [1]. - "Ruderalis origin" of the trait: *Supported* as history, label as a claim. - Autos winning on yield per area per year (except against a dialled-in SOG/SCROG with a nursery): *Supported* by cycle arithmetic and the founder's experience; per-cycle auto yields in g/m² need peer-reviewed data. Photo yield response to light: *Supported* [6]. - Autos testing slightly under photo sisters: founder's observation; no controlled comparison found. - "Autos are easy": *Myth* (house position). ## Sources 1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 3. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 4. Hillig KW. 2005. Genetic evidence for speciation in Cannabis (Cannabaceae). Genetic Resources and Crop Evolution 52:161-180. https://doi.org/10.1007/s10722-003-4452-y 5. Genetic mapping of SNP markers and candidate genes associated with day-neutral flowering in Cannabis sativa L. (preprint). bioRxiv 2023.04.17.537043. https://www.biorxiv.org/content/10.1101/2023.04.17.537043 6. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # Regular, feminised, autoflower or clone: choosing your starting material > Regular seed gives about half males and is what breeders need; feminised seed gives nearly all females and suits growers who want flower; autoflowers flower by age; clones copy one known plant but can carry pests and viroids. Each choice changes what you can do next. - Canonical: https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.html - Category: Basics · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should I buy regular or feminised seeds?** Buy feminised seeds if you just want flowers: nearly every plant is female, which saves space and time. Buy regular seeds if you want to breed, hunt phenotypes or preserve a line, because they give roughly half real males. Regular seed means sexing plants and removing males before they shed pollen. Either way, choose a breeder who can show grow-out data for the batch. **Are feminised seeds more likely to hermie?** Well-made feminised cannabis seed should not hermie more. The GenetixBay breeder position is that herm-prone seed is mainly breeder error: seed from a female that hermed on its own, from S1-on-S1 stacking or from untested 'pollen chucker' batches carries that tendency. Seed from a stable female reversed with silver thiosulfate, then grown out and culled, is different. Ask for the batch's grow-out herm rate. **Are clones better than seeds?** Clones are not simply better than seeds; they are a different tool. A clean, tested clone is the only way to get one known cannabis genotype exactly, with uniform crops. But cuttings can carry hop latent viroid, mites, thrips, aphids and powdery mildew, so ask for a recent negative viroid test and quarantine every clone for 2-3 weeks. The same named cut from two sources can also differ slightly. **What does a seed pack's GB-PKG code mean?** A GB-PKG code is unique to one GenetixBay seed pack, and scanning it activates that pack to your account. The pack links to a GB-BAT record for its batch, showing parent plants, pollination date and whether it is feminised or regular, and to a GB-GEN record for the line. Check the line's evidence level, from L0 to L4, before trusting its stated parentage. **Can I breed with feminised seeds?** You can breed with feminised seeds only in a limited way, because they give no real males. Any cross must use pollen from a sex-reversed female, which makes more all-female seed, and repeated selfing such as S1 on S1 is a main source of herm-prone lines. For proper breeding, pheno hunts or preserving a line, start with regular seed. Buying feminised seed for a breeding project is a common mistake. **Short answer.** If you want flowers, feminised seed saves space and time. If you want to breed, you need regular seed (real males), or you need to plan for feminised-only work. If you want one known plant exactly, a clean, tested clone is the only way. Autoflowering is a separate choice about flowering, and it comes in both regular and feminised seed. ## The options | Material | What you get | Best for | Trade-offs | |---|---|---|---| | Regular seed | ~1:1 males to females, real genetic males | Breeding, pheno hunts, preserving a line | Must sex and remove males | | Feminised seed | Nearly all females, made with pollen from a sex-reversed female [1][2] | Flower production | No males to breed with; only as sex-stable as the reversed donor and the breeder's culling | | Autoflower (regular or feminised) | Flowers by age [4] | Speed, small spaces, high latitudes | Can't usefully clone or keep mothers | | Clone (cutting) | A copy of one genotype | Known performance, uniform crops | Pests, mildew, hop latent viroid (HLVd) [3]; somatic mutations accumulate in long-kept mothers [5] | ## Do feminised seeds hermie more? Well-made feminised seed shouldn't. The GenetixBay breeder position: cannabis is dioecious and stable, and herm-prone seed is mainly breeder error. Feminised seed from a female that hermed on its own (or under stress), from S1-on-S1 stacking, or from a "pollen chucker" who never grew the batch out carries that tendency into every seed, because seed from hermaphroditic flowers is female [1]. Seed made by controlled reversal (silver thiosulfate) of a female proven stable over several runs, then grown out and culled, is a different product. Controlled data comparing intersex rates between well-made feminised and regular seed are scarce, so judge the breeder: ask for the batch's grow-out herm rate. See [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) and [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). > **Buyer's check.** A breeder who meets the GenetixBay breeder's standard can tell you how many plants of the batch were grown out and how many showed intersex flowers. No grow-out data is a warning sign. ## Clones: the hidden costs - **HLVd** spreads through cuttings and contaminated tools, often without symptoms; disinfectants like ethanol and hydrogen peroxide were reported ineffective [3]. Ask for a recent negative test. - **Somatic mutations** build up as a mother is kept for years, so "the same cut" from two sources can differ slightly [5] (*Supported*). - **Pests** (mites, aphids, thrips, root aphids) and powdery mildew travel on cuttings. Quarantine every clone for 2-3 weeks. ## How to read a GenetixBay seed pack - **GB-PKG** on the pack is unique to that pack; scanning it activates it to your account. - The pack links to a **GB-BAT** (the batch: parent plants, pollination date, feminised or regular) and a **GB-GEN** (the line). - Check the line's **evidence level** (L0-L4) before trusting its parentage. See [documenting lineage evidence](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md). ## Common mistakes - Buying feminised seed for a breeding project, then discovering you have no males. - Keeping a feminised plant that hermed as a mother, or saving its seed. - Accepting clones without quarantine. - Trusting a name instead of a source: the same "strain" name from two sellers is often two different genotypes. See [why strain names are unreliable](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md). ## Evidence - Feminised seed mechanism: *Established* [1][2]. - HLVd transmission by cuttings: *Established* [3]. - Somatic mutation in long-kept clones: *Supported* (one genomic study) [5]. - Herm-prone feminised seed comes mainly from careless feminising and selfing, not the method itself: GenetixBay house position (breeder experience); controlled comparisons are scarce. ## Sources 1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 3. Adkar-Purushothama CR, Sano T, Perreault JP. 2023. Hop latent viroid: a hidden threat to the cannabis industry. Viruses 15(3):681. https://doi.org/10.3390/v15030681 4. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 5. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 --- # The cannabis life cycle, stage by stage > Cannabis goes from seed to seedling (1-3 weeks), vegetative growth (2-8+ weeks indoors, set by the grower for photoperiod plants), transition, flowering (about 7-12 weeks for most drug-type cultivars, longer for some tropical types) and ripening, then harvest, drying and curing. Photoperiod plants flower when nights are long enough; autoflowers flower by age. - Canonical: https://genetixbay.com/knowledge/basics/life-cycle.html - Category: Basics · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How long does it take to grow cannabis from seed?** Growing cannabis from seed indoors usually takes about 3-5 months for a photoperiod plant and about 2.5-3.5 months for an autoflower, before drying and curing. The biggest variable is vegetative time, which the grower chooses for photoperiod plants (2-8+ weeks), plus flowering of about 7-12 weeks for most drug-type cultivars and 12-16+ weeks for some tropical lines. **What are the stages of cannabis growth?** Cannabis passes through seven main stages: germination (1-7 days), seedling (1-3 weeks), vegetative growth (2-8+ weeks indoors), transition or stretch (about 2-3 weeks after 12/12), flowering (about 7-12 weeks for most drug-type cultivars), ripening in the last 1-3 weeks, then harvest, drying (7-14 days) and curing (2-8+ weeks). These durations are typical grower ranges, not fixed rules. **When does cannabis start flowering?** A photoperiod cannabis plant starts flowering once nights pass its cultivar-specific threshold, which indoors means switching to about 12 hours of uninterrupted darkness. Flowering does not start on the day of the switch: a transition and stretch follows first, and breeders often count flowering time from the first pistils rather than the flip. Autoflowers instead flower at a set age, regardless of day length. **How long is the vegetative stage?** The vegetative stage of a photoperiod cannabis plant typically lasts 2-8+ weeks indoors, and its length is the grower's choice: plants stay vegetative under long days, usually 18 hours of light, until switched to 12/12. Vegging too long in a small space is a common mistake, because plants can roughly double in height after the flip. Autoflowers skip this choice and flower at a set age. **What is the stretch in early flower?** The stretch is the burst of stem elongation in roughly the first 2-3 weeks after switching photoperiod cannabis to 12/12. Depending on genotype, stems can elongate by 50-200% while flower sites form, so a plant can roughly double in height. Growers plan for it by limiting veg time in small spaces and managing the canopy before and during the transition. **Short answer.** Seed, seedling, vegetative growth, transition, flowering, ripening, harvest. A photoperiod plant stays vegetative under long days (typically 18 h light indoors) and flowers once it gets long, uninterrupted nights (typically 12 h dark indoors). An autoflower flowers at a set age regardless of day length. Indoors, a photoperiod grow from seed usually takes 3-5 months; an autoflower 2.5-3.5 months. ## What's happening Cannabis is a short-day plant: what it actually measures is the length of the dark period. When nights pass a cultivar-specific threshold, the shoot tips switch from vegetative architecture to compact flower clusters [1][2]. Even under long days, plants of flowering age form solitary flowers at the nodes ("pre-flowers"), which is how you can sex plants before switching to 12/12 [1]. ## Stages and timing | Stage | Typical duration (indoor) | What the plant is doing | Grower focus | |---|---|---|---| | Germination | 1-7 days | Radicle emerges, cotyledons open | Warmth 22-26 °C (72-79 °F), moist not wet | | Seedling | 1-3 weeks | First true leaves (1, then 3, then 5 leaflets) | Gentle light, avoid overwatering | | Vegetative | 2-8+ weeks (grower's choice for photoperiods) | Leaf, stem and root growth; nodes stack | Training, root volume, steady feeding | | Transition / stretch | ~2-3 weeks after 12/12 | Stems can elongate 50-200% (genotype dependent); flower sites form | Height planning, canopy management | | Flowering | ~7-12 weeks for most drug-type cultivars; 12-16+ for some tropical lines | Bract and stigma production, resin build-up | Stable climate, no light leaks | | Ripening | Last 1-3 weeks of flower | Stigmas recede and darken; trichome heads turn cloudy, some amber | Decide harvest by trichomes and plan; keep feeding at stage strength (no pre-harvest flush: see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)) | | Harvest, dry, cure | Dry 7-14 days; cure 2-8+ weeks | Water leaves slowly; flavour and smoothness improve | ~18-21 °C (64-70 °F), ~55-62% RH for drying | Durations are typical grower ranges, not laws (*Grower practice*). Breeders' stated flowering times are claims and often optimistic by 1-2 weeks, partly because many count from first pistils rather than the flip: see [the flip isn't day 1 of flower](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md). ## The photoperiod threshold The critical day length varies by cultivar. In a Florida study of 27 hemp cultivars, essential-oil types flowered 1-2 days later when days exceeded 13 h and a further 7-8 days later beyond 14 h; some had a critical day length of 13 h 45 min to 14 h. Very dim civil twilight (~2 µmol/m²/s) was enough to count as "light" for the plant [2]. Indoor growers use 12/12 because it reliably triggers essentially all photoperiod cultivars (*Established* practice). Autoflowering is a different, genetically controlled pathway (a recessive locus, *Autoflower1*, in the populations mapped so far) [4]. See [photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md). ## Male versus female timelines Males usually show sex earlier and open flowers sooner than females from the same seed lot. Males shed pollen within roughly 1-3 weeks of the switch; remove or isolate them before then unless you are making seed (*Grower practice*) [3]. ## Common mistakes - Light leaks during the dark period. Even weak light can delay or disrupt flowering in sensitive cultivars [2]. - Vegging too long in a small space. Plan for the stretch: a plant can roughly double in height after the flip. - Harvesting by the calendar instead of the plant. ## Evidence - Short-day (long-night) flowering and cultivar-specific critical photoperiods: *Established* [1][2]. - Pre-flowers under long days as sex indicators: *Established* [1]. - Stage durations above: *Grower practice*, highly cultivar dependent. - Drying and curing ranges: *Grower practice*; see the harvest-cure category for evidence detail. ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 3. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 4. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 --- # Your first grow: a plan from seed to jar > For a first indoor grow, use one to four plants of a reputable feminised autoflower or photoperiod line in a tent, a good LED, quality soil or coco, a pH and EC meter, and a journal. Keep the targets simple: steady temperature and humidity, light to about 400-600 µmol/m²/s in veg and 600-900 in flower, water by weight, and harvest by trichomes. - Canonical: https://genetixbay.com/knowledge/basics/first-grow-guide.html - Category: Basics · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Soil, Coco - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What do I need for my first cannabis grow?** A first indoor cannabis grow needs a grow tent, one good LED light, a fan and carbon filter, 11-19 L (3-5 gal) pots of quality soil or coco, a pH pen, an EC meter and a journal, plus one to four plants of a well-documented feminised line. Check that home growing is legal where you live first. Most first grows fail from overwatering and overfeeding, not from too little gear. **Should a beginner grow autoflowers or photoperiods?** Either works for a beginner. Feminised autoflowers finish fast, in about 9-14 weeks, and need no light-schedule change, but they have no time to recover from mistakes. Feminised photoperiods give control over size and allow cloning and training practice, but you must flip them to 12/12 and keep the dark period truly dark. Whichever you choose, pick a line with real grow journals. **How much light does cannabis need?** Cannabis grows well indoors at about 150-300 µmol/m²/s PPFD for seedlings, 300-600 in veg and 600-900 in flower, rising to about 1,200 with added CO2 and experience. That works out to a DLI of roughly 10-20, 20-40 and 26-40 mol/m²/day. Research shows yield kept rising roughly linearly with light up to about 1,800 µmol/m²/s, but beginners should not chase that. **How often should I water my plants?** Water cannabis when the pot feels light, not on a fixed schedule. Lift the pot to learn its wet and dry weight, then water to about 10-20% runoff in coco and less in soil. Seedlings need only a small ring of water around the stem. Overwatering is the most common first-grow failure, and drowned roots often look like hunger, which tempts growers into overfeeding too. **Soil or coco for a first grow?** Both soil and coco work for a first cannabis grow in 11-19 L (3-5 gal) pots. Quality organic soil is forgiving, may need plain water only for weeks, and runs at pH 6.2-6.8. Coco needs feeding from early on, at pH 5.8-6.2 and a feed EC rising from about 0.4-0.8 mS/cm for seedlings to 1.6-2.2 mS/cm in flower, watered to 10-20% runoff. **What temperature and humidity should my tent be?** A cannabis grow tent should run about 24-27 °C (75-81 °F) and 65-75% RH for seedlings, 22-28 °C (72-82 °F) and 55-70% RH in veg, and 20-26 °C (68-79 °F) with 45-55% RH in flower, dropping to 40-50% late in flower to cut bud rot risk. Matching VPD targets are about 0.4-0.8, 0.8-1.2 and 1.0-1.5 kPa. **Short answer.** Start small and boring: a tent, one good LED, a fan and carbon filter, 11-19 L (3-5 gal) pots of quality soil or coco, a pH pen and an EC meter. Grow one to four plants of a well-documented feminised line. Write everything down. Most first grows fail from overwatering, too much nutrient and too much fiddling, not from too little gear. **Legal first.** Home growing is legal only in some places, with plant limits and rules about visibility and security. Check your local rules and the GenetixBay regional page before buying seed. ## What's happening A plant needs light, water, air at the roots, nutrients and a stable climate. Each has a "good enough" window. A first grow is about staying inside the windows and learning what your plant looks like when it is happy. ## Choose your genetics | Option | Good for | Watch out | |---|---|---| | Feminised autoflower | Speed (9-14 weeks), small spaces, no light-schedule change | No time to recover from mistakes; don't top late | | Feminised photoperiod | Control over size, cloning, learning training | You must flip to 12/12 and keep the dark period dark | | Regular seed | Breeding later | Half will be males to remove | Pick a line with a GenetixBay record at L2 or higher and real grow journals. See [seed types](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md). ## Numbers that matter | Parameter | Seedling | Veg | Flower | Notes | |---|---|---|---|---| | PPFD (µmol/m²/s) | 150-300 | 300-600 | 600-900 (up to ~1,200 with CO₂ and experience) | Yield rose roughly linearly with light up to ~1,800 in one study [1]; beginners should not chase that | | DLI (mol/m²/day) | 10-20 | 20-40 | 26-40 | DLI = PPFD x hours x 0.0036 | | Photoperiod | 18/6 | 18/6 | 12/12 (photos); 18/6-20/4 (autos) | Dark must be dark [4] | | Air temperature | 24-27 °C (75-81 °F) | 22-28 °C (72-82 °F) | 20-26 °C (68-79 °F) | Net photosynthesis peaked ~25-30 °C in [2] | | RH | 65-75% | 55-70% | 45-55%, 40-50% late | Lower late to reduce bud rot risk | | VPD (kPa) | 0.4-0.8 | 0.8-1.2 | 1.0-1.5 | Leaf-temperature based | | pH (soil / coco) | 6.2-6.8 / 5.8-6.2 | same | same | Measure what goes in and what runs off | | Feed EC (mS/cm, coco) | 0.4-0.8 | 1.0-1.8 | 1.6-2.2 | Organic soil may need water only for weeks [3] | These are *Grower practice* ranges anchored to the cited studies; your cultivar may differ. **Pot size is a trade-off.** Bigger pots give bigger yields within reason and forgive missed waterings; smaller pots can still produce big plants if you water and feed often (the founder has grown 4 oz+ from a 16 oz cup). For a first grow, 11–19 L (3–5 gal) is the forgiving choice. ## Step by step 1. **Set up and test the room for 48 h before seeds.** Log temperature and RH day and night. Fix the climate first. 2. **Germinate** in moist paper towel or directly in a small pot at 22-26 °C (72-79 °F). Plant root-down 0.5-1 cm (¼-½ in) deep. 3. **Seedling (1-3 weeks).** Light gentle, water a small ring around the stem. Do not feed most bagged soils yet. 4. **Veg.** Pot up when roots fill the container. Water when the pot feels light, to 10-20% runoff in coco, less in soil. Begin training (low-stress tying down) on photoperiods. 5. **Flip (photoperiods only).** Change to 12/12 when plants are about half the final height you can fit. Expect them to stretch. The flip isn't day 1 of flower: pistil clusters usually show 10–14 days later, so log both dates (see [the flip-to-flower transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md)). 6. **Flower.** Keep the dark period uninterrupted. Lower RH. Check for pests weekly with a loupe. 7. **Ripening and harvest.** Keep feeding at the strength the stage calls for right up to harvest; if you mix single salts, taper only nitrogen over the last few weeks. Don't flush before harvest: it's a *Myth* that starves the plant while it packs on its final weight, trichomes and resin, so it costs you yield and resin (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). Look at trichome heads with a 60x loupe: harvest when most are cloudy and some amber, not by the stigma colour. 8. **Dry** whole branches at ~18-21 °C (64-70 °F) and ~55-62% RH for 7-14 days, until small stems snap. Trim wet before hanging or dry afterwards: it's grower preference. Dry trimming (brushing the sugar leaf off a dry bud) is easier on the hands; wet trimming suits a humid room. See [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md). 9. **Cure** in airtight jars, opening briefly daily for the first week, then less often, letting the buds' moisture fall slowly. Judge the bud, not the air: a hygrometer reading only counts once the sealed jar has sat 12–24 h (aim for 55–65 %, aw 0.55–0.65). Skip humidity packs; they're a marketing gimmick. ## Common mistakes - Watering on a schedule instead of by pot weight. Drowned roots look like hunger. - Feeding full strength from week one. - Flushing with plain water for the last 1–2 weeks "for taste". It costs yield and resin; taste comes from a healthy plant, slow drying and a proper cure. - Lights too close, especially strong LEDs: bleached tops, upward-cupped leaves. - Changing three things at once when something looks wrong. Change one, log it, wait. - Skipping the journal. A dated, photographed journal is the only way to learn from a grow, and on GenetixBay it is what links your harvest back to the seed pack. ## Evidence - Light-yield relationship indoors: *Supported* (cannabis-specific trials) [1][2]. - Fertiliser rate in coir-based veg: *Supported* [3]. - Climate, VPD and dry/cure ranges: *Grower practice*. - Autoflower timing: *Supported* genetics [5], timing is grower data. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Chandra S, Lata H, Khan IA, ElSohly MA. 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14:299-306. https://doi.org/10.1007/s12298-008-0027-x 3. Caplan D, Dixon M, Zheng Y. 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307-1312. https://doi.org/10.21273/HORTSCI12401-17 4. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 5. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 --- # Damping-off: why seedlings collapse at the soil line > Damping-off is seedling death caused mainly by soil-borne pathogens such as Pythium, Rhizoctonia and Fusarium: the stem pinches, darkens and collapses at the soil line, or seeds rot before emerging. It is a prevention problem: clean containers and new mix, no overwatering, warm medium, good light and airflow. Once a seedling has collapsed it cannot be saved. - Canonical: https://genetixbay.com/knowledge/germination/damping-off.html - Category: Germination · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review - Stage: Seedling · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why did my seedling fall over at the base?** A cannabis seedling that suddenly topples over with a thin, water-soaked or brown stem right at the soil line almost always has damping-off, a disease caused by soil-borne pathogens, most often Pythium and Rhizoctonia. The leaves often stay green as it falls. If the stem is evenly thin and pale instead, low-light stretch is more likely; if the base is firm, suspect overwatering droop. **What is damping off and how do I prevent it?** Damping-off is seedling death from soil-borne pathogens such as Pythium, Rhizoctonia and Fusarium, either rotting the seed before emergence or pinching the stem at the soil line. Extension guidance agrees on prevention: new sterile seedling mix, trays soaked 30 minutes in 10% household bleach and rinsed, watering only when the plug lightens, medium at 21-25 °C (70-77 °F), vented domes and no fertiliser before true leaves. **Can a damped-off seedling be saved?** No. A cannabis seedling that has already collapsed from damping-off cannot be saved, because its stem is pinched and rotted at the soil line. Remove it along with the medium around it, let the tray dry slightly, improve airflow and sanitise before sowing again. Many growers add beneficial root inoculants preventively, though evidence for them in cannabis is limited. **Does cinnamon stop damping off?** No. Cinnamon is a myth as a reliable damping-off control; there is no supporting data for it. The defences that work are preventive and backed by extension consensus: fresh sterile seedling mix, clean containers, no soggy medium, warm roots at 21-25 °C (70-77 °F), strong light and moving air. Fungicides are a last resort for a known recurring problem, since they can stunt seedlings. **Short answer.** If a healthy-looking seedling suddenly **topples over**, with the stem **thin, water-soaked or brown right at the soil line**, it's damping-off. It's caused by soil-borne pathogens, most often ***Pythium*** and ***Rhizoctonia***, also *Fusarium* and *Phytophthora* [1][2][3]; in cannabis, *Pythium* and *Fusarium* are among the documented root and seedling pathogens [5]. A collapsed seedling **can't be saved**. Prevention: **clean containers, fresh mix, no soggy medium, warm roots, strong light, moving air**. ## How to recognise it - **Pre-emergence:** seed rots in the medium; nothing comes up; dig and find a soft, brown seed or radicle. - **Post-emergence:** stem pinched or constricted at the soil line, often darker or translucent; seedling falls over while leaves are still green. - **Pattern:** often patches of a tray, spreading along wet zones. ## Differential diagnosis | Looks like | Distinguish by | |---|---| | Stretch / weak stem from low light | Stem uniformly thin and pale, not pinched or brown at the base | | Overwatering droop | Whole seedling droops but stem base is firm | | Heat or dry-out | Leaves crisp; stem dry, not water-soaked | | Fungus gnat larvae damage | Larvae visible in the top 1–2 cm; roots chewed | ## What drives it - **Free water and saturated media:** *Pythium* needs free water to spread [4]. - **Temperature:** *Pythium* favours wet soils; some species cool, some warm; *Rhizoctonia* acts in warm to cool and even drier conditions [2][3]. - **Slow seedlings:** low light, cold medium, excess fertiliser salts all lengthen the vulnerable phase [1]. - **Contamination:** dirty pots, reused mix, garden soil, hose ends, hands and tools [1]. ## Prevention checklist 1. New, sterile seedling mix; never garden soil [1]. 2. Clean trays and pots: soak 30 min in 10 % household bleach, rinse [1]. 3. Water only when the plug lightens; let the surface dry slightly between waterings [4]. 4. Use clean, room-temperature water; cold water slows growth [1]. 5. Medium at 21–25 °C (70–77 °F); light at seedling levels ([seedling care](https://genetixbay.com/knowledge/germination/seedling-care.md)). 6. Vent domes daily; gentle air movement. 7. No fertiliser until true leaves form [1]. 8. Fungicides only if damping-off is a known recurring problem, and late as possible, since they can stunt seedlings [2]; in many places no products are registered for cannabis, so check local rules. ## If it happens Remove affected seedlings and the medium around them, let the tray dry slightly, improve airflow, and sanitise before the next sowing. Beneficial biological root inoculants (e.g. *Trichoderma*, *Bacillus*) are used preventively by many growers (*Grower practice*; evidence in cannabis is limited). ## Common mistakes - Overwatering "because seedlings are thirsty". - Reusing last run's mix for seedlings. - Cinnamon "cures" (*Myth* as a reliable control; no supporting data). ## Safety Bleach: dilute in a ventilated space, gloves on, never mix with acids or ammonia. ## Evidence Causes, conditions and prevention are *Established* extension consensus [1][2][3][4]. Cannabis pathogen reports are *Established* [5]. ## Sources 1. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 2. NC State Extension. Damping-off in flower and vegetable seedlings. https://content.ces.ncsu.edu/damping-off-in-flower-and-vegetable-seedlings 3. University of Arizona Cooperative Extension AZ1029. Damping-off. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1029.pdf 4. Utah State University Extension. Damping off (vegetable guide). https://extension.usu.edu/vegetableguide/root-crops/damping-off 5. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Germination methods compared: soak, paper towel, plugs, direct sow > Cannabis seed germinates best around 20–30 °C (68–86 °F) with steady moisture and air. Every common method works if those are met: direct sowing is least handling, paper towels let you see radicles, plugs and cubes suit hydro. Lab protocols with 1 % hydrogen peroxide, short soaks or tip scarification sped up germination, mainly for old or hard seeds; they are optional for fresh seed. - Canonical: https://genetixbay.com/knowledge/germination/germination-methods.html - Category: Germination · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the best way to germinate cannabis seeds?** The best way to germinate fresh cannabis seed is usually direct sowing 0.5-1.5 cm (¼-½ in) deep in a moist plug or small pot, because it avoids handling the taproot. Every common method works if it holds warmth, steady moisture and air. Paper towels let you watch radicles appear, rockwool or plugs suit hydro, and peroxide protocols mainly help old or hard seeds. **Should I soak seeds before planting?** Soaking cannabis seeds before planting is optional. A 12-24 hour soak in room-temperature water speeds water uptake, and one study found soaking improved germination, but soaks longer than 24-36 hours risk starving the seed of oxygen. Never soak for days. Fresh seed germinates well without any soak, so soaking is mainly worthwhile for older or harder seeds. **Does hydrogen peroxide help germination?** Hydrogen peroxide can help cannabis germination in some cases. A lab protocol that sterilised, germinated and grew seeds on in 1% hydrogen peroxide gave faster, higher germination than water with no contamination, and helped very old seed. But results conflict: another study found peroxide largely ineffective and hot-water soaking best. For fresh seed it is optional. Wear gloves and eye protection when diluting stock above 3%. **What temperature for germinating cannabis seeds?** Cannabis seeds germinate best at about 22-27 °C (72-81 °F). Hemp research found an optimum band of 19-30 °C with a calculated optimum near 29.6 °C, a base around 3.4 °C and a ceiling near 42.6 °C. Below about 18 °C (64 °F), for example on a cold windowsill, germination slows sharply. Light is not needed until the seedling emerges. **How deep do I plant a cannabis seed?** Plant a cannabis seed 0.5-1.5 cm (¼-½ in) deep, radicle down if it has already sprouted, and cover it lightly with a moist, light seedling mix that holds together but does not drip. Planting too deep is a common mistake. Seeds started in a paper towel are best planted once the radicle is about 0.5-2 cm long, before it gets long enough to break easily. **How long should germination take?** Fresh cannabis seed usually shows a radicle within 1-5 days at 22-27 °C (72-81 °F); old seed can take up to 10 days. Cooler conditions slow it considerably, especially below about 18 °C (64 °F). In a tissue-culture lab setting, disinfection plus tip scarification gave 100% germination within a week. Seedlings then need light once the hook breaks the surface. **Short answer.** Seeds need **warmth (20–30 °C / 68–86 °F)**, **steady moisture** and **air**. In a hemp study the optimum band was **19–30 °C**, with a calculated optimum of ~**29.6 °C**, base ~**3.4 °C** and ceiling ~**42.6 °C** [1]. Any method that holds those conditions works. For fresh seed, **direct sow** in a moist plug or small pot is simplest and avoids handling the taproot. Use a **paper towel** or **1 % hydrogen peroxide** protocol [3] when you want to see results or rescue old seed. ## Methods compared | Method | How | Pros | Cons | Evidence | |---|---|---|---|---| | Direct sow | 0.5–1.5 cm (¼–½ in) deep in moist, light mix or plug | No handling; no transplant of a bare radicle | Can't see what's happening | Grower practice | | Soak, then sow | 12–24 h in water at room temperature, then plant | Speeds water uptake; sinkers are hydrated | Over 24–36 h risks oxygen starvation | Supported: soaking improved germination in one study [5] | | Paper towel | Damp (not wet) towel in a closed dish, dark, warm; plant at 0.5–2 cm radicle | Visible; easy germination test | Radicles break; towels dry out or grow mould | Grower practice | | Rockwool / plug | Pre-soaked cube (pH ~5.5 for rockwool) | Clean start for hydro | Easy to overwater | Grower practice | | 1 % H₂O₂ protocol | Sterilise, germinate and grow on in 1 % hydrogen peroxide | Faster, higher germination than water, no contamination; helped very old seed [3] | Lab protocol; handle peroxide safely | Supported [3] | | Tip scarification + disinfection | Remove seed tip after disinfection (in vitro) | 0 % contamination, 100 % germination within a week in a tissue-culture setting [4] | Fiddly; for in vitro work | Supported (lab) [4] | Results on peroxide and scarification **conflict** across studies: one found hot-water soaking best and peroxide/scarification largely ineffective [5]. The common thread is: fresh seed germinates well without tricks. ## Numbers that matter | Parameter | Target | |---|---| | Temperature | 22–27 °C (72–81 °F); hemp optimum 19–30 °C [1] | | Base temperature | Roughly 0–7 °C depending on model and cultivar [1][2] | | Soak time | ≤ 24 h | | Planting depth | 0.5–1.5 cm (¼–½ in), radicle down | | Expected time to radicle | 1–5 days fresh seed; up to 10 days old seed | | Light | Not needed until the seedling emerges | ## How to do it (direct sow) 1. Moisten a light seedling mix or plug until it holds together but doesn't drip. 2. Plant 0.5–1.5 cm deep; cover lightly. 3. Keep at 22–27 °C under a humidity dome, but vent daily. 4. Turn on light (low intensity, see [seedling care](https://genetixbay.com/knowledge/germination/seedling-care.md)) once the hook emerges. ## Safety Hydrogen peroxide above 3 % irritates skin and eyes; wear gloves and eye protection when diluting stronger stock. Bleach (sodium hypochlorite) used for disinfection must be rinsed off and never mixed with acids or ammonia. ## Common mistakes - Soaking for days. - Paper towels left sopping wet. - Planting too deep. - Cold windowsills (below ~18 °C germination slows sharply). ## Evidence Temperature limits are *Supported* by hemp studies [1][2]. Peroxide and scarification benefits are *Supported* in lab protocols [3][4] but *Contested* across studies [5]. Choice of home method is *Grower practice*. ## Sources 1. Geneve RL, et al., 2022. Temperature limits for seed germination in industrial hemp (Cannabis sativa L.). Crops 2(4):415–427. https://doi.org/10.3390/crops2040029 2. Lisson SN, Mendham NJ, Cornish PS, 2000. Development of a hemp (Cannabis sativa L.) simulation model 1: general introduction and the effect of temperature on the pre-emergent development of hemp. Australian Journal of Experimental Agriculture 40:405–411. https://www.publish.csiro.au/AN/EA99058 3. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 4. Pepe M, Hesami M, Jones AMP, 2021. Machine learning-mediated development and optimization of disinfection protocol and scarification method for improved in vitro germination of cannabis seeds. Plants 10(11):2397. https://pmc.ncbi.nlm.nih.gov/articles/PMC8619272/ 5. Physical and chemical pretreatments on germination efficiency and seedling growth of Cannabis sativa. Nativa (UFMT). https://periodicoscientificos.ufmt.br/ojs/index.php/nativa/article/view/20226 --- # Seed viability and storage: keeping cannabis seeds alive > Cannabis seeds stay viable longest when dry and cold: research on hemp and drug-type seeds recommends about 5 °C (41 °F) storage to keep germination ability for around six years, with low seed moisture and an airtight container. Room temperature and humid storage cost viability within months to a few years. Test old seeds with a small germination test before planting a whole batch. - Canonical: https://genetixbay.com/knowledge/germination/seed-viability-storage.html - Category: Germination · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How long do cannabis seeds last?** Cannabis seeds can stay viable for about six years when stored dry, airtight and cold at around 5 °C (41 °F), based on research by Small and Brookes. At or below 25 °C (77 °F) and 70% RH, hemp seed stayed safe for more than 26 weeks, so room-temperature storage is fine for a season but not for years. Warm, humid, bright storage costs viability within months. **Should I store seeds in the fridge or freezer?** Store cannabis seeds in the fridge at 2-8 °C (36-46 °F), away from the door, in a sealed vial with silica gel desiccant. The freezer at about -18 °C (0 °F) likely works for longer storage, but only for thoroughly dried stock you will rarely open, and freezer results for cannabis are less documented. Always let a cold container reach room temperature before opening it, to avoid condensation. **How do I know if my seeds are still viable?** To check if cannabis seeds are still viable, run a germination test: place 10 seeds on a damp paper towel at 22-26 °C (72-79 °F) in the dark for 7 days, then count radicles. Eight sprouts means 80% germination. The float test is unreliable because it mostly measures trapped air, and colour alone does not prove viability. Test before planting a precious batch. **Do dark seeds germinate better than pale ones?** Darker cannabis seeds are usually mature and harder, but seed colour varies with genetics, so a pale seed is not necessarily a dud and a dark one is no guarantee. Grower practice treats colour as a rough sign of maturity only. The only reliable way to know is a germination test: 10 seeds on a damp towel at 22-26 °C (72-79 °F) in the dark for 7 days. **Can I revive old cannabis seeds?** Old cannabis seeds can sometimes be helped to sprout. In one lab protocol, germinating seeds in 1% hydrogen peroxide gave faster germination and improved results for very old, low-viability seed compared with plain water. Start with a small test batch and count radicles after 7 days. Prevention matters more: dry, airtight, cold storage at about 5 °C (41 °F) keeps seeds viable for around six years. **Short answer.** Keep seeds **dry, cold, dark and airtight**. Small & Brookes recommended **~5 °C (41 °F)** to maintain germination capacity for about **six years** [1]; the general seed rule holds for cannabis: life span rises predictably as **temperature and seed moisture fall** [3]. Hemp seed at **≤ 25 °C (77 °F), ≤ 70 % RH (≤ 10 % seed moisture)** stayed safe for **more than 26 weeks** [2], so room-temperature storage is fine for a season, not for years. Before planting a precious batch, run a **10-seed germination test**. ## What's happening A seed is a living embryo running a very slow metabolism. Heat and moisture speed up the chemical ageing of membranes and DNA. Drop either and ageing slows dramatically. Repeated warming and cooling causes condensation, which is the hidden killer of fridge-stored seeds. ## Numbers that matter | Storage | Expected | Evidence | |---|---|---| | ~5 °C (41 °F), dry, airtight | ~6 years with good germination | Supported [1] | | ≤ 25 °C, ≤ 70 % RH (≤ 10 % moisture) | > 26 weeks safe | Supported [2] | | Freezer (−18 °C / 0 °F) | Likely longer, *only if* seeds are dry before freezing | Grower practice | | Warm, humid, light | Viability falls within months | Supported [3] | | Seed moisture target | ~6–8 % for long storage (≤ 10 % for short term [2]) | | ## How to store 1. Keep seeds in their original sealed packet or a small glass vial. 2. Add a desiccant packet (silica gel) to the outer container. 3. Fridge at 2–8 °C (36–46 °F), not the door. Label with cultivar and date. 4. When removing seeds, let the sealed container reach room temperature **before** opening (prevents condensation). 5. Freezer only for dried, long-term stock you won't open often. ## Testing viability - **Germination test:** 10 seeds on a damp paper towel at 22–26 °C (72–79 °F), in the dark, for 7 days. Count radicles. 8/10 = 80 % germination. - **Old seeds:** a 1 % hydrogen peroxide germination protocol gave faster germination and improved germination of very old, low-viability cannabis seeds vs water in one lab protocol [4] ([germination methods](https://genetixbay.com/knowledge/germination/germination-methods.md)). - **Seed colour/float test:** mature seeds are usually darker and harder, but colour varies with genetics; the float test is unreliable (*Grower practice*: it mostly measures trapped air). ## Common mistakes - Opening a cold container in a warm room. - Storing in a grow room or next to a window. - Buying more seed than you will plant in 2–3 years and storing it warm. ## Evidence Cold, dry storage extending viability is *Supported* by cannabis-specific studies [1][2][3] and *Established* in seed science generally. Freezer outcomes for cannabis are less documented. ## Sources 1. Small E, Brookes B, 2012. Temperature and moisture content for storage maintenance of germination capacity of seeds of industrial hemp, marijuana, and ditchweed forms of Cannabis sativa. Journal of Natural Fibers 9(4):240–255. https://doi.org/10.1080/15440478.2012.737179 2. University of Manitoba (MSc thesis). Safe storage guidelines for industrial hemp (Cannabis sativa) seeds (≤25 °C and ≤70 % RH, ≤10 % moisture, >26 weeks). https://mspace.lib.umanitoba.ca/handle/1993/33358 3. Effect of seed moisture content and storage temperature on seed longevity of hemp (Cannabis sativa), 2014. Indian Journal of Agricultural Sciences. https://epubs.icar.org.in/index.php/IJAgS/article/view/44551 4. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 --- # Seedling care: the first three weeks > Seedlings need moderate light (about 150–300 µmol/m²/s, 18 h, a DLI of 10–19 mol/m²/day), warm and fairly humid air (23–27 °C / 73–81 °F, 65–75 % RH), and small, careful waterings. Most seedling losses come from overwatering, too little light (stretching) or damping-off, not from lack of nutrients. Start feeding lightly once the first two or three sets of true leaves have formed. - Canonical: https://genetixbay.com/knowledge/germination/seedling-care.html - Category: Germination · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why is my seedling stretching and falling over?** A cannabis seedling that stretches into a long, thin, pale stem and flops over is usually getting too little light, or the light is too far away. Raise the light intensity gradually toward 150-300 µmol/m²/s for 18 hours, and at transplant bury the stretched stem deeper in soil or coco. If the stem is pinched and brown at the soil line instead, the cause is damping-off. **How much should I water seedlings?** Water cannabis seedlings in small amounts, in a ring around the stem, only when the plug or small pot feels lighter. Keep the surface just moist rather than wet, and use room-temperature water, since cold water slows growth and raises damping-off risk. Giving a big pot a big watering for a tiny root is a classic mistake that leaves the medium soggy and the seedling drooping. **How far should the light be from seedlings?** The right distance from light to cannabis seedlings is whatever delivers about 150-300 µmol/m²/s at the canopy for 18 hours, a DLI of 10-19 mol/m²/day; the height depends on the fixture, so measure PPFD rather than guessing. Start lower, around 100-200 µmol/m²/s, as cotyledons open. Bleached tips or hard 'praying' leaves mean too close; long, pale stems mean too far. **When should I start feeding seedlings?** Start feeding cannabis seedlings once two or three sets of true leaves have formed, at about quarter to half strength, an EC of 0.4-0.8 mS/cm (200-400 ppm on the 500 scale). Seedlings in inert media with no starter charge, such as coco, rockwool or hydro, need feed earlier. Yellowing cotyledons around days 10-14 are often normal, or a sign an inert medium needs a light feed. **What humidity for cannabis seedlings?** Cannabis seedlings do best at about 65-75% relative humidity with air at 23-27 °C (73-81 °F), giving a leaf VPD of roughly 0.4-0.8 kPa. A humidity dome helps in the first days, but vent it daily: a dome left closed for days invites mould and soft stems. These targets are grower practice rather than cannabis-specific research, so watch how your seedlings respond. **Short answer.** Give seedlings **moderate light** (≈ **150–300 µmol/m²/s for 18 h**, a DLI of **10–19 mol/m²/day**), **warm, fairly humid air** (**23–27 °C / 73–81 °F, 65–75 % RH**, leaf VPD ~0.4–0.8 kPa) and **small waterings** in a ring around the stem. Hold off on feed until **2–3 sets of true leaves** unless the medium has no starter charge (coco, rockwool, hydro). Most losses are **overwatering, stretching from low light, or damping-off**. ## Week by week | Days | What you see | What to do | |---|---|---| | 0–5 | Hook emerges, cotyledons open | Low light (100–200 µmol/m²/s), dome vented daily, keep surface just moist | | 5–10 | First true leaves (single or 3-finger) | 150–250 µmol/m²/s; water small amounts when the plug lightens | | 10–21 | 2nd–4th nodes | 200–300+ µmol/m²/s; start ¼–½ strength feed (EC 0.4–0.8 mS/cm); transplant when roots fill the plug ([transplanting](https://genetixbay.com/knowledge/germination/transplanting.md)) | ## Numbers that matter | Parameter | Target | Evidence | |---|---|---| | PPFD | 150–300 µmol/m²/s, 18 h | Grower practice; consistent with young-plant DLI research in other crops [1] | | DLI | 10–19 mol/m²/day | Plugs below ~8 mol/m²/day are inferior in other crops [1] | | Air temperature | 23–27 °C (73–81 °F) | Grower practice | | RH | 65–75 % | Grower practice | | Medium temperature | 21–25 °C (70–77 °F) | Warm roots grow fast; cold water raises damping-off risk [2] | | First feed EC | 0.4–0.8 mS/cm (200–400 ppm500) | Grower practice; start at true leaves [2] | | Water pH | Soil 6.2–6.8; coco 5.8–6.2; hydro/rockwool 5.5–6.0 | | ## Problems and fixes | Symptom | Likely cause | Fix | |---|---|---| | Long, thin, pale stem, flops over | Light too weak or too far | Raise PPFD gradually; bury the stretched stem deeper at transplant (*Grower practice*) | | Drooping, wet medium | Overwatering | Let it dry; smaller waterings; airier mix | | Stem pinched and brown at the soil line, collapse | Damping-off | See [damping-off](https://genetixbay.com/knowledge/germination/damping-off.md) | | Cotyledons yellow at day 10–14 | Normal as true leaves take over, or no nutrients in inert media | Start light feed | | Leaves praying hard, bleached tips | Too much light/heat | Dim or raise light | | Seed husk stuck on cotyledons | Dry surface | Mist, wait, then gently remove | ## Common mistakes - Big pot + big watering for a tiny root. - Dome left closed for days (mould, soft stems). - Strong nutrients "to get it going". - A cheap light at 1 m away. ## Evidence Young-plant light responses are *Supported* in horticultural research on other crops [1]; cannabis veg responds to high light with compact growth [3]. Temperatures follow hemp germination data [4] and grower practice. Fertiliser timing follows extension guidance [2]. ## Sources 1. Runkle E. The benefits of lighted plugs. Michigan State University Extension (plugs below DLI ~8 inferior; 10–14 mol/m²/day better roots and mass). https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs 2. University of Minnesota Extension. How to prevent seedling damping off (fertiliser after true leaves; avoid cold water). https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 3. Moher M, Llewellyn D, Jones M, Zheng Y, 2021. High light intensities can be used to grow healthy and robust cannabis plants during the vegetative stage of indoor production. Preprints (not peer reviewed). https://doi.org/10.20944/preprints202104.0417.v1 4. Geneve RL, et al., 2022. Temperature limits for seed germination in industrial hemp. Crops 2(4):415–427. https://doi.org/10.3390/crops2040029 --- # Transplanting: when, into what, and avoiding transplant shock > Transplant when roots fill the current container but before they circle: typically seedling plug to 1–3 L at 2–3 weeks, then to the final pot 2–4 weeks before flowering. Move the root ball intact into pre-moistened medium at the same pH and similar EC, water in lightly, and keep light and climate gentle for a few days. Autoflowers do best sown straight into their final pot. - Canonical: https://genetixbay.com/knowledge/germination/transplanting.html - Category: Germination · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Seedling, Veg · Systems: Soil, Coco, Rockwool, Living soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Does pot size limit yield?** Pot size can limit cannabis yield, but it is a trade-off rather than a fixed rule. A meta-analysis across many crops found bigger rooting volume generally means bigger plants, and bigger pots give bigger yields within reason. Yet the GenetixBay founder has grown over 4 oz (about 115 g) from a 16 oz cup using high-frequency fertigation. Small pots simply need more frequent watering and feeding. **When should I transplant my cannabis seedling?** Transplant a cannabis seedling when its roots reach the sides and bottom of the container but before they start circling, typically 2-3 weeks from sprouting or at about 2-4 true-leaf nodes. Lift the plant out to check: white roots at the edge should hold the ball together. Water lightly the day before so the root ball stays intact during the move. **What size pots should I transplant into?** A typical path for photoperiod cannabis is a plug or 0.25-0.5 L cup, then a 1-3 L (0.25-0.8 US gal) pot at 2-3 weeks, then a final pot of 11-25 L in soil or coco 2-4 weeks before the flip. Increase volume about 2-4 times per step, since bigger jumps leave unrooted medium that dries slowly. Autoflowers go straight into an 11-15 L final pot. **How do I avoid transplant shock?** To avoid transplant shock, move the cannabis root ball intact into pre-moistened medium of the same type and pH (soil 6.2-6.8, coco 5.8-6.2), firm gently and water in with a mild solution. Then lower light by about 10-20% and keep RH slightly higher for 2-3 days. Mild drooping for 2-5 days is normal; longer suggests root damage, waterlogging or a pH mismatch. **Can I transplant during flower?** Transplanting cannabis during flower is best avoided. A late emergency pot-up can work, but expect the plant to stall while it recovers. Plan instead to move photoperiod plants into their final 11-25 L pots 2-4 weeks before the flip, so the roots have time to colonise the new medium before flowering begins. This timing is grower practice aligned with extension guidance. **Should I transplant autoflowers?** No. Autoflowers should not be transplanted: sow them straight into an 11-15 L final pot. An auto runs on a fixed clock from germination, so any setback, including transplant shock, costs it time it cannot recover. The GenetixBay founder also finds the autoflower taproot reacts badly to being moved compared with photoperiods. This is grower practice and a GenetixBay house position. **Short answer.** Pot up when roots **reach the sides and bottom** of the container but **before they circle** (lift the plant out: you should see white roots at the edge holding the ball together). Typical path: **plug → 1–3 L (0.25–0.8 US gal) at 2–3 weeks → final pot 2–4 weeks before the flip**. Move the root ball **intact** into **pre-moistened** medium of the same type and pH, water in lightly, and give it **2–4 easy days**. **Autoflowers:** sow straight into the final pot. This is *Grower practice* consistent with general horticulture [1][2]. ## Why pot up at all A small container wets and dries evenly around a small root ball. A giant pot around a seedling stays wet in the zone with no roots (low air, high disease risk [3]). Potting up keeps the moisture cycle matched to root size [2]. ## Numbers that matter | Step | Container | Typical timing | |---|---|---| | Seedling/clone | Plug, cube, 0.25–0.5 L cup | Until 2–4 true-leaf nodes | | First up-pot | 1–3 L | 2–3 weeks from sprout | | Final pot (photoperiod) | 11–25 L soil/coco; slab/block for rockwool | 2–4 weeks before flip | | Autoflower | 11–15 L final | Sow direct into the final pot; don't transplant | | Ratio per step | ~2–4× volume | Bigger jumps = slower drying | > **House position: pot size is a trade-off.** Bigger pots give bigger yields, within reason; across many crops, bigger rooting volume generally means bigger plants (Poorter et al. 2012 meta-analysis). But root volume isn't the whole story: the founder has grown a QP+ (4 oz+, ~115 g+) from a 16 oz (~0.5 L) cup. If you push water and nutrients hard enough (high-frequency fertigation), big things come in small packages. Small pots need more frequent feeding and watering and leave less margin for error; big pots are more forgiving but dry slower. Match the pot to how often you can irrigate. ## How to do it 1. Water the plant lightly the day before so the root ball holds together. 2. Pre-moisten the new medium to "wrung sponge" and pH-correct it (soil 6.2–6.8; coco 5.8–6.2). 3. Make a hole the size of the old container (use an empty pot as a mould). 4. Tip, support the stem between fingers, slide the ball out, set it in. Stretched seedlings can be set deeper in soil or coco (*Grower practice*). 5. Firm gently; water in with a small amount of mild solution. 6. Lower light ~10–20 % and keep RH a little higher for 2–3 days. 7. Rockwool: place the block on the slab; irrigate the block until roots enter the slab. ## How to recognise transplant shock Drooping or slow growth for 2–5 days, mild leaf curl. Lasting longer, check for: root damage, waterlogged new medium, pH mismatch, or a hot, bright light right after the move. ## Common mistakes - Breaking the root ball. - Transplanting into dry or soaking medium. - Transplanting in flower (a late emergency pot-up can work; expect a stall). - Transplanting autoflowers at all. Any setback costs an auto time on its fixed clock, and the founder finds the auto taproot reacts badly to it; sow into the final pot (house position). ## Evidence Container physics is *Established* [2]. Transplant timing and handling is *Grower practice* aligned with extension seedling guidance [1][3]. ## Sources 1. University of Minnesota Extension. Starting seeds indoors (transplanting seedlings, hardening). https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container size and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 3. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 4. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # Airflow: air exchange, canopy air speed and fan placement > Aim for gentle, constant movement across and under the canopy (roughly 0.3–1.0 m/s at leaf level) plus enough exhaust to remove heat and humidity, typically one full tent air exchange every 1–3 minutes for a lit tent. Moving air thins the leaf boundary layer, which raised canopy photosynthesis in non-cannabis research, and dries out the microclimates where mould starts. - Canonical: https://genetixbay.com/knowledge/environment/airflow.html - Category: Environment · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How many fans do I need in a grow tent?** A typical cannabis grow tent needs at least two fan jobs covered: one exhaust fan mounted high to swap out hot, humid air, and one oscillating or clip fan above the canopy blowing across the tops. In flower, add a second circulation fan below the canopy blowing across the pots to dry the lower canopy. This layout is grower practice rather than a researched cannabis standard. **How fast should air move over cannabis leaves?** Air over cannabis leaves should move at roughly 0.3–1.0 m/s (60–200 ft/min) at leaf level, enough that leaves flutter gently but never whip. Research on other crops found that raising air speed above the canopy from 0.1 to 1.0 m/s roughly doubled canopy net photosynthesis, but no cannabis-specific optimum has been published, so the range is grower practice. **What size exhaust fan for my tent?** An exhaust fan for a lit grow tent without added CO₂ should replace the full tent volume every 1–3 minutes. For a 1.2 × 1.2 × 2 m tent (2.9 m³) that is about 60–175 m³/h of raw airflow, plus 25–50 % extra to cover carbon filter and ducting losses. Run it on a speed controller tied to temperature and humidity rather than at full blast. **Can too much wind hurt plants?** Yes, too much wind can hurt cannabis plants: a strong fan pointed straight at them causes windburn, seen as constantly bending top leaves and clawed or tacoed edges on the fan side, while the far side stays stagnant. The fix is gentler, spread-out circulation that keeps leaf-level air speed around 0.3–1.0 m/s, aimed across the canopy rather than down onto it. **Should fans run at night?** Circulation fans in a cannabis grow should run 24 hours a day, including lights-off. Turning them off at night to 'let the plants rest' is a common mistake, because humidity spikes when the lights go off and still air lets moisture build up in dense colas, where bud rot and powdery mildew start. Moving air dries those microclimates and keeps the leaf boundary layer thin. **Short answer.** You need two separate things: **exhaust** (to swap room air and remove heat/humidity) and **circulation** (to move air across and through the canopy). Target leaf-level air speed of about **0.3–1.0 m/s (60–200 ft/min)**: leaves should flutter gently, never whip. In research on other crops, raising air speed above the canopy from 0.1 to 1.0 m/s roughly doubled canopy net photosynthesis [1]. Circulation also dries the pockets where *Botrytis* and powdery mildew start [3]. ## What's happening Every leaf sits inside a thin, still "boundary layer" of air. In still air that layer thickens; CO₂ near the leaf is used up, water vapour builds up, and the leaf can't shed heat. Moving air thins it. Under water stress and low wind, modelled leaves run 8–12 °C (14–22 °F) above air temperature [2]. ## Numbers that matter | Item | Target | Notes | |---|---|---| | Leaf-level air speed | 0.3–1.0 m/s (60–200 ft/min) | | | Exhaust, lit tent (no CO₂) | One full volume every 1–3 min | Tent 1.2 × 1.2 × 2 m = 2.9 m³ → 60–175 m³/h raw; add 25–50 % for a carbon filter and ducting losses | | Exhaust, sealed CO₂ room | Off during lights-on except emergency | Heat and humidity handled by AC and dehumidifier | | Negative pressure | Tent walls slightly sucked in | Keeps odour inside | | Intake area | ≈ 2–3 × exhaust duct area if passive | | | Fans under canopy | Yes, in flower | Dries the lower canopy and pot surface | ## How to set it up 1. Exhaust high (hot air rises), intake low on the opposite side. 2. One oscillating or clip fan above the canopy blowing across, not down. 3. One fan below the canopy in flower, blowing across the pots. 4. In rooms, aim fans to create a circular pattern; avoid dead corners. 5. Run circulation 24 h. At lights-off is when humidity spikes. 6. Put exhaust on a speed controller tied to temperature and RH rather than full blast. ## What to check first - Hang a ribbon or tissue at several canopy points: it should move everywhere, gently. - Feel the top leaves: if they are constantly bending or the edges are clawing/tacoing on the fan side, it's windburn. - Check humidity inside dense colas vs room air. ## Common mistakes - One big fan pointed straight at the plants: windburn on one side, stagnant air on the other. - Exhaust too strong in a sealed CO₂ setup (throws money out the vent). - Fans off at night to "let the plants rest". - Undersized exhaust once a carbon filter is added. ## Evidence Boundary-layer physics and the effect of air speed on gas exchange are *Established* in plant science; the doubling result [1] is from non-cannabis canopies in a closed system. Leaf temperature under low wind is *Supported* by modelling [2]. Air movement as part of disease prevention in cannabis is *Established* extension guidance [3]. Specific air speeds and exchange rates for cannabis are *Grower practice*. ## Sources 1. Kitaya Y, Tsuruyama J, Shibuya T, Yoshida M, Kiyota M, 2003. Effects of air current speed on gas exchange in plant leaves and plant canopies. Advances in Space Research 31(1):177–182. https://www.science.gov/topicpages/a/air+current+speed 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 3. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # CO₂ enrichment: when it pays, how much, and how to stay safe > Raising CO₂ from ambient (~420 ppm) to 800–1,200 ppm during lights-on raises cannabis photosynthesis substantially, but only pays when light is already high (roughly 900+ µmol/m²/s) and the room is sealed enough to hold it. Keep occupied rooms below the 5,000 ppm 8-hour workplace limit and never enter a room above 30,000 ppm. - Canonical: https://genetixbay.com/knowledge/environment/co2-enrichment.html - Category: Environment · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is CO2 worth it for a small grow tent?** CO₂ enrichment is usually not worth it for a small grow tent unless the tent is sealed and already runs high light, roughly 900 µmol/m²/s or more in flower. Below about 600 µmol/m²/s there is little benefit, so money is better spent on light first. A ventilated tent with the exhaust running simply vents the added gas outside. **What ppm CO2 should I run in flower?** For cannabis in flower under 900–1,500 µmol/m²/s, a typical CO₂ target is 900–1,200 ppm during lights-on, with day temperature raised about 2–3 °C (4–5 °F). Between 700 and 900 µmol/m²/s, ambient to 800 ppm is marginal and only worthwhile if sealed. Many growers taper back to ambient in the last 1–2 weeks, which is grower practice without published evidence. **Do I need CO2 above 1000 PPFD?** Cannabis does not strictly need added CO₂ above 1,000 µmol/m²/s PPFD: in one well-run indoor trial, yield kept rising linearly with light up to 1,800 µmol/m²/s even at ambient CO₂. Enrichment to about 900–1,200 ppm acts as a multiplier on high light, letting plants use more photons and tolerate warmer rooms, but a full cannabis CO₂ by light yield trial is still missing. **Is CO2 dangerous to people?** Yes, CO₂ is dangerous to people at high concentrations. The 8-hour workplace exposure limit is 5,000 ppm, the 15-minute short-term limit is 30,000 ppm, and 40,000 ppm is immediately dangerous to life or health. Fit a separate CO₂ alarm at head height, ventilate a sealed grow room before entering, never enter above 5,000 ppm, and keep cylinders strapped upright. **Should CO2 run at night?** No, CO₂ enrichment should not run at night. With the lights off, cannabis plants respire and do not fix carbon, so CO₂ added in the dark period is wasted money and an extra safety risk. Dose only during lights-on, ideally on a controller with a high cut-off that also locks the gas out whenever exhaust fans run. **Short answer.** CO₂ is the raw material of photosynthesis. In cannabis leaves, raising CO₂ from ambient to 750 ppm increased net photosynthesis by about **50 %** and water-use efficiency by about **111 %** [1]. It only turns into yield when **light is the strong side of the equation** (roughly 900–1,500 µmol/m²/s in flower) and the room is **sealed** so the gas stays put. Typical target: **800–1,200 ppm during lights-on only**. Safety: **5,000 ppm** is the 8-hour workplace limit; **40,000 ppm** is immediately dangerous to life [4][5]. ## What's happening At ambient CO₂ (~420 ppm today) and high light, the enzyme Rubisco runs short of CO₂ and wastes energy on photorespiration. More CO₂ fixes more carbon per photon and lets stomata close slightly (cannabis at elevated CO₂ showed lower stomatal conductance and transpiration and higher water-use efficiency [1][2]). The plant can then use more light and tolerate slightly higher temperatures. Cannabis yield kept rising linearly with light up to 1,800 µmol/m²/s **even at ambient CO₂** in one well-run indoor trial [3]. CO₂ is therefore a multiplier on light, not a substitute for it. ## Numbers that matter | Situation | CO₂ target (lights-on) | Notes | |---|---|---| | Light below ~600 µmol/m²/s | Ambient, just ventilate | Little benefit; spend on light first | | Flower 700–900 µmol/m²/s | Ambient to 800 ppm | Marginal; only if sealed | | Flower 900–1,500 µmol/m²/s | 900–1,200 ppm | Raise day temperature 2–3 °C (4–5 °F) | | Above 1,500 µmol/m²/s | 1,200–1,500 ppm | Commercial practice | | Lights-off | None | Plants respire, they don't fix carbon at night | | Last 1–2 weeks of flower | Often tapered to ambient | *Grower practice*, no published evidence | **Human exposure** [4][5] | Level | Meaning | |---|---| | 5,000 ppm | 8-hour time-weighted workplace limit (OSHA PEL, NIOSH REL) | | 30,000 ppm | NIOSH 15-minute short-term limit | | 40,000 ppm | IDLH (immediately dangerous to life or health) | ## How to do it 1. **Seal first.** Exhaust fans must be off (or on a controller that locks out CO₂ when they run). Otherwise you are heating the street with gas. 2. **Measure with an NDIR sensor** at canopy height, not near the emitter. Calibrate yearly (outdoor fresh-air reference ≈ 420 ppm). 3. **Choose a source:** compressed cylinder with regulator and solenoid (clean, no heat); combustion generators add heat and water vapour and need a CO monitor; fermentation/bags give small, uncontrollable amounts. Combustion indoors in a small space is not recommended. 4. **Control:** dose on a controller with a high cut-off; release from above the canopy (CO₂ is denser than air) with circulation fans running. 5. **Safety:** a separate CO₂ alarm at head height outside the canopy; ventilate before entering a sealed room; never enter if the alarm is above 5,000 ppm; cylinders strapped upright. ## How to confirm it worked Readings hold within ±100 ppm of target during lights-on; plants tolerate the higher light without bleaching; dry yield per m² and per kWh improve over a matched run. ## Common mistakes - Running CO₂ with the exhaust on. - Adding CO₂ to a 400 µmol/m²/s tent. - Dosing at night. - Placing the sensor next to the emitter. - Forgetting a people-safety alarm. ## Evidence Leaf-level photosynthetic gains in cannabis are *Supported* [1][2] (single group, a few cultivars, gas exchange not yield). The yield benefit under high light is *Supported* by horticultural consensus and the light-response work [3]; a full cannabis CO₂ × light yield trial is still missing. Exposure limits are *Established* regulation [4][5]. ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 2. Chandra S, Lata H, Khan IA, ElSohly MA, 2011. Photosynthetic response of Cannabis sativa L., an important medicinal plant, to elevated levels of CO2. Physiology and Molecular Biology of Plants 17:291–295. https://doi.org/10.1007/s12298-011-0066-6 3. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 4. OSHA. Carbon dioxide, chemical data (PEL 5,000 ppm TWA). https://www.osha.gov/chemicaldata/183 5. NIOSH Pocket Guide to Chemical Hazards: Carbon dioxide (REL 5,000 ppm TWA; ST 30,000 ppm; IDLH 40,000 ppm). https://www.cdc.gov/niosh/npg/npgd0103.html --- # Heat and light stress: taco leaves, bleaching and foxtails > Heat and light stress show at the top of the plant, closest to the light: leaves curl up or taco, bracts bleach white or yellow, buds may foxtail. Measure leaf temperature and canopy PPFD before blaming nutrients. Typical fixes: dim or raise the light 10–20 %, bring leaf temperature under about 30 °C (86 °F), restore airflow and root-zone water uptake. - Canonical: https://genetixbay.com/knowledge/environment/heat-light-stress.html - Category: Environment · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my top leaves curling up like tacos?** Top cannabis leaves that curl up like tacos or canoes, mainly at mid-day and nearest the light, usually signal heat or high VPD: the plant is folding leaves to cut transpiration. Measure leaf temperature first and aim for 24–29 °C (75–84 °F) at the tops, with leaf VPD of 0.8–1.5 kPa. Add airflow across the canopy and check that roots can drink. **Why are my top buds turning white?** Top cannabis buds turning white or pale yellow, closest to the lamp, are usually light bleaching, a photo-oxidation of chlorophyll from more light than the plant can use under current conditions, made worse by heat. Measure canopy PPFD and dim or raise the light 10–20 %, then lower leaf temperature below about 30 °C (86 °F). Bleached tissue will not recover, so judge by new growth. **Is it light burn or nitrogen toxicity?** Light burn and nitrogen toxicity differ by location. Light or heat damage appears only at the top of the plant, nearest the lamp, while lower leaves stay healthy. Nitrogen toxicity shows dark, glossy, clawed leaves throughout the plant, not just at the top. If old lower leaves are damaged first, check nutrients and pH rather than the light. **What causes foxtailing?** Foxtailing, new calyxes stacking on top of finished buds, is most often blamed on heat or light stress at the top colas in late flower, though some cultivars do it from genetics. That cause is grower practice: no controlled study of foxtailing is known. Keeping top leaf temperature under about 30 °C and not turning lights up in late flower lowers the risk. **How far should my LED be from the canopy?** The right LED distance from the cannabis canopy depends on the fixture, so follow its PPFD map and a measured reading at the tallest tops rather than a fixed rule of thumb. At ambient CO₂, aim for no more than about 1,000–1,200 µmol/m²/s in flower. Any bleaching means it is too much for your conditions, so raise or dim the light 10–20 %. **Short answer.** If the damage is **only at the top, nearest the light**, and lower leaves look fine, suspect light or heat before nutrients. Measure **canopy PPFD** and **leaf temperature** first. Fix by dimming or raising the light 10–20 %, bringing leaf temperature under ~**30 °C (86 °F)** [1], and making sure the plant can transpire (airflow, root zone, VPD). ## How to recognise it | Symptom | Where | Most likely cause | |---|---|---| | Leaf edges curl up, leaves "taco" or "canoe" | Top canopy, mid-day | Heat or high VPD; the plant is cutting transpiration | | Leaves point straight up and stay that way all day | Top | Too much light (*Grower practice* sign) | | Bleached white or pale yellow top leaves/bracts, veins green at first | Top colas closest to lamp | Light bleaching (photo-oxidation); worse with heat | | Crispy brown spots on top leaves only | Top | Light/heat burn | | New calyxes stacking on top of finished buds ("foxtailing") | Top colas | Heat/light stress in late flower, or genetics | | Droop at lights-on, recovers later | Whole plant | Root zone (over/under-watering), not light | Lower canopy healthy + top damaged = light/heat. Old leaves damaged first = check nutrients and pH instead. ## What's happening At high leaf temperature cannabis photosynthesis and water-use efficiency fall; in one gas-exchange study high temperature combined with high light reduced net photosynthesis [1]. When transpiration can't keep the leaf cool (dry air, still air, sick roots), leaf temperature can climb 8–12 °C (14–22 °F) above air [2]. Excess absorbed light then damages chlorophyll (bleaching). UV at high doses also reduced photosystem efficiency (Fv/Fm) in cannabis [4]. Note that the whole-plant yield response to light did not saturate at 1,800 µmol/m²/s in a well-run trial [3], so "too much light" usually means **too much for the conditions**: heat, low CO₂, root problems, or a cultivar that dislikes it. ## Differential diagnosis - **Nitrogen toxicity:** dark, glossy, clawed leaves throughout, not just at the top. - **Calcium/boron issues:** spotting or distorted new growth across the plant, often with pH or low VPD. - **Windburn:** damage on the fan side. - **Root zone:** wilting that tracks irrigation, not light. ## Numbers that matter | Parameter | Target | Alarm | |---|---|---| | Leaf temperature (top) | 24–29 °C (75–84 °F) | > 31 °C (88 °F) | | Canopy PPFD, ambient CO₂ | ≤ 1,000–1,200 µmol/m²/s | Bleaching at any level = too much for your conditions | | Leaf VPD | 0.8–1.5 kPa | > 1.7 kPa | | Light distance | Follow the fixture's PPFD map, not a rule of thumb | | ## How to fix it 1. Dim 10–20 % or raise the light; re-measure PPFD at the tallest tops. 2. Lower air temperature; move drivers out of the tent if possible. 3. Add airflow across the top canopy (not directly onto colas). 4. Check irrigation and roots; a plant that can't drink can't cool. 5. Supercrop or tie down the tallest colas to even the canopy ([HST](https://genetixbay.com/knowledge/training/hst-supercropping.md)). 6. Bleached tissue won't recover. Judge by new growth. ## How to confirm it worked New leaves at the top are flat and green within 3–5 days, leaf temperature at the tallest tops stays within ~2 °C of air, and no new bleached bracts appear. ## Common mistakes - Flushing or changing nutrients for what is a light problem. - One tall cola dictating the light height. - Turning lights up in late flower "for density" just when foxtailing risk is highest. ## Evidence Temperature × light effects on cannabis gas exchange are *Supported* [1]. Leaf temperature physics is *Supported* [2]. Visual diagnostic patterns and foxtailing causes are *Grower practice*; foxtailing has no controlled study we know of. ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 3. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 4. Westmoreland FM, Kusuma P, Bugbee B, 2023. Elevated UV photon fluxes minimally affected cannabinoid concentration in a high-CBD cultivar (Fv/Fm reduced at highest UV). Frontiers in Plant Science 14:1220585. https://doi.org/10.3389/fpls.2023.1220585 --- # Humidity by stage: RH targets from clone to cure > Run about 65–80 % RH for clones and seedlings, 55–70 % in veg, 50–60 % early flower and 40–50 % in late flower, adjusted to hit a leaf VPD band at your temperature. High RH in flower raises bud-rot and mildew risk and, in a 2025 study, delayed flowering and lowered cannabinoids. Dry and cure near 60 % RH. - Canonical: https://genetixbay.com/knowledge/environment/humidity-by-stage.html - Category: Environment · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Transition, Flower, Ripening, Harvest, Cure · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What humidity should I have in flower?** Cannabis in flower does best at about 50–60 % relative humidity in weeks 1–4 at 23–27 °C, dropping to 40–50 % from week 5 to harvest at 20–25 °C. At lights-off, keep RH at or below 55 % and surfaces at least 3 °C above the dew point. These grower-practice bands target a leaf VPD of roughly 0.9–1.5 kPa and limit bud rot. **Is 70 % humidity too high in late flower?** Yes, 70 % relative humidity is too high for cannabis in late flower, where the target is about 40–50 %. Dense buds plus humid nights is how bud rot starts, and a 2025 controlled cannabis study at roughly 78–98 % RH found delayed flowering, lower biomass and lower cannabinoid content compared with 37–58 % RH. **Why does humidity spike when the lights go off?** Humidity spikes when grow lights go off because the air temperature drops: the same amount of water vapour in cooler air means higher relative humidity, and surfaces near the dew point collect condensation. Ramp temperature down over 30–60 minutes instead of a sudden cliff, keep the dehumidifier running in the dark, or add heat during the dark period. **How big a dehumidifier do I need?** As a first estimate, a grow-room dehumidifier should remove about as many litres per day as the plants are irrigated, because most irrigation water is transpired into the air. Four large plants in a 1.2 × 1.2 m tent can add 6–8 L of vapour daily. Size for real conditions: units rated at 30 °C and 80 % RH remove far less at 24 °C and 50 %. **Can low humidity increase trichomes?** No controlled evidence shows that low humidity increases cannabis trichomes. Dropping relative humidity to around 30 % to 'boost trichomes' is a myth as a reliable technique, contested at best, and mainly stresses the plant. Late-flower targets of about 40–50 % RH are set for disease control and a healthy leaf VPD, not for resin. **Short answer.** RH targets only make sense with temperature, so set humidity to hit a [leaf VPD](https://genetixbay.com/knowledge/environment/vpd-explained.md) band. As a starting point: **clones/seedlings 65–80 %**, **veg 55–70 %**, **early flower 50–60 %**, **late flower 40–50 %**, **drying and curing ~55–62 %**. The flower numbers are driven by disease risk: dense buds plus humid nights is how bud rot (*Botrytis cinerea*) starts [2][3]. ## What's happening - Young plants with few roots lose water through leaves faster than they can replace it; high RH lowers that demand. - Bigger plants transpire a lot of water into the room. A plant drinking 2 L a day puts most of that into the air; a 1.2 × 1.2 m (4 × 4 ft) tent of four such plants is adding ~6–8 L of water vapour a day (~90–95 % of irrigation water is transpired in a healthy crop). - At lights-off temperature drops; the same water content now means higher RH, and surfaces near the dew point collect condensation. That is the hour bud rot loves. - A 2025 controlled study of cannabis at roughly 78–98 % RH vs 37–58 % RH found delayed flowering, lower biomass and lower cannabinoid content at high RH [1]. ## Numbers that matter | Stage | RH | At this air temperature | Leaf VPD (≈, LED) | |---|---|---|---| | Unrooted clones (dome) | 75–90 % | 23–26 °C (73–79 °F) | 0.2–0.5 kPa | | Seedlings | 65–75 % | 23–26 °C (73–79 °F) | 0.4–0.7 kPa | | Veg | 55–70 % | 24–28 °C (75–82 °F) | 0.7–1.1 kPa | | Flower wk 1–4 | 50–60 % | 23–27 °C (73–81 °F) | 0.9–1.3 kPa | | Flower wk 5–harvest | 40–50 % | 20–25 °C (68–77 °F) | 1.1–1.5 kPa | | Lights-off in flower | ≤ 55 % and ≥ 3 °C above dew point | | | | Drying | 55–62 % | 15–21 °C (59–70 °F) | see [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) | **Dew-point rule of thumb:** keep every surface (walls, buds, pots) at least 3 °C (5 °F) above the room's dew point. At 22 °C and 60 % RH the dew point is about 14 °C (57 °F) [4]. ## What to check first 1. Calibrate the hygrometer (salt test). 2. Log RH over 48 h; look at the lights-off spike, not the daytime average. 3. Inside the canopy: a hygrometer inside a dense cola zone often reads 5–10 % higher than room air. ## How to fix it - **Too humid:** dehumidifier sized to the transpiration load (litres per day ≈ total irrigation litres per day as a first estimate), more air exchange if outside air is drier, keep the dehumidifier running at lights-off, thin interior leaves, don't leave standing water or runoff trays. - **Too dry:** humidifier on a controller; fewer air exchanges; group plants; raise reservoir lids only briefly. Avoid misting buds. - **Spikes at lights-off:** ramp temperature down over 30–60 minutes instead of a cliff, or run heat in the dark period. ## How to confirm it worked RH trace stays within ±5 % of target through the lights-off transition, no condensation on tent walls, no grey fuzz inside colas at harvest (check by breaking open the largest buds). ## Common mistakes - Undersized dehumidifier rated at test conditions (often 30 °C/80 % RH) that removes far less at 24 °C/50 %. - "Lowering RH to 30 % boosts trichomes." No controlled evidence; it mainly stresses the plant (*Myth* as a reliable technique, *Contested* at best). - Ignoring humidity inside the canopy. ## Evidence Humidity as a driver of bud rot and powdery mildew is *Established* [2][3]. High-RH harm to flowering and cannabinoids is *Supported* by one 2025 cannabis study [1]. Per-stage RH bands are *Grower practice* derived from VPD logic. ## Sources 1. Corredor-Perilla IC, Kwon H, Park J, 2025. High relative humidity effects in cannabis. Frontiers in Plant Science 16:1678142. https://doi.org/10.3389/fpls.2025.1678142 2. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 3. Utah State University Extension. Hemp bud rot (IPM fact sheet). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot.php 4. Allen RG et al., 1998. FAO-56 Chapter 3 (vapour pressure). https://www.fao.org/4/x0490e/x0490e07.htm --- # Light spectrum: blue, red, far-red and UV, what's real > Photon quantity (PPFD/DLI) and fixture efficacy matter far more than spectrum. Less blue slightly increased cannabis yield (about 12 % from 4 % to 20 % blue). Far-red stretches plants; its yield effect is contested and seems to trade off against cannabinoid concentration. UV has repeatedly failed to raise cannabinoids in controlled trials and can cut yield at high doses. - Canonical: https://genetixbay.com/knowledge/environment/light-spectrum.html - Category: Environment · Level: Intermediate - Evidence: Contested · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Does UV light increase THC?** No, UV light does not reliably increase THC; the claim is a myth. Three independent controlled trials across two labs found UV-B, or UV-A plus UV-B, gave no commercially useful rise in yield or cannabinoids, one cultivar lost yield and THC, and the highest dose cut yield. GenetixBay's position matches the trials: UV makes little or no visible difference to cannabis. **Is far-red worth adding to my LED?** Adding far-red to a cannabis LED is contested and not a proven win. One study found a lower red to far-red ratio raised inflorescence yield but lowered cannabinoids and terpenes, another found more height and less yield, and end-of-day far-red helped only some high-THC lines. Far-red reliably stretches plants, so test it side by side with your cultivar, measuring grams and lab potency. **What spectrum is best for flowering cannabis?** For flowering cannabis, a broad white LED spectrum with roughly 5–15 % blue works well; a red-heavy 'bloom' spectrum is not required, and HPS at about 4 % blue also flowers fine. Research shows photon quantity and fixture efficacy in µmol/J matter far more than colour, though yield fell about 12 % as blue rose from 4 % to 20 %. **Do I need a different spectrum for veg and flower?** No, cannabis does not need a different spectrum for veg and flower; one broad white spectrum works for both unless you have a specific reason. More blue gives shorter, more compact plants, but stretch in veg is mostly caused by low light intensity, not by missing blue. Running a dim 'veg spectrum' is a common mistake; raise PPFD instead. **Is a full-spectrum white LED as good as HPS?** Yes, a full-spectrum white LED is as good as HPS for cannabis yield at the same PPFD, according to research comparisons, and better on running costs. Good current LED fixtures exceed 2.5–3 µmol/J against about 1.7 µmol/J for HPS, and they put less heat load on the leaves. Choose a fixture on efficacy and its PPFD map, not on 'full spectrum' marketing. **Do LEDs need more Cal-Mag?** No, LEDs do not create a need for more Cal-Mag; that is a myth. Calcium and magnesium demand in cannabis follows the cultivar, the water source such as RO, coco buffering, root-zone pH and transpiration. Cooler leaves under LED can lower transpiration and calcium delivery, so correct leaf VPD and check water, medium and pH before reaching for a supplement. **Short answer.** Buy photons, not colours. Across three studies, yield **fell about 12 %** as the blue fraction rose from 4 % to 20 %, but the authors concluded that **fixture efficacy (µmol/J) matters more** for cost-effective cannabinoid production [1]. **UV** did not deliver commercially useful gains in yield or cannabinoids in three independent controlled trials and cut yield at high doses [2][3][4]. **Far-red** is genuinely contested: one study saw more yield with lower cannabinoid concentration [5], another saw the opposite on yield [6], and end-of-day far-red helped some high-THC lines [7]. ## What's real, what isn't | Claim | Status | Detail | |---|---|---| | More photons = more yield | *Supported* | See [PPFD and DLI](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md). | | Lower blue fraction slightly increases yield | *Supported* | ~12 % linear drop from 4 % to 20 % blue [1]. More blue gives shorter, more compact plants. | | A "bloom" red-heavy spectrum is required for flower | *Myth* | Broad white LED spectra with ~5–15 % blue flower fine; HPS (~4 % blue) also works [1]. | | UV-B raises THC or visibly improves buds | *Myth* (house position: little or no visible difference, matching the trials) | No commercially relevant increase in yield or cannabinoids from 287 nm UV-B; one cultivar lost yield and THC [2]. UV-A + UV-B: no effect on total THC [3]. High-CBD cultivar: +3–13 %, not significant; highest dose cut yield [4]. | | Far-red increases yield | *Contested* | Lower R:FR (3 vs 12) increased inflorescence yield but decreased cannabinoids and terpenes [5]; an earlier experiment found low R:FR increased height and reduced yield [6]; end-of-day FR raised yield in some high-THC lines and was strongly genotype-specific [7]. | | Far-red stretches plants | *Established* | Shade-avoidance via phytochrome; consistent across studies [5][6]. | | Green light is wasted | *Myth* | Green penetrates deeper into the canopy and drives photosynthesis in lower leaves. | | White LED vs HPS at the same PPFD | *Supported* | Similar yield; LED wins on efficacy and leaf heat load [1][8]. | | LEDs need more Cal-Mag | *Myth* | The light source doesn't create a Ca/Mg need. Demand follows cultivar, water (RO), coco buffering, root-zone pH and transpiration. Cooler leaves under LED can lower transpiration and Ca delivery; fix leaf VPD, not the bottle. See [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md). | ## Practical choices 1. **Choose by µmol/J and uniformity first.** Good current LED fixtures exceed 2.5–3 µmol/J; HPS is ~1.7 µmol/J [8]. 2. **Keep one broad white spectrum** for veg and flower unless you have a specific reason. 3. **Far-red supplement:** if you try it, run it as an end-of-day (EOD) 10–15 min treatment or a modest FR fraction, on a side-by-side trial with your own cultivar, measuring both grams and lab potency. Expect more stretch. 4. **UV:** not recommended as a potency tool. If you use it, protect eyes and skin (UV-B and UV-C are hazardous); the evidence does not justify the cost or risk. ## Common mistakes - Choosing a fixture on "full spectrum" marketing instead of efficacy and PPFD map. - Adding UV and switching off a good fixture for the sake of a colour story. - Running a "veg spectrum" at low intensity: low light, not blue, causes stretch. - Judging spectrum trials by eye: purple-pink light hides deficiencies and pests. - Adding Cal-Mag "because it's an LED". Check water, medium, pH and leaf VPD first ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)). ## Safety UV fixtures and bright blue LEDs can damage eyes. Wear rated glasses when working under lights, never look into UV sources, and switch UV off before working in the canopy. ## Evidence The blue-fraction result is *Supported* (three studies, one lab) [1]. The UV result is *Supported* in its negative direction by three trials across two labs [2][3][4]; the house position is the same: UV-B makes little or no visible difference. Far-red is *Contested*: results depend on cultivar, timing and ratio [5][6][7]. ## Sources 1. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://pmc.ncbi.nlm.nih.gov/articles/PMC7987162/ 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis inflorescence yield and cannabinoid concentration are not increased with exposure to short-wavelength ultraviolet-B radiation. Frontiers in Plant Science 12:725078. https://doi.org/10.3389/fpls.2021.725078 3. Llewellyn D et al., 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 4. Westmoreland FM, Kusuma P, Bugbee B, 2023. Elevated UV photon fluxes minimally affected cannabinoid concentration in a high-CBD cultivar. Frontiers in Plant Science 14:1220585. https://doi.org/10.3389/fpls.2023.1220585 5. Kotiranta S, Sarka A, Kotilainen T, Palonen P, 2025. Decreasing R:FR ratio in a grow light spectrum increases inflorescence yield but decreases plant specialized metabolite concentrations in Cannabis sativa. Environmental and Experimental Botany 229:106059. https://doi.org/10.1016/j.envexpbot.2024.106059 6. Kotiranta S et al., 2024. (Low R:FR increased height and reduced inflorescence yield.) Industrial Crops and Products. https://doi.org/10.1016/j.indcrop.2023.117772 7. Peterswald TJ et al., 2025. The effects of far-red light on medicinal Cannabis. Scientific Reports. https://pmc.ncbi.nlm.nih.gov/articles/PMC12092679/ 8. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # Photoperiod and light leaks: 18/6, 12/12 and the dark period > Photoperiod cannabis stays vegetative under long days (18/6 up to 24/0; no sleep period is needed in veg) and flowers when the uninterrupted night is long enough: 12/12 or 13/11, and some cultivars flower at 14–15 h, usually as ~12 h at high intensity plus sunrise and sunset ramps. Light during the dark period, even very dim, can delay or weaken flowering in sensitive cultivars; leaks can also expose herm-prone genetics, triggering male flowers on susceptible plants. Some cultivars yield more at 13–14 h days, at a possible cost in THC concentration. - Canonical: https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.html - Category: Environment · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why is my plant not flowering on 12/12?** A photoperiod cannabis plant that is not flowering on 12/12 usually has light reaching it during the dark period or a faulty timer. Research shows stray light as dim as 0.01–2 µmol/m²/s can delay flowering in sensitive cultivars. Remember the first pistil clusters normally take about 10–14 days after the flip, so worry only if stretching and leaf growth continue 3–4 weeks in. **How dark does the grow room need to be at night?** A cannabis flowering room needs to be as close to completely dark as you can measure during the night period, and certainly below about 0.01–2 µmol/m²/s of stray light. A hemp study found delays from roughly 2 µmol/m²/s, and conference work saw delays in the most sensitive cultivars at 0.01 µmol/m²/s. If your adapted eyes can see light after five minutes, it is a leak. **Do light leaks cause hermaphrodites?** Light leaks are a commonly reported trigger for hermaphrodite flowers in cannabis, but in GenetixBay's breeder position a leak reveals herm-prone genetics rather than creating them: a stable plant beside the same leak stays female. Controlled evidence is limited, so this is grower practice. Fix the leak, and cull any plant that produced pollen sacs rather than breeding from it. **Can I flower on 13/11 or 14/10?** Yes, many cannabis cultivars flower on 13/11, which GenetixBay endorses, and some flower at 14–15 hours of light. In one study every line flowered at 14 hours and some yielded more, but two high-THC lines lost THC concentration. In practice the house approach is about 12 hours at high intensity plus sunrise and sunset ramps. Trial your own cultivar before committing. **Can I run 24/0 in veg?** Yes, you can run 24/0 lighting in veg; GenetixBay endorses it, because cannabis does not need a sleep period in vegetative growth. As a short-day plant, cannabis measures night length only to decide when to flower, so continuous light simply keeps it vegetative. The trade-off is more electricity per day than 18/6 or 20/4, which is grower practice rather than a measured yield finding. **Do sunrise and sunset ramps count as daylight?** Yes, sunrise and sunset ramps count as daylight for a cannabis plant's flowering clock, even though they add little to the daily light integral. The plant measures the uninterrupted dark that follows, so a 12-hour high-intensity day plus ramps makes a 13–15 hour photoperiod. When calculating DLI, count the ramp periods at their real, lower PPFD. **What photoperiod for autoflowers?** Autoflowering cannabis is usually grown on 18/6 to 20/4 from seed to harvest. Autoflowers are day-neutral, meaning the photoperiod does not trigger their flowering, so there is no need to switch to 12/12. Long days simply give them more total light during their short, fixed life cycle. This schedule is grower practice rather than a result from a controlled trial. **Short answer.** Photoperiod cannabis measures the **night**, not the day. Keep nights short (18/6 is standard veg) to stay vegetative; give a long, **uninterrupted** night to flower. **House position:** 24/0 is fine in veg (cannabis doesn't need a sleep period in veg), and flower doesn't have to be exactly 12/12: **13/11 is endorsed**, and some cultivars flower at 14–15 h of light. Light in the dark period, even very dim, can delay or weaken flowering: a hemp study reports delays from stray light at about **2 µmol/m²/s** [1], and a 2024 conference report saw delays in the most sensitive cannabis cultivars at **0.01 µmol/m²/s (10 nmol)** of continuous white LED light [2]. Make the room truly dark. ## What's happening Phytochrome in the leaf tracks red and far-red light. During a long night the "active" form decays; once the night is longer than the cultivar's critical night length, flowering genes switch on. A pulse of light in the middle of the night resets the clock (that's the "night break" commercial growers use deliberately to keep mothers vegetative with less energy [4]). Critical night length varies by cultivar; many drug-type cultivars flower once nights exceed roughly 10–11 h, which is why 12/12 is the safe default ([1] tested hemp). **Sunrise and sunset.** In practice a GenetixBay flowering day is about **12 h at high intensity**, with dimmed sunrise and sunset ramps adding the rest of a 13–15 h photoperiod. The ramps are low-intensity light, so they add little DLI, but they count as day: the uninterrupted dark that follows is what the plant measures. **The flip isn't day 1 of flower.** Expect roughly 10–14 days of transition before pistil clusters show at the tops; see [the flip-to-flower transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md). ## Numbers that matter | Situation | Schedule | Notes | |---|---|---| | Veg, photoperiod | 18/6, 20/4 or 24/0 | 24/0 endorsed (house position): cannabis doesn't need a sleep period in veg. It costs more energy per day (*Grower practice*) | | Mothers | 18/6, or 12/12 + 1 h night break | Night break can cut veg lighting energy by nearly a third [4] | | Flower, default | 12/12 or 13/11 | 13/11 endorsed (house position); in practice ~12 h at high intensity plus sunrise/sunset ramps | | Flower, cultivar trial | 14/10 or 15/9 | Some cultivars flower at 14–15 h. Some cultivars yielded more at 14 h; two high-THC lines lost THC concentration [3] | | Autoflowers | 18/6 to 20/4 throughout | Day-neutral; photoperiod doesn't trigger flowering | | Dark-period stray light | As close to 0 as you can measure; certainly < 0.01–2 µmol/m²/s | Thresholds from [1][2]; cultivar dependent | ## How to find and fix leaks 1. Sit in the room with the lights off for 5 minutes until your eyes adapt. Anything you can see is a leak. 2. Usual culprits: tent zipper ends, duct ports, power-strip LEDs, controller displays, smoke detector LEDs, phone screens, door gaps, light from a neighbouring veg room. 3. Fix with black tape, foil tape, light-tight duct boots and a black-out curtain on doors. 4. If you must work in the dark period, use a dim green headlamp briefly (*Grower practice*; green is less active on phytochrome than red, but not inactive). 5. Use a timer you trust; check it after power cuts. A drifting mechanical timer is a slow leak. ## How to recognise a problem - Plants keep stretching and making leaves 3–4 weeks into 12/12. - Flowers start, then "re-veg" (rounded single-finger leaves on buds). - Uneven flowering between plants nearest a leak and the rest. - Hermaphrodite flowers (bananas/pollen sacs) late in flower. Light leaks are a commonly reported trigger, along with heat and other stress. In GenetixBay's breeder position the leak *reveals* susceptible genetics: a stable plant beside it stays female. Fix the leak, and cull the plant that hermed (*Grower practice*; controlled evidence is limited). See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). ## Common mistakes - "One minute of light won't matter." For sensitive cultivars it can. - Opening the tent to check on plants at night. - Assuming outdoor street lighting can't reach a greenhouse. ## Evidence The long-night requirement is *Established*. Low-intensity stray light delaying flowering is *Supported* by [1] for hemp and by conference work for cannabis [2] (not yet peer reviewed at time of writing). Longer flowering photoperiods increasing yield in some cultivars is *Supported* by one study [3], which also found lower THC concentration in two high-THC lines, so test your cultivar. 24/0 veg and 13/11 flower are house positions (*Grower practice*, founder-endorsed); no sleep period in veg is consistent with cannabis being a short-day plant that measures night length only to decide when to flower. Leaks triggering hermaphrodite flowers in susceptible plants is *Grower practice*; the genetic basis of susceptibility is the GenetixBay house position. ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis 3. Peterswald TJ, Mieog JC, Azman Halimi R, et al., 2023. Moving away from 12:12; the effect of different photoperiods on biomass yield and cannabinoids in medicinal cannabis. Plants 12(5):1061. https://doi.org/10.3390/plants12051061 4. Examining the night break method in Cannabis sativa horticulture: vegetative daily light integral affects yield of extractable biomass, 2025. Plants 14(19):3095. https://pmc.ncbi.nlm.nih.gov/articles/PMC12525983/ --- # PPFD and DLI by stage, with the evidence > In the best indoor trial, cannabis flower yield rose linearly with canopy PPFD from 120 to 1,800 µmol/m²/s at ambient CO₂ (116 to 519 g/m²) with no change in cannabinoid potency. Practical targets: 100–300 µmol/m²/s for seedlings and clones, 300–700 (up to ~900) in veg, and 800–1,200 in flower, or more with CO₂, as long as the plant shows no stress and the electricity is worth it. - Canonical: https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.html - Category: Environment · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What PPFD should I run in flower?** A practical PPFD for cannabis in flower at ambient CO₂ is 800–1,200 µmol/m²/s at canopy height, rising to 1,000–1,500 µmol/m²/s with 900–1,200 ppm CO₂. Research shows yield kept rising linearly up to 1,800 µmol/m²/s, so the ceiling depends on plant stress, root-zone health and whether the extra electricity pays. Measure with a quantum sensor grid, not the manufacturer's centre-point figure. **What DLI does cannabis need?** Cannabis DLI needs by stage are roughly 3–10 mol/m²/day for unrooted cuttings, 10–19 for seedlings, 19–43 in early veg, 32–58 in late veg and 35–56 in flower at ambient CO₂, or 43–65 with CO₂. Autoflowers on 18–20 hour days run about 39–72. Most of these figures are grower practice, while the flower response is supported by controlled trials. **Does more light increase THC?** No, more light does not increase THC percentage in cannabis. In two controlled indoor trials, raising canopy light from 120 to 1,800 µmol/m²/s multiplied dry flower yield about 4.5 times, from 116 to 519 g/m², while cannabinoid potency per gram stayed flat and terpenes rose only modestly. Extra light buys more grams, not stronger buds. **Is 1500 PPFD too much without CO2?** 1,500 µmol/m²/s PPFD is not automatically too much for cannabis without added CO₂: one trial saw yield keep climbing to 1,800 at ambient CO₂. Still, practical targets at ambient CO₂ are 800–1,200, and pushing past about 1,200 without CO₂ and healthy roots often causes stress. Raise light 10–15 % every 3–5 days and back off at bleaching, tacoing or leaves that stay praying upward. **How do I convert PPFD to DLI?** To convert PPFD to DLI, multiply PPFD in µmol/m²/s by the hours of light and by 0.0036, giving mol/m²/day. For example, 600 µmol/m²/s for 18 hours equals 38.9 mol/m²/day, 900 for 12 hours is also 38.9, and 1,200 for 12 hours is 51.8. Use your measured canopy average, not a fixture's centre-point figure, and count dim ramps at their real PPFD. **What PPFD for seedlings and clones?** Cannabis seedlings do well at about 150–300 µmol/m²/s PPFD on 18-hour days, and unrooted clones at 50–150 µmol/m²/s on 18–24 hours. General horticulture research supports a maximum of roughly 100–150 µmol/m²/s for cuttings at sticking, and young-plant DLI of 10–14 mol/m²/day gives better roots in other crops; the cannabis figures are grower practice. **Short answer.** Light is the single biggest yield lever indoors. In a 2021 trial with LEDs, a 12 h flowering photoperiod and **ambient CO₂**, dry flower yield rose **linearly** from **116 g/m² at 120 µmol/m²/s to 519 g/m² at 1,800 µmol/m²/s** (about 4.5×) and **did not saturate**; cannabinoid potency did not change with light, terpenes rose modestly [1]. A 2022 trial on a high-THC cultivar found the same proportional yield response [2]. Practical targets: **seedlings/clones 100–300, veg 300–700 (up to ~900), flower 800–1,200 µmol/m²/s**, higher with CO₂ if the plants and your power bill tolerate it. ## What's happening - **PPFD** (photosynthetic photon flux density, µmol/m²/s) is the instantaneous photon rate hitting the canopy, 400–700 nm. - **DLI** (daily light integral, mol/m²/day) is the total for the day: `DLI = PPFD × hours × 0.0036`. - Individual leaves saturate well below the canopy's limit; whole-plant yield keeps climbing because lower leaves and bud sites receive more light as the top gets more [1]. Leaf light-response curves are a poor predictor of yield [1]. - Higher light also shortens internodes, thickens leaves and makes denser, more compact plants in veg [3]. ## Numbers that matter | Stage | PPFD (µmol/m²/s) | Hours | DLI (mol/m²/day) | Evidence | |---|---|---|---|---| | Unrooted cuttings | 50–150 | 18–24 | 3–10 | Supported for horticultural cuttings: max ~100–150 at sticking [6] | | Seedlings (cotyledons–2 nodes) | 150–300 | 18 | 10–19 | Grower practice; young-plant DLI 10–14 gives better roots in other crops [5] | | Early veg | 300–500 | 18–24 | 19–43 | Grower practice; 24/0 house-endorsed (no sleep period needed in veg) | | Late veg | 500–900 | 18 | 32–58 | Supported (preprint): healthy, compact growth up to ~900 [3] | | Flower, ambient CO₂ | 800–1,200 | 12–13 | 35–56 | Supported: yield linear to 1,800 [1][2]; 13/11 house-endorsed | | Flower, 900–1,200 ppm CO₂ | 1,000–1,500 | 12 | 43–65 | Supported (gas exchange) [4]; grower practice for yield | | Autoflowers | 600–1,000 | 18–20 | 39–72 | Grower practice | Conversions: 600 µmol at 18 h = 38.9 mol; 900 µmol at 12 h = 38.9 mol; 1,200 µmol at 12 h = 51.8 mol; 400 µmol at 24 h = 34.6 mol. **Photoperiod in practice.** 24/0 is endorsed in veg; 13/11 is endorsed in flower, and some cultivars flower at 14–15 h (see [photoperiod](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)). In practice a GenetixBay flowering day is about **12 h at high intensity**, with dimmed sunrise and sunset ramps adding the rest of a 13–15 h photoperiod. The ramps are low-intensity light, so they add little DLI, but they count as day: the uninterrupted dark that follows is what the plant measures. Count the ramps at their real PPFD when you work out DLI. ### The economics The same 2021 trial estimated ~0.54 g/kWh at 900 µmol/m²/s; doubling light raised yield about 70 % but cut energy-use efficacy about 15 % [1]. Fixture efficacy (µmol/J) matters more than any other lighting specification for cost per gram; current good LEDs exceed 2.5–3 µmol/J [7]. ## How to measure 1. Use a quantum (PAR) sensor, not a lux meter. Lux-to-PPFD conversion depends on spectrum and is only rough. 2. Take a 9- or 16-point grid at canopy top height; record average and min/max. Aim for min ≥ 70–80 % of average. 3. Re-measure when plants grow; the canopy moves toward the light. 4. Phone apps are ±20 % or worse; fine for trends, not for setpoints. ## How to raise light safely Step up 10–15 % every 3–5 days in veg and early flower and watch the top leaves. Signs you've overshot: upward-praying leaves that stay that way at lights-on, bleached or yellow-white top bracts, tacoing, and pale new growth at the top only ([heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md)). ## Common mistakes - Using the manufacturer's centre-point PPFD at 30 cm as "my PPFD". - Hanging lights for the tallest cola and starving the rest. - Pushing above ~1,200 µmol/m²/s without CO₂ and good root-zone health, then blaming the strain. - Expecting more light to raise THC percentage. It raises grams; potency per gram stayed flat [1][2]. ## Evidence Linear yield response to light in flower is *Supported* by two controlled indoor trials from one group [1][2]; it needs replication across more cultivars and with CO₂. No effect of light intensity on cannabinoid concentration is *Supported* [1][2]. Veg targets rely on a non-peer-reviewed preprint [3] and grower practice. Seedling/clone values are *Grower practice* plus general horticulture [5][6]. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 3. Moher M, Llewellyn D, Jones M, Zheng Y, 2021. High light intensities can be used to grow healthy and robust cannabis plants during the vegetative stage of indoor production. Preprints 2021040417 (not peer reviewed). https://doi.org/10.20944/preprints202104.0417.v1 4. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 5. Runkle E. The benefits of lighted plugs (DLI for young plants). Michigan State University Extension. https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs 6. Michigan State University. Lighting of cuttings (rooting-phase PPFD). https://www.canr.msu.edu/uploads/resources/pdfs/lighting-of-cuttings.pdf 7. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # Temperature by stage: day, night and root-zone targets > Run roughly 24–28 °C (75–82 °F) by day in veg, 22–26 °C (72–79 °F) in flower, cooling to 20–24 °C (68–75 °F) in late flower, with nights 3–6 °C (5–10 °F) cooler. Above about 30 °C (86 °F) photosynthesis in cannabis falls unless light and CO₂ are high. Keep the root zone and hydro reservoirs at 18–22 °C (64–72 °F). - Canonical: https://genetixbay.com/knowledge/environment/temperature-by-stage.html - Category: Environment · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Transition, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What temperature should my grow room be in veg and flower?** A cannabis grow room should run about 24–28 °C (75–82 °F) by day in veg, 22–26 °C (72–79 °F) in mid flower and 20–24 °C (68–75 °F) in late flower, read at canopy height with a shaded probe. Add 2–3 °C when running 800–1,200 ppm CO₂. These setpoints are grower practice informed by one cannabis gas-exchange study and greenhouse horticulture. **How much cooler should the night be?** Cannabis grow-room nights are usually run 3–6 °C (5–10 °F) cooler than the day. A smaller day-night difference during the transition weeks helps limit stretch, because a large positive difference lengthens internodes, an effect well documented in ornamentals and grower practice in cannabis. Avoid sharp swings at lights-on and lights-off, which cause condensation and invite bud rot. **Is 30 °C too hot for cannabis?** 30 °C (86 °F) is at the upper edge for cannabis: research shows net photosynthesis and water-use efficiency fall above about 30 °C leaf temperature unless light and CO₂ are high. Sustained air above 30–32 °C is a hard limit in an un-enriched room. CO₂-enriched commercial rooms run 28–30 °C, but copying that setpoint into a tent without CO₂ is a common mistake. **What reservoir temperature should I run?** A hydroponic cannabis reservoir should run at 18–22 °C (64–72 °F), which is established extension guidance for hydroponic root zones. Above 24 °C (75 °F) in DWC or RDWC, root-rot risk rises sharply. Keep a reservoir cool with a chiller, insulation, a larger volume, and by lifting it off a warm floor into shade; healthy roots stay white. **Does a cold night really bring out purple colour?** Yes, cold nights can really bring out purple colour in cannabis, but only in cultivars that carry the genetics for anthocyanin pigments; colour is mostly genetic. Big cold nights also slow ripening and invite condensation and bud rot, so they are a trade-off. Late-flower nights of about 16–20 °C (61–68 °F) are the usual range. **Do cold nights increase terpenes?** No, cold nights do not increase terpenes; that is a myth and the GenetixBay house position unless peer-reviewed data shows otherwise. No published evidence supports more terpenes, flavour or resin from cold. Cooler late-flower days of 20–24 °C may reduce heat losses of volatile terpenes, which is grower practice, but deliberately chilling nights adds colour at most. **Short answer.** Cannabis photosynthesises best somewhere around **25–30 °C (77–86 °F) leaf temperature** when light is strong; above ~30 °C (86 °F) net photosynthesis and water-use efficiency fall in the one cannabis gas-exchange study we have [1]. In practice: **veg 24–28 °C (75–82 °F) day, flower 22–26 °C (72–79 °F) day, late flower 20–24 °C (68–75 °F)**, nights **3–6 °C (5–10 °F) cooler**, root zone **18–22 °C (64–72 °F)**. ## What's happening Temperature sets the speed of every enzyme in the plant. Photosynthesis climbs with temperature until respiration and photorespiration catch up; at high light and high CO₂ the optimum shifts warmer, which is why CO₂-enriched rooms run 2–4 °C hotter [1][2]. Night temperature mostly controls respiration (sugar burnt) and stretch: a warm night relative to day (negative DIF) shortens internodes, a big positive DIF lengthens them (well documented in ornamentals; *Grower practice* in cannabis). Leaf temperature is what matters, and it is not air temperature. Under LEDs well-watered leaves usually run slightly cooler than air; under HID they run warmer [3]. See [VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md). ## Numbers that matter | Stage | Day air | Night air | Root zone / reservoir | Notes | |---|---|---|---|---| | Germination | 22–28 °C (72–82 °F) | same | 22–26 °C (72–79 °F) | Hemp seed optimum ~19–30 °C [5] | | Seedlings / clones | 23–27 °C (73–81 °F) | 20–24 °C (68–75 °F) | 21–24 °C (70–75 °F) for rooting | Warm root zone speeds rooting | | Veg | 24–28 °C (75–82 °F) | 19–23 °C (66–73 °F) | 18–22 °C (64–72 °F) | Add 2–3 °C with CO₂ 800–1,200 ppm | | Transition (flower wk 1–3) | 23–27 °C (73–81 °F) | 19–22 °C (66–72 °F) | 18–22 °C (64–72 °F) | Smaller DIF limits stretch | | Mid flower (wk 4–6) | 22–26 °C (72–79 °F) | 18–22 °C (64–72 °F) | 18–22 °C (64–72 °F) | | | Late flower / ripening | 20–24 °C (68–75 °F) | 16–20 °C (61–68 °F) | 18–21 °C (64–70 °F) | Cooler days avoid heat losses of volatile terpenes (*Grower practice*); cold nights don't add terpenes | | Hard limits | Above 30–32 °C (86–90 °F) sustained, or below 15 °C (59 °F) | | Above 24 °C (75 °F) in DWC/RDWC raises root-rot risk [4] | | ## What to check first 1. Canopy-height reading, shaded probe, moving air. Ceiling and floor readings lie. 2. Leaf temperature with an IR thermometer; compare with air. 3. Day-night swing: plot 48 h. Sharp swings at lights-on/off cause condensation. 4. Reservoir or pot temperature, especially in hydro and fabric pots on warm floors. ## How to fix it - **Too hot:** raise or dim lights 10–20 %, improve exhaust or add cooling, move ballasts/drivers outside the room, run lights during the cooler part of the day. - **Too cold:** insulate, add a thermostatically controlled heater (never an open-element heater near water or plastic), shorten the dark-period swing. - **Warm reservoir:** chiller, insulated reservoir, reservoir off the floor in shade, larger volume. ## How to confirm it worked New growth is evenly spaced (no sudden stretch), leaves don't taco or droop at mid-day, water use is steady, and roots in hydro stay white. ## Common mistakes - Copying a CO₂-enriched commercial setpoint (28–30 °C) into an un-enriched tent. - Ignoring leaf temperature under HID. - Big cold nights to "force purple" or "boost terpenes". Anthocyanin colour is mostly genetic; cold can bring it out in some cultivars (real), but it also slows ripening and invites condensation. More terpenes, flavour or resin from cold: *Myth*. - Warm reservoirs in summer and wondering why roots go brown. ## Evidence The cannabis gas-exchange response to temperature and light is *Supported* by Chandra et al. [1][2] (one cultivar, leaf level, short-term measurements). Stage setpoints and DIF effects are *Grower practice* informed by greenhouse horticulture. Root-zone 18–22 °C for hydroponics is *Established* extension guidance [4]. Germination cardinal temperatures for hemp are *Supported* [5]. Cold nights bring out anthocyanin colour in cultivars that carry it; that's real. Claims that cold nights add terpenes, flavour or resin are a *Myth* (house position) unless peer-reviewed data shows otherwise. ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 2. Chandra S, Lata H, Khan IA, ElSohly MA, 2011. Photosynthetic response of Cannabis sativa L., an important medicinal plant, to elevated levels of CO2. Physiology and Molecular Biology of Plants 17:291–295. https://doi.org/10.1007/s12298-011-0066-6 3. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 4. e-GRO / Colorado State University Extension, Root disease problems and management in hydroponic systems (root-zone 68–72 °F). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 5. Geneve RL et al., 2022. Temperature limits for seed germination in industrial hemp (Cannabis sativa L.). Crops 2(4):415–427. https://doi.org/10.3390/crops2040029 --- # The flip isn't day 1 of flower: the 10–14 day transition and how to count it > Switching to 12/12 starts floral induction, not flowering. In controlled studies the first visible inflorescence (at least three pairs of pistils at the top of the main shoot) appeared roughly 8–14 days after short days began, around 13–14 days on average across many hemp cultivars, and up to three weeks in slow ones. Breeder flowering times often count from that point, so a stated 8 weeks usually means harvest about 9.5–10 weeks after the flip. Count both: days since flip and days of flower. - Canonical: https://genetixbay.com/knowledge/environment/flip-to-flower-transition.html - Category: Environment · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is the first day of 12/12 the first day of flower?** No, the first day of 12/12 is not the first day of flower; this is a myth. The flip starts floral induction, and the shoot tip then spends roughly 10–14 days rebuilding itself before real flowering begins. Counting the flip as day 1 of flower is why many growers harvest about two weeks early because the calendar says 'week 8'. **How long after the flip do pistils show?** Visible pistil clusters at the top of the main shoot usually appear about 8–14 days after the flip to 12/12 in controlled studies. Across 27 hemp cultivars the average was 13–14 days, the fastest essential-oil types took about 13 days and slow cultivars around 21 days or more. Under the microscope, flower primordia were already forming by about day 7–8. **Why does my strain take longer than the breeder says?** A cannabis strain usually takes longer than the breeder's stated flowering time because many breeders count from flower set, the first visible pistil clusters, not from the flip. The 10–14 day transition gets added on top, so a stated 8 weeks typically means harvest about 9.5–10 weeks after switching to 12/12. This counting habit is grower practice and the GenetixBay house position, not a measured survey. **When does flowering actually start after switching to 12/12?** Flowering actually starts when at least three pairs of pistils are visible at the top of the main shoot, the research definition of onset. After switching to 12/12 that typically takes about 10–14 days, though some northern hemp needed only 4–11 days and slow cultivars three weeks. Full flowering on main and side branches took until about day 22 in one study. **Are preflowers the start of flowering?** No, preflowers are not the start of flowering. The single flowers that form in leaf axils during veg are triggered by plant age and internal signals, not by the photoperiod, so they appear under 18/6 or 24/0 too. Research found the first pair formed around the 7th node in one cultivar. They reveal sex and maturity; induced pistil clusters at the shoot tips mark real flowering. **How do I count weeks of flower?** To count weeks of flower, keep two clocks. Days since flip starts at the first long night and is for planning the room, stretch and comparing your own runs. Days of flower starts when three or more pairs of pistils cluster at the top of the main shoot, and is the clock to compare with breeder times and harvest windows. Record both in your journal. **How long does the stretch last?** The cannabis stretch mostly happens in the first two to three weeks after the flip. Research found stem and internode elongation fastest from about day 5 to day 10 of short days. One plant-patent description gives a 50–100 % height gain over that window, and grower reports range from about 1.5× to 3×, so flip at roughly half the final height you can fit. **How will I know my plant is really flowering?** A cannabis plant is really flowering when pistil clusters form at the top nodes and main cola, not lone pairs in leaf axils. Supporting signs are the stretch slowing with short new internodes, new growth switching from fan leaves to stacked bracts, and smaller top leaves with stronger aroma. Photographing the same top cola every 2–3 days from the flip makes the onset date obvious. **Does 13/11 delay flowering?** A 13/11 photoperiod delays cannabis flowering very little: in one study of two THC-dominant cultivars, 13 hours delayed onset by about 1.5 days in one and not at all in the other, while yield rose 1.35× and 1.5×. GenetixBay endorses 13/11. Sensitive cultivars may need a day or two more, and THC fell in some lines at 14 hours, so test your cultivar. **Short answer.** Switching to 12/12 starts **floral induction**. It doesn't start flowering. The shoot tip spends the next week or two rebuilding itself, and the first real pistil clusters at the top of the plant usually show **about 8–14 days after the flip** in controlled studies [1][4], with slow cultivars taking **three weeks or more** [4]. Breeders' flowering times often count from that point, not from the flip. So a breeder's **"8 weeks" usually means harvest about 9.5–10 weeks after the flip.** Count both: days since flip and days of flower. > **House position: the flip isn't day 1 of flower.** The founder's ruling: after the switch to 12/12 there's a transition, generally about 10–14 days, before flowering really begins, and most growers don't account for it. That's why most runs go "longer" than the breeder's stated time by about the same amount: breeder times often count from first visible pistils or "flower set", not from the flip. Count from the flip and add the transition. Jardin and GenetixBay journals track both "days since flip" and "days of flower". The evidence for and against is below. > **The founder, on "how will I know when she's actually flowering?":** "Talk to her." No, seriously: she'll tell you more than you bargained for. ## What's happening after the flip Cannabis is a short-day plant: it measures the uninterrupted night (see [photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)). Once the night is long enough, the shoot apex changes what it builds. - **Under long days** the main shoot keeps making long internodes, big fan leaves and side shoots. Each node carries a pair of single flowers once the plant is old enough [1][2]. - **Under short days** the apex branches intensively, the internodes shrink and bracts stack into a compact inflorescence: the cola [1][3]. In one Israeli study, the apex of a cultivar showed bract and flower primordia under the microscope by about **day 7–8** of short days, but visible pistils at the top of the main shoot didn't appear until **day 12**; another cultivar showed them by **day 8** [1]. Full flowering, with inflorescences on main, second- and third-order branches, took until about **day 22** [1]. The plant is busy from day one. It just isn't visibly flowering yet. The switch itself is fast and reversible. A follow-up study found inflorescence onset needed **at least three consecutive short days**, short days had to continue to keep the inflorescence compact, and returning plants to long days raised gibberellin and auxin at the apex and **pulled the inflorescence apart** [3]. That's the biology of re-veg, and why a leaky dark period in the first two weeks costs you time. ## Preflowers are not the start of flower The single flowers that appear at the nodes in veg ("preflowers") are not induced by the flip. Spitzer-Rimon and colleagues concluded that "induction of solitary flowers is age-dependent and controlled by internal signals, but not by photoperiod" [1]. In seedlings the juvenile-to-adult shift happened autonomously; in the cultivar studied, the first pair of single flowers formed at the **7th node** [2]. Alter et al. confirm that solitary-flower initiation in seedlings is photoperiod-independent [3]. | | Solitary flowers ("preflowers") | Induced inflorescence (real flowering) | |---|---|---| | Trigger | Plant age, internal signals [1][2] | Long uninterrupted nights [1][3][4] | | Appears under 18/6 or 24/0? | Yes | No (photoperiod types) | | Where | One pair per node, in leaf axils | Clustered at the top of the main shoot and branch tips | | What it tells you | Sex, and that the plant is mature | That flowering has started: day 1 of flower | The research definition of flowering onset is the one to use: **at least three pairs of pistils visible at the top of the main shoot** [1][7]. Zhang et al. used the equivalent: forked stigmas protruding from bracts at the apical meristem [4]. ## How long the transition takes: the data | Study | Plants and schedule | Time from short days to flowering onset | |---|---|---| | Spitzer-Rimon et al. 2019 [1] | Three drug-type cultivars, 12/12 | Visible stigmata day 8 (one cultivar) and day 12 (two cultivars); sampling every 5–7 days, so coarse | | Zhang et al. 2021 [4] | 27 hemp cultivars, 12 h days | Averaged **13–14 days**; fastest essential-oil types ~13 days, slowest ~21 days; fibre types from the far south took 21–25 days | | Peterswald et al. 2023 [6] | Three medicinal lines at 10, 12, 14 h | One line had pistils on 60–73 % of plants by the first check; the other two had few or none then, and all three were at 100 % about 9 days later. | | Ahrens et al. 2024 [7] | Two THC-dominant cultivars, 12 h vs 13 h | 13 h delayed onset by about **1.5 days** in one cultivar and not at all in the other (per-treatment day counts are in the paper's figure) | | Lisson et al. 2000 [8] | Two fibre hemp cultivars, 8–16 h | Rapid flowering below about 14 h; flowering delayed more the longer the day, using thermal time from emergence | **Reading the table.** Most cultivars studied showed onset between about one and two weeks after the switch, which matches the house figure of 10–14 days. It isn't universal: some northern hemp flowered in 4–11 days, and slow cultivars took three weeks [4]. Most of the data are hemp or a handful of drug-type cultivars, so treat 10–14 days as the typical case and **measure your own** (*Supported*). ## The stretch belongs to the transition The stretch isn't random; it's part of the switch. Under short days, the main stem and internodes elongated fastest from about **day 5 to day 10**, and short-day plants outgrew long-day plants over the first 14 days, before the condensed inflorescence took over [3]. A US plant-patent description puts the general figure at **50–100 % height gain in the first two to three weeks** after floral induction, and 71 ± 13 % for the cultivar described [10]. That's a breeder's description, not a controlled multi-cultivar trial; grower reports run from about 1.5× to 3× (*Grower practice*). See [stretching](https://genetixbay.com/knowledge/diagnosis/stretching.md). When the stretch slows and the new internodes stay short, the inflorescence is forming. That's a better sign of day 1 of flower than the calendar. ## Cultivar variation and the critical photoperiod Day length decides how fast induction happens, and the threshold varies by cultivar. - Explants of one drug-type genotype flowered best at 12.0 and 13.2 h; the authors concluded it needed **at least 10.8 h of uninterrupted dark** [5]. - In hemp, essential-oil cultivars flowered 1–2 days later above 13 h and 7–8 days later above 14 h; some had a critical photoperiod between **13 h 45 min and 14 h**, and as little as 15 minutes changed floral initiation in some [4]. - At 14 h every line in Peterswald et al. still flowered and made more flower mass, but two high-THC lines fell from 12 % to 7 % and from 10 % to 6 % THC [6]. - At 13 h, one cultivar flowered about 1.5 days later and the other not at all, with 1.35× and 1.5× the inflorescence yield and cannabinoid concentrations equal or higher. The study ended before full commercial maturity [7]. - Major-effect flowering-time loci (*Autoflower1*, *Early1*) have been mapped, so timing is partly simple genetics [9]. Autoflowers skip this question entirely; see [photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md). > **House position: 13/11 is endorsed, and some cultivars flower at 14–15 h** (in practice about 12 h at high intensity, plus sunrise and sunset ramps). The data above support it: 13 h barely moved flowering onset in the cultivars tested [7], and every line flowered at 14 h [6]. Expect a longer photoperiod to add a day or two to the transition in sensitive cultivars [4][7], and watch THC concentration at 14 h [6]. Test your cultivar. ## What she's telling you Signs that flowering has really started, in order of how much they can be trusted: 1. **Pistil clusters at the top nodes and the main cola, not lone preflowers.** Three or more pairs of pistils at the top of the main shoot is the research definition of onset [1][7]. A single pair in a leaf axil doesn't count; those form in veg too [1][2]. 2. **The stretch slows and internodes shorten.** Short days condense the apex: elongation peaks around days 5–10, then the internodes stay short as bracts stack [3]. 3. **New growth switches from fan leaves to bracts.** The apex branches into bract and flower primordia instead of making big leaves and long shoots [1][3]. 4. **Leaf size, aroma and water use change.** New leaves at the tops come in smaller with fewer leaflets, the plant starts to smell, and water use shifts as growth moves from stems to flowers (*Grower practice*; the smaller leaves and fewer leaflets near the inflorescence are consistent with the architecture in [1], the rest is grower observation). **Photo-log tip.** Shoot the same top cola from the same angle, at the same time of day, every 2–3 days from the flip. Side by side, the day the internodes stop growing and the pistil clusters appear is obvious. Note that date in your journal as day 1 of flower. ## How to count: days since flip vs days of flower Keep two clocks. | Clock | Starts | What it's for | |---|---|---| | **Days since flip** | The first long night | Planning the room, light schedules, stretch, comparing with your own past runs | | **Days of flower** | First pistil clusters at the top of the main shoot (3+ pairs) | Comparing with breeder flowering times, harvest windows, trichome checks | Many breeders' stated flowering times appear to count from flower set, not the flip (*Grower practice*, house position). If you don't know which a breeder means, assume flower set and add the transition. ### Worked example: a breeder's "8 weeks" - Stated flowering time: 8 weeks = 8 × 7 = **56 days** of flower. - Transition from flip to flower set: **10–14 days** (house figure; consistent with [1][4]). - 56 + 10 = **66 days**; 56 + 14 = **70 days** after the flip. - 66 ÷ 7 ≈ 9.4 weeks; 70 ÷ 7 = 10 weeks. - **Plan for harvest about 9.5–10 weeks after the flip**, then decide on the day by the trichomes, not the calendar (see [trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md)). If you flower at 13/11 or longer, allow another day or two for a sensitive cultivar [4][7]. ## Common mistakes - Counting the flip as day 1 of flower, then harvesting two weeks early because "it's week 8". - Calling preflowers in veg "flowering". They form under long days [1][2]. - Light leaks or a broken timer in the first two weeks. Induction can stall or reverse while it's still being set up [3]. Make the room dark. - Running out of headroom: most of the stretch comes in this window [3][10]. Flip at about half the final height you can fit. - Comparing your run with a breeder's number without knowing which clock they used. ## Evidence - Short-day induction and cultivar-specific critical photoperiods: *Established* [4][5][6][8]. - Visible inflorescence typically appearing about 1–2 weeks after short days begin: *Supported* [1][4][6]; mostly hemp and a few drug-type cultivars; some cultivars much faster or slower [4]. - Solitary flowers ("preflowers") being age-dependent and photoperiod-independent: *Supported* [1][2][3]. - Induction needing continuous short days, and long days reversing the inflorescence: *Supported* by one study [3]. - Stretch concentrated in the first two to three weeks: *Supported* for timing [3]; size from one patent description [10] and *Grower practice*. - 13 h adding little or no delay: *Supported* by one study of two cultivars [7]; 14 h lowering THC in high-THC lines: *Supported* by one study [6]. - Breeder flowering times counting from flower set, and runs going long by about the transition: house position (founder's experience) and *Grower practice*; not measured in any study we've found. ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Spitzer-Rimon B, Shafran-Tomer H, Gottlieb GH, et al. 2022. Non-photoperiodic transition of female cannabis seedlings from juvenile to adult reproductive stage. Plant Reproduction 35(4):265-277. https://doi.org/10.1007/s00497-022-00449-0 3. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 4. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 5. Moher M, Jones M, Zheng Y. 2021. Photoperiodic response of in vitro Cannabis sativa plants. HortScience 56(1):108-113. https://doi.org/10.21273/HORTSCI15452-20 6. Peterswald TJ, Mieog JC, Azman Halimi R, et al. 2023. Moving away from 12:12; the effect of different photoperiods on biomass yield and cannabinoids in medicinal cannabis. Plants 12(5):1061. https://doi.org/10.3390/plants12051061 7. Ahrens A, Llewellyn D, Zheng Y. 2024. Longer photoperiod substantially increases indoor-grown cannabis' yield and quality. Plants 13(3):433. https://doi.org/10.3390/plants13030433 8. Lisson SN, Mendham NJ, Carberry PS. 2000. Development of a hemp (Cannabis sativa L.) simulation model 2. The flowering response of two hemp cultivars to photoperiod. Australian Journal of Experimental Agriculture 40(3):413-417. https://doi.org/10.1071/EA99059 9. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 10. US Plant Patent PP30,434 (cannabis plant 'LW-BB1'), botanical description of post-induction stretch. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/PP30434 --- # VPD explained: vapour pressure deficit for cannabis growers > VPD is how hard the air pulls water out of the leaf, in kPa. Common targets are about 0.4–0.8 kPa for seedlings and clones, 0.8–1.2 kPa in veg and 1.0–1.5 kPa in flower, calculated from leaf temperature rather than air temperature. Most of these bands come from grower and greenhouse practice; cannabis-specific VPD trials are still scarce. - Canonical: https://genetixbay.com/knowledge/environment/vpd-explained.html - Category: Environment · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is VPD and why does it matter for cannabis?** VPD, vapour pressure deficit, is the gap in kPa between the saturated water vapour inside a cannabis leaf and the vapour actually in the room air. It sets the pull on transpiration, which moves water and calcium to new growth. Too low, below about 0.4 kPa, invites bud rot and mildew; too high, above about 1.6–1.8 kPa, closes stomata and cuts photosynthesis. **What VPD should I run in veg and flower?** Common cannabis VPD targets, calculated from leaf temperature, are about 0.8–1.0 kPa in early veg, 0.9–1.2 kPa in late veg, 1.0–1.4 kPa in flower weeks 1–5 and 1.2–1.5 kPa from week 6 to harvest. These bands are grower practice backed by general plant physiology; no published trial has pinned an optimum VPD per stage for cannabis. **How do I calculate VPD with leaf temperature?** To calculate leaf VPD, find saturation vapour pressure with es(T) = 0.6108 × exp(17.27 × T / (T + 237.3)) in kPa. Leaf VPD equals es at leaf temperature minus es at air temperature × RH/100. Measure leaf temperature with an infrared thermometer at emissivity about 0.95, aimed at a fully lit top leaf, or use a canopy IR sensor. **What humidity do I need at 26 °C to hit 1.2 kPa?** At 26 °C (79 °F) air, you need about 53 % relative humidity to hit 1.2 kPa leaf VPD in a typical LED room where leaves sit about 2 °C below air temperature. Under HID, where leaves are near air temperature, the same target needs roughly 64 % RH. Measure your actual leaf offset with an infrared thermometer before setting the humidifier. **Is leaf VPD or air VPD the right number?** Leaf VPD is the right number, because it is what the cannabis plant actually feels; air VPD assumes the leaf is at air temperature. Under LEDs, healthy leaves often run 1–3 °C cooler than air, so at 26 °C and 60 % RH an app shows 1.34 kPa air VPD while the leaf is only at 0.97 kPa, and growers end up running the room too humid. **My VPD is perfect but plants still look stressed, why?** Cannabis plants can look stressed at a perfect VPD because the cause lies elsewhere. Check the RH sensor with a two-point salt test, since cheap sensors drift 3–5 %; confirm it sits at canopy height in moving air; compare leaf temperatures top to bottom for airflow gaps; and rule out a dry pot, wrong reservoir temperature or root disease. VPD cannot fix a sick root zone. **Short answer.** Vapour pressure deficit (VPD) is the gap between how much water vapour the air inside a leaf holds (saturated, at leaf temperature) and how much the room air actually holds, in kilopascals (kPa). It sets the "pull" on transpiration. Common working targets are **0.4–0.8 kPa for seedlings and clones, 0.8–1.2 kPa in veg, 1.0–1.5 kPa in flower**, calculated with **leaf** temperature. Treat those bands as *Grower practice* backed by general plant physiology, not as cannabis-proven optima. ## What's happening The air spaces inside a leaf are effectively at 100 % RH at the leaf's own temperature. Water moves from high vapour pressure (leaf) to low (room). The bigger the difference, the faster the plant transpires, and the faster water, calcium and other mass-flow nutrients move from root to shoot. - **Too low** (below ~0.4 kPa outside propagation): transpiration stalls, calcium delivery to new growth and buds slows, leaf surfaces stay wet, and fungal pathogens such as *Botrytis* and powdery mildew get their favourite conditions [5]. A 2025 study held cannabis at roughly 78–98 % RH and found delayed flowering, lower biomass and lower cannabinoid content compared with roughly 37–58 % RH [3]. - **Too high** (above ~1.6–1.8 kPa): stomata partially close to save water, CO₂ intake drops, and photosynthesis falls even though the light is on. Leaves taco, edges crisp, and the root zone has to work harder to keep up. RH alone is a poor control target because the same 60 % RH means a very different pull at 20 °C than at 30 °C. VPD folds temperature and humidity into one number. ## The calculation Saturation vapour pressure (kPa) at temperature T (°C), using the FAO-56 form of the Tetens equation [1]: `es(T) = 0.6108 × exp(17.27 × T / (T + 237.3))` - **Air VPD** = es(T_air) × (1 − RH/100) - **Leaf VPD** = es(T_leaf) − es(T_air) × RH/100 Leaf VPD is what the plant feels. Measure leaf temperature with an infrared thermometer on a top, fully lit leaf (set emissivity around 0.95), or read it from a canopy IR sensor. ### How far is the leaf from the air? Well-watered leaves usually sit **within about 2 °C (3.6 °F) of air temperature** under any light source; under water stress and still air the model in [2] puts leaves 8 °C (14 °F) above air under LED and 12 °C (22 °F) above under HPS. In practice: | Situation | Typical leaf offset vs air | Notes | |---|---|---| | LED, healthy transpiring canopy, decent airflow | −1 to −3 °C (−2 to −5 °F) | The usual assumption is −2 °C. Measure your own. | | HPS / double-ended HID | 0 to +2 °C (0 to +4 °F) | Radiant load warms the leaf. | | Water-stressed or still air, any light | +2 to +8 °C or more | Stomata closed; the leaf can't cool itself [2]. | ## Numbers that matter ### Leaf VPD (kPa) with a −2 °C leaf offset (typical LED room) | Air °C (°F) | 40 % | 50 % | 55 % | 60 % | 65 % | 70 % | 75 % | 80 % RH | |---|---|---|---|---|---|---|---|---| | 20 (68) | 1.13 | 0.89 | 0.78 | 0.66 | 0.54 | 0.43 | 0.31 | 0.19 | | 22 (72) | 1.28 | 1.02 | 0.88 | 0.75 | 0.62 | 0.49 | 0.36 | 0.22 | | 24 (75) | 1.45 | 1.15 | 1.00 | 0.85 | 0.70 | 0.56 | 0.41 | 0.26 | | 26 (79) | 1.64 | 1.30 | 1.14 | 0.97 | 0.80 | 0.63 | 0.46 | 0.29 | | 28 (82) | 1.85 | 1.47 | 1.28 | 1.09 | 0.90 | 0.72 | 0.53 | 0.34 | | 30 (86) | 2.08 | 1.66 | 1.45 | 1.23 | 1.02 | 0.81 | 0.60 | 0.39 | ### Leaf VPD (kPa) with no offset (leaf = air; typical HID room) | Air °C (°F) | 40 % | 50 % | 55 % | 60 % | 65 % | 70 % | 75 % | 80 % RH | |---|---|---|---|---|---|---|---|---| | 20 (68) | 1.40 | 1.17 | 1.05 | 0.94 | 0.82 | 0.70 | 0.58 | 0.47 | | 22 (72) | 1.59 | 1.32 | 1.19 | 1.06 | 0.93 | 0.79 | 0.66 | 0.53 | | 24 (75) | 1.79 | 1.49 | 1.34 | 1.19 | 1.04 | 0.90 | 0.75 | 0.60 | | 26 (79) | 2.02 | 1.68 | 1.51 | 1.34 | 1.18 | 1.01 | 0.84 | 0.67 | | 28 (82) | 2.27 | 1.89 | 1.70 | 1.51 | 1.32 | 1.13 | 0.94 | 0.76 | | 30 (86) | 2.55 | 2.12 | 1.91 | 1.70 | 1.49 | 1.27 | 1.06 | 0.85 | The difference between those two tables is the whole point: at 26 °C and 60 % RH, the "air VPD" app says 1.34 kPa, but an LED-lit leaf two degrees cooler is only at 0.97 kPa. ### RH needed for a target leaf VPD (−2 °C leaf offset) | Air °C (°F) | 0.6 kPa | 0.8 kPa | 1.0 kPa | 1.2 kPa | 1.4 kPa | |---|---|---|---|---|---| | 20 (68) | 63 % | 54 % | 46 % | 37 % | 28 % | | 22 (72) | 66 % | 58 % | 51 % | 43 % | 35 % | | 24 (75) | 68 % | 62 % | 55 % | 48 % | 42 % | | 26 (79) | 71 % | 65 % | 59 % | 53 % | 47 % | | 28 (82) | 73 % | 68 % | 62 % | 57 % | 52 % | | 30 (86) | 75 % | 70 % | 66 % | 61 % | 56 % | ### Working targets by stage | Stage | Leaf VPD (kPa) | Typical air / RH that gets you there | Evidence | |---|---|---|---| | Germination, seedlings, unrooted clones | 0.4–0.8 | 22–26 °C (72–79 °F), 65–80 % RH (domes) | Grower practice; propagation horticulture | | Early veg | 0.8–1.0 | 24–27 °C (75–81 °F), 60–70 % RH | Grower practice | | Late veg | 0.9–1.2 | 24–28 °C (75–82 °F), 55–65 % RH | Grower practice | | Flower weeks 1–5 | 1.0–1.4 | 24–27 °C (75–81 °F), 50–60 % RH | Grower practice | | Flower weeks 6+ / ripening | 1.2–1.5 | 20–25 °C (68–77 °F), 40–50 % RH | Grower practice; disease-risk logic [5] | | Lights-off (any stage) | Keep above ~0.5 and stay well above dew point | Raise dehumidification before lights-off | Supported (condensation physics) | ## What to check first 1. **Is the sensor right?** Cheap RH sensors drift 3–5 % RH. Check against a fresh two-point salt test (75 % with sodium chloride, 33 % with magnesium chloride) before you chase numbers. 2. **Where is the sensor?** At canopy height, shaded from direct light, in moving air. A probe in the corner or on the floor reads a different room. 3. **What is the leaf actually doing?** Shoot leaf temperature at the top of the canopy, mid-canopy and lower. Big spreads mean an airflow problem, not a VPD-setpoint problem ([airflow](https://genetixbay.com/knowledge/environment/airflow.md)). 4. **Is the root zone keeping up?** A dry pot, cold or warm reservoir, or root disease looks exactly like "VPD too high". Rule it out before you add humidity. ## How to fix it - **VPD too high (dry/hot):** lower air temperature first if you are above ~28 °C (82 °F); then add humidity (humidifier on a controller, or fewer air exchanges). Raise the light slightly or dim 10–15 % if leaves are above air temperature. - **VPD too low (wet):** dehumidify, then gently raise temperature, then increase air exchange if outside air is drier. In late flower dehumidify on the **dark** period too; that is when RH spikes. - **Big leaf-to-air gap:** improve canopy airflow; thin dense interior leaves ([defoliation](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md)). ## How to confirm it worked Leaves held flat and pointed slightly up, no tacoing, no droplets at lights-on; stable daily water use; new growth free of calcium-type spotting; no condensation on walls or buds at lights-off. Log leaf VPD for a week and check it stays inside your band for at least 80 % of lights-on hours. ## Common mistakes - Using air VPD from an app while running LEDs, then running the room too humid. Low leaf VPD slows calcium delivery to new growth, which is the real story behind the *Myth* that "LEDs need more Cal-Mag" ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)). - Chasing a single number all day. Plants tolerate excursions; sustained extremes are the problem. - Dropping RH hard in early flower at the cost of temperature control. Stable is better than "perfect". - Forgetting the night: lights-off RH spikes are where bud rot starts. - Treating VPD as a cure-all. It won't fix a sick root zone. ## Evidence The physics (Tetens/FAO-56 equation, leaf vs air vapour pressure) is *Established* [1]. Leaf temperature behaviour under different light sources is *Supported* by modelling [2]. Cannabis-specific evidence is thin: one recent study shows very high RH (low VPD) harms flowering, biomass and cannabinoids [3], and humidity is *Established* as a driver of cannabis bud rot and mildew [5]. Gas-exchange work on cannabis shows stomatal conductance and photosynthesis are temperature- and light-dependent [4], but there is no published trial that pins an optimum VPD per stage. The stage bands above are *Grower practice*. ## Sources 1. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 3. Corredor-Perilla IC, Kwon H, Park J, 2025. High relative humidity in cannabis cultivation (effects on flowering, biomass and cannabinoids). Frontiers in Plant Science 16:1678142. https://doi.org/10.3389/fpls.2025.1678142 4. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 5. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # "Bloom boosters" for cannabis: what's real and what's marketing > Most bloom boosters are concentrated phosphorus and potassium. Four independent controlled cannabis trials found no increase in flower yield or cannabinoids from raising phosphorus above roughly 25–60 mg/L, and one found no yield response to potassium anywhere from 60 to 340 mg/L. A complete, balanced flower feed is what matters; extra P and K mostly end up in the runoff and can induce magnesium, calcium, zinc and iron problems. Some boosters have been reported to contain undeclared plant growth regulators, which have no place in a consumable crop. - Canonical: https://genetixbay.com/knowledge/nutrients/bloom-boosters.html - Category: Nutrients · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Do bloom boosters work on cannabis?** Bloom boosters mostly do not work on cannabis beyond what a balanced flower feed already provides. Four independent controlled trials found no gain in flower yield or cannabinoids once solution phosphorus passed roughly 25-60 mg/L, and one trial found no yield response to potassium from 60 to 340 mg/L. The extra phosphorus and potassium largely end up in the runoff. **Should I use a PK booster in week 4 or 5 of flower?** A PK booster in week 4 or 5 of flower is generally not needed if the cannabis base feed is complete. Research puts the useful flower range at about 40-60 mg/L phosphorus and 200-280 mg/L potassium. Stacking a booster on a full bloom base can push P above 100 mg/L and K above 400 mg/L, adding no yield and risking magnesium and calcium problems. **Does high phosphorus increase bud size?** High phosphorus does not increase cannabis bud size once the plant has enough. Controlled trials testing 5-90 mg/L phosphorus found yield plateaued around 25-60 mg/L, and in one study leachate phosphorus rose about twelvefold for a threefold increase in input. Flowers took up more than 1% phosphorus with no benefit, a pattern called luxury uptake. **Are bloom boosters a waste of money?** For growers already running a complete flower feed, bloom boosters are largely a waste of money, according to controlled cannabis research. The money is better spent on light intensity, environment and root-zone control, since cannabis yield rises with light. Anyone who wants to test one should split a room of identical plants of one cultivar, then compare dry flower weight and lab potency. **What is in a bloom booster?** A typical cannabis bloom booster is mostly concentrated phosphorus and potassium, often sold as a 'PK' product. The idea stretches a real fact, that phosphorus and potassium are needed for flowering, past its limit, because need has a ceiling. Some bloom or hardening additives have also been reported to contain synthetic plant growth regulators, sometimes undeclared, so full ingredient disclosure matters. **Are there growth regulators in some cannabis additives?** Some cannabis bloom or hardening additives have been reported to contain synthetic plant growth regulators such as paclobutrazol or daminozide, sometimes undeclared on the label. These chemicals shorten internodes and densify flowers. Daminozide is classed as a probable human carcinogen and is not approved for food crops in many jurisdictions. Use only additives with full ingredient disclosure and check local rules. **Short answer.** Most bloom boosters are concentrated phosphorus and potassium ("PK"). Four independent controlled cannabis trials found no increase in flower yield or cannabinoids from raising P above roughly 25–60 mg/L [1][2][3][4], and one found no yield response to K anywhere from 60 to 340 mg/L [4]. What matters is a complete, balanced flower feed. Extra P and K mostly end up in the runoff [2] and can induce Mg, Ca, Zn and Fe problems. Some boosters have been reported to contain undeclared plant growth regulators, which have no place in a crop people smoke or eat. ## What's happening The bloom-booster idea comes from a real fact stretched too far: P and K are needed for flowering. But "needed" has a ceiling. Once the plant has enough, more does not make more flower. The cannabis evidence: | Study | What was tested | Result | |---|---|---| | Shiponi and Bernstein 2021 [1] | P 5–90 mg/L, two medical genotypes | Biomass highest at 30–90 mg/L; THCA/CBDA concentration highest below 30 and down up to 25% at higher P (mostly dilution) | | Westmoreland and Bugbee 2022 [2] | P 25, 50, 75 mg/L, high-CBD cultivar | No effect on yield or cannabinoids; leachate P up ~12× for 3× input; flower P >1% (luxury uptake) | | Hershkowitz, Westmoreland and Bugbee 2025 [3] | P 15–90 mg/L and 2 vs 4 mS/cm, deep-flow hydro | Neither excess P nor doubled strength improved yield or quality | | Bevan, Jones and Zheng 2021 [4] | N, P, K response surface, DWC flower | Yield optimum ~59 mg/L P; no response to K across 60–340 mg/L | | Velechovsky et al. 2024 [6] | Augmented P, K and Fe | Augmented regime did not substantially increase biomass | | Bernstein et al. 2019 [5] | Enhanced P, enhanced NPK, humic acid | Enhanced NPK raised CBG 71%, lowered CBN; no large THC gains reported. | Meanwhile, high K competes with Ca and Mg at the root, which was seen in cannabis [7], and high P is associated with Zn and Fe problems in many crops (see [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md)). ### Growth regulators Some "bloom" or "hardening" additives have been reported to contain synthetic plant growth regulators such as paclobutrazol or daminozide, which shorten internodes and densify flowers, sometimes undeclared. Daminozide is classed as a probable human carcinogen and is not approved for food crops in many jurisdictions. Use only additives with full ingredient disclosure, and check what your jurisdiction allows on cannabis. ## Numbers that matter | Parameter | Practical target in flower | Notes | |---|---|---| | Solution P | 40–60 mg/L | No gain above this range [1][2][3][4] | | Solution K | 200–280 mg/L | No yield response found 60–340 [4] | | Total EC | 1.6–2.2 mS/cm | 4 mS/cm no better than 2 [3] | | Leaf P when overfed | >1% in flowers | Luxury uptake, no benefit [2] | ## What to do instead 1. Run a complete flower feed at sensible strength (see [building a feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md)). 2. Keep N adequate through mid-flower; many "boosters" are paired with cutting N too early. 3. Spend the money on light, environment and root-zone control. Yield in cannabis rises with light intensity; see the environment articles. 4. If you want to test a booster, split the room: identical plants, same cultivar, half with, half without, weigh dry flower and send both for potency testing. ## Common mistakes - Stacking a booster on a full bloom base, pushing P above 100 mg/L and K above 400 mg/L. - Reading bigger runoff EC as "the plant is eating more". - Trusting before-and-after photos with no side-by-side control. ## Evidence - High P does not increase cannabis yield or cannabinoids: *Established* (four independent controlled trials in different labs and systems [1][2][3][4]). House position agrees: there's a plateau, and past moderate P more doesn't help. - High K does not increase flowering yield: *Supported* (one trial [4]). - "More P = bigger buds": *Myth* beyond sufficiency. - PGR contamination of some additives: *Supported* by grower and media reports ## Sources 1. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323 2. Westmoreland FM, Bugbee B. 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 3. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 4. Bevan L, Jones M, Zheng Y. 2021. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 5. Bernstein N, Gorelick J, Zerahia R, Koch S. 2019. Impact of N, P, K, and humic acid supplementation on the chemical profile of medical cannabis. Frontiers in Plant Science 10:736. https://doi.org/10.3389/fpls.2019.00736 6. Velechovsky J, Malik M, Senkyrik JB, Tlustos P. 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 7. Saloner A, Sacks MM, Bernstein N. 2019. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 --- # Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window > Boron cross-links cell-wall pectin and is needed wherever cells are dividing: shoot tips, root tips and flowers. Deficiency in cannabis causes stunted, distorted new growth, dead growing tips and wilting from root-tip death; toxicity scorches the margins of older leaves. Supply about 0.2–0.5 mg/L B; cannabis tolerated a tenfold dose for weeks but the gap between enough and too much is narrower than for most nutrients. - Canonical: https://genetixbay.com/knowledge/nutrients/boron.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What does boron deficiency look like in cannabis?** Boron deficiency in cannabis shows first at the growing tips: slight stunting, new leaves that are distorted, smaller and narrower at the leaflet base, then dying leaflet margins, leaves curling inward and down, and dead growing tips. In advanced stages the plant wilts because root tips die. In one controlled study biomass fell 28% and leaf boron dropped to about 2.5 mg/kg. **Why are my growing tips twisted and dying?** Twisted, dying cannabis growing tips can come from boron deficiency, calcium deficiency, broad mites, heat stress or root rot. Inspect new growth with a loupe for mites first, then check the roots, confirm your base feed actually contains boron, and make sure soilless pH is not above about 6.5, which reduces boron availability. Glossy, twisted tips point to mites rather than nutrients. **How much boron in hydroponic solution?** A cannabis hydroponic solution should carry about 0.2-0.5 mg/L boron, a grower practice range that matches the roughly 0.49 mg/L used in cannabis research. Count any boron in your irrigation water, since some groundwater carries it. Weigh boron sources carefully: about 2.3 mg/L of boric acid supplies roughly 0.4 mg/L boron, and the feed should not exceed about 0.5 mg/L. **Can boron be toxic to cannabis?** Boron can be toxic to cannabis, although the plant is relatively tolerant. In one controlled study a tenfold dose of about 4.9 mg/L boron took 7 weeks to cause symptoms, with leaf boron near 670 mg/kg. Toxicity shows as yellowing at the margins of lower, older leaves moving inward to the midrib, then brown, dead margins. Stop boron supplements and leach with a boron-free solution. **Why is my plant wilting even though the medium is wet?** A cannabis plant wilting in wet medium usually has a root problem: either root rot or root tips dying from boron deficiency, which collapses root mass. Check the roots for rot first, then confirm the feed supplies about 0.2-0.5 mg/L boron. Wilting caused by boron shortage comes with distorted, dying new growth at the shoot tips, which helps tell the two apart. **Short answer.** Boron cross-links pectin in cell walls and is needed wherever cells divide and expand: shoot tips, root tips and flowers [3]. In cannabis, deficiency caused stunted, distorted new leaves, dead growing tips and wilting caused by dying root tips; biomass fell 28% [1]. Toxicity showed as yellow, then brown, margins on older leaves [1]. Feed about 0.2–0.5 mg/L B. ## What's happening Plants take up B as uncharged boric acid. It moves with the transpiration stream and is **immobile** in the phloem of most species, so deficiency hits growing points first [3]. Because it moves with water, B accumulates at leaf margins and tips where water evaporates, which is why toxicity scorches margins of the oldest leaves [3]. B and Ca disorders look alike because both affect cell walls in growing tissue. B availability falls at high pH [5]. ## How to recognise it - **Deficiency:** slight stunting from the growing tips; new leaves distorted, smaller and narrower at the leaflet base than at the tip; in advanced stages leaflet margins die, leaves curl inward and down at odd angles, growing tips die, and the whole plant wilts because root tips have died and root mass collapses [1]. Leaf B at symptom onset was about 2.5 mg/kg against 59 mg/kg in controls [1]. - **Toxicity:** marginal yellowing of *lower* leaves moving inward to the midrib, then brown, necrotic margins [1]. Symptoms appeared after 7 weeks at a 10× dose (≈4.9 mg/L B), with leaf B around 672 mg/kg. Strawberry shows toxicity at 120 mg/kg, which suggests cannabis is relatively tolerant [1]. - **Differential:** Ca deficiency (new growth, spotting), broad mites (glossy, twisted tips), heat stress, root rot (also wilting; check roots), K deficiency (margins of old leaves, like B toxicity). ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution B | 0.2–0.5 mg/L | Cannabis trials used ≈0.49 mg/L [1]; *grower practice* range | | Toxicity seen at | ~4.9 mg/L in solution, 7 weeks | Cannabis, sand culture [1] | | Leaf B, healthy (most recent mature leaf) | 30–90 mg/kg | NC State floral hemp [2] | | Leaf B at first deficiency symptoms | ~2.5 mg/kg | [1] | | Leaf B at toxicity | ~670 mg/kg | [1] | | Irrigation water B | Test it | Some groundwater carries B; count it in the feed. | ## What to check first 1. **Mites.** Inspect new growth with a loupe before blaming any nutrient. 2. **Roots.** Wilting with wet media: check for rot as well as B shortage. 3. **Feed:** does your base contain B? Some DIY salt recipes skip it. 4. **pH** above ~6.5 in soilless reduces availability [5]. 5. **Water report** for B (for toxicity). ## How to fix it - **Deficiency:** add boric acid (≈17.5% B; 2.3 mg/L product ≈ 0.4 mg/L B) or sodium borate (≈20% B). Do not exceed about 0.5 mg/L B in the feed. - **Toxicity:** stop B-containing supplements; in soilless and soil, leach with balanced, B-free solution; B leaches readily from soilless media. - **Safety:** boric acid is a reproductive toxicant when ingested or inhaled as dust; wear gloves and a dust mask when weighing it. ## How to confirm it worked Healthy new tips form within 7–10 days; roots show new white tips. Already distorted leaves will not straighten. ## Common mistakes - Adding "a pinch" of borax without weighing; the safe range is small. - Calling broad-mite damage boron deficiency. - Ignoring B in well water. ## Evidence - B deficiency and toxicity symptoms in cannabis: *Supported* (one controlled study [1]). - Cannabis relatively tolerant of excess B: *Supported* (one study, compared with strawberry [1]). - B immobility and margin accumulation: *Established* [3][4]. ## Sources 1. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 4. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 5. MSU Extension. pHix it! Getting substrate pH just right. https://www.canr.msu.edu/news/phix-it-getting-substrate-ph-just-right --- # Building a cannabis feed by stage: ppm targets per element and how to hit them > A good mineral cannabis feed runs roughly N 150–200, P 30–60, K 175–250, Ca 150–200, Mg 40–70 and S 60–120 mg/L in veg and flower, plus Fe 1.5–3 and small amounts of Mn, Zn, B, Cu and Mo, at an EC of about 1.2–1.8 mS/cm in veg and 1.6–2.2 in flower. Cannabis research shows no benefit from pushing P or overall strength higher. This article gives the targets, the evidence behind each, and two worked RO-water recipes with a sources table. - Canonical: https://genetixbay.com/knowledge/nutrients/feed-by-stage.html - Category: Nutrients · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Transition, Flower, Ripening · Systems: DWC, RDWC, NFT, Ebb and flow, Drip, Coco, Rockwool, Aeroponics - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How many ppm of each nutrient does cannabis need in veg and flower?** In veg, a mineral cannabis feed runs about N 150-200, P 30-50, K 175-240, Ca 150-200, Mg 35-70 and S 60-100 ppm (mg/L). In mid flower it shifts to roughly N 140-190, P 40-60, K 200-280, Ca 150-200, Mg 40-70 and S 60-120 ppm, plus iron at 1.5-3 ppm and traces of manganese, zinc, boron, copper and molybdenum. **What EC should I run for cannabis in veg and flower?** Cannabis in coco or hydro usually runs about 1.2-1.8 mS/cm in veg and 1.6-2.2 mS/cm through transition and mid flower, easing to 1.2-1.8 mS/cm late in flower. This EC ladder is grower practice. Research in deep-flow hydro found that doubling strength from 2 to 4 mS/cm gave no yield or quality benefit, so higher EC is not better. **How do I make my own cannabis nutrients from salts?** To make cannabis nutrients from salts, get a water analysis, then weigh single salts such as calcium nitrate, potassium nitrate, MKP, magnesium sulfate and potassium sulfate, plus iron DTPA and micronutrient salts. Keep calcium nitrate and iron in an A stock and everything else in B. Add A, stir, add B, stir, then adjust pH and check EC. **What is a good N-P-K ratio for flowering cannabis?** Rather than a fixed N-P-K ratio, flowering cannabis does well on about 140-190 mg/L nitrogen, 40-60 mg/L phosphorus and 200-280 mg/L potassium in mid flower. Controlled trials found a flower nitrogen optimum near 194 mg/L, a phosphorus optimum near 59 mg/L in DWC, and no yield gain above about 60 mg/L phosphorus, so heavy high-P bloom ratios add nothing. **Do I need to change nutrients between veg and flower?** Cannabis needs only modest feed changes between veg and flower, not a switch to a high-phosphorus, low-nitrogen bloom formula. EC rises from about 1.2-1.8 to 1.6-2.2 mS/cm, and potassium and phosphorus increase slightly, but nitrogen should stay near 160-200 mg/L through the stretch. Dropping nitrogen at the flip starves the stretch; taper it only in the final weeks. **What EC for seedlings and clones?** Cannabis seedlings and clones are usually fed at about 0.6-1.0 mS/cm, a grower practice range. At that strength the solution carries roughly 50-100 mg/L nitrogen, 15-30 mg/L phosphorus, 60-120 mg/L potassium, 80-120 mg/L calcium and 25-40 mg/L magnesium. Measure total solution EC including the water, and raise strength toward the veg range of 1.2-1.8 mS/cm as plants establish. **Short answer.** A solid mineral feed for cannabis in coco or hydro runs roughly **N 150–200, P 30–60, K 175–250, Ca 150–200, Mg 40–70, S 60–120 mg/L**, plus Fe 1.5–3 mg/L and traces of Mn, Zn, B, Cu and Mo. Run it at about **1.2–1.8 mS/cm in veg and 1.6–2.2 mS/cm in flower**. Cannabis trials show no benefit from pushing P above about 60 mg/L or from doubling overall strength [4][5][6]. Below: the targets, the evidence, and two worked recipes for RO water. ## Targets by stage All values mg/L (= ppm by mass of the element) in the solution going to the roots, including what your water supplies. EC values are total solution EC at 25 °C. | Element | Seedling / clone | Veg | Transition (flower wk 1–3) | Mid flower (wk 4–7) | Late flower / ripen | Evidence | |---|---|---|---|---|---|---| | EC (mS/cm) | 0.6–1.0 | 1.2–1.8 | 1.6–2.2 | 1.6–2.2 | 1.2–1.8 | *Grower practice*; 4 vs 2 mS/cm gave no gain [6] | | N | 50–100 | 150–200 | 160–200 | 140–190 | 100–150, tapering towards 0 at the finish (see note) | Veg optimum ~160 [1]; flower optimum ~194 [2]; taper is *Grower practice* | | NH₄ share of N | ≤10% | ≤10–20% | ≤10–20% | ≤10–20% | ≤10% | >30% harmful [8] | | P | 15–30 | 30–50 | 40–60 | 40–60 | 30–50 | No gain above ~25–60 [4][5][6]; optimum ~59 in DWC [2] | | K | 60–120 | 175–240 | 180–250 | 200–280 | 180–250 | Veg 175–240 [3]; no flower response 60–340 [2] | | Ca | 80–120 | 150–200 | 150–200 | 150–200 | 130–180 | Standard solutions [9][10]; *Supported* | | Mg | 25–40 | 35–70 | 40–70 | 40–70 | 40–60 | Veg 35–70 [7] | | S | 30–60 | 60–100 | 60–120 | 60–120 | 60–100 | *Supported* (standard solutions) | | Fe | 1.0–2.0 | 1.5–3.0 | 1.5–3.0 | 1.5–3.0 | 1.5–2.5 | Greenhouse standards [9] | | Mn | 0.2–0.5 | 0.3–0.8 | 0.3–0.8 | 0.3–0.8 | 0.3–0.6 | [9] | | Zn | 0.1–0.3 | 0.1–0.5 | 0.1–0.5 | 0.1–0.5 | 0.1–0.4 | [9] | | B | 0.2–0.4 | 0.2–0.5 | 0.2–0.5 | 0.2–0.5 | 0.2–0.5 | [9]; toxicity at ~5 mg/L [10] | | Cu | 0.03–0.05 | 0.03–0.1 | 0.03–0.1 | 0.03–0.1 | 0.03–0.08 | [9] | | Mo | 0.01–0.05 | 0.01–0.05 | 0.01–0.05 | 0.01–0.05 | 0.01–0.05 | [9] | | Na, Cl | As low as possible; Na <50, Cl <50–70 | | | | | See [sodium](https://genetixbay.com/knowledge/nutrients/sodium.md) | Notes: - Per-stage splits within veg and flower are *grower practice*; the research gives single optima per phase, mostly from one or two cultivars per study. - Organic liquid feeds need higher N on paper (one coir trial put the flowering optimum at 212–261 mg/L N) because organic N is less available [see [organic vs mineral](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md)]. - Soil growers: these are solution numbers; soil supplies and buffers its own nutrients. - **Feed through to harvest.** The late flower / ripen column is a real feed, not a wind-down. Don't flush before harvest: pre-harvest flushing is a *Myth* that starves the plant while it packs on its final weight, trichomes and resin, so it costs you yield and resin [see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)]. The only valid flush is a root-zone flush to clear salt build-up, at any stage, when runoff EC says you need one (see [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). - **N and potency are a trade-off.** Lower N in flower can raise cannabinoid and terpene percentage while lowering total yield; yield rose with N up to ~160 mg/L in one controlled trial (Saloner & Bernstein 2021, Industrial Crops and Products 167:113516, https://doi.org/10.1016/j.indcrop.2021.113516). Pick your late-flower N deliberately within the table range; it isn't a reason to flush (see [nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md)). - **Taper N, don't flush.** From about 3 weeks out, ramp N down: ~75 % of late-flower N at week −3, ~50 % at −2, ~25 % at −1, 0–20 mg/L in the final days, with P, K, Ca, Mg, S and micros unchanged (*Grower practice*). That needs single salts with an N-free Ca source (see [hydroponic salts](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md)) or per-element dosing; diluting a 2-part cuts everything. ## Sources table: which salt to use for each element | Element | Main sources | Secondary sources | |---|---|---| | N (nitrate) | Calcium nitrate, potassium nitrate | Magnesium nitrate, nitric acid | | N (ammonium) | Already in calcium nitrate (~1.1% NH₄-N) | MAP, ammonium nitrate (small amounts) | | P | MKP | MAP, phosphoric acid | | K | Potassium nitrate, potassium sulfate | MKP, potassium silicate, KOH | | Ca | Calcium nitrate | Calcium chloride (small amounts) | | Mg | Magnesium sulfate | Magnesium nitrate | | S | Magnesium sulfate, potassium sulfate | Sulfuric acid | | Fe | Fe-DTPA (hydro, coco), Fe-EDDHA (alkaline) | Fe-EDTA (pH < 6.5) | | Mn, Zn, Cu | Sulfate salts or EDTA chelates | | | B | Boric acid | Sodium borate | | Mo | Sodium molybdate | Ammonium molybdate | Salt percentages are in [hydroponic salts explained](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md). ## Worked recipe 1: veg, RO water Per 1,000 L (divide by 10 for 100 L). Assumes RO water with EC < 0.05 mS/cm. | Salt | g per 1,000 L | Supplies (mg/L) | |---|---|---| | Calcium nitrate (15.5% N, 19% Ca) | 840 | N 130, Ca 160 (NH₄-N ≈ 9) | | Potassium nitrate | 380 | N 53, K 147 | | MKP | 175 | P 40, K 50 | | Magnesium sulfate heptahydrate | 500 | Mg 49, S 65 | | Potassium sulfate (44.9% K) | 50 | K 22, S 9 | | **Totals** | | **N 183, P 40, K 220, Ca 160, Mg 49, S 74** | ## Worked recipe 2: flower, RO water | Salt | g per 1,000 L | Supplies (mg/L) | |---|---|---| | Calcium nitrate | 790 | N 123, Ca 150 (NH₄-N ≈ 9) | | Potassium nitrate | 200 | N 28, K 77 | | MKP | 220 | P 50, K 63 | | Magnesium sulfate heptahydrate | 560 | Mg 55, S 73 | | Potassium sulfate | 240 | K 108, S 44 | | **Totals** | | **N 150, P 50, K 248, Ca 150, Mg 55, S 117** | ## Micronutrients for both | Salt | g per 1,000 L | Supplies (mg/L) | |---|---|---| | Fe-DTPA (11% Fe) | 23 | Fe 2.5 | | Manganese sulfate monohydrate | 1.6 | Mn 0.5 | | Zinc sulfate heptahydrate | 1.3 | Zn 0.3 | | Boric acid | 2.3 | B 0.4 | | Copper sulfate pentahydrate | 0.3 | Cu 0.08 | | Sodium molybdate dihydrate | 0.1 | Mo 0.04 | Weigh micros into a 1:1000 stock (for example, 1,000× the per-litre amount in 1 L of water) so you dose millilitres, not milligrams. **Expected EC.** A rule of thumb for nutrient solutions is EC (mS/cm) ≈ sum of cations in meq/L ÷ 10 [9]. Recipe 1 has about 18 meq/L of cations (Ca 8.0, K 5.6, Mg 4.1, NH₄ 0.7), so expect roughly 1.8 mS/cm; recipe 2 ≈ 1.9 mS/cm. Measure; don't trust the arithmetic alone. ## How to use it 1. **Get a water analysis** and subtract what the water supplies (Ca, Mg, S, Na, Cl, alkalinity). See [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md). 2. **Mix A and B stocks separately** (calcium nitrate and iron in A; everything else in B). 3. **Fill the tank, add A, stir, add B, stir, then adjust pH** to 5.6–6.0 (hydro) or 5.8–6.2 (coco). 4. **Check EC** against the target. 5. **Monitor runoff or reservoir** (see [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)) and adjust strength, not ratios, first. 6. **Tissue test** once per cycle if you can (most recent mature leaf): N 3.3–5.0%, P 0.27–0.48%, K 1.8–2.7%, Ca 1.5–2.9%, Mg 0.30–0.65%, S 0.25–0.36% (NC State floral hemp ranges). ## Common mistakes - Copying a feed chart's EC without accounting for tap water EC. - Switching to a high-P, low-N "bloom" feed at the flip and starving the stretch. - Stacking boosters on a complete base (see [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md)). - Assuming more EC means more yield: doubling to 4 mS/cm gave no yield or quality benefit in deep-flow hydro [6]. ## Evidence - N, P, K, Mg optima: *Supported* (controlled cannabis trials, mostly one or two cultivars each [1][2][3][4][5][7]). - P and overall-strength ceilings: *Established* as "no benefit above" across several independent trials [4][5][6]. - Ca, S and micronutrient targets: *Supported* by general greenhouse standards [9] and solutions used in cannabis research [10]; no cannabis dose-response data for most. - Per-stage EC ladder: *Grower practice*. ## Sources 1. Saloner A, Bernstein N. 2020. Response of medical cannabis to nitrogen supply under long photoperiod. Frontiers in Plant Science 11:572293. https://doi.org/10.3389/fpls.2020.572293 2. Bevan L, Jones M, Zheng Y. 2021. Optimisation of nitrogen, phosphorus, and potassium for soilless production of Cannabis sativa in the flowering stage. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 3. Saloner A, Bernstein N. 2022. Effect of potassium (K) supply on cannabinoids, terpenoids and plant function in medical cannabis. Agronomy 12(5):1242. https://doi.org/10.3390/agronomy12051242 4. Shiponi S, Bernstein N. 2021. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323 5. Westmoreland FM, Bugbee B. 2022. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 6. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 7. Morad D, Bernstein N. 2023. Plants 12(14):2676. https://doi.org/10.3390/plants12142676 8. Saloner A, Bernstein N. 2022. Nitrogen source matters. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 9. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 10. Cockson P, et al. 2019. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Cal-Mag: what it is, when you need it and when you don't > Cal-Mag is a calcium and magnesium supplement, usually calcium nitrate and magnesium nitrate, sometimes with iron. You need it when your water and base nutrient together supply too little Ca and Mg: RO or very soft water, new or unbuffered coco, or a base nutrient designed for hard water. How much a plant needs is driven mainly by its cultivar, the water source, the medium (coco's cation exchange), root-zone pH and transpiration. The claim that LED lights create a Cal-Mag need is a myth. You do not need it on hard tap water with a complete base feed, and overusing it adds nitrogen and pushes potassium and magnesium out of balance. - Canonical: https://genetixbay.com/knowledge/nutrients/cal-mag.html - Category: Nutrients · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Coco, DWC, RDWC, NFT, Drip, Rockwool, Soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Do I need Cal-Mag with RO water?** With RO water, cannabis usually needs Cal-Mag or another calcium and magnesium source, because RO supplies essentially none and many base nutrients assume some comes from the tap. Add only the gap between your base and the targets of about 150-200 mg/L total calcium and 40-70 mg/L magnesium. Grower practice is roughly 40-60 mg/L Ca and 15-25 mg/L Mg from the supplement. **How much Cal-Mag should I use in coco?** Cannabis in coco should get enough Cal-Mag to bring total solution calcium to about 150-200 mg/L and magnesium to about 40-70 mg/L, at a calcium to magnesium mass ratio near 3:1 to 4:1. Buffer new coco first, because its exchange sites hold potassium and sodium and soak up calcium and magnesium until saturated. After buffering, a smaller ongoing top-up is often enough. **Do LED lights need more Cal-Mag?** LED lights do not make cannabis need more Cal-Mag; that claim is a myth and contradicts the GenetixBay house position. A photon does not consume calcium. LEDs emit less radiant heat, so leaves can run cooler, transpire less and deliver less calcium to new growth. That is a VPD setting, so raise air temperature a degree or two or lower humidity before adding a supplement. **Why does one strain need Cal-Mag and another doesn't in the same room?** One cannabis cultivar can need Cal-Mag while another does not in the same room because calcium and magnesium demand is largely genetic. In thirteen hemp cultivars grown side by side, leaf calcium varied more than any other nutrient, and two medical genotypes moved nutrients differently on the same potassium feed. When only one plant shows symptoms, suspect the genetics before the bottle. **I switched from HPS to LED and got rust spots: is it Cal-Mag?** Rust spots after switching a cannabis room from HPS to LED are not caused by the LED itself, so do not assume a Cal-Mag shortage. Cooler leaves under LED lower leaf VPD and slow calcium delivery to new growth, so adjust temperature or humidity first. Many growers changed to coco and RO water at the same time, so check water, medium, pH and potassium too. **Can I use too much Cal-Mag?** Yes, too much Cal-Mag harms a cannabis feed. Most products are nitrate-based, adding roughly 1 mg/L nitrogen for every 1.2 mg/L calcium, and overuse pushes potassium and magnesium out of balance; the extra nitrogen is unwanted late in flower. Avoid full-rate doses on hard tap water 'just in case', and never use Cal-Mag to treat broad-mite damage or pH problems. **Should I add Cal-Mag if I have hard tap water?** On hard tap water with a complete base feed, cannabis growers usually should not add Cal-Mag. Water above about 60 mg/L calcium or 25 mg/L magnesium is classed as hard and can supply much of what the plant needs. Read the water report and the base nutrient label, then add only the gap to reach about 150-200 mg/L calcium and 40-70 mg/L magnesium. **Is Cal-Mag the same as Epsom salt?** Cal-Mag is not the same as Epsom salt. Epsom salt is magnesium sulfate only and contains no calcium. Cal-Mag supplements are usually calcium nitrate plus magnesium nitrate, sometimes with a little iron, so they also add nitrogen to the feed. Check the label of any Cal-Mag product to see how much nitrogen it contributes before using it late in flower. **Short answer.** Cal-Mag is a calcium-plus-magnesium supplement, usually calcium nitrate and magnesium nitrate, sometimes with a little iron. You need it when your water plus base nutrient supply too little Ca and Mg: **RO or very soft water, new or unbuffered coco, or a base formulated for hard water.** You do not need it on hard tap water with a complete base feed. Overuse adds nitrogen and pushes K and Mg out of balance. **"LEDs need more Cal-Mag" is a myth.** Demand is set mainly by the **cultivar**, then by your **water**, your **medium**, **root-zone pH** and **transpiration**, not by the light source. ## What's happening Many base nutrients are designed assuming some Ca and Mg come from the tap. Hard water commonly supplies tens of mg/L of each; Purdue classes water above about 60 mg/L Ca or 25 mg/L Mg as hard [3]. RO water supplies essentially none. A feed that is balanced on tap water can therefore be Ca- and Mg-short on RO. Coco makes it worse when new: its exchange sites hold K and Na and soak up Ca and Mg from the feed until they are saturated [4] (see [buffering coco](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md)). Cal-Mag is not Epsom salt. Epsom salt is magnesium sulfate only. Most Cal-Mag products are nitrate-based, so they also add roughly 1 mg/L N for every 1.2 mg/L Ca (from the calcium nitrate) plus N from magnesium nitrate. Check your label. ### What actually drives Ca and Mg demand 1. **Cultivar.** Genetic demand varies. Two cultivars in the same room, on the same feed, can show very different Ca and Mg status. In thirteen hemp cultivars grown side by side, leaf Ca had the widest spread of any nutrient [7], and two medical cannabis genotypes differed in how they took up and moved nutrients on the same K feed [5]. If one plant in a mixed room shows Ca/Mg signs and the rest don't, suspect the genetics before the bottle. 2. **Water source.** RO and soft water bring almost no Ca or Mg; hard tap water can bring most of what the plant needs [3]. 3. **Medium.** Fresh coco's exchange sites are loaded with K and Na and pull Ca and Mg out of the feed until buffered [4]. 4. **Root-zone pH.** Low pH cuts Ca and Mg availability; see [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md). 5. **Transpiration and VPD.** Ca moves only in the transpiration stream [6]. Cool leaves in a humid room transpire little, so new growth gets little Ca whatever the feed holds. > **Greenleaf aside: the LED myth.** "LEDs need more Cal-Mag" is a *Myth*. A photon doesn't consume calcium. The kernel of truth is transpiration: LEDs put out less radiant heat, so leaves often run cooler than under HPS at the same air temperature [8], leaf VPD drops, and Ca delivery to new growth slows [6]. That is an environment setting, not a light-source requirement. Many growers also moved to LEDs at the same time as they moved to coco and RO water, which gets the blame mixed up. If you switch to LEDs, set leaf VPD (raise air temperature a degree or two, or lower RH) and check your water and medium before you reach for a supplement. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Total Ca in solution (water + base + supplement) | 150–200 mg/L | Cannabis research solutions ran 200 mg/L [1] | | Total Mg | 40–70 mg/L | Veg optimum 35–70 mg/L [2] | | Ca:Mg (mass) | ~3:1 to 4:1 | *Grower practice* | | RO base before nutrients (if your base assumes tap) | ~Ca 40–60, Mg 15–25 mg/L | *Grower practice*; roughly EC 0.3–0.4 mS/cm from the supplement. | | Hard-water threshold | >60 mg/L Ca or >25 mg/L Mg | [3] | ## Decision steps 1. **Read your water report** (or measure source EC: RO is usually <0.05 mS/cm, many tap waters 0.2–0.8). 2. **Read the base nutrient label**: what Ca and Mg does it supply at your dose? Many list it as % CaO and % MgO; convert (Ca = CaO × 0.715; Mg = MgO × 0.603). 3. **Add only the gap** between water + base and the targets. 4. **Coco:** buffer first; then a smaller ongoing top-up is often enough. 5. **Re-check K.** If K is very high (PK boosters), you may be fighting K antagonism rather than a Ca/Mg shortage [5]. ## Common mistakes - Adding full-rate Cal-Mag to hard tap water "just in case". - Using Cal-Mag to treat broad-mite damage or pH problems. - Forgetting the extra nitrogen late in flower. - Adding Cal-Mag after the base nutrient in the same concentrate bottle (precipitation with sulfate and phosphate). Add it to the water first, at working strength. ## Evidence - Ca and Mg shortage on RO water and in fresh coco: *Supported* (substrate chemistry [4], water chemistry [3]; no cannabis trial specific to Cal-Mag). - Target Ca and Mg levels: *Supported* [1][2]. - "LEDs need more Cal-Mag": *Myth* (GenetixBay house position). No study shows the light source itself raises Ca or Mg demand; the transpiration effect of cooler leaves [6][8] is a VPD setting, fixed with the environment. - Cultivar differences in Ca and Mg uptake: *Supported* [5][7]. ## Sources 1. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Morad D, Bernstein N. 2023. Response of medical cannabis to magnesium (Mg) supply at the vegetative growth phase. Plants 12(14):2676. https://doi.org/10.3390/plants12142676 3. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 4. Greenhouse Grower. Washed, low-EC, or buffered? How to specify coco substrate for your crop. https://www.greenhousegrower.com/?p=180860 5. Saloner A, Sacks MM, Bernstein N. 2019. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 6. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 7. Kalinowski J, et al. 2020. Augmenting nutrient acquisition ranges of greenhouse grown CBD (cannabidiol) hemp (Cannabis sativa) cultivars. Horticulturae 6(4):98. https://doi.org/10.3390/horticulturae6040098 8. Nelson JA, Bugbee B. 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10):e0138930. https://doi.org/10.1371/journal.pone.0138930 --- # Calcium (Ca) in cannabis: deficiency, transport, targets and sources > Calcium builds cell walls and membranes and moves only in the transpiration stream, so it cannot be moved from old leaves to new ones. Feed about 150–200 mg/L Ca in soilless systems, and remember that most 'calcium deficiency' is a delivery problem (low transpiration, high humidity, root damage, competing K/Mg/NH4) rather than an empty bottle. Classic signs are distorted, stunted new growth and brown spots. - Canonical: https://genetixbay.com/knowledge/nutrients/calcium.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why do my new leaves have brown spots and twisted tips?** Brown spots plus twisted new tips on cannabis often point to calcium deficiency, which causes irregular, distorted new growth, narrow leaflet bases and necrotic spotting. Rule out broad and russet mites first with a 30-60x loupe, since they cause glossy, twisted tips. Boron shortage, heat, herbicide drift, phosphorus or magnesium shortage, leaf septoria and spray burn can look similar. **Calcium deficiency or pH problem?** Calcium deficiency and a pH problem are often the same issue in cannabis, because low root-zone pH cuts calcium uptake. Below about 5.5 in soilless media, calcium and magnesium uptake suffer even when the feed holds enough. Check pH first: keep soilless and hydro at 5.5-6.5 (coco 5.8-6.3) and soil at 6.0-7.0 before adding more calcium. **How much calcium does cannabis need in coco or hydro?** Cannabis in coco or hydro needs about 150-200 mg/L calcium in the solution during veg and flower, counting what the water already supplies; the modified Hoagland solution used in cannabis research carries 200 mg/L. Grower practice for seedlings and clones is lower, about 80-120 mg/L. Healthy recent mature leaves test about 1.5-2.9% calcium by dry weight. **Why does calcium deficiency show up in coco with RO water?** Calcium deficiency shows up in coco with RO water because RO supplies almost no calcium and new or unbuffered coco binds calcium on its exchange sites while releasing potassium and sodium. Together they leave the plant short even on a normal feed. Buffer the coco and bring total solution calcium, water plus feed, to about 150-200 mg/L. **Can high humidity cause calcium deficiency?** Yes, high humidity can cause calcium deficiency in cannabis because calcium moves only with water in the transpiration stream. When relative humidity stays above about 70% with little airflow, leaves transpire less and new growth gets too little calcium even when the feed is fine. Grower practice keeps VPD near 0.8-1.2 kPa in veg and 1.0-1.5 kPa in flower. **Do LED lights cause calcium deficiency?** LED lights do not cause calcium deficiency in cannabis; the idea that LEDs create a Cal-Mag need is a myth and the GenetixBay house position. The light source does not change calcium demand. Leaves can run cooler under LEDs, which lowers transpiration and calcium delivery to new growth, so set leaf VPD correctly rather than adding calcium. **Why does only one strain in my room show calcium deficiency?** Only one cannabis strain may show calcium deficiency because calcium demand and uptake are partly genetic. In thirteen hemp cultivars grown side by side, leaf calcium varied more than any other nutrient, and medical cannabis genotypes differed in uptake and transport on the same feed. If the rest of the room is healthy, suspect the cultivar before changing the whole feed. **Short answer.** Calcium builds cell walls and keeps membranes intact. It travels only with water in the xylem, so new growth depends on transpiration and steady supply, and the plant cannot move it out of old leaves [4]. Feed about 150–200 mg/L Ca in coco and hydro. Most real-world "Ca deficiency" is a delivery problem: low transpiration, root damage, low pH, or too much K, Mg or ammonium competing at the root. ## What's happening Ca²⁺ cross-links pectins in the cell wall, stabilises membranes and acts as a signalling ion [4]. Because it moves almost exclusively in the xylem with the transpiration stream, the fastest-transpiring organs (big mature leaves) get the most; slow-transpiring tissues (young leaves, buds, root tips) get the least [4][5]. Anything that slows transpiration (very high humidity, low VPD, cold leaves, a dark period after a big irrigation) can starve new growth even when the feed is fine. This is *Established* in crops such as lettuce and tomato (tip burn, blossom-end rot) [5]; cannabis-specific transport data are lacking. **Cultivar matters.** Ca demand and uptake are partly genetic: in thirteen hemp cultivars grown side by side, leaf Ca varied more than any other nutrient [8], and medical cannabis genotypes differed in nutrient uptake and transport on the same feed [6]. The other real drivers are water source (RO), coco's cation exchange, root-zone pH and transpiration. **"LEDs need more Cal-Mag" is a *Myth*:** the light source doesn't create a Ca need; cooler leaves under LEDs can lower transpiration, which is fixed by setting leaf VPD (see [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md) and [VPD](https://genetixbay.com/knowledge/environment/vpd-explained.md)). Ca is **immobile** in the phloem, so symptoms appear on new growth first (see [mobile vs immobile](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md)). One caveat: in a DWC flowering trial, withholding Ca produced yellow-ringed necrotic spots on *lower* fan leaves first [2]. Spots on older leaves therefore do not rule Ca out. ## How to recognise it - **Early:** slight stunting; growing tips and newly expanding leaves grow irregularly; the base of new leaflets stays narrow and lighter green than the tip [1]. - **Progressing:** interveinal chlorosis at leaflet bases, marginal necrosis, leaves with odd shapes and orientation [1]. - **Advanced:** growing tips die, causing bushy axillary shoots [1]. In DWC flower: yellow-ringed necrotic spots between veins on lower fan leaves from week 3, margin necrosis by week 5, upward leaf curling by week 6; inflorescence fresh weight about 44% lower than control [2]. - **Differential:** rust spots also come from P or Mg shortage, leaf septoria, and spray burn. See [rust spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md). Twisted new growth also comes from boron shortage, broad mites, heat and herbicide drift. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution Ca, seedlings/clones | 80–120 mg/L | *Grower practice* | | Solution Ca, veg and flower | 150–200 mg/L | Modified Hoagland used in cannabis trials = 200 mg/L [1][7] | | Ca from water | Count it | Hard tap water may supply 40–120 mg/L; RO supplies ~0 | | Leaf Ca, healthy (most recent mature leaf) | 1.5–2.9% dry weight | NC State floral hemp [3]; controls in [1] ran 3.7% | | Leaf Ca at first deficiency symptoms | ~0.39% | Cannabis, sand culture [1] | | VPD to keep Ca moving | ~0.8–1.2 kPa veg; 1.0–1.5 kPa flower | *Grower practice*; see environment articles | | Root-zone pH | Soilless/hydro 5.5–6.5 (coco 5.8–6.3); soil 6.0–7.0 | Low pH lowers Ca availability; accepted practice from extension and grower consensus | ## What to check first 1. **Pests.** Broad and russet mites cause twisted, glossy new growth that looks like Ca deficiency. Check with a 30–60× loupe. 2. **Environment.** Has RH been above ~70% with little airflow? Leaves in still air transpire less. 3. **Water source.** RO or soft water with no Ca added is the commonest true cause. 4. **Coco.** New or unbuffered coco binds Ca and releases K and Na (see [buffering coco](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md)). 5. **pH.** Below about 5.5 in soilless, Ca and Mg uptake suffer. 6. **Competitors.** K above ~300 mg/L, high Mg, ammonium above ~20% of N, or Na from softened water. ## How to fix it - **Mineral feed:** calcium nitrate is the standard source (greenhouse grade ≈19% Ca and 15.5% N; 1 g/L ≈ 190 mg/L Ca and 155 mg/L N). Bring total Ca (water plus feed) to 150–200 mg/L. - **If you can't add more N** (late flower): calcium chloride (≈27% Ca, 48% Cl in the dihydrate) at small doses; keep chloride below about 70 mg/L. - **Soil:** gypsum (calcium sulfate) supplies Ca without raising pH; agricultural or dolomitic lime when the soil is also acidic. Both work slowly. - **Environment:** fix humidity and airflow so leaves transpire. - **Foliar calcium** (calcium chloride or calcium nitrate, ~0.5–1 g/L) can help new leaves in veg; Ca absorbed by leaves barely moves, so coverage matters. Never spray flowers. ## How to confirm it worked New growth emerges flat, evenly green and properly shaped within 7–10 days. Spotted leaves stay spotted. Runoff Ca (lab test) or leaf tissue 1.5–2.9% [3]. ## Common mistakes - Adding Cal-Mag on top of a feed that already supplies 180 mg/L Ca, pushing EC up and creating new problems. - Ignoring broad mites. - Mixing calcium nitrate with sulfates or phosphates in the same concentrated stock: gypsum and calcium phosphate precipitate. Use separate A and B tanks. - Assuming spots on old leaves cannot be Ca. ## Evidence - Ca deficiency symptoms in cannabis (tips, new leaves, spotting): *Established* by two controlled studies [1][2]. - Transpiration-driven Ca supply and humidity-linked Ca disorders: *Established* in horticulture [4][5]; *Supported* (extrapolated) for cannabis. - 150–200 mg/L Ca targets: *Supported* (standard solutions used in cannabis research [1][7]; no cannabis Ca dose-response study found). - K–Ca uptake competition in cannabis: *Supported* [6]. - Cultivar differences in Ca uptake: *Supported* [6][8]. - "LEDs need more Cal-Mag": *Myth* (GenetixBay house position); see [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md). ## Sources 1. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, et al. 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 4. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 5. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 6. Saloner A, Sacks MM, Bernstein N. 2019. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 7. Hoagland DR, Arnon DI. 1950. The water-culture method for growing plants without soil. California Agricultural Experiment Station Circular 347. https://archive.org/details/watercultureme3450hoag/ 8. Kalinowski J, et al. 2020. Augmenting nutrient acquisition ranges of greenhouse grown CBD (cannabidiol) hemp (Cannabis sativa) cultivars. Horticulturae 6(4):98. https://doi.org/10.3390/horticulturae6040098 --- # Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add > Chloride (Cl-) is an essential micronutrient for water splitting, osmotic balance and stomata, but the requirement is tiny and always met by water and fertiliser impurities. In practice chloride is a salinity problem, not a deficiency: keep it below roughly 50–70 mg/L in the feed, watch it in coco and some tap waters, and don't confuse chloride (a nutrient ion) with chlorine or chloramine (disinfectants). - Canonical: https://genetixbay.com/knowledge/nutrients/chlorine.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is chloride bad for cannabis?** Chloride is not bad for cannabis in small amounts; it is an essential micronutrient for photosynthetic water splitting, osmotic balance and stomata. The requirement is tiny and always met by water and fertiliser impurities, so never add it. Chloride becomes harmful as salinity, causing burnt, bronzed margins on older leaves, so keep it below roughly 50-70 mg/L in the feed. **How much chloride is too much in irrigation water?** For cannabis, chloride above roughly 50-70 mg/L in the combined water and feed is too much, according to grower practice and greenhouse guidance. A hydroponic study found more than 5 mM sodium chloride, about 180 mg/L chloride, may reduce yield, and 40 mM, about 1,400 mg/L, damaged growth. Check the water report, especially for coastal wells and softened water. **Is calcium chloride safe to use in a cannabis feed?** Calcium chloride is safe in a cannabis feed only at small doses, not as the main calcium source, because the dihydrate is about 48% chloride and chloride is a salinity risk. It is useful late in flower when you need calcium without nitrogen. Keep total feed chloride below about 50-70 mg/L and use calcium nitrate as the standard source. **What's the difference between chlorine, chloride and chloramine?** Chloride is the nutrient ion that cannabis takes up from salts, water and coco. Chlorine, as gas or hypochlorite, is a tap-water disinfectant that gasses off when water stands. Chloramine is a longer-lasting disinfectant that does not gas off on standing. Letting water sit removes chlorine only; it does not remove chloride or chloramine. **Can coco coir have high chloride?** Yes, coco coir can carry high chloride, along with sodium and potassium, and levels vary widely by source; poorly washed coco can hold a lot. Rinse and buffer coco before use and check runoff EC. Chloride burn looks like general salt stress, with burnt, bronzed margins on older cannabis leaves, often alongside high EC readings. **Short answer.** Chloride (Cl⁻) is an essential micronutrient. It is needed for the water-splitting step of photosynthesis, osmotic balance and stomatal movement [1][3]. The requirement is tiny and always met by water and impurities, so you never need to add it. In practice chloride matters as a *salinity* problem: keep it below roughly 50–70 mg/L in the feed. Chloride is not the same thing as chlorine or chloramine, the disinfectants in tap water. ## What's happening Cl⁻ is highly mobile in soil and plant, and plants take it up readily [1]. White and Broadley put the requirement at a few tenths of a milligram per gram of dry matter, and toxicity at around 4–7 mg/g in sensitive plants and 15–50 mg/g in tolerant ones [1]. That puts the gap between "enough" and "too much" at more than tenfold, and contamination alone supplies the requirement. Because Cl⁻ moves with water and builds up in leaf margins, toxicity looks like salt burn on older leaves. In cannabis, the only controlled salinity data come from sodium chloride: in hydroponic flower, cannabinoid content fell linearly with NaCl, growth was damaged at 40 mM (≈1,400 mg/L Cl), and the authors note that more than 5 mM NaCl (≈180 mg/L Cl) may reduce yield [2]. Sodium and chloride effects were not separated. **Words matter:** - **Chloride (Cl⁻):** the nutrient ion, from salts, water and coco. - **Chlorine (Cl₂ / hypochlorite):** a disinfectant in tap water; gasses off on standing. - **Chloramine:** a longer-lasting disinfectant; does not gas off (see [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md)). ## How to recognise it - **Deficiency:** never documented in cannabis; in other crops, wilting of leaflet tips, chlorosis and stubby roots [3]. - **Toxicity:** burnt, bronzed margins on older leaves, leaf drop, reduced growth, often with high EC; very similar to sodium and general salt stress. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Added Cl | None needed | [1][3] | | Feed Cl (water + fertilisers) | <50–70 mg/L | *Grower practice*/greenhouse guidance | | NaCl that may reduce cannabis yield | >5 mM (≈180 mg/L Cl) | Hydroponic flower [2] | | NaCl phytotoxic in hydro | 40 mM (≈1,400 mg/L Cl) | [2] | | 1 mmol/L Cl | 35.5 mg/L | Unit conversion | ## What to check first 1. **Water report:** chloride in mg/L. Coastal wells and softened water can be high. 2. **Fertilisers:** potassium chloride (muriate of potash), calcium chloride and hydrochloric acid all add Cl. 3. **Coco:** coir's Cl (and Na, K) varies widely by source; poorly washed coco can carry a lot [5]. 4. **Recirculating hydro:** Cl is barely taken up, so it accumulates as you top up. ## How to fix it - Switch to RO water or blend RO with tap to dilute. - Replace KCl with K₂SO₄ or KNO₃; replace CaCl₂ with Ca(NO₃)₂. - Rinse and buffer coco; check runoff EC. - In recirculating systems, dump and refill when Cl (or Na) reaches your limit. ## Common mistakes - Thinking "letting water stand" removes chloride. It removes chlorine gas only. - Using calcium chloride as the main calcium source. - Diagnosing "K deficiency" on margins that are really salt burn. ## Evidence - Cl is an essential micronutrient with requirements met by contamination: *Established* [1][3]. - Cannabis yield and potency decline with NaCl: *Supported* (one controlled study [2]; Na and Cl not separated). - A specific Cl ceiling for cannabis: *Grower practice*. ## Sources 1. White PJ, Broadley MR. 2001. Chloride in soils and its uptake and movement within the plant: a review. Annals of Botany 88(6):967-988. https://doi.org/10.1006/anbo.2001.1540 2. Yep B, Gale NV, Zheng Y. 2020. Aquaponic and hydroponic solutions modulate NaCl-induced stress in drug-type Cannabis sativa L. Frontiers in Plant Science 11:1169. https://doi.org/10.3389/fpls.2020.01169 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 4. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 5. Minnesota Pollution Control Agency. Chemical and physical properties of coir. https://stormwater.pca.state.mn.us/Chemical_and_physical_properties_of_coir --- # Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess > Copper is needed for photosynthetic electron transport, lignin and cell-wall strength. Cannabis copper deficiency showed late as stunted, distorted, slightly yellow new leaves that lost turgor and wilted, with a 45% biomass loss. Supply only about 0.03–0.1 mg/L Cu; excess (from copper fungicides, ionisers or pipework) damages roots first. - Canonical: https://genetixbay.com/knowledge/nutrients/copper.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What does copper deficiency look like in cannabis?** Copper deficiency in cannabis appears late, after about 9 weeks in one controlled study, as stunted, slightly distorted new leaves with narrow, yellowish leaflet bases, then fine interveinal chlorosis and margins curling in and down. New leaves lose turgor and look wilted. Biomass fell 45%, and leaf copper at symptom onset was about 1.4 mg/kg against 4.7 mg/kg in healthy controls. **Why are my new leaves limp and curling down?** Limp new cannabis leaves that curl down can signal copper deficiency, because copper is needed for lignin and cell-wall strength, so deficient leaves lose turgor. Check the roots first, since rot, boron deficiency, underwatering and heat look similar. Then confirm the feed contains copper; DIY salt mixes and RO water with micronutrient-free bases are common causes. **How much copper in a hydro nutrient solution?** A cannabis hydro nutrient solution needs only about 0.03-0.1 mg/L copper, based on greenhouse standards; cannabis trials used about 0.19 mg/L without harm. About 0.3 mg/L of copper sulfate pentahydrate supplies roughly 0.08 mg/L copper. Because the dose is tiny, mix a 1,000x micronutrient stock rather than dosing by pinch, and aim for leaf copper of 5-11 mg/kg. **Is copper toxic to cannabis roots?** Yes, excess copper is toxic to roots, which it damages before any other tissue. Roots become stunted, thick and dark or brown with few fine laterals, and iron-deficiency-like chlorosis then appears on new leaves, because copper damages membranes and induces iron shortage. Cannabis-specific toxicity thresholds have not been published. Remove the source, change the solution and allow 1-2 weeks for recovery. **Can copper pipes or ionisers harm a hydro system?** Yes, new copper pipe and copper-silver ionisers can release copper into a cannabis hydro system, and copper-based fungicide sprays add more. Because plants need only about 0.03-0.1 mg/L, extra copper accumulates in roots and damages them first. Test the water if plumbing is copper, remove the source, change the solution and keep pH in range. **Short answer.** Copper is part of plastocyanin (photosynthetic electron transport) and enzymes that build lignin and strengthen cell walls [3]. Cannabis grown without Cu developed symptoms only after about 9 weeks: stunted, distorted new leaves with narrow, yellowish leaflet bases, fine interveinal chlorosis and a loss of turgor that looked like wilting; biomass fell 45% [1]. Plants need very little: about 0.03–0.1 mg/L Cu. Excess damages roots first. ## What's happening Cu²⁺ is strongly bound by organic matter and roots, and moves poorly to new growth, so new leaves show shortage [3]. Because Cu is needed for lignification, deficient plants have weak cell walls. Cockson et al. linked the odd wilting they saw to "gummi-hemp", a historical name for limp, lodging fibre hemp, and suggested hemp may need more Cu than many species [1]. Excess Cu accumulates in roots, damages membranes and induces Fe deficiency [3]. ## How to recognise it - **Deficiency:** slight stunting; new and expanding leaves slightly distorted, especially at the leaflet base, which is narrower and slightly yellow; later more pronounced narrowing, marginal and then fine interveinal chlorosis, margins curling in and down, and reduced turgidity of new leaves [1]. Leaf Cu at onset was about 1.4 mg/kg against 4.7 in controls [1]. - **Toxicity:** stunted, thick, dark or brown roots with few fine laterals; then Fe-deficiency-like chlorosis on new leaves [3]. Cannabis-specific thresholds are not published. - **Differential:** B deficiency (also distorted tips and wilting from root damage), Ca deficiency, root rot (check roots), underwatering, heat. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution Cu | 0.03–0.1 mg/L | Greenhouse standards [4]; cannabis trials used ≈0.19 mg/L without harm [1] | | Leaf Cu, healthy (most recent mature leaf) | 5–11 mg/kg | NC State floral hemp [2] | | Leaf Cu at first deficiency symptoms | ~1.4 mg/kg | [1] | | Copper from water/plumbing | Test | New copper pipe and some ionisers release Cu. | ## What to check first 1. **Roots** (both deficiency and toxicity show there; rot mimics both). 2. **Feed:** a DIY salt mix with no Cu source, or RO water with base nutrients lacking micros. 3. **Copper sprays or ionisers:** copper-based fungicides or Cu/Ag ionisers in recirculating systems. 4. **pH:** Cu availability falls at high pH in soil and peat; very low pH increases it. ## How to fix it - **Deficiency:** copper sulfate pentahydrate (≈25.5% Cu; 0.3 mg/L product ≈ 0.08 mg/L Cu) or Cu-EDTA (≈14% Cu). Weigh carefully; this is a tiny dose. Mixing a 1,000× micronutrient stock makes accurate dosing possible. - **Toxicity:** remove the source, change the solution, keep pH in range. Root recovery takes 1–2 weeks. - **Safety:** copper sulfate is harmful if swallowed and irritates eyes; gloves and eye protection. ## How to confirm it worked New leaves expand normally and hold turgor within 1–2 weeks. Tissue Cu 5–11 mg/kg [2]. ## Common mistakes - Treating limp new growth as underwatering. - Spraying copper fungicide repeatedly in veg and then wondering about root issues in hydro. - Dosing copper sulfate by "pinch". ## Evidence - Cu deficiency symptoms, including wilting, in cannabis: *Supported* (one controlled study [1]). - Hemp has a high Cu requirement: *Contested/hypothesis* [1]. - Cu toxicity mechanism: *Established* in plant nutrition [3]; cannabis thresholds unknown. ## Sources 1. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 4. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Flushing before harvest: myth (summary) > Pre-harvest flushing is a myth that costs you yield and resin: it starves the plant while it packs on its final weight, trichomes and resin, and controlled studies found no gain in quality, minerals or cannabinoids. Cannabis stores what it takes up in its tissue, so plain water at the end doesn't wash it out. Feed through to harvest at stage-appropriate strength. The one valid flush treats the medium: a root-zone flush to clear salt build-up, at any stage. Full evidence in the flush debate article. - Canonical: https://genetixbay.com/knowledge/nutrients/flushing.html - Category: Nutrients · Level: Beginner - Evidence: Myth · Status: Draft: awaiting expert review - Stage: Ripening, Harvest · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should I flush my cannabis before harvest?** No, you should not flush cannabis before harvest. Pre-harvest flushing is a myth and actively harmful, because the final weeks are when the plant packs on most of its weight, trichomes and resin. Controlled studies found no gain in quality or cannabinoids, and longer nutrient withdrawal tended to cut dry mass and cannabinoid yield. Feed through to harvest at the strength the stage calls for. **Is flushing a myth?** Yes, pre-harvest flushing is a myth, and the GenetixBay house position is that it does more harm than good. Cannabis is a bioaccumulator: nutrients taken up are built into tissue, so plain water at the end strips the leaves, causing the yellowing, while flower nitrogen stays the same. The only valid flush is a root-zone flush that clears salt build-up from the medium. **Does flushing improve taste or make white ash?** Flushing does not improve cannabis taste or produce white ash; controlled studies found no gain in flower quality from it. Taste and ash come from a healthy plant that was never overfed, followed by slow drying and proper curing. Starving the plant with plain water in the final weeks costs yield and resin without removing what is already stored in the bud. **When should I flush my medium?** Flush the growing medium at any stage when salts have built up: runoff EC far above input EC, a visible salt crust, or nutrient lockout. Run 2-3 times the container volume of pH-adjusted water for soil, or a light nutrient solution for coco, rockwool or hydro, check runoff EC, then return straight to normal feeding. This flush treats the medium, not the plant. **Short answer.** Don't flush before harvest. Pre-harvest flushing is a *Myth*, and it costs you yield and resin. The last weeks are when the plant packs on most of its final weight and finishes its trichomes and resin; starving it then does far more harm than good. Controlled studies found no gain in flower quality or cannabinoids, and longer nutrient withdrawal tended to cut dry mass and cannabinoid yield [1][2][3]. Feed through to harvest at the strength the stage calls for. The full evidence, the studies table and the how-to live in one place: **[Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)**. ## The short version - **Cannabis is a bioaccumulator.** What it takes up is built into tissue. Plain water at the end doesn't wash it out of the bud; it strips the leaves (that's the yellowing) while flower nitrogen stays the same [1]. - **Taste and ash** come from a healthy plant that was never overfed, then slow [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) and proper [curing](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md). - **The one valid flush** treats the medium, not the plant: a root-zone flush to wash out accumulated salts when runoff EC is far above input, or there's salt crust or lockout. Run 2–3× the container volume of pH-adjusted water (soil) or a light solution (coco, rockwool, hydro), check runoff EC, then go straight back to normal feeding. Any stage. See [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md). ## Evidence Pre-harvest flushing improves quality: **Myth** (house position). No benefit and a yield cost with longer withdrawal: *Supported* [1][2][3]. Details and caveats in [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Sources 1. Hershkowitz JA. 2024. Nutrient management of cannabis in controlled environments. MS thesis, Utah State University. https://digitalcommons.usu.edu/etd2023/178 2. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 3. Alden MJ. 2025. Horticultural strategies to improve yield and efficiency for controlled-environment cannabis production. PhD dissertation, Clemson University. https://open.clemson.edu/all_dissertations/4161 --- # Hydroponic salts explained: what each fertiliser salt supplies > Almost every mineral cannabis feed is built from about a dozen salts: calcium nitrate, potassium nitrate, monopotassium phosphate (MKP), magnesium sulfate, potassium sulfate, a few others, plus chelated iron and trace salts. Each one supplies known percentages of two elements, so 1 g/L of a salt gives (percent x 10) mg/L of each. Calcium must be kept apart from sulfate and phosphate in concentrated stocks, which is why feeds come as A and B. - Canonical: https://genetixbay.com/knowledge/nutrients/hydroponic-salts.html - Category: Nutrients · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: DWC, RDWC, NFT, Ebb and flow, Drip, Coco, Rockwool, Aeroponics - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What does calcium nitrate supply?** Greenhouse-grade calcium nitrate supplies about 15.5% nitrogen, roughly 1.1% of it as ammonium, and about 19% calcium. At 1 g/L it gives about 155 mg/L nitrogen and 190 mg/L calcium. It is the main calcium source in mineral cannabis feeds and belongs in tank A only, because it precipitates with sulfate and phosphate in concentrated stocks. **How many ppm does 1 gram per litre of MKP give?** One gram per litre of monopotassium phosphate (MKP) gives about 228 ppm phosphorus and 287 ppm potassium, because MKP is 22.8% phosphorus and 28.7% potassium and 1 g/L of any salt supplies its percentage times 10 in mg/L. MKP is mildly acidic and goes in tank B. Check the bag label, which overrides typical values. **Why are nutrients split into part A and part B?** Hydroponic nutrients are split into part A and part B because calcium forms insoluble calcium sulfate (gypsum) and calcium phosphate when concentrated with sulfate or phosphate. At feed strength they stay dissolved, but at 100x concentrate they precipitate. Tank A holds calcium nitrate and iron chelate; tank B holds MKP, magnesium sulfate, potassium sulfate and trace salts. **Which salts do I need to make my own hydro nutrients?** A home-made cannabis hydro feed needs about a dozen salts: calcium nitrate, potassium nitrate, monopotassium phosphate, magnesium sulfate, potassium sulfate, often magnesium nitrate, an iron chelate such as Fe-DTPA, and trace salts for manganese, zinc, copper, boron and molybdenum. Use greenhouse or hydroponic grade, fully soluble salts, since agricultural grades can carry insoluble fillers or heavy metals. **What is the difference between EDTA and DTPA iron?** The difference between EDTA and DTPA iron chelates is pH stability. Fe-EDTA, about 13% iron, stays stable only up to about pH 6.5, while Fe-DTPA, about 11% iron, holds iron available up to about pH 7.5, making it the usual choice for cannabis in hydro and coco. Fe-EDDHA, about 6% iron, is stable to about pH 9. **Is Epsom salt the same as magnesium sulfate?** Yes, Epsom salt is magnesium sulfate heptahydrate, the standard magnesium source in hydroponic feeds. It contains about 9.9% magnesium and 13.0% sulfur, so 1 g/L supplies about 99 mg/L magnesium and 130 mg/L sulfur. It goes in tank B and must never share a concentrate with calcium nitrate, because gypsum would precipitate. **Short answer.** Nearly every mineral cannabis feed, bottled or home-made, is built from about a dozen salts. Each supplies fixed percentages of two elements, so **1 g/L of a salt gives (percent × 10) mg/L of each element**. Calcium nitrate supplies Ca and N; potassium nitrate supplies K and N; MKP supplies P and K; magnesium sulfate supplies Mg and S; potassium sulfate supplies K and S; chelates supply iron and other metals [1]. Calcium must be kept apart from sulfates and phosphates in concentrated stocks, which is why feeds come as part A and part B. ## The salts Percentages are for pure or typical greenhouse-grade material; check your bag's label, which overrides this table. | Salt (formula) | Supplies | 1 g/L gives (mg/L) | Notes | |---|---|---|---| | Calcium nitrate, greenhouse grade (5Ca(NO₃)₂·NH₄NO₃·10H₂O) | 15.5% N (≈1.1% as NH₄), ≈19% Ca | 155 N, 190 Ca | Main Ca source. Tank A only | | Potassium nitrate (KNO₃) | 13.9% N, 38.7% K | 139 N, 387 K | Either tank | | Monopotassium phosphate, MKP (KH₂PO₄) | 22.8% P, 28.7% K | 228 P, 287 K | Tank B; mildly acidic | | Magnesium sulfate heptahydrate, Epsom salt (MgSO₄·7H₂O) | 9.9% Mg, 13.0% S | 99 Mg, 130 S | Tank B | | Potassium sulfate, SOP (K₂SO₄) | 41.5–44.9% K, 17–18.4% S | ~415–449 K, ~170–184 S | Tank B; dissolves slowly | | Magnesium nitrate hexahydrate (Mg(NO₃)₂·6H₂O) | 9.5% Mg, 10.9% N | 95 Mg, 109 N | Mg without S; either tank | | Monoammonium phosphate, MAP (NH₄H₂PO₄) | 12.2% N (all NH₄), 26.9% P | 122 N, 269 P | Adds ammonium; acidifies | | Calcium chloride dihydrate (CaCl₂·2H₂O) | 27.3% Ca, 48.2% Cl | 273 Ca, 482 Cl | Small doses only (see [chloride](https://genetixbay.com/knowledge/nutrients/chlorine.md)) | | Fe-DTPA | ≈11% Fe | 110 Fe | Stable to ~pH 7.5 [3]; hydro and coco | | Fe-EDTA | ≈13% Fe | 130 Fe | Stable to ~pH 6.5 [3] | | Fe-EDDHA | ≈6% Fe | 60 Fe | Stable to ~pH 9 [3]; soil and alkaline water | | Manganese sulfate monohydrate | ≈32.5% Mn | 325 Mn | Trace | | Zinc sulfate heptahydrate | ≈22.7% Zn | 227 Zn | Trace | | Copper sulfate pentahydrate | ≈25.5% Cu | 255 Cu | Trace | | Boric acid (H₃BO₃) | ≈17.5% B | 175 B | Trace | | Sodium molybdate dihydrate | ≈39.7% Mo | 397 Mo | Trace | | Potassium silicate | Varies (Si and K) | Label | Add first; very alkaline (see [silicon](https://genetixbay.com/knowledge/nutrients/silicon.md)) | **Acids and bases are nutrients too.** Nitric acid adds N, phosphoric acid adds P, sulfuric acid adds S (about 14, 31 and 16 mg/L respectively per meq/L of acid used); potassium hydroxide pH-up adds K [4]. Count them. **Tapering N in late flower.** Single salts make this possible: drop calcium nitrate and potassium nitrate, take K from potassium sulfate and MKP, and switch the Ca source to an N-free salt such as calcium chloride (small doses only: 50 mg/L Cl brings just ~28 mg/L Ca, so keep Cl under ~50–70 mg/L; see [chloride](https://genetixbay.com/knowledge/nutrients/chlorine.md)) or calcium sulfate (gypsum) dissolved directly in the final solution. See [nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md) for the ramp. ## Why part A and part B Calcium forms insoluble calcium sulfate (gypsum) and calcium phosphate when concentrated with sulfate or phosphate. At feed strength they stay dissolved; at 100× concentrate they do not [1]. So: - **Tank A:** calcium nitrate, (potassium nitrate), iron chelate. - **Tank B:** MKP, magnesium sulfate, potassium sulfate, (potassium nitrate), trace salts. - Add A to the water, mix, then B. Never mix A and B concentrates directly. ## A worked micro example To hit 2.5 mg/L Fe from Fe-DTPA 11%: 2.5 ÷ (11 × 10) = 0.0227 g/L, i.e. 2.27 g per 100 L. Trace elements are easier with a 1:1000 stock solution because the weights are tiny. ## Reference: a classic solution The modified Hoagland all-nitrate solution used in cannabis deficiency research supplied, in mg/L: N 210, P 31, K 235, Ca 200, Mg 49, S 64, Fe 4.0, Mn 1.0, B 0.49, Zn 0.20, Cu 0.19, Mo 0.01 [5] (converted from the mM/µM values in the paper; based on [2]). See [building a feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) for cannabis targets. ## Safety - Nitrate salts are oxidisers; store away from fuels and organic material, keep dry. - Acids: gloves and eye protection; always add acid to water, never water to acid. - Boric acid, copper and nickel salts are toxic if swallowed; keep away from food and children. ## Common mistakes - Using agricultural-grade salts with insoluble fillers or heavy-metal contamination in hydro. Use greenhouse or hydroponic (fully soluble) grade. - Forgetting the ammonium in calcium nitrate and MAP when calculating NH₄ share. - Mixing calcium nitrate with Epsom salt in the same concentrate. - Ignoring what the water already supplies. ## Evidence - Element percentages: *Established* (stoichiometry; label values vary by grade). - A/B separation: *Established* [1]. - Chelate pH ceilings: *Established* [3]. ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Hoagland DR, Arnon DI. 1950. The water-culture method for growing plants without soil. California Agricultural Experiment Station Circular 347. https://archive.org/details/watercultureme3450hoag/ 3. HortScience. 2025. Iron chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA) in high-pH soilless media. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml 4. NC State Extension. Producing conventional tobacco transplants in greenhouses: water quality. https://content.ces.ncsu.edu/producing-conventional-tobacco-transplants-in-greenhouses-water-quality 5. Cockson P, et al. 2019. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Iron (Fe) in cannabis: yellow new growth, chelates and pH > Iron is needed to make chlorophyll and run electron transport. Deficiency shows as interveinal yellowing of the newest leaves and is almost always caused by high root-zone pH or alkaline water, not a lack of iron in the feed. Supply about 1.5–3 mg/L Fe as a chelate matched to your pH: EDTA up to about 6.5, DTPA to about 7.5, EDDHA to about 9. - Canonical: https://genetixbay.com/knowledge/nutrients/iron.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my new leaves yellow with green veins?** New cannabis leaves that turn yellow between green veins usually show iron deficiency, which starts as slight yellowing at the base of new leaflets while lower and middle foliage stays dark green. It is almost always caused by high root-zone pH or alkaline water rather than a feed lacking iron. Manganese, zinc and sulfur shortages can look similar, so check pH first. **Which iron chelate is best for hydro: EDTA, DTPA or EDDHA?** Fe-DTPA is usually the best iron chelate for cannabis in hydro and coco, because it keeps iron available up to about pH 7.5. Fe-EDTA works only up to about pH 6.5 and fails in a reservoir drifting toward 7, while Fe-EDDHA, stable to about pH 9, suits soil and alkaline water but stains red. Keep chelate stocks and reservoirs dark. **How many ppm iron in a nutrient solution?** A cannabis nutrient solution should carry about 1.5-3 ppm (mg/L) iron, based on grower practice and greenhouse standards; the modified Hoagland solution used in cannabis trials ran about 4 mg/L. To supply 2 mg/L iron from an 11% Fe-DTPA product, dose about 18 mg/L of product. Healthy recent mature leaves test about 70-150 mg/kg iron. **Iron deficiency or high pH?** Iron deficiency in cannabis is usually a high-pH problem rather than a shortage of iron in the feed. Measure root-zone pH in the runoff or reservoir, not just the input; readings above about 6.5 explain most cases, and alkaline water with bicarbonate above roughly 100-150 mg/L as CaCO3 is the classic trigger. Bringing pH back to range often fixes it within 5-7 days. **Can low pH cause iron toxicity?** Low root-zone pH, below about 5.3, makes iron and manganese very soluble, and in iron-efficient crops this causes bronzing, dark speckling and necrotic spots. Iron toxicity in cannabis has not been characterised by research, and it is rare in soilless media at normal pH. Keep soilless pH around 5.5-6.3 to avoid both iron shortage and excess. **Short answer.** Iron is needed to make chlorophyll and to run photosynthetic and respiratory electron transport [7]. Deficiency shows as yellowing between the veins of the *newest* leaves [1]. It is almost always caused by high root-zone pH or alkaline water, not by a feed with no iron [4]. Supply about 1.5–3 mg/L Fe as a chelate that stays stable at your pH: Fe-EDTA up to about pH 6.5, Fe-DTPA to about 7.5, Fe-EDDHA to about 9 [5]. ## What's happening Free Fe³⁺ is nearly insoluble at neutral and alkaline pH; it precipitates as hydroxides and with phosphate. Chelates (EDTA, DTPA, EDDHA) are organic cages that keep iron in solution until a root takes it. Each cage has a pH ceiling above which iron is displaced [5]. Fe is **immobile** in the phloem: once laid down in an old leaf it stays there, so new growth shows the shortage first [4][7]. High bicarbonate (alkaline water) is the classic trigger, because it raises root-zone pH and directly impairs iron uptake [4]. High P, Mn, Zn, Cu and Ca can also compete with or precipitate iron (see [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md)). ## How to recognise it - **Deficiency:** begins as slight marginal yellowing at the base of new leaflets, then interveinal chlorosis on new and expanding leaves while lower and middle foliage stays dark green [1]. Severe cases: almost white new leaves [4]. In a sand-culture cannabis trial, symptoms took about 9 weeks to appear [1]; in a DWC flowering trial, withholding Fe produced no striking symptoms and no significant yield loss, probably because the plants had iron reserves and some contamination [2]. - **Toxicity:** rare in soilless at normal pH. At low pH (below ~5.3) Fe and Mn become very soluble; in iron-efficient crops this causes bronzing, dark speckling and necrotic spots [4]. Cannabis Fe toxicity has not been characterised. - **Differential:** Mn deficiency (similar but more netted, spots, upper and central leaves), Zn (narrow, small leaves, margins), S (whole leaf pale, not interveinal), light bleaching (top only, near lamp). ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution Fe | 1.5–3 mg/L | *Grower practice* and greenhouse standards; modified Hoagland used in cannabis trials ≈4 mg/L [1] | | Root-zone pH, soilless | 5.5–6.3 | Above ~6.5, choose DTPA or EDDHA | | Fe-EDTA stable to | ~pH 6.5 | [5] | | Fe-DTPA stable to | ~pH 7.5 | [5]; common hydro choice | | Fe-EDDHA stable to | ~pH 9 | [5]; soil and alkaline water; stains red | | Leaf Fe, healthy (most recent mature leaf) | 70–150 mg/kg | NC State floral hemp [3] | | Leaf Fe at first deficiency symptoms | ~60 mg/kg | Cannabis, sand culture [1] | | Irrigation water alkalinity flag | >100–150 mg/L CaCO₃ | Acidify (see [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md)) | ## What to check first 1. **pH of the root zone**, not just the input. Runoff or reservoir pH above ~6.5 explains most cases. 2. **Water alkalinity.** Get a water report; bicarbonate is the usual culprit [4]. 3. **Root health and temperature.** Cold, waterlogged or rotting roots fail to take up iron. 4. **Chelate type.** EDTA in a reservoir drifting to 7 is not doing its job. 5. **Light.** Very high-intensity lamps photodegrade Fe-EDTA and Fe-DTPA in clear reservoirs and lines; keep stock and reservoirs dark. ## How to fix it - **Bring pH back to range** (5.5–6.2 hydro, 5.8–6.3 coco). This alone often fixes it in 5–7 days. - **Acidify alkaline water** before mixing nutrients. - **Switch chelate** to DTPA (hydro, coco) or EDDHA (soil, high-pH water). Typical products: Fe-DTPA ≈ 11% Fe, Fe-EDDHA ≈ 6% Fe; 2 mg/L Fe from an 11% DTPA product ≈ 18 mg/L of product. - **Foliar iron** (Fe-DTPA or Fe-EDTA, about 50–100 mg/L Fe) greens existing new leaves quickly in veg; *grower practice*. Not on flowers. ## How to confirm it worked New leaves emerge green within 5–10 days; already-yellow leaves may partly re-green over 1–2 weeks. Tissue Fe 70–150 mg/kg [3]. ## Common mistakes - Adding more iron while pH sits at 7. - Using Fe-EDTA in soil or hard-water systems. - Leaving nutrient stock in clear bottles in the sun. - Confusing Fe (new growth) with Mg (old growth). ## Evidence - New-leaf interveinal chlorosis as the Fe deficiency signature in cannabis: *Established* [1]. - High pH/alkalinity as the usual cause: *Established* in container horticulture [4]; *Supported* for cannabis. - Chelate pH limits: *Established* [5]. - Extra Fe above standard levels improving cannabis yield: *Not supported* (augmented Fe/P/K regime did not substantially increase biomass [6]). ## Sources 1. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, et al. 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 4. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 5. HortScience. 2025. Iron chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA) in high-pH soilless media for calibrachoa and soybean. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml 6. Velechovsky J, Malik M, Senkyrik JB, Tlustos P. 2024. Effect of augmented nutrient composition and fertigation system on biomass yield and cannabinoid content of medicinal cannabis. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 7. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 --- # Magnesium (Mg) in cannabis: interveinal yellowing, targets and the K-Ca competition > Magnesium sits at the centre of chlorophyll. Cannabis trials put the optimum at about 35–70 mg/L Mg in veg, and Mg supply raised cannabinoid and terpene production in flower. Deficiency shows as interveinal yellowing on older leaves with green veins; it is often induced by low pH or by too much potassium or calcium rather than an actual lack of Mg. - Canonical: https://genetixbay.com/knowledge/nutrients/magnesium.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my lower leaves yellow between the veins?** Lower cannabis leaves that yellow between green veins usually show magnesium deficiency, because magnesium is mobile and the plant moves it from old leaves to new growth. The pattern starts faint and becomes a stark green-vein, yellow-blade contrast with necrotic patches. Iron and manganese cause similar chlorosis but on new growth, and potassium deficiency starts at leaf margins instead. **How much magnesium does cannabis need?** Cannabis needs about 35-70 mg/L magnesium in veg, the optimum found in a controlled dose-response trial, and about 40-70 mg/L in flower. Grower practice for seedlings and clones is 25-40 mg/L, with calcium to magnesium kept near 3:1 to 4:1 by mass. Healthy recent mature leaves test about 0.30-0.65% magnesium by dry weight. **Can I use Epsom salt on cannabis? How much?** Yes, Epsom salt (magnesium sulfate heptahydrate, about 9.9% magnesium) is a standard cannabis magnesium source. In the root feed, 0.5 g/L supplies about 50 mg/L magnesium and 65 mg/L sulfur. As a veg foliar spray, grower practice uses about 2-5 g/L with a wetting agent at lights-off or low light. Never spray flowers, and test before repeating doses in soil. **Is it magnesium deficiency or too much potassium?** Magnesium deficiency in cannabis is often induced by too much potassium, because magnesium uptake is weak compared with potassium and calcium; in cannabis, rising potassium supply lowered calcium and magnesium uptake. Check whether a PK booster or extra calcium was added recently. If solution potassium is above about 300 mg/L, bring it down rather than adding more magnesium. **Does magnesium increase THC or terpenes?** Research suggests magnesium supply can increase cannabinoid and terpene production in flowering cannabis: one controlled study spanning 2-140 mg/L magnesium found higher production as supply rose from deficiency. This is supported by a single study, and the exact flower optimum still needs confirming. Practical flower targets are about 40-70 mg/L magnesium in the solution. **Do LED lights need more magnesium?** LED lights do not make cannabis need more magnesium; the claim that LEDs create a Cal-Mag need is a myth and the GenetixBay house position. Magnesium demand tracks the cultivar, the water source, coco's cation exchange and root-zone pH. Genotypes on the same feed take up and move magnesium differently, which explains most plants that seem magnesium-hungry. **Short answer.** Magnesium is the atom at the centre of every chlorophyll molecule. A cannabis dose-response trial found about 35–70 mg/L Mg optimal in veg [1], and a follow-up found Mg supply increased cannabinoid and terpene production in flower [2]. Deficiency shows as yellowing *between* the veins of older leaves while the veins stay green [3]. It is often induced by low pH or by too much potassium, calcium or ammonium, so check those before adding more Mg. ## What's happening Mg²⁺ is part of chlorophyll, activates enzymes including Rubisco and ATPases, and is needed to load sugars into the phloem [7]. It is **mobile**, so the plant pulls it from old leaves to supply new ones; symptoms begin low on the plant. Mg uptake is weak compared with K⁺ and Ca²⁺. When K or Ca is high, or NH₄⁺ is a large share of N, Mg uptake drops. In cannabis, rising K supply was linked to lower Ca and Mg uptake [6]. That is why a PK booster or heavy Cal(cium)-only supplement can produce a Mg deficiency. Mg demand also varies by **cultivar**: genotypes on the same feed take up and move nutrients differently [6]. Together with RO water, coco's cation exchange and root-zone pH, that explains most "Mg-hungry" plants. **"LEDs need more Cal-Mag" is a *Myth*:** the light source doesn't raise Mg demand. See [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md). ## How to recognise it - **Early:** faint interveinal yellowing on lower, older leaves [3]. - **Progressing:** stronger contrast; veins stay green while the tissue between them goes yellow [3]. - **Advanced:** stark green-vein, yellow-blade pattern with necrotic patches [3]. In DWC flower, symptoms began in week 4 on lower fan leaves and later spread to younger leaves by weeks 5–6, with midribs and margins staying green; inflorescence fresh weight was about 33% lower [4]. - **Differential:** iron and manganese also cause interveinal chlorosis, but on *new* growth. K deficiency starts at margins, not between veins. Late-flower senescence is general fading, not a crisp vein pattern. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution Mg, seedlings/clones | 25–40 mg/L | *Grower practice* | | Solution Mg, veg | 35–70 mg/L | Optimum in a cannabis trial [1] | | Solution Mg, flower | 40–70 mg/L | Mg raised cannabinoids and terpenes; the study spanned 2–140 mg/L [2]. | | Ca:Mg ratio (mass) | ~3:1 to 4:1 | *Grower practice*; standard Hoagland is 200:49 ≈ 4:1 | | Leaf Mg, healthy (most recent mature leaf) | 0.30–0.65% dry weight | NC State floral hemp [5] | | Leaf Mg at first deficiency symptoms | ~0.12% | Cannabis, sand culture [3] | ## What to check first 1. **pH.** Soilless below about 5.5 or soil below about 6.0 reduces Mg availability. Keep soilless at 5.5–6.5 and soil at 6.0–7.0 (accepted practice; see [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)). 2. **K and Ca levels.** Did you add a PK booster or extra calcium recently? 3. **Water.** RO water supplies no Mg. Hard water often supplies 10–40 mg/L. 4. **Coco.** Unbuffered coco can bind Mg (see [buffering coco](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md)). 5. **Roots.** Cold or waterlogged roots absorb poorly. ## How to fix it - **Mineral:** magnesium sulfate heptahydrate (Epsom salt, ≈9.9% Mg, 13% S). 0.5 g/L supplies about 50 mg/L Mg and 65 mg/L S. Magnesium nitrate (≈9.5% Mg, 11% N) if you also want N. - **Foliar (veg):** Epsom salt at about 2–5 g/L with a wetting agent, at lights-off or low light; new leaves green faster. *Grower practice.* Do not spray flowers. - **Soil:** dolomitic lime if the soil is also acidic (slow); Epsom salt dissolved in irrigation water for a quick response. - **Rebalance K:** if K is above about 300 mg/L, bring it down instead of adding Mg. ## How to confirm it worked Yellowing stops climbing within a week; new leaves stay fully green. Old interveinal damage stays. Tissue Mg 0.30–0.65% [5]. ## Common mistakes - Adding Epsom salt repeatedly in soil without testing; sulfate and EC build up. - Missing the real cause (K excess or low pH). - Confusing Mg (old leaves) with Fe/Mn (new leaves). ## Evidence - Mg deficiency symptoms on older leaves: *Established* [3][4]. - Veg optimum 35–70 mg/L: *Supported* (one cultivar, one lab [1]). - Mg increases cannabinoid/terpene production: *Supported* (one study [2]). - Foliar Mg as a quick fix: *Grower practice*, consistent with other crops. - "LEDs need more Cal-Mag": *Myth* (GenetixBay house position); Mg demand tracks cultivar, water, medium and pH [6]. ## Sources 1. Morad D, Bernstein N. 2023. Response of medical cannabis to magnesium (Mg) supply at the vegetative growth phase. Plants 12(14):2676. https://doi.org/10.3390/plants12142676 2. Morad D, Bernstein N. 2025. From deficiency to toxicity: magnesium increases cannabinoid and terpene production in cannabis plants. PMC12739851. https://pmc.ncbi.nlm.nih.gov/articles/PMC12739851/ 3. Cockson P, et al. 2019. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 4. Llewellyn D, et al. 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 5. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 6. Saloner A, Sacks MM, Bernstein N. 2019. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 7. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 --- # Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance > Manganese is needed to split water in photosynthesis. Deficiency gives a bright yellow, netted interveinal chlorosis on upper and middle leaves with small tan spots; toxicity, usually from low root-zone pH, gives yellowing and necrosis of older leaf margins. Supply about 0.3–0.8 mg/L Mn and keep pH in range, because Mn availability swings strongly with pH. - Canonical: https://genetixbay.com/knowledge/nutrients/manganese.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What does manganese deficiency look like in cannabis?** Manganese deficiency in cannabis shows as bright yellow, netted interveinal chlorosis on upper and central leaves, starting at the leaflet midrib and spreading outward while the veins stay green. Advanced leaves develop small tan necrotic spots between the veins. Onset took about 6 weeks in a sand-culture study, with leaf manganese near 7.6 mg/kg at first symptoms. **Can low pH cause manganese toxicity?** Yes, low root-zone pH is the usual cause of manganese toxicity in cannabis, because manganese solubility rises steeply as pH falls, so a feed that is fine at pH 6 can become toxic near pH 5. Toxicity shows as yellowing and dying margins on lower leaves, then leaf drop. Keep soilless pH around 5.5-6.3; risk rises below about 5.3. **How much manganese in a hydroponic solution?** A cannabis hydroponic solution should carry about 0.3-0.8 mg/L manganese, a grower practice and greenhouse standard range; cannabis trials used about 1.0 mg/L, and toxicity appeared near 10 mg/L. About 1.5 mg/L of manganese sulfate monohydrate supplies roughly 0.5 mg/L manganese. Healthy recent mature leaves test about 40-158 mg/kg manganese. **Iron or manganese deficiency, how do I tell?** Iron and manganese deficiency in cannabis differ in pattern and position. Iron chlorosis is smoother and paler and concentrates on the very newest leaves. Manganese chlorosis is more netted, sits a little lower on upper-middle leaves, and develops small tan spots. Correct pH first, and never treat manganese deficiency with extra iron, because the two compete. **Why do I have yellow netting between veins on top leaves?** Yellow netting between green veins on upper and middle cannabis leaves is the classic sign of manganese deficiency, often triggered by high root-zone pH, which cuts manganese availability. Very high iron doses can also suppress manganese uptake. Measure runoff or reservoir pH, bring soilless media back to about 5.5-6.3, then add manganese if the feed lacks it. **Short answer.** Manganese runs the water-splitting step of photosynthesis and activates many enzymes [6]. Deficiency shows as bright yellow, *netted* interveinal chlorosis on upper and central leaves, later with small tan spots [1]. Toxicity usually comes from a root zone that has gone too acidic and shows as yellowing and dying margins on lower leaves [1][4]. Supply about 0.3–0.8 mg/L Mn and hold pH in range. ## What's happening Mn²⁺ is the plant-available form. Its solubility rises steeply as pH falls, so the same feed can be deficient at pH 7 and toxic at pH 5 [4][5]. Mn and Fe compete: high Mn can induce Fe deficiency and the reverse [6]. Mn is **poorly mobile**, so deficiency appears on newer and middle leaves. ## How to recognise it - **Deficiency:** bright yellow netted interveinal chlorosis on upper and central foliage, starting at the leaflet midrib and spreading outward; veins stay green; advanced leaves develop small tan necrotic spots between veins [1]. Onset took about 6 weeks in sand culture [1]. In a DWC flowering trial, withholding Mn gave no visible symptoms and no yield or cannabinoid loss even though upper-canopy Mn was very low [2]; reserves from veg may carry plants through a short flower cycle. - **Toxicity:** in a 10× Mn treatment (about 10 mg/L Mn), marginal yellowing of lower leaves moved inward toward the midrib, followed by marginal necrosis and leaf drop [1]. Leaf Mn in those plants was only 48 mg/kg, within normal survey ranges, so tissue tests may not flag it; the authors called for higher-dose work [1]. In other crops, Mn toxicity also shows as brown speckles on older leaves and induced Fe deficiency on new ones [6]. - **Differential vs iron:** Fe chlorosis is smoother and paler, concentrated on the very newest leaves; Mn chlorosis is more netted, sits a little lower (upper-middle), and develops tan spots. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution Mn | 0.3–0.8 mg/L | *Grower practice*/greenhouse standards; cannabis trials used ≈1.0 mg/L [1] | | Toxicity seen at | ~10 mg/L in solution | Cannabis, sand culture, 7 weeks [1] | | Root-zone pH, soilless | 5.5–6.3 (accepted range 5.5–6.5) | Below ~5.3 Mn and Fe toxicity risk rises [4][5] | | Leaf Mn, healthy (most recent mature leaf) | 40–158 mg/kg | NC State floral hemp [3] | | Leaf Mn at first deficiency symptoms | ~7.6 mg/kg | [1] | ## What to check first 1. **pH.** High pH → deficiency; low pH → toxicity. Measure runoff or reservoir. 2. **Iron dose.** Very high Fe can suppress Mn. 3. **Media.** Some peat and soil mixes release Mn when they go acidic or waterlogged (reduced, low-oxygen soils make Mn²⁺ more soluble). 4. **Fungicides.** Mn-containing fungicides (mancozeb-type) add Mn; never use on cannabis flowers. ## How to fix it - **Deficiency:** correct pH first. Then add manganese sulfate monohydrate (≈32% Mn; 1.5 mg/L product ≈ 0.5 mg/L Mn) or Mn-EDTA (≈13% Mn). - **Toxicity:** raise root-zone pH into range (in soil, lime; in soilless, raise feed pH and stop acidic inputs). Root-zone flush with a balanced solution at normal EC, not plain water (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). ## How to confirm it worked New growth emerges green without netting within 7–10 days. For toxicity, no new marginal necrosis on lower leaves after pH correction. ## Common mistakes - Treating Mn deficiency with iron, which can make it worse. - Letting a peat-based mix drift acidic and then adding more acid. - Relying on tissue tests alone to rule out Mn toxicity [1]. ## Evidence - Mn deficiency symptoms in cannabis: *Established* (one sand-culture study [1]); not reproduced in a short DWC flower trial [2]. - Mn toxicity symptoms at ~10 mg/L: *Supported* (one study; threshold not refined [1]). - pH control of Mn availability and Fe–Mn antagonism: *Established* in plant nutrition [4][5][6]. ## Sources 1. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, et al. 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 4. Michigan State University Extension. pHix it! Getting substrate pH just right. https://www.canr.msu.edu/news/phix-it-getting-substrate-ph-just-right 5. Lopez RG, Mickelbart MV, Pasian C. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 6. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 --- # Mobile vs immobile nutrients: reading old vs new leaves > Mobile nutrients (N, P, K, Mg, and also Cl, Mo, Ni) can be moved from old leaves to new ones through the phloem, so their shortages show on the oldest, lowest leaves first. Immobile nutrients (Ca, B, Fe, Mn, Cu, Zn, and partly S) stay where they were first deposited, so shortages show on new growth. It is the first fork in any deficiency diagnosis, with a few cannabis-specific exceptions. - Canonical: https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.html - Category: Nutrients · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Which nutrients are mobile in cannabis?** The mobile nutrients in cannabis are nitrogen, phosphorus, potassium and magnesium, plus chloride, nickel and, moderately, molybdenum. The plant can reload them into the phloem and move them from old leaves to new growth, so their shortages show first on the oldest, lowest leaves. Calcium, boron, iron, manganese, copper and zinc are immobile or low-mobility, and sulfur is intermediate. **Why do deficiencies show on bottom leaves or top leaves?** Cannabis deficiencies show on bottom or top leaves depending on nutrient mobility. Mobile nutrients such as nitrogen, phosphorus, potassium and magnesium are stripped from old leaves to feed new growth, so lower leaves suffer first. Immobile nutrients such as calcium, boron and iron stay where first deposited, so new growth depends on daily root supply and shows shortages first. **Yellow new growth vs yellow old leaves, what does it mean?** Yellow old leaves on cannabis point toward a shortage of a mobile nutrient: nitrogen, magnesium, potassium or phosphorus. Yellow new growth points toward an immobile nutrient: iron, manganese, zinc, calcium, boron, copper or sulfur. Before adding anything, rule out root-zone pH and root health, because most new-growth symptoms in a properly fed plant are pH or root failures. **Is calcium mobile or immobile?** Calcium is immobile in cannabis: it barely enters the phloem, so the plant cannot move it from old leaves to new ones, and symptoms usually start at growing tips and new leaves. There is a cannabis-specific exception, though. In a DWC flowering trial, withholding calcium produced spotting on lower fan leaves first, so spots on old leaves do not rule calcium out. **How do I tell nitrogen from iron deficiency?** Nitrogen deficiency in cannabis starts on the oldest, lowest leaves and yellows the whole leaf, climbing up the plant, because nitrogen is mobile. Iron deficiency starts on the newest, expanding leaves and yellows between green veins, because iron is immobile. Check root-zone pH before treating iron, and remember old-leaf fading near harvest is normal remobilisation. **Short answer.** Some nutrients can be pulled out of old leaves and sent to new growth through the phloem; others stay where they were first laid down [1]. Shortages of **mobile** nutrients (N, P, K, Mg) show first on the oldest, lowest leaves. Shortages of **immobile** nutrients (Ca, B, Fe, Mn, Cu, Zn, and partly S) show first on new growth [1][4]. Where the symptom starts is the first fork in diagnosis. Cannabis has a few exceptions, below. ## What's happening Water and dissolved nutrients rise from the roots in the **xylem**, pulled by transpiration. Everything reaches leaves that way first. What differs is whether the plant can reload a nutrient into the **phloem** (the sugar-transport system) and send it to growing tips [1]. - **Mobile:** N, P, K, Mg, Cl, Mo (moderate), Ni [1][5]. When supply falls, the plant strips them from old leaves. Old leaves yellow; new leaves look normal for a while. - **Immobile:** Ca and B (barely enter phloem in most species), Fe, Mn, Cu, Zn (low mobility) [1][4]. New growth depends on what the roots deliver *today*. New leaves suffer; old leaves stay green. - **Intermediate:** S. Mobility depends on N status; symptoms tend to appear mid-canopy and on newer leaves [1][2]. ## How it shows in cannabis | Nutrient | Mobility | Where symptoms started in cannabis trials | |---|---|---| | N | Mobile | Lower leaves, climbing up [2][3] | | P | Mobile | Lower, older leaves (olive or brown spots) [2][3] | | K | Mobile | Margins of lower leaves [2]; sugar leaves in DWC flower [3] | | Mg | Mobile | Lower leaves, interveinal [2][3] | | S | Intermediate | Middle of plant, then new leaves [2]; upper sugar leaves [3] | | Ca | Immobile | Growing tips and new leaves [2]; **but lower fan leaves in DWC flower** [3] | | Fe | Immobile | New, expanding leaves [2] | | Mn | Low | Upper and central leaves [2] | | Zn | Low | Newer leaves, margins [2] | | Cu | Low | New leaves, distortion and limpness [2] | | B | Immobile | Growing tips, new leaves, root tips [2] | | Mo | Moderate | No visible symptoms in 9 weeks [2] | ## Decision steps 1. **Where did it start?** Oldest leaves → think N, Mg, K, P. New leaves → think Fe, Mn, Zn, Ca, B, Cu, S. 2. **What pattern?** Whole leaf (N, S), between veins (Mg old, Fe/Mn new), margins (K old, Zn new), spots (P, Ca), distortion (Ca, B, Cu). 3. **Then rule out the root zone and pH** before any nutrient: most immobile-nutrient symptoms in a properly fed plant are pH or root failures [4]. See [how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md). ## Common mistakes - Treating mobility as absolute. The Ca result in DWC [3] shows spotting on lower leaves can still be Ca. - Forgetting that pests (broad mites, thrips) and light stress also hit new growth first. - Diagnosing late flower: plants remobilise N, P, K and Mg into flowers by design, so old-leaf fading near harvest is normal. ## Evidence - Phloem mobility classes: *Established* [1]. - Cannabis symptom locations matching the classic pattern: *Established* for most elements [2][3], with the Ca exception noted [3]. ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 3. Llewellyn D, et al. 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 4. Lopez RG, Mickelbart MV, Pasian C. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 5. White PJ, Broadley MR. 2001. Annals of Botany 88(6):967-988. https://doi.org/10.1006/anbo.2001.1540 --- # Molybdenum (Mo) in cannabis: the trace element nitrate depends on > Molybdenum is a cofactor for nitrate reductase, so a nitrate-fed plant cannot use its nitrogen without it. Cannabis needs a minuscule amount (about 0.01–0.05 mg/L Mo); in a 9-week trial, cannabis grown with no Mo showed no visible symptoms at all despite 96% lower leaf Mo. Unlike the other micronutrients, Mo becomes more available as pH rises, so deficiency is a low-pH, acid-soil problem. - Canonical: https://genetixbay.com/knowledge/nutrients/molybdenum.html - Category: Nutrients · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Does cannabis need molybdenum?** Yes, cannabis needs molybdenum, but only in minuscule amounts, about 0.01-0.05 mg/L in solution. Molybdenum is a cofactor for nitrate reductase, the enzyme that turns nitrate into usable nitrogen. A complete micronutrient mix supplies plenty in soilless and hydro systems, and deficiency is rare, mainly a problem of acidic soils below about pH 5.5. **What does molybdenum deficiency look like?** Molybdenum deficiency has not produced visible symptoms in cannabis: in one 9-week trial, plants given no molybdenum showed no symptoms or biomass loss despite 96% lower leaf molybdenum. In other crops it looks like nitrogen deficiency, with pale yellowing of older and middle leaves, marginal scorch and cupped or narrow leaves, called whiptail in brassicas. **How much molybdenum in a hydroponic solution?** A cannabis hydroponic solution needs about 0.01-0.05 mg/L molybdenum; a cannabis trial used about 0.01 mg/L and greenhouse standards use about 0.05 mg/L. Sodium molybdate dihydrate is about 39.7% molybdenum, so 0.1 mg/L of product gives roughly 0.04 mg/L. Make a concentrated stock, because weighing a few milligrams for a tank is impossible on kitchen scales. **Why would a plant fed nitrate still look nitrogen deficient?** A cannabis plant fed plenty of nitrate can still look nitrogen deficient if root-zone pH is off, roots are failing, or, rarely, molybdenum is short. Without molybdenum, nitrate reductase cannot work, so nitrate accumulates in leaves unused. Check pH and roots first; molybdenum sits near the bottom of the list and matters mainly in acidic soils. **Is molybdenum available at low pH?** No, molybdenum becomes less available at low pH, the opposite of most micronutrients. As the molybdate anion it binds to iron and aluminium oxides in acidic soils, so shortages appear below about pH 5.5 in acid mineral soils. Liming the soil raises pH and releases molybdenum, which is the real fix in that situation. **Short answer.** Molybdenum is a cofactor for nitrate reductase, the enzyme that converts nitrate into usable nitrogen, and for a few other enzymes including one in the abscisic-acid pathway [1]. Cannabis needs a minuscule amount: about 0.01–0.05 mg/L Mo in solution. In a 9-week trial, cannabis grown with no Mo showed no visible symptoms and no biomass loss, even though leaf Mo was 96% lower [2]. Deficiency is rare. Unlike most micronutrients, Mo gets *less* available as pH falls. ## What's happening Mo is taken up as the molybdate anion (MoO₄²⁻). Like phosphate, it binds to iron and aluminium oxides in acidic soils, and liming releases it [1]. In soilless and hydro, a complete micronutrient mix supplies plenty. Mo is moderately mobile in the plant [3]. When Mo is short, nitrate accumulates in leaves but cannot be reduced, so a plant fed plenty of nitrate looks N-deficient. Kaiser et al. note the phenotype is often misdiagnosed because symptoms appear as downstream effects of the enzymes it supports [1]. ## How to recognise it - **Cannabis:** no visual symptoms after 9 weeks without Mo; leaf Mo 0.06 vs 1.46 mg/kg in controls [2]. Longer crops or seed-grown plants from Mo-poor parents could behave differently. - **Other crops (for reference):** general pale, N-deficiency-like yellowing of older and middle leaves, marginal scorch, cupped or narrow leaves ("whiptail" in brassicas) [1][3]. - **Toxicity:** plants tolerate high Mo; toxicity is very rare. The concern with excess Mo is for grazing animals, not cannabis. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution Mo | 0.01–0.05 mg/L | Cannabis trial used ≈0.01 mg/L [2]; greenhouse standard ≈0.05 mg/L [4] | | Leaf Mo, survey | 0.5–1.5 mg/kg | Survey range cited in [2]; NC State AG-904 gives no Mo range | | Leaf Mo at 9 weeks with none supplied | ~0.06 mg/kg, no symptoms | [2] | | Soil pH where Mo gets scarce | Below ~5.5 | Acid mineral soils [1] | ## What to check first 1. **N symptoms that don't respond to N:** consider pH, roots and only then Mo. 2. **Acidic soil:** raise pH with lime; that releases Mo [1]. 3. **DIY recipe:** does your micronutrient mix include any Mo source? ## How to fix it - Sodium molybdate dihydrate (≈39.7% Mo): 0.1 mg/L product ≈ 0.04 mg/L Mo. Ammonium molybdate (≈54% Mo) also works. - Make a concentrated micronutrient stock; weighing 4 mg for a 100 L tank is impossible on kitchen scales. For example, 1 g sodium molybdate in 1 L water gives a stock where 1 mL per 10 L ≈ 0.04 mg/L Mo. - In acidic soil, liming is the real fix. ## How to confirm it worked If Mo was limiting, pale leaves green within 1–2 weeks of a feed containing Mo. If nothing changes, the problem was elsewhere. ## Common mistakes - Blaming Mo for any yellowing. It is near the bottom of the differential list. - Overdosing because the number looks tiny. ## Evidence - Mo as a cofactor for nitrate reductase and other enzymes: *Established* [1][3]. - Cannabis showing no visual Mo deficiency in a 9-week trial: *Supported* (one study [2]). - Mo targets for cannabis: *Grower practice* based on general greenhouse standards [4]. ## Sources 1. Kaiser BN, Gridley KL, Brady JN, Phillips T, Tyerman SD. 2005. The role of molybdenum in agricultural plant production. Annals of Botany 96(5):745-754. https://doi.org/10.1093/aob/mci226 2. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 4. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Nickel (Ni) in cannabis: essential, needed in traces, almost never worth adding > Nickel became the most recently accepted essential plant micronutrient in 1987; its known job is activating urease, the enzyme that breaks down urea. Requirements are so small that contamination in salts, water and media normally covers them, and there is no published evidence of nickel deficiency in cannabis. Do not add nickel unless you feed urea in a very pure system; excess nickel is toxic and cannabis is known to accumulate metals. - Canonical: https://genetixbay.com/knowledge/nutrients/nickel.html - Category: Nutrients · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Does cannabis need nickel?** Cannabis, like all higher plants, needs nickel as an essential micronutrient, but only in traces. Nickel was accepted as essential in 1987, after barley grown for three generations without it failed to produce viable grain. Contamination in fertiliser salts, water and media normally covers the requirement, and no nickel deficiency has been published in cannabis. **Should I add nickel to my hydroponic nutrients?** No, you should not add nickel to normal cannabis hydroponic nutrients; the added amount should be 0 mg/L because impurities in salts and water already cover the tiny requirement. The only exception is feeding urea in an unusually pure system, and switching to nitrate nitrogen avoids that need entirely. Excess nickel is toxic and cannabis accumulates metals. **What does nickel do in plants?** Nickel's known job in plants is activating urease, the enzyme that breaks urea down into ammonium. Without it, urea from fertiliser and from the plant's own nitrogen recycling builds up in leaves to toxic levels and can cause tip necrosis in sensitive species. Nickel is mobile in the phloem and moves into seeds, which is why deficiency affected barley seed viability. **Can urea fertilizer cause leaf tip burn without nickel?** In nickel-deficient plants, urea can accumulate and cause leaf tip and margin necrosis, because urease needs nickel to break urea down. This has been documented in other crops but not in cannabis. For tip burn on a urea-containing feed, first rule out overfeeding, high EC, ammonium toxicity and potassium shortage; nickel is the last suspect. **Is nickel toxic to cannabis?** Excess nickel is toxic to plants, causing interveinal chlorosis that resembles iron deficiency, because nickel competes with iron, plus stunted roots and growth. Cannabis and hemp accumulate heavy metals from contaminated soils, which is a reason to keep nickel out. If you suspect toxicity, test water and soil, remove the source, and in soil raise pH to reduce availability. **Short answer.** Nickel is a genuine essential micronutrient: Brown, Welch and Cary showed in 1987 that barley grown for three generations in Ni-depleted conditions failed to produce viable grain [1]. Its known role is activating urease, which breaks urea into ammonium [2]. The requirement is so small that contamination in fertiliser salts, water and media normally covers it. There is no published report of nickel deficiency in cannabis. Do not add nickel unless you feed urea in an unusually pure system. ## What's happening Ni is the metal centre of urease. Without it, urea (from urea fertiliser and from the plant's own nitrogen recycling) builds up in leaves to toxic levels and causes tip necrosis in sensitive species [2]. Ni is mobile in the phloem and moves into seeds [2]. The amount needed is in the range of tens to a few hundred micrograms per kilogram of leaf dry weight [1][2]. Ordinary reagent and fertiliser-grade salts carry more than enough as impurities; that is also why Ni went unrecognised for so long (Epstein made the same point about contaminants and silicon [3]). ## How to recognise it - **Deficiency (other crops):** leaf tip and margin necrosis linked to urea accumulation; in barley, failure of seed viability [1][2]. Not documented in cannabis. - **Toxicity:** interveinal chlorosis similar to iron deficiency (Ni competes with Fe), stunted roots and growth [2]. Cannabis and hemp are effective accumulators of heavy metals from contaminated soils, which is a reason to keep Ni out of the flower, not add more. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution Ni (added) | 0 mg/L for normal feeds | Contaminants suffice; *grower practice* and greenhouse standards | | Solution Ni, if feeding urea in ultra-pure systems | ≤0.01–0.05 mg/L | | | Leaf Ni, sufficiency | ~0.01–0.1 mg/kg range | Order of magnitude from crop literature [1][2] | | Leaf Ni, toxicity in sensitive plants | >10 mg/kg | [2] | ## What to check first - Tip burn on a urea-containing feed: first rule out overfeeding, high EC, ammonium toxicity and K shortage. Ni is the last suspect. - Suspected Ni toxicity: test water and soil (industrial sites, some biosolids, stainless or plated fittings in poor condition). ## How to fix it - **Deficiency (rare):** switch from urea to nitrate-based N, which sidesteps urease entirely. If you must use urea, a trace of nickel sulfate hexahydrate (≈22% Ni) in the micronutrient stock. - **Toxicity:** remove the source; in soil, raising pH reduces Ni availability [2]. - **Safety:** nickel salts are skin sensitisers and suspected carcinogens; gloves, no dust. ## Common mistakes - Adding "complete" trace-element products with Ni to an already complete feed for no reason. - Assuming essential means "must be supplemented". ## Evidence - Ni is essential for higher plants: *Established* [1][2]. - Contaminant Ni covers needs in practice: *Supported* (agronomy consensus [2]); no cannabis study. - Benefit of Ni supplementation in cannabis: *No evidence*. ## Sources 1. Brown PH, Welch RM, Cary EE. 1987. Nickel: a micronutrient essential for higher plants. Plant Physiology 85(3):801-803. https://doi.org/10.1104/pp.85.3.801 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 3. Epstein E. 1994. The anomaly of silicon in plant biology. PNAS 91(1):11-17. https://doi.org/10.1073/pnas.91.1.11 --- # Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets > Nitrogen drives leaf growth and photosynthesis. Cannabis does best on mostly nitrate N (about 150–200 mg/L in soilless veg and early flower), with ammonium kept at or below about 10–30% of total N; above 30% ammonium, cannabis trials show toxicity and lost yield. Deficiency yellows the oldest leaves first; excess gives dark, clawed leaves and soft, leafy growth. - Canonical: https://genetixbay.com/knowledge/nutrients/nitrogen.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Transition, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How much nitrogen does cannabis need in veg and flower?** Cannabis needs roughly 160 mg/L nitrogen in veg, the optimum in a controlled pot trial where 30 mg/L was deficient and 240-320 mg/L was no better. In flower, a mineral DWC trial predicted a yield optimum near 194 mg/L. Liquid organic feeds in coir needed more on paper, about 212-261 mg/L, because organic nitrogen is less available. **Nitrate or ammonium for cannabis?** Cannabis does best on mostly nitrate nitrogen, with ammonium kept at or below about 10-30% of total nitrogen. Nitrate uptake makes the root zone pH rise, while ammonium uptake releases protons and drops pH. In a controlled trial, cannabinoids were highest under pure nitrate, and 10-30% ammonium did not substantially harm secondary metabolism. **Why are my bottom leaves turning yellow?** Bottom cannabis leaves turning evenly pale yellow, with the fade climbing upward, is the classic sign of nitrogen deficiency, because nitrogen is mobile and the plant strips old leaves to feed new growth. Check the stage first: a slow bottom-up fade in the last 2-3 weeks of flower is normal senescence. Also rule out overwatering, cold solution, root rot and pH. **What does nitrogen toxicity look like? Dark green clawed leaves?** Yes, nitrogen excess in cannabis typically shows as very dark green, glossy leaves with tips hooking down, called the claw, plus thin, soft stems and delayed or leafy flowering. Ammonium toxicity adds root browning, leaf-margin necrosis and signs of calcium, magnesium and potassium shortage. Claw can also come from overwatering, heat or pH, so check those too. **How many ppm N in a hydro nutrient solution?** A cannabis hydro nutrient solution typically carries about 150-200 ppm (mg/L) nitrogen in veg and early flower, mostly as nitrate. Seedlings and fresh clones get about 50-100 ppm at low EC of 0.6-1.0 mS/cm, as grower practice. Healthy recent mature leaves should test 3.3-5.0% nitrogen by dry weight; around 1.6% marks first deficiency symptoms. **Is ammonium bad for cannabis?** Ammonium is harmful to cannabis above about 30% of total nitrogen. In a controlled trial at 200 mg/L nitrogen, yield fell 46% as ammonium rose from 0 to 50%, plants at 50% showed toxicity, and plants at 100% died. Small amounts are fine: commercial calcium nitrate carries about 1% ammonium-N, so avoid fixing deficiencies with ammonium sulfate or urea in hydro. **Does lower nitrogen raise THC percentage?** Research shows lower nitrogen in flower can raise cannabinoid and terpene percentage while lowering total yield: in one controlled trial, concentrations were suppressed at higher nitrogen while inflorescence yield rose with nitrogen up to about 160 mg/L. It is a trade-off to set deliberately in the flower recipe, not a reason to flush, which starves the plant and is a myth. **How do I taper nitrogen before harvest?** To taper nitrogen before harvest, cut it over the last 3-4 weeks: about 75% of normal late-flower nitrogen at week minus 3, 50% at minus 2, 25% at minus 1 and 0-20 mg/L in the final days. Keep phosphorus, potassium, calcium, magnesium, sulfur and micros unchanged, using single salts or per-element dosing. This is GenetixBay grower practice, not yet trial-tested. **Short answer.** Nitrogen is the engine of leaf growth. In soilless and hydro systems cannabis does well on roughly 150–200 mg/L N, supplied mostly as nitrate (NO₃⁻), with ammonium (NH₄⁺) capped at about 10–30% of total N [1][2][3]. Too little N yellows the oldest leaves first and cuts yield hard; too much gives dark, glossy, clawed leaves and soft, leafy growth. Ammonium above about 30% of total N caused toxicity in a controlled cannabis trial, and 100% ammonium killed the plants [2]. ## What's happening N is part of every amino acid, protein, nucleic acid and chlorophyll molecule. Plants take it up as nitrate or ammonium. - **Nitrate** is the safe workhorse. Its uptake makes roots release hydroxide or bicarbonate, so the root zone **pH rises** on a nitrate feed (see [pH drift](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md)). - **Ammonium** is taken up fast and assimilated in the roots, which costs sugars. Its uptake releases protons, so the root zone **pH falls**. In excess it is toxic: it competes with K⁺, Ca²⁺ and Mg²⁺ for uptake and can damage roots [2]. In the Saloner and Bernstein NH₄/NO₃ trial (uniform 200 mg/L N, 0–100% ammonium), yield fell 46% as ammonium went from 0 to 50%, plants at 50% showed toxicity, and plants at 100% died. Cannabinoids were highest under pure nitrate; 10–30% ammonium did not substantially harm secondary metabolism, and the authors advise against ratios above 30% NH₄ [2]. ### The nitrogen and potency trade-off In flower, Saloner and Bernstein found that cannabinoid and terpenoid concentrations were suppressed at higher N supply, while inflorescence yield rose with N up to about 160 mg/L [8]. So lower N can raise cannabinoid and terpene **percentage** while lowering **total yield**. It's a trade-off to set deliberately with your flower recipe, not a reason to flush: a pre-harvest flush starves the plant while it is packing on yield and resin, and is a *Myth* (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). ### Late-flower N taper (instead of flushing) GenetixBay tapers N in the last 3–4 weeks, towards zero at the finish, and keeps P, K, Ca, Mg, S and the micros at normal late-flower strength. It puts the trade-off above to deliberate use: a little potency percentage for a little bulk, with the plant otherwise fully fed. *Grower practice*, widely recommended by experienced growers; this ramp hasn't been tested in a controlled trial. | Weeks before harvest | N (mg/L) | Everything else | |---|---|---| | −4 | 100–150 (normal late flower) | Full late-flower feed | | −3 | ~75–110 (about 75 %) | P, K, Ca, Mg, S and micros unchanged | | −2 | ~50–75 (about 50 %) | Unchanged | | −1 | ~25–40 (about 25 %) | Unchanged | | Final days | 0–20 | Unchanged; keep normal runoff | To do it you need per-element control: single salts with an N-free Ca source (see [hydroponic salts](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md)) or a per-element dosing controller. Diluting a 2-part cuts everything, not just N. N is **mobile** in the phloem. When supply falls short, the plant strips old leaves to feed new ones, so deficiency starts at the bottom (see [mobile vs immobile nutrients](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md)). ## How to recognise it **Deficiency.** Slight stunting, then even pale-yellowing of the lower foliage that climbs upward; advanced leaves go fully yellow, necrotic and drop [4]. In DWC flower trials, N deficiency appeared in flower week 3 at the lower fan-leaf tips, spread upward, fan leaves senesced by week 5, and inflorescence fresh weight was about 72% lower than control [5]. Red or purple petioles often accompany it, but that alone is not diagnostic (genetics and cold do it too). **Excess (and ammonium toxicity).** Very dark green, glossy leaves; leaf tips that hook down ("the claw"); thin, soft stems; delayed or leafy flowering. Ammonium toxicity adds root browning, leaf-margin necrosis and symptoms of Ca/Mg/K shortage because ammonium blocks their uptake [2]. Claw also has other causes (overwatering, heat, pH), so see [taco and canoeing leaves](https://genetixbay.com/knowledge/diagnosis/taco-canoeing-leaves.md). ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution N, seedlings and fresh clones | 50–100 mg/L | *Grower practice*; low EC (0.6–1.0 mS/cm) | | Solution N, veg | ~160 mg/L optimum; 150–200 mg/L working range | Pot trial, long photoperiod; 30 mg/L deficient, 240–320 mg/L no better [1] | | Solution N, flower (mineral, DWC) | ~194 mg/L predicted optimum for yield | Response-surface trial, one high-THC cultivar [3] | | Solution N, flower (liquid organic, coir) | 212–261 mg/L N | Organic N is less available; one substrate [6] | | NH₄⁺ share of total N | ≤10–30% | >30% risks toxicity; 50% cut yield 46% [2] | | Leaf N, healthy (most recent mature leaf) | 3.3–5.0% dry weight | NC State floral hemp range [7] | | Leaf N at first deficiency symptoms | ~1.6% | Cannabis, sand culture [4] | ## What to check first 1. **Stage.** A slow bottom-up fade in the last 2–3 weeks of flower is normal senescence, not a problem to fix. 2. **Root zone.** Overwatering, cold solution (<18 °C / 64 °F), root rot or root aphids cause "N deficiency" in a well-fed plant. Check roots before the feed (see [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)). 3. **pH.** Outside about 5.5–6.5 in soilless, uptake of several nutrients suffers. 4. **EC in and out.** Low input EC means real hunger; high runoff EC means salts or poor uptake. 5. **Feed history.** A "bloom" base with very low N switched on at flip is a classic cause of early-flower yellowing. ## How to fix it - **Mineral hydro/coco:** raise N by 10–20% (for example 150 → 170 mg/L), using calcium nitrate or potassium nitrate. Do not double it. - **Keep ammonium modest.** Most commercial calcium nitrate contains about 1% ammonium-N (5–8% of its N); that is fine. Do not "fix" a deficiency with ammonium sulfate or urea in hydro. - **Soil/organic:** liquid organic N or a top-dress (blood meal, feather meal, fish hydrolysate) at label rate; expect 1–2 weeks before response because microbes must mineralise it. - **Toxicity:** cut N 20–30%, feed at lower EC for one or two cycles, check runoff EC. If ammonium-based, switch to a nitrate-dominant feed and raise root-zone pH back into range. ## How to confirm it worked - Yellowing stops climbing within 5–7 days; already-yellow leaves stay yellow. - New leaves come in mid-green. For excess, new leaves stop clawing within about a week. - If you can, a tissue test on the most recent mature leaf lands at 3.3–5.0% N [7]. ## Common mistakes - Feeding more N to a plant with sick roots. - Treating harvest-time fade as a deficiency. - Running high-ammonium "organic-style" salts in DWC and then chasing a falling pH. - Assuming dark green always means healthy. ## Evidence - Bottom-up yellowing as the N deficiency signature in cannabis: *Established* (two controlled studies in different systems [4][5]). - Veg optimum near 160 mg/L N and flower optimum near 190–200 mg/L N in mineral feeds: *Supported* (single-cultivar trials [1][3]); organic feeds need higher N because availability is lower [6]. - Ammonium above ~30% of N harms cannabis: *Supported* (one rigorous trial, consistent with other crops [2]). - Purple petioles as a reliable N sign: *Contested*. - Lower N in flower raising cannabinoid and terpene percentage while lowering yield: *Supported* (one controlled trial [8]); a trade-off, not a reason to flush. - Tapering N towards zero over the last 3–4 weeks while feeding everything else: *Grower practice* (GenetixBay house approach). ## Sources 1. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 2. Saloner A, Bernstein N. 2020. Response of medical cannabis (Cannabis sativa L.) to nitrogen supply under long photoperiod. Frontiers in Plant Science 11:572293. https://doi.org/10.3389/fpls.2020.572293 3. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 4. Bevan L, Jones M, Zheng Y. 2021. Optimisation of nitrogen, phosphorus, and potassium for soilless production of Cannabis sativa in the flowering stage using response surface analysis. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 5. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 6. Llewellyn D, Golem S, Jones AMP, Zheng Y. 2023. Foliar symptomology, nutrient content, yield, and secondary metabolite variability of cannabis grown hydroponically with different single-element nutrient deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 7. Caplan D, Dixon M, Zheng Y. 2017. Optimal rate of organic fertilizer during the flowering stage for cannabis grown in two coir-based substrates. HortScience 52(12):1796-1803. https://doi.org/10.21273/HORTSCI12401-17 8. Suchoff D, McGinnis M, Davis J, Whipker B, Hicks K. 2026. Hemp leaf tissue nutrient ranges: refinement of reference standards for floral hemp. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges --- # Nutrient antagonism and Mulder's chart: what the evidence actually says > Mulder's chart is a mid-20th-century wheel of nutrient interactions. It is a useful reminder that excess of one nutrient can suppress another, but it is a teaching sketch, not a quantitative tool. A review of 117 published interactions found synergy far more often than antagonism; the antagonisms that reliably matter in practice are among cations (K, Ca, Mg, NH4, Na), phosphorus with zinc and iron, and iron with manganese. - Canonical: https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is Mulder's chart?** Mulder's chart is a circular diagram, attributed to the Dutch soil scientist D. Mulder in the early 1950s, showing which plant nutrients suppress or help each other. It is a useful teaching sketch that reminds growers excess of one nutrient can cause shortage of another, but it has no doses and is not a quantitative tool for adjusting a cannabis feed. **Does too much potassium lock out magnesium?** Yes, too much potassium can suppress magnesium and calcium uptake through cation competition at the root, an established effect in plant nutrition that has also been observed in cannabis. A standard Hoagland-type solution runs about 235 mg/L potassium, 200 mg/L calcium and 49 mg/L magnesium; antagonism bites when potassium climbs far above calcium, as happens when PK boosters are stacked. **What is nutrient lockout and is it real?** Nutrient lockout is real in a narrow sense, but most cases growers call lockout are actually root-zone pH or root failures. Genuine antagonism mostly involves competing cations, phosphorus with zinc and iron, and iron with manganese. Fix pH before any lockout theory, confirm with runoff EC or a lab test, and flush only for real salt build-up. **Which nutrients compete with each other?** The nutrient competitions that reliably matter are among cations, where potassium, ammonium and sodium suppress calcium and magnesium and calcium suppresses magnesium, plus phosphorus with zinc and iron, iron with manganese, and copper and zinc with iron. A review of 117 published interactions found synergy more often than antagonism: 43 synergistic against 17 antagonistic. **Can too much phosphorus cause zinc deficiency?** Excess phosphorus is associated with reduced zinc effectiveness and poorer iron movement in many crops, through precipitation and interference inside the plant. This is supported by general crop research but has not been tested in cannabis. Keeping solution phosphorus at moderate levels and not stacking bloom boosters avoids the risk. **Short answer.** Mulder's chart is a circular diagram, attributed to the Dutch soil scientist D. Mulder in the early 1950s, showing which nutrients suppress (antagonise) or help (synergise) each other [7]. It is a good reminder that excess of one nutrient can cause shortage of another. But it is a teaching sketch, not a calculator. A review of 117 published interactions found synergy more often than antagonism; the antagonisms that reliably matter are among the cations (K, Ca, Mg, NH₄, Na), phosphorus with zinc and iron, and iron with manganese [1][6]. ## What's happening "Antagonism" covers several different mechanisms that the chart lumps together: 1. **Competition at root uptake.** Ions with similar charge compete for transporters and for the root's charge balance. K⁺, NH₄⁺ and Na⁺ suppress Ca²⁺ and Mg²⁺ uptake; Ca²⁺ suppresses Mg²⁺ [6]. In cannabis, higher K supply was linked to lower Ca and Mg uptake [3], and high ammonium reduced cation uptake and yield [4]. 2. **Precipitation in the root zone or tank.** Ca with phosphate or sulfate; Fe with phosphate at high pH. That is chemistry, not physiology, and pH controls most of it (see [pH and availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)). 3. **Interference inside the plant.** High P is associated with reduced Zn effectiveness and Fe translocation in many crops [6]; Fe and Mn compete; Cu and Zn compete. 4. **Dilution.** Adding a growth-limiting nutrient makes the plant bigger, which lowers the *concentration* of others in tissue without any real antagonism. Shiponi and Bernstein saw P supply reshape the whole cannabis ionome, partly this way [5]. Rietra et al. reviewed 94 papers describing 117 interactions across all macro- and micronutrients: 43 were synergistic, 17 antagonistic, 35 zero-interaction, the rest non-significant or negative. Antagonistic effects on yield were found most often for divalent cations [1]. The authors also note that the number of studied interactions is low, which makes firm conclusions difficult [1]. ## The interactions worth knowing | Excess of | Can suppress | Mechanism | Strength of evidence | |---|---|---|---| | K | Mg, Ca | Cation competition | *Established* [6]; observed in cannabis [3] | | NH₄⁺ | K, Ca, Mg | Cation competition, root damage | *Established* [6]; cannabis [4] | | Ca | Mg, (K) | Cation competition | *Established* [6] | | Na | K, Ca | Cation competition, membrane displacement | *Established* [6] | | P | Zn, Fe, (Cu) | Precipitation and in-plant interference | *Supported* in crops [6]; untested in cannabis | | Fe | Mn (and the reverse) | Uptake competition | *Supported* [6] | | Cu, Zn | Fe | Competition | *Supported* [6] | | N (adequate) | Most others improve | Synergy via growth | *Established* [1] | | High bicarbonate/pH | Fe, Mn, Zn, Cu, B, P | Solubility, not antagonism | *Established*; see [pH and availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) | ## How to use this 1. **Keep ratios sensible.** A standard Hoagland-type solution runs roughly K 235, Ca 200, Mg 49 mg/L (K:Ca:Mg ≈ 1.2:1:0.25). Big departures from that, especially K far above Ca, are where antagonism bites. 2. **Fix pH before any "lockout" theory.** Most so-called lockout is pH or root-zone failure. 3. **Don't stack boosters.** A PK booster plus a bloom base plus Cal-Mag can push K, P and Ca far beyond need. 4. **Confirm with numbers.** Runoff EC, a lab solution test, or a leaf tissue test beat reading a wheel. ## Common mistakes - Treating Mulder's chart as quantitative. It has no doses. - Calling every deficiency "lockout" and flushing with plain water, which removes everything. A root-zone flush is for real salt build-up (runoff EC far above input), done with a light solution in soilless media (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). - Ignoring dilution when reading tissue tests. ## Evidence - Cation antagonism (K/NH₄/Na vs Ca/Mg): *Established* in plant nutrition [6], *Supported* in cannabis [3][4]. - Synergism being more common than antagonism in yield studies: *Supported* (one large review [1]). - Mulder's chart as a diagnostic tool: *Grower practice*; origin details - Fageria 2001 citation details ## Sources 1. Rietra RPJJ, Heinen M, Dimkpa CO, Bindraban PS. 2017. Effects of nutrient antagonism and synergism on yield and fertilizer use efficiency. Communications in Soil Science and Plant Analysis 48(16):1895-1920. https://hub.ifdc.org/handle/20.500.14297/2410 2. Fageria VD. 2001. Nutrient interactions in crop plants. Journal of Plant Nutrition 24(8):1269-1290. https://doi.org/10.1081/PLN-100106981 3. Saloner A, Sacks MM, Bernstein N. 2019. Response of medical cannabis genotypes to K supply under long photoperiod. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 4. Saloner A, Bernstein N. 2022. Nitrogen source matters. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 5. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323 6. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 7. ICL Growing Solutions. Interactions between plant nutrients: a deep understanding. https://icl-growingsolutions.com/agriculture/knowledge-hub/interactions-between-plant-nutrients-a-deep-understanding/ --- # Organic vs mineral nutrition for cannabis: what the trials show > Plants absorb the same ions whether they came from a bag of salts or from compost; the differences are in speed, precision and what else comes along. Controlled cannabis trials show mineral feeds deliver nutrients more efficiently and organic liquid feeds need higher nominal N to match them. Organic and lower-input regimes can keep cannabinoid content per gram up while yield falls. Plants mostly don't care where the ions come from; slight differences in flavonoids or terpenes are possible but unproven, and no controlled blind trial shows organic flower tastes better. - Canonical: https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is organic or synthetic nutrients better for cannabis?** Neither organic nor synthetic nutrients is inherently better for cannabis; the GenetixBay house position is that plants mostly don't care where the ions come from. Mineral feeds give immediate availability and precise control, suiting hydro and coco, while organic feeds are slower and more forgiving in living soil. A controlled trial found mineral fertiliser delivered nutrients more efficiently. **Does organic cannabis taste better?** No controlled blind trial has shown that organic cannabis tastes or smokes better than mineral-fed cannabis. Slight differences in flavonoids or terpenes are possible but unproven, and roots absorb the same ions from either source. Judge on your own outcomes, including blind taste comparisons with a friend, rather than on labels. **Can I use organic nutrients in hydroponics?** Organic nutrients suit recirculating hydroponics such as DWC, NFT and aero poorly, because they cause biofilm, odour and clogging and supply little nitrate until microbes mineralise them. Pouring sugary or protein-rich organics into a DWC reservoir can grow root rot. Specialised organic-compatible systems with biofilters exist, but mineral salts are the usual choice for recirculating hydro. **Why do organic feeds need more nitrogen?** Organic feeds need more nominal nitrogen because most of their nitrogen sits in organic molecules that microbes must mineralise before roots can use it. In coir trials, a liquid organic fertiliser had a veg optimum near 389 mg/L nitrogen and a flower optimum of 212-261 mg/L, compared with about 160 mg/L for mineral feeds in veg. **Do humic acids help cannabis?** Humic acids gave cannabis no big potency gain in controlled research. One study found humic acid supplementation reduced the natural variation of cannabinoids across different parts of the plant, while enhanced NPK raised CBG by 71% and lowered CBN. Neither treatment was a major win for THC, so humic acids are best seen as optional. **Short answer.** Roots absorb the same ions (nitrate, ammonium, phosphate, potassium and so on) whether they came from salts or compost [6]. The differences are speed, precision and what else comes along: microbes, organic matter and variability. Controlled cannabis trials show mineral feeds deliver nutrients more efficiently, organic liquid feeds need higher nominal N to match them, and lower-input regimes can keep cannabinoid content per gram up while yield falls [1][2][3]. **House position: plants mostly don't care where the ions come from.** There may be slight differences in flavonoids or terpenes, but that's unproven; no controlled blind trial has shown organic flower tastes or smokes better. ## What's happening - **Mineral (salt-based) feeds** dissolve as plant-available ions immediately. You control exact ppm and ratios, which makes hydro and coco precise and repeatable. The cost is no buffer: mistakes hit the roots at once. - **Organic feeds** (manures, meals, composts, fish and plant hydrolysates) hold most of their N, P and S in organic molecules. Microbes must mineralise them first. Release depends on temperature, moisture, oxygen and soil life, so it is slower and harder to predict, but more forgiving in soil. What the cannabis research shows: - **Nutrient efficiency.** In an indoor CBD trial comparing mineral and organic fertiliser at three rates in flower, the organic fertiliser had lower nutrient acquisition and utilisation efficiency, and differences in CBD yield between fertiliser types appeared at final harvest, attributed to uptake limits from the organic nutrient forms [1]. - **Lower input, similar CBD.** In the same trial, lower nutrient levels reduced flower yield but raised CBD concentration enough that plants kept about 95% of CBD yield with one-third less fertiliser [1]. - **Organic N rates.** Liquid organic fertiliser (2.0-0.87-3.32) in coir: veg optimum about 389 mg/L N [2]; flower optimum 212–261 mg/L N in one substrate, with higher rates boosting yield but diluting cannabinoids [3]. Mineral optima are lower (about 160 mg/L N in veg) [5], consistent with lower availability of organic N. - **Humic acid.** Humic acid supplementation reduced the natural spatial variability of cannabinoids across the plant; enhanced NPK raised CBG by 71% and lowered CBN [4]. Neither is a big win for potency. ## Comparison | | Mineral | Organic | |---|---|---| | Availability | Immediate | Delayed; microbe-dependent | | Control of ppm and ratios | Precise | Approximate | | Buffer against mistakes | Low | High in living soil | | Suits DWC, NFT, aero | Yes | Poorly: biofilm, odour, clogging, low nitrate | | Suits living soil | Unnecessary, can harm soil life at high EC | Yes | | Runoff and waste | Recoverable; P leaching if overfed | N and P can leach from manures too | | Flavour or "smoothness" | Possible slight flavonoid/terpene differences, unproven | Same | ## How to choose 1. **System first.** Recirculating hydro: mineral (or specialised organic-compatible systems with biofilters). Coco and drip: either; mineral is easier to dial. Living soil: organic amendments and top-dressing. 2. **Measure anyway.** Organic growers still benefit from pH and runoff EC checks; soil tests every cycle or two. 3. **Don't mix philosophies at random.** Salt feeds at high EC in a living soil can stress its microbes; a little supplemental mineral feeding is common and fine. 4. **Judge on your outcomes**: yield, potency test, and blind taste comparisons with a friend, not labels. ## Common mistakes - Feeding organic liquids at mineral N rates and getting N-deficient plants [2][3]. - Pouring sugary or protein-rich organics into a DWC reservoir and growing root rot (see [root rot](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md)). - Believing "chemical" nutrients leave residues that organic ones don't. The ions in the plant are identical, and neither is "flushed out" with plain water at the end: pre-harvest flushing is a *Myth* that costs yield and resin (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). ## Evidence - Plants take up inorganic ions regardless of source: *Established* [6]. - Mineral feeds more efficient than organic in controlled cannabis trials: *Supported* (one trial [1], consistent with N-rate studies [2][3][5]). - Lower input sustaining cannabinoid yield: *Supported* [1]. - Plants mostly don't care where the ions come from: house position, consistent with [6]. - Organic tastes or smokes better, or differs in flavonoids/terpenes: unproven; no controlled blind trial found. ## Sources 1. Massuela DC, Munz S, Hartung J, Nkebiwe PM, Graeff-Honninger S. 2023. Cannabis Hunger Games: nutrient stress induction in flowering stage - impact of organic and mineral fertilizer levels on biomass, cannabidiol (CBD) yield and nutrient use efficiency. Frontiers in Plant Science 14:1233232. https://doi.org/10.3389/fpls.2023.1233232 2. Caplan D, Dixon M, Zheng Y. 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307-1312. https://doi.org/10.21273/HORTSCI11903-17 3. Caplan D, Dixon M, Zheng Y. 2017. Optimal rate of organic fertilizer during the flowering stage for cannabis grown in two coir-based substrates. HortScience 52(12):1796-1803. https://doi.org/10.21273/HORTSCI12401-17 4. Bernstein N, Gorelick J, Zerahia R, Koch S. 2019. Impact of N, P, K, and humic acid supplementation on the chemical profile of medical cannabis. Frontiers in Plant Science 10:736. https://doi.org/10.3389/fpls.2019.00736 5. Saloner A, Bernstein N. 2020. Frontiers in Plant Science 11:572293. https://doi.org/10.3389/fpls.2020.572293 6. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 --- # Per-element feeding tricks: what growers adjust, stage by stage > Experienced growers change single elements by stage rather than just turning the whole feed up or down: tapering nitrogen in late flower, cutting the ammonium share after the flip, a little extra calcium through the stretch, small magnesium, boron and zinc bumps in flower, silicon in veg. Most of these tricks are grower practice with little or no controlled research behind them. Two popular ones are contradicted by research: extra phosphorus above about 30–60 mg/L and potassium 'ramps' above about 250 mg/L did not raise yield or cannabinoids in controlled cannabis trials. Sugars and molasses feed soil microbes only, not the plant, and do harm in hydro. The GenetixBay approach is to taper nitrogen and keep everything else fed, which needs single salts or per-element dosing. - Canonical: https://genetixbay.com/knowledge/nutrients/per-element-tricks.html - Category: Nutrients · Level: Advanced - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Veg, Transition, Flower, Ripening · Systems: Coco, Rockwool, DWC, RDWC, NFT, Ebb and flow, Drip, Aeroponics - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What nutrient tricks do growers use in late flower?** In late flower, experienced cannabis growers change single elements rather than the whole feed: tapering nitrogen towards zero over the last 3-4 weeks, swapping calcium nitrate for an N-free calcium source, a small magnesium bump to about 65-75 mg/L, and slight boron and zinc increases. Most of these are grower practice with little controlled testing; the GenetixBay rule is taper nitrogen, keep everything else fed. **Should I raise potassium in late flower?** Raising potassium in late flower is not supported by research: a controlled deep-water cannabis trial found no yield response anywhere between 60 and 340 mg/L potassium. Pushing potassium above about 300 mg/L commonly induces magnesium deficiency and calcium problems through cation competition. Keep potassium near 200-270 mg/L, with calcium at or above potassium in charge terms. **Does more phosphorus in flower make bigger buds?** More phosphorus in flower does not make bigger cannabis buds once the feed supplies about 30-60 mg/L; that claim is a myth. Four independent controlled trials agree: in one, 30 mg/L already gave about 80% of maximum yield, and in another, 25, 50 and 75 mg/L gave the same yield while leachate phosphorus rose. Hold 40-60 mg/L. **How much ammonium should be in a flowering feed?** A flowering cannabis feed should keep ammonium at or below about 10% of total nitrogen, dropping towards 0-5% in late flower, after 10-20% in veg. In a controlled trial cannabinoids were highest under pure nitrate. Cutting ammonium makes root-zone pH drift up faster, so plan more pH-down and use sulfuric or phosphoric acid rather than nitric. **Should I add extra calcium during the stretch?** Adding extra calcium during the stretch, raising it from about 150 to 170-190 mg/L in flower weeks 1-3, is grower practice with no cannabis dose-response study behind it. The mechanism is sound, since fast growth builds a lot of new cell wall, but most stretch-time calcium deficiency is a delivery problem. Fix VPD and roots first. **Does sulfur increase terpenes or skunky smell?** Extra sulfur does not increase terpenes; terpenes are hydrocarbons containing no sulfur, so that claim is a myth as a mechanism. The skunky note does come from volatile sulfur compounds, chiefly 3-methyl-2-butene-1-thiol, but no one has shown that feeding more sulfate raises them. Raising sulfur to 150-200 mg/L is untested grower practice. **Should I keep silica in flower?** Whether to keep silica in cannabis flower is unresolved: stopping it around flower week 3-5 and running it to harvest are both grower practice with no evidence behind either. Growers commonly use 20-50 mg/L silicon from potassium silicate in veg and early flower. If you stop it, remember potassium silicate also supplied some potassium. **Does molasses make buds sweeter?** No, molasses does not make cannabis buds sweeter or fatter; that is a myth. Molasses and sugars feed soil microbes only, because plants make their own sugars by photosynthesis and do not take up meaningful sucrose through the roots. Taste comes from terpenes, plant health, drying and curing. In hydro, sugars feed biofilm, strip dissolved oxygen and raise root rot risk. **Should I put plants in darkness before harvest?** No, putting cannabis in 24-72 hours of darkness before harvest is a myth, and the GenetixBay founder calls it complete and utter nonsense. It cuts photosynthesis in the final, most critical days while the plant is still finishing resin. The founder has offered seeds for 20+ years to anyone who finds an unbiased peer-reviewed study showing a benefit; nobody has claimed it. **Do cold nights increase terpenes?** Cold nights do not increase terpenes, flavour or resin; those claims are a myth until peer-reviewed data shows otherwise. Night temperatures of about 15-18 C (59-64 F) in the last 1-2 weeks do bring out real anthocyanin colour, but only in cultivars that carry it. Going too cold slows ripening. **Should I drop EC before harvest or just cut nitrogen?** Cut only nitrogen before harvest rather than dropping the whole EC. A 20-40% whole-feed cut in the last 1-2 weeks lowers nitrogen but also starves potassium, calcium, magnesium, sulfur and micros while flowers are still adding weight and resin. The GenetixBay position is an element-specific taper. The one valid reason to lower input EC late is a salty root zone. **How do I taper nitrogen without dropping calcium?** To taper nitrogen without dropping calcium, replace calcium nitrate with an N-free source. Gypsum at 0.6 g/L supplies about 140 mg/L calcium and 110 mg/L sulfur but must dissolve directly in the final solution, not a concentrate. Small doses of calcium chloride can fine-tune, keeping chloride below about 50-70 mg/L. Hold calcium at 130-180 mg/L. **Short answer.** Good growers don't just turn the whole feed up or down. They move single elements: nitrogen tapered towards zero in the last 3–4 weeks, less ammonium after the flip, a little extra calcium through the stretch, small magnesium, boron and zinc bumps in flower, silicon in veg. Most of these are *Grower practice*: sensible, widely used, and barely tested. Two popular tricks are flatly contradicted by controlled cannabis trials: **more phosphorus** above about 30–60 mg/L and **potassium ramps** above about 250 mg/L did not raise yield or cannabinoids [3][4][5][6]. Sugars and molasses do nothing useful in mineral hydro. GenetixBay's own rule is simple: **taper nitrogen, don't flush, keep everything else fed**. A bottled 2-part can't do that; single salts or per-element dosing (what Jardin is built for) can. ## How to read this article Every trick below is a **change from a base feed**, not a recipe on its own. The base is the flower recipe in [building a feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md): roughly N 150, P 50, K 250, Ca 150, Mg 55, S 115, Fe 2.5, Mn 0.5, Zn 0.3, B 0.4, Cu 0.08, Mo 0.04 mg/L at about 1.8–2.0 mS/cm. All amounts are mg/L (ppm by mass of the element) in the solution going to the roots. Salt percentages are in [hydroponic salts explained](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md); 1 g/L of a salt gives (percent × 10) mg/L of each element. Two rules before you touch anything: 1. **Change one thing at a time** and write it down. If you move N, K and Mg in the same week, you'll never know which one did what. 2. **Every cation you add competes with the others.** Raising K pushes down Ca and Mg uptake; raising Mg or Ca pushes down K; ammonium pushes down all three. See [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md). ## The tricks at a glance | Trick | Stage | Change from base | Evidence | |---|---|---|---| | N taper | Last 3–4 weeks | N stepped down to ~25 % then 0–20 mg/L; everything else unchanged | *Grower practice* (house approach); N/potency trade-off *Supported* [1] | | Lower ammonium share | Flip onwards | NH₄ 10–20 % of N in veg → ≤10 % in flower | *Supported* [2] | | "More P in flower" / PK weeks | Mid flower | P raised to 80–150+ mg/L | *Myth* beyond ~30–60 mg/L [3][4][5][6] | | K ramp | Mid–late flower | K 250 → 300–400 mg/L | *Contested*: no yield response 60–340 mg/L [6] | | Extra Ca in the stretch | Flower wk 1–3 | Ca 150 → 170–190 mg/L | *Grower practice* | | N-free Ca source late | Taper weeks | Swap calcium nitrate for gypsum / a little CaCl₂ | *Established* chemistry; needed for the taper | | Late Mg bump | Flower wk 5–end | Mg 55 → 65–75 mg/L | *Grower practice*; Mg–cannabinoid link *Supported* (one lab) | | Extra S for aroma | Mid–late flower | S 115 → 150–200 mg/L | *Grower practice*, untested; "S for terpenes" *Myth* as a mechanism | | Si in veg, stop in flower | Veg → mid flower | 20–50 mg/L Si, then 0 | *Grower practice*; stopping or keeping both untested | | Fe chelate by pH | Any | EDTA / DTPA / EDDHA by root-zone pH | *Established* | | B and Zn bump | Flower | B 0.4 → 0.5–0.6; Zn 0.3 → 0.4–0.5 | *Grower practice* | | Mn, Mo, Cu | Any | Don't push | Caution: narrow windows | | Cl, Na | Any | Keep low (Cl < 50–70, Na < 50) | *Supported* | | Crop-steering EC ramp | Flip, late flower | Input EC up 0.4–0.8 mS/cm for generative steer | *Grower practice* | | Late-flower EC drop | Last 1–2 weeks | Whole feed −20–40 % | *Grower practice*; inferior to an N-only taper | | Molasses / sugars | Flower | 1–5 mL/L | Feeds soil microbes only, not the plant; *Myth* for the plant, harmful in hydro | | Amino acids, fulvic/humic | Any | Label rate | *Contested* | | Cold nights, darkness, drought | Last 1–2 weeks | Non-nutrient | Cold: colour real, terpene/resin gain *Myth*; darkness *Myth*; mild drought *Supported*, house-endorsed | ## Nitrogen ### 1. The late-flower N taper **What and when.** From about 4 weeks before harvest, step N down: ~75 % of late-flower N at week −3, ~50 % at −2, ~25 % at −1, 0–20 mg/L in the final days. P, K, Ca, Mg, S and micros stay at normal late-flower strength. **Claimed benefit and mechanism.** Lower N late in flower shifts the plant from building leaf and protein towards secondary metabolism and senescence of the fan leaves. In a controlled cannabis trial, higher N suppressed cannabinoid and terpenoid concentrations while inflorescence yield rose with N up to about 160 mg/L [1]. So less N trades a little bulk for a little potency percentage. The taper puts that trade to deliberate use at the stage when the plant has finished building its canopy. **Evidence.** The N/potency trade-off: *Supported* (one controlled trial [1]). The taper ramp itself: *Grower practice*, widely recommended by experienced growers, not tested as a ramp. It is the **GenetixBay house approach**, and the reason Jardin doses per element. **Risks.** Start too early (more than ~4 weeks out) and you cut yield, because the plant still needs N to fill flowers. Fan leaves will yellow from the bottom; that's expected. Purple stems and leaves at this stage are mostly genetics and cold, not a sign to stop. **With single salts.** Drop calcium nitrate and potassium nitrate step by step. Take K from potassium sulfate and MKP, and Ca from an N-free source (trick 6). Full table and reasoning: [nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md). Why not to flush instead: [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). Pre-harvest flushing is a *Myth*, and a harmful one: it starves the plant while it is packing on its final weight and resin. ### 2. N form: the ammonium share **What and when.** Run 10–20 % of total N as ammonium (NH₄⁺) in veg, then cut to ≤10 % from the flip and towards 0–5 % in late flower. **Claimed benefit and mechanism.** Two things. **pH:** nitrate uptake makes roots release hydroxide and bicarbonate, so the root zone pH climbs; ammonium uptake releases protons and pulls pH down. A small ammonium share balances the two and holds pH steady in hydro without constant acid [10]. **Quality:** in a controlled cannabis trial (200 mg/L N, 0–100 % NH₄), cannabinoids were highest under pure nitrate; 10–30 % NH₄ was tolerated, 50 % cut yield by 46 % and showed toxicity, 100 % killed the plants [2]. **Evidence.** *Supported* (one rigorous cannabis trial [2], consistent with greenhouse practice [10]). The veg 10–20 % / flower ≤10 % split is *Grower practice* built on that. **Risks and antagonisms.** Ammonium competes with K⁺, Ca²⁺ and Mg²⁺ for uptake. Too much gives Ca/Mg/K-shortage symptoms on a well-fed plant and a sliding pH. Cutting ammonium in flower means **pH will drift up faster**; plan for more pH-down, which itself adds N (nitric acid), P (phosphoric) or S (sulfuric). Count it. **With single salts.** Greenhouse calcium nitrate already supplies about 7 % of its N as ammonium. To add more in veg, use small amounts of MAP or ammonium nitrate. In flower, use only calcium nitrate and potassium nitrate, and use sulfuric or phosphoric acid for pH-down during the taper so you're not sneaking N back in. ## Phosphorus ### 3. "More P in flower" and bloom boosters **What growers do.** Raise P from about 50 to 80–150 mg/L or more in mid flower, often as a "PK week" with a concentrated booster. **Claimed benefit.** Bigger, denser flowers, because P is in ATP and "flowering needs phosphorus". **What the research says.** It doesn't work above moderate P. Four independent controlled trials agree: - Shiponi and Bernstein tested 5–90 mg/L P in two cultivars: 30 mg/L gave about 80 % of maximum yield, flower P stopped rising above 30 mg/L, and cannabinoid concentration was highest below 30 mg/L, falling as yield rose (largely a dilution effect) [3]. - Westmoreland and Bugbee tested 25, 50 and 75 mg/L P: no significant effect on flower yield or cannabinoid concentration, but significantly more P in the leachate. Leaves took up 35 % more P and flowers 11 % more, with nothing to show for it [4]. - Hershkowitz et al. found the same again, and that raising overall nutrient concentration did not raise yield or cannabinoids either [5]. - Bevan et al. predicted a flower optimum near 59 mg/L P in deep-water culture [6]. **Evidence.** "More P = bigger buds" beyond ~30–60 mg/L: *Myth*. The yield plateau: *Established* (four trials). See ["bloom boosters": what's real](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) and [phosphorus](https://genetixbay.com/knowledge/nutrients/phosphorus.md). **Risks and antagonisms.** More runoff P (an environmental cost and money down the drain), and higher salinity. High P inducing **Zn and Fe deficiency** is well known in other crops [10]; in cannabis it is *possible but not shown*: the Shiponi and Bernstein ionome data didn't show a clear fall in flower Zn or Fe at 90 mg/L P [3]. Calcium phosphate also precipitates in concentrates and in high-pH solution. See [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md). **With single salts.** Don't add P. If you want a flower P setting, hold 40–60 mg/L from MKP. During the N taper, MKP and phosphoric acid are your N-free P sources, so the taper doesn't touch P. ## Potassium ### 4. The K ramp and the K:Ca:Mg balance **What growers do.** Raise K from about 250 to 300–400 mg/L from mid flower (weeks 4–8), usually with potassium sulfate or a PK booster. **Claimed benefit and mechanism.** K drives sugar transport into flowers, stomatal control and water relations, so more K should mean denser, heavier buds. **What the research says.** In a flowering deep-water trial, yield showed **no response to K anywhere between 60 and 340 mg/L** [6]. One trial, one cultivar, but it's the only dose-response data in flower, and it doesn't support the ramp. **Evidence.** K ramp for yield: *Contested* (strong grower lore; the one controlled trial found nothing [6]). K–Ca–Mg competition: *Established* in plant nutrition [10]. **Risks and antagonisms.** This is the real danger of the trick. K, Ca and Mg compete for uptake; pushing K above ~300 mg/L is a common cause of **induced Mg deficiency** (interveinal yellowing on older leaves) and Ca problems in late flower. Keep the cations balanced. A workable rule for soilless flower feeds, in meq/L: **K about 5–7, Ca about 7–9, Mg about 3.5–5**, i.e. Ca at or above K in charge terms. By mass, that is roughly K 200–270, Ca 140–180, Mg 45–60 mg/L. If you raise K, raise Mg a little with it (trick 7). See [potassium](https://genetixbay.com/knowledge/nutrients/potassium.md) and [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md). **With single salts.** If you want a modest K lift, add potassium sulfate: 0.11 g/L adds about 50 mg/L K and 20 mg/L S. During the N taper, K comes from potassium sulfate and MKP instead of potassium nitrate, which keeps K steady while N falls. ## Calcium ### 5. Extra Ca through the stretch and early flower **What and when.** Raise Ca from 150 to 170–190 mg/L in flower weeks 1–3, when the plant can double in height. **Claimed benefit and mechanism.** Ca builds cell walls and membranes, and fast stretch growth means a lot of new wall. Ca moves only in the transpiration stream and can't be moved from old leaves, so growers front-load it. **Evidence.** *Grower practice*. No cannabis Ca dose-response study exists. The mechanism is sound; whether the extra 20–40 mg/L matters is untested. Most stretch-time "Ca deficiency" is a **delivery** problem (low transpiration from high RH, cold or damaged roots, too much K, Mg or NH₄), not an empty tank. Fix VPD and roots first. See [calcium](https://genetixbay.com/knowledge/nutrients/calcium.md). **Risks.** More calcium nitrate also means more N at a time when the stretch is already leafy. Ca competes with Mg and K. The idea that LEDs create a need for extra Cal-Mag is a *Myth* (house position); demand is cultivar-, water- and medium-driven ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)). **With single salts.** 0.1 g/L calcium nitrate adds about 19 mg/L Ca and 16 mg/L N. If you don't want the N, use gypsum (below). ### 6. Switching to an N-free Ca source late **What and when.** During the N taper, replace calcium nitrate with an N-free calcium source so Ca stays at 130–180 mg/L while N falls. **Why.** Calcium nitrate is the main Ca source in nearly every feed. Cut it to cut N and you cut Ca too, in the weeks when the flowers are still building tissue. Without this switch, a taper turns into a Ca starvation. **Evidence.** The chemistry is *Established*; the need follows directly from the taper. **Options and limits.** - **Calcium sulfate (gypsum, CaSO₄·2H₂O, ≈23 % Ca, ≈18.6 % S).** 0.6 g/L gives about 140 mg/L Ca and 110 mg/L S. It dissolves only to about 2 g/L and slowly, so it can't go in a concentrate. Dissolve it straight into the final solution or dose it from a stirred slurry. It roughly doubles S; with Epsom and potassium sulfate also present, total S can pass 250 mg/L. That's tolerated by most crops but raises EC, so trim potassium sulfate if needed. - **Calcium chloride (CaCl₂·2H₂O, 27 % Ca, 48 % Cl).** Small doses only. 50 mg/L Cl brings just ~28 mg/L Ca, so use it to top up, not as the main source. Keep total Cl below ~50–70 mg/L ([chloride](https://genetixbay.com/knowledge/nutrients/chlorine.md)). - A blend works best: gypsum for the bulk, a little CaCl₂ to fine-tune. ## Magnesium ### 7. The late-flower Mg bump **What and when.** Raise Mg from about 55 to 65–75 mg/L from flower week 5 to harvest. **Claimed benefit and mechanism.** Mg is the centre of chlorophyll and activates the enzymes that fix carbon. Growers claim it keeps upper fans green longer, supports resin, and prevents the late-flower Mg fade. Magnesium supply did change cannabinoid and terpene production in Bernstein's lab (see [magnesium](https://genetixbay.com/knowledge/nutrients/magnesium.md)); the veg optimum is 35–70 mg/L [7]. **Evidence.** *Grower practice*. The bump itself hasn't been tested in flower. The claim that it "raises THC" isn't shown; the claim that it prevents a late-flower Mg shortage is plausible, especially if K is high. Much late-flower Mg yellowing is induced by too much K or Ca, or low pH, not by too little Mg in the tank. **Risks.** Mg competes with Ca and K. Above ~80–100 mg/L, Ca uptake suffers. Don't stack a Mg bump on a K ramp on a Ca bump: that's three cations all pushing up EC and each other. **With single salts.** Epsom salt (magnesium sulfate heptahydrate): 0.1 g/L adds about 10 mg/L Mg and 13 mg/L S. Avoid magnesium nitrate during the taper: it adds N. ## Sulfur ### 8. Extra S for aroma (terpenes and thiols) **What growers do.** Raise S from about 115 to 150–200 mg/L in mid and late flower, for a louder nose. **Claimed benefit and mechanism.** Two claims, and they need separating. - **"S raises terpenes."** Terpenes are hydrocarbons; they contain no sulfur. S feeds them only indirectly (enzymes, general metabolism). Once S is sufficient, there's no mechanism for more S to make more terpenes. Calling this a sulfur trick is a *Myth* as a mechanism. - **"S raises skunk."** This one has a real basis. The skunky note in cannabis comes from prenylated volatile sulfur compounds, chiefly 3-methyl-2-butene-1-thiol, which peak at maturity and in curing [8]. They do contain sulfur. But nobody has shown that feeding more sulfate raises them; they're present at tiny concentrations, so ordinary S supply is very unlikely to be limiting. **Evidence.** *Grower practice*, untested. The compounds are *Established* [8]; the feeding link isn't. See [sulfur](https://genetixbay.com/knowledge/nutrients/sulfur.md). **Risks.** Higher sulfate raises EC and can push Ca sulfate out of solution at high Ca. It does little harm at 150–200 mg/L, so it's a cheap experiment if you want to run one, side by side, same cultivar. **With single salts.** Swap some potassium nitrate for potassium sulfate (more S, same K), or use Epsom salt. During the taper, S rises anyway as nitrates come out and sulfates go in. ## Silicon ### 9. Si in veg; stop or keep in flower **What and when.** 20–50 mg/L Si from potassium silicate in veg and early flower for stiffer stems; many growers stop around flower week 3–5, others run it to harvest. **Claimed benefit and mechanism.** Silicon is deposited in cell walls and is beneficial in many crops against abiotic stress and some fungal disease. Cannabis does take it up (see [silicon](https://genetixbay.com/knowledge/nutrients/silicon.md)). **Evidence.** Si as a beneficial element: *Established* in other crops. Yield, stem strength or quality benefits in cannabis: *Grower practice*, no direct cannabis trial found. Stopping in flower (claims about ash, trichomes or "hard" buds) and keeping it in flower are both *Grower practice*; neither has evidence behind it. **Risks.** Potassium silicate is very alkaline and must go in first, into plain water, then pH-correct after everything else. It adds K, so count it against your K:Ca:Mg balance. It can precipitate with Ca in concentrates. **With single salts.** Dose from a separate stock, first in the mix. If you stop it in flower, remember you've also removed some K. ## Micronutrients ### 10. Iron chelate choice versus pH Choose the chelate for your root-zone pH, not for the price: **Fe-EDTA** holds iron to about pH 6.5, **Fe-DTPA** to about 7.5, **Fe-EDDHA** to about 9 [10]. In hydro and coco at pH 5.6–6.2, EDTA or DTPA is fine; DTPA gives headroom if pH drifts up (likelier once ammonium is cut in flower). In soil or with hard, alkaline water, use EDDHA. *Established*. No ramp is needed: hold 1.5–3.0 mg/L Fe. Too much iron competes with Mn. See [iron](https://genetixbay.com/knowledge/nutrients/iron.md). ### 11. Boron and zinc during flowering **What.** Small bumps from mid flower: B 0.4 → 0.5–0.6 mg/L, Zn 0.3 → 0.4–0.5 mg/L. **Claim.** B is needed for pollen tubes, cell walls and sugar transport; Zn for auxin and enzyme function. Growers bump them for flower set and density. **Evidence.** *Grower practice*. There's no cannabis flowering dose-response data. Sinsemilla doesn't make pollen tubes, so the classic boron-for-seed-set argument doesn't apply to unpollinated flowers. **Risks.** **Boron has the narrowest safe window of any nutrient**: toxicity starts around 5 mg/L in solution in cannabis work, and leaf-tip burn can show well below that in recirculating systems where B accumulates. Never "bump" boron without measuring what's already there. Zn rises are mild but compete with Fe and Cu. See [boron](https://genetixbay.com/knowledge/nutrients/boron.md) and [zinc](https://genetixbay.com/knowledge/nutrients/zinc.md). **With single salts.** Boric acid (17.5 % B) and zinc sulfate heptahydrate (22.7 % Zn) from a 1:1000 micro stock: 0.6 g boric acid in 1 L of stock, dosed at 1 mL/L, adds about 0.1 mg/L B. ### 12. Manganese, molybdenum and copper: caution Don't play with these. **Mn** competes with Fe (and excess Fe or Zn suppresses Mn); above about 1 mg/L in solution you risk Fe-like yellowing. **Mo** is needed in hundredths of a mg/L; there's no benefit to more. **Cu** is toxic to roots at low concentrations; stay within 0.03–0.1 mg/L, and watch copper pipes and copper-based "root" products, which add more than you think. Hold all three at the base-feed levels in [building a feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md). ### 13. Chloride and sodium: limits, not tricks Keep **Cl below about 50–70 mg/L** and **Na below about 50 mg/L** in the feed, counting what your water brings. Both are salinity, not nutrition, at these levels. The one deliberate chloride use is small doses of calcium chloride during the N taper (trick 6). Sodium has no use; don't choose sodium-based pH-up or borate for a feed. See [chloride](https://genetixbay.com/knowledge/nutrients/chlorine.md) and [sodium](https://genetixbay.com/knowledge/nutrients/sodium.md). ## Whole-feed strength ### 14. Crop-steering EC ramps **What.** In drain-to-waste coco and rockwool, growers raise input EC from about 1.8–2.4 mS/cm (vegetative steer) to 2.4–3.2 mS/cm (generative steer) at the flip to hold back the stretch and again in late flower, and let substrate EC climb on purpose with bigger drybacks. **Mechanism and evidence.** Water and salt stress shift assimilates towards generative growth; *Supported* in greenhouse horticulture, *Grower practice* in cannabis for the specific numbers. One cannabis study found controlled late-flower drought raised THCA and CBDA concentration by about 12–13 %. Raising nutrient concentration overall did not raise yield or cannabinoids in recirculating hydro [5]. So EC is a steering lever (water and salt stress), not a way to feed more. Full method: [drain-to-waste and crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md). **Risks.** Tip burn, stalled growth and midday wilting from over-steering; substrate EC more than ~1.5 mS/cm above input needs a flush shot (root-zone management, not a pre-harvest flush). ### 15. Late-flower EC drops versus element-specific changes **What growers do.** Cut the whole feed by 20–40 % in the last 1–2 weeks (for example 2.0 → 1.3 mS/cm), as a softer version of a flush. **What it actually does.** It lowers N, which is the part you wanted, but it also cuts K, Ca, Mg, S and micros in the weeks when the flowers are still adding weight and resin. It's a blunt version of the N taper, and it sits on the same slope as flushing: the further you cut, the closer you get to starving the plant. **Evidence.** *Grower practice*. There's no controlled evidence for a benefit; long nutrient withdrawal costs dry mass and cannabinoid yield ([the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). **GenetixBay position.** Prefer the element-specific taper: **N down, everything else at normal late-flower strength**. Total EC will fall somewhat as nitrates come out; that's fine. The one legitimate reason for a lower input EC in late flower is a root zone that has run salty (high runoff or substrate EC); then lower the input to bring the root zone back into range, and fix the cause. ## Additives ### 16. Carbohydrates: molasses and sugars **What growers do.** 1–5 mL/L molasses or other sugars in the last weeks, to "sweeten" or "fatten" buds. **What's real.** Molasses and sugars feed soil microbes only, not the plant (house position). Plants make their own sugars by photosynthesis and don't take meaningful amounts of sucrose up through the roots to feed flowers. Taste comes from terpenes, plant health, drying and curing, not from sugar in the root zone. In living soil, molasses does feed microbes, which may speed nutrient cycling; molasses also carries some K, Ca, Mg and S. **Evidence.** "Molasses sweetens or fattens buds" or feeds the plant: *Myth*. As a microbial food in living soil: *Grower practice*; that's the only thing it does. **Risks.** In hydro and recirculating systems, sugars feed bacteria and biofilm, strip dissolved oxygen and raise the risk of root rot. Don't use them there. See [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md). ### 17. Amino acids, fulvic and humic acids **What.** Amino-acid biostimulants, fulvic acid and humic acid at label rates, sold for uptake, stress tolerance and "chelation". **What's real.** Humic and fulvic substances do complex metals and can improve micronutrient availability in soil. In the one cannabis study, humic acid supplementation didn't raise cannabinoids; it reduced the natural spatial variability of cannabinoids through the plant [9]. Amino-acid products have very little cannabis data. **Evidence.** *Contested*. Plausible in soil and soilless with poor micronutrient availability; no consistent yield or quality benefit shown in cannabis mineral feeds. **Risks.** **Amino acids are nitrogen.** A label-rate amino product can add 10–30 mg/L N without your noticing, which quietly undoes an N taper. Count them. Humics stain roots and reservoirs and can feed microbes in hydro. ## Non-nutrient finishing tricks Briefly, because they aren't about elements: - **Cold nights** in the last 1–2 weeks (for example 15–18 °C / 59–64 °F) bring out anthocyanin colour, but only in cultivars that carry it. The colour is real. Claims of more terpenes, flavour or resin from cold are a *Myth* until peer-reviewed data shows otherwise (house position). Too cold slows ripening. See [temperature by stage](https://genetixbay.com/knowledge/environment/temperature-by-stage.md). - **A 24–72 h dark period before harvest** to "boost trichomes": *Myth* (house position). It cuts photosynthesis in the final, most critical days. See [trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md). > **Greenleaf's standing challenge: darkness before harvest.** Putting plants in 24–72 h of darkness before the chop is a *Myth*, and the founder's verdict is "complete and utter nonsense": why cut photosynthesis in the most critical part of the life cycle, while the plant is still finishing its resin? For more than 20 years the founder has offered a standing challenge: find a peer-reviewed study showing a benefit (not a single-plant study, not biased or skewed) and a 50-pack of seeds is yours, no questions asked. Nobody has claimed it. - **Mild late-flower drought**: one study found higher cannabinoid concentration; *Supported* (Caplan et al. 2019) and house-endorsed: the founder uses it, and some cultivars thrive when allowed to go a bit dry. Every cultivar responds differently, so test on one plant first ([crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md)). - **Stem snapping (supercropping)**: *Grower practice*, house-endorsed; the founder does it all the time for better buds ([HST and supercropping](https://genetixbay.com/knowledge/training/hst-supercropping.md)). - **UV-B**: little or no visible difference in controlled trials; see [light spectrum](https://genetixbay.com/knowledge/environment/light-spectrum.md). - **Flushing**: *Myth*, and harmful ([the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). ## A worked late-flower example (single salts, RO water) Base flower feed from [feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) recipe 2, then the final week of the N taper with Ca held by gypsum. Per 1,000 L. | Salt | Base (g) | Week −1 (g) | Week −1 supplies (mg/L) | |---|---|---|---| | Calcium nitrate | 790 | 200 | N 31, Ca 38 | | Potassium nitrate | 200 | 0 | — | | Gypsum (calcium sulfate dihydrate) | 0 | 500 | Ca 116, S 93 | | MKP | 220 | 220 | P 50, K 63 | | Magnesium sulfate heptahydrate | 560 | 600 | Mg 59, S 78 | | Potassium sulfate | 240 | 420 | K 189, S 77 | | **Totals** | **N 150, P 50, K 248, Ca 150, Mg 55, S 117** | | **N 31, P 50, K 252, Ca 154, Mg 59, S 248** | Micros unchanged. Dissolve the gypsum directly in the tank and stir well; it won't go into a concentrate. pH-down with phosphoric or sulfuric acid, not nitric. Measure EC; the arithmetic is a guide. ## Common mistakes - Running several tricks at once and crediting the wrong one. - Ramping K and forgetting that it pushes Mg and Ca out. - Stacking a PK booster on a complete base feed. - "Tapering N" by diluting a 2-part, which cuts every element. - Dropping calcium nitrate for the taper with no other Ca source. - Adding amino acids or nitric acid during the taper and putting the N back in. - Sugars in a recirculating system. - Bumping boron without knowing what the water and the reservoir already hold. ## Evidence - N/potency trade-off: *Supported* [1]. N taper ramp: *Grower practice* (GenetixBay house approach). - Ammonium ≤10–30 % of N; cannabinoids highest on nitrate: *Supported* [2]. NH₄ pH effects: *Established* [10]. - No yield or cannabinoid gain above ~30–60 mg/L P: *Established* (four trials [3][4][5][6]). "More P in flower": *Myth*. High P inducing Zn/Fe shortage: *Established* in other crops [10], not demonstrated in cannabis [3]. - K ramp for yield: *Contested*; no response 60–340 mg/L K in one flower trial [6]. K–Ca–Mg competition: *Established* [10]. - Extra Ca in stretch, late Mg bump, B/Zn bumps, Si on/off: *Grower practice*. Mg veg optimum 35–70 mg/L: *Supported* [7]. - Volatile sulfur compounds behind skunk aroma: *Established* [8]; S feeding raising them: untested. "S raises terpenes": *Myth* as a mechanism. - Chelate pH limits: *Established* [10]. - Higher overall concentration not raising yield or cannabinoids: *Supported* [5]. Crop-steering EC numbers: *Grower practice*. - Pre-harvest darkness: *Myth* (house position). Cold nights: colour real, terpene/resin gain *Myth*. Mild late drought: *Supported*, house-endorsed; cultivars vary. Supercropping: *Grower practice*, house-endorsed. UV-B: little or no visible difference. - Molasses feeding the plant: *Myth*; it feeds soil microbes only. Molasses in hydro: harmful. Humic acid: *Contested* [9]. Amino acids: *Contested*, little data. ## Sources 1. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 2. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 3. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323 4. Westmoreland FM, Bugbee B. 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 5. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 6. Bevan L, Jones M, Zheng Y. 2021. Optimisation of nitrogen, phosphorus, and potassium for soilless production of Cannabis sativa in the flowering stage using response surface analysis. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 7. Morad D, Bernstein N. 2023. Response of medical cannabis to magnesium (Mg) supply at the vegetative growth phase. Plants 12(14):2676. https://doi.org/10.3390/plants12142676 8. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47). https://doi.org/10.1021/acsomega.1c04196 9. Bernstein N, Gorelick J, Zerahia R, Koch S. 2019. Impact of N, P, K, and humic acid supplementation on the chemical profile of medical cannabis (Cannabis sativa L). Frontiers in Plant Science 10:736. https://doi.org/10.3389/fpls.2019.00736 10. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough > Phosphorus powers energy transfer (ATP), roots and flowering, but cannabis needs far less than 'bloom' marketing implies. Controlled trials found no yield or cannabinoid gain above roughly 25–60 mg/L P in solution; extra P just ends up in the runoff and can tie up zinc, iron and calcium. Deficiency shows as dark, dull, olive-spotted older leaves and stunting. - Canonical: https://genetixbay.com/knowledge/nutrients/phosphorus.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How much phosphorus does cannabis need in flower?** Cannabis in flower needs about 30-60 mg/L phosphorus in the solution. Four controlled trials found no gain in flower yield or cannabinoids above roughly 25-60 mg/L, and a deep-water trial predicted a yield optimum near 59 mg/L. Healthy recent mature leaves test about 0.27-0.48% phosphorus by dry weight; extra phosphorus just ends up in the runoff. **Does more phosphorus make bigger buds?** More phosphorus does not make bigger cannabis buds past moderate levels, according to research and the GenetixBay house position. In one trial, raising phosphorus from 25 to 75 mg/L had no effect on yield or cannabinoids while leachate phosphorus rose about 12-fold, and flowers fed 75 mg/L held over 1% phosphorus with no benefit. Pushing 100-200 mg/L wastes money. **What does phosphorus deficiency look like in cannabis?** Phosphorus deficiency in cannabis starts with slight stunting, then olive-green spots in an irregular pattern on lower, older leaflets that enlarge, look sunken and almost water-soaked, with some marginal necrosis. In a DWC flowering trial, spots merged into necrotic lesions, leaflets curled by week 6, and inflorescence fresh weight fell about 63%. Purple stems alone are not a reliable sign. **Why do my lower leaves have dark olive or brown spots?** Dark olive or brown spots on lower cannabis leaves often indicate phosphorus deficiency, frequently caused by cold roots, since uptake drops sharply in cold media, or by high pH where phosphorus precipitates with calcium. Aim for a 20-24 C (68-75 F) root zone. Calcium deficiency, leaf septoria, potassium scorch and nutrient burn can look similar. **Can too much phosphorus cause zinc or iron deficiency?** High phosphorus is associated with induced zinc and iron shortages in many crops, and it can precipitate calcium in the reservoir. This is supported in other crops but not tested in cannabis. Excess phosphorus rarely shows symptoms of its own, so keeping solution phosphorus near 30-60 mg/L avoids the risk and the wasted runoff. **Short answer.** Cannabis needs phosphorus, but not much. Controlled trials found no gain in flower yield or cannabinoids above roughly 25–60 mg/L P in the feed, and plants fed more simply flushed it out in the runoff [1][2][3]. Keep solution P around 30–60 mg/L in veg and flower. Deficiency shows on older leaves as dark, dull foliage with olive-to-brown sunken spots, and stunting. ## What's happening P is the backbone of ATP (the cell's energy currency), DNA, RNA and membrane phospholipids. It is critical for root growth, cell division and seed and flower development. Plants take it up as H₂PO₄⁻ (dominant at pH below about 7.2) and HPO₄²⁻. P is **mobile** in the plant, so shortages show on old leaves first. In the root zone, P readily precipitates with calcium at high pH, and with iron and aluminium at low pH in mineral soils. That is why P "disappears" in alkaline water or limed soil (see [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)). The cannabis-specific evidence is now fairly consistent: - Shiponi and Bernstein (5–90 mg/L P, two medical genotypes): inflorescence biomass was highest at 30–90 mg/L; THCA and CBDA *concentrations* were highest below 30 mg/L and fell up to 25% at higher P, which the authors attribute mostly to yield dilution [1]. - Westmoreland and Bugbee (25, 50, 75 mg/L P, high-CBD cultivar): no effect on flower yield or cannabinoids; leachate P rose about 12-fold for a 3-fold increase in input [2]. - Hershkowitz, Westmoreland and Bugbee (15–90 mg/L P, two EC levels, deep-flow hydro): neither excess P nor a doubled nutrient strength improved yield or quality [3]. - Bevan et al. (20–100 mg/L P in DWC flower): predicted yield optimum at 59 mg/L P [4]. ## How to recognise it **Deficiency.** Slight stunting first. Then olive-green spots in an irregular pattern on lower, older leaflets; spots enlarge, look sunken and almost water-soaked, with some marginal necrosis; advanced leaves carry large necrotic areas [5]. In DWC flower, P deficiency appeared in week 3 as small chlorotic spots on lower fan leaves that merged into necrotic lesions; leaflets curled by week 6; inflorescence fresh weight was about 63% lower than control [6]. Purpling was minor in that study, so do not rely on purple stems as a P sign [6]. **Excess.** Rarely shows as its own symptom. It shows indirectly: high P can precipitate calcium in the reservoir, and is associated with induced zinc and iron shortages in many crops (see [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md)). It also wastes money and pollutes runoff [2]. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution P, seedlings/clones | 15–30 mg/L | *Grower practice* | | Solution P, veg | 30–50 mg/L | Hoagland-type solutions run ~31 mg/L [5] | | Solution P, flower | 30–60 mg/L | No gain above ~25–60 mg/L in three trials [1][2][3][4] | | Leaf P, healthy (most recent mature leaf) | 0.27–0.48% dry weight | NC State floral hemp range [7] | | Leaf P at first deficiency symptoms | ~0.09% | Cannabis, sand culture [5] | | Flower P when fed 75 mg/L | >1% | Luxury uptake, no benefit [2] | ## What to check first 1. **Cold roots.** P uptake drops sharply in cold media; seedlings in cold rooms often look P-deficient. Aim for 20–24 °C (68–75 °F) root zone. 2. **pH.** In soil above ~7.0 or with very hard water, P precipitates with Ca. 3. **Spots on lower leaves have a differential**: Ca deficiency spots, leaf septoria, K deficiency scorch, and nutrient burn. See [rust spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md). 4. **Feed history.** A plain Cal-Mag-and-water regime has no P at all. ## How to fix it - **Mineral:** bring solution P to 40–50 mg/L using monopotassium phosphate (MKP, KH₂PO₄: 1 g/L supplies about 228 mg/L P and 287 mg/L K) or monoammonium phosphate (MAP; adds ammonium). See [hydroponic salts](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md). - **Soil/organic:** bone meal, rock phosphate (slow and needs acidic soil), guano. Mineralisation is slow; expect weeks. - **Warm the root zone** before adding more P. ## How to confirm it worked New leaves show no spotting within 7–10 days; the oldest damaged leaves will not recover. Tissue test 0.27–0.48% P [7]. ## Common mistakes - Pushing "bloom" P to 100–200+ mg/L expecting bigger buds. The trials say no [1][2][3] (see [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md)). - Mixing concentrated phosphate and calcium nitrate in the same stock tank. They precipitate as calcium phosphate. Keep them in separate A and B stocks. - Diagnosing P deficiency from purple stems alone. ## Evidence - Cannabis yield plateaus at modest P (≈25–60 mg/L in solution): *Established* (four independent controlled trials with consistent results [1][2][3][4]); house position agrees. - High P lowers cannabinoid concentration: *Supported* (one study, largely a dilution effect [1]); not seen in [2][3]. - P deficiency symptoms on older leaves: *Established* [5][6]. - High P inducing Zn/Fe deficiency: *Supported* in other crops; not tested in cannabis. ## Sources 1. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323 2. Westmoreland FM, Bugbee B. 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 3. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 4. Bevan L, Jones M, Zheng Y. 2021. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 5. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 6. Llewellyn D, et al. 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 7. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges --- # Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance > Potassium runs water relations, stomata and sugar transport. Cannabis grows well on roughly 175–240 mg/L K in veg, and a flowering DWC trial found no yield response anywhere between 60 and 340 mg/L K, so more is not better. Deficiency scorches the margins and serrations of older leaves; excess K mainly does harm by suppressing calcium and magnesium uptake. - Canonical: https://genetixbay.com/knowledge/nutrients/potassium.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How much potassium does cannabis need in flower?** Cannabis in flower does well on about 150-300 mg/L potassium in the solution. A flowering DWC trial found no yield response anywhere from 60 to 340 mg/L, so adequate matters but extra does not; the upper part of the range is grower practice. Healthy recent mature leaves test about 1.8-2.7% potassium by dry weight. **Why are the edges of my lower leaves yellow and crispy?** Yellow, crispy edges on lower cannabis leaves often mean potassium deficiency, but check runoff EC first, because salt build-up, drought, heat, and manganese or boron toxicity cause similar marginal scorch. Then check pH and roots. If solution potassium is below about 100 mg/L in flower, raise it in steps of 20-40 mg/L with potassium sulfate or potassium nitrate. **Can too much potassium cause magnesium or calcium deficiency?** Yes, too much potassium can cause magnesium and calcium deficiency in cannabis, because these cations compete for root uptake; one cannabis study found calcium and magnesium uptake fell as potassium supply rose. Watch for interveinal yellowing on old leaves and distorted new growth. Grower practice keeps potassium to calcium near 1:1 to 1.5:1 by mass. **Do PK boosters help cannabis?** PK boosters generally do not help cannabis on a full bloom feed. Yield showed no response to potassium from 60 to 340 mg/L in a flowering trial, and adding a booster on top of a complete base can raise potassium to 400+ mg/L, inducing magnesium deficiency. Crowding out calcium and magnesium is the main practical risk of these products. **What does potassium deficiency look like?** Potassium deficiency in cannabis starts as yellowing along the margins and serrated tips of lower, older leaflets, moving inward towards the midrib and turning into tan, necrotic edges. In a DWC flowering trial it appeared in week 3 as dark brown lesions on sugar leaves, then browned fan-leaf tips; inflorescence fresh weight fell about 52%. **Short answer.** Potassium controls water movement, stomatal opening and sugar transport into flowers. In veg, cannabis does well at about 175–240 mg/L K [1][2]; in a flowering DWC trial, yield did not respond to K anywhere from 60 to 340 mg/L [3]. So adequate matters; extra does not. Deficiency scorches the margins and serrated tips of older leaves. Excess K mostly hurts by crowding out calcium and magnesium [1]. ## What's happening K⁺ is the main cation in plant cells. It is not built into structures; it works as an osmotic and charge regulator. It drives turgor and cell expansion, opens and closes stomata, activates dozens of enzymes, and moves sugars through the phloem into sinks such as flowers [7]. K is highly **mobile**, so older leaves show shortage first. At the root, K⁺, Ca²⁺, Mg²⁺ (and NH₄⁺, Na⁺) compete for uptake. In cannabis, Saloner et al. reported competition between K and both Ca and Mg uptake as K supply increased [1]. That is the main practical risk of PK boosters. ## How to recognise it **Deficiency.** Yellowing of the leaf margin, especially the saw-teeth of leaflets, on lower and older foliage; it moves inward toward the midrib and turns into tan necrosis along the margin [4]. In DWC flower, K deficiency showed in week 3 as dark brown lesions on sugar leaves, then fan-leaf tip and margin browning; most non-flower leaves were brown by week 7 and inflorescence fresh weight was about 52% lower [5]. In veg, 15 mg/L K was clearly deficient with visible symptoms in two genotypes [1]. **Excess.** Rarely toxic on its own. Watch for induced Mg deficiency (interveinal yellowing of old leaves) and Ca problems (distorted new growth, spotting) when K is pushed high, and for salt stress (high EC, burnt tips). The response is genotype-dependent: 240 mg/L K harmed one cultivar and stimulated another [1]. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution K, seedlings/clones | 60–120 mg/L | *Grower practice* | | Solution K, veg | 175–240 mg/L | Pot trials, two genotypes [1][2] | | Solution K, flower | 150–300 mg/L | No yield response 60–340 mg/L in DWC [3]; upper part is *grower practice* | | Leaf K, healthy (most recent mature leaf) | 1.8–2.7% dry weight | NC State floral hemp [6] | | Leaf K at first deficiency symptoms | ~0.41% | Cannabis, sand culture [4] | | K:Ca ratio in solution (mass) | ~1:1 to 1.5:1 | *Grower practice*; above ~2:1 watch for Ca/Mg problems. | ## What to check first 1. **Is it really K?** Marginal scorch also comes from high EC/salt build-up, drought, Mn or B toxicity (both gave marginal yellowing of lower leaves in trials [4]), and heat. Check runoff EC first. 2. **pH and roots.** Wet, cold or rotted roots absorb poorly. 3. **Coco.** Unbuffered coco releases K, so K deficiency in coco is rare; Ca/Mg shortage is common (see [buffering coco](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md)). 4. **Feed.** Is your K below ~100 mg/L in flower? ## How to fix it - **Mineral:** raise K with potassium sulfate (K₂SO₄, ~41–45% K, also supplies S) or potassium nitrate (KNO₃, ~38% K, 13% N); MKP adds K with P. Raise in steps of about 20–40 mg/L. - **Soil/organic:** sulfate of potash, kelp meal, wood ash (very alkaline; small amounts and only in acidic soil). - **Excess:** reduce K and check Ca and Mg are at 150–200 and 40–70 mg/L respectively. ## How to confirm it worked No new marginal scorch on leaves above the damage within 7–10 days; damaged edges stay brown. Tissue K lands at 1.8–2.7% [6]. ## Common mistakes - Adding a PK booster on top of a full bloom feed, raising K to 400+ mg/L and inducing Mg deficiency. - Blaming K for tip burn that is really overfeeding. - Using wood ash in alkaline soil. ## Evidence - K deficiency symptoms on older leaf margins: *Established* [4][5]. - Veg optimum ~175–240 mg/L K: *Supported* (two genotypes, one lab [1][2]). - No flower yield response across 60–340 mg/L K in DWC: *Supported* (one trial, one cultivar [3]). - K–Ca–Mg uptake competition: *Established* in plant nutrition [7], observed in cannabis [1]. ## Sources 1. Saloner A, Sacks MM, Bernstein N. 2019. Response of medical cannabis (Cannabis sativa L.) genotypes to K supply under long photoperiod. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 2. Saloner A, Bernstein N. 2022. Effect of potassium (K) supply on cannabinoids, terpenoids and plant function in medical cannabis. Agronomy 12(5):1242. https://doi.org/10.3390/agronomy12051242 3. Bevan L, Jones M, Zheng Y. 2021. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 4. Cockson P, et al. 2019. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 5. Llewellyn D, et al. 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 6. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 7. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Silicon (Si) for cannabis: beneficial, not essential, and how to dose it > Silicon is a beneficial element, not an essential one. It strengthens cell walls and reduces abiotic and some disease stress in many crops, and cannabis does take it up, but cannabis-specific evidence for yield or quality benefits is thin. If you use it, add potassium silicate first to the water at about 20–50 mg/L Si, before other nutrients, and correct pH afterwards because it is strongly alkaline. - Canonical: https://genetixbay.com/knowledge/nutrients/silicon.html - Category: Nutrients · Level: Intermediate - Evidence: Contested · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Does cannabis need silica?** Cannabis does not need silica to complete its life cycle; silicon is a beneficial element, not an essential one. In many crops it strengthens cell walls and reduces drought, salt, metal and some fungal stress, and research shows cannabis does take it up and deposit it. No controlled cannabis trial has shown silicon raises flower yield or cannabinoids, so use is grower practice. **How much silica to add to a hydro reservoir?** Grower practice for a cannabis hydro reservoir is about 20-50 mg/L silicon from potassium silicate. Staying below roughly 56 mg/L silicon avoids polymerisation, where silica gels out of solution. Remember that potassium silicate also supplies potassium, so count it in the feed, and expect the strongly alkaline stock, around pH 11-12, to raise reservoir pH. **Why do I add silica first when mixing nutrients?** Silica goes in first, into plain water, because potassium silicate is strongly alkaline and adding it to a mixed, acidic nutrient solution creates local pH spikes that precipitate calcium and iron, while silicic acid polymerises at low pH. Stir it in, wait a few minutes, add the A and B nutrients, then adjust pH last. **Does silicon prevent powdery mildew in cannabis?** Silicon preventing powdery mildew in cannabis is plausible but unproven. Soluble silicon suppresses powdery mildew well in cucurbits and cereals, but no cannabis trial has tested it, so the evidence for cannabis is contested. At best silicon is a preventive aid, and it will not rescue an existing outbreak. **Silica ppm SiO2 vs Si, what's the difference?** Silica labels often quote SiO2 rather than elemental silicon, and silicon is only 0.467 of the SiO2 weight. So 100 mg/L SiO2 equals about 47 mg/L Si. Reading ppm SiO2 as ppm Si leads growers to overdose by about two times, so convert before dosing toward the 20-50 mg/L silicon target. **Short answer.** Silicon is a *beneficial* element, not an essential one: plants complete their life cycle without it. In many crops it strengthens cell walls and reduces drought, salt, metal and some fungal stress [1][4][5]. Cannabis does take up and deposit Si [2], but cannabis-specific evidence for yield or quality gains is thin. If you use it, dose about 20–50 mg/L Si as potassium silicate, added to the water first, then correct the pH. ## What's happening Soil solutions normally contain silicic acid at concentrations similar to K and Ca, so field plants always have Si. Hydroponic plants are the odd ones out: Epstein pointed out that solution-cultured plants contain only contaminant Si, which may distort research and plant performance [1]. Si is taken up as monosilicic acid, deposited as amorphous silica in cell walls and trichome bases, and is immobile once deposited [5]. Cannabis evidence: - Guerriero et al. identified the aquaporin gene family in cannabis, including channels associated with Si transport, and found Si accumulating in tissues [2]. Cannabis is not a strong Si accumulator like rice or horsetail. - In short-term hemp hydroponics, added Si did not improve growth after one week but reduced cadmium accumulation in all organs and improved water-use efficiency [3]; similar work tested Zn stress. - No controlled cannabis trial showing Si raises flower yield or cannabinoids was found. - Powdery mildew suppression by soluble Si is well documented in cucurbits and cereals [4]. A cannabis trial was not found; treat it as *plausible, unproven*. ## How to recognise it There is no deficiency syndrome. Silicon "toxicity" is not a thing at practical doses; the real problems are pH spikes and precipitation in the tank. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution Si | 20–50 mg/L Si | *Grower practice*; staying below ~56 mg/L Si avoids polymerisation | | Monosilicic acid solubility | ~2 mM (≈56 mg/L Si) at 25 °C | Above this, silica polymerises and gels out. | | Si vs SiO₂ | Si = 0.467 × SiO₂ | Labels often quote SiO₂; 100 mg/L SiO₂ = 47 mg/L Si | | Potassium silicate stock pH | ~11–12 | Strongly alkaline; raises reservoir pH | | K added | Count it | Potassium silicate supplies K as well as Si | ## How to use it 1. Fill the reservoir with water. 2. Add potassium silicate first and stir well. 3. Wait a few minutes, then add the A and B nutrients. 4. Check and adjust pH last. 5. In coco and soil, apply at the same concentration in the feed. Adding silicate to a mixed, acidic nutrient solution makes local pH spikes that precipitate Ca and Fe, and at low pH silicic acid polymerises. ## Common mistakes - Adding silicate after the base nutrients and getting cloudy, gelled or precipitated solution. - Reading "ppm SiO₂" as "ppm Si" and overdosing by 2×. - Expecting Si to rescue a mildew outbreak. It is at best a preventive aid; see [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md). - Forgetting that the pH-up effect of silicate means you then add more acid. ## Evidence - Si is beneficial, not essential: *Established* [1][5]. - Cannabis takes up Si: *Supported* [2]. - Si reduces metal uptake in hemp under stress: *Supported* (short-term studies [3]). - Si improves cannabis yield or potency: *No direct evidence found*; *grower practice*. - Si protects cannabis from powdery mildew: *Contested* (strong in other crops [4]; no cannabis trial found). ## Sources 1. Epstein E. 1994. The anomaly of silicon in plant biology. PNAS 91(1):11-17. https://doi.org/10.1073/pnas.91.1.11 2. Guerriero G, Deshmukh R, Sonah H, Sergeant K, Hausman JF, Lentzen E, Valle N, Siddiqui KS, Exley C. 2019. Identification of the aquaporin gene family in Cannabis sativa and evidence for the accumulation of silicon in its tissues. Plant Science 287:110167. https://doi.org/10.1016/j.plantsci.2019.110167 3. Luyckx M, et al. 2021. Silicon reduces cadmium accumulation in hemp (Cannabis sativa) in short-term nutrient-solution culture. UCLouvain repository. https://research.dial.uclouvain.be/handle/2078.5/104395 4. Fauteux F, Remus-Borel W, Menzies JG, Belanger RR. 2005. Silicon and plant disease resistance against pathogenic fungi. FEMS Microbiology Letters 249(1):1-6. https://doi.org/10.1016/j.femsle.2005.06.034 5. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 --- # Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add > Sodium is not essential for cannabis. It can partly substitute for potassium in some plants, but in cannabis the controlled data show only harm: cannabinoids fall linearly as NaCl rises, and more than about 5 mM NaCl (115 mg/L Na) may reduce yield in hydro. Keep sodium below about 50 mg/L in the feed, never use ion-exchange softened water, and watch it build up in coco and recirculating systems. - Canonical: https://genetixbay.com/knowledge/nutrients/sodium.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is sodium bad for cannabis?** Sodium is bad for cannabis beyond trace levels; it is not an essential nutrient for the crop. Sodium competes with potassium and calcium at the root, displaces calcium from membranes and raises osmotic pressure, making water harder to take up. In hydroponic flower, cannabinoid content fell linearly as sodium chloride rose, so keep sodium below about 50 mg/L in the feed. **Can I use softened water on cannabis?** No, do not use ion-exchange softened water on cannabis. Household softeners swap calcium and magnesium for sodium, often leaving 100-300+ mg/L sodium, far above the roughly 50 mg/L feed limit. Softened water is established as harmful to container crops. Use a bypass tap, RO water or rainwater instead. **How much sodium is too much in irrigation water?** For cannabis, sodium above about 50 mg/L (roughly 2 mM) in the combined water and inputs is too much, per grower practice and greenhouse guidance. Research found more than 5 mM sodium chloride, about 115 mg/L sodium, may reduce yield in hydro, and 40 mM, about 920 mg/L, was phytotoxic. Check the water report for sodium and chloride. **Does salt stress increase THC?** No, salt stress does not increase THC; the controlled data contradict that grower idea. In a hydroponic flowering study, THCA fell by about 0.037 percentage points for every mM of sodium chloride added, and plants were damaged at 40 mM. Another study found osmotic-stress steering reduced height but also reduced yield. Deliberately salting plants for potency backfires. **Why does sodium build up in recirculating hydro?** Sodium builds up in recirculating hydro because cannabis takes it up slowly, so it accumulates while the nutrients around it are consumed, especially when reservoirs are topped up for weeks with sodium-rich tap water. Change the solution on a schedule or when lab tests show sodium nearing about 50 mg/L, and use potassium-based rather than sodium-based pH-up. **Short answer.** Sodium is not essential for cannabis. It is essential for some C4 and salt-adapted plants and can stand in for potassium in a few others, which is why it has been called a "functional" nutrient [3]. For cannabis, the controlled data show only harm: in hydroponic flower, cannabinoid content fell linearly as NaCl rose, and more than about 5 mM NaCl (≈115 mg/L Na) may reduce yield [1]. Keep Na below about 50 mg/L in the feed. ## What's happening Na⁺ competes with K⁺ and Ca²⁺ at the root and inside cells, displaces Ca from membranes, and raises osmotic pressure in the root zone, making water harder to take up [4]. It is taken up slowly, so in any system that recycles solution or holds salts (recirculating hydro, coco, pots without runoff) it **accumulates** while the nutrients around it are consumed. Cannabis data: - Yep et al. applied 1–40 mM NaCl in flower. Cannabinoids decreased linearly with NaCl in both hydroponic (−0.037% THCA per mM) and aquaponic (−0.026% per mM) solutions; hydroponic plants were damaged at 40 mM; the authors advise staying below the 40 mM phytotoxic level and note >5 mM may reduce yield [1]. - Allred, Fatzinger and Bugbee found cannabis highly tolerant of osmotic stress, but using it to steer (reduce height) reduced yield, with cultivar-dependent responses [2]. - The grower idea that salt stress boosts THC is *not supported* by these data [1]. ## How to recognise it Salt stress, not a unique sodium signature: slower growth, darker, smaller leaves, then burnt margins and tips on older leaves, wilting in the heat of the day, and high runoff EC. Induced K and Ca shortages may appear [4]. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Na in feed (water + inputs) | <50 mg/L (~2 mM) | *Grower practice* and greenhouse guidance | | May reduce yield | >5 mM NaCl (≈115 mg/L Na) | Hydro flower [1] | | Phytotoxic in hydro | 40 mM NaCl (≈920 mg/L Na) | [1] | | 1 mmol/L Na | 23 mg/L | Unit conversion | | Softened water | Often 100–300+ mg/L Na | Depends on original hardness; ion-exchange swaps Ca/Mg for Na. | ## What to check first 1. **Water report:** Na and Cl in mg/L. 2. **Softener:** is the grow water coming through a household ion-exchange softener? Use a bypass tap or RO. 3. **Coco:** Na varies widely by source and washing [5]; check runoff EC on new coco. 4. **Inputs:** sodium nitrate, sodium bicarbonate, sodium hydroxide pH-up, some "organic" liquid feeds and seaweed products add Na. 5. **Recirculating hydro:** how long since a full change? ## How to fix it - Use RO, rainwater, or blend RO with tap to bring Na down. - Use potassium hydroxide (KOH) or potassium silicate rather than sodium-based pH-up. - Buffer and rinse new coco (see [buffering coco](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md)). - Change recirculating solution on a schedule, or when lab tests show Na approaching your limit. - In pots, irrigate to 10–20% runoff to keep salts moving out (see [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). ## Common mistakes - Using softened water because it "tastes better". - Topping up a recirculating reservoir for weeks with sodium-rich tap water. - Deliberately salting plants for potency. ## Evidence - NaCl reduces cannabis cannabinoids and, at higher levels, yield: *Supported* (one controlled study [1]; consistent with [2]). - Na as a functional nutrient in some species: *Established* [3]; not relevant to cannabis in practice. - Softened water harming container crops: *Established* in horticulture [4]. ## Sources 1. Yep B, Gale NV, Zheng Y. 2020. Aquaponic and hydroponic solutions modulate NaCl-induced stress in drug-type Cannabis sativa L. Frontiers in Plant Science 11:1169. https://doi.org/10.3389/fpls.2020.01169 2. Allred J, Fatzinger B, Bugbee B. 2025. Crop steering through osmotic stress can reduce height but reduced yield in medical cannabis. PMC12625080. https://pmc.ncbi.nlm.nih.gov/articles/PMC12625080/ 3. Subbarao GV, Ito O, Berry WL, Wheeler RM. 2003. Sodium: a functional plant nutrient. Critical Reviews in Plant Sciences 22(5):391-416. https://doi.org/10.1080/713610858 4. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 5. Minnesota Pollution Control Agency. Chemical and physical properties of coir. https://stormwater.pca.state.mn.us/Chemical_and_physical_properties_of_coir --- # Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources > Sulfur is part of the amino acids cysteine and methionine and of glutathione; cannabis also makes sulfur-containing aroma compounds. Feeds usually supply 50–120 mg/L S as sulfate without trying, via magnesium and potassium sulfate. Deficiency yellows the middle and newer leaves evenly, strongest at the leaflet base, and is rare unless a feed is built entirely from nitrates and chlorides. - Canonical: https://genetixbay.com/knowledge/nutrients/sulfur.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What does sulfur deficiency look like in cannabis?** Sulfur deficiency in cannabis starts as slight, even yellowing mid-plant, strongest at the base of leaflets, then intensifies on newly expanding leaves until they turn very pale yellow around the midrib. In a DWC flowering trial, upper sugar leaves yellowed from week 4, upper fan leaves angled upward by week 5, and inflorescence fresh weight fell about 34%. **Why is the middle of my plant turning pale yellow?** Pale, even yellowing in the middle of a cannabis plant points to sulfur deficiency, because sulfur is only partly mobile and shortages show mid-canopy and on newer leaves. Check the feed recipe: a mix built only from calcium, potassium and magnesium nitrates supplies zero sulfur. Then check pH and roots before adding magnesium or potassium sulfate. **How much sulfur does cannabis need?** Cannabis needs about 50-120 mg/L sulfur in the solution during veg and flower, usually supplied as sulfate through magnesium and potassium sulfate; Hoagland-type solutions run about 64 mg/L. Around 200 mg/L is a practical upper limit, beyond which sulfate mainly raises EC. Healthy recent mature leaves test about 0.25-0.36% sulfur by dry weight. **Does sulfur make cannabis smell stronger?** Feeding more sulfur has not been shown to make cannabis smell stronger; that idea is untested grower practice. The skunky aroma does come from volatile sulfur compounds such as 3-methyl-2-butene-1-thiol, which research has confirmed in cannabis, but no study has linked sulfate feeding to higher levels of them. Ordinary sulfur supply is very unlikely to be limiting. **Sulfur deficiency or nitrogen deficiency?** Sulfur and nitrogen deficiency both cause pale, even yellowing in cannabis, but location tells them apart. Nitrogen is mobile, so its deficiency starts at the bottom leaves and climbs. Sulfur is only partly mobile, so its deficiency shows in the middle and upper canopy and on new leaves, strongest at the leaflet base. Over-feeding nitrogen for mid-canopy yellowing is a common mistake. **Short answer.** Sulfur is needed for the amino acids cysteine and methionine, for glutathione (the plant's main antioxidant buffer) and for many enzymes [4]. Most feeds supply 50–120 mg/L S as sulfate simply because magnesium and potassium sulfate are in them. Deficiency gives an even pale yellowing of the middle and newer leaves, strongest at the leaflet base [1]. It is uncommon unless a feed uses only nitrates and chlorides. ## What's happening Plants take S up as sulfate (SO₄²⁻) and reduce it in the leaves. S is only partly mobile: the plant does not readily strip it from old leaves, so deficiency tends to show in the middle and upper canopy, unlike N, which starts at the bottom [1][4]. That location is the main way to tell them apart. Cannabis also produces volatile sulfur compounds, including prenylated thiols such as 3-methyl-2-butene-1-thiol, which contribute to the "skunky" aroma of some cultivars [5]. Whether S feeding changes their levels has not been tested. Treat "more sulfur, more skunk" as *Grower practice* with no evidence behind it. ## How to recognise it - **Early:** slight overall yellowing, especially mid-plant; yellowing is strongest at the base of leaflets [1]. - **Progressing:** yellowing intensifies on newly expanding leaves [1]. - **Advanced:** very pale yellow leaves, especially around the midrib and leaflet base [1]. In DWC flower: yellowing of upper sugar leaves from week 4, upper fan leaves angling upward by week 5, later interveinal chlorosis on lower fan leaves; inflorescence fresh weight about 34% lower [2]. - **Differential:** N deficiency (starts at the bottom), Fe deficiency (interveinal, new leaves, veins green), light bleaching (top of canopy nearest the lamp, whitish). ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution S, veg and flower | 50–120 mg/L | Hoagland-type ≈64 mg/L [6]; *grower practice* above that is common and tolerated | | Upper practical limit | ~200 mg/L | Above this, sulfate mainly raises EC and risks gypsum precipitation with Ca. | | Leaf S, healthy (most recent mature leaf) | 0.25–0.36% dry weight | NC State floral hemp [3] | | Leaf S at first deficiency symptoms | ~0.11% | Cannabis, sand culture [1] | ## What to check first 1. **Where on the plant?** Middle/new = S candidate; bottom = N. 2. **Feed recipe.** Does it contain any sulfate salt? Magnesium nitrate plus potassium nitrate plus calcium nitrate supplies zero S. 3. **pH and roots.** As always. ## How to fix it - **Mineral:** magnesium sulfate (≈13% S; 0.5 g/L ≈ 65 mg/L S) or potassium sulfate (≈17–18% S). Using sulfuric acid as a pH-down also adds S (1 meq/L of acid adds 16 mg/L S). - **Soil:** gypsum (calcium sulfate) for S without pH change; elemental sulfur only to lower soil pH, and only slowly (bacteria oxidise it over weeks). - Expect new growth to green within 7–10 days. ## How to confirm it worked New leaves green up evenly; middle-canopy yellowing stops spreading. Tissue S at 0.25–0.36% [3]. ## Common mistakes - Treating mid-canopy yellowing as N deficiency and over-feeding N. - Keeping a very high sulfate feed with high calcium in one concentrate: gypsum (calcium sulfate) has limited solubility, roughly 2 g/L, and drops out of concentrated stocks. - Sulfur burning or vaporising near plants: sulfur vapour applied for mildew can damage tissue and should not be used on flowers. ## Evidence - S deficiency symptoms and their mid/upper-plant location in cannabis: *Established* (two controlled studies [1][2]). - S solution target ranges: *Supported* (standard solutions; no cannabis S rate study found). - S feeding raises skunky volatile sulfur compounds: *Untested* (the compounds are real [5], the feeding link is not). ## Sources 1. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, et al. 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 4. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 5. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196 6. Hoagland DR, Arnon DI. 1950. Circular 347. https://archive.org/details/watercultureme3450hoag/ --- # Zinc (Zn) in cannabis: small leaves, margin burn and the phosphorus link > Zinc is needed for many enzymes and for making the growth hormone auxin. Deficiency in cannabis shows late, as yellowing and then tan necrosis along the toothed margins of new leaves, often with small leaves and short internodes elsewhere in the literature. Supply about 0.1–0.5 mg/L Zn; high pH and very high phosphorus are the usual reasons a fed plant runs short. - Canonical: https://genetixbay.com/knowledge/nutrients/zinc.html - Category: Nutrients · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What does zinc deficiency look like in cannabis?** Zinc deficiency in cannabis shows late, after about 9 weeks without zinc in one controlled study, as yellowing along the toothed margins of newer and expanding leaves that develops into tan, irregular necrotic patches along the edge. Leaf zinc at first symptoms was about 10.7 mg/kg. Small leaves and short internodes are reported in other crops but not yet confirmed in cannabis. **Why are my new leaves small with burnt edges?** Small new cannabis leaves with burnt, yellow-to-tan edges along the leaf teeth can point to zinc deficiency, usually caused by high root-zone pH or very high phosphorus rather than a feed lacking zinc. Check pH, and whether a bloom booster pushes phosphorus above 100 mg/L. Potassium deficiency also burns margins, but on old leaves; broad mites distort new growth. **How much zinc in a hydro feed?** A cannabis hydro feed needs about 0.1-0.5 mg/L zinc, a grower practice range; cannabis trials used about 0.2 mg/L. Zinc sulfate heptahydrate is about 22.7% zinc, so 1.3 mg/L of product supplies roughly 0.3 mg/L. Healthy recent mature leaves test about 33-60 mg/kg zinc. Keep phosphorus at or below about 60 mg/L to protect zinc uptake. **Can too much phosphorus cause zinc deficiency?** Heavy phosphorus is one of the better-documented antagonisms in crops, depressing zinc uptake, although it has not been tested in cannabis. Since phosphorus above about 60 mg/L adds no yield, running high phosphorus 'for buds' only risks inducing zinc and iron shortages. Trim phosphorus back to 30-60 mg/L and correct pH when new-leaf margins burn. **Is zinc toxic to cannabis?** Excess zinc can harm cannabis: in hydroponic hemp, about 6.5 mg/L zinc for one week was used as a stress treatment and raised stress markers, and in many crops excess zinc induces iron deficiency with interveinal chlorosis on new leaves. Galvanised pipe, trays or fittings in recirculating systems can leach zinc, so remove them and replace the solution. **Short answer.** Zinc activates many enzymes and is needed to make auxin, the hormone that drives stem and leaf expansion [3]. In cannabis, deficiency showed late (after about 9 weeks without Zn) as yellowing and then tan necrosis along the toothed margins of new leaves [1]. Supply about 0.1–0.5 mg/L Zn. When a fed plant runs short, high pH or very high phosphorus is usually to blame. ## What's happening Zn²⁺ is taken up by roots and moves poorly once in a leaf, so new growth shows shortage first [3]. Classic Zn deficiency in other crops causes "little leaf" and "rosetting": small, narrow leaves on short internodes, because auxin production falls [3]. In cannabis the documented sign was marginal, along the leaf teeth [1]. Zn availability drops as pH rises, and heavy P fertilisation is one of the better-documented antagonisms in crops (P–Zn) [3][4]. ## How to recognise it - **Deficiency:** marginal yellowing on newer and expanding leaves, concentrated along the toothed margins; it develops into tan, irregular necrotic patches along the edge [1]. Biomass was not significantly reduced at symptom onset [1]. Small, crinkled or narrow new leaves and shortened internodes are reported in other crops - **Toxicity:** in hydroponic hemp, 100 µM Zn (≈6.5 mg/L) for a week was used as a stress treatment, raising stress markers [5]. Excess Zn induces Fe deficiency (interveinal chlorosis on new leaves) in many crops [3]. Galvanised fittings in recirculating systems can leach Zn. - **Differential:** K deficiency (margins too, but on *old* leaves), Ca and B (distorted new growth), heat or light stress (tip curl at canopy top), and broad mites. ## Numbers that matter | Parameter | Target | Conditions / notes | |---|---|---| | Solution Zn | 0.1–0.5 mg/L | *Grower practice*; cannabis trials used ≈0.2 mg/L [1] | | Stress-level Zn | ~6.5 mg/L | Hemp, hydroponic, 1 week [5] | | Leaf Zn, healthy (most recent mature leaf) | 33–60 mg/kg | NC State floral hemp [2] | | Leaf Zn at first deficiency symptoms | ~10.7 mg/kg | [1] | | Solution P | ≤60 mg/L | Higher P adds no yield and may depress Zn uptake (see [phosphorus](https://genetixbay.com/knowledge/nutrients/phosphorus.md)) | ## What to check first 1. **pH** of the root zone (soil above ~7.0, soilless above ~6.5). 2. **P level** in the feed: is a bloom booster pushing P above 100 mg/L? 3. **Water and plumbing:** galvanised pipe (excess) or RO with a micronutrient-free feed (shortage). 4. **Pests:** broad mites mimic new-growth distortion. ## How to fix it - Correct pH and trim P back to 30–60 mg/L. - Add zinc sulfate heptahydrate (≈22.7% Zn; 1.3 mg/L of product ≈ 0.3 mg/L Zn) or Zn-EDTA (≈14% Zn). - **Foliar (veg only):** zinc sulfate at about 0.1–0.5 g/L of product; *grower practice*. Test on one leaf first. - **Toxicity:** remove the Zn source (galvanised parts), replace the solution, keep pH in range. ## How to confirm it worked New leaves emerge full-size with clean margins within 7–14 days. Tissue Zn 33–60 mg/kg [2]. ## Common mistakes - Running very high P "for buds" and inducing Zn and Fe shortages. - Over-correcting with multiple micronutrient products. - Using galvanised steel trays or pipe in recirculating hydro. ## Evidence - Zn deficiency symptoms in cannabis (new-leaf margins): *Supported* (one controlled study [1]). - P–Zn antagonism: *Established* in crops [3][4]; *untested* in cannabis. - Zn targets: *Supported* (standard solutions; no cannabis Zn rate study found). ## Sources 1. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Suchoff D, et al. 2026. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 4. Rietra RPJJ, Heinen M, Dimkpa CO, Bindraban PS. 2017. Effects of nutrient antagonism and synergism on yield and fertilizer use efficiency. Communications in Soil Science and Plant Analysis 48(16):1895-1920. https://hub.ifdc.org/handle/20.500.14297/2410 5. Luyckx M, Hausman JF, Isenborghs A, Guerriero G, Lutts S. 2022. Silicon and zinc stress in industrial hemp (hydroponic study). UCLouvain repository. https://research.dial.uclouvain.be/handle/2078.5/105352 --- # Buffering coco coir: why it matters and how to do it > Coco coir has a high cation exchange capacity that arrives loaded with potassium and sodium. Unbuffered, it grabs calcium and magnesium from your feed and releases K and Na, causing early Ca/Mg deficiency. Buffering means soaking washed coco in a calcium (and usually magnesium) nitrate solution so the exchange sites are filled with Ca and Mg before planting, then rinsing. It is standard grower and industry practice with sound chemistry behind it, though controlled studies on cannabis are lacking. - Canonical: https://genetixbay.com/knowledge/ph-ec/buffering-coco.html - Category: pH and EC · Level: Intermediate - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg · Systems: Coco - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Do I need to buffer coco coir?** Yes, you should buffer coco coir unless a runoff test confirms a 'pre-buffered' bag is ready. Coco has a high cation exchange capacity, about 32–130 cmol/kg, that arrives loaded with potassium and sodium, and unbuffered coco pulls calcium and magnesium from your feed for the first few weeks. The chemistry is established; the cannabis benefit is grower practice without controlled trials. **How do I buffer coco with Cal-Mag or calcium nitrate?** To buffer coco, start with washed coco, then soak it in calcium nitrate plus a magnesium salt, or a strong Cal-Mag product, at roughly 150–300 mg/L calcium and 50–100 mg/L magnesium, EC about 1.2–2.0 mS/cm, adjusted to pH 5.8–6.0. Soak 8–24 hours, drain, rinse with low-EC water, and test runoff for EC below about 0.6–1.0 mS/cm. These strengths are grower practice. **Why does my plant get calcium deficiency in new coco?** Cannabis plants often show calcium deficiency in new coco because unbuffered coir's exchange sites grab calcium and magnesium from the feed and release potassium and sodium in exchange. The extra potassium then competes further with calcium and magnesium uptake. Buffering beforehand, and feeding slightly more calcium and magnesium for the first 2–3 weeks, prevents it. **What is the difference between washed and buffered coco?** Washed coco has been rinsed with fresh water to remove soluble salts and lower its EC, but washing cannot fully clear the potassium and sodium held on the coir's exchange sites. Buffered coco has also been soaked in a calcium and usually magnesium solution, so divalent calcium displaces those monovalent ions, which are then rinsed away. Buffering needs washed coco first. **How long should I soak coco to buffer it?** Coco coir is usually soaked for 8–24 hours to buffer it, mixed once or twice so it saturates evenly; one retailer protocol uses about 45 g of calcium nitrate in 7 L of water for a 600 g block over 12 hours. Very high-potassium or high-sodium coco may need a second soak. Confirm the result by testing runoff EC and pH afterwards. **Can I reuse coco without buffering?** Yes, reused coco usually does not need full re-buffering, because its exchange sites are already loaded with your previous feed's calcium and magnesium. Rinse it well, check that runoff EC has come down, and remove old roots before replanting. This is grower practice rather than a tested protocol, so a runoff check is the best guide. **Short answer.** Coco coir has a high cation exchange capacity (CEC) that comes loaded with potassium and sodium from the coconut and from salt water used in processing [1][2]. Unbuffered, it pulls calcium and magnesium out of your feed and releases K and Na, so young plants show Ca/Mg deficiency in the first weeks. **Buffering** means soaking washed coco in a calcium (usually plus magnesium) nitrate solution so the exchange sites fill with Ca and Mg before planting, then rinsing [3]. The chemistry is sound; cannabis-specific trials are lacking, so the method is *grower practice*. ## What's happening Coir particles carry negative charges that hold cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) and swap them with the solution. Reported coir properties vary widely by source: CEC about 32–130 cmol/kg, pH 4.9–6.9, total K about 0.4–2.4% of dry weight, with large source-to-source differences in Na and Cl [2]. Abad et al. found commercial coir dusts suitable as peat substitutes but chemically variable, with high K and Na in some lots [1]. - **Washing** (with fresh water) removes soluble salts, lowering EC, but cannot fully clear ions held on exchange sites [3]. - **Buffering** uses mass action: flood the coco with Ca²⁺ (and Mg²⁺). Divalent Ca is held more strongly than K⁺ and Na⁺; each Ca²⁺ adsorbed displaces two monovalent ions, which you then rinse away [3]. If you skip it, the coco buffers itself using *your feed*, for the first few weeks: Ca and Mg disappear onto the coco, K and Na come out, and high K competes further with Ca and Mg uptake [4][5]. ## Numbers that matter | Parameter | Value | Notes | |---|---|---| | Coir CEC | ~32–130 cmol(+)/kg dry | [2]; varies by source and age | | Coir pH | ~4.9–6.9 | [2] | | Coir total K | ~0.4–2.4% dry weight | [2] | | Rough Ca needed to load 1 kg dry coco | ~10–25 g Ca (≈50–130 g calcium nitrate) | Back-of-envelope from CEC 50–130 cmol/kg assuming full exchange; real exchange is partial. | | Example supplier protocol | ~45 g calcium nitrate in 7 L for a 600 g block, 12 h | One retailer guide [6]; equals ~75 g per kg dry coco | | Buffering solution, home practice | Ca 150–300 mg/L + Mg 50–100 mg/L, EC ~1.2–2.0 mS/cm | *Grower practice*; often a Cal-Mag product at strong rate. | | Target runoff after buffering | EC <0.6–1.0 mS/cm, pH 5.8–6.5 | *Grower practice* | ## How to buffer coco 1. **Start with washed coco.** If the bag says "unwashed", rinse with fresh water until runoff EC is below about 0.5 mS/cm. 2. **Mix the buffer solution**: calcium nitrate (plus magnesium sulfate or magnesium nitrate) in water, or a Cal-Mag product, to the strength above. Adjust to pH 5.8–6.0. 3. **Soak** the coco fully for 8–24 hours, mixing once or twice so it saturates evenly. 4. **Drain**, then **rinse** with plain or low-EC water to remove the released K and Na. 5. **Test runoff** EC and pH. Optional but useful: one lab test of runoff for K, Na and Ca on a new coco supplier. 6. **Optional second soak** for very high-K/Na coco. 7. **Plant, and feed with a full nutrient solution from day one,** slightly higher in Ca and Mg for the first 2–3 weeks. Reused coco: it has been loaded with your feed's cations already; rinse well, check runoff EC, and remove old roots. It usually does not need full re-buffering. *Grower practice.* ## Common mistakes - Treating "pre-buffered" bags as guaranteed. Test runoff anyway. - Buffering with plain water and calling it done. - Planting into buffered coco and then giving plain water for a week; the seedlings still need Ca and Mg. - Using salty tap water to rinse, undoing the job (see [sodium](https://genetixbay.com/knowledge/nutrients/sodium.md)). ## Evidence - Coir has a variable, often high CEC and variable K, Na and Cl: *Established* [1][2]. - Calcium-loading displaces K and Na from exchange sites: *Established* chemistry [5]; practical protocols are *grower and industry practice* [3]. - Buffering improves cannabis outcomes: *Grower practice*; no controlled cannabis study found. ## Sources 1. Abad M, Noguera P, Puchades R, Maquieira A, Noguera V. 2002. Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology 82(3):241-245. https://doi.org/10.1016/S0960-8524(01)00189-4 2. Minnesota Pollution Control Agency. Chemical and physical properties of coir. https://stormwater.pca.state.mn.us/Chemical_and_physical_properties_of_coir 3. Greenhouse Grower. Washed, low-EC, or buffered? How to specify coco substrate for your crop. https://www.greenhousegrower.com/?p=180860 4. Saloner A, Sacks MM, Bernstein N. 2019. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 5. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 6. Living Seeds. Washed coco coir block: buffering instructions (retailer guide). https://www.livingseeds.co.za/600g-cocopeat-block --- # EC vs PPM: the 500 and 700 scales, CF, and how to convert > EC (electrical conductivity, in mS/cm) is what every meter actually measures. 'PPM' or TDS readings are EC multiplied by an assumed factor: 0.5 on the 500 (NaCl) scale, 0.7 on the 700 (442 or KCl-style) scale, sometimes 0.64. So 1.0 mS/cm reads 500 ppm on one meter and 700 ppm on another. Always talk in EC, or state the scale. Feed charts quoting ppm without a scale are ambiguous by 40%. - Canonical: https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.html - Category: pH and EC · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I convert EC to ppm?** To convert EC to ppm, multiply EC in mS/cm by your meter's factor: 500 for the 500 or NaCl scale, 700 for the 700 scale, or 640 used by some agricultural sources. For example, 1.4 mS/cm equals 700 ppm on the 500 scale and 980 ppm on the 700 scale. To switch scales, multiply 500-scale ppm by 1.4. **What is the difference between the 500 and 700 ppm scales?** The 500 and 700 ppm scales differ only in the factor a meter multiplies EC by: 0.5 on the 500 scale, based on sodium chloride and common in North America, and 0.7 on the 700 scale, common in Europe and Australia. The same solution at 1.0 mS/cm reads 500 or 700 ppm, a 40 % gap. Neither is the true ppm of your nutrients. **Is my meter 500 or 700 scale?** To tell whether your meter is 500 or 700 scale, check the manual or settings menu, or test it in a 1.413 mS/cm calibration standard: a 500-scale meter reads about 707 ppm and a 700-scale meter about 990 ppm. If the meter can display EC directly, switch to EC and stop using ppm altogether. **What is CF in hydroponics?** CF, conductivity factor, is another unit for electrical conductivity used in hydroponics, equal to EC in mS/cm multiplied by 10. So 1.0 mS/cm is CF 10, 1.8 mS/cm is CF 18 and 2.2 mS/cm is CF 22. Like ppm, CF describes the same meter measurement; it says nothing about which nutrient ions are present. **What EC is 1000 ppm?** 1,000 ppm equals 2.0 mS/cm EC on the 500 scale, about 1.56 mS/cm on the 640 scale and about 1.43 mS/cm on the 700 scale. That is why a 1,000 ppm feed chart written on the 700 scale overfeeds by about 40 % when followed with a 500-scale meter. Check which scale the chart uses, or work in EC. **mS/cm vs µS/cm vs dS/m?** mS/cm, µS/cm and dS/m are all units of electrical conductivity. 1 mS/cm equals 1,000 µS/cm, and 1 mS/cm equals exactly 1 dS/m and 1 mmho/cm. So a 1,413 µS/cm calibration standard is 1.413 mS/cm. EC readings should be temperature-corrected to 25 °C, so readings from meters without compensation are not comparable. **Short answer.** Every "ppm" or TDS meter actually measures electrical conductivity (EC) and then multiplies by an assumed factor [1]. On the **500 scale** (NaCl) the factor is 0.5; on the **700 scale** (often called 442 or KCl-style) it is 0.7; some agricultural sources use 0.64 [1][2]. So the same solution at **1.0 mS/cm reads 500 ppm on one meter and 700 ppm on another.** Talk in EC (mS/cm), or always state the scale. ## What's happening Dissolved salts conduct electricity; more ions, more conductivity. EC is measured in siemens per distance and corrected to 25 °C. It does not tell you *which* ions are present, only the total charge-carrying load. "PPM" (TDS, total dissolved solids, mg/L) is an estimate: different salts conduct differently per gram, so no single factor is right for every solution. NDSU notes the true factor for natural waters rises with conductivity, from about 0.65 at 1,000 µS/cm to about 0.82 at 10,000 µS/cm [1]. Meter makers just pick one: - **500 scale (NaCl, factor 0.5):** common in North America. - **700 scale (factor 0.7):** common in Europe and Australia; often based on a "442" reference mix of sodium sulfate, sodium bicarbonate and sodium chloride. - **640:** used in some agricultural and extension material [2]. None is the "true" ppm of your nutrients. A nutrient solution's ppm-by-element (e.g. N 180 mg/L) is a different thing again. ## Units | Unit | Equals | |---|---| | 1 mS/cm | 1,000 µS/cm | | 1 mS/cm | 1 dS/m | | 1 mS/cm | 1 mmho/cm | | CF (conductivity factor) | EC (mS/cm) × 10 | ## Conversion table | EC (mS/cm) | CF | ppm 500 scale | ppm 640 | ppm 700 scale | |---|---|---|---|---| | 0.2 | 2 | 100 | 128 | 140 | | 0.4 | 4 | 200 | 256 | 280 | | 0.6 | 6 | 300 | 384 | 420 | | 0.8 | 8 | 400 | 512 | 560 | | 1.0 | 10 | 500 | 640 | 700 | | 1.2 | 12 | 600 | 768 | 840 | | 1.4 | 14 | 700 | 896 | 980 | | 1.6 | 16 | 800 | 1,024 | 1,120 | | 1.8 | 18 | 900 | 1,152 | 1,260 | | 2.0 | 20 | 1,000 | 1,280 | 1,400 | | 2.2 | 22 | 1,100 | 1,408 | 1,540 | | 2.5 | 25 | 1,250 | 1,600 | 1,750 | | 3.0 | 30 | 1,500 | 1,920 | 2,100 | Formulas: ppm₅₀₀ = EC × 500; ppm₇₀₀ = EC × 700; ppm₇₀₀ = ppm₅₀₀ × 1.4; ppm₅₀₀ = ppm₇₀₀ × 0.714. ## How strong should a cannabis feed be? Typical working ranges are 0.6–1.0 mS/cm for seedlings and clones, 1.2–1.8 in veg and 1.6–2.2 in flower (see [building a feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md)); these are *grower practice*. The research supports not going higher: in deep-flow hydro, doubling input from 2 to 4 mS/cm raised solution nutrients but not yield or quality [3]; in rockwool, yield did not differ between 1.8 and 3 mS/cm, while 12 mS/cm cut yield about threefold [4]. ## How to tell which scale your meter uses 1. Check the manual or the meter's setting menu (many let you choose). 2. Test a calibration standard: 1.413 mS/cm (1,413 µS/cm) solution should read ~707 ppm on the 500 scale and ~990 ppm on the 700 scale. 3. If the meter can display EC, switch it to EC and forget ppm. ## Common mistakes - Following a "1,000 ppm" feed chart written on the 700 scale with a 500-scale meter, and overfeeding by 40%. - Forgetting that tap water already has EC; feed charts usually mean *total* EC, but some mean "added". Read the chart notes. - Comparing EC readings taken at different temperatures on a meter without automatic temperature compensation. - Thinking EC tells you nutrient balance. It doesn't; sodium chloride has EC too. ## Evidence - Meters measure EC and convert with an assumed factor; the factor varies with solution: *Established* [1]. - 500, 640 and 700 conventions: *Established* industry and extension usage [1][2]. - No cannabis yield gain above roughly 2–3 mS/cm: *Supported* (two studies [3][4]). ## Sources 1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test 2. University of California Cooperative Extension, Ventura County. Salinity units and conversions (640 ppm = 1 dS/m). https://ucanr.edu/node/125832 3. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 4. Baas R, Wijnen D. 2023. Effects of EC on cannabis in rockwool (1.8 to 12 mS/cm). Acta Horticulturae 1377. https://www.ishs.org/ishs-article/1377_97 5. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # pH and EC meter calibration: buffers, slope, storage and when to replace a probe > Calibrate pH meters with at least two fresh buffers that bracket your readings (pH 7 then pH 4 for growing), before any session where decisions matter and at least weekly. Store glass pH probes wet in storage solution or pH 4/7 buffer, never in RO water or dry. Check EC meters against a 1.413 mS/cm standard. A pH probe with a slope below about 90-95% or one that can no longer be adjusted to buffer should be replaced; typical glass electrodes last one to two years. - Canonical: https://genetixbay.com/knowledge/ph-ec/meter-calibration.html - Category: pH and EC · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I calibrate a pH pen?** To calibrate a pH pen, rinse the probe with distilled or RO water and blot it without wiping the bulb, place it in fresh pH 7.00 buffer to set the offset, rinse, then use pH 4.01 buffer to set the slope. Re-read pH 7 afterwards; it should be within ±0.05. Keep buffers and samples near the same temperature. **How often should I calibrate my pH meter?** A handheld pH meter should be calibrated before every session where readings drive a decision and at least weekly, plus immediately whenever readings seem odd. Continuous in-reservoir pH probes should be checked weekly against a freshly calibrated handheld and recalibrated monthly, or sooner if the two disagree by more than 0.1–0.2 pH units. **How should I store a pH probe?** A glass pH probe should be stored wet, in storage solution, usually 3 M potassium chloride, or in pH 4 or 7 buffer. Never store it dry or in distilled or RO water, which leaches the reference electrolyte and shortens probe life. Keep the meter out of heat. A dried-out probe may recover after soaking several hours in storage solution. **Why does my pH meter drift?** A pH meter drifts mainly because the glass membrane and reference junction degrade with age, and drying out, storage in pure water, biofilm and nutrient salt crusts in the junction speed that up. Slow responses over 30–60 seconds point to a dirty junction or old probe. Calibration with two fresh buffers corrects drift until the probe can no longer be adjusted. **What is pH probe slope and offset?** pH probe offset is the voltage the probe makes at pH 7, which should be close to 0 mV, ideally within ±15 mV. Slope is the probe's millivolts per pH unit as a percentage of the theoretical 59.16 mV at 25 °C; a healthy probe reads 95–102 %. A two-point calibration sets both, and most meters display them afterwards. **How do I calibrate an EC meter?** To calibrate an EC meter, rinse and shake the probe dry, immerse it in a fresh 1.413 mS/cm standard at 25 °C, or 2.77 mS/cm for strong feeds, let the temperature settle and adjust the meter to match. Recalibrate after battery changes, drops or odd readings. For a rough check, about 1.7 g table salt in 0.94 L distilled water reads roughly 3.2–3.6 mS/cm. **When should I replace my pH probe?** Replace a pH probe when it can no longer be adjusted to match buffer, or when its slope stays below about 90–95 % after cleaning; an offset beyond ±30 mV at pH 7 is another warning sign. Glass pH electrodes typically last about one to two years when stored wet in buffer or storage solution. Exact limits vary by manufacturer. **Short answer.** Calibrate a pH meter with **at least two fresh buffers that bracket your readings** (pH 7, then pH 4, for growing) before any session where decisions matter, and at least weekly [1][3]. **Store glass pH probes wet** in storage solution or pH 4/7 buffer, never dry or in RO water [1]. Check EC meters against a **1.413 mS/cm** standard. Replace a pH probe that can no longer be adjusted to buffer [1] or whose slope has fallen below about 90–95%. Glass electrodes typically last about two years with good storage [1]. ## What's happening A glass pH electrode makes a voltage that changes about 59 mV per pH unit at 25 °C. Calibration tells the meter two things: - **Offset (zero point):** the voltage at pH 7. A healthy probe reads close to 0 mV; drift here shifts every reading. - **Slope:** mV per pH unit compared with the theoretical 59.16 mV. Expressed as a percentage. New probes are near 100%; ageing, dirty or dried-out probes fall. Most meters show both after a two-point calibration. Probes age because the glass membrane and reference junction degrade; drying out, storing in pure water (which leaches the reference electrolyte), biofilm and nutrient salts in the junction speed this up [1]. EC meters are simpler: two electrodes and a temperature sensor. They drift less but still need checking, and readings must be temperature-compensated to 25 °C. ## How to calibrate a pH meter 1. **Use fresh buffers.** Single-use sachets or freshly poured buffer; never pour used buffer back. Buffers 7.00 and 4.01 bracket growing ranges; add 10.01 only if you measure alkaline water [1][3]. 2. **Rinse** the probe with distilled or RO water and gently blot (don't wipe the glass bulb; it causes static and scratches). 3. **pH 7 first** (sets offset). Wait for a stable reading, confirm. 4. **Rinse, then pH 4** (sets slope). Wait, confirm. 5. **Check the slope and offset** if your meter shows them. 6. **Verify:** re-read pH 7. It should be within ±0.05. 7. **Match temperature:** buffers and samples near the same temperature; most meters compensate automatically, but buffer values themselves shift slightly with temperature. **When:** before every session that drives a decision; at least weekly for handheld pens; immediately if readings seem odd [1]. Continuous in-reservoir probes: check against a freshly calibrated handheld weekly and recalibrate monthly or when they disagree by >0.1–0.2. ## How to calibrate an EC meter 1. Rinse the probe, shake dry. 2. Immerse in a fresh standard: **1.413 mS/cm (1,413 µS/cm)** at 25 °C is the common one; 2.77 mS/cm is useful for strong feeds. 3. Let temperature settle; adjust the meter to the standard. 4. Calibrate after battery changes, drops, or if readings look wrong [4]. 5. For a rough field check with no standard, NDSU gives a homemade NaCl solution (about 1.7 g table salt in 0.94 L distilled water ≈ 3.2–3.6 mS/cm) [4]. ## Numbers that matter | Parameter | Good | Act | Notes | |---|---|---|---| | pH slope | 95–102% | <90–95%: clean; if no better, replace | General lab guidance | | pH offset at pH 7 | within ±15 mV | >±30 mV: clean or replace | | | Buffer spacing | Bracket samples, ≤3–4 pH units apart | | USP <791> summary [3] | | Response time | <30–60 s to stable | Slow = dirty junction or old probe | | | pH probe life | ~1–2 years | | Stored in buffer, not dry [1] | | EC temperature correction | ~2% per °C to 25 °C | | Typical for nutrient solutions. | ## Storage and cleaning - **Store wet** in storage solution (usually 3 M potassium chloride) or pH 4 or 7 buffer [1]. Never in distilled or RO water. - **Dried-out probe:** soak in storage solution for several hours before calibrating; it may recover. - **Cleaning nutrient or biofilm residue:** soak in a probe-cleaning solution or warm, mild detergent; for salt crusts, a brief soak in dilute acid per manufacturer instructions; rinse well and recondition in storage solution. - **Keep meters out of heat**; a cool box in a hot room or vehicle helps [1]. ## Common mistakes - Single-point calibration at pH 7 only. - Reusing old or contaminated buffer. - Storing the pen dry with the cap empty. - Trusting a cheap pen for months without checking. - Calibrating in cold buffer and measuring warm nutrient solution with no temperature compensation. ## Evidence - Two-buffer calibration and wet storage: *Established* (extension [1], USGS [2], pharmacopoeia guidance [3]). - Specific slope and offset thresholds: *Established* as general lab practice; exact numbers vary by manufacturer. - EC calibration practice: *Established* [4]. ## Sources 1. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download 2. US Geological Survey. National Field Manual for the Collection of Water-Quality Data, Chapter A6.4: pH. https://www.usgs.gov/mission-areas/water-resources/science/national-field-manual-collection-water-quality-data-nfm 3. Mettler-Toledo. pH measurement and USP <791> (white paper). https://www.mt.com/my/en/home/library/white-papers/lab-analytical-instruments/pH-measurement-USP-791.html 4. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test --- # pH and nutrient availability: what pH really controls, by medium > pH controls how soluble each nutrient is and how well roots absorb it. The accepted ranges are soil about 6.0–7.0 and soilless/hydro about 5.5–6.5 (sweet spots: 5.5–6.2 in hydro, 5.8–6.3 in coco and rockwool, 6.2–6.8 in soil), and drift within the range is normal. High pH starves plants of iron, manganese, zinc, boron and phosphorus; low pH makes iron and manganese overly available and reduces calcium, magnesium and molybdenum. The classic availability bar chart was built for mineral soils and overstates the effect in chelated soilless feeds. The ranges are broadly agreed accepted practice, from extension and grower consensus. - Canonical: https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.html - Category: pH and EC · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What pH should I use for cannabis in soil, coco and hydro?** Cannabis grows best at about pH 6.2–6.8 in soil, within the accepted 6.0–7.0 range; about 5.8–6.3 at the feed in coco and rockwool, with runoff at 5.8–6.5; and 5.5–6.2 in DWC, RDWC, NFT and aeroponic reservoirs. These ranges are accepted practice from extension guidance and grower consensus, and the GenetixBay house position. **What is nutrient lockout from pH?** Nutrient lockout from pH happens when root-zone pH moves far enough out of range that nutrients become insoluble or roots absorb them poorly, so the plant shows deficiencies even though the feed contains them. At high pH, iron, manganese, zinc and copper form insoluble compounds; at low pH, calcium, magnesium and molybdenum drop. Measure before blaming every deficiency on lockout. **Why is the hydro pH range lower than soil?** The hydro pH range is lower than soil because soilless media and hydroponics lack the clays and aluminium chemistry of mineral soils that make pH 6.0–7.0 best, and their micronutrients are supplied as chelates. Extension sources give about 5.4–6.2 for typical soilless crops, so cannabis hydro sits at about 5.5–6.2 and coco at 5.8–6.3. **Is the pH nutrient availability chart accurate?** The classic pH nutrient availability chart is accurate only as a direction, not a law: it was drawn for mineral soils and overstates the effect in chelated soilless feeds. In coco and hydro, chelated iron, manganese, zinc and copper stay available further up the scale; for example, iron-EDTA holds to about pH 6.5, iron-DTPA to about 7.5 and iron-EDDHA to about 9. **What happens if my pH is too high?** If root-zone pH is too high, above about 6.5 in soilless media or about 7.3 in soil, cannabis runs short of iron, manganese, zinc, boron and copper, and phosphorus precipitates with calcium. The first sign is usually interveinal chlorosis on new growth. Bicarbonate-rich alkaline water makes it worse by reducing iron uptake directly and pushing pH up over weeks. **What happens if my pH is too low?** If root-zone pH is too low, below about 5.3 in soilless media or 5.8 in soil, iron and manganese become overly available and can reach toxic levels, while calcium, magnesium and molybdenum run short and root membranes are damaged. Typical signs are leaf speckling, necrosis along old-leaf margins and distorted new growth. **Is it OK if my pH drifts?** Yes, pH drift is fine as long as it stays within the accepted range, about 5.5–6.5 for soilless and hydro or 6.0–7.0 for soil; drift within the range is normal and healthy, and some movement helps. Treating pH as one perfect number is a common mistake. Act on a sustained trend outside the band, measured in the root zone with a calibrated meter. **Short answer.** pH sets how soluble each nutrient is and how easily roots absorb it. The accepted ranges are **soil 6.0–7.0** and **soilless/hydro 5.5–6.5**; within them, aim for about **5.5–6.2 in hydro, 5.8–6.3 in coco and rockwool, and 6.2–6.8 in soil**. Drift within the range is normal and healthy. High pH starves plants of Fe, Mn, Zn, B and P; low pH makes Fe and Mn overly available and cuts Ca, Mg and Mo [1][2][6]. The classic availability bar chart was drawn for mineral soils and overstates the effect in chelated soilless feeds. These ranges are accepted practice, from extension and grower consensus. ## What's happening pH is the hydrogen-ion activity of the solution around the roots. It changes nutrient chemistry in three ways: 1. **Solubility and precipitation.** At high pH, iron, manganese, zinc and copper form insoluble hydroxides and phosphates; calcium phosphate precipitates. At low pH, aluminium and manganese dissolve (in soils) and molybdate binds to iron oxides [1][6][7]. 2. **Chemical form.** Phosphate shifts from H₂PO₄⁻ (preferred) to HPO₄²⁻ above about pH 7.2. Chelates hold metals only up to a ceiling: Fe-EDTA to about 6.5, Fe-DTPA to about 7.5, Fe-EDDHA to about 9 [4]. 3. **Root function.** Very low pH damages root membranes and reduces Ca and Mg uptake; very high pH reduces Fe uptake directly, especially with bicarbonate present [1]. **Why soil and soilless differ.** Mineral soils have clays and aluminium chemistry that make pH 6.0–7.0 best. Soilless media (peat, coco, rockwool, hydro) lack them, and micronutrients are supplied chelated, so the best range sits lower: extension sources give 5.4–6.2 for typical soilless crops [3], with iron-efficient species tolerating 6.0–6.6 [1]. **The availability chart caveat.** The familiar chart with tapering bars was built for mineral soils. In soilless systems with chelated micros, Fe, Mn, Zn and Cu stay available further up the scale than the bars suggest [4]. Use it as a direction, not a law. ## High pH vs low pH | Root-zone pH | Likely problems | Who's affected first | |---|---|---| | Above ~6.5 (soilless) / ~7.3 (soil) | Fe, Mn, Zn, B, Cu shortage; P precipitation with Ca | New growth: interveinal chlorosis [1][2] | | 5.5–6.3 (soilless) | Broad availability | Target | | Below ~5.3 (soilless) / ~5.8 (soil) | Fe and Mn toxicity; Ca, Mg, Mo shortage; root damage | Speckling, old-leaf margin necrosis; distorted new growth [1][2][6] | ## Numbers that matter | System | Target pH | Measure where | Notes | |---|---|---|---| | DWC, RDWC, NFT, aero | 5.5–6.2 | Reservoir | Recommendation cited for cannabis hydro 5.5–6.0 [5]; let it drift within the band | | Coco, rockwool, drip | 5.8–6.3 (feed), runoff 5.8–6.5 | Feed and runoff | Soilless recommendation 5.5–6.5 [5] | | Peat-based mixes | 5.8–6.4 | Pour-through | Extension general group 5.8–6.4 [1] | | Soil and living soil | 6.0–7.0 (sweet spot 6.2–6.8) | Soil slurry or pour-through | Accepted practice; don't pH-adjust living soil inputs aggressively | | Irrigation water | 5.0–7.0 before nutrients | Source | Water pH matters less than alkalinity [1] | ## What to check first 1. **Calibrate the meter** (see [meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)). A drifting probe causes more "pH problems" than chemistry does. 2. **Measure the root zone,** not only the input: reservoir, runoff, or pour-through. 3. **Know your water alkalinity.** Alkaline water pushes pH up over days and weeks regardless of the input pH [1] (see [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md)). 4. **Look at N form.** Nitrate feeds push pH up; ammonium pushes it down (see [pH drift](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md)). ## How to fix it - **Hydro:** adjust with acid (phosphoric, nitric or sulfuric) or base (potassium hydroxide, potassium silicate) in small steps; recheck after 15–30 minutes of circulation. - **Coco/rockwool:** adjust each batch of feed; if runoff keeps climbing, acidify the water to reduce alkalinity, or increase the ammonium share slightly (stay ≤20% of N). - **Soil:** raise pH with agricultural or dolomitic lime, lower with elemental sulfur; both take weeks. Do not chase soil pH with acid in every watering. - **Lockout with high runoff EC:** if salts have built up as well, a root-zone flush resets the medium: 2–3× the container volume of a light, correctly pH-adjusted solution (coco, rockwool) or pH-adjusted water (soil), then check runoff pH and EC and resume normal feeding (see [the root-zone flush](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). - **Safety:** concentrated acids and hydroxides burn skin and eyes. Gloves and goggles; add acid to water. ## Common mistakes - Treating pH as one perfect number. A band is fine; drift within the range is normal and some movement helps. - Adjusting pH before adding nutrients (the salts change it). - Measuring pH of plain water with a meter and assuming that's the root zone. - Blaming every deficiency on "pH lockout" without measuring. ## Evidence - pH effects on micronutrient and P solubility and chelate ceilings: *Established* [1][2][4][6][7]. - Soilless crops do best at lower pH than soils: *Established* in container horticulture [1][3]. - Cannabis pH ranges (soil 6.0–7.0, soilless/hydro 5.5–6.5): *Established* as accepted practice from extension and grower consensus [1][3][5]; GenetixBay house position. ## Sources 1. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 2. Michigan State University Extension. pHix it! Getting substrate pH just right. https://www.canr.msu.edu/news/phix-it-getting-substrate-ph-just-right 3. Michigan State University Extension. pH and EC issues still a problem in some greenhouses. https://www.canr.msu.edu/news/ph_and_ec_issues_still_a_problem_in_some_greenhouses 4. HortScience. 2025. Iron chelates in high-pH soilless media. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml 5. Velechovsky J, Malik M, Senkyrik JB, Tlustos P. 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 6. Kaiser BN, et al. 2005. The role of molybdenum in agricultural plant production. Annals of Botany 96(5):745-754. https://doi.org/10.1093/aob/mci226 7. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 --- # pH drift in hydro: why reservoir pH rises (and sometimes falls) > Reservoir pH usually rises because plants absorb nitrate and release hydroxide or bicarbonate to stay electrically balanced; aeration driving off CO2, alkaline top-up water and algae add to it. Ammonium does the opposite. A steady upward drift of a few tenths per day in a healthy, growing system is normal. Manage it with a small ammonium share (5–15% of N), acidifying alkaline water, and letting pH ride within 5.5–6.2 rather than chasing a single number. A fast unexplained fall, or a rise with brown roots, points to root or microbial trouble. - Canonical: https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.html - Category: pH and EC · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: DWC, RDWC, NFT, Ebb and flow, Aeroponics, Drip - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why does my hydro pH keep going up?** Hydro reservoir pH keeps going up mainly because cannabis absorbs nitrate faster than cations and releases hydroxide or bicarbonate to stay electrically balanced; this is established plant chemistry. Aeration driving off dissolved CO₂, alkaline top-up water and algae in a lit reservoir add to the rise. A steady climb of a few tenths per day in a healthy system is normal. **Why is my DWC pH dropping?** DWC pH usually drops because of an ammonium-heavy feed, nitrifying bacteria in biofilm or organic additives converting ammonium to nitrate, decaying organic matter, or dying roots releasing organic acids. A sudden fall with brown, slimy roots or a bad smell is a root-rot warning, according to grower observation. Inspect the roots and check the reservoir temperature, ideally 18–22 °C. **How often should I adjust pH in hydro?** Adjust hydro pH only when it leaves the 5.5–6.2 working band, not several times a day. Let it ride upward inside the band and reset it to the bottom when needed. After mixing a fresh reservoir, aerate for 30–60 minutes before the final adjustment, because CO₂ loss raises pH in the first hours. Chasing an exact 5.8 is a common mistake. **Is pH drift a sign of a problem?** No, steady upward pH drift is usually a sign of a healthy, feeding hydro system, typically about 0.1–0.4 pH units per day in DWC, especially with falling EC. Drift becomes a warning when pH falls quickly for no clear reason, or rises alongside brown roots or a bad smell, which points to root disease or microbial trouble. Check the meter's calibration first. **How do I stop pH swings in RO water?** pH swings bigger in RO-based hydro because RO water with nutrients has little buffering, so the same nutrient uptake moves pH further. Steady them with a small ammonium share of about 5–15 % of total nitrogen, more reservoir litres per plant, and a 5.5–6.2 band rather than a fixed number. Keep ammonium below about 30 %, which harms cannabis. **Does an air stone raise pH?** Yes, an air stone can raise reservoir pH, because strong aeration strips dissolved CO₂, which otherwise forms carbonic acid. The effect is largest in the first hours after mixing, especially with carbonated groundwater, and its size depends on the water's alkalinity. Aerate a fresh mix for 30–60 minutes before the final pH adjustment so the reading settles first. **Short answer.** Reservoir pH usually rises because plants absorb nitrate (an anion) faster than cations, and release hydroxide or bicarbonate to stay electrically balanced [1][5]. Aeration driving off dissolved CO₂, alkaline top-up water and algae add to the rise. Ammonium uptake does the opposite and pushes pH down [5]. A steady upward drift of a few tenths per day in a healthy, growing system is normal. Manage it, don't fight it: a small ammonium share, acidified water, and a 5.5–6.2 band. ## What's happening **1. Nitrate uptake (the main driver).** A nitrate-based feed supplies most N as NO₃⁻. To take up one negative ion without becoming charged, the root exports OH⁻ or HCO₃⁻. In nitrate-based recirculating systems, pH climbs as plants grow [1][5]. Faster growth means faster drift, which is why drift increases in late veg and early flower. **2. Ammonium uptake (pushes pH down).** NH₄⁺ uptake exports H⁺. Rhizosphere pH can drop by up to about two units under ammonium nutrition [5]. A small ammonium share balances the nitrate effect. Bugbee's group stabilised recirculating solutions with automated additions of nitric acid plus ammonium nitrate, reporting stable root-zone pH and no anion accumulation at a 1:2 molar ratio of ammonium nitrate to nitric acid [2]. Cannabis tolerates up to about 10–30% of N as ammonium; above 30% it is harmful [3]. **3. CO₂ loss.** Dissolved CO₂ forms carbonic acid. Strong aeration strips CO₂ toward equilibrium with air, so freshly mixed solution (especially from carbonated groundwater) rises in pH for the first hours. *Established* chemistry; magnitude depends on alkalinity. **4. Alkalinity in water.** Topping up with bicarbonate-rich tap water adds base every day [4] (see [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md)). **5. Algae and biofilm.** Photosynthesising algae in a lit reservoir consume CO₂ and raise pH. Light-proof reservoirs and lines. **6. Low buffering.** RO water with a nutrient mix has little buffering, so the same uptake moves pH further. That is the trade-off for precision. **When pH falls instead:** ammonium-heavy feeds; nitrifying bacteria in biofilm or organic additives converting ammonium to nitrate (releases acid); decaying organic matter; or root death releasing organic acids. A sudden fall with brown, slimy roots or a bad smell is a root-rot warning (see [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)). ## Numbers that matter | Parameter | Typical | Notes | |---|---|---| | Working band | 5.5–6.2 | Let pH ride up inside it, reset to the bottom | | Normal drift, healthy DWC | ~0.1–0.4 pH units/day | *Grower practice*; depends on plant size vs reservoir volume. | | NH₄ share to slow drift | 5–15% of total N | Cannabis safe up to ~10–30% [3] | | Reservoir temperature | 18–22 °C (64–72 °F) | Warmer: less O₂, more microbial activity | | Alkalinity of top-up water | <1 meq/L (50 mg/L CaCO₃) | Acidify above this | ## What to check first 1. **Is the meter right?** Calibrate (see [meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)). 2. **Direction and speed.** Steady rise = normal uptake. Rapid rise right after mixing = CO₂ off-gassing or silicate. Fall = ammonium, biology, or roots. 3. **Roots and smell.** White and earthy is good. 4. **EC trend at the same time.** EC falling with pH rising = plants feeding normally. EC rising with pH rising = plants drinking more water than nutrients; top up with plain water. 5. **Top-up water alkalinity.** ## How to fix it - **Accept drift inside the band.** Adjust when pH leaves 5.5–6.2, not every hour. - **Mix, wait, adjust.** After mixing a fresh tank, aerate 30–60 minutes before final pH adjustment. - **Add a small ammonium share** (calcium nitrate already gives ~5%; a little ammonium nitrate or MAP takes it to 10%). - **Acidify top-up water** to reduce alkalinity, rather than repeatedly dosing the reservoir. - **Size the reservoir**: more litres per plant means slower drift. - **Dose pH-down with nitric or phosphoric acid**; account for the N or P added. Potassium hydroxide for pH-up. - **Light-proof everything.** - **Safety:** wear gloves and goggles with acids and hydroxides; add acid to water. ## Common mistakes - Chasing an exact 5.8 several times a day. - Using strong pH-up made from sodium hydroxide (adds sodium). - Adding potassium silicate last, then fighting a pH spike. - Ignoring a falling pH with brown roots. ## Evidence - Nitrate uptake raises and ammonium uptake lowers root-zone pH: *Established* [1][5]. - Nitric acid plus ammonium dosing stabilises recirculating systems: *Supported* (controlled studies, non-cannabis crops [2]). - Cannabis ammonium tolerance: *Supported* [3]. - Drift within the 5.5–6.5 band is normal and harmless: accepted practice (extension and grower consensus). - Typical daily drift rates: *Grower practice*. ## Sources 1. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 2. Langenfeld NJ, Bugbee B. 2025. pH control in recirculating hydroponics with nitric acid and ammonium nitrate. HortScience 60(9):1555. https://journals.ashs.org/view/journals/hortsci/60/9/article-p1555.xml 3. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 4. Lopez RG, Mickelbart MV, Pasian C. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 5. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 6. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Runoff testing: how to measure root-zone pH and EC and what the numbers mean > Runoff (leachate) pH and EC tell you what the roots are actually sitting in, which is often different from what you fed. Use the pour-through method: water to full saturation, wait 30 minutes to 2 hours, then pour a measured amount of water on top and collect about 50 mL. Compare runoff EC with input EC: higher means salts are building up, much lower means the plant is hungry or you are over-leaching. Track the trend over weeks rather than reacting to one reading. - Canonical: https://genetixbay.com/knowledge/ph-ec/runoff-testing.html - Category: pH and EC · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Soil, Coco, Rockwool, Drip, Living soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I test runoff pH and EC?** To test runoff pH and EC, irrigate the pot to full saturation, wait 30 minutes to 2 hours, then pour enough clean water evenly on top to collect about 50 mL from the bottom. Measure pH and EC promptly, because leachate pH can change within about 2 hours. Also measure your irrigation water, and sample the same 3–5 plants each time. **What should my runoff EC be compared to my input?** Cannabis runoff EC is normally about equal to the input EC, up to roughly 0.5 mS/cm higher. Runoff more than 0.8–1.0 mS/cm above input and rising means salts are accumulating, while runoff well below input means uptake exceeds supply or you are leaching heavily. These targets are grower practice for soilless media, consistent with general greenhouse practice. **Why is my runoff EC higher than what I feed?** Runoff EC climbs above feed EC because cannabis takes up water faster than some ions, so salts concentrate in the medium between irrigations. If runoff is more than about 0.8–1.0 mS/cm above input and rising, lower feed EC by 10–20 % or increase runoff volume. Sampling a dry pot with a small splash exaggerates the reading. **Why is my runoff pH different from my feed pH?** Runoff pH differs from feed pH because chemistry changes inside the pot: nitrate uptake pushes pH up, ammonium pushes it down, alkaline water raises it over time, and peat and fresh coco have their own chemistry. Runoff rising more than 0.5 above input over weeks calls for acidified water or a small ammonium share; runoff falling below about 5.5 suggests ammonium, acidic organics or root problems. **What is the pour-through method?** The pour-through method is an extension technique for measuring root-zone pH and EC in containers. After irrigating to container capacity and waiting 30 minutes to 2 hours, you pour a set volume of water on top, for example about 350 mL for a 12 L pot, which pushes roughly 50 mL of the pot's held solution out of the bottom for testing. It is established in container horticulture. **How much runoff should I get in coco?** In drain-to-waste coco and rockwool, a common target is 10–20 % of the applied volume as runoff each day, increased in hot conditions or when runoff EC is climbing. That figure is grower practice rather than a cannabis-specific trial result. Constant heavy leaching wastes fertiliser and, with phosphorus, pollutes, so fix the feed rather than over-leaching every watering. **How do I flush salt build-up out of my medium?** To flush salt build-up, run about 2–3 times the container volume through slowly in several passes: pH-adjusted plain water at about 6.3–6.8 for soil, or a light solution at EC 0.4–0.8 mS/cm with calcium and magnesium, pH 5.8–6.0, for coco and rockwool. Stop when runoff EC is within about 0.3–0.5 mS/cm of the input, then resume normal feeding. **Should I flush before harvest?** No, you should not flush cannabis before harvest. Pre-harvest flushing is a myth that costs yield and resin by starving the plant during its final weeks, so feed through to harvest. The only valid flush is a root-zone flush that washes accumulated salts out of the medium when runoff EC is high or lockout appears, and it can be done at any stage. **Short answer.** Runoff (leachate) pH and EC tell you what the roots are actually sitting in, which can be very different from what you fed. Use the **pour-through method**: irrigate to full saturation, wait 30 minutes to 2 hours, pour a measured amount of water on top, and collect about 50 mL from the bottom [1]. Compare runoff EC with input EC: higher means salts are building up; much lower means the plant is hungry or you are leaching hard. Watch the trend over weeks, not one reading. ## What's happening In any container, water and salts are not uniform. Plants take up water faster than some ions, so salts concentrate between irrigations. Water draining from the bottom after a fresh pour displaces the solution held in the bottom of the pot (the perched water table) and gives an average reading of what the roots experience [1]. pH also shifts in the pot: nitrate uptake pushes it up, ammonium down; alkaline water pushes it up over time; peat and fresh coco have their own chemistry [3]. ## The pour-through method From NC State's nursery procedure [1]: 1. **Irrigate thoroughly** as normal, to container capacity. 2. **Wait 30 minutes to 2 hours.** 3. **Place a saucer** under the pot. 4. **Pour clean water** (or your normal feed, but be consistent) evenly on the surface, enough to push out about 50 mL. Guide volumes: | Container | Pour | Collect | |---|---|---| | 4 L (1 gal) | ~120 mL | ~50 mL | | 12 L (3 gal) | ~350 mL | ~50 mL | | 19 L (5 gal) | ~600 mL | ~50 mL | | 27 L (7 gal) | ~825 mL | ~50 mL | | 38 L (10 gal) | ~1,200 mL | ~50 mL | 5. **Measure pH and EC promptly**; leachate pH can change within about 2 hours [2]. 6. **Measure your irrigation water too** and subtract its EC to see what comes from fertiliser [1]. 7. **Sample the same 3–5 representative plants** each time and log it. Drain-to-waste coco and rockwool growers usually just catch the drain from the irrigation itself. That works, but the first runoff after a dry-back is saltier than the last; mix the whole catch or always sample the same way. ## Reading the numbers These ranges are *grower practice* for cannabis in soilless media; extension ranges exist for ornamentals but not cannabis. | Runoff vs input | What it usually means | What to do | |---|---|---| | Runoff EC ≈ input to +0.5 mS/cm | Normal | Nothing | | Runoff EC >+0.8–1.0 mS/cm above input, rising | Salts accumulating; plant drinking more water than nutrients | Lower feed EC 10–20% and/or increase runoff volume | | Runoff EC well below input | Plant uptake exceeds supply, or heavy leaching | Raise feed EC slightly; check runoff volume | | Runoff pH >0.5 above input, rising over weeks | Nitrate uptake and/or alkaline water | Acidify water; slightly lower input pH; small ammonium share | | Runoff pH falling below ~5.5 | Ammonium-heavy feed, acidic organics, or root problems | Raise input pH; review N form; check roots | | Runoff EC very high with burnt tips | Salt stress | Root-zone flush (below); see [burnt tips](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) | **Runoff volume** in coco and rockwool drain-to-waste: 10–20% of applied volume per day is common *grower practice*; more in hot conditions or when EC is climbing. **Soil and living soil:** pour-through still works, but organic soil EC is lower and pH more stable; use it to catch trends and sodium or salt build-up rather than to steer daily. ## When runoff says flush the medium A **root-zone flush** washes accumulated salts out of the medium so you can start fresh. It treats the medium, not the plant, and can be done at any stage. Use it when runoff EC is far above input (roughly +1.0 mS/cm or more and rising), when salt crusts the surface, or when you see lockout symptoms despite a full feed. 1. Record input and runoff pH and EC. 2. **Soil:** pH-adjusted plain water (pH ~6.3–6.8). **Coco, rockwool, hydro media:** a light solution (EC ~0.4–0.8 mS/cm, with Ca and Mg) at pH ~5.8–6.0; plain water strips Ca and Mg from coco. 3. Run about **2–3× the container volume** through slowly, in several passes. 4. Check runoff EC on the last pass: stop when it's within ~0.3–0.5 mS/cm of the flush input and runoff pH is in range. 5. Go straight back to normal feeding, and fix the cause (feed EC, runoff volume, water hardness). This is not a pre-harvest flush. Flushing before harvest is a *Myth* that costs you yield and resin; feed through to harvest (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). ## Common mistakes - Testing runoff from a dry pot with a small splash: you get the most concentrated salts and panic. - Changing feed in response to one reading. - Measuring hours later after the sample has sat in the sun. - Using an uncalibrated meter (see [meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)). - Over-leaching every watering to "fix" a high runoff: one proper root-zone flush, then fix the feed. Constant heavy leaching wastes fertiliser and, with P, pollutes [4]. ## Evidence - Pour-through gives representative substrate EC and pH: *Established* in container horticulture [1][2]. - Interpreting runoff EC relative to input EC for cannabis: *Grower practice*; consistent with general greenhouse practice [5]. ## Sources 1. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download 2. Cavins TJ, Whipker BE, Fonteno WC, Harden B, McCall I, Gibson JL. Monitoring and managing pH and EC using the PourThru extraction method. NC State University Horticulture Information Leaflet 590. Cited via MSU Extension: https://www.canr.msu.edu/uploads/resources/pdfs/measuring_ph_and_ec_of_crops_grown_in_large_containers.pdf 3. Lopez RG, Mickelbart MV, Pasian C. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 4. Westmoreland FM, Bugbee B. 2022. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 5. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine > Get a water report before choosing a feed. Alkalinity (bicarbonate), not water pH, is what pushes root-zone pH up over time; above about 100–150 mg/L as CaCO3 (2–3 meq/L) it should be partly neutralised with acid. Tap water may also add useful Ca and Mg, or harmful sodium, chloride and boron. RO water removes nearly everything, which gives precise control but means you must add back Ca and Mg. Chloramine does not evaporate; remove it with long-contact or catalytic carbon or ascorbic acid if you run living soil or beneficial microbes. - Canonical: https://genetixbay.com/knowledge/ph-ec/water-quality.html - Category: pH and EC · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should I use RO water or tap water for cannabis?** Use RO water for cannabis when your tap water has high sodium, chloride or boron, alkalinity you cannot economically acidify, or when you need exact recipes; otherwise good tap water, often 0.2–0.8 mS/cm, can supply useful calcium and magnesium. RO is under 0.05 mS/cm, so you must add calcium and magnesium back and expect easier pH swings. Many growers blend the two. **What is alkalinity and why does it matter?** Alkalinity is water's capacity to neutralise acid, mostly from bicarbonates and carbonates, and it matters because it, not water pH, pushes root-zone pH up over time. High-alkalinity water acts like adding lime at every irrigation. One meq/L equals 50 mg/L as CaCO₃; extension guidance says to partly neutralise water above about 2–3 meq/L, or 100–150 mg/L. **How much acid do I need to treat hard water?** To treat high-alkalinity water, 1 meq/L of acid neutralises 1 meq/L of alkalinity, so subtract the buffer you want to keep, about 0.5–1 meq/L for hydro, from the measured alkalinity and dose that difference. Use an extension alkalinity calculator, count the sulfur, nitrogen or phosphorus each acid adds, always add acid to water, and re-test every season. **Does chloramine hurt cannabis or soil microbes?** Whether chloramine at tap-water levels hurts cannabis is contested: no cannabis study was found. The main concern is soil biology, compost teas and beneficial inoculants, which are sensitive to disinfectants, while mineral hydro run with sterile intent is less affected. Living-soil growers should remove chloramine with long-contact or catalytic carbon or ascorbic acid; the US limit is 4 mg/L. **Does letting tap water sit remove chloramine?** No, letting tap water sit does not remove chloramine. Chlorine gasses off from standing water, but chloramine does not, and boiling or adding salt does not remove it either. Use granular activated carbon with long contact time, about 10 minutes or more, catalytic carbon, or ascorbic acid. Standard RO does not reliably remove chloramine. **What is a good EC for source water?** A good source water EC for cannabis is below about 0.5 mS/cm; above 0.8 mS/cm it leaves little room for nutrients before total feed EC gets too high. Also check the report for sodium, ideally under 30 mg/L, chloride under 30 mg/L and boron under about 0.3 mg/L, since EC alone does not show which ions are present. **Short answer.** Get a water report before you choose a feed. **Alkalinity** (mostly bicarbonate), not water pH, is what pushes root-zone pH up over time [1]; above roughly 100–150 mg/L as CaCO₃ (2–3 meq/L) neutralise part of it with acid [1][2]. Tap water may add useful Ca and Mg, or harmful Na, Cl and B. **RO** removes nearly everything: precise, but you must add back Ca and Mg. **Chloramine** does not evaporate; remove it with long-contact or catalytic carbon or ascorbic acid if you run living soil or beneficial microbes [3][4][5]. ## What's happening ### pH vs alkalinity pH is the hydrogen-ion level right now. Alkalinity is the water's capacity to neutralise acid, its buffer, from carbonates and bicarbonates [1]. Water at pH 7.5 with low alkalinity barely affects the root zone; water at pH 7.5 with high alkalinity acts like adding lime every irrigation [1]. Purdue's summary: water pH has minimal effect on root-zone pH; alkalinity has a large one [1]. Alkalinity units confuse everyone [1][2]: - 1 meq/L alkalinity = 50 mg/L (ppm) as CaCO₃ = 61 mg/L as HCO₃⁻. - Hardness (Ca + Mg) often tracks alkalinity but is not the same thing. ### RO vs tap | | Tap / well | RO | |---|---|---| | EC | Often 0.2–0.8 mS/cm | <0.05 mS/cm | | Ca, Mg | May supply a useful share | ~0 (add back; see [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)) | | Alkalinity | Low to very high | ~0; pH swings easily | | Na, Cl, B | Variable; can be limiting | Removed | | Chlorine / chloramine | Present in municipal water | Chlorine damages thin-film RO membranes; use a carbon prefilter. RO does not reliably remove chloramine [3] | | Cost, waste | Low | Equipment, membranes, reject water | Use RO when your tap water has high Na or Cl, high B, high alkalinity you can't economically acidify, or when you need exact recipes. Many growers blend RO and tap to hit a target. ### Chloramine Utilities use chlorine or chloramine to disinfect. Chlorine gasses off from standing water; **chloramine does not**, and boiling or adding salt does not remove it either [3]. The US EPA limit is 4 mg/L (as Cl₂) [3]. Removal: granular activated carbon with long contact time (a bed contact time of about 10 minutes or more may be needed with ordinary carbon), catalytic carbon, or ascorbic acid (vitamin C) [3][4][5]. The USDA Forest Service describes ascorbic acid and sodium ascorbate as effective dechlorinators that slightly lower dissolved oxygen in the treated water [5]. Aquarium guides quote roughly 2.5–2.8 parts vitamin C per part chlorine by weight. Does it harm cannabis? At drinking-water levels, no cannabis study was found. The main concern is for soil biology, compost teas and beneficial inoculants, which are disinfectant-sensitive; mineral hydro with sterile intent is less affected. *Contested.* ## Numbers that matter | Parameter | Good | Act if | Notes | |---|---|---|---| | Source EC | <0.5 mS/cm | >0.8 mS/cm | Leaves little room for nutrients | | Alkalinity | 0.5–1.5 meq/L (25–75 mg/L CaCO₃) | >2–3 meq/L (100–150 mg/L CaCO₃) | Extension guidance 50–120 mg/L CaCO₃ after treatment for many crops [1][2]; for hydro keep ~0.5–1 meq/L buffer [6] | | Bicarbonate | <60–120 mg/L HCO₃⁻ | >180 mg/L | Purdue: low <80, moderate 100–200, high >200 mg/L [1] | | Na | <30 mg/L | >50 mg/L | >5 mM NaCl (115 mg/L Na) may cut cannabis yield [7] | | Cl | <30 mg/L | >50–70 mg/L | See [chloride](https://genetixbay.com/knowledge/nutrients/chlorine.md) | | B | <0.3 mg/L | >0.5 mg/L | Count it in the feed. | | Ca, Mg | Note the values | | Subtract from recipe | | Chloramine | 0 for living soil | Any, if using biology | [3] | ## How to treat high alkalinity 1. **Test** alkalinity (lab report or a drop-count alkalinity kit). 2. **Decide how much to remove.** Leave about 0.5–1 meq/L as a buffer in hydro [6]; neutralise the rest. 3. **Choose the acid** and count the nutrient it adds: sulfuric (adds S), nitric (adds N), phosphoric (adds P; the P limits how much you can use). NC State notes sulfuric is the most common for bicarbonate neutralisation [2]. 1 meq/L of acid neutralises 1 meq/L of alkalinity. 4. **Calculate the dose** with an alkalinity calculator (Purdue, NC State and New Hampshire developed one [1]) or the NC State formula [2]. Add acid to the water, mix, wait, measure pH. 5. **Re-test** every season: well water alkalinity changes with drought and rain [1]. **Safety:** concentrated acids cause severe burns and nitric acid fumes are toxic. Gloves, goggles, ventilation. Always add acid to water, never the reverse. ## Common mistakes - Adjusting water pH and ignoring alkalinity. - Running high-sodium softened water (see [sodium](https://genetixbay.com/knowledge/nutrients/sodium.md)). - Letting chloramine water "stand overnight" for living soil. - Using a base nutrient designed for hard water with RO, and then blaming the plant. ## Evidence - Alkalinity, not pH, drives substrate pH: *Established* [1]. - Extension alkalinity targets and acid methods: *Established* for container crops [1][2]; *Supported* (extrapolated) for cannabis. - Chloramine persistence and removal methods: *Established* [3][4]. - Chloramine harming cannabis at tap levels: *Contested*; no study found. ## Sources 1. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 2. NC State Extension. Producing conventional tobacco transplants in greenhouses: water quality. https://content.ces.ncsu.edu/producing-conventional-tobacco-transplants-in-greenhouses-water-quality 3. Massachusetts Department of Environmental Protection. Public notification template when switching from chlorine to chloramines. https://www.mass.gov/doc/public-notification-template-when-switching-from-chlorine-to-chloramines/download 4. Water Quality Association. 2014. Chloramine fact sheet. https://wqa.org/wp-content/uploads/2022/09/2014_Chloramine.pdf 5. USDA Forest Service. Vitamin C dechlorination. https://www.fs.usda.gov/t-d/pubs/html/05231301/05231301.html 6. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 7. Yep B, Gale NV, Zheng Y. 2020. Frontiers in Plant Science 11:1169. https://doi.org/10.3389/fpls.2020.01169 --- # Bottom-watering, soak trays and wick (self-watering) systems > Bottom-watering lets pots draw solution up from a tray, either by a timed soak (flood 2–5 cm for 10–30 minutes, then drain) or by a constant shallow level held by a float valve or wick. It is gentle and labour-saving and suits soil, but salts accumulate at the top of the pot, so feed at lower EC than top-feeding and top-water to runoff every week or two. - Canonical: https://genetixbay.com/knowledge/systems/bottom-watering-wick.html - Category: Systems · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Soil, Coco, Living soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is bottom watering good for cannabis?** Bottom watering is a good, gentle way to water cannabis in soil or airy coco blends, as long as you manage salts. Pots drink from a tray, either by a 15–30 minute soak at 2–5 cm depth or from a constant shallow level. Evaporation pulls salts to the top of the pot, so feed weaker and top-water to runoff every 7–14 days. **Do self-watering pots work for cannabis?** Self-watering wick and float-valve pots do work for cannabis grown in soil or a free-draining coco and perlite mix, and they suit busy growers. Feed about 20–30% below top-feed strength (grower practice), give the tray a dry day every 7–10 days to re-oxygenate the pot base, and avoid dense media, which wick too much water and stay soggy. **Why is there white crust on top of my bottom-watered pots?** White crust on bottom-watered pots is accumulated fertiliser salt. Extension research shows evaporation draws salts upward in subirrigated pots, so the top layer can reach several times the EC of the rest of the root zone. Fix it by top-watering to 10–20% runoff and lowering feed EC, and switch to heavy top-watering gradually so the salt layer doesn't hit the roots at once. **Should I bottom water seedlings?** Cannabis seedlings in large pots should be top-watered first, not bottom-watered. Water from above until the roots reach the bottom of the pot, then switch to tray soaks or a wick. Bottom-watering a big pot before roots reach the base is a common mistake, because the wet lower mix has no roots to use the water and stays soggy. **Short answer.** Pots stand in a tray and drink from below. Two flavours: **soak** (fill the tray 2–5 cm / 1–2 in for 10–30 min, drain, repeat 1–2× a day as needed) and **constant level** (a float valve or wick keeps a shallow reservoir topped up) [4]. It's the gentlest method on hardware and roots and suits soil well [4]. The catch: evaporation pulls salts to the **top** of the pot, where EC can reach several times the rest of the root zone [1][2][3]. **Feed weaker than you would top-feed** and **top-water to runoff every 7–14 days**. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Soak depth | 2–5 cm (1–2 in) | [4] | | Soak dwell | 15–30 min, then drain | [4] | | Feed EC | ~20–30 % below top-feed equivalent | | | Top-water flush | Every 7–14 days, to 10–20 % runoff | Pushes the salt layer down and out | | Constant-level systems | "Dry the tray" day every 7–10 days | Re-oxygenates the pot base [4] | | Media | Soil, airy coco/perlite blends | Dense media wick too much, stay soggy | ## How to run it 1. Start seedlings top-watered until roots reach the pot bottom; then switch. 2. Use a free-draining mix with a coarse bottom layer for wick/float systems. 3. Weigh pots or use a VWC probe to decide soak frequency. 4. Sample EC from the top layer separately if tips burn; discard the top 1–2 cm when sampling the root zone [3]. 5. Keep trays clean; standing nutrient solution grows algae and fungus gnats. ## Failure modes | Problem | Sign | Response | |---|---|---| | Salt crust on top | White crust, burnt leaf tips | Top-water flush; lower EC | | Waterlogged base | Slow growth, brown bottom roots | Dry-tray days; airier mix | | Stagnant tray | Smell, algae | Refresh; Jardin can add an air-stone option [4] | | Tray overflow | Water on floor | Level sensor + leak pad [4] | A warning when switching methods: if you stop bottom-watering and start heavy top-watering, the salt layer moves down into the roots at once [3]. Flush gradually. ## Jardin notes Jardin method "Sub-irrigation / soak / wick": tray level (float or pressure) and reservoir mass required; soak = fill to level, dwell, drain (max-on timer 1.5 × learned fill); wick = continuous hold with periodic dry days. Time-to-harm: days. Automation level 3 [4]. ## Common mistakes - Hydro-strength feed in a wick system. - Never top-watering. - Bottom-watering seedlings in big pots before roots reach the base. ## Evidence Top-layer salt accumulation and the switching risk are *Established* extension knowledge [1][2][3]. Cannabis-specific EC reductions are *Grower practice*. ## Sources 1. UMass Extension. Subirrigation for greenhouse crops. https://www.umass.edu/agriculture-food-environment/greenhouse-floriculture/fact-sheets/subirrigation-for-greenhouse-crops 2. NC State University. Subirrigation (top-layer EC). https://hortscans.ces.ncsu.edu/uploads/s/u/subirrig_51e435ff2e468.pdf 3. University of Arkansas. Greenhouse management, Unit 9 §6 (salts in the upper inch; risk when switching to overhead watering). https://greenhouse.hosted.uark.edu/Unit09/Section06.html 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Choosing your growing system: soil, coco, rockwool or hydro > Choose by how much attention and measurement you can give, not by yield claims. Soil and living soil forgive mistakes for days; coco and drip need daily feeding; DWC, NFT and aeroponics grow fast but can lose roots within hours if a pump or air supply fails. No controlled study shows one system out-yielding the others when light and climate are equal. - Canonical: https://genetixbay.com/knowledge/systems/choosing-a-system.html - Category: Systems · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the best growing system for a beginner?** Soil or coco is the best growing system for most beginner cannabis growers. Soil buffers mistakes for days and needs little more than pH-checked water, while coco gives hydro-like speed but needs daily feeding with pH and EC checks. For a first hydroponic grow, deep water culture or the pump-free Kratky method is the usual starting point. **Is hydro better than soil for cannabis?** Hydro is not proven better than soil for cannabis. No controlled study shows one system out-yielding another at equal light and climate, and research points to light and plant density as the strongest yield drivers. Hydro trades forgiveness for speed: soil buffers mistakes for days, while deep water culture can lose roots in 2–12 hours if the air supply stops. **Which system gives the biggest yield?** No growing system reliably gives the biggest cannabis yield on its own. A meta-analysis of cannabis yield factors found light and plant density among the strongest drivers, and controlled trials showed yield rising linearly with light. Claims that one system out-yields another are grower practice, not research, so invest in lighting and climate before chasing a 'high-yield' system. **Coco or soil?** Choosing coco or soil comes down to attention. Soil forgives mistakes for days, runs at pH 6.2–6.8 and needs only occasional runoff checks, making it the safer first grow. Coco runs at pH 5.8–6.2, needs daily feeding with pH and EC checks, and can harm plants within 12–36 hours if irrigation stops, but rewards that attention with fast, hydro-like growth. **Which hydroponic system is easiest?** Kratky and deep water culture are the easiest hydroponic systems for cannabis. Kratky needs no pump, so nothing can fail, though you still check level, EC and water temperature. Deep water culture is cheap and fast but needs pH, EC and temperature checks and loses roots within 2–12 hours if the air stops. Ebb and flow is also forgiving, since its media buffer pump failures for days. **Short answer.** Pick the system whose **failure mode you can live with**. Soil and living soil buffer mistakes for **days**; coco and rockwool for **12–48 hours**; DWC for **2–12 hours** if the air stops; NFT and LPA for **1–4 hours**; HPA for **tens of minutes** [5]. Yield follows **light, climate and the grower** far more than the system: a meta-analysis of cannabis yield factors found light and plant density among the strongest drivers [1], and yield rose linearly with light in controlled trials [2]. There is no controlled study showing one system out-yields another at equal light. Beginners: **soil or coco**. First hydro: **DWC or Kratky**. ## Side-by-side | System | Forgiveness (time-to-harm on actuator failure) [5] | Daily attention | Measurement needed | Cost | Typical pH | Best for | |---|---|---|---|---|---|---| | [Soil (bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) | Days | Low | pH of water; occasional runoff EC | Low | 6.2–6.8 | First grow | | [Living soil](https://genetixbay.com/knowledge/systems/living-soil.md) | Days | Low | Moisture | Low–medium | 6.3–7.0 (not controlled) | Low-input, organic | | [Bottom-water / wick](https://genetixbay.com/knowledge/systems/bottom-watering-wick.md) | Days | Very low | Tray level; occasional top EC | Low | Medium-dependent | Busy growers, soil | | [Coco](https://genetixbay.com/knowledge/systems/coco.md) (hand or drip) | 12–36 h | Daily | pH, EC, runoff | Low–medium | 5.8–6.2 | Fast growth, hydro-like control | | [Rockwool](https://genetixbay.com/knowledge/systems/rockwool.md) | 24–48 h | Daily | VWC/EC probe | Medium | 5.5–6.0 | Precision, crop steering | | [Ebb & flow](https://genetixbay.com/knowledge/systems/ebb-and-flow.md) | Days | Low–medium | pH, EC, reservoir | Medium | 5.6–6.2 | Many small plants, SOG | | [Recirculating drip](https://genetixbay.com/knowledge/systems/recirculating-drip.md) | 12–36 h | Medium | pH, EC, runoff, refresh | Medium | Per medium | Water/nutrient saving | | [Drain-to-waste + steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) | 12–36 h | Medium–high | VWC/EC probe | Medium–high | Per medium | Advanced/commercial | | [Kratky](https://genetixbay.com/knowledge/systems/kratky.md) | n/a (no pump) | Low | Level, EC, water temp | Very low | 5.6–6.2 | Hydro on a budget, autos | | [DWC](https://genetixbay.com/knowledge/systems/dwc.md) | 2–12 h (air) | Medium | pH, EC, water temp | Low | 5.6–6.0 | Fast veg, first hydro | | [RDWC](https://genetixbay.com/knowledge/systems/rdwc.md) | 2–12 h (air) | Medium | pH, EC, water temp, flows | Medium–high | 5.6–6.0 | Multiple large plants | | [NFT](https://genetixbay.com/knowledge/systems/nft.md) | 1–3 h | Medium | Flow, pH, EC | Medium | 5.6–6.0 | Clones, mothers, small plants | | [LPA](https://genetixbay.com/knowledge/systems/lpa-aeroponics.md) | 1–4 h | Medium | Chamber RH, pH, EC | Medium | 5.6–6.0 | Aero without the risk of HPA | | [HPA](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) | Tens of minutes to hours | High | Pressure, RH, battery | High | 5.6–6.0 | Experienced tinkerers | | [Fogponics](https://genetixbay.com/knowledge/systems/fogponics.md) | Hours (as sole method) | Medium | Tank level, EC | Low | n/a | Supplement only | ## Decision guide 1. **Will you be away for 2+ days without automation?** → Soil, living soil or bottom-watering. 2. **Can you check pH and EC daily?** → Coco or DWC become options. 3. **Is your power or water supply unreliable?** → Avoid NFT and HPA; prefer media-based systems. 4. **Hot room in summer (reservoir above 24 °C / 75 °F)?** → Media-based systems, or budget for a chiller [4]. 5. **Many small plants (SOG)?** → Ebb & flow or coco drip. 6. **Want to steer for yield and quality with data?** → Rockwool or coco on drain-to-waste with a VWC/EC probe. ## Common mistakes - Choosing hydro "for yield" and then running it in a hot, poorly lit room. - Mixing system advice: soil pH and feed schedules in coco, or hydro-strength EC in soil. - Building aeroponics before mastering a forgiving system. ## Evidence Failure-margin times are engineering estimates from GenetixBay's Jardin design [5]. The dominance of light and density over system choice is *Supported* [1][2]. Root-disease risk in warm recirculating systems is *Established* [4]. Comparative yield claims between systems are *Grower practice*. ## Sources 1. Backer R, Schwinghamer T, Rosenbaum P, et al., 2019. Closing the yield gap for cannabis: a meta-analysis of factors determining cannabis yield. Frontiers in Plant Science 10:495. https://doi.org/10.3389/fpls.2019.00495 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 3. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 4. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 5. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Deep water culture (DWC) > In DWC roots hang in an aerated nutrient solution. It grows fast but depends on two things: dissolved oxygen (keep above about 6 mg/L, ideally near saturation) and solution temperature (18–22 °C / 64–72 °F). Warm, poorly aerated water is how Pythium root rot starts. Run pH 5.6–6.0 and EC 0.8–2.0 mS/cm by stage, and treat the air pump as life support. - Canonical: https://genetixbay.com/knowledge/systems/dwc.html - Category: Systems · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: DWC - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should my reservoir be sterile or full of beneficial microbes?** GenetixBay prefers a beneficial-microbe reservoir for DWC, because bacteria will turn up in any reservoir whatever you do, so you may as well have the good ones. A sterile reservoir is a valid choice only if you commit fully, with a continuous oxidiser or UV or ozone, clean top-ups and no organics. Mixing the two, such as routine peroxide on top of microbes, is what fails. **What water temperature for DWC?** DWC water temperature should be 18–22 °C (64–72 °F), with 24 °C (75 °F) as the alarm point. Warm water holds less oxygen, about 9 mg/L at 20 °C versus 8 mg/L at 25 °C, and extension research links warm, poorly aerated solution to Pythium root rot. In summer, use a chiller or keep the reservoir in a cooler room. **How much air does a DWC bucket need?** A DWC bucket needs about 1–2 litres per minute of air per 10 litres of solution, a grower rule of thumb, enough to keep dissolved oxygen above 6 mg/L and ideally at 7–9 mg/L. Size the air pump for all buckets plus margin, put air stones on the bottom, and keep a backup pump, because roots suffer within 2–12 hours if the air stops. **Why are my DWC roots brown and slimy?** Brown, slimy DWC roots with a swampy smell are root rot, usually Pythium, which is favoured by warm, low-oxygen solution; tan roots alone can be normal nutrient staining. Respond by cooling the water to 18–22 °C, raising dissolved oxygen, cleaning the system, removing dead roots and using biological root treatments. Wide daily pH swings are often an early warning sign. **How often should I change the DWC reservoir?** Change a DWC reservoir every 7–14 days, or on mass-balance rules if you track what the plants actually take up. Between changes, top off with plain or quarter-strength water as plants drink, and keep checking pH and EC. If pH swings widely from day to day, inspect the roots for rot before simply buffering and refreshing the solution. **What pH for DWC cannabis?** DWC cannabis runs best at pH 5.6–6.0, letting the pH drift within that band rather than chasing exactly 5.8. Treat readings below 5.4 or above 6.4 as an alarm. This sits within the accepted hydroponic range of 5.5–6.5. Wide daily pH swings often point to root rot, so inspect the roots before adding more pH adjuster. **Short answer.** Roots hang in a bucket of nutrient solution kept oxygenated by an air pump and air stones. It is fast and cheap to build, and unforgiving of two things: **low dissolved oxygen (DO)** and **warm water**. Keep solution at **18–22 °C (64–72 °F)** and DO **above ~6 mg/L (ideally 7–9 mg/L, near saturation)** [1][2][4]. Run **pH 5.6–6.0**, **EC 0.6–1.0 mS/cm (seedling) to 1.4–2.0 (flower)**. If the air pump stops, roots are in trouble within **2–12 hours** [5]. ## How it works Roots respire and need oxygen. Water holds little of it, and less as it warms (about 9 mg/L at 20 °C, 8 mg/L at 25 °C at sea level). Bubbles mix the water and keep it near saturation. Warm, low-oxygen solution suppresses roots and favours *Pythium*, which turns roots brown and slimy [1][2]. Leafy-green extension data show growth inhibition below ~4 mg/L DO and failure below ~3 mg/L [3][4]; cannabis-specific thresholds aren't published. > **House position: living reservoir preferred.** Bacteria will turn up in any reservoir whatever you do, so you may as well have the good ones: GenetixBay prefers a beneficial-microbe reservoir. A sterile reservoir is a valid choice, but only if you commit to it fully (continuous oxidiser or UV/ozone, clean top-ups, no organics) and never mix the two. It's a personal choice; the half-way house is what fails. See [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) for both approaches. ## Numbers that matter | Parameter | Target | Alarm | |---|---|---| | Solution temperature | 18–22 °C (64–72 °F) | > 24 °C (75 °F) | | Dissolved oxygen | ≥ 6 mg/L; 7–9 ideal | < 4 mg/L | | pH | 5.6–6.0 (let it drift within band) | < 5.4 or > 6.4 | | EC, seedling/clone | 0.6–1.0 mS/cm | | | EC, veg | 1.0–1.6 mS/cm | | | EC, flower | 1.4–2.0 mS/cm | | | Air | ~1–2 L/min of air per 10 L solution | | | Gap between net pot and water | 2–5 cm once roots are established | Roots above water get air | | Reservoir refresh | Every 7–14 days or on mass-balance rules | | ## How to run it 1. Opaque bucket (light causes algae), lid, net pot with clay pebbles, air pump sized for all buckets plus margin, air stones on the bottom. 2. Start with the water touching the net pot base; lower it as roots grow. 3. Top off with plain or quarter-strength water as plants drink; full refresh on schedule. 4. Watch roots weekly: white and fuzzy is good, tan from nutrients is normal, brown slime with a swampy smell is root rot. 5. In summer, use a chiller or keep the reservoir in a cooler room. ## Failure modes | Problem | Sign | Response | |---|---|---| | Air pump failure | Wilting within hours, roots dulling | Restart, keep a backup pump; Jardin alerts on zero pump power draw [5] | | Root rot (*Pythium*) | Brown slimy roots, wilting despite water, smell | Cool the water, raise DO, clean system; biological root treatments; remove dead roots | | pH swings | Wide daily drift | Check for root rot first; then buffer and refresh | | Algae | Green film, roots stained | Light-proof everything | ## Jardin notes Jardin method "DWC": air pump on a monitored plug (power draw = proof of life), chiller plug, level floats, top-off, DO proxy from air-pump power and water temperature. On air failure Jardin escalates alerts, keeps the chiller on, and switches on a second pump if one is plugged into a spare port. Time-to-harm: 2–12 h for air, days for chemistry [5]. ## Safety Water and mains electricity share the space. Use GFCI/RCD-protected outlets, drip loops on every cable and keep pumps above reservoir level where possible. ## Common mistakes - Warm reservoir in summer. - One air pump, no backup. - Adding hydrogen peroxide routinely on top of beneficial microbes (they cancel). - Chasing pH 5.8 exactly instead of letting it drift within band. ## Evidence Temperature and DO effects on hydroponic root disease are *Established* in extension literature for other crops [1][2][3][4]. The hydro pH band (5.5–6.5, with drift inside it normal) is accepted practice from extension and grower consensus; cannabis-specific DO and temperature targets are *Grower practice*. ## Sources 1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems (68–72 °F). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 2. e-GRO Alert (Cornell / collaborators). Pythium root rot on hydroponically grown basil and spinach (cool solution 68–72 °F; DO near 8 ppm). https://www.hortidaily.com/article/6040777/pythium-root-rot-on-hydroponically-grown-basil-and-spinach 3. Cornell CEA. Hydroponic lettuce handbook (dissolved oxygen; stress below ~4 mg/L). https://cea.cals.cornell.edu/ 4. Cornell CEA, 2016. Leafy greens (GPN): DO ~7–8 ppm, failure below 3 ppm. https://cea.cals.cornell.edu/files/2019/06/GPNOctober2016_LeafyGreens.pdf 5. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Drain-to-waste drip and crop steering (generative vs vegetative dryback) > Drain-to-waste drip sends fresh solution every shot and discards runoff, so you control the root zone by irrigation timing, shot size and substrate EC measured with a VWC/EC probe. Vegetative steering uses earlier first shots, larger shots and small overnight drybacks (about 10–15 % VWC); generative steering delays the first shot, uses smaller shots, longer P3 and larger drybacks (about 20–35 %) with higher substrate EC. The ranges are grower practice; one cannabis study found controlled late-flower drought raised cannabinoid concentration. - Canonical: https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.html - Category: Systems · Level: Advanced - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Drip, Coco, Rockwool - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is crop steering?** Crop steering is controlling cannabis growth through irrigation timing, shot size, dryback and substrate EC, measured with a substrate moisture and EC probe. In drain-to-waste drip every shot is fresh solution, so the root zone becomes the control surface, and growers push the plant toward leafy bulking or toward flowering. The specific ranges are grower practice adapted from greenhouse tomato work. **What is generative vs vegetative steering?** Vegetative steering pushes leaf and stem growth: first shot 0.5–1.5 hours after lights-on, larger shots, a small 10–15% VWC overnight dryback and input EC around 1.8–2.4 mS/cm. Generative steering pushes flowering and tighter internodes: first shot 2–3 hours after lights-on, smaller shots, last shot 4–6 hours before lights-off, a 20–35% dryback and EC 2.4–3.2 mS/cm. **What are P1, P2 and P3 irrigation phases?** P1, P2 and P3 are the three daily irrigation phases in crop steering. P1 is the ramp-up from lights-on, with small shots every 15–30 minutes until the substrate reaches field capacity and runoff starts. P2 is maintenance, shooting whenever moisture falls 2–4% below the daily maximum. P3 is the dry-down, with no shots from a set time before lights-off so the substrate dries overnight. **How much dryback should I run in flower?** Dryback in flower depends on the steer. Grower practice uses a vegetative 10–15% VWC overnight dryback for bulking in flower weeks 3–5, and a generative 20–35% dryback at the flip and in late flower. Push dryback a few points at a time, watch for midday wilting, and pull back toward 15% if leaf tips burn or growth stalls. **Do I need a substrate sensor for crop steering?** A substrate sensor is effectively required for crop steering, because steering means acting on measured volumetric water content and substrate EC; steering by feel is a common mistake. Use a calibrated probe in a representative pot, not an edge pot or the biggest plant. Two or three probes with median voting are better, and spend the first 2 days learning field capacity. **Does drought stress increase THC?** Controlled drought stress late in flower can increase THC concentration, according to one cannabis study. Researchers found controlled late-flower drought raised THCA and CBDA concentration by roughly 12–13% and increased inflorescence dry weight, but warned against generalising to every cultivar. GenetixBay endorses mild late drought: dry back a few points at a time and stop at the first sign of stalling. **Short answer.** In drain-to-waste (DTW), each shot is fresh solution and runoff is discarded, so reservoir chemistry is simple and the **root zone** becomes the control surface. With a substrate **VWC/EC probe** you steer the plant: **vegetative** = earlier first shot, bigger shots, small overnight dryback (~**10–15 % VWC**), lower substrate EC; **generative** = later first shot, smaller shots, earlier last shot, larger dryback (~**20–35 %**), higher substrate EC [5]. These numbers are *Grower practice* adapted from greenhouse tomato work. The one controlled cannabis study we have found that a **controlled drought late in flower** raised THCA and CBDA concentration by roughly 12–13 % [1]. ## The vocabulary - **VWC:** volumetric water content of the substrate (%). - **Field capacity:** max VWC after drainage. Learned per pot/slab in the first days. - **Dryback:** drop in VWC between the last shot of one day and the first of the next (overnight), or across the day. - **P1 (ramp-up):** from lights-on, small shots every 15–30 min until VWC hits field capacity and runoff starts. - **P2 (maintenance):** shots whenever VWC falls a set amount (2–4 %) below the daily max. - **P3 (dry-down):** no shots from a set time before lights-off; the substrate dries overnight. - **Vegetative steer:** encourages leaf/stem growth and bulking. **Generative steer:** encourages flowering, tighter internodes, and is used in transition and late flower. ## Numbers that matter From Jardin's steering table [5]: | Lever | Vegetative steer | Generative steer | |---|---|---| | First shot after lights-on | 0.5–1.5 h | 2–3 h | | Last shot before lights-off | 2–3 h before | 4–6 h before | | Overnight dryback | 10–15 % VWC | 20–35 % VWC | | Shot size (% pot/slab volume) | Larger, fewer (4–6 %) | Smaller, more in P1 (2–3 %), longer P3 | | Input EC (coco/rockwool) | 1.8–2.4 mS/cm | 2.4–3.2 mS/cm (slab EC drifts up on purpose) | | Day/night temperature difference | Small (1–2 °C / 2–4 °F) | Larger (4–6 °C / 7–11 °F) | A common schedule: vegetative steer in veg and in flower weeks ~3–5 for bulking; generative at the flip (to control stretch) and in late flower [5]. **Mild late drought (house-endorsed).** Letting plants go a bit dry in late flower is *Supported* by one cannabis study, in which controlled drought raised inflorescence dry weight and cannabinoid content [1], and it's house-endorsed: the founder uses it, and some cultivars thrive when allowed to go a bit dry. Every cultivar responds differently. Push dryback a few points at a time, watch for midday wilting, and stop at the first sign of stalling. ## How to run it 1. Install a calibrated probe in a **representative** pot (not the edge, not the biggest plant). Two or three probes with median voting are better. 2. Spend 2 days learning field capacity: shoot until runoff, record the plateau VWC. 3. Set P1 to reach field capacity in 3–6 shots; P2 to hold within 2–4 % of max; P3 to hit your dryback target by lights-on. 4. Track substrate EC daily. If it runs above input + 1.5 mS/cm, add a flush shot or more runoff. 5. Change one lever at a time and keep notes. Plants answer over 3–7 days. ## Failure modes | Problem | Sign | Jardin response [5] | |---|---|---| | Probe fault or out of the pot | Implausible flat or jumpy readings; VWC doesn't rise after a shot | Fall back to schedule-only recipe; alert | | Waste tank full | Float trips | Pump lockout before next shot | | Substrate EC runaway | EC > input + 1.5 | Automatic flush shot with plain water | | Over-steering generative | Leaf tip burn, stalled growth, wilting by mid-day | Bring dryback back toward 15 %, lower EC | ## Jardin notes Jardin method "Drip, drain-to-waste + crop steering": required substrate VWC/EC/temperature probe, runoff mass or flow, waste tank float, reservoir mass. Fresh reservoir every 3–7 days (no uptake model needed). Time-to-harm 12–36 h. Level 2 at launch; Level 3 steering is unlocked only after 10 logged steered grows on that substrate and genetic [5]. ## Common mistakes - **Flushing before harvest.** Pre-harvest flushing is a *Myth* that costs you yield and resin: it starves the plant while it packs on its final weight, trichomes and resin. Feed through to harvest at stage strength. The only valid flush is a root-zone flush to clear salt build-up, at any stage (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). A flush shot when substrate EC runs away is root-zone management, not a pre-harvest flush; in coco, a light solution protects Ca and Mg better than plain water. - Steering without a probe, by feel. - Copying a commercial dryback onto a small pot that dries 3× faster. - Running generative all of flower and losing bulk. - Mistaking a dry corner pot for the room average. ## Evidence The mechanism (water and salt stress shift assimilate partitioning toward generative growth) is *Supported* in greenhouse horticulture [3]. Controlled drought late in flower raising cannabinoid concentration is *Supported* by one cannabis study, which its authors say should not be generalised to all cultivars [1], and mild late drought is house-endorsed with the same caveat: every cultivar responds differently; reduced irrigation frequency saved water with little impact on yield or THC in another [2]. The specific P1/P2/P3 ranges are *Grower practice* [4][5]. ## Sources 1. Caplan D, Dixon M, Zheng Y, 2019. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience 54(5):964–969. https://doi.org/10.21273/HORTSCI13510-18 2. Stemeroff J, 2018. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 3. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (irrigation in soilless production). https://doi.org/10.1016/C2015-0-01807-5 4. Greenhouse Grower. The details behind crop steering in cannabis production. https://www.greenhousegrower.com/production/the-details-behind-crop-steering-in-cannabis-production/ 5. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Ebb and flow (flood and drain) > A pump floods a table or tray of pots to a standpipe height, then the solution drains back to the reservoir. Each flood refreshes water and pulls fresh air into the medium as it drains. Typical schedules: clay pebbles 3–6 floods per light period of 10–15 minutes, coco or rockwool 1–3. It is robust because the media buffer pump failures for days, but salts can build up at the top of the medium. - Canonical: https://genetixbay.com/knowledge/systems/ebb-and-flow.html - Category: Systems · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Ebb and flow - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How often should I flood an ebb and flow table?** Flood an ebb and flow table 3–6 times per light period for clay pebbles, or 1–3 times for rockwool or coco, with none or one short flood at night. These are grower-practice starting points to verify for your own medium. Avoid night floods in rockwool, which keep it saturated, and adjust frequency to how fast the medium dries. **What media works in ebb and flow?** Ebb and flow works with clay pebbles in net or mesh pots, rockwool blocks, or coco in pots with a drainage layer. Clay pebbles hold the least water and need the most floods, while rockwool and coco hold more and need only 1–3 floods per light period. Because the media hold water, a dead pump buys you days rather than hours. **How long should each flood last?** Each ebb and flow flood should last about 10–15 minutes in total, covering fill, dwell and drain, with the solution reaching about two-thirds of pot or block height as set by the standpipe. Time the first fill and set a pump max-on timer at about 1.5 times that. As the table drains, fresh air is pulled into the medium. **Why are salts building up on top of my pots?** Salts build up on top of ebb and flow pots because subirrigation carries water upward and evaporation leaves fertiliser salts in the upper layer, which extension research shows can reach about 10 times the EC elsewhere in the pot. Run EC slightly lower than for top-feeding, and hand-water each pot with plain water every week or two to push salts down and take runoff. **Short answer.** A pump floods a tray to an overflow standpipe; after a set time it stops and the solution drains back by gravity. Draining pulls fresh air into the medium, so every flood is a water-and-oxygen exchange. Jardin's starting schedule: **clay pebbles 3–6 floods per light period, 10–15 min each; rockwool or coco 1–3; none or one short flood at night** [4]. Because the media hold water, a dead pump buys you **days**, not hours [4]. The trade-off: subirrigation concentrates salts at the **top** of the medium [1][2][3]. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Flood depth | To ~2/3 of pot or block height | Standpipe sets it | | Flood time | 10–15 min | Fill + dwell + drain | | Floods per light period | Clay 3–6; rockwool/coco 1–3 | [4] | | Reservoir volume | ≥ 1.5–2 × the volume to fill the table | Level must stay above the pump during a flood | | pH | 5.6–6.2 (media dependent) | | | EC | Slightly lower than top-feed | Salts concentrate on top [1][2] | | Drain confirmation | Reservoir back within ~2 % of pre-flood mass in 20 min | Jardin rule [4] | ## How to run it 1. Table above the reservoir; overflow standpipe plus a fill/drain fitting; a screen on the drain. 2. Media: clay pebbles in net pots or mesh pots, rockwool blocks, or coco in pots with a drainage layer. 3. Learn your fill time on the first flood; set a pump max-on timer at ~1.5 × that. 4. Top-water each pot by hand with plain water every week or two to push surface salts down (and take runoff). 5. Inspect the table for root mats and clean the standpipe every reservoir change. ## Failure modes | Problem | Sign | Jardin response [4] | |---|---|---| | Standpipe blocked / float stuck | Table overflows | Reservoir mass drop exceeds flood mass → pump off, alert; leak pad cuts rail | | Drain blocked | Table stays full, roots sit in water | No further floods; alert "roots sitting in water" | | Pump dead | No floods | Alert; media buy days | | Salt crust | White crust, burnt tips on lower leaves | Lower EC, periodic top-water flush | ## Jardin notes Jardin method "Flood & drain": reservoir mass, table high float, fill-line flow meter required; flood scheduler by medium and stage; pH/EC hold between floods. Time-to-harm: days. Automation level 3 [4]. ## Common mistakes - Reservoir too small, pump sucks air mid-flood. - Running hydro-strength EC and ignoring the salt layer. - Night floods in rockwool that keep it saturated. ## Evidence Subirrigation behaviour and top-layer salt accumulation are *Established* extension knowledge [1][2][3]. Cannabis flood schedules are *Grower practice*. ## Sources 1. UMass Extension. Subirrigation for greenhouse crops. https://www.umass.edu/agriculture-food-environment/greenhouse-floriculture/fact-sheets/subirrigation-for-greenhouse-crops 2. NC State University. Subirrigation (top-layer EC up to ~10× elsewhere in the pot). https://hortscans.ces.ncsu.edu/uploads/s/u/subirrig_51e435ff2e468.pdf 3. University of Arkansas. Greenhouse management, Unit 9 §6: sampling subirrigated media (salts in the upper layer). https://greenhouse.hosted.uark.edu/Unit09/Section06.html 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Fogponics: ultrasonic fog for roots (a supplement, not a system) > Fogponics uses ultrasonic transducers to make a 5–10 µm water fog that is blown into a root chamber. Fog carries very little dissolved nutrient (salts stay behind and concentrate in the fogger tank), transducers wear out in roughly 1,000–3,000 hours and run hot, so GenetixBay treats fog as a humidity supplement for cloning domes and aeroponic chambers, not as a standalone way to feed a flowering plant. - Canonical: https://genetixbay.com/knowledge/systems/fogponics.html - Category: Systems · Level: Intermediate - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg · Systems: Aeroponics - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Does fogponics work for cannabis?** Fogponics does not work well as a standalone way to grow cannabis to harvest. Fog is mostly water, dissolved salts stay behind in the tank, and roots in pure fog grow fine hair but little mass. There is no published support for fogponics as a complete cannabis system; it works as a humidity supplement in cloning domes or alongside aeroponics or NFT. **Can foggers feed plants nutrients?** Ultrasonic foggers deliver very little nutrient to plants. The fog is mostly water, and dissolved salts largely stay behind and concentrate in the fogger tank, crusting the discs and cutting fog output. Use plain or very weak solution in the fogger, dump the tank when its EC passes 1.5 times the input EC, and feed the roots by another method. **How long do ultrasonic foggers last?** Ultrasonic fogger transducers typically last about 1,000–3,000 hours, an engineering estimate worth checking against your transducer's datasheet, and should be replaced on schedule. They run hot, which warms the tank, and running them dry destroys them. Fit a float switch interlock so the fogger cuts out when the tank level falls below minimum. **Is fogponics good for clones?** Fogponics is good for clones because ultrasonic fog keeps cuttings and new roots at near 100% humidity, with the chamber at 95% RH or higher. Fog into the cloning dome or chamber, but vent daily to prevent soggy stems and mould. Fog carries very little nutrient, so treat it as humidity support rather than a feeding method. **Short answer.** Ultrasonic discs make a very fine fog (**~5–10 µm**) that a fan pushes into a root chamber [2]. It keeps roots and cuttings at near 100 % RH, which is why it's popular for cloning. As a **sole** feeding method it's weak: fog is mostly water; dissolved salts largely stay behind and **concentrate in the fogger tank**; transducers **run hot and die in ~1,000–3,000 h**; and roots in pure fog tend to grow fine hair but little mass [2]. GenetixBay and Jardin treat fog as a **humidity supplement** alongside LPA, HPA or NFT, or in cloning domes [2]. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Fog droplet size | ~5–10 µm | Ultrasonic; finer than HPA's ~10–100 µm [1] | | Chamber RH | ≥ 95 % | [2] | | Fogger tank EC | Dump when > 1.5 × input EC | Salts concentrate as water fogs off [2] | | Transducer life | ~1,000–3,000 h | Replace on schedule [2] | | Tank level | Always above minimum | Dry-running destroys transducers [2] | ## How to use it well 1. Use plain or very weak solution in the fogger; feed roots by another method. 2. Float switch interlock on the fogger relay. 3. Keep the fogger tank cool; transducer heat warms it. 4. For clones: fog into the dome or chamber, but vent daily to prevent soggy stems and mould. ## Failure modes | Problem | Sign | Jardin response [2] | |---|---|---| | Transducer dead | RH stops rising with relay on | Alert | | Tank dry | Float trips | Relay cut | | Tank EC climbing | Crust on discs, fog output drops | Dump and refill | ## Jardin notes Jardin method "Fogponics": supplement only. The UI says "supplementary" wherever fog is configured as the only method. Time-to-harm: hours if it is the sole method [2]. ## Common mistakes - Feeding a flowering plant by fog alone. - Running discs dry. - Never replacing transducers. ## Evidence Aeroponics in general is *Established* [1]. Fogponics as a complete cannabis growing system has no published support we can cite; the limitations above are physical and from engineering experience (*Grower practice*). ## Sources 1. Lakhiar IA, Gao J, Syed TN, Chandio FA, Buttar NA, 2018. Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics. Journal of Plant Interactions 13(1):338–352. https://doi.org/10.1080/17429145.2018.1472308 2. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Growing in coco coir > Coco coir is a hydroponic substrate that looks like soil: inert-ish, airy, and fed every irrigation with a complete mineral solution at pH 5.8–6.2 and EC 1.2–2.4 mS/cm with 10–20 % runoff. Use pre-washed, buffered coco or buffer it yourself with a calcium/magnesium solution, because raw coir holds potassium and sodium and grabs calcium and magnesium. - Canonical: https://genetixbay.com/knowledge/systems/coco.html - Category: Systems · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Coco - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What size pot for coco?** Coco pot size is a trade-off against how often you can irrigate. Bigger pots generally give bigger plants, as a meta-analysis of rooting volume across crops found, and they dry slower and forgive more. Small pots can still grow big plants with high-frequency fertigation, which coco suits best, but need more irrigations per day (2–6 in flower) and leave less margin for error. **Do I need to buffer coco coir?** Coco coir needs buffering unless it is sold pre-washed and buffered. Raw coir's exchange sites are loaded with potassium and sodium and will pull calcium and magnesium from your feed, causing early deficiency spots. Rinse until runoff EC is below about 0.5 mS/cm, soak 8–24 hours in a calcium-magnesium solution, then rinse again. Some substrate experts argue well-processed coir needs no buffering. **What pH for coco?** The best pH for coco is 5.8–6.2 at the input, or 5.8–6.0 for seedlings and clones. That sits inside the accepted 5.5–6.5 soilless range, and gentle drift within it is normal. Don't use the pH 6.5 figures from soil guides, and check runoff pH a few times a week alongside runoff EC to see what the root zone is actually doing. **How often should I water coco?** Coco should be watered when the pot has lost about 30–50% of its available water, always to 10–20% runoff, with full nutrients every time. In practice that is about once a day for seedlings, 1–3 irrigations a day in veg and 2–6 a day in flower, with smaller pots needing more frequent shots. Never let coco dry out completely. **Why do my coco plants get calcium deficiency?** Coco plants usually show calcium deficiency because raw, unbuffered coir swaps potassium and sodium off its exchange sites and holds on to calcium and magnesium from the feed. Rust spots on newer leaves in weeks 1–3 are the classic sign. RO water, low root-zone pH and cultivar demand also drive it; blaming LED lighting is a myth. Check runoff before adding more calcium-magnesium. **Can coco dry out completely?** Coco should never dry out completely. Fully dry coir becomes hydrophobic and hard to re-wet, and plants can crash after a single hot day. Letting it dry out 'to make roots search' is a common mistake. Irrigate when about 30–50% of the available water is gone, and use a moisture probe if you can't check pots often enough. **Coco vs soil for beginners?** For beginners, coco is less forgiving than soil because it behaves like hydroponics in a pot and has no starter nutrient charge. Coco needs a complete mineral feed at EC 1.2–2.4 mS/cm every irrigation with 10–20% runoff, and can harm plants within 12–36 hours if watering stops. Feeding coco like soil, with plain-water days and low EC, is a common beginner error. **Short answer.** Treat coco as **hydroponics in a pot**. Feed a complete mineral solution at **pH 5.8–6.2**, **EC 1.2–2.4 mS/cm** (600–1,200 ppm500 / 840–1,680 ppm700) depending on stage, **every irrigation**, with **10–20 % runoff**, and never let it dry to dust. Use coco that is washed and **buffered** (exchange sites pre-loaded with calcium/magnesium), or buffer it yourself, because raw coir carries potassium and sodium and will take calcium and magnesium out of your feed [1][2]. ## How it works Coir pith holds a lot of water while staying airy, so roots get both. It has a modest cation exchange capacity that, when raw, is loaded with K⁺ and Na⁺ from the coconut husk [1]. Feed it calcium and it swaps calcium onto the exchange sites and releases potassium (and sodium) into the root zone, which is why fresh, unbuffered coco produces early calcium/magnesium deficiency symptoms. Buffering soaks the coir in a calcium (often calcium nitrate) or calcium-magnesium solution, then rinses [2]. Coco dries fast, so it rewards frequent small irrigations (high-frequency fertigation). Once fully dry it becomes hydrophobic and hard to re-wet. ## Numbers that matter | Parameter | Seedling/clone | Veg | Flower | Notes | |---|---|---|---|---| | Input pH | 5.8–6.0 | 5.8–6.2 | 5.8–6.2 | Jardin coco band 5.8–6.2 [5] | | Input EC (mS/cm) | 0.6–1.0 | 1.2–1.8 | 1.8–2.4 | ppm500 = EC × 500; ppm700 = EC × 700 | | Runoff | 10–20 % per day | 10–20 % | 10–20 % | Less if drain-to-waste is steered ([crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md)) | | Runoff EC vs input | ±0.3–0.5 | ±0.5 | ±0.5–1.0 | Higher = salts building, irrigate more volume | | Irrigations/day | 1 | 1–3 | 2–6 | Smaller pots need more | | Ca:Mg in early weeks | Slightly higher Ca/Mg | | | Jardin "buffer check" in week 1 [5] | | Perlite | 0–30 % | | | Adds air; reduces water holding | > **House position: pot size is a trade-off.** Bigger pots give bigger yields, within reason; across many crops, bigger rooting volume generally means bigger plants (Poorter et al. 2012 meta-analysis). But root volume isn't the whole story: the founder has grown a QP+ (4 oz+, ~115 g+) from a 16 oz (~0.5 L) cup. If you push water and nutrients hard enough (high-frequency fertigation, which coco suits best), big things come in small packages. Small pots need more frequent feeding and watering and leave less margin for error; big pots are more forgiving but dry slower. Match the pot to how often you can irrigate. ## How to run it 1. **Prep:** hydrate the brick, rinse until runoff EC is below ~0.5 mS/cm, then soak 8–24 h in a buffering solution and rinse again. Pre-buffered commercial coco can skip this. 2. **First feed:** full mineral nutrients from day one at the seedling EC. Coco has no starter charge. 3. **Irrigate** when the pot has lost ~30–50 % of its available water, to light runoff. Never let it dry out fully. 4. **Measure runoff** EC and pH a few times a week. Adjust volume, not just strength. 5. **Reuse?** Possible after rinsing and re-buffering; root debris increases water holding and disease risk. ## Failure modes | Problem | Likely cause | First check | |---|---|---| | Rust spots on new-ish leaves, weeks 1–3 | Calcium/magnesium pulled by unbuffered coco | Runoff Ca/Mg or runoff EC; was it buffered? | | Burnt tips, runoff EC far above input | Too little runoff, salts accumulate | Root-zone flush with a light solution (EC ~0.4–0.8, with Ca/Mg), then more runoff volume | | Droop with wet pots | Over-watering, low air porosity | Pot size vs plant size, perlite | | Plants crash after a hot day | Coco dried out | Irrigation frequency, a VWC probe | ## Jardin notes Jardin treats coco as a "hydro-behaving medium": dryback plus EC control from VWC, with the irrigation method chosen separately (recirculating drip, drain-to-waste with steering, or flood & drain). Time-to-harm on pump failure: 12–36 h. Automation level 3 [5]. ## Common mistakes - **Flushing before harvest.** Pre-harvest flushing is a *Myth* that costs you yield and resin: it starves the plant while it packs on its final weight, trichomes and resin. Feed through to harvest at stage strength. The only valid flush is a root-zone flush to clear salt build-up, at any stage (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). - **Root-zone flushing coco with plain water.** It strips Ca and Mg from the exchange sites. Flush with a light solution (EC ~0.4–0.8 mS/cm, pH ~5.8–6.0) and check runoff EC. - Feeding coco like soil (plain water days, low EC). - Skipping buffering, then adding more cal-mag blindly instead of checking runoff. - Blaming the LEDs for Ca/Mg spotting. That's a *Myth*: in coco the usual drivers are unbuffered coir, RO water, low pH and the cultivar's own demand ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)). - Letting coco dry fully between waterings "to make roots search". - Reading the label pH 6.5 from soil guides. ## Evidence Coir's high K/Na and exchange behaviour is *Established* [1][4]. Buffering practice is *Supported* by industry and substrate experts, though some argue well-processed coir needs no calcium buffering [2]. Cannabis responses to organic feed rates in coir-based substrates are *Supported* by [3]. The pH band (soilless 5.5–6.5, coco sweet spot 5.8–6.2) is accepted practice from extension and grower consensus; EC bands and irrigation frequency are *Grower practice*. ## Sources 1. Abad M, Noguera P, Puchades R, Maquieira A, Noguera V, 2002. Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology 82(3):241–245. https://doi.org/10.1016/S0960-8524(01)00189-4 2. Greenhouse Grower, 2023. Washed, low-EC, or buffered? How to specify coco substrate for your crop. https://www.greenhousegrower.com/?p=180860 3. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17 4. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 5. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). 6. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # Growing in rockwool (stonewool cubes and slabs) > Rockwool is an inert, unbuffered mineral fibre that holds a lot of water and air and gives precise control over the root zone. Pre-soak at pH about 5.5, run pH 5.5–6.0 and EC 1.8–3.0 mS/cm in flower, and manage it by volumetric water content and slab EC. It is the native medium of crop steering, and it punishes neglect quickly because nothing buffers mistakes. - Canonical: https://genetixbay.com/knowledge/systems/rockwool.html - Category: Systems · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Rockwool - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Do I need to pre-soak rockwool?** Rockwool does need pre-soaking, because fresh stonewool is slightly alkaline and releases alkalinity on first wetting. Soak it for 12–24 hours in solution at pH about 5.5 and EC 0.5–1.0 mS/cm, then let it drain to field capacity before planting. Skipping the soak and starting seedlings at high pH is a common mistake. **What pH for rockwool?** Rockwool runs best at an input pH of 5.5–6.0, at the lower end of the accepted 5.5–6.5 soilless range, after a pre-soak at about pH 5.5. Because rockwool is inert and unbuffered, it does not absorb pH errors the way soil does, so a wrong pH shows up within a day rather than over weeks. **How do I know when to water rockwool slabs?** Water rockwool slabs by measuring them, not by feel: install a moisture and EC probe in a representative block or slab, or weigh it. Irrigate in shots of 2–6% of substrate volume, aiming for daily runoff that keeps slab EC within input plus 1.5 mS/cm. Overnight dryback ranges from 10–15% VWC points for a vegetative steer to 20–35% for generative. **Rockwool vs coco for cannabis?** Rockwool gives the most precise root-zone control of any medium and is where crop steering developed, but it is inert and unbuffered, so mistakes show within a day. Coco is more forgiving, though it needs buffering for calcium and magnesium. Rockwool runs at pH 5.5–6.0 against coco's 5.8–6.2, and rockwool is not compostable while coco can be rinsed and reused. **Is rockwool dust dangerous?** Rockwool fibres and dust irritate skin, eyes and airways, so handle dry stonewool with care. Wet the material before cutting it, and wear gloves, long sleeves and a dust mask rated FFP2 or N95 when working with dry wool. Rockwool also isn't compostable, so dispose of used slabs responsibly rather than mixing them into garden soil. **Short answer.** Rockwool is spun mineral fibre: sterile, inert, unbuffered, with high water-holding and air capacity. Pre-soak at **pH ~5.5**, run **pH 5.5–6.0**, input **EC 1.2–1.8 mS/cm in veg and 1.8–3.0 in flower** (Jardin default bands), and manage it by **VWC (volumetric water content) and slab EC** [3]. It gives the most precise root-zone control of any medium and is where crop steering was developed, but it has no buffer: a mistake shows within a day. ## How it works Fresh rockwool is slightly alkaline (it releases some alkalinity on first wetting), which is why growers pre-soak at pH ~5.5 [1][2]. After that it contributes nothing chemically. Its water content after drainage is high (product-dependent) with a stable air fraction, so roots can sit at high moisture without suffocating, as long as the slab drains. Every irrigation replaces part of the slab solution. If you water little, slab EC climbs (deliberately, in generative steering); if you water a lot, slab EC approaches input EC. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Pre-soak | pH 5.5, EC 0.5–1.0, 12–24 h | Then let drain to field capacity | | Input pH | 5.5–6.0 | Jardin rockwool band [3] | | Input EC, veg | 1.2–2.0 mS/cm | | | Input EC, flower | 1.8–3.0 mS/cm | Steering range 1.8–3.2 [3] | | Slab EC | Input +0 to +1.5 | Above input +1.5 Jardin triggers a flush shot [3] | | Overnight dryback | 10–15 % (vegetative) to 20–35 % (generative) VWC points | See [crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) | | Root-zone temperature | 18–23 °C (64–73 °F) | Slabs on cold floors stall roots | ## How to run it 1. Cube (2.5–4 cm) for seeds/clones → block (10 cm) → slab or larger block. Don't let small cubes dry out; don't keep them soaking either. 2. Put a block on a slab only once roots show through the block bottom; irrigate the block, not the slab, until roots enter. 3. Install a VWC/EC probe in a representative block or slab. Without one, weigh. 4. Irrigate in shots of 2–6 % of substrate volume; aim for a daily runoff that keeps slab EC in your target band. 5. Dispose of slabs responsibly; rockwool is not compostable. ## Failure modes | Problem | Sign | Fix | |---|---|---| | Slab EC runaway | Burnt tips, slab EC ≫ input | More runoff shots or a flush shot | | Water-logged | Slow growth, brown roots, algae | Fewer/smaller shots, check drainage slit, raise slab off floor | | Dry spots | Probe reads fine but plants wilt | Probe placement; drip emitter clogged | ## Jardin notes Jardin medium "Rockwool" (with any drip method): dryback + slab EC loop; VWC/EC probe strongly recommended; P3 dryback matters more than in coco. Time-to-harm on pump failure: 24–48 h. Automation level 3 [3]. ## Safety Fibres irritate skin, eyes and airways. Wet the material before cutting, wear gloves, long sleeves and a dust mask (FFP2/N95) when handling dry wool. ## Common mistakes - **Flushing before harvest.** Pre-harvest flushing is a *Myth* that costs you yield and resin: it starves the plant while it packs on its final weight, trichomes and resin. Feed through to harvest at stage strength. The only valid flush is a root-zone flush to clear salt build-up, at any stage (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). In rockwool, a flush shot when slab EC runs above input + 1.5 is that root-zone flush. - Using it without measurement, like soil. - Not pre-soaking and starting seedlings at high pH. - Keeping propagation cubes soaked. - Copying slab EC numbers from vegetable greenhouses without adjusting for cannabis. ## Evidence Material behaviour is *Established* horticultural knowledge [1][2]. The pH band (soilless 5.5–6.5, run 5.5–6.0 in rockwool) is accepted practice from extension and grower consensus. Cannabis-specific EC and dryback bands are *Grower practice*; Jardin's ranges are flagged ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (mineral wool chapter). https://doi.org/10.1016/C2015-0-01807-5 2. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 3. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Growing in soil (potting mix with bottled feed) > Soil (a peat- or compost-based potting mix fed with dilute bottled nutrients) is the most forgiving system: it buffers pH and nutrients and holds water for days. Water to light runoff when the pot is light, feed at EC 0.8–1.6 mS/cm with water at pH 6.2–6.8, and remember that over-watering, not under-feeding, kills most soil plants. - Canonical: https://genetixbay.com/knowledge/systems/soil.html - Category: Systems · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Does a bigger pot give a bigger yield?** A bigger pot gives a bigger cannabis yield within reason: a meta-analysis of rooting volume across many crops found bigger root volume generally means bigger plants. Pot size is a trade-off with feeding frequency, though. GenetixBay's founder has grown over 4 ounces from a 16-ounce cup using high-frequency fertigation. Big pots are more forgiving but dry slower; small ones need frequent feeding. **What pH should I water my soil plants at?** Water cannabis in soil at pH 6.2–6.8, within the accepted soil range of about 6.0–7.0. Compost and peat in the potting mix buffer pH, so a slightly off irrigation pH is absorbed for weeks. If you see mixed deficiencies despite feeding, check runoff pH and correct the water pH gradually rather than with harsh swings. **How often should I water cannabis in soil?** Water cannabis in soil when the pot feels light and the top 2–3 cm (1 inch) is dry, rather than on a fixed schedule. Water slowly until 10–20% runs out, then discard the runoff. Learn the rhythm by lifting pots: water at roughly 40–50% of just-watered weight above dry weight. Daily small sips that never fully wet the pot are a common mistake. **Can I use hydro nutrients in soil?** Mineral nutrients can be used in soil only at soil strength, never at hydro strength on top of a fertilised mix. Wait until the mix's starter charge runs out, usually 2–4 weeks, then start at half the label rate, feeding at EC 0.8–1.6 mS/cm every second or third watering. Check runoff EC monthly, because a rising reading means salts are building up. **What size pot do I need?** Photoperiod cannabis in soil usually finishes in an 11–25 litre (3–7 US gallon) pot, while autoflowers suit 11–15 litres (3–4 US gallons) planted directly into the final pot to avoid transplant stalls. Match the pot to how often you can water: smaller pots need more frequent feeding and watering, while bigger pots dry slower and forgive more. **Why are my soil plants drooping when the soil is wet?** Soil plants droop when the soil is wet because they are over-watered: a saturated pot has little air-filled porosity, so roots suffocate and the plant wilts as if dry. Signs are droopy but firm-looking leaves, a heavy pot, slow growth and fungus gnats. Water less often, add perlite or pumice to the mix, and consider fabric pots. **Short answer.** "Soil" indoors means a bagged **potting mix** (peat or coco plus compost, perlite and a starter charge of fertiliser), not garden dirt. It is the most forgiving system: the mix buffers pH and holds nutrients and water for days. Water at **pH 6.2–6.8**, feed lightly (**EC 0.8–1.6 mS/cm**, i.e. 400–800 ppm500 / 560–1,120 ppm700) and only once the mix's own charge runs out, and water when the pot is **light**, to **10–20 % runoff**. ## How it works The mix has three jobs: hold water, hold air, and hold nutrients on its exchange sites (cation exchange capacity). Compost and peat buffer pH, so a slightly off irrigation pH is absorbed for weeks. Roots need air as much as water: a saturated pot has little air-filled porosity and roots suffocate. That is why over-watering looks like wilting [1]. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Irrigation pH | 6.2–6.8 | Jardin "Soil (bottled feed)" band 6.3–6.8 [4] | | Feed EC (when feeding) | 0.8–1.6 mS/cm | Jardin caps soil at ≤ 1.2 as default [4]; never hydro-strength | | Runoff EC | Within ~0.5–1.0 of input | Rising runoff EC = salt build-up | | Pot size, photoperiod | 11–25 L (3–7 US gal) final | Bigger pots dry slower and yield more within reason; smaller pots work if you water and feed more often (see note) | | Pot size, autoflower | 11–15 L (3–4 US gal), plant directly | Avoid transplant stalls | | Watering trigger | Pot ~40–50 % of its just-watered weight above dry weight | Learn by lifting | | Root-zone temperature | 18–24 °C (64–75 °F) | | > **House position: pot size is a trade-off.** Bigger pots give bigger yields, within reason; across many crops, bigger rooting volume generally means bigger plants (Poorter et al. 2012 meta-analysis). But root volume isn't the whole story: the founder has grown a QP+ (4 oz+, ~115 g+) from a 16 oz (~0.5 L) cup. If you push water and nutrients hard enough (high-frequency fertigation), big things come in small packages. Small pots need more frequent feeding and watering and leave less margin for error; big pots are more forgiving but dry slower. Match the pot to how often you can irrigate. ## How to run it 1. **Mix:** a quality potting mix with 20–35 % perlite or pumice. Garden soil compacts and carries pathogens [3]. 2. **Start:** the mix's starter charge usually feeds seedlings for 2–4 weeks. Water only, pH-adjusted. 3. **Water:** when the pot is light and the top 2–3 cm (1 in) is dry. Slowly, until 10–20 % runs out. Discard runoff; don't let pots sit in it. 4. **Feed:** begin at half the label rate when lower leaves start to pale; feed every second or third watering ("feed, water, feed" is common). 5. **Check monthly:** pour-through or runoff EC/pH. If runoff EC climbs well above input, do a root-zone flush: 2–3× the pot volume of pH-adjusted water (pH ~6.3–6.8), slowly, then check runoff EC and go back to normal feeding. ## Failure modes | Problem | Sign | Fix | |---|---|---| | Over-watering | Droopy, firm-looking leaves, wet heavy pot, slow growth, fungus gnats | Water less often, more air in mix, fabric pots | | Under-watering | Limp, papery droop, very light pot | Water slowly in stages so the mix re-wets | | Salt build-up | Burnt tips, runoff EC high | Root-zone flush (2–3× pot volume), then normal feed | | pH drift | Mixed deficiencies despite feeding | Check runoff pH; adjust water pH, not with harsh swings | ## Jardin notes Jardin medium "Soil (bottled feed)": moisture-based irrigation by VWC with long dry-downs, dosing caps halved, pH control on the water only, no reservoir pH-down below 6.0. Time-to-harm on pump failure: days. Automation level 2 [4]. ## Common mistakes - **Flushing before harvest.** Pre-harvest flushing is a *Myth* that costs you yield and resin: it starves the plant while it packs on its final weight, trichomes and resin. Feed through to harvest at stage strength. The only valid flush is a root-zone flush to clear salt build-up, at any stage (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). - Small cups watered daily "a little bit": the pot never dries and never fully wets. - Hydro nutrient strength on top of a fertilised mix. - Chasing every leaf spot by changing nutrients before checking runoff pH and watering rhythm. ## Evidence Container-media physics is *Established* [1]. Feed ranges for mineral-fed soil are *Grower practice*; for organic liquid feed in coir-based organic substrates, ~389 mg N/L maximised veg yield in one study [2], which shows how much higher organic N rates can run than people expect, but it is not a mineral-soil recipe. ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 2. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17 3. University of Minnesota Extension. How to prevent seedling damping off (sanitation; avoid garden soil in containers). https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). 5. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # High-pressure aeroponics (HPA) > HPA atomises nutrient solution at roughly 80–100 psi (5.5–7 bar) through fine nozzles into a root chamber, giving fine droplets (about 10–100 µm) and very high root oxygen. It can grow outstanding root systems but has the shortest failure margin of any system: roots can be damaged within tens of minutes if misting stops. It needs an accumulator, pressure monitoring, filtration, anti-drip nozzles and a backup plan. - Canonical: https://genetixbay.com/knowledge/systems/hpa-aeroponics.html - Category: Systems · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Aeroponics - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What pressure for high-pressure aeroponics?** High-pressure aeroponics runs at about 80–100 psi (5.5–7 bar), stored in an accumulator and released through solenoids and fine nozzles to make droplets of roughly 10–100 µm. Monitor pressure with a transducer plus a mechanical switch, and filter to 5 µm before the solenoids. A 40 psi pump with fogger nozzles is not true HPA. **What mist cycle for HPA cannabis?** A typical HPA mist cycle for cannabis is seconds on, minutes off, for example 2–5 seconds every 2–5 minutes, which you should verify for your own chamber. Chamber humidity should stay near 100% between bursts, because that is the proof the mist is working. Measuring pressure decay per burst helps spot clogged or leaking zones. **Is HPA worth it over LPA or DWC?** HPA is worth it only for experienced growers who will build in pressure monitoring, filtration, anti-drip nozzles and a backup. It grows outstanding root systems, but no published study compares cannabis flower yield from HPA with LPA or DWC, so '30–50% more yield' claims are marketing. DWC tolerates 2–12 hours without air, while HPA roots can be harmed in tens of minutes. **What happens if my HPA pump fails?** If an HPA pump fails, pressure decays, chamber humidity drops and roots can be damaged within tens of minutes, the shortest failure margin of any system. Protect the crop with battery-backed misting, a loud alarm and a lifeboat: a shallow pool with a small pump that keeps roots wet until misting is restored. Without a backup, one power cut can mean one dead crop. **Short answer.** A pump charges an **accumulator to ~80–100 psi (5.5–7 bar)**; solenoids release short bursts through fine nozzles, producing a true mist with droplets of roughly **10–100 µm** [1][2]. Roots hang in air with a thin water film and get superb oxygen. The price is fragility: time-to-harm if misting stops is **tens of minutes to hours** [4]. Only build HPA if you'll fit pressure monitoring, filtration, anti-drip nozzles and a backup (battery-backed misting or a "lifeboat" pool) [4]. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | System pressure | 80–100 psi (5.5–7 bar) | Pressure transducer + mechanical switch [4] | | Droplet size | ~10–100 µm (aeroponic range) | [1][2] | | Mist timing | Seconds on, minutes off (e.g. 2–5 s every 2–5 min) | | | Filtration | 5 µm before solenoids | [4] | | Input EC | 0.6–1.4 mS/cm (Jardin default) | Thin films concentrate salts on roots | | Solution temperature | 18–22 °C (64–72 °F) | | | Chamber RH | ~100 % between bursts | RH is the proof of mist [4] | ## Design essentials 1. Demand pump → accumulator → relief valve → 5 µm filter → direct-acting solenoids per zone → anti-drip nozzles. 2. Measure pressure decay per burst to diagnose clogged or leaking zones. 3. A lifeboat: a shallow pool and small pump that keeps roots wet if HPA fails, plus battery backup for the mister [4]. 4. Flush lines with plain water before each new batch mix [4]. ## Failure modes | Problem | Sign | Response | |---|---|---| | Pump or power failure | Pressure decays, RH drops | Battery misting, lifeboat pump, loud alarm | | Clogged nozzle | Zone pressure decay changes, dry roots in one spot | Filter, clean nozzles | | Leaking solenoid | Constant drip, pressure loss | Replace; anti-drip nozzles | | Salt build-up on roots | Brown tips on roots, leaf tip burn | Lower EC, flush mist | ## Jardin notes Jardin method "HPA": pressure transducer, chamber RH, flow meter and battery required; burst scheduler, pressure loop, lifeboat. Automation level 3 with battery [4]. ## Safety Pressurised water lines can burst. Use rated fittings and accumulators, a relief valve, eye protection when working on pressurised lines, and GFCI/RCD on every pump. ## Common mistakes - Calling a 40 psi pump with fogger nozzles "HPA". - No backup: one power cut, one dead crop. - Hydro-strength EC in a fine mist. ## Evidence HPA physics and root benefits are *Supported* [1][2]; cannabis roots grow very large in aeroponics [3]. There is no published cannabis flower-yield comparison of HPA vs other systems; HPA claims of "30–50 % more yield" are *Grower practice/marketing* until tested. ## Sources 1. Lakhiar IA, Gao J, Syed TN, Chandio FA, Buttar NA, 2018. Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics. Journal of Plant Interactions 13(1):338–352. https://doi.org/10.1080/17429145.2018.1472308 2. Eldridge BM, Manzoni LR, Graham CA, et al., 2020. Getting to the roots of aeroponic indoor farming. New Phytologist 228:1183–1192. https://doi.org/10.1111/nph.16780 3. Ferrini F et al., 2021. Yield, characterization, and possible exploitation of Cannabis sativa L. roots grown under aeroponics cultivation. Molecules. https://pmc.ncbi.nlm.nih.gov/articles/PMC8401984/ 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Kratky (passive, non-circulating hydroponics) > Kratky is hydroponics with no pump: the plant sits above a container of nutrient solution, drinks it down, and the growing air gap gives the upper roots oxygen. It was developed and published for lettuce and tomatoes at the University of Hawaii. Cannabis can be grown this way, but its large water use means big containers, careful refills that keep the air gap, and close attention to water temperature and EC drift. - Canonical: https://genetixbay.com/knowledge/systems/kratky.html - Category: Systems · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: DWC - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Can you grow cannabis with the Kratky method?** Cannabis can be grown with the Kratky method, though that is grower practice; the published research covers lettuce and tomatoes. Kratky uses no pump or air stone: the plant drinks the solution down and the growing air gap gives the upper roots oxygen. It suits autoflowers, small photoperiod plants, mothers and clones, kept in large containers with solution at 18–22 °C. **How big a Kratky container for cannabis?** A full-size cannabis plant in Kratky needs a large container, roughly 40–100 litres per plant, a grower estimate worth verifying. Cannabis drinks far more than lettuce, and a big photoperiod plant can empty a 20-litre tote within days in flower. Use an opaque, light-tight container, and choose smaller plants such as autoflowers if space is limited. **Should I refill a Kratky reservoir to the top?** Do not refill a Kratky reservoir to the top. As the level drops, the upper roots adapt to the humid air gap, and refilling to the brim submerges those air roots, inviting rot. Refill only partway, to about half to two-thirds of the original level, or with weak solution, a grower approach extrapolated from Kratky's tomato research. **Why are my Kratky roots rotting?** Kratky roots usually rot because the air roots were submerged by topping up too high, or because the solution got too warm. With no aeration, Kratky has less margin than DWC, so keep the solution at 18–22 °C (64–72 °F) in a light-tight container. If roots turn brown and slimy, add an air stone and convert the system to DWC. **Short answer.** Kratky needs **no pump, no air stone and no electricity**: a net pot sits in a lid over nutrient solution; the plant drinks the level down, and the expanding **air gap** gives the upper roots oxygen while the lower roots keep drinking [1][2]. It's proven for lettuce and was extended to tomatoes with refills [3]. Cannabis drinks far more than lettuce, so you need **large containers**, refills that **don't drown the air-root zone**, and **cool solution**. ## How it works At the start the solution touches the bottom of the net pot. As the plant drinks, roots follow the water down; the upper root mass becomes "air roots" in a humid gap. Refilling to the top would submerge those air roots, which are not adapted to anaerobic water, inviting rot [1][3]. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Starting level | Just touching net pot base | [1] | | Refill | Only partway (e.g. to ~1/2–2/3 of the original level), or with weak solution | | | Solution temperature | 18–22 °C (64–72 °F) | No aeration = less margin than DWC | | pH | 5.6–6.2 | Drifts up as plants feed | | EC | Start 0.8–1.4 mS/cm | EC often rises as water use outpaces uptake | | Container | Opaque, light-tight | Algae otherwise | ## How to run it 1. Best for **autoflowers, small photoperiod plants, mothers and clones**. 2. Start with a seedling or rooted clone in a net pot with clay pebbles. 3. Check level, pH and EC every few days; add plain water if EC climbs fast, weak feed if it falls. 4. Keep the container cool and dark. 5. If roots go brown and slimy, convert to DWC with an air stone. ## Jardin notes Jardin method "Kratky (monitor only)": a Root node in monitor mode reads pH/EC/water temperature and level or mass; dosing is disabled in software and channels unmapped, so no actuator can misbehave. Alerts like "EC rising fast, add water" and "water temp 26 °C". Automation level 0. It's the cheapest entry to the data side and the natural path to DWC [4]. ## Common mistakes - Topping up to the brim. - Small containers for big photoperiod plants (they drink a 20 L tote in days in flower). - Clear containers. ## Evidence The method is *Established* for lettuce and *Supported* for tomatoes with refills [1][2][3]. Kratky for cannabis is *Grower practice*. ## Sources 1. Kratky BA, 2004. A suspended pot, non-circulating hydroponic method. Acta Horticulturae 648:83–89. https://www.ctahr.hawaii.edu/hawaii/downloads/A_Suspended_Pot_Non-circulating_Hydroponic_Method.pdf 2. Kratky BA, 2009. Three non-circulating hydroponic methods for growing lettuce. Acta Horticulturae 843:65–72. https://www.ctahr.hawaii.edu/Hawaii/downloads/Three_Non-circulating_Hydroponic_Methods_for_Growing_lettuce.pdf 3. Kratky BA, Maehira GT, Cupples RJ, Bernabe CC, 2005. Non-circulating hydroponic methods for growing tomatoes. Proc. National Agricultural Plastics Congress 32:31–36. https://www.ctahr.hawaii.edu/Hawaii/downloads/Non-Circulating_Hydroponic_methods_for_growing_tomatoes.pdf 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Living soil (no-till, water-only organic growing) > Living soil is a large, biologically active, amended organic soil that is reused without tilling and watered with plain dechlorinated water; soil organisms release nutrients. It is forgiving and low-input once established but slow to correct, so build it well, keep it moist and mulched, never use salt-based nutrients or sanitisers on it, and don't chase pH. Most of its claims are grower practice rather than tested in cannabis. - Canonical: https://genetixbay.com/knowledge/systems/living-soil.html - Category: Systems · Level: Intermediate - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Living soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is living soil and how is it different from regular soil?** Living soil is a large volume of compost-rich, amended organic soil that is reused without tilling and watered with plain dechlorinated water, while soil microbes and invertebrates release nutrients from organic matter. Regular indoor soil is a bagged potting mix fed with dilute bottled nutrients and usually replaced each run. Living soil relies on biology, mulch and top-dressing rather than salt-based feeds. **Do I need to pH water for living soil?** You generally do not need to pH-adjust water for living soil. Organic matter and carbonates buffer the root zone, and plants and microbes work around a near-neutral pH of roughly 6.3–7.0. Use dechlorinated water as it is unless it is very alkaline. Adjusting water to pH 6.0 out of habit is a common mistake rather than accepted living-soil practice. **How big a container for living soil?** Living soil needs a container of at least 50–100 litres (15–25 US gallons) per plant, or a raised bed, according to grower practice. Small pots lack the biological and nutrient buffering that makes living soil forgiving, and small pots of 'living soil' fed like hydro are a common mistake. Keep the volume evenly moist and covered with 3–5 cm of mulch. **Can I use bottled nutrients in living soil?** Salt-based bottled mineral nutrients should not be used in living soil, because they bypass and can disrupt the soil biology that the system depends on. Feed the soil instead: top-dress organic amendments such as compost, worm castings, seed meals, kelp or bone and fish meal, and water them in. Fast-acting organic inputs like fish hydrolysate or kelp extract can bridge short gaps. **How do I fix a deficiency in living soil?** Fix a living-soil deficiency by diagnosing before amending, because pH or watering problems and cold soil cause most apparent deficiencies; biology slows below about 15 °C. If a nutrient really is short, top-dress the right amendment and water it in, then bridge the days to weeks it takes to release with a fast-acting organic input such as fish hydrolysate, kelp extract or a light foliar spray. **Short answer.** Living soil is a **large volume of compost-rich, amended soil** that you **reuse without tilling** and water with **plain, dechlorinated water**. Soil microbes and invertebrates mineralise organic matter into plant-available nutrients. Done well, it needs little more than water, mulch and a top-dress between runs. Don't pH-adjust aggressively, don't add salt fertilisers, and don't sanitise it. The evidence base is mostly *Grower practice*: soil-health principles from agronomy are well established [1], but controlled cannabis comparisons of living soil vs other systems are scarce. ## How it works - **Nutrients** come from organic amendments (compost, worm castings, seed meals, rock dusts, kelp, bone/fish meal) released by biology. Release speed depends on moisture, temperature and organism activity, so it lags by days to weeks. - **pH** is buffered by organic matter and carbonates; plants and microbes work around a near-neutral pH. Jardin leaves living-soil pH uncontrolled at ~6.3–7.0 [4]. - **No-till** keeps fungal networks and soil structure intact between runs; a mulch layer and optionally a cover crop keep the surface moist and alive (directly echoing NRCS principles: minimise disturbance, keep soil covered, keep living roots, maximise diversity [1]). ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Container volume | ≥ 50–100 L (15–25 US gal) per plant, or beds | Small pots lack buffering; *Grower practice* | | Water | Dechlorinated (stand 24 h or carbon filter for chloramine) | pH as-is unless very alkaline | | Soil moisture | Evenly moist; never dry, never saturated | Jardin uses VWC + soil temperature, dosing disabled [4] | | Soil temperature | 18–24 °C (64–75 °F) | Biology slows below ~15 °C | | Mulch | 3–5 cm (1–2 in) straw, leaves or living cover | | | Top-dress | Between runs and mid-veg; weeks before need | Organic N release is slow | ## How to run it 1. **Build** (or buy) a mix of roughly equal parts aeration (pumice/perlite), compost/castings and peat or coco, plus a balanced amendment package. Let it "cook" moist and warm for 2–4 weeks. 2. **Plant** directly; water gently; mulch. 3. **Water** by weight or VWC; living soil wants steady moisture. 4. **Feed the soil, not the plant:** top-dress amendments and water in; compost teas or extracts by hand if you use them. 5. **Between runs:** cut stems at soil level, leave roots, top-dress, re-mulch, replant. ## Fixing problems - Diagnose before amending: in living soil, pH or water problems and cold soil cause most "deficiencies". - Fast-acting organic inputs (fish hydrolysate, kelp extract, a light foliar) bridge a gap while a top-dress breaks down. - Pests: fungus gnats love moist mulch; use sticky traps and predatory mites or *Bacillus thuringiensis israelensis* rather than drying the soil out. ## Jardin notes Jardin medium "Living soil": dosing disabled in software, EC targets hidden; Jardin runs moisture, climate, photos and IPM monitoring. Time-to-harm on pump failure: days. Automation level 3 for water [4]. ## Common mistakes - **Flushing living soil before harvest.** There's nothing to flush, and pre-harvest flushing is a *Myth* that costs yield and resin. Keep watering normally (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). - Small pots of "living soil" fed like hydro. - Chlorinated or hydrogen-peroxide water, or sanitisers poured on the bed. - pH-ing water to 6.0 out of habit. - Over-amending (hot soil) and burning seedlings. ## Evidence Soil-health principles are *Established* agronomy [1]. Organic feeding can produce high cannabis yields when N supply is adequate (~389 mg N/L liquid organic feed maximised veg yield in coir-based organic media [2]). Claims specific to living soil (better terpenes, "cleaner" smoke, microbial-driven quality) are *Grower practice* with no controlled cannabis data we can cite. ## Sources 1. USDA Natural Resources Conservation Service. Soil health principles (minimise disturbance, keep soil covered, maintain living roots, maximise biodiversity). https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soil/soil-health 2. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17 3. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (organic substrates and compost chapters). https://doi.org/10.1016/C2015-0-01807-5 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Low-pressure aeroponics (LPA) > LPA uses an ordinary submersible pump and spray heads to drench roots hanging in a dark chamber with coarse droplets. It is essentially a spray-assisted hydro system: forgiving (a pool on the chamber floor keeps roots wet for hours), cheap, and easier than true high-pressure aeroponics. Run sprays continuously or on short cycles such as 1 minute on, 4 off, with a chamber humidity watchdog and solution at 18–22 °C. - Canonical: https://genetixbay.com/knowledge/systems/lpa-aeroponics.html - Category: Systems · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Aeroponics - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is low-pressure aeroponics?** Low-pressure aeroponics is a hydro system in which an ordinary submersible pump feeds 360° sprayers or a spray bar inside a dark root chamber, drenching hanging roots with large droplets of hundreds of micrometres. True aeroponics research uses much finer droplets of about 10–100 µm made at high pressure, so low-pressure aeroponics is better described as spray-assisted hydroponics. **LPA vs HPA: which is better?** Low-pressure aeroponics is the better choice for most growers because it is cheaper and far more forgiving: the pool on the chamber floor keeps roots wet for 1–4 hours if the pump fails. High-pressure aeroponics makes a true 10–100 µm mist and outstanding roots, but roots can be harmed in tens of minutes. No published study compares their cannabis flower yields. **What spray cycle for low-pressure aeroponics?** Low-pressure aeroponics usually sprays continuously or on a short cycle such as 1 minute on and 4 minutes off, a grower setting to verify for your chamber. Spray continuously for clones until roots are well developed. Keep chamber humidity at about 95–100% during the cycle with a humidity watchdog, and keep the solution at 18–22 °C (64–72 °F). **Why do my aeroponic sprayers keep clogging?** Aeroponic sprayers clog with fertiliser salts and root fragments. Fit a fine screen on the pump intake, run a daily plain-water spray cycle to flush the lines, keep roots from wrapping the sprayers, and clean the heads between runs with a dilute acid soak and a rinse, wearing gloves and goggles. A slow fall in chamber humidity or dry root patches signals a clog. **Short answer.** A standard submersible pump feeds 360° sprayers or a spray bar inside a closed, dark root chamber. Droplets are **large (hundreds of µm)**, so the chamber is a constant drizzle rather than a mist [4]. True aeroponics researchers work with much finer droplets, roughly 10–100 µm, produced at high pressure [1]. LPA is forgiving: the pool on the chamber floor keeps roots wet, so a pump failure buys **1–4 hours** [4]. Spray **continuously, or ~1 min on / 4 min off** with a humidity watchdog; solution **18–22 °C (64–72 °F)** [3][4]. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Spray cycle | Continuous, or 1 on / 4 off | [4] | | Chamber RH | ~95–100 % during cycle | Falling RH = clog or pump issue | | Solution temperature | 18–22 °C (64–72 °F) | Pump heat warms the reservoir | | pH / EC | pH 5.6–6.0; EC as DWC | | | Filter | Fine screen on pump intake | Sprayers clog with salts and roots | | Daily line flush | Plain water spray cycle | Jardin default [4] | ## How to run it 1. Light-proof chamber; sprayers that cover every root zone; drainage back to the reservoir. 2. Start clones in neoprene collars or small net pots; spray continuously until roots are well developed. 3. Keep roots from wrapping sprayers; trim if needed. 4. Clean sprayers between runs (dilute acid soak, rinse; gloves and goggles). ## Failure modes | Problem | Sign | Jardin response [4] | |---|---|---| | Pump dead | RH falls | Alert; LPA buys hours | | Sprayer clogs | Slow RH decline, dry patches | Daily flush cycle; clean heads | | Chamber overflow | Float trips | Pump off | | Root rot | Brown roots | Cool solution; sanitation | ## Jardin notes Jardin method "LPA": chamber RH/temperature, pump current, reservoir mass and chamber overflow float; spray scheduler with RH watchdog. Time-to-harm 1–4 h. Automation level 3 [4]. ## Common mistakes - Calling LPA "aeroponics" and expecting HPA root behaviour. - No intake filter. - Warm reservoir from a submerged pump in a small tank. ## Evidence Aeroponics as a method is *Established* in the literature [1]; cannabis roots grow vigorously in aeroponics (13- to 64-fold more root dry weight than soil in one study focused on root products) [2]. Head-to-head LPA vs other systems for cannabis flower yield is not published; LPA settings are *Grower practice*. ## Sources 1. Lakhiar IA, Gao J, Syed TN, Chandio FA, Buttar NA, 2018. Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics. Journal of Plant Interactions 13(1):338–352. https://doi.org/10.1080/17429145.2018.1472308 2. Ferrini F, Fraternale D, Donati Zeppa S, et al., 2021. Yield, characterization, and possible exploitation of Cannabis sativa L. roots grown under aeroponics cultivation. Molecules 26(16):4889. https://pmc.ncbi.nlm.nih.gov/articles/PMC8401984/ 3. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Nutrient film technique (NFT) > In NFT a thin, continuous film of nutrient solution runs down sloped channels past bare roots. It is efficient and well proven for lettuce and herbs, but large cannabis root masses can dam the channel, and roots dry within one to three hours if the pump stops. Keep flow continuous (about 1–2 L/min per channel), slope about 1:30 to 1:100, and solution at 18–22 °C. - Canonical: https://genetixbay.com/knowledge/systems/nft.html - Category: Systems · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: NFT - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Does NFT work for cannabis?** NFT works for cannabis clones, mothers, short-veg sea-of-green and small plants, but it struggles with full-size flowering plants. Large cannabis root masses build mats that dam the channel, and roots can dry within 1–3 hours if flow stops. NFT is well established for lettuce and herbs, while NFT for big flowering cannabis remains grower practice with no published comparisons. **What flow rate for an NFT channel?** An NFT channel for cannabis typically runs about 1–2 litres per minute of continuous flow, a starting default similar to leafy-green guidance that should be verified per system. The film should be only a few millimetres deep, since a deep, slow film causes root rot. At lights-off you can reduce flow, but never stop it, and confirm return flow at every channel daily. **What slope should NFT gullies have?** NFT gullies should slope about 1:30 to 1:100, which is a 1–3% fall, so solution runs as a thin film past the roots; check the figure against hydroponic reference texts. Keep channels no longer than about 10–15 metres, because long runs deplete oxygen and nutrients at the far end. Use wide, flat-bottomed, light-proof channels for cannabis. **What happens if my NFT pump stops?** If an NFT pump stops, the thin film drains away and bare cannabis roots can dry out within 1–3 hours, so plants wilt within hours. NFT has almost no buffer, unlike media-based systems. Fit a flow alarm on the return, put a backup pump on the same manifold if you can, and confirm return flow at every channel daily or by sensor. **Short answer.** A pump sends a **thin film** of solution down a gently sloped channel; roots sit in the film with their upper surface in air, so they get water and oxygen at once. It is a mature system for leafy greens [1][2]. For cannabis it works best for **clones, mothers, short-veg SOG and small plants**; big flowering plants build root mats that dam the channel, and the system has almost no buffer: roots can dry in **1–3 hours** without flow [4]. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Flow per channel | 1–2 L/min | Jardin default | | Slope | 1:30–1:100 (1–3 %) | | | Channel length | ≤ 10–15 m | Long channels deplete O₂ and nutrients at the far end | | Film depth | A few mm | Deep, slow film = root rot | | Solution temperature | 18–22 °C (64–72 °F) | [3] | | pH / EC | pH 5.6–6.0; EC as DWC | | | Lights-off | Reduce flow if desired, never stop | [4] | ## How to run it 1. Wide, flat-bottomed channels for cannabis; lids that block light. 2. Start plants in rockwool or a small net pot so the root ball sits in the film. 3. Confirm return flow at every channel daily (or by sensor). 4. Prune or redistribute root mass if it starts to pond. 5. Backup pump on the same manifold if you can. ## Failure modes | Problem | Sign | Jardin response [4] | |---|---|---| | Pump failure | No return flow, wilting within hours | Switch to backup pump; escalate alert | | Channel blocked by roots | Water at the inlet end rises/overflows | Inlet high float → pump off, "channel blocked" | | Film too deep/slow | Brown roots at outlet end | Flow and temperature trend | | Warm solution | Root rot | Chiller, shade the channels | ## Jardin notes Jardin method "NFT": flow meter on the return is the proof that a film exists; pump current; inlet-end high float; a 30 s loss of return flow with pump current = blockage or split; with zero current = pump dead. Automation level 3 [4]. ## Safety Water + electricity: GFCI/RCD, drip loops, leak trays under the reservoir. ## Common mistakes - Using lettuce channels for big flowering plants. - Narrow channels that dam within weeks. - No flow alarm. ## Evidence NFT for leafy crops is *Established* [1][2]. NFT for full-size flowering cannabis is *Grower practice* with no published comparisons we can cite. ## Sources 1. Cornell CEA. Hydroponic lettuce handbook. https://cea.cals.cornell.edu/ 2. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press (NFT chapter). https://doi.org/10.1201/9781003133254 3. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Recirculating deep water culture (RDWC) > RDWC links several DWC sites to a control bucket and circulates the solution with a pump, so one reservoir sets pH, EC and temperature for every plant and a single chiller cools the lot. It adds circulation and plumbing failure modes to DWC's oxygen and temperature risks. Targets match DWC: 18–22 °C, DO above 6 mg/L, pH 5.6–6.0. - Canonical: https://genetixbay.com/knowledge/systems/rdwc.html - Category: Systems · Level: Advanced - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: RDWC - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should my reservoir be sterile or full of beneficial microbes?** GenetixBay prefers a beneficial-microbe RDWC reservoir, since bacteria arrive in shared recirculating water whatever you do, so you may as well have the good ones. Running sterile is valid only with full commitment: a continuous oxidiser or UV or ozone, clean top-ups and no organics. In RDWC any outbreak reaches every site, so never mix the two approaches. **What is the difference between DWC and RDWC?** The difference is that RDWC plumbs several DWC sites together and pumps solution through a shared control bucket, while DWC keeps each plant in its own bucket. RDWC gives one place to correct pH, EC and temperature, one chiller and more stable chemistry. The cost is plumbing risk: a leak, blocked return or stopped pump, or a root disease, affects every plant. **How big should the RDWC control bucket be?** An RDWC control bucket is usually about 20–30% of the total system volume, a grower rule of thumb worth verifying for your build. It needs room for the pH and EC probes, the dosing inlet and the top-off. Pair it with return plumbing of at least 25 mm (1 inch) on small systems, because undersized returns overflow the sites. **How fast should the RDWC pump circulate?** An RDWC pump should turn the total system volume over about 1–4 times per hour, a grower rule of thumb. Circulating too fast adds pump heat to the water, which matters when you are holding 18–22 °C, while circulating too slowly leaves stagnant, warming sites. Circulation does not replace aeration: keep air stones in every site, not only the control bucket. **One plant in my RDWC has root rot; what now?** Root rot in one RDWC site means system-wide action, because every site shares the same water and the disease spreads to all of them. Cool the solution to 18–22 °C, keep dissolved oxygen above 6 mg/L, check roots in every site and remove dead root material. Clean and sterilise the whole system between runs to stop the pathogen carrying over. **Short answer.** RDWC is DWC with the buckets plumbed together and a pump circulating solution through a **control bucket**. You get one place to measure and correct **pH, EC and temperature** and one chiller for every plant, plus larger total volume (more stable chemistry). The cost is plumbing: a split fitting, a blocked return or a stopped pump now affects every plant. Targets are the same as [DWC](https://genetixbay.com/knowledge/systems/dwc.md): **18–22 °C (64–72 °F)**, **DO > 6 mg/L**, **pH 5.6–6.0**. ## How it works Each site has its own air stones. Solution is pumped from the control bucket into the sites (or the reverse), and returns by gravity through bulkhead fittings near the bottom. Because every site shares water, a root-disease outbreak in one site spreads to all [1]. > **House position: living reservoir preferred.** Bacteria will turn up in any reservoir whatever you do, so you may as well have the good ones: GenetixBay prefers a beneficial-microbe reservoir. A sterile reservoir is a valid choice, but only if you commit to it fully (continuous oxidiser or UV/ozone, clean top-ups, no organics) and never mix the two. It's a personal choice; the half-way house is what fails. See [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) for both approaches. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Solution temperature | 18–22 °C (64–72 °F) | Chiller sized for pump heat + room | | DO | ≥ 6 mg/L | Air in every site, not only the control bucket [2] | | pH / EC | As DWC | | | Circulation | Turn total volume over ~1–4 times per hour | Too fast heats water; too slow leaves stagnant sites | | Control bucket | 20–30 % of system volume | Room for probes and top-off | | Return plumbing | ≥ 25 mm (1 in) for small systems | Undersized returns overflow sites | ## How to run it 1. Level all sites; test with plain water for 24 h and check every joint before plants go in. 2. Probes, dosing inlet and top-off live in the control bucket. 3. Inspect roots in every site weekly; any brown slime means system-wide action. 4. Refresh on schedule; drain via a pump, not by tipping buckets. ## Failure modes | Problem | Sign | Jardin response [4] | |---|---|---| | Split line / leak | One site's level drops while control bucket holds | Per-site level floats flag it; leak pad cuts the pump rail | | Circulation pump dead | Return flow stops; sites stagnate and warm | "Stagnant bucket" alarm; proof-of-life by current | | Air failure | DO falls in all sites | Alert, chiller stays on, backup pump if fitted | | Root rot | Spreads through system | Clean and sterilise between runs; cool water | ## Jardin notes Jardin method "RDWC": as DWC plus per-bucket level floats, circulation-pump proof-of-life and a stagnant-bucket alarm. Time-to-harm: 2–12 h for air, days for chemistry. Automation level 3 [4]. ## Safety As DWC: GFCI/RCD on every outlet, drip loops, leak trays. RDWC systems hold hundreds of litres; plan for a full spill. ## Common mistakes - Relying on air only in the control bucket. - Undersized return lines. - Mixing plants of different vigour on one system (one EC for all). ## Evidence Root-disease spread and DO/temperature behaviour in recirculating hydroponics are *Established* [1][2][3]. RDWC-specific design numbers are *Grower practice*. ## Sources 1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 2. Cornell CEA, 2016. Leafy greens (GPN): DO and pH guidance. https://cea.cals.cornell.edu/files/2019/06/GPNOctober2016_LeafyGreens.pdf 3. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Recirculating drip (top-feed, runoff returns) > A pump pushes nutrient solution through drip emitters into pots of coco, rockwool or clay pebbles and the runoff returns to the reservoir. It saves water and nutrients but the reservoir slowly drifts as runoff brings back salts and root exudates, so monitor runoff and refresh when reservoir chemistry diverges. Typical shots are 2–6 % of pot volume, first shot 1–2 h after lights-on, none in the dark. - Canonical: https://genetixbay.com/knowledge/systems/recirculating-drip.html - Category: Systems · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Drip - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How many drip emitters per plant?** Most cannabis drip setups use 2–4 emitters per plant, each delivering about 2–8 litres per hour, spread around the pot so the medium wets evenly. Use pressure-compensating emitters on long lines and a filter of at least 120 mesh before the manifold. Calibrate weekly by collecting one emitter's output for one minute, since a clogged emitter can leave one plant dry. **Should I recirculate drip runoff?** Recirculating drip runoff saves water and fertiliser, but it comes with two costs. The reservoir drifts as plants take up ions unevenly and runoff returns salts and root exudates, and recirculation spreads any root pathogen to every plant. Recirculate only if you will monitor runoff and reservoir EC, refresh on schedule, and never return runoff from a diseased plant. **How often should I change a recirculating reservoir?** Change a recirculating drip reservoir every 7–14 days, or sooner when runoff and input EC diverge by more than about 0.5 mS/cm. Rising reservoir EC with a steady feed is another refresh trigger. Between changes, top off with plain water or weak feed, and remember 'it's recirculating, it's fine' is a common mistake that lets chemistry drift. **What shot size for drip irrigation in coco?** Drip shots in coco typically run about 2–6% of the pot volume per shot in veg, a grower starting point to verify for your setup. Give the first shot 1–2 hours after lights-on and the last 2–4 hours before lights-off, with no shots in the dark by default. Aim for 10–30% runoff overall and keep coco input pH at 5.8–6.2. **Short answer.** Drip emitters (typically **2–4 per plant, 2–8 L/h each**) feed pots of coco, rockwool or clay; runoff drains back to the reservoir [4]. You reuse water and fertiliser, but the reservoir drifts: plants take up ions unevenly and runoff returns salts and exudates. Watch reservoir vs runoff EC and **refresh when they diverge by more than ~0.5 mS/cm** (Jardin rule) [4]. Recirculation also spreads root pathogens to every plant [2]. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Emitters | 2–4 per plant, 2–8 L/h | Spread around the pot to wet it evenly | | Shot size | 2–6 % of pot volume per shot (veg) | | | First shot | 1–2 h after lights-on | | | Last shot | 2–4 h before lights-off | | | Night shots | None by default | | | Runoff | 10–30 % of applied, returned | | | Refresh trigger | Runoff/input EC divergence > 0.5 mS/cm, or every 7–14 days | [4] | | pH / EC | Per medium (coco 5.8–6.2, rockwool 5.5–6.0) | | ## How to run it 1. Size the pump for all emitters at pressure; use pressure-compensating emitters on long lines. 2. Filter (≥ 120 mesh) before the manifold; emitters clog. 3. Calibrate: collect one emitter for 1 minute and confirm flow; repeat weekly. 4. Return runoff through a screen; consider UV or slow-sand filtration at commercial scale. 5. Top off with plain water or weak feed; full refresh on trigger. ## Failure modes | Problem | Sign | Jardin response [4] | |---|---|---| | Emitter clog | One plant dry, shot volume low | Raise shot time up to +50 %; alert at −40 % | | Line split | Shot volume high, reservoir mass drops without return | Close zone | | Runoff tray overflow | Float trips | Pump off | | Pump dead | No current | Alert; media buy 12–36 h | | Reservoir EC creeping | Rising EC with steady feed | Refresh | ## Jardin notes Jardin method "Drip, recirculating": flow meter per manifold, reservoir mass, runoff tray float required; one VWC probe per zone turns it into a steered system. Time-to-harm 12–36 h. Automation level 3 [4]. ## Common mistakes - **Flushing before harvest.** Pre-harvest flushing is a *Myth* that costs you yield and resin: it starves the plant while it packs on its final weight, trichomes and resin. Feed through to harvest at stage strength. The only valid flush is a root-zone flush to clear salt build-up, at any stage (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). In recirculating systems the reset is a fresh reservoir plus a light-solution flush of the pots. - No filter → clogged emitters → one dead plant. - Never refreshing ("it's recirculating, it's fine"). - Recirculating from a plant with root disease. ## Evidence Closed-system drift and pathogen spread are *Established* hydroponic knowledge [1][2][3]. Cannabis-specific shot sizes and timing are *Grower practice*. ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press (closed vs open systems). https://doi.org/10.1201/9781003133254 2. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems (recirculation spreads pathogens). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 3. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins). --- # Defoliation and lollipopping: what to remove, when, and the evidence > Lollipopping strips small branches and leaves from the shaded lower third at or near the flip; defoliation removes fan leaves that shade bud sites or block airflow. In a controlled study on large plants, neither defoliation three weeks before harvest nor lower-branch removal changed flower or cannabinoid yield per plant, and defoliation improved cannabinoid uniformity. Stripping within reason doesn't hurt yield, but in the founder's experience tucking helps more: tuck and train first. Whether tucking beats stripping, and whether defoliation raises cannabinoids, is an open GenetixBay trial question. - Canonical: https://genetixbay.com/knowledge/training/defoliation-lollipopping.html - Category: Training · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should I defoliate my cannabis plant?** Defoliate cannabis only within reason, and tuck first. GenetixBay's position is that fan leaves are the solar farm powering the buds: tuck them under or behind bud sites and spread branches before removing anything. Pluck only leaves you cannot tuck that shade buds, crowd a humid interior, touch the medium or are damaged. Cultivars vary a lot, so learn how yours reacts before defoliating hard. **When should I lollipop?** Lollipop cannabis at the flip to 12/12 or up to about day 21 of flower. Remove the small shoots and leaves in the lower third of the plant that will never reach good light, since that growth makes airy, low-potency buds. Research found lower-plant cannabinoids correlated with poor light penetration, and lower-third removal gave the most uniform cannabinoids when combined with defoliation. **Does defoliation increase yield?** No. Defoliation does not increase cannabis yield per plant in the best controlled data. A study of large greenhouse plants found neither defoliation three weeks before harvest nor lower-third removal at the flip significantly changed flower or cannabinoid yield, and at commercial density yield per m² matched the control. It doesn't hurt within reason either, but the founder finds tucking leaves helps more. **How many leaves can I remove?** Remove no more than about 20-30% of a cannabis plant's leaf area in one session, and only after tucking leaves out of the way first. That limit is grower practice rather than research. Avoid 'schwazzing', stripping almost all leaves twice in flower, especially on stressed or deficient plants or a cultivar you haven't tested, and don't strip autoflowers during their short veg. **What is the day 21 defoliation?** The day 21 defoliation is a grower practice of thinning fan leaves around the 21st day of flower. GenetixBay advises tucking large fan leaves away from bud sites at that point and removing only those you cannot tuck that crowd a dense, humid interior, where bud rot and powdery mildew thrive. The day-21 timing itself is grower practice; no controlled study has tested it specifically. **Tuck or pluck fan leaves?** Tuck, don't pluck, is the GenetixBay house position on cannabis fan leaves. Tucking leaves under or behind bud sites keeps the plant's full leaf area working while still letting light reach the buds. Controlled trials found stripping within reason neither hurt nor helped yield, and the founder's side-by-sides suggest tucking helps more. Whether tucking truly beats stripping is an open GenetixBay trial question. **Does defoliation increase THC or cannabinoids?** It is unproven whether defoliation increases THC or cannabinoids in indoor drug-type cannabis. In a controlled study on large plants, defoliation did not change cannabinoid yield per plant but made cannabinoids more uniform through the plant. A hemp study found early-flower defoliation raised total cannabinoid concentration while veg or late-flower timing did not, but it simulated hail. GenetixBay lists this as an open trial question. **Short answer.** **Lollipopping** removes small branches and leaves from the bottom third of the plant at or just after the flip, because that growth gets little light and makes airy, low-potency buds. **Defoliation** removes fan leaves that shade bud sites or block airflow. The best controlled data (large ~2.5 m greenhouse plants of a CBD-dominant medical cultivar): **defoliation 3 weeks before harvest** and **removing the lower third at the flip** did **not** significantly change flower or cannabinoid yield per plant, and defoliation **improved cannabinoid uniformity** across the plant [1]. Lower cannabinoids at the bottom of the plant correlated with low light penetration [1]. So stripping within reason doesn't hurt yield, and it doesn't boost it either. In the founder's experience **tucking helps more**. > **House position: tuck first, strip within reason.** Leaves are the solar farm that powers the buds. Stripping within reason doesn't hurt yield (the trials above agree), but the founder, after a lifetime of side-by-sides, finds that tucking fan leaves under or behind bud sites and training branches out of each other's shade helps more than removing them. Responses vary by cultivar: some clones can lose most of their leaves with no effect, or even grow faster, while others suffer. Learn how your cultivar reacts before you defoliate hard. > **Open question: a GenetixBay trial.** Two things nobody has settled for indoor drug-type cannabis: does **tucking beat stripping** for dry yield, and does **defoliation raise cannabinoid content** (the hemp data in [3] hints it might, at one timing)? This is exactly what the Bay Trials are for: matched clones, split tent, tuck vs strip, dry weight and lab COAs on both sides. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md) for the open trials. ## What the research shows | Treatment (Danziger & Bernstein 2021 [1]) | Flower yield/plant | Cannabinoid yield/plant | Uniformity | |---|---|---|---| | Defoliation 3 weeks before harvest | No significant change | No significant change | Improved | | Lower-third branch + leaf removal at flip ("lollipopping") | No significant change | No significant change | Not improved alone; best when combined with defoliation | | Lower-third removal + defoliation | No significant change | No significant change | Most uniform of non-branch-removal treatments | | Removing all primary branches (single stem) | −up to 99 % | ~3 % of others | High (but pointless) | At commercial density, defoliation gave yields per m² similar to the control [2]. In hemp, defoliation in early flower raised total cannabinoid concentration while veg or late-flower defoliation did not [3]; this was a simulated-hail study and may not transfer to indoor drug-type cannabis. ## How to do it 1. **Lollipop** at flip to ~day 21 of flower: remove small shoots and leaves from the lower ~⅓ that will never reach the light. 2. **Veg: tuck first.** Tuck fan leaves under or behind shaded shoots, and spread branches with [LST](https://genetixbay.com/knowledge/training/lst.md). Remove only leaves that touch the medium or are damaged. If you do remove healthy leaves, take no more than ~20–30 % of leaf area at once (*Grower practice*). 3. **Around day 21 of flower:** tuck large fan leaves away from bud sites. Remove only those you can't tuck and that crowd a dense, humid interior. 4. **Late flower:** only remove leaves that are dying, mouldy, or blocking airflow in dense colas. 5. Sterilise scissors between plants. ## Numbers that matter | Item | Typical | Evidence | |---|---|---| | Lollipop zone | Lower ~⅓ | Supported [1] | | Max leaf removal per session | ~20–30 %, and only after tucking | Grower practice; tuck-first is the house position | | Timing | Flip, ~day 21, ~3 weeks before harvest | Supported for the last [1]; others Grower practice | ## Why airflow matters Dense, humid canopies favour *Botrytis* bud rot and powdery mildew [4]. Thinning the interior lowers canopy humidity ([humidity](https://genetixbay.com/knowledge/environment/humidity-by-stage.md), [airflow](https://genetixbay.com/knowledge/environment/airflow.md)). ## Common mistakes - "Schwazzing" (stripping almost all leaves twice in flower), especially on stressed or deficient plants or on a cultivar you haven't tested. Some clones shrug it off; others suffer. - Plucking a leaf you could have tucked. - Removing leaves from autoflowers in a short veg. - Taking healthy leaves when the real problem is too few, too dim lights. ## Evidence Effects on per-plant yield and uniformity are *Supported* by controlled studies on large plants [1][2]. Hemp timing effects are *Supported* for hemp only [3]. Session limits and day-21 timing are *Grower practice*. "Tuck first" is the house position: the controlled trials found stripping within reason neither hurt nor helped yield [1][2], and the founder finds tucking helps more. Tuck vs strip, and any cannabinoid gain from defoliation, are *open questions* for a GenetixBay trial; cultivar responses vary. ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 2. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 3. Sandoval SM et al., 2024. Defoliation timing effects on phytocannabinoids in hemp (simulated hail). Industrial Crops and Products; MSc thesis version, Colorado State University. https://mountainscholar.org/bitstreams/a8421af5-2146-4d67-8751-397a58816f1b/download 4. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # FIM: pinching most of the tip for multiple tops > FIM removes roughly 70–80 % of the newest growth at the tip instead of cutting cleanly above a node. When it works, three to five shoots grow from the same point; when it doesn't, you get one or two, like a sloppy top. It is less predictable than topping and has no controlled research behind its yield claims. - Canonical: https://genetixbay.com/knowledge/training/fim.html - Category: Training · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Veg · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is FIMing?** FIMing is a cannabis training technique that pinches or snips off about 70-80% of the newest, still-folded growth at the main tip, leaving the bottom quarter in place. Done at 4-6 nodes on a healthy plant, the leftover tissue often splits into several new shoots within 5-7 days. It is grower practice, with no controlled cannabis research behind its yield claims. **FIM vs topping: which gives more colas?** FIM can give more colas than topping, typically 2-5 new shoots from one point versus topping's reliable two, but the result is a gamble. One or two shoots is common after FIM, while topping is predictable. No controlled cannabis study has compared them. Either way, any yield benefit comes from a flatter canopy with more tops in good light, not from the cut itself. **How much of the tip do I cut for FIM?** For a FIM, cut or pinch across the newest tight cluster of leaves at the cannabis plant's main tip, removing roughly the top three-quarters and leaving the bottom quarter. Cut too little and the tip simply regrows as one; cut too much and it becomes an ordinary top with two shoots. Wait 5-7 days to see the split, and leave at least 7-10 days before the flip. **Why did my FIM only grow one top?** A FIM that grows only one top usually means too little of the tip was removed, so the dominant growing point survived and simply regrew. Cutting too much instead gives an ordinary two-shoot top. FIM results are inconsistent even when done well, and slow or stressed plants respond poorly. You can FIM the new top again, since the technique can be repeated, or train it out with LST. **Short answer.** "FIM" is a partial top: pinch or snip off about **70–80 % of the newest, still-folded growth** at the very tip, leaving the base of that tip. Often several tiny buds at the base grow out together, giving **3–5 new shoots** from one point. Results are inconsistent; one or two shoots is common. The method is *Grower practice*: there is no controlled cannabis study of FIM vs topping. Topping gives a predictable result; FIM gives a gamble with more tops. ## How to do it 1. Plant with 4–6 nodes, healthy. 2. Find the newest tight cluster of leaves at the main tip. 3. Pinch or cut across it, removing the top ~¾ of the cluster; leave the bottom ~¼. 4. Wait 5–7 days; the cluster should split into several shoots. 5. Train the new shoots apart with [LST](https://genetixbay.com/knowledge/training/lst.md). ## Numbers that matter | Item | Typical | |---|---| | Timing | 4–6 nodes; can be repeated on new tops | | Expected shoots | 2–5 (variable) | | Recovery | Usually faster than a full top (*Grower practice*) | | Last FIM before flip | ≥ 7–10 days | ## Why it may work The leftover tip tissue still contains several axillary meristems; damaging the dominant one without removing all of them can release more than two. Like topping, the yield benefit (where any) comes from a flatter canopy with more tops in good light [1][2]. ## Common mistakes - Cutting too little (the tip just regrows) or too much (it's just a top). - FIMing slow or stressed plants. - Expecting four colas every time. ## Evidence Apical dominance is *Established*. FIM-specific outcomes are *Grower practice*. Benefits of an even, well-lit canopy and of pruning are *Supported* [1][2]. ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # HST and supercropping: controlled stem crushing > Supercropping pinches and gently crushes a green stem until the inner tissue softens, then bends it over so the tip sits lower. It is used to tame tall shoots in late veg and early stretch. Done right the stem forms a firm knuckle in a few days. Stem snapping gives better buds in the founder's long experience: *Grower practice*, house-endorsed, though no controlled study has measured a potency gain yet. Every cultivar responds differently. - Canonical: https://genetixbay.com/knowledge/training/hst-supercropping.html - Category: Training · Level: Intermediate - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Veg, Transition · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is supercropping?** Supercropping is a high-stress training method: squeeze a green, flexible cannabis stem between finger and thumb, roll it until the inner fibres soften, then bend it 45-90° so the tip sits lower. The skin should stay intact. The branch keeps growing and forms a hard knuckle in 3-7 days. Growers use it to level the canopy so more bud sites sit in good light. **When should I supercrop?** Supercrop cannabis in late veg and the first two weeks of flower, when shoots are still green and pliable and the stretch is pushing tall tops toward the light. Pick a section 5-15 cm (2-6 in) below the tip. Avoid woody stems, which snap, and avoid late flower or plants already under stress. Keep the environment easy for a few days afterwards. **Does supercropping increase THC?** No controlled study has measured whether supercropping increases THC, so a potency gain is untested, not disproven. The one cannabis study of deliberate stress used controlled drought, which raised cannabinoid concentration, but that result does not transfer to mechanical crushing. The supported benefit is canopy levelling, which puts more bud sites in good light, and light is what yield follows. **Does snapping stems give better buds?** Yes, in GenetixBay's view: stem snapping (supercropping) gives better buds in the founder's long experience, and they do it all the time. That is grower practice, house-endorsed, rather than research; no controlled study has yet measured the effect. Snap it, don't break it: a good supercrop leaves the skin intact and the branch upright within a day or two. Every cultivar responds differently. **What do I do if I snap a branch?** If you accidentally split or snap a cannabis branch while supercropping, tape or splint it back into position; most heal. Keep the environment easy for a few days, with no other stress and no feeding changes, while a firm knuckle forms over 3-7 days. Crushing so hard that the stem is cut right through is the main way to lose the branch, so squeeze gently next time. **Is HST bad for autoflowers?** HST should be used only lightly, and early, on autoflowers. An autoflower runs on a strict countdown from germination and cannot be vegged longer to recover, so heavy stress costs yield it cannot regain. If an auto has one shoot that is too tall, a gentle supercrop in early growth is acceptable, but low-stress training is the safer main method for autos. **Short answer.** Supercropping = squeeze a green, flexible stem between finger and thumb, roll it gently until the inner fibres soften (you'll feel it give), then **bend it 45–90°**. The tip now sits lower and the branch keeps growing; a hard "knuckle" forms in **3–7 days**. Use it to bring tall shoots down in **late veg and the first 2 weeks of flower**. It's a **canopy-levelling tool**, and GenetixBay endorses it for better buds: the founder snaps stems all the time. That's *Grower practice*, house-endorsed; no controlled study has yet measured supercropping's effect on cannabinoids, and the one cannabis study of deliberate stress used **drought**, not crushing [3]. Every cultivar responds differently, so watch how yours recovers. > **Greenleaf aside.** Snap it, don't break it. A good supercrop leaves the skin intact and the branch upright again within a day or two, with a knuckle that carries the cola through flower. ## How to do it 1. Pick a stem section that is green and still pliable, 5–15 cm (2–6 in) below the tip. 2. Squeeze and roll gently, rotating, until it softens. Don't split the skin. 3. Bend over and, if needed, tie in place. 4. Keep the environment easy for a few days (no other stress, no feeding changes). 5. If it splits: tape or splint it; most heal. ## Numbers that matter | Item | Typical | |---|---| | Timing | Late veg to flower week 2 | | Recovery | 2–4 days to stand up; knuckle in 3–7 days | | Autoflowers | Light use only, early | ## Why bother Tall shoots close to the light suffer heat/light stress while the rest of the canopy is under-lit ([heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md)). Levelling the canopy puts more bud sites in good light, which is what yield follows [1][2]. ## Common mistakes - Supercropping woody stems (they snap). - Crushing so hard the stem is cut through. - Doing it in late flower. - Using it on stressed plants. ## Evidence Supercropping technique, recovery and better buds: *Grower practice*, house-endorsed (founder's long experience). No controlled study has measured a cannabinoid gain from supercropping; that's untested, not disproven. The canopy-light rationale is *Supported* [1][2]. Controlled drought (a different stress) raised cannabinoid concentration in one study [3], which doesn't transfer to mechanical stress. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 3. Caplan D, Dixon M, Zheng Y, 2019. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience 54(5):964–969. https://doi.org/10.21273/HORTSCI13510-18 --- # LST: low-stress training > Low-stress training bends and ties stems outward and down so the plant grows as a flat, even canopy, without cutting anything. It is the safest training method, suits autoflowers, and works with topping and SCROG. Start in early veg, adjust ties every few days, and stop bending hard once stems lignify in mid-stretch. - Canonical: https://genetixbay.com/knowledge/training/lst.html - Category: Training · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Veg, Transition · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I LST a cannabis plant?** To LST a cannabis plant, gently flex the main stem, bend it outward toward the pot edge and tie it down with soft plant ties or plastic-coated wire anchored to the pot rim or stakes. As side branches grow, tie them outward like spokes so their tops stay level, ideally within about 10-15 cm (4-6 in) of each other. Re-tie or turn the pot every 2-4 days. **When should I start low stress training?** Start low-stress training cannabis in early veg, at about 3-5 nodes, while stems are still soft and flexible. Starting too late, once stems turn woody, makes bending harder and risks snapping. Keep adjusting ties every 2-4 days through veg, and finish your hard bending by mid-stretch, around flower week 2-3, when stems stiffen. **Is LST good for autoflowers?** Yes. LST is the default training method for autoflowers because nothing is cut, so recovery time is near zero. An auto runs on a fixed countdown from germination and cannot afford the recovery that topping or heavy stress demands. Starting at 3-5 nodes, tie branches outward to build several tops in the brightest light, and avoid hard bending once stems stiffen. **Can I LST in flower?** You can keep guiding cannabis branches in early flower, but stop hard bending by mid-stretch, around flower week 2-3, when stems lignify and stiffen. During the stretch, tuck tops under a SCROG net or gently steer them rather than forcing sharp bends. Bending woody stems later risks creasing or snapping them; if a stem creases, tape it, and it usually heals. **What do I tie plants down with?** Tie cannabis plants down with soft plant ties or plastic-coated wire, anchored to small holes drilled in the pot rim or to stakes. Avoid thin wire or string, which can cut into stems. Check and loosen ties as stems thicken, because forgotten ties can girdle a branch. During the stretch, a SCROG net can take over the job of holding branches in place. **Short answer.** Bend the main stem and branches **outward and down** and tie them in place so the side shoots rise to the same height under the light. Nothing is cut, so recovery time is near zero, which makes LST the default for **autoflowers** and beginners. Start in **early veg (3–5 nodes)**, adjust every **2–4 days**, and finish shaping by **mid-stretch** (around flower week 2–3), when stems stiffen. > **Tuck first.** LST is the house alternative to stripping leaves. Tuck fan leaves under or behind bud sites and spread branches so every leaf works: leaves are the solar farm for the buds. Stripping within reason doesn't hurt yield, but in the founder's experience tucking helps more, and it's safe on every cultivar; responses to heavy defoliation vary. Tuck vs strip (yield and cannabinoids) is an open GenetixBay trial question (see [defoliation](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md)). ## Why it works Bending the main stem horizontal reduces its apical dominance (the tip is no longer the highest point), so side branches turn upward and grow out. The result is many tops in the brightest light zone rather than one tall cola shading the rest. Light drives yield [1], and lower, shaded buds in cannabis have lower and less uniform cannabinoid content [2]. ## How to do it 1. Use soft plant ties or plastic-coated wire; anchor to the pot rim (drill small holes) or to stakes. 2. Gently bend the main stem toward the pot edge; flex it between fingers first to make it supple. 3. Tie branches outward like spokes as they grow; keep the tops level. 4. Turn the pot or re-tie every few days. 5. In stretch, tuck tops under a [SCROG](https://genetixbay.com/knowledge/training/scrog.md) net or just guide them; stop hard bending. ## Numbers that matter | Item | Typical | |---|---| | Start | 3–5 nodes | | Adjust | Every 2–4 days | | Target canopy evenness | Tops within ~10–15 cm (4–6 in) of each other | | Last bending | Flower week 2–3 | ## Common mistakes - Thin wire or string that cuts into stems. - Bending too sharply too early and snapping the stem (if it creases, tape it; it usually heals). - Starting too late when stems are woody. - Forgetting the ties as stems thicken (girdling). ## Evidence The mechanism (gravity and position effects on apical dominance) is *Established* plant physiology. LST yield benefits are *Grower practice*; the even-canopy rationale is *Supported* by light-response and architecture studies [1][2]. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ --- # Mainlining and manifolding: building a symmetrical plant > Mainlining (manifolding) tops a young plant down to the third node, removes all lower growth, and then tops each arm repeatedly to build a symmetrical hub feeding 8 or 16 evenly matched colas. It produces a very even canopy at the cost of 2–4 extra weeks of veg. It is grower practice with no controlled studies; the closest research found double pruning increased yield per plant. - Canonical: https://genetixbay.com/knowledge/training/mainlining-manifolding.html - Category: Training · Level: Advanced - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Veg · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is mainlining cannabis?** Mainlining is a cannabis training method that tops a young plant above the third node, removes all growth at nodes 1-2, then trains the two remaining arms flat and tops each one repeatedly. Every top is fed through one central 'manifold' junction, so the colas grow evenly matched. It is also called manifolding and is grower practice, with no controlled studies testing it directly. **How long does mainlining add to veg?** Mainlining usually adds about 2-4 extra weeks of vegetative growth, because each topping round needs 5-7 days of recovery and the arms must grow 2-3 nodes between rounds. Start at 5-6 nodes on a healthy plant, and flip once the tops are even and the space is about 70% full. The extra time is why mainlining is not recommended for autoflowers. **How many colas can I get from mainlining?** Mainlining usually gives 8 evenly matched colas, and 16 on large plants in big spaces. Each round of topping doubles the tops: 2 arms from the first top above node 3, then 4, then 8, then 16, all fed through one central hub. Going beyond 8 means more veg time, because each round needs 5-7 days of recovery before the next. **Mainlining vs topping and LST?** Mainlining builds a more symmetrical, even canopy than simple topping or LST, but costs roughly 2-4 extra weeks of veg and more work. Topping gives a quick, predictable split, and LST bends without cutting. Mainlining combines repeated topping with LST for 8-16 equal colas. None has been compared head to head in a controlled study; the closest research found double pruning raised yield per plant. **Short answer.** Let the plant reach **5–6 nodes**, top it **above the 3rd node**, and remove everything below that node (the shoots and leaves at nodes 1–2). Train the two remaining arms horizontally. When each arm has grown 2–3 nodes, top each one again, giving **4**, then **8**, then **16** tops, all fed through one central "manifold" junction. The goal is perfectly equal colas in an even canopy. It costs roughly **2–4 extra weeks of veg** (*Grower practice*). No study tests mainlining directly; the closest research found **double pruning** raised yield per plant and lower-canopy removal had no yield penalty in large plants [1]. ## How to do it 1. Top above node 3 at 5–6 nodes; remove growth at nodes 1–2 (keep the node-3 pair). 2. Tie the two arms flat, opposite each other. 3. Let each arm grow 2–3 nodes; top each above its 1st node of new growth → 4 tops. 4. Clean everything inside the hub that isn't one of the main arms. 5. Repeat for 8 (and 16 in big spaces). Recover 5–7 days between rounds. 6. Flip when tops are even and the space is ~70 % full. ## Numbers that matter | Item | Typical | |---|---| | Start | 5–6 nodes | | Tops | 8 (common), 16 (large plants) | | Extra veg | 2–4 weeks | | Recovery per topping round | 5–7 days | | Autoflowers | Not recommended | ## Common mistakes - Starting on a weak plant. - Uneven arms (one arm dominates for the rest of the grow); correct with LST early. - Flipping too early with tiny arms. ## Evidence Technique is *Grower practice*. The architecture logic (even canopy in good light, pruning increasing per-plant yield) is *Supported* [1][2]. ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # SCROG: screen of green > SCROG uses a horizontal net 20–40 cm above the pots to spread a few plants into a flat, even canopy: shoots are tucked under the net through veg and early stretch, then allowed to grow up through it. It suits small rooms and plant-count limits, at the cost of longer veg. Fill about 70–80 % of the net before flipping, since plants stretch to fill the rest. - Canonical: https://genetixbay.com/knowledge/training/scrog.html - Category: Training · Level: Intermediate - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How does SCROG work?** SCROG (screen of green) works by fixing a horizontal net above the pots and tucking every shoot that pokes through back under it, sideways, throughout veg. The plant spreads across the screen into a flat, even canopy where all the tops sit in good light. After the flip, growers keep tucking for about two weeks of stretch, then let the tops grow up through the net. **How high should the SCROG net be?** Set a SCROG net about 20-40 cm (8-16 in) above the pots, with mesh squares of 5-10 cm (2-4 in). Install it taut and level before the plant reaches it. For heavy colas, a second net about 20-30 cm higher adds support in flower. Below the net, strip small shaded growth around day 21 of flower to reduce larf and mould risk. **When do I flip a SCROG to flower?** Flip a SCROG to 12/12 when the net is about 70-80% full. Many cultivars stretch 1.5-2.5 times after the flip, and that stretch fills the remaining space; flipping with a full net leaves you out of room. Keep tucking sideways for the first 10-14 days of stretch, then let the tops grow up through the screen. **SCROG vs SOG: which yields more?** No published head-to-head trial shows whether SCROG or SOG yields more. In both, light and canopy evenness drive yield, and research shows planting density strongly affects yield per area and cannabinoid uniformity. SCROG gets a few plants, about 1-4 per m², to fill a space, which suits plant-count limits but adds veg time and labour. **How many plants for a SCROG?** A SCROG typically uses 1-4 cannabis plants per square metre, or one plant per 0.25-1 m², with 4-8 weeks of veg depending on pot size and space. Fewer plants means longer veg to fill the net, which suits plant-count limits but costs more time and power. Where plant numbers aren't limited, using too few plants for the space is a common mistake. **Short answer.** Fix a net (5–10 cm / 2–4 in squares) **20–40 cm (8–16 in)** above the pots. Through veg, tuck every shoot that pokes through back under, sideways, so the plant spreads across the screen. Flip to 12/12 when the net is **~70–80 % full**; tuck for the first **~2 weeks of stretch**, then let tops grow up. Below the net, strip small shaded growth ([lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md)). SCROG makes **few plants** fill a space evenly, which helps under plant-count limits; it trades extra veg time and labour for that. Head-to-head yield vs SOG is not published; light and canopy evenness drive both [1][3]. ## How to do it 1. Top once or twice, then LST the branches outward ([topping](https://genetixbay.com/knowledge/training/topping.md), [LST](https://genetixbay.com/knowledge/training/lst.md)). 2. Install the net before the plant reaches it; make it taut and level. 3. Tuck daily or every other day; always tuck sideways along the net. 4. Flip at 70–80 % fill; tuck for 10–14 days of stretch. 5. Around day 21 of flower, remove growth below the net that gets little light. 6. A second net 20–30 cm higher supports heavy colas. ## Numbers that matter | Item | Typical | |---|---| | Net height above pots | 20–40 cm (8–16 in) | | Net mesh | 5–10 cm (2–4 in) | | Plants per m² | 1–4 (1 per 0.25–1 m²) | | Veg time | 4–8 weeks depending on pot size and space | | Fill at flip | ~70–80 % | | Stretch | Many cultivars stretch 1.5–2.5× after flip (*Grower practice*) | ## Common mistakes - Flipping with a full net, then running out of space in stretch. - Tucking upward or twisting stems. - Leaving dense, dark growth under the net (larf and mould risk). - Too few plants for the space under a plant-count-free setup (longer veg = more power). ## Evidence The canopy-light rationale is *Supported* [1]; planting density strongly affects yield per area and uniformity [2][3]. SCROG technique and fill rules are *Grower practice*. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 3. Backer R, Schwinghamer T, Rosenbaum P, et al., 2019. Closing the yield gap for cannabis: a meta-analysis of factors determining cannabis yield. Frontiers in Plant Science 10:495. https://doi.org/10.3389/fpls.2019.00495 --- # SOG: sea of green > Sea of green packs many small plants, usually clones, into the space and flowers them after little or no veg, so each plant makes one main cola. Higher planting density increases yield per square metre but lowers cannabinoid uniformity between plants, according to controlled research. Typical densities are 9–25 plants per m² with 0–14 days of veg; check local plant-count rules first. - Canonical: https://genetixbay.com/knowledge/training/sog.html - Category: Training · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is sea of green?** Sea of green (SOG) is a cannabis growing method that packs many small plants, usually uniform rooted clones of one cultivar, close together and flowers them after little or no veg. Each plant makes one dominant cola, so the canopy fills with tops quickly and cycles run shorter. Plants usually sit in small 1-4 L containers, rockwool blocks or an ebb and flow table, with no topping. **How many plants per square metre for SOG?** A sea of green typically runs 9-25 cannabis plants per square metre, about 1-2.3 plants per square foot. Belgian yield trials used 12-20 plants per square metre. Higher density raises yield per area but lowers cannabinoid uniformity between plants, according to controlled research, and airflow at the base gets harder as plants crowd together. **How long to veg for SOG?** Veg a sea of green for 0-14 days under 18/6 before switching to 12/12, often flipping rooted clones almost straight away. Short veg is what keeps each plant to one main cola and shortens the cycle, giving more harvests per year. Vegging too long is a common mistake that recreates a crowded SCROG with uneven, shaded growth. **Is SOG legal where I live?** SOG may not be legal for home growers where you live, because it needs many plants, usually 9-25 per square metre, and plant-count limits in many jurisdictions make that illegal at home. Check your local plant-count rules before planning a sea of green. Even where it is legal, SOG needs a reliable clone supply, and one sick plant spreads disease quickly to its packed neighbours. **Does higher planting density increase yield?** Yes, higher planting density increases cannabis yield per square metre, according to controlled research on drug-type cannabis, and density is among the strongest yield drivers in a meta-analysis of the cannabis literature. The trade-off is lower cannabinoid uniformity between plants and canopy positions, plus harder airflow at the base and faster spread of disease between neighbouring plants. **Short answer.** Grow **many small plants** close together and flower them after **0–14 days of veg**, so each plant makes one dominant cola and the canopy fills with tops quickly. Higher density **raises yield per m²** but **reduces cannabinoid uniformity** between plants and positions, in controlled work on drug-type cannabis [1]; density is among the strongest yield drivers in the cannabis literature [2]. Typical SOG density is **9–25 plants/m² (about 1–2.3 per ft²)**; Belgian yield trials used 12–20 plants/m² [3][4]. **Plant-count limits** in many jurisdictions make SOG illegal for home growers; check your local rules. ## How to do it 1. Use uniform, rooted clones of one cultivar (seed plants vary too much in height and timing). 2. Small containers: 1–4 L (0.25–1 US gal), rockwool blocks, or an ebb & flow table ([ebb and flow](https://genetixbay.com/knowledge/systems/ebb-and-flow.md)). 3. Veg 0–14 days under 18/6, then 12/12. 4. Strip the lower third (lollipop) at or soon after the flip; these buds would be larf ([lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md)). 5. No topping; maybe light supercropping to level outliers. ## Numbers that matter | Item | Typical | |---|---| | Density | 9–25 plants/m² | | Veg | 0–14 days | | Container | 1–4 L | | Cycle time | Shorter by the veg weeks saved; more harvests per year | | PPFD | Full flowering intensity from day one ([PPFD](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md)) | ## Trade-offs - **Pros:** fast cycles, even canopy, less training labour, simple irrigation. - **Cons:** many plants (legal and clone-supply issues), uniformity drops with density [1], one sick plant spreads disease to its neighbours, airflow at the base is harder. ## Common mistakes - Mixed cultivars or seed plants (uneven stretch). - Too long a veg, recreating a crowded SCROG. - No airflow under the canopy. ## Evidence Density effects on yield per area and on uniformity are *Supported* [1][2][3]. SOG-specific densities and veg times are *Grower practice*. ## Sources 1. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 2. Backer R, Schwinghamer T, Rosenbaum P, et al., 2019. Closing the yield gap for cannabis: a meta-analysis of factors determining cannabis yield. Frontiers in Plant Science 10:495. https://doi.org/10.3389/fpls.2019.00495 3. Vanhove W, Van Damme P, Meert N, 2011. Factors determining yield and quality of illicit indoor cannabis (Cannabis spp.) production. Forensic Science International 212(1–3):158–163. https://doi.org/10.1016/j.forsciint.2011.06.006 4. BELSPO MARCANT project summary (plant densities 12–20 plants/m² in yield trials). https://www.belspo.be/Belspo/fedra/DR/DR92_MARCANT_summ_en.pdf --- # Topping: cutting the main tip for more colas > Topping removes the main growing tip above a node so the two shoots below take over, breaking apical dominance and producing a flatter plant with more main colas. Top healthy plants with 4–6 nodes, cut just above the chosen node, and allow 5–10 days of recovery before flipping to flower. In one controlled study, pruning twice (at transplant and at the switch to flower) gave the highest flower and cannabinoid yield per plant. - Canonical: https://genetixbay.com/knowledge/training/topping.html - Category: Training · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Veg · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **When should I top my cannabis plant?** Top a cannabis plant once it has 4-6 nodes, roughly 3-4 weeks from seed, and is healthy, well rooted and growing vigorously. Topping weak seedlings earlier stalls growth, and topping stressed, root-bound or sick plants is a common mistake. Do the last top at least 7-10 days before switching to 12/12, and avoid topping in flower, which costs yield time. **Where exactly do I cut when topping?** When topping, cut the main stem 3-5 mm (⅛-¼ in) above the chosen node, leaving both side shoots at that node intact. Use clean, sharp scissors wiped with 70% alcohol. Cutting below the node removes the very shoots you wanted to grow. Within about a week, two shoots at the cut node should be growing at equal speed. **Does topping increase yield?** Topping can increase cannabis yield, but the evidence is one controlled study. On large greenhouse plants of a CBD-dominant cultivar, pruning twice, at transplant and again at the switch to flower, was the only architecture treatment that raised flower yield per plant, with CBDA rising from 14.1 g to 22.5 g per plant. Small indoor plants and high-THC cultivars may respond differently. **Can I top autoflowers?** No. Don't top autoflowers; use low-stress training instead. An autoflower runs on a fixed clock from germination, so the recovery time topping demands, typically 3-7 days before visible regrowth, comes straight out of its growing time. The GenetixBay house position is that topping will never produce what proper LST does on an auto. This is grower practice rather than controlled research. **How many times can I top a plant?** You can top a cannabis plant repeatedly, topping each new main shoot again after it grows 2-3 new nodes, which doubles the tops each round: 2, then 4, then 8. Each round needs 3-7 days before visible regrowth, so every extra top adds veg time. Finish the last top at least 7-10 days before the flip, and combine topping with LST to spread tops apart. **Topping vs FIM: which is better?** Topping is the more predictable choice: cutting cleanly above a node reliably gives two co-dominant shoots. FIM, which pinches off most of the tip instead, can give three to five shoots but often gives only one or two. No controlled cannabis study has compared them. Either way, the gain comes from a flatter canopy with more tops in good light, so pair either one with LST. **Short answer.** Snip the main stem's growing tip just **above a node** once the plant has **4–6 nodes** and is growing vigorously. The two side shoots at that node become co-dominant, and lower branches catch up, giving a flatter canopy with more tops at similar height. Let the plant recover **5–10 days** before flipping to flower. In a controlled trial on large greenhouse plants, **pruning twice** (at transplant, leaving six main branches, and again at the switch to short days) was the only architecture treatment that increased flower yield per plant over the control; cannabinoid yield rose too (e.g. CBDA 22.5 g vs 14.1 g per plant) [1]. ## What's happening The apical tip makes auxin that flows down the stem and suppresses side buds (apical dominance). Remove the tip and the suppression lifts; the nearest buds grow out. An even canopy also matters because light falls off with depth, and yield follows light [3]; lower, shaded buds in cannabis have lower cannabinoid concentration [1]. ## How to do it 1. Plant healthy, well rooted, 4–6 nodes (or 3–4 weeks from seed). 2. Use clean, sharp scissors (wipe with 70 % alcohol). 3. Cut the main stem 3–5 mm (⅛–¼ in) above the chosen node, leaving both side shoots intact. 4. Optional: top again on each new main shoot after 2–3 new nodes (gives 4, 8, …). 5. Combine with [LST](https://genetixbay.com/knowledge/training/lst.md) to spread new tops apart. ## Numbers that matter | Item | Typical | Notes | |---|---|---| | First top | 4–6 nodes | Earlier tops on weak seedlings stall growth | | Recovery | 3–7 days before visible regrowth | | | Last top before flip | ≥ 7–10 days before 12/12 | Avoid topping in flower; costs yield time (*Grower practice*) | | Autoflowers | Don't top; use LST | Topping never produces what proper LST does on an auto, and it costs recovery time on a fixed clock (house position, *Grower practice*) | ## How to confirm it worked Within a week two (or more) shoots at the cut node are growing at equal speed; by flip the tops sit within ~10–15 cm (4–6 in) of each other. ## Common mistakes - Topping a stressed, root-bound or sick plant. - Cutting below the node (removes the side shoots you wanted). - Topping in flower. - Topping autoflowers. Use [LST](https://genetixbay.com/knowledge/training/lst.md) instead. - Topping, then leaving the canopy uneven with no LST. ## Evidence Apical dominance is *Established* plant physiology. Yield increase from double pruning is *Supported* by one controlled study on large (~2.5 m) greenhouse plants of a CBD-dominant medical cultivar [1]; small indoor plants and high-THC cultivars may respond differently. Topping vs not topping at commercial densities shows that density and architecture interact [2]. ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 2. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 3. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # Aphids on cannabis: species, life tables, population growth and IPM > Three aphids matter on cannabis: the cannabis-only cannabis aphid (Phorodon cannabis), the green peach aphid (Myzus persicae) and the cotton/melon aphid (Aphis gossypii). All breed without mating and give live birth, with intrinsic rates of increase of about 0.25-0.53 per day at 25 C, so a colony doubles every 1.3-2.8 days. Identify the species, then release the matching parasitoid early; keep sprays out of flower. - Canonical: https://genetixbay.com/knowledge/pests/aphids.html - Category: Pests · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How fast do aphids multiply on cannabis?** Aphids on cannabis multiply very fast because every adult is a female that gives live birth without mating. In lab life tables at 25 °C, the cannabis aphid had an intrinsic rate of increase of 0.355 per day on hemp, a doubling time of about 2 days, and the cotton aphid reached 0.526 per day on cucumber. Unchecked, 10 cannabis aphids become roughly 17,000 in three weeks. **Which aphids attack cannabis?** Three aphids do most of the damage on cannabis leaves and buds. The cannabis aphid (Phorodon cannabis) develops only on Cannabis and is the most common aphid on hemp in Colorado. The green peach aphid (Myzus persicae) and the cotton or melon aphid (Aphis gossypii) are generalists of greenhouses and indoor rooms. Root-feeding species such as rice root aphid live mostly below ground and need a different approach. **What temperature do aphids like best?** Aphid temperature optima differ by species. The cannabis aphid on hemp grew fastest at 25 °C (77 °F) and nearly stopped growing at 30 °C (86 °F), where its intrinsic rate of increase fell to 0.019 per day. The green peach aphid peaked near 25-27 °C, with an upper developmental threshold of about 37 °C. The cotton aphid keeps a high growth rate up to about 30 °C. **Which parasitic wasp should I use for aphids on cannabis?** Match the parasitoid to the aphid species. Aphidius colemani is the standard choice for the small green peach aphid and cotton or melon aphid, developing egg to adult in about 10 days at 25 °C. Aphidius ervi and Aphelinus abdominalis target larger foxglove and potato aphids. For the cannabis aphid, industry reports favour Aphidius matricariae, reports on A. colemani are mixed, and peer-reviewed trials are lacking. **Does Aphidoletes work under 12/12 light?** Aphidoletes aphidimyza, the aphid predatory midge, can enter diapause under short days, so under 12/12 cannabis flowering light it may fail to produce a second generation. Extension advice says larvae need at least 15.5 hours of light to avoid diapause. In one strain, temperatures of 25 °C or more prevented diapause at any day length. Night-break lighting is not an option: it disrupts cannabis flowering. **Why do aphids suddenly grow wings?** Aphids produce winged adults mainly when colonies get crowded, when the host plant declines in quality, and when natural enemies disturb them. Winged females fly or drift on air currents to new plants and start fresh colonies without mating. On outdoor hemp, large numbers of winged cannabis aphids appear in September, and shortening days may add to the trigger. Yellow sticky cards catch these winged dispersers. **Why are my cannabis leaves sticky and black?** Sticky, shiny cannabis leaves mean honeydew, the sugary excretion of phloem-feeding aphids, whiteflies or soft scales. Black, sooty patches on that honeydew are sooty mould fungi growing on the sugar. Look directly above the sticky leaves for aphid colonies on leaf undersides and stems, and for white cast skins. Honeydew in buds is a quality and mould problem, so infested buds are best removed. **How often should I spray aphids with soap?** Repeat contact sprays such as insecticidal soap on cannabis every 5-7 days, at least three times, in vegetative growth only. Soaps kill only aphids hit on the day of spraying. Survivors' newborn nymphs start reproducing in about 6-8 days at 25 °C (4-5 days for cotton aphid at 30 °C), so the next spray must land before then. Follow the label and local law. **Are aphids resistant to insecticides?** The green peach aphid is one of the most insecticide-resistant insects known, with documented resistance to many chemical classes including pyrethroids. Because aphids reproduce clonally, one resistant female produces a whole colony of identical resistant daughters within weeks. Rotate modes of action by IRAC group, use soaps, oils and biological control, and check that any product is legal on cannabis where you grow. **Do aphids lay eggs indoors?** Indoors under long days, the green peach aphid, cotton aphid and cannabis aphid reproduce by live birth, with no egg stage. Eggs appear only when sexual forms are produced. The cannabis aphid can produce males and egg-laying females indoors after the switch to short-day flowering light, according to Colorado State University. How long such eggs survive in warm rooms is unknown. **Short answer.** Aphids are soft, pear-shaped sap feeders with two tail pipes (cornicles), found in clusters on leaf undersides, stems and later in buds, with white cast skins and sticky [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md) below them. On cannabis the three that matter are the cannabis aphid (*Phorodon cannabis*), the green peach aphid (*Myzus persicae*) and the cotton/melon aphid (*Aphis gossypii*). Every adult is a female that gives live birth without mating, and at 25 °C (77 °F) colonies double every 1.3-2.8 days in lab life tables [7][8][10]. Identify the species, release the matching [parasitoid](https://genetixbay.com/knowledge/glossary/parasitoid.md) early, and keep sprays out of flower. ## Aphid numbers at a glance | Parameter | Cannabis aphid (*P. cannabis*) | Green peach aphid (*M. persicae*) | Cotton/melon aphid (*A. gossypii*) | |---|---|---|---| | Host range | Cannabis only [2][18] | Hundreds of hosts, 40+ families [23] | Very broad (cotton, cucurbits, many ornamentals) | | Lab host for data | Hemp cv. Henola [7] | Pepper [8] | Cucumber [10]; cotton [11][12] | | Birth to first reproduction, 25 °C | 6.4 days [7] | 8.3 days (pre-adult) [8] | about 5 days [12] | | Lower developmental threshold | No published value found (GenetixBay estimate 10-13 °C, see below) | 3.9 °C [8]; 6.5 °C [9] | 6.0 °C [10]; 6.2 °C [11]; 6.3 °C [12] | | Degree-days, birth to adult | No published value found | 174 DD [8] | 92.6 DD [10]; 108.9 DD [11] | | Optimum for population growth | 25 °C [7] | 25 °C [8]; 26.7 °C [9] | 22.5-30 °C [10]; 28.6 °C [12] | | Upper limit | r_m near zero at 30 °C [7] | Upper threshold 37.3 °C; lethal 38.5 °C [9] | Constant 35 °C lethal to nymphs [10][11] | | Lifetime fecundity | 111.6 nymphs/female at 25 °C [7] | R0 32.5 at 25 °C; 61.6 at 22 °C [8] | 82.1 nymphs/female at 25 °C [10] | | Peak daily fecundity | 7.5 nymphs/day at 25 °C [7] | No per-day value extracted | No per-day value extracted | | Intrinsic rate of increase r_m, 25 °C | 0.355 /day [7] | 0.250 /day [8]; 0.356 /day at optimum [9] | 0.526 /day [10] | | Doubling time (ln2 / r_m), 25 °C | 1.95 days | 2.77 days [8] | 1.32 days | | Sex ratio | All female while clonal; males only in autumn/short days [4] | All female while clonal | All female while clonal | The [intrinsic rate of increase](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md) r_m is the per-day exponential growth rate of an unchecked population; [doubling time](https://genetixbay.com/knowledge/glossary/doubling-time.md) is ln 2 divided by r_m. These are constant-temperature lab values on single host plants, not field measurements on cannabis, except the cannabis aphid data, which come from hemp [7]. ## Which aphids attack cannabis, and how do I tell them apart? Three aphids cause most above-ground damage on cannabis: the cannabis aphid, the green peach aphid and the cotton/melon aphid. Cranshaw and colleagues name the cannabis aphid one of the two most damaging sap-feeding pests of US hemp, alongside hemp russet mite [4]. Cotton/melon aphid has been recovered from greenhouse hemp in Virginia and is reported abundant in indoor cannabis production in the south-eastern United States [4]. **Cannabis aphid (*Phorodon cannabis*).** Pale yellow forms predominate, with light green less common; pale pink and light brown forms appear indoors after the switch to short-day light and outdoors late in the season [18]. It develops only on *Cannabis* [18]. Full ID, life history and control are in [Cannabis aphid](https://genetixbay.com/knowledge/pests/cannabis-aphid.md). **Green peach aphid (*Myzus persicae*).** A generalist on hundreds of host plants in more than 40 families, and a major virus vector worldwide [17][23]. Winged adults are about 1.8-2.1 mm, with a black head and thorax and a yellowish-green abdomen [23]. It is resistant to many insecticides, including pyrethroids [16][17]. **Cotton/melon aphid (*Aphis gossypii*).** A small generalist of greenhouse crops. It tolerates heat best of the three, keeping high growth rates up to 30 °C (86 °F) [10][11]. **Others.** Bean aphid (*Aphis fabae*) was found on hemp in one eastern Colorado field [4]. Rusty plum aphid (*Hysteroneura setariae*) was the only aphid recorded on cultivated cannabis in a 1989 Mississippi survey [4]. Larger species such as potato and foxglove aphid matter mainly because they need different parasitoids [5]. Rice root aphid, the commonest aphid in indoor marijuana production in Colorado, lives mostly on roots [4]; see [Root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md). **Why species ID matters.** The parasitoid you buy must match the aphid. A pale green, unstriped cannabis aphid can be mistaken for green peach aphid, leading growers to *Aphidius colemani*, which one trade article calls less effective on cannabis aphid than *A. matricariae* (trade press; Contested). Many extension labs identify slide-mounted samples. ## How do aphids damage cannabis? Aphids damage cannabis by sucking phloem sap, which at high, sustained numbers slows growth and causes wilting and yellowing [18]. Their stylets slip between cells to the phloem, so there is no stippling or scarring of the kind left by spider mites or thrips [18]. **Honeydew and sooty mould.** Aphids excrete surplus sugar as honeydew, which lands as small shiny droplets on leaves below the colony [18]. Sooty mould fungi grow black on honeydew, and ants tend aphids for it and fend off their natural enemies [1]. **Buds.** Cannabis aphid infests maturing flowers and nearby leaflets late in the season and into harvest in Colorado; large numbers of aphids and their eggs can end up in harvested flower, with abundant honeydew [4]. Yield effects are unknown [4]. **Viruses.** The cannabis aphid can transmit cucumber mosaic virus and alfalfa mosaic virus to hemp [2]. Colorado State notes that the main viruses described from Cannabis are mechanically transmitted, through wounds and cuttings, and cannot be spread by aphids [18]. See [Hop latent viroid and viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). ## How do I recognise aphids on cannabis? Recognise aphids on cannabis by clusters of soft-bodied insects on leaf undersides, along veins, stems and growing tips, with two cornicles at the rear. Supporting signs: - White cast skins on leaves below colonies, often mistaken for dandruff, mealybugs or mould [18]. - Small shiny honeydew droplets on leaf tops below colonies; later black sooty mould [1][18]. - Ants walking up stems [1]. - Winged aphids on yellow sticky cards [18]. - Swollen tan, bronze or golden "mummies": aphids killed by parasitoid wasps, a good sign [1][5]. Do not confuse with whiteflies (fly up when disturbed; see [Whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md)), mealybugs (waxy, white, slow), or thrips (slender, fast, silvery scars). ## What is the aphid life cycle in numbers? The aphid life cycle indoors is birth, four nymphal instars and a reproducing adult, with no egg and no pupa. At 25 °C (77 °F) a newborn cannabis aphid starts reproducing after 6.4 days on hemp [7], a green peach aphid becomes adult in 8.3 days on pepper [8], and a cotton aphid matures in about 5 days [12]. **Viviparous [parthenogenesis](https://genetixbay.com/knowledge/glossary/parthenogenesis.md).** Under long days, the colony is all female, and each female gives birth to live, genetically identical daughters without mating [1][18]. UC IPM gives up to 12 nymphs a day and up to 80 offspring a week per adult in warm weather [1]. **Telescoping generations.** A newborn aphid already carries developing embryos of her own daughters, so the next generation is under way before the current one is born. This is why generation time is so short. ### Development and reproduction by temperature | Temp | Cannabis aphid on hemp: pre-reproductive (d) / fecundity / r_m [7] | Green peach aphid on pepper: pre-adult (d) / R0 / r_m [8] | Cotton aphid: immature development / r_m | |---|---|---|---| | 15 °C (59 °F) | No data | No data (18 °C: 12.4 d / 52.3 / 0.189) | 10.8 d, r_m 0.208 on cucumber [10]; 12.0 d, r_m 0.177 on cotton [11] | | 20 °C (68 °F) | 11.0 / 54.5 / 0.153 | 22 °C: 9.6 / 61.6 / 0.233 | First progeny at 8 d on cotton [12] | | 25 °C (77 °F) | 6.4 / 111.6 / 0.355 | 8.3 / 32.5 / 0.250 | First progeny at 5 d [12]; r_m 0.526 on cucumber [10] | | 28 °C (82 °F) | 6.0 / 27.8 / 0.244 | 8.1 / 16.6 / 0.214 | Optimum 28.6 °C on cotton [12] | | 30 °C (86 °F) | 5.4 / 2.4 / 0.019 | 8.5 / 3.4 / 0.108 | 4.1-4.5 d [10][11]; r_m 0.413 on cotton [11] | | 32-35 °C | No data | 32 °C: 13.0 / 0.22 / -0.097 | 32.5 °C: r_m 0.132 [10]; 35 °C lethal to nymphs [10][11] | For the cannabis aphid, "fecundity" is mean nymphs per female; for green peach aphid, R0 is the [net reproductive rate](https://genetixbay.com/knowledge/glossary/net-reproductive-rate.md) (daughters per female, survival included). Conditions: cannabis aphid at 65 ± 5% RH, 16L:8D [7]; green peach aphid at 60 ± 5% RH, 16L:8D [8]. **Longevity.** Cannabis aphid adults lived 24.6 days in total at 25 °C and 15.1 days at 30 °C, with 15.2 reproductive days at 25 °C [7]. Green peach aphid adults on pepper lived about 21 days at 25 °C and about 31 days at 22 °C (read from the published table [8]). **Nymph survival.** For the cannabis aphid, 98% of nymphs reached maturity at 20 °C, 71% at 25 °C, 61% at 28 °C and 43% at 30 °C [7]. **[Degree-days](https://genetixbay.com/knowledge/glossary/degree-day.md).** Green peach aphid needs 174 degree-days above 3.9 °C from birth to adult on pepper [8]. Cotton aphid needs 92.6 DD above 6.0 °C on cucumber [10] or 108.9 DD above 6.2 °C on cotton [11]. For the cannabis aphid, no published threshold was found; a linear fit of the 20, 25 and 28 °C pre-reproductive times in [7] gives roughly 10 °C and 100 DD (two-point fit 20-25 °C: 13 °C and 77 DD). That is a GenetixBay calculation from three points, not a published value. ## What triggers winged aphids, and what are holocyclic and anholocyclic cycles? Winged aphids are triggered mainly by crowding, poor host-plant nutrition and disturbance by natural enemies or other insects, as reviewed by Müller, Williams and Hardie [15]. Most adults in a colony are wingless; winged forms appear when populations are high or food quality declines [1]. **Short days.** Large numbers of winged cannabis aphids appear on outdoor hemp in September, and Colorado State suggests shortening day length may raise the proportion of winged forms [18]. **Holocyclic.** A holocyclic aphid has a sexual generation once a year: males and egg-laying females (oviparae) mate and lay overwintering eggs. Green peach aphid overwinters as eggs on *Prunus* (peach and relatives) in the northern United States [17]. Cannabis aphid is holocyclic on the crop itself outdoors, with winged males and wingless oviparae from early September [4]. **Anholocyclic.** An anholocyclic population skips the sexual phase and stays clonal all year. Green peach aphid in the south-eastern United States lays no eggs and reproduces by live birth year-round, with up to 30 generations a year [17]. Under indoor long days all three species stay clonal; the cannabis aphid can sustain asexual reproduction year-round under adequate lighting [4]. **Grow-room consequence.** The switch to 12/12 is a short-day signal. Cannabis aphid can produce sexual forms and eggs indoors after the flip [18]. Green peach aphid and cotton aphid have no such reported response on cannabis (no published data found). ## Why do temperature and humidity matter for aphids? Temperature controls aphid generation time and growth rate; humidity matters mostly through the natural enemies. Between about 18 and 25 °C, warmer rooms raise r_m for all three species [7][8][10]. Above 25 °C the species split: the cannabis aphid collapses by 30 °C (86 °F), green peach aphid declines from 28 °C, and cotton aphid keeps growing fast to about 30 °C [7][8][11]. **Heat tolerance differs.** At 30 °C the cannabis aphid's r_m fell to 0.019 per day and fecundity to 2.4 nymphs per female [7]. Cotton aphid on cotton still reached its highest r_m, 0.413 per day, at 30 °C [11]. A hot room that suppresses cannabis aphid can favour cotton aphid. **Fluctuating temperatures.** Green peach aphid survived daily excursions above its calculated lethal temperature of 38.5 °C for an hour per day, and a constant-temperature model failed to predict development under fluctuating temperatures (R² 0.01) [9]. Lab optima are guides, not set-points. **Grow-room set-points.** Typical veg rooms run 24-28 °C (75-82 °F) at 60-70% RH; flower 22-26 °C (72-79 °F) at 45-55% RH; late flower 40-50% RH. Every one of those temperatures is inside the fast-growth window for all three aphids. **Humidity.** No published direct effect of RH on cannabis aphid development was found. Humidity matters for control: entomopathogenic fungi need relatively high humidity to work [18], parasitoids perform best at about 70-85% RH [5], and Aphidoletes at 50-85% RH [5]. See [VPD](https://genetixbay.com/knowledge/glossary/vpd.md). **Diapause in the predator.** Short days do not stop aphids indoors, but they can put the predatory midge Aphidoletes aphidimyza into [diapause](https://genetixbay.com/knowledge/glossary/diapause.md) (see biological control below) [5][14]. ## How fast can an aphid population grow? A worked example An unchecked aphid colony grows as N(t) = N0 × e^(r_m × t). Starting from 10 cannabis aphids at 25 °C (r_m 0.355 per day [7]), that is about 120 after one week, 1,440 after two and 17,300 after three. At 20 °C (r_m 0.153) the same 10 aphids reach about 250 after three weeks. **Method.** Take N0 = 10, the r_m from the life table, t in days. Example: 10 × e^(0.355 × 21) = 10 × 1,728 ≈ 17,300. | Species, temperature (r_m /day) | Doubling time | Day 7 | Day 14 | Day 21 | Day 28 | |---|---|---|---|---|---| | Cannabis aphid, 20 °C (0.153) [7] | 4.5 d | 29 | 85 | 249 | 725 | | Cannabis aphid, 25 °C (0.355) [7] | 2.0 d | 120 | 1,440 | 17,285 | 207,437 | | Cannabis aphid, 28 °C (0.244) [7] | 2.8 d | 55 | 304 | 1,680 | 9,270 | | Cannabis aphid, 30 °C (0.019) [7] | 36.5 d | 11 | 13 | 15 | 17 | | Green peach aphid, 22 °C (0.233) [8] | 3.0 d | 51 | 261 | 1,334 | 6,813 | | Green peach aphid, 25 °C (0.250) [8] | 2.8 d | 58 | 331 | 1,906 | 10,966 | | Cotton aphid, 25 °C, cucumber (0.526) [10] | 1.3 d | 397 | 15,781 | 626,927 | 24.9 million | | Cotton aphid, 30 °C, cotton (0.413) [11] | 1.7 d | 180 | 3,244 | 58,430 | 1.05 million | **Read this as an upper bound.** These numbers assume no predators, no disease, unlimited food and no winged emigration. Real colonies crowd, grow wings and leave, and plants decline. The point stands: two weeks of not looking at 25 °C is the difference between ten aphids and over a thousand. ## Where do aphids hide, how do they spread, and how do they get in? Aphids get into indoor cannabis mainly on infested plant material: clones, mother plants and transplants. Colorado State notes that once a facility is cleared, the only likely route back for cannabis aphid is introduced Cannabis material carrying live aphids [18]. **Hiding places.** Leaf undersides along the midrib, growing tips, stems and leaf axils; later inside buds [4][18]. **Winged dispersal.** Winged aphids are weak fliers and largely carried by air currents faster than about 3 mph (about 1.3 m/s) [18]. Airflow direction steers where they settle in a greenhouse: they collect where air flows towards and avoid strong headwinds [18]. See [aerial dispersal](https://genetixbay.com/knowledge/glossary/aerial-dispersal.md). **Outdoors and intake air.** Generalist aphids migrate from weeds, vegetables and ornamentals; green peach aphid also from *Prunus* in spring [17]. Unscreened intakes and open greenhouse vents let winged aphids in. **People and pets.** Aphids walk slowly and starve within a few days without a host plant [18]. Clothing can carry them from an infested room or garden to a clean one (Grower practice: clean room first, dirty room last). **Ants.** Ants move and guard aphid colonies outdoors and in greenhouses [1]. **[Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md).** Keep new plant material isolated for several weeks and inspect for honeydew, cast skins, live aphids and winged aphids on cards before it joins the main room [18]. ## How do I scout for aphids? Scout for aphids on cannabis at least twice a week during rapid growth, as UC IPM advises for aphid-prone plants [1]. Turn leaves over and check stems and growing tips, using a 10x lens. Look first for honeydew droplets and cast skins, then trace them upward to the colony [18]. **Where to look.** Leaf undersides of upper and middle canopy, new growth, stems, and plants near intake air and doors. Flag every infested plant. **Lens power.** 10-20x confirms an aphid and spots mummies. Separating cannabis aphid from hop aphid needs a microscope (about 40-60x) to see the head and antennal tubercles [2]. **[Sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md).** Yellow sticky cards catch winged aphids and show when they disperse; telling winged aphids from fungus gnats and small parasitoid wasps takes magnification and practice [18]. Hang them near, but not touching, plants [22]. No cannabis-specific card density was found; 1 card per 10-20 m² (about 100-200 ft²), changed weekly, is common greenhouse grower practice. **[Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md).** No action threshold has been researched for aphids on hemp or cannabis [2]. Grower practice indoors: act on the first confirmed colony, because the growth table above leaves no room to wait. **Record keeping.** Count aphids and mummies on a fixed set of flagged leaves each visit. Rising mummies and falling live aphids mean biocontrol is working. ## How do I control aphids by life stage? Control aphids indoors by targeting nymphs and adults, which are the only stages present while colonies are clonal. There is no egg or pupa to shelter survivors, so contact tactics work, provided they are repeated before newborn survivors start breeding [1][7]. **Nymphs and adults.** Squash or wipe early colonies; prune heavily infested leaves into a bag. A strong water spray dislodges aphids in veg (Grower practice). Insecticidal soaps (potassium salts of fatty acids) and horticultural oils kill by smothering and only kill aphids present on the day of spraying; coverage of leaf undersides is essential [1]. **Re-application interval.** Spray again before nymphs born just after a spray can reproduce. From the life tables, that is about 6 days for cannabis aphid at 25 °C [7], 8 days for green peach aphid at 25 °C [8], and 4-5 days for cotton aphid at 25-30 °C [10][11][12]. At 20 °C cannabis aphid takes 11 days [7]. Practical rule: every 5-7 days, at least three applications, in veg only. **Eggs.** Eggs exist only after sexual reproduction, outdoors in autumn or, for cannabis aphid, indoors after short days [4][18]. No published data were found on how contact sprays affect cannabis aphid eggs. Removing plant debris after harvest removes laid eggs [18]. **Mummies.** Parasitised mummies contain developing wasps. Leave them on the plant. **[Pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md).** Green peach aphid has evolved resistance to many insecticide classes, including pyrethroids [16][17]. Clonal reproduction multiplies a resistant genotype into a uniform colony within weeks. Rotate [modes of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md) by IRAC group, never repeat one group across consecutive aphid generations, and lean on soaps, oils and biological control. Registrations on cannabis vary by jurisdiction; many places permit none. Follow the label and local law. **Botanicals and fungi.** Azadirachtin (neem-derived) is reported to control aphids on hemp, with efficacy still under study [2]. Entomopathogenic fungi such as *Beauveria bassiana* and *Isaria fumosorosea* infect aphids and need relatively high humidity [18]. See [entomopathogenic fungi](https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.md). ## How does biological control of aphids work in depth? Biological control of aphids on cannabis works best when the parasitoid or predator matches the aphid species and is released early, at the first colony or before it. Aphidius colemani for green peach and cotton aphid is the standard first choice [5][6]. ### Parasitoid and predator matching | Aphid | First-choice parasitoid | Other enemies | Notes | |---|---|---|---| | Green peach aphid | *Aphidius colemani* [5] | *A. matricariae* [5]; Aphidoletes; lacewings | A. colemani egg-to-adult 9.8 d at 25 °C on this host [13] | | Cotton/melon aphid | *Aphidius colemani* [5] | Aphidoletes; lacewings; lady beetles | A. colemani egg-to-adult 10.0 d at 25 °C on this host [13] | | Cannabis aphid | No proven commercial parasitoid; industry reports favour *A. matricariae*, with mixed reports on *A. colemani* [22] | Lady beetles, lacewings, syrphids, Aphidoletes (field) [4] | See [Cannabis aphid](https://genetixbay.com/knowledge/pests/cannabis-aphid.md) | | Potato aphid, foxglove aphid | *Aphidius ervi*, *Aphelinus abdominalis* [5] | Aphidoletes | A. colemani is not effective on these [5][6] | ### Aphidius colemani *Aphidius colemani* is a 2-3 mm braconid wasp that lays an egg inside an aphid; the larva kills it, and the aphid becomes a bronze mummy [20]. Egg to adult takes about 10 days at 25 °C [13], with a lower developmental threshold near 2.7-3.0 °C [13]. Parasitism peaked at 25 °C and declined at 30 °C [13]; extension notes it is less effective above 30 °C (86 °F) [5]. **Climate window.** Active from 15 °C; optimum 18-25 °C (64-77 °F) at 60-80% RH (biocontrol supplier technical sheet [20]). UConn gives 18-25 °C (65-77 °F) and 70-85% RH for aphid parasitoids generally [5]. **Release rates.** Biocontrol supplier technical sheets give 0.15-0.25 wasps/m² per release every 1-2 weeks preventively, and 0.5-2 wasps/m² weekly for at least three releases after aphids are found [20]. Mummies should appear 10-14 days after the first release, and control is typically achieved once parasitism reaches about 80% [20]. **[Banker plants](https://genetixbay.com/knowledge/glossary/banker-plant.md).** Wheat or barley carrying bird cherry-oat aphid (*Rhopalosiphum padi*), a cereal aphid, keeps A. colemani breeding before cannabis is attacked [6]. Suppliers suggest 1-10 banker plants per 10,000 ft² (about 930 m²); start them up to 6 weeks before production, transfer aphids to fresh pots every 2 weeks, and replace declining plants [6]. *R. padi* is too small to support *A. ervi*, so this system serves A. colemani only [6]. ### Aphidius ervi and Aphelinus abdominalis *Aphidius ervi* is about twice the size of A. colemani and, with the aphelinid *Aphelinus abdominalis*, targets large aphids such as foxglove and potato aphid [5]. No published cannabis trials were found for either on cannabis pests. ### Aphidoletes aphidimyza, the predatory midge *Aphidoletes aphidimyza* larvae eat more than 60 aphid species, with an optimum of 16-27 °C (60-80 °F) and 50-85% RH [5]. Larvae drop to moist substrate to pupate [5]. It was observed feeding on cannabis aphid in Colorado hemp fields [4]. One supplier's cannabis program lists 1 midge/m² weekly from first detection [21]. **Short-day diapause.** UConn states larvae need at least 15.5 hours of light to avoid diapause, with no second generation in short days [5]. In a Chinese strain, diapause occurred mainly at 15-20 °C under 8-14 h of light, reached 88.7% at 15 °C, and was 0% at 25 and 30 °C under every photoperiod [14]. A Japanese strain had a critical day length of 12.7 h at 20 °C [14]. **Cannabis consequence.** Under 12/12, expect the midge to work as a single release generation unless the room runs at 25 °C or more (strain-dependent; Contested). Night-break lighting, the greenhouse trick for keeping Aphidoletes active, interrupts the long night that cannabis needs to flower. Do not use it in a flowering room. See [Light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md). ### Lacewings and lady beetles Green lacewing larvae (*Chrysoperla*, *Chrysopa* spp.) reduce aphids in about 2 weeks and leave greenhouses above 35 °C (95 °F) [5]. Lady beetle larvae may eat 500-1,000 aphids each [5]. Field-collected convergent lady beetles (*Hippodamia convergens*) often arrive semi-dormant and may take a few weeks to lay eggs [18]. **[Predator:prey ratios](https://genetixbay.com/knowledge/glossary/predator-prey-ratio.md).** No published predator:prey or parasitoid:aphid release ratio for cannabis was found. Use supplier per-m² rates and the 80% parasitism target as the working benchmark [20]. **Spray compatibility.** Soaps and oils kill exposed adult wasps and predator larvae on contact but leave little residue [1]. Spray, let it dry, then release (Grower practice). Check residue history before releases [20]. ## How can the room environment be used against aphids? The room environment slows aphids only modestly, because every common indoor set-point is inside their growth window. The useful levers are favouring the parasitoids, steering winged aphids with airflow, and starving the colony of soft growth and ants. **Temperature.** At 20 °C (68 °F) cannabis aphid r_m is 0.153 per day versus 0.355 at 25 °C [7]: doubling time stretches from 2 to 4.5 days. Running mother rooms and clone areas at 20-22 °C buys time for scouting. **Do not run hot to fight aphids.** Cannabis aphid collapses at 30 °C in the lab [7], but cotton aphid is near its optimum there [11], A. colemani loses effectiveness above 30 °C [5], and the plant suffers. See [Heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md). **Humidity for beneficials.** Parasitoids prefer 60-85% RH [5][20]. That fits veg (60-70% RH) and mother rooms. In flower, 45-55% RH is a compromise against [botrytis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) and [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md); do not raise flower humidity to help beneficials. **Airflow.** Winged aphids ride air currents above about 3 mph (1.3 m/s) [18]. Positive pressure and filtered intakes keep them out; strong headwinds keep them off clean zones. **Nitrogen.** Soft, high-N growth is a better aphid host (Grower practice; USU advises avoiding excess nitrogen [3]). Poor host quality triggers winged forms [15], so a declining plant sends aphids to its neighbours. ## What should I not do about aphids in flower? In flower, do not spray soaps, oils or botanicals onto buds. Residues stay on harvested flower, and wet buds invite bud rot. Rely on beneficials released before or at the flip, removal of infested branches, and early harvest of badly infested plants. **No systemics.** Systemic insecticides are not registered on cannabis in most places and persist into flower. Follow the label and local law. **No night-break lights.** Lighting to keep Aphidoletes out of diapause breaks the 12-hour night and risks reverting or [hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) flowers. **No humidity raises.** Raising RH for fungi or parasitoids in late flower trades an aphid problem for a bud-rot problem. **Cut out honeydew-coated buds.** Honeydew and sooty mould in buds lower quality and feed mould [4]. Bag and remove those sections. **Watch for eggs after the flip.** Cannabis aphid can produce sexual forms and eggs under short days [18]. Clean all debris after harvest [18]. ## What are the common myths about aphids on cannabis? The common aphid myths concern lady beetles, wasp choice, eggs, heat and viruses. Evidence labels follow the GenetixBay ladder. - **"Garden-centre ladybugs will clean up indoor aphids."** *Myth* for indoor rooms. Field-collected convergent lady beetles arrive semi-dormant and may take weeks to lay eggs; larvae do most of the eating [5][18]. - **"Any Aphidius kills any aphid."** *Myth.* A. colemani is not effective on large foxglove and potato aphids [5][6]; cannabis aphid lacks a proven commercial match [4][19]. - **"Aphids lay eggs that hatch after you spray."** *Myth* indoors under long days: the colonies are clonal and viviparous [1][18]. Eggs appear only with sexual forms [4][18]. - **"Run the room hot to kill aphids."** *Contested.* Cannabis aphid collapses at 30 °C [7], but cotton aphid thrives there [11] and the plant and parasitoids suffer [5]. - **"Aphids spread hop latent viroid."** *Myth.* The main Cannabis viruses described are mechanically transmitted [18]; cannabis aphid carries cucumber mosaic and alfalfa mosaic virus [2]. ## Common mistakes - Buying a parasitoid before identifying the aphid. - Waiting for "a few more" aphids: at 25 °C a colony doubles in 2-3 days. - Ignoring ants, which guard aphids from beneficials [1]. - Spraying soap once and stopping; one spray only kills what it touches [1]. - Releasing Aphidoletes into a cool 12/12 room and expecting a second generation [5][14]. - Bringing in clones without quarantine [18]. - Using broad-spectrum sprays that kill established parasitoids and cause a rebound. ## Evidence - Viviparous parthenogenesis, honeydew, winged dispersal: *Established* [1][15][18]. - Cannabis aphid life table on hemp: *Supported*, one lab study at four constant temperatures, 65% RH, 16L:8D [7]. - Green peach and cotton aphid life tables: *Established* across several studies; values vary with host plant and clone [8][9][10][11][12]. - Aphidius colemani for green peach and cotton aphid: *Established* in greenhouse crops [5][13]; cannabis-specific trials sparse. - Biocontrol of cannabis aphid by specific parasitoids: *Grower practice* and trade reports [22]; peer-reviewed data minimal [4][19]. - Aphidoletes short-day diapause: *Established*; thresholds strain-dependent [5][14]. - Action thresholds on cannabis: none researched [2]. ## Sources 1. Flint ML. 2013. Pest Notes: Aphids. UC ANR Publication 7404. UC Statewide IPM Program. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html 2. Pulkoski M, Burrack H. 2020. Cannabis Aphid in Industrial Hemp. NC State Extension. https://content.ces.ncsu.edu/cannabis-aphid-in-industrial-hemp 3. Utah State University Extension. Cannabis Aphids (hemp IPM note). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-cannabis-aphid.php 4. Cranshaw W, Schreiner M, Britt K, Kuhar TP, McPartland J, Grant J. 2019. Developing insect pest management systems for hemp in the United States: a work in progress. Journal of Integrated Pest Management 10(1):26. https://doi.org/10.1093/jipm/pmz023 5. UConn IPM. Biological Control of Aphids. University of Connecticut Extension. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-aphids/ 6. UConn IPM. Aphid Banker Plants. University of Connecticut Extension. https://ipm-cahnr.media.uconn.edu/wp-content/uploads/sites/3216/2024/08/aphidbankerplants.pdf 7. Durak R, Jedryczka M, Czajka B, Dampc J, Wielgusz K, Borowiak-Sobkowiak B. 2021. Mild abiotic stress affects development and stimulates hormesis of hemp aphid Phorodon cannabis. Insects 12(5):420. https://doi.org/10.3390/insects12050420 8. Bas FH, Ozgokce MS. 2026. Life table and development parameters of green peach aphid Myzus persicae at six different temperatures on pepper (Capsicum annuum L.). Plant Protection Science 62(3):252-267. https://doi.org/10.17221/96/2025-PPS 9. Davis JA, Radcliffe EB, Ragsdale DW. 2006. Effects of high and fluctuating temperatures on Myzus persicae (Hemiptera: Aphididae). Environmental Entomology 35(6):1461-1468. https://doi.org/10.1603/0046-225X(2006)35[1461:EOHAFT]2.0.CO;2 10. Satar S, Kersting U, Uygun N. 2005. Effect of temperature on development and fecundity of Aphis gossypii Glover (Homoptera: Aphididae) on cucumber. Journal of Pest Science 78(3):133-137. https://doi.org/10.1007/s10340-005-0082-9 11. Kersting U, Satar S, Uygun N. 1999. Effect of temperature on development rate and fecundity of apterous Aphis gossypii Glover reared on Gossypium hirsutum L. Journal of Applied Entomology 123(1):23-27. https://doi.org/10.1046/j.1439-0418.1999.00309.x 12. Parajulee MN. 2007. Influence of constant temperatures on life history parameters of the cotton aphid, Aphis gossypii, infesting cotton. Environmental Entomology 36(4):666-672. https://academic.oup.com/ee/article/36/4/666/462257 13. Zamani AA, Talebi A, Fathipour Y, Baniameri V. 2007. Effect of temperature on life history of Aphidius colemani and Aphidius matricariae, two parasitoids of Aphis gossypii and Myzus persicae. Environmental Entomology 36(2):263-271. https://doi.org/10.1603/0046-225X-36.2.263 14. Dai X, Wang Y, Liu Y, et al. 2024. Molecular correlates of diapause in Aphidoletes aphidimyza. Insects 15(5):299. https://doi.org/10.3390/insects15050299 15. Muller CB, Williams IS, Hardie J. 2001. The role of nutrition, crowding and interspecific interactions in the development of winged aphids. Ecological Entomology 26:330-340. https://doi.org/10.1046/j.1365-2311.2001.00321.x 16. Bass C, Puinean AM, Zimmer CT, et al. 2014. The evolution of insecticide resistance in the peach potato aphid, Myzus persicae. Insect Biochemistry and Molecular Biology 51:41-51. https://doi.org/10.1016/j.ibmb.2014.05.003 17. Baker J. 2013 (rev. 2023). Green Peach Aphid. NC State Extension. https://content.ces.ncsu.edu/green-peach-aphid 18. Colorado State University. 2018. Pest Management of Hemp in Enclosed Production: Cannabis Aphid (Phorodon cannabis). https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Cannabis%20Aphid%20Management_.pdf 19. Ong M, Su C, Yaqub S, Feng A, Buirs L, Gries G. 2025. Rice root aphids, Rhopalosiphum rufiabdominale, and cannabis aphids, Phorodon cannabis, are parasitised by Aphelinus varipes. The Canadian Entomologist 157:e39. https://doi.org/10.4039/tce.2025.10024 20. Biocontrol supplier technical sheet: Aphidius colemani (2022). Release rates, development time and climate range. 21. Biocontrol supplier cannabis biological-control program sheet (2020). Aphidoletes aphidimyza release rate for cannabis aphid. 22. Reeves A. 2022. Cannabis aphids on the rise. Greenhouse Canada, 18 November 2022. https://www.greenhousecanada.com/cannabis-aphids-on-the-rise/ 23. Capinera JL. Green peach aphid, Myzus persicae (Sulzer). Featured Creatures EENY-222, University of Florida IFAS Extension (rev. 2023). https://journals.flvc.org/edis/article/view/111002 --- # Broad mites on cannabis: life table, spread and control (plus russet mite summary) > Broad mites (Polyphagotarsonemus latus) twist, glaze and harden cannabis new growth. At 25 C a generation takes about 4.4 days from egg to adult and populations can double in about 2.2 days (grape-leaf lab data), so control rests on clean stock, quarantine, preventive predatory mites (Amblyseius swirskii, Neoseiulus cucumeris, N. californicus) and repeat treatments timed to the life cycle. Hemp russet mite has its own article. - Canonical: https://genetixbay.com/knowledge/pests/broad-russet-mites.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my new cannabis leaves twisted and shiny but my feed is fine?** Twisted, glossy, stunted new cannabis leaves with normal feed and pH usually point to broad mites (Polyphagotarsonemus latus). Their toxic saliva hardens and distorts the youngest leaves, and the damage keeps showing after the mites are gone. Adult females are about 0.2 mm long, so check shoot tips at 20x or more, ideally 40 to 60x, for pale mites and eggs studded with white tufts. **How fast do broad mites breed?** Broad mites breed extremely fast in warm rooms. On grape leaf discs at 65% RH, egg-to-adult took 7.3 days at 18 C, 4.4 days at 25 C and 3.3 days at 28 C. The intrinsic rate of increase peaked at 0.31 per day at 25 C, a doubling time of about 2.2 days, and fell to 0.12 per day at 32 C. No cannabis-specific life table has been published. **Broad mites or calcium deficiency?** Broad mite damage and calcium deficiency both twist and distort new cannabis growth, so check the root zone first: input and runoff pH, EC and root health. If those are fine, inspect the newest leaves at 40 to 60x. Pale oval mites, and eggs about 0.08 mm long covered in rows of white tufts, confirm broad mites. Chasing a deficiency with ever more Cal-Mag is a common mistake. **How do broad mites spread between cannabis plants?** Broad mites spread on infested clones, on workers' hands and clothing, by plant-to-plant contact and on air currents. They also hitch rides on whitefly adults and some aphids, a habit called phoresy. Within a plant, males carry quiescent female nymphs to fresh shoot tips, which drives much of the local spread. Quarantine incoming cuttings and work clean rooms before infested ones. **When should I repeat a broad mite spray?** Repeat a contact broad mite treatment after surviving eggs have hatched but before the new females start laying. At 25 C, eggs hatch in about 2.3 days and females lay from about 4.7 days after the egg was laid, so a 3 to 4 day interval fits. At 18 C, eggs take about 3.9 days and egg-to-first-egg about 9 days, so 4 to 7 days. Follow the label and local law. **Which predatory mites control broad mites?** Amblyseius swirskii, Neoseiulus cucumeris and Neoseiulus californicus are the predatory mites used against broad mites in greenhouses, released preventively before damage shows. In sweet pepper trials, A. swirskii suppressed broad mites, eating up to about 18 per day in the lab. Its eggs need humidity: half fail to hatch at about 63% RH. Amblyseius andersoni is also used, with less broad-mite data behind it. **Does hot water kill broad mites on cuttings?** Hot water kills broad mites on plant material in other crops: University of Florida guidance gives immersion at 43 to 49 C (109 to 120 F) for 15 minutes. No validated protocol exists for cannabis cuttings, and those temperatures may injure soft cannabis tissue. A Colorado trial on hemp cuttings at 41 to 43 C for 10 to 15 minutes reduced russet mites without killing them all. Test on a few cuttings first. **What is the difference between broad mite and cyclamen mite?** Broad mite (Polyphagotarsonemus latus) and cyclamen mite (Phytonemus pallidus) are both tarsonemid mites that distort buds and new leaves. Broad mite favours warm, humid rooms and lays eggs covered in white tufts; cyclamen mite favours cool, humid conditions and lays smooth pale eggs. Broad mite is the one documented on cannabis; cyclamen mite is rarely reported there. Both need 20x or more to see. **Can broad mites be controlled in flower?** Broad mites are hard to control in cannabis flower because oils, soaps and sulfur must not go on buds and most miticides are not registered for cannabis. The mites also sit inside buds and distorted tips where contact sprays miss. Rely on predatory mites released in veg, remove badly infested plants, consider an early harvest and never take clones from infested plants. Follow the label and local law. **What are russet mites and are they the same as broad mites?** Hemp russet mites (Aculops cannabicola) are not broad mites. They are eriophyid mites with only two pairs of legs, feed only on Cannabis, and bronze leaves and curl edges upward from the lower canopy, while broad mites twist new growth at the top. Russet mites need about 55x to count reliably. See the dedicated hemp russet mite article for life table and control. **Short answer.** If new growth is twisted, glossy, stiff and stalled while pH and feed check out, put a 40-60x scope on the shoot tips before you touch the nutrients. Broad mites (*Polyphagotarsonemus latus*) are about 0.2 mm long, finish a generation in about 4.4 days at 25 °C (77 °F) and can double their numbers every 2.2 days in the lab [1]. They arrive on clones, hands and whitefly adults. Prevention, early predatory mites and repeat treatments timed to the life cycle are the whole game. Hemp russet mite is a different animal; it has [its own article](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md) and a summary below. ## What is a broad mite and what does it do to cannabis? A broad mite is *Polyphagotarsonemus latus*, a tarsonemid ("thread-footed") mite that feeds on the youngest leaves, shoot tips and buds of hundreds of crops [2][7]. It injects a toxic saliva as it feeds, and the plant responds with twisted, hardened, distorted growth out of all proportion to the number of mites [3]. Terminal buds can die. The damage persists long after the mites are gone [3][4]. That is why "it still looks bad" tells you nothing about whether a treatment worked; judge only new growth. Gerson's review found no evidence that broad mites transmit plant viruses [4]. The harm is the toxin and the feeding, not a disease. ## How do you recognise broad mite damage on cannabis? Broad mite damage on cannabis shows first at the top: newest leaves narrow, cup, twist and turn glossy or glassy, leaf edges pucker downward, and internodes shorten so tips look bunched [3][2]. Lower leaf surfaces may bronze. Damage often appears suddenly and is spotty across a room, because populations start on one plant or one clone line [3]. | Sign | What you see | Source | |---|---|---| | Where first | Newest growth, shoot tips, flower buds | [2][3] | | Leaf shape | Narrow, twisted, cupped; edges pucker downward; thick and brittle | [3] | | Colour | Glossy then bronze on lower surface; leaves may turn coppery or purplish | [2][3] | | Growth habit | Shortened internodes, extra lateral buds breaking, stalled tips | [2] | | Mites | Females ~0.2 mm, oval, pale amber to green with a faint pale stripe; males ~0.11 mm, faster | [2] | | Eggs | ~0.08 mm, clear, elliptical, with 29-37 white tufts in rows ("rows of diamonds") | [2][3] | | Magnification | Hard to see below 10x; 20x workable with practice; microscope preferred | [2][3][7] | **Differentials.** Broad mite injury mimics calcium or boron deficiency, herbicide drift (2,4-D, glyphosate), cold injury and physiological disorders [3][7]. On cannabis add heat or light stress at the tips, genetic leaf mutations on a single cut, and viroid or virus infection: see [kb-diseases-hop-latent-viroid-and-viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). ## How is broad mite different from cyclamen mite and russet mite? Broad mite and cyclamen mite (*Phytonemus pallidus*) are both tarsonemids that feed in buds and distorted tissue, but broad mite favours warm, humid conditions while cyclamen mite does best in cool, humid ones [7]. Broad mite eggs carry rows of white tufts; cyclamen mite eggs are smooth, pale ovals about half the adult's length [7]. Broad mite bodies taper and are widest between the second pair of legs; cyclamen mite sides are nearly parallel [7]. Cyclamen mite on cannabis is rarely reported; most "cyclamen mite" calls on cannabis turn out to be broad mite or hemp russet mite. See [cyclamen mite](https://genetixbay.com/knowledge/glossary/cyclamen-mite.md). Hemp russet mite (*Aculops cannabicola*) is an eriophyid: carrot-shaped, only two pairs of legs at the front, feeds only on *Cannabis*, and starts low and inside the plant, bronzing leaves and curling edges upward [15]. Details below and in [kb-pests-hemp-russet-mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md). ## Numbers that matter for broad mites | Parameter | Value | Conditions and source | |---|---|---| | Female length | ~0.2 mm (0.008 in) | [2] | | Male length | ~0.11 mm | [2] | | Egg length | ~0.08 mm | [2] | | Egg-to-adult at 25 °C | 4.4 days (females 4.5, males 4.1) | Grape leaf discs, 65 ± 10% RH, lab [1] | | Lower developmental threshold, egg-adult | 9.71 °C | Grape, lab [1] | | Thermal constant, egg-adult | 62.73 degree-days | Grape, lab [1] | | Upper developmental threshold | 33-35 °C | Citrus, Jones & Brown 1983, as cited in [1] | | Fecundity | 44.3 eggs/female at 25 °C | Grape, lab [1] | | Eggs per day | about 5 | Extension summary [2] | | Sex ratio | ~4 females : 1 male (mated females); unmated females lay only males | [2] | | r_m peak | 0.31 per day at 25 °C (doubling ~2.2 days) | Grape, lab [1] | | Favoured climate | 21-27 °C (70-80 °F), 80-90% RH | Extension [3] | | Action threshold | None published for cannabis | Any confirmed find is significant (Grower practice) | ## What is the broad mite life cycle in numbers? The broad mite life cycle runs egg, larva, quiescent "pupa" (often called nymph), adult, and at 25 °C (77 °F) the whole egg-to-adult run takes about 4.4 days on grape leaves [1]. The best life table with five temperatures comes from Ferreira and colleagues on grape (*Vitis vinifera*) leaf discs at 65 ± 10% RH and 12 h light [1]. No cannabis-specific life table has been published, so treat these as the closest lab proxy. | Temp | Egg (d) | Larva (d) | Quiescent (d) | Egg-adult (d) | Eggs/female | Female longevity (d) | r_m (/day) | Doubling (d) | Generation time T (d) | |---|---|---|---|---|---|---|---|---|---| | 18 °C | 3.9 | 1.7 | 1.3 | 7.3 | 16.5 | 27.9 | 0.10 | 6.9 | 25.7 | | 22 °C | 2.7 | 1.2 | 0.9 | 5.1 | no published value found | – | – | – | – | | 25 °C | 2.3 | 0.9 | 0.7 | 4.4 | 44.3 | 15.8 | 0.31 | 2.2 | 10.8 | | 28 °C | 1.6 | 0.8 | 0.5 | 3.3 | no published value found | – | – | – | – | | 32 °C | 1.8 | 0.8 | 0.5 | 3.5 | 13.3 | 7.7 | 0.12 | 6.0 | 8.2 | | 15 °C, 20 °C, 35 °C | no published value found | | | | | | | | | All values from [1]; doubling time computed here as ln2 / r_m. Net reproductive rate R0 was 13.2 at 18 °C, 30.1 at 25 °C and 2.6 at 32 °C [1]. **Pre-oviposition is very short.** Females started laying 0.3 days after emerging at 25 °C, 1.1 days at 32 °C and 1.8 days at 18 °C [1]. Egg-laying peaked at 4.3 eggs on day 3 of adult life at 25 °C [1]. **Other hosts give similar numbers.** On lemon at 27.5 °C, immatures took 3.6-3.7 days; on cotton at 28.5 °C, about 4.1 days; on lime at 25 °C, 8.5 days with an r_m of 0.427 per day (as cited in [1]). Host plant clearly matters. **Adult males live 5-9 days; females lay 30-76 eggs over 8-13 days and then die** (extension summary across hosts) [2]. The grape lab study found lower fecundity, a reminder that host and method shift every number [1]. ## How do broad mites reproduce and why does that matter for resistance? Broad mites reproduce by [arrhenotoky](https://genetixbay.com/knowledge/glossary/arrhenotoky.md): unmated females lay eggs that become males, and mated females lay about four female eggs for every male egg [2]. One overlooked female can therefore found a colony by producing sons and mating with them. Males do a strange job. Quiescent female larvae attract males, which pick them up with enlarged hind legs, carry them at right angles to their bodies to fresh foliage and mate the moment the female emerges [2]. The males' "frenzy" to carry females accounts for much of the dispersal within a plant [2]. [Haplodiploidy](https://genetixbay.com/knowledge/glossary/haplodiploidy.md), short generations and high r_m are the classic recipe for fast [pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md): a surviving resistant female's sons carry her genes unmasked. Rotate modes of action and never rely on one product class. ## Why do temperature and humidity matter so much for broad mites? Temperature sets broad mite speed: egg-to-adult falls from 7.3 days at 18 °C to 3.3 days at 28 °C, and r_m peaks near 25 °C at 0.31 per day before dropping to 0.12 per day at 32 °C because fecundity and female lifespan collapse in the heat [1]. Above roughly 33-35 °C development stops (citrus data cited in [1]). **Degree-days.** With a lower threshold of 9.71 °C and 62.73 degree-days per egg-to-adult, a room averaging 25 °C delivers 15.3 degree-days a day and a generation in about 4.1 days; at 22 °C about 5.1 days; at 18 °C about 7.6 days [1]. See [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md) and [developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md). **Humidity.** Extension sources say 80-90% RH at 21-27 °C favours broad mites [3], and leaves "collected during humid conditions are more likely to have mites" [3]. The lab life table above was run at 65 ± 10% RH, so its r_m does not test dry rooms. Jones & Brown (1983) measured broad mite reproduction across constant temperature-humidity regimes (as cited in [1]) (egg sensitivity to low RH is widely repeated but no accessible primary value found). **Grow-room set-points.** A veg room at 24-28 °C and 60-70% RH sits right on the broad mite optimum. A flower room at 22-26 °C and 45-55% RH is drier but still within the mite's thermal sweet spot; temperature alone will not save you. See [kb-pests-temperature-humidity-and-pest-population-growth](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) and [VPD](https://genetixbay.com/knowledge/glossary/vpd.md). No [diapause](https://genetixbay.com/knowledge/glossary/diapause.md) is known in broad mites; they are tropical and subtropical and "generally don't survive outdoors" in cold winters, so northern indoor infestations come in on plants [3]. ## How fast can 10 broad mites become a problem? Ten broad mites at 25 °C can become roughly 7,400 in three weeks if nothing stops them, compared with about 80 at 18 °C and about 110 at 32 °C. The method is N(t) = N0 × e^(r_m × t), using the grape-leaf r_m values of 0.1005, 0.3149 and 0.1159 per day at 18, 25 and 32 °C [1]. | Temp | r_m (/day) | Doubling (d) | Day 14 | Day 21 | Day 28 | |---|---|---|---|---|---| | 18 °C | 0.1005 | 6.9 | 41 | 83 | 167 | | 25 °C | 0.3149 | 2.2 | 822 | 7,446 | 67,493 | | 32 °C | 0.1159 | 6.0 | 51 | 114 | 257 | | 25 °C, lime (cited in [1]) | 0.427 | 1.6 | 3,947 | 78,400 | 1,557,488 | This is the unchecked exponential upper bound: no predators, unlimited young tissue, constant temperature. Real populations crash when tips die. The point stands: at room temperature, a clone carrying a handful of mites can be a visibly sick plant within three weeks. ## Where do broad mites hide, how do they spread and how do they get in? Broad mites hide where tissue is youngest and most folded: shoot tips, unfolding leaves, flower buds and the undersides of new leaves [2][3]. They crowd into crevices and buds, which shelters them from contact sprays [2]. **Clones and plant material** are the main way in. UConn notes the species generally does not survive outdoors in the US Northeast and "may be introduced on vegetatively propagated material" [3]. **Hands, clothing and tools** carry them between plants; UConn advises entering infested areas last [3]. **Air currents and plant contact** move them within a crop [3]. **Insects.** Broad mites ride whiteflies (*Bemisia*, *Trialeurodes*) and the green peach aphid *Myzus persicae* from plant to plant (Fan & Petitt 1998; Palevsky et al. 2001, as cited in [1] and [2]). A whitefly problem is therefore also a broad mite distribution network. See [kb-pests-whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md) and [kb-pests-aphids](https://genetixbay.com/knowledge/pests/aphids.md). **Within the plant**, males carrying quiescent females to new foliage drive much of the spread [2]. ## How do you scout for broad mites? Scout for broad mites by examining the newest leaves and shoot tips under 40-60x at least weekly, and every incoming clone before it joins the room. Extension guidance says eggs can be seen at 20x with practice and good light, but a microscope is preferred [3]. - **What to sample.** The youngest unfolded leaves, shoot tips and lower surfaces; leaves collected during humid conditions are more likely to carry mites [3]. - **Lens.** 10x is not enough for confident ID; 20x minimum; 40-60x clip-on lens or a USB microscope is the practical choice (Grower practice, consistent with [2][3]). - **Frequency.** Weekly in veg and mothers; every incoming plant during [quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) (Grower practice). - **Sticky cards** do not catch broad mites usefully, but yellow cards tell you about whiteflies and aphids that can carry them. - **Action threshold.** No published threshold exists for cannabis. Any confirmed broad mite on a mother or clone line is an action point (Grower practice). See [action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md). - **Lab ID.** Extension plant diagnostic labs will identify mites from a sample. ## Which broad mite controls hit which life stage? Contact treatments (soaps, oils, sulfur) hit mobile larvae and adults they touch, but broad mite eggs and quiescent stages hidden in buds largely escape, so every contact program needs at least two or three timed applications. UConn advises high-volume and repeat applications, and translaminar products where labelled [3]. Cloyd notes contact miticides struggle because the mites sit in meristematic tissue [14]. **Timing the repeat at your temperature.** The second application must land after eggs that survived the first have hatched, and before females from those eggs start laying. From the grape life table [1]: | Room temp | Egg hatch (d) | Egg-adult (d) | Pre-oviposition (d) | First new eggs at (d) | Repeat window | |---|---|---|---|---|---| | 18 °C | 3.9 | 7.3 | 1.8 | ~9.1 | day 4-8 | | 22 °C | 2.7 | 5.1 | no published value (between 0.3 and 1.8) | ~5.5-7 | day 3-5 | | 25 °C | 2.3 | 4.4 | 0.3 | ~4.7 | day 3-4 | | 28-32 °C | 1.6-1.8 | 3.3-3.5 | ~1.1 at 32 °C | ~4.4-4.6 | day 2-4 | Plan three applications in that rhythm, then re-inspect. This is a calculation from lab data, not a tested cannabis protocol (Grower practice informed by [1]). **Modes of action.** Miticides labelled for broad mite in greenhouse ornamentals come from several IRAC groups, including 6 (avermectins), 13 (pyrrole uncoupler), 21A (mitochondrial complex I inhibitors) and 23 (tetronic/tetramic acid derivatives) [14]. Many have no cannabis registration. Rotate by class, never repeat one class back-to-back across generations, and follow the label and local law. See [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md). ## How do predatory mites control broad mites? Predatory mites control broad mites only when released preventively, before populations build and before the tips are damaged [3]. The species with the best broad mite record are *Amblyseius swirskii*, *Neoseiulus cucumeris* and *Neoseiulus californicus*; all are generalists that also eat pollen and so can be released before broad mites are found [3]. | Predator | Temperature window | Humidity | Broad mite evidence | |---|---|---|---| | [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md) | Development 11.3-37.4 °C, optimum ~31.5 °C; population growth 15.5-37 °C, optimum ~30 °C; slow below 20 °C [8] | 50% of eggs fail to hatch at ~63% RH, the most drought-sensitive of six species tested [9] | Suppressed broad mites on sweet pepper [5]; up to ~18 broad mites/day and 1.2 eggs/day on a broad-mite diet; on pepper, control lagged two weeks after release [6] | | [Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md) | Lower development threshold ~10.3-11 °C on pollen diets [11] | Needs high RH for egg hatch | As effective as *A. swirskii* on begonia, cleared broad mites within a week [6]; used on pepper (Weintraub et al. 2003, cited in [6]) | | [Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md) | Prefers 10-33 °C (50-91 °F) [10] | Tolerates 40-80% RH, prefers the upper end [10] | Develops and reproduces on broad and cyclamen mites [10]; used against broad mite on pepper in Florida and Israel [6] | | *Amblyseius andersoni* | Eggs did not hatch at 16 °C (one Chinese population); fecundity peaked at 25 °C (45.7 eggs/female) [12] | Low-RH sensitive | Little published broad mite data; more often used against russet and spider mites | **Release rates.** Published trials used 25 predators per plant twice on begonia and 60 then 100 per plant on sweet pepper [6]. For cannabis, follow the biocontrol supplier technical sheet; no cannabis-specific rate has been published. **Predator:prey and lag.** On pepper, broad mite suppression took two weeks after the first *A. swirskii* release [6]. With prey doubling every 2.2 days at 25 °C, a two-week lag means curative releases arrive too late; this is why predators go in at transplant (Grower practice informed by [1][6]). **Compatibility.** Most miticides, sulfur and oils harm predatory mites. Leave the label's re-entry interval for beneficials before releasing, and never spray sulfur on a predator program. **Trichomes.** On tomato, *A. swirskii* established mainly on leaves where glandular trichomes had collapsed (russet mite study, [kb-pests-hemp-russet-mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md)). Cannabis is also glandular and sticky; expect predators to work better in veg than on resinous flowers (Grower practice). ## How can the environment be used against broad mites? Use the environment to favour predators rather than to "dry out" broad mites. The predatory mites that eat broad mites need humid air for their eggs (*A. swirskii* 50% hatch failure at ~63% RH) [9], while broad mites are favoured by warm, humid rooms [3]. There is no setting that helps one and hurts the other cleanly. - **Veg and mothers:** 24-26 °C and 65-70% RH supports *A. swirskii* and *N. cucumeris* egg hatch. It also suits broad mites, so the predators must already be there (Grower practice). - **Cooler mother rooms** at 20-22 °C slow broad mites (egg-adult 5.1 days at 22 °C versus 4.4 at 25 °C) [1] but also slow *A. swirskii*, which grows slowly below 20 °C [8]. *N. cucumeris* and *N. californicus* cope better with cool rooms [10][11]. - **Flower:** drop RH to 45-55%, then 40-50% in late flower, for [botrytis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) and [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) control. That will not stop broad mites, and it shortens predator egg survival. Accept it; bud rot costs more than a flower-stage mite fight. - **Do not run veg above ~30 °C to "cook" mites.** r_m does fall at 32 °C [1], but the plant suffers too and other pests (spider mites) thrive in heat. ## What should you not do about broad mites in flower? Do not spray oils, soaps or sulfur onto flowering buds; residues and wet buds invite botrytis and can fail testing. Do not reach for unregistered miticides; the residue can fail compliance testing and the use may be illegal. Follow the label and local law; registrations on cannabis vary by jurisdiction. - Do not try to "spray through" broad mites in mid to late flower; the mites sit inside buds where sprays miss. - Do not keep an infested mother "because she's the keeper"; every clone carries the problem. - Do not take clones from infested plants, even "clean-looking" tips. - Do isolate the plant, remove the worst, consider an early harvest, and restart from clean stock. ## What are the common myths about broad mites? The common broad mite myths are that a 10x loupe is enough, that twisted tips mean calcium deficiency, that clones are the only route in, and that low humidity or one hot dip will clear them. - **"A 10x loupe will show broad mites."** *Myth.* Females are ~0.2 mm and eggs ~0.08 mm; extension calls for 20x or more and prefers a microscope [2][3]. - **"Twisted new growth is calcium deficiency."** *Myth* as a default. Broad mite injury mimics calcium and boron deficiency [3]; check pH, root zone and then the scope. - **"Broad mites only come in on clones."** *Myth.* Clones are the main route, but hands, clothing, air and whitefly or aphid adults also carry them [1][3]. - **"Hot water dips clean cuttings."** *Contested* for cannabis. 43-49 °C for 15 minutes is documented for broad mite on plant material in other crops [2]. On hemp cuttings, 41-43 °C (106-109 °F) for 10-15 minutes reduced russet mites but did not eliminate them, with no rooting damage [13]. No cannabis broad-mite protocol exists. - **"Drop the humidity and they die."** *Contested.* High RH favours broad mites [3], but no study shows low RH eliminates them, and low RH kills predator eggs [9]. - **"Damaged leaves recover after treatment."** *Myth.* Distortion persists after the mites are dead [3][4]. ## Hemp russet mite: the short version Hemp russet mite (*Aculops cannabicola*, family Eriophyidae) feeds only on *Cannabis* and is described by Colorado State as one of the most injurious arthropods in industrial hemp [15]. It bronzes, shrinks and stiffens leaves, curls edges upward, starts low and inside the plant and moves up into buds as numbers rise [15]. It needs at least 15-20x to glimpse and about 55x to count [15] ([kb-pests-hemp-russet-mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md)). - **Life cycle:** about one week in favourable conditions [15]; no published *A. cannabicola* life table. The tomato russet mite (*Aculops lycopersici*) is the closest proxy: egg-to-adult 5.5 days and r_m 0.286 per day at 25 °C on tomato leaves. - **Spread:** wind from leaf edges, clones and cuttings, people and tools [15]. - **Control:** clean mothers and seed starts, quarantine, removal of infested plants, oils in veg; predatory mites gave mixed results in field hemp [13]. The full life table, worked growth example, scouting method and control program are in [kb-pests-hemp-russet-mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md). ## How do you confirm broad mite control worked? Confirm broad mite control by watching new growth and repeating microscope checks. New leaves should emerge flat and normal-coloured within one to two weeks; old distorted leaves stay distorted [3]. - Re-inspect the same tips at 40-60x weekly for at least three weeks; no live mites, no fresh eggs. - Three weeks covers four to five broad mite generations at 25 °C [1]. - Run the next cycle from clean stock and check again at two and four weeks. ## Common mistakes - Chasing a "calcium deficiency" with ever more Cal-Mag. - Looking with a 10x lens and declaring the plant clean. - Spraying once, or twice a week apart; at 25 °C the second spray lands after new eggs are already laid. - Releasing predators after damage shows; there is a two-week lag [6]. - Ignoring whiteflies and aphids that ferry broad mites [1]. - Keeping the infested mother. ## Evidence - Broad mite biology, damage, and male carrying behaviour: *Established* (extension consensus and lab studies) [2][3][4]. - Temperature-dependent development and r_m: *Established* for grape and other hosts [1]; *extrapolated* to cannabis (no cannabis life table). - Humidity preference (80-90% RH): *Supported* by extension [3]; egg sensitivity to low RH: *Contested/unverified*. - Phoresy on whiteflies and aphids: *Established* (cited in [1][2]). - Hot water treatment: *Supported* in other crops [2]; *Grower practice/untested* for cannabis broad mite. - Preventive predatory mites: *Supported* in pepper and begonia [5][6]; *extrapolated* to cannabis. ## Sources 1. Ferreira, R.C.F., de Oliveira, J.V., Haji, F.N.P. & Gondim Jr., M.G.C. 2006. Biologia, exigencias termicas e tabela de vida de fertilidade do acaro-branco Polyphagotarsonemus latus (Banks) em videira cv. Italia. Neotropical Entomology 35(1): 126-132. https://doi.org/10.1590/S1519-566X2006000100017 (full text: https://www.alice.cnptia.embrapa.br/alice/bitstream/doc/156985/1/Haji2006.pdf) 2. Fasulo, T.R. Broad mite, Polyphagotarsonemus latus (Banks). UF/IFAS Featured Creatures EENY-183 (rev. 2025). https://doi.org/10.32473/edis-in340-2005 3. Pundt, L. Managing Broad Mites on Greenhouse Crops. UConn Extension IPM (rev. June 2024). https://ipm.cahnr.uconn.edu/ipm-managing-broad-mites-on-greenhouse-crops 4. Gerson, U. 1992. Biology and control of the broad mite, Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae). Experimental and Applied Acarology 13: 163-178. https://doi.org/10.1007/BF01194934 5. van Maanen, R., Vila, E., Sabelis, M.W. & Janssen, A. 2010. Biological control of broad mites (Polyphagotarsonemus latus) with the generalist predator Amblyseius swirskii. Experimental and Applied Acarology 52: 29-34. https://doi.org/10.1007/s10493-010-9343-2 6. Buitenhuis, R., Shipp, L. & Scott-Dupree, C. 2010. Biocontrol for broad mites. Greenhouse Canada, September 2010. https://www.greenhousecanada.com/september-2010-2417/ 7. UC IPM. Broad mite and cyclamen mite (home and landscape). University of California ANR. https://ipm.ucanr.edu/home-and-landscape/broad-mite-and-cyclamen-mite/ 8. Lee, H.-S. & Gillespie, D.R. 2011. Life tables and development of Amblyseius swirskii (Acari: Phytoseiidae) at different temperatures. Experimental and Applied Acarology 53: 17-27. https://profils-profiles.science.gc.ca/en/publication/life-tables-and-development-amblyseius-swirskii-acari-phytoseiidae-different 9. Ferrero, M., Gigot, C., Tixier, M.-S., van Houten, Y.M. & Kreiter, S. 2010. Egg hatching response to a range of air humidities for six species of predatory mites. Entomologia Experimentalis et Applicata 135: 237-244. https://esploro.umontpellier.fr/esploro/outputs/journalArticle/Egg-hatching-response-to-a-range/9993063809311 10. Rhodes, E.M. & Liburd, O.E. Predatory mite, Neoseiulus californicus (McGregor). UF/IFAS EENY-359 (rev. Dec 2023). https://edis.ifas.ufl.edu/publication/IN639 11. Yazdanpanah, S. et al. 2022. Modeling temperature-dependent development rate of Neoseiulus cucumeris (Acari: Phytoseiidae). Environmental Entomology 51(1): 145-152. https://doi.org/10.1093/ee/nvab130 12. Li, Y.-J., Liu, Q.-Y., Chang, J., Jia, Y.-H. & Meng, R.-X. 2019. Effects of temperature on a Chinese population of Amblyseius andersoni (Acari: Phytoseiidae) fed with Tetranychus urticae. Acarologia 59(4): 475-483. https://doi.org/10.24349/acarologia/20194344 13. Hayes, C. 2022. Developing integrated pest management (IPM) strategies for hemp russet mite (Aculops cannabicola Farkas) on hemp (Cannabis sativa L.). Thesis, Colorado State University. https://doi.org/10.25675/3.04334 14. Cloyd, R.A. Broad mite and cyclamen mite management in greenhouses and nurseries (MF2938). Kansas State University Research and Extension. https://bookstore.ksre.ksu.edu/download/broad-mite-and-cyclamen-mite-management-in-greenhouses-and-nurseries_MF2938 15. Colorado State University. Hemp russet mite, Aculops cannabicola. https://agsci.colostate.edu/agbio/ipm-pests/29895-2/ --- # Budworms on cannabis: corn earworm and tobacco budworm in numbers > The 'budworm' that ruins outdoor cannabis colas in the US is mostly the corn earworm (Helicoverpa zea), with the tobacco budworm (Chloridea virescens) mixed in; both need about 422 Celsius degree-days above 12.6 C to go from egg to adult (about 34 days at 25 C), lay up to ~1,500 eggs per female singly on flowers, and open the door to bud rot, so growers trap moths from late July, scout buds weekly in flower and hit hatchlings with Bt within the first week after egg hatch. - Canonical: https://genetixbay.com/knowledge/pests/budworms-corn-earworm.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Transition, Flower, Ripening · Systems: Soil, Living soil, Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the budworm that eats cannabis buds?** On outdoor cannabis and hemp in the United States, the budworm is mostly the corn earworm, Helicoverpa zea, with the tobacco budworm, Chloridea (Heliothis) virescens, sometimes mixed in. Moths lay single eggs on flowers and bracts; larvae bore into colas, leave dark frass and let bud rot in. Virginia Tech calls corn earworm one of the most important hemp pests in the state. **How long does a corn earworm take to develop?** Corn earworm needs about 422 Celsius degree-days (760 Fahrenheit degree-days) above a lower threshold of 12.6 C (54.7 F) to go from egg to adult, using the USDA MOTHZV-2 model listed by UC IPM. That is roughly 57 days at a steady 20 C, 34 days at 25 C and 24 days at 30 C. Eggs take about 3 days and larvae about 16 days at 25 C. **How many eggs does a corn earworm moth lay?** A corn earworm female lays up to about 25 to 35 eggs a day and roughly 1,500 in her lifetime of two to three weeks, according to Oregon State and the Pacific Northwest Insect Management Handbook. Eggs are laid singly, about 0.5 mm across, on flower buds, bracts, pistils and nearby leaves, which is why one moth can seed damage across many colas. **When should I hang corn earworm pheromone traps for hemp?** Hang one Heliothis-type trap baited with a corn earworm lure at the field edge by late July or early August and keep it through harvest, per Oregon State Extension. Check it about twice a week and change the lure every two weeks. In Virginia, catches peaked around mid-August as moths left maturing corn. No trap-count treatment threshold has been published for hemp. **When is Bt most effective on budworms?** Bt (Bacillus thuringiensis) works on budworms only while larvae are small and still feeding on the bud surface, so Utah State advises using it on caterpillars under about 12 mm (0.5 in). With the UC IPM model, first to third instars last about a week at 25 C after a 3-day egg stage. Bt often persists under seven days in sunlight, so treatments must repeat during flights. **Why do budworms cause bud rot?** Budworm larvae tunnel into dense colas and leave wet frass inside, and those wounds and droppings give Botrytis (grey mould) an entry point. Virginia Tech linked corn earworm infestations in CBD hemp with more flower bud rot. That is why losses are often larger than the chewing alone: a single larva can turn a fist-sized section of cola into brown mush within days. **Is Bt resistance a problem in corn earworm?** Yes, partly. Britt and Kuhar (2020) found that kurstaki-strain Bt killed only 32 to 35% of field-collected third-instar corn earworm larvae on hemp in four days, versus 60 to 68% of lab-reared larvae, and attributed the gap to widespread Cry1Ab resistance in Virginia populations. A product containing the aizawai strain killed 67.5% of field larvae, the best of the Bt products tested. **Is there a treatment threshold for corn earworm in hemp?** No treatment threshold has been established for corn earworm in hemp, according to Colorado State, Utah State and the Pacific Northwest Insect Management Handbook. Growers instead combine pheromone trap counts with weekly inspection of flowering buds for eggs, young larvae and frass, and treat when moths are flying and eggs or small larvae are being found. Utah State suggests using your own trap history. **Can I use sweet corn as a trap crop for budworms in hemp?** A Maryland grower trial funded by SARE (FNE20-951) found that sweet corn borders did not protect hemp from corn earworm. In a lab choice test the moths laid more eggs on hemp than on sweet corn, and in the field larvae were most numerous in the hemp rows next to the corn, falling with distance from 12 to 60 ft. Treat trap cropping as unproven. **Do budworms get into indoor and greenhouse cannabis?** Budworms are uncommon indoors because the moths fly in from outdoor hosts at night. Greenhouses and light-deprivation houses with open, unscreened vents or doors during late-summer moth flights can be hit hard, since flowering cannabis is attractive to egg-laying females. Screen vents and doors, keep doors shut at dusk, and scout colas weekly from the first pistils. **Short answer.** The "budworm" that hollows out outdoor colas in the United States is mostly the corn earworm, *Helicoverpa zea*, with the tobacco budworm, *Chloridea* (formerly *Heliothis*) *virescens*, mixed in. A generation needs about 422 Celsius degree-days above 12.6 °C, roughly 34 days at 25 °C. Females lay up to ~1,500 single eggs on flowers. Trap moths from late July, inspect buds weekly in flower, and hit hatchlings with Bt in their first week, before they tunnel in and let bud rot follow. For the wider caterpillar picture (European corn borer, hemp borer, armyworms, loopers) see [Caterpillars on cannabis](https://genetixbay.com/knowledge/pests/caterpillars.md). ## Which budworms attack cannabis? Two closely related heliothine moths cause nearly all budworm damage on outdoor cannabis and hemp in the United States. The corn earworm (*Helicoverpa zea*, also called cotton bollworm and tomato fruitworm) is the main one; Virginia Tech surveys found it among the most prevalent and consistent hemp pests in the state [2][16]. The tobacco budworm (*Chloridea virescens*) is listed as a hemp caterpillar in the Pacific Northwest handbook [4] and is sometimes mixed into corn earworm populations in the Southeast [9]. The two are hard to tell apart as larvae in the field. Both are striped, 25 mm (1 in) when grown, and highly variable in colour; on hemp corn earworm larvae are mostly green [1]. Separating them reliably needs a lens on the larval skin or the adult moth, and for cannabis management the difference rarely matters: they lay eggs in the same places and need nearly the same heat to develop [5][6]. The practical difference is insecticide resistance in field crops. NC State notes corn earworm is now resistant to pyrethroids in North Carolina, and tobacco budworm has long been resistant to them [9]. That matters if you ever rotate classes outdoors. The glossary entry is at [corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md); the broader term is [caterpillar](https://genetixbay.com/knowledge/glossary/caterpillar.md). ## Budworm numbers at a glance | Parameter | Corn earworm (*H. zea*) | Tobacco budworm (*C. virescens*) | Source / conditions | |---|---|---|---| | Lower developmental threshold | 12.6 °C (54.7 °F) | 12.6 °C (MOTHZV-2); 12.8 °C (Arizona field); 13.3 °C (lab diet) | [5][6] | | Upper developmental threshold | 33.3 °C (91.9 °F) | 33.3 °C (MOTHZV-2); 30.0 °C (Arizona); 33.0 °C (lab) | [5][6] | | Egg | 40.5 °C-DD (72.9 °F-DD) | 40.5 °C-DD (MOTHZV-2); 41.2 °C-DD (lab) | [5][6] | | Small larvae (instars 1-3) | 81.7 °C-DD | 81.7 °C-DD | [5][6] | | Large larvae (instars 4-5) | 120.6 °C-DD | 120.6 °C-DD | [5][6] | | Pupa | 179.5 °C-DD | 179.5 °C-DD (MOTHZV-2); 182.1 °C-DD (lab) | [5][6] | | Egg to adult | 422.3 °C-DD (760.1 °F-DD) | 422.3 °C-DD (MOTHZV-2); 413.3 °C-DD (lab) | [5][6] | | Adult to adult (incl. pre-oviposition 62.6 °C-DD) | 484.9 °C-DD (872.8 °F-DD) | 484.9 °C-DD | [5][6] | | Eggs per female | up to 25-35/day; ~1,500 lifetime | no separate value verified | [1][4] | | Adult female life | 2-3 weeks | no separate value verified | [1] | | Generations per year | 2-4 in Utah; 3-4 in North Carolina | not reported for hemp | [3][9] | | Mature larva | ~25 mm (1 in) | ~25 mm | [1][4] | | Bt size window | larvae under ~12 mm (0.5 in) | same | [3] | | Treatment threshold in hemp | none established | none established | [3][4][10] | | Intrinsic rate of increase r_m | no published value found | no published value found | closest relative: *H. armigera* 0.147/day at 27.5 °C [11] | The MOTHZV-2 model (Hartstack et al. 1976, USDA) was built for both species together, which is why its stage values are identical for the two [5][6]. UC IPM uses the single-sine method with an intermediate cutoff for it and advises testing any model locally for a season before relying on it [5]. A brief often-quoted figure of "about 690 °F degree-days" per generation does not match the models UC IPM lists: egg to adult is 760 °F-DD, and adult to adult 873 °F-DD [5]. ## How long does a budworm generation take at each temperature? A corn earworm generation takes about 34 days egg to adult at a constant 25 °C (77 °F), and about 39 days adult to adult, using the 422.3 °C-DD and 484.9 °C-DD values above a 12.6 °C threshold [5]. Days are degree-days divided by (temperature − 12.6). This is a linear estimate; real development near the threshold is slower and less predictable than the arithmetic suggests. | Constant temperature | Egg (days) | Larva, instars 1-5 (days) | Pupa (days) | Egg to adult (days) | Adult to adult (days) | |---|---|---|---|---|---| | 15 °C (59 °F) | ~17 | ~84 | ~75 | ~176 (unreliable near threshold) | ~202 | | 20 °C (68 °F) | 5.5 | 27 | 24 | 57 | 66 | | 25 °C (77 °F) | 3.3 | 16 | 14.5 | 34 | 39 | | 30 °C (86 °F) | 2.3 | 12 | 10 | 24 | 28 | | 35 °C (95 °F) | above upper threshold; model caps at ~22 days | | | ~22 | ~26 | Computed from the Hartstack et al. (1976) model as listed by UC IPM [5]. Not cannabis data: the model was fitted to field data from College Station, Texas. The 35 °C row is the model's cutoff talking, not biology. In the closest lab study, on the Old World bollworm *Helicoverpa armigera*, no eggs completed development to adult at constant temperatures outside 17.5-32.5 °C, though alternating day-night regimes widened that to 10-35 °C [11]. Hot days with cool nights are survivable; a constant 35 °C is not. Host plant changes the numbers. Butler (1976) found corn earworm larvae needed 273 °C-DD on corn, 207 on wheat-germ diet and 432 on cotton (with a lower 7.7 °C threshold on cotton) [5]. No cannabis-specific development study was found; flowers are a high-quality food, so corn-like values are a reasonable working assumption, not a measured one. ## What does the full corn earworm life cycle look like on cannabis? Corn earworm passes egg, five (sometimes six) larval instars, a pupa in the soil and a night-flying moth [1][4]. Eggs are laid singly, about 0.5 mm across, white to pale green, turning darker with ridges as they mature [10]. Extension sources give egg hatch as 2-4 days in summer [4] to "about a week" [1]; the degree-day model gives 3.3 days at 25 °C and 5.5 days at 20 °C [5]. Young larvae (first and second instars) are about 2 mm long, dark, with black bristles, and cluster near flowers [4][10]. Larvae reach full size, about 25 mm, in two to three weeks [1][4]. Mature larvae drop to the soil and pupate; summer moths emerge about two weeks later [1]. Corn earworm overwinters as a pupa in the soil where winters allow. Utah State reports pupae survive winter in central and southern Utah but not in northern Utah [3]. Northern populations are rebuilt each year by moths migrating north [3][10]. In North Carolina, overwintered pupae produce moths in April and May; the first generation develops on whorl-stage corn and wild hosts, the second on corn ears, and second-generation moths leave cornfields from mid-July into early to mid-August, looking for soybean, cotton, peanut and other hosts [9]. That mass exodus from maturing corn is the flight that meets early-flowering outdoor cannabis. Virginia trap data show the same pattern: catches near Blacksburg peaked around mid-August with moths emerging from cornfields and eased by late August [8]. ## Why do temperature and humidity matter for budworms? Temperature sets how fast budworms cycle: at 30 °C a corn earworm generation takes about 24 days, at 20 °C about 57 days [5]. Warm Augusts therefore mean more overlapping larvae in the crop and less time between egg hatch and larvae boring in. At 25 °C the surface-feeding window (egg hatch to end of third instar) is about 6.6 days; at 20 °C it is about 11 days [5]. Above roughly 33 °C development slows (the model's upper threshold) [5], and for the related *H. armigera* the intrinsic rate of increase peaked at 27.5 °C (0.147/day) and adult life fell from 34.4 days at 15 °C to 7.6 days at 35 °C [11]. Mid-summer heat waves therefore do not make budworms unstoppable; mild, warm late summers are the danger. Humidity matters mainly through the plant, not the insect. Larval tunnels and frass inside dense colas plus cool, humid autumn nights are what turns a caterpillar wound into Botrytis bud rot [2][17]. Outdoors you cannot set humidity, but you can avoid making it worse: no late-day sprays that leave colas wet overnight. Diapause: corn earworm overwinters as a pupa in the soil [1][9], and pupae do not survive northern Utah winters [3]. The exact day-length and temperature triggers for hemp-feeding populations have not been studied (no published value found). In practice, warm regions can still see larvae in October while northern plots go quiet once nights cool (Grower practice). Indoor set-points (flower ~22-26 °C, 45-55% RH) are well inside the comfortable range for budworms. Indoors the defence is exclusion, not climate. ## How fast can a budworm problem grow? A budworm problem grows mostly by immigration, not by local breeding: moths fly in from corn and wild hosts every night of a flight, and each female can lay up to ~1,500 eggs [1][9]. A single generation in the crop takes 24-57 days depending on temperature [5], so most outdoor cannabis sees one, at most two, local generations between first flowers and harvest. No intrinsic rate of increase (r_m) has been published for *H. zea* that we could verify. The closest life-table data are for *Helicoverpa armigera*: r_m 0.147/day at 27.5 °C constant (lab, artificial diet) [11]. Used only as a proxy, the unchecked exponential N(t) = N0 × e^(r_m × t) gives: | Start | r_m (/day) | Doubling time (ln 2 / r_m) | After 21 days | After 42 days | |---|---|---|---|---| | 10 eggs/larvae | 0.147 (27.5 °C constant) | 4.7 days | ~219 | ~4,800 | | 10 eggs/larvae | 0.139 (alternating regime, same mean) | 5.0 days | ~185 | ~3,400 | Proxy species and lab conditions; not cannabis data [11]. This is an upper bound with no predators, no parasitoids and unlimited food. The real-world lesson is different from mites. Outdoors, one moth flight can put dozens of eggs on a single plant in a week regardless of what bred there last month. What you control is how many eggs hatch into larvae that reach the inside of a cola. ## Where do budworms come from and how do they get in? Budworm moths fly in at night from corn, cotton, soybean, tomato and wild hosts, and from overwintering pupae in nearby soil [1][9][10]. Northern regions are repopulated each year by migrating moths [3]. Cannabis is a preferred egg-laying site once it flowers: in a Maryland grower trial, moths laid more eggs on hemp than on sweet corn in a two-choice lab test [12]. Distance from corn reduces pressure but does not remove it. In the same Maryland trial, hemp rows next to a sweet corn border had the most larvae, and numbers fell from 12 to 60 ft away [12]. Virginia trap catches peaked as moths left maturing cornfields [8]. Clones are not a vector; eggs and larvae arrive on flowering plants. Indoors and in greenhouses, moths come in through unscreened intakes, roof vents and doors left open at dusk. Light-deprivation greenhouses that flower in August are as exposed as open fields if vents are unscreened (Grower practice). Moving cut plants is a vector in one sense: harvested branches can carry live larvae into a drying room, where they keep feeding until the bud dries. Shake or inspect branches before hanging (Grower practice). ## How do I scout for budworms on cannabis? Scout outdoor cannabis for budworms weekly from the first pistils to harvest, and twice weekly during a moth flight: inspect the upper third of the colas, bracts and pistils for single pale eggs, 2 mm larvae, small holes and dark frass [1][3][10]. A 10x hand lens is enough to see eggs; larvae are visible to the naked eye once past about 5 mm. Pheromone traps tell you when to look harder. Oregon State's protocol: one Heliothis-type net trap with a corn earworm lure at the field border by late July or early August, maintained through harvest, checked about twice a week (for example Tuesday and Friday), lure changed every two weeks [1]. Utah State starts traps in July and checks every 3-5 days [3]. Lures attract males only [10]. There is no trap-count threshold for hemp [3][4][10]. Utah State suggests building your own: record catches each year and use them to identify high-risk weeks [3]. Regional networks such as Virginia's county-level corn earworm trap reports can warn you a flight is under way before your own trap catches it [18]. Signs inside the bud: a single dead sugar leaf poking out of a cola, a brown or wilted section, webbing-free tunnels with granular frass, or frass dropping onto leaves below. Open suspect buds; damage hides inside [1][3]. Action threshold: none published for cannabis or hemp [3][4][10]. Grower practice: treat when the trap shows a flight and you find eggs or first-instar larvae on buds, because that is the only stage you can still reach. Moths are active only at night, so without a trap you will rarely see them [1]. Black-light traps catch them too, but also catch many other species. ## How do I control budworms at each life stage? Budworm control works only on eggs and small surface-feeding larvae; once a larva is inside a cola, sprays rarely reach it [1][3]. At 25 °C that window is about 3 days of egg plus about 6.6 days of first to third instars [5]. Time everything to the flight and the hatch. | Stage | What reaches it | Notes | |---|---|---| | Egg (3-6 days) | Egg parasitoids (*Trichogramma pretiosum*); generalist predators; hand removal | *T. ostriniae* gives little parasitism of corn earworm eggs [14] | | Larva instars 1-3 (~1 week at 25 °C), on surface | Bt (IRAC 11A); Helicoverpa NPV (IRAC 31); spinosyns (IRAC 5) where registered | Must be eaten; coverage of buds is everything [2][7] | | Larva instars 4-5, inside colas | Hand removal; cutting out damaged section | Sprays largely fail; Bt weak on big larvae [3][7] | | Pupa (in soil, ~2 weeks summer) | Tillage and residue removal where practical | Reduces local overwintering only [10] | | Moth | Exclusion (netting, screened vents); monitoring traps | Traps do not control [1] | ### How often should budworm treatments be repeated? Repeat budworm treatments at an interval shorter than the egg stage plus the surface-feeding window, and shorter than the residual of the product, for as long as moths are flying. At 25 °C, eggs hatch in about 3.3 days and larvae stay small for about 6.6 days [5], while Bt residue often lasts under seven days in sunlight [1]. That arithmetic explains the extension advice. Oregon State suggests spraying likely twice a week during outbreaks [1]; Virginia Tech advises reapplying Bt every 2-3 days, early morning or late evening, and notes dead larvae may not show until 48 hours after the first application [2]. A weekly interval leaves a gap in which eggs laid just after a spray can hatch and bore in before the next. At cooler late-season temperatures the window widens: at a 20 °C mean, egg plus instars 1-3 is about 16.5 days [5], so the limiting factor becomes product residual, not development. ### Which product classes work, and what about resistance? Rotate budworm controls by mode-of-action class, follow the label and local law, and check what is registered on cannabis or hemp where you grow; registrations vary by state and country and most residues are tested for on cannabis [15]. No brands or rates are given here. - **Bt (IRAC 11A).** Two subspecies are used: kurstaki and aizawai [2]. In Britt and Kuhar's 2019 lab bioassays on hemp seed heads, kurstaki-strain products killed 32.5-35% of field-collected third-instar corn earworm in four days, and an aizawai-plus-kurstaki product 67.5% [7]. With lab-reared larvae, kurstaki products killed 60-67.5%. The authors attribute the gap to widespread Cry1Ab resistance in Virginia field populations [7]. - **Helicoverpa nucleopolyhedrovirus (NPV, IRAC 31).** Specific to heliothine larvae. Slow: in the same bioassay it killed 10% within 96 hours, and the authors note it often takes longer than 96 hours on larger larvae [7]. Oregon trials found it useful [1]. - **Spinosyns (IRAC 5).** The spinosad product was the only one giving effective control in Virginia's 2019 field trial and killed 95-97.5% in bioassays [2][7], but it was not legal on hemp in Virginia at the time [2]. Legality is the deciding factor, not efficacy. - **Diamides (IRAC 28).** A major field-crop class against heliothines; NC State asked growers to limit its use in soybean to protect its value in cotton [9]. We found no cannabis registration data; check locally. - **Pyrethrins and pyrethroids (IRAC 3A).** Corn earworm is now pyrethroid-resistant in North Carolina, and tobacco budworm has long been [9]. Virginia authors expected pyrethrins to underperform on field larvae for the same reason [7]. - **Beauveria bassiana (fungal biological).** Tested in Virginia field trials; did not give effective control alone [2]. Resistance in budworms comes from huge, mobile, multi-generation populations exposed to Bt crops and insecticides across the corn, cotton and soybean belt, not from your garden. You inherit it. The rotation rule still applies: do not lean on one class for an entire flight. ## Which natural enemies attack budworms? Budworms have a large natural-enemy community outdoors: big-eyed bugs, damsel bugs and lady beetles eat eggs and small larvae; *Trichogramma* wasps parasitize eggs; and the tachinid fly *Archytas marmoratus* and the braconid wasp *Microplitis croceipes* parasitize larvae [4]. Their role on hemp has not been fully studied [4]. Conservation (no broad-spectrum sprays, flowering borders) is the cheapest biological control you have. ### Do Trichogramma releases work against corn earworm? Trichogramma egg-parasitoid releases against corn earworm are supported in corn but unproven in cannabis, and the species matters. In Brazilian corn, three releases of 100,000 *Trichogramma pretiosum* adults per hectare (about 40,000 per acre) raised parasitism of *H. zea* eggs up to fivefold and cut ear damage by 26% [13]. The species sold for European corn borer, *Trichogramma ostriniae*, is not a substitute. Cornell reports little or no substantial parasitism of corn earworm eggs by it, an ideal development range of 82-91 °F (28-33 °C), highest parasitism within about 100 ft of release points, and no established rates for hemp [14]. Biocontrol supplier technical sheets for *Trichogramma* generally advise releases timed to the start of egg laying, repeated weekly through the flight (supplier technical sheet, cited generically). Parasitism reduces hatch; it does not stop eggs laid between releases. Wasps are compatible with Bt and NPV, which do not harm adults on contact, but not with broad-spectrum contact insecticides (Grower practice). [Parasitoid](https://genetixbay.com/knowledge/glossary/parasitoid.md) and [biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) are defined in the glossary. ## Can I use the environment against budworms? Outdoors the environment is mostly out of your hands, so the "environment" levers for budworms are exclusion and timing, not set-points. Exclusion is the strongest tactic: fine insect netting over flowering plants, or screened vents and doors in greenhouses, keeps moths off the buds entirely (Grower practice; strong in principle, little cannabis research). Timing: Virginia catches peaked in mid-August [8] and NC second-generation moths leave corn mid-July to mid-August [9]. Light-deprivation scheduling or cultivar choice can move flowering earlier or later than your local peak (Grower practice; check your own trap history, as Utah State advises [3]). Earlier-finishing plants also spend fewer late, humid nights with larvae inside. Site: keep plantings away from corn and from last year's infested ground where possible; larval numbers fell with distance from corn in the Maryland trial [12]. Controlling weeds before planting reduces overwintering pupae and alternative food [10]. Cultivar: Virginia Tech notes damage depends on the variety grown [16]. Looser, airier colas give larvae fewer protected tunnels and dry faster after rain (Grower practice). Trade-off: netting raises humidity a little and cuts airflow round colas, which matters for Botrytis in a wet autumn. Use the coarsest mesh that still stops moths, and leave the netting off the plant surface. ## What should I not do for budworms in flower? Do not spray broad-spectrum synthetic insecticides on flowering cannabis; most are not registered on cannabis, residues fail testing, and corn earworm is already resistant to pyrethroids in parts of the US [9][15]. Follow the label and local law. Do not spray once at first flower and assume protection; Bt often lasts under a week in sunlight and moths keep arriving for weeks [1]. Do not spray Bt on large larvae inside colas and expect a result; it must be eaten, and kurstaki-strain Bt killed only about a third of field-collected third instars in Virginia tests [7]. Do not apply sprays late in the day that leave dense colas wet overnight in cool weather; that feeds bud rot [17]. Do not leave damaged sections on the plant. Cut out the brown section with a margin of clean tissue and bag it, since larvae and Botrytis spores travel with it [17]. Do not hang unchecked branches in the drying room; larvae keep feeding and rot keeps spreading (Grower practice). ## What are the common myths about budworms? - **"Bt kills any caterpillar in the bud."** *Myth.* Bt must be eaten; large larvae inside colas eat little treated tissue, and Cry1Ab resistance cuts kurstaki-strain efficacy in Virginia field populations [3][7]. - **"One spray at the start of flower protects the crop."** *Myth.* Residual is under a week in sunlight and flights last weeks [1][2]. - **"Pheromone traps control budworms."** *Myth.* Lures catch males only and serve to time scouting [1][10]. - **"Budworms only hit plants next to corn."** *Myth.* Distance helps, but moths preferred hemp to sweet corn in a Maryland trial and migrants reach isolated plots [3][12]. - **"Sweet corn borders protect hemp."** *Contested to unsupported.* The only hemp trial found was a grower trial, and it did not support the idea [12]. - **"Corn earworm and tobacco budworm need different tactics on cannabis."** *Supported that they do not.* Same egg-on-flower habit and near-identical degree-day needs [5][6]; resistance differences matter only for synthetic classes [9]. ## Common mistakes - Starting scouting after brown patches appear; by then larvae are inside. - Hanging a trap and never recording counts, so next year's timing is guesswork. - Using one Bt strain all season against populations known to carry Cry1Ab resistance [7]. - Spacing treatments a week apart during a peak flight at 25 °C, longer than egg plus small-larva window [5]. - Ignoring the rot that follows larvae, and drying infested branches with healthy ones. ## Evidence - Corn earworm biology, fecundity and lack of hemp thresholds: *Established* by multiple extension services [1][3][4][10]. - Degree-day thresholds and stage requirements: *Established* for cotton, corn and diet; *not validated on cannabis* [5][6]. - Bt, NPV and spinosyn efficacy on hemp: *Supported* by Virginia field trial and lab bioassays [2][7]. - Cry1Ab resistance reducing Bt kill: *Supported*, author interpretation in a bioassay report [7]. - Trichogramma for corn earworm: *Supported* in corn [13]; *untested* in cannabis. - Exclusion netting and light-dep timing: *Grower practice*. - Trap cropping with sweet corn: *Contested*; one negative grower trial [12]. ## Glossary terms used here - Glossary: [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md), [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md), [parasitoid](https://genetixbay.com/knowledge/glossary/parasitoid.md), [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md), [action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md) ## Sources 1. Shrestha, G. 2022. Corn earworm management in hemp (EM 9626). Oregon State University Extension. https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 2. Kuhar, T., Britt, K., Doughty, H. 2019. Corn earworm pest problems on hemp and results of recent insecticide tests. Virginia Tech Ag Pest Advisory. https://ag-pest-advisory.vaes.vt.edu/corn-earworm-pest-problems-on-hemp-and-results-of-recent-insecticide-tests/ 3. Utah State University Extension. Corn Earworm (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-corn-earworm 4. Pacific Northwest Insect Management Handbook. Hemp: caterpillars. https://pnwhandbooks.org/insect/agronomic/hemp/hemp-caterpillars 5. UC IPM. Corn earworm / cotton bollworm / tomato fruitworm phenology models (Hartstack et al. 1976; Coop et al. 1993; Butler 1976). https://ipm.ucanr.edu/weather/phenology-models-description/corn-earworm-cotton-bollworm-tomato-fruitworm/ 6. UC IPM. Tobacco budworm phenology models (Potter et al. 1981; Hartstack et al. 1976; Butler & Hamilton 1979). https://ipm.ucanr.edu/PHENOLOGY/ma-tobacco_budworm.html 7. Britt, K.E., Kuhar, T.P. 2020. Laboratory bioassays of biological/organic insecticides to control corn earworm on hemp in Virginia, 2019. Arthropod Management Tests 45(1): tsaa102. https://doi.org/10.1093/amt/tsaa102 8. Kuhar, T., Britt, K. 2020. Corn earworm moth trap catch around Blacksburg, VA and results of an insecticide evaluation on hemp. Virginia Tech Ag Pest Advisory. https://ag-pest-advisory.vaes.vt.edu/?p=5110 9. Reisig, D. 2020 (rev. 2024). Corn earworm in soybean. NC State Extension. https://content.ces.ncsu.edu/corn-earworm-in-soybean 10. Colorado State University. Corn earworm, Helicoverpa zea (hemp IPM). https://agsci.colostate.edu/agbio/ipm-pests/corn-earworm/ 11. Mironidis, G.K., Savopoulou-Soultani, M. 2008. Development, survivorship, and reproduction of Helicoverpa armigera under constant and alternating temperatures. Environmental Entomology 37(1): 16-28. https://academic.oup.com/ee/article/37/1/16/547157 12. Edwards, K., Zebelo, S. 2022. Managing corn earworm in hemp field by using sweet corn as a trap crop (SARE FNE20-951 final report). https://projects.sare.org/project-reports/fne20-951/ 13. Nogueira de Sá, L.A., Parra, J.R.P. 1993. Effect of the number and interval between releases of Trichogramma pretiosum on the parasitism and control of Helicoverpa zea in corn. Scientia Agricola 50(3): 355-359. https://revistas.usp.br/sa/article/view/20130 14. Cornell IPM. Trichogramma ostriniae biocontrol agent fact sheet. https://cals.cornell.edu/integrated-pest-management/outreach-education/fact-sheets/trichogramma-ostriniae-biocontrol-agent-factsheet 15. IRAC. Mode of Action Classification (online). https://irac-online.org/mode-of-action/classification-online/ 16. Britt, K., Taylor, S., Kuhar, T. 2019. Corn earworm, Helicoverpa zea, a pest of hemp, Cannabis sativa, in Virginia (ENTO-328NP). Virginia Cooperative Extension. https://pubs.ext.vt.edu/ENTO/ENTO-328/ENTO-328.html 17. Utah State University Extension. Hemp bud rot. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot 18. Malone, S. 2025. Expanded corn earworm pheromone trap monitoring network for Virginia. Virginia Tech Ag Pest Advisory. https://ag-pest-advisory.vaes.vt.edu/expanded-corn-earworm-pheromone-trap-monitoring-network-for-virginia/ --- # Cannabis aphid (Phorodon cannabis): ID, life table, overwintering and control > The cannabis aphid (Phorodon cannabis) develops only on Cannabis. It was first recognised as a pest in North America on Colorado hemp from 2015. On hemp at 25 C it starts breeding 6.4 days after birth, produces about 112 nymphs per female and doubles every 2 days (r_m 0.355/day), but it nearly stops growing at 30 C. Short days trigger males and egg-laying females outdoors and after the indoor flip. Quarantine clones; no parasitoid has been proven against it in peer-reviewed trials. - Canonical: https://genetixbay.com/knowledge/pests/cannabis-aphid.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the cannabis aphid?** The cannabis aphid (Phorodon cannabis), also called hemp aphid or bhang aphid, is an aphid that develops only on Cannabis. It is pale yellow to light green, turning pink or light brown under short days, and lives on leaf undersides, stems and later in buds. Cranshaw and colleagues rank it among the two most damaging sap-feeding pests of US hemp, with hemp russet mite. **How fast does the cannabis aphid reproduce?** In a lab life table on hemp at 25 °C (77 °F), cannabis aphid nymphs began reproducing after 6.4 days, each female produced about 112 nymphs at up to 7.5 a day, and the intrinsic rate of increase was 0.355 per day. That is a doubling time of about 2 days, so 10 aphids can become roughly 17,000 in three weeks if nothing checks them. **Does heat kill cannabis aphids?** Heat suppresses but does not quickly kill cannabis aphids. On hemp in the lab, the intrinsic rate of increase fell from 0.355 per day at 25 °C to 0.244 at 28 °C and 0.019 at 30 °C (86 °F), where females produced only 2.4 nymphs each. Running a room at 30 °C stresses cannabis and beneficials, and does nothing against heat-tolerant cotton aphids. **How do I tell cannabis aphid from green peach aphid or hop aphid?** Cannabis aphid is pale yellow to light green, often with a pale stripe along the back, and lives only on Cannabis. Green peach aphid is a generalist, usually green. The hop aphid looks almost identical; separating it needs a microscope to see the cannabis aphid's horn-like antennal tubercles and bulb-tipped head hairs. A misidentified cannabis aphid can lead to the wrong parasitoid. **Do cannabis aphids lay eggs indoors?** Yes, cannabis aphids can lay eggs indoors. Colorado State University reports that the cannabis aphid can produce winged males and egg-laying females indoors when the lighting shifts to short days, as in a 12/12 flowering room. Outdoors these sexual forms appear from early September and lay eggs on stems and flower buds. How long eggs survive in warm rooms is unknown. **How does the cannabis aphid survive winter?** Outdoors, the cannabis aphid survives winter as eggs laid by mated females in September and October on stems, buds and seed capsules. The eggs stay on crop debris and hatch in spring, colonising volunteer Cannabis seedlings nearby. Indoors, it can breed asexually year-round under long days. Removing debris and volunteer plants breaks the outdoor cycle. **What parasitic wasp works on cannabis aphid?** No parasitoid has been proven against cannabis aphid in peer-reviewed greenhouse trials. Industry reports favour Aphidius matricariae; reports on Aphidius colemani are mixed. Colorado State observed unidentified parasitic wasps attacking it. A 2025 lab study found Aphelinus varipes parasitised only 3% of cannabis aphids offered. Release early, at low aphid numbers, and confirm control by counting mummies. **How do I get rid of cannabis aphids in a grow room?** Get rid of cannabis aphids in a grow room by quarantining all incoming clones for several weeks, removing infested leaves, releasing parasitoids or lacewings early, and using contact sprays such as insecticidal soap only in veg, every 5-7 days. Because the aphid lives only on Cannabis and starves within days, removing all plants from a room clears it. Follow the label and local law. **Short answer.** The cannabis aphid (*Phorodon cannabis*) is a pale yellow to light green aphid that develops only on *Cannabis* [3]. On hemp at 25 °C (77 °F) it starts breeding 6.4 days after birth and doubles every 2 days (r_m 0.355 per day) [4]. Short days trigger males and egg-laying females, outdoors in September and indoors after the flip [2][3]. Quarantine clones, release natural enemies early, and keep sprays out of flower. General aphid biology and the other species are in [Aphids](https://genetixbay.com/knowledge/pests/aphids.md). ## Cannabis aphid numbers at a glance | Parameter | Value | Conditions / source | |---|---|---| | Host range | *Cannabis* only | [3][5][6] | | Birth to first reproduction | 11.0 d at 20 °C; 6.4 d at 25 °C; 6.0 d at 28 °C; 5.4 d at 30 °C | Hemp cv. Henola, lab, 65% RH, 16L:8D [4] | | Lower developmental threshold | No published value found; GenetixBay estimate 10-13 °C | Linear fit of [4] | | Degree-days to first reproduction | No published value found; GenetixBay estimate 77-100 DD | Linear fit of [4] | | Lifetime fecundity | 54.5 (20 °C); 111.6 (25 °C); 27.8 (28 °C); 2.4 (30 °C) nymphs/female | [4] | | Peak daily fecundity | 7.5 nymphs/day at 25 °C; 3.7 at 20 °C | [4] | | Adult longevity (total lifespan) | 25.7 d (20 °C); 24.6 d (25 °C); 18.2 d (28 °C); 15.1 d (30 °C) | [4] | | Nymph survival to maturity | 98% (20 °C); 71% (25 °C); 61% (28 °C); 43% (30 °C) | [4] | | Intrinsic rate of increase r_m | 0.153 (20 °C); 0.355 (25 °C); 0.244 (28 °C); 0.019 (30 °C) per day | [4] | | Doubling time | 4.5 d (20 °C); 1.95 d (25 °C); 2.8 d (28 °C); 36.5 d (30 °C) | [4] | | Net reproductive rate R0 | 26.7 (20 °C); 58.0 (25 °C); 12.2 (28 °C); 1.2 (30 °C) | [4] | | Mean generation time T | 21.5 d (20 °C); 11.4 d (25 °C); 10.3 d (28 °C); 8.2 d (30 °C) | [4] | | Sex ratio | All female under long days; winged males and wingless oviparae under short days | [2][3] | | Starvation | Dies within a few days without a host plant | [3] | | Action threshold | None established | [5] | ## What is the cannabis aphid, and where did it come from? The cannabis aphid (*Phorodon cannabis* Passerini), also called hemp aphid or bhang aphid, is an Old World aphid that develops only on *Cannabis* [1][3]. It is the aphid most consistently reported as a pest of hemp worldwide, and McPartland, Clarke and Watson's *Hemp Diseases and Pests* reviews it among the insects of the crop [11]. **First North American records.** Cranshaw and colleagues reported it in 2018 as a newly recognised pest in North America, observed in Colorado hemp since 2015, when significant outdoor production began [1]. Halbert (2016) recorded it as new to the Western Hemisphere (as cited in [4]). **Pest status.** In Colorado it has produced high late-summer populations in some fields every season since 2016 [2]. Cranshaw and colleagues name it, with hemp russet mite, one of the two most damaging sap-feeding pests of US hemp [2]. See [Hemp russet mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md). **Indoors.** It can be a common pest wherever hemp has an indoor phase, such as clone propagation or transplant production [2]. In Canadian licensed production it is described as quickly becoming one of the most prevalent pests on cannabis crops [7]. ## How do I identify the cannabis aphid? Identify the cannabis aphid by a pale yellow, soft-bodied aphid on Cannabis leaf undersides and stems, often with a pale stripe along the back, plus honeydew droplets and cast skins on the leaves below [3][6]. Confirming the species needs a microscope. **Colour forms.** Pale yellow forms predominate; light green is less common [3]. Pale pink and light brown forms occur indoors after the shift to short-day lighting and outdoors late in the season [3]. NC State describes early-season aphids as light cream to pale yellow, and late-season ones as light green, pale pink or light brown [5]. **Colour and reproduction.** Colorado State suspects the pale yellow form is the normal asexual one, and that coloured forms (pink, brown, green) may be sexual forms, including egg-laying oviparae [3]. *Contested*: this is a stated hypothesis, not a measured result. **Stripes and spots.** Wingless forms may carry a pale yellow stripe beside a thin green stripe along the back; winged forms have some dark spotting [3][6]. Greenhouse Canada describes winged forms as mostly brown and green, with harder bodies [7]. **Eggs.** Yellow-green at first, turning black as they harden [5]. **Microscope ID.** The cannabis aphid is very similar to the hop aphid (*Phorodon humuli*). Separating them needs a microscope to see the horn-like projections at the base of the antennae and the bulb-tipped hairs on the head, thorax and antenna bases [5]. Use 40-60x or send a sample to an extension lab. **Commonest mix-up.** A green, unstriped cannabis aphid can be mistaken for green peach aphid, which leads growers to *Aphidius colemani*; one trade article calls that a less effective choice for cannabis aphid than *A. matricariae* [14] (page blocked). ## Where on the plant does it live, and what damage does it do? The cannabis aphid lives on leaf undersides and stems, and late in the season infests maturing flowers and nearby leaflets [2][3]. It feeds on phloem, so it leaves no stippling or scarring; damage comes from sap loss, which at high, sustained numbers causes slowed growth, wilting and yellowing [3]. **Buds at harvest.** Large numbers of aphids and their eggs can be incorporated into harvested flower, and the aphid produces abundant honeydew [2]. Effects on yield are unknown [2]. **Honeydew as a sign.** Honeydew falls as tiny droplets that show as small shiny spots on leaves below the colony, together with white cast skins; both are excellent diagnostic signs [3]. See [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md). **Viruses.** The cannabis aphid can transmit cucumber mosaic virus and alfalfa mosaic virus to hemp [5]. Colorado State notes the main viruses described from Cannabis are mechanically transmitted and cannot be spread by aphids [3]. See [Hop latent viroid and viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). ## What is the cannabis aphid life cycle in numbers? The cannabis aphid life cycle under long days is clonal: females give live birth to genetically identical daughters, nymphs moult through four instars, and at 25 °C (77 °F) they begin reproducing 6.4 days after birth [3][4]. The only published life table is Durak and colleagues' 2021 study on hemp [4]. **Study conditions.** Hemp cultivar Henola, 6-week-old plants, 20, 25, 28 and 30 °C, 65 ± 5% RH, 16L:8D, 50 aphids per temperature [4]. Values are lab means, not field rates. | Temp | Pre-reproductive (d) | Reproductive period (d) | Total lifespan (d) | Fecundity (nymphs/female) | r_m (/day) | R0 | T (d) | Doubling time (d) | |---|---|---|---|---|---|---|---|---| | 20 °C (68 °F) | 11.0 | 14.7 | 25.7 | 54.5 | 0.153 | 26.7 | 21.5 | 4.5 | | 25 °C (77 °F) | 6.4 | 15.2 | 24.6 | 111.6 | 0.355 | 58.0 | 11.4 | 1.95 | | 28 °C (82 °F) | 6.0 | 9.6 | 18.2 | 27.8 | 0.244 | 12.2 | 10.3 | 2.8 | | 30 °C (86 °F) | 5.4 | 2.1 | 15.1 | 2.4 | 0.019 | 1.2 | 8.2 | 36.5 | Source: [4]. 15 and 35 °C were not tested; no published values found. **Extension estimates.** Colorado State gives a looser field picture: maturity within one to two weeks of birth, 1-5 young per day, and a likely maximum adult life of 3-4 weeks [3]. The lab figure of 7.5 nymphs per day at 25 °C [4] is higher, as expected on young plants without enemies. **Thresholds.** No published lower developmental threshold or degree-day requirement was found for the cannabis aphid. A linear fit of the pre-reproductive times at 20, 25 and 28 °C [4] gives roughly 10 °C and 100 degree-days; a two-point fit at 20-25 °C gives 13 °C and 77 DD. Both are GenetixBay calculations from very few points. See [developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md). **Proxy for missing temperatures.** For 15-18 °C and 32 °C, the closest well-studied relative is the green peach aphid. *Proxy only, a different species on pepper*: green peach aphid reached adulthood in 12.4 days at 18 °C and 13.0 days at 32 °C, with r_m 0.189 at 18 °C and -0.097 at 32 °C [9]. ## Why do temperature and humidity matter for the cannabis aphid? Temperature sets how fast the cannabis aphid multiplies: on hemp its r_m more than doubled from 0.153 per day at 20 °C to 0.355 at 25 °C, then fell to 0.244 at 28 °C and almost zero at 30 °C [4]. Of the common cannabis aphids, it is the least heat tolerant. **Heat stress.** At 30 °C (86 °F) the reproductive period shrank to 2.1 days, females produced 2.4 nymphs each, and 57% of nymphs died before maturity [4]. **Grow-room set-points.** Veg rooms at 24-28 °C (75-82 °F) and flower rooms at 22-26 °C (72-79 °F) sit in or near the cannabis aphid's 25 °C optimum. Mother and clone rooms at 20-22 °C slow it, but do not stop it. **Humidity.** No published effect of RH on cannabis aphid development was found; the only life table used 65% RH [4]. Humidity matters through control agents: entomopathogenic fungi need relatively high humidity [3], and aphid parasitoids prefer about 70-85% RH [10]. See [VPD](https://genetixbay.com/knowledge/glossary/vpd.md). **Day length.** Short days are the trigger that matters. Declining day length triggers males and egg-laying females outdoors in September and October [3]. Indoors, the switch to short-day lighting can do the same [3]. Short days may also raise the share of winged forms [3]. ## How fast can a cannabis aphid colony grow? A worked example A cannabis aphid colony unchecked by enemies grows as N(t) = N0 × e^(r_m × t). Ten aphids at 25 °C (r_m 0.355 per day [4]) become about 120 in one week, 1,440 in two and 17,300 in three. At 20 °C (r_m 0.153) they reach only about 250 in three weeks. **Method.** N0 = 10; r_m from [4]; t in days. Example at 28 °C, 21 days: 10 × e^(0.244 × 21) = 10 × 168 ≈ 1,680. | Temperature (r_m /day) | Day 7 | Day 14 | Day 21 | Day 28 | |---|---|---|---|---| | 20 °C (0.153) | 29 | 85 | 249 | 725 | | 25 °C (0.355) | 120 | 1,440 | 17,285 | 207,437 | | 28 °C (0.244) | 55 | 304 | 1,680 | 9,270 | | 30 °C (0.019) | 11 | 13 | 15 | 17 | **Upper bound only.** The model assumes unlimited food, no predators, no disease and no winged emigration. Real colonies slow as plants decline and aphids crowd. The lesson holds: at 25 °C, three weeks without scouting turns a few aphids into thousands. ## Where does the cannabis aphid hide, how does it spread, and how does it get in? The cannabis aphid gets into a clean indoor facility almost only on Cannabis plant material carrying live aphids, because it develops on no other host and starves within a few days without one [3]. Clones, mother plants and transplants are the main vector. **Hiding places.** Leaf undersides, stems, and later maturing flowers and leaflets [2][3]. Eggs, when laid, go on stems, flower buds and seed capsules [3][5]. **Winged dispersal.** Winged forms disperse over long distances and most readily colonise new plants [3]. They are weak fliers carried by winds above about 3 mph (1.3 m/s); greenhouse airflow largely controls where they settle [3]. **Outdoors to indoors.** Outdoor fields and volunteer hemp carry the aphid into nearby propagation areas. Overwintering eggs survive on crop debris and hatch onto volunteer seedlings in spring [2][3]. **Clothing and pets.** No published data were found. Because the aphid starves quickly and walks slowly, people moving from infested outdoor plants to clean rooms are a plausible but minor route (Grower practice: visit clean rooms first). **[Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md).** Hold new plant material separately for several weeks and inspect it for honeydew droplets, cast skins, live aphids and winged aphids on sticky traps before it joins clean stock [3]. ## How do I scout for cannabis aphid? Scout for cannabis aphid by looking for honeydew droplets and cast skins on leaf tops, then inspecting leaf undersides and stems directly above them [3]. Check mother plants and clones weekly at minimum, and twice weekly in rapid growth (Grower practice; UC IPM gives twice weekly for aphid-prone plants, see [Aphids](https://genetixbay.com/knowledge/pests/aphids.md)). **Lens.** 10-20x to confirm aphids, cast skins and mummies; 40-60x microscope to separate cannabis aphid from hop aphid [5]. **[Sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md).** Yellow sticky traps capture winged cannabis aphids and show when winged forms disperse; distinguishing them from fungus gnats and parasitoid wasps needs magnification [3]. Place cards near, not touching, plants [7]. **After the flip.** Watch for colour change to pink or brown and for winged males: they signal sexual forms and possible eggs [3]. **Threshold.** No action threshold has been researched for hemp [5]. Indoors, act on the first confirmed colony (Grower practice). ## How do I control the cannabis aphid by life stage? Control the cannabis aphid by attacking nymphs and adults with contact tactics and natural enemies under long days, and by removing eggs and debris once short days have produced sexual forms [3]. Indoors under long days, there is no egg stage to shelter survivors. **Nymphs and adults.** Remove infested leaves into a bag; squash small colonies. Insecticidal soaps (potassium salts of fatty acids), pyrethrins and azadirachtin are among the materials with aphid activity allowed on cannabis in some US states [3]. Greenhouse Canada reports insecticidal soap as the most effective registered option in Canadian production, needing thorough coverage of leaf undersides [7]. **Re-application interval.** Newborn nymphs that survive a spray begin reproducing in 6.4 days at 25 °C and 11 days at 20 °C [4]. Re-spray every 5-6 days at 25-28 °C, or every 7-9 days at 20-22 °C, for at least three applications, in veg only. **Eggs.** No published data on egg mortality from sprays were found. Remove all plant debris after harvest, because eggs are laid on Cannabis tissue [3]. **Room clear-out.** Removing all Cannabis plants from a room should kill all remaining aphids within a few days, since both winged and wingless forms starve quickly [3]. **Resistance.** No published insecticide resistance data were found for the cannabis aphid. Its clonal reproduction means any resistant female founds a uniform resistant colony. Rotate [modes of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md) by IRAC group, and see [Aphids](https://genetixbay.com/knowledge/pests/aphids.md) for the resistance record of green peach aphid. Registrations on cannabis vary by jurisdiction; follow the label and local law. **Fungi.** *Isaria fumosorosea* and *Beauveria bassiana* infect aphids; relatively high humidity is essential to their effect [3]. ## What biological control works on the cannabis aphid? Biological control of the cannabis aphid outdoors comes mostly from native lady beetles, lacewings, hover flies and the midge Aphidoletes, which in Colorado built up enough to control late-season outbreaks [2][3]. Indoors those enemies are absent unless released, and no parasitoid has yet been proven in peer-reviewed trials [3][8]. **Field enemies.** Convergent lady beetle (*Hippodamia convergens*) and multicoloured Asian lady beetle (*Harmonia axyridis*) were most important in Colorado, with at least four other lady beetle species, three green lacewings, at least four syrphid species and *Aphidoletes aphidimyza* [2]. Braconid parasitism and fungal infection were observed only infrequently [2]. **Purchased predators for indoor use.** Colorado State lists green lacewings (sold as eggs), the aphid predatory midge and convergent lady beetle as among the more effective [3]. Field-collected lady beetles arrive semi-dormant and may take weeks to lay eggs [3]. Greenhouse Canada reports that green lacewings did not control infestations and that Aphidoletes is not recommended in Canadian cannabis production [7]. *Contested*. ### Parasitoids: what the evidence says | Parasitoid | Evidence on cannabis aphid | Label | |---|---|---| | *Aphidius matricariae* | Trade press: shown effective against cannabis aphid specifically, with more quantitative study needed for other parasitoids [14]; named with A. colemani as the most successful by Greenhouse Canada, but tends to leave greenhouses in warm months [7] | *Supported* (industry) | | *Aphidius colemani* | Named among the most successful [7]; stays while suitably sized aphids are present [7]; one trade article calls it less effective than A. matricariae on this aphid [14]; development 10 d at 25 °C on other hosts | *Contested* (industry) | | *Aphidius ervi* | Sold for aphids generally; Colorado State lists it as available [3] | *Grower practice* | | *Aphelinus varipes* | 3% parasitism of cannabis aphid nymphs in a 2025 lab study; may be the first record on a *Phorodon* species [8] | Research only | | Unidentified braconids | Seen attacking cannabis aphid in Colorado; species not determined [2][3] | *Established* (observation) | **Bottom line.** Is *Aphidius colemani* effective against cannabis aphid? Industry sources disagree, and no published trial settles it [7][14]. *A. matricariae* has the stronger trade-press support [14]. A mixed release of both, made early and checked by counting mummies after 10-14 days, is the cautious choice (Grower practice). **Release rates.** No cannabis-aphid-specific rates are published. Biocontrol supplier technical sheets for A. colemani give 0.25 wasps/m² every 1-2 weeks preventively, and 0.5-2 wasps/m² weekly for at least three releases after detection [13]. Greenhouse Canada reports weekly or biweekly re-releases being needed when prey is scarce [7]. **Climate.** A. colemani works from 15 °C, best at 18-25 °C and 60-80% RH (supplier sheet [13]); parasitoids generally prefer 70-85% RH [10]. **Aphidoletes and 12/12.** Aphidoletes larvae need about 15.5 h of light to avoid diapause [10]; one strain did not diapause at 25 °C or above at any day length [12]. Night-break lighting is not an option in a flowering room. See [Aphids](https://genetixbay.com/knowledge/pests/aphids.md). **[Predator:prey ratio](https://genetixbay.com/knowledge/glossary/predator-prey-ratio.md).** No published ratio for cannabis aphid was found. ## How can the environment be used against the cannabis aphid? The environment slows the cannabis aphid most in propagation, where cooler rooms at 20-22 °C stretch its doubling time from 2 days at 25 °C to about 4.5 days at 20 °C [4]. That buys scouting time but does not replace control. **Mother and clone rooms.** Keep them at 20-22 °C and 60-70% RH: slower aphids, better parasitoid humidity [4][10]. **Do not run hot.** Lab data show the cannabis aphid collapsing at 30 °C [4], but plants, parasitoids and beneficials suffer there too, and cotton aphid thrives. See [Heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md). **Airflow and screening.** Winged aphids ride air above about 3 mph [3]; filtered intakes and positive pressure keep outdoor migrants out. **Break the host chain.** The aphid lives only on Cannabis. Remove volunteer hemp near outdoor plots, clean up crop debris after harvest, and avoid overlapping old and new crops [2][3][5]. **Nitrogen.** USU advises avoiding excess nitrogen [6] (Grower practice for aphids generally). **Flower trade-off.** Do not raise flower humidity above 45-55% RH to help fungi or parasitoids; [botrytis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) risk outweighs the gain. ## What should I not do about cannabis aphids in flower? In flower, do not spray soaps, oils, pyrethrins or neem products onto buds; residues stay on harvested flower and wet buds invite bud rot. Release beneficials before or at the flip, remove infested branches, and cut out honeydew-coated buds. **Expect sexual forms.** After the flip to 12/12, the cannabis aphid can produce winged males and egg-laying females [3]. Eggs on stems and buds can end up in harvested flower [2]. **Clean thoroughly after harvest.** Remove all plant debris and leave the room empty for several days before restocking [3]. **No systemics, no night-break lights.** Systemic insecticides are not registered on cannabis in most places. Night-break lighting disrupts flowering. ## What are the common myths about the cannabis aphid? Common cannabis aphid myths are about identity, reinfestation, parasitoids and eggs. - **"Cannabis aphids are just green peach aphids."** *Myth.* It is a distinct, Cannabis-only species [1][3]; mistaking it can lead to a less suitable parasitoid [14]. - **"Weeds outside will reinfest a clean room."** *Myth.* It develops only on Cannabis and starves within days without it; reinfestation comes from Cannabis plant material [3]. - **"Aphidius colemani is proven against cannabis aphid."** *Contested.* One industry report names it among the most successful [7], another calls it less effective than A. matricariae [14]; no peer-reviewed greenhouse trial was found, and Colorado State could not name the parasitoid species seen in the field [3]. - **"Eggs only happen outdoors."** *Myth.* Short-day lighting indoors can trigger sexual forms and eggs [3]. - **"Indoor eggs survive indefinitely."** *Contested.* USU states eggs survive better indoors [6]; Colorado State says egg survival indoors at warm temperatures is unknown [3]. ## Common mistakes - Treating it as green peach aphid and buying the wrong parasitoid [14]. - Skipping quarantine on clones from another facility [3]. - Leaving plant debris and old mother plants in the room after harvest [3]. - Waiting for numbers to build: doubling time is 2 days at 25 °C [4]. - Missing the colour change to pink or brown after the flip [3]. ## Evidence - Host specificity, Colorado biology, holocycle on the crop: *Established* in extension and review literature [1][2][3][5]. - Life table on hemp at 20-30 °C: *Supported*, one lab study [4]. - Short-day sexual forms indoors: *Supported*, extension observation [3]. - Parasitoid efficacy: *Grower practice* and industry reports [7][14]; peer-reviewed data minimal [8]. - Action threshold: none researched [5]. ## Sources 1. Cranshaw WS, Halbert SE, Favret C, Britt KE, Miller GL. 2018. Phorodon cannabis Passerini (Hemiptera: Aphididae), a newly recognized pest in North America found on industrial hemp. Insecta Mundi 0662:1-12. https://journals.flvc.org/mundi/article/view/0662 2. Cranshaw W, Schreiner M, Britt K, Kuhar TP, McPartland J, Grant J. 2019. Developing insect pest management systems for hemp in the United States: a work in progress. Journal of Integrated Pest Management 10(1):26. https://doi.org/10.1093/jipm/pmz023 3. Colorado State University. 2018. Pest Management of Hemp in Enclosed Production: Cannabis Aphid (Phorodon cannabis). https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Cannabis%20Aphid%20Management_.pdf 4. Durak R, Jedryczka M, Czajka B, Dampc J, Wielgusz K, Borowiak-Sobkowiak B. 2021. Mild abiotic stress affects development and stimulates hormesis of hemp aphid Phorodon cannabis. Insects 12(5):420. https://doi.org/10.3390/insects12050420 5. Pulkoski M, Burrack H. 2020. Cannabis Aphid in Industrial Hemp. NC State Extension. https://content.ces.ncsu.edu/cannabis-aphid-in-industrial-hemp 6. Utah State University Extension. Cannabis Aphids. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-cannabis-aphid.php 7. Reeves A. 2022. Cannabis aphids on the rise. Greenhouse Canada. https://www.greenhousecanada.com/cannabis-aphids-on-the-rise/ 8. Ong M, Su C, Yaqub S, Feng A, Buirs L, Gries G. 2025. Rice root aphids, Rhopalosiphum rufiabdominale, and cannabis aphids, Phorodon cannabis, are parasitised by Aphelinus varipes. The Canadian Entomologist 157:e39. https://doi.org/10.4039/tce.2025.10024 9. Bas FH, Ozgokce MS. 2026. Life table and development parameters of green peach aphid Myzus persicae at six different temperatures on pepper. Plant Protection Science 62(3):252-267. https://doi.org/10.17221/96/2025-PPS 10. UConn IPM. Biological Control of Aphids. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-aphids/ 11. McPartland JM, Clarke RC, Watson DP. 2000. Hemp Diseases and Pests: Management and Biological Control. CABI Publishing, Wallingford, UK. 12. Dai X, Wang Y, Liu Y, et al. 2024. Molecular correlates of diapause in Aphidoletes aphidimyza. Insects 15(5):299. https://doi.org/10.3390/insects15050299 13. Biocontrol supplier technical sheet: Aphidius colemani (2022). 14. Cannabis Business Times. Axe aphids with biological controls (trade article). https://www.cannabisbusinesstimes.com/pests/aphids/article/15693525/axe-aphids-with-biological-controls --- # Caterpillars on cannabis: species, degree-days and control > Caterpillars on cannabis are mostly an outdoor, late-season problem: corn earworm budworms bore into colas and start bud rot, European corn borer and Eurasian hemp borer tunnel stems and buds, and armyworms and loopers chew leaves. Each species has a degree-day clock (lower thresholds about 10-14 C), so trap the moths, scout for eggs and hatchlings, exclude moths with netting, and use Bt or other biologicals on newly hatched larvae before they bore in. - Canonical: https://genetixbay.com/knowledge/pests/caterpillars.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Veg, Transition, Flower, Ripening · Systems: Soil, Living soil, Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What caterpillars attack cannabis?** The main caterpillars on outdoor cannabis and hemp in North America are the corn earworm (Helicoverpa zea), which bores into buds, the European corn borer (Ostrinia nubilalis) and Eurasian hemp borer (Grapholita delineana), which tunnel stems and buds, and leaf-chewers such as beet armyworm and cabbage looper. Tobacco budworm joins corn earworm in the Southeast. Indoors, caterpillars are uncommon and arrive through open vents or doors. **Why is there brown mush inside my cola?** Brown mush inside a cannabis cola is bud rot, and if dark frass pellets and tunnels are present a caterpillar started it, usually a corn earworm budworm. Larvae bore into the bud and their wounds and frass let Botrytis in, so the loss is often more rot than chewing. Rot without frass is plain bud rot. Cut out the damaged section with a margin and bag it. **When is Bt most effective on caterpillars?** Bt (Bacillus thuringiensis) is most effective on young caterpillars that are still feeding on the plant surface, because it must be eaten. Utah State advises using it on corn earworm larvae under about 12 mm (0.5 in), and stem borers such as European corn borer and hemp borer are exposed only for days after hatching. Bt often lasts under seven days in sunlight, so repeat it during flights. **What is a degree-day model for caterpillars?** A degree-day model adds up heat above a species' lower developmental threshold to predict hatch, larval stages and moth flights. Corn earworm needs about 422 Celsius degree-days above 12.6 C from egg to adult, cabbage looper about 440 above 10 C, and beet armyworm about 490 above 12.2 C. European corn borer flights in Vermont start near 374 Fahrenheit degree-days, base 50 F. **How fast do caterpillars develop on cannabis?** At a steady 25 C, corn earworm takes about 34 days from egg to adult, beet armyworm about 27 days on sugar beet in the lab, and cabbage looper about 29 days, based on UC IPM degree-day models and published life tables. At 20 C the same generations take roughly 44 to 63 days. These are crop and lab figures; no cannabis-specific development study has been published. **When should I spray for European corn borer in hemp?** For European corn borer in hemp, University of Vermont Extension advises targeting newly hatched caterpillars before they bore into stems, typically mid-June in the Northeast, and suggests treating if 15% or more of plants show larvae or fresh feeding, rechecking after 4 to 7 days. Egg laying begins at about 450 Fahrenheit degree-days, base 50 F. Follow the label and local law. **Do Trichogramma wasps work on cannabis caterpillars?** Trichogramma egg parasitoids work against European corn borer in corn, where Cornell and UConn trials with Trichogramma ostriniae at 30,000 to 120,000 wasps per acre gave 65 to 100% egg mass parasitism. That species gives little control of corn earworm, which needs Trichogramma pretiosum. No release rates have been established for hemp, so treat it as promising but unproven in cannabis. **Do I need to spray loopers and armyworms on cannabis?** Usually not. The Pacific Northwest Insect Management Handbook says damage from caterpillars other than corn earworm, such as cabbage looper and alfalfa looper, is usually minor on mature hemp and generally does not require control. Loopers and armyworms chew ragged holes in leaves; a healthy plant tolerates moderate leaf loss. Act when young plants are being stripped or larvae move into flowers. **Can netting keep caterpillars off cannabis?** Yes. Fine insect netting over outdoor plants, or screened vents and doors on greenhouses, keeps the egg-laying moths off cannabis entirely, which no spray can match. It is grower practice with little cannabis-specific research, but strong in principle because every caterpillar starts as an egg laid by a flying moth. Fit netting before the first flowers and before local moth flights start. **Is there a treatment threshold for caterpillars on hemp?** There is no established treatment threshold for corn earworm in hemp, according to Colorado State, Utah State and the Pacific Northwest handbook. For European corn borer, University of Vermont Extension suggests a working threshold of 15% of plants with larvae or fresh feeding. For other caterpillars, growers act on what they find while scouting, combined with pheromone trap counts that show moth flights. **Short answer.** If a cola has a brown, dead patch with dark crumbs (frass) inside, a caterpillar bored in and bud rot followed; outdoors in North America it is usually the corn earworm. Stem borers (European corn borer, Eurasian hemp borer) wilt and swell stems; loopers and armyworms chew leaves. All of them start as eggs laid by night-flying moths, all run on a degree-day clock, and all are only reachable for a few days after hatch. Trap the moths, scout for eggs and hatchlings, net the plants where you can, and use Bt on small larvae. The main bud-boring species has its own deep article: [Budworms: corn earworm and tobacco budworm](https://genetixbay.com/knowledge/pests/budworms-corn-earworm.md). ## Which caterpillars attack cannabis? Five groups of caterpillars matter on cannabis and hemp in North America, and they split by where they feed. Bud borers ruin flowers; stem borers weaken and wilt shoots; leaf chewers mostly cost leaf area. | Species | Family | Feeds on | Importance on cannabis | Source | |---|---|---|---|---| | Corn earworm, *Helicoverpa zea* | Noctuidae | Flowers, inside colas; seed heads | Key outdoor pest in the US; bud rot follows | [1][2][3] | | Tobacco budworm, *Chloridea (Heliothis) virescens* | Noctuidae | Flowers | Listed for hemp; mixed with corn earworm in the Southeast | [6] | | European corn borer, *Ostrinia nubilalis* | Crambidae | Stems, petioles, buds | Stem breakage and wilt, worst near corn; Northeast and Midwest | [8] | | Eurasian hemp borer, *Grapholita delineana* | Tortricidae | Stems and flower buds | Specialist on hemp; eastern Colorado and elsewhere; late-summer generation most damaging | [7] | | Beet armyworm, *Spodoptera exigua* | Noctuidae | Leaves, sometimes flowers | Leaf chewer of warm regions (no hemp-specific damage data found) | [10][12] | | Cabbage looper, *Trichoplusia ni*; alfalfa looper | Noctuidae | Leaves | Usually minor on mature hemp; generally no control needed | [6] | | Others: bertha armyworm, spotted cutworm, false corn earworm | Noctuidae | Leaves, flower buds | False corn earworm recently found on buds in southern Oregon | [6] | Indoors, caterpillars are uncommon. They arrive as moths through unscreened intakes, roof vents or doors left open at dusk, or as larvae on branches brought in from outside. The glossary entry is [caterpillar](https://genetixbay.com/knowledge/glossary/caterpillar.md); for the main budworm see [corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md). ## How do I recognise caterpillar damage on cannabis? Caterpillar damage on cannabis shows as chewed holes, frass (dark, granular droppings) and dying tissue, and the pattern tells you which group you have. - **Bud borers (corn earworm, tobacco budworm).** Brown, wilted or dead sections of a cola, sometimes a single dead sugar leaf poking out of a bud; dark frass inside the bud and on leaves below; larvae up to 25 mm, mostly green on hemp, striped along the body [1][3]. - **European corn borer.** Bored holes and stem wounds, sawdust-like frass at the hole, wilting above the entry; larvae light grey to faint pink with a dark head and dark spots, up to about 25 mm [8]. - **Eurasian hemp borer.** Stem swelling, wilting, dieback and protruding frass; late larvae red-orange and small, 6-8 mm when grown [7]. - **Loopers and armyworms.** Ragged holes and edges in leaves [6]; loopers walk with a looping arch. Leaf feeding rarely reaches buds. Differential: frass and tunnels mean caterpillar. Rot without frass is plain [bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md). Wilting with no hole may be a root or vascular problem; see [How to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md). ## Caterpillar life cycles in numbers Every caterpillar species on cannabis has a lower developmental threshold between about 10 and 14 °C and needs roughly 340-550 Celsius degree-days to go from egg to adult. Below are the best-documented values. None were measured on cannabis. | Parameter | Corn earworm | European corn borer | Beet armyworm | Cabbage looper | Eurasian hemp borer | |---|---|---|---|---|---| | Lower threshold | 12.6 °C [9] | 10 °C (50 °F) [8][19] | 12.2 °C (field model) [10]; 13.1 °C (r_m model) [12] | 10.0 °C [11] | no published value found | | Upper threshold | 33.3 °C [9] | no value verified | 32.2 °C (r_m model) [12] | 32.2 °C [11] | no published value found | | Egg to adult | 422.3 °C-DD [9] | ~556 °C-DD egg-to-egg (derived, see below) [8] | 490 °C-DD females, 543 males [10] | 439.7 °C-DD [11] | no published value found | | Egg to adult at 25 °C | ~34 days (model) | no value verified | 27.2 days (lab, sugar beet) [12] | ~29 days (model) | no published value found | | Egg to adult at 30 °C | ~24 days (model) | no value verified | 16.9 days (lab) [12] | ~22 days (model) | no published value found | | Eggs per female | up to 25-35/day; ~1,500 lifetime [1][6] | 200-500 over 2-3 weeks [8] | R0 377.7 female offspring at 25 °C [12] | no value verified | several hundred over a couple of weeks [7] | | r_m (/day) | no published value for *H. zea*; *H. armigera* 0.147 at 27.5 °C [13] | no value verified | 0.149 at 20 °C; 0.276 at 30 °C [12] | no value verified | no published value found | | Mean generation time T | no value verified | no value verified | 35.9 days at 20 °C; 15.1 days at 33 °C [12] | no value verified | no published value found | | Generations per year | 2-4 (Utah) [3] | 1-2 (Northeast), 3rd possible in Kentucky [8][19] | no value verified | no value verified | multiple, most damaging in late summer (Colorado) [7] | | Overwinters as | pupa in soil [1] | larva in crop debris [8] | no value verified | no value verified | grown larva in stems and seed-head leaf folds [7] | Sources and conditions: corn earworm from the USDA MOTHZV-2 field model (Texas) [9]; beet armyworm from a Californian cotton field model [10] and a lab life table on sugar beet leaves (Iran) [12]; cabbage looper from a lab artificial-diet model (Riverside, California) [11]; European corn borer from Vermont field degree-days [8]. The European corn borer egg-to-egg figure is derived, not measured: first eggs at about 450 °F-DD and second-generation first eggs at about 1,450 °F-DD (base 50 °F) give ~1,000 °F-DD, or ~556 °C-DD, per generation in Vermont [8]. Beet armyworm's two thresholds are not a contradiction: 12.2 °C is the developmental base of a field flight model [10]; 13.1 °C is where the fitted population growth rate reaches zero [12]. ## How do degree-day models time caterpillar flights? A degree-day model sums daily heat above a species' lower threshold, and stage transitions happen at fixed totals. For European corn borer in Vermont (base 50 °F, accumulated from early spring), first moths fly at about 374 °F-DD, egg laying begins at about 450 and peak flight is about 631; the second flight starts around 1,400, with eggs at 1,450 and hatch at 1,550 [8]. Corn earworm stage requirements above 12.6 °C are 40.5 °C-DD for eggs, 81.7 for small larvae (instars 1-3), 120.6 for large larvae, 179.5 for pupae and 62.6 for pre-oviposition adults [9]. Add up to the stage you care about. The useful one for spraying is egg plus small larvae: about 122 °C-DD, roughly 10 days at 25 °C. Calculation method matters. UC IPM uses the single-sine method with stated cutoffs; Kentucky's corn borer model counts degrees above 50 °F per 24 h from 1 January [9][19]. Use the method the model was built with, from a weather station near your field. Caveats: models were built on corn, cotton, beet or artificial diet; UC IPM advises testing any model for a season or more locally before relying on it [9]. Corn borer distributions are patchy, so regional data should not replace your own trap [8]. Migrant species (corn earworm in the north) arrive on the wind, so a degree-day clock started on 1 January predicts the local generation after they arrive, not the arrival itself. See [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md) and [developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md). ## Why do temperature and humidity matter for caterpillars? Temperature controls how fast caterpillars cycle and how long the vulnerable surface-feeding window lasts. Beet armyworm on sugar beet leaves took 27.2 days from egg to adult at 25 °C and 16.9 days at 30 °C; its intrinsic rate of increase rose from 0.149/day at 20 °C to 0.276/day at 30 °C; no development occurred at 12 or 36 °C [12]. Heat speeds things up only to a point. For *Helicoverpa armigera*, the closest well-studied relative of corn earworm, r_m peaked at 27.5 °C (0.147/day), constant temperatures outside 17.5-32.5 °C prevented development to adult, and adult life fell from 34.4 days at 15 °C to 7.6 days at 35 °C [13]. Alternating day-night temperatures widened the survivable range to 10-35 °C, which is why field populations tolerate hot afternoons [13]. Humidity mostly works through the plant. Larval frass and tunnels inside dense colas, plus wet, cool autumn nights, turn caterpillar wounds into Botrytis bud rot [2][5]. Indoor flower set-points (22-26 °C, 45-55% RH, 40-50% in late flower) are comfortable for caterpillars, so indoors you exclude them rather than climate them out. Diapause decides who survives winter. Corn earworm overwinters as a pupa in soil only where winters are mild (central and southern Utah, not northern) [3]; European corn borer and hemp borer overwinter as larvae in plant residue [7][8]. That is why residue removal works on the borers and not on migrant earworms. ## How fast can a caterpillar population grow? A caterpillar population on cannabis grows mainly by moths flying in, not by local generations, because one generation takes 17-57 days depending on species and temperature [9][12]. Still, life-table r_m values show why warm late summers are dangerous. Method: N(t) = N0 × e^(r_m × t), doubling time = ln 2 / r_m. Start with 10 beet armyworm eggs on sugar beet leaves (lab, constant temperature) [12]. | Temperature | r_m (/day) | Doubling time | After 21 days | After 42 days | |---|---|---|---|---| | 20 °C (68 °F) | 0.149 | 4.7 days | ~229 | ~5,200 | | 30 °C (86 °F) | 0.276 | 2.5 days | ~3,300 | ~1,080,000 | | 27.5 °C (*H. armigera* proxy for corn earworm) | 0.147 [13] | 4.7 days | ~219 | ~4,800 | This is the unchecked exponential upper bound: no predators, parasitoids or disease, unlimited food, and a population already at stable age distribution. Real outdoor numbers are far lower. The practical point: 10 °C of extra warmth roughly halves beet armyworm doubling time. In flower, what counts is not the 42-day projection but how many eggs hatch into larvae that reach the inside of a bud before you find them. ## Where do caterpillars come from and how do they get in? Caterpillars on cannabis come from eggs laid by moths that fly in at night, from corn, weeds, vegetable crops and wild or feral hemp. Corn earworm migrates north each year and leaves maturing corn in large flights; Virginia catches peaked around mid-August with moths emerging from cornfields [3][20]. European corn borer may shift to other hosts when corn planting is delayed, and crops near corn are at higher risk [8]. Eurasian hemp borer is a weak flier, so heavy infestations appear near wild hemp or fields grown to hemp in previous years, and infestations usually begin at field edges [7]. Drying sheds can act as overwintering sites; CSU advises siting them at least half a mile from crops [7]. Clones are not the usual vector, but harvested or transplanted material can be. Larvae ride on branches into drying rooms and keep feeding (Grower practice). Hemp borer larvae overwinter in stems and seed-head leaf folds, so moving residue moves them [7]. Indoors and in greenhouses, the entry points are unscreened vents and doors during late-summer flights. Lit greenhouses at night attract moths (Grower practice). ## How do I scout for caterpillars? Scout cannabis for caterpillars weekly from early flower to harvest, and twice weekly during moth flights. Check the upper third of colas, bracts and pistils for single pale eggs, 2 mm hatchlings, small holes and frass [1][3]. Check stems for swelling, entry holes and sawdust-like frass, and leaf top and underside on low and high parts of the plant for borer eggs [7][8]. A 10x lens shows eggs; larvae are visible by eye. ### How do pheromone traps help with caterpillars? Pheromone traps catch male moths of one species and tell you when a flight has started, so you know when to scout harder and when to time Bt. They do not control anything [1][8]. - **Corn earworm:** one Heliothis-type net trap with a corn earworm lure at the field border by late July or early August; check twice weekly; change the lure every two weeks; keep it to harvest [1]. Utah State starts in July and checks every 3-5 days [3]. - **European corn borer:** two Heliothis-type net traps at least 50 ft apart along the field edge, the trap bottom above grassy weeds and no more than about 4 in above the vegetation, not over bare ground. Bait one with each strain's lure (New York and Iowa strains occur in New England). Check once or twice a week and change lures every other week [8]. - **Eurasian hemp borer:** CSU does not list a trap; it suggests scouting for moths, sweep netting, and black lights [7]. Light traps (black-light traps) catch adults of many moth species at once. They are useful for monitoring and confirming activity but costly and unselective [7]; they are not a control. ### What are the action thresholds for caterpillars? There is no established treatment threshold for corn earworm in hemp [3][6]. For European corn borer, University of Vermont Extension suggests treating if 15% or more of plants have larvae or fresh feeding damage, and treating again if infestation is still above 15% after 4-7 days [8]. That figure is a working extension threshold, not a cannabis economic threshold. For loopers and armyworms on mature plants, the PNW handbook says control is generally not needed [6]. See [action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md), [scouting](https://genetixbay.com/knowledge/glossary/scouting.md) and [sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md). ## How do I control caterpillars at each life stage? Caterpillar control is a race to the hatchling: eggs and first instars on the plant surface are reachable, larvae inside stems or colas mostly are not [3][7][8]. Match the tactic to the stage. | Stage | What works | Notes | |---|---|---| | Egg | *Trichogramma* egg parasitoids; generalist predators; hand removal of egg masses (corn borer) | Species-matched wasps only [15][17] | | Newly hatched larva on surface | Bt (IRAC 11A), NPV for Helicoverpa (IRAC 31), spinosyns (IRAC 5) where registered | Must be eaten; full bud and stem coverage [2][14] | | Larva inside stem or bud | Cut out and bag; hand-pick bud borers at dusk or dawn | Sprays largely fail once inside [7][8] | | Overwintering larva/pupa | Remove and destroy residue; tillage where allowed | Strong for borers, weak for migrant earworm [7][8] | | Moth | Exclusion netting, screened vents; traps for timing | [1] | ### Why does Bt work best on young larvae? Bt (*Bacillus thuringiensis*) is a stomach poison: the larva must eat a crystal protein toxin; IRAC classes it as a microbial disruptor of insect midgut membranes [18]. It therefore works best on young caterpillars that feed on treated surfaces, and poorly on large larvae that feed inside tissue [3][14]. Utah State advises Bt only on corn earworm under about 12 mm (0.5 in) [3]. The instar window is short. For corn earworm, first to third instars take about 82 °C-DD above 12.6 °C, about 6.6 days at 25 °C [9]. European corn borer larvae feed on leaves for about a week before boring into stems [8]. Eurasian hemp borer larvae are exposed only briefly after hatching, so CSU says applications must be timed to egg hatch [7]. Strain matters. In Virginia lab bioassays on hemp, kurstaki-strain Bt killed 32.5-35% of field-collected third-instar corn earworm in four days and an aizawai-plus-kurstaki product 67.5%; the authors blame widespread Cry1Ab resistance in field populations [14]. For corn earworm see the [budworm article](https://genetixbay.com/knowledge/pests/budworms-corn-earworm.md). Residual is short: Bt often lasts under seven days on plants in sunlight [1]. Virginia Tech advises reapplying every 2-3 days, early morning or late evening, during heavy pressure [2]. Glossary: [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md). ### How often should caterpillar treatments be repeated? Repeat caterpillar treatments at an interval shorter than egg hatch time plus the surface-feeding window, and within the product's residual, for as long as moths are flying. For corn earworm at 25 °C that is egg about 3.3 days plus small larvae about 6.6 days [9], against Bt residual under seven days [1]: twice weekly in a flight, as Oregon State suggests [1]. For European corn borer, Vermont's 15% re-check after 4-7 days [8] works because larvae spend about a week feeding on leaves before boring in. At cooler late-season temperatures, development slows (corn earworm egg plus small larvae is about 16 days at 20 °C) [9], so product breakdown, not hatching, sets the interval. ### Which product classes are used, and how do I rotate? Rotate caterpillar controls by IRAC mode-of-action group, never repeat one group through a whole flight, and use only what is registered on cannabis or hemp where you grow. Follow the label and local law. No brands or rates are given here [18]. | Class | IRAC group | Notes on cannabis | |---|---|---| | *Bacillus thuringiensis* (kurstaki, aizawai) | 11A | Most widely permitted biological on hemp; short residual; strain choice matters [2][14] | | Baculoviruses (Helicoverpa NPV) | 31 | Species-specific; slow kill on large larvae [14] | | Spinosyns | 5 | Best kill in Virginia tests but not legal on hemp in Virginia at the time [2][14] | | Diamides | 28 | Major field-crop class against caterpillars; no cannabis registration data found | | Pyrethrins / pyrethroids | 3A | Resistance widespread in corn earworm in parts of the US (see budworm article) | | Azadirachtin (neem extract) | UN | Unknown or uncertain mode of action per IRAC [18] | The *Beauveria bassiana* fungus was tested on hemp in Virginia and did not give effective control of corn earworm alone [2]. Resistance in caterpillars is inherited from field-crop selection on huge, mobile populations. A home or craft grower cannot create much of it, but can waste a season using a class the local population already shrugs off. Glossary: [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md), [pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md). ## Which natural enemies control caterpillars? Caterpillars on outdoor cannabis are attacked by big-eyed bugs, damsel bugs and lady beetles (eggs and small larvae), *Trichogramma* egg parasitoids, and larval parasitoids such as the tachinid fly *Archytas marmoratus* and the braconid wasp *Microplitis croceipes*; their role on hemp is not fully investigated [6]. Spiders, lacewings and birds add to it. Broad-spectrum sprays remove all of them. ### How do Trichogramma releases work? *Trichogramma* wasps lay their eggs inside moth eggs, preventing them from hatching [8]. They are bought as parasitized host eggs on cards and released when moths begin laying, within a week of the start of the flight [8]. They do not overwinter well and must be released each season [15]. For European corn borer, *Trichogramma ostriniae* has the best data. Cornell lists 30,000-60,000 wasps per acre over three weekly releases in sweet corn and 100,000-120,000 per acre in peppers and potatoes; there are no established rates for hops or hemp [15]. New York trials (UConn summary) gave 80-100% parasitism in most inundatively released fields at 120,000 per acre, and 65% average egg-mass parasitism from a single inoculative release of 30,000 per acre [16]. Dispersal and temperature: highest parasitism within about 100 ft of release points, so release points about 100 ft apart; ideal development 82-91 °F (28-33 °C); reduced parasitism in prolonged cool, rainy weather [15]. Wasps moved up to 340 ft and persisted up to 30 days in New York trials [16]. Species matter. *T. ostriniae* gives little or no substantial parasitism of corn earworm eggs [15]. For corn earworm, three releases of 100,000 *T. pretiosum* per hectare in Brazilian corn raised egg parasitism up to fivefold and cut ear damage by 26% [17]. Compatibility: Bt and NPV are compatible with *Trichogramma* (Grower practice; supplier technical sheets agree). Broad-spectrum contact insecticides are not. Glossary: [parasitoid](https://genetixbay.com/knowledge/glossary/parasitoid.md), [biological control](https://genetixbay.com/knowledge/glossary/biological-control.md). ## Can I use the environment against caterpillars? The most powerful environmental tool against caterpillars is a physical barrier: fine insect netting outdoors, or screened vents and doors on greenhouses and light-dep houses, keeps egg-laying moths off the plants entirely (Grower practice; strong in principle, little cannabis research). Fit it before flowering and before local flights. Timing: plant date, transplant timing and light-deprivation scheduling can move flowering away from the local peak flight. Transplanting early lets seedlings harden before pests arrive [8]. Your own trap records are the best guide [3]. Site and sanitation: plant away from corn and from last year's hemp ground; remove and destroy stems and stalks after harvest to kill overwintering hemp borer and corn borer larvae; remove wild hemp nearby; work residue into soil where allowed [7][8]. Keep weeds down, since they host first-generation borers and leaf-feeders [8]. Climate indoors: caterpillars tolerate any set-point cannabis tolerates. Indoors, the levers are screens, door discipline and quarantine of outdoor material, not temperature or humidity. Trade-off: netting slightly raises humidity and reduces airflow around colas, which matters for Botrytis in wet autumns. Keep netting off the plant surface and open it on dry, sunny days if pressure allows. ## What should I not do for caterpillars in flower? Do not use broad-spectrum synthetic insecticides on flowering cannabis; most are not registered on cannabis and residues fail testing. Follow the label and local law. Do not spray once and assume protection; Bt breaks down within days in sunlight [1]. Do not spray Bt at large larvae inside colas or stems and expect a kill; it must be eaten [3]. Do not spray late in the day in a way that leaves buds wet overnight in cool weather; that feeds bud rot [5]. Do not leave damaged bud sections on the plant; cut a margin of clean tissue around them and bag them [5]. Do not leave infested stalks in or near the field over winter; that is where borers wait for spring [7][8]. ## What are the common myths about caterpillars on cannabis? - **"Bt kills caterpillars on contact."** *Myth.* Bt must be eaten [3]. - **"Caterpillars are only an outdoor problem."** *Myth.* Greenhouses with open vents and indoor rooms with unscreened intakes get them (Grower practice). - **"Pheromone traps control moths."** *Myth.* They attract males only and serve for timing [1][8]. - **"Leaf holes in veg mean a ruined harvest."** *Myth.* Looper and armyworm feeding on mature hemp usually needs no control [6]. - **"Removing crop debris reduces next year's borers."** *Established.* Hemp borer and corn borer overwinter as larvae in residue [7][8]. - **"Trichogramma works on every caterpillar."** *Myth.* Species matching matters; *T. ostriniae* barely touches corn earworm [15]. ## Common mistakes - Waiting until buds rot to start scouting. - Spraying Bt on large larvae already inside buds or stems. - Buying the corn borer *Trichogramma* species for a corn earworm problem. - Running a degree-day model from a distant weather station or with the wrong calculation method. - Leaving last year's hemp stalks at the field edge. - Ignoring the rot that follows larvae and letting it spread in the drying room. ## Evidence - Species list and hemp damage: *Established* from multiple extension sources [1][3][6][7][8]. - Degree-day thresholds and requirements: *Established* on other crops and diets; *not validated on cannabis* [9][10][11]. - Life-table r_m values: *Supported*, lab data on sugar beet and diet [12][13]. - Bt, NPV and spinosyn efficacy on hemp: *Supported* by Virginia trials and bioassays [2][14]. - European corn borer 15% threshold: *Grower practice / extension guidance*, not a cannabis economic threshold [8]. - *Trichogramma*: *Established* for corn borer in sweet corn [15][16]; *Supported* for corn earworm in corn [17]; *untested* in cannabis. - Exclusion netting: *Grower practice*; little cannabis-specific research. ## Glossary terms used here - Glossary: [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [intrinsic rate of increase](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [doubling time](https://genetixbay.com/knowledge/glossary/doubling-time.md), [diapause](https://genetixbay.com/knowledge/glossary/diapause.md), [parasitoid](https://genetixbay.com/knowledge/glossary/parasitoid.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) ## Sources 1. Shrestha, G. 2022. Corn earworm management in hemp (EM 9626). Oregon State University Extension. https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 2. Kuhar, T., Britt, K., Doughty, H. 2019. Corn earworm pest problems on hemp and results of recent insecticide tests. Virginia Tech. https://ag-pest-advisory.vaes.vt.edu/corn-earworm-pest-problems-on-hemp-and-results-of-recent-insecticide-tests/ 3. Utah State University Extension. Corn Earworm (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-corn-earworm 4. Cranshaw, W. 2020. Hemp pests (CSU talk). https://webdoc.agsci.colostate.edu/bspm/InsectInformation/Talks2020/HempPests.pdf 5. Utah State University Extension. Hemp bud rot. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot 6. Pacific Northwest Insect Management Handbook. Hemp: caterpillars. https://pnwhandbooks.org/insect/agronomic/hemp/hemp-caterpillars 7. Colorado State University. Eurasian hemp borer, Grapholita delineana. https://agsci.colostate.edu/agbio/ipm-pests/eurasian-hemp-borer 8. University of Vermont Extension (SARE LNE16-348, ONE19-333). The European corn borer in hops and hemp. https://projects.sare.org/media/pdf/E/u/r/European-Corn-Borer-Hemp-Hops-factsheet-FINAL.pdf 9. UC IPM. Corn earworm phenology models. https://ipm.ucanr.edu/weather/phenology-models-description/corn-earworm-cotton-bollworm-tomato-fruitworm/ 10. UC IPM. Beet armyworm phenology model (Hogg & Gutierrez 1980). https://ipm.ucanr.edu/PHENOLOGY/ma-beet_armyworm.html 11. UC IPM. Cabbage looper phenology models (Toba et al. 1973; Butler et al. 1975). https://ipm.ucanr.edu/weather/phenology-models-description/cabbage-looper/ 12. Karimi-Malati, A., Fathipour, Y., Talebi, A.A., Bazoubandi, M. 2014. Life table parameters and survivorship of Spodoptera exigua at constant temperatures. Environmental Entomology 43(3): 795-803. https://doi.org/10.1603/EN11272 13. Mironidis, G.K., Savopoulou-Soultani, M. 2008. Development, survivorship, and reproduction of Helicoverpa armigera under constant and alternating temperatures. Environmental Entomology 37(1): 16-28. https://academic.oup.com/ee/article/37/1/16/547157 14. Britt, K.E., Kuhar, T.P. 2020. Laboratory bioassays of biological/organic insecticides to control corn earworm on hemp in Virginia, 2019. Arthropod Management Tests 45(1): tsaa102. https://doi.org/10.1093/amt/tsaa102 15. Cornell IPM. Trichogramma ostriniae biocontrol agent fact sheet. https://cals.cornell.edu/integrated-pest-management/outreach-education/fact-sheets/trichogramma-ostriniae-biocontrol-agent-factsheet 16. Seaman, A. 1999 (rev. 2012). Using Trichogramma and Bt for European corn borer control. UConn IPM. https://ipm.cahnr.uconn.edu/using-trichogramma-and-bt-for-european-corn-borer-control 17. Nogueira de Sá, L.A., Parra, J.R.P. 1993. Releases of Trichogramma pretiosum against Helicoverpa zea in corn. Scientia Agricola 50(3): 355-359. https://revistas.usp.br/sa/article/view/20130 18. IRAC. Mode of Action Classification (online). https://irac-online.org/mode-of-action/classification-online/ 19. Bessin, R. Predicting European corn borer development (ENTFACT-106). University of Kentucky. https://entomology.mgcafe.uky.edu/ef106 20. Kuhar, T., Britt, K. 2020. Corn earworm moth trap catch around Blacksburg, VA. Virginia Tech. https://ag-pest-advisory.vaes.vt.edu/?p=5110 --- # Fungus gnats: the watering problem with wings > Fungus gnats (Bradysia impatiens, B. coprophila) breed in constantly wet, organic, microbially active media. At about 25 C a generation takes roughly 17-22 days and the population can double about every 6 days (r_m 0.111/day). Larvae chew roots of seedlings and clones and can carry Pythium; adults do not. Dry the top of the medium, then use Bti, Steinernema feltiae, Stratiolaelaps scimitus or Dalotia coriaria, with yellow cards and potato slices to count. - Canonical: https://genetixbay.com/knowledge/pests/fungus-gnats.html - Category: Pests · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Flower · Systems: Soil, Coco, Living soil, Rockwool - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What are the little black flies in my grow?** Small dark flies that run over the growing medium and flit up when you water are almost always fungus gnats, usually Bradysia impatiens or B. coprophila. Adults are about 2-3 mm, grey-black, with long legs, long beaded antennae and a Y-shaped wing vein. Their larvae, up to about 6 mm with a shiny black head, live in the top few centimetres of moist, organic media. Stockier flies with spotted wings are shore flies. **Are fungus gnats harmful to cannabis?** Adult fungus gnats are harmless to cannabis, but their larvae chew root hairs and roots and tunnel into the stems of young cuttings. Damage is worst on seedlings, fresh clones and plugs in wet media, which wilt, stall or yellow. Mature plants in large containers rarely show damage. In lab studies larvae transmitted Pythium to seedlings, so a big larval population in propagation deserves action. **How long is the fungus gnat life cycle?** The fungus gnat life cycle (Bradysia impatiens) takes about 17-22 days from egg to adult at 24-25 C: eggs hatch in 3-4 days, four larval instars feed for 10-14 days and pupae last 3.5-4 days. At 12.8 C development takes about 49 days, and below about 10 C it stops. Adults live only about 6 days but each female lays roughly 75-200 eggs. **How fast do fungus gnats multiply?** Fungus gnats (Bradysia impatiens) multiply fastest at about 20-25 C, where the intrinsic rate of increase is 0.103-0.111 per day on rice bran in the lab. That means the population doubles roughly every 6-7 days. Ten gnats left unchecked at 25 C become about 100 in 3 weeks and about 1,000 in 6 weeks. At 16 C or 30 C growth is about half as fast. **How do I get rid of fungus gnats in soil or coco?** Get rid of fungus gnats by drying the top of the medium first: water less often but fully, and in soil let the top 2-5 cm dry. Then treat larvae: Bti drenches every 5-7 days for at least three rounds, or Steinernema feltiae nematodes every 14 days, or a preventive release of Stratiolaelaps scimitus mites. In coco and rockwool, which stay wet, rely on these biologicals. Count adults weekly on yellow cards. **Do fungus gnats cause root rot?** Fungus gnats do not cause root rot by themselves, but their larvae wound roots and can carry root-rot organisms. In lab tests, Bradysia impatiens larvae ingested Pythium aphanidermatum oospores and passed them to seedlings, with up to 65% transmission on filter paper but under 6% in potting mix. Adult gnats did not transmit Pythium. A gnat outbreak also signals the wet medium that favours rot. **What temperature kills fungus gnats?** No grow-room temperature kills fungus gnats without hurting the plant. Bradysia impatiens develops from about 10 C up to 32-35 C, and 32.2 C already damaged eggs, larvae and pupae in the lab. Its population grows fastest near 25 C, which is right in the cannabis veg and flower range. Control gnats through substrate moisture and biologicals, not air temperature. **Does Bti kill fungus gnat eggs and adults?** Bti (Bacillus thuringiensis subsp. israelensis) kills only feeding fungus gnat larvae, mostly young first-instar larvae, after they eat the toxin crystals. It does not kill eggs, pupae or adults, and it stays active in the medium for only about 2 days. That is why it is repeated every 5-7 days for at least three rounds, so each new cohort is hit while it is still feeding. **When should I use nematodes versus predatory mites for fungus gnats?** Use Steinernema feltiae nematodes when fungus gnat larvae are already numerous: they kill larvae in 1-2 days, stay active about 10-14 days and are reapplied every 2 weeks. Use Stratiolaelaps scimitus mites preventively at planting while numbers are low; they establish in the top 2.5 cm of medium and need at least about 14-15 C. Both work best in moist media. **Does a layer of sand stop fungus gnats?** A layer of sand or diatomaceous earth on the medium did not stop fungus gnats in published tests: adult emergence and egg laying were unaffected because the gaps between grains still let larvae pupate and females lay eggs. A thick layer of coarse recycled-glass aggregate reduced adult emergence over time. Drying the top of the medium works better than any cover. **Short answer.** Small dark flies running over the medium and flitting up when you water are fungus gnats, usually *Bradysia impatiens* or *B. coprophila* [4]. Adults are harmless and live about six days. The larvae eat root hairs and young roots, which hurts seedlings and fresh clones, and in lab tests they carried *Pythium* into seedlings [7]. At 25 C a gnat population can double about every 6 days [3]. The fix is the substrate, not the air: dry the top few centimetres between irrigations, then use Bti, *Steinernema feltiae* nematodes, *Stratiolaelaps scimitus* mites or *Dalotia coriaria* rove beetles, with yellow cards and potato slices to count. ## Fungus gnats at a glance: which numbers matter? The fungus gnat numbers that matter most are a 17-22 day generation at 24-25 C, a population doubling time of about 6 days near 25 C, and a lower developmental limit of about 10 C. Values below are for *Bradysia impatiens* unless stated; all come from lab rearing on artificial diets, not cannabis. | Parameter | Value | Conditions and source | |---|---|---| | Species in greenhouses | *Bradysia impatiens*, *B. coprophila* (and *B.* sp. nr. *coprophila*) | [4] | | Adult size | ~2-3 mm (1/16-1/8 in) | [8] | | Mature larva | up to ~6 mm (1/4 in), shiny black head | [8][9] | | Egg to adult | ~21.6 d (sum of stage means) | ~24 C (75 F), ground soybean diet [1] | | Egg to adult | ~17 d (egg 3, larva 10, pupa 4) | 75 F (24 C), extension summary [8] | | Egg to adult (females) | 21.4 d at 25 C; 93.3 d at 11 C | rice bran [3] | | Egg to adult | 48.8 d at 12.8 C; 19.9 d at 29.4 C; 19.2 d at 18.9-30 C fluctuating | [2] | | Lower / upper developmental limit | ~10 C / 32.2-35 C | constant temperatures [2] | | Degree-days per generation | no published value found | | | Adult longevity | ~5.9 d | ~24 C [1]; longest at 12.8 C [2] | | Lifetime fecundity | ~75 eggs/female (range 12-156) | 75 F (24 C) [1] | | Eggs laid in 48 h | 141 ± 9.3 (range 21-217) | *B.* sp. nr. *coprophila* in soilless media [12] | | Intrinsic rate of increase r_m | 0.103/day at 20 C; 0.111/day at 25 C | rice bran [3] | | Doubling time (ln2 / r_m) | ~6.7 d at 20 C; ~6.2 d at 25 C | calculated from [3] | | Sex ratio | no published value found for *B. impatiens* in the sources checked | sciarids have unusual chromosome systems [5] | | Bti activity in medium | ~2 days | [11] | | *S. feltiae* activity in medium | ~10-14 days; reapply every 2 weeks | [10][11] | | Dry-back for soil pots | top 2-5 cm (1-2 in) dry between waterings | Grower practice | ## What are fungus gnats and which species attack cannabis? Fungus gnats are small flies in the family Sciaridae; the species that matter in greenhouses and grow rooms are *Bradysia coprophila* and *Bradysia impatiens* [4]. They are flies with a full metamorphosis: egg, four larval instars, pupa, adult [1][8]. Fungus gnat larvae feed mainly on fungi and decaying plant matter. They also eat healthy roots, tunnel into the stems of young cuttings and seedlings, and feed in the crowns of mature plants [4]. A fungal food source appears critical for good development and reproduction [5]. Fungus gnats are a propagation pest. Problems are mostly tied to excessive moisture, which is normal while cuttings and plugs root [4]. Losses of 20-40% of plants in propagation have been reported in ornamentals [23] (*Supported* outside cannabis). No published study of fungus gnats on cannabis specifically was found. The biology here comes from ornamental crops and lab diets and is extrapolated to cannabis (*Supported*). Punja and colleagues recovered *Pythium* and *Fusarium* from roots of commercially grown cannabis, so anything that wounds roots in wet media matters [21]. ## How do I recognise fungus gnat adults and larvae? Fungus gnat adults are delicate grey-black flies about 2-3 mm long, with long slender legs, beaded antennae longer than the head, and a Y-shaped vein in clear to light-grey wings [8]. They fly weakly, run over the medium and rest on pots and leaves. Fungus gnat larvae are legless, translucent white to clear, up to about 6 mm long, with a shiny black head capsule [8]. They live in the top few centimetres of medium. In very wet, heavily infested pots they leave shiny slime trails on the surface [8]. **Plant signs.** Seedlings and clones in a wet medium wilt, stall, yellow or fail to root. Wilting with wet media is more often root rot or plain overwatering than gnats alone, so check roots [8]. See [kb-diagnosis-drooping-overwatering-vs-underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md). **Differential: shore flies.** Shore flies (*Scatella* spp.) are stockier, like tiny house flies, with short bristle-like antennae and about five pale spots on each dark wing. Their larvae are yellow-brown with no black head and feed on algae [8]. See [kb-pests-shore-flies](https://genetixbay.com/knowledge/pests/shore-flies.md). **Differential: root aphids.** Winged root aphids on cards look like small aphids, not flies, and wingless ones sit on roots covered in white wax. See [kb-pests-root-aphids](https://genetixbay.com/knowledge/pests/root-aphids.md). ## What is the fungus gnat life cycle in numbers? The fungus gnat life cycle (*Bradysia impatiens*) runs about 17-22 days from egg to adult at 24-25 C, slowing to about 49 days at 12.8 C and stopping below about 10 C [1][2][3][8]. Females start laying within a day of emerging if males are present [1]. ### How long does each stage last? At about 24 C (75 F) on a ground-soybean diet, Wilkinson and Daugherty measured these mean stage durations for *B. impatiens* [1]: | Stage | Mean duration (days) | |---|---| | Egg | 4.0 | | Larva I | 3.3 | | Larva II | 3.1 | | Larva III | 1.8 | | Larva IV | 5.9 | | Pupa | 3.5 | | Adult (longevity) | 5.9 | | Egg to adult (sum) | ~21.6 | Extension summaries give similar figures: eggs hatch in about 3 days at 75 F, larvae feed about 10 days and adults emerge about 4 days after pupation, for roughly 17 days egg to adult [8]. UConn gives 21-28 days egg to adult depending on temperature, with eggs hatching in 4-6 days and larvae feeding about 2 weeks at 72 F (22 C) [9]. Strains differ. Kennedy (1974) reported a *B. impatiens* strain that developed in 15.6 days at 25 C and was more fecund than the Wilkinson and Daugherty population (cited in [19]). ### How does temperature change fungus gnat development and growth? Fungus gnat development speeds up with heat until about 29 C and then fails; the population growth rate peaks near 25 C. These are the constant-temperature results for *B. impatiens*: | Temperature | Egg to adult (days) | r_m (/day) | Doubling time (days) | Source and conditions | |---|---|---|---|---| | 11 C | 93.3 (females) | 0.004 | ~173 | rice bran [3] | | 12.8 C | 48.8 | - | - | [2] | | 16 C | no value in abstract | 0.058 | ~12.0 | rice bran [3] | | 20 C | no value in abstract | 0.103 | ~6.7 | rice bran [3] | | ~24 C (75 F) | ~21.6 | - | - | soybean diet [1] | | 25 C | 21.4 (females) | 0.111 | ~6.2 | rice bran [3] | | 29.4 C | 19.9 | - | - | [2] | | 30 C | no value in abstract | 0.062 | ~11.2 | rice bran [3] | | 32.2 C | injurious to eggs, larvae, pupae and adults | - | - | [2] | | 18.9-30 C fluctuating | 19.2 (best of all regimes) | - | - | [2] | Doubling times are ln2 / r_m, calculated here from the published r_m values. Development data at 15, 20 and 35 C exactly were not found. Wilkinson and Daugherty put the lower limit for development at about 10 C and the upper limit at 32.2-35 C [2]. The optimum for each stage differed: about 29.4 C for eggs and pupae, 23.9 C for larvae, and 12.8 C for the longest adult life [2]. No published degree-day total for a *B. impatiens* generation was found. Do not apply the shore fly figure (about 213 degree-days above 6.4 C) to gnats. ### How many eggs does a fungus gnat lay? A *B. impatiens* female laid about 75 eggs on average (range 12-156) at 75 F in the original life-history study [1]. Fecundity was about the same from 12.8 to 29.4 C and fell at 32.2 C [2]. Other populations lay more. Mated *Bradysia* sp. nr. *coprophila* females laid 21-217 eggs, mean 141 ± 9.3, within 48 hours in soilless growing media [12]. Wisconsin extension gives up to 200 eggs per female, laid in clusters on moist media [22]. Adults are short-lived: about 5.9 days at 24 C [1] and about one week in greenhouse descriptions. Longevity increases as temperature drops [2]. ## Why do temperature and substrate moisture matter for fungus gnats? For fungus gnats, temperature sets the speed of the cycle but substrate moisture decides whether the cycle happens at all. Every immature stage lives in the medium, where the air is close to saturated whatever the room RH, so air humidity matters far less than how wet the top few centimetres stay. ### Why does grow-room temperature favour fungus gnats? Cannabis grow-room temperatures sit right on the fungus gnat optimum. Veg rooms at about 24-28 C and flower rooms at about 22-26 C match the 20-25 C band where *B. impatiens* r_m is 0.103-0.111/day [3]. The 32-35 C needed to harm gnats [2] would harm the crop first. Cool rooms slow gnats but do not stop them. At 16 C r_m is still 0.058/day, a doubling every 12 days [3]. A cold propagation area mainly slows your clones' rooting, which lengthens the wet, vulnerable window. No diapause has been described for greenhouse *Bradysia* in the sources checked. Indoors they breed all year with overlapping generations [8][11]. Outdoors in inland California they peak in winter and spring, when soils are wetter [8]. ### How does a wet medium increase fungus gnat numbers? A constantly wet medium raises fungus gnat survival. In a greenhouse trial, about 2.6 times as many adult *Bradysia* sp. nr. *coprophila* emerged from pots kept "constantly saturated" (9.9 ± 1.4 adults) as from pots only "initially saturated" (3.8 ± 1.0) [13]. The type of medium mattered as much as moisture. In the same trials, one peat-based mix produced 3-7 times fewer adults than another [13], and in a later study larval survival differed between two other commercial peat-based mixes [14]. The reasons (drainage, air-filled porosity, microbial load) were not separated. Microbially active media attract egg-laying females. Composts, vermicompost, blood meal and kelp attract adults, and 2-5 times as many adults may emerge from microbially active media [11]. Immature composts less than a year old are a known source [11]. Females lay in media rather than on bare surfaces. In choice tests, *B.* sp. nr. *coprophila* laid far more eggs in three soilless mixes than on filter paper, with no clear preference among the mixes; the authors suggested moisture and volatiles drive the choice [12]. ### Does air humidity matter for fungus gnats? Air humidity is a minor factor for fungus gnats. In the classic temperature study, chamber RH ran 50-90% while the rearing cells were close to 100% [2], and development still followed temperature. Room RH matters indirectly: high RH and low VPD slow how fast the medium surface dries. **Tie to set-points.** A propagation dome at 80-90% RH keeps the plug surface wet all day. Once clones root, venting the dome and dropping to 60-70% RH in veg lets the top layer dry between irrigations (*Grower practice*). See [kb-term-vpd](https://genetixbay.com/knowledge/glossary/vpd.md) and [kb-term-dryback](https://genetixbay.com/knowledge/glossary/dryback.md). ## How fast can a fungus gnat population grow? (worked example) Ten fungus gnats left unchecked at 25 C can become about 100 in 3 weeks and about 1,000 in 6 weeks. This uses N(t) = N0 × e^(r_m × t) with the *B. impatiens* r_m values from Ishihara and Tagami (rice bran, constant temperature) [3]. | Temperature | r_m (/day) | Day 14 | Day 21 | Day 28 | Day 42 | |---|---|---|---|---|---| | 16 C | 0.058 | 23 | 34 | 51 | 114 | | 20 C | 0.103 | 42 | 87 | 179 | 756 | | 25 C | 0.111 | 47 | 103 | 224 | 1,058 | | 30 C | 0.062 | 24 | 37 | 57 | 135 | Starting number N0 = 10; values rounded. For example, at 25 C after 21 days: 10 × e^(0.111 × 21) = 10 × e^2.33 ≈ 103. This is an unchecked exponential upper bound. It assumes unlimited food and moisture, no predators and a stable age structure. Real pots plateau, and a drying surface or a predator breaks the curve. The table shows why 20-25 C is the danger band and why 30 C is not a cure: growth at 30 C is slower, but still about 13 times in 6 weeks. Compare shore flies, which multiply far faster (r_m 0.263/day at 25 C for *Scatella stagnalis*); see [kb-pests-shore-flies](https://genetixbay.com/knowledge/pests/shore-flies.md). ## Where do fungus gnats hide, how do they spread and how do they get in? Fungus gnats hide as eggs, larvae and pupae in the top few centimetres of moist medium, and as adults on the medium surface, pot rims and lower leaves. Most of the population at any moment is below the surface, not flying. **Bagged media.** Commercial bagged soilless media and rooted plugs can arrive carrying fungus gnats (Cloyd and Zaborski, cited in [9]). Store bags closed, dry and off the floor [8][11]. **Clones and plugs.** Rooted cuttings and plugs move larvae in their root balls. Inspect incoming plugs for larvae and feeding damage [11]. **Compost and organic amendments.** Unfinished compost, worm castings, blood meal and kelp attract females and can carry eggs [8][11]. Pasteurise or age compost before use [8]. **Debris and cull piles.** Adults can emerge from discarded media and plant debris and migrate to the crop; keep waste in sealed bins or outside [4][11]. **Wet floors, algae and spills.** Puddles, algae under benches and spilled media are breeding sites [4][11]. **Flight.** Adults fly weakly and stay near pots, but they still spread locally and are attracted to light [8]. Open windows and doors let outdoor gnats in; screen and seal them [8]. ## How do I scout for fungus gnats? Scout fungus gnats with two tools: yellow sticky cards for adults and raw potato pieces for larvae, both checked weekly. **Yellow sticky cards.** Lay cards horizontally at the medium surface, or stand small pieces on skewers just above it; check and change weekly [9][11]. Wisconsin extension suggests about 10 traps per 1,000 sq ft (about 1 per 9 m²) for gnats and shore flies [22]. Use a 10x hand lens to confirm the Y-shaped wing vein and long antennae. **Potato slices or plugs.** Press raw potato pieces, cut side down, onto the medium. UConn uses plugs at least 2.5 cm (1 in) across and checks after 48 hours; thin "French fry" strips suit small plugs [9]. Count larvae under each piece, then discard it. A potato-based larval monitoring technique was published for *B. coprophila* in floriculture [18]. **Where to place them.** Put cards and potato pieces in propagation first, then in a fixed sample of veg pots, and always in the wettest pots and near any algae. **Action thresholds.** No research-based threshold exists for cannabis; growers set their own [11]. Supplier guidance used by growers is about 20 adults per card per week as a trigger for predatory mites, and about 50-75 to switch to nematodes (*Grower practice*). In propagation, any larvae under potato slices on rooting clones justify action, because larvae there can carry *Pythium* (*Grower practice*, based on [7]). **Trend, not snapshot.** Record counts per card per week. A rising trend after a watering change means the source is somewhere else: a wetter bench, a compost-rich pot or a floor drain. ## How do fungus gnats spread plant diseases? Fungus gnat larvae can spread soil-borne pathogens, but adults are poor vectors of *Pythium*. Laboratory work shows a clear split by life stage. **Larvae and Pythium.** *B. impatiens* larvae ingested *Pythium aphanidermatum* oospores and transmitted the pathogen to geranium seedlings in 65% of filter-paper assays, but in under 6% of plug cells with potting mix [7]. Strains with few oospores transmitted less, and strains without oospores were not transmitted [7]. **Gut passage.** Passing through a larval gut increased germination of *P. aphanidermatum* oospores [7]. *Pythium* DNA was detected in larvae and pupae but not in adults [6]. **Adults and Pythium.** Adult *B. impatiens* did not pick up infectious *Pythium* from diseased plants and transmit it in any experiment [6]. *Pythium* produces no aerial spores for adults to carry [4]. **Adults and fungi with aerial spores.** Adult fungus gnats can carry spores of fungi that sporulate above ground, including *Botrytis cinerea*, *Fusarium avenaceum*, *Thielaviopsis basicola* and *Verticillium* spp. [4]. Adult gnats, shore flies and moth flies carried *F. avenaceum* macroconidia to healthy lisianthus, which then died [20]. **Larvae and other fungi.** Larvae have been shown to transmit *Thielaviopsis basicola*, *Fusarium* and *Verticillium* in lab work [4]. **What this means in a grow room.** Transmission may be less important in real greenhouses than in lab dishes, and it varies with the *Pythium* species [4][7]. Treat gnats in propagation as a disease risk, and fix the wet medium that favours both. See [kb-diseases-root-rot-pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) and [kb-diseases-fusarium](https://genetixbay.com/knowledge/diseases/fusarium.md). ## Which fungus gnat controls hit which life stage? Fungus gnat controls work almost entirely on larvae; nothing practical kills eggs or pupae in the medium. This is why every control is repeated on a schedule set by development time. | Control | Eggs | Larvae | Pupae | Adults | Notes | |---|---|---|---|---|---| | Drying the top layer | reduces laying and survival | reduces survival | - | - | the main tool [4][13] | | Bti drench | no | yes, mainly young larvae | no | no | active ~2 days [11] | | *Steinernema feltiae* drench | no | yes | limited | no | kills larvae in 1-2 days [9] | | *Stratiolaelaps scimitus* | - | yes, prefers 1st instars | - | no | preventive [10] | | *Dalotia coriaria* | - | yes | - | - | preventive [10][14] | | Yellow sticky cards | - | - | - | yes | monitoring, minor removal | | Potato pieces | - | trap and count | - | - | monitoring [8][9] | ### How often should I reapply fungus gnat treatments? Reapply fungus gnat larvicides on a schedule that hits every new cohort while it is still feeding. At 24-25 C eggs hatch in 3-4 days, larvae feed for about 10-14 days, and pupae last 3.5-4 days [1][8][9]. **Bti schedule.** Bti stays toxic in the medium for about 2 days [11]. Applied every 5-7 days, every larval cohort is exposed at least once during its 10-14 day feeding window. Extension guidance is that 2-3 repeat applications may be needed [9][11]; three rounds over about 3 weeks cover one full generation (*Grower practice*, derived from the stage durations above). **Nematode schedule.** *S. feltiae* stays active about 10-14 days [10], and UConn recommends repeat applications every two weeks [11]. Because larval feeding lasts 10-14 days, a 14-day interval keeps infective nematodes present through each cohort. **Cooler rooms stretch the schedule.** At about 16-18 C development is roughly half as fast [2][3], so larval windows are longer. Spacing can stretch slightly, but keep at least three rounds. ### Do fungus gnats become resistant to insecticides? Fungus gnats can develop insecticide resistance with repeated use, and few products still work against adults because of resistance [4][11]. Their short generations (about 3 weeks) and high egg output favour it. Rotate by mode-of-action class, not by product name. Classes used against fungus gnat larvae elsewhere include microbial disruptors of the insect midgut (Bti, IRAC 11A), and insect growth regulators such as cyromazine (IRAC 17), diflubenzuron (IRAC 15) and azadirachtin (IRAC UN) [11][22]. Registrations on cannabis vary by jurisdiction: follow the label and local law. ## Which biological controls work against fungus gnats, and in what conditions? Four biological controls are established against fungus gnats in greenhouse crops: Bti, the nematode *Steinernema feltiae*, the soil mite *Stratiolaelaps scimitus* and the rove beetle *Dalotia coriaria* [4][9][10]. All are used in moist media and work best preventively [11]. Their use on cannabis is extrapolated from ornamentals (*Supported*). ### Bti (Bacillus thuringiensis subsp. israelensis) Bti is a bacterial larvicide whose protein crystals must be eaten by fungus gnat larvae; larvae stop feeding and die [11]. It is most effective against young first-instar larvae and is toxic for only about 2 days [9][11]. It is toxic only to fly larvae such as mosquitoes, black flies and fungus gnats [8]. See [kb-term-bti](https://genetixbay.com/knowledge/glossary/bti.md). Bti does not affect eggs, pupae or adults. It is a curative tool on an established population, often combined with mites or nematodes [10]. Bti is not a reliable shore fly control; see [kb-pests-shore-flies](https://genetixbay.com/knowledge/pests/shore-flies.md). ### Steinernema feltiae (entomopathogenic nematode) *Steinernema feltiae* infective juveniles enter fungus gnat larvae and kill them within 1-2 days [9]. They remain active in the medium for about 10-14 days [10], so they are reapplied every two weeks [11]. Apply as a drench to moist medium, ideally in low light or on overcast days [10][11]. See [kb-term-steinernema-feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md). *S. feltiae* is a cool-adapted nematode. In lab assays it infected hosts over roughly 8-30 C, a narrower range than other steinernematids [17]. Biocontrol supplier technical sheets give activity at about 10-31 C with best results at about 14-26 C. Root-zone temperatures above about 30 C, common in hot pots under strong light, reduce its performance. Rate, timing, potting medium and host plant all changed *S. feltiae* efficacy against *B. coprophila* in floriculture trials (Jagdale et al. 2004, cited in [4]). Do not mix nematodes with oxidising sanitisers such as hydrogen peroxide or chlorine. ### Stratiolaelaps scimitus (soil predatory mite) *Stratiolaelaps scimitus* (formerly *Hypoaspis miles*) is a soil-dwelling mite about 0.4 mm long that eats fungus gnat larvae and thrips prepupae and pupae, up to about 30 prey per day [16]. It lives in the top 2.5 cm (1 in) of the medium [16]. See [kb-term-stratiolaelaps-scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md). **Temperature window.** Development takes 10 days at 28 C, 12 days at 24 C, 18 days at 20 C and 34 days at 15 C [16]. The optimum for development and reproduction is 15-30 C, and activity drops below about 14 C [16]. UConn puts the minimum media temperature at about 15-16 C (60 F) [10]. **Reproduction.** Females lay up to three eggs per day; populations are 50-70% female; unfertilised females produce only males [16]. Adults survive 3-4 weeks without food and eat algae and debris when prey is scarce [16]. **How to use it.** Release early, when gnat numbers are low; one release can establish for a whole crop cycle [16]. *S. scimitus* alone usually does not manage an established gnat population, so pair it with watering changes [16]. Release rates vary by supplier; follow the biocontrol supplier technical sheet. ### Dalotia coriaria (rove beetle) *Dalotia coriaria* (formerly *Atheta coriaria*) is a generalist rove beetle about 3 mm long whose adults and larvae eat fungus gnat larvae, shore fly larvae and thrips pupae in the medium [10][11]. **Life history.** In growing medium in the lab, egg, larva and pupa took 2.2, 7.1 and 7.8 days, 17.0 days egg to adult; females laid 90.2 eggs on average; females lived 47.8 days and males 60.3; sex ratio 1:1 [15]. UConn gives the optimum as 18-27 C (65-80 F) and 50-85% RH [10]. **Moisture and medium.** In the lab, one or two beetles per pot halved gnat emergence (2.7 and 2.3 adults vs 5.4 in controls), but in the greenhouse the beetle effect was not significant, while moisture and medium were [13]. In later greenhouse trials, 10 adult beetles per 15.2 cm pot (2 L medium) regulated larval numbers [14]. **Compatibility.** UConn describes *S. scimitus*, *S. feltiae* and *D. coriaria* as mutually compatible [11]. Kansas State notes that *D. coriaria* will eat *S. scimitus* and advises against releasing both at once [16] (*Contested*). Beetles are nocturnal; release in the evening [9]. ### What else eats fungus gnats? The hunter fly *Coenosia attenuata* catches adult gnats and shore flies in flight, and its larvae prey on larvae in the medium [10]. It is not sold commercially but turns up in unsprayed greenhouses [10]. ## How do I use the environment against fungus gnats? The environmental weapon against fungus gnats is a dry top layer of medium, not a room set-point. A constantly saturated medium produced about 2.6 times as many adults as one allowed to dry back [13]. **Soil and living soil.** Water less often and more completely, and let the top 2-5 cm (1-2 in) dry between waterings (*Grower practice*, consistent with [8][11]). Lift pots: a light pot is ready for water. See [kb-guides-watering-how-much-how-often](https://genetixbay.com/knowledge/guides/watering-how-much-how-often.md). **Coco coir and rockwool.** Coco and rockwool are run wet by design with frequent fertigation, so drought is not an option. Rely on biologicals, and keep the surface drier with drip emitters under a cover or by increasing dry-back between the last and first shots (*Grower practice*). See [kb-term-coco-coir](https://genetixbay.com/knowledge/glossary/coco-coir.md) and [kb-term-rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md). **Bottom watering.** Watering from below keeps the top layer drier than top watering (*Grower practice*). See [kb-term-bottom-watering](https://genetixbay.com/knowledge/glossary/bottom-watering.md). **Media choice.** Use well-drained media and do not compact it [4][11]. Add perlite to improve drainage [8]. Avoid immature compost and heavy surface dressings of blood meal, kelp or worm castings in propagation [11]. **Physical covers.** Sand and diatomaceous earth on the surface did not reduce emergence or egg laying in tests [4]. A thick layer of coarse recycled-glass aggregate reduced adult emergence over time, depending on thickness [4]. Fitted collars or discs over the medium are *Grower practice*. **Trade-off in flower.** Drying the top layer has no downside for botrytis or powdery mildew; it lowers local humidity at the base of the plant. The risk is overcorrecting into drought stress in mid-flower, when water demand peaks. Dry the surface, not the root ball. See [kb-diseases-botrytis-bud-rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md). **Temperature is not a lever.** Room temperatures that suit cannabis (22-28 C) suit gnats [3]. Root-zone cooling below about 18 C slows gnats but also slows roots. ## What should I not do against fungus gnats in flower? In flower, do not drench residual insecticides into the root zone. Most are not registered on cannabis, and residues can show up in compliance tests. Follow the label and local law. Do not starve flowering plants of water to kill gnats. Drought stress in weeks 3-7 of flower costs more yield than gnats do on established plants. Dry only the top few centimetres. Do not use strong hydrogen peroxide or chlorine drenches as a gnat cure. They are poorly supported against gnats, can damage roots, and kill the nematodes and soil microbes you may be relying on (*Grower practice / Contested*). See [kb-term-hydrogen-peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md). Biological drenches (Bti, nematodes) and soil predators act in the medium, not on buds, and are generally fine through flower. Check that what you use is allowed on cannabis where you live. ## How do I know the fungus gnat treatment worked? A fungus gnat treatment has worked when weekly sticky-card counts fall for 2-3 consecutive weeks and stay low, potato pieces show no larvae, and seedlings and clones root normally. Expect a lag. Adults already present, and pupae that Bti and nematodes do not reach, keep appearing on cards for about one generation (2-3 weeks at 24-25 C) after larvae are controlled [1][8]. ## What are the common myths about fungus gnats? **"Sand or diatomaceous earth on top stops gnats."** *Myth.* In tests, neither reduced adult emergence or egg laying, because larvae and females use the gaps [4]. Only a thick coarse aggregate layer helped [4]. **"Adult gnats spread Pythium."** *Myth.* Adults did not transmit *Pythium* and carried no *Pythium* DNA; larvae can, mainly in lab assays [6][7]. Adults can carry fungi with aerial spores, such as *Fusarium* and *Botrytis* [4][20] (*Established*). **"Gnats always mean overwatering."** *Contested.* Wet media are the main driver [4][13], but microbially active media can produce 2-5 times as many adults [11]. Coco and rockwool are wet by design. **"Hydrogen peroxide drenches cure gnats."** *Grower practice / Contested.* No controlled trial against *Bradysia* was found. **"Sticky cards control gnats."** *Myth.* Adults live about 6 days [1]; most of the population is in the medium. Cards are for counting. **"Fabric softener sheets repel gnats."** *Supported (lab only).* Dryer sheets repelled adults in a lab study, linked to volatiles such as linalool, but they kill nothing and adults move elsewhere [4]. ## What are the common mistakes with fungus gnats? - Killing adults with cards and ignoring the larvae in the medium. - One Bti or nematode application, then stopping before the next cohort hatches. - Not changing the watering habit, or the compost-rich top dressing, that created the problem. - Treating gnats while ignoring the root rot they signal. - Releasing predators into a medium that never dries and expecting them to fix it alone. - Mistaking shore flies for gnats and using Bti against them. ## Evidence - Biology, life-stage durations and temperature limits of *B. impatiens*: *Established* (lab rearing on soybean and rice-bran diets) [1][2][3]. - Damage to seedlings and cuttings, association with wet and microbially active media: *Established* in greenhouse crops [4][11][13]; extrapolated to cannabis (*Supported*). - Larval transmission of *Pythium*: *Established* in the lab, weaker in potting mix [6][7]; adult *Pythium* vectoring: *Myth* [6]. - Bti, *S. feltiae*, *S. scimitus* and *D. coriaria* as controls: *Established* in greenhouse ornamentals [4][9][10][16]; on cannabis *Supported* (extrapolated). - Re-application intervals derived from stage durations: *Grower practice* built on published development times. - Action thresholds: *Grower practice*; no published cannabis threshold. ## Sources 1. Wilkinson, J.D. & Daugherty, D.M., 1970. The biology and immature stages of Bradysia impatiens (Diptera: Sciaridae). Annals of the Entomological Society of America 63(3):656-660. https://doi.org/10.1093/aesa/63.3.656 2. Wilkinson, J.D. & Daugherty, D.M., 1970. Comparative development of Bradysia impatiens (Diptera: Sciaridae) under constant and variable temperatures. Annals of the Entomological Society of America 63(4):1079-1083. https://doi.org/10.1093/aesa/63.4.1079 3. Ishihara, Y. & Tagami, Y., 2019. Effect of temperature on development and reproduction of Bradysia sp. and Bradysia impatiens (Diptera: Sciaridae). Japanese Journal of Applied Entomology and Zoology 63(2):57-67. https://doi.org/10.1303/jjaez.2019.57 4. Cloyd, R.A., 2015. Ecology of fungus gnats (Bradysia spp.) in greenhouse production systems associated with disease-interactions and alternative management strategies. Insects 6(2):325-332. https://doi.org/10.3390/insects6020325 5. Harris, M.A., Gardner, W.A. & Oetting, R.D., 1996. A review of the scientific literature on fungus gnats (Diptera: Sciaridae) in the genus Bradysia. Journal of Entomological Science 31(3):252-276. https://doi.org/10.18474/0749-8004-31.3.252 6. Braun, S.E., Castrillo, L.A., Sanderson, J.P., Daughtrey, M.L. & Wraight, S.P., 2010. Transstadial transmission of Pythium in Bradysia impatiens and lack of adult vectoring capacity. Phytopathology 100(12):1307-1314. https://doi.org/10.1094/PHYTO-04-10-0117 7. Braun, S.E., Sanderson, J.P. & Wraight, S.P., 2012. Larval Bradysia impatiens (Diptera: Sciaridae) potential for vectoring Pythium root rot pathogens. Phytopathology 102(3):283-289. https://doi.org/10.1094/PHYTO-09-11-0262 8. UC IPM, 2013. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf 9. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ 10. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ 11. Pundt, L., 2024. Managing Fungus Gnats and Shore Flies in Commercial Greenhouse Vegetable Transplant Production. UConn Extension. https://doi.org/10.61899/ucext.v1.060.2024 12. Meers, T.L. & Cloyd, R.A., 2005. Egg-laying preference of female fungus gnat Bradysia sp. nr. coprophila (Diptera: Sciaridae) on three different soilless substrates. Journal of Economic Entomology 98(6):1937-1942. https://doi.org/10.1603/0022-0493-98.6.1937 13. Herrick, N.J. & Cloyd, R.A., 2017. Effects of growing medium type and moisture level on predation by adult rove beetle, Dalotia coriaria, on fungus gnat, Bradysia sp. nr. coprophila, larvae under laboratory and greenhouse conditions. HortScience 52(5):736-741. https://doi.org/10.21273/HORTSCI11842-17 14. Herrick, N.J. & Cloyd, R.A., 2018. Effects of growing medium type and predator:prey ratio on rove beetle, Dalotia coriaria, adult predation on fungus gnat, Bradysia sp. nr. coprophila, larvae. HortScience 53(10):1441-1446. https://doi.org/10.21273/HORTSCI13268-18 15. Echegaray, E.R. & Cloyd, R.A., 2013. Life history characteristics of the rove beetle, Dalotia coriaria (Coleoptera: Staphylinidae) under laboratory conditions. Journal of the Kansas Entomological Society 86(2):145-154. https://doi.org/10.2317/JKES120927.1 16. Cloyd, R.A., 2023. Stratiolaelaps scimitus: Biological Control Agent of Fungus Gnats and the Western Flower Thrips. Kansas State University MF3632. https://bookstore.ksre.ksu.edu/download/stratiolaelaps-scimitus-biological-control-agent-of-fungus-gnats-and-the-western-flower-thrips_MF3632 17. Grewal, P.S., Selvan, S. & Gaugler, R., 1994. Thermal adaptation of entomopathogenic nematodes: niche breadth for infection, establishment, and reproduction. Journal of Thermal Biology 19(4):245-253. https://doi.org/10.1016/0306-4565(94)90047-7 18. Harris, M.A., Oetting, R.D. & Gardner, W.A., 1995. Use of entomopathogenic nematodes and a new monitoring technique for control of fungus gnats, Bradysia coprophila, in floriculture. Biological Control 5(3):412-418. https://doi.org/10.1006/bcon.1995.1049 19. University of Florida EDIS. EENY-215 Darkwinged fungus gnats, Bradysia spp. https://journals.flvc.org/edis/article/download/113282/108458/157298 20. El-Hamalawi, Z.A. & Stanghellini, M.E., 2005. Disease development on lisianthus following aerial transmission of Fusarium avenaceum by adult shore flies, fungus gnats, and moth flies. Plant Disease 89(6):619-623. https://doi.org/10.1094/PD-89-0619 21. Punja, Z.K. et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/pdf 22. Liesch, P.J. Fungus gnats and shore flies. University of Wisconsin-Madison Extension (XHT1128). https://hort.extension.wisc.edu/articles/fungus-gnats-and-shore-flies/ 23. Lindquist, R.K. Management of fungus gnats and shore flies. Connecticut Greenhouse Newsletter (Ohio State University/OARDC). https://hortscans.ces.ncsu.edu/uploads/m/a/manageme_53bac7fbd3ee4.pdf --- # Hemp russet mite (Aculops cannabicola): life cycle, detection and control > Hemp russet mite (Aculops cannabicola) is a 0.11-0.21 mm eriophyid mite that lives only on Cannabis, bronzes and curls leaves upward from the lower canopy and moves into buds. It is invisible below about 15-20x and needs about 55x to count. No life table exists for it; its relative the tomato russet mite completes egg-to-adult in 5.5 days at 25 C with an r_m of 0.286 per day. Clean stock and quarantine are the main defences; most growers treat it as zero tolerance in mothers and clones. - Canonical: https://genetixbay.com/knowledge/pests/hemp-russet-mite.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is hemp russet mite?** Hemp russet mite (Aculops cannabicola) is an eriophyid mite, 110 to 210 micrometres long, pale, carrot-shaped and with only two pairs of legs at the front. It feeds only on Cannabis. Feeding bronzes and stiffens leaves, curls edges upward, stunts plants and, in heavy infestations, invades buds and cuts yield and cannabinoid content. It is one of the most damaging arthropods in industrial and indoor hemp. **How do I know if I have russet mites?** You know you have hemp russet mites when leaves bronze, dull, go brittle and curl their edges upward, starting low and inside the plant and moving up, and a scope shows tiny pale carrot-shaped mites. Colorado State says at least 15 to 20x is needed to see them; a Kentucky counting study needed at least 55x. A 10x loupe shows nothing. Tan powdery cast skins appear in heavy infestations. **How fast do russet mites reproduce?** Hemp russet mite can complete its life cycle in about one week in favourable conditions, according to Colorado State and Kentucky extension. No temperature life table for Aculops cannabicola has been published. Its close relative, the tomato russet mite, develops from egg to adult in 5.5 days at 25 C and 17 days at 15 C, with a peak intrinsic rate of increase of 0.286 per day at 25 C. **How do russet mites get into a grow room?** Hemp russet mites get into indoor grows mainly on infested clones and cuttings, because they feed only on Cannabis and are invisible without strong magnification. Inside the room they move on wind and fan currents from leaf edges, on hands, clothing and tools, and by crawling between touching plants. Seeds do not sustain them, so starting from seed is the cleanest way to begin. **Why are russet mites zero tolerance for clones?** Russet mites are zero tolerance in clone stock because one infested mother infests every cutting, mites are invisible at normal inspection power, populations persist year-round indoors and no treatment reliably eradicates them. A Colorado trial of hot-water and soap dips on hemp cuttings reduced mites but eliminated none. Treat any confirmed find on a mother as a reason to retire her and restart clean. **Can you get rid of russet mites in flower?** Hemp russet mites usually cannot be cleared from cannabis in mid to late flower. Oils, soaps and sulfur must not go on buds, unregistered miticides may be illegal and fail residue testing, and research on controls is limited. Isolate infested plants, remove the worst, consider an early harvest, never take clones from them, and restart the next cycle from clean stock. Follow the label and local law. **Do predatory mites work on russet mites?** Predatory mites give partial control of hemp russet mite at best. In Colorado field hemp, mass releases of Neoseiulus fallacis and Amblyseius swirskii significantly reduced russet mites, while N. californicus and Amblyseius andersoni did not, and none of the predators reproduced on infested plants. On tomato russet mite, iolinid mites established with pollen worked best. Use predators as prevention, not rescue. **Does hot water kill russet mites on cuttings?** Hot water reduces but does not eliminate hemp russet mites on cuttings. In a Colorado State thesis, hemp cuttings dipped at 41 C (106 F) or 43 C (109 F) for 10 or 15 minutes had significantly fewer mites and rooted normally, but no treatment killed all mites. A dip can lower the load on a valuable cut; it does not make an infested mother safe to clone. **Does humidity help or hurt russet mites?** The humidity effect on hemp russet mite is contested. Colorado State lists high humidity and temperature as favourable, while Kentucky advises limiting heat and humidity in propagation. For tomato russet mite, lab work at 30 to 33% RH gave the fastest growth, and high humidity slowed development and egg laying at high temperatures. No humidity study exists for Aculops cannabicola itself. **Is sulfur effective on hemp russet mite?** Sulfur sprays suppressed hemp russet mite by up to 98% in Colorado field hemp, raising yield by up to 33%, with the best result from two applications, one in July in veg and one in August at flowering onset. Sulfur harms predatory mites, must never be combined with or applied near oils, and should not go on indoor flowering buds. Follow the label and local law. **Short answer.** If cannabis leaves bronze, dull, go brittle and curl their edges upward, starting low and inside the plant, and your feed and pH are fine, you are probably looking at hemp russet mite. You will not see it with a 10x loupe; you need 15-20x to glimpse it and about 55x to count it [1][6]. It lives only on *Cannabis*, travels in clones and on air currents, and has no reliable cure once it is in flowers. Clean stock is the cure. Most serious growers treat it as zero tolerance in mothers and clones. ## What is hemp russet mite? Hemp russet mite is *Aculops cannabicola*, an eriophyid mite that feeds only on *Cannabis* (hemp and drug-type cannabis) [1][2]. Colorado State calls it one of the most injurious arthropods in industrial hemp [1], and Kentucky calls it a key pest of hemp [3]. Lab attempts to establish it on related Cannabaceae plants failed [2]. Eriophyids are an odd family of mites: wormlike, carrot-shaped, with only two pairs of legs crowded at the front end, where spider mites and broad mites have four pairs as adults [1][3]. They make no webbing [1]. Biology is poorly studied, and little research exists on effective chemical or biological controls [14]. Every extension source says so, and the life cycle is "believed to be similar" to the tomato russet mite, *Aculops lycopersici* [2][4]. This article uses tomato russet mite data as the life-table proxy and labels them every time. ## How do you recognise hemp russet mite damage? Hemp russet mite damage starts on lower and inner leaves and moves up: leaves turn dull, greyish, bronze or rusty, become smaller and brittle, and curl their edges upward (sometimes downward) [1][2][3][13]. Petioles may turn golden or bronze [4]. At low densities there is no visible damage at all [1]. | Sign | What you see | Source | |---|---|---| | Where first | Lower leaf undersides, then upper surfaces, petioles, stems, flower stalks and buds | [3] | | Leaf shape | Edges curl upward (or downward), leaves smaller and brittle | [1][3] | | Colour | Dull, greyish, bronzed or rusty; later yellow and wilting | [1][2] | | Residue | Tan to brown powdery cast skins (exuviae) on leaves and stems in heavy infestations | [1][3] | | Growth | Stunting; populations peak in apical meristems and can kill seedlings and young clones | [3] | | In flower | Fewer, smaller buds; lower yield and cannabinoid content | [1][2][3] | | Webbing | None | [1] | **Differentials.** Russet damage is mistaken for magnesium or potassium problems, heat or light stress, broad mite, spider mite without webbing, and viroid or virus infection [2][4]. Broad mite twists the top of the plant first; russet mite bronzes from the bottom up. See [kb-pests-broad-russet-mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) and [kb-diseases-hop-latent-viroid-and-viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). ## Numbers that matter for hemp russet mite | Parameter | Value | Source | |---|---|---| | Adult length | 110-210 µm; females 170-210 µm, males 160-165 µm | [2][3][4] | | Legs | 2 pairs, at front end (nymphs and adults) | [1][3] | | Life stages | Egg, two nymphal stages, adult | [3] | | Life cycle | ~1 week in favourable conditions; 7-10 days optimal; up to ~30 days in poor conditions | [1][2][3][4] | | Adult lifespan | Up to ~30 days | [3] | | Magnification to see | At least 15-20x | [1] | | Magnification to count reliably | At least 55x | [6] | | Survival without a host | Remaining mites die within about a month | [1] | | Host range | *Cannabis sativa* only | [1][2] | | Action threshold | None established | [2][4] | | r_m, development thresholds | No published value found for *A. cannabicola* | – | ## What is the hemp russet mite life cycle in numbers? The hemp russet mite life cycle runs egg, two nymphal stages and adult, and extension sources put the whole cycle at about one week in favourable conditions [1][3]. No temperature-dependent life table for *Aculops cannabicola* has been published (no published value found). The closest proxy is the tomato russet mite, *Aculops lycopersici*, in the same genus. **Proxy, clearly labelled: tomato russet mite on tomato leaves, constant temperatures, 30-33% RH, lab (Japan)** [8][9]. | Temp | Egg (d) | Nymphs (d) | Egg-adult (d) | Female longevity (d) | Eggs/female | R0 | Generation T (d) | r_m (/day) | Doubling (d) | |---|---|---|---|---|---|---|---|---|---| | 15 °C | 8.26 | 8.78 | 17.07 | 32.2 | 21.9 | 17.5 | 20.7 | 0.138 | 5.0 | | 17.5 °C | 5.85 | 6.05 | 11.76 | – | – | – | – | – | – | | 20 °C | 4.59 | 4.06 | 8.66 | 29.7 | 31.9 | 24.4 | 20.2 | 0.158 | 4.4 | | 22.5 °C | 3.57 | 3.62 | 7.16 | – | – | – | – | – | – | | 25 °C | 3.14 | 2.40 | 5.48 | 25.7 | 51.7 | 38.7 | 12.8 | 0.286 | 2.4 | | 27.5 °C | 2.57 | 2.21 | 4.79 | – | – | – | – | – | – | | 30 °C | 2.23 | 2.36 | 4.57 | 17.3 | 42.7 | 27.1 | 13.0 | 0.253 | 2.7 | | 35 °C | no published value found | | | | | | | | | Doubling time computed here as ln2 / r_m. Values from Kawai & Haque's review of their lab work [8][9]. **Thresholds (proxy).** Development rate rose linearly from 15 to 27.5 °C. Egg-to-adult required 81.2 degree-days above a developmental zero of 10.5 °C [8][9]. A separate Chinese study reported 9.15 °C and 105.6 degree-days, with peak r_m of 0.265 per day at 26 °C (Acta Entomologica Sinica 2006, as summarised in a secondary index). **Upper limit (proxy).** Nymph survival fell from 88-93% at 25-27.5 °C to 56% at 30 °C [8]. That is the first sign of an upper limit; no 35 °C data exist. **Sex ratio (proxy).** 70-80% females regardless of temperature [8]. **Note the abstract-versus-table discrepancy.** Kawai & Haque's abstract gives r_m 0.253 at 25 °C; their table gives 0.286 at 25 °C and 0.253 at 30 °C [8]. This article uses the table. **On whole plants (proxy).** On greenhouse tomato plants, 100 released adults grew exponentially at an r_m of 0.175 per day to a peak of 187,286 mites per plant at six weeks [8]. ## Why do temperature and humidity matter for hemp russet mite? Temperature drives hemp russet mite speed: if it behaves like its tomato relative, generations shrink from about 17 days at 15 °C to about 5.5 days at 25 °C, and r_m roughly doubles from 0.138 to 0.286 per day [8]. A grow room at 24-28 °C sits at the proxy's optimum. **Degree-day estimate (proxy).** With 81.2 degree-days above 10.5 °C [8][9], egg-to-adult takes about 8.5 days at 20 °C, 7.1 days at 22 °C, 5.6 days at 25 °C and 4.6 days at 28 °C. See [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md). **Humidity is contested.** Colorado State lists high relative humidity and high temperature as favourable [1]. Kentucky advises limiting high temperature and humidity in propagation, since both favour reproduction [3]. LSU says the mite reproduces faster in dry, warm conditions [12]. **Tomato russet mite data side with dry air.** The proxy life table was run at 30-33% RH, and high humidity retarded development and reduced egg numbers at high temperatures; 30-60% RH suited reproduction [8]. Kawai & Haque expected field growth at high humidity to be slower than the lab table [8]. **What that means for set-points.** Humid propagation domes (often 70-90% RH at 24-26 °C) are exactly where Kentucky says to be careful [3]. Flower rooms at 45-55% RH and then 40-50% RH are within the range where the proxy reproduces well [8]. No set-point controls this mite; clean stock does. **Diapause and winter.** No diapause has been described. Indoors it persists year-round on a constant supply of plants [1][2][4]. Outdoor overwintering is unknown: Colorado State says it overwinters in crop debris [1], NC State says survival between field plantings is uncertain [2], and the PNW handbook calls field overwintering unclear [4]. Eriophyid mites on perennial hosts often overwinter as females under bud scales, but no study documents this for *A. cannabicola*, an annual-host specialist (no published value found). ## How fast can 10 russet mites become a problem? Ten russet mites at 25 °C could become about 4,000 in three weeks if they grow like tomato russet mite on leaf discs, versus about 280 at 20 °C. The method is N(t) = N0 × e^(r_m × t), using the proxy r_m values [8]. | Scenario (proxy) | r_m (/day) | Doubling (d) | Day 14 | Day 21 | Day 28 | |---|---|---|---|---|---| | 15 °C, leaf disc | 0.138 | 5.0 | 69 | 181 | 477 | | 20 °C, leaf disc | 0.158 | 4.4 | 91 | 276 | 834 | | 25 °C, leaf disc | 0.286 | 2.4 | 548 | 4,059 | 30,049 | | 30 °C, leaf disc | 0.253 | 2.7 | 345 | 2,030 | 11,927 | | Whole greenhouse plant | 0.175 | 4.0 | 116 | 394 | 1,343 | This is the unchecked exponential upper bound, with no predators and unlimited tissue. Kawai & Haque calculated that the whole-plant rate means a 1,914-fold increase in 30 days [8]. A clone carrying a few dozen invisible mites into week one of veg can carry tens of thousands into flower. ## Where do russet mites hide, how do they spread and how do they get in? Hemp russet mites hide on leaf undersides, in petioles and stems, and at high density on upper surfaces, flower stalks and buds [2][3]. Populations peak in the apical meristems [3]. **Clones and cuttings are the main way in.** The mites are likely carried on propagules as eggs or mobile stages [3], and Colorado State lists cloning and tools as spread routes [1]. They cannot be sustained on seeds [2]. **Wind and fans.** Russet mites move to leaf edges and are carried on wind currents [1][2]. In greenhouses, ventilation can spread high densities quickly [3]. **People, tools and supplies.** Restrict movement between infested and clean areas [1][2]. **Crawling** between touching plants over short distances [1]. **Outdoors**, in Kentucky field hemp, high populations occur from August to October, coinciding with flower development [3]. ## Why is hemp russet mite zero tolerance in clone stock? Hemp russet mite is zero tolerance in clone stock because every property of the mite defeats normal inspection and treatment. It is invisible below 15-20x [1]; fairly high populations can cause no visible injury [2]; it persists indefinitely indoors on mother plants [1][2]; and no treatment eradicates it from cuttings [5]. **The dip data.** Hayes (Colorado State) dipped hemp cuttings in water at 41 °C (106 °F) or 43 °C (109 °F) for 10 or 15 minutes, or in 1.0% or 0.1% plant-based soap. All treatments reduced russet mites significantly and none damaged rooting, but none eliminated the mites [5]. **The arithmetic.** One mother feeds dozens of cuttings a cycle. If even one survives per cutting, the proxy r_m of 0.175-0.286 per day [8] rebuilds a full population inside the next veg. **The house rule.** A confirmed russet mite find on a mother means retire her, or keep her only in strict isolation as a source for tissue culture or seed (Grower practice). Do not trade or sell cuts from an infested line. ## How do you scout for hemp russet mite? Scout for hemp russet mite by examining leaflets from the lower and middle canopy under 55x or more, weekly in mothers and veg and on every incoming cutting. Colorado State says 15-20x is the minimum to see them [1]; the Kentucky counting study found a 14x smartphone too weak and set 55x as the working minimum [6]. - **What to sample.** Lower and inner leaves first, both surfaces, petioles and stems; later the buds [1][3]. - **Kentucky photo method.** Photograph the basal and middle sections of the central leaflet with a handheld digital microscope; counts correlated with microscope counts (r > 0.7) and took 0.4-1.3 minutes per leaflet. Sample at least 22 leaflets per event for a reliable estimate [6]. - **Washing.** Rinse leaves in soapy water or 70% ethanol and examine the wash against a dark background [2]. - **Brushing.** A mite-brushing machine can estimate infestation levels [2][4]. - **The tape test.** Growers press clear tape on leaf undersides and view it under a microscope (Grower practice). It is quick, but no published validation exists for eriophyids on hemp. Stem-encircling sticky tape traps were rated unsuitable for eriophyids on hemp in the Kentucky methods comparison [6]. - **Sticky cards** do not catch russet mites usefully. - **Action threshold.** None established [2][4]. In mothers and clones, the threshold is one mite (Grower practice). - **Lab ID.** Extension diagnostic labs will confirm from a sample [2]. Cornell's hemp program also stresses microscopy for confirmation [15]. ## Which russet mite controls hit which life stage? Contact treatments (oils, soaps, sulfur) kill the russet mites they touch but have no residual activity and miss eggs and mites deep in petioles and buds, so coverage and repeats matter [2]. No ovicidal data exist for *A. cannabicola* (no published value found). **Timing the repeat (proxy).** Using tomato russet mite at 25 °C, eggs hatch in about 3.1 days and egg-to-adult takes 5.5 days [8]. A second application at day 3-5 lands after surviving eggs hatch and before most new adults lay. At 20 °C (egg 4.6 days, egg-adult 8.7 days) a 5-7 day interval fits. Pre-oviposition for *A. lycopersici* was not reported in the accessible source (no published value found). **What has worked in trials (classes only).** - **Sulfur:** up to 98% suppression in Colorado field hemp, up to 33% more yield and 45% more cannabinoid content than untreated; two applications, in July (veg) and August (start of flowering), worked best [5]. - **Refined mineral oil and a *Beauveria bassiana* product** were the most effective in Kentucky 2021 trials [3]. - **Refined mineral and seed oils** have been used; none have residual activity [2]. **Modes of action.** Very few miticides are registered on hemp or cannabis. As of December 2021 the US EPA had approved 58 biopesticides and one conventional insecticide/miticide for hemp [3]. Rotate by class (for example sulfur IRAC UN, oils as physical action, fungal biopesticides) and follow the label and local law. Never use sulfur within the label interval of an oil. **Resistance.** Fast generations and a single-host specialist life in sealed rooms favour resistance to any repeated chemistry. Rotation and non-chemical tactics are the defence. See [pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md). ## Which biological controls work on hemp russet mite? Biological control of hemp russet mite is partial at best, and only as prevention. Colorado State notes *Amblyseius andersoni* is known to feed on it, while *Phytoseiulus persimilis* and *N. californicus* are not effective [1]. NC State lists *A. andersoni* as feeding on other russet mites in greenhouses [2]. The PNW handbook suggests *A. swirskii* may have potential, based on its effect on tomato russet mite [4]. **Field trial, Colorado** [5]. Mass releases of *Neoseiulus fallacis* and *Amblyseius swirskii* significantly reduced russet mites. *N. californicus* and *A. andersoni* did not significantly reduce them. No release changed yield or cannabinoid content, and none of the predators reproduced on infested plants. **Lab assays.** A 2025 review in *Agronomy* reports no-choice predation and oviposition assays with *A. swirskii*, *A. andersoni*, *N. californicus* and *Galendromus occidentalis* on *A. cannabicola* [11]. **Tomato russet mite lessons (proxy)** [10]: - Curative releases of *N. californicus*, *A. andersoni* and *N. fallacis* at 500 per plant weekly for four weeks gave the strongest damage reduction, but survived poorly and did not eradicate the pest; repeated releases were judged too costly. - *A. swirskii* established only on leaves where glandular trichomes had collapsed. Cannabis is a glandular plant too. - Iolinid mites (*Pronematus ubiquitus*, *Homeopronematus anconai*), released preventively with cattail pollen at 0.15 g per plant weekly, kept tomato plants damage-free. *H. anconai* ate an average of 69.3 tomato russet mite deutonymphs per day in the lab [8]. No iolinid trial on cannabis has been published (no published value found). **Fungus.** *Hirsutella thompsonii* was found infecting hemp russet mite in Kentucky in 2021; inoculated mites showed infection by day 8 and about 28% were discoloured by day 14 [7]. It is not yet a commercial tool. See [entomopathogenic fungi](https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.md). **Predator windows.** For temperature and humidity ranges of *A. swirskii*, *N. californicus*, *N. cucumeris* and *A. andersoni*, see the predator table in [kb-pests-broad-russet-mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). Key point: *A. swirskii* eggs fail at about 63% RH and below, which clashes with low-RH flower rooms. ## How can the environment be used against hemp russet mite? The environment is a weak weapon against hemp russet mite. No set-point has been shown to stop it, and the humidity evidence conflicts [1][3][8]. - **Propagation.** Kentucky advises limiting high temperature and humidity in propagation [3]. Keep domes vented and do not run cuttings warmer than needed (Grower practice). - **Mother rooms.** A cooler mother room (20-22 °C) slows the proxy from 5.5 to 7-9 days per generation [8]. It slows, not stops. - **Host-free period.** Without hosts, remaining mites die within about a month [1]. A fully plant-free room for four or more weeks after cleaning is the strongest environmental move available (Grower practice informed by [1]). - **Flower.** Keep RH at 45-55% and 40-50% late for botrytis and powdery mildew control; do not raise humidity to "slow mites". See [botrytis bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md). ## What should you not do about russet mites in flower? Do not spray oils, soaps or sulfur on flowering buds, and do not use unregistered miticides; residues fail testing and the use may be illegal. The Colorado sulfur result came from field hemp with a last spray at flowering onset [5], not from sprays into ripening indoor buds. Follow the label and local law. - Do not try to "spray through" a russet infestation in mid-late flower. - Do isolate infested plants, remove the worst, and consider an early harvest. - Do bag plants before carrying them through clean rooms. - Do not take clones from any plant in an infested room. - Do run the room plant-free for at least a month after cleanout [1]. ## What are the common myths about hemp russet mite? The common hemp russet mite myths are that a 10x loupe will find them, that seeds carry them, that predators or dips can clean an infested line, and that they live on other plants. - **"A 10x loupe will show russet mites."** *Myth.* 15-20x minimum to see, 55x to count [1][6]. - **"Russet mites come in on seed."** *Myth.* They cannot be sustained on seeds [2]; starting from seed is the best prevention. - **"Predatory mites will wipe them out."** *Myth.* Some predators reduced field populations; none eradicated them or reproduced on infested hemp [5]. - **"A hot-water or soap dip cleans an infested clone."** *Myth.* Dips reduced mites; none eliminated them [5]. - **"They live on other plants in the room."** *Myth.* Host specific to *Cannabis*; they die within about a month without hosts [1][2]. - **"Russet mites like dry rooms."** *Contested.* Colorado State says high humidity favours them [1]; tomato russet mite data favour low humidity [8]. - **"Russet mites transmit viruses."** *Contested.* Eriophyids as a group include virus vectors [12], but no virus transmission by *A. cannabicola* has been shown (no published value found). ## How do you confirm russet mite control worked? Confirm hemp russet mite control by repeated high-power counts, not by leaf appearance. Bronzed leaves stay bronzed. - Sample at least 22 leaflets per check at 55x or more, using the basal and middle sections of the central leaflet [6]. - Repeat weekly for at least four weeks; four weeks covers four or more generations at 25 °C (proxy) [8]. - New growth should emerge flat and green. Any live mite in mothers or clones means the line is still infested. ## Common mistakes - Looking with a 10x loupe and declaring the plant clean. - Treating bronzing as magnesium or potassium deficiency without a scope. - Keeping an infested mother and dipping her cuttings. - Spraying once; contact products have no residual activity [2]. - Releasing *P. persimilis* or *N. californicus* and expecting russet control [1][5]. - Restarting the room without a host-free period. ## Evidence - Host specificity, damage, spread on wind and clones: *Established* in extension literature [1][2][3][4]. - Life cycle of about one week: *Supported* (extension consensus) [1][3]; no *A. cannabicola* life table. - Temperature-development, r_m, fecundity: *Established for tomato russet mite* [8][9]; *extrapolated* to hemp russet mite. - Humidity effect: *Contested* [1][3][8][12]. - Detection at 55x and the photo method: *Supported* (one peer-reviewed study) [6]. - Sulfur suppression in field hemp: *Supported* (one thesis) [5]; predatory mites: *Contested/partial* [5][10]. - Hot-water and soap dips: *Supported* as reduction, *Myth* as eradication [5]. - *Hirsutella thompsonii*: early research [7]. ## Sources 1. Colorado State University, Agricultural Biology. Hemp russet mite, Aculops cannabicola. https://agsci.colostate.edu/agbio/ipm-pests/29895-2/ 2. Pulkoski, M. & Burrack, H. 2020. Hemp Russet Mite in Industrial Hemp. NC State Extension. https://content.ces.ncsu.edu/hemp-russet-mite-in-industrial-hemp 3. Villanueva, R., Viloria, Z., Ochoa, R. & Ulsamer, A. Hemp russet mite, a key pest of hemp in Kentucky. University of Kentucky ENTFACT-162. https://entomology.mgcafe.uky.edu/ef162 4. Pacific Northwest Insect Management Handbook (Oregon State University, Washington State University, University of Idaho). Hemp russet mite (Aculops cannibicola). https://pnwhandbooks.org/insect/agronomic/hemp/hemp-mite-russet 5. Hayes, C. 2022. Developing integrated pest management (IPM) strategies for hemp russet mite (Aculops cannabicola Farkas) on hemp (Cannabis sativa L.). Thesis, Colorado State University (advisors P. Nachappa, W. Cranshaw). https://doi.org/10.25675/3.04334 6. Falcon-Brindis, A., Villanueva, R.T., Viloria, Z. & Bradley, C.L. 2023. A novel approach to tally Aculops cannabicola (Acari: Eriophyidae) for field and laboratory studies. Journal of Economic Entomology 116(2): 591-598. https://doi.org/10.1093/jee/toad004 7. Ricciardi, M.M., Smith, H., Viloria, Z., Dixon, E., Szarka, D., Pearce, R., Gauthier, N. & Villanueva, R.T. 2024. First report of Hirsutella thompsonii as an entomopathogenic fungus of hemp russet mite (Aculops cannabicola) in Kentucky. Plant Health Progress 25(1): 92-94. https://doi.org/10.1094/PHP-04-23-0035-BR 8. Kawai, A. & Haque, M.M. 2004. Population dynamics of tomato russet mite, Aculops lycopersici (Massee) and its natural enemy, Homeopronematus anconai (Baker). JARQ 38(3): 161-166. https://doi.org/10.6090/jarq.38.161 9. Haque, M.M. & Kawai, A. 2003. Effect of temperature on development and reproduction of the tomato russet mite, Aculops lycopersici (Massee). Applied Entomology and Zoology 38(1): 97-101. https://doi.org/10.1303/aez.2003.97 10. Pijnakker, J. et al. 2022. Evaluation of phytoseiid and iolinid mites for biological control of the tomato russet mite Aculops lycopersici (Acari: Eriophyidae). Insects 13(12): 1146. https://doi.org/10.3390/insects13121146 11. Sustainable management strategies for acarine pests of industrial hemp (Cannabis sativa subsp. sativa L.). 2025. Agronomy 15(12): 2785. https://doi.org/10.3390/agronomy15122785 12. LSU AgCenter. Aculops cannibicola, Hemp Russet Mite. https://www.lsuagcenter.com/articles/page1649168950500 13. Utah State University Extension. Hemp Russet Mite. https://extension.usu.edu/planthealth/ipm/notes_ag/veg-hemp-russet-mite 14. Alabama Cooperative Extension. Russet Mites in Hemp (ANR-2763). https://www.aces.edu/wp-content/uploads/2021/07/ANR-2763_RussetMitesinHemp_070721L-G.pdf 15. Britt, K. Insects and mites of hemp (webinar slides). Cornell University Hemp Program, 2024. https://hemp.cals.cornell.edu/files/2024/01/Cornell-webinar-INSECTS-AND-MITES-Kadie-Britt-compressed-098e2a10d08cdaea.pdf --- # Integrated pest management (IPM) for cannabis: a complete programme for home and small commercial growers > A cannabis IPM programme is a written routine: keep pests out (clean stock, a 14-21 day quarantine, clean-room-first workflow), find them early (weekly leaf and card scouting with set thresholds), act by life stage and temperature (predators first, contact tools only in veg, rotation by mode-of-action group), and record every count so the next run starts smarter. - Canonical: https://genetixbay.com/knowledge/pests/integrated-pest-management-program.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is IPM for cannabis?** Integrated pest management (IPM) for cannabis is a planned system, not a spray: prevention and quarantine to keep pests out, scouting on a fixed schedule to find them early, written action thresholds, and control chosen by pest, life stage and room temperature, with biological control first and chemical tools last and by mode-of-action class. Records of every count tie it together and improve each run. **How long should I quarantine new cannabis clones?** Quarantine new cannabis clones for at least 14 days, and 21 days for cuts from unknown sources, in a separate space with its own tools. Fourteen days at 20-25 C covers one full spider mite generation from egg, so hidden eggs hatch and show. Inspect leaf undersides with 10-20x every 3-4 days and growing tips at 40-60x at day 7 and day 14 for broad and russet mites. **How often should I scout my grow for pests?** Scout a cannabis grow at least once a week, and twice a week when the room runs above about 26 C (79 F), because pest doubling times then shrink to 2-4 days. Each check: change or read sticky cards, turn over leaves on a fixed sample of plants, look at growing tips with 40-60x, check the medium surface, and write the counts down. **How many sticky cards do I need for a grow room?** Extension greenhouse guides recommend at least one sticky card per 1,000 sq ft (about 93 m2), and better three to four, plus extra cards near doors and intakes. For a home tent of 1-2 m2, use one yellow card at canopy height and one laid flat at the medium surface for fungus gnats; add blue for thrips. Change cards weekly and record counts. **What is an action threshold for cannabis pests?** An action threshold is the pre-set pest count that triggers a specific step. No published thresholds exist for indoor cannabis, so growers set their own: for example any spider mite colony triggers a predator release, any confirmed broad or russet mite in a mother room triggers isolation or destruction, and rising weekly thrips counts on blue cards trigger extra predators. Thresholds tighten as flower approaches. **Why does my spray schedule need to match room temperature?** A spray schedule must match room temperature because pest development runs on heat, not days. Most contact sprays miss eggs, so the second application has to land after surviving eggs hatch but before the new adults lay. For two-spotted spider mites that gap is roughly 4-5 days at 27-30 C but 7-10 days at 20 C, based on lab life tables. **How do I stop pests becoming resistant to sprays?** To slow pest resistance, rotate between mode-of-action groups (IRAC numbers) so that no group is used on two successive pest generations, use non-chemical tools first, and spray only when a threshold is crossed. Spider mites and thrips evolve resistance fast because of short generations and haplodiploidy. Different brands often share one group, so rotate by group number. Follow the label and local law. **What is a clean-room-first workflow?** A clean-room-first workflow means entering the cleanest areas first each day: propagation and mothers, then veg, then flower, and quarantine last. Change gloves or wash hands between rooms, wear clean clothing, and never go from an outdoor garden or another grower's room into yours on the same day. Mites, thrips and aphids ride on sleeves, hair, pets and tools. **When should I release predatory mites?** Release predatory mites preventively in veg, before pests are seen, or at the first confirmed colony, never after the population has exploded. Generalists such as Neoseiulus californicus or Amblyseius swirskii suit preventive releases; Phytoseiulus persimilis suits spider mite hot spots. Check that the room climate suits the species (persimilis needs above about 60% RH and below about 30 C) and avoid residual sprays. **What pest records should a grower keep?** Keep dated records for each room: sticky card counts by pest, leaf-sample counts of pests and predators, plant IDs affected, temperature and RH (or VPD), every release or treatment with its mode-of-action group and stage, and the outcome a week later. On GenetixBay, log them in the grow journal against the batch and plant IDs so patterns and sources can be traced. **Short answer.** Integrated pest management is a written routine, not a product. Keep pests out with clean stock, a 14-21 day quarantine and a clean-room-first workflow. Find them early with weekly scouting of leaves, tips and sticky cards. Act on pre-set thresholds, matching the tactic to the pest's life stage and your room temperature: predators first, contact tools in veg only, and chemical classes rotated by mode of action. Write every count down. This article is the programme; each pest article gives the species detail. Pesticide registrations on cannabis differ by country, state and province, and many products are not legal on cannabis at all. This article names classes, not products or rates. Always follow the label and local law. ## What is IPM, and why does cannabis need it more than most crops? IPM for cannabis is a system of prevention, monitoring, thresholds and layered control, with chemicals as the last layer. Cannabis needs it more than most crops because the harvested part is the flower, which is smoked or extracted, so residues matter more than in a crop that is peeled or cooked, and because few pesticides are registered on it [1]. Indoor cannabis also hands pests ideal conditions. Rooms run at 24-28 C (75-82 F) all year, with no winter to reset populations. The crop is propagated as clones, so pests travel with the plant material. Cranshaw and colleagues name the two-spotted spider mite a key pest wherever cannabis has an indoor or greenhouse phase, and note that problems often involve mother plants used for cloning [1]. Three facts drive the whole programme: 1. **Pests grow exponentially.** At 25-30 C, spider mites and aphids can double in 2-4 days in lab life tables. A week of not looking can mean a four- to eightfold increase. See [temperature, humidity and pest population growth](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md). 2. **Options shrink in flower.** Almost every contact tool is off the table once buds form. Problems must be solved in veg. 3. **Prevention is cheaper than cure.** Most indoor infestations are introduced, not spontaneous. ## How do pests get into an indoor grow? Most pests enter an indoor cannabis grow on plants, with clones as the main route, followed by people, pets, air intakes and reused media. Cranshaw et al. describe mother plants used for cloning as a common focus of spider mite problems [1], and the same logic holds for broad mites, hemp russet mites and root aphids, which are hard or impossible to see on a cutting. | Entry route | Typical pests | Prevention | |---|---|---| | Clones and rooted cuttings | Spider mites, broad and russet mites, root aphids, thrips pupae in plugs, mealybugs | Trusted source, quarantine 14-21 days, dip or inspect | | Seeds | Almost none | Seeds are the cleanest start | | People and clothing | Spider mites, thrips, aphids, whiteflies | Clean-room-first, clean clothes, no garden visits before the grow room | | Pets | Spider mites, thrips | Keep pets out of grow spaces | | Houseplants and outdoor plants | Spider mites, aphids, mealybugs, whiteflies | No houseplants in or next to the room | | Air intakes, doors, vents | Thrips, aphids, whiteflies, moths, leafhoppers | Fine insect screening on intakes; sticky cards at doors [2] | | Reused soil or media, bags of compost | Fungus gnats, root aphids, shore flies | New or pasteurised media; store bags closed | | Wind and silk (outdoors, between rooms) | Spider mites, russet mites | Airflow from clean to dirty areas | ## How long should new plants stay in quarantine? New cannabis plants should stay in quarantine for at least 14 days, and 21 days when the source is unknown or the plants are heading for a mother room (Grower practice, derived from life tables). The logic is life-cycle timing: a spider mite egg laid the day before you collect a clone hatches in roughly 3-6 days at 20-25 C and becomes an egg-laying adult in about 10-17 days, so 14 days lets one hidden cohort show itself (see [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md)). Quarantine only works if it is real: - **Separate space.** A different room or tent, ideally with its own air, not a corner of the veg room. - **Separate tools and clothing.** Or quarantine is visited last each day. - **Inspections on a schedule.** Day 0, day 3-4, day 7, day 10, day 14 (and day 21). Leaf undersides at 10-20x; growing tips and petioles at 40-60x for broad and hemp russet mites on days 0, 7 and 14; roots of one sacrificial plug or the root ball edge for root aphids on day 14. - **Sticky cards.** One yellow card in the quarantine space from day 0. - **Indicator leaves.** Tape-sample a few upper leaves onto clear tape and examine under magnification for eriophyid mites. | Source of plants | Minimum quarantine | Extra checks | |---|---|---| | Own seed | None needed for pests | Check medium for gnats | | Own clones moved between rooms | 0-7 days | Tip check at 40-60x if the mother room had any history | | Trusted clean-stock nursery with records | 14 days | 40-60x tip check days 0, 7, 14 | | Friend, swap or unknown source | 21 days | All of the above, plus root check | | Any plant with confirmed russet or broad mites | Destroy or full treatment cycle before release | Treat as zero tolerance | Some growers dip incoming cuttings in a contact solution (soap, oil or other classes legal where they live) before quarantine. A dip reduces mobiles but rarely kills all eggs, so it shortens nothing: the quarantine clock still runs (Grower practice). ## What does a clean-room-first workflow look like? A clean-room-first workflow orders every visit from the cleanest area to the dirtiest: propagation and mothers first, then veg, then flower, then quarantine, then any room with a known problem. It is the cheapest prevention there is (Grower practice, standard in greenhouse IPM). - Wash hands or change gloves between rooms. - Wear clean clothes that have not been in a garden, a barn or another grow that day; a dedicated overshirt or lab coat per room is better. - Keep pets out of grow spaces. - Disinfect pruning tools between rooms and between suspect plants. - Never carry an infested leaf through a clean room. Bag it where you cut it. - Set airflow from clean areas toward dirty ones, not the reverse, because spider mites disperse on air (see [aerial dispersal](https://genetixbay.com/knowledge/glossary/aerial-dispersal.md)). ## What should a scouting round include? A cannabis scouting round includes four checks: sticky cards, leaf undersides, growing tips and the root zone, each done the same way every time and written down. Doing it the same way matters more than doing it perfectly, because the goal is a trend line. | Check | Tool | What you are looking for | Pests found this way | |---|---|---|---| | Sticky cards (yellow, plus blue for thrips) | Eye, 10x lens | Flying adults per card per week | Thrips, whiteflies, fungus gnats, shore flies, winged aphids, leafhoppers, moths | | Leaf undersides, lower and mid canopy | 10-20x lens | Mites, eggs, nymphs, cast skins, stippling | Spider mites, thrips larvae, whitefly nymphs, aphids | | Growing tips, petioles, upper leaves | 40-60x loupe or microscope, or clear tape lift | Tiny wedge or translucent mites, eggs with dimples | Broad mites, hemp russet mites | | Medium surface and root ball edge | Eye, potato slice, 10x | Larvae, white wax, algae | Fungus gnats, root aphids, shore flies, root mealybugs | | Whole plant | Eye | Honeydew, webbing, twisted tips, wilting, frass | Aphids, mealybugs, spider mites, caterpillars | UConn Extension notes that sticky cards catch only flying adults; spider mites, broad mites, mealybugs and wingless aphids will never appear on them, and immature thrips and whiteflies are not caught either [2]. Cards supplement plant inspection; they do not replace it. ## How often should you scout, and how many plants? Scout weekly as a minimum and twice weekly when the canopy runs above about 26 C (79 F) or when a pest is already present. At 27-30 C, spider mite, aphid and thrips doubling times are a few days in lab life tables, so a weekly check can miss a doubling or two. UConn Extension likewise recommends spot-checking cards twice a week as temperatures rise [2]. | Grow size | Plants to inspect each round | Cards | |---|---|---| | Home tent, 1-4 plants | Every plant: 5 leaves each (2 lower, 2 mid, 1 top) plus 2 tips | 1 yellow at canopy, 1 flat at medium surface | | Home room, 5-20 plants | Every plant, 3 leaves each, plus 2 tips on a third of plants | 2-3 yellow, 1 blue | | Small commercial room, 50-500 plants | At least 10% of plants, chosen on a walking pattern, plus every plant near doors, intakes and lamps | 3-4 per 1,000 sq ft (93 m2), plus doors and vents [2][3] | | Mother room | Every mother, every week, including 40-60x tip checks | 1 per bench | Rules for good scouting (Grower practice, in line with greenhouse extension guidance [2][3]): - Walk the same route at the same day and time each week. - Flag every positive plant with tape or a tag and re-check it at the next round. - Pick up cards one or two days after a release of winged parasitoids, not the same evening, so you do not trap the beneficials [2]. - Place cards 10-15 cm (4-6 in) above the canopy and raise them as the plants grow [2]. For fungus gnats, lay a card horizontally just above the medium [2]. - Change cards weekly; they lose catch as dust builds up [2]. ## What action thresholds should a cannabis grower use? No published action thresholds exist for indoor cannabis, so the thresholds below are grower-set starting points to be adjusted with your own records (Grower practice). They are deliberately low, because the harvested flower has almost no damage tolerance and options shrink in flower. See [action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md). | Pest | Veg threshold (triggers action) | Flower threshold | Typical first action | |---|---|---|---| | Spider mites | Any colony (adults plus eggs) on one leaf | Any colony | Predator release on hot spot; remove leaf; climate check | | Broad or hemp russet mites | Any confirmed mite | Any confirmed mite | Isolate; in mothers, destroy or full treatment cycle; zero tolerance | | Thrips | Rising blue-card counts over 2 weeks, or larvae on 10% of sampled leaves | Any rising trend | Extra predatory mites; check medium for pupae | | Fungus gnats | More than about 10 adults per card per week, or larvae in potato slices | Same | Dry top layer; soil-dwelling predators, nematodes or Bti class | | Aphids | Any colony with nymphs | Any colony | Parasitoid matched to species; spot removal | | Root aphids | Any confirmed | Any confirmed | Isolate; drench-class biologicals in veg; break cycle between runs | | Whiteflies | Rising yellow-card counts, or nymphs on leaf undersides | Any rising trend | Parasitoids or predators by temperature | | Caterpillars | Any larva, frass or bored stem; moths in the room | Same | Remove by hand; Bt class on young larvae in veg and early flower | Threshold tightening by stage: whatever count triggers action in week 2 of veg should trigger it earlier as the flip approaches, because the last safe window for contact sprays is the end of veg. ## How do you decide what to do once a pest is found? The decision runs in five steps: confirm the pest, check the stage of the crop, check the room climate, choose the tactic that hits the life stages present, then schedule the follow-up from the pest's development time at your temperature. ``` 1. Confirm ID - Lens: 10-20x for spider mites, thrips, aphids, whiteflies; 40-60x for broad/russet mites. - Not sure? Don't treat yet. Tape-lift and look again, or ask for ID. 2. What stage is the crop? - Propagation / mothers / veg -> all IPM tools available (step 3) - Flower weeks 1-3 -> biologicals, removal, climate; contact tools only where legal and non-residual - Flower week 4 to harvest -> biologicals, removal, climate only; consider early harvest if severe 3. Is the room climate inside the predator's window? - Yes -> release the matched predator/parasitoid at the hot spot plus preventive rate across the room - No -> fix climate first (see "environment as a weapon" in the pest article), or choose a predator that tolerates the room (e.g. N. californicus for warm, dry rooms) 4. Is the infestation above the threshold where predators alone can catch up? - Predator:prey worse than about 1:20 for spider mites, or webbing present -> knock down first in veg (water wash, contact class compatible with the predator), then release predators after any residue period on the label 5. Schedule follow-up from development time at YOUR temperature - Re-check in half the egg-to-adult time; re-apply contact tools before survivors lay - Rotate mode-of-action group every pest generation - Record everything ``` ## How do you time repeat treatments to the pest's life cycle? Time repeat treatments so the second application lands after eggs that survived the first have hatched, and before the resulting juveniles mature and lay. Most soaps, oils and many other contact classes kill mobile stages but not eggs, so a single treatment always leaves a cohort behind (Established in greenhouse IPM). The window comes from the life table at your temperature: - **Earliest useful repeat** = egg development time (the eggs must have hatched). - **Latest safe repeat** = egg development time + juvenile development time + pre-oviposition period of the first survivors, minus a margin. For two-spotted spider mites, lab life tables put egg development at very roughly 3 days at 30 C and 6-7 days at 20 C, and egg-to-adult at roughly 6-8 days at 30 C and 14-17 days at 20 C (see the life-table section of [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md) for the cited values). That gives: | Room temperature | Repeat window for mobile-only tools (spider mites) | Practical schedule | |---|---|---| | 20 C (68 F) | about day 7 to day 12 | Every 7 days, three applications | | 25 C (77 F) | about day 4 to day 8 | Every 5 days, three applications | | 30 C (86 F) | about day 3 to day 6 | Every 3-4 days, three to four applications | These windows are estimates from lab data on non-cannabis hosts; confirm with your own scouting. Degree-day thinking makes the point general: heat, not the calendar, sets the pace [7]. ## How do you rotate pesticides to slow resistance? Rotate by mode-of-action group, so no group is used on two successive generations of the same pest. That is the core IRAC recommendation, which also warns that metabolic resistance can cause cross-resistance between groups [6]. Rotate by group number on the label, not by product name, because different brands often share one group. Spider mites and thrips need the strictest rotation. Both are haplodiploid: males develop from unfertilised eggs and carry one set of chromosomes, so resistance genes are exposed to selection in every male (see [haplodiploidy](https://genetixbay.com/knowledge/glossary/haplodiploidy.md)). UC IPM notes that spider mites develop resistance quickly and that some sprays make outbreaks worse by killing their predators [4]. Practical rotation rules (Grower practice built on IRAC principles [6]): - Count pest generations, not sprays. At 27 C a spider mite generation is about a week: three weekly sprays of one group expose three generations. - Use non-chemical layers (predators, removal, climate) so that sprays are rare. - Never use a group again in the same run if it failed; assume resistance. - Record the group number of every application in the journal. - Follow the label and local law; many groups are not legal on cannabis anywhere. ## How do biological controls fit into the programme? Biological controls are the backbone of cannabis IPM: predators and parasitoids keep working in flower, leave no residues and do not select pesticide resistance. They work best preventively, released before pests are seen or at the first colony, and only inside their temperature and humidity window. | Pest | Main beneficials (class) | Climate notes | |---|---|---| | Spider mites | Phytoseiulus persimilis (specialist); Neoseiulus californicus, N. fallacis (generalists); predatory midges | Persimilis needs above about 60% RH and suffers above about 30 C; californicus tolerates warmer, drier rooms [5] | | Broad mites | Amblyseius swirskii, Neoseiulus californicus, N. cucumeris | Swirskii prefers warm rooms | | Hemp russet mites | Generalist phytoseiids (evidence limited) | See [hemp russet mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md) | | Thrips | N. cucumeris, A. swirskii, Orius; soil predators for pupae | Some Orius strains diapause under short days | | Fungus gnats, shore flies | Stratiolaelaps scimitus, Dalotia coriaria, Steinernema feltiae, Bti class | Keep media moist enough for nematodes, not soggy | | Aphids | Aphidius species matched to aphid, Aphelinus, aphid midge, lacewings | Aphid midge diapauses under short days without supplemental light | | Whiteflies | Encarsia formosa, Eretmocerus eremicus, A. swirskii | Encarsia prefers moderate warmth; Eretmocerus handles heat | | Caterpillars | Trichogramma (eggs), Bt class (young larvae) | Outdoors and greenhouses mainly | Judge progress with a [predator:prey ratio](https://genetixbay.com/knowledge/glossary/predator-prey-ratio.md) counted on marked leaves weekly. For spider mites, extension guides describe control when predators reach roughly one per 10-20 pest mites [5]. Check pesticide compatibility before any spray near a release; many contact classes and sulfur harm predatory mites. ## How should the room climate support IPM? Run the room climate so it slows the main pests and suits the beneficials, within the limits set by the crop stage. The crop wins every conflict: late-flower humidity stays at 40-50% RH regardless of what mites prefer, because bud rot costs more (see [botrytis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)). | Stage | Typical set-point | IPM angle | |---|---|---| | Propagation | 22-26 C, 70-85% RH | Good for most predators; watch fungus gnats and shore flies in wet plugs | | Veg | 24-27 C, 60-70% RH | Avoid canopy above 28 C to slow spider mites; keeps persimilis viable | | Early flower | 23-26 C, 50-60% RH | Last window for preventive releases of humidity-sensitive predators | | Late flower | 20-24 C, 40-50% RH | Prioritise bud-rot prevention; use dryness-tolerant predators | Hot spots matter more than averages. A canopy 3 C hotter than the room under a lamp is where spider mites start. Measure leaf temperature with an infrared thermometer and fix hot spots with airflow (see [VPD](https://genetixbay.com/knowledge/glossary/vpd.md)). ## How do you clean up between runs? Between runs, empty the room completely, remove all plant debris and media, clean every surface and wait before restocking, so that no generation bridges two crops. Spider mites, root aphids and thrips pupae survive in debris, cracks, reused media and on mother plants kept in the same space. 1. Remove all plants and media; bag them inside the room. 2. Vacuum and wipe surfaces, ducting, fan guards and tent seams; clean or replace intake filters and screening. 3. Wash or replace trays, pots and irrigation lines; root aphids and gnat larvae shelter in trays. 4. Disinfect surfaces with a sanitiser suitable for the material (see [sanitation and prevention](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md)); wear gloves and eye protection. 5. Leave the room empty and dry for several days if you can (Grower practice); without food, mobile mites die within days to weeks depending on temperature. 6. Restock only from quarantined or own clean stock. Mother plants are the weak point. Never keep mothers in a room with a known infestation, and treat the mother room as the cleanest room in the building. ## How should pest records tie into a GenetixBay grow journal? Log every scouting round, count, release and treatment in the GenetixBay grow journal, against the batch and plant IDs, so that sources, trends and what worked can be traced across runs. A count without a date and a plant ID is a memory, not a record. | Field | Example | Why | |---|---|---| | Date, room, stage, day of flower | 2026-11-04, Room B, flower day 12 | Ties pests to crop timing | | Temperature, RH, leaf temperature or VPD | 26 C, 58% RH, leaf 24.5 C | Explains pest speed and predator success | | Card counts by pest | Yellow 1: 4 gnats, 0 whitefly; Blue 1: 7 thrips | Trend lines | | Leaf sample counts | 5 of 30 leaves with spider mites; 2 persimilis seen | Predator:prey ratio | | Plants flagged | IDs or tag numbers | Spread pattern | | Action | Released 1 predator class at hot spot; removed 6 leaves | What was done | | Product class and IRAC group, if any | Contact soap class; group not applicable | Rotation record | | Source of plants | Clone batch ID and origin | Traces introductions | | Outcome 7 days later | 1 of 30 leaves; 6 predators seen | Did it work? | Weekly pest-check results are already part of the recommended journal routine; see [grow journal 101](https://genetixbay.com/knowledge/guides/grow-journal-101.md). Shared journals turn one grower's lesson into everyone's data: when several members report hemp russet mite on the same clone line, that is a provenance warning. ## What are the common myths about IPM? - **"A weekly preventive spray is IPM."** *Myth.* Calendar spraying without scouting selects resistance and kills beneficials [4][6]. - **"Clones from a reputable source don't need quarantine."** *Myth.* Clones are the main route for mites and root aphids into indoor rooms, and eriophyid and tarsonemid mites are invisible without 40-60x magnification [1]. - **"Sticky cards will tell you if you have mites."** *Myth.* Mites and wingless aphids do not fly and are never caught [2]. - **"Predators are a cure-all."** *Myth.* They fail outside their climate window or when released too late [5]. - **"Bugs appear from the soil."** *Myth.* Indoor pests are introduced. Fungus gnats arrive as adults or in bagged media; they do not form from wet soil. - **"Spraying in flower is fine if it's organic."** *Myth.* Organic classes still leave residues and wet buds; the issue is residue and moisture, not origin. ## Common mistakes - No quarantine, or a quarantine corner sharing air with the main room. - Scouting by feel instead of on a schedule with written counts. - Waiting for webbing, honeydew or twisted tips: those are late signs. - Repeating sprays on a fixed weekly calendar regardless of temperature. - Rotating products that share a mode-of-action group. - Releasing humidity-sensitive predators into a hot, dry room. - Visiting the outdoor garden, then the mother room. ## Evidence - Clones and mother plants as a focus for spider mite problems in cannabis: *Supported* by a hemp pest review [1]; generalised to other mites and root aphids as *Grower practice*. - Sticky card density, placement, change interval and what cards cannot catch: *Established* in greenhouse extension guidance [2][3]. - Mode-of-action rotation to slow resistance: *Established* [6]; rapid resistance in spider mites *Established* [4]. - Quarantine lengths and cannabis action thresholds: *Grower practice*, derived from life tables; no cannabis trials. - Re-application windows: calculated from non-cannabis lab life tables [7][8]; *Supported* as method, approximate as numbers. ## Sources 1. Cranshaw, W., Schreiner, M., Britt, K., Kuhar, T.P., McPartland, J. and Grant, J., 2019. Developing insect pest management systems for hemp in the United States: a work in progress. Journal of Integrated Pest Management 10(1):26. https://doi.org/10.1093/jipm/pmz023 2. UConn Extension IPM Program. Using Sticky Cards to Monitor for Greenhouse Insects. https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019stickycardsfactsheet-1.pdf 3. Michigan State University Extension. Integrated Pest Management in Greenhouse Crops (Bulletin E3296). https://www.canr.msu.edu/resources/integrated_pest_management_in_greenhouse_crops_e3296 4. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 5. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf 6. Insecticide Resistance Action Committee. Mode of Action classification. https://irac-online.org/modes-of-action/ 7. UC IPM. Degree-Days: About Degree-Days. https://ipm.ucanr.edu/WEATHER/ddconcepts.html 8. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605 --- # Leafhoppers on cannabis: beet leafhopper, curly top and hopperburn > Leafhoppers matter on cannabis for one reason above all: the beet leafhopper (Circulifer tenellus) spreads beet curly top virus, which was found in 81% of symptomatic hemp samples in Colorado in 2019 and has no cure. Potato leafhopper causes hopperburn but is usually a minor pest. Protect young outdoor plants with barriers, control weed hosts, monitor with yellow sticky cards and rogue infected plants; insecticides cannot stop a virus transmitted within hours. - Canonical: https://genetixbay.com/knowledge/pests/leafhoppers.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Transition, Flower · Systems: Soil, Living soil, Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Do leafhoppers hurt cannabis?** Most leafhoppers found on cannabis and hemp do little harm, but two matter. The beet leafhopper (Circulifer tenellus) spreads beet curly top virus, a serious, incurable disease of outdoor hemp in the western United States. The potato leafhopper (Empoasca fabae) causes hopperburn, yellow and scorched leaf tips, in the Midwest and East. Colorado's commonest hemp leafhopper, Ceratagallia uhleri, causes no significant injury. **What is beet curly top virus in cannabis?** Beet curly top virus (BCTV) is a leafhopper-spread curtovirus that stunts outdoor cannabis and hemp, yellows and mottles leaves and twists new growth into a witches' broom. The beet leafhopper is its only vector in North America. In Colorado in 2019 it was detected in 81% of symptomatic hemp leaf samples from 12 counties. Infected plants do not recover; young plants are most vulnerable. **How fast does a beet leafhopper transmit curly top?** A beet leafhopper can pick up beet curly top virus within about one hour of feeding on an infected plant, and after a latent period of about four hours it can infect new plants, according to the EPPO datasheet. It keeps the virus for weeks, up to 30 days in one study, and extension sources say for life. Because transmission is that fast, insecticides cannot prevent infection. **How long does a beet leafhopper take to develop?** The beet leafhopper needs about 361 Celsius degree-days above 14.4 C (58 F) to go from egg to adult, using the Harries and Douglass sugar beet model listed by UC IPM. That is roughly 64 days at a steady 20 C, 34 days at 25 C and 23 days at 30 C. Eggs take about 111 degree-days and the five nymphal instars about 250. **How many eggs does a beet leafhopper lay?** In laboratory work by Meyerdirk and Moratorio (1987), beet leafhopper females laid about 105 eggs at 20 C, 99 at 25 C, 116 at 28 C and 197 at 32 C, and 163 under fluctuating 19 to 36 C greenhouse conditions. Pre-oviposition fell from 13 days at 20 C to 5 days at 32 C. The Pacific Northwest handbook gives 300 to 400 eggs under optimal conditions. **What is hopperburn on cannabis?** Hopperburn on cannabis is yellowing and scorching of leaf tips, followed by curling and twisting, caused by potato leafhopper (Empoasca fabae) feeding on the undersides of leaves. Purdue reports it on Indiana hemp in 2021 and notes that no economic threshold exists. UConn says damage can go from first symptoms to dead leaves in four to five days. Confirm by finding pale, sideways-running nymphs under affected leaves. **How do I monitor leafhoppers in hemp?** Monitor leafhoppers in hemp with yellow sticky cards at field edges, checked weekly and replaced as needed, plus a sweep net, as Colorado State and Oregon State advise. Identify beet leafhopper with a hand lens: it is 3.3 to 3.6 mm, pale green to yellow and has no head markings. Other leafhoppers are common on cards, so counts are meaningless without identification. **Can insecticides stop beet curly top in cannabis?** No. Colorado State's Whitney Cranshaw states that insecticides are ineffective against beet curly top in hemp because beet leafhoppers are highly mobile and transmit the virus within a couple of hours, and Colorado State adds that beet leafhoppers are resistant to many pesticides used on sugar beet. Management relies on barriers over young plants, weed-host control, reflective mulch and removing infected plants. **Can I get curly top indoors from clones?** Yes, potentially. The beet leafhopper is an outdoor insect, so indoor rooms rarely see new infections, but the Pacific Northwest Plant Disease Handbook lists vegetative propagation, such as cuttings from an infected mother plant, as a transmission route for beet curly top virus. Do not take clones from outdoor plants with curled, yellowed new growth, and test suspect mothers by PCR. **When are leafhoppers active on outdoor hemp?** Beet leafhoppers move into crops in early spring from overwintering weeds or, in Colorado, from migrations out of New Mexico, and complete about three generations a year in Oregon and Washington. Potato leafhoppers migrate north from the Gulf states, arriving in Connecticut from June, and Utah State lists June through harvest as their time of concern. Young transplants are most at risk. **Short answer.** Most leafhoppers on cannabis are harmless passers-by. The one that matters is the beet leafhopper (*Circulifer tenellus*, also *Neoaliturus tenellus*), which carries [beet curly top virus](https://genetixbay.com/knowledge/glossary/beet-curly-top-virus.md): incurable, worst on young plants, and found in 81% of symptomatic Colorado hemp samples in 2019. The potato leafhopper (*Empoasca fabae*) causes hopperburn, usually minor. Protect transplants with barriers, kill the weed hosts, watch yellow sticky cards and pull infected plants. Sprays cannot outrun a virus that moves in hours. ## Which leafhoppers are found on cannabis? Leafhoppers on cannabis are small (about 3-4 mm), wedge-shaped, jumping sap-feeders of the family Cicadellidae. Over a dozen species have been found in Colorado hemp fields, most of them transients that do not breed in the crop [1]. Three are worth knowing. | Species | Where | Harm to cannabis | Source | |---|---|---|---| | Beet leafhopper, *Circulifer (Neoaliturus) tenellus* | Arid western US: Colorado West Slope, Columbia Basin, southern Idaho, central Oregon, Utah, Arizona, New Mexico, California | Only known vector of beet curly top virus to hemp; feeding itself causes little injury | [1][2][3][4] | | Potato leafhopper, *Empoasca fabae* | Midwest and East, migrating north each year; also Utah | Hopperburn: yellow, scorched leaf tips, curling; usually low threat | [16][17][18] | | *Ceratagallia uhleri* | Colorado (most common hemp leafhopper there) | Breeds on hemp but causes no significant injury and transmits nothing known | [1][2] | | Others: *Empoasca* spp., *Ceratagallia* spp., aster leafhopper *Macrosteles quadrilineatus* | Pacific Northwest hemp | Role unknown | [3] | Glossary: [leafhopper](https://genetixbay.com/knowledge/glossary/leafhopper.md), [plant virus](https://genetixbay.com/knowledge/glossary/plant-virus.md). ## How do I recognise beet curly top and hopperburn? Beet curly top in cannabis shows as pale green to yellow foliage, upward curling and puckering of leaves, twisted new growth and stunting; mid-season infection shortens internodes into a witches' broom, and badly stunted plants may die late in the season [2][4]. Severity is greater the earlier the plant is infected [4]. Hemp shows some odd variants. Plants can be "bisymptomatic": a twisted, stunted main stem with normal-looking side branches, though virus is detectable in both [1]. Some plants appear to outgrow symptoms [1][4]. Symptoms vary with variety, growth stage, temperature and virus strain [4]. Hopperburn from potato leafhopper starts as yellowing at the tips of serrated leaves, then scorching, curling and twisting; plants may be stunted [17][18]. Under UConn's description, damage can progress from first symptoms to leaf death in four to five days [18]. Light white stippling is of little consequence [16]. Differential diagnosis: curly top mimics herbicide drift, nutrient problems and [broad mite](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) damage; confirm by PCR test [4][7]. Hopperburn resembles drought, senescence or [spider mite](https://genetixbay.com/knowledge/pests/spider-mites.md) damage, so look under the leaves for the insects [16]. See [How to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md). ## Leafhopper life cycle in numbers Both important leafhoppers pass egg (inserted into leaf or stem tissue), five nymphal instars and a winged adult [2][18]. Development thresholds are 14.4 °C for beet leafhopper and 11.4 °C for potato leafhopper in the UC IPM models [8][13]. | Parameter | Beet leafhopper (*C. tenellus*) | Potato leafhopper (*E. fabae*) | Source / conditions | |---|---|---|---| | Lower developmental threshold | 14.4 °C (58 °F) | 11.4 °C (52.5 °F); 8.4 °C immatures under fluctuating temps | [8] sugar beet; [13] alfalfa lab; [14] | | Upper developmental threshold | 35.0 °C (95 °F) | 30.0 °C (86 °F) | [8][13] | | Egg | 111.1 °C-DD | 7-14 days in summer | [8]; [18] | | Nymphs (5 instars) | 250.0 °C-DD | no DD split verified | [8] | | Egg to adult | 361.1 °C-DD (650 °F-DD) | 435 °C-DD lab; 459 field (783 / 826 °F-DD) | [8][13] | | Pre-oviposition | 13.1 d at 20 °C; 8.2 at 25; 6.4 at 28; 5.0 at 32 | no value verified | [9] lab | | Eggs per female | 105 at 20 °C; 99 at 25; 116 at 28; 197 at 32; 163 at 19-36 °C fluctuating; 300-400 under optimal conditions | no lifetime value verified | [9]; [3] | | Eggs per female per day (derived) | ~2.2 at 25 °C; ~5.0 at 32 °C | no value verified | from [9]: eggs ÷ (longevity − pre-oviposition) | | Female longevity | 58.1 d at 20 °C; 52.7 at 25; 41.9 at 28; 44.8 at 32; 96.3 fluctuating | no value verified | [9] | | Oviposition threshold | no value verified | ~9.5 °C (laid at 10 °C, not 9 °C) | [15] | | Generations per year | ~3 in Oregon and Washington | 4-5 in Utah; 2+ in Connecticut | [3]; [16][18] | | Intrinsic rate of increase r_m | no published value found | measured by Hogg (1985), highest in the warmest regime; value not retrieved | [14] | | Sex ratio | no published value found | no value verified | | Sources and conditions: beet leafhopper degree-days from Idaho lab and field work on sugar beet (Harries & Douglass 1948) [8]; fecundity and longevity from constant-temperature lab work (Meyerdirk & Moratorio 1987) [9]; potato leafhopper from Illinois work on alfalfa (Kouskolekas & Decker 1966) [13]. No leafhopper life table has been measured on cannabis. ### How long does a generation take at each temperature? | Constant temperature | Beet leafhopper egg (days) | Beet leafhopper nymphs (days) | Beet leafhopper egg to adult (days) | Potato leafhopper egg to adult (days) | |---|---|---|---|---| | 15 °C (59 °F) | ~185 | ~417 | not viable as a linear estimate (0.6 °C above threshold) | ~121 | | 20 °C (68 °F) | 20 | 45 | 64 | 51 | | 25 °C (77 °F) | 10.5 | 24 | 34 | 32 | | 30 °C (86 °F) | 7.1 | 16 | 23 | 23 | | 35 °C (95 °F) | 5.4 | 12 | 17.5 | above upper threshold | Computed as degree-days ÷ (temperature − lower threshold) from [8] and [13]. Linear estimates are unreliable near the threshold. For potato leafhopper under cool fluctuating regimes (8-19, 10-21 and 13-24 °C), eggs took about 35, 29 and 16 days and nymphs about 47, 39 and 23-25 days [15]. ## Why do temperature and humidity matter for leafhoppers? Warmth drives beet leafhopper reproduction hard: pre-oviposition shortened from 13.1 days at 20 °C to 5.0 days at 32 °C, and eggs per female nearly doubled from 99 at 25 °C to 197 at 32 °C [9]. Generation time drops from about 64 days at 20 °C to 23 days at 30 °C [8]. Hot, dry western summers are its home climate. Cool weather shuts beet leafhoppers down. Arizona extension notes they become less active when daily highs fall below about 60 °F (15.6 °C) and stay on their overwintering weed or crop hosts [11]. That is why disease pressure is a spring and early-summer problem in the west. Winter moisture in the breeding grounds matters more than your field. Colorado's beet leafhoppers are largely spring migrants from New Mexico and possibly Arizona, where winter-annual mustards feed them; a wet winter there, as in 2019, means more migrants carrying virus [1]. Potato leafhopper damage is worse in warm conditions, and drought worsens the injury [18]. Hogg (1985) found intrinsic and finite rates of increase highest in the warmest regime (23-34 °C) on a per-day basis, while gross and net reproductive rates peaked in the coolest (13-24 °C) [14]. Humidity: no published humidity effect on either species was found. Leafhoppers are rarely an indoor problem, so indoor set-points (veg 24-28 °C / 60-70% RH, flower 22-26 °C / 45-55%) are not a control lever; screening and clean mothers are. ## How fast can a beet leafhopper population grow? No intrinsic rate of increase has been published for the beet leafhopper, so a true exponential projection cannot be computed. A per-generation ceiling can be, from the lab fecundity data [9] and the degree-day model [8]. Method: maximum multiplication per generation = eggs per female × fraction female × survival. Assume a 1:1 sex ratio (assumption; no published value found) and 100% survival (impossible in reality, so this is a ceiling). | Temperature | Eggs per female [9] | Ceiling multiplication per generation | Generation length (egg to adult + pre-oviposition) | Ceiling r = ln(multiplication) ÷ generation | |---|---|---|---|---| | 20 °C | 105 | 52.5x | 64.5 + 13.1 ≈ 78 days | ~0.051/day (doubling ~13.6 days) | | 25 °C | 98.9 | 49.5x | 34.1 + 8.2 ≈ 42 days | ~0.092/day (doubling ~7.5 days) | | 28 °C | 115.7 | 57.9x | 26.6 + 6.4 ≈ 33 days | ~0.123/day (doubling ~5.6 days) | | 32 °C | 196.9 | 98.5x | 20.5 + 5.0 ≈ 25.5 days | ~0.180/day (doubling ~3.9 days) | Derived figures, not published r_m; the generation length ignores the spread of egg laying, so these ceilings run high. The point for growers is not the local breeding rate. CSU observed only adults in hemp fields and doubts the species reproduces on the crop [1], though a CSU lab study found beet leafhoppers survived 7-day periods on hemp and laid eggs that developed [5]. Either way, your risk is set by how many virus-carrying migrants arrive from weeds and rangeland, not by how many breed in your rows. ## How does beet curly top spread to cannabis? Beet curly top reaches cannabis when a beet leafhopper that has fed on an infected plant feeds on hemp; the leafhopper is the only insect vector in North America [1][10]. The virus is persistent and circulative but does not multiply in the insect [10]. A leafhopper can acquire it within an hour of feeding and transmit after a latent period of about four hours [10]. Retention is long. EPPO cites up to 30 days [10]; Soto and Gilbertson tracked a related curtovirus in leafhoppers held on a non-host for up to 30 days [12]; Arizona extension says leafhoppers transmit for the rest of their lives [11]. The virus is not passed to offspring [11]. Weed reservoirs feed the cycle. In Colorado, prickly lettuce, dandelion and chicory most often tested positive among 41 weed species surveyed [5]. In the Pacific Northwest, kochia, Russian thistle and tumble mustard are key leafhopper hosts [3]; in Colorado, winter-annual mustards (flixweed, pepperweed) support overwintering and kochia is where summer leafhoppers are easiest to find [1]. Other routes: grafting and vegetative propagation, such as cuttings from an infected mother, transmit the virus; tools are not thought to; preliminary evidence suggests infected seed may [4]. Two strains, BCTV-Worland and BCTV-Colorado, have been found alone and mixed in Colorado hemp [6]. Scale: BCTV was detected in 81% of hemp leaf samples from 12 Colorado counties in 2019, and earlier at western sites than northern ones [5][6]. It was formally reported on *Cannabis sativa* in western Colorado in 2020 [7]. In the PNW it is common in the Columbia Basin, southern Idaho and central Oregon, and less so west of the Cascades [4]. ## Where do leafhoppers come from and how do they get in? Beet leafhoppers fly into cannabis fields in early spring from overwintering sites on weeds [3], and in Colorado mostly arrive as long-distance migrants from the south [1]. Potato leafhoppers overwinter in the Gulf states and arrive in the north on warm winds, reaching Connecticut from June; non-reproductive adults are carried south again in autumn [18]. Utah State lists June through harvest as their season [16]. Both are flying, wind-borne adults, so distance from source habitat matters more than hygiene. Purdue advises avoiding sites next to alfalfa for potato leafhopper [17]. For beet leafhopper, weedy rangeland and field edges with kochia, Russian thistle or mustards are the sources [1][3]. Indoors, leafhoppers are rare. The realistic indoor risk is not the insect but the virus arriving in a cutting from an infected outdoor or greenhouse mother [4]. ## How do I scout for leafhoppers? Scout outdoor hemp for leafhoppers with yellow sticky cards at the field edge, checked weekly and replaced as needed, plus a sweep net through the canopy [2][20]. Colorado State says sweep netting is the best way to detect beet leafhoppers in hemp [1]. Identification is the whole job. Beet leafhoppers are 3.3-3.6 mm (about 1/8 in), pale green in summer, wedge-shaped, with no head markings [2][3]. Many other leafhoppers land on the same cards, so a hand lens or microscope is needed [2][20]. Colorado's common *Ceratagallia uhleri* looks superficially similar but is harmless [1]. For beet leafhopper, scout the weeds as well as the crop: regular surveys of kochia patches in western Colorado show when migrations have arrived [1]. CSU suggests treating breeding areas in nearby weeds before leafhoppers move into hemp [2]. For potato leafhopper, inspect leaf undersides from June for pale, wingless nymphs that run sideways, and check scorched leaf margins and curled leaves [16][18]. Shaking plants or sweeping collects adults [18]. Action thresholds: none established for either species in hemp [2][17]. Utah State reports potato leafhopper has generally not damaged Utah hemp enough to warrant treatment [16]. For beet leafhopper, the "threshold" is effectively any viruliferous leafhopper on a young plant, which is why prevention is all that works (Grower practice). Glossary: [sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [scouting](https://genetixbay.com/knowledge/glossary/scouting.md). ## How do I control leafhoppers on cannabis? For beet leafhopper and curly top, control means keeping infected leafhoppers off young plants, because once a plant is infected it cannot be cured and insecticides cannot stop a transmission that takes a couple of hours [1][2]. CSU adds that beet leafhoppers are resistant to many pesticides used on sugar beet [2]. | Tactic | Target | Evidence | |---|---|---| | Physical barriers (row covers, insect netting) over seedlings and transplants | Keeps migrants off when plants are most susceptible | Recommended by CSU [2]; Grower practice for timing | | Weed-host control (kochia, Russian thistle, mustards, prickly lettuce) | Removes breeding and virus reservoirs | "Likely the most important option" per PNW, though often impractical [3]; [5] | | Reflective mulch | Deters leafhoppers from landing | "May reduce" spread [1][4] | | Rogueing infected plants | Removes virus source | [4] | | Trap crops (sugar beet at field edges) | Concentrates leafhoppers for targeted treatment | Suggested by CSU [2]; untested in hemp | | Clean planting stock | Stops clone-borne virus | [4] | ### Which insecticide classes are used on leafhoppers? Insecticides used against sap-feeding hoppers in other crops come mainly from IRAC groups 4A (neonicotinoids), 4C (sulfoximines), 3A (pyrethroids and pyrethrins), 9B (pymetrozine) and 29 (flonicamid) [19]. Most are not registered on cannabis, residues fail cannabis testing, and none prevents virus transmission [1]. Follow the label and local law; no brands or rates are given here. For potato leafhopper nymphs on leaf undersides, contact materials such as [insecticidal soap](https://genetixbay.com/knowledge/glossary/insecticidal-soap.md) and [horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md) are grower practice in veg; we found no hemp efficacy data. Purdue notes chemical control used in other crops is not an option for hemp producers in Indiana [17]; Utah State says approved insecticides exist if populations and damage are high [16]. Rotate by mode of action if you do treat. Glossary: [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md), [contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md). ## Which natural enemies attack leafhoppers? Leafhoppers are attacked by generalist predators (green lacewings, spiders, assassin bugs, big-eyed bugs), egg parasitoid wasps of the families Mymaridae and Trichogrammatidae, and big-headed flies (Pipunculidae) [2][3]. Conservation (flowering borders, no broad-spectrum sprays) is the only practical biological tactic. No commercial release programme or release rate has been established for leafhoppers on cannabis (no published value found). Predators eat leafhoppers but cannot stop a single viruliferous adult from infecting a plant within hours, so biological control does not manage curly top on its own. ## Can I use the environment against leafhoppers? Outdoors, timing and site are the environmental levers against beet leafhopper. Plant away from weedy rangeland and field edges with kochia, Russian thistle and mustards [1][3]. Keep transplants under cover through the spring migration, because young plants are most vulnerable and severity is greater with early infection [2][4]. Planting-date logic from other crops: in Arizona spinach and beets, delaying planting until leafhoppers become inactive (daily highs below about 60 °F / 15.6 °C) reduces curly top [11]. For a summer crop like cannabis the equivalent is protecting plants through the main spring flight, not avoiding it. Local timing varies; use your own sticky-card records (Grower practice). For potato leafhopper, reduce plant stress, since drought worsens hopperburn [17][18], and avoid fields next to alfalfa [17]. Cultivar: there is currently no information on hemp varietal resistance to BCTV [4]. Purdue suspects cultivars bred for western states may be more stressed, and more damaged, in the Midwest [17]. Trade-off: row covers on transplants raise temperature and humidity underneath; vent or remove them once plants are established and the main flight has passed (Grower practice). ## What should I not do about leafhoppers in flower? Do not spray broad-spectrum insecticides on flowering cannabis to "stop curly top"; the virus is already in the plant, the spray cannot prevent new transmissions and residues fail testing [1]. Do not take clones from plants with curled, yellowed or twisted new growth; cuttings carry the virus [4]. Do not keep infected plants in the field to "see if they grow out of it"; they remain virus sources even when side branches look healthy [1][4]. Do not mistake hopperburn for nutrient burn and change feeding; look under the leaves first [16]. Do not count every leafhopper on a sticky card as beet leafhopper; most species in hemp are harmless [1]. ## What are the common myths about leafhoppers on cannabis? - **"Spraying leafhoppers prevents curly top."** *Myth.* Transmission takes hours and migrants keep arriving [1][10]. - **"Curly top only spreads by leafhoppers."** *Myth.* Grafting and cuttings also transmit it; seed transmission is under investigation [4]. - **"Hopperburn is nutrient burn."** *Myth.* Same look, different cause; find the insects [16][17]. - **"Beet leafhoppers breed in hemp fields."** *Contested.* CSU field observations found adults only [1]; CSU lab work showed oviposition and development on hemp [5]. - **"Every leafhopper on the card is a threat."** *Myth.* Over a dozen species occur in Colorado hemp and only beet leafhopper transmits a known hemp pathogen [1]. ## Common mistakes - Transplanting unprotected seedlings next to weedy rangeland during the spring flight. - Spraying after curly top symptoms appear instead of rogueing. - Treating sticky-card totals as beet leafhopper counts without identification. - Cloning from outdoor mothers in curly top regions without testing. - Blaming nutrients for hopperburn. ## Evidence - Beet leafhopper as sole vector of BCTV and its prevalence in Colorado hemp: *Established* [1][5][6][7][10]. - Transmission speed (1 h acquisition, 4 h latent) and retention: *Established* in other crops [10][11][12]. - Degree-day models and fecundity: *Established* on sugar beet and alfalfa; *not measured on cannabis* [8][9][13]. - Insecticides ineffective against BCTV in hemp: *Supported* by CSU expert assessment [1][2]. - Reflective mulch and row covers: *Supported* in principle; untested in hemp [1][2][4]. - Hopperburn on hemp: *Established* as a symptom; yield impact unknown [17]. - Whether beet leafhopper reproduces on hemp in the field: *Contested* [1][5]. ## Glossary terms used here - Glossary: [beet curly top virus](https://genetixbay.com/knowledge/glossary/beet-curly-top-virus.md), [leafhopper](https://genetixbay.com/knowledge/glossary/leafhopper.md), [plant virus](https://genetixbay.com/knowledge/glossary/plant-virus.md), [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [fecundity](https://genetixbay.com/knowledge/glossary/fecundity.md), [parasitoid](https://genetixbay.com/knowledge/glossary/parasitoid.md) ## Sources 1. Cranshaw, W. 2020. Beet leafhopper and beet curly top virus (Insects/mites that feed on hemp). Colorado State University. https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Curly%20Top%20Beet%20Leafhopper%202020.pdf 2. Colorado State University. Beet leafhopper (Neoaliturus tenellus) and beet curly top virus. https://agsci.colostate.edu/agbio/ipm-pests/beet-leafhopper-beet-curly-top-virus/ 3. Pacific Northwest Insect Management Handbook. Hemp: leafhoppers. https://pnwhandbooks.org/node/25831 4. Frost, K., Ocamb, C.M. Hemp (Cannabis sativa) - Curly top. Pacific Northwest Plant Disease Management Handbook. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-curly-top 5. Chiginsky, J. 2021. Beet curly top virus - beet leafhopper dynamics in hemp in Colorado. M.S. thesis, Colorado State University. https://mountainscholar.org/items/690318d0-f830-4090-b0a5-c1e18581d7b5/full 6. Chiginsky, J., et al. 2021. First insights into the virus and viroid communities in hemp (Cannabis sativa). Frontiers in Agronomy 3: 778433. https://doi.org/10.3389/fagro.2021.778433 7. Giladi, Y., Hadad, L., Luria, N., Cranshaw, W., Lachman, O., Dombrovsky, A. 2020. First report of beet curly top virus infecting Cannabis sativa in western Colorado. Plant Disease 104(3). https://doi.org/10.1094/PDIS-08-19-1656-PDN 8. UC IPM. Beet leafhopper phenology model (Harries & Douglass 1948, Ecological Monographs 18: 47-79). https://ipm.ucanr.edu/weather/phenology-models-description/beet-leafhopper/ 9. Meyerdirk, D.E., Moratorio, M.S. 1987. Circulifer tenellus (Baker), the beet leafhopper: laboratory studies on fecundity and longevity. The Canadian Entomologist 119(5): 443-447. https://doi.org/10.4039/Ent119443-5 10. EPPO Global Database. Beet curly top virus (BCTV00) datasheet. https://gd.eppo.int/taxon/BCTV00/datasheet 11. Nischwitz, C., Olsen, M. 2011. Beet curly top disease (Curtoviruses) in spinach and table beets in Arizona (AZ1552). University of Arizona Cooperative Extension. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1552.pdf 12. Soto, M.J., Gilbertson, R.L. 2003. Distribution and rate of movement of the curtovirus Beet mild curly top virus in the beet leafhopper. Phytopathology 93(4): 478-484. https://doi.org/10.1094/PHYTO.2003.93.4.478 13. UC IPM. Potato leafhopper phenology model (Kouskolekas & Decker 1966, Ann. Entomol. Soc. Am. 59: 292-298). https://ipm.ucanr.edu/PHENOLOGY/ma-potato_leafhopper.html 14. Hogg, D.B. 1985. Potato leafhopper immature development, life tables, and population dynamics under fluctuating temperature regimes. Environmental Entomology 14(3): 349-355. https://doi.org/10.1093/ee/14.3.349 15. Sher, R.B., Shields, E.J. 1991. Potato leafhopper oviposition and development under cool fluctuating temperatures. Environmental Entomology 20(4): 1113-1120. https://academic.oup.com/ee/article/20/4/1113/2394359 16. Utah State University Extension. Potato leafhopper (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-potato-leafhopper 17. Bolt, M. 2021. Potato leafhopper on hemp. Purdue Pest&Crop newsletter 2021.16. https://extension.entm.purdue.edu/newsletters/pestandcrop/article/potato-leafhopper-on-hemp 18. Legrand, A. 2023. Beware of hopperburn. UConn Extension. https://extension.uconn.edu/publication/beware-of-hopperburn-2 19. IRAC. Mode of Action Classification (online). https://irac-online.org/mode-of-action/classification-online/ 20. Oregon State University Extension. Monitoring for beet leafhopper adults helps halt spread of plant virus (EM 9618). https://extension.oregonstate.edu/catalog/em-9618-monitoring-beet-leafhopper-adults-helps-halt-spread-plant-virus --- # Mealybugs and root mealybugs on cannabis: ID, life cycle in numbers and IPM > Mealybugs are occasional, slow-building pests of indoor cannabis, usually the citrus mealybug (Planococcus citri), sometimes the longtailed mealybug or root mealybugs (Rhizoecus). They are slow: about 4 weeks egg to adult at 25 °C and an r_m near 0.084/day (doubling in about 8 days, lab data on grapevine), with development failing at 35 °C. Wax shields them from contact sprays, ants farm them, and control rests on clean clones, ant control, and Cryptolaemus and Leptomastix released above about 20 °C. - Canonical: https://genetixbay.com/knowledge/pests/mealybugs.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the white cottony stuff on my cannabis stems?** White cottony tufts in cannabis branch crotches, leaf axils and along stems, with slow-moving oval insects 3-4 mm long underneath, are usually citrus mealybugs (Planococcus citri). Females lay their eggs inside those cottony ovisacs. Sticky honeydew, sooty mould and ants on the plant support the diagnosis. Powdery mildew is flat and has no insects; spider mite webbing is fine silk with tiny mites. **How fast do mealybugs reproduce on cannabis?** Citrus mealybugs reproduce slowly compared with mites or aphids. On grapevine at 25 °C, Kına and colleagues measured an intrinsic rate of increase of 0.084 per day, a mean generation time of 41 days and 32 offspring per individual. That means a doubling about every 8 days. Egg to adult takes about 28 days at 25 °C. No cannabis-specific life table has been published. **What temperature do mealybugs like?** Citrus mealybugs develop between roughly 10 and 33 °C, with fastest population growth near 25 °C. Studies on coffee, coleus and citrus put the lower developmental threshold at about 7 to 11 °C and the upper limit near 33.6 °C; at 35 °C all nymphs died on coffee. On coleus, fecundity peaked at 23 °C and population growth at 25 °C. Typical cannabis rooms at 22-28 °C suit them well. **Why don't sprays kill mealybugs?** Contact sprays often fail on mealybugs because adult females are coated in water-repellent wax and their eggs sit inside cottony ovisacs, so droplets never reach the insect. UC IPM notes the wax makes contact insecticides less effective and that young crawlers are the most susceptible stage. Contact treatments must be repeated two or more times, in veg only, to catch nymphs hatching from protected eggs. **Do ants cause mealybugs?** Ants do not cause mealybugs, but they make infestations worse. Ants collect the sugary honeydew mealybugs excrete and in return guard them against predators and parasitoids such as Cryptolaemus and Leptomastix, and may move them between plants. UC IPM advises controlling ants before or alongside any biological control release. In a cannabis room, ant trails up stems are a sign to look for mealybugs or aphids. **What is the best biological control for mealybugs?** For citrus mealybug on indoor cannabis, the standard pairing is the mealybug destroyer beetle Cryptolaemus montrouzieri plus the parasitoid wasp Leptomastix dactylopii. Cryptolaemus develops and reproduces fastest at 22-25 °C and 70-80 % RH and slows greatly below 20 °C; it needs egg masses to breed. Leptomastix prefers third-instar and young adult citrus mealybugs. Control ants first, and expect weeks, not days. **How long does Cryptolaemus take to control mealybugs?** Cryptolaemus montrouzieri takes weeks to control mealybugs because its egg-to-adult development takes about 4 to 6 weeks in warm conditions, according to UC IPM. Each larva can eat over 250 mealybug nymphs or 1,000 eggs. A single release mainly works through adult and larval feeding; real suppression comes from the next generation, so plan a program of 6-10 weeks and repeat releases where egg sacs persist. **What are root mealybugs and how are they different from root aphids?** Root mealybugs (Rhizoecus species) are bluish-grey to white, elongate-oval insects up to about 2.4 mm long that live on roots, leaving white cottony wax especially between the pot wall and the rootball. Unlike root aphids, they have no tail-pipes (cornicles), move slowly, and take 2 to 4 months egg to adult. Rice root aphids are olive-green to brown, faster and develop in days. **Can I use rubbing alcohol on mealybugs on cannabis?** Dabbing isopropyl alcohol on mealybugs is a houseplant method: UC IPM suggests 70 % or weaker alcohol on a swab for individual insects. It can work on a few veg cannabis plants with a handful of colonies, but it is labour-heavy, can burn tissue, and misses hidden crawlers. Never use it on flowers. Check that alcohol is legal as a pest treatment on cannabis where you grow. **How long should I keep treating mealybugs?** Mealybug treatments must cover the whole egg-laying window, not just the visible insects. Citrus mealybug females lay eggs over 10 to 20 days, and egg to adult takes about four weeks at 25 °C. A contact program in veg therefore needs repeats every 5-7 days for at least four weeks, and a biological program 6-10 weeks, followed by weekly scouting until two consecutive checks find no live insects or fresh ovisacs. **Short answer.** White cottony tufts in branch crotches and along stems, with slow oval insects underneath, are mealybugs, on indoor cannabis usually the citrus mealybug (*Planococcus citri*). They are slow: about four weeks egg to adult at 25 °C and a population doubling roughly every 8 days [6]. Their wax shrugs off contact sprays, ants protect them, and they hide in places you do not look. Control rests on clean clones, ant control, repeated treatment across the 10-20 day egg-laying window in veg [1], and *Cryptolaemus* plus *Leptomastix* in rooms kept above about 20 °C [7][8]. ## Which mealybugs attack cannabis? Mealybugs on indoor cannabis are occasional pests, not key pests: Colorado State University's list of key hemp pests does not include them [14], and we found no published cannabis-specific mealybug life table. The species involved are the general greenhouse mealybugs, brought in on plants. *Supported* (extension consensus for greenhouses; cannabis evidence anecdotal). | Species | Where on the plant | How to tell it | Reproduction | |---|---|---|---| | Citrus mealybug, *Planococcus citri* | Stems, leaf axils, branch crotches, under leaves, buds | Oval, white wax, short equal-length side filaments, sometimes a darker line down the back [1][2] | 300-600 eggs in a cottony ovisac [2] | | Longtailed mealybug, *Pseudococcus longispinus* | Stems and foliage | Two tail filaments as long as or longer than the body; 17 pairs of marginal filaments; female up to about 3 mm (1/8 inch) [1][2] | Live young; no egg masses [1] | | Root mealybugs, *Rhizoecus* spp. | Roots, rootball surface | Bluish-grey to bluish-white, elongate-oval, up to 2.35 mm, short antennae, nearly eyeless, white cottony wax between pot and rootball [2][12] | 17-83 young per female in 1-3 litters (*R. hibisci*) [12] | | Solenopsis mealybug, *Phenacoccus solenopsis* | Stems and foliage | Host lists include *Cannabis sativa* [13] | Mainly outdoor/warm-climate; not well documented indoors | **Mealybugs are true bugs (Hemiptera: Pseudococcidae).** Females are wingless and stay mobile through their lives, unlike armoured scales. Males are tiny, winged, short-lived and do not feed [2]. **Many species can reproduce without mating** [1]. A single female arriving on a clone can start a colony. ## How do you recognise mealybug damage on cannabis? Mealybug damage on cannabis shows as white cottony masses, sticky honeydew, sooty mould and slow, weak growth near colonies. Mealybugs suck phloem sap, and heavy colonies reduce plant growth [1]. - **Cottony tufts** in leaf axils, branch crotches, on stems and on the undersides of fan leaves. Citrus mealybug ovisacs are the tell [1][2]. - **Honeydew** makes leaves below colonies shiny and sticky; black sooty mould grows on it [1]. - **Ants** walking up stems are often the first visible sign [1]. - **In flower,** colonies inside dense colas are almost impossible to remove; contaminated buds are unsaleable. - **Root mealybugs** show no specific top symptom; plants decline slowly. The infestation is not evident until the rootball is removed from the pot [12]. **Differentials.** Powdery mildew is flat, powdery and has no bodies (see [white powder on leaves](https://genetixbay.com/knowledge/diagnosis/white-powder-on-leaves.md)). Spider mite webbing is fine silk. Whitefly nymphs are flat, scale-like ovals under leaves. On roots, see the next section. ## How do you tell root mealybugs from root aphids and perlite? Root mealybugs (*Rhizoecus*) are slow, bluish-white oval insects with cottony wax and no tail-pipes; root aphids are olive-green to brown, faster and have cornicles. Under a 10x lens the difference takes seconds. | Feature | Root mealybug (*Rhizoecus*) | Rice root aphid | Perlite | |---|---|---|---| | Colour | Bluish-grey to bluish-white under wax [2][12] | Dark olive-green to brown | Bright white, glassy | | Shape and size | Elongate-oval, up to about 2.4 mm [12] | Round, pear-shaped aphid | Angular grains | | Cornicles (tail-pipes) | None | Present | n/a | | Wax | White cottony wax on rootball surface, especially against the pot wall [12] | Little wax; white cast skins | n/a | | Movement | Very slow, slower than springtails [2] | Walks when disturbed | None | | Development | 2-4 months egg to adult (*R. hibisci*) [12] | 4-21 days, temperature-dependent | n/a | See [root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md) for the full root comparison, including fungal hyphae. ## What are the citrus mealybug life-cycle numbers? Citrus mealybug life-table data come from lab studies on coffee, coleus, citrus and grapevine; none used cannabis. The figures agree on the big picture: development stalls below about 10 °C, runs fastest at 25-28 °C and fails at 35 °C. | Parameter | Value | Host, conditions and source | |---|---|---| | Female nymphal development (crawler to adult) | 76.6 days at 15 °C; 35.2 at 20 °C; 23.2 at 25 °C; 30.0 at 30 °C | Coffee, lab, 70 % RH [3] | | Male nymphal development | 37.9 days at 20 °C; 24.1 at 25 °C; 19.8 at 30 °C | Coffee, lab [3] | | Egg to adult (preadult) | 28.3 days (females), 26.3 (males) at 25 °C | Grapevine, lab, 65-70 % RH [6] | | Nymphal mortality | 80 % at 15 °C; 45 % at 20 °C; 30 % at 25 °C; 72.5 % at 30 °C; 100 % at 35 °C | Coffee [3] | | Temperature range for completing development | Females 15-32 °C; males 18-32 °C; no first instars survived at 10, 12 or 37 °C | Coleus, lab [5] | | Lower developmental threshold | 10.6 °C, female nymphal period, 334.9 degree-days | Coffee [3] | | Lower developmental threshold | 7.15 °C, egg to adult, 526.3 degree-days | Citrus, lab [4] | | Optimum and upper threshold | Optimum 27.85 °C; upper 33.64 °C | Citrus, lab [4] | | Eggs per female | 300-600, in an ovisac | Extension [2]; UC: 100-200 or more for most mealybugs [1] | | Egg-laying period | 10-20 days | Extension [1] | | Egg hatch | Within a few days | Extension [2] | | Adult longevity | 14.8 days (total adult); 34.0 days whole life | Grapevine, 25 °C [6] | | Peak fecundity | 23 °C | Coleus [5] | | Net reproductive rate R0 | 32.1 offspring per individual at 25 °C | Grapevine [6] | | Intrinsic rate of increase r_m | 0.084 per day at 25 °C | Grapevine [6]; on coleus r_m peaked at 25 °C [5] | | Finite rate of increase λ | 1.087 per day at 25 °C | Grapevine [6] | | Mean generation time T | 41.4 days at 25 °C | Grapevine [6] | | Doubling time | 8.3 days (ln 2 / 0.084) at 25 °C | Calculated from [6] | | Generations per year | 2-6 outdoors; continuous indoors | Extension [1] | | Sex ratio | No published value found in the abstracts used | — | **Degree-day check.** Using 526.3 degree-days above 7.15 °C [4], egg to adult is about 41 days at 20 °C, 29 days at 25 °C and 23 days at 30 °C. The 25 °C figure matches the 28.3 days measured on grapevine [6]. The linear model overestimates speed near the upper limit: on coffee, female nymphs took longer at 30 °C than at 25 °C [3]. **Longtailed mealybug and root mealybugs.** We found no comparable temperature-dependent life table for *Pseudococcus longispinus* in the sources used. For *Rhizoecus hibisci*, egg to adult takes about 2-4 months, adult females live 27-57 days and eggs hatch in under 24 hours [12]. ## Why do temperature and humidity matter for mealybugs? Temperature sets how fast citrus mealybugs breed, and normal cannabis rooms sit in their sweet spot. On coleus, fecundity peaked at 23 °C and population growth at 25 °C [5]; the citrus study put the optimum near 27.85 °C [4]. Veg rooms at 24-28 °C and flower rooms at 22-26 °C both suit them. **Heat helps them until about 30 °C.** Above 30 °C nymphal mortality climbs (72.5 % at 30 °C on coffee) and at 35 °C all nymphs died [3]. The upper threshold estimate is 33.64 °C [4]. No cannabis room should run that hot for long. **Cool slows them hard.** At 15 °C female nymphs took 76.6 days on coffee, with 80 % mortality [3]. Cool nights in a dark period slow development but do not stop it. **Humidity.** The lab studies ran at 65-80 % RH [3][5][6]. We found no published study isolating RH effects on citrus mealybug development. Wax protects mealybugs from desiccation, so dry flower rooms (45-55 % RH, late flower 40-50 %) do not stop them (Grower practice). **Humidity matters more for the natural enemies.** *Cryptolaemus* develops and reproduces fastest at 22-25 °C (72-77 °F) and 70-80 % RH [7], and *Leptomastix* prefers warm, sunny, humid conditions [8]. Late-flower rooms at 40-50 % RH and cooler nights are below the beetle's comfort zone. **No diapause indoors.** Under warm indoor conditions all stages are present year-round [1]. ## How fast can a mealybug population grow? A worked example Ten citrus mealybugs at 25 °C become about 58 in three weeks and about 1,500 in 60 days, in the unchecked exponential model. The calculation uses N(t) = N0 × e^(r_m × t) with r_m = 0.084 per day at 25 °C on grapevine [6]. | Days | Mealybugs at 25 °C (r_m 0.084/day) | |---|---| | 7 | about 18 | | 14 | about 32 | | 21 | about 58 | | 42 | about 340 | | 60 | about 1,500 | | 90 | about 19,000 | **Method.** N0 = 10; r_m = 0.084 per day [6]; doubling time = ln 2 / 0.084 = 8.3 days. At 60 days: 10 × e^(0.084 × 60) = 10 × e^5.04 ≈ 1,545. **The authors' own projection is lower.** Kına and colleagues projected 357 individuals at 60 days from 10 eggs [6]. Their stage-structured projection starts from eggs, which take weeks to start reproducing; the simple exponential assumes the stable age mix from day 1. Both are upper bounds with no natural enemies. **Compare with fast pests.** Rice root aphid at 25 °C has an r_m of 0.432 per day (see [root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md)), five times higher. Mealybugs are slow, which is why a cannabis crop of 10-14 weeks often finishes before a small infestation becomes a disaster, and why infestations go unnoticed in mother rooms that run for years. ## Where do mealybugs hide, how do they spread and how do they get in? Mealybugs reach indoor cannabis almost always on plants: rooted clones, mothers, houseplants and ornamentals carried into the grow [2]. Adult females cannot fly, so they do not blow in. - **Clones and mothers.** Long-lived mothers are the classic reservoir: slow pests build up in plants kept for years (Grower practice). - **Houseplants and ornamentals.** Citrus mealybug is common on citrus, indoor ornamentals and greenhouse crops and is usually brought indoors on an infested plant [2]. - **Crawlers.** First-instar crawlers walk between touching plants and are carried on hands, clothing, tools and air currents (Grower practice). - **Ants.** Ants move and guard mealybugs [1]. - **Root mealybugs** spread via purchased infested plants, crawlers from nearby hosts, reused pots, reused media and irrigation water [12]. **Hiding places.** Leaf axils, branch crotches, under bark-like lower stems, the base of the stem at the medium surface, inside trellis knots and plant ties, pot rims, under trays and in cracks in benches (Grower practice). Root mealybugs hide between the pot wall and the rootball [12]. ## How do you scout for mealybugs? Scout for mealybugs by checking stems, axils and crotches of every incoming plant and of mothers weekly, by watching for ants and honeydew, and by unpotting a sample of plants for root mealybugs. No published action threshold exists for cannabis; any confirmed colony on a mother or in flower warrants action (Grower practice). 1. **Incoming plants.** Inspect every clone and plant for cottony tufts, stems and leaf axils, and unpot to look at roots. Quarantine for at least four weeks, about one egg-to-adult cycle at 25 °C [6]. *Grower practice.* 2. **Weekly mother checks.** Look into branch crotches and at stem bases with a 10x lens. *Grower practice.* 3. **Ants and honeydew.** Ant trails or sticky shiny leaves trigger a close search [1]. 4. **Root checks.** For root mealybugs, slide plants out and look at the rootball surface against the pot wall [12]. 5. **Sticky cards** catch winged male mealybugs only; they do not show females and are a poor monitoring tool for mealybugs (Grower practice). 6. **White card trick.** A white, non-sticky card near infestations attracts *Cryptolaemus* adults [7], which shows where released beetles are active. **Lens.** 10x shows crawlers, filaments and ovisacs; 20x helps confirm young crawlers and parasitoid exit holes in mummies. ## How do you control mealybugs by life stage? Mealybug control by life stage comes down to one fact: eggs in ovisacs and waxed adults are shielded, crawlers are exposed. UC IPM notes that wax makes contact insecticides less effective and younger nymphs are more susceptible [1]; NC State adds that contact products usually need two or more applications to catch nymphs hatching from protected eggs [2]. | Stage | Exposure | What reaches it | |---|---|---| | Eggs in ovisac | Protected by cottony wax | Physical removal; Cryptolaemus adults and larvae eat eggs [7] | | Crawlers (1st instar) | Most exposed, least wax | Contact sprays in veg; predators | | Older nymphs | Increasingly waxed | Leptomastix (prefers 3rd instar) [8]; older Cryptolaemus larvae [7] | | Adult females | Heavily waxed, in crevices | Leptomastix (young adults) [8]; Cryptolaemus; hand removal | | Longtailed mealybug | Live-bearing, no ovisac [1] | Crawlers appear continuously | **Registrations differ by jurisdiction.** Follow the label and local law. No products or rates here. **Repeat interval.** Each female lays eggs over 10-20 days [1] and eggs hatch within a few days [2]. In veg, a contact program (insecticidal soap, horticultural oil) must repeat every 5-7 days for at least four weeks to keep killing new crawlers until the last protected eggs have hatched and before those crawlers mature (about 23-29 days to adult at 25 °C [3][6]). *Calculation from [1][3][6]; Grower practice for interval.* **The program is long because the pest is slow.** A six-week generation time [6] means you need a six- to ten-week campaign, not a one-off. Stopping after two sprays because the cotton is gone is the common failure. **Resistance.** Mealybugs breed slowly, so resistance builds slowly, but parthenogenetic reproduction [1] means survivors pass on their traits intact. Rotate [modes of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md) by class; IRAC group numbers on any registered label identify the class. Systemic classes are the "reliable" option in ornamentals [2] but are unregistered on cannabis in most places. **Spot treatments.** UC IPM suggests swabbing individual mealybugs on houseplants with 70 % or weaker isopropyl alcohol [1]. On a few veg plants, it works; on a room, it does not; on flowers, never. ## Which biological controls work on mealybugs? Biological control of citrus mealybug indoors rests on the predatory beetle *Cryptolaemus montrouzieri* and the parasitoid wasp *Leptomastix dactylopii*, often released together [8]. *Anagyrus* parasitoids add coverage. All need warmth, egg masses or the right host stage, and ant control. ### Cryptolaemus montrouzieri (mealybug destroyer) - **What it eats.** Adults and young larvae mainly eat mealybug eggs and young nymphs; older larvae eat mealybugs of any age. Each larva can eat over 250 nymphs or 1,000 eggs [7]. - **Temperature and RH.** Fastest development and reproduction at about 22-25 °C (72-77 °F) and 70-80 % RH; below 20 °C (68 °F) and with short day lengths, reproduction slows greatly [7]. One lab study on *P. citri* found a lower developmental threshold of 11.5 °C, an upper of 25.5 °C and 400 degree-days for the immature stages [9]. - **Development.** Eggs hatch in about 5 days at 27 °C (80 °F); larvae feed 3-4 weeks; egg to adult takes 4-6 weeks in warm conditions [7]. - **Reproduction.** Females live about 2 months and lay 200-400 eggs; eating the waxy eggs of egg-sac-producing insects stimulates laying [7]. Release where egg sacs are plentiful. - **Release.** UC IPM suggests one or more releases of several beetles per square foot of growing area or per plant where egg masses are present in greenhouses and interiorscapes [7]. Check the sex ratio: healthy shipments are about 50:50; females have black to dark-brown front legs, males orange [7]. - **Look-alike warning.** Cryptolaemus larvae are covered in long wax filaments and look like large mealybugs. Brush the wax: beetle larvae have visible legs and mouthparts [7]. Do not spray them. ### Leptomastix dactylopii (parasitoid wasp) - **Hosts.** Best known as a citrus mealybug parasitoid. UC's Pest Note says it kills only citrus mealybug [1]; UC's natural enemies gallery says it attacks at least 50 mealybug species, including longtailed mealybug [8]. UF EDIS notes that females reared on vine mealybug produce fewer, smaller offspring than on citrus mealybug [11]. Use it for *P. citri*. *Contested* breadth. - **Stages attacked.** Prefers third-instar nymphs and young adult females; one egg per host; the host becomes a mummy [8]. - **Development.** About 3 weeks egg to adult at warm temperatures [8]; 15-16 days egg to adult on vine mealybug third instars (UF EDIS citing Muştu et al. 2022) [11]. - **Fecundity.** Each female parasitises about 60-100 mealybugs in her life [8]. - **Temperature.** Progeny production rose and adult longevity fell as temperature increased from 18 to 30 °C [10]. It prefers warm, sunny, humid environments [8]. ### Anagyrus spp. - *Anagyrus pseudococci* (in the 1989 study) is another encyrtid parasitoid of *Planococcus* mealybugs; like *Leptomastix*, its progeny production rose with temperature from 18 to 30 °C [10]. Its temperature-dependent development on vine mealybug has been modelled [15]. Use it alongside *Leptomastix* where suppliers offer it. ### What the natural enemies need - **Ant control first.** Ants attack mealybug natural enemies [1][8]. - **Warmth.** Keep the room above about 20 °C during release periods for Cryptolaemus [7]. - **No broad-spectrum, persistent insecticides** [7][8]. Soaps and oils kill exposed beetle larvae and wasps on contact; time any spray before releases. - **Reduce dust** and offer nectar sources where possible [7][8]. - **Expect weeks.** With a 4-6 week beetle generation [7] and a 3-week wasp generation [8], suppression takes one to two natural-enemy generations. **Root mealybugs** are not reached by Cryptolaemus or Leptomastix. In other crops, hot-water immersion of potted plants (49 °C water until the rootball reaches 46 °C) was 100 % effective on palms [12]; that is unsuitable for cannabis roots. Discard infested plants and media. ## How can you use the environment against mealybugs? Environment is a weak lever against citrus mealybug in cannabis, because its optimum of 25-28 °C [4][5] is a normal cannabis set-point. The real environmental play is making the room good for the natural enemies. - **Keep release rooms at 22-26 °C and 60-70 % RH in veg** to suit Cryptolaemus (fastest at 22-25 °C, 70-80 % RH [7]). - **Do not chill rooms to slow mealybugs.** Cooling to 15-18 °C slows the pest (76.6 days nymphal at 15 °C [3]) but stops Cryptolaemus reproducing below 20 °C [7] and slows the crop. - **Do not heat rooms to kill them.** Development fails at 35 °C [3], which is crop-damaging heat. - **In flower,** hold normal humidity (45-55 %, late flower 40-50 %) for botrytis and powdery mildew control, and accept that natural enemies will work more slowly. ## What not to do about mealybugs in flower In flower, contain mealybugs; do not try to spray them out of buds. - **Do not spray soaps, oils or alcohol on flowers.** Residues stay on trichomes and wet buds invite botrytis. - **Do not use systemic insecticides.** Most are unregistered on cannabis and persist into harvest. - **Do not take clones from an infested plant,** and do not keep it as a mother. - **Do:** remove and bag heavily infested branches, release Cryptolaemus where egg sacs are present, control ants, isolate plants, and inspect harvested material before drying. - **After harvest:** bag plant waste in the room, clean benches, trellis and pots, and restart with inspected clones. ## What are the common myths about mealybugs? - **"Mealybugs explode like spider mites."** *Myth.* r_m is about 0.084 per day at 25 °C [6], several times lower than mites or aphids. Their danger is that they go unnoticed. - **"One spray clears them."** *Myth.* Wax and ovisacs shield adults and eggs; repeats are required [1][2]. - **"Leptomastix only attacks citrus mealybug."** *Contested.* UC sources disagree [1][8]; it performs best on citrus mealybug [11]. - **"Cryptolaemus works in any room."** *Myth.* Reproduction slows greatly below 20 °C [7]. - **"Ants are harmless."** *Myth.* Ants guard mealybugs and attack their natural enemies [1][8]. - **"Sticky cards will show mealybugs."** *Grower practice says no.* Only winged males are caught. ## How do you confirm mealybug control worked? - Two consecutive weekly checks, at least four weeks after the last live female was seen (one egg-to-adult cycle at 25 °C [6]), find no live crawlers, nymphs, adults or fresh white ovisacs. - Old ovisacs are empty or contain parasitoid-killed mummies with round exit holes. - No fresh honeydew and no ant trails. - Root checks show no bluish-white insects or fresh wax against the pot wall. ## Common mistakes - Treating cotton, not insects: the wax stays after the mealybugs die, and new ovisacs look the same. - Stopping after two sprays when the egg-laying window is 10-20 days [1]. - Releasing biological control without killing the ant trail first. - Spraying Cryptolaemus larvae because they look like mealybugs. - Releasing Cryptolaemus into a cool or late-flower room below 20 °C. - Keeping an infested mother for years. - Bringing houseplants or citrus trees into the grow area. ## Evidence - Citrus mealybug development, survival and population growth versus temperature: *Established* for coffee, coleus, citrus and grapevine in the lab [3][4][5][6]; not measured on cannabis. - Wax reducing contact-spray efficacy, crawlers as the susceptible stage, ant protection: *Established* (extension consensus) [1][2]. - Cryptolaemus and Leptomastix biology: *Established* [7][8][9][10][11]; release efficacy on cannabis: *Grower practice*. - Leptomastix host range: *Contested* [1][8][11]. - Mealybugs as cannabis pests: *Supported* by host records [13] and grower reports; not a key pest in university hemp lists [14]. - Root mealybug biology: *Supported* for ornamentals [12]. ## Sources 1. Flint, M.L., 2016 (updated). Pest Notes: Mealybugs. UC ANR Publication 74174. University of California IPM. https://ipm.ucanr.edu/PMG/PESTNOTES/pn74174.html 2. Frank, S. and Baker, J., 2010 (revised 2022). Mealybugs. NC State Extension. https://content.ces.ncsu.edu/publication/mealybugs 3. Correa, L.R.B., Santa-Cecília, L.V.C., Souza, B. and Cividanes, F.J., 2008. Heat requirements of the white mealybug Planococcus citri on coffee plants. Arquivos do Instituto Biológico 75(1). https://doi.org/10.1590/1808-1657v75p0532008 4. Al-Shammari, A. and Al-Zubaidy, H., 2017. Growth threshold and degree days requirement for development and growth of citrus mealybug Planococcus citri. Iraqi Journal of Agricultural Sciences 48(2). https://doi.org/10.36103/ijas.v48i2.415 5. Goldasteh, S., Talebi, A.A., Fathipour, Y. et al., 2009. Effect of temperature on life history and population growth parameters of Planococcus citri on coleus. Archives of Biological Sciences 61(2):329-336. https://doi.org/10.2298/ABS0902329G 6. Kına, E., Kara, H. and Özgökçe, M.S., 2018. Life table and some biological features of Planococcus citri on 41-B grapevine variety. Yüzüncü Yıl Üniversitesi Tarım Bilimleri Dergisi 28(5):247-256. https://gcris.yyu.edu.tr/items/e8a214c2-7537-41e7-9003-45ba37fe362d 7. UC IPM. Natural Enemies Gallery: Mealybug destroyer (Cryptolaemus montrouzieri). https://ipm.ucanr.edu/natural-enemies/mealybug-destroyer/ 8. UC IPM. Natural Enemies Gallery: Mealybug parasitoid Leptomastix dactylopii. https://ipm.ucanr.edu/natural-enemies/mealybug-leptomastix-parasitoid/ 9. Saeedi, M. and Damavandian, M.R., 2015. [Temperature-dependent development of Cryptolaemus montrouzieri reared on Planococcus citri] (descriptive title). Arthropods. https://doaj.org/article/ad165c15745246e3851188c8716e76eb 10. Entomophaga 34:111-120 (1989). Progeny production and adult longevity of the mealybug parasitoids Anagyrus pseudococci, Leptomastix dactylopii and Leptomastidea abnormis in relation to temperature. https://doi.org/10.1007/BF02372594 11. University of Florida IFAS EDIS IN1420. Leptomastix dactylopii Howard (Hymenoptera: Encyrtidae): parasitoid of mealybugs. https://journals.flvc.org/edis/article/view/134441 12. Hara, A.H. and Niino-DuPonte, R. Rhizoecus hibisci: Rhizoecus root mealybug. Crop Knowledge Master, University of Hawaii CTAHR. https://cms.ctahr.hawaii.edu/ckm/Home/Insects-and-Other-Pests/Mealybugs/Rhizoecus-hibisci 13. ScaleNet. Phenacoccus solenopsis Tinsley, 1898: catalogue entry and host list. https://scalenet.info/catalogue/Phenacoccus%20solenopsis/ 14. Cranshaw, W., 2020. Hemp pests (presentation). Colorado State University. https://webdoc.agsci.colostate.edu/bspm/InsectInformation/Talks2020/HempPests.pdf 15. Daane, K.M., Malakar-Kuenen, R.D. and Walton, V.M., 2004. Temperature-dependent development of Anagyrus pseudococci as a parasitoid of the vine mealybug, Planococcus ficus. Biological Control 31(2):123-132. https://doi.org/10.1016/j.biocontrol.2004.04.010 --- # Root aphids (rice root aphid) on indoor cannabis: ID, life cycle in numbers and IPM > The 'root aphid' of indoor cannabis in North America is mainly the rice root aphid (Rhopalosiphum rufiabdominale). At 25 °C it doubles in about 1.6 days (r_m 0.432/day, lab data from Tsai and Liu 1998), it reproduces only asexually indoors, and winged alates spread it plant to plant. Control rests on clean clones, removing every root between runs, a plant-free gap, and fungal drenches; nematodes and soil predators are unproven. - Canonical: https://genetixbay.com/knowledge/pests/root-aphids.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Veg, Transition, Flower · Systems: Soil, Coco, Rockwool, Living soil, DWC, RDWC - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why is my cannabis plant slowly yellowing and wilting when pH and EC are fine?** A cannabis plant that slowly stalls, droops between waterings and yellows while root-zone pH, EC and watering all check out may have rice root aphids, so slide it out of the pot and inspect the roots with a 10x lens. Cranshaw and Wainwright-Evans found no unique symptom, only general decline and slower growth. Rule out cheaper causes first: runoff pH and EC, overwatering and Pythium root rot. **What are the small bugs on my cannabis roots?** Small, round, dark olive-green to brownish insects clustered on cannabis roots, often at the edge of the rootball and the drainage holes, are usually rice root aphids (Rhopalosiphum rufiabdominale) in North American indoor grows. A 10x lens shows six legs, antennae and short tail-pipes (cornicles). Worm-like larvae with shiny black heads are fungus gnats; slow, bluish-white insects in cottony wax are root mealybugs. **How fast do root aphids multiply?** Rice root aphids multiply very fast at grow-room temperatures. In laboratory work by Tsai and Liu (1998), the population at 25 °C had an intrinsic rate of increase of 0.432 per day, a doubling time of 1.61 days and a mean generation time of 8.7 days. Unchecked, 10 aphids could become roughly 87,000 in 21 days. Nymphs reached adulthood in 4.4 days at 30 °C and 20.7 days at 10 °C. **How do root aphids get into an indoor grow?** Rice root aphids usually arrive on rooted clones or in root balls of bought plants, then spread inside the room as winged females (alates) that fly to new plants and give birth on stems and leaves. Cranshaw and Wainwright-Evans list reused pots with live roots, roots left after harvest, surface mulches and poor isolation of new plantings as outbreak factors. Grasses and sedges are also hosts. **How do I get rid of root aphids in cannabis?** Rice root aphids are hard to clear from a running cannabis room, so the decisive step is breaking the cycle between runs. Bag infested plants with their medium, remove every root and pot, clean surfaces, and keep the room free of all plants and weeds for at least two to four weeks. In veg, fungal drenches with Beauveria bassiana or Isaria fumosorosea had the best observed results, though controlled trials are lacking. **Do beneficial nematodes kill root aphids?** Entomopathogenic nematodes are a poor bet against root aphids. In the only field test we found, on the woolly apple aphid, a Steinernema carpocapsae broadcast spray cut root colonies only marginally (P = 0.10) and topdressing did nothing. Later work by Berkvens and colleagues (2014) showed the nematodes fail to parasitise that aphid because its body suppresses their symbiotic bacteria. No trial on rice root aphid exists. **Root aphids or fungus gnats on my sticky cards?** Winged rice root aphids and fungus gnats both land on yellow sticky cards, but they look different under a 10x lens. A root aphid alate has a compact, dark aphid body, short legs and two pairs of clear wings held over the back, with cornicles at the rear. A fungus gnat is a slender, long-legged fly with long beaded antennae and one pair of smoky wings. Confirm by checking roots. **Is the white stuff on my cannabis roots root aphids, root mealybugs or perlite?** White specks on cannabis roots can be perlite, cast aphid skins, mealybug wax or beneficial fungal threads. Under a 10x lens perlite is hard, angular and glassy; cast aphid skins are papery, hollow and aphid-shaped; root mealybug wax is cottony and sits on slow, bluish-white oval insects, often between pot wall and rootball; fungal hyphae are fine, thread-like webs. Heavy powdery wax colonies fit lettuce-root-aphid-type Pemphigus, not typical rice root aphid. **How long should a grow room sit empty to kill root aphids?** No published starvation study gives a safe plant-free period for rice root aphid. Adults live about 9 days at 30 °C and 30 days at 10 °C in the lab, and Hesler and Kindler saw them survive 24 days on caged potato without reproducing. A gap of at least two weeks after removing every root is the minimum; four weeks, with no weeds or houseplants, is safer (Grower practice). **What temperature do root aphids like?** Rice root aphids grow best at 20 to 25 °C (68 to 77 °F), which is exactly a cannabis root-zone set-point. Tsai and Liu (1998) found the highest net reproductive rate at 20 °C (57 offspring per female) and the fastest population growth at 25 °C. The lower developmental threshold is about 6 to 7 °C, and nymphs did not develop past the fourth instar at 35 °C. **Short answer.** If cannabis plants slowly stall, droop and yellow even though pH, EC and watering check out, tip one out and look at the roots. Small, round, olive-green to brownish aphids clustered on roots are root aphids, in North America almost always the rice root aphid, *Rhopalosiphum rufiabdominale* [1]. At 25 °C a colony can double in about 1.6 days [2]. They are hard to clear from a running room, so the decisive moves are clean clones, removing every root between runs, a real plant-free gap, and fungal drenches started early. ## What is the "root aphid" on indoor cannabis? The root aphid on indoor cannabis in North America is mainly the rice root aphid, *Rhopalosiphum rufiabdominale* (also spelled *rufiabdominalis*) [1]. Cranshaw and Wainwright-Evans first saw it on cannabis in northeastern Colorado in 2011 and have since found it in California, Florida, Maine, Michigan, Nevada, Oregon and Washington; they suspect it occurs across the continental USA [1]. *Established.* The species name means "red abdomen". It is known in North America since at least 1900, first recorded in the USA on cotton roots in 1937, and is mainly a pest of grasses (Poaceae) and sedges (Cyperaceae), with records on squash, peppers, celery and dieffenbachia [1]. A 2020 Colorado State University talk lists it among the key hemp pests in Colorado [6]. Much online "root aphid" material is wrong. Cranshaw notes that cannabis forum posts borrowed images and biology from *Pemphigus* species (such as the lettuce root aphid) and from grape phylloxera, which are different insects with different life cycles [5]. **Other root aphids on cannabis.** We found no published record of *Pemphigus* spp., *Aphis armoraciae* or *Smynthurodes betae* as established root pests of cannabis. If you find a heavily waxed root aphid, send a sample to a diagnostic lab rather than assume. **Indoors it is anholocyclic.** In Asia the species alternates between *Prunus* trees (sexual generation, overwintering eggs) and grasses. On indoor cannabis it is anholocyclic: females give birth to live female young without mating, all year, and there are no eggs [1][4]. There are no North American records on *Prunus* [1]. **Not an outdoor hemp pest.** Rice root aphid has not been found on outdoor hemp [1]; it occurs in soil, coco coir, rockwool and aeroponics indoors [1][5]. ## How do you recognise rice root aphid damage? Rice root aphid causes no unique symptom on cannabis. Cranshaw and Wainwright-Evans report general decline, slower growth and, sometimes, discoloured lower leaves on heavily infested plants [1]. That is why it is so often misread as a nutrient, watering or root-rot problem. - **Above ground.** Slow, uneven growth, mild wilting between waterings, yellowing that does not respond to feeding [1][4]. Yield loss is possible at high populations [5]. - **On the roots.** Colonies sit on fine roots, typically at the rootball edge against the pot wall and around drainage holes. USU describes the aphid as dark olive-green with a round body [4]. A 10x lens shows antennae, legs and the paired tail-pipes (cornicles) that mark any aphid. - **At the stem base.** Adults gather at the plant base and on lower stems; alates (winged females) appear on stems and leaves, particularly as plants flower and near maturity [1]. - **On foliage.** Foliage colonies are rare and small. Most young born up top migrate down to the roots [1]. In hydro (DWC, RDWC, aero), check the root mass at the net pot and the waterline. Heavily infested squash roots in aeroponics showed discolouration and decay [1], so root browning in hydro is not always Pythium. ## What is the white stuff on the roots: root aphids, root mealybugs or perlite? White material on cannabis roots is most often perlite, cast aphid skins, root mealybug wax or fungal threads, and a 10x lens tells them apart in a minute (Grower practice). | What you see under 10x | Most likely | Notes | |---|---|---| | Hard, angular, glassy white grains that do not move | Perlite | The most common false alarm | | Papery, hollow, aphid-shaped white shells | Cast skins (exuviae) of rice root aphid | Aphids moult four times; skins pile up near colonies | | Round olive-green to brown bodies, legs, cornicles | Rice root aphid | Live aphids move when disturbed | | Slow, bluish-white oval insects in cottony wax, often between pot wall and rootball | Root mealybug (*Rhizoecus* spp.) | No cornicles; see [mealybugs](https://genetixbay.com/knowledge/pests/mealybugs.md) | | Clustered colonies under heavy white powdery wax | *Pemphigus*-type root aphid | UC IPM describes lettuce root aphid colonies this way [7] | | Fine branching threads, web-like | Fungal hyphae (often beneficial or saprophytic) | No bodies inside | The heavy white wax that forum photos show belongs to *Pemphigus*-type aphids, whose colonies are "covered with a white powdery wax" [7]. Rice root aphid colonies are mostly visible as dark aphids plus their white cast skins (Grower practice). ## What are the rice root aphid life-cycle numbers? Rice root aphid life-table data come from one laboratory study, Tsai and Liu (1998), run at constant temperatures from 10 to 35 °C (Environmental Entomology; host is rice per the title) [2], plus a conference abstract by Ridland (2006) [3]. No cannabis-specific life table has been published. These are the best numbers available. | Parameter | Value | Conditions and source | |---|---|---| | Development, 1st instar to adult | 20.7 days at 10 °C; 4.4 days at 30 °C | Lab, constant temperature [2] | | Development, birth to first reproduction | 4.2 days at 30 °C (shortest observed) | Lab, nine constant temperatures 10-35 °C [3] | | Development at 15, 20, 25 °C | No published value found in accessible abstracts | Estimate below | | Lower developmental threshold | 7.0 °C (1st instar), 6.2 (2nd), 6.3 (3rd), 5.1 (4th), 6.1 °C (all immatures) | [2]; Ridland gives 7.3 °C birth to adult [3] | | Upper limit | Nymphs did not develop past the 4th instar at 35 °C | [2] | | Degree-days, birth to adult | No published value found; about 80-105 degree-days above 6.1 °C back-calculated by us from [2] | Our arithmetic, not a published constant | | Immature survival | 52.7-90.2 % across 10-30 °C | [2] | | Adult longevity | 29.7 days at 10 °C; 9.4 days at 30 °C | [2]; USU: "about a month" [4] | | Lifetime offspring per female | 63.3 nymphs at 20 °C; 31.9 at 30 °C | [2] | | Net reproductive rate R0 | Highest, 57.2, at 20 °C | [2] | | Intrinsic rate of increase r_m | 0.432 per day at 25 °C (highest tested) | [2] | | Doubling time | 1.61 days at 25 °C | [2]; USU: "roughly every 2 days" [4] | | Mean generation time T | 8.7 days at 25 °C | [2] | | Optimum for population growth | 20-25 °C | [2] | | Sex ratio | 100 % female indoors (no males produced) | Anholocyclic [1][4] | | Eggs | None indoors; live birth | [1][4] | **Our development-time estimate.** Using the 6.1 °C threshold and about 93 degree-days (the middle of our back-calculated range), birth to adult takes roughly 10 days at 15 °C, 7 days at 20 °C and 5 days at 25 °C. Treat these as estimates; the published anchor points are 20.7 days at 10 °C and 4.4 days at 30 °C [2]. ## Why do temperature and moisture matter for rice root aphids? Rice root aphid grows best at 20 to 25 °C (68 to 77 °F) [2], and that is exactly the root-zone temperature a well-run cannabis room holds. There is no environmental window where the crop is comfortable and the aphid is not. **Heat speeds generations up to about 30 °C.** Development falls from 20.7 days at 10 °C to 4.4 days at 30 °C [2]. Above about 30 °C fecundity drops (31.9 offspring per female at 30 °C against 63.3 at 20 °C), and at 35 °C nymphs fail to finish development [2]. No cannabis root zone should run that hot anyway. **Cool root zones slow, not stop, them.** The lower threshold of about 6 °C [2] is far below any useful cannabis root-zone temperature. Dropping a root zone from 24 °C to 18 °C roughly lengthens development from about 5 to about 8 days (our degree-day estimate), which slows a colony but does not control it. **Air RH and VPD barely reach them.** Rice root aphids live in the medium, so canopy RH (veg 60-70 %, flower 45-55 %, late flower 40-50 %) and VPD have little direct effect on them. No published study links rice root aphid survival to substrate moisture. **Moisture matters for the fungi you use against them.** Entomopathogenic fungi need moist conditions to germinate and infect. A medium kept evenly moist (not waterlogged) after a fungal drench gives the spores a better chance (Grower practice; see [entomopathogenic fungi](https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.md)). **Mulches help the aphid.** Cranshaw and Wainwright-Evans list surface mulches and near-optimal temperatures among outbreak factors [1]. Mulch keeps the top of the medium dark, humid and undisturbed. ## How fast can a rice root aphid population grow? A worked example Ten rice root aphids at 25 °C can, in theory, become about 87,000 in three weeks. The calculation uses N(t) = N0 × e^(r_m × t), with r_m = 0.432 per day at 25 °C from Tsai and Liu [2]. | Days after 10 aphids arrive | Population at 25 °C (r_m 0.432/day) | |---|---| | 7 | about 210 | | 14 | about 4,200 | | 21 | about 87,000 | | 28 | about 1.8 million | **Method.** N0 = 10; r_m = 0.432 per day; doubling time = ln 2 / 0.432 = 1.60 days, matching the published 1.61 days [2]. At 14 days: 10 × e^(0.432 × 14) = 10 × e^6.05 ≈ 4,200. **This is the upper bound.** It assumes no predators, no fungi, unlimited roots and constant 25 °C. Real colonies run out of root surface, crowd, and push out alates. The point stands: one infested clone on day 1 can mean a room-wide problem by the time anyone notices slow growth. **No r_m is published for other temperatures** in the accessible abstract [2]. At 20 °C the net reproductive rate is higher (57.2) but generations are slower, so growth is slower than at 25 °C [2]. ## Where do root aphids hide, and how do they spread and get in? Rice root aphids get into indoor grows mainly on rooted clones and plants with root balls, then spread inside as winged alates and via reused material [1]. Every route is something you carry in or leave behind. - **Clones and bought plants.** Poor isolation of new plantings is a named outbreak factor [1]. A rooted clone hides the aphids inside the plug. - **Winged alates.** Alates are produced periodically and in particular abundance as plants flower and near maturity [1]. They fly to new plants and give birth on stems and leaves; the young walk down to the roots [1]. A flowering room therefore seeds the next room. - **Reused pots and roots left behind.** Reused pots with live roots and uncut roots left after harvest are named outbreak factors [1]. - **Reused medium.** Old coco or soil carries root fragments and aphids into the next run (Grower practice; consistent with [1]). - **Weeds and other hosts.** Grasses and sedges are main hosts [1][4]. USU advises weed control in and around crop areas, especially grasses and sedges [4]. Hesler and Kindler saw survival for 24 days on caged potato without reproduction [1], so other plants can carry them through a gap. - **Hydro water.** Aphids at the waterline of shared reservoirs can move between sites (Grower practice). **Where they hide on the plant.** Rootball edges against the pot wall, drainage holes, the root collar just under the surface, and in hydro the net pot and root mass near the water line. ## How do you scout for root aphids? Scout for rice root aphids by checking roots of every incoming clone, checking a sample of plants weekly, and running yellow sticky cards and stem bands. There is no published action threshold; any confirmed colony warrants action (Grower practice). 1. **Incoming clones.** Unpot or break open the plug of every incoming clone and look at the roots with a 10x lens. Quarantine for at least two weeks, which covers about two generations at 25 °C (8.7-day generation time [2]). *Grower practice.* 2. **Weekly root checks.** In each room, slide a few plants out of their pots each week, prioritising mothers and slow plants. Look at the rootball edge and drainage holes. *Grower practice.* 3. **Yellow sticky cards** at canopy height and just above pot level catch alates [1][4]. Grower practice is about one card per 10 m² plus one near each mother plant, changed every one to two weeks. 4. **Sticky bands on lower stems** catch aphids moving up from the soil or down from foliage [1]. 5. **Map hits.** Trace affected plants back to a mother, a clone batch or a bench. **Lens.** 10x is enough to see rice root aphids; 20x helps separate cast skins from perlite and to see cornicles. ## How do you control root aphids by life stage? Rice root aphids indoors have no egg stage: every individual is a nymph or a live-bearing adult female on the roots, or a winged alate on the canopy [1]. That means a contact treatment hits every stage it touches, but misses whatever it does not reach in a dense rootball. **Registrations differ by jurisdiction.** Many root drenches and all systemic insecticides are unregistered on cannabis in most places. Follow the label and local law. No products or rates here. **Repeat interval.** A contact drench (soap, fungal spores) must be repeated before survivors' young mature and reproduce. At 25 °C a newborn reaches adulthood in about 5 days (estimate) and the generation time is 8.7 days [2], so repeat contact drenches every 4-5 days for at least three applications (two to three generations). At 20 °C stretch to about 6-7 days. *Calculation from [2]; Grower practice for the count.* **Fungal drenches need repeats too.** Fungal spores take several days to kill; repeated drenches at 5-7 day intervals keep inoculum present across generations (Grower practice). **Resistance.** All indoor rice root aphids are clones of their mothers (parthenogenesis; see [parthenogenesis](https://genetixbay.com/knowledge/glossary/parthenogenesis.md)). A colony that survives a treatment is a population of identical survivors. Rotate [modes of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md) by class; for registered chemistry, IRAC group numbers on the label identify the class. *Established principle* (see [pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md)). **Alates on foliage.** Alates are exposed and can be hit by foliar contact sprays in veg. In flower, rely on cards and stem bands. ## Which biological controls work on root aphids? Biological control of rice root aphid in containers is weak: Cranshaw and Wainwright-Evans found few effective biological controls, with *Beauveria bassiana* and *Isaria fumosorosea* showing the greatest efficacy among commercial products [1]. No controlled cannabis trial exists for any agent. ### Entomopathogenic fungi - ***Beauveria bassiana* and *Isaria fumosorosea*** drenches had the best observed results in cannabis facilities [1]. *Supported* (observational). - ***Lecanicillium lecanii*** infected rice root aphids on aeroponic squash, and a similar-looking fungus was seen on aphids on cannabis in California [1]. - **Beauveria plus azadirachtin.** UC IPM reports that a *B. bassiana* product with azadirachtin gave good control of root aphids in crops similar to lettuce [7]. Azadirachtin use on cannabis is jurisdiction-dependent. - ***Metarhizium*.** Against the lettuce root aphid (*Pemphigus bursarius*), a *Metarhizium* isolate was pathogenic and sporulated abundantly on cadavers in bioassays, while *Lecanicillium* (then *Verticillium*) isolates were only weakly pathogenic [8]. That is a different aphid; no *Metarhizium* data on rice root aphid exist. - **Conditions.** Keep the medium moist after a drench, avoid fungicide drenches for several days before and after, and treat early while colonies are small (Grower practice). See [Beauveria bassiana](https://genetixbay.com/knowledge/glossary/beauveria-bassiana.md). ### Entomopathogenic nematodes: questionable Entomopathogenic nematodes (*Steinernema*, *Heterorhabditis*) are not a reliable root aphid control. Against the root-feeding woolly apple aphid, a *S. carpocapsae* broadcast spray reduced root colonies only marginally (P = 0.10) and topdressing had no effect [9]. Berkvens and colleagues later showed the nematodes fail to parasitise that aphid because their symbiotic bacteria are suppressed [10]. Aphids, being small sap-feeders, are poor nematode hosts. *Contested to Myth* for rice root aphid; no trial exists. ### Soil predators: unproven - ***Stratiolaelaps scimitus*** eats fungus gnat larvae, thrips pupae, springtails and shore fly larvae, and is inactive below about 15 °C (59 °F) [11]. No published study tests it against root aphids. It may take small nymphs; treat it as a fungus gnat and thrips tool (Grower practice). See [Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md). - ***Dalotia coriaria*** (rove beetle) survives best at 18-27 °C (65-80 °F) and 50-85 % RH and mainly eats fungus gnat and shore fly larvae and thrips pupae [11]. No root aphid data. - **Ants.** The ponerine ant *Hypoponera opacior* was observed in a Colorado facility, apparently preying on rice root aphid [1]. Not a release option. ### Parasitoids for alates Some growers release *Aphidius* species against alates on foliage. Evidence on rice root aphid in cannabis is anecdotal (Grower practice). See [Aphidius](https://genetixbay.com/knowledge/glossary/aphidius.md). ## How do you break the root aphid cycle between runs? Breaking the cycle between runs is the single most effective rice root aphid control, because the outbreak factors Cranshaw and Wainwright-Evans list (reused pots with live roots, uncut roots after harvest, poor isolation of new plantings) are all carry-over [1]. 1. **Bag plants with their medium** in the room before moving them. Do not walk infested root balls through clean areas. 2. **Remove every root.** Pull roots out of pots, net pots, rockwool slabs and hydro sites. Uncut roots left after harvest are a named outbreak factor [1]. 3. **Do not reuse medium** from an infested room in another cannabis room. 4. **Clean and disinfect** pots, trays, reservoirs, lines and floors. 5. **Keep the room plant-free.** No weeds, no houseplants, no grasses near intakes [4]. No published starvation-survival time exists for rice root aphid. Adults live up to about 30 days at 10 °C and 9 days at 30 °C [2], and they survived 24 days on a non-host [1]. A gap of at least two weeks with zero plant material is the minimum; four weeks is safer. *Grower practice, informed by [1][2].* 6. **Restart with inspected clones** from a clean mother, quarantined. **Mothers are the reservoir.** If a mother room is infested, the whole facility is. Replace mothers from clean stock or tissue culture rather than treating them forever. ## How can you use the environment against root aphids? Environmental control of rice root aphid is limited, because its optimum (20-25 °C [2]) overlaps the cannabis root zone. A few levers help. - **Do not run hot root zones.** Above 26 °C the aphid develops faster (4.4 days to adult at 30 °C [2]), and Pythium risk rises. Keep root zones at 18-22 °C. - **Skip surface mulches** in rooms with a history, because mulches favour outbreaks [1]. - **Keep moisture even after fungal drenches** to help spores infect, without waterlogging (which invites Pythium). - **Canopy RH and VPD** do not affect root colonies directly; keep normal stage set-points (veg 60-70 % RH, flower 45-55 %, late flower 40-50 %) to protect against botrytis and powdery mildew. - **Avoid excess nitrogen** [4]. ## What not to do about root aphids in flower In flower, contain rice root aphids rather than trying to eradicate them. - **Do not drench residual or systemic insecticides** into the root zone. Most are unregistered on cannabis and leave residues. - **Do not spray buds** to hit alates. Use cards and stem bands. - **Do not raise humidity** to help fungi; that invites botrytis in dense flowers. - **Do not keep infested plants as mothers** or take clones from them. - **Do:** isolate infested plants, keep them watered and fed, harvest, bag everything in the room, and break the cycle with a full clean-out and plant-free gap. ## What are the common myths about root aphids? - **"Cannabis root aphids are lettuce root aphids or phylloxera."** *Myth.* The cannabis species is mainly rice root aphid; forum biology was borrowed from *Pemphigus* and phylloxera [1][5]. - **"Beneficial nematodes kill root aphids."** *Myth* on current evidence. Marginal field effect on woolly apple aphid [9]; nematode bacteria suppressed [10]; no rice root aphid trial. - **"A one-week break kills them."** *Contested.* No starvation data; adults can live about a month in cool conditions [2] and 24 days on a non-host [1]. - **"Fungal drenches work."** *Supported* by observation [1], not by controlled cannabis trials. - **"Root aphids are an outdoor problem."** *Myth.* Not found on outdoor hemp [1]. - **"The white fluff on roots is root aphids."** *Contested.* Usually perlite, cast skins, mealybug wax or fungi; rice root aphids themselves are olive-green to brown [4]. ## How do you confirm root aphid control worked? - Root checks every week for at least three weeks (two to three generations at 25 °C [2]) show no live aphids, only old cast skins. - No alates on yellow cards or stem bands for three weeks. - New growth vigour returns, and runoff pH and EC stay normal. - In a room with a history, recheck every incoming clone and every cycle. ## Common mistakes - Chasing nutrient fixes for weeks without looking at roots. - Calling winged root aphids fungus gnats because both appear on cards. - Panicking at perlite. - Moving clones from an infested mother into a clean room. - Leaving roots in pots, net pots or slabs after harvest. - Starting the next cycle the day after harvest in the same room. - Relying on nematodes or soil predatory mites alone. - Treating once and stopping, when survivors double every 1.6 days at 25 °C [2]. ## Evidence - Identity of the main indoor root aphid on cannabis in North America, anholocyclic indoor life cycle, alate behaviour and outbreak factors: *Established* [1]. - Temperature-dependent development, survival, fecundity and r_m: *Established* for rice in the lab [2][3]; not measured on cannabis. - Damage symptoms: *Supported* [1][4]. - Fungal drenches: *Supported* by observation [1]; no controlled cannabis trial. - Nematodes against aphids: *Contested to Myth* [9][10]. - Soil predatory mites and rove beetles against root aphids: no published data (*Grower practice*). - Plant-free gap length: *Grower practice*, informed by longevity data [1][2]. ## Sources 1. Cranshaw, W. and Wainwright-Evans, S., 2020. Cannabis sativa as a host of rice root aphid (Hemiptera: Aphididae) in North America. Journal of Integrated Pest Management 11(1):15. https://doi.org/10.1093/jipm/pmaa008 2. Tsai, J.H. and Liu, Y.-H., 1998. Effect of temperature on development, survivorship, and reproduction of rice root aphid (Homoptera: Aphididae). Environmental Entomology 27(3):662-666. https://doi.org/10.1093/ee/27.3.662 3. Ridland, P.M., 2006. The influence of temperature on the development, growth and fertility of Rhopalosiphum rufiabdominalis and R. insertum (Hemiptera: Aphididae). Entomological Society of America Annual Meeting abstract. https://esa.confex.com/esa/2006/techprogram/paper_25420.htm 4. Utah State University Extension. Rice Root Aphids (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-rice-root-aphid 5. Cranshaw, W., 2020. Rice root aphid: an insect surprise on indoor-grown cannabis. Entomology Today, 24 July 2020. https://entomologytoday.org/2020/07/24/rice-root-aphid-indoor-grown-cannabis-integrated-pest-management/ 6. Cranshaw, W., 2020. Hemp pests (presentation). Colorado State University. https://webdoc.agsci.colostate.edu/bspm/InsectInformation/Talks2020/HempPests.pdf 7. UC IPM. Lettuce pest management guidelines: Lettuce root aphid. University of California ANR. https://ipm.ucanr.edu/agriculture/lettuce/lettuce-root-aphid/ 8. Chandler, D., 1992. Entomopathogenic fungi against the lettuce root aphid, Pemphigus bursarius (descriptive title). Phytoparasitica 20. https://doi.org/10.1007/BF02980401 9. Brown, M.W., Jaegers, J.J., Pye, A.E. and Schmitt, J.J., 1992. Control of edaphic populations of woolly apple aphid using entomopathogenic nematodes and a systemic aphicide. Journal of Entomological Science 27(3):224-232. https://jes.kglmeridian.com/view/journals/ents/27/3/article-p224.xml 10. Berkvens, N., Van Vaerenbergh, J., Maes, M., Beliën, T. and Viaene, N., 2014. Entomopathogenic nematodes fail to parasitize the woolly apple aphid Eriosoma lanigerum as their symbiotic bacteria are suppressed. Journal of Applied Entomology 138(9):644-655. Listing: https://www.pestinfo.org/ISPIdata/public/publications/6S1962B118 11. UConn IPM. Biological control of fungus gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ --- # Shore flies: algae farmers in your propagation tray > Shore flies (Scatella stagnalis, S. tenuicosta) breed in algae on wet media, rockwool, benches and floors. Larvae eat algae, not roots, but larvae and adults carry Pythium, Thielaviopsis, Fusarium and Verticillium in their gut and frass. At 25 C S. stagnalis goes egg to adult in 11.4 days and multiplies at r_m 0.263/day. Control is algae and puddle management first; Bti and soil mites do little, rove beetles and repeated nematode drenches help. - Canonical: https://genetixbay.com/knowledge/pests/shore-flies.html - Category: Pests · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Rockwool, Coco, Soil, Living soil, Ebb and flow, Drip, NFT - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the difference between shore flies and fungus gnats?** Shore flies (Scatella spp.) are stout, about 3 mm long, like tiny house flies, with dark wings carrying about five pale spots, short bristle-like antennae, short legs and strong flight. Fungus gnats are delicate, long-legged, with long beaded antennae and clear wings. Shore fly larvae are yellow-brown with no black head and live in algae; fungus gnat larvae are white with a shiny black head. **Are shore flies harmful to cannabis?** Shore flies do not eat cannabis roots; their larvae feed on algae and decaying matter on wet surfaces. The harm is indirect. Larvae and adults can carry Pythium, Thielaviopsis, Fusarium and Verticillium in their gut and droppings, and adults move these between plants in propagation. Black fecal specks on leaves are cosmetic. In clone and seedling areas, large numbers deserve control. **How long is the shore fly life cycle?** The shore fly Scatella stagnalis develops from egg to adult in about 15.9 days at 20 C and 11.4 days at 25 C in rockwool, and about 10 days at a fluctuating 23-34 C. Development needs about 213 degree-days above 6.4 C. Females start laying about 3 days after emerging, lay about 315 eggs each at 25 C and live about 15 days. **How fast do shore flies multiply?** Shore flies multiply much faster than fungus gnats. Scatella stagnalis has an intrinsic rate of increase of 0.263 per day at 25 C in rockwool, so ten flies can become about 400 in two weeks and about 2,500 in three weeks if unchecked. The related S. tenuicosta reached 0.430 per day at 28.5 C, doubling about every 1.6 days. **Does Bti kill shore flies?** Bti is not a reliable shore fly control. It is a fungus gnat larvicide, and no published trial showing good control of Scatella larvae was found. University extension guides for shore flies list algae control, rove beetles, nematodes and insect growth regulators instead. If you have both pests, Bti will treat the gnats and leave the shore flies, which is a common reason growers think Bti failed. **How do I get rid of shore flies?** Get rid of shore flies by removing their food: algae. Keep floors, benches, trays and slabs free of standing water and green film, let the media surface dry between irrigations, cover rockwool and slab tops, and avoid excess fertiliser runoff. Then add rove beetles (Dalotia coriaria) preventively, use yellow sticky cards or tape to trap adults, and repeat nematode drenches. **Why do I have shore flies in my hydroponic or rockwool system?** Shore flies appear in hydroponic and rockwool systems because wet, lit, nutrient-rich surfaces grow algae, and Scatella larvae eat algae. Exposed rockwool cube tops, slab cuts, drippers, trays, channels and reservoir lids under light are typical breeding sites. Shore fly larvae survive even submerged, which many predators cannot. Covering wet surfaces from light is the single most effective fix. **Do predatory mites control shore flies?** Soil predatory mites such as Stratiolaelaps scimitus do eat shore fly larvae, but Kansas State extension reports they are usually not effective at regulating shore fly populations. Shore fly larvae live in saturated algae and even standing water, where the mites cannot survive. Mites may help in pots that dry between irrigations, but rove beetles and algae control are better choices. **Can nematodes control shore flies?** Entomopathogenic nematodes (Steinernema species) infect shore fly larvae, but extension services rate the control as inconsistent or insufficient because the nematodes are poorly adapted to the semi-aquatic algae mats. Some growers use repeated high-rate drenches of Steinernema carpocapsae. In one trial, nematodes disappeared quickly from rockwool, which lowered control compared with peat. **Short answer.** Shore flies (*Scatella stagnalis*, and in some greenhouses *S. tenuicosta*) are stout little black flies with pale-spotted wings that breed in algae on wet rockwool, trays, benches and floors [8][9]. Their larvae eat algae, not roots [8]. The risk is disease: larvae and adults carry *Pythium*, *Thielaviopsis*, *Fusarium* and *Verticillium* in their gut and droppings [5][6][7]. At 25 C *S. stagnalis* goes from egg to adult in 11.4 days and can double in under 3 days [1]. Kill the algae and the puddles first; Bti and soil mites do little, rove beetles and sticky traps help. ## Shore flies at a glance: which numbers matter? The shore fly numbers that matter are an 11-16 day generation at 20-25 C, about 300 eggs per female, and an r_m of 0.263/day at 25 C, more than twice the fungus gnat rate. Values are for *Scatella stagnalis* in rockwool unless stated [1]. | Parameter | Value | Conditions and source | |---|---|---| | Common species | *Scatella stagnalis*; also *S. tenuicosta* | [1][2][12] | | Adult size | ~3.1 mm (1/8 in), black body, reddish eyes | [8][11] | | Wings | dark, with about 5-6 pale spots each | [8][9] | | Mature larva | ~6.3 mm (1/4 in), yellow-brown, no head capsule, forked rear breathing tubes | [8][9] | | Larval instars | 3 | [8] | | Egg to adult | 15.9 d at 20 C; 11.4 d at 25 C; 10.1 d at 23-34 C (mean 28.5 C) | rockwool [1] | | Lower developmental threshold | 6.4 ± 2.7 C | [1] | | Degree-days egg to adult | 212.8 DD above 6.4 C | [1] | | Upper limit | no value found; pupal mortality 29% at mean 28.5 C (vs 7-10% at 20-25 C) | [1] | | Pre-oviposition period | ~3 days | [9] | | Female longevity | 15.5 d at 25 C (males 22.0 d) | [1] | | Fecundity | 315 ± 19 eggs/female (20.4 eggs/female/day) at 25 C | [1] | | Sex ratio | 0.521 female | [1] | | Net reproductive rate R0 | 126.1 female eggs/female at 25 C | [1] | | Generation time T | 18.4 d at 25 C | [1] | | r_m | 0.263/day at 25 C | [1] | | Doubling time | 2.6 d (ln2 / r_m; the paper reports 5.3 d) | calculated from [1] | ## What are shore flies and where do they live? Shore flies are flies of the family Ephydridae, and *Scatella stagnalis* is the most common species in US greenhouses [11][12]. In the wild they live along wetland margins and feed on algae and microbes [4]. Shore fly larvae are trophic generalists on algae. On monocultures of 17 algae, 13 supported development to adult, with egg-to-adult times from 12.1 days on a diatom to 23.0 days on a blue-green alga [3]. In a grow, shore flies breed wherever algae grow on wet, lit, nutrient-rich surfaces: exposed rockwool cubes and slab tops, propagation trays, capillary mats, drippers and channels, under benches and on wet floors [8][9]. They thrive under moist conditions and are most common in propagation [8]. Shore flies often appear after fungus gnat numbers start to fall in a crop [12]. That timing tricks growers into thinking a gnat treatment failed. No published study of shore flies on cannabis was found. Everything here comes from greenhouse ornamentals, vegetables and rockwool cucumber work and is extrapolated (*Supported*). ## How do I tell shore flies from fungus gnats? Tell shore flies from fungus gnats by body shape and wings. Shore flies are robust, house-fly-shaped, about 3 mm long, with short legs, short bristle-like antennae and dark wings with about five pale spots [8][9][14]. Fungus gnats are delicate and mosquito-like, with long legs, long beaded antennae and clear or grey wings with a Y-shaped vein [14]. | Feature | Shore fly (*Scatella*) | Fungus gnat (*Bradysia*) | |---|---|---| | Body | stout, house-fly-like | slender, mosquito-like | | Antennae | short, bristle-like, shorter than head | long, beaded, longer than head | | Wings | dark, ~5 pale spots each | clear to grey, Y-shaped vein | | Flight | strong, fast; flies up when disturbed | weak; runs on the medium | | Larva | yellow-brown, no head capsule, forked rear tubes | white-clear, shiny black head | | Larval food | algae, decaying matter at the surface | fungi, organic matter, roots | | Main harm | frass specks, pathogen spread | root feeding, pathogen spread | Sources: [8][9][11][14]. On a sticky card, shore flies look like tiny dark house flies and fungus gnats like thin mosquitoes. A 10x hand lens shows the wing spots [11]. The predatory hunter fly (*Coenosia attenuata*) is about twice the size of a shore fly, with clear unspotted wings, and perches on leaves to ambush prey [9]. Do not kill it. ## What is the shore fly life cycle in numbers? The shore fly life cycle runs egg, three larval instars, pupa and adult, and *Scatella stagnalis* completes it in 15.9 days at 20 C and 11.4 days at 25 C in rockwool [1][8]. ### How does temperature change shore fly development? Shore fly development speeds up steadily with temperature, and a simple degree-day model fits the published data. These are the published values: | Species | Temperature | Egg to adult (days) | Female longevity (days) | Eggs/female | r_m (/day) | Source and conditions | |---|---|---|---|---|---|---| | *S. stagnalis* | 20 C | 15.9 | - | - | - | rockwool [1] | | *S. stagnalis* | 25 C | 11.4 | 15.5 | 315 | 0.263 | rockwool [1] | | *S. stagnalis* | 23-34 C (mean 28.5) | 10.1 | - | - | - | rockwool, fluctuating [1] | | *S. tenuicosta* | 20 C | 14.5 | 21.8 | 379 | - | algae on filter paper [2] | | *S. tenuicosta* | 26 C | 8.2 | 19.9 | 710 | - | algae on filter paper [2] | | *S. tenuicosta* | 28.5 C | 7.0 | 15.0 | 477 | 0.430 (highest) | algae on filter paper [2] | No development data at 15, 30 or 35 C were found for either species. For *S. stagnalis*, 212.8 degree-days above 6.4 C [1] predict about 13.6 days at 22 C and 9.9 days at 28 C (calculated here; the model reproduces the measured 11.4 days at 25 C). *S. tenuicosta* needs about 154 degree-days [2]; its threshold was not given in the abstract. Extension summaries agree: about 8 days at 78 F (26 C) and 14 days at 68 F (20 C) [9], or 15-20 days per generation depending on medium temperature [8][11]. ### How many eggs does a shore fly lay and how long do adults live? A *Scatella stagnalis* female lays about 315 eggs at 25 C, about 20 per day, and lives about 15.5 days; males live about 22 days [1]. Extension sources give 300-500 eggs per female [9][11]. *S. tenuicosta* lays more when warm: 379 eggs at 20 C, 710 at 26 C and 477 at 28.5 C, with peak daily output of 33.5 eggs at 26 C [2]. The authors considered 26 C near optimal for reproduction [2]. Eggs are laid in algae or very wet areas and hatch in 2-3 days [9][11][13]. Larvae feed about 7-10 days, and adults emerge 4-5 days after pupation [11][13]. Females need about 3 days to mature before laying [9]. This short window is why adult sprays alone fail. ### What are the shore fly life-table parameters? At constant 25 C in rockwool, *Scatella stagnalis* has a net reproductive rate of 126.1 female eggs per female, a generation time of 18.4 days and an intrinsic rate of increase of 0.263/day [1]. The proportion of females was 0.521 [1]. The paper gives the doubling time as 5.3 days. ln2 / 0.263 is 2.6 days, and ln(126.1) / 18.4 confirms r_m = 0.263, so the 2.6-day figure is consistent with the other published parameters. Use 2.6 days for planning. *S. tenuicosta* had its highest R0 (329.6) at 26 C and its highest r_m (0.430/day) at 28.5 C, with a generation time of 12.4 days and a doubling time of 1.6 days [2]. Stage-specific mortality stayed at or below 5.7% [2]. Heat costs *S. stagnalis* pupae. Pupal mortality rose from 7% at 20 C and 10% at 25 C to 29% at a fluctuating mean of 28.5 C [1]. ## Why do temperature and moisture matter for shore flies? For shore flies, moisture and algae decide whether a population exists, and temperature decides how fast it grows. Every life stage is found on or near algae [9]. **Temperature.** Cannabis rooms at 22-28 C are where shore flies grow fastest. *S. stagnalis* develops in 11-14 days across that range [1] (calculated for 22 C), and *S. tenuicosta* reproduces best near 26 C [2]. Propagation heat mats under trays speed both the algae and the flies. **Lower limit.** The *S. stagnalis* threshold of about 6.4 C [1] is far below grow-room temperatures. Cooling is not a control. **Surface moisture.** Shore flies tolerate saturated and even submerged conditions that most predators cannot [8]. A surface that dries between irrigations stops algae and removes the habitat [9]. **Light on wet surfaces.** Algae need light, water and nutrients. Exposed rockwool, white trays and clear channels under strong LEDs grow algae fastest (*Grower practice*). Covering wet surfaces from light starves the larvae. **Fertiliser.** Use the minimum fertiliser level that grows the crop well and avoid excess runoff, which feeds algal blooms [11]. **Air humidity.** Room RH is a minor factor. High RH and low VPD in propagation domes slow surface drying, so algae and shore flies build up there. See [kb-term-vpd](https://genetixbay.com/knowledge/glossary/vpd.md). **Diapause.** No diapause has been described for greenhouse *Scatella* in the sources checked; indoors they breed continuously. ## How fast can a shore fly population grow? (worked example) Ten shore flies left unchecked at 25 C can become about 400 in 2 weeks and about 2,500 in 3 weeks. This uses N(t) = N0 × e^(r_m × t) with the published r_m values [1][2]. | Species and temperature | r_m (/day) | Day 7 | Day 14 | Day 21 | |---|---|---|---|---| | Fungus gnat *B. impatiens*, 25 C (for comparison) | 0.111 | 22 | 47 | 103 | | *S. stagnalis*, 25 C, rockwool | 0.263 | 63 | 397 | 2,504 | | *S. tenuicosta*, 28.5 C, algae | 0.430 | 203 | 4,116 | 83,499 | N0 = 10; values rounded. Example: 10 × e^(0.263 × 21) = 10 × e^5.52 ≈ 2,504. Fungus gnat r_m is from Ishihara and Tagami; see [kb-pests-fungus-gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md). This is an unchecked exponential upper bound: unlimited algae, no predators, a stable age structure. Real populations level off when algae run out. The point is speed: a shore fly problem can appear within two weeks of algae appearing. ## How do shore flies spread plant diseases? Shore fly larvae and adults carry soil-borne pathogens in their gut and frass, and adults move them to healthy plants. The evidence is from lab and greenhouse-crop studies. **Pythium.** *S. stagnalis* larvae fed on cucumber roots colonised by *Pythium aphanidermatum*; 97% of first and second instars, 20% of third instars and pupae, and 10% of adults carried mature oospores in the gut [5]. Excreted oospores germinated, and both larvae and adults transmitted the pathogen to healthy cucumber plants [5]. **Other soil-borne fungi.** Adult shore flies were shown to be aerial vectors of *Verticillium dahliae*, *Fusarium oxysporum* f. sp. *basilici* and *Thielaviopsis basicola* [6]. Adults were attracted to sporulating cultures and infected tissue and picked up spores within 10-20 minutes [6]. **Inoculum load.** One adult deposited about 2.4 × 10^7 viable *V. dahliae* spores per day in frass, and spread the pathogen over about 2.2 cm² per hour [6]. **Fusarium on lisianthus.** Adult shore flies, fungus gnats and moth flies picked up *Fusarium avenaceum* spores from infected stems and carried them to healthy lisianthus; 75% of plants were infected within 4 days [7]. **Field relevance.** Extension sources note that disease transmission may be less likely under real greenhouse conditions than in the lab [8][9]. In cannabis propagation, where *Pythium* and *Fusarium* are already present in many facilities, treat a shore fly outbreak as a sanitation alarm (*Supported*). See [kb-diseases-root-rot-pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md). ## Where do shore flies hide and how do they get in? Shore flies hide as eggs, larvae and pupae in algae mats on wet media surfaces, under benches, in floor puddles, drains and capillary mats, and as adults on leaves and walls near those sites [8][9]. **Infested media and plants.** Large numbers move between greenhouses in infested growing medium [8]. Inspect incoming plugs and cubes for larvae and algae [11]. **Flight.** Adults are strong fliers but usually stay close to breeding sites [11]. They come in through doors and vents from wet outdoor areas. **Wet structures.** Uneven floors that pool water, leaking emitters, open reservoirs and algae-covered trays keep a population going between crops [9]. ## How do I scout for shore flies? Scout shore flies with yellow sticky cards checked weekly, and by looking for larvae and pupae in algae on wet surfaces. **Sticky cards.** Place yellow cards near the media surface and just above the canopy, and count adults weekly with a 10x lens [8][11]. Wisconsin extension suggests blue cards for shore flies and about 10 traps per 1,000 sq ft (about 1 per 9 m²) [13]. **Sticky tape.** Yellow sticky tape along walls or above the crop, especially in propagation, both monitors and mass-traps adults [8][9]. **Larvae and pupae.** Look in green or brown algae films for yellow-brown larvae with forked rear tubes and dark, spindle-shaped pupae [9]. Potato slices attract fungus gnat larvae, not shore fly larvae; a clean potato slice with flies on the cards points to shore flies (*Grower practice*). **Frass.** Black specks of droppings on leaves near wet areas are a shore fly sign [8][9]. **Thresholds.** No published action threshold exists for shore flies on any crop in the sources checked. Record counts per card per week, and act on a rising trend in propagation (*Grower practice*). ## Which shore fly controls hit which life stage? Shore fly controls that work target the algae habitat and the larvae; adult sprays fail because females lay eggs about 3 days after emerging and the puparium resists insecticides [9][11]. | Control | Eggs | Larvae | Pupae | Adults | Evidence | |---|---|---|---|---|---| | Algae and puddle removal | removes laying sites | removes food | removes habitat | fewer emerge | *Established* [8][9][11] | | Dry media surface | yes | yes | - | - | *Established* [9] | | *Dalotia coriaria* rove beetles | yes | yes | - | - | *Supported* [9] | | *Steinernema* nematodes | - | infects | - | - | inconsistent [8][9] | | *Stratiolaelaps scimitus* | - | eats | - | - | mostly not effective [8] | | Bti | - | no reliable effect found | - | - | *Inconclusive* | | Insect growth regulators | - | suppress | - | - | *Supported* [9] | | Sticky cards and tape | - | - | - | trap | *Established* [8][9] | **Re-application timing.** Larvae feed for about 7-10 days and the generation turns over in 11-16 days at 20-25 C [1][11]. Any larval treatment needs repeating at least every 7-10 days through two generations, about 3-4 weeks, while algae control takes effect (*Grower practice*, derived from [1]). **Resistance.** Shore flies breed fast (r_m 0.263/day [1]), so repeated use of one insecticide class invites resistance. Rotate by mode-of-action class only. Insect growth regulators such as cyromazine (IRAC 17) and diflubenzuron (IRAC 15) are listed as drenches for both shore flies and fungus gnats [13]. Registrations on cannabis vary: follow the label and local law. ## Which biological controls work against shore flies? Biological control of shore flies is weaker than for fungus gnats, because shore fly larvae live in saturated algae and even standing water where most natural enemies cannot survive [8]. Use biologicals preventively and together with algae control [9]. ### Rove beetles (Dalotia coriaria) *Dalotia coriaria* (formerly *Atheta coriaria*) is the best-supported predator for shore flies. Adults and larvae feed on shore fly eggs and larvae, as well as fungus gnats and thrips pupae, in the growing medium [9][15]. Release adults in the evening; they are nocturnal [9]. *Dalotia* develops from egg to adult in about 17 days at 26 C (79 F), lays about 90 eggs per female, and does best at 18-27 C and 50-85% RH [15]. Release rates vary by supplier; follow the biocontrol supplier technical sheet. ### Entomopathogenic nematodes (Steinernema) *Steinernema* nematodes infect shore fly larvae but do not give sufficient control, because they are poorly adapted to the semi-aquatic breeding habitat [9]. Kansas State extension describes lab results as inconsistent and dependent on greenhouse conditions [8]. Some growers use repeated drenches of *Steinernema carpocapsae* at high rates against shore flies [9]. Do not mix nematodes with oxidising sanitisers. In peat and rockwool trials against *S. tenuicosta*, both *S. feltiae* and *S. carpocapsae* were tested; in rockwool the best control was 83-84% in the second week after two applications, and control was lower than in peat because nematodes disappeared quickly from rockwool [16] (year and journal not confirmed). ### Soil predatory mites (Stratiolaelaps scimitus) *Stratiolaelaps scimitus* eats shore fly larvae [10][15], but Kansas State extension reports that soil mites, including *S. scimitus* and *Hypoaspis aculeifer*, are in most cases not effective at regulating shore fly populations [8]. An older extension note says the mite can control shore flies only where there is no standing water [11]. Use mites for fungus gnats and thrips pupae, not as the main shore fly tool. ### Bti Bti is not a shore fly tool. It is a larvicide used against fungus gnats [10][14], and no published trial showing good control of *Scatella* larvae was found. Extension shore fly guides from Kansas State and UConn list algae control, rove beetles, nematodes and insect growth regulators, not Bti [8][9]. The bacterial product tested against *S. tenuicosta* in the peat and rockwool trial was a different subspecies, *B. thuringiensis* var. *thuringiensis* [16]. ### Natural enemies that arrive on their own The hunter fly *Coenosia attenuata* catches adult shore flies and fungus gnats in flight; it is not sold commercially but moves between greenhouses on plants [9]. The parasitoid wasp *Hexacola neoscatellae* (spelled *Hexacloa neoscatella* in the UConn sheet) can help regulate shore flies in unsprayed greenhouses [9]. ## How do I use the environment against shore flies? The environmental weapon against shore flies is a grow with no algae: no standing water, no lit wet surfaces, and media that dry at the surface between irrigations [9][11]. **Floors and benches.** Level floors so water drains and does not pool; clean up standing water on and under benches and walks [9][11]. Landscape or weed fabric under benches reduces algae, and with it fungus gnats and shore flies [18]. **Cover wet surfaces.** Cover rockwool cube and slab tops, trays and channels from light with opaque film or covers (*Grower practice*). Keep reservoirs lidded and lightproof. **Irrigation.** Avoid overwatering, especially early in a crop, so the upper surface dries between irrigations [9]. Fix leaking drippers. **Media.** Choose free-draining media and do not compact it [9]. **Disinfectants for algae.** Use disinfectants in pre-crop clean-up on surfaces and walkways [9]. Hydrogen peroxide can reduce algal growth and so shore fly numbers, but some disinfectants can harm plants [8]. The effect of hydrogen peroxide on algae, seedlings and shore fly reproduction in rockwool was studied directly by Vänninen and Koskula [17]. See [kb-term-hydrogen-peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md). **Trade-off in flower.** Removing algae and puddles has no downside for botrytis or powdery mildew; drier floors lower humidity around plant bases. The only risk is drying the root zone instead of the surface. See [kb-diseases-botrytis-bud-rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md). ## What should I not do against shore flies in flower? In flower, do not spray adult shore flies with insecticides. Adults are not the source, females lay within about 3 days of emerging, and residues on buds can fail compliance tests [9]. Follow the label and local law. Do not pour strong oxidisers or algaecides onto the root zone of flowering plants. Treat floors, benches, trays and covers, not the medium around live roots [8]. Do not starve flowering plants of water to dry out algae. Cover and dry the surfaces instead. Rove beetles, sticky tape and algae control are fine through flower. ## What are the common myths about shore flies? **"Shore flies eat roots like fungus gnats."** *Myth.* Shore fly larvae feed on algae and decaying matter and do not consume roots [8]. Their harm is pathogen spread and frass [5][6]. **"Bti controls shore flies too."** *Contested.* No trial showing good control was found, and extension shore fly guides do not list Bti [8][9]. **"Shore flies are only cosmetic."** *Myth.* Larvae and adults carry and transmit *Pythium aphanidermatum*, *Thielaviopsis basicola*, *Fusarium* and *Verticillium* in lab studies [5][6][7]. **"Spraying adults clears shore flies."** *Myth.* Insecticides do not effectively suppress shore flies because the puparium resists them and new adults lay within days [9][11]. **"Soil predatory mites handle shore flies."** *Contested.* Mites eat larvae but are usually not effective because they cannot live in standing water [8][11]. ## What are the common mistakes with shore flies? - Treating shore flies as fungus gnats and using Bti or potato traps. - Spraying adults instead of removing algae. - Leaving rockwool tops, trays and channels uncovered under strong light. - Ignoring puddles under benches and leaking emitters. - Using algaecides or strong peroxide on live root zones. ## Evidence - Biology and life tables of *S. stagnalis* in rockwool and *S. tenuicosta* on algae: *Established* (lab and greenhouse conditions) [1][2][3]. - Larvae feed on algae, not roots: *Established* [3][8]. - Pathogen transmission by larvae and adults: *Established* in the lab [5][6][7]; importance in commercial greenhouses: *Contested* [8][9]. - Algae and moisture control as the main tactic: *Established* [8][9][11]. - Rove beetles: *Supported*; nematodes and soil mites: inconsistent [8][9]. - Bti against shore flies: *Inconclusive* (no trial found). - All extrapolated to cannabis; no cannabis-specific study found. ## Sources 1. Vänninen, I., 2001. Biology of the shore fly Scatella stagnalis in rockwool under greenhouse conditions. Entomologia Experimentalis et Applicata 98(3):317-328. https://doi.org/10.1046/j.1570-7458.2001.00788.x 2. Ugine, T.A., Sanderson, J.P. & Wraight, S.P., 2007. Developmental times and life tables for shore flies, Scatella tenuicosta (Diptera: Ephydridae), at three temperatures. Environmental Entomology 36(5):989-997. https://bioone.org/journals/environmental-entomology/volume-36/issue-5/0046-225X(2007)36[989:DTALTF]2.0.CO;2/Developmental-Times-and-Life-Tables-for-Shore-Flies-Scatella-tenuicosta/10.1603/0046-225X(2007)36[989:DTALTF]2.0.CO;2.full 3. Zack, R.S. & Foote, B.A., 1978. Utilization of algal monocultures by larvae of Scatella stagnalis. Environmental Entomology 7(4):509-511. https://doi.org/10.1093/ee/7.4.509 4. Foote, B.A., 1995. Biology of shore flies. Annual Review of Entomology 40:417-442. https://doi.org/10.1146/annurev.en.40.010195.002221 5. Goldberg, N.P. & Stanghellini, M.E., 1990. Ingestion-egestion and aerial transmission of Pythium aphanidermatum by shore flies (Ephydrinae: Scatella stagnalis). Phytopathology 80(11):1244-1246. https://doi.org/10.1094/Phyto-80-1244 6. El-Hamalawi, Z.A., 2008. Attraction, acquisition, retention and spatiotemporal distribution of soilborne plant pathogenic fungi by shore flies. Annals of Applied Biology 152(2):169-177. https://doi.org/10.1111/j.1744-7348.2007.00191.x 7. El-Hamalawi, Z.A. & Stanghellini, M.E., 2005. Disease development on lisianthus following aerial transmission of Fusarium avenaceum by adult shore flies, fungus gnats, and moth flies. Plant Disease 89(6):619-623. https://doi.org/10.1094/PD-89-0619 8. Cloyd, R.A., 2017. Greenhouse Pests: Shore Fly. Kansas State University MF3384. https://bookstore.ksre.ksu.edu/download/shore-fly_MF3384 9. Pundt, L., 2023. Managing Shore Flies in the Greenhouse. UConn Extension IPM. https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2023/11/2023shorefliesinthegreenhousefinal.pdf 10. Pundt, L., 2024. Managing Fungus Gnats and Shore Flies in Commercial Greenhouse Vegetable Transplant Production. UConn Extension. https://doi.org/10.61899/ucext.v1.060.2024 11. Cloyd, R.A., 1994. Shore flies. Floriculture Indiana 8(3):4-5, Purdue University. https://hortscans.ces.ncsu.edu/uploads/s/h/shore_fl_53bc05844e37a.pdf 12. Lindquist, R.K. Management of fungus gnats and shore flies. Connecticut Greenhouse Newsletter (Ohio State University/OARDC). https://hortscans.ces.ncsu.edu/uploads/m/a/manageme_53bac7fbd3ee4.pdf 13. Liesch, P.J. Fungus gnats and shore flies. University of Wisconsin-Madison Extension (XHT1128). https://hort.extension.wisc.edu/articles/fungus-gnats-and-shore-flies/ 14. UC IPM, 2013. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf 15. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ 16. Vänninen, I. & Koskula, H. Biological control of the shore fly (Scatella tenuicosta) with steinernematid nematodes and Bacillus thuringiensis var. thuringiensis in peat and rockwool. AGRIS record. https://agris.fao.org/search/ru/records/65df84a863b8185d9cad183c 17. Vänninen, I. & Koskula, H., 1998. Effect of hydrogen peroxide on algal growth, cucumber seedlings and the reproduction of shore flies (Scatella stagnalis) in rockwool. Crop Protection 17(6):547-553. https://doi.org/10.1016/S0261-2194(98)00060-X 18. Cloyd, R.A., 2015. Ecology of fungus gnats (Bradysia spp.) in greenhouse production systems associated with disease-interactions and alternative management strategies. Insects 6(2):325-332. https://doi.org/10.3390/insects6020325 --- # Slugs and snails: night shift on your seedlings > Slugs and snails, above all the gray field slug Deroceras reticulatum, chew smooth-edged holes in cannabis seedlings and young transplants at night in cool, wet weather. They lay clutches of about 10-40 eggs and do best near 17-20 C. Scout at night or under boards, protect seedlings with iron phosphate baits, copper barriers and traps, and remove hiding places. - Canonical: https://genetixbay.com/knowledge/pests/slugs-and-snails.html - Category: Pests · Level: Beginner - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg · Systems: Soil, Living soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is eating holes in my cannabis seedlings at night?** If cannabis seedlings or young transplants have irregular holes with smooth edges, or are clipped off overnight, and you see silvery slime trails in the morning, slugs or snails are the likely cause. The gray field slug Deroceras reticulatum is the most common culprit outdoors and in greenhouses. Confirm by checking with a flashlight two to three hours after dark, especially after watering or rain. **When are slugs most active?** Slugs are most active at night and on cloudy, foggy or rainy days, when the ground and leaves are wet. They hide from sun, heat and dry air under boards, mulch, pots and debris. In cold weather they shelter in the topsoil, and hot, dry periods stop activity. The gray field slug Deroceras reticulatum develops and lays eggs best at about 17-20 C. **How many eggs do slugs lay?** A gray field slug (Deroceras reticulatum) lays clutches of about 10-40 eggs, typically around 20, in soil cracks and under debris. In a Korean lab study a slug laid about 217 eggs in total at 20 C but only 105 at 16 C, and field estimates reach about 500 eggs a year. Eggs hatch in roughly 2-4 weeks depending on temperature. **Are iron phosphate slug baits safe around pets?** Iron phosphate slug baits are considered safer around children, pets and wildlife than metaldehyde baits, which are highly poisonous to dogs and cats. Slugs stop feeding soon after eating iron phosphate but take several days to a week to die, often out of sight, so you rarely see bodies. Some iron phosphate products are allowed in organic growing; follow the label and local law. **Do beer traps work for slugs?** Beer traps catch slugs, but only those within a few feet of the trap, so they are a monitoring and small-garden tool rather than a field solution. Use a deep-sided container sunk with its rim at soil level, covered with a lid that has entry holes, and refill it every few days. A sugar-water and yeast mixture works in place of beer. **Do copper barriers stop slugs?** Copper barriers deter slugs and snails when they are tall enough and kept clean. UC IPM recommends a copper strip at least 5 cm (2 in) tall, buried 2.5-5 cm (1-2 in) into the soil so slugs cannot go under it. Copper bands on pots and planters work until they tarnish; clean them with vinegar. Barriers fail if a slug is already inside. **Why are seedlings most at risk from slugs?** Seedlings are most at risk from slugs because a cannabis seedling has only a few small, succulent leaves and a soft stem, so one night of feeding can remove all its growing points or cut it off at the base. Older plants lose some leaf area but survive. Protect seedlings and transplants until stems firm up, usually the first 2-4 weeks outdoors. **How long do slugs live and how many generations do they have?** The gray field slug Deroceras reticulatum lives about a year and has one to two generations a year. A Korean lab study found egg-to-death lifespans of 151-216 days at 16-28 C, with juveniles taking 51-68 days to mature. UC IPM gives 3-6 months from hatching to maturity, depending on species. Mixed-age populations peak in spring and autumn. **Short answer.** Smooth-edged holes and clipped seedlings overnight, with silvery slime in the morning, mean slugs or snails, most often the gray field slug *Deroceras reticulatum* [1]. They feed at night in cool, wet weather and hide by day. Seedlings and fresh transplants are the ones that die. Scout with a flashlight or boards, protect young plants with iron phosphate baits and copper barriers, trap, and remove hiding places [1]. ## Which slugs and snails attack cannabis? The slugs that attack cannabis outdoors and in greenhouses are the same garden slugs that attack vegetables: the gray field slug *Deroceras reticulatum*, banded and three-band garden slugs (*Lehmannia* spp.), the tawny slug *Limacus flavus* and the greenhouse slug *Milax gagates* [1]. The brown garden snail is the common snail [1]. No published study of slug damage to cannabis specifically was found; the biology below is from vegetable and lab studies and is extrapolated (*Supported*). ## How do I recognise slug and snail damage? Slug and snail damage on cannabis is irregular holes with smooth edges, chewed leaf margins, and seedlings cut off at the base overnight [1]. Silvery mucus trails on leaves, pots and soil confirm slugs or snails, because earwigs and caterpillars make similar holes [1]. See [kb-pests-caterpillars](https://genetixbay.com/knowledge/pests/caterpillars.md). Seedlings are most at risk because slugs prefer succulent tissue and a seedling has little to lose [1]. Older plants lose leaf area but survive (*Grower practice*). ## What is the slug life cycle in numbers? The gray field slug lives about a year, lays clutches of about 10-40 eggs and develops best near 17-20 C. All land slugs and snails are hermaphrodites and lay eggs after mating [1]. | Parameter | Value | Conditions and source | |---|---|---| | Eggs per clutch | 3-40 (slugs generally) | extension summary [1] | | Eggs per clutch, *D. reticulatum* | mean 22 (range 9-49) | field, Carrick 1938, cited in [5] | | Eggs per clutch, *D. reticulatum* | ~20 at 20 C; ~10 at 28 C | lab [2] | | Eggs per clutch, *D. reticulatum* | 21-43 | lab [3] | | Lifetime eggs | 217 at 20 C; 105 at 16 C | lab [2] | | Eggs per year | up to ~500 | field estimate, cited in [5] | | Egg hatch | 12-19 d | lab, 16-28 C [2] | | Egg hatch | 23-27 d (hatchability 79-97%) | lab [3] | | Hatch rate | 95% at 20 C (highest) | lab [2] | | Juvenile period | 51-68 d | lab [2] | | Time to maturity | 3-6 months, by species | [1] | | Total lifespan | 216 d at 20 C; 193 d at 24 C; 170 d at 16 C; 151 d at 28 C | lab [2] | | Best temperature | ~20 C for egg laying, development and longevity | lab [2] | | Growth optimum | ~17-19 C, detrimental above | literature summary in [4] | | Generations per year | 1 (lab) to 2 (UK field) | [3][4] | | Snail clutches (brown garden snail) | up to 6 per year, ~80 eggs each | [1] | | r_m, doubling time | no published value found | | Slug populations are mixed-age. Spring and autumn peaks in *D. reticulatum* numbers may reflect a mixed-age population responding to good conditions rather than two distinct generations [4]. ## Why do temperature and moisture matter for slugs? Moisture decides when slugs feed and temperature decides how fast they breed. Slugs are most active at night and on cloudy or foggy days, and hide from heat and bright light [1]. In cold weather they shelter in the topsoil; hot, dry periods stop activity [1]. The gray field slug performs best near 20 C: egg laying, development and longevity peaked there in the lab, and 28 C shortened life and halved clutch size [2]. Cool, wet spring and autumn weather is slug season outdoors. In greenhouses and polytunnels, wet floors, mulch, damp pots and drip lines keep slugs active all year (*Grower practice*). Mild coastal climates allow year-round activity outdoors [1]. ## How do I scout for slugs? Scout slugs at night and under traps, because by day they are hidden. Search with a flashlight after dark; watering the area in late afternoon draws them out [1]. Lay boards raised about 2.5 cm (1 in) on runners, or inverted melon rinds, and check underneath every morning; scrape off and destroy what you find [1]. Check daily at first, then weekly once numbers fall [1]. There is no published action threshold for slugs on cannabis. Grower practice is to act on any slug found near seedlings or transplants. ## How do I control slugs and snails on cannabis? Control slugs and snails by combining baits, barriers, traps and habitat removal; no single method holds them alone [1]. Follow the label and local law for any bait. **Iron phosphate baits.** Iron phosphate baits are safer around children, pets and wildlife, and some are allowed in organic growing [1]. Slugs stop feeding soon after eating them but take several days to a week to die, usually hidden [1]. Iron phosphate has been field-tested as a molluscicide [6]. Scatter baits around seedlings, not in piles. **Other bait classes.** Ferric sodium EDTA baits work like iron phosphate but faster, in about 3 days instead of 7, and are not organic [1]. Metaldehyde baits are highly poisonous to dogs and cats and should be kept away from pets, children and edible plants [1]. **Bait timing.** Baits work poorly in very hot, very dry or cold weather [1]. Light irrigation before baiting encourages slugs to forage; heavy watering after baiting makes pellets mouldy [1]. **Copper barriers.** Use a copper strip at least 5 cm (2 in) tall, buried 2.5-5 cm (1-2 in) into the soil [1]. Bands on pots and planters work until they tarnish; clean with vinegar [1]. Remove slugs inside the barrier first. **Beer traps.** Sink deep-sided containers with the rim at soil level and a lid with entry holes; they attract slugs within a few feet and need refilling every few days [1]. Sugar water with yeast works too [1]. **Handpicking.** Pick at night with gloves and drop slugs into soapy water [1]. Repeat regularly. **Habitat.** Remove boards, debris, dense weeds and thick mulch near seedlings, and water in the morning rather than the evening (*Grower practice*, consistent with [1]). **Predators.** Ground beetles, toads, snakes, birds and others eat slugs but rarely give enough control in gardens [1]. Penned poultry can reduce snail problems [1]. Do not release decollate snails where they are restricted [1]. ## What should I not do against slugs? Do not use metaldehyde baits where dogs, cats or children can reach them, and do not put any bait on the plants themselves [1]. Do not salt the soil to kill slugs; salt damages soil and plants (*Grower practice*). Do not rely on beer traps alone around a field of seedlings. ## What are the common myths about slugs? **"Salt is a good slug control."** *Myth.* It kills on contact but harms soil and plants. **"Beer traps clear a garden."** *Myth.* They draw slugs only from a few feet away [1]. **"Iron phosphate does not work because there are no bodies."** *Myth.* Slugs die over several days, out of sight [1]. **"Copper always keeps slugs out."** *Contested.* It works only tall, clean, continuous and with no slugs already inside [1]. ## Evidence - Species, damage, behaviour and control options: *Established* (extension) [1]. - Temperature effects on *D. reticulatum* development and egg laying: *Established* in the lab [2][3][4]. - Use on cannabis: extrapolated from vegetables and gardens (*Supported*). ## Glossary terms used here - Glossary: [slugs and snails](https://genetixbay.com/knowledge/glossary/slugs-and-snails.md) ## Sources 1. Wilen, C.A. & Flint, M.L., 2018. Pest Notes: Snails and Slugs. UC ANR Publication 7427. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7427.html 2. Kim, H.J. et al., 2009. Effects of temperature on the development and longevity of the gray field slug, Deroceras reticulatum. Korean Journal of Applied Entomology 48(4):541-546. https://db.koreascholar.com/Article/Detail/10254 3. Biology, food consumption and control of the gray garden slug Deroceras reticulatum, 2015. Annals of Agricultural Science, Moshtohor 53(4):719-726. https://doi.org/10.21608/assjm.2015.109952 4. Shirley, M., Howlett, S. & Port, G., 2020. Not all slugs are the same: variation in growth and development of the slug Deroceras reticulatum. Insects 11(11):742. https://doi.org/10.3390/insects11110742 5. McDonald-Howard, K., Williams, C.D., Jones, H. & Rae, R. A method of culturing and breeding slugs through several generations. Liverpool John Moores University repository. https://researchonline.ljmu.ac.uk/15832/3/A%20method%20of%20culturing%20and%20breeding%20slugs%20through%20several%20generations.pdf 6. Speiser, B. & Kistler, C., 2002. Field tests with a molluscicide containing iron phosphate. Crop Protection 21(5):389-394. https://doi.org/10.1016/S0261-2194(01)00120-X --- # Spider mites on cannabis: life tables, ID and IPM > The twospotted spider mite (Tetranychus urticae) causes pale stippling and, at high numbers, webbing on cannabis. In lab life tables its intrinsic rate of increase roughly doubles from about 0.16 per day at 20 °C to about 0.30 per day at 30 °C, so 10 females can become several thousand in three weeks in a warm room. Control rests on early scouting, cooler and less dry veg rooms, predatory mites released early, and contact sprays timed to the egg stage and kept out of flower. - Canonical: https://genetixbay.com/knowledge/pests/spider-mites.html - Category: Pests · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What are the tiny dots on my cannabis leaves?** Tiny pale dots on the upper surface of cannabis leaves are usually stippling from twospotted spider mites (Tetranychus urticae); each dot is an emptied leaf cell. Turn the leaf over: a 10 to 20x lens shows oval mites about 0.5 mm long with two dark side blotches, plus round clear eggs. No mites and no eggs means look at thrips, russet mites or nutrient spotting instead. **How fast do spider mites reproduce at different temperatures?** Twospotted spider mites develop from egg to adult in about 26 to 29 days at 15.5 °C but about 6 to 7 days at 29.4 °C on cotton in the lab. Their intrinsic rate of increase rises from about 0.16 per day at 20 °C to about 0.30 per day at 30 °C on apple leaves, so a population doubles roughly every 4.3 days at 20 °C and every 2.3 days at 30 °C. **How many spider mites will I have in three weeks?** Ten female twospotted spider mites growing unchecked would become about 290 females in 21 days at 20 °C but about 5,700 at 30 °C, using lab intrinsic rates of increase of 0.161 and 0.302 per day on apple leaves. That is an upper bound with unlimited food and no predators. Host plant matters: on peach leaves the same mite grew far slower. **What temperature stops spider mites?** Twospotted spider mite development stops below a lower threshold of roughly 8 to 14 °C, depending on population and host, and no eggs hatched at 13 °C on peach leaves. Development still completes at 35 to 37 °C, but net reproduction falls sharply: about 12 daughters per female at 35 °C versus 84 at 30 °C on apple. No cannabis-specific threshold has been published; grow rooms never get cold enough to stop them. **Does humidity help control spider mites?** Humidity slows twospotted spider mites but does not control them. In greenhouse cucumber trials, spider mite densities were up to three times higher at about 55% RH than at about 80% RH. Higher humidity mainly helps predatory mites, whose eggs dry out below about 60 to 70% RH. In veg, 60 to 70% RH is workable; in late flower, bud rot risk rules and RH stays at 40 to 50%. **How often should I spray for spider mites?** Re-spray contact treatments for twospotted spider mites at the egg-hatch interval for your room temperature, because soaps and oils do not reliably kill eggs. Using lab thermal constants from apple leaves, eggs hatch in about 6 days at 20 °C, 4 days at 25 °C and 3 days at 30 °C. Three applications at that interval catch hatching larvae before they mature and lay. Follow the label and local law. **Which predatory mite should I use for spider mites?** For twospotted spider mites, Phytoseiulus persimilis is the specialist for established hot spots: it eats 5 to 20 prey a day but its eggs need RH above about 60 to 75% and it falls behind above about 30 °C. Neoseiulus californicus works more slowly but survives on pollen and other prey, tolerates about 40 to 80% RH, and suits preventive release. Many growers combine the two. **How many predatory mites do I need for spider mites?** A common extension guideline for spider mites is about one predator per 10 spider mites, and a strawberry study found an initial 1:10 ratio of Neoseiulus californicus to twospotted spider mites gave season-long control. On greenhouse roses, about 26 Phytoseiulus persimilis plus 24 N. californicus per square metre controlled an established infestation where either alone failed. No cannabis-specific release rate has been published; confirm rates with the supplier. **Why are some spider mites orange or red?** Orange-red twospotted spider mites are often diapausing females: short days, cool temperatures and poor food make adult females stop laying, turn bright orange-red and hide in cracks. Diapause was induced at 12 hours light and 17 to 20 °C on peach leaves but not at 25 °C or above. Others may be the red (carmine) form of T. urticae or the predator Phytoseiulus persimilis, which lacks dark spots. **Why do spider mites become resistant to miticides so quickly?** Twospotted spider mites evolve miticide resistance quickly because of a short life cycle, very high egg output and arrhenotoky: males hatch from unfertilised eggs and carry one set of chromosomes, so a resistance mutation is exposed to selection at once. The species also has expanded detoxification gene families. Rotate acaricide modes of action by IRAC group, use biological control, and follow the label and local law. **How do spider mites spread between plants and rooms?** Twospotted spider mites spread mainly on infested clones and cuttings, on clothing, hands and tools, and by walking along touching leaves. Mated females also disperse by air: they climb to plant tops, raise their forelegs and are carried by wind, sometimes on silk. At high density and food shortage, mites gather at the plant apex in silk balls that can be carried away by air or animals. **Short answer.** Fine pale speckles on the upper leaf surface, tiny moving dots underneath, and later silk webbing: that is almost always the twospotted spider mite, *Tetranychus urticae*. In lab life tables its population roughly doubles every 2.3 days at 30 °C (86 °F) and every 4.3 days at 20 °C (68 °F) [9], so a warm room turns a handful of mites into thousands in three weeks. Find them early, take the heat and the driest air out of veg, release predatory mites while numbers are low, and time any contact spray to egg hatch. Sprays stay out of flower. ## Spider mite numbers at a glance | Parameter (T. urticae) | Value | Conditions and source | |---|---|---| | Adult female size | ~0.4-0.5 mm | Visible as a dot; confirm at 10-20x [4][5] | | Egg-to-adult, 15.5 °C | 25.8-29.0 days (females) | Cotton cotyledons, lab [7] | | Egg-to-adult, 20 °C | 15.5 days (females) | Apple leaves, lab [9] | | Egg-to-adult, 23.8 °C | ~10.5-10.7 days | Cotton, lab [7] | | Egg-to-adult, 29.4 °C | 6.1-6.7 days | Cotton, lab [7] | | Egg-to-adult, 35 °C | 6.5 days (females) | Apple, lab [9] | | Egg-to-adult, 37 °C | 5.3 days | Eggplant, lab [10] | | Lower developmental threshold | 8.4-13.8 °C (47-57 °F) | Population and host vary [9][10][11] | | Degree-days, egg-to-adult | 80.5-172 DD | Eggplant 80.5 [10]; peach 136 [11]; apple 172 [9] | | Upper threshold | No published value found | Development still completes at 37 °C [10] | | Lifetime eggs per female | 64-141 (8-40 on peach) | 103 at 23.8 °C, 64 at 29.4 °C (cotton) [7]; 141 at 27 °C (eggplant) [10]; peach [11] | | Eggs per female per day | ~2-5 | 4.6 at 25 °C, apple [9]; 2-3 on peach [11] | | Female adult longevity | ~4-15 days in lab | 14.7 d at 23.8 °C, 9.7 d at 29.4 °C (cotton) [7]; 3.6-12.9 d (peach) [11] | | Sex ratio | ~63-88% female | Peach [11]; about 3 females per male [4] | | r_m (per day) | 0.08 (15 °C) to ~0.30-0.32 (30 °C) | [8][9] | | Doubling time | ~8.7 d at 15 °C; ~2.2-2.3 d at 30 °C | ln2 / r_m, computed | | Cannabis action threshold | None published | Act on first confirmed colony (Grower practice) [3][5] | No life table for *T. urticae* on *Cannabis sativa* has been published that we could find. Every number above is from another host plant in the lab, and host plant changes the numbers a lot (see the peach-leaf caveat below). ## What are spider mites doing to a cannabis plant? Twospotted spider mites pierce cannabis leaf cells from the underside and suck out the contents, leaving a pale dot (stippling) on the upper surface for each emptied cell [1][3]. Thousands of dots bronze and yellow the leaf, photosynthesis falls, and leaves dry and drop [3][5][6]. Heavy infestations reduce flower growth, and webbing over colas is cosmetic damage that buyers notice [5][6]. Utah State rates the twospotted spider mite a high threat to indoor hemp and a moderate one outdoors [3]; Colorado State calls it a significant indoor pest that is rarely a problem in field hemp [6]. ## How do you recognise spider mites on cannabis? Spider mites on cannabis show first as fine white-yellow stippling on the upper leaf surface, with mites, round eggs and cast skins on the underside [1][4]. Webbing comes later, when numbers are already large. - **Leaf tops:** scattered pale stippling, often first near lamps, walls, fans and other hot, dry spots [4]. - **Leaf undersides:** at 10-20x, oval mites about 0.5 mm, yellow-green with two dark side blotches; round, clear to pale eggs [4][5]. - **Shake test:** tap a branch over white paper; moving specks that streak when smeared are mites [3][6]. - **Heavy populations:** silk at leaf tips and over colas, a dusty, dirty look, and mites massing at the top of the web [3][6]. - **Orange-red females:** in cool, short-day conditions, adult females may turn bright orange-red and stop feeding (diapause) [4][5]. Do not confuse with: broad and russet mites (twisted or bronzed growth, mites invisible at 10x; see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) and [hemp russet mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md)), thrips (silvery scars and black fecal specks; see [thrips](https://genetixbay.com/knowledge/pests/thrips.md)), or nutrient spotting (no mites, no eggs; see [rust spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md)). For green versus red spider mites, see [two-spotted vs carmine mite](https://genetixbay.com/knowledge/pests/two-spotted-vs-carmine-mite.md). ## What is the spider mite life cycle in numbers? The twospotted spider mite passes through egg, six-legged larva, two eight-legged nymphal stages (protonymph and deutonymph) with resting stages between, and adult [1][5]. Egg-to-adult takes about 26 to 29 days at 15.5 °C and 6 to 7 days at 29.4 °C on cotton in the lab [7]. ### Development time by temperature | Temperature | Egg-to-adult (days) | Host, lab | Source | |---|---|---|---| | 15.5 °C (60 °F) | 25.8-29.0 (females) | Cotton | [7] | | 17 °C (63 °F) | 25.8 | Eggplant | [10] | | 17 °C (63 °F) | 30.3 (females) | Peach | [11] | | 20 °C (68 °F) | 15.5 (females) | Apple | [9] | | 23.8 °C (75 °F) | ~10.5-10.7 | Cotton | [7] | | 25 °C (77 °F) | ~10.4 (computed from 172.41 DD above 8.43 °C) | Apple | [9] | | 29.4 °C (85 °F) | 6.1-6.7 (females) | Cotton | [7] | | 35 °C (95 °F) | 6.5 (females) | Apple | [9] | | 37 °C (99 °F) | 5.3 | Eggplant | [10] | Males develop slightly faster than females [7][9]. On cotton, temperature, not host, dominated development time [7]. ### Thresholds and degree-days The lower developmental threshold for twospotted spider mite ranges from about 8.4 to 13.8 °C depending on population and host [9][10][11]. Kasap estimated 10.78 °C and 57.8 degree-days (DD) for the egg, and 8.43 °C and 172.41 DD for egg-to-adult, on apple [9]. Kim and colleagues found 12.5 °C and 80.5 DD for females on eggplant [10]. Riahi and colleagues found 13.79 °C and 136.43 DD on peach, and no eggs hatched at 13 °C [11]. No published upper developmental threshold was found for *T. urticae*. Development still completed at 35 °C on apple [9] and 37 °C on eggplant [10], although egg hatch was poor at 37 °C [10]. ### Reproduction and life-table parameters | Temperature | r_m (/day) | R0 (daughters/female) | Mean generation time T (days) | Host, source | |---|---|---|---|---| | 15 °C | 0.080 | - | - | Lab, [8] (host not stated in abstract) | | 20 °C | 0.161 | 67.0 | 26.0 | Apple, [9] | | 23.8 °C | 0.219 | 74.8 | 19.7 | Cotton, [7] | | 25 °C | 0.231-0.243 | 92.2 | - | Apple cultivars, [9] | | 25 °C | 0.144 | 16.9 | 19.3 | Peach, [11] | | 27 °C | 0.213 | 12.1 | 11.7 | Peach, [11] | | 29.4 °C | ~0.29 | - | - | Cotton, [7] (0.293-0.295 across three species) | | 30 °C | 0.302 | 84.3 | - | Apple, [9] | | 30 °C | 0.321 | - | - | Lab, [8] | | 35 °C | - | 12.0 | 9.9 | Apple, [9] | Doubling time is ln2 / r_m: about 8.7 days at 15 °C, 4.3 days at 20 °C, 3.2 days at 23.8 °C, 2.9 days at 25 °C (apple) and 2.2-2.3 days at 30 °C. One study on eggplant reported r_m rising to 0.565 per day at 37 °C [10]. Treat that as an outlier tied to fast development on that host; on apple, net reproduction at 35 °C collapsed to 12 daughters per female [9]. **The peach-leaf caveat.** On peach leaves, the same species laid only 40 eggs per female at 25 °C and 8 at 30 °C, and r_m peaked at 0.213 at 27 °C [11]. Host plant quality can halve or triple the numbers. Cannabis has not been measured, so use the apple and cotton values as a working range and assume the worse case. ### Fecundity, longevity and sex ratio Twospotted spider mite females laid 103 eggs each at 23.8 °C and 64 at 29.4 °C on cotton [7], and 141 at 27 °C on eggplant [10]. Extension sheets quote up to about 100-200 eggs per female [4][5]. Female adults lived 14.7 days at 23.8 °C and 9.7 days at 29.4 °C on cotton [7]. UConn gives about one month for a female in greenhouse conditions [4]. About 63-88% of offspring were female on peach [11], and UConn describes females as three times more abundant than males [4]. The first eggs a female lays are mostly males; later eggs are mostly females [11]. ## Why do temperature and humidity matter so much for spider mites? Temperature sets the speed of the twospotted spider mite: r_m roughly doubles from about 0.16 per day at 20 °C to about 0.30 per day at 30 °C on apple [9]. Dry air adds to it: spider mites develop faster at low humidity [12][13], while their main predators need humid air. ### Heat Between the lower threshold (about 8-14 °C) and about 30 °C, every degree speeds twospotted spider mite development [7][9]. Above about 33-35 °C, net reproduction falls: 12 daughters per female at 35 °C versus 84 at 30 °C on apple [9], and 8 eggs per female at 30 °C on peach [11]. A cannabis room never gets hot enough to control mites without cooking the crop. Heat above about 30 °C hurts the plant and the predators before it hurts the mite. ### Humidity Low humidity favours twospotted spider mites. Boudreaux showed in 1958 that relative humidity affects spider mite egg-laying, hatching and survival [13], and later work confirmed spider mites develop faster at low than high humidity [12]. In greenhouse cucumber, spider mite densities were up to three times higher at about 55% RH than at about 80% RH [12]. UConn notes egg-to-adult in as little as 7 days above 29 °C (85 °F) at 30-50% RH [4]. High humidity favours the predators. Phytoseiulus persimilis eggs held at 27 °C hatched 7.5% at 40% RH versus 99.7% at 80% RH [14]. The humidity at which 50% of eggs die (LH50) is about 66-70% for both P. persimilis and Neoseiulus californicus [12]. The surprise: in the same greenhouse trials, both predators still controlled spider mites at an average of about 55% RH, probably because humidity rose at night and the leaf boundary layer is more humid than room air [12]. Short humid periods compensate for dry ones [12]. ### Diapause Diapause is a hormonally controlled resting state. In twospotted spider mites, short days, cool temperatures and declining food make adult females stop feeding and laying, turn bright orange-red and hide in cracks [4][5]. NC State gives fewer than 10 hours of light or cooler temperatures as triggers [5]. On peach leaves at 12 h light, immature mites reared at 17 and 20 °C became winter-type (diapausing) females that laid no eggs; at 25 °C and above, none did [11]. One strain had a critical photoperiod of about 13.5 h at 18 °C [23]. That matters for cannabis. A 12/12 flower room is a short day for a spider mite. In a warm flower room (24-26 °C lights on), diapause is unlikely [11]. In a cool room or a cool dark period near 17-20 °C, some females may diapause, stop laying, and survive the clean-out in cracks and under trays (*Supported*, inferred from lab data, not tested on cannabis). Diapause ability varies between populations and can be lost in tetranychid mites kept without winter [22]. Greenhouse and indoor populations may barely diapause at all; nobody has surveyed cannabis-room populations. ### What the set-points mean in practice | Room state | Mite r_m (approx., lab) | Predator outlook | Note | |---|---|---|---| | Veg, 24-28 °C, 60-70% RH | ~0.22-0.30 /day | P. persimilis and N. californicus both workable | Best window for biocontrol | | Flower, 22-26 °C, 45-55% RH | ~0.20-0.25 /day | P. persimilis eggs at risk; N. californicus better | Night RH helps the predator | | Late flower, 40-50% RH | ~0.20-0.25 /day | Predators struggle; dry air favours mites | Bud rot outranks mites; do not raise RH | | Hot room, >30 °C, <45% RH | ~0.30 /day | P. persimilis falls behind | Worst case | r_m values are read from the apple and cotton tables above [7][9]. See [VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md) and [humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md). ## How fast can a spider mite population grow? A worked example Ten female twospotted spider mites growing without limits for 21 days become about 290 females at 20 °C and about 5,700 at 30 °C, using r_m of 0.161 and 0.302 per day from apple-leaf life tables [9]. Warm rooms do not add mites; they multiply them. **Method.** Unchecked exponential growth: N(t) = N0 × e^(r_m × t). N0 = 10 adult females, t in days. r_m counts female offspring per female per day, so N is females; add about a third more for males. | Temperature (r_m, source) | Day 7 | Day 14 | Day 21 | Day 28 | Doubling time | |---|---|---|---|---|---| | 15 °C (0.080, [8]) | 18 | 31 | 54 | 94 | 8.7 d | | 20 °C (0.161, [9]) | 31 | 95 | 294 | 907 | 4.3 d | | 23.8 °C (0.219, [7]) | 46 | 215 | 994 | 4,604 | 3.2 d | | 25 °C (0.243, [9]) | 55 | 300 | 1,645 | 9,014 | 2.9 d | | 30 °C (0.302, [9]) | 83 | 686 | 5,679 | 47,032 | 2.3 d | | 30 °C (0.321, [8]) | 95 | 895 | 8,464 | 80,064 | 2.2 d | | 30 °C on peach (0.108, [11]) | 21 | 45 | 97 | 206 | 6.4 d | **Reading it.** At 30 °C, three weeks gives about 19 times more mites than at 20 °C (5,679 vs 294). One week at 30 °C multiplies the population about 8-fold; at 20 °C about 3-fold. **Caveats.** This is the unchecked upper bound: no predators, no sprays, unlimited leaf, constant temperature. Real populations crash when leaves are exhausted. The peach row shows how much host plant matters [11]. No cannabis r_m has been published. ## Where do spider mites hide, how do they spread and how do they get in? Twospotted spider mites get into cannabis rooms mainly on infested clones and cuttings, then spread on hands, clothing and tools, along touching leaves, and through the air [4][5][20][21]. They hide on leaf undersides, under webbing, and as diapausing females in cracks [4]. - **Clones and cuttings:** the main door. Quarantine and inspect every incoming plant [4] (*Grower practice*; established in greenhouse IPM). - **People:** mites ride on workers and clothing; scout and work infested areas at the end of the day [4]. - **Weeds and outdoor plants:** weeds are a source; control them inside and around the facility [4][6]. The species feeds on hundreds of plants [5]. - **Dust:** dust on webbing makes refuges from predators; field hemp infestations are often worse near dusty drive paths [5][1]. - **Walking:** mites walk between plants whose leaves touch [4]. - **Air:** mated females climb to the top of the plant and take off in wind in a "take-off posture", forelegs raised [21]. Lower leaf surfaces facing down are favoured take-off sites [21]. - **Silk balls:** under food shortage and high density, mites gather at the plant apex and form collective silk balls (141 to 2,162 mites, mean about 794; 98.9% immatures) that can be carried by wind or animals [20]. - **Hiding places:** leaf undersides near the midrib, under webs, in cracks, under trays and in debris (diapausing females) [4][6]. Indoors, mites can stay active year-round [6]. Outdoors, females overwinter in leaf litter and under bark [6][1]. ## How should I scout for spider mites? Scout cannabis for twospotted spider mites at least weekly by turning leaves over with a 10-20x hand lens, starting in hot, dry spots and on plants that showed mites before [4][5]. Sticky cards are useless for spider mites; use a lens and a shake test. - **Frequency:** weekly random inspections are the extension baseline [4]; twice weekly in warm rooms is sensible (*Grower practice*). At 30 °C a population can double in about 2.3 days [9]. - **Where:** hot spots near lamps, walls and fans; plants not overhead-watered; susceptible cultivars [4]. Check mid-canopy and lower leaves where stippling starts. - **Lens:** 10x minimum [5]; 14x was used in strawberry scouting [15]; 10-20x shows all stages [4]. Use 40-60x (a clip-on scope) to tell spider mite eggs from predator eggs, which are larger and oval [4][2]. - **Shake test:** tap stems over white paper or a cloth tray and count what falls [3][6]. - **Indicator plants:** tag infested plants and re-check them to judge control [4]. - **Sampling scale:** strawberry growers in Florida sample 100 leaflets weekly per field block [15]; in a room, aim for at least 10-20 leaves per plant group (*Grower practice*). - **Records:** note leaf counts, location and room temperature, so you can see the curve bend. **Action thresholds.** No action threshold has been published for spider mites on hemp or cannabis [5]. USU advises acting at the first sign of damage or when low numbers are found [3]. In strawberry, the release rate is scaled to the share of leaflets infested (1-5% low, 6-10% moderate) [15]. In cannabis, treat first confirmed colonies (*Grower practice*). ## How do you control spider mites by life stage? Twospotted spider mite eggs survive most contact sprays, so any soap or oil programme must re-spray after the surviving eggs hatch and before the new larvae mature and lay [4][6]. That interval depends on room temperature. ### Which tactic hits which stage | Stage | Contact soap | Horticultural oil | Mite growth inhibitors (IRAC 10A/10B) | Predatory mites | |---|---|---|---|---| | Egg | Poor | Some (smothering) | Yes (ovicidal/larvicidal classes) | P. persimilis eats eggs | | Larva, nymph | Yes, on contact | Yes | Yes | Yes | | Adult | Yes, on contact | Yes | Weak on adults | Yes | | Diapausing female in cracks | No | No | No | Soil predators near walls (*Grower practice*) [4] | Soaps and oils need full coverage of leaf undersides, high volume and repeat applications because they work only on contact and do little to eggs [5][6]. ### Timing the re-spray to your temperature Using Kasap's apple-leaf thermal constants [9] (egg: 57.8 DD above 10.78 °C; egg-to-adult: 172.41 DD above 8.43 °C) and a pre-oviposition period of about 1.3-1.6 days [11]: | Room temperature | Egg hatch (days) | Egg to adult (days) | Re-spray interval | |---|---|---|---| | 20 °C (68 °F) | ~6.3 | ~14.9 | every 6-7 days | | 24 °C (75 °F) | ~4.4 | ~11.1 | every 4-5 days | | 25 °C (77 °F) | ~4.1 | ~10.4 | every 4 days | | 28 °C (82 °F) | ~3.4 | ~8.8 | every 3-4 days | | 30 °C (86 °F) | ~3.0 | ~8.0 | every 3 days | **The logic.** Spray 1 kills mobiles. Eggs laid just before spray 1 hatch within the egg period; spray 2 at that interval kills the hatchlings before they become adults. Spray 3 catches survivors that coverage missed. On a faster host (eggplant, 80.5 DD above 12.5 °C [10]) egg-to-adult at 25 °C is only about 6.4 days, so err short. Three applications at the egg-hatch interval is the usual pattern (*Grower practice*, consistent with extension advice to repeat [1][3][6]). Always follow the label and local law. ### Resistance Twospotted spider mites evolve resistance to acaricides fast because of a short life cycle, abundant progeny and arrhenotoky [18]. Arrhenotoky is a form of [haplodiploidy](https://genetixbay.com/knowledge/glossary/haplodiploidy.md): unfertilised eggs become haploid males, fertilised eggs become females [4][7]. Haploid males carry one copy of each gene, so a resistance mutation is expressed and selected immediately [4]. The genome also shows expanded families of detoxification genes linked to polyphagy and pesticide tolerance [19]. Repeated miticide use selects resistant populations [6]. Mites often flare after broad-spectrum insecticides that kill predators [1]. **Rotate by class.** Acaricide modes of action in the IRAC scheme include groups 6, 10A, 10B, 12, 13, 20, 21A, 23 and 25; sulfur is in group UN [24]. Never use the same group on consecutive mite generations. Very few of these are registered on cannabis anywhere; registrations differ by country, state and province. Follow the label and local law. ## Which biological controls work against spider mites? Phytoseiulus persimilis, a specialist predatory mite, is the main biological control for twospotted spider mite hot spots, with Neoseiulus californicus as the slower, hardier preventive partner [2][4][12]. Release early, when mites are first seen [4]. ### Predator windows | Predator | Type | Temperature | RH | Notes | |---|---|---|---|---| | Phytoseiulus persimilis | Specialist mite | Optimum above 20 °C; falls behind above ~30 °C (86 °F) [4] | Eggs shrivel below ~60%; optimum >75% [4] | Egg-to-adult 25 d at 15 °C, 5 d at 30 °C [14]; eats 5-20 prey/day [2]; no diapause [4] | | Neoseiulus californicus | Generalist mite | Active 8-35 °C (46-95 °F) [4]; develops 10-33 °C [15] | 40-80% [4] | ~3 eggs/day, 10-12 d life cycle at 25-27 °C [15]; survives on pollen and other mites [4][15] | | Neoseiulus fallacis | Generalist mite | 9-29 °C (48-85 °F) [4] | >50%, dense canopy [4] | Also eats cyclamen mites [4] | | Amblyseius andersoni | Generalist mite | 6-40 °C (42-104 °F) [4] | No value given | Cool-tolerant; also eats broad and eriophyid mites [4] | | Galendromus occidentalis | Mite | 10-46 °C (50-115 °F) [4] | 30-60% [4] | Drier, hotter rooms [4] | | Feltiella acarisuga | Predatory midge | Egg-to-adult 10 d at 27 °C, 34 d at 15 °C [4] | 60-95%; optimum 80% [4] | Larvae feed; adults fly to hot spots [4] | | Stethorus punctillum | Lady beetle | 16-32 °C (61-90 °F) [4] | No value given | Flies to colonies; use with predatory mites [4] | Ranges are from extension fact sheets for greenhouse crops, not cannabis trials. ### Phytoseiulus persimilis: strengths and limits P. persimilis feeds on all twospotted spider mite stages and cannot survive on anything else, so it starves or leaves when prey run out [2][4]. Expect to re-release when mites return [2]. Its development is faster than the spider mite's at most temperatures: about 5 days at 30 °C, 9 days at 20 °C and 25 days at 15 °C [4][14]. Cornell reports it reproduces faster than spider mites above 28 °C [14], yet UConn reports it cannot keep up above 30 °C (86 °F) [4]. The likely reason is humidity: hot rooms are usually dry rooms, and dry air kills its eggs [4][14]. Treat 28-30 °C as the edge. It spreads best where leaves of neighbouring plants touch; dispersal drops by about 70% when plants barely touch [14][2]. Tag hot spots and release onto them [4]. ### Release rates and ratios - **Ratio:** UC IPM gives about one predator per 10 spider mites as a guideline [1]. An initial ratio of about 1:10 N. californicus to twospotted spider mites gave season-long control in Florida strawberry [16]. - **Combined releases:** on greenhouse cut roses, simultaneous releases of about 26 P. persimilis and 24 N. californicus per m² controlled an infestation of 23.9 mites per leaf through the season; either species alone failed [17]. - **Per plant:** strawberry guidance is one N. californicus per plant for low to moderate infestations, avoiding releases below 7.2 °C (45 °F) or above 29.5 °C (85 °F) [15]. - **Per area:** biocontrol supplier technical sheets typically give about 5-25 P. persimilis per m² (0.5-2 per ft²) for light to heavy infestations, more on hot spots. Confirm rates with the supplier [4]. - **Establishment:** colonies should shrink within 2-3 weeks of a P. persimilis release [4]. Look for shrivelled, sucked-dry spider mites [4]. No release rate has been published for cannabis. These are greenhouse-crop figures. ### Compatibility with sprays Sulfur harms predatory mites; keep it out of programmes that rely on them (*Supported*). Avoid broad-spectrum and persistent pesticides before and after release [2]. Check supplier side-effect databases for any product you plan to use [4]. ## How can the grow-room environment be used against spider mites? Use the environment to slow twospotted spider mites and help predators in veg: keep leaf temperature below about 28 °C (82 °F) and RH at 60-70%, with humid nights [12][4]. In flower, bud-rot risk caps humidity, so lean on predators that tolerate drier air. - **Veg (24-28 °C, 60-70% RH):** the best biocontrol window. Release P. persimilis on hot spots and N. californicus preventively. Moderate the hottest corners, because r_m at 25 °C is still about 0.23-0.24 on apple [9]. - **Kill the hot spots:** spider mites start near lamps, walls and stagnant corners [4]. Even air mixing (see [airflow](https://genetixbay.com/knowledge/environment/airflow.md)) removes the hot, dry microclimates that breed them. - **Night humidity:** short humid periods compensate predator eggs for dry days [12]. A slightly higher night RH in veg is a cheap advantage. - **Water and dust:** water-stressed plants are more susceptible, and dust triggers outbreaks [1][5]. Water properly and keep surfaces clean. - **Flower (22-26 °C, 45-55% RH):** N. californicus copes better than P. persimilis with drier air [4][12]. Do not chase predator humidity at the expense of bud rot ([botrytis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md), [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md)). - **Late flower (40-50% RH):** accept that conditions favour the mite. Your defence is a clean start, not climate. - **Cool flower rooms:** dark periods near 17-20 °C at 12/12 may induce diapause in some females [11], which then hide and survive between runs. Clean cracks and trays between cycles. - **Between runs:** a fully emptied, cleaned room with no green plant material breaks the cycle (*Grower practice*). ## What should you not do about spider mites in flower? Do not spray soaps, oils, sulfur or miticides onto developing cannabis buds: residues end up in the product, wet buds invite botrytis, and most miticides are not registered on cannabis [1][3]. In flower, rely on predators, leaf removal and acceptance of some damage. - No residual or systemic miticides in flower; residues fail compliance testing in regulated markets. - No oils above about 32 °C (90 °F) or on water-stressed plants; no sulfur within 30 days of an oil [1]. - Do not raise RH in late flower to slow mites; bud rot costs more ([kb-diseases-botrytis-bud-rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)). - Do not shake or move heavily infested plants through clean rooms. Bag them in place. - Do not release P. persimilis into a hot, dry late-flower room and expect miracles [4]. - If a late-flower infestation is severe, harvest early rather than spray (*Grower practice*). ## What are the common myths about spider mites? The most common spider mite myth is that humidity alone will control them; it only slows them, by up to about three times on cucumber [12]. - **"Spider mites cannot survive high humidity."** *Myth.* High RH slows them (up to 3 times lower densities at about 80% vs 55% RH [12]) but does not stop them. - **"A weekly spray matches the life cycle."** *Myth.* Egg hatch takes about 3 days at 30 °C but about 6 days at 20 °C [9]. Time sprays to temperature. - **"Red or orange mites are predators."** *Myth.* Diapausing females and the red form of T. urticae are also orange-red [4][22]. Predators have no dark side spots and run fast. - **"Spider mites love heat."** *Established*, with a ceiling: r_m roughly doubles from 20 to 30 °C; net reproduction falls above about 33-35 °C [9][11]. - **"P. persimilis works in any room."** *Myth.* Its eggs fail in dry air [14] and it falls behind above about 30 °C [4]. - **"Neem or one heavy spray wipes them out."** *Myth.* Contact products miss eggs; plan three timed applications [5][6]. - **"Mites come from nowhere."** *Myth.* They arrive on clones, people, weeds and air [4][21]. ## Common mistakes - Waiting for webbing; by then the population is large [3]. - Spraying on a fixed weekly calendar instead of the egg-hatch interval for your temperature. - Treating only the plants with visible damage; mites walk and fly [4][21]. - Releasing P. persimilis into a hot, dry room, then blaming the supplier [4]. - Rotating products within the same IRAC group [24]. - Mistaking orange diapausing spider mites for predators, or the reverse [4]. - Mistaking broad or russet mite damage for spider mites ([kb-pests-broad-russet-mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md)). ## Evidence - Life cycle, stippling and webbing: *Established* [1][3][4][5]. - Temperature-dependent development and r_m: *Established* in multiple lab life tables on cotton, apple, eggplant and peach [7][8][9][10][11]; not measured on cannabis. - Low humidity favouring spider mites: *Established* [12][13]. - P. persimilis humidity needs and heat limit: *Established* in greenhouse crops [2][4][14]; the exact heat cut-off conflicts between sources. - Diapause at 12/12 and cool temperatures in cannabis rooms: *Supported*, inferred from lab data [11][23]. - Re-spray intervals: computed from thermal constants [9]; the three-spray pattern is *Grower practice*. - Release rates and ratios: *Supported* in strawberry and roses [16][17]; supplier rates are guidance; no cannabis trials. - Cannabis action thresholds: none published [5]; first-sighting action is *Grower practice*. ## Glossary terms used here - Glossary: [intrinsic rate of increase](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [diapause](https://genetixbay.com/knowledge/glossary/diapause.md), [arrhenotoky](https://genetixbay.com/knowledge/glossary/arrhenotoky.md), [predator:prey ratio](https://genetixbay.com/knowledge/glossary/predator-prey-ratio.md), [Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md), [Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) ## Sources 1. Godfrey LD. 2011. Pest Notes: Spider Mites. UC ANR Publication 7405. University of California Statewide IPM Program. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 2. UC IPM. Natural Enemies Gallery: Phytoseiulus predatory mites. University of California ANR. https://ipm.ucanr.edu/natural-enemies/phytoseiulus-predatory-mites/ 3. Utah State University Extension. Two-Spotted Spider Mite (hemp). Utah Pests. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php 4. Pundt L. 2019. Biological Control of Two-Spotted Spider Mites. UConn Extension IPM. https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf 5. Pulkoski M, Burrack H. 2020. Twospotted Spider Mite in Industrial Hemp. NC State Extension. https://content.ces.ncsu.edu/twospotted-spider-mite-in-industrial-hemp 6. Colorado State University, Agricultural Biology. 2022. Twospotted spider mite, Tetranychus urticae (controlled environment agriculture pests). https://agsci.colostate.edu/agbio/ipm-pests/twospotted-spider-mite/ 7. Carey JR, Bradley JW. 1982. Developmental rates, vital schedules, sex ratios and life tables for Tetranychus urticae, T. turkestani and T. pacificus (Acarina: Tetranychidae) on cotton. Acarologia 23(4):333-345. https://www1.montpellier.inrae.fr/CBGP/acarologia/article.php?id=2789 8. Bounfour M, Tanigoshi LK. 2001. Effect of temperature on development and demographic parameters of Tetranychus urticae and Eotetranychus carpini borealis (Acari: Tetranychidae). Annals of the Entomological Society of America 94(3):400-404. https://doi.org/10.1603/0013-8746(2001)094[0400:EOTODA]2.0.CO;2 9. Kasap I. 2004. Effect of apple cultivar and of temperature on the biology and life table parameters of the twospotted spider mite Tetranychus urticae. Phytoparasitica 32(1):73-82. https://doi.org/10.1007/BF02980863 10. Kim J, Lee SK, Kim JM, Kwon YR, Kim TH, Kim JS. 2008. Effect of temperature on development and life table parameters of Tetranychus urticae Koch (Acari: Tetranychidae) reared on eggplants. Korean Journal of Applied Entomology 47(2):163-168. https://doi.org/10.5656/KSAE.2008.47.2.163 11. Riahi E, Shishehbor P, Nemati AR, Saeidi Z. 2013. Temperature effects on development and life table parameters of Tetranychus urticae (Acari: Tetranychidae). Journal of Agricultural Science and Technology 15(4):661-672. https://jast.modares.ac.ir/article-23-9684-en.html 12. Messelink G, Leman A. 2020. Are low humidity levels a limiting factor for spider mite control by phytoseiid predators under fluctuating climatic conditions? IOBC-WPRS Bulletin 149:101-102. https://edepot.wur.nl/519096 13. Boudreaux HB. 1958. The effect of relative humidity on egg-laying, hatching, and survival in various spider mites. Journal of Insect Physiology 2(1):65-72. https://doi.org/10.1016/0022-1910(58)90029-5 14. Hoffmann MP, Frodsham AC. 1993. Phytoseiulus persimilis. In: Natural Enemies of Vegetable Insect Pests. Cornell Cooperative Extension; Biological Control: A Guide to Natural Enemies in North America. https://biocontrol.entomology.cornell.edu/predators/Phytoseiulus.php 15. Rondon SI, Price JF, Liburd OE, Francis R, Cantliffe DJ. 2004. Neoseiulus californicus McGregor: a predatory mite species for controlling twospotted spider mites in strawberries. UF/IFAS EDIS HS1001. https://journals.flvc.org/edis/article/download/114203/109514/158938 16. Fraulo AB, Liburd OE. 2007. Biological control of twospotted spider mite, Tetranychus urticae, with predatory mite, Neoseiulus californicus, in strawberries. Experimental and Applied Acarology 43:109-119. https://doi.org/10.1007/s10493-007-9109-7 17. Blümel S, Walzer A. 2002. Efficacy of different release strategies of Neoseiulus californicus and Phytoseiulus persimilis for the control of two-spotted spider mite on greenhouse cut roses. Systematic and Applied Acarology 7:35-48. https://www.nhm.ac.uk/hosted_sites/acarology/saas/saa/abst07/saa07_05.html 18. Van Leeuwen T, Vontas J, Tsagkarakou A, Dermauw W, Tirry L. 2010. Acaricide resistance mechanisms in the two-spotted spider mite Tetranychus urticae and other important Acari: a review. Insect Biochemistry and Molecular Biology 40(8):563-572. https://doi.org/10.1016/j.ibmb.2010.05.008 19. Grbić M, Van Leeuwen T, Clark RM, et al. 2011. The genome of Tetranychus urticae reveals herbivorous pest adaptations. Nature 479:487-492. https://doi.org/10.1038/nature10640 20. Clotuche G, Mailleux AC, Astudillo Fernández A, Deneubourg JL, Detrain C, Hance T. 2011. The formation of collective silk balls in the spider mite Tetranychus urticae Koch. PLoS ONE 6(4):e18854. https://doi.org/10.1371/journal.pone.0018854 21. Osakabe M, Isobe H, Kasai A, et al. 2008. Aerodynamic advantages of upside down take-off for aerial dispersal in Tetranychus spider mites. Experimental and Applied Acarology 44:165-183. https://doi.org/10.1007/s10493-008-9141-2 22. Auger P, Migeon A, Ueckermann EA, Tiedt L, Navajas M. 2013. Evidence for synonymy between Tetranychus urticae and Tetranychus cinnabarinus (Acari, Prostigmata, Tetranychidae): review and new data. Acarologia 53(4):383-415. https://doi.org/10.1051/acarologia/20132102 23. Amini MY, Daneshyar JA, Mohammadi MM, Memlawal R. 2023. Simulation of diapause induction in spider mites (Tetranychus urticae and T. kanzawai) by reproducing field environments in the laboratory. Nangarhar University International Journal of Biosciences 2(02):53-60. https://doi.org/10.70436/nuijb.v2i02.43 24. IRAC. Mode of Action Classification (online). Insecticide Resistance Action Committee. https://irac-online.org/mode-of-action/classification-online/ --- # Temperature, humidity and pest population growth in cannabis: every major pest compared > Room temperature is the single biggest lever on how fast cannabis pests multiply: between about 20 and 30 C, most mites, aphids and thrips double every 2-4 days in lab life tables, while mealybugs and fungus gnats double every 6-8 days. Humidity matters mostly through the predators and pathogens that control pests, so set-points should be chosen for the beneficials as much as against the pest. - Canonical: https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.html - Category: Pests · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Which cannabis pest multiplies fastest?** In lab life tables the fastest-multiplying cannabis pests are aphids: cotton aphid reached an intrinsic rate of increase of 0.53 per day at 25 C on cucumber, rice root aphid 0.43 and cannabis aphid 0.36 on hemp, meaning a doubling every 1.3-2 days. Broad mites (0.31) and spider mites (0.24-0.30) follow. Mealybugs (0.08) and fungus gnats (0.11) are among the slowest. **How much faster do spider mites grow at 30 C than at 20 C?** Two-spotted spider mites grow about twice as fast at 30 C as at 20 C. Lab life tables on apple leaves give an intrinsic rate of increase of 0.161 per day at 20 C and 0.302 at 30 C, doubling every 4.3 versus 2.3 days. Ten mites become about 290 in three weeks at 20 C but about 5,700 at 30 C, with no predators. **Does lowering the temperature stop pests in a grow room?** Lowering grow-room temperature slows pests but does not stop them, because most cannabis pests have lower developmental thresholds of about 6-13 C, far below any room set-point. Spider mites still double every 4 days or so at 20 C. Cooling from 30 C to 24 C can roughly halve the growth rate of mites and thrips, which helps predators catch up, but it never replaces them. **Why does heat sometimes reduce pest numbers?** Heat reduces some pests because each species has an optimum above which egg-laying and survival fall. Cannabis aphid growth collapsed to 0.019 per day at 30 C on hemp, broad mite growth fell from 0.31 at 25 C to 0.12 at 32 C, and 96% of western flower thrips larvae died at 35 C. Spider mites are the exception: they still grow fast at 30-32 C. **Does high humidity kill spider mites?** High humidity does not kill spider mites, but it slows them and helps their predators. Greenhouse cucumber trials found up to three times more mites at about 55% RH than at about 80% RH. The bigger effect is on Phytoseiulus persimilis, whose eggs mostly fail below about 60% RH. Raising humidity is a veg-stage tactic only; in flower it invites bud rot. **What humidity do predatory mites need?** Most predatory mites need about 60-75% RH around their eggs. Phytoseiulus persimilis egg hatch fell to about 8% at 40% RH versus nearly 100% at 80% RH at 27 C, and Amblyseius swirskii lost half its eggs at about 63% RH. Neoseiulus californicus tolerates roughly 40-80% RH, which is why it suits drier cannabis rooms and flower. **What is a degree-day and how do I use it indoors?** A degree-day is one day spent one degree above a pest's lower developmental threshold. Indoors, divide the pest's degree-day requirement by room temperature minus threshold to get days per stage. Western flower thrips need about 268 degree-days above 7.9 C per generation, so a generation takes about 16 days at 25 C and about 12 days at 30 C. **Do short days in flower affect pests and beneficials?** Short days in flower can push some pests and beneficials into diapause. Two-spotted spider mite females may enter diapause under short days and cool temperatures, turning orange and hiding. Some Orius strains entered diapause at 57% at 12:12 and 20 C, and the aphid midge needs about 15.5 hours of light to stay active, so it often fails in 12:12 rooms. **Why should spray intervals change with temperature?** Spray intervals should change with temperature because development time does. Most contact sprays miss eggs, so the follow-up must land after survivors hatch and before they reproduce. Broad mites go from egg to adult in about 7 days at 18 C but 3.3 days at 28 C on lab leaf discs; a weekly interval that works in a cool room is far too slow in a hot one. **Which predators work best in hot, dry cannabis rooms?** In hot, dry cannabis rooms, Neoseiulus californicus (active about 8-35 C at 40-80% RH) is the most robust spider mite predator, Amblyseius swirskii suits warm rooms against thrips, whiteflies and broad mites, and Eretmocerus eremicus beats Encarsia formosa against whiteflies above about 27 C. Phytoseiulus persimilis and the aphid midge struggle in hot, dry conditions. **Short answer.** Temperature sets the speed of every cannabis pest. Between about 20 and 30 C (68-86 F), spider mites, broad mites, thrips and aphids double every 2-4 days in lab life tables, while mealybugs and fungus gnats take 6-8 days. Humidity matters less to the pests directly than to the predators and fungi that kill them. So choose set-points for the beneficials as much as against the pest, and time every repeat treatment from development time at your own temperature. Each pest's article has the full life table; this page puts them side by side. All life-table figures here are from lab studies at constant temperature, mostly on hosts other than cannabis (bean, apple, cucumber, grape, eggplant). Only the cannabis aphid figures come from hemp. Treat them as the unchecked upper limit of what a pest can do; real rooms with predators, crowding and plant defences run slower. ## How fast does each cannabis pest multiply at 25 C? At 25 C (77 F), the intrinsic rate of increase (r_m) of common cannabis pests ranges from about 0.08 per day for citrus mealybug to about 0.53 per day for cotton aphid, a doubling time from 8 days down to 1.3 days. Aphids, broad mites and spider mites are the fast group; thrips and whiteflies are intermediate; mealybugs, fungus gnats and moths are slow per day but lay many eggs. | Pest | Egg (or birth) to adult at 25 C | Eggs or young per female | r_m at ~25 C (/day) | Doubling time | Lower / upper threshold | Favoured RH | Data source | |---|---|---|---|---|---|---|---| | Two-spotted spider mite (*Tetranychus urticae*) | ~6.4-10.4 d | 64-141 | 0.231-0.243 | ~2.9 d | 8.4-13.8 C / none published (develops at 35-37 C) | Low (~30-55%) | Apple, eggplant, cotton [3][4] | | Carmine (red) form of *T. urticae* | 12.8 d at 29.4 C | ~4 per day | 0.183 at 29.4 C | ~3.8 d | as green form | Low | Carnation, 42% RH; see [two-spotted vs carmine](https://genetixbay.com/knowledge/pests/two-spotted-vs-carmine-mite.md) | | Broad mite (*Polyphagotarsonemus latus*) | 4.4 d | ~44 | 0.31 | ~2.2 d | 9.7 C / ~33-35 C | High (80-90%) | Grape leaf discs [6] | | Hemp russet mite (*Aculops cannabicola*) | ~5.5 d (proxy) | ~52 (proxy) | 0.286 (proxy) | ~2.4 d | 10.5 C / none published | Contested | Tomato russet mite on tomato, proxy only [7] | | Western flower thrips (*Frankliniella occidentalis*) | 15.9 d | ~102 | 0.23 | ~3.0 d | 7.9 C / ~31-35 C | No direct effect found | Chrysanthemum, cabbage [8][9] | | Greenhouse whitefly (*Trialeurodes vaporariorum*) | ~22.8 d | up to ~400 | 0.035-0.072 (poor host) | 10-20 d | 8.3 C / declines from ~26 C | No value found | Bean, degree-day model [11] | | Silverleaf whitefly (*Bemisia tabaci*) | ~21-23 d | 324 at 20 C | 0.192 | ~3.6 d | 11-13 C / ~35 C | No value found | Eggplant, cotton [10] | | Cannabis aphid (*Phorodon cannabis*) | 6.4 d to first birth | ~112 | 0.355 | ~2.0 d | ~10-13 C (fitted) / ~30 C | No data (65% RH only) | **Hemp**, lab [12] | | Green peach aphid (*Myzus persicae*) | ~8.3 d | R0 ~33 | 0.250 (0.356 at 26.7 C) | ~2.0-2.8 d | 3.9-6.5 C / 37.3 C | No value found | Pepper, lab [14] | | Cotton/melon aphid (*Aphis gossypii*) | ~5 d | ~82 | 0.526 | ~1.3 d | 6.0 C / ~35 C lethal | No value found | Cucumber, lab [13] | | Rice root aphid (*Rhopalosiphum rufiabdominale*) | ~5 d (estimate) | 63 at 20 C | 0.432 | ~1.6 d | 6.1 C / ~35 C | Lives in the medium | Rice, lab [15] | | Citrus mealybug (*Planococcus citri*) | ~26-28 d | 300-600 | 0.084 | ~8.3 d | 7.2-10.6 C / ~33.6 C | Not isolated | Grapevine, lab [16] | | Fungus gnat (*Bradysia impatiens*) | ~17-21 d | ~75 (up to ~200) | 0.111 | ~6.2 d | ~10 C / 32-35 C | Wet medium matters, not air RH | Rice bran, lab [17] | | Shore fly (*Scatella stagnalis*) | 11.4 d | ~315 | 0.263 | ~2.6 d | 6.4 C / not published | Wet, algae-covered media | Rockwool, lab; see [shore flies](https://genetixbay.com/knowledge/pests/shore-flies.md) | | Corn earworm (*Helicoverpa zea*) | ~34 d (model) | ~1,500 | no published value | - | 12.6 C / 33.3 C | Indirect (bud rot) | Degree-day model [19] | | Beet armyworm (*Spodoptera exigua*) | 27.2 d | R0 ~378 | ~0.21 (between 0.149 at 20 C and 0.276 at 30 C) | ~3.3 d | 13.1 C / 32.2 C | No value found | Sugar beet, lab [18] | | Beet leafhopper (*Circulifer tenellus*) | ~34 d (model) | ~99 | no published value | - | 14.4 C / 35 C | No value found | Degree-day model [20] | Notes: R0 is the net reproductive rate (daughters per female per generation). A dash means no published value was found. Where a range is shown, values differ by host plant; host quality alone can change r_m by half, as the spider mite data on apple versus peach show (see [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md)). ## Why does temperature matter so much for pest growth? Temperature matters because insects and mites cannot regulate their body temperature, so every step of development and egg-laying runs on the heat around them. Between the lower developmental threshold and the optimum, development rate rises roughly in a straight line with temperature, which is the basis of [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md) models [2]. Heat raises r_m in two ways at once. Generations get shorter, and females start laying sooner. Since r_m is roughly the natural log of R0 divided by generation time, halving generation time doubles r_m even if each female lays the same number of eggs [1]. Above the optimum, the picture flips. Egg-laying and survival fall faster than development speeds up: - **Cannabis aphid on hemp:** r_m 0.355 per day at 25 C, 0.244 at 28 C, 0.019 at 30 C [12]. - **Broad mite:** 0.31 at 25 C, 0.12 at 32 C [6]. - **Western flower thrips:** 96% of larvae died at 35 C, with development fastest near 31 C [8]. - **Two-spotted spider mite:** still 0.30-0.32 per day at 30 C [3][4]; daughters per female fell sharply only at 35 C [3]. That is why spider mites are the signature pest of hot cannabis rooms. They keep accelerating up to temperatures where aphids and broad mites are already slowing down. ## How much faster do pests grow at 30 C than at 20 C? Pests with published data grow roughly 1.5 to 2 times faster at 30 C than at 20 C, except those whose optimum is below 30 C. The worked example below starts with 10 females and uses N(t) = N0 x e^(r_m x t), the unchecked exponential model from life tables [1]. | Pest | Temperature | r_m (/day) | Doubling time | After 14 days | After 21 days | After 28 days | |---|---|---|---|---|---|---| | Two-spotted spider mite | 20 C | 0.161 | 4.3 d | ~95 | ~290 | ~910 | | Two-spotted spider mite | 25 C | 0.237 | 2.9 d | ~280 | ~1,450 | ~7,600 | | Two-spotted spider mite | 30 C | 0.302 | 2.3 d | ~690 | ~5,700 | ~47,000 | | Broad mite | 18 C | 0.10 | 6.9 d | ~40 | ~80 | ~160 | | Broad mite | 25 C | 0.31 | 2.2 d | ~770 | ~6,700 | ~59,000 | | Broad mite | 32 C | 0.12 | 5.8 d | ~50 | ~120 | ~290 | | Cannabis aphid (hemp) | 20 C | 0.153 | 4.5 d | ~85 | ~250 | ~730 | | Cannabis aphid (hemp) | 25 C | 0.355 | 2.0 d | ~1,400 | ~17,000 | ~210,000 | | Cannabis aphid (hemp) | 30 C | 0.019 | 36 d | ~13 | ~15 | ~17 | | Tomato russet mite (proxy for hemp russet mite) | 20 C | 0.158 | 4.4 d | ~90 | ~280 | ~830 | | Tomato russet mite (proxy) | 30 C | 0.253 | 2.7 d | ~350 | ~2,000 | ~12,000 | | Western flower thrips | 25 C | 0.23 | 3.0 d | ~250 | ~1,250 | ~6,300 | | Citrus mealybug | 25 C | 0.084 | 8.3 d | ~30 | ~60 | ~105 | **Method.** Doubling time = 0.693 / r_m. Population at day t = 10 x e^(r_m x t). For example, spider mites at 30 C for 21 days: 0.302 x 21 = 6.34; e^6.34 = 568; 568 x 10 = about 5,700. Sources: spider mite [3], broad mite [6], cannabis aphid [12], tomato russet mite [7], thrips [9], mealybug [16]. **What the numbers mean.** These are ceilings, not forecasts. They assume unlimited food, no predators, no crowding and a constant temperature. Their use is comparative: three weeks of neglect at 30 C produces about 20 times more spider mites than three weeks at 20 C. See [intrinsic rate of increase](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md) and [doubling time](https://genetixbay.com/knowledge/glossary/doubling-time.md). ## How do developmental thresholds and degree-days help a grower? Developmental thresholds and degree-days let a grower convert one temperature's life cycle into another's. Days per stage = degree-days required / (temperature minus lower threshold), valid between the lower and upper thresholds [2]. See [developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md). | Pest | Lower threshold | Degree-days (C) | Days at 20 C | Days at 25 C | Days at 30 C | Stage covered | |---|---|---|---|---|---|---| | Two-spotted spider mite (apple) | 8.43 C | 172.4 | 14.9 | 10.4 | 8.0 | Egg to adult [3] | | Broad mite (grape) | 9.71 C | 62.7 | 6.1 | 4.1 | 3.1 | Egg to adult [6] | | Western flower thrips | 7.9 C | 268 | 22.1 | 15.7 | 12.1 | Generation [8] | | Shore fly (rockwool) | 6.4 C | 212.8 | 15.6 | 11.4 | 9.0 | Egg to adult; see [shore flies](https://genetixbay.com/knowledge/pests/shore-flies.md) | | Greenhouse whitefly | 8.3 C | 380.7 | 32.5 | 22.8 | 17.5 | Egg to adult [11] | | Citrus mealybug (citrus) | 7.15 C | 526.3 | 41.0 | 29.5 | 23.0 | Egg to adult [28] | | Corn earworm | 12.6 C | 422.3 | 57.1 | 34.1 | 24.3 | Egg to adult [19] | | Beet leafhopper | 14.4 C | 361.1 | 64.5 | 34.1 | 23.1 | Egg to adult [20] | The 30 C column for the spider mite and broad mite is close to measured values (about 6-7 days and 3.3-3.5 days), which is a useful sanity check [3][6]. Linear models overestimate speed near the upper threshold, so trust them least above about 30 C. ## How does humidity affect cannabis pests and their enemies? Humidity affects cannabis pests far less than temperature does, but it decides which predators and pathogens can work. The clearest effects are on predatory mite eggs and on insect-killing fungi, both of which need high humidity, and on spider mites, which do better in dry air. **Spider mites prefer dry air.** In greenhouse cucumber, spider mite densities were up to three times higher at about 55% RH than at about 80% RH [5]. Dry air helps mites shed the excess water they take in while feeding; humid air slows feeding and egg-laying. Low humidity is a contributing factor, not a cause. **Broad mites prefer humid air.** UConn and other extension sources give 80-90% RH at 21-27 C as favourable; see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). **Hemp russet mite is contested.** Extension sources disagree; the tomato russet mite proxy grew fastest at 30-60% RH [7]. See [hemp russet mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md). **Fungus gnats and shore flies respond to substrate moisture, not air RH.** A wet top layer of the medium drives them; see [fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md). **Predatory mite eggs need humidity.** Phytoseiulus persimilis egg hatch was about 8% at 40% RH versus nearly 100% at 80% RH at 27 C [22]. The humidity at which half the eggs of persimilis and Neoseiulus californicus die was about 66-70% RH in Wageningen trials [5]. Amblyseius swirskii lost half its eggs at about 63% RH (see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md)). **Insect-killing fungi need humid leaf surfaces** for hours to germinate, which conflicts with flower-room humidity targets. See [entomopathogenic fungi](https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.md). ## What are the climate windows of the main beneficials? Each beneficial has a temperature and humidity window, and releasing it outside that window wastes money. The table below summarises extension and research values; supplier technical sheets give similar ranges. | Beneficial | Target pests | Temperature window | RH window | Notes | |---|---|---|---|---| | *Phytoseiulus persimilis* | Spider mites | Above ~20 C; struggles above ~30 C | Above ~60%, optimum >75% | Specialist; starves when prey run out [21][22] | | *Neoseiulus californicus* | Spider mites, broad mites | ~8-35 C | ~40-80% | Best for warm, dry rooms and preventive use [21] | | *Neoseiulus fallacis* | Spider mites, russet mites | ~9-29 C | Above ~50% | Cooler rooms [21] | | *Amblyseius andersoni* | Mites | ~6-40 C | Not well defined | Wide temperature tolerance [21] | | *Galendromus occidentalis* | Spider mites | ~10-46 C | ~30-60% | Hot, dry conditions [21] | | *Feltiella acarisuga* (midge) | Spider mite hot spots | Moderate | ~60-95%, optimum ~80% | Flies to colonies [21] | | *Stethorus* (lady beetle) | Spider mite hot spots | ~16-32 C | - | Needs high prey density [21] | | *Amblyseius swirskii* | Thrips, whiteflies, broad mites | Develops 11-37 C, optimum ~30 C | Eggs fail below ~63% | Warm rooms [23] | | *Neoseiulus cucumeris* | Thrips, broad mites | ~24-29 C best | Above ~65%, ideally 75% | Eats first-instar thrips only; see [thrips](https://genetixbay.com/knowledge/pests/thrips.md) | | *Orius insidiosus* | Thrips | ~20-29 C | - | 57% of females diapaused at 12:12 and 20 C [24] | | *Encarsia formosa* | Greenhouse whitefly | ~21-27 C; no flight below ~18 C | ~50-80% | Whitefly outpaces it below ~17 C [11][25] | | *Eretmocerus eremicus* | Whiteflies | ~25-29 C | - | Better than Encarsia in heat [25] | | *Aphidius colemani* | Green peach and cotton aphids | ~18-25 C; poor above ~30 C | ~60-80% | Match species to aphid [26] | | *Aphidoletes aphidimyza* (midge) | Aphids | ~16-27 C | ~50-85% | Needs ~15.5 h light or diapauses [26] | | *Cryptolaemus montrouzieri* | Mealybugs | ~22-25 C best; slows below 20 C | ~70-80% | Needs egg masses to breed [27] | | *Stratiolaelaps scimitus* | Fungus gnats, thrips pupae | Inactive below ~15 C | Moist medium | Top 2.5 cm of medium [17] | | *Steinernema feltiae* (nematode) | Fungus gnats, thrips pupae | ~8-30 C, best ~14-26 C | Moist medium | Poor in hot pots above ~30 C; see [fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md) | ## How do short days and diapause affect a flower room? Short days can trigger diapause in some pests and beneficials, so a 12:12 flower room is a different biological environment from an 18:6 veg room, not just a different light schedule. See [diapause](https://genetixbay.com/knowledge/glossary/diapause.md). - **Two-spotted spider mites.** Females reared under short days and cool temperatures can enter diapause, turn orange-red, stop laying and hide in debris and cracks; they are the survivors that restart the next run. Many greenhouse strains diapause weakly. See [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md). - **Orius insidiosus.** In a lab study at 20 C, 57% of females entered reproductive diapause at 12:12 and nearly all at 10:14 [24]. Use non-diapausing strains in flower rooms or rely on predatory mites. - **Aphidoletes aphidimyza.** The aphid midge needs about 15.5 hours of light to avoid diapause [26]. Night-break lighting to prevent it would disrupt cannabis flowering, so the midge is a veg-room tool. - **Cannabis aphid.** Sexual forms and eggs can appear indoors after the flip to short days; see [cannabis aphid](https://genetixbay.com/knowledge/pests/cannabis-aphid.md). ## How should grow-room set-points be chosen for pest control? Choose set-points that keep the crop first, then nudge the room toward the predator's window and away from the pest's optimum. The crop's needs win every conflict: late-flower humidity stays at 40-50% RH regardless of what mites prefer, because bud rot costs more [21]. | Stage | Typical set-point | Pests favoured | Beneficials favoured | IPM adjustment | |---|---|---|---|---| | Propagation | 22-26 C, 70-85% RH | Fungus gnats, shore flies, broad mites | Persimilis, cucumeris, swirskii, soil predators | Dry the top of plugs; release soil predators | | Veg | 24-27 C, 60-70% RH | Spider mites (at the hot end), aphids, thrips | Most predatory mites | Keep canopy below ~28 C; hold 60-70% RH where safe | | Early flower | 23-26 C, 50-60% RH | Spider mites, thrips | Californicus, swirskii | Last window for preventive releases | | Late flower | 20-24 C, 40-50% RH | Spider mites (dry air) | Californicus, G. occidentalis | Do not raise RH; accept slower mite control | Leaf temperature matters more than air temperature. A canopy hot spot 3-4 C above the room under a lamp runs spider mites at the 30 C row of the growth table while the thermostat reads 26 C. Check with an infrared thermometer, and see [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) and [leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md). ## How do you set re-application intervals from these numbers? Set the repeat interval of a contact treatment that misses eggs to fall after the eggs hatch and before the survivors become egg-laying adults. Take egg development time as the earliest repeat and egg-to-adult time (plus the pre-oviposition period) as the latest, then aim for the middle. The [IPM programme](https://genetixbay.com/knowledge/pests/integrated-pest-management-program.md) explains the logic. | Pest | 20 C interval | 25 C interval | 30 C interval | Based on | |---|---|---|---|---| | Two-spotted spider mite | ~7 d | ~5 d | ~3-4 d | Egg-to-adult 14.9 / 10.4 / 8.0 d [3] | | Broad mite | ~3-4 d | ~2-3 d | ~2 d | Egg-to-adult 6.1 / 4.1 / 3.1 d [6] | | Western flower thrips (foliar stages) | ~7-10 d | ~5-7 d | ~4-5 d | Generation 22 / 16 / 12 d; pupae in medium need a separate tool [8] | | Aphids (live birth, no eggs) | ~5-7 d | ~3-5 d | ~3-5 d | Birth to first birth ~11 / 6.4 / 5.4 d (cannabis aphid) [12] | These intervals are calculated from non-cannabis lab data (except the cannabis aphid) and are a starting point to confirm by scouting, not a label instruction. Whatever the interval, follow the label and local law, and rotate mode-of-action groups by pest generation; see [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md). ## What are the common myths about temperature, humidity and pests? - **"Mites die in winter."** *Myth* for indoor rooms. Rooms never drop below spider mite thresholds of about 8-14 C [3][4]; outdoors, diapausing females survive in debris. - **"Just raise humidity to beat spider mites."** *Myth* as a cure. High RH slows mites and helps persimilis [5][22], but it does not eliminate them and is dangerous in flower. - **"Hotter always means more pests."** *Myth.* Cannabis aphid, broad mites and thrips decline above their optimum [6][8][12]; spider mites keep going. - **"A cold room stops pests."** *Myth.* Cooling slows them; development continues down to thresholds of roughly 6-13 C. - **"Lab r_m values predict what will happen in my room."** *Myth.* They are upper bounds on non-cannabis hosts, best used for comparisons and timing. - **"Temperature makes the most difference to pest growth."** *Established* [1][2]. ## Common mistakes - Using air temperature at the thermostat instead of leaf temperature at the canopy. - Keeping one weekly spray interval all year, whatever the room temperature. - Releasing humidity-sensitive predators into a dry flower room. - Relying on the aphid midge or diapausing Orius under 12:12. - Treating lab r_m values as forecasts instead of upper bounds. ## Evidence - Temperature-driven development and the degree-day method: *Established* [1][2]. - Pest life-table values: *Supported* from lab studies, mostly on non-cannabis hosts; only the cannabis aphid data are from hemp [12]. - Humidity effects on spider mites and predatory mite eggs: *Supported* by greenhouse trials and lab data [5][22]. - Diapause in Orius and Aphidoletes under short days: *Established* in the cited studies [24][26]; cannabis-specific trials absent. - Hemp russet mite growth figures: proxy only (tomato russet mite) [7]. ## Sources 1. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605 2. UC IPM. Degree-Days: About Degree-Days. https://ipm.ucanr.edu/WEATHER/ddconcepts.html 3. Kasap, I., 2004. Effect of apple cultivar and of temperature on the biology and life table parameters of the twospotted spider mite, Tetranychus urticae. Phytoparasitica 32:73-82. https://doi.org/10.1007/BF02980863 4. Bounfour, M. and Tanigoshi, L.K., 2001. Effect of temperature on development and demographic parameters of Tetranychus urticae and Eotetranychus carpini borealis. Annals of the Entomological Society of America 94(3):400-404. https://doi.org/10.1603/0013-8746(2001)094[0400:EOTODA]2.0.CO;2 5. Messelink, G. and Leman, A., 2020. Are low humidity levels a limiting factor for spider mite control by phytoseiid predators under fluctuating climatic conditions? IOBC-WPRS Bulletin 149:101-102. https://edepot.wur.nl/519096 6. Ferreira, R.C.F., Oliveira, J.V., Haji, F.N.P. and Gondim, M.G.C., 2006. Biology, thermal requirements and fertility life table of the broad mite Polyphagotarsonemus latus on grape. Neotropical Entomology 35:126-132. https://doi.org/10.1590/S1519-566X2006000100017 7. Kawai, A. and Haque, M.M., 2004. Population dynamics of tomato russet mite, Aculops lycopersici, and its natural enemy, Homeopronematus anconai. JARQ 38:161-166. https://doi.org/10.6090/jarq.38.161 8. McDonald, J.R., Bale, J.S. and Walters, K.F.A., 1998. Effect of temperature on development of the western flower thrips, Frankliniella occidentalis. European Journal of Entomology 95:301-306. https://www.eje.cz/pdfarticles/406/eje_095_2_301_McDonald.pdf 9. Ding, T., Chi, H., Gokce, A., Gao, Y. and Zhang, B., 2018. Demographic analysis of arrhenotokous parthenogenesis and bisexual reproduction of Frankliniella occidentalis. Scientific Reports 8:3346. https://pmc.ncbi.nlm.nih.gov/articles/PMC5820284/ 10. Wang, K. and Tsai, J.H., 1996. Temperature effect on development and reproduction of silverleaf whitefly. Annals of the Entomological Society of America 89(3):375-384. https://doi.org/10.1093/aesa/89.3.375 11. Osborne, L.S., 1982. Temperature-dependent development of greenhouse whitefly and its parasite Encarsia formosa. Environmental Entomology 11(2):483-485. https://doi.org/10.1093/ee/11.2.483 12. Durak, R. et al., 2021. Mild abiotic stress affects development and stimulates hormesis of hemp aphid Phorodon cannabis. Insects 12(5):420. https://doi.org/10.3390/insects12050420 13. Satar, S., Kersting, U. and Uygun, N., 2005. Effect of temperature on development and fecundity of Aphis gossypii on cucumber. Journal of Pest Science 78:133-137. https://doi.org/10.1007/s10340-005-0082-9 14. Davis, J.A., Radcliffe, E.B. and Ragsdale, D.W., 2006. Effects of high and fluctuating temperatures on Myzus persicae. Environmental Entomology 35(6):1461-1468. https://doi.org/10.1603/0046-225X(2006)35[1461:EOHAFT]2.0.CO;2 15. Tsai, J.H. and Liu, Y.H., 1998. Effect of temperature on development, survivorship, and reproduction of rice root aphid. Environmental Entomology 27(3):662-666. https://doi.org/10.1093/ee/27.3.662 16. Kina, A., Kara, H. and Ozgokce, M.S., 2018. Life table of Planococcus citri on grapevine. Yuzuncu Yil University Journal of Agricultural Sciences 28:247-256. https://gcris.yyu.edu.tr/items/e8a214c2-7537-41e7-9003-45ba37fe362d 17. Ishihara, Y. and Tagami, Y., 2019. Effect of temperature on development and reproduction of Bradysia sp. and Bradysia impatiens. Japanese Journal of Applied Entomology and Zoology 63(2):57-67. https://doi.org/10.1303/jjaez.2019.57 18. Karimi-Malati, A., Fathipour, Y., Talebi, A.A. and Bazoubandi, M., 2014. Life table parameters and survivorship of Spodoptera exigua at constant temperatures. Environmental Entomology 43(3):795-803. https://doi.org/10.1603/EN11272 19. UC IPM. Corn earworm / cotton bollworm / tomato fruitworm phenology model. https://ipm.ucanr.edu/weather/phenology-models-description/corn-earworm-cotton-bollworm-tomato-fruitworm/ 20. UC IPM. Beet leafhopper phenology model. https://ipm.ucanr.edu/weather/phenology-models-description/beet-leafhopper/ 21. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf 22. Cornell University Biological Control. Phytoseiulus persimilis. https://biocontrol.entomology.cornell.edu/predators/Phytoseiulus.php 23. Lee, H.S. and Gillespie, D.R., 2011. Life tables and development of Amblyseius swirskii at different temperatures. Experimental and Applied Acarology 53:17-27. https://profils-profiles.science.gc.ca/en/publication/life-tables-and-development-amblyseius-swirskii-acari-phytoseiidae-different 24. Ruberson, J.R., Bush, L. and Kring, T.J., 1991. Photoperiodic effect on diapause induction and development in Orius insidiosus. Environmental Entomology 20(3):786-789. https://doi.org/10.1093/ee/20.3.786 25. UConn IPM. Biological Control of Whiteflies. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-whiteflies 26. UConn IPM. Biological Control of Aphids. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-aphids/ 27. UC IPM. Natural Enemies Gallery: Mealybug destroyer. https://ipm.ucanr.edu/natural-enemies/mealybug-destroyer/ 28. Al-Shammari, A. and Al-Zubaidy, H., 2017. Growth threshold and degree days requirement for development and growth of citrus mealybug Planococcus citri. Iraqi Journal of Agricultural Sciences 48(2). https://doi.org/10.36103/ijas.v48i2.415 --- # Thrips on cannabis: life table, temperature, scouting and biological control > Thrips rasp leaf cells and leave silvery scars dotted with black fecal specks. Western flower thrips needs about 268 degree-days above 7.9 °C per generation (about 16 days at 25 °C) and can grow by r = 0.12-0.23 per day. Eggs sit inside leaf tissue and most pupae sit in the medium, so control has two levels: predators that eat larvae on the foliage, and soil predators or nematodes for the pupae, all set up in veg. - Canonical: https://genetixbay.com/knowledge/pests/thrips.html - Category: Pests · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What are the silver streaks with black dots on my cannabis leaves?** Silver or bronze papery streaks dotted with tiny black specks on cannabis leaves are thrips feeding scars and droppings. Thrips are slender insects of about 1.2 to 1.5 mm that pierce surface cells and suck out the contents, mostly on the upper leaf surface. On indoor cannabis the onion thrips is the species most often confirmed. Shake a leaf over white paper to see pale larvae and darker winged adults. **How long is the thrips life cycle at grow-room temperatures?** Western flower thrips takes about 16 days from egg to adult at 25 °C (77 °F), 22 days at 20 °C and 12 days at 30 °C, in a laboratory study on chrysanthemum leaf discs. Development needs about 268 degree-days above a lower threshold of 7.9 °C. Females start laying about 2 days after emerging, so in a 26 °C veg room a new generation starts roughly every 2.5 weeks. **How fast do thrips multiply?** Western flower thrips populations grow at an intrinsic rate of about 0.12 to 0.23 per day at 25 to 27 °C in laboratory life tables, depending on the host plant. At 0.23 per day numbers double every 3 days, so 10 thrips could become about 1,200 in 3 weeks with no predators. At 15 °C the population barely grows. These are unchecked upper bounds, not field predictions. **How do I get rid of thrips on cannabis?** Get rid of thrips on cannabis with a two-level attack, because eggs sit inside leaves and most western flower thrips pupate in the growing medium. On the foliage, release predatory mites such as Neoseiulus cucumeris or Amblyseius swirskii early in veg. In the medium, add soil predatory mites, rove beetles or Steinernema nematodes against pupae. Count blue sticky cards weekly and quarantine incoming clones for about a month. **Why do thrips keep coming back after I spray?** Thrips come back after spraying because contact sprays miss two stages: eggs inserted inside leaf tissue and prepupae and pupae in the medium, where about 98% of western flower thrips pupated in one bean study. At 25 °C those survivors hatch or emerge within about 4 days. Fast generations and haploid males also select resistance quickly, and western flower thrips resists several insecticide classes. **Do Orius pirate bugs work in flower under 12/12?** Orius insidiosus can stall under 12/12 because short days trigger reproductive diapause in many strains. In a laboratory study at 20 °C, 56.8% of females entered diapause at 12 hours of light and nearly 100% at 10 hours, with a critical day length between 12 and 13 hours. Release Orius in veg, ask the supplier for a non-diapausing strain, and do not count on it in flower. **Blue or yellow sticky cards for thrips?** Blue sticky cards are more attractive to thrips than yellow and show the small insects more clearly, according to Colorado State University hemp guidance. Yellow cards also catch thrips plus whiteflies, fungus gnats and winged aphids, so many growers hang both. Cards catch only flying adults, never larvae or pupae, so use them to track trends weekly, not as control. Echinothrips is better caught on green cards. **Which predatory mite should I use for thrips?** For thrips on cannabis, Neoseiulus cucumeris is the cheaper choice for cooler rooms and short days, and works best at 24 to 29 °C with RH above 65%. Amblyseius swirskii does better in warm, long-day rooms around 21 to 27 °C and 70% RH, and also eats whitefly eggs. Both eat only first-instar thrips larvae, so release them preventively in veg, before thrips are seen. **Are thrips dangerous to cannabis?** Thrips damage cannabis by scarring leaves and cutting photosynthesis. In a Canadian trial on indoor cannabis, plants started with five onion thrips yielded less fresh flower than plants started with none. No thrips-transmitted tospoviruses are known to infect cannabis, according to Colorado State University, so the risk is direct feeding damage, which builds fast in warm indoor rooms where natural enemies are absent. **Can a cool room stop thrips?** A cool room slows thrips but does not stop them. Western flower thrips develops above about 7.9 to 9.4 °C, does not enter diapause, and still finished egg to adult in about 37 days at 15 °C in laboratory studies. Dropping a room from 28 °C to 22 °C stretches a generation from about 13 to 19 days, which buys predators time but is no cure on its own. **Short answer.** Silvery, papery patches on leaves sprinkled with tiny black dots are thrips feeding scars and droppings. Western flower thrips (*Frankliniella occidentalis*) needs about 268 degree-days above 7.9 °C to go from egg to adult, which is about 16 days at 25 °C (77 °F) [2]. Its population can grow by 12–23% a day in laboratory life tables [4][5][6]. Eggs sit inside leaf tissue and most pupae sit in the medium, so leaf sprays alone keep failing. Hit both levels: predatory mites up top from early veg, soil predators or nematodes below, blue sticky cards to track the trend, and clean stock so they never get in. ## Thrips numbers at a glance | Parameter | Value | Conditions and source | |---|---|---| | Adult length | ~1.2–1.5 mm | Onion and western flower thrips [8] | | Egg to adult, 25 °C | 15.9 days | WFT, chrysanthemum leaf discs, lab [2] | | Egg to adult, 20 / 30 °C | 21.6 / 11.8 days | Same study [2] | | Lower developmental threshold | 7.9 °C (egg 9.9 °C) | Linear model, 10–35 °C [2]; 9.4 °C on cucumber [3]; 8.9 °C on lima bean [7] | | Degree-days per generation (egg to adult) | 268 DD above 7.9 °C | [2]; 199–233 DD on lima bean [7] | | Upper limit | 96% larval mortality at 35 °C | [2] | | Lifetime eggs per female | ~102 | Bisexual females, purple cabbage, 25 °C [4] | | Adult longevity, 25 °C | females 17.8 d, males 9.8 d | [4] | | Pre-oviposition period | ~1.8 days after adult emergence | 25 °C [4] | | Sex ratio | ~71% female (mated mothers) | [4]; 57–59% female at 27.3 °C [5] | | r (intrinsic rate of increase) | 0.23 /day | 25 °C, purple cabbage [4] | | r | 0.18 /day | 27.3 °C constant [5] | | r | 0.12 /day | 26 °C, bean pods [6] | | Doubling time | 3.0–5.7 days | ln 2 / r, from the three r values above | | Diapause | none | WFT overwinters active [2] | | Share pupating in the medium | ~98% | French bean pots [10] | | Published action threshold for cannabis | none | See scouting section | ## What do thrips look like and which species attack cannabis? Thrips on cannabis are slender insects about 1.2–1.5 mm long with pale yellow wingless larvae and light-brown to dark winged adults [8]. Two species turn up most: onion thrips (*Thrips tabaci*) and western flower thrips (*Frankliniella occidentalis*). Colorado State University has confirmed onion thrips in multiple indoor cannabis samples and calls it the primary indoor species; western flower thrips is likely present on some indoor crops too [8]. Onion thrips is the main confirmed indoor cannabis thrips in Canada as well: a trial in a commercial indoor facility found it proliferating on the crop [9]. Western flower thrips is the classic greenhouse thrips and the species with the best life-table data, so most numbers in this article come from it. Treat them as a close guide for onion thrips, not a substitute (*Supported*). Onion thrips populations are often reported to be mostly female and to reproduce without mating. *Echinothrips americanus* is a third greenhouse thrips worth knowing. It is dark brown to black, about 1.6 mm, with orange bands between the abdominal segments and white patches at the base of the wings [13]. All its life stages stay on the leaves, usually along the midvein, and it pupates on the leaf rather than in the medium [13]. No published record on cannabis was found; it matters because nematodes and soil predators do nothing against it. ## What does thrips damage look like on cannabis? Thrips damage on cannabis is a silvery or bronze, papery scar, often along veins, sprinkled with black fecal specks [1][8]. Thrips pierce surface cells and suck out the contents, which leaves pale stippled patches that later turn brown [1]. Thrips feed more on the upper leaf surface than spider mites do [8]. Feeding on expanding leaves can distort them [8]. In flower, thrips can hide in buds, and damage often shows before you see the insect [1]. Indoors, where natural enemies are absent, high populations build and are sustained, so scars accumulate into extensive leaf scarring [8]. In a Canadian indoor trial, plants started with five onion thrips yielded less fresh flower than plants started with none [9]. No thrips-transmitted virus (tospovirus) is known to infect cannabis [8]. The damage is direct feeding. **Differentials.** Spider mites leave round pale stipples, no black specks, and webbing at high numbers. Russet and broad mites bronze or twist growth without scars ([kb-pests-broad-russet-mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md)). Nutrient spotting has no specks and no insects ([kb-diagnosis-rust-spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md)). ## What is the thrips life cycle in numbers? The western flower thrips life cycle runs egg (inserted into leaf tissue), two feeding larval instars, two non-feeding stages (propupa and pupa), then the winged adult [1][15]. At 25 °C the whole run takes about 16 days in a lab study on chrysanthemum leaf discs at 18 h light [2]. **Development time by temperature (days, mean).** McDonald, Bale and Walters reared western flower thrips on chrysanthemum leaf discs at six constant temperatures [2]. Values below are read from their Table 1. | Temperature | Egg | Larvae (L1+L2) | Propupa | Pupa | Egg to adult | |---|---|---|---|---|---| | 10 °C (50 °F) | 31.3 | 59 | 9.4 | 22.1 | 118.6 | | 15 °C (59 °F) | 9.2 | 17.0 | 3.9 | 7.8 | 37.1 | | 20 °C (68 °F) | 6.7 | 9.4 | 1.6 | 3.8 | 21.6 | | 25 °C (77 °F) | 4.1 | 7.8 | 1.3 | 2.8 | 15.9 | | 30 °C (86 °F) | 3.1 | 6.3 | 1.1 | 1.9 | 11.8 | | 35 °C (95 °F) | 2.5 | 96% died | – | – | only 4 adults | **Thresholds and degree-days.** Development rate rose linearly with temperature: rate (1/days) = 0.0037 × T − 0.029 [2]. That gives 268 degree-days above 7.9 °C from egg to adult [2]. Stage thresholds were 9.9 °C for eggs, 6.1 °C for larvae, 5.2 °C for propupae and 9.2 °C for pupae [2]. Other studies put the egg-to-adult threshold at 9.4 °C on cucumber [3] and 8.9 °C on lima bean, with 199–233 degree-days [7]. Larvae develop best near 31 °C [2]. **Adults.** At 25 °C on purple cabbage, mated females lived 17.8 days, males 9.8 days, and females started laying about 1.8 days after emerging [4]. At 28 °C females live about 26 days, some up to 5 weeks [15]. Adult longevity is shortest at 30 °C and longest at 15 °C on cucumber [3]. **Reproduction.** Mated females laid about 102 eggs each at 25 °C, about 71% of them daughters [4]. Other hosts give fewer: 58.7 first instars per female at 27.3 °C [5] and 35 eggs per female on bean pods at 26 °C [6]. Food quality matters as much as temperature [2]. **Population growth.** The intrinsic rate of increase was 0.23 per day at 25 °C on cabbage [4], 0.18 per day at 27.3 °C [5] and 0.12 per day at 26 °C on bean pods [6]. On cucumber, r_m peaked at 30 °C, and at 15 °C the population was nearly stable [3]. No cannabis-specific life table has been published. ## How does thrips reproduction work, and why does it matter? Western flower thrips is arrhenotokous: unmated females lay unfertilised eggs that all become males, and mated females produce mostly daughters [4]. This is [haplodiploidy](https://genetixbay.com/knowledge/glossary/haplodiploidy.md): males are haploid. A single unmated female can still found a colony. Virgin females first produce sons, then mate with those sons and start producing daughters [4]. One escaped thrips on a clone is enough. Haploid males carry one copy of each gene, so a resistance allele is fully expressed in them and selected fast. This is a standard explanation for quick resistance in thrips and mites (*Supported*; see [kb-term-arrhenotoky](https://genetixbay.com/knowledge/glossary/arrhenotoky.md) and [kb-term-pesticide-resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md)). ## Why do temperature and humidity matter for thrips? Temperature sets the speed of every thrips generation: from about 22 days at 20 °C to 12 days at 30 °C in lab rearing [2]. Growth peaks near 30 °C and collapses near 35 °C, where 96% of larvae died [2]. Western flower thrips has no diapause and simply slows in the cold [2]. **Grow-room set-points, converted to generation time.** Using 268 degree-days above 7.9 °C [2], at constant temperature: | Room | Set-point | Days egg to adult | |---|---|---| | Veg, warm | 28 °C (82 °F) | 13.3 | | Veg, typical | 26 °C (79 °F) | 14.8 | | Flower | 24 °C (75 °F) | 16.6 | | Late flower | 22 °C (72 °F) | 19.0 | | Cool room | 18 °C (64 °F) | 26.5 | These are linear-model estimates; real rooms with a cooler night run a little slower. Calculate with your own day/night average. **Humidity.** No strong published effect of RH on western flower thrips growth rate was found for the grow-room range. RH matters mainly through the predators. Neoseiulus cucumeris reproduces best above 65% RH (ideally 75%), and its eggs shrivel and die at low RH [12]. A. swirskii wants about 70% RH [12]. Entomopathogenic fungi also need moisture at the leaf surface. **VPD trade-off.** A veg room at 24–28 °C and 60–70% RH (roughly 0.9–1.5 kPa air VPD) suits predatory mites. A flower room at 45–55% RH, and 40–50% in late flower, does not. That is one more reason to build predator numbers in veg ([kb-term-vpd](https://genetixbay.com/knowledge/glossary/vpd.md)). **Day length.** Short days matter for the predators, not the thrips: some Orius insidiosus strains and some N. cucumeris strains enter diapause under short days [8][11]. ## How fast can a thrips population grow? A worked example Ten western flower thrips can become about 1,200 in three weeks at 25 °C if nothing eats them, using r = 0.23 per day [4]. The method is the exponential model N(t) = N0 × e^(r × t), with N0 = 10 founding thrips and t in days. | Scenario | r (per day) | Doubling time | Day 14 | Day 21 | Day 28 | Day 42 | |---|---|---|---|---|---|---| | 25 °C, cabbage [4] | 0.23 | 3.0 d | 249 | 1,239 | 6,177 | ~154,000 | | 27.3 °C [5] | 0.18 | 3.8 d | 126 | 446 | 1,580 | ~19,900 | | 26 °C, bean pods [6] | 0.12 | 5.7 d | 54 | 127 | 296 | 1,611 | | 15 °C, cucumber [3] | ~0 | – | ~10 | ~10 | ~10 | ~10 | This is the unchecked upper bound: no predators, unlimited food, a stable age structure. Real rooms grow slower once leaves are damaged, predators arrive or numbers crowd. Read the table for what it shows about timing. At r = 0.12–0.23, the gap between "a few on one card" and "every leaf scarred" is two to four weeks. A clone brought in at the start of veg can be a crop-wide problem by the flip. Host plant changes r by a factor of two [4][6]. Cannabis has no published value, so treat the range as the planning band. ## Where do thrips hide, how do they spread and how do they get in? Thrips enter a cannabis room mainly on clones and other live plants, and through vents and openings in the warm season [8]. Winged adults move between plants and are small enough to pass through tiny gaps; thrips-proof screening must be very fine mesh [8]. **Hiding places.** Eggs are inside leaf tissue [1]. Larvae feed on leaves, often along veins. Prepupae and pupae of most species drop to the medium or leaf litter, or wedge into crevices [1]; on French beans about 98% of western flower thrips left the plant to pupate in the soil [10]. In flower, thrips shelter inside buds [1]. Echinothrips stays on the leaf for its whole life [13]. **Vectors.** Clones, cuttings and potted plants [8]. Cut flowers and houseplants. Weeds near intakes and in the room, which support thrips [8]. Clothing after time in a garden (Grower practice). **Starve-out.** Colorado State University advises a host-free period of at least 3–4 weeks, weeds included, to let residual thrips die out between crops [8]. **Quarantine.** Hold new plants in a separate area for at least a month, inspect them regularly and hang traps before they enter a thrips-free room [8]. One month covers about two generations at 25 °C, which is long enough for eggs and pupae that came in to show up. ## How do I scout for thrips? Scout for thrips weekly with a lens, a tap test and sticky cards, and record counts so you can see the trend. A rising card count week on week, or fresh scars on new leaves, is the signal to act. **Lens.** A 10x lens shows adults and larvae; 20x helps tell thrips larvae from mites and see the black specks. Species ID (onion vs western flower vs Echinothrips) needs 40–60x or a lab. **Tap test.** Tap a branch or bud over white paper or a dark card; count larvae and adults (Grower practice). **Sticky cards.** Blue cards attract thrips better than yellow and make them easier to see; yellow also works and catches other pests [8]. Thin adhesive makes thrips easier to count [8]. Hang cards just above the canopy and raise them as plants grow (Grower practice). Change or read them weekly. Cards catch only flying adults, never larvae or pupae [8]. **Card density.** Greenhouse guidance uses about 1 card per 1,000 ft² (~93 m²) for monitoring whiteflies, which is far too sparse for a tent ([kb-pests-whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md)). In small rooms, growers use about 1 card per 1–2 m² plus one by each door and intake (Grower practice). **Echinothrips.** Adults are sedentary and weak fliers, so they may not show on cards; green cards are reported to catch them better than yellow or blue [13]. Look along the leaf midvein instead. **Thresholds.** No action threshold has been published for thrips on cannabis. The Canadian trial found that five founding onion thrips per plant reduced yield [9]. A workable rule: in veg, any confirmed thrips starts the program; in flower, act on rising counts, not on a single card (Grower practice). ## How do I control thrips by life stage? Thrips control works stage by stage because each stage hides in a different place. Contact sprays and foliar predators hit larvae and adults; soil predators and nematodes hit propupae and pupae; nothing practical hits eggs inside the leaf. | Stage | Where it is | What reaches it | |---|---|---| | Egg | Inside leaf tissue | Nothing practical; wait for hatch | | Larva 1 | Leaf surface | N. cucumeris, A. swirskii, Orius, contact sprays | | Larva 2 | Leaf surface | Orius, contact sprays; too big for predatory mites [12] | | Propupa, pupa | Medium, leaf litter (WFT, onion thrips) or leaf (Echinothrips) | Stratiolaelaps, Dalotia, Steinernema feltiae [12]; foliage-only for Echinothrips [13] | | Adult | Leaves, buds, flying | Orius, sticky cards, contact sprays | **Re-application interval.** Match it to your temperature. A contact spray kills exposed larvae and adults. Survivors are eggs in the leaf, which hatch within about 4 days at 25 °C, and pupae in the medium, which emerge within about 4 days and lay about 2 days later [2][4]. So the next spray must land while those hatchlings are still larvae: the interval must be shorter than the larval period. The whole program must run at least one full generation plus the pre-oviposition period. | Room temperature | Larval period [2] | Max spray interval | Program length | Applications | |---|---|---|---|---| | 20 °C | 9.4 d | ~7 d | ≥ 24 d | 4 (days 0, 7, 14, 21) | | 25 °C | 7.8 d | ~5 d | ≥ 18 d | 4 (days 0, 5, 10, 15) | | 30 °C | 6.3 d | ~4 d | ≥ 14 d | 4 (days 0, 4, 8, 12) | This schedule is a calculation from the life table, not a label. The label interval and local law come first. **Resistance.** Western flower thrips is notorious for resistance [2][12]. A greenhouse strain from Almería, Spain, was 356,547-fold resistant to spinosad, an IRAC Group 5 spinosyn, compared with a susceptible lab strain [14]. Haploid males and 2–3-week generations make resistance fast. **Mode-of-action rotation.** Rotate by IRAC group, never by brand, and change group after each generation-length window, not after each spray. Products, rates and registrations for cannabis vary by jurisdiction: follow the label and local law. This article names classes only. **Least-toxic contact options in veg.** Insecticidal soaps and horticultural oils kill only what they touch, so coverage of leaf undersides and buds-to-be matters ([kb-term-insecticidal-soap](https://genetixbay.com/knowledge/glossary/insecticidal-soap.md), [kb-term-horticultural-oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md)). Fungal biopesticides such as Beauveria bassiana act on contact and are compatible with many predators ([kb-term-beauveria-bassiana](https://genetixbay.com/knowledge/glossary/beauveria-bassiana.md)). ## Which biological controls work against thrips? Biological control of thrips on cannabis uses foliar predatory mites against first-instar larvae, Orius bugs against larvae and adults, and soil predators or nematodes against pupae [8][12]. All of them work best released preventively in veg. Release rates below are generic ranges from biocontrol supplier technical sheets; check the sheet for the strain you buy. | Agent | Stage eaten | Temperature | RH | Notes | |---|---|---|---|---| | Neoseiulus cucumeris | L1 larvae only | 24–29 °C (75–85 °F) optimum | > 65%, ideally 75% | Egg to adult 8 d at 25 °C, 11 d at 20 °C; adults live ~3 weeks [12]; some strains diapause in short days [8] | | Amblyseius swirskii | L1 larvae; whitefly eggs and crawlers | 21–27 °C (70–80 °F) | ~70% | Outperforms cucumeris in warm, long-day conditions; costs more [12] | | Orius insidiosus | All mobile stages | 20–29 °C (68–85 °F) | – | Needs pollen; up to 8–10 weeks to establish [12]; short-day diapause [11] | | Stratiolaelaps scimitus | Pupae in medium; fungus gnat larvae | – | Moist medium | Single preventive release at planting [12] | | Dalotia coriaria | Pupae in medium | – | – | Rove beetle; also fungus gnats [12] | | Steinernema feltiae | Pupae in medium | – | Moist medium | Drench, then weekly; useless against Echinothrips [12][13] | ### Neoseiulus cucumeris N. cucumeris eats only first-instar thrips larvae; second instars are too big [12]. Second instars still feed less with mites around, about 30% of the time in one Canadian study, so damage drops [12]. Release N. cucumeris at planting or at the start of veg, before thrips are found [12]. Slow-release sachets keep mites emerging for 4–6 weeks [12]. Hang sachets inside the canopy, not in bright light: sun heats them, dries them and kills the predator eggs [12]. Supplier technical sheets commonly give 50–100 mites per m² per release preventively, repeated every 2 weeks, and up to 100–250 per m² on hot spots (biocontrol supplier technical sheet). Some N. cucumeris strains go dormant under short days [8]. Ask for a non-diapausing strain before the flip to 12/12. ### Amblyseius swirskii A. swirskii is the warm-room choice. In winter short days on chrysanthemum, swirskii and cucumeris controlled thrips equally, so cucumeris is the economical choice for cool rooms [12]. In summer, with heat, strong light and long days, swirskii ate and laid more [12]. It also eats whitefly eggs and crawlers, broad mites and spider mites ([kb-term-amblyseius-swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md)). ### Orius insidiosus and short-day diapause Orius insidiosus, the insidious flower bug, eats all mobile thrips stages [12]. Females lay about 129 eggs over a ~35-day adult life, and egg to adult takes at least 20 days under optimum conditions [16]. It needs pollen when prey is scarce and can take 8–10 weeks to establish [12]. Release it in early morning or evening, away from bright light [12]. **Diapause under 12/12.** In a laboratory culture at 20 °C, nearly 100% of Orius insidiosus females entered reproductive diapause at 10 h light, 56.8% at 12 h, 29.7% at 13 h and 5.3% at 14 h; the critical photoperiod fell between 12 and 13 h [11]. A cannabis flower room at 12/12 sits right on that line. Strains differ by origin, and non-diapausing strains are sold. Use Orius in veg (18/6) and treat flower as a bonus. Sinsemilla cannabis makes little pollen, so Orius has little alternative food on a seedless crop (*Grower practice*). ### Soil predators and nematodes against pupae In French bean pots, 5 Hypoaspis miles per pot caused at least 44.9% mortality of soil-dwelling thrips stages and 10 caused 61%, while 20 H. aculeifer caused 80.5% [10]. The commercial "H. miles" is now Stratiolaelaps scimitus ([kb-term-stratiolaelaps-scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md)). Steinernema feltiae nematodes drenched into the medium also hit thrips pupae; start with a drench, then spray or drench weekly [12]. Apply early or late, keep lights off for at least 2 hours after application, and keep the medium moist ([kb-term-steinernema-feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md)) [12]. ### Compatibility Orius also eats predatory mites [12]. Most residual insecticides kill predators for weeks; check side-effect tables and phase out residual sprays before release. Soaps and oils are less harmful once dry but still kill predators they hit (*Supported*). ## How can I use the environment as a weapon against thrips? The environment helps against thrips mainly by favouring the predators, not by stopping the thrips. You cannot cool a cannabis room enough to halt thrips without hurting the plant: they still develop at 15 °C [2]. **Veg: run humid, moderate.** Hold 24–26 °C and 60–70% RH. At 25 °C a thrips generation takes 16 days [2], while N. cucumeris develops in 8 days [12], so the predator gets two generations for each thrips generation. RH above 65% keeps predator eggs alive [12]. **Avoid hot spots.** At 28–30 °C a thrips generation takes 12–13 days [2]. Lamps close to the canopy and dead-air corners create these spots. **Flower: accept a drier room.** RH at 45–55%, and 40–50% in late flower, protects buds from botrytis ([kb-diseases-botrytis-bud-rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)) and powdery mildew ([kb-diseases-powdery-mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md)). Bud rot costs more than thrips. Predators carry on inside the canopy, where leaf-surface humidity is higher than room air (*Supported*). **Late flower: run a little cooler.** Dropping from 26 °C to 22 °C stretches a generation from 15 to 19 days [2]. That buys time; it does not fix anything. **Medium surface.** Pupae need a medium to pupate in. A dry, coarse top layer may reduce pupation success (Grower practice; no published value found for cannabis media). ## What should I not do about thrips in flower? Do not spray cannabis buds in flower. Soaps, oils and other residues stay in dense buds, wet buds invite botrytis, and most residual insecticides are not registered on cannabis. - **Do not raise RH in late flower** to help predators or fungal biopesticides. Keep 40–50% RH. - **Do not start predators in week 5 of flower** and expect a rescue. N. cucumeris and A. swirskii do not eat adults or second instars [12]. Build numbers in veg. - **Do not count on Orius in 12/12** without a non-diapausing strain [11]. - **Do not drench nematodes into a medium you are drying back** for ripening; they need moisture [12]. - **If a late infestation is heavy,** remove scarred fan leaves, keep cards up, and plan an early, clean harvest rather than spraying. ## What are the common myths about thrips? **"Sticky cards control thrips."** *Myth.* Cards catch only flying adults [8]. Eggs, larvae and pupae never touch them. Mass trapping with many cards can slow populations, but cards are a monitoring tool [8]. **"Weekly leaf sprays will wipe out thrips."** *Myth.* Eggs are inside leaf tissue [1] and about 98% of western flower thrips pupated in the soil in a bean study [10]. **"Thrips will give cannabis a virus."** *Myth* (for now). Thrips spread tospoviruses in other crops, but none are known to infect cannabis [8]. **"Pirate bugs work just as well in flower."** *Myth.* About 57% of females of one lab strain entered diapause at 12:12 [11]. **"A cold room kills thrips."** *Myth.* Western flower thrips develops above about 8 °C and overwinters active [2]. **"Predatory mites can rescue a heavy infestation."** *Myth.* N. cucumeris and A. swirskii eat only first-instar larvae, not second instars or adults [12]. They prevent; they do not rescue. ## Common mistakes - Treating only the foliage and ignoring pupae in the medium [10][12]. - Releasing N. cucumeris after adults are everywhere; it does not eat adults [12]. - Spraying at a fixed 7–10-day interval in a 28 °C room, where larvae can finish in about 6–7 days [2]. - Rotating brands instead of IRAC groups, then wondering why resistance builds [14]. - Releasing Orius under 12/12 and calling it a failure of biocontrol [11]. - Bringing in clones without a month of quarantine [8]. - Hanging sachets in direct light, which bakes the mites [12]. ## Evidence - Life cycle, pupation in media and damage signs: *Established* [1][8][15]. - Development times, thresholds and degree-days of western flower thrips: *Established* in lab studies on chrysanthemum, cucumber and lima bean [2][3][7]; no cannabis data. - Population growth rates: *Established* for the hosts tested (r = 0.12–0.23 per day) [4][5][6]; cannabis value unknown. - Onion thrips as the main indoor cannabis species and its yield effect: *Supported* by Colorado extension and one Canadian trial [8][9]. - Predatory mites, Orius and soil predators against western flower thrips: *Established* in greenhouse crops [10][12]; cannabis trials sparse (*Supported* by extrapolation). - Short-day diapause in Orius insidiosus: *Established* for the strain studied [11]; strain-dependent. - Spinosad resistance: *Established* in Spanish greenhouse populations [14]; local status varies. ## Glossary terms used here - Glossary: [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md), [intrinsic rate of increase](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [doubling time](https://genetixbay.com/knowledge/glossary/doubling-time.md), [diapause](https://genetixbay.com/knowledge/glossary/diapause.md), [arrhenotoky](https://genetixbay.com/knowledge/glossary/arrhenotoky.md), [sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md), [Orius](https://genetixbay.com/knowledge/glossary/orius.md) ## Sources 1. Bethke, J.A., Dreistadt, S.H. & Varela, L.G. 2014. Pest Notes: Thrips (Publication 7429). UC Statewide IPM Program. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html 2. McDonald, J.R., Bale, J.S. & Walters, K.F.A. 1998. Effect of temperature on development of the Western Flower Thrips, Frankliniella occidentalis (Thysanoptera: Thripidae). European Journal of Entomology 95: 301-306. https://www.eje.cz/pdfarticles/406/eje_095_2_301_McDonald.pdf 3. Gaum, W.G., Giliomee, J.H. & Pringle, K.L. 1994. Life history and life tables of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), on English cucumbers. Bulletin of Entomological Research 84: 219-224. https://doi.org/10.1017/S0007485300039729 4. Ding, T., Chi, H., Gökçe, A., Gao, Y. & Zhang, B. 2018. Demographic analysis of arrhenotokous parthenogenesis and bisexual reproduction of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Scientific Reports 8: 3346. https://pmc.ncbi.nlm.nih.gov/articles/PMC5820284/ 5. Ullah, M.S. & Lim, U.T. 2015. Life history characteristics of Frankliniella occidentalis and Frankliniella intonsa (Thysanoptera: Thripidae) in constant and fluctuating temperatures. Journal of Economic Entomology 108: 1000-1009. https://doi.org/10.1093/jee/tov035 6. Wang, H.-H., Xue, Y. & Lei, Z.-R. 2014. Life tables for experimental populations of Frankliniella occidentalis under constant and fluctuating temperature. Scientia Agricultura Sinica 47: 61-68. https://www.chinaagrisci.com/EN/Y2014/V47/I1/61 7. Badenhorst, J.A. 1996. A study of the biology and control of the western flower thrips, Frankliniella occidentalis Pergande. MSc thesis, University of Stellenbosch. https://scholar.sun.ac.za/items/7e23dfff-03a1-447f-ad19-45574781dcdc/full 8. Cranshaw, W. (Colorado State University). Pest Management of Hemp in Enclosed Production: Thrips. https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Thrips%20extra%20info.pdf 9. McCune, F., Murphy, C., Eaves, J. & Fournier, V. 2021. Onion thrips, Thrips tabaci (Thysanoptera: Thripidae), reduces yields in indoor-grown cannabis. Phytoprotection 101(1). https://doi.org/10.7202/1076365ar (preprint: https://www.biorxiv.org/content/10.1101/2020.05.11.088997v1) 10. Berndt, O., Meyhöfer, R. & Poehling, H.-M. 2004. The edaphic phase in the ontogenesis of Frankliniella occidentalis and comparison of Hypoaspis miles and Hypoaspis aculeifer as predators of soil-dwelling thrips stages. Biological Control 30: 17-24. https://agris.fao.org/search/en/records/65df23394c5aef494fe04031 11. Ruberson, J.R., Bush, L. & Kring, T.J. 1991. Photoperiodic effect on diapause induction and development in the predator Orius insidiosus (Heteroptera: Anthocoridae). Environmental Entomology 20: 786-789. https://doi.org/10.1093/ee/20.3.786 12. Pundt, L. 2024. Biological Control of Western Flower Thrips. UConn Extension IPM. https://ipm-cahnr.media.uconn.edu/wp-content/uploads/sites/3216/2024/08/biologicalcontrolthrips.pdf (web version: https://ipm.cahnr.uconn.edu/ipm-biological-control-of-western-flower-thrips/) 13. Pundt, L. 2024. Echinothrips americanus. UConn Extension IPM. https://ipm-cahnr.media.uconn.edu/wp-content/uploads/sites/3216/2024/06/echinothripsamericanus-3.pdf 14. Bielza, P., Quinto, V., Contreras, J., Torné, M., Martín, A. & Espinosa, P.J. 2007. Resistance to spinosad in the western flower thrips, Frankliniella occidentalis (Pergande), in greenhouses of south-eastern Spain. Pest Management Science 63: 682-687. https://doi.org/10.1002/ps.1388 15. Reitz, S.R. 2009. Biology and ecology of the western flower thrips (Thysanoptera: Thripidae): the making of a pest. Florida Entomologist 92: 7-13. https://doi.org/10.1653/024.092.0102 16. Cornell University. Biological Control: A Guide to Natural Enemies in North America. Orius insidiosus. https://biocontrol.entomology.cornell.edu/predators/Orius.php --- # Two-spotted vs carmine spider mite: one species or two, and does it matter? > The carmine spider mite (Tetranychus cinnabarinus) is now usually treated as the red form of the twospotted spider mite, Tetranychus urticae, because red and green mites interbreed, overlap in every morphological character and do not separate in DNA studies. Some researchers still use the old name. For a cannabis grower the colour form changes almost nothing: the same predators, the same humidity and temperature logic and the same acaricide rotation apply; resistance depends on a population's spray history, not its colour. - Canonical: https://genetixbay.com/knowledge/pests/two-spotted-vs-carmine-mite.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the difference between two-spotted and carmine spider mites?** The carmine spider mite (Tetranychus cinnabarinus) is usually treated today as the red form of the twospotted spider mite, Tetranychus urticae, not a separate species. A 2013 review by Auger and colleagues concluded the two interbreed, overlap in body characters and do not separate in DNA studies. Active red-form females are carmine to dark red; green-form females are yellowish to dark green with two dark spots. **Is Tetranychus cinnabarinus the same as Tetranychus urticae?** Tetranychus cinnabarinus is treated by most acarologists as a synonym of Tetranychus urticae, forming its red form. Auger and colleagues reviewed morphology, crosses, diapause, host range and DNA in 2013 and found no consistent difference: red and green mites produce viable hybrids, and COI sequences do not cluster by colour. Some studies, especially in China, still use the separate name, so the debate is not fully closed. **How do I tell red and green spider mites apart?** Red and green forms of the twospotted spider mite are told apart mainly by the colour of active adult females under a 10 to 20x lens: carmine to dark red versus yellowish to dark green, both with dark side spots. Males and juveniles of both forms look alike, and eggs differ only slightly in tint. Colour shifts with age, diet and cold, so it is a clue, not proof. **Are orange spider mites the carmine mite?** Bright orange spider mites without dark side spots are usually diapausing females of the twospotted spider mite, either colour form, not carmine mites. Short days, cool temperatures and poor food make females stop feeding and laying and turn orange. Active carmine-form females are deep red with dark spots. The orange-red predatory mite Phytoseiulus persimilis is pear-shaped, long-legged, fast and also lacks spots. **Is the red spider mite harder to kill?** There is no published evidence that the red form of the twospotted spider mite is inherently more pesticide-resistant than the green form. A 2013 taxonomic review noted that resistance had not been compared between colour forms and that differences probably reflect spray history. Both forms belong to a species that evolves acaricide resistance fast, so rotate modes of action by IRAC group and follow the label and local law. **Does the carmine mite tolerate heat better?** The red form of the twospotted spider mite is reported mainly from warm temperate and subtropical regions and greenhouses, and the green form from cooler latitudes, which suggests heat adaptation. No direct comparison of upper temperature limits between the forms was found. In the field, hibernating green-form females were far more cold-resistant than red-form ones, which often lack true diapause. **Do red spider mites go dormant in winter?** Many red-form populations of the twospotted spider mite do not enter true diapause: they turn orange in autumn but resume feeding within days of warmth. Yet diapause has been induced in red-form strains from Italy and Greece, at short days and 19 °C for the Greek strain, and Lebanese mountain populations diapause at 1,500 m. Indoor mites of either colour may have lost diapause. **What other spider mites attack cannabis or hemp?** University extension sheets on hemp from Utah, North Carolina and Colorado list only the twospotted spider mite, Tetranychus urticae, as the spider mite pest of hemp. We found no verified record of the strawberry spider mite (T. turkestani) or Pacific spider mite (T. pacificus) on cannabis. Both feed on cotton and many other crops in western North America, so outdoor hemp there could meet them. **How do strawberry and Pacific spider mites compare with twospotted mites?** On cotton at 23.8 °C, Carey and Bradley found the strawberry spider mite (T. turkestani), Pacific spider mite (T. pacificus) and twospotted spider mite developed at similar rates. Twospotted females laid the most eggs, 103 versus 85 and 79, and r_m was 0.219 per day versus 0.204 and 0.207. At 29.4 °C all three reached r_m of about 0.29 per day. **Short answer.** The carmine or "red" spider mite, *Tetranychus cinnabarinus*, is now usually treated as the red form of the twospotted spider mite, *Tetranychus urticae* [1]. Red and green mites interbreed, overlap in every body character used to separate them, and do not split in DNA studies [1]. For a cannabis grower the colour changes almost nothing. The same predators, set-points and acaricide rotation apply, and resistance follows a population's spray history, not its colour [1][11]. The full pest article is [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md). ## Red vs green form at a glance | Feature | Green form (classic T. urticae) | Red form ("T. cinnabarinus", carmine mite) | Source | |---|---|---|---| | Active adult female colour | Yellowish-green to dark green, two dark side spots | Carmine red to dark red, dark spots | [1] | | Male colour | Indistinguishable between forms | Indistinguishable | [1] | | Larvae and nymphs | Pale, then green when feeding; never orange or red | Similar to green form | [1] | | Eggs | Clear, translucent, becoming yellowish | Amber with a pink-reddish tint | [1] | | Diapausing female | Bright orange, spots reduced or absent | Similar when diapause occurs | [1][7] | | Dorsal skin lobes | Broader, rounded or oblong | Smaller, more triangular; overlaps | [1] | | Typical climate | Cold temperate | Warm temperate, subtropical, greenhouses | [1] | | True diapause | Usually yes (varies by population) | Often absent; present in some populations | [1] | | Interbreeding | Produce viable hybrids with red form in many crosses | Same | [1] | | Pesticide resistance difference | Not investigated | Not investigated | [1] | | Recorded on hemp (extension) | Yes | Not reported separately | [8][9][10] | ## Is the carmine mite a separate species from the twospotted spider mite? The carmine mite is not a separate species in the view of most acarologists: Auger and colleagues concluded in 2013 that *T. cinnabarinus* should be treated as a synonym of the polymorphic species *T. urticae*, of which it is the red form [1]. Some authors still disagree. ### Where the two names came from The red mite was described by Boisduval in 1867, mainly by its colour [1]. Since then, about 44 species names have been synonymised with *T. urticae*, which shows how variable this mite is [1]. For decades, authors used colour, the shape of tiny lobes on the skin folds of the back, the shape of the male's aedeagus (copulatory organ), leg hairs, diapause and host plant to separate the two [1]. Each criterion has been used both to split and to lump them [1]. ### What the 2013 review found Auger and colleagues found that every morphological character used to separate red and green mites varies within and between populations and overlaps with no clear cut-off [1]. The aedeagus, the key character for telling *Tetranychus* species apart, showed this most clearly [1]. They found no consistent link between body colour and the other characters [1]. Their own crosses between red and green populations, checked free of *Wolbachia* bacteria that can cause crossing failures, produced compatible offspring [1]. Phylogenetic studies based on the mitochondrial COI gene did not split mites by colour [1]. Instead, *T. urticae* falls into two major COI lineages that each contain red and green mites [1]. ### Why the debate is not closed Molecular work partly revived the controversy: one 2009 study argued for the validity of *T. cinnabarinus* [1]. Auger and colleagues point out that many GenBank sequences labelled *T. cinnabarinus* are misidentified, which corrupts such analyses [1]. Crossing results are mixed. Several older studies found sterile or partly sterile hybrids between some red and green strains [1]. Gotoh and colleagues (1993) found partial compatibility between a non-diapausing red strain and green mites, but none between a diapausing red strain and the others [1]. Incompatibility between populations is common within spider mite species, so it does not by itself prove two species [1]. **Label:** synonymy is *Supported* (strong review, majority view); separate-species status is *Contested*. Chinese and some applied literature still reports "T. cinnabarinus" as a distinct pest [1]. ## How do you tell red and green spider mites apart on cannabis? Red and green twospotted spider mites are told apart by the colour of active adult females under a 10-20x lens: carmine to dark red versus yellowish to dark green [1][7]. Colour is a clue, not a diagnosis. ### Colour, and why it misleads Spider mite colour comes mainly from carotenoid pigments and from the food in the gut, which shows as dark spots [1]. Both forms carry the same pigments in different amounts [1]. Colour darkens with age, shifts with diet, and fades or turns orange in diapausing and cold-exposed females [1]. Hybrids between red and green mites come in many shades: F1 females are pale red to dark red and never green, and later generations range from yellowish-green to bronze [1]. Males of the two forms cannot be told apart by colour [1]. Larvae and nymphs of both forms are pale to green and never orange or red [1]. ### Skin lobes and aedeagus Under a compound microscope, the dorsal skin folds of green-form females carry broader, rounded lobes, and red-form females smaller, more triangular ones [1]. The two overlap. Lobe density also changes with environment: green-form females reared at 35 °C and 15% RH had more lobes per 30 µm than those at 20 °C and 70% RH (Mollet and Sevacherian 1984, cited in [1]). Hibernating females of both forms have smooth folds without lobes [1]. The aedeagus shape varies within populations and overlaps between colour forms [1]. None of this is a field method. ### Three look-alikes that are not carmine mites - **Diapausing twospotted females:** bright orange-red, spots reduced or absent, not feeding, often hiding in cracks [7][8]. - **Phytoseiulus persimilis:** bright orange-red, pear-shaped, long-legged and fast, with no dark spots; eggs are larger and oval [7]. - **Predatory midge larvae (Feltiella):** orange, legless maggots in colonies [7]. ## Does red vs green matter for spider mite control? Red vs green form makes no practical difference to cannabis spider mite control: the same predatory mites, environment set-points and acaricide rotation apply [1][7][13]. What matters is how resistant your population is, which depends on its spray history. ### Pesticide resistance Resistance has not been compared between the two colour forms [1]. Auger and colleagues note that existing data cannot tell whether resistance in a colour form comes from innate capacity or from different spray pressure [1]. The whole species evolves acaricide resistance quickly because of short generations, high fecundity and arrhenotoky (males from unfertilised eggs) [11]. Assume any mite on a clone from someone else's room is resistant to something. Rotate by IRAC group (6, 10A, 10B, 12, 13, 20, 21A, 23, 25; sulfur is UN) [13]. Follow the label and local law. ### Heat tolerance The red form is reported mostly from warm temperate and subtropical zones and from greenhouses in northern countries; the green form from cold temperate latitudes [1]. That hints at heat adaptation, but no direct comparison of upper thermal limits between the forms was found. Cold tolerance differs more clearly. In field studies, hibernating green-form females were far more cold-resistant than red-form ones [1]. ### Diapause Diapause is the trait that most often separated the forms, and it fails as a species marker [1]. Many red-form populations do not enter true diapause: they turn orange in autumn but resume feeding and red colour within days of warmth [1]. Yet diapause has been induced in red-form strains from Italy and Greece, the Greek strain at short days and 19 °C [1]. In Lebanon, red-form females diapause on mountains at 1,500 m but breed all year at lower altitude [1]. Diapause ability can be lost by tetranychid populations kept without winter [1]. Green-form diapause also varies with latitude [1]. One green-form strain had a critical photoperiod of about 13.5 h at 18 °C [12]. **Cannabis implication.** A 12/12 flower room is a short day. A strongly diapausing green-form population in a cool room may produce orange females that stop laying and hide; a red-form or long-indoor population may simply keep breeding. Either way, clean cracks and trays between runs (*Supported*, inferred, not tested on cannabis). ### Host range Red-form mites were long associated with carnation, which green mites were once thought unable to use [1]. Later work found green populations on carnation too, with success varying by cultivar [1]. Host adaptation varies between populations, not colours [1]. ## What are the life-table numbers for the red form? One published life table for the red form ("T. cinnabarinus") on carnation leaves at 29.4 °C and 42% RH gave egg-to-adult development of 12.8 days, r_m of 0.183 per day and 3.9 eggs per female per day [3]. That is slower than green-form figures on cotton or apple, but host plant differs. | Parameter | Red form, carnation, 29.4 °C, 42% RH [3] | Green form, cotton, 29.4 °C [2] | Green form, apple, 30 °C [4] | |---|---|---|---| | Egg-to-adult (days) | 12.84 | 6.1-6.7 (females, range across 3 species) | ~8.0 (computed from thermal constant) | | Egg-to-adult survival | 80.2% | - | - | | Female offspring | 76.3% | ~74% | - | | Female longevity (days) | 24.3 | 9.7 | - | | Eggs per female per day | 3.92 | - | - | | Lifetime eggs | - | 64.3 | - | | R0 (daughters/female) | 40.8 | - | 84.3 | | Mean generation time (days) | 20.2 | - | - | | r_m (/day) | 0.183 | ~0.29 | 0.302 | | Doubling time (days, ln2/r_m) | 3.8 | ~2.4 | 2.3 | Doubling times are computed here. No study has compared red and green forms on the same host at the same temperature that we could verify, and none on cannabis. Do not read the slower red-form numbers as "carmine mites are slower"; carnation is a different host and the authors used a different lab set-up [3]. ## What other Tetranychus spider mites could turn up on cannabis? University hemp extension sheets from Utah, North Carolina and Colorado list only the twospotted spider mite as the spider mite pest of hemp [8][9][10]. We found no verified record of other *Tetranychus* species on cannabis. Two western North American relatives are worth knowing because they feed on cotton and many other field crops near where outdoor hemp is grown: - **Strawberry spider mite, Tetranychus turkestani.** UC IPM's degree-day model uses a lower threshold of 12.0 °C (53.6 °F), 112.1 DD (°C) egg-to-adult and 125.9 DD egg-to-egg on cotton [6]. - **Pacific spider mite, Tetranychus pacificus.** UC IPM's model uses a lower threshold of 11.1 °C (52.0 °F) and 121.0 DD (°C) egg-to-adult on cotton [5]. No published record of either on cannabis was found in the sources checked; treat them as possible outdoor visitors, not known cannabis pests. Telling them from *T. urticae* needs a slide-mounted male and a specialist. ### Comparative life tables on cotton Carey and Bradley reared all three species side by side on cotton cotyledons at 15.5 to 29.4 °C [2]. | Parameter | T. urticae | T. turkestani | T. pacificus | Conditions | |---|---|---|---|---| | Female egg-to-adult, 15.5 °C | 25.8-29.0 days (range across species) | same range | same range | [2] | | Female egg-to-adult, 29.4 °C | 6.1-6.7 days (range across species) | same range | same range | [2] | | Lifetime eggs, 23.8 °C | 103.3 | 84.6 | 78.9 | [2] | | Lifetime eggs, 29.4 °C | 64.3 | 73.5 | 68.3 | [2] | | Female longevity, 23.8 °C | 14.71 d | 12.46 d | 12.71 d | [2] | | Female longevity, 29.4 °C | 9.71 d | 8.79 d | 8.91 d | [2] | | Female offspring | ~74% | ~55% | ~57% | [2] | | r_m, 23.8 °C (/day) | 0.219 | 0.204 | 0.207 | [2] | | r_m, 29.4 °C (/day) | 0.293-0.295 (range across species) | same range | same range | [2] | Development rates were similar across the three species, and males developed slightly faster [2]. The twospotted spider mite's edge at 23.8 °C came from more eggs and a more female-biased sex ratio [2]. The sex-ratio values are read from a scanned copy of the paper; check the original if you need them exactly. ## Which spider mite looks like what? A quick key 1. **Mite oval, ~0.5 mm, slow, two dark side spots, colour yellow-green:** green form of T. urticae. 2. **Same shape and spots, deep red to carmine:** red form of T. urticae ("carmine mite"). 3. **Bright orange, spots faint or absent, not feeding, in cracks or on old leaves:** diapausing T. urticae female (either form) [7]. 4. **Bright orange-red, pear-shaped, long legs, runs fast, no spots:** Phytoseiulus persimilis, a predator; leave it [7]. 5. **Mites invisible at 10x, twisted or bronzed new growth:** not spider mites; see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) and [hemp russet mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md). Steps 1 and 2 are managed identically. ## What are the common myths about red and green spider mites? The most common myth is that red spider mites are a tougher, separate species; the best current evidence treats them as a colour form of the twospotted spider mite with no proven extra resistance [1]. - **"Red spider mites are a different, tougher species."** *Myth* for most purposes: synonymy is the majority view, and resistance has never been compared by colour [1]. - **"You can identify the species by colour."** *Myth.* Colour varies with age, diet, cold and hybrid origin [1]. - **"Orange mites are carmine mites."** *Myth.* Bright orange females are usually diapausing females [1][7]. - **"Red forms never go dormant."** *Myth.* Many fail to diapause, but some populations do [1]. - **"Green and red forms need different control."** *Established* that they do not, in the sense that every tactic in the [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md) article applies to both [1][7]. ## Common mistakes - Changing products because "it's the red one now"; check instead whether your rotation repeated an IRAC group [13]. - Killing Phytoseiulus persimilis because it is red [7]. - Counting orange diapausing females as "dead" or "gone"; they come back when it warms [1][7]. - Assuming a clean colour means a clean clone; males and juveniles look the same in both forms [1]. ## Evidence - Synonymy of T. cinnabarinus with T. urticae: *Supported* by a comprehensive review with new crossing and morphological data [1]; *Contested* by some molecular and crossing studies cited there [1]. - Morphological overlap and colour variability: *Established* [1]. - Diapause variability within both forms: *Established* [1][12]. - Resistance differences between colour forms: *no published comparison* [1]. - Heat tolerance differences: *no direct comparison found*; distribution data only [1]. - Red-form life table: one study on carnation [3]; not comparable host-for-host with green-form data [2][4]. - Other Tetranychus on cannabis: *no verified record found*; extension hemp sheets list only T. urticae [8][9][10]. ## Glossary terms used here - Glossary: [diapause](https://genetixbay.com/knowledge/glossary/diapause.md), [arrhenotoky](https://genetixbay.com/knowledge/glossary/arrhenotoky.md), [life table](https://genetixbay.com/knowledge/glossary/life-table.md), [intrinsic rate of increase](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md), [two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) ## Sources 1. Auger P, Migeon A, Ueckermann EA, Tiedt L, Navajas M. 2013. Evidence for synonymy between Tetranychus urticae and Tetranychus cinnabarinus (Acari, Prostigmata, Tetranychidae): review and new data. Acarologia 53(4):383-415. https://doi.org/10.1051/acarologia/20132102 2. Carey JR, Bradley JW. 1982. Developmental rates, vital schedules, sex ratios and life tables for Tetranychus urticae, T. turkestani and T. pacificus (Acarina: Tetranychidae) on cotton. Acarologia 23(4):333-345. https://www1.montpellier.inrae.fr/CBGP/acarologia/article.php?id=2789 3. Tello-M V, Vargas-M R, Araya-C J. 2009. Life history parameters of Tetranychus cinnabarinus (Acari: Tetranychidae) on leaves of carnation, Dianthus caryophyllus. Revista Colombiana de Entomología 35(1):47-51. https://doi.org/10.25100/socolen.v35i1.9188 4. Kasap I. 2004. Effect of apple cultivar and of temperature on the biology and life table parameters of the twospotted spider mite Tetranychus urticae. Phytoparasitica 32(1):73-82. https://doi.org/10.1007/BF02980863 5. UC IPM. Degree-day model description: Pacific spider mite. University of California ANR. https://ipm.ucanr.edu/PHENOLOGY/ma-pacific_spider_mite.html 6. UC IPM. Degree-day model description: Strawberry spider mite. University of California ANR. https://ipm.ucanr.edu/weather/phenology-models-description/strawberry-spider-mite/ 7. Pundt L. 2019. Biological Control of Two-Spotted Spider Mites. UConn Extension IPM. https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf 8. Pulkoski M, Burrack H. 2020. Twospotted Spider Mite in Industrial Hemp. NC State Extension. https://content.ces.ncsu.edu/twospotted-spider-mite-in-industrial-hemp 9. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php 10. Colorado State University, Agricultural Biology. 2022. Twospotted spider mite, Tetranychus urticae. https://agsci.colostate.edu/agbio/ipm-pests/twospotted-spider-mite/ 11. Van Leeuwen T, Vontas J, Tsagkarakou A, Dermauw W, Tirry L. 2010. Acaricide resistance mechanisms in the two-spotted spider mite Tetranychus urticae and other important Acari: a review. Insect Biochemistry and Molecular Biology 40(8):563-572. https://doi.org/10.1016/j.ibmb.2010.05.008 12. Amini MY, Daneshyar JA, Mohammadi MM, Memlawal R. 2023. Simulation of diapause induction in spider mites (Tetranychus urticae and T. kanzawai) by reproducing field environments in the laboratory. Nangarhar University International Journal of Biosciences 2(02):53-60. https://doi.org/10.70436/nuijb.v2i02.43 13. IRAC. Mode of Action Classification (online). https://irac-online.org/mode-of-action/classification-online/ --- # Whiteflies on cannabis: life table, temperature, parasitoids and IPM > Whiteflies are tiny white moth-like sap feeders that rise in a cloud when you shake a plant; nymphs sit flat under leaves and drip honeydew. Greenhouse whitefly needs about 381 degree-days above 8.3 °C per generation (about 23 days at 25 °C) and prefers moderate rooms; silverleaf whitefly grows fastest at 25-27 °C (r about 0.19 per day). Identify the species, monitor with yellow cards, and release Encarsia formosa (greenhouse whitefly, rooms above about 18-20 °C) or Eretmocerus (silverleaf, warm rooms) plus A. swirskii early in veg, keeping sprays out of flower. - Canonical: https://genetixbay.com/knowledge/pests/whiteflies.html - Category: Pests · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What are the tiny white flies on my cannabis?** Tiny white moth-like insects that rise in a puff when you shake a cannabis plant are whiteflies. Adults are about 1.5 mm with four white, waxy wings and rest on leaf undersides, while flat, oval, translucent nymphs sit motionless below. Indoors the two main species are greenhouse whitefly and silverleaf whitefly. Unlike aphids, whiteflies lack tail pipes and fly readily when disturbed. **How long is the whitefly life cycle?** Greenhouse whitefly needs about 381 degree-days above 8.3 °C from egg to adult, which works out to roughly 33 days at 20 °C, 23 days at 25 °C and 18 days at 30 °C by a linear model. Silverleaf whitefly took 105 days at 15 °C and 14 days at 30 °C on eggplant in the lab. Eggs alone take about 5 to 7 days to hatch. **How fast do whiteflies multiply?** Silverleaf whitefly populations grew at about 0.19 per day at 25 to 27 °C on eggplant in a laboratory life table, doubling every 3.6 days, so 10 adults could become about 560 in 3 weeks with no enemies. Greenhouse whitefly on poor bean cultivars grew far slower, 0.035 to 0.072 per day. Host plant matters, and no cannabis life table has been published. **How do I get rid of whiteflies indoors?** Get rid of whiteflies indoors by monitoring with yellow sticky cards near the canopy, identifying the species, and releasing the matching natural enemy early in veg: Encarsia formosa for greenhouse whitefly, Eretmocerus eremicus for silverleaf whitefly and hot rooms, and Amblyseius swirskii for eggs and crawlers. Phase out residual insecticides first. Quarantine incoming plants and keep houseplants and vegetable seedlings out. **Encarsia or Eretmocerus for whiteflies?** Choose Encarsia formosa for greenhouse whitefly in rooms of about 21 to 27 °C (70 to 80 °F) and 50 to 80% RH; its adults stop flying below about 18 °C (65 °F). Choose Eretmocerus eremicus for silverleaf whitefly and for warm rooms of about 25 to 29 °C (77 to 84 °F). Encarsia attacks silverleaf whitefly less reliably. Release weekly until 80 to 90% of nymphs are parasitised. **Why does Encarsia fail in a cool room?** Encarsia formosa fails in cool rooms because it develops above 12.7 °C while greenhouse whitefly develops above 8.3 °C. By linear degree-day models, below about 17 °C the whitefly completes a generation faster than the wasp, and adults of Encarsia stop flying below about 18 °C. At 25 °C the wasp needs about 15 days per generation against about 23 for the whitefly. **Why are my cannabis leaves sticky with black mould?** Sticky cannabis leaves with black mould are coated in honeydew, sugary waste from sap-feeding insects, on which black sooty mould grows. Whiteflies and aphids both cause it. Shake the plant: a cloud of tiny white flies means whiteflies, while clusters of soft pear-shaped insects with tail pipes mean aphids. Check the leaves directly above the mould for the source. **Greenhouse whitefly or silverleaf whitefly: how do I tell?** Tell greenhouse whitefly from silverleaf whitefly by the fourth-instar nymph and the adult wings under a 10 to 20x lens. Greenhouse whitefly nymphs carry long waxy filaments and a marginal fringe, and adults hold their wings flat. Silverleaf whitefly nymphs lack filaments and fringe, and adults hold wings slightly tilted, showing the yellow body. A lab can confirm species and biotype. **How often should I spray whiteflies?** Spray contact products against whiteflies at intervals shorter than the egg stage, because eggs and the last nymphal stage survive most contact sprays. For greenhouse whitefly at 25 °C eggs take about 7 days and the whole immature cycle about 23 days, so spray roughly every 6 to 7 days for at least 4 rounds. Follow the label and local law, and stop before flowers form. **Do whiteflies spread broad mites?** Whiteflies can spread broad mites between cannabis plants because broad mites hitch rides on whitefly adults, according to UConn Extension. A whitefly problem in a room with broad mites can therefore move the far more damaging mite into clean plants. Control whiteflies in mother and clone rooms, and check new growth for the twisted, glossy leaves typical of broad mites. **Short answer.** Shake a plant and a puff of tiny white flies lifts off: whiteflies. They are less common on cannabis than mites or thrips (Grower practice), but they breed steadily indoors, drip honeydew and can carry broad mites between plants [11]. Greenhouse whitefly needs about 381 degree-days above 8.3 °C per generation, roughly 23 days at 25 °C [2]; silverleaf whitefly grows fastest at 25–27 °C [4]. Monitor with yellow cards, work out which species you have, and release the matching parasitoid or predator early in veg. Keep sprays to veg. ## Whitefly numbers at a glance | Parameter | Greenhouse whitefly (T. vaporariorum) | Silverleaf whitefly (B. tabaci, MEAM1 / "B") | |---|---|---| | Adult length | ~1.5 mm | ~1.5 mm | | Lower developmental threshold | 8.3 °C [2] | 12.5 °C on eggplant [4]; 11.1 °C cotton, 13.2 °C cantaloupe [5] | | Degree-days egg to adult | 380.7 DD (sum of stages) [2] | 312.5 DD cotton, 250 DD cantaloupe [5] | | Egg to adult, 25 °C | ~23 d (model from [2]) | ~21–23 d (models from [5]) | | Egg to adult, 30 °C | ~18 d (model from [2]) | 14 d on eggplant [4] | | Egg to adult, 15 °C | ~57 d (model from [2]) | 105 d on eggplant [4] | | Upper limit | Longevity 5.9 d and lowest r at 26 °C on bean [3] | No development at 35 °C on cotton or cantaloupe [5]; r 0.073 at 35 °C on eggplant [4] | | Eggs per female | Up to ~400 [10]; 8.6–127 on bean cultivars [3] | 324 at 20 °C, 22 at 35 °C [4]; up to 280 at 18 °C on cotton [7] | | Adult female longevity | 22.6 d at 19 °C, 5.9 d at 26 °C (bean) [3] | 44 d at 20 °C, 10 d at 35 °C [4] | | Sex ratio | ~54% female (average across hosts) [3] | no value verified here | | r (intrinsic rate of increase) | 0.035–0.072 /day on bean [3] | 0.192 /day at 25–27 °C on eggplant [4] | | Doubling time | 9.6–20 d (poor bean hosts) | 3.6 d | | Best parasitoid | Encarsia formosa [8] | Eretmocerus eremicus [8] | | Published action threshold for cannabis | none | none | ## What do whiteflies look like on cannabis? Whiteflies on cannabis are tiny, about 1.5 mm, with four white wings dusted in mealy wax; they rest on leaf undersides and fly up when the plant is disturbed [1]. They are Hemiptera, related to aphids, not true flies [1]. **Nymphs.** The first instar, the "crawler", moves for a few hours and then settles [1]. Later nymphs are flat, oval, immobile scales with tiny legs [1]. The fourth instar, often called the "pupa", thickens and shows red eyes, and is the easiest stage to identify [1]. **Greenhouse whitefly (Trialeurodes vaporariorum).** Fourth-instar nymphs carry very long waxy filaments and a marginal fringe [1]. Adults hold their wings flat over the body (*Supported*). **Silverleaf or sweetpotato whitefly (Bemisia tabaci).** Fourth-instar nymphs lack the filaments and fringe [1]. Adults hold their wings slightly tilted, so the yellow body shows [1]. B. tabaci is a complex of look-alike species; the greenhouse ones are usually called MEAM1 (formerly "B") and MED (formerly "Q"). **Exit holes.** A healthy adult leaves a T-shaped slit in the empty nymph skin; a parasitoid leaves a round or oval hole [1]. **Parasitised nymphs.** Encarsia-parasitised greenhouse whitefly nymphs turn black [8]. Eretmocerus-parasitised silverleaf whitefly nymphs turn light brown [8]. Colour alone is not proof, because some healthy nymphs are dark [1]. ## What damage do whiteflies do to cannabis? Whiteflies damage cannabis by sucking phloem sap and dripping honeydew, which turns leaves sticky and grows black sooty mould [1]. Large nymph populations cause yellowing, drying or leaf drop; adults alone rarely cause much damage [1]. Honeydew attracts ants, which protect whiteflies from natural enemies [1]. Broad mites hitch rides on whitefly adults [11]. In a clone room with both, whiteflies can move the mite into clean plants ([kb-pests-broad-russet-mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md)). Honeydew in flower sticks to trichomes and supports mould. That alone justifies control before the flip (Grower practice). **Differentials.** Aphids have tail pipes (cornicles), cluster on stems and new growth and rarely fly up in a cloud ([kb-pests-aphids](https://genetixbay.com/knowledge/pests/aphids.md)). Fungus gnats are dark, long-legged and hover over the medium ([kb-pests-fungus-gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md)). ## What is the whitefly life cycle in numbers? The whitefly life cycle runs egg, crawler, two more flat nymphal instars, a fourth instar ("pupa"), then the winged adult [1]. For greenhouse whitefly, egg to adult takes about 23 days at 25 °C and 33 days at 20 °C by a degree-day model [2], and 3–4 weeks under favourable greenhouse conditions [10]. ### Greenhouse whitefly by temperature Osborne measured greenhouse whitefly development above a threshold of 8.3 °C: 122.9 degree-days for the egg, 63.9 for the first instar, 38.4 for the second, 40.1 for the third and 115.4 for the fourth, about 381 in total [2]. Converted to days at constant temperature: | Temperature | Egg | Instars 1–3 | Instar 4 ("pupa") | Egg to adult | |---|---|---|---|---| | 15 °C (59 °F) | 18.3 | 21.3 | 17.2 | 56.8 | | 20 °C (68 °F) | 10.5 | 12.2 | 9.9 | 32.5 | | 25 °C (77 °F) | 7.4 | 8.5 | 6.9 | 22.8 | | 30 °C (86 °F) | 5.7 | 6.6 | 5.3 | 17.5 | These are linear-model values; near the upper limit real development is slower than the model says. Colorado State University gives eggs hatching in 5–7 days and a non-feeding pupal stage of almost a week [10], which matches the 25 °C row. **Greenhouse whitefly dislikes heat.** On a bean cultivar at about 75% RH, adult longevity fell from 22.6 days at 19 °C to 5.9 days at 26 °C, and r peaked at 22 °C (0.061 per day) and fell to 0.035 at 26 °C [3]. Female output was 8.6, 32.6 and 33.3 eggs at 19, 22 and 26 °C on that cultivar, but 127.2 at 19 °C on a better cultivar [3]. Host plant changed r by more than half [3]. Colorado State University gives up to 400 eggs per female over up to two months on favourable hosts [10]. ### Silverleaf whitefly by temperature Wang and Tsai reared silverleaf whitefly (Bemisia argentifolii, now B. tabaci MEAM1) on eggplant at six constant temperatures [4]. | Temperature | Egg to adult | Survival egg to adult | Female lifespan | Eggs per female | r (per day) | |---|---|---|---|---|---| | 15 °C | 105 d | 40% | – | – | – | | 20 °C | – | – | 44 d | 324 | – | | 25 °C | – | 89% | – | – | 0.192 | | 27 °C | – | – | – | – | 0.192 | | 30 °C | 14 d | – | – | – | – | | 35 °C | prolonged | 37% | 10 d | 22 | 0.073 | Dashes mean the value is not in the abstract; the shared threshold for all immature stages was 12.5 °C [4]. Mean generation time fell from 46 days at 20 °C to 18 days at 30 °C, and the best range for population growth was 20–30 °C [4]. On cotton and cantaloupe from 20 to 32 °C, egg to adult took 14.6–37.9 days, with thresholds of 11.1 °C (cotton, 312.5 degree-days) and 13.2 °C (cantaloupe, 250 degree-days) [5]. No whitefly developed at 35 °C or on pepper [5]. Fecundity at 30 °C was 117–158 eggs per female on cotton and cantaloupe but 2–41 on pepper [5]. On cotton, females laid up to 280 eggs at 18 °C and only 5 at 37.2 °C [7]. Wagner's 31-temperature cotton study gives the full development-rate model [6]. No whitefly life table on cannabis has been published. The pepper result is a warning: host suitability can swing from excellent to almost nil [5]. **Reproduction.** Whiteflies are haplodiploid: unmated females lay sons, mated females lay both sexes. Greenhouse whitefly averages about 54% females across hosts [3]. ## Why do temperature and humidity matter for whiteflies? Temperature sets whitefly speed and also picks the species that wins. Greenhouse whitefly does best near 22 °C and lives and breeds less at 26 °C [3]; silverleaf whitefly grows fastest at 25–27 °C and still develops at 30–32 °C [4][5]. **Grow-room set-points, converted to generation time** (degree-day models, constant temperature): | Room | Set-point | Greenhouse whitefly [2] | Silverleaf, cotton model [5] | Encarsia formosa [2] | |---|---|---|---|---| | Cool | 18 °C (64 °F) | 39 d | 45 d | 36 d (adults barely fly) | | Late flower | 22 °C (72 °F) | 28 d | 29 d | 20 d | | Flower | 24 °C (75 °F) | 24 d | 24 d | 17 d | | Veg | 26 °C (79 °F) | 22 d | 21 d | 14 d | | Warm veg | 28 °C (82 °F) | 19 d | 19 d | 12 d | **The Encarsia crossover.** Encarsia formosa develops above 12.7 °C and needs 188.9 degree-days; greenhouse whitefly develops above 8.3 °C and needs about 381 [2]. Solving the two models, they run at the same speed at about 17 °C. Below that, the whitefly out-breeds its parasitoid; above it, the wasp gets ahead. That is why Encarsia programs fail in cold rooms, together with the fact that Encarsia adults do not fly below about 18 °C (65 °F) [8]. **Humidity.** No published effect of RH on whitefly growth rate in the grow-room range was found. RH matters through the natural enemies: Encarsia works best at 50–80% RH [8], A. swirskii at about 70% [8], and fungal biopesticides need moisture at the leaf surface. **Light.** Encarsia searches for hosts in light, and growers report poor performance under low light. Sachets and cards belong in shaded lower canopy to avoid drying [8]. **Grow-room translation.** Veg at 24–28 °C and 60–70% RH (about 0.9–1.5 kPa VPD) suits Encarsia, Eretmocerus and A. swirskii. Flower at 45–55% RH, and 40–50% late, is drier than the predators like ([kb-term-vpd](https://genetixbay.com/knowledge/glossary/vpd.md)). ## How fast can a whitefly population grow? A worked example Ten silverleaf whiteflies can become about 560 in three weeks at 25–27 °C if nothing eats them, using r = 0.192 per day [4]. The method is N(t) = N0 × e^(r × t), with N0 = 10 and t in days. | Scenario | r (per day) | Doubling time | Day 14 | Day 21 | Day 28 | Day 42 | |---|---|---|---|---|---|---| | Silverleaf, 25–27 °C, eggplant [4] | 0.192 | 3.6 d | 147 | 564 | 2,162 | ~31,800 | | Silverleaf, 35 °C, eggplant [4] | 0.073 | 9.5 d | 28 | 46 | 77 | 215 | | Greenhouse WF, 19 °C, good bean cultivar [3] | 0.072 | 9.6 d | 27 | 45 | 75 | 206 | | Greenhouse WF, 22 °C, poor bean cultivar [3] | 0.061 | 11.4 d | 23 | 36 | 55 | 130 | | Greenhouse WF, 26 °C, poor bean cultivar [3] | 0.035 | 19.8 d | 16 | 21 | 27 | 43 | This is the unchecked upper bound: no enemies, unlimited food, stable age structure. The greenhouse whitefly rows come from bean cultivars that suit it poorly [3]. On favourable hosts such as eggplant or tomato its r is higher. Treat the silverleaf row as the planning case until cannabis data exist. Practical reading: whiteflies are slower than thrips or spider mites, which gives parasitoids time, but a silverleaf infestation at 26 °C still goes from "a few on a card" to "honeydew everywhere" in about a month. ## Where do whiteflies hide, how do they spread and how do they get in? Whiteflies enter cannabis rooms on plants: clones, houseplants, vegetable transplants and bedding plants. Greenhouse whitefly has more than 250 ornamental and vegetable hosts [10]. **Hiding places.** Eggs, nymphs and pupae sit on leaf undersides [1]. Adults gather on the youngest leaves, where females lay, so the oldest nymphs are on lower, older leaves (*Supported*). **Dispersal.** Adults fly, but not far; you need several cards to detect them [1]. Air movement and people carry them around a room (Grower practice). Adults carry broad mites [11]. **Outdoors.** In warm climates greenhouse and silverleaf whiteflies breed year-round outdoors [1], so intakes near gardens and weeds are a route in. **Quarantine.** Isolate new plants for 1–2 weeks [10]. Given 23 days egg to adult at 25 °C [2], three weeks of isolation with weekly underside checks is the safer choice (Grower practice). **Starve-out.** A host-free period of 2–3 weeks starves an established infestation, weeds included [10]. ## How do I scout for whiteflies? Scout for whiteflies weekly by turning leaves, shaking plants and reading yellow sticky cards. Record counts, so you see the trend rather than a single snapshot. **Leaf checks.** Turn 3–5 upper and lower leaves per plant on 10% of plants, or all plants in a small room (Grower practice). Young upper leaves show adults and eggs; lower leaves show older nymphs and parasitised pupae. **Lens.** 10x shows adults and nymphs; 20x shows the waxy filaments that separate the species [1]. Biotype ID needs a lab. **Yellow sticky cards.** Hang cards sticky side toward plants, out of direct light, level with the infestation [1]. Colorado State University uses 1 card per 1,000 ft² (~93 m²), replaced weekly, for greenhouses [10]; UC IPM suggests one trap per one or two plants in a home setting [1]. In small rooms, use about 1 card per 1–2 m² (Grower practice). **Cards and parasitoids.** Yellow cards trap Encarsia too. Take cards down before release and put them back 3–4 days later [8]. **Thresholds.** No action threshold has been published for whiteflies on cannabis. Practical rule: first adults on cards plus nymphs on leaves starts the program (Grower practice). ## How do I control whiteflies by life stage? Whitefly control works stage by stage. Contact sprays and predators hit adults, crawlers and young nymphs; eggs and the fourth instar tolerate most contact sprays; parasitoids lay in the nymphs. | Stage | Where | What reaches it | |---|---|---| | Egg | Undersides of young leaves | A. swirskii, Delphastus [8]; contact sprays poorly | | Crawler, instars 1–2 | Undersides | A. swirskii, Delphastus, soaps and oils, fungi [8] | | Instars 3–4 | Undersides, older leaves | Encarsia (prefers instars 3–4), Eretmocerus, fungi [8] | | Adult | Young leaves, flying | Yellow cards, vacuuming, fungi, Delphastus, soaps [1][8] | **Re-application interval.** Survivors of a contact spray are eggs and fourth instars. The next spray must land before the hatchlings from surviving eggs reach the tolerant fourth instar, so the interval must be shorter than the egg stage plus the crawler window. Run the program at least one full generation. | Room temperature | Egg stage [2] | Max interval | Program length | Applications | |---|---|---|---|---| | 20 °C | 10.5 d | ~9–10 d | ≥ 33 d | 4–5 | | 25 °C | 7.4 d | ~6–7 d | ≥ 23 d | 4–5 | | 30 °C | 5.7 d | ~5 d | ≥ 18 d | 4–5 | These intervals come from the greenhouse whitefly model [2]. Colorado State University recommends repeating oils, soaps and neem every 7–10 days until eggs and nymphs are gone [10], which fits the 20–25 °C rows. Use soaps and oils only when plants are not drought-stressed and below about 32 °C (90 °F) [1]. **Resistance.** Both species have long histories of insecticide resistance, and B. tabaci MED is noted for it. Rotate by IRAC group, never by brand, and change group after each generation-length window. Registrations on cannabis vary by jurisdiction: follow the label and local law. No products or rates are given here. **Residuals vs parasitoids.** Encarsia is very sensitive to pesticide residues, including long-residual products [8]. Phase residual sprays out well before release. ## Which biological controls work against whiteflies? Biological control of whiteflies on cannabis uses a parasitoid matched to the species plus a predator for eggs and crawlers: Encarsia formosa for greenhouse whitefly, Eretmocerus eremicus for silverleaf whitefly, and Amblyseius swirskii for both [8]. Release in veg, when whiteflies are first found. | Agent | Target | Temperature | RH | Notes | |---|---|---|---|---| | Encarsia formosa | Greenhouse whitefly instars 3–4 | 21–27 °C (70–80 °F); no flight < 18 °C; survival falls > 30 °C | 50–80% | Threshold 12.7 °C, 188.9 DD [2]; 25 d at 21 °C [9]; pupae black [8] | | Eretmocerus eremicus | Silverleaf whitefly (also greenhouse) | 25–29 °C (77–84 °F) | – | Desert origin; host-feeds; no direct sun [8] | | Amblyseius swirskii | Eggs, crawlers; also thrips | ~21 °C and up | ~70% | Prefers eggs and first instars [8] | | Delphastus (lady beetle) | All stages, prefers eggs and nymphs | 24–27 °C (75–80 °F); no flight < 13 °C | – | Avoids parasitised whiteflies [8] | | Beauveria bassiana, Cordyceps (Isaria) fumosorosea | All stages | – | needs leaf-surface moisture | Start when populations are low [8] | ### Encarsia formosa Encarsia formosa is a tiny wasp that lays in greenhouse whitefly nymphs, preferring the third and fourth instars [8]. Parasitised nymphs turn black and release a wasp through a round hole [1][8]. At 21 °C on greenhouse whitefly, development from egg to adult wasp took 25 days [9]. Females lay about 5 eggs a day and about 59 in a lifetime of about 12 days [9]. They also kill about 3 nymphs a day by host-feeding, about 95 over a lifetime [9]. Populations are all-female (thelytokous) because of Wolbachia bacteria [9]. Every wasp you release lays eggs. Release weekly from first detection until 80–90% of the nymphs are parasitised [8]. Supplier and university schedules use either a regular low "dribble" of about 1 parasitised nymph per plant, or larger releases when whiteflies appear [9]. Banker plants have been used at 1 per 352 crop plants in tomato [9]. Encarsia also attacks silverleaf whitefly. Against B. argentifolii, under 2 wasps per plant per week was reported to work in some trials, while more than 3 failed in others [9]. Eretmocerus is still the usual first choice for silverleaf [8]. ### Eretmocerus eremicus Eretmocerus eremicus comes from the deserts of southern California and Arizona and tolerates 25–29 °C (77–84 °F) [8]. It has been sold since the 1990s for Bemisia [8]. Females also kill nymphs by host-feeding [8]. Do not release it in direct light; replace yellow cards four days after release [8]. A quality check: hold a card in a shaded, screened container at room temperature for two weeks; about 95% of adults should emerge [8]. ### Amblyseius swirskii A. swirskii eats whitefly eggs and first-instar nymphs, plus thrips larvae, broad mites and pollen [8]. It works best around 21 °C and 70% RH [8]. In poinsettia, A. swirskii combined with Eretmocerus suppressed whiteflies better than either alone [8]. On cannabis it does double duty against thrips ([kb-pests-thrips](https://genetixbay.com/knowledge/pests/thrips.md)). ### Delphastus Delphastus is a 1.3–1.4 mm dark lady beetle that eats all whitefly stages, preferring eggs and nymphs; optimum 24–27 °C, no flight below about 13 °C (55 °F) [8]. It avoids parasitised whiteflies, so it fits with wasps [8]. Growers use it on hot spots, because a beetle needs many prey (Grower practice). ### Predatory mirid bugs: caution Macrolophus and Dicyphus are omnivorous mirid bugs used against whiteflies in tomato. They also feed on plants when prey run short (no cannabis data found). Do not release them on cannabis without trial evidence. ### Fungi Beauveria bassiana and Cordyceps (formerly Isaria) fumosorosea infect whiteflies; infected nymphs turn brown or pink [8]. Start when populations are low [8]. They need humidity at the leaf surface to infect. Do not raise room RH in flower for them ([kb-term-entomopathogenic-fungi](https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.md)). ## How can I use the environment as a weapon against whiteflies? The environment helps against whiteflies by keeping the room in the parasitoid's favour, not by killing the pest. Encarsia gets ahead of greenhouse whitefly above about 17 °C and does best at 21–27 °C [2][8]. **Greenhouse whitefly room: moderate and steady.** Hold 22–26 °C. At 24 °C Encarsia needs about 17 days per generation against 24 for the whitefly [2]. Avoid nights below about 18 °C, where Encarsia adults stop flying [8]. **Silverleaf whitefly room: Eretmocerus likes it warm.** Silverleaf grows fastest at 25–27 °C [4], and Eretmocerus tolerates 25–29 °C [8]. Do not try to cook silverleaf out: at 35 °C it still grew at r = 0.073 per day on eggplant [4], and the crop suffers more than the pest. **Greenhouse whitefly and heat.** At 26 °C on bean, greenhouse whitefly adults lived only 5.9 days [3]. A warm veg room at 26–28 °C slows it, but never trade that against heat stress or spider mites ([kb-pests-spider-mites](https://genetixbay.com/knowledge/pests/spider-mites.md)). **Flower trade-off.** RH at 45–55%, and 40–50% late, protects buds from botrytis ([kb-diseases-botrytis-bud-rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)) and powdery mildew ([kb-diseases-powdery-mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md)). Parasitoids keep working in the drier room; fungal sprays do not. ## What should I not do about whiteflies in flower? Do not spray cannabis buds in flower. Residues stay in dense buds, wet buds invite botrytis, and most residual and systemic insecticides are not registered on cannabis. - **Do not use systemic insecticides.** Not registered on cannabis in most places, and residues persist. - **Do not raise RH in late flower** to help fungal biopesticides. Keep 40–50% RH. - **Do not hang dozens of fresh yellow cards right after a parasitoid release;** wait 3–4 days [8]. - **Do not let the room drop below about 18 °C at night** if you rely on Encarsia [8]. - **In flower, rely on parasitoids and predators established in veg.** Vacuum adults from lower leaves early in the morning, when they are sluggish (Grower practice). ## What are the common myths about whiteflies? **"Yellow cards will control whiteflies."** *Myth.* Cards are for monitoring and detection [1]. Eggs and nymphs keep developing under the leaves. **"Encarsia works on any whitefly."** *Myth.* Encarsia is the greenhouse whitefly specialist; it attacks silverleaf whitefly less reliably, and Eretmocerus is the usual choice there [8][9]. **"Whiteflies love heat, so cool the room."** *Myth.* Silverleaf whitefly does well in heat [4], but greenhouse whitefly breeds less at 26 °C [3]. Cooling below about 17–18 °C helps greenhouse whitefly more than Encarsia [2][8]. **"One spray clears whiteflies."** *Myth.* Eggs and fourth instars survive, and eggs hatch within about a week at 25 °C [2]. **"Whiteflies are harmless apart from honeydew."** *Myth.* Large nymph populations cause yellowing and leaf drop [1], and adults carry broad mites [11]. ## Common mistakes - Releasing Encarsia against silverleaf whitefly and expecting greenhouse-whitefly results [8][9]. - Releasing Encarsia into a cool room or one with fresh pesticide residues [2][8]. - Relying on cards for control instead of monitoring [1]. - Spraying once, seeing adults vanish, and stopping before eggs hatch [2]. - Ignoring ants that farm honeydew and protect whiteflies [1]. - Keeping houseplants or vegetable seedlings in the grow room [10]. ## Evidence - Biology, identification and honeydew damage: *Established* [1][10]. - Greenhouse whitefly and Encarsia degree-day models: *Established*, from one lab study [2]; linear models overestimate speed near the upper limit. - Silverleaf whitefly temperature responses: *Established* on eggplant, cotton and cantaloupe [4][5][6][7]. - Greenhouse whitefly r on bean: *Established* for those cultivars [3]; low values reflect poor hosts. - Encarsia and Eretmocerus biology and temperature windows: *Established* in greenhouse crops [8][9]. - Use on cannabis: *Supported* by extrapolation; no cannabis trials or life tables found. ## Glossary terms used here - Glossary: [parasitoid](https://genetixbay.com/knowledge/glossary/parasitoid.md), [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md), [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md), [intrinsic rate of increase](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md), [biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) ## Sources 1. Flint, M.L. 2015. Pest Notes: Whiteflies (Publication 7401). UC Statewide IPM Program. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7401.html 2. Osborne, L.S. 1982. Temperature-dependent development of greenhouse whitefly and its parasite Encarsia formosa. Environmental Entomology 11: 483-485. https://doi.org/10.1093/ee/11.2.483 3. Manzano, M.R. & van Lenteren, J.C. 2009. Life history parameters of Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) at different environmental conditions on two bean cultivars. Neotropical Entomology 38: 452-458. https://doi.org/10.1590/S1519-566X2009000400002 4. Wang, K. & Tsai, J.H. 1996. Temperature effect on development and reproduction of silverleaf whitefly (Homoptera: Aleyrodidae). Annals of the Entomological Society of America 89: 375-384. https://doi.org/10.1093/aesa/89.3.375 5. Nava-Camberos, U., Riley, D.G. & Harris, M.K. 2001. Temperature and host plant effects on development, survival, and fecundity of Bemisia argentifolii (Homoptera: Aleyrodidae). Environmental Entomology 30: 55-63. https://doi.org/10.1603/0046-225X-30.1.55 6. Wagner, T.L. 1995. Temperature-dependent development, mortality, and adult size of sweetpotato whitefly biotype B (Homoptera: Aleyrodidae) on cotton. Environmental Entomology 24: 1179-1188. https://doi.org/10.1093/ee/24.5.1179 7. Wagner, T.L. 1994. Temperature-dependent reproduction of sweetpotato whitefly, Bemisia tabaci. Proceedings of the Beltwide Cotton Conferences (abstract). https://www.cotton.org/beltwide/proceedings/8395/abstracts/4366.cfm 8. Pundt, L. 2024. Biological Control of Whiteflies. UConn Extension IPM. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-whiteflies 9. Cornell University. Biological Control: A Guide to Natural Enemies in North America. Encarsia formosa. https://biocontrol.entomology.cornell.edu/parasitoids/encarsia.php 10. Cranshaw, W.S. 1999 (reviewed 2025). Greenhouse Whitefly. Colorado State University Extension Fact Sheet 5.587. https://extension.colostate.edu/topic-areas/insects/greenhouse-whitefly-5-587/ 11. UConn Extension IPM. Managing Broad Mites on Greenhouse Crops. https://ipm.cahnr.uconn.edu/ipm-managing-broad-mites-on-greenhouse-crops --- # Botrytis (bud rot / grey mould) in cannabis > Bud rot is Botrytis cinerea rotting dense colas from the inside, favoured by cool-to-moderate temperatures (10–27 °C, optimum near 20 °C), high humidity and free water on tissue. There is no cure in flower: prevent it with RH below about 50 % in late flower, dew-point control at lights-off, airflow, open canopies and fast removal of infected buds. - Canonical: https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.html - Category: Diseases · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Flower, Ripening, Harvest, Cure · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What does bud rot look like on cannabis?** Bud rot on cannabis first shows as a single sugar leaf or small cluster of pistils on a cola turning dull, yellow, then brown and dry while the rest stays green, and it pulls out easily. Inside, the core is brown, mushy or dusty grey. Late infections produce grey-brown fuzzy mould that releases a spore cloud when disturbed. **Why are my cannabis buds turning brown inside?** Cannabis buds turning brown and mushy inside are almost always infected with Botrytis cinerea, the grey mould fungus. It germinates in free water or very high humidity and enters through senescing pistils, wounds and the wet core of dense colas, so by the time it shows outside the inside is gone. Normal ripening browns pistils evenly while the bud stays firm. **How do I stop bud rot spreading on cannabis?** Stop cannabis bud rot spreading by cutting infected buds out with at least 5 to 10 cm (2 to 4 in) of healthy-looking stem below, bagging them at the plant to avoid shaking spores, and sanitising pruners between cuts. Then drop humidity to 40 to 45%, push air through the canopy and inspect every cola of that cultivar and its neighbours daily until harvest. **What humidity prevents bud rot in cannabis?** Relative humidity of about 40 to 50% in mid to late flower helps prevent cannabis bud rot, and extension sources recommend keeping greenhouse humidity below 50%. Night-time spikes matter most: keep bud surfaces at least 2 to 3 °C above the dew point, ramp temperature down over 30 to 60 minutes at lights-off and dehumidify before and during the dark period. **Can I save cannabis buds with botrytis?** Cannabis buds with botrytis cannot be saved; there is no cure in flower, and removing only the visible brown part leaves rot deeper inside. Cut the infected bud out with a healthy margin and discard it. Do not spray buds to kill the fungus, because wetting dense flowers spreads spores. Biological antagonists work only as prevention. **Is it safe to smoke cannabis buds with bud rot?** Cannabis buds with bud rot are not safe to smoke, vape or extract. Mouldy flower carries spores and mycotoxin-producing contaminants, which is why regulated markets test for yeast and mould counts, according to published research. Discard infected buds rather than trimming around them, and check dried buds by breaking them open: a clean core with no grey dust or musty smell. **Short answer.** Bud rot is the fungus *Botrytis cinerea* rotting your densest colas from the inside out [1][2]. It needs cool-to-moderate temperatures, high humidity and free water on the tissue: the PNW Handbook gives 10–27 °C (50–80 °F) with an optimum near 20 °C (68 °F) [2]. You can't cure it in flower. You prevent it with humidity below about 50 % late in flower [2][3], no condensation at lights-off, moving air, open canopies, and by cutting out infected buds the moment you see them. ## What's happening *B. cinerea* is a necrotroph: it kills tissue and lives on the dead remains. Airborne spores land on flowers, germinate in free water or very high humidity, and infect through senescing pistils, damaged tissue and the cosy wet core of a fat cola. By the time you see it outside, the inside of the bud is already gone. Grey fuzzy sporulation then releases millions of spores to the rest of the room. It also causes stem cankers and damping-off of cuttings [2]. Wounds help it. Caterpillar feeding inside colas is a classic entry point outdoors [4] (see [caterpillars](https://genetixbay.com/knowledge/pests/caterpillars.md)). Dense, high-calyx, late-maturing cultivars are reported to be most vulnerable (*Grower practice*). ## How to recognise it - **Earliest sign:** a single sugar leaf or small cluster of pistils on a cola turns dull, yellow then brown and dry while the rest is green. Tug it: it pulls out easily. - **Inside:** pry the bud apart. Brown, mushy or dusty grey tissue at the core, sometimes along the stem inside. - **Late:** grey-brown fuzzy mould with a dusty spore cloud when disturbed. Stem above the lesion may wilt. - **Stems:** tan, water-soaked cankers that girdle a branch; everything above wilts. - **Look-alikes:** normal pistil browning at ripeness (uniform, bud stays firm), nutrient-related leaf yellowing (whole leaves, not inside the bud), Fusarium bud rot (pinkish-white mould; see [fusarium](https://genetixbay.com/knowledge/diseases/fusarium.md)), PM on buds (white powder on the surface, no internal rot). ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Temperature favouring infection | 10–27 °C (50–80 °F), optimum ~20 °C (68 °F) | PNW Handbook [2]; cool nights in late flower are high-risk | | RH, mid to late flower | 40–50 % | Keep below 50 % in greenhouse production [2][3] | | VPD, late flower | 1.2–1.6 kPa | Higher VPD = drier leaf surfaces (*Grower practice*) | | Leaf/bud surface vs dew point | Keep surface temperature ≥ 2–3 °C (4–5 °F) above dew point | Condensation is free water; free water favours infection [2] (*Supported*, margin is grower practice) | | Lights-off transition | Ramp temperature down over 30–60 min; dehumidify before and during | Night RH spikes are the most common trigger (*Grower practice*) | | Drying room | 15–21 °C (60–70 °F), 55–62 % RH | Common drying targets; above ~65 % RH with poor air exchange, botrytis can continue in drying buds | | Outdoor | Rain or fog during the last 2–4 weeks of flower | Highest-risk window (*Supported*) | ## What to check first 1. **Confirm:** pull the suspect bud apart. Internal brown rot = botrytis until proven otherwise. 2. **Check your climate log at lights-off** and the first two hours of dark. RH climbing past 60–65 % or temperature falling toward dew point is the usual culprit. 3. **Look at the position:** biggest top colas near cool surfaces (walls, AC outlets, vents) or wet zones (under leaks, near humidifiers). 4. **Check for caterpillars or frass** in affected colas, especially outdoors. 5. **Check for overwatering and wet floors** raising room RH. ## How to fix it ### Immediately - **Cut infected buds out with a margin** of at least 5–10 cm (2–4 in) of healthy-looking stem below. Bag them at the plant before removing to avoid shaking spores. Sanitise pruners between cuts. - **Inspect every cola** of the same cultivar, then neighbours, every day until harvest. - **Drop RH** to 40–45 % and increase airflow through, not just over, the canopy. ### Cultural and environmental (prevention) - Open the canopy: defoliate and lollipop before week 3 of flower so air moves through colas. - Space plants. Support colas so they don't fold into each other. - Dehumidification sized for the transpiration load (roughly the water you feed per day, minus runoff). - Avoid cold surfaces, cold air blowing directly onto buds, and late-day irrigation that raises night RH. - Choose cultivars with looser flower structure for humid climates and greenhouses. - Harvest promptly. Botrytis risk rises as flowers senesce. - Sanitise between cycles; remove plant debris (see [sanitation](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md)). ### Biological and least-toxic options Products and registrations differ by jurisdiction; Utah State notes that no fungicides were available for bud rot there [3], while the PNW Handbook lists a few biological options for hemp in Oregon [2]. Check local regulations and labels before using anything. - **Biological antagonists** (*Bacillus* spp., *Clonostachys rosea* [formerly *Gliocladium roseum*], *Trichoderma* spp.) are used against botrytis in other crops and some are trialled on hemp [2]. *Supported in other crops*, limited cannabis evidence. They are preventive only. - **Plant-extract biofungicides** (e.g. *Reynoutria sachalinensis* extract) are listed for hemp in the PNW [2]. Preventive. - **UV-C, ozone, air purifiers:** may lower airborne spore load; no peer-reviewed cannabis efficacy for bud rot prevention found. ### What not to do in flower - **Don't spray buds** to "kill" botrytis. Wetting dense flowers spreads spores and feeds the next infection. - **Don't keep infected buds.** Mouldy flower is not safe to smoke, vape or extract; spores and mycotoxin-producing contaminants are a health concern, and regulated markets test for yeast and mould counts [1]. - **Don't shake or blow** infected colas before bagging them. - **Don't raise humidity in late flower** for "terpenes". Anything above about 55 % RH in late flower is a gamble with dense genetics. ## How to confirm it worked - No new brown sugar leaves or soft spots in daily inspections for 7–10 days. - Night RH stays within target and surfaces stay above dew point (a cheap IR thermometer plus a dew-point calculator, or a controller that logs it). - Dried buds break open clean at the core, with no grey dust or musty smell. ## Common mistakes - Removing only the visible brown bit. The rot extends further inside. - A big night-time temperature drop with no dehumidification. - Fans blowing across the top of the canopy while the cores stay stagnant. - Hanging wet, whole plants in a crowded, humid dry room. - Letting caterpillar damage go unchecked outdoors. ## Evidence - *Established:* *B. cinerea* causes bud rot in cannabis indoors, in greenhouses and outdoors [1][2][3]. - *Established:* cool-moderate temperature, high humidity and free water favour infection; greenhouse RH below 50 % is recommended [2][3]. - *Supported:* wounds and insect feeding increase infection [4]. - *Supported in other crops*, limited cannabis data: biological antagonists. - *Grower practice:* dew-point margins, lights-off ramping, drying-room numbers. - *Myth:* "Bud rot only happens outdoors." It is common in indoor rooms with night-time RH spikes [1]. ## Sources 1. Punja ZK et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker 3. Utah State University Extension. Hemp bud rot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot 4. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp --- # Fusarium in cannabis: wilt, crown rot and bud rot > Fusarium fungi cause three different problems in cannabis: vascular wilt (F. oxysporum), root and crown rot (mainly F. solani), and a pinkish-white bud rot. There is no cure once a plant is infected; remove it, stop root-zone stress, sanitise pots and water, and source clean clones and media. - Canonical: https://genetixbay.com/knowledge/diseases/fusarium.html - Category: Diseases · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why is my cannabis plant wilting on one side?** A cannabis plant wilting on one side or one branch, during the day and without recovering, is a classic sign of Fusarium vascular wilt, caused by Fusarium oxysporum colonising the xylem and blocking water flow. Lower leaves yellow and drop, and there is typically no obvious root rot. Cut the stem near the base: brown or reddish-brown streaks in the wood confirm it. **What does Fusarium look like in cannabis?** Fusarium in cannabis looks different depending on the disease. Vascular wilt shows yellowing, wilting leaves and brown streaks inside the stem. Crown rot shows a dark, soft or sunken lesion at the stem base, sometimes with white-pink growth, plus brown roots and stunting. Fusarium bud rot appears as whitish to pinkish mould on or inside buds in warm, humid late flower. **Why is the inside of my cannabis stem brown?** Brown or reddish-brown streaking in the wood of a cannabis stem, seen when cut near the base, points to Fusarium vascular wilt, according to extension sources. Verticillium wilt causes similar streaking and can only be told apart by a lab culture or molecular test. Clean, pale wood with rotten roots instead suggests root rot from Pythium or Fusarium. **Is Fusarium wilt in cannabis curable?** Fusarium wilt is not curable in an infected cannabis plant, and extension sources note few or no fungicides are registered for it on hemp. Remove the wilting plant with its roots and media, bagged, and do not compost it on site. Then fix root-zone stress, disinfect reused pots with a 10 to 15% household bleach solution and use pasteurised media and clean clones. **How can I tell Fusarium from Pythium in cannabis?** Fusarium and Pythium in cannabis differ mainly in the roots and stem. Pythium makes roots slimy, with an outer layer that sloughs off, and causes no vascular streaking. Fusarium wilt causes brown streaks inside the stem, often with no obvious root rot, while Fusarium crown rot softens and discolours the stem base. Research shows both can infect the same plant. **What causes pink mould on cannabis buds?** Whitish to pinkish mould on or inside cannabis buds, especially in warm, humid late flower, is typical of Fusarium bud rot. Research recovered Fusarium solani and Fusarium oxysporum from cannabis buds, where they add to yeast and mould counts and may produce mycotoxins. Treat mouldy flower as waste, and keep late-flower humidity at about 40 to 50% to prevent it. **Short answer.** "Fusarium" covers three different problems in cannabis. **Vascular wilt** (*Fusarium oxysporum*) blocks the plant's plumbing so it wilts, often one branch or one side first, with brown streaks inside the stem [3]. **Root and crown rot** (mainly *F. solani*) rots roots and the stem base [4]. **Fusarium bud rot** shows as pinkish-white mould in flowers [2]. None is curable in an infected plant. Remove it, fix the root-zone stress that let it in, sanitise, and start from clean clones and clean media. ## What's happening *Fusarium* species live in soil, plant debris, unpasteurised media and water. They enter through root tips and wounds (transplant damage, fungus gnat feeding, salt burn) [2][5]. - **Wilt:** *F. oxysporum* (formae speciales *cannabis* and *vasinfectum* reported on hemp) colonises the xylem. Water flow stops; leaves yellow and wilt from the bottom or on one side. There is typically no obvious root rot [3]. - **Crown and root rot:** *F. solani* (primarily), *F. equiseti* and *F. graminearum* rot the roots and soften and discolour the crown just above the soil line [4]. In hydroponic cannabis, *F. oxysporum*, *F. solani* and *F. brachygibbosum* caused root browning, crown and pith discolouration, stunting and yellowing [1][2]. - **Bud rot:** *F. solani*, *F. oxysporum* and other species were recovered from cannabis buds and can contribute to yeast-and-mould counts [2]. Stress, warm and wet or alternately wet-and-droughty media, and poor drainage favour wilt and crown rot [3][4][8]. ## How to recognise it - **Wilt:** lower leaves yellow and drop; a branch or one side of the plant wilts during the day and doesn't recover; whole plant can collapse in flower. **Cut the stem near the base:** brown or reddish-brown streaking in the wood (xylem) is the giveaway. - **Crown rot:** dark, soft or sunken lesion at the stem base, sometimes with white-pink fungal growth; roots brown and rotting; plant stunted and yellow. - **Hydro root infection:** root browning with crown and pith discolouration [1]. - **Bud rot:** whitish to pinkish mycelium on or inside buds, often in warm, humid late flower. - **Look-alikes:** Pythium (slimy roots that slough, no vascular streaking — see [root rot](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md)); Verticillium wilt (similar streaking, favoured by consistently moist soils [8]; lab test needed); drought or overwatering wilt (recovers when corrected; no streaking); stem borer damage outdoors. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Root-zone moisture | Even, with dry-back; no waterlogging, no extreme drought cycles | Overly wet or droughty soils favour Fusarium wilt [8] | | Solution temperature (hydro) | 18–21 °C (65–70 °F) | Reduces root stress and Pythium co-infection (*Supported*) | | Disinfection of reused pots/trays | 10–15 % household bleach solution | Utah State recommendation [3]; clean off soil first | | Field rotation after wilt | 2–3 years (Utah) to ≥ 4 years (Oregon) out of hemp | Sources differ [3][8] | | Late-flower RH (bud rot) | 40–50 % | Same targets as botrytis (*Supported*) | | Pasteurised media | Use new or pasteurised coco/peat | Unpasteurised coco can carry fungal contaminants [2] | ## What to check first 1. **Cut a stem section** at the base of a wilting plant (or a lower branch you can spare). Streaks in the wood = vascular wilt. Clean wood + rotten roots = root rot (Pythium or Fusarium). 2. **Check the root zone:** waterlogging, saucers, compacted media, drought cycles, salt burn from high EC. 3. **Check for fungus gnat larvae** and root aphids in the media; both wound roots. 4. **Check the source:** new clones, reused soil, unpasteurised media, untreated surface water. 5. **Send a sample to a plant diagnostic lab** if you need certainty. Fusarium and Verticillium can only be told apart reliably by culture or molecular test. ## How to fix it ### Infected plants - **Remove wilting plants with their roots and media**, bagged, out of the grow. Utah State recommends removing infected plants with roots [3]. Don't compost them on site. - In recirculating hydro, isolate the plant's site from the loop immediately. ### Cultural and environmental - Water by weight or sensor; allow dry-back; never leave pots sitting in drainage. - Avoid root damage: gentle transplants, no cultivating near stems, manage gnats. - Use new pots and trays, or disinfect reused ones [3]. Clean equipment between rooms or fields [3]. - Use pasteurised media and clean planting stock from a reliable source [7]. - Outdoors: avoid heavy, poorly draining soils [8]; rotate out of hemp as above. - Late flower: open canopy and keep RH below 50 % against bud rot. ### Biological and least-toxic options Utah State and NC State note that no or very few fungicides are registered for these diseases on hemp [3][5]. Registration varies; check local regulations and labels. - **Root-zone biologicals** applied preventively: *Trichoderma* spp., *Bacillus* spp., *Streptomyces* spp., *Gliocladium/Clonostachys*. *Supported in other crops* for Fusarium suppression; limited cannabis-specific evidence. - **Compost-amended or living soils** may suppress some root pathogens (*Supported in other crops*), but poorly made compost can also introduce them. - **Resistant genetics:** no tested resistant cannabis cultivars are documented in these sources. ### What not to do in flower - **Don't try to nurse a wilting, streaked plant to harvest** in a shared space; it sheds spores into media and water. - **Don't drench with unregistered fungicides.** Residues, legality, and they don't cure vascular infection. - **Don't harvest or process buds with pink or white internal mould.** Fusarium species can produce mycotoxins; treat mouldy flower as waste [2]. - **Don't reuse that plant's media** in flower or next cycle. ## How to confirm it worked - No new wilting in neighbouring plants over 2–3 weeks. - Stem cuts from suspect plants show clean, pale wood. - Next crop in disinfected pots and fresh media establishes without lower-leaf yellowing or crown lesions. - If you sent a sample, a lab result tells you which pathogen to plan for. ## Common mistakes - Watering a Fusarium-wilted plant harder because it's wilting. - Reusing soil and pots from an infected crop without treatment. - Assuming every wilt is Fusarium (or every root rot is Pythium). Both can co-occur [1]. - Buying cheap, unpasteurised media. - Ignoring fungus gnats. ## Evidence - *Established:* *F. oxysporum*, *F. solani* and *F. brachygibbosum* infect cannabis roots and crowns; *F. solani* and *F. oxysporum* occur in cannabis buds [1][2]. - *Established:* wilt and crown rot are distinct diseases with different species and symptoms [3][4]. - *Supported:* poor drainage, overwatering and drought stress increase risk [3][4][8]. - *Contested:* rotation length outdoors (2–3 years vs ≥ 4 years) [3][8]. - *Supported in other crops*, limited cannabis data: biological suppression. ## Sources 1. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 2. Punja ZK et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 3. Utah State University Extension. Hemp Fusarium wilt (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-fusarium-wilt 4. Utah State University Extension. Hemp Fusarium crown rot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-fusarium-crown-rot 5. NC State Extension Plant Pathology. Root diseases prevalent in industrial hemp. https://plantpathology.ces.ncsu.edu/news/root-diseases-prevalent-in-industrial-hemp/ 6. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Root and Crown Rot. https://pnwhandbooks.org/node/12931 7. BC Ministry of Agriculture. Diseases of cannabis in British Columbia (factsheet). https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/agriculture-and-seafood/animal-and-crops/plant-health/disease-factsheets/specialty-crops/diseases_of_cannabis_in_british_columbia.pdf 8. Oregon State University Extension, hemp disease guidance. https://extension.oregonstate.edu/node/190521 --- # Hop latent viroid (HLVd, 'dudding') and other cannabis viruses > Hop latent viroid is a tiny infectious RNA that spreads through sap on tools, hands, clones, recirculating water and seed, and causes 'dudding': stunting, brittle stems and small, low-resin flowers. There is no cure in a plant. Test mothers (roots and leaves) by RT-PCR/RT-qPCR, discard positives, disinfect tools with bleach or heat (not alcohol), and use meristem tissue culture to rescue valuable genetics. - Canonical: https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.html - Category: Diseases · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is cannabis clone decline real or is it HLVd?** Cannabis clone decline is, in the GenetixBay position, almost always a pathogen such as hop latent viroid, not genetic drift. Apart from pathogens, a cut does not decline; the founder keeps cuts more than 40 years old with no loss. Cuts taken from shaded lower branches can behave differently (position effect), so take cuts from consistent locations and test weak mothers. **What is hop latent viroid in cannabis?** Hop latent viroid (HLVd) is a tiny, naked loop of infectious RNA, roughly 256 nucleotides long with no protein coat, that the cannabis plant's own enzymes copy. It is mechanically transmitted in sap and needs no insect. Research shows it is common in clone-based grows, though how common is contested, and it causes the flower problem growers call dudding. **What are the symptoms of HLVd or dudding in cannabis?** HLVd symptoms in cannabis cannot be diagnosed by eye, and many infected plants show none, especially in veg. Some show stunting, shorter internodes, smaller narrower leaves, mild chlorosis and brittle stems that snap rather than bend. In flower, dudding means smaller, looser buds with reduced trichome density and lower cannabinoid and terpene content, and uneven performance within one clone. **How does HLVd spread between cannabis plants?** HLVd spreads between cannabis plants through sap: on blades and scissors, hands, clones from infected mothers, roots sharing recirculating water, and seed. One researcher reported 100% infection in rooted clones from infected mothers. Defoliating a whole room with one pair of scissors is the fastest way to spread it, so disinfect blades between plants, not just between rooms. **Does alcohol kill hop latent viroid on tools?** Alcohol does not kill hop latent viroid on tools: Oregon State tests found 70% ethanol, hydrogen peroxide, peroxymonosulfate disinfectants and even autoclaving were not effective. What did inactivate HLVd was 10 to 20% household bleach, hypochlorous acid at 1000 ppm or more, or heating blades to 160 °C (320 °F) for 10 minutes. Dip or swap blades for every mother. **How do I test my cannabis mother plants for HLVd?** Test cannabis mother plants for HLVd by RT-PCR or RT-qPCR through an accredited lab, sending roots plus leaves from several positions (top, side and bottom). The viroid can be unevenly distributed, so a single leaf can miss it, and research shows roots are a reliable tissue. Test new clones after rooting and before they enter mother or veg rooms. **Can you cure HLVd in cannabis?** HLVd cannot be cured in a cannabis plant; no spray or product clears viroids. Discard or quarantine positive mothers and all their clones. Valuable genetics can be rescued through meristem tip culture, which research shows yields a high rate of viroid-free plantlets at genotype-dependent rates. Retest each plantlet twice and keep clean mothers in a separate room. **Can HLVd spread through cannabis seeds?** HLVd can spread through cannabis seeds from infected mothers or pollen, according to extension sources, though published transmission rates are scarce; one trade report suggested up to 30 to 40% of seed from infected mothers, which is unpublished. Buy seed from sources that test parents, and treat lines from untested parents as potential carriers. **What viruses infect cannabis?** Viruses reported in cannabis include beet curly top virus, spread by the beet leafhopper in outdoor western US hemp, and lettuce chlorosis virus, spread by whiteflies on Israeli farms and mimicking nutrient deficiency. Cucurbit chlorotic yellows virus and tobacco streak virus have also been detected. Insecticides do not stop transmission well, so control vectors and remove infected plants. **Short answer.** Hop latent viroid (HLVd) is a tiny, naked loop of infectious RNA with no protein coat. It moves in sap: on blades, hands, clones, roots sharing recirculating water, and in seed [1][2][3]. Infected plants can look normal in veg, then "dud" in flower: stunted, brittle, with small, airy, low-resin buds [1][2]. There is no cure in a plant. Test your mothers by RT-PCR or RT-qPCR (sample roots as well as leaves), discard positives, disinfect tools with bleach or heat rather than alcohol, and rescue precious genetics through meristem tissue culture [3][4]. ## What's happening Viroids are the smallest known plant pathogens: HLVd is roughly 256 nucleotides of circular RNA that is copied by the plant's own enzymes and moves through the plant's vascular and cell-to-cell connections [1]. It doesn't need an insect; it is mechanically transmitted. Once in a mother, every clone taken from her carries it: Punja has reported 100 % HLVd in rooted clones from infected mothers [5]. In hydroponics it is especially troublesome because it spreads through shared water and matted roots [5]. In mother plants, the viroid can be unevenly distributed, so a single leaf sample can miss it; roots are a reliable tissue to include [4][5]. Losses are real but poorly quantified. Industry estimates of prevalence (25–50 % of North American facilities' plants) and of annual losses vary enormously and come mostly from trade sources [1][5]. The PNW Handbook notes data on the extent and incidence of HLVd are lacking [2]. *Supported* that it is common; *Contested* how common. ## How to recognise it HLVd cannot be diagnosed by eye. Symptoms are suggestive at best, and many infected plants show none, especially in veg [1][2]. - **Veg:** sometimes stunting, shorter internodes, smaller and narrower leaves, mild chlorosis, brittle stems (snap rather than bend) [2]. Mothers that "got weak" over successive generations: this is what growers call "clone decline". GenetixBay's position is that, apart from pathogens like HLVd, a cut doesn't drift or decline; the founder keeps cuts more than 40 years old with no loss (see [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md)). Two things get mistaken for decline: a rare somatic mutation (which doesn't mean a loss) and a position effect (topophysis), where cuts from shaded lower branches behave differently from cuts off vigorous leaders. Take cuts from consistent locations, so that a weak clone points to a pathogen rather than to where the cut came from. - **Flower ("dudding"):** smaller, looser flowers, reduced trichome density and lower cannabinoid and terpene content, uneven canopy where some plants of the same clone underperform [1]. - **Rooting:** clones from infected mothers root more slowly. - **Differential:** the same picture comes from root-zone problems, light deficits, nutrient issues and root aphids. Rule those out first ([slow growth](https://genetixbay.com/knowledge/diagnosis/slow-growth.md), [root rot](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md)), then test. ## Other viruses reported in cannabis | Agent | Spread by | Typical symptoms | Where reported | |---|---|---|---| | Beet curly top virus (BCTV) | Beet leafhopper | Stunting, leaf curling/twisting, pale green to yellow foliage | Outdoor hemp, western US; 81 % of Colorado leaf samples in 2019 [6][7] | | Lettuce chlorosis virus (LCV) | Whitefly (*Bemisia tabaci*) | Interveinal chlorosis, brittle older leaves, necrosis; mimics nutrient deficiency | Licensed cannabis farms, Israel [8] | | Cucurbit chlorotic yellows virus (CCYV) | Whitefly | Yellowing, leaf-edge necrosis in mixed infection with LCV | Israel | | Tobacco streak virus | Thrips/pollen (in other crops) | Variable | Detected in Colorado hemp viromes [7] | Insecticides do not stop virus transmission by vectors well; vector control plus removing infected plants is the strategy [6]. Manage [whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md), [aphids](https://genetixbay.com/knowledge/pests/aphids.md) and [thrips](https://genetixbay.com/knowledge/pests/thrips.md) for this reason as well as their direct damage. Russet mites can transmit plant viruses in other crops (see [broad/russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md)). ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Test method | RT-PCR or RT-qPCR from an accredited lab | Visual diagnosis is unreliable [1][2] | | Tissue to test (mothers) | Roots plus leaves from several positions (top, side, bottom) | Uneven distribution; roots reliable [4][5] | | Clone test timing | After rooting, before entering mother or veg rooms | *Grower practice* | | Retest mothers | Every 4–8 weeks | Re-infection from tools or water | | Tool disinfection | 10–20 % household bleach, or ≥ 1000 ppm hypochlorous acid, or heat blades to 160 °C (320 °F) for 10 min | Inactivated HLVd in Oregon State tests [3]; contact time for bleach dip | | What doesn't work on HLVd | 70 % ethanol, hydrogen peroxide, peroxymonosulfate disinfectants, autoclaving | Not effective per Oregon State [3] | | Seed transmission | Possible from infected mothers or pollen | [2][3]; trade report of up to 30–40 % of seed from infected mothers [5] | | Meristem tip culture | High rate of viroid-free plantlets, genotype-dependent | [4] | ## What to check first 1. **Rule out cheaper explanations** for poor vigour or "duds": pH and EC, root zone, light (PPFD), temperature, root aphids. 2. **Is it clone-specific?** If one cultivar or one mother line consistently underperforms while others in the same room thrive, suspect HLVd. 3. **Test the mother**, not just the sick plant, using roots and multiple leaf positions. 4. **Audit the workflow:** shared blades between plants, defoliating with the same scissors across rooms, shared recirculating water, hands moving from mothers to clones. ## How to fix it There is no treatment that cures a plant of HLVd [1][2]. 1. **Discard or quarantine positive mothers** and all clones from them. Don't sell, gift or swap cuttings from untested plants. 2. **Rescue genetics with meristem tip culture** (the tiny growing tip, often with a heat or cold step) through a tissue-culture lab, then retest the plantlets twice before use [4]. Success depends on cultivar [4]. 3. **Re-establish clean stock:** start new mothers from tested-negative material and keep them in a separate, clean room. 4. **Disinfect between plants**, not just between rooms: dip or swap blades for every mother; use bleach, hypochlorous acid or heat [3]. See [sanitation](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md). 5. **Break water connections:** don't share recirculating solution between mothers and production; disinfect systems between cycles. 6. **Seeds:** buy from sources who test parents; treat seed lines from untested parents as potential carriers [2][3]. Seed surface disinfection does not remove viroid inside the seed. 7. **Outdoor viruses (BCTV):** remove symptomatic plants; reflective mulches may help deter leafhoppers; insecticides are ineffective against transmission [6]. ### What not to do in flower - **Don't take clones from a flowering "dud"** to see if it was a fluke. Test instead. - **Don't spray anything** hoping to "boost" an infected plant out of it. No product cures viroids or viruses. - **Don't defoliate a whole room with one pair of scissors.** That is the single fastest way to spread HLVd. ## How to confirm it worked - Mothers and production plants test negative on two consecutive tests at least 4 weeks apart. - Uniform canopy and flower size across plants of the same clone. - Clones root at a normal rate. ## Common mistakes - Trusting looks: asymptomatic carriers are common. - Testing a single leaf from a mother. - Disinfecting with alcohol or peroxide and believing tools are clean for HLVd [3]. - Bringing in "just one" untested clone from a friend. - Treating tissue culture as a guarantee; retest every plantlet. ## Evidence - *Established:* HLVd infects cannabis, is mechanically transmitted and moves with clones [1][2][4]. - *Supported:* HLVd reduces vigour, flower size and secondary metabolites; many infections are asymptomatic [1][2]. - *Supported:* bleach, hypochlorous acid and heat inactivate HLVd on surfaces; ethanol and peroxide do not [3]. - *Supported:* meristem tip culture yields viroid-free plants at genotype-dependent rates [4]. - *Supported:* seed transmission occurs [2][3]; rates are not well published. - *Contested:* prevalence and economic loss figures [1][2][5]. - *Established:* BCTV (leafhopper) and LCV (whitefly) infect cannabis/hemp [6][7][8]. ## Sources 1. Adkar-Purushothama CR, Sano T, Perreault J-P, 2023. Hop latent viroid: a hidden threat to the cannabis industry. Viruses 15(3):681. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10053334/ 2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Viroid Diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases 3. Oregon State University Extension. Hop latent viroid in hemp (EM 9570). https://extension.oregonstate.edu/catalog/em-9570-hop-latent-viroid-hemp 4. Punja ZK et al., 2025. Hop latent viroid transmission, spread and longevity in cannabis; meristem tip culture. Plants 14(5):830. https://www.mdpi.com/2223-7747/14/5/830 5. Cannabis Business Times, 2024. Hop latent viroid spread (report of Z. Punja talk). https://www.cannabisbusinesstimes.com/news/hop-latent-viroid-spread-zamir-punja 6. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Curly Top. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-curly-top 7. Colorado State University (Mountain Scholar). Beet curly top virus - beet leafhopper dynamics in hemp in Colorado. https://mountainscholar.org/items/690318d0-f830-4090-b0a5-c1e18581d7b5/full 8. Hadad L, Luria N, Smith E, et al., 2019. Lettuce chlorosis virus disease: a new threat to cannabis production. Viruses 11(9):802. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6784094/ --- # Powdery mildew in cannabis > Powdery mildew is a leaf-surface fungus (mainly Golovinomyces ambrosiae) that thrives in still, humid, moderate-temperature canopies and spreads by airborne spores. Prevent it with airflow, stable humidity, clean clones and resistant genetics; treat early in veg with least-toxic contact options, because once it reaches flowers there is no clean fix. - Canonical: https://genetixbay.com/knowledge/diseases/powdery-mildew.html - Category: Diseases · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the white powder on my cannabis leaves?** White powder on cannabis leaves that forms round, flour-like spots, wipes off and returns in the same place within a few days is usually powdery mildew, a leaf-surface fungus that in indoor and greenhouse cannabis is mostly Golovinomyces ambrosiae. It often starts on lower or middle fan leaves in the shadiest, least-ventilated part of the canopy. Confirm with a 30 to 60x loupe. **How do I get rid of powdery mildew on cannabis?** Get rid of powdery mildew on cannabis by fixing the environment first: oscillating fans above and below the canopy, thinning inner growth, bagging infected leaves and stabilising humidity at lights-off. In veg, least-toxic contact options such as potassium bicarbonate or horticultural oils need full coverage repeated every 7 to 10 days. Check local registration and labels before applying anything. **Can I spray for powdery mildew in cannabis flower?** Do not spray sulfur, oils or bicarbonates on cannabis buds after the first 2 to 3 weeks of flower, according to grower consensus. They leave residue, change flavour and can fail testing, and home remedies such as milk, vinegar or peroxide wet the buds and invite botrytis. Remove the worst branches or plants instead, and accept the loss. **Is powdery mildew systemic in cannabis?** Whether powdery mildew is systemic in cannabis is contested. The fungus lives mostly on the leaf surface, feeding through haustoria in the outer cells, but growers report it reappearing on clones from infected mothers even when leaves looked clean. Latent infection or persistent spores could explain this, as a true internal phase has not been demonstrated. Treat clones from infected mothers as infected. **What humidity causes powdery mildew on cannabis?** Powdery mildew on cannabis thrives in humid microclimates and still air, and its spores germinate in high humidity without needing free water. The risk peaks with night-time spikes to 70 to 80% humidity around lights-off. Grower practice keeps humidity at 55 to 70% in veg and 40 to 50% in mid to late flower, avoids VPD below 0.6 kPa and limits night temperature drops to 5 °C. **Are there powdery mildew resistant cannabis strains?** Powdery mildew resistant cannabis does exist. Research mapped PM1, a single dominant gene that gave complete resistance to a Pacific Northwest isolate, and PM2, a second locus that suppresses infection and sporulation. Breeders are also exploring loss of function in MLO susceptibility genes. Ask breeders for tested resistance data rather than relying on mould-resistant marketing claims. **Short answer.** Powdery mildew (PM) is a fungus that lives on the leaf surface and shows up as white, flour-like patches that wipe off and come back. In indoor and greenhouse cannabis it is mostly *Golovinomyces ambrosiae* [1][2]. It loves still air, moderate temperatures and humid microclimates inside dense canopies. Prevent it with airflow, steady humidity, clean starting material and resistant genetics. Treat it early in veg with contact options. Once it is in the flowers, the honest answer is: you can slow it, not clean it. ## What's happening PM fungi are obligate biotrophs: they feed on living cells through tiny feeding structures (haustoria) pushed into the leaf's outer layer, while the white mycelium and chains of spores (conidia) sit on top. Spores are airborne and land on new tissue, germinate without needing a film of water, and produce a new crop of spores in roughly a week under favourable conditions (5–10 days is typical for related PM fungi on other crops). That short cycle is why "a few spots" becomes a room-wide problem in two or three weeks. Older literature and some growers' guides call the cannabis pathogen *Golovinomyces cichoracearum* or *G. spadiceus*; recent work and the PNW Handbook use *G. ambrosiae* [1][2]. The PNW Handbook also lists *Podosphaera macularis* (the hop PM fungus, bright white colonies) on hemp [2]. Practically, management is the same. Is PM "systemic"? *Contested.* The fungus is mostly external, but growers report PM reappearing on clones taken from infected mothers even after the leaves looked clean. Latent infection of buds and stems, and persistent spores on the plant, are plausible explanations; a systemic, inside-the-plant phase has not been demonstrated. Treat clones from infected mothers as infected. ## How to recognise it - **First signs:** small, round, white-to-grey powdery spots on the upper leaf surface, often on lower or middle fan leaves in the shadiest, least-ventilated part of the canopy. Sometimes on the underside first. - **Progression:** spots merge into a felt-like coating; leaves yellow under the colonies, then brown and drop. Stems and petioles get coated. In flower, sugar leaves and bracts turn dusty white. - **The wipe test:** rub with a damp finger. PM smears off and comes back in a few days in the same place. Trichomes do not wipe off; mineral residue from sprays does not regrow. - **Look-alikes:** spray residue or hard-water spots (no regrowth, often on top surfaces only in droplet shapes), trichome-heavy sugar leaves (glandular heads under a 30–60x loupe), spider mite webbing (moving dots, stippling), downy mildew (rare on cannabis; grey-purple growth on the underside, yellow angular patches on top). See [white powder on leaves](https://genetixbay.com/knowledge/diagnosis/white-powder-on-leaves.md). ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Day air temperature | 24–28 °C (75–82 °F) veg; 22–26 °C (72–79 °F) flower | PM develops readily in moderate temperatures; temperature alone does not prevent it | | RH, veg | 55–70 % | Avoid wide swings; PM spores germinate in high humidity without free water | | RH, mid to late flower | 40–50 % | Also limits botrytis | | VPD | 0.8–1.2 kPa veg; 1.0–1.5 kPa flower | Very low VPD (< 0.6 kPa) and still air favour leaf-surface fungi (*Grower practice*) | | Air movement | Visible leaf flutter throughout canopy, including lower third | Dead air pockets are where PM starts (*Grower practice*) | | Day–night temperature drop | ≤ 5 °C (≤ 9 °F) | Large drops spike RH at lights-off | | Silicon (root-applied) | Reduced PM severity in soilless trials | PNW Handbook reports reduced severity in upper and mid canopy [2]; rates are crop/medium-specific, follow product guidance | | UV-C (night) | 70–200 J/m² in other crops | Suppressed PM in grape, strawberry and cucumber [6]; **no published cannabis dose** — | ## What to check first 1. **Confirm it's PM.** Wipe test plus a loupe. Mycelium and spore chains look like tangled cotton threads and beaded chains; trichomes are stalks with round heads. 2. **Map where it is.** Lower canopy and corners = airflow and microclimate problem. Everywhere at once = high spore load, probably came in on clones or mothers. 3. **Check the climate log** for RH at lights-off and the hour after. A night-time spike to 70–80 % RH is common and is when spores germinate. 4. **Check canopy density.** Leaves touching leaves, no light reaching the lower third, no air movement under the canopy. 5. **Trace the source.** New clones in the last 2–4 weeks? Mother plants with a history? Outdoor air intake with no filtration? 6. **Rule out the root zone and nutrition** for the plant's overall health, but don't expect them to explain PM. Stressed, soft, over-fed (high-nitrogen) plants are reported to be more susceptible (*Grower practice*). ## How to fix it ### Cultural and environmental (always, first) - **Airflow:** oscillating fans above and below the canopy; no dead corners. - **Defoliate and thin** inner and lower growth that never sees light. Bag infected leaves at the plant and remove them; don't shake them over the canopy. - **Stabilise RH**, especially around lights-off: dehumidify on a schedule, ramp temperature down slowly. - **Space plants;** don't overlap crops. The PNW Handbook notes epidemics build when young plants sit next to older infected plants [2]. - **Remove infected mothers** or retire them. Clones from an infected mother start infected. ### Genetics - *Established:* resistance exists. **PM1**, a single dominant gene, gave complete resistance to a Pacific Northwest isolate [3]; **PM2** is a second locus that suppresses infection and sporulation [4]. Loss-of-function in susceptibility genes (*CsMLO1*, *CsMLO4* candidates) is another route breeders are exploring [5]. Ask breeders for tested resistance, not "mould resistant" marketing. ### Biological and least-toxic options (veg, early transition) Registration and allowed uses for cannabis differ by country, state and province. Check local regulations and the product label before applying anything; many labels do not allow use on cannabis, and licensed producers have strict lists. - **Bicarbonates (potassium bicarbonate):** contact action; raises leaf-surface pH and dries colonies. Needs full coverage, repeated every 7–10 days [2]. - **Horticultural and plant-derived oils:** smother colonies; full coverage essential. Do not apply below 10 °C (50 °F), above 32 °C (90 °F), on stressed or wet plants, or close to sulfur applications (phytotoxic combination) [2]. - **Sulfur:** protectant; works best before infection. Not for use under hot lights or close to oils. Never in flower (residue and smell). - **Biofungicides:** *Bacillus* spp. (e.g. *B. subtilis*, *B. amyloliquefaciens* strains) and plant-extract resistance inducers are listed for hemp PM in some jurisdictions [2]; efficacy varies and some trials showed no effect [2]. *Supported* in other crops, limited cannabis data. - **Resistance inducers / silicon:** root-applied silicon reduced severity in soilless hemp [2]. *Supported.* - **UV-C at night:** *Supported in other crops* (grape, strawberry, cucumber) [6]; no peer-reviewed cannabis dose found. Treat as experimental and test on a few plants for leaf injury first. ### What not to do in flower - **No sulfur, no oils, no bicarbonate sprays on buds** after the first 2–3 weeks of flower (grower consensus; label pre-harvest intervals vary). They leave residue, change flavour, and residue on flower can fail testing where testing is required. - **No home remedies on flowers** (milk, vinegar, hydrogen peroxide). Wet buds plus PM is an invitation to botrytis. - **Don't spray to "clean up" a PM'd crop before harvest.** Remove the worst plants or branches and accept the loss. PM-coated flower is not something to smoke or extract; mould spores and residues end up in the product. - **Don't raise humidity** with foliar sprays in late flower. Ever. ## How to confirm it worked - No new colonies on new growth for 14 days, checked every 2–3 days with a loupe on the lower canopy. - Old spots stay dry and grey rather than fresh white and expanding. - RH logs show no night-time spikes above your targets. - Next cycle: a sticky-tape lift from lower leaves under a 60x loupe shows no spore chains. ## Common mistakes - Treating only visible spots. Spores are already on neighbouring leaves; treat the whole plant and neighbours. - Relying on one spray. Contact options need repeat coverage. - Keeping an infected mother "because she's the keeper". She will re-seed every cycle. - Huge night-time temperature drops in a sealed room. - Mixing or rotating oil and sulfur too closely: burned leaves. - Buying "PM resistant" seeds without any test data. ## Evidence - *Established:* *G. ambrosiae* is the main cannabis PM pathogen in North American indoor and greenhouse production [1][2]; dense canopies, stable humid microclimates and overlapping crop cycles promote epidemics [2]. - *Established:* single-gene resistance (PM1) and a second locus (PM2) exist in cannabis [3][4]; MLO genes are susceptibility candidates [5]. - *Supported:* root-applied silicon reduces severity [2]; bicarbonates and oils give contact suppression [2]. Cannabis efficacy data for many products are lacking [3]. - *Supported in other crops, unknown in cannabis:* night-time UV-C [6]. - *Contested:* whether PM persists "systemically" inside cannabis plants. - *Myth:* "Milk spray cures PM." Some suppression is reported on cucurbits; it is not a cure, and has no place on flowers. ## Sources 1. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 2. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew 3. Mihalyov PD, Garfinkel AR, 2021. Discovery and genetic mapping of PM1, a powdery mildew resistance gene in Cannabis sativa L. Frontiers in Agronomy 3:720215. https://www.frontiersin.org/articles/10.3389/fagro.2021.720215/full 4. Seifi et al., 2025. Mapping of a second powdery mildew resistance locus (PM2) in Cannabis sativa. Frontiers in Plant Science 16:1543229. https://www.frontiersin.org/articles/1543229 5. Pépin N, Hebert FO, Joly DL, 2021. Genome-wide characterization of the MLO gene family in Cannabis sativa reveals two genes as strong candidates for powdery mildew susceptibility. Frontiers in Plant Science 12:729261. https://frontiersin.org/articles/10.3389/fpls.2021.729261/full 6. Gadoury D. et al. Use of UV light to suppress powdery mildew (grapevine and strawberry). IVES Open Science. https://ives-openscience.eu/session-11_gadoury_use-of-uv-light --- # Root rot and Pythium in cannabis > Pythium root rot is a water mould that thrives in warm, low-oxygen root zones and swims between plants in recirculating water. Brown, slimy roots whose outer layer slides off, plus wilting with a wet root zone, are the signature. Fix the root-zone conditions first: solution at about 18–21 °C (65–70 °F), high dissolved oxygen, clean water and no overwatering; then remove dead roots and re-establish beneficial microbes. - Canonical: https://genetixbay.com/knowledge/diseases/root-rot-pythium.html - Category: Diseases · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: DWC, RDWC, NFT, Ebb and flow, Drip, Aeroponics, Coco, Rockwool, Soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my DWC cannabis roots brown and slimy?** Brown, slimy DWC cannabis roots with a foul smell and an outer sheath that slides off are usually Pythium root rot, a water mould rather than a true fungus. Research identified Pythium dissotocum, P. myriotylum and P. aphanidermatum in hydroponic cannabis. It wins when the solution is warm and short of oxygen, most commonly above 22 °C (72 °F). **What water temperature prevents Pythium root rot?** Grower practice keeps DWC, RDWC and NFT solutions at 18 to 21 °C (65 to 70 °F), and below 22 °C (72 °F), to prevent Pythium root rot. Cooler water holds more oxygen: saturation is about 9.1 mg/L at 20 °C versus 8.3 mg/L at 25 °C. Research in hydroponic spinach found the aggressive warm-water species took over above about 23 °C. **How do I treat Pythium in cannabis hydroponics?** Treat Pythium in cannabis hydroponics by fixing root-zone conditions first: cool the solution to 18 to 21 °C, maximise aeration, change the solution completely and clean the reservoir and lines. Trim the worst rotten roots with sanitised scissors, rinse gently and black out any light reaching the water. Then choose either a beneficial-microbe or a fully sterile approach, never both. **Is brown root colour from nutrients or root rot?** Brown cannabis roots that stay firm, with intact tips and no smell, are often just tea-coloured from additives, dyes or organics, according to grower practice. Root rot is soft and slimy, smells rotten, and its outer layer pulls off between the fingers leaving a thin white strand. The belief that brown roots always mean Pythium is a myth. **Can I use hydrogen peroxide for cannabis root rot?** Hydrogen peroxide is one of the oxidiser classes used in hydroponics and can reduce free-swimming Pythium spores, but it does not cure infected roots, may alter pH and nutrient availability, and kills beneficial microbes. Never shock-dose living roots at high concentration, since that burns them too. Use oxidisers only as part of a fully committed sterile approach. **Should a cannabis hydro reservoir use beneficial microbes or be sterile?** GenetixBay prefers a beneficial-microbe reservoir, because bacteria will turn up in any reservoir regardless, so it may as well host good ones such as Bacillus, Trichoderma, Pseudomonas and Streptomyces. A sterile reservoir is valid only if fully committed, with continuous oxidiser or UV and ozone and no organics. Mixing the two fails, because oxidisers kill the microbes. **Why is my cannabis plant wilting when the soil is wet?** A cannabis plant wilting in wet soil is drowning, not thirsty: chronic overwatering, poor drainage and compacted media starve roots of oxygen and allow root rot, and fungus gnat larvae wound the roots further. Do not top up the plant. Let the media dry back, clear drainage, empty full saucers, manage gnats and consider preventive root-zone biologicals. **Short answer.** In hydroponic cannabis, "root rot" is usually *Pythium* (a water mould, not a true fungus), sometimes with *Fusarium* alongside [1][2]. It wins when the root zone is warm and short of oxygen, and in recirculating systems its swimming spores reach every plant. Brown, slimy roots with an outer sheath that slides off, a foul smell, and a plant that wilts while sitting in water are the signature. Fix the conditions first, keep the solution near 18–21 °C (65–70 °F) with dissolved oxygen high, then clean up roots and re-establish beneficial microbes. ## What's happening *Pythium* species (in cannabis: *P. dissotocum*, *P. myriotylum*, *P. aphanidermatum*) infect root tips and the outer root tissue (cortex) [1][2]. The cortex rots and sloughs, leaving the inner thread of the root. Water and nutrient uptake collapse, so the plant wilts and shows deficiency-like yellowing even when the solution is perfect. Spores called zoospores swim through water and are attracted to root exudates, which is why one sick bucket in an RDWC loop becomes a whole system [3]. Warm water holds less oxygen and speeds pathogen growth; stressed, oxygen-starved roots leak more exudate and resist less. In hydroponic spinach, 23 °C was the transition at which the aggressive warm-water species *P. aphanidermatum* came to dominate [4]. The same logic applies to cannabis (*Supported*, extrapolated from other crops). In soil and coco, root rot follows chronic overwatering, poor drainage and compacted media; fungus gnat larvae wound roots and carry spores [6]. ## How to recognise it - **Roots:** healthy hydro roots are white to cream, firm, with fuzzy fine hairs. Pythium roots are tan to brown, slimy, and the outer layer pulls off between your fingers leaving a thin white strand. Smell: rotten or sewer-like. - **Plant:** wilting during lights-on that doesn't recover with water; slow growth; lower-leaf yellowing; then rapid collapse in warm weather. Seedlings and fresh clones may damp off (stem pinches at the base). - **Solution:** cloudy, slimy biofilm on surfaces, pH drifting, foaming. - **Stain vs rot:** brown roots that are **firm** with intact tips and no smell are often tea-coloured from additives, dyes or organics (*Grower practice*). Rot is soft and slides off. See [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md). ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Solution temperature (DWC/RDWC/NFT) | 18–21 °C (65–70 °F); keep below 22 °C (72 °F) | Cooler water slows Pythium and holds more oxygen [3]; above ~23 °C warm-water species dominate [4] | | Dissolved oxygen (DO) | ≥ 6 mg/L, ideally near saturation | Saturation is about 9.1 mg/L at 20 °C and 8.3 mg/L at 25 °C (fresh water); high DO reduces zoospore survival [3] | | Solution change interval | 7–14 days, or top-off by EC | Grower practice; also restart after any outbreak | | pH (hydro) | 5.6–6.2 | Out-of-range pH stresses roots; not itself protective (*Supported*) | | Media moisture (soil/coco) | Allow partial dry-back; 10–20 % runoff in coco | Saturated, airless media favour root rot (*Grower practice*) | | Room temperature effect | Every 1 °C on the air heats reservoirs | Chillers or insulated, opaque reservoirs in warm rooms | | Light on solution | Zero | Light feeds algae, which consume oxygen at night and add organic load | ## What to check first 1. **Water temperature right now and at peak** (late in the lights-on period). Above 22 °C (72 °F) is the most common root cause. 2. **Aeration:** are air stones clogged, pumps undersized, return lines delivering? Measure DO if you can. 3. **Pull a root sample:** white and firm vs brown and slimy. Rinse; firm brown = stain, soft = rot. 4. **pH and EC:** rule out salt burn (very high EC also browns root tips) and pH crashes. 5. **Light leaks** into reservoirs or buckets. 6. **In soil/coco:** pot weight before watering, drainage holes, saucers sitting full, fungus gnats. 7. **History:** new clones, contaminated water source, shared tools or pots. 8. **If roots look clean but plants stunt:** consider [hop latent viroid](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md), [root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md) or [fusarium](https://genetixbay.com/knowledge/diseases/fusarium.md). ## How to fix it ### Root-zone conditions (first, always) 1. **Cool the solution** to 18–21 °C (65–70 °F): chiller, insulated reservoir, move reservoir off a warm floor, reduce room heat. 2. **Max out oxygen:** larger air pump, clean stones, waterfall/return turbulence. In soil/coco: water less often, increase drainage, bigger air-porosity media. 3. **Change the solution** entirely; clean the reservoir and lines (see below). 4. **Trim the worst rotten root mass** with sanitised scissors in DWC; rinse gently with fresh, cool, pH-adjusted water. 5. **Black out** any light reaching the solution. ### Sanitation and water treatment (choose one approach, not a mix) > **House position: living reservoir preferred.** Bacteria will turn up in any reservoir whatever you do, so you may as well have the good ones: GenetixBay prefers a beneficial-microbe reservoir. A sterile reservoir is a valid choice, but only if you commit to it fully (continuous oxidiser or UV/ozone, clean top-ups, no organics) and never mix the two. It's a personal choice; the half-way house is what fails. Water-treatment classes used in hydroponics include chlorination, ozonation, copper ionisation, UV and oxidisers such as hydrogen peroxide [3]. They can change pH and nutrient availability, and most also kill beneficial microbes [3]. Follow manufacturer guidance and local rules. Wear gloves and eye protection when handling concentrated oxidisers; never mix chlorine products with acids or ammonia. - **Biological approach first (house preference)**, see below. **Sterile approach:** oxidiser or UV/ozone kept running continuously in recirculating systems. Effective at reducing free-swimming spores; does not cure infected roots. - **Biological approach:** beneficial microbes (*Bacillus* spp., *Trichoderma* spp., *Pseudomonas* spp., *Streptomyces* spp.) colonise roots and compete with or suppress pathogens. *Supported in other hydroponic crops*; cannabis-specific trial data are limited. Do not add them to an oxidiser-treated solution; the oxidiser kills them. - **After an outbreak:** drain, scrub, disinfect, rinse, restart with fresh solution, then reintroduce biologicals if you use them. ### In soil and coco - Let media dry back; don't top up a wilting plant in wet media (it is drowning, not thirsty — see [drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md)). - Manage [fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md), whose larvae wound roots. - Root-zone biologicals (*Trichoderma*, *Bacillus*) are commonly used preventively (*Grower practice*, *Supported in other crops*). ### What not to do in flower - **Don't keep heavily infected plants in a shared recirculating system.** Isolate or remove them; the rest of the loop pays otherwise. - **Don't shock-dose oxidisers** at high concentrations on living roots hoping to "burn it out". You burn the roots too. - **Don't add fungicides of unknown registration** to the reservoir. Residues can end up in flower, and most are not legal for cannabis. - **Don't push heavy feeding** to "fix" the yellowing; damaged roots can't take it up and EC climbs. ## How to confirm it worked - New root tips appear white and firm within 5–10 days. - Plants stop wilting during lights-on; turgor returns. - Solution stays clear; pH drifts slowly and predictably. - Water temperature log stays below 22 °C (72 °F) at peak. ## Common mistakes - Treating the symptom with additives while the water sits at 25 °C (77 °F). - Mixing oxidisers and beneficial microbes in the same reservoir. - Translucent reservoirs and light leaks. - Topping off forever without ever changing or cleaning. - Assuming all brown roots are rot (and all white roots are healthy — HLVd and root aphids can hide in white roots). - Overwatering soil and coco "because it's flowering". ## Evidence - *Established:* *P. dissotocum*, *P. myriotylum* and *P. aphanidermatum* cause root rot, stunting, yellowing and wilt in hydroponic cannabis in Canada [1][2]. - *Established in other crops:* cooler, oxygen-saturated solutions reduce Pythium [3][4]. - *Supported:* water-treatment classes (chlorination, ozone, UV, copper, oxidisers) reduce pathogens in recirculating systems but have side effects [3]. - *Supported in other crops*, limited cannabis data: beneficial microbes for suppression. Preferring a living reservoir: house position; sterile is valid if fully committed. - *Grower practice:* exact solution temperature targets of 18–21 °C, change intervals. - *Myth:* "Brown roots always mean Pythium." Stains from additives are common. ## Sources 1. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 2. Punja ZK et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 3. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic leafy greens and its management (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 4. Phytopathology 75:333, 1985 (abstract). Temperature and predominance of Pythium aphanidermatum vs P. dissotocum on hydroponic spinach. https://www.apsnet.org/publications/phytopathology/backissues/Documents/1985Abstracts/Phyto75_333.htm 5. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Root and Crown Rot. https://pnwhandbooks.org/node/12931 6. UConn Extension IPM. Managing fungus gnats in the greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ --- # Sanitation and disease prevention for cannabis grows > Most cannabis disease problems are brought in on clones, tools, hands, media or water, and then helped along by humid, stagnant rooms. Quarantine and test incoming plants, work clean-to-dirty, clean then disinfect with the right chemical class for the pathogen (bleach or hypochlorous acid or heat for viroids; alcohol and peroxide do not inactivate HLVd), treat recirculating water, and keep the climate out of the disease zone. - Canonical: https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.html - Category: Diseases · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I sterilise my cannabis grow room between cycles?** To sterilise a cannabis grow room between cycles, remove and bag all plant material, media and debris, then wash every surface with detergent and scrub biofilm from reservoirs, lines, drippers and trays. Disinfect with a suitable class, respecting contact time, then rinse. Run a line cleaner through irrigation, replace filters, clean ducting and fans, and leave the room empty and dry for several days. **What kills hop latent viroid on scissors?** Hop latent viroid on scissors is inactivated by 10 to 20% household bleach, hypochlorous acid at 1000 ppm or more, or heating blades to 160 °C (320 °F) for 10 minutes, according to Oregon State tests. Clean sap off first, because organic matter neutralises chlorine. For mother plants, disinfect blades between every plant or rotate several pairs through a dip. **How long should I quarantine new cannabis clones?** Quarantine new cannabis clones in a separate space for at least 2 to 3 weeks, which grower practice treats as long enough for a pest generation and latent powdery mildew to show. Inspect leaf undersides with a 30 to 60x loupe for mites, thrips, whitefly eggs and mildew, and test for hop latent viroid using roots and leaves before clones enter the mother room. **Which is better for cleaning grow tools, bleach, hydrogen peroxide or alcohol?** Bleach is the better choice for cleaning cannabis grow tools when hop latent viroid is the concern, because 70% alcohol and hydrogen peroxide do not inactivate it in Oregon State tests. Alcohol and peroxide still work on most fungi and bacteria. Bleach corrodes metal, so rinse tools afterwards and mix fresh daily, since it degrades in light and with organic matter. **How do I prevent powdery mildew and bud rot in a cannabis grow?** Prevent powdery mildew and bud rot in cannabis by controlling climate and spore entry together. Keep humidity at 55 to 70% in veg and 40 to 50% in mid to late flower, limit night-time humidity spikes at lights-off to under 10 percentage points, and keep leaves fluttering through every canopy layer. Quarantine clones, defoliate for airflow before week 3 of flower and use resistant genetics. **Is it safe to mix bleach with other cleaners in a grow room?** Bleach is not safe to mix with other grow-room cleaners. Mixing bleach with acids such as pH-down, vinegar, peracetic acid or some descalers, or with ammonia or quaternary ammonium cleaners, releases toxic chlorine or chloramine gas. Do not mix disinfectants with each other at all, wear gloves and eye protection, ventilate, and store concentrates labelled away from nutrients. **Short answer.** Diseases rarely appear from nowhere. They arrive on clones, tools, hands, shoes, media and water, then the climate decides whether they take off [3]. Quarantine and test anything coming in. Work from clean areas to dirty ones. Clean first, then disinfect with a chemical that actually works on your target: for hop latent viroid that means bleach, hypochlorous acid or heat, because 70 % alcohol and hydrogen peroxide do not inactivate it [1]. Treat recirculating water. Keep humidity and airflow out of the zone where mildews and moulds win. ## What's happening Disease needs three things: a pathogen, a susceptible host, and the right environment (the disease triangle). Sanitation removes the pathogen; genetics and plant health change the host; climate control removes the environment. You need all three because none is perfect. Main entry routes in cannabis: - **Clones and mothers:** powdery mildew, HLVd, Fusarium, pests [2][3][8]. - **Tools and hands:** HLVd and other sap-transmitted agents [1][2]. - **Media:** unpasteurised coco fibre carries fungal communities that can contaminate flowers [3]. - **Water:** Pythium zoospores and HLVd in recirculating systems [4][8]. - **Air:** powdery mildew and botrytis spores [6][7]. - **People and pets** moving between outdoor gardens and indoor rooms. ## How to recognise a sanitation problem - The same disease returns each cycle in the same room or on the same cultivar. - Problems start a few weeks after new clones arrive. - Disease follows the path of a person, a tool or a water line. - Root problems appear system-wide in a shared reservoir. ## Numbers that matter ### Disinfectant classes Always **clean first**: scrub off soil, root mats, sap and biofilm with detergent and water. Organic matter neutralises most disinfectants, especially chlorine. | Class | Typical use concentration | Contact time | Works on | Notes | |---|---|---|---|---| | Sodium hypochlorite (household bleach) | 10 % v/v of household bleach (≈ 0.5–0.8 % NaOCl depending on starting strength); 10–20 % for HLVd [1][8] | 10 min on hard surfaces; tool dip time for HLVd | Fungi, bacteria, oomycetes, viruses, **HLVd** [1] | Corrodes metal; rinse tools after; make fresh daily (degrades in light and with organics). 10–15 % for pots/trays [5] | | Hypochlorous acid | ≥ 1000 ppm for HLVd on tools [1] | | Broad, including HLVd [1] | Less corrosive than bleach; unstable, check strength | | Heat | Tool blades 160 °C (320 °F) for 10 min [1] | 10 min | Including HLVd [1] | Note: autoclaving did not inactivate HLVd in Oregon State tests [1] | | Alcohol (ethanol, isopropanol) | 70 % | ≥ 30 s wet | Most fungi and bacteria | **Not effective against HLVd** [1]; flammable | | Hydrogen peroxide / peracetic acid | Per label | Per label | Fungi, bacteria, spores, biofilm | **Hydrogen peroxide not effective against HLVd** [1]; peracetic acid | | Potassium peroxymonosulfate | Per label | Per label | Broad | **Not effective against HLVd** in Oregon State tests [1] | | Quaternary ammonium | Per label | Per label (often 10 min) | Many fungi, bacteria | Efficacy on HLVd not shown; leaves residue; don't let it contact roots | **Safety:** wear gloves and eye protection when mixing disinfectants; ventilate. **Never mix bleach with acids** (pH-down, vinegar, peracetic acid, some descalers) **or with ammonia or quaternary ammonium cleaners**: this releases toxic chlorine or chloramine gas. Don't mix disinfectants with each other at all. Store concentrates labelled, away from nutrients and pH-down. Rinse before plants or roots touch treated surfaces. ### Climate guard rails | Parameter | Target | Protects against | |---|---|---| | RH, veg | 55–70 % | PM germination at the high end | | RH, mid–late flower | 40–50 % | Botrytis, PM [6][7] | | Night RH spike at lights-off | < 10 percentage points | Botrytis, PM | | Solution temperature | 18–21 °C (65–70 °F) | Pythium [4] | | Dissolved oxygen | ≥ 6 mg/L, ideally near saturation (~9 mg/L at 20 °C) | Pythium [4] | | Airflow | Leaf flutter through all canopy layers | PM, botrytis | ## What to check first 1. **Where did the last problem come from?** Clones, media, water, tools, people. 2. **Which disinfectant do you use**, and does it work on what you're worried about? (Alcohol for HLVd is the classic gap.) 3. **Is there a clean-to-dirty flow?** Do you go from flowering rooms back to mothers? 4. **Are mothers tested?** 5. **What does the night-time RH log say?** ## How to fix it: a working sanitation programme ### 1. Quarantine incoming plants - Keep all new clones and plants in a separate space for at least 2–3 weeks (*Grower practice*; long enough for a pest generation and latent PM to show). - Inspect with a 30–60x loupe: leaf undersides for mites, thrips, whitefly eggs, PM. - Test for HLVd (roots and leaves) before they enter the mother room [2][8]. - Prefer seeds or tested clean stock from tissue culture over untested cuttings. ### 2. Clean room workflow - **Order of work:** clone/propagation → mothers → veg → flower → drying. Never go backwards in a day without changing clothes and washing hands (*Grower practice*). - **Dedicated tools per room**, or disinfect between rooms. For HLVd-sensitive stock (mothers), **disinfect blades between every plant** with bleach, hypochlorous acid or heat, or rotate several pairs through a dip [1]. - Wash hands or change nitrile gloves between plants when taking cuttings. - Clean clothing or coveralls; shoe covers or dedicated footwear for mother rooms. - Keep pets and outdoor garden clothing out of the grow. - Sticky traps at doors and inside rooms to monitor what comes in (see [thrips](https://genetixbay.com/knowledge/pests/thrips.md), [fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md)). ### 3. Between cycles 1. Remove all plant material, media and debris; bag it out. 2. Dry-clean then wash every surface with detergent; scrub biofilm in reservoirs, lines, drippers, trays. 3. Disinfect with an appropriate class; respect contact time; rinse. 4. Run a disinfectant (or appropriate line cleaner) through irrigation lines; flush with clean water. 5. Leave the room empty and dry for several days if possible; a plant-free period also starves some pests (*Grower practice*; e.g. root aphids — see [root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md)). 6. Replace filters and clean ducting and fan blades that collected spores. ### 4. Media and water - Use new or pasteurised media; don't reuse media from diseased crops [3][5]. - Source water: municipal or well water is usually low-risk; surface water and rainwater collection can carry Pythium and Phytophthora (*Supported in other crops*). - **Recirculating systems:** choose a treatment class: UV, ozone, chlorination, copper ionisation, slow sand filtration or oxidisers [4]. Each can affect pH, micronutrients and beneficial microbes [4]. Don't combine an oxidiser with live biological inoculants in the same water. - Opaque, lidded reservoirs; no light on solution. ### 5. Plant-level prevention - Resistant genetics where data exist (e.g. powdery mildew PM1/PM2 — see [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md)). - Don't overwater; manage dry-back. - Defoliate for airflow before week 3 of flower. - Avoid wounding; manage chewing and sucking pests ([caterpillars](https://genetixbay.com/knowledge/pests/caterpillars.md), [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md)). - Preventive beneficials where legal and suitable: root-zone microbes in non-sterile systems, predatory mites for pests. ### What not to do in flower - Don't spray disinfectants on or near flowering plants. They are for surfaces, tools and water. - Don't fog or "bomb" a room with plants in it. - Don't bring clones or mothers into a flowering room to "save space". - Don't start a deep clean during late flower that raises humidity (mopping a room full of plants at lights-off is a botrytis invitation). ## How to confirm it worked - The repeating problem doesn't repeat next cycle. - Mothers test HLVd-negative on consecutive tests. - Sticky-trap counts stay flat after new plants enter. - Reservoirs stay clear, roots white. ## Common mistakes - Disinfecting dirty surfaces (no cleaning step). - Using alcohol for viroids. - Mixing bleach with pH-down or other cleaners. - Old, diluted bleach that has lost strength. - Skipping quarantine "because it's from a friend". - Going from the flower room to the mother room. - Reusing coco or soil from a crop with root disease. ## Evidence - *Supported:* 10–20 % bleach, ≥ 1000 ppm hypochlorous acid and dry heat inactivate HLVd; ethanol, hydrogen peroxide, peroxymonosulfate and autoclaving did not [1]. Contact-time details for tool dips need confirmation. - *Established:* clones, tools and recirculating water spread HLVd and root pathogens [1][2][4][8]. - *Supported:* unpasteurised coco carries fungal contaminants [3]. - *Established:* bleach mixed with acids or ammonia releases toxic gases (general chemical safety). - *Grower practice:* quarantine length, work order, plant-free fallow periods. ## Sources 1. Oregon State University Extension. Hop latent viroid in hemp (EM 9570). https://extension.oregonstate.edu/catalog/em-9570-hop-latent-viroid-hemp 2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Viroid Diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases 3. Punja ZK et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 4. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic production (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 5. Utah State University Extension. Hemp Fusarium wilt (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-fusarium-wilt 6. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew 7. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker 8. Cannabis Business Times. Hop latent viroid spread: Zamir Punja. https://www.cannabisbusinesstimes.com/news/hop-latent-viroid-spread-zamir-punja 9. BC Ministry of Agriculture. Diseases of cannabis in British Columbia. https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/agriculture-and-seafood/animal-and-crops/plant-health/disease-factsheets/specialty-crops/diseases_of_cannabis_in_british_columbia.pdf --- # Septoria leaf spot (yellow leaf spot) in cannabis > Septoria leaf spot (Septoria cannabis) starts as small brown spots with bright yellow halos on lower, older leaves and climbs the plant in wet, humid weather by rain and water splash. It is mainly an outdoor and greenhouse problem; manage it with clean lower canopies, dry foliage, mulch, airflow and debris removal, and protectants only where registered. - Canonical: https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.html - Category: Diseases · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Soil, Living soil, Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What causes brown spots with yellow halos on lower cannabis leaves?** Small brown spots with bright yellow halos on the lowest, oldest cannabis leaves, enlarging and merging into blotches, are the typical sign of septoria leaf spot, according to extension sources. Look with a 10 to 20x lens for tiny black fruiting bodies (pycnidia) in older lesions. The disease climbs the plant during rain, overhead watering and high humidity. **What is septoria leaf spot on cannabis?** Septoria leaf spot, also called yellow leaf spot, is a fungal disease caused by Septoria cannabis, which infects only cannabis and hemp. It overwinters on infected plant debris and spreads by spores splashed from black fruiting bodies onto wet leaves. Kentucky extension reports it as the most common leaf spot of field hemp; it is mainly an outdoor and greenhouse problem. **Is it leaf spot disease or a nutrient deficiency on my cannabis?** Leaf spot disease and nutrient deficiency on cannabis differ in pattern. Septoria spots have yellow halos and black dots, start on the oldest leaves and spread leaf to leaf after wet weather. Nutrient spots usually lack halos and black dots and follow a symmetrical pattern by leaf age, such as new leaves for calcium. Check pH and the root zone first. **How do I stop leaf spot spreading up my cannabis plant?** Stop septoria leaf spot spreading up a cannabis plant by removing and bagging spotted lower leaves, lifting the lowest leaves to about 20 to 30 cm above the soil, mulching to stop splash, and watering at the base in the morning so foliage dries. Space and prune for airflow. New spots should stop on middle and upper leaves within 7 to 14 days. **Does septoria affect cannabis buds or yield?** Septoria usually has a modest effect on cannabis yield when it arrives late in the season; Utah State extension notes no cannabinoid yield losses observed from leaf spots in other states. Severe early infection is different, causing stunting and loss of vigour according to Kentucky extension. A few spotted lower leaves in late flower are a cosmetic problem, not an emergency. **Short answer.** Septoria leaf spot is caused by the fungus *Septoria cannabis*, which only infects cannabis/hemp [1]. It starts on the lowest, oldest leaves as small brown spots with bright yellow halos that enlarge and merge into blotches [2]. Spores move upward in rain splash and overhead watering, so wet, humid weather spreads it fast [1]. It is mostly an outdoor and greenhouse disease. Keep foliage dry, clean up the lower canopy, mulch the soil, and remove debris; use protectants only where registered. ## What's happening The fungus overwinters on infected plant debris. In spring and summer, spores are released from tiny black fruiting bodies (pycnidia) in old lesions and splash onto nearby leaves. Infection needs leaf wetness, and spread is rapid during extended rain or high humidity [1]. Lower leaves get hit first because they are closest to splash and stay wet longest. Kentucky reports it as the most common leaf spot of field hemp there [1]; Florida lists it among the most common hemp leaf spots [3]. Yield impact is usually modest when it arrives late. Utah State notes no cannabinoid yield losses observed from leaf spots in other states [2], while Kentucky notes stunting and loss of vigour with severe early infection [1]. ## How to recognise it - **Where:** lower, older fan leaves first; moves upward. - **What:** small (a few mm) round-to-angular brown or tan spots with a bright yellow halo [2]. Spots enlarge and coalesce into irregular brown blotches; leaflets yellow and drop. - **Hand lens (10–20x):** tiny black dots (pycnidia) in the centre of older lesions are a strong sign of Septoria. - **Pattern:** worst after rain, on the side facing irrigation splash, on plants in the wettest part of the garden. ### Look-alikes (differential) | Looks like | How to tell | |---|---| | Calcium or magnesium issue, "rust spots" | Nutrient spots usually lack yellow halos and black dots; often appear on new (Ca) or mid (Mg) leaves symmetrically. Check pH first. See [rust spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md) | | Nitrogen deficiency | Uniform yellowing of whole lower leaves, no discrete spots. See [yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) | | Spray or light burn | Pattern matches droplets or the hottest canopy spot; doesn't spread from leaf to leaf | | Other leaf spots (*Cercospora*, *Alternaria*, bacterial) | Lab confirmation needed; management is similar [3] | | Pest stippling | Tiny pale dots, insects or mites on undersides | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Leaf wetness duration | Minimise; foliage dry within 1–2 h after watering or rain | Infection requires wetness (*Established* for Septoria genus) | | Irrigation | Drip or soil-level watering | Splash spreads spores [1] | | Lowest leaves | Keep 20–30 cm (8–12 in) above soil outdoors | Reduces splash infection (*Grower practice*) | | Plant spacing | Leaves of neighbouring plants not touching | Airflow and faster drying [2] | | Indoor RH | 55–70 % veg, 40–50 % late flower | Indoors Septoria is uncommon with dry foliage (*Grower practice*) | ## What to check first 1. **Old or new leaves?** Septoria starts low and old. Spots appearing first on new growth point elsewhere (pH, calcium, pests). 2. **Look for halos and black dots** with a hand lens. 3. **Check pH and the root zone** before concluding it's a disease, because nutrient spotting and fungal spotting are confused often. 4. **Check the weather and watering:** recent rain, overhead watering, foliar sprays. 5. **Is it spreading leaf to leaf?** Disease spreads; nutrient problems follow a pattern by leaf age. ## How to fix it ### Cultural (first, and usually enough) - **Remove spotted lower leaves** and bag them; don't leave them on the ground. - **Lift the skirt:** remove the lowest leaves that touch or sit near soil. - **Mulch** the soil surface (straw, wood chips) to stop splash. - **Water at the base**, in the morning, so foliage dries during the day. - **Space and prune** for airflow [2]. - **End of season:** remove and destroy all debris; don't till infected residue into next year's bed without a gap. Rotate outdoor beds where practical [1]. ### Biological and least-toxic options Registrations vary by jurisdiction; Utah State notes not all listed materials are registered for edible crops [2]. Check local regulations and the label before using anything. - **Protectant classes** listed for hemp leaf spots include sulfur, copper-based products and biofungicides (e.g. *Bacillus*-based) [2]. They protect healthy leaves; they don't cure spots. - **Biofungicides (*Bacillus* spp., *Streptomyces* spp.):** *Supported in other crops*; limited cannabis data. ### What not to do in flower - **No copper or sulfur sprays on buds.** Residue on flowers is unacceptable and can fail testing where required. - **No foliar feeding or overhead watering** once spotting starts, and none on flowers ever. - **Don't strip a flowering plant bare** to remove every spotted leaf. Remove the worst; leaves still feed the buds. A few spotted lower leaves in late flower are a cosmetic problem, not an emergency. ## How to confirm it worked - New spots stop appearing on middle and upper leaves within 7–14 days of drier conditions and lower-leaf cleanup. - New growth is clean. - Next season, fewer early spots after debris removal and mulching. ## Common mistakes - Treating halo spots as calcium deficiency and adding more Cal-Mag. - Leaving fallen leaves under plants. - Watering with a hose wand over the foliage at dusk. - Spraying protectants after the disease is everywhere instead of fixing wetness and splash. ## Evidence - *Established:* *Septoria cannabis* causes leaf spot on hemp, starting on lower leaves and spreading in wet weather [1][2][3]. - *Supported:* cultural controls (debris removal, spacing, avoiding splash) reduce disease [1][2]. - *Supported:* yield impact is often limited when infection is late [2]; early severe infection reduces vigour [1]. - *Grower practice:* lifting lower canopy, mulching, numeric splash heights. ## Sources 1. University of Kentucky Plant Pathology. Septoria leaf spot of hemp (PPFS-AG-H-01). https://plantpathology.mgcafe.uky.edu/files/ppfs-ag-h-01.pdf 2. Utah State University Extension. Hemp leaf spot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-leaf-spot 3. University of Florida IFAS Plant Pathology. Hemp diseases. https://plantpath.ifas.ufl.edu/extension/hemp-diseases/ 4. Punja ZK et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full --- # Brown or burnt leaf tips on cannabis: a differential > Crispy brown tips on otherwise healthy leaves usually mean too much salt in the root zone (EC too high, or salts building up because of low runoff or drying out), not a deficiency. Check runoff or reservoir EC against input first, then watering rhythm, then heat and low humidity, and only then K or B disorders. - Canonical: https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.html - Category: Diagnosis · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are the tips of my cannabis leaves brown and crispy?** Brown, crispy tips on otherwise dark green cannabis leaves usually mean salt burn: root-zone EC is too high, or salts are concentrating because the medium dries out or gets too little runoff. Leaf tips sit at the end of the water path, so they die first. Check runoff or reservoir EC against input first, then watering rhythm, heat and low humidity, and only then potassium or boron. **Is brown tip burn on cannabis nutrient burn?** Brown tip burn on cannabis is most often nutrient (salt) burn, especially when 1 to 3 mm of the tip is brown on dark green, newest mature leaves. Confirm it by measuring runoff EC: runoff more than about 1.0 mS/cm above input points to salt build-up, while runoff within about 0.5 mS/cm of input means heat, low humidity or a potassium problem is more likely. **Why do cannabis seedlings get burnt tips?** Cannabis seedlings and fresh clones get burnt tips at feed strengths that a flowering plant would find light. Grower practice keeps seedling feed at roughly 0.4 to 0.8 mS/cm EC (200 to 400 ppm on the 500 scale). If seedling tips brown, lower the feed EC, avoid letting the medium dry hard between waterings and keep humidity up, because dry air worsens tip burn. **How does high EC cause tip burn on cannabis?** High root-zone EC lowers the osmotic potential around cannabis roots, making water uptake harder, and salts concentrate further as the medium dries. Heat and low humidity raise transpiration and carry even more salt to the leaf tips and margins, where cells die first. Grower practice treats runoff EC more than about 1.0 mS/cm above the input EC as a sign of salt build-up. **What is the difference between brown leaf edges and brown tips on cannabis?** Brown tips alone on dark green, newer mature cannabis leaves point to salt burn from high EC. Brown margins with a yellow band that start on the lower, older leaves point to potassium deficiency, which controlled trials show yellows the serrated edge before it browns. Brown edges combined with upward cupping at the top of the canopy suggest heat or light stress instead. **How do I flush salt build-up from cannabis pots?** A root-zone flush washes salt build-up out of the medium, not the plant, and is fine at any stage. In coco or rockwool, run 2 to 3 times the container volume of a light solution (EC about 0.4 to 0.8 mS/cm, with calcium and magnesium, pH 5.8 to 6.0) in passes until runoff EC is within about 0.5 mS/cm of input. In soil, use pH-adjusted plain water at pH 6.3 to 6.8. **Short answer.** Brown, crispy tips on leaves that are otherwise dark green is classic salt (nutrient) burn: the root zone is too concentrated, so water is pulled out of the leaf margins first. Measure runoff or reservoir EC and compare it with what you are feeding. If EC is fine, look at watering rhythm (pots drying out concentrates salts), heat and very low humidity, and only then at potassium or boron disorders. ## What's happening Leaf tips and margins are the end of the water path. Anything that limits water supply or concentrates salts there kills those cells first. High root-zone EC lowers the osmotic potential around roots; in drying media the salts concentrate further. Heat and low RH raise transpiration demand and deliver more salts to the tip. True K deficiency starts on *lower* leaves with yellowing of the serrated margin before browning [1]; in DWC flowering trials K deficiency caused scorching of fan-leaf tips and margins and dark lesions on sugar leaves [2]. Boron *toxicity* caused marginal yellowing then browning on lower leaves [1]. ## How to recognise it | Pattern | Most likely | Also consider | |---|---|---| | Tips only, 1–3 mm brown, leaves dark green, newest mature leaves | Mild salt/nutrient burn (EC high) | Feed too strong for seedlings | | Tips plus dark, glossy leaves curling down at tips ("claw") | Excess N plus high EC | See [clawing](https://genetixbay.com/knowledge/diagnosis/clawing-leaves.md) | | Brown margins with yellow band, lower leaves first | Potassium deficiency [1] | Salt build-up, Mn/B toxicity | | Brown edges plus upward cupping at top of canopy | Heat or light stress | Low RH, see [taco](https://genetixbay.com/knowledge/diagnosis/taco-canoeing-leaves.md) | | Brown tips across many plants after a dry spell | Drought plus salt concentration | Irrigation failure | | Brown spots in the leaf body, not just tips | Not tip burn: see [rust spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md) | Ca, P, leaf septoria | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Seedling feed EC | ~0.4–0.8 mS/cm (200–400 ppm500) | Grower practice | | Veg feed EC | ~1.0–1.8 mS/cm (500–900 ppm500; 700–1260 ppm700) | Grower practice; DWC trial used 1.8 dS/m [2] | | Flower feed EC | ~1.6–2.4 mS/cm (800–1200 ppm500) | Grower practice | | Runoff EC vs input | within ~0.5 mS/cm | Grower practice; > 1.0 above input = build-up | | Runoff volume (coco/rockwool, drain-to-waste) | 10–30% of irrigation | Grower practice | | RH, veg | ~55–70% | Grower practice; very low RH worsens tip burn | | Air temperature | photosynthesis declined above ~30 °C (86 °F) in one cultivar | [5] | ## What to check first 1. **Runoff/reservoir EC** versus input EC. The single most useful reading. 2. **Feed strength vs stage.** Seedlings and fresh clones burn at EC that a flowering plant would find light. 3. **Watering rhythm.** Coco or rockwool allowed to dry hard between irrigations concentrates salts; small sips with no runoff build salts. 4. **Climate.** Leaf temperature and RH at the canopy. Hot, dry rooms produce tip burn at moderate EC. 5. **pH.** Rarely the direct cause of tip burn, but out-of-range pH changes which salts accumulate; targets are 5.5–6.0 in hydro and 5.5–6.5 in soilless media [4]. 6. **Pattern by leaf age** to separate K deficiency (old leaves, yellow band first) from burn (newest mature leaves, tips first). ## How to fix it - **Hydro:** dilute or replace the reservoir to a lower EC (drop 0.2–0.4 mS/cm). Top up evaporation losses with plain pH-adjusted water, not full-strength feed. - **Coco/rockwool:** do a **root-zone flush**: run about 2–3× the container volume of a light solution (EC ~0.4–0.8 mS/cm, with Ca and Mg, pH ~5.8–6.0) through in several passes until runoff EC is within ~0.5 mS/cm of the flush input. Then go back to normal feed with consistent runoff. Plain water strips Ca and Mg from coco. - **Soil:** root-zone flush with 2–3× the pot volume of pH-adjusted plain water (pH ~6.3–6.8), slowly and in passes, then check runoff EC and resume normal feeding once the top few cm dry. Do not drown a pot that is already wet. This root-zone flush treats the medium, not the plant, and is fine at any stage (see [the root-zone flush](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). It is not a pre-harvest flush, which is a *Myth* that costs yield and resin. - **Climate:** raise RH towards the stage target, lower leaf temperature, reduce light intensity if leaves are hot. - **True K deficiency (confirmed by pattern and normal EC):** increase K in the feed modestly. Bevan et al. found flowering yield in soilless cannabis was relatively insensitive across moderate K rates, so big K additions are rarely justified [3]. ## How to confirm it worked - New leaves develop without brown tips (5–10 days). - Runoff EC trends toward input EC over 2–3 irrigations. - Existing burnt tips stay burnt; they do not spread inward if fixed. ## Common mistakes - Reading the brown tip as hunger and feeding harder. - Topping up a hydro reservoir with full-strength nutrient; EC creeps up as water evaporates. - Ignoring runoff in coco. No runoff = salts with nowhere to go. - Cutting off every crispy tip; harmless, but pointless. ## Evidence - Salt stress causing marginal and tip necrosis is *Established* horticultural physiology. Specific cannabis EC limits are *Grower practice*. - K deficiency and B toxicity patterns in cannabis are *Established* in controlled trials [1][2]. - Heat effects on cannabis photosynthesis are *Supported* [5]. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Bevan L, Jones M, Zheng Y., 2021. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 4. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 5. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x --- # Brown roots in hydroponics (DWC, RDWC, NFT): a differential > Healthy hydro roots are white to cream and firm. Brown roots that are still firm and odourless are often just stained by nutrients or additives; brown, slimy, smelly roots whose outer layer slips off are root rot, usually Pythium, favoured by warm, oxygen-poor solution. Check solution temperature and dissolved oxygen first, then root texture and smell. - Canonical: https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: DWC, RDWC, NFT, Ebb and flow, Aeroponics - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my DWC roots turning brown?** DWC roots turn brown either from harmless staining or from root rot. Firm, branching, odourless brown roots with new white tips are usually stained by nutrients, organic additives or tannins. Soft, slimy, sour-smelling roots are root rot, most often Pythium, which research has isolated from hydroponic cannabis. Warm, oxygen-poor solution above about 23 to 24 °C is the usual enabler. **What causes brown slimy roots in cannabis hydroponics?** Brown, slimy roots in cannabis hydroponics whose outer layer slips off between the fingers, leaving a thin thread, are Pythium root rot, sometimes with Fusarium. Research on hydroponic cannabis links these pathogens to root browning, stunting, yellowing and daytime wilting. Pythium zoospores swim through the solution, so in recirculating systems the infection spreads quickly between plants. **How can I tell root rot from stained roots in hydro?** To tell root rot from stained roots in hydro, pull a root gently between finger and thumb and smell it. Stained roots stay firm, branch normally, have no odour and still show new white tips, and the plant above is healthy. Rotting roots feel soft and slimy, smell sour, and their outer cortex slides off while the plant wilts by day. **What water temperature prevents root rot in cannabis hydro?** A nutrient solution temperature of about 18 to 22 °C (65 to 72 °F) helps prevent root rot in cannabis hydroponics. Extension guidance shows cool solution holds more dissolved oxygen and reduces Pythium zoospore survival, while research in other hydroponic crops found risk rises above about 23 to 24 °C (73 to 75 °F). Keep dissolved oxygen near saturation as well. **Why does my hydro reservoir smell and my cannabis plants wilt?** A smelly hydro reservoir with wilting cannabis plants usually means root rot in warm, oxygen-poor solution, often with bacterial slime and biofilm. Cool the solution toward 18 to 22 °C, clean or replace air stones and add pump capacity, change the reservoir and clean surfaces. A peroxide dose alone will not fix it if the solution stays warm. **Short answer.** Healthy hydro roots are white to cream, firm and fuzzy with fine root hairs. Brown roots that are still firm, branching and odourless are often just stained by nutrients, organic additives or tannins. Brown, slimy, smelly roots whose outer layer slides off between your fingers are root rot, most often Pythium, sometimes with Fusarium [1][2]. Warm, oxygen-poor solution is the usual enabler. Check solution temperature and dissolved oxygen first, then texture and smell, then act fast: in recirculating systems it spreads through the water. ## What's happening Pythium species produce swimming zoospores that move through nutrient solution and infect root tips. In hydroponically grown cannabis in Canada, Punja and Rodriguez isolated *Pythium dissotocum*, *P. myriotylum* and *P. aphanidermatum*, and *Fusarium oxysporum* and *F. solani*, which caused root browning, crown and pith discolouration, stunting, yellowing and wilting [1][2]. Warm solution holds less oxygen and favours the more aggressive, warm-loving Pythium species (in hydroponic spinach, ~23 °C marked the shift between *P. dissotocum* and *P. aphanidermatum* dominance [4]). Extension guidance for hydroponic crops is to keep solution cool (~20–22 °C) and near oxygen saturation, which reduces zoospore survival and infection [3]. HLVd also accumulates in roots and spreads in shared hydroponic water [5]; it does not brown roots by itself but is worth knowing when plants share a system. ## How to recognise it | Root appearance | Smell | Plant above | Most likely | |---|---|---|---| | White/cream, firm, fuzzy tips | Earthy or none | Healthy | Fine | | Tan/brown but firm, branching, new white tips present | None | Healthy | Staining (nutrients, organics, tannins) | | Brown, soft, slimy; outer cortex slips off leaving a thin thread | Sour, rotten | Wilting by day, yellowing, stunting | Pythium root rot [1] | | Brown roots plus discoloured crown and brown pith in stem | Variable | Wilt, yellowing | Fusarium (often with Pythium) [1] | | Roots matted in a brown, gelatinous mass; biofilm on surfaces | Rotten | Decline | Rot plus bacterial slime; low DO | | Few roots, tips dead, crust on roots | None | Burnt tips | High EC / salt damage | | Browning only where light hits roots, green algae | Earthy | Fine | Light leak into reservoir | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Solution temperature | ~18–22 °C (65–72 °F) | [3]; above ~23–24 °C (73–75 °F) risk rises [4] | | Dissolved oxygen | as close to saturation as possible; ~8 mg/L at ~25 °C | [3] | | pH, hydro | 5.5–6.0 | Grower practice and cited literature | | EC, veg DWC | ~1.2–1.8 mS/cm | Llewellyn et al. used 1.8 dS/m [6] | | Reservoir change interval | 7–14 days | Grower practice; weekly in [6] | | Light into reservoir | none | Algae and root browning | ## What to check first 1. **Solution temperature** at the warmest time of day. 2. **Dissolved oxygen** (meter), or at least: are the air pump and stones working and bubbling evenly? 3. **Smell** of reservoir and roots. 4. **Texture.** Pull a root gently between finger and thumb. Firm = probably staining. Outer layer slips = rot. 5. **New tips.** White new root tips among brown roots = staining or a recovering system. 6. **Plant symptoms.** Daytime wilting, yellowing, stunting on plants with brown roots = rot. 7. **Additives.** Organic teas, molasses, humic/fulvic products stain roots and can feed microbes. 8. **Light leaks** into the reservoir or net pot. ## How to fix it - **Cool the solution** to ~18–22 °C (chiller, insulation, bigger reservoir volume, keep the reservoir off warm floors). - **Maximise oxygen:** clean or replace air stones, add air pump capacity, keep return lines splashing in RDWC. - **Change the reservoir** and clean surfaces of biofilm. - **Trim** dead, slimy root masses with sterilised scissors only if they are clearly detached; leave anything firm. - **Water treatment classes** used in commercial hydroponics: chlorination, ozonation, copper/silver ionisation, UV and oxidisers such as hydrogen peroxide. Extension sources warn that some alter pH or nutrient availability and many harm beneficial microbes [3]. Check local regulations and the label for your crop. - **Beneficial microbes** (e.g. root-colonising *Bacillus* and *Trichoderma* products) are used as a preventive in clean systems; evidence in cannabis is limited. See [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md). - **Isolate** badly affected plants in RDWC by removing them from the shared circuit. - **Sanitise between runs.** See [sanitation and prevention](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md). ## How to confirm it worked - New white root tips appear within 3–7 days. - Plants stop wilting in the afternoon. - The reservoir no longer smells and DO stays near saturation at the warmest point of the day. ## Common mistakes - Panicking over firm, stained roots and dosing harsh oxidisers that kill healthy root tips. - Fixing smell with a peroxide dose but leaving the solution at 26 °C. - Adding sugar-rich organic additives to DWC. - Sharing one recirculating system across mother plants and production plants (pathogens and HLVd spread through water). ## Evidence - Pythium and Fusarium as root pathogens of hydroponic cannabis: *Established* [1][2]. - Temperature and oxygen effects on Pythium: *Established* in other hydroponic crops [3][4]; extrapolated to cannabis. - Water treatment efficacy in cannabis systems: *Grower practice*; little cannabis-specific data. ## Sources 1. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 2. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 3. University of Kentucky Cooperative Extension, E706 (hydroponic Pythium and oxygen management). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 4. Phytopathology 75:333 (1985) abstract on Pythium species and solution temperature in hydroponic spinach. https://www.apsnet.org/publications/phytopathology/backissues/Documents/1985Abstracts/Phyto75_333.htm 5. Adkar-Purushothama CR, Sano T, Perreault JP., 2023. Hop Latent Viroid: A Hidden Threat to the Cannabis Industry. Viruses 15(3):681. https://doi.org/10.3390/v15030681 6. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422 (DWC method reference). https://doi.org/10.3390/plants12030422 --- # Cannabis bud problems: the master decision tree > Check buds for rot first: a brown, dead sugar leaf in a healthy cola, or grey fuzz inside, is Botrytis and needs the bud cut out today. Then look for white powder (powdery mildew), bananas or seeds (a hermaphrodite: a genetic defect, never normal), frass and holes (caterpillars), white or bleached tops (too much light), foxtails, and loose, airy buds (usually too little light at the bud site). Most bud problems are decided by where on the plant they appear and what the canopy climate was. - Canonical: https://genetixbay.com/knowledge/diagnosis/bud-problems-decision-tree.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Flower, Ripening, Harvest · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why does my cannabis bud have a brown dead leaf sticking out?** A single brown, dry sugar leaf poking out of an otherwise healthy cannabis cola is the classic first sign of Botrytis bud rot, which starts deep inside dense buds. Gently pull the bud apart: a brown, mushy core or grey fuzz confirms it. Cut the whole bud out at least 5 cm below the rot, bag it in the room, and drop relative humidity below 50%. **Are bananas in late flower normal?** No. Bananas (exposed anthers, also called nanners) in late cannabis flower are a hermaphrodite trait and a sign of unstable genetics from poor breeding, not normal plant behaviour. Stress such as light leaks or heat can reveal the trait, but stable lines do not produce them. Remove the anthers or harvest early to limit seeding, never breed from the plant, and note the cultivar in your journal. **Why are the top buds on my cannabis turning white?** Top cannabis buds that turn white or bone-coloured while lower buds stay green are usually light bleaching: the colas nearest the fixture receive more light, and often more heat, than the tissue can handle. Measure PPFD at the tops and raise or dim the light. Bleached tissue does not recover. White fuzz or powder you can rub off is mildew, not bleaching. **Why are my cannabis buds airy and loose?** Airy, loose cannabis buds are most often caused by too little light at the bud site: lower and inner buds may get only a fraction of the canopy-top intensity. Heat above about 30 °C, harvesting too early, root-zone or feeding problems and cultivars that naturally grow loose flowers are the other causes. Measure PPFD at the bud itself, not at the top of the plant. **Why are there seeds in my cannabis buds with no males around?** Seeds in sinsemilla cannabis buds with no male in the room almost always come from a hermaphrodite plant in the same room, often anthers hidden deep in the buds, or from pollen brought in on clothes or through intake air. Search every plant for anthers, then review light leaks and stress. Seeds from a hermaphrodite carry the trait and should not be grown on. **Why are my pistils turning brown early?** Cannabis pistils turning brown early, in the first half of flower, are usually physical or environmental: touching or handling, heat and low humidity near the light, light stress at the tops, or pollination, which browns pistils within days. Ripeness is judged by the trichomes, not the pistils. Check canopy temperature and PPFD at the tops, and look for seeds forming in the calyxes. **Short answer.** Check for rot first, every time. A single brown, dead sugar leaf in an otherwise healthy cola, or grey fuzz inside a bud, is Botrytis bud rot: cut that bud out today [1][2][3]. Then look, in order, for white powder (powdery mildew), bananas or seeds (a hermaphrodite), frass and holes (caterpillars), bleached white tops (too much light), foxtails, and loose, airy buds, which usually got too little light at the bud site [5][6]. ## What's happening? Buds are the most valuable and the most vulnerable tissue on the plant. Dense colas trap moisture, so fungi that need free water or high humidity, chiefly *Botrytis cinerea*, start from the inside and are invisible until late [1][2]. Powdery mildew can colonise sugar leaves and bracts in still, humid canopies [1][10]. Buds sit closest to the light, so excess light and heat show there first as bleaching and foxtailing [5]. Flowers are also where sex expression shows: anthers in a female inflorescence mark a hermaphrodite, which Punja and Holmes documented forming viable pollen and seed [4]. Finally, bud size and density depend on the light each bud site receives; yield rose roughly in proportion to canopy PPFD in controlled indoor trials [5][6]. The GenetixBay position on hermaphrodites is firm: they are mainly a breeding defect that stress *reveals*, not normal cannabis behaviour, and late-flower bananas are not normal. See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). ## Which bud problem do I have? (the decision tree) 1. **Is any bud soft, brown inside, or showing grey fuzz?** Look for a single dry, brown sugar leaf or a bract cluster that turns tan in an otherwise green cola. Pull it gently: if it comes away easily with a brown, mushy core, it is **Botrytis bud rot** [2][3]. **Critical urgency.** Go straight to the fix below. 2. **Is there white powder on sugar leaves or bracts that smears off?** → **Powdery mildew** in the buds [1][10]. If you also see it on fan leaves, it moved up. See [white or grey coatings](https://genetixbay.com/knowledge/diagnosis/white-grey-coatings-decision-tree.md). 3. **Is there pinkish-white mould with a brown core, especially after high humidity?** → possibly **Fusarium bud rot** [1]. Treat as bud rot and send a sample to a lab if it recurs. See [Fusarium](https://genetixbay.com/knowledge/diseases/fusarium.md). 4. **Are there holes, small dark pellets (frass), webbing or a caterpillar inside?** → **Caterpillars**, mostly outdoors and in greenhouses [8]. Their wounds and frass start rot, so check for step 1 at the same spot. See [caterpillars](https://genetixbay.com/knowledge/pests/caterpillars.md). 5. **Are there yellow or pale green banana-shaped anthers, or pollen sacs among the pistils?** → **Hermaphrodite** [4]. See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). 6. **Are there seeds forming (swollen calyxes splitting to show a seed) but no anthers you can find?** → hidden **hermaphrodite** flowers on this or another plant, or pollen brought in. Search every plant, including inner buds ([seeds in buds](https://genetixbay.com/knowledge/answers/why-are-there-seeds-in-my-buds.md)). 7. **Are only the top colas nearest the light white, bone or pale yellow, with no fuzz?** → **light bleaching**, often with heat [5]. Measure PPFD and leaf temperature at the tops. 8. **Are new spires of calyxes growing out of mature buds?** - Only on the tops nearest the light → **stress foxtailing** (heat and light). - Evenly through the canopy, including shaded buds → **cultivar trait**. See [foxtails](https://genetixbay.com/knowledge/diagnosis/foxtails.md). 9. **Are pistils browning in the first half of flower?** → handling, heat or light stress at the tops, or pollination ([pistils turning brown early](https://genetixbay.com/knowledge/answers/pistils-turning-brown-early.md)). 10. **Are buds loose, airy or larfy?** - Mostly lower and inner sites → **too little light at the bud site** [5][6][9]. - Whole plant, with hot canopy → **heat** above ~30 °C (86 °F) [7]. - Whole plant, with yellowing, stunting or brown roots → a **root-zone or feeding** problem; go to [root problems](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md). - Cultivar known for open, sativa-style flowers → **genetics**. 11. **Are buds ripening slowly, still putting out white pistils at the breeder's stated finish?** → count from the flip and add the ~10–14 day transition before flowering really starts (house position); also check for light leaks, which can delay ripening, and low light. See [flip-to-flower transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md). 12. **Do dried buds smell of hay or ammonia?** → that is a drying or curing problem, not a plant problem: drying too fast or too wet, or bacterial activity in the jar. See [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) and [curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md). ## How do I tell bud problems apart? (differential table) | Pattern | Most likely | Rule out first | Key test | |---|---|---|---| | One brown, dry sugar leaf in a green cola | Botrytis bud rot [2] | Mechanical damage, normal leaf ageing | Pull the bud apart: mushy brown core, grey spores | | White powder on sugar leaves | Powdery mildew [10] | Trichomes, residue | Rub test; 30–60x lens shows hyphae, not glass-bead heads | | Pink-white mould, brown core | Fusarium bud rot [1] | Botrytis | Lab culture | | Holes, dark pellets, webbing in buds | Caterpillars [8] | Spider-mite webbing | Open the bud: larvae and frass; check for rot nearby | | Banana-shaped yellow anthers | Hermaphrodite [4] | Pistils, bract tips | Lens: anthers hang from a short stalk and may shed pollen | | Seeds, no anthers seen | Hidden herm or stray pollen | — | Inspect every plant, inner buds included | | White or bone tops nearest the light | Light bleaching [5] | PM, thrips silvering | PPFD at the tops; nothing rubs off | | Calyx spires on top colas only | Stress foxtailing | Cultivar trait | Are shaded buds foxtailing too? | | Calyx spires everywhere | Cultivar trait | Heat stress | Same as above | | Brown pistils in weeks 2–5 | Handling, heat, pollination | Ripeness (it is not) | Check calyxes for seeds; canopy temperature | | Airy lower buds | Low PPFD at the bud [5][9] | Root-zone problem | PPFD measured at the bud | | Airy everywhere, hot canopy | Heat [7] | Low light | Leaf temperature at the tops | | Still pushing pistils at stated finish | Counted from the wrong day; light leaks | Low light | Days since flip vs breeder time + ~10–14 days | ## Which numbers matter? | Parameter | Target or threshold | Notes | |---|---|---| | RH, late flower | Below ~50% | Botrytis prevention [2][3] | | Botrytis range | ~10–27 °C (50–81 °F), optimum near 20 °C (68 °F) | With high RH or free water [1][2] | | Lights-off dew risk | Keep leaf temperature above the dew point; avoid RH spikes at lights-off | See [VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md) | | PPFD at canopy top, flower | ~800–1,200 µmol/m²/s without added CO₂ | Grower practice; yield kept rising to ~1,800 in one trial [5] | | PPFD where bleaching appears | Often reported above ~1,200–1,500 µmol/m²/s at the tops, worse with heat | Grower observation. | | Canopy air temperature, flower | ~22–28 °C (72–82 °F) | Photosynthesis declined above ~30 °C in one cultivar [7] | | Cut margin for rotted buds | At least 5 cm (2 in) below visible rot | Grower practice; extension advises removing infected material [3] | | Flip-to-flower transition | ~10–14 days before flowering really begins | House position; see [flip transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) | ## What should I check first? 1. **Rot check.** Run your eyes over every cola for a dead sugar leaf; squeeze large colas gently for soft spots. Do this every 2 days from about week 5 of flower. 2. **Climate log.** Night-time RH and the RH spike at lights-off are the usual Botrytis trigger. 3. **Lens check** of sugar leaves for powder, anthers and insects. 4. **Light at the tops and at the lower buds.** A PAR meter, or a calibrated phone method ([measure PPFD without a PAR meter](https://genetixbay.com/knowledge/answers/measure-ppfd-without-a-par-meter.md)). 5. **Leaf temperature at the tops** with an IR thermometer. 6. **Light leaks** during the dark period (see [light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)). 7. **Root zone and feed** only if the whole plant is affected. ## How do I fix each one? - **Botrytis bud rot (critical).** Cut the bud out at least 5 cm (2 in) below visible rot with a sanitised blade, bag it inside the room before carrying it out, and wipe the blade between cuts. Lower RH below ~50%, raise air movement through the canopy, and remove leaves that trap moisture inside dense colas. If more than a few colas are infected near the finish, harvest early; it is better than losing the crop. Never consume rotted material [2][3]. See [bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md). - **Powdery mildew in buds.** No clean fix in flower; sprays land on what you consume. Remove affected buds, harvest affected plants early if needed, and fix airflow and RH for the next run [10]. See [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md). - **Caterpillars.** Hand-pick, open suspect buds, and use Bt (*Bacillus thuringiensis* var. *kurstaki* or *aizawai*) while larvae are small, where legal and within its label; it must be eaten and breaks down in sunlight within days [8]. Netting excludes moths outdoors. - **Hermaphrodite.** Remove the anthers with tweezers if few, mist them first so pollen does not fly, or harvest early if they keep coming. Fix light leaks and big stresses. Do not breed from the plant, and record the cultivar. See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) and [preventing hermaphrodites](https://genetixbay.com/knowledge/answers/how-to-prevent-hermaphrodites.md). - **Light bleaching.** Raise the fixture or dim it until top-of-canopy PPFD is back in the ~800–1,200 µmol/m²/s range, and bring leaf temperature down. Bleached tissue does not recover; harvest it with the rest. - **Stress foxtails.** Same as bleaching: reduce light and heat at the tops. Cultivar foxtails need no fix. - **Brown pistils early.** Stop touching buds; lower canopy heat; check for pollination. - **Airy buds.** Lift light to the lower sites by raising the light-reaching part of the canopy (training, SCROG), removing sites that will never get light, and checking PPFD at the bud [5][9]. Keep feeding at stage strength through to harvest: pre-harvest flushing is a *Myth* that starves the plant while it packs on final weight and resin (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). - **Slow ripening.** Count from the flip and add the transition; fix light leaks; judge ripeness by trichomes ([trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md)). ## How do I know the fix worked? - **Botrytis:** no new brown sugar leaves or soft spots on 2-day inspections; RH log stays below ~50% at night. - **PM:** no new powder on sugar leaves for 10–14 days. - **Caterpillars:** no new frass or holes after 7 days. - **Herm:** no new anthers on 2-day inspections; no new seeds swelling. - **Bleaching and foxtails:** new calyxes at the tops stay green and tight. - **Airy buds:** next run, lower-bud PPFD readings rise and dry weight of those sites increases. ## What are the common mistakes? - Waiting "a few more days" on a rotted cola. Botrytis spores spread to neighbouring buds. - Mistaking trichome frost on sugar leaves for mildew, or mildew for frost. Use a lens. - Calling late-flower bananas "normal". They are a hermaphrodite trait. - Starting a pre-harvest flush to "fix" anything. It fixes nothing in the bud and costs yield and resin. - Turning the light up to fix airy lower buds when the tops are already bleaching. Fix light distribution, not intensity. - Judging ripeness by pistil colour instead of trichomes. - Spraying anything on buds in flower. ## How strong is the evidence? - Botrytis and PM in cannabis flowers, and the conditions that favour them, are *Established* [1][2][3][10]. - Hermaphroditism with viable pollen in female cannabis inflorescences is *Established* [4]; the GenetixBay reading that herm-prone lines come mainly from poor breeding practice, with stress revealing susceptibility, is the house position, consistent with observed cultivar differences in that study. - Yield and bud size rising with light at the bud is *Established* [5][6]; lower-canopy buds receiving less light and lower quality is *Supported* [9]. - Light-bleaching and stress-foxtail thresholds are *Grower practice*; no controlled cannabis study gives a threshold. - Caterpillar damage and Bt use are *Established* in hemp extension [8]. ## Sources 1. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker 3. Utah State University Extension. Hemp bud rot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot 4. Punja ZK, Holmes JE., 2020. Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences: Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 5. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 6. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 7. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x 8. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 9. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 10. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew --- # Cannabis lookalike problems: how to tell them apart > Many cannabis problems look alike in a photo. The ones growers confuse most are Ca vs Mg vs K, nitrogen toxicity vs overwatering claw, light bleaching vs Mg deficiency, spider-mite stippling vs calcium spots, heat vs light stress, Pythium vs low dissolved oxygen, Fe vs Mn, and nutrient burn vs K deficiency. Each pair separates on three things: where on the plant it started, the exact pattern, and one cheap test (a lens, a runoff EC reading, a root check, a light meter or a lifted pot). - Canonical: https://genetixbay.com/knowledge/diagnosis/lookalikes.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I tell calcium, magnesium and potassium deficiency apart in cannabis?** Look at where it starts and the pattern. Magnesium yellows between the veins of old, lower leaves while veins stay green. Potassium yellows then browns the margins and serrated tips of old leaves. Calcium hits new or recently matured growth with distorted leaves and brown spots, and is usually a delivery problem (pH, low transpiration, root damage) rather than an empty feed. Check root-zone pH before dosing any of them. **Is my cannabis clawing from too much nitrogen or overwatering?** Nitrogen toxicity gives very dark, glossy green leaves whose tips hook down like a claw, on a plant that is otherwise vigorous, with high runoff EC and a recent feed increase. Overwatering gives drooping, swollen-looking leaves that curl down along their whole length, a heavy pot, a medium still wet two to three days after watering and perkier leaves once it dries. Lift the pot and read runoff EC to separate them. **Is it light bleaching or magnesium deficiency on my cannabis?** Light bleaching is pale-to-white leaves and bracts only at the tops nearest the lamp, often with green veins at first, while lower leaves are fine. Magnesium deficiency starts on old, lower leaves with green veins and yellow blades and climbs upward. If the damage sits where PPFD is highest, measure it and raise or dim the light; if it starts at the bottom, check pH and the Mg in the feed. **Are these tiny spots from spider mites or calcium deficiency?** Spider mite stippling is hundreds of pin-prick pale dots, usually starting near the leaf midrib, with mites, eggs or fine silk visible underneath through a 10 to 30x lens. Calcium spots are fewer, larger, irregular tan-to-brown patches, often with a yellow halo, on new or recently matured leaves and with no insects underneath. A lens check of the leaf underside settles it in under a minute. **How do I tell Pythium root rot from low dissolved oxygen in hydro?** Low dissolved oxygen gives limp, tan roots and afternoon wilting that recover within a day or two once you cool the solution and add air. Pythium gives brown, slimy roots whose outer sheath slips off leaving a thin white thread, a sour or rotten smell, and decline that continues after oxygen is fixed. Warm solution above about 23 °C (73 °F) drives both, and low oxygen often comes first. **Is it iron or manganese deficiency on my cannabis?** Both cause interveinal yellowing on new growth with green veins. Iron chlorosis is smooth, pale and concentrated on the very newest leaves, which can turn almost white. Manganese chlorosis is more netted, sits a little lower on the upper and middle leaves, and develops small tan spots between the veins. Both are usually caused by high root-zone pH, so check pH before adding either. **Is brown leaf edge nutrient burn or potassium deficiency?** Nutrient burn starts as dry brown tips on the newest mature leaves and creeps back along the margin, with high input or runoff EC. Potassium deficiency starts on older, lower leaves as yellow margins and serration tips that then go tan, with a normal or low EC. A runoff EC reading compared with input EC usually separates them: runoff well above input means salt, not hunger. **Short answer.** Most misdiagnoses happen between a handful of pairs that look the same in a photo. They almost always separate on three things: **where the symptom started** (old leaves, new leaves, top of the canopy, whole plant), **the exact pattern** (between the veins, margins, tips, spots, stipples), and **one cheap test**: a 10–30× lens under the leaf, a runoff EC and pH reading, a root check, a light meter, or simply lifting the pot. This page puts each pair side by side. ## What's happening Cannabis has a limited vocabulary of distress. Chlorophyll fades (yellowing), cells die (brown necrosis), leaves change angle (clawing, tacoing, drooping), and pigments show through (purple, red). Very different causes speak that same vocabulary. The way to separate them is the clinician's method in [how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md): location first, because nutrient mobility decides whether a shortage shows on old or new growth [3]; then pattern; then the test that rules one side out. Two controlled cannabis studies give us the reference pictures for single-element shortages: Cockson et al. in soilless sand culture [1] and Llewellyn et al. in deep-water culture through flower [2]. They do not always agree on timing, and several deficiencies (Fe, Mn, Mo) produced weak or no symptoms in the shorter hydroponic flower trial [2], so treat any "textbook" picture as a starting point, not proof. ## How do I tell calcium, magnesium and potassium deficiency apart? **Magnesium yellows between the veins of old leaves; potassium burns the margins of old leaves; calcium distorts and spots new or recently matured leaves.** Mg and K are mobile and are stripped from old leaves first; Ca moves only in the transpiration stream and cannot be remobilised, so its damage lands on growth that is expanding while supply is short [1][3]. | Feature | Calcium (Ca) | Magnesium (Mg) | Potassium (K) | |---|---|---|---| | Where it starts | New and recently matured leaves, growing tips; in DWC flower, also lower fan leaves from week 3 [2] | Old, lower fan leaves [1][2] | Old, lower fan leaves; in DWC flower, sugar leaves early [2] | | Pattern | Irregular brown spots with yellow halos, distorted or cupped new leaves, dead growing tips in severe cases [1] | Interveinal yellowing, veins and midrib stay green [1][2] | Yellow margins and serration tips, moving inward, then tan crispy scorch [1] | | Colour | Rust to tan spots | Lemon yellow blade, green "skeleton" | Yellow edge, then tan to brown | | Speed | Fast in high humidity or after root damage | Slow, climbs upward over 1–3 weeks | Slow; shows from flower week 3 in DWC [2] | | Typical readings | Low root-zone pH, RH above ~70%, unbuffered coco, RO water | Low root-zone pH, excess K or Ca, RO water | Low input EC, or salt stress mimicking it | | Healthy leaf tissue | ~1.0–2.5% Ca | ~0.40–0.81% Mg [1] | ~1.8–2.9% K [1] | | The separating test | Look at *which* leaves: new growth means Ca, old growth means Mg or K. Then read runoff pH | Interveinal and lower: Mg | Margin and lower: K | | Fix | Correct pH, raise transpiration (VPD 0.8–1.2 kPa), Ca to ~150–200 mg/L | Correct pH, then magnesium sulfate to ~40–70 mg/L Mg | Confirm EC is not high, then raise K toward ~175–240 mg/L | **Why the confusion.** All three can end in brown, dead leaf tissue, and all three are commonly induced rather than real shortages. Excess K suppresses Mg and Ca uptake, and excess Ca suppresses Mg and K: cation antagonism is one of the few interactions that reliably matters in practice [3][15]. Cal-Mag thrown at every spot often makes K worse. The house position applies: LEDs do not create a Cal-Mag need; demand is driven by cultivar, water source, coco cation exchange and pH (see [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)). ## Is it nitrogen toxicity or overwatering claw? **Nitrogen toxicity makes leaves very dark and glossy with downward-hooked tips on an otherwise vigorous plant; overwatering makes leaves droop and curl down along their whole length on a heavy, wet pot.** The first is a feed problem confirmed by EC and the feed record; the second is a root-oxygen problem confirmed by weight and by recovery as the pot dries. | Feature | Nitrogen toxicity | Overwatering | |---|---|---| | Where it starts | Upper and middle leaves first, then whole plant | Whole plant at once, usually hours after watering | | Pattern | Leaf *tips* hook downward ("claw"); leaf blade stays firm; long petioles; soft lush growth | Whole leaf droops from the petiole and curls down; leaves look swollen and firm but hang | | Colour | Very dark, almost blue-green, glossy | Normal to slightly pale green; yellowing follows if it persists | | Speed | Builds over days after a feed increase | Appears within hours of watering; eases as the pot dries | | Readings | High input or runoff EC; ammonium above ~30% of total N is a known cause of toxicity in cannabis (see [nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md)) | Normal EC; pot still heavy 2–3 days after watering; medium smells sour if chronic | | Separating test | Read runoff EC and check the feed record | Lift the pot: heavy and wet means overwatering | | Fix | Cut N 20–30% or drop to a lower-N formula; if runoff EC is high, do a root-zone flush with pH'd water | Let the pot dry until noticeably light; improve drainage and air (perlite, fabric pots); water less often, not less per watering | | Confirm | New leaves emerge mid-green and flat in 5–7 days | Leaves lift within a day of the medium drying | **Watch for the third option.** A waterlogged root zone and an N-heavy feed often occur together in heavy-fed soil. Twisted, clawed new growth with glassy, shiny leaflets is neither of these: think broad mites (see below and [clawing leaves](https://genetixbay.com/knowledge/diagnosis/clawing-leaves.md)). ## Is it light bleaching or magnesium deficiency? **Light bleaching is pale-to-white tissue confined to the canopy tops closest to the fixture; magnesium deficiency starts on the lowest, oldest leaves and climbs.** The location settles it before any test does. | Feature | Light bleaching | Magnesium deficiency | |---|---|---| | Where it starts | Top colas, upper fan and sugar leaves, directly under the hottest part of the fixture | Old, lower fan leaves [1][2] | | Pattern | Leaves and bracts fade from the centre or tips; early leaves may keep green veins, which is why it gets mistaken for Mg | Crisp interveinal yellowing with green veins and midrib | | Colour | Pale yellow to bone white, bracts and pistils included | Lemon yellow; later necrotic patches | | Speed | Days after a light raise, a canopy gaining height or a heat spike | Weeks, steady upward progress | | Readings | Top-canopy PPFD high for the conditions; leaf temperature well above air | Low root-zone pH, high K or Ca, RO water | | Separating test | Measure PPFD at the tallest top versus a healthy spot lower down; check whether lower leaves are fine | Check the bottom third of the plant: if it is clean, it is not Mg | | Fix | Raise or dim the light 10–20%, cool the canopy, even out tall colas | Correct pH; magnesium sulfate to bring Mg to ~40–70 mg/L | **The numbers.** Cannabis yield kept rising up to about 1,800 µmol/m²/s in a well-run trial [10], so bleaching usually means *too much light for the conditions*: heat, low CO₂, sick roots or a sensitive cultivar. In one gas-exchange study, net photosynthesis fell when high temperature and high light were combined [11]. Bleached tissue does not recover; judge the fix by new growth. See [heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md). ## Is it spider mite stippling or calcium spotting? **Spider mite stippling is many pin-prick pale dots with mites, eggs or silk under the leaf; calcium spots are fewer, larger, irregular brown patches with no insects underneath.** Flip the leaf and look through a lens before you touch the feed. | Feature | Two-spotted spider mite | Calcium spotting | |---|---|---| | Where it starts | Often lower and inner leaves, near the midrib and leaf base; hot, dry, still spots in the room [7] | New and recently matured leaves; in DWC flower, lower fan leaves [1][2] | | Pattern | Hundreds of tiny pale-yellow or white specks (stipples), merging into a speckled, dusty look; fine webbing at heavy infestations [7] | A few to dozens of irregular spots 1–5 mm across, often with yellow halos, plus margin necrosis or distorted new leaves | | Colour | Pale yellow to white stipples, later bronze or grey leaves | Tan to rust brown | | Speed | Explosive in heat: populations can double in days above ~27 °C (80 °F) | Steady; tracks humidity, pH and root health | | Readings | Low RH, high temperature | Low pH, high RH (low transpiration), RO or unbuffered coco | | Separating test | 10–30× lens on the leaf underside: moving 0.5 mm mites, round eggs, cast skins, silk [7] | Lens shows nothing alive; spots are dead tissue | | Fix | Isolate, wash or treat in veg, release predatory mites; see [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md) | Correct pH and VPD; Ca ~150–200 mg/L; buffer coco | Thrips damage is the other stippling lookalike: silvery, papery streaks with tiny black faecal dots rather than round stipples ([thrips](https://genetixbay.com/knowledge/pests/thrips.md)). Septoria spots have dark margins and, through a lens, tiny black fruiting bodies ([septoria](https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.md)). ## Is it heat stress or light stress? **Heat stress shows wherever the air or leaf is hottest, including leaves far from the lamp; light stress shows only where the light is most intense, usually the top of the canopy directly under the fixture.** The two often arrive together, because high light raises leaf temperature. | Feature | Heat stress | Light stress (excess PPFD) | |---|---|---| | Where it starts | Whole upper canopy and any hot pocket: near walls, drivers, poor airflow; also leaves far from the fixture | The tops nearest the fixture's peak PPFD, often the centre of the footprint | | Pattern | Leaves taco (fold upward along the midrib) or canoe, edges curl up, droop by late afternoon; foxtailing on colas | Leaves point up toward the light ("praying" if mild), then pale and bleach; bracts bleach | | Colour | Green with crispy, curled edges; brown edges if severe | Pale yellow to white, often with green veins early | | Speed | Hours; worst at the end of the photoperiod | Days | | Readings | Air above ~30 °C (86 °F), leaf VPD above ~1.5–1.7 kPa, leaf temperature above air | High PPFD at the top; leaf temperature may be normal under LED | | Separating test | IR thermometer on the leaves and a thermometer at canopy height: hot leaves = heat | PAR meter at the tops: high PPFD with normal leaf temperature = light | | Fix | Lower air temperature, raise RH to bring VPD to 0.8–1.5 kPa, add airflow across the canopy | Dim or raise the light; level the canopy | Under LEDs, leaf temperature at a given air temperature is lower than under HPS because there is less radiant heat [9], so growers often run warmer air under LED. A leaf that is hot to the IR gun under LED usually means poor transpiration (dry air, still air, sick roots), not radiant heat. ## Is it Pythium root rot or low dissolved oxygen? **Low dissolved oxygen gives limp, tan roots and afternoon wilting that recover within a day or two of cooling and aerating the solution; Pythium gives brown, slimy roots whose outer sheath slips off, a rotten smell, and a decline that continues after oxygen is fixed.** Warm solution drives both: oxygen solubility falls as temperature rises, and Pythium thrives in warm, oxygen-poor water [5][6]. | Feature | Low dissolved oxygen | Pythium root rot | |---|---|---| | Where it starts | Whole root mass, worst at the bottom of the reservoir | Patches of root, spreading; often after a hot spell | | Root look | Tan or cream, limp, fewer fuzzy white tips; no slime | Brown, soft, slimy; outer cortex slides off leaving a thin white stele [4] | | Smell | Flat or slightly stale | Sour, rotten, "swampy" | | Plant above | Mild wilting in the afternoon, slow growth | Wilting by day, yellowing lower leaves, stunting [4] | | Speed | Hours after a pump or air failure; recovers in 24–48 h once fixed | Days to a week; progresses despite aeration | | Readings | Solution above ~23–24 °C (73–75 °F), DO below ~6 mg/L (grower threshold) | Same warm solution; pH may drift oddly | | Separating test | Fix air and temperature first, then re-check roots in 48 h: new white tips mean it was oxygen | Pull a root and rub it: the sheath slipping off is the hallmark [4] | | Fix | Air stones and pump checked, solution to 18–22 °C (65–72 °F), clean reservoir | Same, plus remove rotted roots, sanitise or establish beneficial microbes; see [root rot](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) | House position: a beneficial-microbe reservoir is preferred to a half-hearted sterile one; a sterile reservoir works only if you commit to it fully. Fusarium can join Pythium in hydro cannabis [4]; brown pith in the stem base points to it ([fusarium](https://genetixbay.com/knowledge/diseases/fusarium.md)). Light leaking into the reservoir browns roots too, with algae and no slime ([root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)). ## Is it iron or manganese deficiency? **Both cause interveinal yellowing on new growth; iron chlorosis is smooth, pale and concentrated on the very newest leaves, while manganese chlorosis is netted, sits on the upper-middle leaves and develops small tan spots.** Both are usually caused by high root-zone pH, not an empty bottle [1][3]. | Feature | Iron (Fe) deficiency | Manganese (Mn) deficiency | |---|---|---| | Where it starts | Newest, still-expanding leaves at the shoot tips [1] | Upper and central foliage, a little below the tip [1] | | Pattern | Starts as yellowing at the base of new leaflets, then smooth interveinal chlorosis; fine veins stay green [1] | Netted interveinal chlorosis spreading out from the midrib; tan necrotic spots develop between veins [1] | | Colour | Pale yellow to nearly white in severe cases | Bright yellow mesh, then tan flecks | | Speed | Slow: about 9 weeks in sand culture [1] | About 6 weeks in sand culture [1] | | Readings | Root-zone pH above ~6.5 in soilless, alkaline water, cold or waterlogged roots, very high P | Same high pH; excess Fe can compete with Mn | | Separating test | Read root-zone pH first; a leaf tissue test separates them reliably (healthy ranges in [12]) | As left; spots on the yellowed tissue favour Mn | | Fix | Bring pH to 5.5–6.2 (hydro) or 6.2–6.8 (soil); use a chelate matched to pH (EDTA ≤ ~6.5, DTPA ≤ ~7.5, EDDHA above) at 1.5–3 mg/L Fe | Same pH correction; Mn ~0.3–0.8 mg/L | In a DWC flowering trial, withholding Fe or Mn produced weak or no symptoms and no significant yield loss, probably because plants carried reserves from veg [2]. If you see sharp new-growth chlorosis in a short hydro run, rule out pH, a cold or waterlogged root zone and light bleaching before blaming the feed. Zinc and sulfur are the other new-growth lookalikes: Zn gives small, narrow leaves with margin necrosis; S yellows the whole new leaf evenly rather than between the veins ([yellow new growth](https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.md)). ## Is it nutrient burn or potassium deficiency? **Nutrient burn starts as dry brown tips on the newest mature leaves with high EC; potassium deficiency starts as yellowing margins and serration tips on old, lower leaves with normal or low EC.** A runoff EC reading against input EC usually separates them in one watering. | Feature | Nutrient (salt) burn | Potassium deficiency | |---|---|---| | Where it starts | Tips of the newest fully expanded leaves, then down the margin; whole plant | Old, lower leaves first [1] | | Pattern | A thin, dry, brown tip of a few mm, often slightly twisted; a yellow line ahead of the brown | Yellow along the margin and saw-teeth, moving inward, then tan crispy scorch [1] | | Colour | Brown tips on otherwise dark-green leaves | Yellow then tan; leaf otherwise fades | | Speed | Days after a feed increase or as runoff EC climbs | Weeks | | Readings | Runoff EC well above input (more than ~0.5 mS/cm above is a common warning sign [16]); high input EC | Low input EC, low K in the recipe, or high Na/Ca/Mg competing | | Separating test | Pour-through or runoff EC versus input EC | Normal EC plus the old-leaf margin pattern; a tissue test confirms (healthy ~1.8–2.9% K [1]) | | Fix | Lower feed EC 10–20%; if runoff is far above input, a root-zone flush with pH'd water to clear salts | Raise K toward ~175–240 mg/L in veg; check Na and coco buffering | The root-zone flush here treats the medium, not the plant, and is valid at any stage. A pre-harvest "flush" is a different thing and is a *Myth* that costs yield and resin ([flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). See [brown or burnt tips](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md). ## Is my plant overwatered or underwatered? **Lift the pot: a heavy pot with drooping leaves is overwatered, a light pot with limp, papery leaves is underwatered.** Both droop, but the leaves feel different and the timing is opposite. | Feature | Overwatering | Underwatering | |---|---|---| | Leaf feel | Firm, swollen, curled down along the length | Thin, limp, papery, hanging from the petiole | | Timing | Within hours of watering; improves as it dries | Before watering; recovers within an hour or two of water | | Pot | Heavy, wet 2–3+ days after watering | Light; medium pulling away from the pot wall | | Long-term signs | Yellowing lower leaves, fungus gnats, sour smell, root rot | Crispy edges, slow growth, salt concentration | | Fix | Water less often, improve drainage and air | Water thoroughly to 10–20% runoff, then on a schedule | A plant that wilts while the medium is wet is neither: check the roots for rot or the stem base for wilt disease ([drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md)). ## Is it nitrogen deficiency or normal late-flower fade? **Uniform yellowing from the bottom up in the last 2–3 weeks of flower is normal senescence; the same pattern in veg or before about week 5–6 of flower is nitrogen shortage or a root problem.** Timing is the test. | Feature | Nitrogen deficiency | Late-flower fade | |---|---|---| | When | Veg or early to mid flower | Final 2–3 weeks of flower | | Pattern | Pale to lemon yellow, whole leaf, climbing fast; red-brown petioles in severe DWC cases [2] | Slow yellowing and sometimes purpling of fan leaves; sugar leaves and buds keep developing | | Buds | Small, slow | Swelling, trichomes maturing | | Fix | Rule out roots and pH, then raise N 10–20% | Keep feeding P, K, Ca, Mg and micros; taper N; no pre-harvest flush | The GenetixBay approach is to taper nitrogen in late flower while keeping everything else fed, which per-element dosing makes possible ([yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md)). ## Is twisted new growth broad mites, heat or calcium? **Broad and russet mites twist and glaze the newest growth with no visible insect; heat curls the upper canopy where it is hottest; calcium (or boron) distorts new growth alongside spotting and pH or humidity problems.** Broad mites are about 0.2 mm long and need 20× or more to see, or a microscope [8]. | Feature | Broad / russet mites | Heat stress | Calcium or boron shortage | |---|---|---|---| | Where | Shoot tips and newest leaves, spreading plant to plant | Top of the canopy, hot spots | New growth across the plant | | Pattern | Leaves twisted, cupped, glossy or glassy, edges curled down; bronzed, rusty stems on russet mites; buds stall [8] | Taco and canoe, edges up; fine at night | Distorted, cupped new leaves with brown spots; dead tips | | Spread | Moves between touching plants | Follows the heat map | Follows pH and humidity | | Test | 40–60× magnification on the newest leaf and petiole | IR thermometer and canopy thermometer | Runoff pH, RH reading | | Fix | Isolate; predatory mites or approved treatment; see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) | Cool the canopy | Correct pH, VPD, Ca or B supply | ## Is it septoria leaf spot or a calcium or phosphorus spot? **Septoria spots are round to angular with dark brown margins, start on lower leaves in humid conditions, and show tiny black fruiting bodies through a lens; nutrient spots have no fruiting bodies and follow pH and feed.** [14] | Feature | Septoria | Ca spots | P shortage | |---|---|---|---| | Where | Lower leaves, moving up in wet, crowded canopies [14] | New and recently matured leaves | Old, lower leaves | | Look | Pale yellow spots that turn brown with darker margins, often with a yellow halo; black specks (pycnidia) inside [14] | Irregular rust spots, yellow halo, no specks | Dark, dull, olive to purple-brown blotches; dark leaves overall | | Test | 10–30× lens for pycnidia; spots on many leaves at once after leaf wetness | Lens shows nothing; pH and RH readings | Root-zone pH and temperature; feed record | | Fix | Remove affected leaves, cut leaf wetness and RH, improve airflow; see [septoria](https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.md) | Correct pH and VPD | Correct pH, warm cold roots; P is rarely truly short | ## Is it powdery mildew or residue and trichomes? **Powdery mildew is a flat, white, flour-like coating that wipes off and comes back in circles on leaf surfaces; residue does not regrow, and trichomes are stalked glands you can see as tiny mushrooms under a lens.** [13] | Feature | Powdery mildew | Spray or water residue | Trichomes | |---|---|---|---| | Where | Upper surfaces of fan leaves first, then stems and buds | Wherever spray landed; drip edges | Sugar leaves, bracts, buds | | Look | Fuzzy white spots spreading to patches | Dry crusty film or rings | Glistening, stalked glands | | Wipe test | Wipes off, reappears in days | Wipes off, does not return | Does not wipe off cleanly; sticky | | Lens | Cobweb-like hyphae, chains of spores | Crystals, no structure | Clear stalks with round heads | | Fix | RH below ~55% in flower, airflow, remove infected leaves; see [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) | Nothing; change spray practice | Nothing; that is the crop | ## What to check first 1. **Where did it start?** Old leaves, new leaves, top of the canopy, or the whole plant. 2. **Lens on the underside** of three affected leaves (10–30×; 40–60× for broad mites). 3. **Lift the pot** or check reservoir temperature and air. 4. **pH and EC of input and runoff**, on a calibrated meter ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). 5. **Air and leaf temperature, RH and PPFD** at the affected spot. 6. **Only then** compare nutrient lookalikes. ## How to fix it Fix the cause the separating test pointed to, one change at a time, and write it in your journal. Changing pH, feed, light and watering on the same day makes it impossible to know which one worked. The individual fixes are in the tables above and the linked articles. ## How to confirm it worked - New growth emerging after the fix is clean; damaged leaves do not heal and are not the measure. - The symptom stops spreading to new leaves within 5–7 days for nutrients, 1–2 days for watering and oxygen, and 3–5 days for light and heat. - Readings stay in range at the next two checks. ## Common mistakes - Diagnosing from one leaf. Look at the whole plant and the neighbouring plants. - Skipping the lens. Mites and thrips cause many "deficiencies". - Treating several lookalikes at once with Cal-Mag plus a bloom booster plus a pH change. - Judging a photo taken under purple or warm LED light; colours lie. See [how to describe your plant's problem](https://genetixbay.com/knowledge/diagnosis/how-to-describe-your-plants-problem.md). ## Evidence - The old-versus-new location rule for mobile and immobile nutrients is *Established* plant nutrition [3] and holds in cannabis trials [1][2]. - Cannabis-specific deficiency pictures for Ca, Mg, K, Fe and Mn are *Supported* by two controlled studies; Fe and Mn gave weak or no symptoms in short hydro flower runs [1][2]. - Pythium on hydro cannabis roots is *Established* [4]; the dissolved-oxygen threshold for cannabis is *Grower practice* extrapolated from other crops [5][6]. - Spider mite and broad mite signs are *Established* extension guidance [7][8]. - Leaf temperature differences between LED and HPS are *Established* [9]. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 4. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 5. University of Kentucky Cooperative Extension, E706 (hydroponic Pythium and oxygen management). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 6. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-in-hydroponic-systems/ 7. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php 8. UConn IPM. Managing Broad Mites on Greenhouse Crops. https://ipm.cahnr.uconn.edu/ipm-managing-broad-mites-on-greenhouse-crops 9. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 10. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 11. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x 12. Suchoff D, et al. 2026. Hemp leaf tissue nutrient ranges. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 13. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 14. University of Kentucky Plant Pathology. Septoria leaf spot of hemp (PPFS-AG-H-01). https://plantpathology.mgcafe.uky.edu/files/ppfs-ag-h-01.pdf 15. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 16. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction --- # Cannabis root problems: the master decision tree > Healthy cannabis roots are white to cream, firm and smell earthy or of nothing. Brown, slimy roots whose outer skin slides off and smell rotten are root rot (usually Pythium), driven by warm, oxygen-poor water or waterlogged media. Firm, odourless tan roots are usually stained, not sick. Check solution temperature (target 18–21 °C) and dissolved oxygen first, then texture and smell, then insects. Root problems show above ground as drooping with a wet root zone, yellowing and stunting. - Canonical: https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Soil, Coco, Rockwool, DWC, RDWC, NFT, Ebb and flow, Drip, Aeroponics, Living soil - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What do healthy cannabis roots look like?** Healthy cannabis roots are white to cream, firm, branched and covered in fine root hairs, with bright white growing tips. They smell earthy in soil and coco, and of nothing or slightly sweet in hydro. Firm roots tinted tan or brown by nutrients, tannins or additives are usually fine. Brown roots that are soft, slimy, smell rotten and lose their outer skin when pulled are rotting. **Why are my cannabis roots brown and slimy?** Brown, slimy cannabis roots whose outer layer slips off between your fingers, often with a rotten or sewer smell, are root rot, most commonly Pythium in hydro and overwatered media. Warm solution above about 22 to 24 °C, low dissolved oxygen and stagnant or overwatered media are the usual causes. Cool the solution to 18 to 21 °C, raise aeration, remove dead roots and clean the system. **How warm is too warm for a cannabis reservoir?** A cannabis hydro reservoir is too warm above about 22 to 24 °C (72 to 75 °F). Warm water holds less oxygen, about 9.1 mg/L at 20 °C versus 8.3 mg/L at 25 °C at saturation, while roots and microbes use more, so Pythium root rot becomes much more likely. Aim for 18 to 21 °C (65 to 70 °F) with strong aeration. **How do I know if my cannabis is root-bound?** A cannabis plant is root-bound when roots circle the outside of the root ball in a dense mat, water runs straight through, the pot dries out in hours, and growth slows despite good feed and light. Slide the plant out to check. Up-pot into a container two to three times the volume, gently loosening circling roots, or increase watering frequency if you plan to finish in that pot. **Can a cannabis plant recover from root rot?** A cannabis plant can recover from root rot if it is caught early and the conditions are corrected. Cool the solution to 18 to 21 °C, raise dissolved oxygen, trim away dead brown roots, change and clean the reservoir, and re-establish beneficial microbes or commit fully to a sterile system. Recovery shows as new bright white root tips within 5 to 10 days. **What happens if my aeroponic pump fails?** If a high-pressure aeroponic pump or timer fails, cannabis roots hanging in air can dry and be damaged within tens of minutes, and the plant wilts soon after. Treat it as an emergency: restore misting, or mist roots by hand with nutrient solution until it is fixed. A pressure alarm, accumulator and backup pump are the only reliable protection. **Short answer.** Healthy cannabis roots are white to cream, firm and smell of earth or of nothing. Brown, slimy roots whose outer skin slides off and smell rotten are root rot, usually *Pythium* [1][2]. Firm, odourless tan roots are usually just stained. Check solution temperature and dissolved oxygen first (target 18–21 °C / 65–70 °F, strong aeration) [3][4], then root texture and smell, then insects. Above ground, root trouble looks like drooping with a wet root zone, yellowing and stunting. ## What's happening? Roots need oxygen to respire, and respiration powers nutrient and water uptake [11]. Anything that starves roots of oxygen (waterlogged media, warm or stagnant solution, a failed air pump) stops uptake within hours and weakens the root cells. Oomycetes such as *Pythium* and fungi such as *Fusarium* then invade the weakened tissue; both were isolated from rotting roots of hydroponic cannabis in British Columbia [1]. *Pythium* swims between plants in recirculating water, so one sick plant becomes a whole system [3][4]. Water temperature matters twice. Warm water holds less oxygen: about 9.1 mg/L at 20 °C (68 °F) and 8.3 mg/L at 25 °C (77 °F) at full saturation in fresh water [5]. At the same time, roots and microbes use oxygen faster as temperature rises, and the warm-loving *Pythium* species grow faster [3]. That is why hot reservoirs and summer heat waves bring root rot. Not every root problem is a pathogen. Roots also suffer from salt burn (high EC kills the tips), being root-bound, insects (root aphids, fungus gnat larvae) and, in high-pressure aeroponics, simply drying out when the misting stops [7][8][10]. ## How do I find the root problem? (the decision tree) 1. **What does the plant do above ground?** - Droops while the medium or solution is wet → root zone is short of oxygen, or roots are rotting. Go to step 2. - Droops while the pot is light and dry → underwatering, not a root disease ([drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md)). - Slow, stunted, no droop → go to step 5 (root-bound, insects, cold). - Sudden collapse of the whole plant in HPA or aeroponics → step 6, now. 2. **Look at and touch the roots.** In hydro, lift the net pot. In soil or coco, slide the plant out of the pot. - White to cream, firm, fine hairs, white tips → roots are healthy; the problem is elsewhere (pH, EC, climate, light). - Tan to brown but firm, tips still white, no smell → **staining** by nutrients, tannins or additives. Usually harmless ([root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)). - Brown, soft, slimy, outer skin slides off leaving a thin white core thread → **root rot**, most often *Pythium* [1][3]. - Brown or reddish discolouration at the crown and stem base, plant wilting, often in soil → **Fusarium crown or root rot** [1][6]. - Roots short with brown, burnt tips but firm elsewhere → **salt burn** from high EC. 3. **Do the smell test.** Put your nose to the roots or the reservoir. - Earthy or nothing → healthy. - Sour, rotten, sewer or swampy → **anaerobic rot**. Rot plus smell plus wet medium is the strongest root-rot signal there is. 4. **Take the readings.** - Solution temperature above ~22–24 °C (72–75 °F) → **hot reservoir** is the driver [3][4]. - Dissolved oxygen below ~5–6 mg/L, or air pump off, stones clogged, little surface agitation → **low dissolved oxygen**. - Soil or coco: pot stays heavy for more than 3 days, or water pools on top → **overwatering anoxia**. - Runoff EC far above input (more than ~0.5 mS/cm) → **salt build-up** ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). 5. **Look for insects and root-bound roots.** - Small pear-shaped insects, often with white waxy residue, on roots or at drainage holes → **root aphids** [7] ([root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md)). - Thin, clear larvae with shiny black heads in the top few cm, adults flying over wet media → **fungus gnat larvae**, which chew root hairs of seedlings and clones and open wounds for *Pythium* [8] ([fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md)). - A dense mat of roots circling the outside of the root ball, water runs straight through → **root-bound** [9]. - Few roots, cold medium below ~18 °C (65 °F) → **cold root zone**. 6. **HPA or aeroponics: is the mist running?** No pressure, blocked nozzles or a failed timer → **pump failure: critical**. Roots can be damaged within tens of minutes of drying [10]. Restore misting first, diagnose later ([HPA aeroponics](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md)). ## How do I tell root problems apart? (differential table) | Pattern | Most likely | Rule out first | Key test | |---|---|---|---| | Brown, slimy, skin slides off, rotten smell | Pythium root rot [1][3] | Staining | Pull a root between fingers; smell test | | Tan or brown, firm, odourless, white tips | Staining | Early rot | Texture and smell; new white tips present? | | Wilting with wet medium, no rot yet | Low oxygen (overwatering, low DO) | Fusarium wilt | Lift the pot; DO meter or check air pump | | Reservoir above 24 °C, rot spreading | Hot reservoir driving Pythium [3] | — | Thermometer at the warmest time of day | | Brown crown and stem base, soil grow | Fusarium crown rot [6] | Pythium, physical damage | Cut the stem base: brown internal streaks; lab test | | Burnt brown root tips, roots firm | Salt burn | Rot | Runoff or reservoir EC vs target | | White woolly residue, small insects on roots | Root aphids [7] | Root mealybugs, perlite dust | 10–20x lens | | Larvae with black heads in top 5 cm | Fungus gnats [8] | Shore flies | Potato slice trap for 48 h; yellow card | | Dense circling root mat | Root-bound [9] | Root aphids | Slide plant out of the pot | | Roots drying in an aero chamber | Pump or nozzle failure (critical) | — | Pressure gauge; listen for misting | | Few roots, slow, cold medium | Cold root zone | Overwatering | Probe thermometer in the medium | ## Which numbers matter? | Parameter | Target or threshold | Notes | |---|---|---| | Solution temperature, hydro | 18–21 °C (65–70 °F); trouble above ~22–24 °C (72–75 °F) | [3][4]; see [root rot](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) | | DO at saturation, fresh water | ~9.1 mg/L at 20 °C; ~8.3 mg/L at 25 °C; ~7.6 mg/L at 30 °C | Physical constants [5] | | DO target, hydro | Above ~5–6 mg/L, ideally near saturation | Extension practice [3]. | | Root-zone temperature, soil and coco | ~18–22 °C (65–72 °F) | Grower practice | | Runoff EC above input | More than ~0.5 mS/cm = salt build-up | Grower practice | | Soil/coco pot weight | Water when the pot is noticeably light; heavy for 3+ days = overwatering | Grower practice | | HPA pressure | ~80–100 psi (5.5–7 bar) | See [HPA](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) | | HPA failure margin | Roots damaged within tens of minutes without mist | [10]; grower practice | | Up-pot size | 2–3x the current volume | Grower practice; growth scales with rooting volume [9] | ## What should I check first? 1. **Plant behaviour vs root-zone moisture.** Wet and wilting is a root-zone emergency; dry and wilting is thirst. 2. **Solution temperature** at the warmest point of the day. 3. **Air supply.** Pump running, stones bubbling evenly, surface agitated, no clogged lines. 4. **Root colour, texture and smell.** 5. **Reservoir or runoff EC and pH** with calibrated meters. 6. **A lens on the roots** and the top 5 cm of the medium for insects. 7. **Pot weight and drainage** in soil and coco. ## How do I fix each one? - **Pythium root rot.** Cool the solution to 18–21 °C (65–70 °F) with a chiller, frozen bottles in an emergency, or moving the reservoir off the warm floor. Raise dissolved oxygen: bigger pump, more stones, surface agitation. Trim dead, slimy roots with sanitised scissors. Drain, clean and sanitise the system, then refill with fresh solution. Then choose: re-establish a beneficial-microbe reservoir (the GenetixBay preference, because bacteria arrive regardless) or commit fully to a sterile reservoir, keeping in mind that oxidisers such as hydrogen peroxide kill beneficial microbes too [3][4]. See [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md). - **Staining.** Nothing to fix; keep the solution cool and the oxygen high. - **Low dissolved oxygen.** Increase air pump capacity, clean or replace stones, raise surface agitation, and lower solution temperature. - **Hot reservoir.** Insulate it, shade it, keep it off warm floors, and chill to 18–21 °C. - **Overwatering anoxia (soil, coco).** Stop watering until the pot is noticeably light; improve drainage (more perlite, fabric pots, no saucers of standing water). Water to 10–20% runoff and let it dry back. - **Fusarium crown rot.** There is no cure for an infected plant. Remove it with its medium, sanitise pots and tools, and avoid root-zone stress in the rest [1][6]. See [Fusarium](https://genetixbay.com/knowledge/diseases/fusarium.md). - **Salt burn.** Do a root-zone flush (the one valid flush: it treats the medium, not the plant) with pH-adjusted water to 20–30% runoff until runoff EC is near input EC, then resume a slightly lower feed. In hydro, replace the reservoir at target EC. - **Root aphids.** See [root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md); soil-applied entomopathogenic fungi and predators are the main tools [7]. - **Fungus gnats.** Fix watering first, then Bti drenches, *Steinernema feltiae* nematodes or soil predatory mites, with yellow cards to monitor [8]. - **Root-bound.** Up-pot into a container 2–3x the volume and loosen circling roots gently. If you plan to finish in a small pot, water more often instead: big plants can come from small pots if you push water and feed frequently (house position on pot size) [9]. - **Cold root zone.** Warm the medium to ~20 °C (68 °F) with a heat mat under the pot or by raising pots off a cold floor. - **HPA pump failure.** Restore misting immediately; hand-mist roots with nutrient solution until fixed. Fit an accumulator, a pressure alarm and a spare pump. ## How do I know the fix worked? - New bright white root tips appear within 5–10 days after rot or anoxia is corrected. - Wilting with a wet root zone stops within 1–3 days of correcting oxygen or watering. - The reservoir smells clean at the next change. - Runoff EC falls within ~0.5 mS/cm of input after a salt flush. - Insect counts fall on cards and traps week on week. - Up-potted plants push faster node growth within 7–10 days. ## What are the common mistakes? - Adding nutrients or "root boosters" to rotting roots. They cannot absorb, and EC climbs. - Dosing hydrogen peroxide into a reservoir that relies on beneficial microbes, then reseeding them the same day. - Calling stained roots rot, then tearing healthy roots out. - Watering a wilting, wet plant because it "looks thirsty". - Ignoring the reservoir temperature at the warmest time of day; a morning reading misses afternoon peaks. - Running HPA without a pressure alarm or backup. - Up-potting a seedling straight into a huge pot that then stays wet (it causes the overwatering it was meant to prevent). ## How strong is the evidence? - *Pythium* and *Fusarium* causing root rot of hydroponic cannabis is *Established* [1][2]. - Warm, oxygen-poor solution favouring *Pythium* is *Established* in hydroponic crops [3][4]; cannabis-specific temperature thresholds are *Supported* by extrapolation. - Dissolved oxygen solubility values are *Established* physics [5]; cannabis DO targets are *Grower practice*. - Root aphids and fungus gnats harming cannabis roots are *Established* [7][8]. - Growth scaling with rooting volume is *Established* across species [9]. - HPA failure margins are *Supported* by aeroponics reviews [10] and grower practice. - Beneficial-microbe reservoirs over sterile ones is the house position; both are valid if done properly. ## Sources 1. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 2. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 3. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic leafy greens and its management (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 4. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 5. US Geological Survey. Dissolved oxygen solubility tables (DOTABLES). https://water.usgs.gov/water-resources/software/DOTABLES/ 6. Utah State University Extension. Hemp Fusarium crown rot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-fusarium-crown-rot 7. Utah State University Extension. Rice Root Aphids (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-rice-root-aphid.php 8. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ 9. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 10. Lakhiar IA, Gao J, Syed TN, Chandio FA, Buttar NA, 2018. Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics. Journal of Plant Interactions 13(1):338-352. https://doi.org/10.1080/17429145.2018.1472308 11. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Clawing leaves on cannabis: a differential > Leaves that curl down at the tips like a talon, especially if dark green and glossy, most often mean excess nitrogen and high EC, or a waterlogged, oxygen-starved root zone. Check watering and runoff EC first; distorted, crinkled clawing on new growth instead points to broad mites, calcium/boron problems or a viroid. - Canonical: https://genetixbay.com/knowledge/diagnosis/clawing-leaves.html - Category: Diagnosis · Level: Intermediate - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my cannabis leaves clawing down?** Cannabis leaves that claw down at the tips most often have too much nitrogen combined with high root-zone EC, or a waterlogged root zone short of oxygen. Lift the pot and check runoff EC before cutting nitrogen. If the clawing is on new growth that is also crinkled, twisted or shiny, broad mites, calcium or boron disorders, or a viroid are more likely causes. **Why are dark green cannabis leaves curling down at the tips?** Very dark, glossy green cannabis leaves with tips hooked downward are the classic grower sign of excess nitrogen, usually alongside high EC and often with burnt tips. This is grower practice rather than a controlled-trial finding. Trials do show cannabis yield plateaus well before the highest nitrogen rates, so over-supply is easy; reduce nitrogen and bring runoff EC back toward input. **Is the claw always nitrogen toxicity in cannabis?** The claw in cannabis is not always nitrogen toxicity. Nitrogen excess fits only when leaves are very dark green; pale clawing does not support it. Overwatering causes droopy, clawed leaves in heavy pots, broad mites twist and crinkle new growth, controlled trials show boron and copper deficiency curl leaves down, and hop latent viroid can cause small, clawed, brittle leaves on single plants. **What makes cannabis leaves point down like eagle talons?** Cannabis leaves that hook down like eagle talons are usually reacting to excess nitrogen and high EC, which produce soft, water-rich, very dark growth under osmotic stress. A soggy, oxygen-starved root zone can look similar because the plant loses turgor. Grower practice targets veg feed EC around 1.0 to 1.8 mS/cm and runoff EC within about 0.5 mS/cm of input. **Why do cannabis leaves claw after a transplant?** Clawing that appears on cannabis right after a transplant or a big feed increase is usually transplant stress or salt shock, and it normally resolves on its own within 3 to 7 days. Keep light intensity moderate and the climate stable, avoid extra feeding, and do not overwater the new pot. New leaves should emerge flat and mid-green within 5 to 10 days. **Short answer.** "The claw" (leaflet tips bending sharply down while the leaf is dark, glossy green) is the textbook grower sign of too much nitrogen, usually alongside high root-zone EC. The other common cause is a soggy, oxygen-starved root zone. Check how wet the pots are and what the runoff EC says before cutting nitrogen. If the clawing is on new growth and the leaves are also crinkled, twisted or shiny, think broad mites, calcium/boron disorders or viroid infection instead. ## What's happening Excess ammonium and nitrate drive soft, very dark green growth with high water content; combined with high EC and the osmotic stress it brings, leaflets curl down at the tips. This is widely reported by growers but has not been characterised in a controlled cannabis N-toxicity trial that we could find (*Grower practice*). Cannabis N trials do show that yield plateaus well before the highest N rates, so over-supply is easy [2]. Waterlogging deprives roots of oxygen; the plant loses turgor and leaves droop and curl, which can look like clawing. In controlled trials, B deficiency curled new leaves inward and down at odd angles, and Cu deficiency slightly curled leaf margins in and down [1]; Ca deficiency produced upward curling in DWC [3]. ## How to recognise it | Pattern | Most likely | Also consider | |---|---|---| | Dark, glossy green, tips hooked down, whole plant, often with burnt tips | Excess N and high EC | Overwatering | | Leaves droopy and clawed, pots heavy and wet, slow growth | Overwatering / low root oxygen | Root rot | | Clawing only after transplant or a big feed increase | Transplant stress / salt shock | Self-resolves in days | | New growth twisted, crinkled, shiny, edges curled down | Broad mites [4] | Ca/B deficiency | | New growth narrow, distorted, tips dying | Boron or calcium deficiency [1] | Broad mites | | Clawed, small leaves, short internodes, brittle, one plant | Viroid (HLVd) | Root aphids | | Leaves at the top only, cupped down under a hot light | Heat/light stress | VPD too low | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | N supply, mineral, veg | ~150–250 mg/L N | Grower practice; trial optima vary [2] | | N supply, mineral, flower | ~160 mg/L N maximised yield in one soilless trial | [2] | | Feed EC veg / flower | ~1.0–1.8 / ~1.6–2.4 mS/cm | Grower practice | | Runoff EC above input | < ~0.5 mS/cm | Grower practice | | Dissolved oxygen (hydro) | near saturation, ≥ 6 mg/L | [5] | | Container dry-back before next irrigation (soil) | pot noticeably lighter; top 2–3 cm dry | Grower practice | ## What to check first 1. **Pot weight and moisture.** Heavy for days = overwatering. Fix that before touching nutrients. 2. **Runoff or reservoir EC** versus input. 3. **Feed N.** Veg formula into flower? Organic top-dress plus liquid N? Recently added a nitrogen-rich amendment? 4. **Leaf colour.** Very dark green supports N excess; pale clawing does not. 5. **New growth with a 20× lens** for broad mites if leaves are twisted or shiny. 6. **Pattern across plants.** One plant only and stunted: consider root disease or viroid. ## How to fix it - **Overwatering:** water less often, to runoff, and let the pot dry back. Improve drainage and aeration (more perlite, fabric pots). In hydro, raise DO and cool the solution. - **Excess N / high EC:** - Hydro: replace the reservoir at a lower EC with a lower-N formula. - Coco/rockwool: irrigate to 20–30% runoff at a reduced EC until runoff EC is near input. - Soil: plain pH-correct water for one or two cycles; skip N-rich top-dresses. - **Transplant shock:** keep light moderate and climate stable; it typically resolves in 3–7 days. - **Broad mites:** act quickly, see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). - **Ca/B issues:** check pH and root zone first; confirm the feed contains Ca and B. ## How to confirm it worked - New leaves emerge flat with a normal mid-green colour within 5–10 days. - Existing clawed leaves may relax partly but often stay curled. - Runoff EC trends toward input. ## Common mistakes - Flushing a soil pot that is already waterlogged. A root-zone flush is for salt build-up (high runoff EC), not for every symptom. - Dropping all nutrients to zero; mild hunger replaces mild excess. - Misreading broad-mite damage as N toxicity while the mites multiply. ## Evidence - N-toxicity "claw" is *Grower practice*; we found no controlled cannabis N-toxicity description. - N over-supply relative to yield optimum is *Supported* [2]. - B, Cu and Ca curling patterns are *Established* in trials [1][3]. - Broad mite distortion is *Established* in extension literature [4]. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Bevan L, Jones M, Zheng Y., 2021. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 3. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 4. UConn IPM. Managing Broad Mites on Greenhouse Crops. https://ipm.cahnr.uconn.edu/ipm-managing-broad-mites-on-greenhouse-crops 5. University of Kentucky Cooperative Extension, E706 (hydroponic Pythium and oxygen management). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf --- # Drooping cannabis: overwatering vs underwatering > Lift the pot: a heavy pot with firm, swollen-looking drooping leaves is overwatered (roots short of oxygen); a light pot with limp, papery leaves is underwatered. If the medium is moist and the plant still wilts, especially one plant at a time or in hydro, suspect root rot or vascular wilt and look at the roots. - Canonical: https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.html - Category: Diagnosis · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Soil, Coco, Rockwool, DWC, RDWC, Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is my cannabis overwatered or underwatered?** Lift the pot to tell whether cannabis is overwatered or underwatered. A heavy pot with firm, thick, dark leaves drooping along the petioles is overwatered, because the roots are short of oxygen. A very light pot with thin, limp, papery leaves is underwatered, and that plant usually perks up within 30 to 120 minutes of watering. **Why is my cannabis plant drooping after watering?** A cannabis plant that droops more after watering is usually overwatered: saturated media fill the air spaces, roots respire without enough oxygen and take up less water. Stop watering until the pot is clearly lighter, then water to light runoff less often. If the plant still does not recover once the pot dries back, inspect the roots for rot. **Why are cannabis leaves drooping when the soil is wet?** Cannabis leaves that droop while the soil is wet point to a root problem, not thirst. Waterlogging starves roots of oxygen, and if the pot is a normal weight but the plant still wilts, especially one plant at a time, research links that pattern to Pythium or Fusarium root rot or vascular wilt. Check roots: white and firm is healthy, brown and slimy is rot. **How often should I water cannabis in fabric pots?** Water cannabis in fabric pots by weight rather than on a fixed schedule. Grower practice is to irrigate when the pot is about 40 to 50% lighter than its just-watered weight, and to check moisture 5 cm down and at the bottom. Fabric pots aerate well, which helps prevent overwatering, but small plants in large pots still stay wet longest. **Why is my cannabis plant wilting in DWC?** A cannabis plant wilting in DWC usually has low dissolved oxygen or warm solution, which also favours Pythium root rot. Keep the reservoir at 18 to 22 °C (65 to 72 °F) with dissolved oxygen of at least 6 mg/L, check air pumps and stones, change the solution and inspect roots. Brown, soft roots whose outer layer slips off indicate root rot. **Short answer.** Lift the pot. Heavy pot, leaves drooping but firm and slightly swollen, petioles curving down along their length: overwatered, roots short of oxygen. Light pot, leaves limp, thin and papery, plant perks up within an hour of watering: underwatered. If the medium is moist, the pot is a normal weight and the plant still wilts, especially one plant at a time, look at the roots: that pattern fits root rot or vascular wilt [1][3]. ## What's happening Roots need oxygen to absorb water. Saturated media fill the air spaces with water; roots respire anaerobically, take up less, and the plant droops even though water is everywhere. Repeated waterlogging also favours Pythium and Fusarium root rot, and fungus gnat larvae, which damage roots further [1][2][5]. Underwatering is simpler: the plant loses turgor as the medium dries past what roots can extract. In hydro, the same physics applies to dissolved oxygen: warm solution holds less oxygen and favours Pythium zoospores [4]. ## How to recognise it | Clue | Overwatered | Underwatered | Root disease / wilt | |---|---|---|---| | Pot weight | Heavy, stays heavy for days | Very light | Normal or heavy | | Leaf feel | Firm, thick, dark, curling down | Thin, limp, papery | Limp, often yellowing | | Petioles | Droop along their length | Hang from the stem | Wilt, may not recover overnight | | After watering | Gets worse | Recovers in 30–120 min | No recovery | | Media surface | Wet, algae, fungus gnats | Dry, pulling away from pot edge | Variable | | Roots | Few white tips, may smell sour | Dry but white | Brown, soft, outer layer sloughs off; or brown vascular tissue in stem | | Pattern | Whole room on same schedule | Whole room or smallest pots | Often single plants, spreading | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Irrigate when (soil, pots) | pot ~40–50% lighter than just-watered weight | Grower practice | | Runoff per irrigation (coco/rockwool) | 10–30% | Grower practice | | Coco irrigation frequency | from 1/day (small plants) to several/day (large plants, flower) | Grower practice; coco tolerates frequent watering if it drains | | Hydro solution temperature | 18–22 °C (65–72 °F) | [4] | | Dissolved oxygen | ≥ 6 mg/L, ideally near saturation | [4] | | Container aeration | ≥ ~20–30% air-filled porosity | Grower practice for container media | ## What to check first 1. **Lift the pot** (or weigh it). Compare with a freshly watered pot of the same size. 2. **Finger or moisture probe** 5 cm down; check the bottom of the pot, not just the top. 3. **Time since watering** and watering schedule. Small plants in big pots stay wet longest. 4. **Drainage.** Holes clear, pot not standing in its runoff tray. 5. **Roots.** Slide the plant out or pull the net pot. White and firm = fine. Brown, soft, slimy, outer root cortex slipping off = root rot [1]. Insects on roots = root aphids [6]. Larvae in the top few cm = fungus gnats [5]. 6. **Stem.** Cut a wilted lower branch: brown streaks in the vascular tissue with no root rot suggests Fusarium wilt [3]. 7. **Climate.** Very high temperature and VPD can wilt a plant with a perfectly good root zone. ## How to fix it - **Overwatered:** - Stop watering until the pot is clearly lighter. Increase airflow over the medium. - Next time, water to light runoff, less often. Use a more aerated mix (perlite, fabric pots) for future crops. - Don't transplant a waterlogged plant unless the pot has no drainage. - **Underwatered:** - Water slowly in two or three passes so the medium rewets evenly (dry coco and peat repel water at first). - Then shorten the interval or use larger volumes. Automate drip if you can't keep up. - **Hydro wilting:** cool the reservoir towards 18–22 °C, check air pumps and stones, change the solution and inspect roots. See [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md). - **Root rot or wilt confirmed:** see [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) and [Fusarium](https://genetixbay.com/knowledge/diseases/fusarium.md). Isolate the plant. ## How to confirm it worked - Overwatered plants stand back up within 1–3 days once the pot dries back, and new root tips are white. - Underwatered plants recover within hours. - If neither happens, the roots are damaged; reassess for disease. ## Common mistakes - "It's drooping, give it water" without lifting the pot. - Giving seedlings or fresh clones a huge pot that never dries. - Daily small sips with no runoff in coco (salts) or daily drenching in soil (drowning). - Adding hydrogen peroxide to a soil pot as a reflex; it doesn't fix the watering rhythm. ## Evidence - Root hypoxia from waterlogging is *Established* plant physiology. - Pythium/Fusarium root rot causing wilt, yellowing and stunting in hydro cannabis is *Established* [1][2]. - Fusarium wilt in hemp and its risk in overwatered or poorly drained conditions is *Supported* [3]. - Pot-weight and runoff targets are *Grower practice*. ## Sources 1. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 2. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 3. Utah State University Extension. Fusarium Wilt (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-fusarium-wilt 4. University of Kentucky Cooperative Extension, E706 (hydroponic Pythium and oxygen management). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 5. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ 6. Utah State University Extension. Rice Root Aphids. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-rice-root-aphid.php --- # Foxtailing buds on cannabis: genetics or stress? > Foxtails (new calyx spires growing out of mature buds) are either a cultivar trait, which appears evenly through the canopy, or a stress response to heat and intense light, which shows mostly on the top colas nearest the fixture. Measure canopy leaf temperature and PPFD at the tops; evidence is mainly grower observation. - Canonical: https://genetixbay.com/knowledge/diagnosis/foxtails.html - Category: Diagnosis · Level: Intermediate - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my cannabis buds foxtailing?** Cannabis buds foxtail, growing spires of fresh calyxes out of mature buds, for one of two reasons. If spires appear evenly on every bud, including lower ones, it is a cultivar trait, common in long-flowering equatorial lines. If they appear mainly on the top colas nearest the light, often with bleached bracts, grower observation points to heat or light stress. **Is foxtailing on cannabis caused by heat or light?** Foxtailing on cannabis top colas is linked by grower practice to both heat and intense light, though no controlled study has confirmed it. Heat is the better supported stressor: research shows cannabis photosynthesis declined above about 30 °C (86 °F). Measure leaf temperature and PPFD at the cola tips; grower practice targets about 24 to 28 °C and 800 to 1200 µmol/m²/s at ambient CO2. **Is foxtailing in late flower genetic?** Foxtailing in late flower is often genetic when the spires appear uniformly across the whole canopy, including lower buds, and the cultivar has foxtailed in earlier grows. Long-flowering, sativa-leaning or equatorial-heritage cultivars commonly do it naturally, according to grower practice. Genetic foxtails can simply be accepted, recorded in the plant journal or selected against when pheno hunting and breeding. **Do foxtails mean my cannabis plant is a hermaphrodite?** Foxtails do not mean a cannabis plant is a hermaphrodite; they are stacked new calyxes, not male flowers. Inspect them anyway, because stressed late-flower buds can also grow yellow, banana-shaped anthers, which is a separate and more serious problem. If anthers are present, the plant is intersex, and it should not be kept as a mother or used for breeding. **How can I prevent foxtails on cannabis?** To prevent stress foxtails on cannabis, reduce heat and light at the tallest colas: raise or dim the fixture, bend or supercrop tall colas down to canopy level, and improve air movement so leaf temperature stays below about 30 °C. Measure PPFD at the tallest cola, not average canopy height. Nutrients will not fix it, and genetic foxtails cannot be prevented by environment. **Short answer.** Foxtails are towers of fresh calyxes growing out of, or on top of, a bud that was already mature. If they appear evenly on every bud in the canopy, it is almost certainly the cultivar. If they appear mainly on the top colas closest to the light, with bleaching or tacoed leaves, it is heat or light stress. Measure leaf temperature and PPFD at the cola tips. The evidence base is mostly grower observation; we found no controlled cannabis study of foxtailing. ## What's happening Cannabis inflorescences keep producing new flowers as long as conditions favour growth. Stressed tips (too hot, too bright) appear to restart calyx production in stacked spires. Rodriguez-Morrison et al. noted morphological responses of inflorescences at high light levels in their PPFD trial Heat is the best-supported stressor: cannabis photosynthesis declined above ~30 °C (86 °F) in one cultivar [2], and a Colorado State study reported heat treatment of young flowers reduced cannabinoid precursor (CBGA) production [4]. Long-flowering, equatorial-heritage cultivars commonly foxtail by nature (*Grower practice*). Foxtails are not hermaphroditism, but inspect them: anthers (bananas) emerging in stressed late-flower buds are a separate, more serious issue [3]. Stress reveals a plant that is genetically prone to herm; if you find anthers, don't keep that plant as a mother or breed from it. ## How to recognise it | Pattern | Most likely | Also consider | |---|---|---| | Uniform spires throughout the canopy, including lower buds | Genetics | Extended flowering time | | Top colas only, nearest the light, with bleached bracts | Light/heat stress | Light too close | | Spires plus fresh white pistils after the plant looked done | Re-vegging or late stress | Light leaks, photoperiod change | | Spires with yellow banana-shaped structures | Hermaphrodite anthers | See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) | | Airy spires plus long flowering weeks | Sativa-leaning or long-season cultivar | Normal | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Canopy leaf/bud temperature, lights on, late flower | ~24–28 °C (75–82 °F) | Grower practice; photosynthesis declined above ~30 °C [2] | | PPFD at top colas (ambient CO₂) | ~800–1200 µmol/m²/s | Grower practice; yield rose to 1800 [1] but stress depends on climate | | Night temperature, late flower | ~18–22 °C (64–72 °F) | Grower practice | | Distance hottest cola to fixture | per fixture spec; re-measure PPFD | Generic | ## What to check first 1. **Where are the foxtails?** Whole plant vs top only. 2. **Canopy temperature** at the tallest colas during the hottest part of the light period. 3. **PPFD at the cola tops.** Tall colas often sit far above the measured canopy. 4. **Cultivar history.** Does this genetic foxtail in other grows? 5. **Inspect for anthers.** 6. **Photoperiod integrity.** Light leaks or timer faults cause re-vegging-like regrowth. ## How to fix it - **Lower stress at the tops:** raise or dim the fixture, or bend/supercrop the tallest colas down to canopy level. - **Cool the canopy:** improve air exchange and air movement across the tops; avoid > ~30 °C leaf temperature. - **Genetic foxtails:** accept them, or select against them in your breeding and pheno hunts. Record in the plant journal. - **Do not** try to "fix" foxtailing with nutrients; there is no evidence for a nutrient cause. ## How to confirm it worked - No new spires forming on the tops in the following 7–10 days. - Bud tops look uniform with the lower canopy. ## Common mistakes - Treating genetic foxtails as a problem and stressing the plant further. - Measuring PPFD at the average canopy height, not at the tallest cola. - Missing anthers inside foxtails. ## Evidence - Foxtailing from heat/light stress: *Grower practice*. No controlled cannabis study located; vendor sources make strong claims without data. - Heat reducing cannabis photosynthesis and cannabinoid precursor production: *Supported* [2][4]. - Genetic foxtailing: *Grower practice*. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x 3. Punja ZK, Holmes JE., 2020. Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences: Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 4. Greenhouse Grower, How Environmental Stresses Can Impact Cannabinoid Production (report on Colorado State University heat-stress work). https://www.greenhousegrower.com/?p=159152 --- # Hermaphrodite cannabis (bananas and nanners): what to do > Hermaphroditic flowers are anthers (often banana-shaped) or pollen sacs forming on a female plant. Cannabis is a dioecious species, and a well-bred female should stay female; herm-prone plants are mainly the product of bad breeding (repeated selfing, careless feminising, untested 'pollen chucker' seed). Stress such as light leaks or heat reveals that weakness rather than causing it in sound genetics. Fix the environment, remove the plant if it sheds pollen, and never keep it as a mother or breed from it. - Canonical: https://genetixbay.com/knowledge/diagnosis/hermaphrodites.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Transition, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **My cannabis plant is growing bananas: what do I do?** If a cannabis plant grows a few closed bananas (bare anthers) in late flower, pluck them carefully with tweezers, lightly mist the area, and inspect every 2 to 3 days. If it has many anthers, pollen-sac clusters or is shedding pollen, bag it and remove it from the room. Then fix light leaks or heat, and never keep the plant as a mother. **Why did my cannabis plant turn hermaphrodite?** A cannabis plant turns hermaphrodite mainly because its genetics are herm-prone, usually from repeated selfing, careless feminising or untested seed from people who never cull. Stress such as light leaks, a skipped dark period or heat then reveals that weakness. If one plant hermed while others in identical conditions stayed female, the environment exposed it, but the genetics are the real problem. **Are cannabis hermaphrodites genetic or caused by stress?** Cannabis hermaphrodites are mainly genetic, with stress acting as the trigger that reveals susceptible plants. Research links interrupted darkness, altered photoperiods, low temperatures and chemicals to male flowers on females, yet the same light leak leaves a stable clone beside it untouched. Hemp studies show sex expression is heritable and responds to selection, which is why GenetixBay treats herm-prone lines as breeder error. **Can light leaks cause cannabis hermaphrodites?** Light leaks can trigger hermaphrodite flowers on susceptible cannabis plants, since research links interrupted darkness to sex reversal, but they do not make a well-bred female herm. Keep the 12-hour dark period fully light-tight: sit in the room for about 10 minutes with eyes adjusted and look for gaps in seals, vents and equipment indicator LEDs. Check timer and controller logs too. **Are nanners in late cannabis flower a problem?** Nanners in late cannabis flower are a real problem: they are staminate flowers producing pollen that looked normal and germinated 10 to 30% in vitro in a controlled study. That pollen can seed buds, lowering quality, and research shows hermaphrodite pollen produced all-female seed that carries the same tendency. Treat them as a genetic defect to record and report, not a harmless finishing quirk. **Will a hermaphrodite pollinate my whole cannabis room?** A hermaphrodite that opens and sheds pollen can pollinate other flowering cannabis plants, and seeded buds are lower in quality because seed formation diverts resources. Research found seeded inflorescences held 22 to 48 seeds. Bag the plant before moving it to contain pollen, remove it from the room, and inspect every plant for new anthers and seeds over the following 7 to 14 days. **Should I keep or breed a cannabis plant that hermed?** A cannabis plant that hermed should not be kept as a mother, cloned, reversed or used for breeding, even if it is your best plant. Research shows hermaphrodite pollen gave only female progeny, so its seed is feminised seed carrying the same weakness. The GenetixBay breeder standard is to cull it, record the event and tell the breeder of the line. **Are late-flower bananas normal on cannabis?** Late-flower bananas are not normal on cannabis; the claim that they are is a myth. A banana is a staminate flower reduced to its anthers, forming inside a female bud, which is intersex expression. Cannabis is a dioecious species with an XY system, and a well-bred female stays female even through a long finish. GenetixBay holds this as a firm house position. **Is it OK to have a few nanners at the end of cannabis flower?** A few closed nanners in the last days of cannabis flower can be managed to finish the run, but the plant is still a herm. Pluck them with tweezers and monitor closely, then record it, take no cuts and make no seed from it. On GenetixBay, a line whose tester grows herm above 2% does not qualify for Bay Lines, the Seed Club or featuring. **Short answer.** A "hermie" is a female plant that also makes male flower parts: small yellow-green, banana-shaped anthers poking out among the pistils, or full pollen-sac clusters. Cannabis is a dioecious species with a long-established XY system [2][3]; a well-bred female stays female. Herm-prone plants are **mainly breeder error**: lines built on repeated selfing, careless feminising, or untested seed from "pollen chuckers". Stress (light leaks, heat, a missed dark period) reveals that weakness; it doesn't create it in sound genetics. Fix the trigger, pluck a few closed anthers in late flower or remove the plant if it's shedding pollen, and **never** keep it as a mother or breed from it. > **Breeder's standard.** A plant that throws male flowers under normal room conditions is culled from the breeding programme, along with any clone of it. It is never used as a pollen donor, a seed mother or a reversal donor. Its herm rate is recorded and disclosed with any seed from the same line. GenetixBay treats this as an ethics standard, not a preference: see [record-keeping and naming ethics](https://genetixbay.com/knowledge/breeding/record-keeping-naming-ethics.md). ## What's happening Cannabis has been a dioecious plant, with separate males and females, for as long as people have grown it. Its sex chromosomes are old and the Y is strongly degenerated [2][3]. Separate sexes are the species' stable, normal state. An intersex female is an unwanted outlier, not the plant "doing what plants do". Drug-type cannabis has been recorded as dioecious throughout its history: growers and writers have always distinguished male from female plants, and ancient Chinese texts already used separate names for male and female hemp [5]. Monoecious hemp, with both sexes on one plant, exists only because 20th-century fibre breeders selected for it on purpose; it is not the norm and says nothing about how drug-type cannabis behaves. Selfing, too, was historically an emergency measure, used to save a line when no male was left, not a trait anyone wanted. Why do some modern plants herm so readily, then? The GenetixBay breeder position, drawn from decades of growing and breeding: - **Repeated selfing (S1 on S1).** Selfing a plant that has already shown intersex flowers concentrates whatever makes it do so. See [S1s and selfing](https://genetixbay.com/knowledge/breeding/s1-selfing.md). - **Careless feminising.** Reversing a female that hasn't been proven stable across several runs, or collecting pollen from a stress herm instead of a controlled reversal, puts that tendency into every seed. See [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md). - **"Pollen chuckers".** People who cross whatever is in the room and release the seed without growing out and culling. Unstable genetics then spread widely under popular names. What the research shows fits that picture. Punja and Holmes characterised hermaphroditism in commercial indoor cannabis: anthers formed in clusters in bract tissue next to the stigmas, from about week 4 of flower through harvest; anther and pollen looked like those of normal males; pollen germinated 10–30% in vitro; seeded inflorescences held 22–48 seeds; whole inflorescences converting to anthers was rare (~2 in 1000 plants) [1]. They saw this on roughly 5–10% of plants across three cultivars in one commercial facility [1]. We read that rate as evidence of poor genetics in that operation's cultivars, not as normal cannabis behaviour. The founder has grown thousands of cultivars and doesn't see it in older lineages, only in the recent wave of low-quality releases. They cite older work linking male flowers to applied chemicals (gibberellins, silver compounds, cobalt chloride) and to stresses such as altered photoperiods, interrupted darkness and low temperatures [1]. We read that as stress *revealing* susceptible genetics. The same light leak that makes one clone herm leaves a stable clone beside it untouched. Seed from hermaphrodite pollen gave only female progeny in the strains tested [1], which is why a herm in the room passes its tendency straight into the next generation of "feminised" seed. ## Late-flower "bananas" are not normal > **House position (firm): late nanners are a herm, and they're unwanted.** You'll hear it in every grow forum: "a few bananas at the end are normal, the plant is just trying to seed itself." It isn't normal. A female that grows anthers in its buds late in flower is expressing male flowers: it's intersex, a herm. That holds even if it's the best plant you've ever grown, the loudest gas in the room, the keeper you've hunted for years. It's a sign of poor genetics, from bad breeding or pollen-chucking behaviour, and base lines that are prone to it got that way through bad practice early on. You can sometimes breed it out of a line with patient selection, but usually that isn't the approach: **cull it, don't keep it as a mother, and don't breed from it.** The founder will die on this hill. **What a late banana actually is.** The yellow "banana" is a staminate flower reduced to its anthers, forming inside a pistillate inflorescence. Punja and Holmes found these anthers in clusters in bract tissue next to the stigmas, from about week 4 of flower right through to harvest, with pollen that looked like a normal male's and germinated 10–30 % in vitro [1]. Late timing doesn't make it a different thing. It's the same intersex expression, showing up when the plant is under the most pressure. **Why we call it genetics, with the evidence:** - **Sex expression is heritable.** In monoecious hemp, how much male and female flowering a plant shows varies between cultivars and has a genetic basis [7]; genome-wide work has mapped loci associated with sex expression [8]. That's hemp, not drug-type cannabis, but it's the same species and the same flowering machinery. - **It responds to selection.** Monoecious hemp exists because 20th-century fibre breeders selected for plants that make both sexes [10]. If selection can push the species towards both sexes on one plant, careless breeding can drift a line that way, and careful breeding can keep it female. - **Herm pollen makes herm-prone "feminised" seed.** Seed from hermaphrodite pollen gave only female progeny in the strains tested [1], and controlled reversal with silver does the same thing on purpose [9]. A late banana that drops pollen in your room has just made feminised seed carrying its own tendency. Selfing such plants, or reversing them for "fem" seed, is how the trait spreads through the market. See [S1s and selfing](https://genetixbay.com/knowledge/breeding/s1-selfing.md) and [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md). - **Stable plants don't do it under the same conditions.** In one facility, intersex flowers turned up on roughly 5–10 % of plants [1]; we read that as a sign of poor genetics in those cultivars, not as a normal rate. Under the same lights, the same feed and the same long finish, a well-bred female stays female. **The honest part.** Research does show that stress can trigger intersex flowers: interrupted darkness, altered photoperiods, low temperatures, and chemicals such as silver compounds or gibberellins have all been linked to male flowers on females [1][9]. Late flower is a stressful time, especially if a plant is run past its window. We don't deny that. We read it the way a breeder does: **stress reveals susceptible genetics; it doesn't make a stable plant herm.** The light leak or the extra two weeks was the test, and the plant failed it. What hasn't been published is a heritability estimate for intersex tendency in drug-type cannabis specifically, so the genetic case rests on the hemp work, the breeding history and long breeder experience. **What to do.** If it's a handful of closed anthers in the last days and you're finishing the run, pluck and monitor. But record it, don't take cuts from it, don't make seed with it, and tell the breeder. On GenetixBay, herm testing has two tiers: a 10-plant screening grow where any herm fails the line for Bay Lines, the Seed Club and featuring; then pooled community grow reports, and only at about 150 plants or more can a line earn "Verified under 2% herm rate" (ten plants can't tell 2 % from 10 %; see [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md)). See [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md). ## How to recognise it | What you see | What it is | Urgency | |---|---|---| | A few yellow "bananas" (bare anthers) poking from buds, late flower | Hermaphroditic anthers | Medium: pluck, monitor, flag the genetics | | Clusters of round, pale green balls on stalks at nodes (pollen sacs) | Male flowers on a female | High: remove plant or branch | | Pollen dust on leaves below | Pollen release | High: isolate immediately | | Fresh calyx spires, no anthers | Foxtailing | See [foxtails](https://genetixbay.com/knowledge/diagnosis/foxtails.md) | | Seeds in buds at harvest | Pollination happened weeks ago | Find the source | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Dark period in flower | 12 h, uninterrupted, light-tight | Grower practice; light interruptions linked to sex reversal [1] | | Light leak test | no visible light after ~10 min eyes adjusted in the dark | Grower practice | | Canopy temperature | < ~30 °C (86 °F) | Heat stress [6]; grower practice links heat to hermies in susceptible plants | | Typical onset | ~week 4 of flower onwards | [1] | | Observed incidence | ~5–10% of plants, 3 commercial cultivars, one facility | [1]; not a "normal" rate for well-bred lines | | Pollen germination | 10–30% in vitro | [1] | | Runs a mother must stay clean before breeding | at least 2 | GenetixBay breeder's standard | ## What to check first 1. **Light leaks.** Sit in the room or tent in the dark for 10 minutes. Check door seals, LEDs on equipment, vents. 2. **Timer and controller logs.** A night with the light on, or a skipped dark period, is the classic trigger for a susceptible plant. 3. **Heat and light stress** at the tops. 4. **Other stresses:** severe root problems, pests, drought, extreme pruning in flower. 5. **Plant history.** Where did the seed come from? Is it an S1 of an S1, a feminised line from an unproven donor, or a "freebie" from someone who doesn't cull? Has this clone done it before? 6. **The neighbours.** If one plant hermed and the rest of the room under identical conditions did not, the environment exposed it; the genetics are the problem. ## How to fix it - **Isolated bananas, late flower, not open:** pluck them carefully with tweezers, mist the area lightly with water to deactivate any loose pollen (grower practice), and inspect every 2–3 days. - **Many anthers, male flower clusters, or pollen shedding:** remove the plant from the room (bag it first to contain pollen). Harvest early if it is near maturity. - **Fix the trigger:** seal light leaks, replace faulty timers, correct heat stress. That protects the rest of the room. - **Fix the genetics:** cull the clone; don't keep it as a mother. Record the event (week, trigger if any, photos) in your journal. If it came from a seed line, tell the breeder and note it publicly on the line record. - **Seeded buds:** quality is reduced; seed formation diverts resources [1]. Don't save or sell the seed. ## How to confirm it worked - No new anthers on any plant over the next 7–14 days of inspection (hand lens, focus on bud interiors and node sites). - At harvest, few or no seeds. - Next run, with the trigger fixed and the culprit gone, a clean room. ## Common mistakes - Treating hermies as normal cannabis behaviour. They are not; they are a defect to breed out. - Calling late-flower bananas "normal" and keeping the plant because it smokes well. - Blaming only the light leak, and keeping the clone. The leak was the test; the clone failed it. - Saving "free feminised seed" from a hermed bud. Every seed carries the tendency. - Missing light leaks from equipment indicator LEDs. - Confusing foxtails with anthers. ## Evidence - Cannabis is dioecious with an XY system: *Established* [2][3]. - Morphology, timing, pollen viability and progeny sex of intersex flowers: *Established* by one controlled study [1]. Its 5–10% incidence describes one facility's cultivars and is read here as a sign of poor genetics, not a normal rate. - Drug-type cannabis recorded as dioecious through history; monoecious hemp a deliberate modern breeding product: *Established* [5]. - Stress and chemical triggers: *Supported* by older literature cited in [1]; specific thresholds are *Grower practice*. - Herm-prone lines arise mainly from breeding practice (repeated selfing, careless feminising, no culling): GenetixBay house position, grounded in long breeder experience. Selfing was historically an emergency measure to save a line, not a desirable trait. Rule: cull herm-prone plants and don't breed from them. - Sex expression having a genetic basis and responding to selection: *Supported* in hemp [7][8], and by the deliberate breeding of monoecious hemp [10]. - "Late-flower bananas are normal": *Myth* (house position). They are intersex flowers [1]; stress can trigger them, which we read as stress revealing susceptible genetics. ## Sources 1. Punja ZK, Holmes JE., 2020. Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences: Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 3. Prentout D, Razumova O, Rhone B, et al. 2020. An efficient RNA-seq-based segregation analysis identifies the sex chromosomes of Cannabis sativa. Genome Research 30(2):164-172. https://doi.org/10.1101/gr.251207.119 4. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 5. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 6. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x 7. Faux AM, Berhin A, Dauguet N, Bertin P. 2014. Sex chromosomes and quantitative sex expression in monoecious hemp (Cannabis sativa L.). Euphytica 196(2):183-197. https://doi.org/10.1007/s10681-013-1023-y 8. Petit J, Salentijn EMJ, Paulo MJ, Denneboom C, Trindade LM. 2020. Genetic architecture of flowering time and sex determination in hemp (Cannabis sativa L.): a genome-wide association study. Frontiers in Plant Science 11:569958. https://doi.org/10.3389/fpls.2020.569958 9. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 10. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # How to describe your plant's problem so it can be diagnosed > A plant problem can be diagnosed quickly only if the description says where on the plant it started (old or new growth), the exact pattern, how fast it is spreading, and the readings: pH and EC of input and runoff, temperature, RH, light intensity or distance, medium, system, water source, stage with the day count from the flip, and anything you changed in the last week. Add a whole-plant photo and a close-up of the top and underside of an affected leaf, taken in white light. - Canonical: https://genetixbay.com/knowledge/diagnosis/how-to-describe-your-plants-problem.html - Category: Diagnosis · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review - Stage: Seedling, Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What information do I need to diagnose a cannabis plant problem?** To diagnose a cannabis problem you need where it started (old lower leaves, new top growth or the whole plant), the pattern (between veins, edges, tips, spots, curling), how fast it is spreading, and the readings: pH and EC going in and coming out, air temperature, humidity, light distance or PPFD, medium, system, water source, stage and days since the flip, plus every change made in the last 7 to 10 days. **How do I take a good photo of a sick cannabis plant?** Take cannabis problem photos in white or natural light, never under purple or very warm LED light, which hides yellowing and fakes purple. Shoot three photos: the whole plant, a close-up of the top of an affected leaf, and its underside, in focus and with a coin or ruler for scale. Then photograph the same leaf again in two or three days to show progression. **Why does it matter if old or new leaves are affected?** Old versus new leaves matters because nutrients that move in the plant (nitrogen, phosphorus, potassium, magnesium) are stripped from old leaves first, while immobile ones (calcium, iron, manganese, zinc, boron) show on new growth. That single detail roughly halves the list of possible causes, and it is the first question any good diagnosis asks. **Should I give pH and EC readings when asking for help with my plant?** Yes. Give both the input and the runoff or reservoir pH and EC, and state your EC scale or the ppm scale your meter uses (500 or 700), because the same reading differs by 40% between scales. Say whether the meter was calibrated recently. Without root-zone readings, pH lockout and salt build-up cannot be ruled out, and they cause many apparent deficiencies. **What does 'what changed recently' mean in plant diagnosis?** Recent changes means anything done to the plant or room in the last 7 to 10 days: a new nutrient or strength, a different water source, a transplant, training or defoliation, a light raised or dimmed, a heatwave, a new clone brought in, a spray, or the flip to 12/12. Plants answer slowly, so the cause of today's symptom is usually something done three to five days ago. **Can a GenetixBay journal fill in my plant readings automatically?** A GenetixBay journal stores your stage, days since flip, medium, system, water source and logged pH, EC, temperature and RH, so the symptom checker and the Professor can read them instead of asking. When a Jardin controller is connected, its sensors log climate and reservoir readings continuously, so the history before a symptom appeared is already there. **Short answer.** Say **where it started** (old lower leaves, new top growth, the whole plant), **what it looks like** (between veins, edges, tips, spots, curling, coating), **how fast it is spreading**, and give the **readings**: pH and EC going in and coming out, temperature, RH, light intensity or distance, medium, system, water source, stage with days since the flip, and anything you changed in the last week. Add three photos in white light: the whole plant, the top of an affected leaf, and its underside. "My plant is yellow, help" can mean twenty different things. A good description narrows it to two or three in one reply, and often answers itself. ## Why does the description matter so much? A diagnosis is a process of elimination, and each detail you give removes causes from the list. Location alone splits nutrient problems in half: mobile nutrients (N, P, K, Mg) show on old leaves, immobile ones (Ca, Fe, Mn, Zn, B) on new growth [1][2]. Root-zone pH and EC rule pH lockout and salt build-up in or out. A lens check rules pests in or out. Without those facts, any helper, human or AI, is guessing from a picture, and many problems look identical in a picture ([lookalikes](https://genetixbay.com/knowledge/diagnosis/lookalikes.md)). ## Which leaves are affected: old or new growth? **State whether the problem started on the oldest, lowest leaves, the newest leaves at the tops, or everywhere at once.** That is the single most useful sentence you can write. - **Old growth:** the big fan leaves at the bottom and inside of the plant, the first ones that grew. - **New growth:** the youngest leaves at the shoot tips and the top of the canopy. - **Middle:** recently matured leaves, a few nodes down from the tip. - **Whole plant:** everything at once, often a watering, root or climate problem rather than a nutrient. - **Top only, nearest the lamp:** usually light or heat. - **One side only:** a fan, a wall, a light hotspot, or one root section. Also say whether it is **one plant or several**, and if several, whether they share a reservoir, a water source or a cultivar. A problem on one plant among many identical ones points to that plant (roots, a pest, HLVd); a problem on every plant points to the room or the feed. ## What words should I use for the pattern? **Use the specific pattern words below rather than "sick" or "burnt".** Each one maps to a different set of causes. | Say this | It means | Points toward | |---|---|---| | Uniform yellow | The whole leaf fades evenly, veins too | N, S, overwatering, senescence | | Interveinal yellowing | Yellow between the veins, veins stay green | Mg (old leaves), Fe or Mn (new leaves) | | Margin yellowing or scorch | Edges and serrations yellow then brown | K, salts, Mn toxicity | | Brown tips | Only the very tip of each leaflet is dry and brown | Salt build-up, nutrient burn | | Spots | Distinct round or irregular patches; say size and colour | Ca, P, septoria, spray burn | | Stippling | Hundreds of pin-prick pale dots | Spider mites, thrips | | Clawing | Leaf tips hook down | High N, overwatering | | Taco or canoe | Leaf folds up along the midrib | Heat, high VPD, light | | Drooping or wilting | Leaves hang from the petiole; say whether firm or limp | Watering, roots | | Twisted or glassy new growth | Deformed, shiny tips | Broad mites, Ca or B, heat | | Coating | Powder, fuzz, web, sticky film; say if it wipes off | PM, mites, honeydew | Add **colour** (pale, lemon yellow, white, rust, bronze, purple, black), **texture** (crispy, papery, soft, slimy) and **speed** ("appeared overnight", "climbing one node a week"). ## How do I take photos that help? **Take three photos in white or natural light: the whole plant, a close-up of the top of an affected leaf, and the underside of the same leaf.** Purple and warm-white LEDs hide yellowing and fake purpling, so switch to a white work light, a phone torch or daylight. 1. **Whole plant**, so the helper can see the gradient from top to bottom. 2. **Close-up, upper surface**, in sharp focus, filling the frame. 3. **Close-up, underside.** Mites, thrips, eggs and septoria fruiting bodies live here [6]. 4. **Scale:** a coin, ruler or fingertip in the close-ups. 5. **Roots** if you are in hydro or the plant wilts in wet media: one photo of the root mass. 6. **The same leaf again in 2–3 days**, from the same angle. Progression is often the deciding clue. Avoid photos taken with a filter, heavy zoom, or under the grow light alone. If you have a phone lens clip or loupe, a 10–30× macro shot of the underside is worth more than ten wide shots. ## Which readings should I include? **Include root-zone readings, not just what you put in.** Input pH and EC tell you what you fed; runoff or reservoir readings tell you what the roots are actually sitting in, and they are often different [4]. | Reading | Give | Why it matters | |---|---|---| | pH in and out | Input pH and runoff (or reservoir) pH | pH lockout causes many apparent deficiencies | | EC in and out | Both values, in mS/cm, or ppm **with the scale** (500 or 700) | A ppm figure without its scale is ambiguous by 40% [5]; runoff far above input means salt build-up | | Meter calibration | When you last calibrated | Uncalibrated meters cause false alarms | | Air temperature | Lights-on and lights-off, at canopy height, in °C or °F | Heat, cold, VPD | | RH | Lights-on and lights-off | VPD, mould risk, Ca delivery | | VPD (if you track it) | kPa, leaf or air | Taco, slow growth, Ca spots | | Light | PPFD at the tops (µmol/m²/s) if you have a meter; otherwise fixture wattage and distance | Bleaching, stretch; cannabis responds to light up to high PPFD when conditions allow [7] | | Reservoir temperature (hydro) | °C or °F | Root rot and dissolved oxygen | ## What setup details should I include? **Give the system, the medium, the water and the plant's age.** The same symptom has different usual causes in soil and in DWC. - **Medium:** soil (bagged or living), coco (buffered or not), rockwool, clay pebbles. - **System:** hand-watered pots, drip to waste, DWC, RDWC, NFT, ebb and flow, aeroponics. - **Pot size** and pot type (fabric or plastic). - **Water source:** tap, well, RO, rain; any water report figures (alkalinity, sodium). - **Watering:** how often, how much, to how much runoff; how heavy the pot feels now. - **Nutrients:** type (mineral or organic, one-part or two-part) and strength; no brand needed, just the EC and any additives. - **Stage and age:** seedling, veg, or flower; days from seed; and **days since the flip** (plus days since first pistils if you track it). - **Cultivar or seed source**, and whether it is an autoflower. - **Recent changes** in the last 7–10 days: new feed, water source, transplant, training, defoliation, light moved, heatwave, new clone, sprays. ## What does a good problem report look like? **A good report fits in a dozen lines and answers every question a helper would ask.** Compare these two. **Not enough to diagnose:** > My plant has yellow leaves and brown spots. What's wrong? Using LED. Help! **Diagnosable:** > **Where:** Lower and middle fan leaves on 2 of 4 plants; tops are fine. > **Looks like:** Yellow between the veins, veins green, a few tan spots 2–3 mm. Started 5 days ago, now 3 nodes up. > **Underside:** Checked with a 30× loupe, no insects or webbing. > **Stage:** Flower day 32 from flip (day 20 of flower), photoperiod. > **Setup:** Coco, 11 L fabric pots, drip to waste 3×/day to ~15% runoff. RO water. > **Feed:** Mineral two-part plus Cal-Mag. Input EC 1.8 mS/cm, pH 5.8. Runoff EC 2.1, pH 5.3. > **Climate:** 27 °C / 55% lights on, 21 °C / 60% lights off. PPFD ~900 at tops. > **Changes:** Switched to the bloom part of the feed 7 days ago. > **Photos:** whole plant, leaf top, leaf underside (white light). That second report nearly diagnoses itself: interveinal yellowing on older leaves, low runoff pH and a recent feed change point to magnesium uptake suppressed by low root-zone pH, with a possible K-heavy bloom feed adding to it. The first report could be any of a dozen causes. ## Copy-paste template ``` WHERE: (old/lower leaves, new/top growth, middle, whole plant, one side) — how many plants of how many LOOKS LIKE: (pattern, colour, texture) — started (date), spreading how fast UNDERSIDE (lens): (insects, eggs, webbing, black specks, nothing) STAGE: (seedling / veg / flower) — days from seed: __ — days since flip: __ — auto or photo CULTIVAR / SEED SOURCE: MEDIUM + SYSTEM: — pot size: — watering how often, how much runoff: WATER SOURCE: (tap / well / RO / rain) — water report if any: FEED: (mineral/organic, strength) — input pH __ EC __ (scale: mS/cm / ppm500 / ppm700) ROOT ZONE: runoff or reservoir pH __ EC __ — reservoir temp (hydro) __ METER LAST CALIBRATED: CLIMATE: lights-on temp __ RH __ — lights-off temp __ RH __ — VPD __ LIGHT: PPFD at tops __ (or fixture watts and distance) ROOTS (if checked): colour, smell, slime CHANGES IN LAST 7–10 DAYS: PHOTOS: whole plant / leaf top / leaf underside / roots — white light, with scale ``` ## How can a GenetixBay journal fill this in for me? **A GenetixBay journal already holds most of the template, so the symptom checker and the Professor can read it instead of asking you.** Stage, days since flip, days of flower, medium, system, pot size, water source and cultivar come from your journal setup; logged pH, EC, temperature, RH and watering come from your entries ([grow journal 101](https://genetixbay.com/knowledge/guides/grow-journal-101.md)). The checker then only asks what it cannot know: where on the plant, the pattern, and what the lens shows. When a Jardin controller is connected to the journal, its sensors log climate and reservoir readings continuously, so the conditions in the days *before* the symptom appeared are already on record. That history is often the deciding clue: the heat spike two nights ago, or the pH that drifted for three days. Jardin is in development; until then, manual journal entries do the same job. ## What should I check before asking for help? 1. **Lens on the underside** of three affected leaves. 2. **Lift the pot** or check the reservoir temperature and air. 3. **Calibrate and read** input and runoff pH and EC ([meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md), [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). 4. **Read climate at canopy height**, lights on and off. 5. **Write down what changed.** Then fill in the template. Doing these five checks first often solves the problem before you post it ([how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md)). ## Common mistakes - Photos under the grow light only; colour is distorted. - One close-up of one leaf, with no whole-plant view. - "pH is fine" without a number, or input pH only. - A ppm figure with no scale. - Leaving out recent changes, especially a new feed, a flip or a transplant. - Removing all the damaged leaves before asking; they are the evidence. - Changing three things at once after asking, so nobody learns which fix worked. ## Evidence - The old-versus-new growth rule is *Established* plant nutrition [1] and holds in cannabis trials [2][3]. - Root-zone sampling by pour-through or runoff as the reading that matters is *Established* extension practice [4]. - The 40% difference between ppm scales is *Established* meter physics [5]. - The report template and photo rules are *Grower practice*, built for GenetixBay's symptom checker. ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 3. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 4. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction 5. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality 6. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php 7. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # How to diagnose any cannabis plant problem > Diagnose in a fixed order: confirm it is a real problem, note where on the plant it started (old vs new growth) and the pattern, then rule out root zone and pH, then environment and light, then pests and disease, and only then blame a nutrient. Change one thing at a time and judge the fix on new growth. - Canonical: https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.html - Category: Diagnosis · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I figure out what is wrong with my cannabis plant?** Figure out what is wrong with a cannabis plant by answering four questions: where on the plant the symptom started, what it looks like, how it is moving, and what changed in the last 7 to 14 days. Write the answers in a plant journal, then rule out causes in a fixed order, from root zone and pH through environment, pests and disease, before blaming a nutrient. **Is it a nutrient deficiency or a pH problem?** Most cannabis symptoms that look like a nutrient deficiency are really an uptake problem, often pH, rather than a shortage in the pot. Measure input and runoff or reservoir pH with a freshly calibrated meter first. Targets are 5.5 to 6.0 in hydro and 5.5 to 6.5 in soilless media; above 6.5, phosphorus, iron and manganese availability falls, and below 5.5 manganese toxicity becomes a risk. **What should I check first when my cannabis plant looks sick?** When a cannabis plant looks sick, first confirm it is a real problem, since lower fan leaves yellowing in late flower is normal senescence. Then check water and roots: pot weight, drainage, and in hydro the root colour, reservoir smell, solution temperature and air pump. After that check pH, EC, environment, light, pests and disease, in that order, from cheapest and most likely onward. **Why do growers say check pH before adding nutrients to cannabis?** Growers check pH before adding nutrients because a cannabis plant at the wrong root-zone pH cannot take up elements that are already in the pot. Adding more fertiliser to that plant raises EC, stresses the roots further and makes the next symptom worse. Research and grower consensus both support fixing the root zone and pH first, then waiting 5 to 7 days. **What does it mean when old cannabis leaves or new leaves show symptoms first?** Where a cannabis symptom starts reveals nutrient mobility. Mobile nutrients (nitrogen, phosphorus, potassium, magnesium) are moved out of old leaves to feed new growth, so shortages show first on lower, older leaves. Immobile ones (calcium, iron, manganese, zinc, copper, boron) cannot be moved, so shortages show first on new growth. Controlled cannabis trials match this established pattern. **Short answer.** Work like a clinician, not a shopper. Note *where* the symptom started (oldest leaves, newest growth, or everywhere), *what* it looks like and *how fast* it is moving. Then rule out the cheap, common causes in order: root zone (water, oxygen, roots), pH, EC, environment and light, pests and disease. Only after that blame a single nutrient. Change one variable, then judge the result on growth that appears *after* the change. ## What's happening Most "deficiencies" growers see are not a shortage of fertiliser in the pot. They are a plant that cannot take up what is already there, because the roots are drowning, rotting, too cold, or sitting at a pH where an element is unavailable. Adding more nutrient to that plant raises EC, stresses the roots further and makes the next symptom worse. That is why every GenetixBay diagnosis tree starts below the soil line. Two pieces of plant biology do most of the diagnostic work *(Established)*: - **Mobility.** Mobile nutrients (N, P, K, Mg) are moved out of old leaves to feed new growth, so their shortage shows first on **lower, older leaves**. Immobile or poorly mobile nutrients (Ca, Fe, Mn, Zn, Cu, B, S to a degree) cannot be moved, so their shortage shows first on **new growth**. Controlled cannabis trials match this pattern: N, P, K and Mg deficiency began on lower foliage; Ca, B, Cu, Fe, Mn and Zn began on upper or expanding foliage [1][2]. - **Pattern.** Uniform symptoms across the whole room point to something shared (water, pH, feed, climate, light). Symptoms on one plant, or spreading plant to plant, point to that plant's roots, a pest or a pathogen. Symptoms only under the hottest part of the light point to light or heat. ## How to recognise it (the four questions) 1. **Where on the plant?** Old/lower leaves, new/top growth, leaves nearest the light, random, or the whole plant. 2. **What does it look like?** Uniform yellowing, interveinal yellowing (veins green), spots (with or without halos), margins and tips burnt, curling (up, down, clawing), stippling (tiny pale dots), powder, webbing, wilting. 3. **How is it moving?** Up the plant, down from the top, outward from one plant, or static. 4. **What changed in the last 7–14 days?** New feed, new water source, transplant, heat wave, new light or height, new clones in the room. Write the answers down. A plant journal turns guesses into evidence. ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Root-zone pH, hydro/DWC | 5.5–6.0 [3] | Grower practice often allows drift to 6.2 | | Root-zone pH, soilless (coco, rockwool) | 5.5–6.5 [3] | Below 5.5, risk of Mn toxicity; above 6.5, P, Fe and Mn availability falls [3] | | Root-zone pH, mineral soil | 6.0–7.0 | Grower practice | | Feed EC, veg | ~1.0–1.8 mS/cm (500–900 ppm500; 700–1260 ppm700) | Grower practice; cultivar and stage dependent. Llewellyn et al. used 1.8 dS/m in veg DWC [2] | | Runoff/root-zone EC vs input | within ~±0.5 mS/cm of input | Grower practice; rising runoff EC = salt build-up | | Nutrient solution temperature | ~18–22 °C (65–72 °F) | Warmer water holds less oxygen and favours Pythium [5] | | Dissolved oxygen | ≥ 6 mg/L, ideally near saturation (~8 mg/L at 25 °C) | Extension guidance for hydro crops [5] | | Air temperature | ~22–28 °C (72–82 °F) lights-on | Grower practice; see environment articles | | Time for new growth to show a fix | 5–10 days | New leaves only; damaged leaves do not recover | ## What to check first Cheapest and most likely first. Do not skip ahead. 1. **Is it actually a problem?** Lower fan leaves yellowing in late flower is normal senescence. One or two old leaves dying in veg is not an emergency. Purple stems on a single genetic line may simply be genetics. 2. **Water and roots.** Pot weight (too heavy for days = overwatered; very light = underwatered). Drainage holes clear. In hydro: smell the reservoir, look at the roots (white and firm good; brown, slimy, smelly bad), check solution temperature and air pump. 3. **pH.** Measure input *and* runoff (or reservoir). Calibrate the meter first (two-point, pH 7 and pH 4 buffers). A meter that has not been calibrated in a month is a guess. 4. **EC.** Input and runoff/reservoir. Too high = burn, clawing, slow growth. Too low = genuine hunger. 5. **Environment.** Air temperature, RH, VPD, night temperature, airflow, and canopy temperature under the light. 6. **Light.** Distance or measured PPFD at the top of the canopy. Bleaching or upward taco near the light is light/heat stress, not a nutrient. 7. **Pests.** Hand lens (10–20×) on the *undersides* of leaves, especially new growth. Yellow sticky cards. Shake a branch over white paper. Spider mites can complete a generation in under a week when warm [6]. 8. **Disease.** Powder, spots with halos, rotting stems, browning roots, wilting with moist media. 9. **Only now: a single-nutrient deficiency or toxicity.** Match the pattern to the controlled-trial descriptions [1][2]. Consider a tissue test if the problem is persistent or commercial. ## How to fix it - **Change one thing at a time.** If you correct pH, change feed and move the light on the same day, you will never know which one worked. - **Fix the root zone before you feed.** Correct watering rhythm, aeration, temperature and pH, then wait 5–7 days. - **In hydro, a fresh reservoir is a cheap reset.** Mix to target EC and pH; it removes drift and imbalance in one move. - **Salt build-up or lockout: flush the medium, not the plant.** If runoff EC is far above input or runoff pH is well out of range, a root-zone flush resets it: 2–3× the container volume of a light solution (coco/rockwool, EC ~0.4–0.8 mS/cm with Ca and Mg) or pH-adjusted plain water (soil), then check runoff EC and resume normal feeding. Any stage; *Grower practice* (see [the root-zone flush](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). Pre-harvest flushing for taste is a different thing, and a *Myth*. - **In soil, slow down.** Soil buffers changes; don't flush a pot that is already waterlogged, and don't flush repeatedly. Correct pH of inputs and allow drying between waterings. - **Remove nothing yet.** Leave damaged leaves until you have confirmed the cause; they tell you whether the problem is still spreading. ## How to confirm it worked - New leaves that form after the fix are normal in colour and shape (5–10 days). - The symptom stops advancing up or down the plant. Old damage stays; that is expected. - Runoff or reservoir pH and EC stay in range for at least two checks. - For pests: counts on sticky cards and leaf samples fall over two consecutive weekly checks. ## Common mistakes - Treating the oldest damaged leaves as the test. They will never turn green again; watch new growth. - Adding Cal-Mag, then bloom booster, then micronutrients in a week. EC climbs, roots burn, symptoms multiply. - Trusting an uncalibrated pH pen or pH test drops alone in hydro. - Diagnosing from one photo under a coloured grow light. Look under white light. - Ignoring the calendar: late-flower fade, autoflower stress and genetic colour are not problems. ## Evidence - Mobility-based diagnosis (old vs new growth) is *Established* plant nutrition and matches cannabis-specific trials in sand culture [1] and DWC hydroponics [2]. Note that in Llewellyn et al. Mn deficiency produced no visible symptoms, while in Cockson et al. it produced bright netted interveinal chlorosis on upper foliage [1][2]: cultivar and system matter. - pH ranges for hydro and soilless are *Supported* by horticultural literature cited in cannabis research [3]; there is little cannabis-specific pH dose–response work. - "Root zone and pH first" is *Supported* (consistent with plant physiology and pathogen literature [4][5]) and is strong grower consensus. - EC targets are *Grower practice*; nutrient-rate trials (e.g. N rate) exist but EC optima vary by cultivar and system. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Velechovský J, Malík M, Šenkyřík JB, Tlustoš P., 2024. Effect of augmented nutrient composition and fertigation system on biomass yield and cannabinoid content of medicinal cannabis. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 4. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 5. University of Kentucky, Hydroponic root health / Pythium in nutrient solutions (E706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 6. UC IPM Pest Notes: Spider Mites (Pest Note 7405). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # Purple or red stems and leaves on cannabis: a differential > Purple or red stems and petioles on a healthy, growing plant are usually genetics, cool nights or bright light, and need no fix. Treat it as a problem only when it comes with something else: lower-leaf yellowing (nitrogen), dark or bronzed spotting on old leaves (phosphorus), or slow growth with a cold or wet root zone. Check root-zone temperature and pH before adding phosphorus. - Canonical: https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.html - Category: Diagnosis · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my cannabis stems purple?** Purple cannabis stems are usually anthocyanin pigments caused by genetics, cool nights or bright light, and need no fix on a plant that is green-leafed and growing well. Treat purple as a symptom only when it comes with yellowing lower leaves, olive or bronze spotting on old leaves, or stalled growth with a cold, wet root zone below about 18 °C (65 °F). **Are red cannabis petioles a sign of phosphorus deficiency?** Red cannabis petioles alone are a weak sign of phosphorus deficiency. In a controlled hydroponic study, phosphorus deficiency caused only moderate petiole purpling, while nitrogen deficiency turned petioles of the worst leaves red-brown. In sand culture the main phosphorus sign was olive-green, sunken spotting on lower leaves. Red petioles with lower leaves yellowing upward point to nitrogen instead. **Why do cannabis leaves turn purple in late flower?** Cannabis leaves and bracts that purple in late flower on an otherwise healthy plant are normally genetics combined with senescence and cool nights, and need no action. Cultivars that carry anthocyanin genes colour more when the night drop is larger than the usual 3 to 6 °C (5 to 10 °F). The colour is cosmetic and does not affect quality. **Do cold nights make cannabis turn purple?** Cold nights do make some cannabis turn purple: nights below about 15 °C (59 °F) increase anthocyanin in cultivars that carry it, which is established across many crops and grower practice in cannabis. The colour is real, but the idea that cold adds terpenes, flavour or resin is a myth. Dropping nights hard can slow growth and reduce phosphorus uptake. **Should I add phosphorus to fix purple cannabis stems?** Do not add phosphorus for purple cannabis stems unless phosphorus deficiency is confirmed by olive or bronze spotting on old leaves and slow growth. First check root-zone temperature (18 to 22 °C) and pH, since both limit phosphorus uptake. Most complete feeds have enough phosphorus, and large bloom-booster doses can antagonise zinc and iron uptake. **Short answer.** Purple or red stems, petioles and even leaves are pigments called anthocyanins. Plenty of cultivars make them on their own, and many more do so under cool nights or strong light. If the plant is green-leafed, growing well and only the stems are purple, leave it alone. Treat purple as a symptom only when it travels with something else: yellowing lower leaves (nitrogen), olive or bronze spotting on old leaves (phosphorus), or stalled growth with a cold, wet root zone. ## What's happening Anthocyanin accumulation is a general plant stress and light response, and is strongly genotype-dependent (*Established* in plant biology; cannabis-specific genetics are only partly mapped). In a controlled DWC study, nitrogen deficiency turned petioles of the worst-affected leaves red-brown and then browned stems, while phosphorus deficiency produced *moderate* purpling of petioles with little other anthocyanin [1]. Neither produced the dramatic all-purple plant that growers often blame on P. In sand culture, P deficiency's main sign was olive-green, sunken spotting on lower leaves rather than purple [2]. So purple alone is a weak sign of P deficiency (*Supported*). Cold root zones and high pH reduce P uptake even when P is present (*Established* in horticulture), which is why "phosphorus" purpling often coincides with cold rooms. ## How to recognise it | Pattern | Most likely | Action | |---|---|---| | Stems/petioles purple, leaves healthy, growth normal | Genetics or light | None | | Purple appears after nights fall below ~15 °C (59 °F) | Cold-induced anthocyanin | Optional: warm nights if growth slows | | Leaves and bracts purpling in late flower, plant healthy | Genetics plus senescence and cool nights | None | | Red-brown petioles with lower leaves yellowing upward | Nitrogen deficiency [1] | See [yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) | | Purpling petioles with olive/bronze spots on old leaves, slow growth | Phosphorus deficiency or P uptake failure [1][2] | Check root temp, pH, feed P | | Purple and stunted, roots brown | Root damage | See [drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) | | Purple-red and dark leaves at the very top under strong light | Light stress | Consider lowering PPFD if growth suffers | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Night air temperature, veg | ~18–22 °C (64–72 °F) | Grower practice | | Night drop vs day, flower | ~3–6 °C (5–10 °F) | Grower practice; larger drops increase colour on susceptible cultivars | | Root-zone temperature | 18–22 °C (65–72 °F) | Below ~16 °C P uptake slows (horticultural) | | pH, hydro / soilless | 5.5–6.0 / 5.5–6.5 | Above 6.5, P availability falls [3] | | Leaf P, healthy | ~0.24–0.49% dry weight | [2] | ## What to check first 1. **Is anything else wrong?** No yellowing, no spotting, normal growth rate: it is cosmetic. 2. **Genetics.** Do siblings or the same clone in another room colour the same way? 3. **Night and root temperature.** Cold floors and unheated tents at night are common. 4. **pH at the root zone.** High pH limits P. 5. **Leaf pattern.** Bottom-up yellowing = N. Olive/bronze sunken spots on old leaves = P. 6. **Root health.** Brown or sparse roots limit everything. ## How to fix it - **Cosmetic purple:** nothing to fix. Many growers like it. - **Cold:** raise night temperature or insulate pots off cold floors. Keep the root zone ~18–22 °C. - **pH:** bring the root zone into range before changing the feed. - **Nitrogen deficiency:** see [yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md). - **Phosphorus deficiency confirmed:** modestly increase P (most complete feeds have enough; in one hydroponic study flower P stopped rising above ~30 mg/L P supply, cited by later work). Avoid large "bloom booster" P doses; excess P can antagonise zinc and iron uptake (*Established* in horticulture). ## How to confirm it worked - New growth is green with normal-coloured petioles (if the purple was a symptom). - Spotting and yellowing stop progressing within 5–10 days. - Cosmetic, genetic purple will not change, and that's fine. ## Common mistakes - Dropping nights hard to "boost terpenes". Cold brings out colour in cultivars that carry it; it doesn't add terpenes or resin (*Myth*). - Dumping high-P bloom boosters on a plant with genetic purple stems. - Ignoring a cold root zone and blaming the bottle. - Judging colour under a pink/purple LED; look under white light. ## Evidence - N and P deficiency petiole colour in cannabis: *Established* in one DWC study [1]; P deficiency primarily as spotting: *Established* in sand culture [2]. - "Purple stems = phosphorus deficiency": *Myth* as a standalone rule. - Cool nights increasing anthocyanin: *Established* across many crops; *Grower practice* in cannabis. The colour is real; cold adding terpenes, flavour or resin: *Myth* (house position). ## Sources 1. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 2. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 3. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 4. Westmoreland FM, Kusuma P, Bugbee B., 2021. PLOS ONE 16(3):e0248988. https://doi.org/10.1371/journal.pone.0248988 --- # Purple, red, bronze or dark leaves on cannabis: the master discolouration decision tree > Most purple and red on a healthy, growing cannabis plant is anthocyanin: genetics, cool nights or strong light, and no fix is needed. Discolouration is a problem only alongside another sign: red-brown petioles with bottom-up yellowing (nitrogen), dull dark leaves with olive-bronze spots and slow growth (phosphorus uptake, often a cold or high-pH root zone), very dark glossy clawed leaves (nitrogen excess), bronze, brittle, upward-curling leaves (russet mites, or late Mg or K deficiency), or reds and oranges as leaves fade in late flower (normal senescence). - Canonical: https://genetixbay.com/knowledge/diagnosis/discolouration-decision-tree.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my cannabis leaves turning purple?** Purple cannabis leaves on a healthy, growing plant are usually anthocyanin pigment from genetics, cool nights or strong light, and need no fix. Purple is a problem only with other signs: dull dark leaves with olive or bronze spots and slow growth suggest phosphorus uptake failure, often from a cold or high-pH root zone. Check root temperature and pH before adding phosphorus. **Do purple stems mean phosphorus deficiency in cannabis?** Purple stems alone do not mean phosphorus deficiency in cannabis. In a controlled hydroponic trial, phosphorus deficiency caused only moderate purpling of petioles, while the main sign in substrate was olive-green, sunken spots on lower leaves. Many cultivars have purple stems from genetics or cool nights. Suspect phosphorus only when purple comes with spotting, dark dull leaves and slow growth. **Why are my cannabis leaves turning bronze?** Bronze, dull cannabis leaves that go brittle and curl their edges upward, starting low and inside the plant, are the classic sign of hemp russet mites, which need 30× or stronger magnification to see. Late-stage magnesium or potassium deficiency and heat stress can bronze leaves too. Check under magnification first, because mites spread fast, then check runoff pH and EC. **Why are my cannabis leaves very dark green?** Very dark, glossy cannabis leaves with tips clawing down usually mean excess nitrogen, often with high root-zone EC. Dark, dull, blue-grey-green leaves that stop growing, with spots on the older ones, suggest phosphorus uptake problems instead. Measure input and runoff EC and look at the feed's nitrogen rate; lowering nitrogen by 10 to 20 percent is usually enough. **Do cold nights make cannabis purple?** Cold nights make cannabis purple only in cultivars that carry the genetics for anthocyanin; nights about 5 to 10 °C cooler than days bring the colour out. A cultivar without those genes stays green however cold it gets. Cold for colour is real, but claims that cold nights add terpenes, flavour or resin are a myth unless peer-reviewed data shows otherwise. Purple is bag appeal, not potency. **Short answer.** If the plant is growing well and nothing else is wrong, purple and red are almost always anthocyanin: genetics, cool nights or strong light. Leave it alone. Discolouration only matters with a second sign. Red-brown petioles with yellowing from the bottom: nitrogen. Dull dark leaves, olive-bronze spots, slow growth: phosphorus uptake, usually a cold or high-pH root zone. Very dark, glossy, clawed leaves: too much nitrogen. Bronze, brittle, edges curling up: russet mites until proven otherwise. Reds and oranges fading in late flower: normal ripening. The GenetixBay symptom checker treats colour the same way: it asks for the second sign before it suggests a nutrient. ## What makes cannabis leaves change colour? Cannabis leaf colour is the balance of three pigment groups. Chlorophyll is green; carotenoids are yellow and orange; anthocyanins are red, purple or blue, stored in the cell vacuole [3]. Whether a plant can make much anthocyanin is mainly genetic; cool temperatures, high light and the breakdown of chlorophyll in late flower bring it out [3][4]. Nutrient shortages change colour either by removing chlorophyll (yellowing) or by stressing the plant into making anthocyanin, as phosphorus and nitrogen shortage can [1][5]. Bronzing is different again: it is a dull, metallic surface caused by damaged epidermal cells, typical of russet-mite feeding [6]. ## The discolouration decision tree, step by step ### Fork 1: Is the plant otherwise healthy? | Growth rate | Other symptoms | Verdict | |---|---|---| | Normal, vigorous | None | Cosmetic. Genetics, cool nights or light. No fix | | Slow, or stalled | Yes (yellowing, spots, curling) | Fork 2 | | Normal | Bronze, brittle leaves or twisted tips | Fork 2, bronze row: check for mites | ### Fork 2: What colour, and where? | Colour and location | Go to | |---|---| | Purple or red stems and petioles | Fork 3A | | Purple or red leaf blades | Fork 3B | | Bronze, dull metallic leaves | Fork 3C | | Very dark green | Fork 3D | | Grey or blue-grey cast | Fork 3E | | Red, orange and yellow fading together, late flower | Normal senescence | ### Fork 3A: Purple or red stems and petioles | Clue | Cause | |---|---| | Healthy plant, whole run, sibling or same clone does the same | Genetics | | Appears after nights below ~15 °C (59 °F) | Cold-induced anthocyanin | | Red-brown petioles on the worst lower leaves, yellowing climbing up | Nitrogen deficiency [1] | | Moderate petiole purpling, olive or bronze spots on old leaves, slow | Phosphorus uptake problem [1][2] | | Purple stems on young plants under very strong light | Light response; harmless unless growth slows | ### Fork 3B: Purple or red leaf blades | Clue | Cause | |---|---| | Sugar leaves and bracts purpling in late flower, plant healthy | Genetics plus cool nights and senescence [3][4] | | Whole leaves dark, dull, purpling, with sunken spots on lower leaves | Phosphorus uptake, often cold root zone or high pH [2][5] | | Top leaves red-purple, nearest the light | Light stress [9] (see [heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md)) | | Purple with stunting, brown roots | Root damage (see [root problems](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md)) | ### Fork 3C: Bronze leaves Check under 30× or stronger magnification before anything else [6]. | Clue | Cause | |---|---| | Bronze, brittle, edges curling up, starting low and inside the plant | Hemp russet mites [6] | | Bronze-tan margins on older leaves, after yellowing at the edges | Late potassium deficiency [2] | | Bronze-brown between veins of older leaves, after interveinal yellowing | Late magnesium deficiency [1][2] | | Bronze top leaves, crisp, nearest the light | Heat or light stress | | Bronze, stunted single plant | Consider HLVd testing [10] | ### Fork 3D: Very dark green | Clue | Cause | |---|---| | Dark, glossy, tips clawing down, soft growth, high EC | Nitrogen excess (see [curling and clawing](https://genetixbay.com/knowledge/diagnosis/curling-clawing-decision-tree.md)) | | Dark, dull, blue-green, growth stalled, spots on old leaves | Phosphorus uptake problem | | Dark green, otherwise healthy, broad-leaved cultivar | Normal for that cultivar | ### Fork 3E: Grey or blue-grey cast A grey cast on the leaf surface that wipes off is a coating, not a colour: powdery mildew or residue (see [white and grey coatings](https://genetixbay.com/knowledge/diagnosis/white-grey-coatings-decision-tree.md)). A dull grey-green that does not wipe off, with stalled growth, points to phosphorus uptake or a cold root zone. Grey-brown, dry patches on leaves facing a fan are wind burn. ### Fork 4: Readings | Reading | Interpretation | |---|---| | Root zone below ~16–18 °C (61–64 °F) | P uptake slows; purple and dark growth follow (*Established* in horticulture [5]) | | Runoff pH above ~6.5 (soilless) / ~7.0 (soil) | P less available [7] | | Runoff EC far above input, leaves dark | Nitrogen and salt excess | | Input EC low, red petioles, yellow bottom | Genuine nitrogen shortage | | Night temperature 5–10 °C (9–18 °F) below day | Colour in susceptible cultivars [3][4] | ## The discolouration differential table | Symptom pattern | Most likely | Rule out first | Key test | |---|---|---|---| | Purple stems, healthy plant | Genetics | Cold nights | Compare siblings; night temperature log | | Purple after cold nights | Cold-induced anthocyanin | P uptake | Night and root temperature | | Red-brown petioles plus bottom yellowing | Nitrogen deficiency | Overwatering, root rot | Pot weight, roots, input EC | | Dark dull leaves, olive-bronze spots, purple petioles | Phosphorus uptake | Cold roots, high pH | Root-zone temperature, runoff pH | | Very dark glossy clawed leaves | Nitrogen excess | Overwatering | Runoff EC, feed N | | Bronze, brittle, edges up | Russet mites | Mg, K, heat | 30–60× magnification | | Bronze margins, old leaves | Potassium (late) | Salt build-up | Runoff EC vs input | | Red-purple tops nearest the light | Light stress | Genetics | Canopy PPFD | | Reds and oranges, late flower, slow fade | Normal senescence | Early N cut | Weeks since flip | | Grey that wipes off | Powdery mildew or residue | — | Wipe test, lens | ## What numbers matter for discolouration? | Parameter | Target | Notes | |---|---|---| | Night air temperature, veg | ~18–22 °C (64–72 °F) | Grower practice | | Day–night difference, flower | ~3–6 °C (5–10 °F); bigger for colour | Grower practice; colour needs the genetics [3][4] | | Root-zone temperature | 18–22 °C (65–72 °F) | Below ~16 °C P uptake slows | | Root-zone pH, hydro / soilless | 5.5–6.0 / 5.5–6.5 | Above 6.5, P availability falls [7] | | Root-zone pH, soil | 6.0–7.0 | Grower practice | | Feed P | ~30–60 mg/L | More P does not raise yield; see [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) | | Feed N, veg/early flower | ~150–200 mg/L | See [nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md) | | Leaf P, healthy | ~0.24–0.49% dry weight | [2] | | Canopy PPFD, flower (no added CO₂) | ~800–1200 µmol/m²/s | Grower practice | ## What should I check first when leaves change colour? Ask whether anything else is wrong before chasing a colour. 1. **Growth rate.** Normal growth and no other symptoms: stop, it's cosmetic. 2. **Siblings and history.** Does the same cultivar or clone colour the same way elsewhere? 3. **Night and root-zone temperature.** Cold floors and cold reservoirs are the usual hidden cause. 4. **Calibrated runoff pH and EC.** 5. **Magnification on bronzed leaves**, 30× or better. 6. **Feed record.** N rate, P rate, any recent "bloom" switch. 7. **Stage.** Late flower colour change is often just ripening. ## How do I fix discolouration in cannabis? - **Genetics or cool nights:** nothing to fix. If growth slows, raise night temperature to ~18–20 °C (64–68 °F). - **Phosphorus uptake:** warm the root zone to 18–22 °C; correct high pH; make sure the feed supplies ~30–60 mg/L P. Do not pile on a bloom booster; extra P adds nothing and can tie up zinc and iron (see [phosphorus](https://genetixbay.com/knowledge/nutrients/phosphorus.md)). - **Nitrogen deficiency:** fix watering and roots first, then raise N about 10–20%. - **Nitrogen excess:** lower N 10–20% or feed EC by 0.2–0.4 mS/cm; keep ammonium at or below about 10–30% of total N. - **Russet mites:** isolate; see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). Act fast; in flower your options narrow. - **Late Mg or K bronzing:** check pH and runoff EC first, then correct the feed (see [magnesium](https://genetixbay.com/knowledge/nutrients/magnesium.md), [potassium](https://genetixbay.com/knowledge/nutrients/potassium.md)). - **Light stress:** raise or dim the fixture until top-leaf colour and temperature settle. - **Late-flower colour:** keep feeding. The GenetixBay approach is to taper nitrogen while keeping P, K, Ca, Mg, S and micros fed [8]. Do not flush: pre-harvest flushing is a *Myth* that costs yield and resin. ## How do I know the fix worked? Cosmetic colour needs no confirmation. For phosphorus, new leaves come in mid-green and growth picks up within 7–10 days of warming the root zone and correcting pH; spotted old leaves stay spotted. For nitrogen, red petioles stop appearing on new leaves within a week. For mites, repeat magnified checks show none for three weekly scouts and new leaves stay free of bronzing. ## What are the common mistakes with purple or bronze leaves? - Adding phosphorus to a plant that is simply purple by genetics. - Treating russet-mite bronzing as magnesium deficiency for weeks while the mites spread. - Running cold nights for "more terpenes"; colour is real, terpene and resin gains are a *Myth* without peer-reviewed data [4]. - Confusing bag appeal with quality: purple is not potency. - Forcing late-flower colour with a flush or darkness. Both are myths that cost the crop. ## How strong is the evidence? - Anthocyanin as the cause of purple and red, set by genetics and enhanced by cool temperatures, is *Established* [3][4]. - Phosphorus deficiency in cannabis producing only moderate petiole purpling and mainly olive spotting is *Supported* by two controlled trials [1][2]. - Nitrogen deficiency producing red-brown petioles in DWC cannabis is *Supported* [1]. - Cold root zones and high pH reducing P uptake are *Established* in plant nutrition [5]; cannabis thresholds are *Grower practice*. - Russet-mite bronzing is *Established* by extension [6]. - Cold nights raising terpenes or resin: *Myth* (unsupported); anthocyanin and yield have different temperature optima [4]. ## Sources 1. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 2. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 3. Bassolino L, Fulvio F, Pastore C, et al. 2023. When Cannabis sativa L. turns purple: biosynthesis and accumulation of anthocyanins. Antioxidants 12(7):1393. https://doi.org/10.3390/antiox12071393 4. Kim SR, Basnet P, Kovaleski AP, Ellison SL. 2025. Anthocyanin accumulation, inflorescence dry weight and total cannabidiol content have different temperature optima in Cannabis sativa. Journal of Cannabis Research 7:51. https://doi.org/10.1186/s42238-025-00311-w 5. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 6. Utah State University Extension. Hemp Russet Mite. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-hemp-russet-mite-.php 7. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 8. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 9. Westmoreland FM, Kusuma P, Bugbee B., 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLOS ONE 16(3):e0248988. https://doi.org/10.1371/journal.pone.0248988 10. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa)-Viroid Diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases --- # Rust-coloured spots on cannabis leaves: a differential > Rusty brown spots are most often a calcium or phosphorus uptake problem driven by pH or root-zone stress, but leaf septoria (spots with yellow halos on lower leaves, spreading in humidity) and spider-mite stippling look similar. Check pH and root zone, then turn the leaf over with a hand lens, then decide between Ca, P, Mg/Mn and disease. - Canonical: https://genetixbay.com/knowledge/diagnosis/rust-spots.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why does my cannabis have rust spots on the leaves?** Rust-coloured spots on cannabis leaves usually come from calcium uptake failure, phosphorus shortage, a fungal leaf spot such as septoria, or mite feeding. The nutrient causes are almost always driven by pH or a stressed root zone rather than an empty bottle. Check pH and roots first, then inspect the leaf underside with a 10 to 20x lens before reading the spot shape. **Are brown spots on cannabis leaves from calcium or disease?** Brown spots on cannabis leaves are more likely disease when they start on the lowest leaves and spread upward in a humid room, and more likely calcium when they appear scattered on mid-lower fan leaves after a pH or root-zone problem. Always flip the leaf first: pale stippling with mites, eggs or webbing underneath is pest damage, not either one. **What causes rusty spots with a yellow halo on cannabis leaves?** Rusty spots with bright yellow halos on cannabis leaves that start on the oldest leaves, enlarge, merge and spread in rain or high humidity are typical of septoria leaf spot, according to extension sources. Look for tiny black dots (pycnidia) in the lesions with a hand lens. Calcium deficiency can also make yellow-ringed spots but they do not spread from plant to plant. **Why do cannabis plants in coco get brown spots on lower leaves?** Cannabis in coco often gets brown spots on lower leaves when root-zone pH falls below about 5.5, which reduces calcium and magnesium availability, or when soft or RO water is used with a base nutrient lacking calcium. Keep coco pH at 5.5 to 6.5, warm and aerate the roots, and grower practice aims for roughly 100 to 200 mg/L calcium in soilless feeds. **Is it calcium deficiency or septoria on my cannabis?** Calcium deficiency and septoria on cannabis differ in pattern. Calcium spots, with brown centres and yellow rings, appeared on lower fan leaves from week 3 of flower in a controlled hydroponic study and do not carry fruiting bodies. Septoria spots have bright yellow halos, tiny black pycnidia, start on the lowest leaves and spread upward in humid conditions. Removing affected leaves only stops septoria. **Short answer.** Rusty or bronze spots usually come from one of four things: calcium uptake failure, phosphorus shortage, a fungal leaf spot such as septoria, or pest feeding (spider mites, russet mites). The first two are almost always driven by pH or a stressed root zone rather than an empty bottle. Check pH and roots first, then flip the leaf and look with a 10–20× lens, then read the spot shape. ## What's happening Calcium moves only in the transpiration stream, so anything that slows transpiration or root function (high RH, cold or wet roots, low pH in soilless media) starves fast-growing leaves. In DWC cannabis, Ca deficiency produced spots with yellow rings and brown centres on lower fan leaves from week 3 of flower, then margin necrosis and upward curling [2]; in sand culture it distorted new growth [1]. Phosphorus deficiency in sand culture caused olive-green spots on lower leaves that became sunken, almost wet-looking, then necrotic [1]; in DWC, tiny chlorotic spots on lower fan leaves became necrotic lesions [2]. Advanced Mg and Mn disorders also leave tan necrotic flecks between veins [1]. Septoria leaf spot (*Septoria cannabis*) starts on lower, older leaves as small brown spots with bright yellow halos that enlarge and merge, and spreads quickly in rain or high humidity [4][5]. Spider mites leave pale stippling that bronzes with time, on the upper surface, with mites and eggs underneath [6]. ## How to recognise it | Spot appearance | Where | Most likely | Confirm by | |---|---|---|---| | Brown centre, yellow ring, scattered, mid/lower fan leaves | Mid-lower, often after week 3 flower | Calcium uptake | pH, RH, root health; Ca level in feed | | Olive/bronze, sunken, irregular, with dark petioles | Lower, older | Phosphorus | Feed P, pH, cold root zone | | Tan flecks between green veins | Lower (Mg), upper/mid (Mn) | Mg or Mn disorder | Interveinal pattern first | | Brown spot with bright yellow halo, enlarging, merging; may have tiny black dots (pycnidia) | Lowest leaves first, moving up | Septoria leaf spot [4][5] | Hand lens for pycnidia; humid history | | Fine pale stippling turning bronze, webbing | Any; worst on upper surface of leaves | Spider mites [6] | Mites/eggs on underside | | Bronzed, dull leaves, edges curling up, no webbing | Lower, moving up | Hemp russet mite | 40× lens or microscope | | Brown spot exactly where water droplets sat under light | Top | Light lens effect / spray burn | History of foliar sprays | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | pH, hydro | 5.5–6.0 | [3] | | pH, coco/rockwool | 5.5–6.5 | Low pH reduces Ca and Mg availability (Established in horticulture) | | Leaf Ca, healthy | ~1.5–4.4% | Survey range in [1]; deficient 0.39% | | Leaf P, healthy | ~0.24–0.49% | [1]; deficient 0.09% | | RH, late flower | ~40–50% | Grower practice; high RH slows Ca transport and favours septoria | | Root-zone temperature | 18–22 °C (65–72 °F) | Cold roots reduce P uptake (Established in horticulture) | ## What to check first 1. **Flip the leaf.** 10–20× lens on the underside. Moving dots, eggs or webbing = mites. Do this before anything else. 2. **Spot shape.** Yellow halo plus spread from the bottom in a humid room = suspect septoria; remove one leaf and check for tiny black fruiting bodies. 3. **pH of root zone.** Coco below ~5.5 is a common cause of Ca/Mg spotting. 4. **Root zone.** Wet, cold or damaged roots cut Ca and P uptake. 5. **RH and airflow.** Very high RH (Ca transport) or very still air. 6. **Feed.** RO or very soft water with a base nutrient lacking Ca; P-light veg formula carried into flower. ## How to fix it - **Mites:** follow [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md) or [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). - **Septoria:** remove affected lower leaves, bag them, improve airflow, lower RH, avoid wetting foliage. See [septoria leaf spot](https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.md). - **Calcium:** correct pH, warm and aerate roots, keep RH in range so the plant transpires, then make sure the feed supplies Ca (RO water users typically need a Ca/Mg source). Grower practice: aim for roughly 100–200 mg/L Ca in soilless feeds. - **Phosphorus:** warm the root zone, correct pH, and check the flower feed actually supplies P. Note: P uptake into flowers plateaued at about 30 mg/L P in one hydroponic study; more P than that did not raise flower P (Shiponi and Bernstein 2021, cited by later work). - **Mg/Mn:** follow the patterns in [yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) and [yellow new growth](https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.md). ## How to confirm it worked - No new spots on leaves that expand after the fix (5–10 days). - For septoria: no new lesions above the removed leaves for two weeks. - For mites: no live mites on 10 sampled leaves at the weekly check. ## Common mistakes - Dosing Cal-Mag for every spot; it does nothing for septoria or mites and can push EC too high. - Blaming the LED. "LEDs need more Cal-Mag" is a *Myth*; real Ca/Mg spotting follows cultivar, RO water, unbuffered coco, low pH or low transpiration ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)). - Foliar spraying a humid canopy, which spreads septoria spores. - Ignoring the underside of the leaf. - Expecting spotted leaves to heal. They won't; judge new growth. ## Evidence - Ca and P spotting patterns in cannabis are *Established* in two controlled studies, though they look different in sand vs DWC [1][2]. - Septoria leaf spot description and conditions are *Established* by extension [4][5]. - Ca targets in feed are *Grower practice*. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 4. Utah State University Extension. Hemp Leaf Spot. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-leaf-spot 5. University of Kentucky Plant Pathology. Septoria leaf spot of hemp (PPFS-AG-H-01). https://plantpathology.mgcafe.uky.edu/files/ppfs-ag-h-01.pdf 6. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php --- # Slow or stunted cannabis growth: a differential > When a plant just isn't growing, the cause is usually the root zone (overwatering, cold, small or rotting roots), too little light, or a cool room; nutrient shortages come later. Plants that stay stunted with small leaves and short internodes while neighbours thrive should be tested for hop latent viroid and checked for root aphids. - Canonical: https://genetixbay.com/knowledge/diagnosis/slow-growth.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why is my cannabis growing so slowly?** Slow cannabis growth is usually caused by the root zone (overwatering, cold media, small or rotting roots), too little light, or a cool room, with nutrient shortages coming later. Check watering and roots, then air and root-zone temperature, then PPFD and photoperiod, then pH and EC. Research shows indoor cannabis yield rose linearly with light up to 1800 µmol/m²/s, so under-lit plants grow slowly. **Why did my cannabis seedling stop growing?** A cannabis seedling that stops growing is most often sitting in a pot that is too big and stays wet, so its small root system is short of oxygen; it looks droopy and pale. Lift the pot, let it dry back, and up-pot in steps next time. Also check that seedling light is about 150 to 300 µmol/m²/s and the root zone is near 18 to 22 °C. **Why is my cannabis plant stunted with small leaves?** A cannabis plant stunted with small leaves and short internodes while neighbours on the same feed thrive points to a plant-specific problem: hop latent viroid, root rot or root aphids. Extension sources describe infected plants as stunted, sometimes with chlorosis and brittle stems. Inspect the roots for browning and insects, and test the plant for the viroid by RT-PCR. **Why is my cannabis clone not growing after rooting?** A cannabis clone that sits for 1 to 2 weeks after transplant is usually still establishing roots, a delay made worse by over-sized pots and cold media. Keep the root zone around 20 °C, water lightly so the pot dries back, and give moderate light. If one clone stays stunted long after its siblings recover, test it and its mother for hop latent viroid. **Is my cannabis plant stunted by hop latent viroid?** A cannabis plant may be stunted by hop latent viroid if it stays small with smaller leaves, shorter internodes and brittle stems while its neighbours grow normally, though many infected plants show no symptoms. Only a lab test (RT-PCR or RT-qPCR, often on root samples) confirms it. There is no cure, so remove positives from propagation and restart from clean, tested stock. **Why is my autoflower so small?** An autoflower stays small when anything slows it in the first three to four weeks, because it flowers on a fixed countdown from germination and cannot extend veg to catch up. Common causes are transplant shock, overwatering a seedling in a big pot, low light, a cold root zone and early heavy feeding. Plant autos straight into their final pot and keep stress near zero. **Can a pot that is too big slow down a cannabis seedling?** Yes. A cannabis seedling in a very large pot often stalls because its small root system cannot use the water held in all that medium, so the root zone stays wet and short of oxygen. Water only a small circle around the stem until roots spread, or start in a smaller pot and up-pot in steps. Autoflowers are the exception: plant them in the final pot and water carefully. **Short answer.** A plant that sits still is usually telling you about its roots or its light. Check, in order: watering and root health, root-zone and air temperature, light intensity and photoperiod, pH and EC, and pests on the roots and new growth. If one plant stays small with tiny leaves and short internodes while its neighbours on the same feed thrive, test it for hop latent viroid (HLVd); it is common in clone-based grows and often has no other obvious sign [3][4]. ## What's happening Growth is the product of light captured, carbon fixed and roots able to supply water and nutrients. Any one of these sets the ceiling. Yield in indoor cannabis rose linearly with canopy PPFD up to 1800 µmol/m²/s in one trial [1], so under-lit plants are slow plants. Temperature also matters: photosynthesis responded to temperature, and above ~30 °C (86 °F) it declined in one cultivar [2]. Root problems (overwatering, Pythium/Fusarium root rot in hydro [6], root aphids [5]) restrict everything above ground. HLVd-infected plants may be symptomless or show stunting, smaller leaves, shorter internodes, chlorosis and brittle stems [4]; it spreads through propagation from infected mothers [3]. ## Why has my plant stopped growing? (the master decision tree) Work through the forks in order. Each fork is cheaper and more likely than the next; stop when one fits and confirm it with the key test in the table below. 1. **Is it the whole room, or one or a few plants?** - **Whole room, all plants equally slow** → a shared input: light, temperature, photoperiod, water source, feed or pH. Go to step 2. - **One or a few plants, neighbours fine on the same feed** → a plant-specific cause: roots, a root pest, a viroid or genetics. Go to step 6. 2. **What stage, and what type of plant?** - **Seedling (first 2–3 weeks)** → step 3. - **Freshly rooted clone or just transplanted** → expect 5–14 days of slow top growth while roots establish; check the medium is not cold or soggy. Beyond ~2 weeks, go to step 4. - **Autoflower** → any setback costs it permanently, because it flowers on a countdown from germination (house position). Look for a transplant, a soggy start, low light or early heavy feeding in weeks 1–4 ([why is my autoflower small](https://genetixbay.com/knowledge/answers/why-is-my-autoflower-small.md)). - **Veg or flower photoperiod plant** → step 4. 3. **Seedling forks.** - Big pot that stays wet, droopy, pale → **overwatering a small root system**. The commonest seedling stall. - Stem pinched and dark at the soil line, collapsing → **damping-off**, a seedling disease [9] ([damping-off](https://genetixbay.com/knowledge/germination/damping-off.md)). - Stretched, pale, leaning to the light → **too little light** (below ~150 µmol/m²/s). - Tight, dark, slow, leaves praying hard under a very close light → **too much light** for the stage. - Tiny flies over wet media → **fungus gnat larvae** chewing root hairs ([fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md)). 4. **Roots and water (always before nutrients).** Lift the pot or inspect the roots. - Heavy for 3+ days, sour smell, brown roots → **overwatering or root rot** ([root problems](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md)). - Roots circling in a dense mat, pot dries in hours → **root-bound** [8]. - Medium cold to the touch, below ~18 °C (65 °F) → **cold root zone**. 5. **Climate, light and chemistry (whole-room causes).** - Air below ~20 °C (68 °F) in lights-on, or above ~30 °C (86 °F) → **temperature** [2]. - PPFD at canopy below the stage target, or DLI below ~25 mol/m²/day in veg → **low light / low DLI** [1] ([PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md)). - Veg on fewer than ~16–18 h of light → **short photoperiod**. - Runoff or reservoir pH outside the system range → **pH lockout** [10]. - Input EC very low and lower leaves pale → **underfeeding**; runoff EC far above input → **salt build-up**. 6. **Plant-specific causes.** - Twisted, glossy, hard new growth → **broad or russet mites** ([broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md)). - White waxy residue and small insects on roots → **root aphids** [5]. - Small leaves, short internodes, brittle stems, no other cause found, clone-based grow → **hop latent viroid**; test it [3][4]. - Seed-grown plant, healthy roots, just small and slow beside siblings → **genetic variation** (a runt). Not every seed is a keeper. - Dead growing tip and extra side shoots → **Ca or B** problem at the meristem [7], often a delivery problem (low transpiration, root damage) rather than an empty feed. ## How to recognise it | Pattern | Most likely | Also consider | |---|---|---| | Seedling in a big wet pot, droopy, pale | Overwatering | Damping-off, fungus gnats | | Whole room slow, no other symptoms | Light too low or room too cool | Short photoperiod in veg | | Whole room slow, pale lower leaves | N shortage or root-zone limitation | pH out of range | | One or few plants stunted, small leaves, short internodes, maybe brittle | HLVd [4] | Root rot, root aphids | | Stunting with wilting, yellowing, brown roots | Root rot [6] | Root aphids | | Stunted with twisted, shiny new growth | Broad/russet mites | Ca/B deficiency | | Clones sitting 1–2 weeks after transplant | Root establishment | Over-sized pots, cold media | | Stalled growing tip, extra side branching | Ca or B deficiency killing the tip [7] | Mechanical damage | ## What is the most likely cause, and what proves it? (differential table) | Pattern | Most likely | Rule out first | Key test | |---|---|---|---| | Seedling in a big pot, wet, droopy | Overwatering a small root system | Damping-off | Lift the pot; is it heavy 2+ days after watering? | | Seedling stem pinched and dark at the base | Damping-off [9] | Physical damage | Look at the stem at the soil line | | Whole room slow, nothing else wrong | Low PPFD or DLI [1] | Cool room | PAR meter at canopy; DLI = PPFD × hours × 0.0036 | | Whole room slow, cool room | Low air or root-zone temperature [2] | Low light | Min/max thermometer; probe in the medium | | Plant dries in hours, roots circle | Root-bound [8] | Root aphids | Slide the plant out | | Wilting with wet medium, brown roots | Root rot [6] | Low DO, overwatering | Root texture and smell | | Pale, slow, runoff pH off range | pH lockout [10] | Calibration error | Calibrate the meter, re-test runoff | | Pale lower leaves, low input EC | Underfeeding | Overwatering | Input and runoff EC | | One plant stunted, small leaves, clone grow | HLVd [3][4] | Root rot, root aphids | RT-PCR or RT-qPCR test | | Twisted, glossy new growth | Broad/russet mites | Ca/B, heat | 40–60x lens on the newest leaves | | Small autoflower, early stress | Transplant or early-stress stunting | Low light | Journal: what happened in weeks 1–4? | | Single runt among healthy seed siblings | Genetic variation | HLVd, roots | Healthy roots, no pests, no test positive | ## How does each cause slow a plant down? - **Overwatering and over-potting.** Roots need oxygen; a big pot full of wet medium around a small root system keeps roots short of it, and uptake of water and nutrients stalls [11]. Growth scales with rooting volume only when roots can use that volume [8]. - **Cold root zone.** Cool roots absorb water and nutrients more slowly and grow slowly, even when the air is warm [11]. Concrete floors and cold reservoirs are the usual culprits. - **Low light and low DLI.** Growth tracks the daily light integral. Yield in indoor cannabis rose linearly with PPFD in controlled trials [1], so a veg canopy at 200 µmol/m²/s grows far slower than one at 600. - **pH out of range.** pH sets nutrient availability; high pH starves the plant of Fe, Mn, Zn, B and P, and low pH cuts Ca, Mg and Mo [10]. See [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md). - **HLVd.** The viroid replicates in the plant and reduces vigour; symptoms range from none to clear stunting [3][4]. See [HLVd](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). - **Autoflower stress.** Autos switch to flower on age, not day length, so lost veg time is never recovered. The founder's observation is that transplanting autos is almost a no-no because of how the taproot reacts; plant directly in the final pot (house position). ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | PPFD, seedling/clone | ~150–300 µmol/m²/s | Grower practice | | PPFD, veg | ~400–700 µmol/m²/s | Grower practice | | DLI, veg (18 h) | ~25–45 mol/m²/day | Grower practice; 600 µmol/m²/s × 18 h ≈ 39 mol/m²/day | | Air temperature, lights on | ~22–28 °C (72–82 °F) | Grower practice; decline above ~30 °C [2] | | Root-zone temperature | 18–22 °C (65–72 °F) | Cold media slow everything | | pH, hydro / soilless / soil | 5.5–6.0 / 5.5–6.5 / 6.0–7.0 | See [how to diagnose](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) | | Typical veg growth (healthy photoperiod plant) | new node every ~2–4 days | Grower practice; cultivar dependent | | Seedling pot size before up-potting | ~0.5–1 L (16–32 oz) for photoperiods | Grower practice; autos go straight into the final pot | | Up-pot step | 2–3x the current volume | Grower practice [8] | | Clone or transplant establishment | ~5–14 days of slow top growth | Grower practice | | Overwatering signal | Pot still heavy 3+ days after watering | Grower practice | | DLI formula | PPFD × hours × 0.0036 = mol/m²/day | Physics; e.g. 400 × 18 × 0.0036 ≈ 26 | ## What to check first 1. **Watering and pot size.** Lift the pot; small root systems in big wet pots are the classic seedling stall. 2. **Roots.** Colour, smell, quantity. Insects on roots. 3. **Temperature** of air and root zone, day and night. 4. **Light.** Measure PPFD at canopy; calculate DLI. Check the timer actually gives 18/6 in veg. 5. **pH and EC** of input and runoff/reservoir. 6. **New growth with a lens** for mites. 7. **Compare plants.** Same treatment, one plant stunted = plant-specific problem (disease, viroid, genetics). 8. **Test** suspect mothers and stunted clones for HLVd (RT-PCR or RT-qPCR; root samples are often recommended). ## How to fix it - **Root zone:** correct watering rhythm, warm media, use appropriately sized containers (up-pot in steps). - **Light:** raise PPFD in steps of ~100 µmol/m²/s per few days, watching for stress; extend photoperiod to 18 h in veg. - **Temperature:** bring air into ~22–28 °C and roots to ~20 °C. - **pH/EC:** correct as per system. - **Root aphids or mites:** see [root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md), [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). - **Over-potted seedling:** water only a small ring around the stem until roots reach the pot edge, and let the pot dry back between waterings. - **Root-bound:** up-pot into 2–3x the volume, or water more often if you plan to finish in that pot [8]. - **Cold root zone:** lift pots off cold floors, use a heat mat set to ~20 °C (68 °F) under seedling trays, keep reservoirs at 18–21 °C. - **Autoflower stunted early:** you cannot recover lost time. Keep the plant stress-free, keep light and feed at stage targets, and plan the next run with direct sowing into the final pot. - **Runt seedling with healthy roots:** accept genetic variation; cull or grow on, but don't select it as a mother. - **HLVd positive:** there is no cure for an infected plant. Remove positives from propagation, sanitise tools with an agent shown to inactivate viroids, and restart from clean, tested stock. See [HLVd](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). ## How to confirm it worked - Node spacing and leaf size increase on new growth within 7–10 days. - Root mass visibly increases (white tips at the pot edge or in the net pot). - HLVd: clean stock tests negative on repeat tests and grows at the expected rate. ## Common mistakes - Feeding harder to "kick-start" a plant with a root problem. - Blaming genetics before checking light and temperature. - Keeping a slow, "just a weak pheno" mother that is actually viroid-infected and seeding the whole facility. - Putting a seedling straight into a large pot and watering the whole pot every time. - Transplanting autoflowers, and topping them instead of using LST. - Trusting the light's wattage instead of measuring PPFD at the canopy. - Reading pH from an uncalibrated meter, then "fixing" a lockout that isn't there. ## Evidence - Light-limited yield is *Established* for cannabis [1]. - Temperature effects are *Supported* [2]. - HLVd stunting and spread via propagation: *Established*, though symptom severity varies widely and incidence estimates are *Contested* [3][4]. - Root aphid on indoor cannabis: *Established* [5]. Root rot in hydro: *Established* [6]. - Growth scaling with rooting volume is *Established* across species [8]; over-potting stalling seedlings is *Grower practice* consistent with root-oxygen physiology [11]. - Damping-off in seedlings is *Established* [9]. pH effects on availability are *Established* [10]. - Autoflower sensitivity to early stress and to transplanting is the house position (founder observation); controlled studies are lacking. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x 3. Adkar-Purushothama CR, Sano T, Perreault JP., 2023. Hop Latent Viroid: A Hidden Threat to the Cannabis Industry. Viruses 15(3):681. https://doi.org/10.3390/v15030681 4. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa)-Viroid Diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases 5. Cranshaw WS, Wainwright-Evans S., 2020. Cannabis sativa as a Host of Rice Root Aphid (Hemiptera: Aphididae) in North America. Journal of Integrated Pest Management 11(1):15. Summary: https://entomologytoday.org/2020/07/24/rice-root-aphid-indoor-grown-cannabis-integrated-pest-management/ 6. Punja ZK, Rodriguez G., 2018. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 7. Cockson P, et al., 2019. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 8. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 9. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 10. Velechovsky J, Malik M, Senkyrik JB, Tlustos P. 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 11. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Spots, brown patches and dead edges on cannabis leaves: the master decision tree > Cannabis leaf spots and dead tissue sort into four groups: pest feeding (pale stippling or silver scars, seen with a 10–20× lens under the leaf), disease (spots with yellow halos and tiny black dots, spreading from the bottom in humidity), nutrient or root-zone disorders (Ca, P, K, Mn, B, salts, in a pattern tied to leaf age) and physical damage (spray droplets, fans, heat, light). Flip the leaf first, then check runoff pH and EC, and only then pick a nutrient. - Canonical: https://genetixbay.com/knowledge/diagnosis/spots-necrosis-decision-tree.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What causes brown spots on cannabis leaves?** Brown spots on cannabis leaves come from four groups of causes: pests such as spider mites and thrips, diseases such as septoria leaf spot, nutrient or pH problems with calcium, phosphorus, potassium or manganese, and physical damage from spray droplets, fans or heat. Turn the leaf over with a 10–20× lens first, then check runoff pH and EC before adding any nutrient. **Is it calcium deficiency or spider mites on my cannabis?** Spider-mite damage on cannabis is many tiny pale dots, evenly peppered across the upper leaf, with moving mites, eggs or fine webbing on the underside under a 10–20× lens. Calcium spots are fewer, larger, irregular brown blotches with no insects present, usually on newer or middle leaves, and often follow low pH, high humidity or root damage. Always look under the leaf first. **What do septoria leaf spots look like on cannabis?** Septoria leaf spot on cannabis appears as round to angular tan or grey-brown spots, often with a yellow halo, that start on the lowest, oldest leaves and climb in humid, wet conditions. Under a lens, mature spots show tiny black dots, the fungal fruiting bodies. Nutrient spots do not show fruiting bodies and do not spread from leaf to leaf in wet weather. **Why are my cannabis leaf edges brown and crispy?** Brown, crispy edges on cannabis leaves usually mean salt stress from high root-zone EC, or potassium shortage on older leaves, which scorches the margins and serrations. Edges burnt only on the top leaves under a strong light or near a fan point to heat, light or wind. Compare runoff EC with input EC first; more than about 1.0 mS/cm above input points to salt build-up. **Do brown spots on cannabis leaves go away?** Brown spots and dead tissue on cannabis leaves never heal or turn green again, because the cells are dead. Judge any fix by whether new spots stop appearing on fresh growth over the next 7 to 14 days. Remove badly diseased leaves to cut spore load, but keep mildly marked healthy leaves, which still photosynthesise and feed the buds. **Short answer.** Spots and dead (necrotic) tissue on cannabis come from four places: pests feeding, a leaf disease, a nutrient or root-zone disorder, or physical damage. The fastest split is a 10–20× lens under the leaf: moving dots, eggs, webbing or black specks mean pests. Spots with yellow halos and tiny black dots that climb from the bottom in humidity mean disease. Spots tied to leaf age, with readings out of range, mean the root zone or a nutrient. Droplet-shaped or one-sided burns mean sprays, fans, heat or light. The GenetixBay symptom checker follows the same order, so answers you gather here carry straight over. ## What is leaf necrosis on cannabis? Necrosis is dead tissue: brown, tan, black or bleached patches that crack and crumble. It is the end stage of many problems, so its *shape* and *location* matter more than its colour. Nutrient necrosis usually follows a yellowing phase and keeps to a pattern (margins, between veins, tips). Pest necrosis starts as many tiny pale feeding points that merge. Disease spots expand as rings with a defined edge and often a halo. Physical burns are sharp-edged and match the shape of whatever caused them [3][6]. ## The spots decision tree, step by step ### Fork 1: Flip the leaf. What is underneath? Turn over five affected leaves from different parts of the plant and look with a 10–20× lens. | Under the leaf | Suspect | Go to | |---|---|---| | Tiny moving dots, round eggs, fine silk | Spider mites [5] | [Spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md) | | Slender fast insects, silver scars, black frass specks | Thrips [10] | [Thrips](https://genetixbay.com/knowledge/pests/thrips.md) | | Sticky honeydew, soft-bodied insects | Aphids or whiteflies | [Aphids](https://genetixbay.com/knowledge/pests/aphids.md), [whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md) | | Nothing visible, but new growth twisted and glossy | Broad or russet mites (need 30–60×) | [Broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) | | Nothing | Fork 2 | | ### Fork 2: What does a single spot look like? | Spot appearance | Suspect | |---|---| | Many pinpoint pale dots merging into a speckled, bleached area | Mite stippling (even if no mites seen, check again) | | Silvery, papery streaks with black dots | Thrips scarring | | Round to angular tan or grey-brown spots with a yellow halo; tiny black dots in older spots | Septoria leaf spot [4] | | Irregular rusty-brown blotches, no halo, on newer or middle leaves | Calcium uptake problem [1] | | Dark, dull, olive to brown spots on older leaves, purple petioles | Phosphorus [1][2] | | Yellow then tan scorch on margins and serrations of older leaves | Potassium [1] | | Small tan specks within netted interveinal yellowing, upper-middle leaves | Manganese deficiency | | Brown-black specks along veins of older leaves, low pH | Manganese toxicity [3][7] | | Marginal yellowing then necrosis of older leaves, boron-rich water or feed | Boron toxicity [1] | | Crispy tips on otherwise healthy leaves | Salt stress / high EC (see [brown tips](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md)) | | Round or teardrop spots where spray droplets sat, on the light-facing side | Foliar or pesticide burn | | Dry, papery, torn patches on leaves facing a fan | Wind burn | | Bleached or crisp edges on the top leaves only | Heat or light stress | ### Fork 3: Where on the plant, and how is it spreading? | Location and spread | Points to | |---|---| | Oldest leaves first, climbing slowly, worse in humid weeks | Septoria, or a mobile nutrient (P, K, Mg) | | Newest or middle leaves, appearing in flushes after humid or wet-root days | Calcium (transpiration-limited) | | Whole plant, all ages, many tiny dots | Mites | | Top of canopy only | Heat, light, foliar spray under lights | | One side only, facing a fan or vent | Wind burn | | One plant first, then neighbours | Pests or disease; isolate | ### Fork 4: What do the root-zone readings say? Readings decide between nutrient look-alikes. Calcium spots at runoff pH 5.2 are a pH problem. Potassium scorch with runoff EC 3.5 mS/cm over a 1.8 input is salt build-up. | Reading | Interpretation | |---|---| | Runoff pH below ~5.5 (soilless) | Ca and Mg less available; Mn can rise to toxic | | Runoff pH above ~6.5 (soilless) or ~7.0 (soil) | P, Mn, Zn, Fe less available | | Runoff EC more than ~1.0 mS/cm above input | Salt build-up; tips and margins burn | | RH above ~70% for days, little airflow | Ca transport falls; septoria spreads | | Root-zone temperature below ~16–18 °C (61–64 °F) | P uptake slows | ## The spots and necrosis differential table | Symptom pattern | Most likely | Rule out first | Key test | |---|---|---|---| | Fine pale stippling, upper surface | Spider mites | Ca spotting | 10–20× lens underside | | Silver streaks with black specks | Thrips | Mites, PM residue | Lens; blue or yellow sticky card | | Halo spots climbing from the bottom | Septoria | P or K deficiency | Lens for black fruiting dots; spread with humidity | | Rust blotches, new/middle leaves | Calcium | Low pH, high RH, root damage, mites | Runoff pH, RH log, lens | | Olive-brown spots, old leaves, dull dark leaves | Phosphorus | Cold roots, high pH | Root-zone temperature, runoff pH | | Margin scorch, old leaves | Potassium | Salt build-up, B or Mn toxicity | Runoff EC vs input | | Black-brown vein specks, old leaves | Mn toxicity | Septoria | Runoff pH (low), tissue test | | Tip burn only | High EC / salts | K deficiency | Runoff EC vs input | | Droplet-shaped burns | Foliar or pesticide burn | Septoria | Spray log, pattern on light side | | Torn, papery patches near fan | Wind burn | Heat | Fan position | | Crisp top-canopy edges | Heat or light stress | K | Leaf temperature, PPFD | ## What numbers matter for spots and necrosis? | Parameter | Target | Notes | |---|---|---| | Root-zone pH, hydro | 5.5–6.0 | [8] | | Root-zone pH, coco/rockwool | 5.5–6.5 | Low pH reduces Ca and Mg availability | | Root-zone pH, soil | 6.0–7.0 | Grower practice | | Runoff EC vs input | within ~0.5 mS/cm | > 1.0 above input = build-up (grower practice) | | Feed Ca, soilless | ~150–200 mg/L | See [calcium](https://genetixbay.com/knowledge/nutrients/calcium.md) | | Feed P | ~30–60 mg/L | Higher P adds nothing and can tie up Zn and Fe | | Feed B | ~0.2–0.5 mg/L | Narrow margin to toxicity; see [boron](https://genetixbay.com/knowledge/nutrients/boron.md) | | Feed Mn | ~0.3–0.8 mg/L | See [manganese](https://genetixbay.com/knowledge/nutrients/manganese.md) | | RH, veg / flower | ~55–70% / ~40–55% | Grower practice; high RH favours septoria and slows Ca | | Leaf temperature, lights on | ~24–28 °C (75–82 °F) | Photosynthesis fell above ~30 °C in one cultivar [9] | | Leaf Ca, healthy | ~1.5–4.4% dry weight | [1] | | Leaf P, healthy | ~0.24–0.49% | [1] | ## What should I check first when I see spots? Check for pests and disease before nutrients, because they spread and nutrients don't. 1. **Lens under the leaf**, five leaves, top, middle and bottom. 2. **Spot shape.** Halo plus black dots = disease. Pinpoint speckle = pests. Droplet shapes = spray. 3. **Spray and equipment log.** Anything sprayed in the last 7 days? Fan moved? Light lowered? 4. **Calibrated runoff pH and EC.** 5. **RH and leaf temperature log** for the past week. 6. **Root inspection** if spots come with wilting or slow growth. 7. **Only now** choose between Ca, P, K, Mn and B by location and pattern. ## How do I fix spots and necrosis on cannabis? - **Mites and thrips:** follow the pest articles; act early, because populations double in days in warm rooms. Predatory mites are the backbone of indoor control. - **Septoria:** remove the worst lower leaves (bag them, don't drop them), lower RH below ~60%, increase airflow under the canopy, stop wetting foliage; see [septoria leaf spot](https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.md). - **Calcium:** correct pH first; lower RH towards range so the plant transpires; feed about 150–200 mg/L Ca in soilless; buffer new coco; add Ca only if the recipe and water report are short. - **Phosphorus:** warm the root zone to 18–22 °C; correct high pH; P at about 30–60 mg/L is enough. Bloom boosters are not the fix (see [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md)). - **Potassium:** confirm EC is not excessive; if the feed is short, move towards ~175–240 mg/L K (see [potassium](https://genetixbay.com/knowledge/nutrients/potassium.md)). - **Mn toxicity:** raise root-zone pH into range; Mn availability falls sharply as pH rises. - **Boron toxicity:** check the water report; switch water or reduce B-containing additives; a root-zone flush of the medium. - **Salt build-up:** root-zone flush with pH-adjusted, low-EC solution until runoff EC is near input, then resume normal feed. - **Foliar or pesticide burn:** stop spraying under lights; spray at lights-off, at label rate, test on one branch first; never combine sulfur and oil products within about two weeks of each other. - **Wind burn:** angle fans across, not at, the canopy; leaves should flutter, not thrash. - **Heat or light:** raise or dim the light; bring leaf temperature under ~28–30 °C (82–86 °F). ## How do I know the fix worked? Dead spots stay dead; success is no new spots on growth that emerged after the fix, usually within 7–14 days. Pest fixes are confirmed by repeated lens checks showing no live mites or thrips for three consecutive weekly scouts. Septoria is confirmed when spots stop climbing. Nutrient fixes are confirmed when runoff readings stay in range and new leaves come in clean. ## What are the common mistakes with leaf spots? - Adding Cal-Mag for mite stippling. The lens costs less than the bottle. - Spraying anything under hot lights, then blaming a deficiency for the burn. - Stripping healthy leaves with a few old spots; they still feed the buds. - Trusting one leaf; diagnose from the pattern across the plant. - Treating septoria with nutrients, or calcium spots with fungicide. - Assuming Cal-Mag is needed because you run LEDs; that is a *Myth*. Ca and Mg needs depend on cultivar, water source and medium. ## How strong is the evidence? - Nutrient spot and necrosis patterns (Ca, P, K, Mg, Mn, B, Zn) in cannabis are *Established* by controlled trials in substrate and DWC [1][2]; Mn toxicity specks are *Established* in horticulture [3][7] and *Supported* for cannabis. - Septoria symptoms and spread on cannabis/hemp are *Established* by extension [4][6]. - Mite and thrips damage patterns are *Established* [5][10]. - Foliar burn and wind burn patterns are *Grower practice*: obvious, but rarely studied in cannabis. - Heat thresholds come from one photosynthesis study [9] and grower practice: *Supported*. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 4. University of Kentucky Plant Pathology. Septoria leaf spot of hemp (PPFS-AG-H-01). https://plantpathology.mgcafe.uky.edu/files/ppfs-ag-h-01.pdf 5. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php 6. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 7. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 8. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 9. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x 10. Cranshaw W. Hemp pests (Colorado State University, 2020). https://webdoc.agsci.colostate.edu/bspm/InsectInformation/Talks2020/HempPests.pdf --- # Stretchy, leggy cannabis: a differential > Long internodes and thin stems mean the plant is reaching for light: PPFD too low, light too far away, a low red-to-far-red ratio (shade or crowding), or warm days relative to nights. Some stretch in the first 2–3 weeks after the switch to 12/12 is normal and cultivar dependent. Measure PPFD and day/night temperatures before blaming genetics. - Canonical: https://genetixbay.com/knowledge/diagnosis/stretching.html - Category: Diagnosis · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Transition · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why is my cannabis seedling so stretched?** A stretched cannabis seedling, tall, thin, floppy and pale, is usually getting too little light because the fixture is too weak or too far away. Grower practice targets about 150 to 300 µmol/m²/s and a DLI of 10 to 20 mol/m²/day for seedlings. A hot humidity dome or high temperature adds to stretch. At transplant, bury the stretched stem deeper. **Why is my cannabis plant leggy with long gaps between nodes?** A leggy cannabis plant with long internodes is reaching for light. The usual causes are low PPFD, shading from crowded neighbours or a far-red-rich spectrum that lowers the red to far-red ratio, and warm days with cool nights. Shade avoidance through phytochrome is established plant biology. Measure PPFD and day and night temperatures before blaming genetics. **How much do cannabis plants stretch in flower?** Cannabis plants commonly stretch about 1.5 to 3 times their height in the first 2 to 3 weeks after the switch to 12/12, according to grower practice, though no controlled cannabis data exist and the amount depends heavily on cultivar. Plan for it by flipping at about half the final height your space allows, and use a trellis, SCROG or supercropping to manage it. **Does far-red light cause cannabis stretching?** Far-red light can cause cannabis stretching. A low red to far-red ratio triggers the shade-avoidance response, lengthening stems and reducing branching, which is established in plant biology and shown for far-red in many species, though cannabis-specific data are grower practice. If you run far-red supplements and stretch is unwanted, reduce them or confine them to end of day. **How can I stop cannabis from stretching?** Stop cannabis stretching by giving more light, keeping temperatures even and spacing plants. Raise PPFD to about 400 to 700 µmol/m²/s in veg, narrow the day and night temperature gap to 3 °C (5 °F) or less, which is extrapolated from ornamentals, and avoid crowding. Topping and low-stress training control height, and gentle air movement strengthens stems. **Short answer.** A stretched plant is a plant looking for more light. The usual causes are low PPFD (light too weak or too far away), shade from neighbours or a light spectrum rich in far-red, and warm days with cool nights. Seedlings stretch fastest. Some stretch after the switch to 12/12 is normal: many cultivars grow substantially taller in the first 2–3 weeks of flower. Measure light and temperature before blaming genetics. ## What's happening Plants sense shade through phytochrome: a low ratio of red to far-red light (from neighbouring leaves or far-red-rich sources) triggers stem elongation and less branching, the "shade avoidance" response (*Established* in plant biology; far-red promotes elongation in many species [3]). Low overall photon flux does the same. Temperature matters too: in many ornamental crops, a warmer day than night (positive DIF) increases internode length, and the day–night difference has more effect than the average (*Supported* outside cannabis [3]). Blue light generally restrains elongation; Westmoreland et al. tested blue fractions in cannabis and found fixture efficacy mattered more for yield than spectrum [2]. Post-flip stretch is a developmental phase. Its size depends heavily on cultivar (*Grower practice*: roughly 1.5× to 3× height gain; no controlled cannabis data located). ## How to recognise it | Pattern | Most likely | Also consider | |---|---|---| | Seedlings tall, thin, floppy, pale | PPFD too low / light too far | High temperature; too warm a humidity dome | | Lower and inner plants taller and thinner than edges | Crowding/shade (low R:FR) | Uneven light footprint | | Whole room elongated, light measured fine | Warm days vs cool nights; far-red-rich spectrum | Genetics | | Big height gain weeks 1–3 after 12/12 | Normal flower stretch | Cultivar trait | | Stretch with pale lower leaves | Low light plus N limitation | See [yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | PPFD, seedlings | ~150–300 µmol/m²/s | Grower practice | | PPFD, veg | ~400–700 µmol/m²/s | Grower practice | | PPFD, flower | ~800–1200+ µmol/m²/s | Yield increased linearly to 1800 [1] | | DLI, seedlings | ~10–20 mol/m²/day | Grower practice | | Day–night difference (DIF) | 0 to small positive (≤ 3 °C / 5 °F) to limit stretch | Extrapolated from ornamentals [3] | | Air temperature | ~22–28 °C (72–82 °F) lights on | [4] for photosynthesis response | ## What to check first 1. **Measure PPFD** at the top of the seedling or canopy. Phone apps are rough; a quantum sensor is better. 2. **Distance** from light vs the fixture's recommended height. 3. **Day and night temperatures.** A hot day and a cold night stretch plants. 4. **Spacing.** Crowded plants shade each other. 5. **Spectrum.** Supplemental far-red, or old fluorescent tubes with low output. 6. **Calendar.** Is this the normal first 2–3 weeks of flower? ## How to fix it - **Seedlings:** lower the light or increase intensity to ~200–300 µmol/m²/s; bury a stretched seedling's stem deeper at transplant (it will root along the buried stem in soil and coco; grower practice); add gentle air movement to strengthen stems. - **Veg:** increase PPFD; space plants; train (top, LST) to control height. - **Temperature:** narrow the day–night gap; a brief cool period at lights-on is a grower trick extrapolated from ornamental "DIP" practice. - **Flower stretch:** plan for it. Flip at about half the final height you can accommodate (grower practice); use a trellis or SCROG; supercrop if needed. - **Far-red:** if you run far-red supplements, reduce or confine them to end-of-day if stretch is unwanted. ## How to confirm it worked - Next internodes are shorter and stems thicker within 5–7 days. - Canopy evens out; inner plants stop outgrowing the edges. ## Common mistakes - Keeping seedlings under a weak light "so they don't burn". - Flipping a tall cultivar to flower with no headroom left. - Assuming "sativa genetics" when the PPFD is 150 µmol/m²/s. ## Evidence - Low light increasing elongation and light-limited yield: *Established* [1]. - Far-red and DIF effects: *Established* in other crops [3]; *Grower practice* for cannabis. - Spectrum effects on cannabis yield are smaller than efficacy effects: *Supported* [2]. - Size of post-flip stretch: *Grower practice*. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Westmoreland FM, Kusuma P, Bugbee B., 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLOS ONE 16(3):e0248988. https://doi.org/10.1371/journal.pone.0248988 3. Horticultural Science (Prague), 2020, 47(3):169-179. Selection of cut-flower species affected in promotion of flowering and stem elongation by far-red lighting or heat. https://doi.org/10.17221/174/2018-HORTSCI 4. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x --- # Taco or canoeing leaves on cannabis: a differential > Leaflets folding upward along the midrib (taco, canoe) on the top of the canopy are almost always heat or light stress, often with low humidity (high VPD). Measure leaf temperature, PPFD and RH at the canopy before anything else; if the whole plant is affected, check the root zone, then calcium and magnesium. - Canonical: https://genetixbay.com/knowledge/diagnosis/taco-canoeing-leaves.html - Category: Diagnosis · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my cannabis leaves folding up like a taco?** Cannabis leaves fold up like a taco to reduce the leaf area exposed to light and cut water loss, almost always because the top of the canopy is too hot, the light is too intense or the air is too dry. Measure leaf temperature, PPFD and humidity at the canopy top first. Research shows cannabis photosynthesis declined above about 30 °C (86 °F). **Why are cannabis leaves canoeing under an LED?** Cannabis leaves canoeing under an LED, mainly on the top leaves closest to the fixture, usually means the light is too close or too intense for the leaf temperature and humidity. Raise the fixture or dim it by 10 to 20% and re-measure PPFD at the canopy. Grower practice targets about 800 to 1200 µmol/m²/s in flower without added CO2. **Why are the edges of my cannabis leaves curling up?** Cannabis leaf edges curl up when hot leaves transpire faster than the roots can supply water, so turgor drops along the margins. Heat, intense light and dry air are the usual causes, with high EC or weak roots adding to it. Upward curling with dull bronzing and brittle lower leaves points instead to hemp russet mites, according to extension sources. **Is taco leaf on cannabis heat stress or calcium deficiency?** Taco leaves on cannabis are usually heat or light stress when only the top leaves nearest the light fold, often with bleaching. Calcium deficiency is more likely when upward curling follows rusty spots on lower and mid fan leaves; in a controlled hydroponic study it appeared by week 6 of flower, after spotting. Fix climate first, then pH and root health, before adding calcium. **What VPD stops cannabis leaves curling?** Grower practice keeps cannabis VPD at about 0.8 to 1.2 kPa in veg and 1.0 to 1.5 kPa in flower to prevent heat and dryness curling, with leaf temperature around 24 to 28 °C (75 to 82 °F). Very dry air plus heat drives high VPD and leaf folding. Raise humidity to bring VPD into range, but take care in late flower, where bud rot risk rises. **Short answer.** When the leaflets at the top of the canopy fold upward along the midrib like a taco shell, the plant is reducing the leaf area it exposes: it is too hot, the light is too intense, or the air is too dry. Measure leaf temperature, PPFD and RH at the top of the canopy. If the folding is all over the plant, including shaded leaves, look at the roots and then at calcium. ## What's happening Leaves fold to cut light interception and water loss. Hot leaves under high PPFD transpire hard; if the roots cannot keep up (dry air, high EC, weak roots), turgor drops along the leaf edges and they rise. In one study, photosynthesis in a high-THC cultivar declined at temperatures above about 30 °C (86 °F) [1]. High PPFD itself is productive: yield kept rising up to 1800 µmol/m²/s in one trial [2] and was higher at 900 than at 750 µmol/m²/s in another [3], but only when temperature, CO₂, water and nutrients keep pace. In DWC, Ca deficiency led to upward leaf curling by week 6 of flower, after spotting [4]. Hemp russet mite feeding causes upward leaf-edge curling with bronzing and brittle leaves [5]. ## How to recognise it | Pattern | Most likely | Also consider | |---|---|---| | Top leaves only, closest to light, edges up, maybe bleaching | Light and/or heat stress | Low RH | | Whole canopy, hot room, crispy edges | Heat stress, high VPD | High EC | | Upward curl plus rusty spots on lower/mid fan leaves | Calcium uptake problem [4] | pH, RH | | Upward curl plus dull bronzing, brittle leaves, worse low on plant | Hemp russet mite [5] | Mg/K deficiency | | Wavy, edges up, under a fan's direct blast | Wind burn | Move or redirect fan | | Folding in the afternoon only, recovers at night | Transient heat/VPD | Climate control at peak | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Leaf temperature, lights on | ~24–28 °C (75–82 °F) | Grower practice; photosynthesis fell above ~30 °C in one cultivar [1] | | VPD, veg | ~0.8–1.2 kPa | Grower practice | | VPD, flower | ~1.0–1.5 kPa | Grower practice | | PPFD, veg | ~400–700 µmol/m²/s | Grower practice | | PPFD, flower (no added CO₂) | ~800–1200 µmol/m²/s | Yield still rose to 1800 in [2]; leaf stress depends on cultivar and climate | | RH, flower | ~40–55% | Grower practice; trade-off with bud rot risk | ## What to check first 1. **Leaf temperature at the top of the canopy** (IR thermometer) and air temperature. 2. **PPFD at the top of the canopy** (quantum sensor or phone meter as a rough guide). Is the light closer than the manufacturer's recommended distance? 3. **RH and VPD.** Very dry air plus heat is the usual combination. 4. **Pattern.** Top only = light/heat. Whole plant = climate, roots, or a nutrient/pest. 5. **Root zone and EC.** Weak roots and high EC limit water supply. 6. **Hand lens** on lower leaves if bronzing is present. ## How to fix it - **Light:** raise the fixture or dim by 10–20%; re-measure PPFD. Use the canopy, not the hottest spot, as your reference. - **Heat:** improve extraction, run lights in the cooler part of the day, and keep leaf temperature under ~30 °C. - **Humidity:** raise RH to bring VPD back into range (humidifier in veg; careful in late flower where bud rot risk rises). - **Airflow:** gentle, constant movement across and under the canopy; no direct blast on leaves. - **Calcium:** correct pH and root health first, then check Ca supply. See [rust spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md). - **Russet mites:** see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). ## How to confirm it worked - Leaves flatten within hours to a day for climate causes; new growth stays flat. - Leaf temperature stays below ~30 °C at the brightest point through the lights-on period. - No new bleaching at the tops. ## Common mistakes - Feeding Cal-Mag for what is a light-height problem. - Measuring temperature at the wall instead of at the canopy. - Pushing PPFD to the maximum without the climate or CO₂ to support it. ## Evidence - Leaf folding under heat and light stress is *Established* plant physiology; cannabis-specific thresholds are *Grower practice*. - Temperature effects on cannabis photosynthesis are *Supported* [1]. - Yield response to PPFD is *Established* across two independent cannabis studies [2][3]. - Ca and russet mite causes are *Supported* [4][5]. ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 3. Westmoreland FM, Kusuma P, Bugbee B., 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLOS ONE 16(3):e0248988. https://doi.org/10.1371/journal.pone.0248988 4. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 5. Utah State University Extension. Hemp Russet Mite. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-hemp-russet-mite-.php --- # White or grey coating on cannabis: the master decision tree > A white or grey coating on cannabis is, in order of how often it matters: powdery mildew (flour-like patches that smear and return), spray or hard-water residue (follows the drip lines), trichomes (on buds and sugar leaves only), thrips silvering, spider-mite webbing, or grey Botrytis fuzz on buds and stems. On the medium, white fuzz is usually harmless mycelium and a hard crust is salt. A rub test and a 20–60x lens settle most cases in two minutes. - Canonical: https://genetixbay.com/knowledge/diagnosis/white-grey-coatings-decision-tree.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the white powder on my cannabis leaves?** White powder on cannabis leaves is most often powdery mildew: round, flour-like patches on the upper leaf surface that wipe off and come back within days. If the white sits in dried drip lines on leaves you sprayed, it is residue from hard water, foliar feed or silica. If it is only on buds and sugar leaves and looks like glass beads under a lens, it is trichomes. **Is grey fuzz on my cannabis buds bud rot?** Grey, fuzzy growth on cannabis buds, often with a brown dead sugar leaf poking out of an otherwise healthy cola, is Botrytis bud rot. It starts inside dense buds when humidity is high and temperatures are around 15 to 25 °C. Cut the whole bud out at least 5 cm below the visible rot, bag it inside the room, drop RH below 50% and do not consume rotted material. **Why are my cannabis leaves silvery?** Silvery, shiny patches on cannabis leaves, dotted with tiny black specks, are thrips feeding damage: the insects rasp cells empty and they fill with air. Look under the leaves with a 10 to 20x lens for slender yellow or brown insects and black frass dots. Fine pale speckling with no shine and fine silk under the leaf points to spider mites instead. **What is the white fuzz on top of my cannabis soil?** White fuzz on top of cannabis soil is usually harmless saprophytic fungal mycelium feeding on organic matter in a surface that stays wet. It is not powdery mildew and rarely harms the plant, but it signals overwatering or still air, which also breeds fungus gnats. Let the top 3 to 5 cm dry. A hard, crunchy white crust is salt, not fungus. **Why are my cannabis leaves sticky and black?** Sticky cannabis leaves with a black, soot-like film are honeydew from sap-sucking insects, usually whiteflies or aphids, growing sooty mould. The mould is cosmetic but blocks light, and the insects are the real problem. Shake the plant to see if whiteflies rise, and check leaf undersides with a lens for aphids or whitefly nymphs. **Short answer.** A white or grey coating on a cannabis plant is usually one of six things: powdery mildew, spray or hard-water residue, trichomes, thrips silvering, spider-mite webbing, or grey Botrytis mould on buds. Where it sits and what it does when you rub it decide most cases. Flour-like circles that smear off and return are powdery mildew [1][2]. White on the medium is usually harmless mycelium (fuzz) or salt (crust). A 20–60x lens settles the rest. ## What's happening? "White stuff" is a symptom family, not a diagnosis. Three very different processes produce it: - **A living organism on the surface.** Powdery mildew (*Golovinomyces ambrosiae* and relatives) grows on the outside of leaves and sends feeding structures into epidermal cells [1][2]. *Botrytis cinerea* grows grey, dusty spore masses on dying tissue, mostly inside dense buds [1][3]. Saprophytic fungi grow white mycelium on wet organic media. - **Insect damage or insect products.** Thrips rasp cells empty so they fill with air and look silver [4]. Spider mites spin silk [5]. Whiteflies and aphids drip honeydew that grows black sooty mould [6]. Mealybugs and root aphids coat themselves in white wax [7][8]. - **Non-living deposits.** Dissolved minerals in hard water, foliar feeds, silica and sulfur products dry into white films [10]. Salts wick to the top of the medium and crystallise. The danger split is clear: powdery mildew and Botrytis are urgent, insects are urgent within days, and residues are cosmetic unless they block light or come from overfeeding. ## Where is the white, and what does it do when you rub it? (the decision tree) Work through the forks in order. Stop at the first one that fits, then confirm with the key test. 1. **Is it on the medium, pots or reservoir, not the plant?** - Soft, cottony, spreads on a wet surface, smells earthy → **saprophytic mycelium**. Harmless in itself; dry the top 3–5 cm and move air ([white fuzz on soil](https://genetixbay.com/knowledge/answers/white-fuzz-on-soil.md)). - Hard, crunchy, white or off-white crust at the rim or top, worse where water evaporates → **salt crust**. Measure runoff EC ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). - Green or brown slime on wet media, net pots or in the reservoir → **algae**, from light reaching nutrient solution ([algae in the reservoir](https://genetixbay.com/knowledge/answers/algae-in-reservoir.md)). - White woolly flecks on roots when you lift the plant, small pear-shaped insects → **root aphids** or **root mealybugs** [8] ([root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md)). 2. **Is it grey and fuzzy, on or inside a bud, or on a stem wound?** → **Botrytis (grey mould)**. Usually a single sugar leaf turns brown or tan and pulls out easily, then grey spores appear inside the cola [1][3]. This is critical urgency in flower: go to [bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md). 3. **Is it only on buds and sugar leaves, glittery, and fixed in place?** → **Trichomes**. Under a lens they are stalks with clear, cloudy or amber glass-bead heads. Healthy, and the point of the exercise. 4. **Does it rub off as a flour-like powder, in round patches, mainly on upper leaf surfaces, and come back within days?** → **Powdery mildew** [1][2]. Patches start small and circular, often on lower and inner leaves in still air, then merge until the leaf looks dusted. 5. **Does it rub off as a film but follow drip lines, leaf edges and the surfaces you sprayed?** → **Residue** (hard water, foliar feed, silica, sulfur, oils or soap). It does not regrow, has no circular pattern and sits on whatever the spray hit. 6. **Is it shiny silver or pewter, flat, and does not rub off?** → **Thrips feeding scars**, usually with tiny black frass dots on the patch [4] ([thrips](https://genetixbay.com/knowledge/pests/thrips.md)). 7. **Is it fine pale speckling with fine silk under leaves or between bud tips?** → **Spider mites** [5] ([spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md)). Heavy webbing over the tops is a late, severe infestation. 8. **Is it a sticky shine, then a black soot film?** → **Honeydew and sooty mould** from whiteflies or aphids [6] ([whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md), [aphids](https://genetixbay.com/knowledge/pests/aphids.md)). 9. **Is it white cottony tufts in leaf axils and along stems, with slow-moving oval insects?** → **Mealybugs** [7]. Uncommon indoors on cannabis, more common where houseplants share the room. 10. **Is it a pale grey-violet fuzz on the underside of yellow, angular leaf patches?** → possibly **downy mildew**. ## How do I tell them apart? (differential table) | Pattern | Most likely | Rule out first | Key test | |---|---|---|---| | Round flour-like patches, upper leaf surface, return after wiping | Powdery mildew [2] | Residue, trichomes | Rub test, then check 48 h later; lens shows cottony hyphae | | White film in drip lines, only where sprayed | Hard-water or spray residue | Powdery mildew | Wet a cloth and wipe: residue dissolves or flakes, never regrows | | Glittering heads on buds and sugar leaves only | Trichomes | PM on sugar leaves | 30–60x lens: glass-bead heads on stalks | | Grey dusty fuzz inside a cola; brown sugar leaf pulls out | Botrytis bud rot [3] | Normal senescence of a sugar leaf | Pull the bud open: brown, mushy core | | Silver, flat, shiny patches with black dots | Thrips [4] | Mite stippling, sun bleaching | 10–20x lens under the leaf; tap leaves over white paper | | Fine pale dots, silk under leaves | Spider mites [5] | Ca spotting, thrips | Lens on the underside: moving dots, eggs | | Sticky shine, black film | Whiteflies or aphids (honeydew) [6] | Sap from damage, spray oil | Shake the plant; yellow card for 48 h | | White cottony tufts in axils | Mealybugs [7] | PM, wax from aphids | Lens: segmented oval insects under the wax | | White wool on roots | Root aphids or root mealybugs [8] | Root hairs, mycelium | Lens on roots; check the pot base and drainage holes | | Soft white fuzz on top of the medium | Saprophytic mycelium | PM spores on media (rare) | It sits only on wet organic surface; dry back 3–5 cm | | Hard white crust on medium or pot rim | Salt build-up | Lime from hard water | Runoff EC vs input EC | | Green slime on media or in reservoir | Algae | Biofilm | Is light reaching the solution? | ## Which numbers matter? | Parameter | Target or threshold | Notes | |---|---|---| | RH, late flower | Below ~50% | Botrytis prevention [3]; see [humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) | | Botrytis growth range | ~10–27 °C (50–81 °F), optimum near 20 °C (68 °F) | With high humidity and free water [1][3] | | PM-favouring conditions | Moderate temperatures, still air, humid canopy; free water is not needed | Established for PM in general; cannabis-specific optima are thin [1][2] | | Lens magnification | 10–20x for insects; 30–60x for mildew hyphae and trichome heads | Grower practice | | Water alkalinity | Above ~100–150 mg/L as CaCO₃ leaves white mineral residue and raises root-zone pH | [10]; see [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md) | | Runoff EC above input | More than ~0.5 mS/cm suggests salt build-up | Grower practice; see [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) | | Top of medium dry-back | ~3–5 cm (1–2 in) between waterings | Discourages mycelium and fungus gnats [11] | | Spider mite outbreak conditions | Hot, dry air (roughly above 27 °C and below 50% RH) | [5] | ## What should I check first? Do these in order, cheapest first. They take about five minutes. 1. **Location.** Medium vs plant; buds vs fan leaves; upper vs lower surface; top of canopy vs interior. 2. **Rub test.** Wipe with a damp finger or cloth. Powder that smears = mildew or residue. Fixed silver = thrips. Fixed glitter = trichomes. 3. **Spray history.** Did anything get sprayed or misted on these leaves in the last 2 weeks? Hard tap water in a mister alone can leave white films. 4. **Lens check under the leaf.** 10–20x for insects, eggs, silk and black frass; 30–60x for mildew hyphae. 5. **Shake test.** Shake a branch over white paper. Whiteflies rise in a cloud; mites and thrips fall and move. 6. **Watch for 48 hours.** Wipe a marked patch. Mildew returns; residue does not. 7. **Climate log.** RH and temperature at lights-off, when the canopy is coolest and dew is most likely. ## How do I fix each one? - **Powdery mildew.** In veg: remove the worst leaves into a bag, raise airflow through (not just over) the canopy, keep RH stable, and use a least-toxic contact option that is legal where you live, such as potassium bicarbonate or a horticultural oil, at label rate, testing on one leaf first. In flower there is no clean fix: anything sprayed lands on what you consume. Remove affected material and decide whether to harvest early. See [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) and [home remedies for PM](https://genetixbay.com/knowledge/answers/home-remedies-for-powdery-mildew.md). - **Botrytis.** Cut the infected bud out at least 5 cm (2 in) below visible rot, bag it inside the room, sanitise the blade between cuts, drop RH below ~50% and increase airflow [3]. Never eat or extract rotted buds. Inspect every cola every 2 days until harvest. See [bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md). - **Residue.** Switch foliar sprays to RO or low-alkalinity water; stop foliar feeding in flower. A gentle wipe with a damp cloth removes heavy films on fan leaves. Residue blocks a little light but does no other harm. - **Thrips.** Predatory mites on foliage plus a soil-level predator or nematodes for the pupae, blue or yellow cards, and remove heavily scarred leaves [4]. See [thrips](https://genetixbay.com/knowledge/pests/thrips.md). - **Spider mites.** Act the day you see silk: isolate, knock numbers down in veg with a contact option, release predatory mites, and lower canopy temperature and raise RH within safe limits [5]. See [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md). - **Whiteflies, aphids and sooty mould.** Treat the insect, not the mould. Yellow cards, parasitoid wasps or predators, contact options in veg [6]. Wipe the sooty film off fan leaves with a damp cloth. - **Mealybugs.** Remove by hand with a cotton swab in isopropyl alcohol on small infestations in veg; quarantine incoming houseplants. - **Root aphids and root mealybugs.** See [root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md); soil-applied entomopathogenic fungi and predators are the usual approaches [8]. - **Mycelium on the medium.** Water less often, let the top 3–5 cm dry, move air over the pots. Scrape off if you prefer; it is not a disease of the plant. - **Salt crust.** Scrape it off and do a root-zone flush (the one valid flush, which treats the medium, not the plant) with pH-adjusted water to 20–30% runoff until runoff EC is near input EC, then resume the normal feed. - **Algae.** Block all light from the reservoir, lines and net-pot tops; clean and sanitise between runs. ## How do I know the fix worked? - **PM:** no new patches on wiped or new leaves for 10–14 days. Spores can lurk; keep checking weekly. - **Botrytis:** no new brown sugar leaves or soft spots in colas on 2-day inspections until harvest. - **Insects:** card counts fall week on week; no new stippling, silvering or honeydew on new leaves. - **Residue:** new leaves stay clean after the spray-water change. - **Salt crust:** runoff EC falls to within ~0.5 mS/cm of input and stays there for two checks. - **Mycelium:** surface fuzz stops returning once the top dries between waterings. ## What are the common mistakes? - Spraying a fungicide on residue or trichomes. Rub, lens, wait 48 hours. - Treating sooty mould instead of the whiteflies or aphids making the honeydew. - Spraying anything on buds in flower. It ends up in the smoke. - Leaving a Botrytis bud on the plant "to finish". Spores spread to the next cola within days. - Shaking or carrying infected material through the room, which spreads PM and Botrytis spores. - Calling white soil fuzz "mould" and drenching the medium with peroxide, which kills beneficial microbes too. - Missing thrips because the damage looks like bleaching. Bleaching is on the top of the canopy facing the light; thrips scars are random and carry black dots. ## How strong is the evidence? - Powdery mildew and Botrytis identification and the conditions that favour them in cannabis are *Established* by pathology surveys and extension guides [1][2][3][9]. - Thrips silvering, spider-mite stippling and webbing, and honeydew with sooty mould are *Established* general IPM knowledge, confirmed on hemp and cannabis by extension [4][5][6]. - Root aphids on cannabis are *Established* [8]; root and foliar mealybugs on indoor cannabis are *Supported* (scattered reports). - Downy mildew on indoor cannabis is *Contested* (rare, mostly hemp field reports). - The rub test, 48-hour regrowth check and drip-line pattern for residue are *Grower practice*. - Least-toxic PM options (bicarbonates, oils) are *Supported* in other crops; cannabis-specific efficacy data are limited [1][9]. ## Sources 1. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 2. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew 3. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker 4. UC IPM Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html 5. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php 6. UC IPM Pest Notes: Whiteflies (Publication 7401). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7401.html 7. UC IPM Pest Notes: Mealybugs (Publication 74174). https://ipm.ucanr.edu/PMG/PESTNOTES/pn74174.html 8. Utah State University Extension. Rice Root Aphids (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-rice-root-aphid.php 9. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857-3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 10. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 11. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ --- # White powder or white spots on cannabis leaves: a differential > Flour-like circular white patches that smear off and come back are powdery mildew until proven otherwise. Rule out spray or hard-water residue (on the surfaces you sprayed, dries in drip lines), trichomes (on sugar leaves and buds, glassy under a lens), silvery thrips scarring and mite stippling. Confirm with a 20-60x lens before treating. - Canonical: https://genetixbay.com/knowledge/diagnosis/white-powder-on-leaves.html - Category: Diagnosis · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is the white powder on my cannabis leaves?** White powder on cannabis leaves that forms round, flour-like patches on the upper surface, smears off with a finger and returns within 2 to 5 days is powdery mildew until proven otherwise. It is caused mainly by Golovinomyces fungi and does not need free water on the leaf. Rule out spray or hard-water residue, trichomes, thrips scarring and mite stippling with a 20 to 60x lens. **Is it powdery mildew or trichomes on my cannabis?** Powdery mildew and trichomes look very different under a 20 to 60x lens. Trichomes are glassy, mushroom-shaped resin glands with a stalk and head, found on sugar leaves, buds and petioles, and they sparkle. Powdery mildew shows cottony threads and chains of spores, forms fuzzy patches that spread across fan leaves and stems, and smears when rubbed. Trichomes need no treatment. **Why are there white spots on cannabis leaves after spraying?** White spots on cannabis leaves after spraying are usually dried spray or hard-water mineral residue: an even, crusty or chalky film in a drip-line pattern, only on sprayed surfaces, that does not grow. Wipe it with a damp cloth; residue stays gone, while powdery mildew returns. Use softer water for foliar sprays, spray only in veg and not under strong light. **What causes silver streaks on cannabis leaves?** Silver streaks on cannabis leaves are usually thrips feeding damage: silvery, papery patches on the upper surface dotted with tiny black specks of frass, according to extension guidance. Confirm by shaking a branch over white paper and looking for slender insects, and check sticky cards. Spider mites cause tiny pale dots and fine webbing instead, with mites on the underside. **How do I confirm powdery mildew on cannabis?** Confirm powdery mildew on cannabis with a wipe test and a lens. Rub a patch: mildew smears, leaves a faint mark and regrows within days, while residue stays gone. Under 20 to 60x magnification, mildew shows cottony threads and spore chains. Mark an affected leaf and recheck in 3 days for spread, and avoid wiping patches, which spreads spores. **Short answer.** Round, flour-like white patches on the upper leaf surface that smear off with a finger and come back within days are powdery mildew (PM) until you prove otherwise. Before treating, rule out the look-alikes: dried spray or hard-water residue, normal trichomes on sugar leaves, silvery thrips scarring, and spider-mite stippling. A 20–60× lens settles most cases in a minute. ## What's happening Cannabis powdery mildew is caused mainly by *Golovinomyces* species (reported as *G. cichoracearum* / *G. ambrosiae*) [1][2], and in the Pacific Northwest *Podosphaera macularis* has also been reported on hemp [1]. The fungus lives on the leaf surface and sends feeding structures into epidermal cells; its chains of spores give the powder look. Unlike most fungi, PM does not need free water on the leaf. It was the major foliar pathogen in a Canadian survey of commercial cannabis [2]. Resistance genes exist (PM1, PM2), so cultivar susceptibility varies a lot [3]. Look-alikes are not infections: mineral residue, trichomes (resin glands), feeding scars from thrips (silvery with black frass dots) [4], spider-mite stippling (pale dots, webbing) [5], and whitefly honeydew or waxy nymph cases on undersides [6]. ## How to recognise it | Appearance | Where | Most likely | Confirm | |---|---|---|---| | Circular, fuzzy, flour-like patches, expanding and merging; smear off and return in 2–5 days | Upper surface first, older/shaded leaves, also stems and buds | Powdery mildew | Lens: cottony threads and chains of spores | | Even, crusty or chalky film, drip-line pattern, does not grow | Only on sprayed surfaces | Spray or hard-water residue | Wipe with damp cloth; doesn't return | | Glassy, mushroom-shaped glands, sparkle | Sugar leaves, buds, petioles | Trichomes (normal) | Lens: stalk and head | | Silvery, papery patches with tiny black dots | Upper surface | Thrips feeding [4] | Shake onto paper; slender insects | | Tiny pale dots, fine webbing, bronze cast | Upper surface; mites underneath | Spider mites [5] | Lens on underside | | White waxy flecks, tiny white flying insects when shaken | Underside | Whiteflies [6] | Yellow sticky card | | White crust on media surface | Medium, pot edges | Salt build-up | Runoff EC high | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | Lens magnification | 20–60× | Generic | | RH, veg | ~55–70% | Grower practice; PM favoured by humid canopies with dry leaf surfaces and moderate temperatures ( | | RH, flower | ~40–55% | Grower practice | | Canopy air movement | continuous, leaves visibly flutter | Grower practice | | Day–night temperature swing | small; avoid dew-point events at lights-off | Grower practice | ## What to check first 1. **Wipe test.** Rub a patch with a fingertip. PM smears, leaves a faint mark, and regrows within days. Residue stays gone. 2. **Lens.** Threads and spore chains (PM) vs glassy glands (trichomes) vs crystals (residue). 3. **Location.** Only where you sprayed? On sugar leaves only? Leaf undersides? 4. **Insects.** Shake a branch over white paper and check sticky cards. 5. **Spread.** Mark a leaf and look again in 3 days. 6. **Climate log.** Humid nights, stagnant corners, crowded canopy. ## How to fix it - **Powdery mildew confirmed:** remove and bag the worst leaves, increase airflow, lower RH, open the canopy, and follow [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) for least-toxic treatment classes and what not to do in flower. Check product registration and labels in your jurisdiction. - **Residue:** use softer water for foliar sprays, spray only in veg, and don't spray under strong light. - **Trichomes:** nothing to fix; that's the crop. - **Thrips, spider mites, whiteflies:** see [thrips](https://genetixbay.com/knowledge/pests/thrips.md), [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md), [whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md). - **Salt crust:** check runoff EC; if it is far above input, do a root-zone flush of the medium (see [the root-zone flush](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)) and see [brown or burnt tips](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) for runoff EC management. ## How to confirm it worked - PM: no new colonies on marked leaves for 10–14 days; new growth clean. - Residue: new leaves clean once spraying stops. - Pests: sticky-card and leaf counts fall over two weekly checks. ## Common mistakes - Spraying anything on buds in flower to "treat" what turns out to be trichomes. - Wiping PM off leaves and spreading spores across the room. - Treating PM only on the leaves you can see; it is usually further along than it looks. - Raising RH to fix tip burn in a room with PM history. ## Evidence - PM pathogens on cannabis and its importance: *Established* [1][2]. - Genetic resistance: *Established* for specific loci [3]. - Look-alike distinctions: *Established* extension guidance [4][5][6]. - Cannabis-specific RH/temperature thresholds for PM: *Grower practice*. ## Sources 1. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa)-Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew 2. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 3. Mihalyov PD, Garfinkel AR., 2021. Discovery and Genetic Mapping of PM1, a Powdery Mildew Resistance Gene in Cannabis sativa L. Frontiers in Agronomy 3:720215. https://doi.org/10.3389/fagro.2021.720215 4. UC IPM Pest Notes: Thrips (Pest Note 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html 5. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php 6. UMass Extension. Whiteflies on Greenhouse Crops. https://www.umass.edu/agriculture-food-environment/greenhouse-floriculture/fact-sheets/whiteflies-on-greenhouse-crops --- # Why are my cannabis leaves curling? The master curling and clawing decision tree > Which way a cannabis leaf curls is the first clue. Edges folding up (taco, canoe) at the top of the canopy is heat, light or high VPD. Tips hooking down like a talon on dark, glossy leaves is excess nitrogen with high EC; whole leaves curling down and puffy on a heavy pot is overwatering. Twisted, crinkled, stunted new growth is broad or russet mites, calcium or boron delivery, a viroid, or growth-regulator herbicide drift. Leaves angled up and flat at lights-on ('praying') is healthy. - Canonical: https://genetixbay.com/knowledge/diagnosis/curling-clawing-decision-tree.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are my cannabis leaves curling up?** Cannabis leaves that curl up at the edges, folding along the midrib like a taco or canoe, are almost always reacting to heat, too much light or very dry air at the top of the canopy. The plant is cutting its exposed area to save water. Measure leaf temperature and PPFD at the canopy top; keep leaves under about 28 to 30 °C and VPD near 1.0 to 1.5 kPa in flower. **Why are my cannabis leaves clawing down?** Cannabis leaf tips that hook down like a talon, on leaves that are very dark green and glossy, usually mean too much nitrogen with a high root-zone EC. Whole leaves curling down and looking swollen on a heavy, wet pot mean overwatering and low root oxygen. Check pot weight and runoff EC first; lower nitrogen by 10 to 20 percent only once watering is right. **What causes twisted new growth on cannabis?** Twisted, crinkled or blistered new growth on cannabis usually comes from broad or russet mites, which are too small to see without 30 to 60× magnification, from calcium or boron failing to reach the growing tips, from hop latent viroid, or from growth-regulator herbicide drift. Check the growing tips under strong magnification before adding calcium, because mites spread fast and nutrients don't. **Are praying cannabis leaves good or bad?** Praying cannabis leaves, held high and angled upward with flat, firm leaflets, are a sign of a healthy plant with good water status and light, especially at the start of the light period. They are not a stress symptom. Upward-folding, cupped or crisp leaflets at the canopy top are different: that is taco or canoe curling from heat or light stress. **Will curled cannabis leaves flatten out again?** Curled cannabis leaves often flatten again within hours to a few days if the cause was heat, light or watering and it has been fixed, because the leaf was folded, not damaged. Clawed leaves from nitrogen excess usually stay clawed, so judge by new growth. Twisted leaves from mites, calcium, boron or herbicides do not recover; the next leaves should come in normal once the cause is removed. **Short answer.** Look at which way the leaf bends and which leaves do it. Edges folding up at the top of the canopy (taco, canoe) is heat, light or dry air. Tips clawing down on dark, glossy leaves is too much nitrogen with high EC. Whole leaves curling down and looking puffy on a heavy pot is overwatering. Twisted, crinkled new growth is mites, calcium or boron, a viroid, or herbicide drift. Leaves held up and flat at lights-on ("praying") is a healthy plant showing off. The GenetixBay symptom checker asks the same direction-then-location questions, so the answers you collect here transfer directly. ## Why does leaf curl direction matter? Leaf curl direction matters because each direction has a different mechanism. Upward folding along the midrib is an active water-saving response: the leaf cuts its exposed area when it is losing water faster than roots supply it, or when it is overheated [4][11]. Downward clawing of the tips comes from uneven expansion of the leaf blade, typical of excess nitrogen (especially ammonium) and soft, over-hydrated tissue [1][8]. Downward curling of the whole leaf with a firm, swollen look is turgid tissue on roots short of oxygen [9]. Twisting and crinkling of new growth is damage to dividing cells at the growing tip, from mites injecting saliva, or from the calcium and boron the new cell walls need [3][6]. ## The curling decision tree, step by step ### Fork 1: Which way does the leaf bend? | Direction | Go to | |---|---| | Edges up, leaflets folding like a taco or canoe | Fork 2A | | Tips hooking down like a claw | Fork 2B | | Whole leaf drooping and curling down from the petiole | Fork 2C | | Twisted, crinkled, cupped or blistered | Fork 2D | | Leaves angled up, flat and firm | Healthy: "praying" (see [praying leaves](https://genetixbay.com/knowledge/answers/praying-leaves.md)) | ### Fork 2A: Edges folding up Upward taco curl at the top of the canopy, worst on leaves nearest the light, is heat, light or VPD stress. Measure leaf temperature (IR thermometer), canopy PPFD and RH. A canopy under LEDs can run cooler than the air; under HPS the leaf can run hotter than the air [11]. | Clue | Cause | |---|---| | Only top leaves, nearest the light, shiny upper surface pointing away | Light stress (PPFD too high for this cultivar and climate) | | Top leaves, leaf temperature above ~30 °C (86 °F) | Heat stress [4] | | All levels, RH below ~40%, VPD above ~1.6 kPa | Low humidity / high VPD | | Whole plant, with edges browning, after a fan was moved | Wind | | Whole plant, leaf edges yellow then brown, old leaves | Potassium, Mg late stage, or salt stress: check runoff EC | | Whole plant, readings normal, wet or damaged roots | Root zone: see [root problems](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md) | ### Fork 2B: Tips clawing down | Clue | Cause | |---|---| | Very dark green, glossy leaves, soft growth, high input or runoff EC | Nitrogen excess [1] | | Same, with ammonium above ~30% of N in the feed | Ammonium toxicity [8] | | Claw on a pot that stays heavy for days | Overwatering, low root oxygen | | Claw with tip burn and runoff EC far above input | Salt build-up | | Claw on new growth only, crinkled, no dark green | Fork 2D (mites, Ca, B) | ### Fork 2C: Whole leaf curling down and drooping Heavy pot and firm, puffy leaves means overwatering. Light pot and limp leaves means underwatering. Wet medium and wilting anyway means roots are failing: root rot, Fusarium wilt or pump failure. See the [drooping and wilting decision tree](https://genetixbay.com/knowledge/diagnosis/drooping-wilting-decision-tree.md). ### Fork 2D: Twisted, crinkled or blistered new growth Check this fork with the best magnification you have before buying anything. Broad and russet mites are around 0.1–0.2 mm and invisible to the naked eye [6][7]. | Clue | Cause | |---|---| | Glossy, twisted, stunted tips; bronzing of older leaves; nothing seen at 10× | Broad or russet mites [6][7] | | Cupped, distorted new leaves with brown spots, high RH or weak roots | Calcium delivery | | Thick, brittle, distorted new leaves; dead growing tips | Boron [3] | | Stunted, small, curled new leaves on one plant among healthy siblings | Hop latent viroid [10] | | Narrow, strap-like, twisted leaves and bent stems after outdoor spraying nearby or using contaminated compost or manure | Growth-regulator herbicide injury | | Odd, single-bladed or mottled leaves on young seedlings only | Genetic or seedling quirk; usually grows out | ## The curling and clawing differential table | Symptom pattern | Most likely | Rule out first | Key test | |---|---|---|---| | Taco curl, top canopy only | Heat or light stress | Low RH | Leaf temperature, PPFD, VPD | | Taco curl, whole plant | High VPD or root zone | Salt build-up, K | RH log, runoff EC, roots | | Dark glossy claw | Nitrogen excess | Overwatering, high EC | Input and runoff EC, feed N and NH₄ share | | Downward curl, puffy, heavy pot | Overwatering | Root rot | Pot weight, root smell | | Twisted glossy new growth | Broad/russet mites | Ca, B, HLVd | 30–60× lens on growing tips | | Cupped new leaves with brown spots | Calcium delivery | Low pH, high RH, mites | Runoff pH, RH, lens | | Thick brittle new growth, dead tips | Boron | Calcium | Feed recipe, tissue test | | One stunted curled plant | HLVd | Root problem | Lab test | | Strap-like leaves, bent stems | Herbicide drift or contaminated inputs | Mites | History of sprays, manure or compost | | Leaves up and flat at lights-on | Healthy | Nothing | None | ## What numbers matter for curling leaves? | Parameter | Target | Notes | |---|---|---| | Leaf temperature, lights on | ~24–28 °C (75–82 °F) | Photosynthesis fell above ~30 °C in one cultivar [4] | | VPD, veg | ~0.8–1.2 kPa | Grower practice | | VPD, flower | ~1.0–1.5 kPa | Grower practice | | RH, veg / flower | ~55–70% / ~40–55% | Grower practice | | PPFD, veg | ~400–700 µmol/m²/s | Grower practice | | PPFD, flower (no added CO₂) | ~800–1200 µmol/m²/s | Yield still rose to ~1800 in [5]; stress threshold is cultivar-dependent | | Ammonium share of total N | ≤ ~10–30% | Above ~30%, toxicity and lost yield in cannabis [8] | | Feed EC, veg / flower | ~1.0–1.8 / ~1.6–2.2 mS/cm | Grower practice | | Runoff EC vs input | within ~0.5 mS/cm | Grower practice | | Dissolved oxygen, hydro | ≥ ~6 mg/L | [9] | ## What should I check first when cannabis leaves curl? Check the cheap physical readings first: they explain most curling. 1. **Direction and location.** Write down which way, and which leaves (top, bottom, new, old, whole plant). 2. **Leaf temperature and RH at canopy height.** Gives you VPD. 3. **Canopy PPFD and fixture distance.** Did you just lower the light? 4. **Pot weight.** Heavy for days, or light and dry? 5. **Input and runoff EC and pH.** Calibrated meters. 6. **Growing tips under 30–60× magnification.** Especially for twisted growth. 7. **Feed recipe.** N rate, ammonium share, Ca and B. 8. **History.** New fan position, new compost or manure, outdoor herbicide spraying nearby, new clones brought in. ## How do I fix curling or clawing cannabis leaves? - **Heat or light stress:** raise or dim the light by 10–20%; bring leaf temperature below ~28 °C (82 °F); improve canopy airflow. See [heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md). - **High VPD:** add humidity towards ~55–65% in veg or ~45–55% in flower, or lower air temperature (see [VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md)). - **Nitrogen excess:** lower N by about 10–20% or the feed EC by 0.2–0.4 mS/cm; keep ammonium at or below about 10–30% of total N [8]. Don't do a big plain-water flush; a moderate correction is enough. If runoff EC is far above input, a root-zone flush clears the salts. - **Overwatering:** dry back to a noticeably lighter pot; water less volume or less often; improve drainage and aeration. - **Broad or russet mites:** isolate, act immediately; see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). - **Calcium delivery:** correct pH, bring RH into range so the plant transpires, keep roots healthy, feed ~150–200 mg/L Ca in soilless. Cal-Mag is only needed on RO or soft water or unbuffered coco, not because of LEDs (that claim is a *Myth*). - **Boron:** feed ~0.2–0.5 mg/L B; do not overshoot, the margin to toxicity is narrow. - **HLVd:** test, then remove positive plants; see [hop latent viroid](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). - **Herbicide injury:** no cure; remove the source (contaminated compost or manure, drift). New growth will tell you whether the plant grows out. ## How do I know the fix worked? Taco and heat curl should relax within hours to a day once leaf temperature and VPD are back in range. Overwatering curl lifts within 1–3 days after the pot dries back. Nitrogen claw doesn't reverse on affected leaves; new leaves should open flat and mid-green within 7–10 days. For mites, the next new growth opens normally and repeat inspections show no mites. For Ca and B, new growth comes in undistorted within 7–14 days. ## What are the common mistakes with curling leaves? - Treating heat taco with nutrients. Measure the leaf, not the room. - Calling clawing "nitrogen toxicity" on an overwatered plant and starving it. - Missing broad mites because nothing shows at 10×. Use 30–60×. - Adding Cal-Mag to twisted growth before checking for mites. - Big plain-water flushes to "fix" claw. Moderate the feed instead; save the flush for salt build-up. - Mistaking healthy praying leaves for a problem. ## How strong is the evidence? - Nitrogen excess and ammonium toxicity producing dark, clawed leaves in cannabis are *Supported* by controlled trials [1][8]. - Heat and high light reducing photosynthesis and causing leaf folding are *Supported* [4][5]; specific leaf temperature thresholds are *Grower practice*. - Broad and russet mites twisting new growth are *Established* by extension [6][7]. - Calcium and boron causing distorted new growth are *Established* in plant nutrition [3] and *Supported* for cannabis [1][2]. - HLVd stunting is *Established* [10]. - Herbicide injury symptoms on cannabis are *Grower practice* with extension support in other crops. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 4. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x 5. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 6. UConn IPM. Managing Broad Mites on Greenhouse Crops. https://ipm.cahnr.uconn.edu/ipm-managing-broad-mites-on-greenhouse-crops 7. Utah State University Extension. Hemp Russet Mite. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-hemp-russet-mite-.php 8. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 9. University of Kentucky Cooperative Extension, E706 (hydroponic Pythium and oxygen management). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 10. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa)-Viroid Diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases 11. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10):e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # Why is my cannabis drooping or wilting? The master decision tree > Drooping cannabis is diagnosed by one question: is the root zone wet or dry? A light, dry pot with limp leaves is underwatering; a heavy, wet pot with firm, curled-down leaves is overwatering. Wilting while the roots sit in water means the roots are failing: Pythium root rot, low dissolved oxygen, a hot reservoir, Fusarium wilt, or (in DWC and especially HPA) a failed pump, which is an emergency measured in minutes to hours. Transplant shock, unrooted clones, heat, stem damage and salt stress complete the list. - Canonical: https://genetixbay.com/knowledge/diagnosis/drooping-wilting-decision-tree.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why is my cannabis plant drooping?** A drooping cannabis plant is either short of water or unable to use the water it has. Lift the pot: if it is light and the leaves are limp and papery, it is underwatered. If it is heavy and the leaves are firm and curled down, it is overwatered and the roots lack oxygen. If the medium is moist and it still wilts, inspect the roots for rot or wilt disease. **How do I tell overwatering from underwatering in cannabis?** Overwatered cannabis has a heavy pot, wet medium for days, and firm, swollen-looking leaves that curl down from the petiole. Underwatered cannabis has a light pot, dry medium pulling from the pot wall, and limp, thin, papery leaves that perk up within an hour or two of watering. Overwatered plants do not perk up after watering; they get worse. **Why is my DWC cannabis wilting with roots in water?** DWC cannabis that wilts with its roots in water is suffocating or rotting. Check the air pump and stones first, then the solution temperature: above about 22 °C (72 °F) water holds less oxygen and Pythium takes over. Brown, slimy roots with a rotten smell confirm root rot. Cool the solution to 18 to 21 °C, restore strong aeration and change the reservoir. **What should I do if my HPA pump fails?** If an HPA pump fails, treat it as an emergency: roots in high-pressure aeroponics can be damaged within tens of minutes once misting stops. Restore misting immediately, or drop roots into a shallow pool of pH-adjusted solution with an air stone or small pump until the system is fixed. Battery-backed misting and an alarm are the only real protection. **Is drooping after transplant normal for cannabis?** Mild drooping for one to three days after transplanting cannabis is normal while roots grow into the new medium, especially if some roots were disturbed. Keep light gentle, water lightly in a ring around the root ball, and don't feed heavily. Drooping that lasts beyond about four days, or a pot that stays soaked, usually means overwatering the new, larger volume. **Short answer.** Start with one question: is the root zone wet or dry? Light pot and limp leaves is underwatering. Heavy pot and firm, curled-down leaves is overwatering. A plant that wilts while its roots sit in water has failing roots: Pythium root rot, low dissolved oxygen, a hot reservoir, Fusarium wilt or, in DWC and above all HPA, a failed pump. **If an HPA or DWC pump has stopped, act now:** HPA roots can be damaged within tens of minutes. The GenetixBay symptom checker shows an "act now" banner for pump failure and spreading root rot for exactly this reason. ## What is the difference between drooping and wilting? Drooping and wilting describe the same thing, leaves hanging below their normal angle, but they come from opposite water states. A drooping overwatered leaf is full of water and stiff, curling down from the petiole; the roots are short of oxygen and their signalling makes the leaf hang [3][10]. A wilting underwatered leaf has lost turgor: it is thin, soft and papery, and recovers within an hour or two of water. Wilting with a wet root zone is the dangerous one: water is present, but damaged roots or blocked vessels cannot move it [1][2][4]. ## The drooping and wilting decision tree, step by step ### Fork 1: Is this an emergency? | Situation | Action | |---|---| | HPA misting stopped, chamber humidity falling | **Critical.** Restore misting or pool the roots in aerated solution now | | DWC or RDWC air pump or chiller stopped | **High.** Restore air; DWC tolerates roughly 2–12 hours without air, depending on temperature | | Reservoir above ~24 °C (75 °F) and plants wilting | **High.** Cool the solution; rot follows | | Several hydro plants wilting at once, brown slimy roots | **Critical.** Root rot spreading through shared water | | None of these | Fork 2 | ### Fork 2: Lift the pot or check the roots. Wet or dry? | Root zone | Leaves | Go to | |---|---|---| | Light, dry, medium shrinking from the pot wall | Limp, thin, papery | Underwatering (Fork 3A) | | Heavy, wet for 3+ days | Firm, curled down, swollen | Overwatering (Fork 3B) | | Moist or in water | Wilting anyway | Root failure (Fork 3C) | | Normal | Drooping at the top only, under strong light | Heat or light (Fork 3D) | ### Fork 3A: Dry root zone Underwatering. Water slowly until 10–20% runoff (coco and rockwool) or until the whole volume is moist (soil). If water runs straight through a bone-dry pot, it has gone hydrophobic: water in several small passes, or bottom-water for 20–30 minutes. Recovery within 1–2 hours confirms it. Repeated dry-outs also concentrate salts: check runoff EC. ### Fork 3B: Wet root zone, firm drooping leaves Overwatering. The roots lack oxygen because the pores are full of water. Let the pot dry back until noticeably lighter, about 40–50% of its just-watered extra weight gone, before watering again. Common causes: pots too large for the plant, no drainage, saucers left full, dense mix with little perlite, watering on a schedule instead of by weight. Persistent overwatering invites root rot and fungus gnats. ### Fork 3C: Wet root zone, wilting anyway The roots or the stem are failing. Inspect them. | Root and stem clue | Cause | |---|---| | Brown, slimy roots, outer sheath slides off, foul smell | Pythium root rot [1][5] | | Roots tan, not slimy, solution warm, few air bubbles | Low dissolved oxygen / hot reservoir [3] | | Healthy-looking roots, but one plant or one branch wilts; brown streaks in the stem when cut | Fusarium vascular wilt [2][4] | | Brown, soft crown at the soil line | Crown rot (Fusarium or Pythium) [2] | | Small insects and white waxy residue on roots | Root aphids [9] | | Clean roots, stem cracked, kinked or chewed at the base | Physical stem damage, cutworms | | Roots fine, very high runoff EC | Salt (osmotic) stress [7] | ### Fork 3D: Root zone fine, top drooping under the light Heat or light. Leaves at the canopy top droop, taco and feel hot. Measure leaf temperature; photosynthesis fell above about 30 °C (86 °F) in one cannabis study [8]. Raise or dim the light and cool the canopy. ### Fork 4: Special cases | Situation | Normal or not | |---|---| | Fresh clone, day 1–3, drooping | Normal; keep 75–90% RH and light at 50–150 µmol/m²/s (see [clones wilting](https://genetixbay.com/knowledge/answers/why-are-my-clones-wilting.md)) | | Clone still wilting after day 4–5, stem soft and brown at the base | Not normal; stem rot in a soggy plug | | 1–3 days after transplant | Normal mild shock; longer means the bigger pot is overwatered | | Autoflower after a transplant | Avoid: autos lose days they can't get back. Sow directly into the final pot | | Seedling flopped at the soil line, stem pinched | Damping-off (see [damping-off](https://genetixbay.com/knowledge/germination/damping-off.md)) | | Leaves droop gently at lights-off and lift at lights-on | Normal diurnal leaf movement | ## The drooping and wilting differential table | Symptom pattern | Most likely | Rule out first | Key test | |---|---|---|---| | Limp, papery, light pot | Underwatering | Hydrophobic medium | Pot weight; recovery after water | | Firm, curled down, heavy pot | Overwatering | Root rot | Pot weight; root smell | | Wilting in DWC, warm water | Low DO / hot reservoir | Pump failure | Solution temperature, air pump check | | Wilting, brown slimy roots | Pythium root rot | Staining from nutrients | Root inspection and smell | | One plant or branch wilts, roots look fine | Fusarium wilt | Stem damage | Cut stem: brown vascular streaks | | HPA, chamber dry | Pump or nozzle failure | None: act | Pressure gauge, chamber RH | | Wilting with tip burn, very high runoff EC | Salt stress | Underwatering | Runoff EC vs input | | Top drooping under light | Heat or light stress | Root zone | Leaf temperature, PPFD | | Clone drooping day 1–3 | Normal | Low RH | Dome RH | | Post-transplant droop 1–3 days | Transplant shock | Overwatering | Pot weight | ## What numbers matter for drooping and wilting? | Parameter | Target | Notes | |---|---|---| | Irrigate when (pots) | pot ~40–50% lighter than just-watered | Grower practice | | Runoff per irrigation, coco/rockwool | 10–30% | Grower practice | | Solution temperature, DWC/RDWC/NFT | 18–21 °C (65–70 °F), below 22 °C (72 °F) | [3]; Pythium favoured above ~23 °C | | Dissolved oxygen | ≥ 6 mg/L, ideally near saturation | Saturation ~9.1 mg/L at 20 °C, ~8.3 mg/L at 25 °C [3] | | HPA pressure | ~80–100 psi (5.5–7 bar) | [6]; see [HPA aeroponics](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) | | HPA time to root harm without mist | tens of minutes to hours | [6] | | Clone dome RH | ~75–90% | Grower practice | | Leaf temperature, lights on | ~24–28 °C (75–82 °F) | [8] and grower practice | | Runoff EC vs input | within ~0.5 mS/cm | Grower practice | | NaCl causing yield loss in hydro cannabis | above ~5 mM (~115 mg/L Na) | [7] | ## What should I check first when cannabis droops? Check whether it is an emergency, then the water state, then the roots. 1. **System check (hydro):** pump running, air stones bubbling, HPA pressure holding, chamber misting, chiller on. 2. **Lift the pot** or weigh it against a just-watered pot of the same size. 3. **Moisture 5 cm down** and at the bottom of the pot, not just the surface. 4. **Solution temperature** and, if you have a meter, dissolved oxygen. 5. **Root look and smell:** white and earthy is good; brown, slimy and rotten is rot. 6. **Runoff EC** against input. 7. **Leaf temperature and PPFD** if only the top droops. 8. **The stem:** base for rot or damage; cut a wilted branch to look for brown vascular streaks. ## How do I fix a drooping cannabis plant? - **Underwatering:** water slowly to full saturation and 10–20% runoff; bottom-water a hydrophobic pot; then water by weight. - **Overwatering:** stop watering until the pot is noticeably lighter; tilt or raise pots off saucers; for the next run, add perlite (coco 20–30%, soil 20–40%) and size pots to the plant. - **Pump or air failure:** restore it immediately; keep a spare air pump, a battery backup for HPA and an alarm. - **Hot reservoir / low DO:** cool to 18–21 °C, add air stones, insulate and shade the reservoir. - **Pythium root rot:** see [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md): cool, aerate, change the solution, trim dead roots, re-establish beneficial microbes, and keep it out of shared water. - **Fusarium wilt:** no cure; remove the plant, bag it, sanitise pots and tools (see [Fusarium](https://genetixbay.com/knowledge/diseases/fusarium.md)). - **Salt stress:** a root-zone flush of the medium until runoff EC is near input, then resume normal feeding. This is the one valid flush. - **Heat or light:** raise or dim the light 10–20%; cool and move air across the canopy. - **Transplant shock:** gentle light, light watering around the root ball, no heavy feed for a few days. ## How do I know the fix worked? Underwatered plants recover within 1–2 hours. Overwatered plants lift within 1–3 days as the pot dries. Hydro plants recovering from low DO or a hot reservoir show new white root tips within 3–7 days. Root-rot recovery is confirmed by new white roots and no further wilting over 7–14 days. If a plant keeps wilting with good water, temperature and oxygen, assume disease and isolate it. ## What are the common mistakes with drooping cannabis? - Watering a drooping plant without lifting the pot. Overwatered plants get worse. - Feeding a drooping plant. Damaged roots cannot use it and EC climbs. - Running an HPA system with no pressure alarm or backup. - Treating root rot with nutrients or sugar products; molasses and sugars feed microbes, not the plant, and in hydro they feed the problem. - Transplanting autoflowers. Sow them in the final pot. - Calling Fusarium wilt "underwatering" and watering more. ## How strong is the evidence? - Pythium and Fusarium causing root rot and wilting in hydroponic cannabis is *Established* [1][2]. - Warm, low-oxygen solutions favouring Pythium is *Established* in hydroponic horticulture [3][5]. - Fusarium vascular wilt symptoms in cannabis/hemp are *Established* by extension [4]. - HPA time-to-harm figures are *Supported* from aeroponics reviews [6], not from cannabis trials. - Salt stress reducing cannabis yield and cannabinoids is *Supported* by controlled hydro trials [7]. - Pot-weight watering and dry-back targets are *Grower practice*, consistent with soilless culture principles [10]. ## Sources 1. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 2. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 3. University of Kentucky Cooperative Extension, E706 (hydroponic Pythium and oxygen management). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 4. Utah State University Extension. Hemp Fusarium wilt (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-fusarium-wilt 5. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-in-hydroponic-systems/ 6. Lakhiar IA, Gao J, Syed TN, Chandio FA, Buttar NA, 2018. Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics. Journal of Plant Interactions 13(1):338-352. https://doi.org/10.1080/17429145.2018.1472308 7. Yep B, Gale NV, Zheng Y. 2020. Aquaponic and hydroponic solutions modulate NaCl-induced stress in drug-type Cannabis sativa L. Frontiers in Plant Science 11:1169. https://doi.org/10.3389/fpls.2020.01169 8. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x 9. Utah State University Extension. Rice Root Aphids (hemp IPM note). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-rice-root-aphid.php 10. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Why is my cannabis turning yellow? The master yellowing decision tree > Cannabis yellowing is diagnosed in four forks: where it started (old leaves = mobile N, Mg, K; new leaves = immobile Fe, S, Mn, Zn, Ca, B), the pattern (uniform, interveinal, margins, spots, bleached tops), the root-zone readings (pH, EC, moisture, root colour) and the stage. Most yellowing in practice is roots that cannot absorb (overwatering, cold, rot, pH out of range) rather than a missing nutrient; late-flower fade and top-only bleaching under strong light are not deficiencies. - Canonical: https://genetixbay.com/knowledge/diagnosis/yellowing-decision-tree.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling, Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why is my cannabis plant turning yellow?** Cannabis turns yellow when chlorophyll is lost, and the location tells you the cause. Old, lower leaves yellowing first points to a mobile nutrient (nitrogen, magnesium, potassium) being pulled to new growth; new, upper leaves yellowing points to an immobile one (iron, sulfur, manganese, zinc) or high pH. In most cases the real cause is the root zone: overwatering, cold, rot or wrong pH. **Is yellowing at the top or the bottom of my cannabis plant worse?** Yellowing at the top of a cannabis plant is usually more urgent, because new growth is where yield is built and immobile nutrients like iron cannot be moved back once missing. Bottom yellowing from nitrogen or magnesium spreads slowly upward and is easy to correct. Top yellowing confined to leaves nearest a strong light, with green leaves lower down, is light bleaching, not a deficiency. **How do I tell nitrogen from magnesium yellowing on cannabis?** Nitrogen yellowing on cannabis turns the whole older leaf evenly pale, veins included, and climbs from the bottom. Magnesium yellowing leaves the veins green with yellow between them, also on older leaves, and often follows low root-zone pH or excess potassium or calcium. Controlled cannabis trials describe exactly these two patterns. Check pH before adding either nutrient. **Should I flush my cannabis if the leaves turn yellow?** Do not flush a yellowing cannabis plant as a reflex. A root-zone flush is only for salt build-up, when runoff EC is well above input EC, and it treats the medium, not the plant. Pre-harvest flushing to force yellowing is a myth that costs yield and resin. Most yellowing needs a watering, pH or root fix, then normal stage-strength feeding. **Is it normal for cannabis leaves to turn yellow in late flower?** Gradual yellowing from the bottom of a cannabis plant in the last two to three weeks of flower is normal ripening: the plant remobilises nitrogen into the buds. It needs no fix. Yellowing that starts before about week five or six of flower, or races up the plant in days, is not normal and usually means nitrogen was cut too early or the roots are failing. **Short answer.** Yellowing is loss of chlorophyll, and where it starts tells you most of the story. Old, lower leaves first means a *mobile* nutrient (N, Mg, K) is being pulled up to feed new growth; new, upper leaves first means an *immobile* one (Fe, S, Mn, Zn, Ca, B) is not arriving. But in real grow rooms the commonest cause of both is a root zone that cannot absorb: wet, cold, rotting or at the wrong pH. Work through the four forks below in order, and check roots and pH before you buy a single bottle. The GenetixBay symptom checker asks the same questions in the same order, so if you answer them here you will get the same answer there. ## What does yellowing actually mean on a cannabis leaf? Yellowing on a cannabis leaf means chlorophyll is being broken down or not being made, which exposes the yellow carotenoids underneath. Nitrogen and magnesium are part of the chlorophyll molecule itself; iron, manganese, sulfur and zinc are needed to build it or run the machinery around it [3]. So a shortage of any of these, or anything that stops roots taking them up, shows as yellow. Whether the old or the new leaves go first depends on phloem mobility. N, P, K and Mg move readily in the phloem, so the plant strips them from old leaves when supply runs short. Ca, B, Fe, Mn, Cu and Zn move poorly once deposited, so shortages show in the newest tissue [3]. Sulfur sits in between; cannabis trials found S deficiency yellowed middle and new leaves evenly [1][2]. This single fork, old versus new, is *Established* plant physiology and is the first question in any yellowing diagnosis (see [mobile vs immobile nutrients](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md)). ## The yellowing decision tree, step by step Answer each fork before moving to the next. Do not skip to fork 4. ### Fork 1: Where did the yellowing start? | Where it started | Go to | |---|---| | Oldest, lowest leaves, moving up | Fork 2A (mobile pattern) | | Newest leaves at the tops and branch tips | Fork 2B (immobile pattern) | | Whole plant at once, evenly pale | Fork 2C (whole-plant pale) | | Only leaves nearest the light, top of canopy | Fork 2D (light) | | Random leaves, in patches, one side of the plant | Fork 2E (local cause: pests, disease, physical) | ### Fork 2A: Old leaves yellowing first. What pattern? | Pattern on old leaves | Suspect | Cannabis evidence | |---|---|---| | Even pale-to-lemon yellow, veins too, climbing upward | Nitrogen | Lower foliage yellowed, then necrosis and drop [1]; began at lower fan tips around flower week 3 in DWC [2] | | Yellow between veins, veins green | Magnesium | Interveinal chlorosis of lower leaves [1][2] | | Yellow at margins and serration tips, then tan scorch | Potassium | Marginal yellowing then necrosis of lower leaves [1] | | Dark, dull leaves with brown-olive spots, purple petioles | Phosphorus | See [rust spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md) | | Marginal yellowing and scorch of older leaves, high Mn or B in the feed | Mn or B toxicity | Both produced marginal chlorosis of lower leaves in [1] | | Slow fade from the bottom in the last 2–3 weeks of flower | Normal senescence | Not a disorder | ### Fork 2B: New leaves yellowing first. What pattern? | Pattern on new leaves | Suspect | Notes | |---|---|---| | Interveinal yellow, fine green veins, sharp contrast | Iron | Almost always high pH or alkaline water, not an empty feed [9] | | Netted yellow between veins, small tan spots, upper and middle leaves | Manganese | Mn availability swings with pH; see [manganese](https://genetixbay.com/knowledge/nutrients/manganese.md) | | Even pale yellow, strongest at the leaflet base, middle and new leaves | Sulfur | Rare unless the feed lacks sulfate [1] | | Yellow then tan along the toothed margins of new leaves, short internodes | Zinc | Shown late in cannabis trials [1] | | Yellowing with twisted, stunted or dead tips | Calcium or boron | Often a transpiration or root problem; also rule out broad mites | | Pale, small new leaves on one stunted plant among healthy ones | Viroid (HLVd) | Test; see Fork 3 | ### Fork 2C: The whole plant is evenly pale Whole-plant paleness, all leaves at once, with slow growth, usually means the roots are failing or the plant is simply underfed. Seedlings in plain starter mix often go pale at weeks 2–3 when the cotyledon and mix reserves run out. Rule out, in this order: overwatering, cold root zone below about 18 °C (64 °F), pH far out of range, then low feed EC. See [whole-plant pale green](https://genetixbay.com/knowledge/answers/whole-plant-pale-green.md). ### Fork 2D: Only the leaves closest to the light Yellow or white leaves at the very top, nearest the fixture, with healthy green leaves below them, are light bleaching. The pattern follows light intensity, not leaf age: if a lower branch is pulled up into the same spot, it bleaches too. In one indoor trial, yield kept rising to about 1800 µmol/m²/s, but leaf-level stress depends on cultivar, temperature and CO₂ [6]. Check canopy PPFD before treating it as iron or magnesium (see [lookalikes](https://genetixbay.com/knowledge/diagnosis/lookalikes.md)). ### Fork 2E: Patchy, random or one-sided yellowing Yellowing in patches rather than by leaf age points away from nutrition. Flip the leaf and use a 10–20× lens: pale speckles with tiny moving dots and fine webbing are spider mites; silvery scars with black specks are thrips; sticky honeydew is aphids or whiteflies. Yellow spots with darker centres and halos spreading from the bottom in a humid room suggest [septoria leaf spot](https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.md). One-sided yellowing on one stem can be a damaged or kinked stem, or a vascular wilt. ### Fork 3: What do the root-zone readings say? This fork overrides fork 2. A textbook magnesium pattern at pH 5.0 is a pH problem, not a magnesium problem. | Reading | What it means | Next step | |---|---|---| | Pot heavy and wet for 3+ days, sour smell | Overwatering, low root oxygen | Dry back before any feed change | | Hydro roots tan/brown, slimy, smell of rot | Root rot (Pythium/Fusarium) [5] | See [root problems](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md) | | Small pear-shaped insects on roots, white waxy residue | Root aphids [8] | See [root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md) | | Runoff pH above ~6.5 (soilless) or ~7.0 (soil) | Fe, Mn, Zn, P lockout likely | Correct pH and alkalinity | | Runoff pH below ~5.5 (soilless) or ~6.0 (soil) | Mg, Ca, Mo shortfall; Mn excess | Correct pH | | Runoff EC more than ~1.0 mS/cm above input | Salt build-up | Root-zone flush, then reset feed | | Input EC well below stage target | Genuine underfeeding | Raise feed 10–20% | | Root zone below ~18 °C (64 °F) | Cold roots absorb poorly | Warm the root zone | ### Fork 4: Stage and history Late flower plus slow bottom-up fade is senescence. A recent switch to a "bloom" feed with little nitrogen, weeks of plain water, a recent transplant, a pH meter that hasn't been calibrated in a month, or a new tap-water source: any of these explains yellowing better than a leaf chart does. ## The yellowing differential table | Symptom pattern | Most likely | Rule out first | Key test | |---|---|---|---| | Uniform yellow, old leaves, climbing | Nitrogen shortage | Overwatering, root rot, cold roots, root aphids | Pot weight, root inspection, input EC | | Interveinal, old leaves | Magnesium | Low pH, excess K or Ca | Runoff pH, feed recipe | | Margins and tips, old leaves, then scorch | Potassium | Salt build-up, Mn/B toxicity | Runoff EC vs input | | Interveinal, new leaves, sharp | Iron | High pH, alkaline water, wet roots | Runoff pH, water report alkalinity | | Netted interveinal with tan specks, upper-middle | Manganese | High pH (deficiency) or low pH (toxicity) | Runoff pH, tissue test | | Uniform pale, middle-new leaves | Sulfur | Nitrogen (older leaves) | Feed recipe for sulfate | | Top leaves bleached white/yellow nearest light | Light bleaching | Fe, Mg | Canopy PPFD, distance | | Whole plant pale, slow | Root zone or underfeeding | Cold, overwatering, pH | Root-zone temperature, input EC | | Single stunted pale plant | HLVd | Root problem on that plant | Lab viroid test | | Speckled yellow, underside dots | Spider mites | Ca spotting | 10–20× lens | | Late-flower bottom fade | Normal senescence | Early N cut | Count weeks since flip | ## What numbers matter when cannabis turns yellow? | Parameter | Target | Notes | |---|---|---| | Root-zone pH, hydro | 5.5–6.0 | [4] | | Root-zone pH, coco/rockwool | 5.5–6.5 | Above ~6.5 Fe and Mn availability falls [4][9] | | Root-zone pH, soil | 6.0–7.0 | Grower practice | | Water alkalinity | < ~100–150 mg/L as CaCO₃ | Above this, acidify; it drives pH up over time [9] | | Feed EC, veg / flower | ~1.0–1.8 / ~1.6–2.2 mS/cm | Grower practice; cultivar-dependent | | Runoff EC vs input | within ~0.5 mS/cm | Grower practice | | Root-zone / solution temperature | 18–22 °C (65–72 °F) | Warmer water holds less oxygen | | Leaf N, healthy recent mature leaf | ~3.3–4.8% dry weight | Survey range in [1] | | Leaf Mg, healthy | ~0.40–0.81% | [1] | | Leaf Fe, healthy | ~100–150 mg/kg | [1] | | Canopy PPFD, flower (no added CO₂) | ~800–1200 µmol/m²/s | Grower practice; bleaching thresholds vary by cultivar | ## What should I check first when my cannabis turns yellow? Check the root zone and pH first, because in practice they explain more yellowing than any nutrient. The order below is cheapest and most likely first. 1. **Lift the pot** or look at the roots. Heavy and wet for days, or brown roots in hydro, ends the search. 2. **Calibrate your pH meter** with fresh buffers, then measure input and runoff (or reservoir) pH. 3. **Measure input and runoff EC.** High runoff EC means salts; low input EC means hunger. 4. **Measure root-zone temperature.** Cold floors and cold reservoirs are underrated causes. 5. **Turn over five leaves** with a 10–20× lens. Mites and thrips cause yellowing too. 6. **Check the canopy PPFD** if only the top is yellow. 7. **Read your feed record and water report.** Bloom-formula switch, RO water without Ca/Mg, new tap source. 8. **Only now** use the leaf pattern to choose between N, Mg, K, Fe, S, Mn and Zn. ## How do I fix yellowing cannabis leaves? Fix the cause the readings point to, then feed normally at stage strength. - **Overwatering:** let the pot dry until noticeably lighter (about 40–50% of its just-watered extra weight gone); improve drainage; water smaller volumes more often only once roots are active. - **Root rot (hydro):** see [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md). Cool the solution to 18–22 °C, maximise aeration, change the reservoir. - **High pH or alkaline water:** bring root-zone pH into range; acidify water with alkalinity above ~100–150 mg/L CaCO₃ [9]; in soilless, use an iron chelate suited to your pH (EDTA up to ~6.5, DTPA to ~7.5, EDDHA above) at about 1.5–3 mg/L Fe (see [iron](https://genetixbay.com/knowledge/nutrients/iron.md)). - **Low pH:** raise to range; Mg and Ca recover as pH rises. A magnesium sulfate supplement at label rate if the feed is genuinely short (see [magnesium](https://genetixbay.com/knowledge/nutrients/magnesium.md)). - **Genuine nitrogen shortage:** raise N by about 10–20% of the current rate, not double. Organic growers: liquid organic N or a top-dress, which acts more slowly (see [nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md)). - **Salt build-up:** a root-zone flush to clear the medium (this is the one valid flush; it treats the medium, at any stage), then resume full feed. See [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md). - **Light bleaching:** raise or dim the fixture until top-canopy PPFD is back in range and leaf temperature is below about 28–30 °C (82–86 °F). - **Late-flower fade:** nothing. Keep feeding P, K, Ca, Mg, S and micros; the GenetixBay approach is to taper nitrogen, not to flush. - **Cal-Mag:** add it when your water is RO or very soft, or your coco is unbuffered. LED lighting does not create a Cal-Mag need; that claim is a *Myth* (see [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)). ## How do I know the fix worked? The fix worked when the yellowing stops spreading and new growth comes in green, usually within 5–7 days for mobile nutrients and 7–14 days for iron or manganese. Already-yellow leaves do not turn green again; judge by the new leaves above the damage. Runoff pH and EC should stay in range at the next two checks. If nothing changes after two weeks with good readings, re-check the roots and consider a leaf tissue test or an HLVd test. ## What are the common mistakes with yellow cannabis leaves? - Adding nutrients to a plant with wet, cold or rotting roots. It cannot use them and the EC climbs. - Trusting an uncalibrated pH meter or pH drops in a coloured feed. - Treating bleached tops as iron deficiency and adding iron to a plant that has plenty. - Chasing late-flower fade with nitrogen, or forcing it with a pre-harvest flush. - Stripping every yellow leaf before diagnosing; the leaves are the evidence and still hold reserves. - Reading one leaf. Look at the whole plant and the pattern over several days. ## How strong is the evidence? - Old-versus-new location as the first fork is *Established* plant physiology [3], confirmed for cannabis by controlled single-element trials in substrate and DWC [1][2]. - The specific leaf patterns for N, Mg, K, S, Fe, Mn and Zn in cannabis are *Established* by two independent controlled studies [1][2], though both used few cultivars. - High pH and alkalinity causing Fe and Mn chlorosis is *Established* in horticulture [9]; exact cannabis thresholds are *Supported*. - Root rot causing yellowing and stunting in hydro cannabis is *Established* [5]. - HLVd causing stunting and pale growth is *Established*; it needs a lab test to confirm [7]. - Nitrogen supply shaping late-flower fade and cannabinoid percentage is *Supported* [10]. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 4. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 5. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 6. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 7. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa)-Viroid Diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases 8. Utah State University Extension. Rice Root Aphids (hemp IPM note). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-rice-root-aphid.php 9. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 10. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 --- # Yellow new growth on cannabis: a differential > Yellowing at the top of the plant points to an immobile nutrient (Fe, S, Mn, Zn, Cu, B, Ca) that the roots are failing to deliver, and the usual cause is high root-zone pH or a wet, cold or damaged root zone rather than a lack of fertiliser. Rule out light bleaching, broad/russet mites and viroid stunting before adding micronutrients. - Canonical: https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.html - Category: Diagnosis · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are the new leaves on my cannabis yellow?** Yellow new leaves on cannabis mean the plant is short of an immobile nutrient, such as iron, sulfur, manganese, zinc, copper, boron or calcium, that it cannot move from old leaves. In most grows the feed contains these, so the real cause is failed uptake: root-zone pH too high or roots that are wet, cold or damaged. Rule out light bleaching and mites first. **Why is the top of my cannabis plant yellow but the bottom green?** A cannabis plant yellow at the top and green at the bottom has an uptake problem with immobile nutrients. Controlled trials show iron deficiency yellows new leaves between the veins while lower foliage stays dark green. First check whether only the tops nearest the light are pale (bleaching), then root-zone pH, which should stay within 5.5 to 6.5 in coco or rockwool. **Is yellow new growth on cannabis iron deficiency?** Yellow new growth on cannabis is iron deficiency when the yellowing is interveinal with sharply green veins at the top only, but in coco and hydro it is usually pH-induced rather than a true shortage. Iron and manganese availability falls above about pH 6.5. Correct root-zone pH first; adding iron to a pH 7 pot precipitates and does nothing. **Why are the tops of my cannabis bleached white under an LED?** Bleached white tops directly under an LED, with the lower canopy fine, are light and heat bleaching, not a nutrient problem. It starts as pale, then white, leaves and bracts at the very top. Raise the fixture 10 to 15 cm or dim it, keep leaf temperature below about 30 °C (86 °F), and measure PPFD. Bleached tissue will not recover. **What causes twisted yellow new growth on cannabis?** Twisted, shiny, glassy or bronzed yellow new growth on cannabis is most often broad or russet mites, which are nearly invisible without a 20x or stronger lens, according to extension sources. Calcium or boron deficiency can also distort new leaflets and kill tips. Inspect the growing tips with a lens before spraying micronutrients, because mites move fast and keep feeding. **Short answer.** If the top is yellow and the bottom is green, the plant is short of something it cannot move from old leaves: iron, sulfur, manganese, zinc, copper, boron or calcium. In most grow rooms the fertiliser contains all of these; what has failed is uptake, usually because root-zone pH is too high or the roots are wet, cold or damaged. Before you buy micronutrients, rule out light bleaching (tops nearest the light), broad or russet mites (twisted, shiny, glassy new growth) and viroid infection (stunted, pale, brittle plants). ## What's happening Immobile elements must arrive fresh through the roots to every new leaf. Any interruption shows first at the growing tips. In cannabis trials, Fe deficiency produced interveinal chlorosis on new and expanding leaves while lower foliage stayed dark green [1]; Mn deficiency produced bright yellow netted interveinal chlorosis on upper and central foliage in sand culture [1] but no visible symptoms in DWC [2]; Zn deficiency produced marginal yellowing of new leaves turning to tan necrosis [1]; S deficiency gave general paling with the base of leaflets most yellow, intensifying on new leaves [1], and in DWC flowering plants it yellowed upper sugar leaves first [2]; Ca and B deficiency distorted new growth, narrow leaflet bases and dying tips [1]. Iron and manganese availability falls as pH rises above ~6.5 in soilless media [3], which is why "iron deficiency" in coco or hydro is so often a pH problem. ## How to recognise it | Pattern on new growth | Most likely | Also consider | |---|---|---| | Interveinal yellow, veins sharply green, top only | Iron (often pH-induced) | Mn; cold, wet roots | | Netted yellow between veins, small tan specks | Manganese | Fe; pH high | | Pale overall, leaflet base yellowest, top half | Sulfur | N if spreading from bottom too | | Yellow margins on new leaves, then tan edges | Zinc | Heat/light stress | | Distorted, narrow, crinkled leaflets; dying tips | Calcium or boron | Broad/russet mites, herbicide drift, HLVd | | White/bleached tops directly under light, lower canopy fine | Light/heat bleaching | Not a nutrient at all | | Twisted, shiny, glassy, bronzed new growth; leaves cupping | Broad or russet mites [5] | Ca/B deficiency | | Whole plant stunted, small pale leaves, short internodes, brittle stems | Hop latent viroid [6] | Root rot, root aphids | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | pH, hydro | 5.5–6.0 | [3] | | pH, coco/rockwool | 5.5–6.5 | Above 6.5, Fe and Mn availability falls [3] | | Leaf Fe, healthy | ~100–150 mg/kg | Survey range in [1]; deficient plants 60 mg/kg | | Leaf Mn, healthy | ~41–93 mg/kg | [1] | | Leaf Zn, healthy | ~24–52 mg/kg | [1] | | Leaf S, healthy | ~0.17–0.41% | Survey 0.17–0.26%; controls 0.41% [1] | | Canopy PPFD | flower ~900–1500 µmol/m²/s | Yield rose linearly to 1800 in one trial [4], but bleaching occurs on some cultivars at high PPFD | | Canopy leaf temperature | < ~30 °C (86 °F) | Grower practice | ## What to check first 1. **Light.** Are the yellow/white tops only the ones closest to the fixture? Measure PPFD or raise the light 10–15 cm. Bleaching starts as pale, then white, leaves and bracts at the very top. 2. **pH at the root zone.** Runoff or reservoir, calibrated meter. A pH of 6.8 in coco is a likely Fe/Mn lockout. 3. **Root zone.** Cold (< 18 °C / 64 °F), waterlogged, or rotting roots. New growth suffers first when roots are compromised. 4. **Hand lens on new growth.** 20× or better. Broad mites are nearly invisible to the eye [5]; look for shine, bronzing and twisted tips. 5. **Whole-plant pattern.** One plant stunted and pale in a room of healthy ones (same feed) suggests a pathogen or viroid; test if it is a mother or a clone source. 6. **Feed check.** Is it a complete fertiliser with micronutrients? RO water with an incomplete base nutrient can genuinely lack S or micros. ## How to fix it - **Light:** raise or dim to reduce top-of-canopy PPFD and leaf temperature. Bleached tissue will not recover. - **pH:** bring the root zone back into range. In coco, irrigate to 20–30% runoff with correctly pH'd solution; in hydro, change the reservoir. Fe and Mn uptake typically recovers in days. - **Root zone:** warm it, aerate it, water less often. See [drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) and [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md). - **True micronutrient shortage (rare with complete feeds):** use a chelated micronutrient product at label rate. A chelated iron foliar spray can green new growth in veg within days; do not spray flowers. - **Sulfur:** most complete feeds supply it via sulfate salts (e.g. magnesium sulfate). Check your base nutrient label. - **Mites:** see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). Do not delay; they move fast. - **Suspected viroid:** isolate, test (RT-PCR on roots and leaves), and remove positives from propagation. See [HLVd](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). ## How to confirm it worked - The next pair of leaves at each tip emerges green, within 5–10 days. - The yellowing does not spread to further new growth. - With mites, new growth stops twisting within 1–2 weeks of control. ## Common mistakes - Adding iron to a pH 7 coco pot. It precipitates and the plant still can't use it. - Mistaking light bleaching for nitrogen or iron shortage. - Spraying micronutrients on a plant with broad mites while the mites keep feeding. - Overdosing boron or zinc "just in case"; boron toxicity in cannabis caused marginal yellowing and necrosis of lower leaves [1]. ## Evidence - Upper-leaf symptoms of Fe, Mn, S, Zn, Ca and B deficiency in cannabis are *Established* in sand culture [1], with partial confirmation in DWC [2]. The Mn result differs between studies: *Contested* how often Mn deficiency is visible. - pH-induced Fe/Mn unavailability is *Established* in horticulture and *Supported* for cannabis [3]. - Light bleaching thresholds are *Grower practice*; yield responses to high PPFD are *Supported* [4]. - Broad mite and HLVd symptoms are *Supported* by extension sources [5][6]. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 4. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 5. UConn IPM. Managing Broad Mites on Greenhouse Crops. https://ipm.cahnr.uconn.edu/ipm-managing-broad-mites-on-greenhouse-crops 6. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa)-Viroid Diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases --- # Yellowing lower leaves on cannabis: a differential > Lower-leaf yellowing is usually nitrogen shortage or, far more often, roots that cannot take nitrogen up (overwatering, cold or rotting roots, pH out of range). Uniform yellow climbing from the bottom suggests N; green veins with yellow between them suggests Mg; yellow-then-brown margins suggest K. In late flower, gradual fade is normal. - Canonical: https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.html - Category: Diagnosis · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower, Ripening · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why are the bottom leaves of my cannabis turning yellow?** The bottom leaves of cannabis turn yellow when a mobile nutrient, usually nitrogen and sometimes magnesium or potassium, is pulled from old leaves to feed new growth. The commonest reason is roots that cannot absorb, being overwatered, cold, rotting or at the wrong pH, rather than an empty feed. Check watering, roots and root-zone pH before adjusting the feed. **Is lower leaf yellowing on cannabis nitrogen deficiency?** Lower leaf yellowing on cannabis is nitrogen deficiency when the whole leaf turns evenly pale to lemon yellow and the yellowing climbs from the bottom, as controlled trials describe. Healthy recent mature leaves hold about 3.3 to 4.8% nitrogen by dry weight. The same pattern also comes from overwatering, root rot, a cold root zone or root aphids, so rule those out first. **Why are the bottom cannabis leaves yellow with green veins?** Yellow lower cannabis leaves with green veins point to magnesium deficiency, shown as interveinal yellowing of lower leaves in controlled trials. In soilless and hydro systems, low root-zone pH is a common cause, as is excess potassium or calcium competing with magnesium. Check pH first, then add a magnesium sulfate supplement at label rate if the feed is genuinely short. **Is yellowing normal in late cannabis flower?** A slow fade from the bottom of cannabis in the last 2 to 3 weeks of flower is normal ripening. It is not a deficiency to chase with extra nitrogen, and it is no reason for a pre-harvest flush, which is a myth that costs yield and resin. Yellowing that starts before about week 5 or 6 of flower may mean nitrogen was cut too early. **Should I add more nitrogen if my cannabis lower leaves are yellow?** Add more nitrogen for yellow lower cannabis leaves only after ruling out overwatering, root problems and pH, because roots that cannot absorb will not use it and the EC simply rises. If nitrogen is genuinely low, raise it modestly, about 10 to 20% of the current rate. One hydroponic flowering trial predicted a yield optimum near 194 mg/L mineral nitrogen. **Short answer.** Yellowing that starts on the oldest, lowest leaves means a *mobile* nutrient is being pulled out of them to feed new growth: most often nitrogen, sometimes magnesium or potassium. But the commonest reason a plant runs short is not an empty feed bottle; it is roots that cannot absorb (overwatered, cold, rotting, or pH out of range). Check water and pH first. In the last 2–3 weeks of flower, a slow fade from the bottom is normal. ## What's happening N, Mg and K are mobile in the phloem. When supply at the roots falls short, the plant cannibalises old leaves. In controlled cannabis trials, N deficiency began as pale yellowing of the lower foliage that climbed upward, then leaves turned fully yellow, necrotic and dropped [1]; in DWC it began at lower fan-leaf tips around week 3 of flower, with red-brown petioles on the worst leaves [2]. Mg deficiency showed as interveinal yellowing of lower leaves with veins staying green [1][2]. K deficiency started as yellowing on the leaf margins and serrations of lower leaves, then tan scorch [1]. ## How to recognise it | Pattern on lower leaves | Most likely | Also consider | |---|---|---| | Even, pale-to-lemon yellow, whole leaf, climbing up | Nitrogen shortage | Overwatering, root rot, cold root zone, root aphids | | Yellow between veins, veins green | Magnesium | pH too low (soilless/hydro), excess K or Ca antagonism | | Yellow margins and serration tips, then brown scorch | Potassium | Salt build-up, Mn or B toxicity (marginal yellowing of lower leaves in trials [1]) | | Brown/olive spots, sunken, on lower leaves | Phosphorus (see rust spots) | Calcium spots, leaf septoria | | One or two leaves, shaded, deep in the canopy | Shade senescence | Nothing; normal | | Whole bottom third, late flower, slow | Normal ripening fade | N cut too early if before week 5–6 | ## Numbers that matter | Parameter | Target | Notes | |---|---|---| | pH, hydro | 5.5–6.0 | [3] | | pH, coco/rockwool | 5.5–6.5 | Mg uptake falls at low pH | | pH, soil | 6.0–7.0 | Grower practice | | N supply, mineral feed, flower | ~194 mg/L N predicted optimum in one DWC flowering trial | Bevan et al. [4]; organic feeds needed more (~260 mg/L in flower) | | Leaf N, healthy (most recent mature leaf) | ~3.3–4.8% dry weight | Survey range cited by Cockson et al. [1]; deficient plants had 1.6% | | Leaf Mg, healthy | ~0.40–0.81% | [1] | | Leaf K, healthy | ~1.8–2.9% | Survey 1.83–2.35%; controls 2.85% [1] | | Solution temperature (hydro) | 18–22 °C (65–72 °F) | Warmer = less oxygen, more root disease | ## What to check first 1. **Stage.** Late flower (last 2–3 weeks) and slow bottom-up fade: probably normal. Stop here, and keep feeding at stage strength; don't force the fade with a pre-harvest flush, which is a *Myth* that costs yield and resin (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). 2. **Watering.** Is the pot heavy and wet for more than 2–3 days? Is the medium sour-smelling? Overwatered roots absorb poorly (see [drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md)). 3. **Roots.** Hydro: are they white, or tan/brown and slimy? Brown roots with yellowing and stunting are classic Pythium/Fusarium root rot in hydro cannabis [5]. Soil/coco: tip a plant out; look for white roots at the edges, and for root aphids (small, pear-shaped insects on roots, often with white waxy residue) [6]. 4. **pH of input and runoff.** Calibrated meter. 5. **EC of input and runoff.** Very low input EC = genuine hunger. Very high runoff EC = salts, often with tip burn too. 6. **Feed record.** Did you switch to a "bloom" formula with low N in early flower, or plain water for weeks (a "flush")? 7. **Only then** decide between N, Mg and K from the leaf pattern. ## How to fix it - **Root zone first.** Let overwatered pots dry back until the pot is noticeably lighter; improve aeration; warm a cold root zone to ~20 °C (68 °F); in hydro, change the reservoir and check the air supply. - **Correct pH** to the system range, measured at the root zone (runoff or reservoir), not just the input. - **If N is genuinely low:** raise the N in the feed modestly, about 10–20% of the existing rate, rather than doubling. In one hydroponic flowering trial, mineral N around 194 mg/L was the predicted yield optimum [4]. Organic growers: top-dress or liquid organic N; it is slower to act. - **If Mg:** check pH first; then a magnesium sulfate supplement at label rate for your system. A foliar Mg spray can green up new leaves faster in veg; avoid foliar sprays on buds. - **If K:** confirm EC is not excessive (salt stress mimics K burn), then adjust to a formula with more K in flower. - **Organic/living soil:** do not chase with bottled salts. Check moisture and pH, top-dress, and give the soil biology time (1–2 weeks). ## How to confirm it worked - The yellowing stops climbing within 5–7 days. Already-yellow leaves stay yellow. - New leaves emerge mid-green, not pale. - For Mg, the next leaves above the damage have no interveinal yellowing. - Runoff pH and EC stay in range at the next two checks. ## Common mistakes - Adding nitrogen to an overwatered or root-rotted plant. It won't be absorbed and the EC rises. - Calling late-flower fade a deficiency and pushing N into ripening buds. - Using Cal-Mag as a cure-all; excess Ca can compete with Mg and K. - Defoliating every yellow leaf before diagnosing; you lose the evidence and the plant's reserves. ## Evidence - Bottom-up yellowing as the signature of N, Mg and K shortage in cannabis is *Established* by two controlled studies in different systems [1][2]. - Root rot in hydro producing yellowing and stunting is *Established* [5]. - N rate optima are *Supported* (single cultivar trials; organic and mineral differ) [4]. - Soil pH 6.0–7.0 for cannabis is *Grower practice*. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824 4. Bevan L, Jones M, Zheng Y., 2021. Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 5. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 6. Utah State University Extension. Rice Root Aphids (hemp IPM note). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-rice-root-aphid.php --- # Curing and burping: jars, humidity and how long > Curing is a slow, steady decline in the bud's moisture content and water activity, not a constant hold: start around aw 0.62–0.65 and let it settle towards 0.55–0.58 over two to eight weeks, burping daily at first, then weekly. Jar RH is only a proxy for the bud, valid once a sealed jar has equilibrated (aw ≈ RH / 100). Check with the stem snap, an equilibrated hygrometer and weight. Humidity packs are a marketing gimmick; if a jar is too dry, add a fresh bud. - Canonical: https://genetixbay.com/knowledge/harvest-cure/curing-burping.html - Category: Harvest and cure · Level: Beginner - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Cure · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How long should I cure cannabis?** Cannabis should cure for at least 2 weeks, and 4–8 weeks is common, according to grower practice. Over that time the bud's water activity should fall slowly from about 0.62–0.65 towards 0.55–0.58. Longer cures help within reason by letting aroma settle and limiting further terpene loss, but curing chemistry is not well studied, and no cure can rescue a badly dried crop. **How often should I burp jars?** Burp curing jars by opening them for 10–15 minutes once or twice a day in the first week, every 2–3 days in the second week, and weekly after that. Sniff each time: an ammonia or musty smell means the buds are too wet and at risk of mould, so spread them out to dry immediately rather than just burping more. **What humidity should my curing jars be?** Curing jars should read 55–65% RH once sealed and left undisturbed for 12–24 hours, starting near 62–65% and drifting slowly towards 55–58%. Jar RH is only a proxy for the bud's water activity and is valid only after equilibration; a reading taken right after burping measures the air. If an equilibrated jar reads above about 65–68%, take the buds out and dry them more. **What water activity should cured buds be?** Cured cannabis buds should sit at a water activity of 0.55–0.65, the range set by the ASTM D8197 standard to guard against mould without making flower brittle. Start the cure near 0.62–0.65 and let it fall slowly to about 0.55–0.58; above 0.68 the flower needs further drying. A dedicated water-activity meter is the gold standard for measuring it. **What moisture content should cured cannabis have?** Cured cannabis at water activity 0.55–0.65 holds roughly 8–12% water by weight, though the figure depends on the measuring method. One lab's method-validation data puts cured flower at 5–9% by water-specific methods, while the common 10–12% figure partly comes from hot-oven testing that also counts lost terpenes as water. That is why water activity, not moisture percentage, is the standard. **How do I know my buds are dry enough to jar?** Buds are dry enough to jar when small stems snap cleanly with a little fibre instead of bending, the flower springs back when squeezed, and a sample sealed in a jar for 12–24 hours reads a stable 60–65% RH. By then the flower usually weighs about 20–25% of its wet weight. If a jar spikes to 75% or more overnight, the buds went in too wet. **Do humidity packs work for curing?** Two-way humidity packs are a marketing gimmick in GenetixBay's view, not a better way to cure. The only data claiming a terpene benefit is a pack maker's own company-commissioned, non-peer-reviewed test, and no independent study exists either way; in the founder's experience packs cost terpenes. If a jar drops below about 55%, add a fresh, slightly moister bud for a day instead. **Should jar humidity stay constant during a cure?** Jar humidity should not stay constant during a cure. Curing is a slow, steady decline in the bud's moisture content and water activity, from about aw 0.62–0.65 at the start towards 0.55–0.58 over several weeks, and holding one number for months is a common mistake. Weighing jars weekly confirms the decline: small, steady losses are right, and a gain means moisture got in. **Is water curing worth it?** Water curing is not worth it according to GenetixBay, which labels it contested and does not recommend it. Neither water curing nor freeze drying is proven to give better flower than a slow hang dry in the dark followed by a jar cure, which remains the standard. A cure works by slowly lowering the bud's water activity, from about 0.62–0.65 towards 0.55–0.58. **Why does my cure smell like hay?** A cure that smells like hay points to bacteria, over-drying or drying too fast, and in GenetixBay's experience that smell never truly comes out; curing won't remove it. Prevent it with a slow 7–14 day dry and by never letting buds fall below water activity 0.55. An ammonia or musty smell is different: it means the buds are too wet and at risk of mould. **Can curing fix a bad dry?** Curing cannot fix a bad dry. Long cures help within reason, letting moisture equalise and aroma settle, but the harsh smoke and hay or grassy smell from a 3-day hot dry stay with the flower. A cure adds no terpenes either; it only limits further loss. Get the dry right first: in the dark, at about 15–21 °C and 55–62% RH, for 7–14 days. **Short answer.** Cure the **bud's moisture**, not the jar's air. Put properly dried buds (small stems snap, aw ~0.60–0.65) loosely into airtight jars **about ¾ full**, with a salt-tested hygrometer. Keep jars dark at **15–21 °C (60–70 °F)**. **Burp** (open for 10–15 minutes) **once or twice a day for the first week**, then every few days, then weekly. Start with the buds at about **aw 0.62–0.65** and let them fall slowly towards **0.55–0.58** over the cure: curing is a steady decline, not a constant hold. The jar's RH tells you the bud's aw **only once the sealed jar has equilibrated** (aw ≈ RH / 100). If an equilibrated jar reads **above ~65–68 %**, take the buds out and dry them more; ASTM notes aw above 0.68 calls for further drying [1][2]. Cure **2–8 weeks**. Smoother smoke and rounder aroma are widely reported, but the chemistry of curing is *Grower practice*, not well studied. > **House position: a cure never fixes a bad dry.** Long cures help, within reason. But a **hay smell** means bacteria, over-drying, or drying too fast, and it never truly comes out. Get the [dry](https://genetixbay.com/knowledge/harvest-cure/drying.md) right first. > **House position: curing is a slow decline, not a hold.** A cure slowly reduces the bud's moisture content and water activity over time; it doesn't hold them constant. Start at the top of the range (aw ~0.62–0.65) and let it fall steadily towards ~0.55–0.58 over the weeks. **Humidity packs are a marketing gimmick.** The only data saying they help is a pack maker's own test, and in the founder's experience they cost you terpenes. If a jar has gone too dry, put a fresh, slightly moister bud in with it for a day instead. (Packs vs a fresh bud vs nothing is an open GenetixBay trial.) ## The bud, not the jar: moisture content and water activity What you are curing is the **bud**. Two numbers describe its water: - **Moisture content (MC):** how much water is in it, as % of its weight (w/w). - **Water activity (aw):** how "available" that water is, from 0 to 1.0. It is what mould and bacteria respond to, and it is what the ASTM D8197 range (**0.55–0.65**) is written in [1]. **Jar RH is only a proxy.** A hygrometer measures the air in the jar, not the bud. Once a sealed jar has **equilibrated** (the reading has stopped moving, usually after 12–24 h undisturbed), the air and the bud agree, and **aw ≈ equilibrium RH / 100**: a stable 60 % means the bud is at about aw 0.60. Read it straight after burping or after you've just filled the jar and it tells you about the air, not the flower. Hygrometers also drift; salt-test yours. **What that means in moisture.** At aw 0.55–0.65, cured flower holds roughly **8–12 % water by weight** [5]. The exact link between aw and MC (the moisture sorption isotherm) differs a little by cultivar and bud density, which is why aw, not %, is the standard. ### How to check the bud | Check | How | What "ready" looks like | |---|---|---| | **Stem snap** | Bend a small stem from inside the jar | Snaps cleanly with a little fibre; a bend means too wet, a powdery crumble means too dry | | **Equilibrated hygrometer** | Seal the jar, leave it untouched 12–24 h, then read | Stable 55–65 % (aw 0.55–0.65); start the cure at the top of that, let it fall slowly | | **Weight** | Weigh a tagged branch or a jar's buds wet, then track | Finished flower ends at roughly **20–25 % of its wet weight**; a slow, steady fall in weight over the cure is the "decline" you want | | **Feel** | Squeeze a bud gently | Springs back; not spongy, not crispy | A dedicated water-activity meter is the gold standard, but an equilibrated, salt-tested hygrometer gets you close enough at home. ## What's happening - **Moisture equalisation:** after drying, the core of a bud is wetter than the outside. Sealed, the moisture redistributes; burping releases the excess so the jar doesn't climb into mould territory. - **Chlorophyll and sugars:** growers attribute the loss of a fresh "green" note to slow breakdown of chlorophyll and starches during a slow dry and cure. This is plausible but not well documented in cannabis (*Grower practice*). - **Hay smell:** a true hay smell comes from bacteria, over-drying or drying too fast. The cure won't remove it (house position). - **Terpenes:** volatile monoterpenes keep escaping during drying and storage, with sesquiterpenes becoming a larger share [3]. Terpenes are more affected by drying method than by storage in hemp; cannabinoids more by storage [4]. A cure doesn't add terpenes; it limits further loss and lets aroma settle. ## Numbers that matter | Parameter | Target | |---|---| | Jar fill | ~¾ full, loose | | Bud aw (equilibrated jar RH / 100) | Start 0.62–0.65, decline slowly to 0.55–0.58 (0.55–0.65 overall) [1] | | Bud moisture content | ~8–12 % w/w at that aw (method dependent) [5] | | Too wet | Equilibrated jar > 65–68 % → remove and dry [2] | | Too dry | < 55 % → add a fresh, slightly moister bud for a day; no humidity packs | | Finished weight | Roughly 20–25 % of wet weight | | Temperature | 15–21 °C (60–70 °F) | | Burping | Week 1: 1–2×/day; week 2: every 2–3 days; after: weekly | | Duration | 2 weeks minimum; 4–8 weeks common | - Freeze drying and water curing: *Contested*; not recommended (see [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md)). ## How to do it 1. Check dryness on the bud: stems snap, then seal a sample jar with a hygrometer for 12–24 h untouched. Only that equilibrated reading counts. 2. Fill jars ¾, add a calibrated mini hygrometer, seal, label with date and cultivar. 3. Burp on schedule; sniff each time. An ammonia or musty smell = too wet, mould risk: spread buds out to dry immediately. 4. Don't add humidity packs: they're a marketing gimmick (house position). Let the bud's aw drift down slowly, reading the jar only after it has sat sealed long enough to equilibrate; if it drops below ~55 %, add a fresh bud for a day. 5. Track weight: weigh each jar's buds when you fill it and again each week. Small, steady losses mean the cure is declining as it should; a gain means moisture got in. 6. After the cure, move to [long-term storage](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md). > **Greenleaf's standing challenge: darkness before harvest.** Putting plants in 24–72 h of darkness before the chop is a *Myth*, and the founder's verdict is "complete and utter nonsense": why cut photosynthesis in the most critical part of the life cycle, while the plant is still finishing its resin? For more than 20 years the founder has offered a standing challenge: find a peer-reviewed study showing a benefit (not a single-plant study, not biased or skewed) and a 50-pack of seeds is yours, no questions asked. Nobody has claimed it. ## Common mistakes - Jarring buds too wet (the jar spikes to 75 %+ overnight). - Packing jars tight. - Leaving jars in sunlight. - Expecting the cure to fix a 3-day hot dry, or a hay smell. It won't. - Plastic bags (static strips trichomes; poor vapour barrier). - Reading the hygrometer right after burping and calling it the bud's humidity. Only an equilibrated jar tells you about the bud. - Trying to hold the jar at one number for months. ## Evidence The aw range and the "dry further above 0.68" rule are *Established* standards [1][2]. Terpene loss over time is *Supported* [3][4]. Burping schedules, duration and sensory claims are *Grower practice*. aw ≈ equilibrium RH / 100 is the definition of water activity, so an equilibrated jar reading is a fair proxy; the moisture-content figure for a given aw depends on the measuring method (*Supported* by one lab's method-validation data [5]). A slowly declining bud aw rather than a constant hold: house position (*Grower practice*). Humidity packs are a marketing gimmick (house position). The only pro-pack data is the manufacturer's own: a pack maker reports higher terpene levels with its packs in a company-commissioned jar test (not peer reviewed), and we have not found an independent study either way. ASTM D8197 lists salt-based sachets as one way to bring under-range flower back up [2]; that is a storage-spec convenience, not evidence that packs improve flower. Freeze drying and water curing: *Contested*, not recommended. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (salt-based humidity control sachets for aw below 0.68). https://sn.astm.org/node/2445/printable/print 3. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa (monoterpene loss on drying and storage). Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 4. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp (terpenes affected by drying, cannabinoids by storage). https://openscholar.uga.edu/record/27813 5. Modern Canna Laboratories. 2025. Validation of moisture content and water activity methods in cannabis flower (method-validation white paper; cured flower typically 5-9 % moisture by water-specific methods at aw 0.45-0.60; 103 °C oven loss-on-drying overstates moisture). https://moderncanna.com/wp-content/uploads/2026/04/Method_Validation_Study_Moisture_Content_and_Water-Activity_in_Cannabis_Flower.pdf --- # Drying cannabis: the 60/60 method and water activity > Dry slowly and in the dark at about 15–21 °C (60–70 °F) and 55–62 % RH, the popular 60/60 target, for 7–14 days until small stems snap and buds reach a water activity of about 0.60–0.65. ASTM D8197 sets 0.55–0.65 aw as the range that protects against mould without making flower brittle. Judge the bud (stem snap, an equilibrated jar reading, weight), not the room. Wet vs dry trim is grower preference. Fast, warm drying loses volatile monoterpenes, and wet, still air grows mould. - Canonical: https://genetixbay.com/knowledge/harvest-cure/drying.html - Category: Harvest and cure · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Harvest · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is freeze drying better for cannabis?** Freeze drying is not proven better for cannabis. GenetixBay rates it contested and does not recommend it, and a slow hang dry followed by a proper jar cure remains the standard. The main goal of any drying method is keeping volatile monoterpenes, which research shows shift and escape during air-drying, so a slow, cool, dark dry matters more than the equipment. **Why does my weed smell like hay?** Weed smells like hay when it was dried too fast, over-dried or affected by bacteria. A 3-day hot dry crisps the outside while volatile terpenes evaporate with the water, and over-drying below water activity 0.55 strips aroma further. The smell never truly comes out and curing won't fix it, so dry slowly at 15–21 °C and 55–62% RH. **What is the 60/60 drying method?** The 60/60 drying method means hanging cannabis in the dark at about 60 °F (15–16 °C) and about 60% relative humidity, with gentle air movement that doesn't hit the buds, for roughly 7–14 days. It is grower practice rather than a researched optimum, but slow, cool drying helps keep volatile monoterpenes. One grower survey averaged about 65 °F and 53% RH. **How long should cannabis dry?** Cannabis should dry for about 7–14 days, according to grower practice. Start testing small stems from day 5: a bend means wait, a clean snap means nearly ready. The dry is finished when a sample sealed in a jar for 12–24 hours reads a stable 58–65% RH and the flower weighs about 20–25% of its wet weight. **What humidity and temperature for drying?** Dry cannabis at 15–21 °C (60–70 °F) and 55–62% relative humidity, in the dark, with gentle room circulation and air exchange to remove moisture but no fans blowing on the buds. Too warm or too fast loses terpenes, while too slow, too warm or still, wet air invites Botrytis and other moulds. Never dry in the grow tent with lights or heat running. **What water activity should dried cannabis have?** Dried cannabis should reach a water activity of about 0.60–0.65 before curing and settle within 0.55–0.65 overall, the range in the ASTM D8197 standard. Below 0.65 guards against mould, above 0.55 avoids brittle, crumbling flower, and above 0.68 means more drying is needed. Measure with a sealed sample: once equilibrated, the jar's RH divided by 100 equals water activity. **Should I wet trim or dry trim?** Wet or dry trimming is grower preference, and both make excellent flower. Wet trim dries buds faster, saves hanging space and suits humid rooms with high mould risk. Dry trim slows the dry because sugar leaves act as a jacket, suits dry rooms where buds would crisp, and is far easier on the hands at volume. Pick the method that suits your room and workload. **Is dry trimming better than wet trimming?** Dry trimming is not proven better than wet trimming; no independent peer-reviewed study compares their terpene or trichome retention, so GenetixBay treats it as an open trial. The founder prefers dry trim after hand-trimming hundreds of pounds, because brushing a dry bud is easier than scissoring a wet, sticky one, and they accept slight trichome loss since the trim goes to hash or edibles. **How much weight does cannabis lose when drying?** Cannabis loses roughly three-quarters of its wet weight when drying, finishing at about 20–25% of its harvest weight, because fresh flower is about 75–80% water; the exact figure varies with cultivar, bud density and how much stem is weighed. Tag and weigh one branch at the chop and every day or two afterwards: a slow, even fall in weight marks a good dry. **My buds dried in 3 days, are they ruined?** Buds dried in 3 days usually lose quality rather than being lost outright: expect harsher smoke, fewer volatile terpenes and a hay or grassy smell. A fast dry crisps the outside while the inside can stay wet, so seal a sample jar for 12–24 hours and check it stays below about 65% RH. A cure will never fully fix a bad dry, so slow the next one down. **Short answer.** Hang whole plants or branches in the **dark** at about **15–21 °C (60–70 °F)** and **55–62 % RH** ("60/60": ~60 °F, ~60 % RH), with gentle air movement that doesn't hit the buds, for **7–14 days**. Done when small stems **snap** rather than bend and buds read **~0.60–0.65 water activity (aw)**. ASTM D8197 specifies **0.55–0.65 aw**: below 0.65 to guard against mould, above 0.55 to avoid brittle, crumbling flower [1][2]. Slow drying is about **keeping volatile monoterpenes**; air-drying measurably shifts oil composition away from monoterpenes [3]. > **Greenleaf's standing challenge: darkness before harvest.** Putting plants in 24–72 h of darkness before the chop is a *Myth*, and the founder's verdict is "complete and utter nonsense": why cut photosynthesis in the most critical part of the life cycle, while the plant is still finishing its resin? For more than 20 years the founder has offered a standing challenge: find a peer-reviewed study showing a benefit (not a single-plant study, not biased or skewed) and a 50-pack of seeds is yours, no questions asked. Nobody has claimed it. ## What's happening At harvest, flower is ~75–80 % water (typical fresh-to-dry weight ratio ~4:1 to 5:1). Water leaves the surface first; the inside dries by diffusion through the stem and bud. Dry too fast and the outside crisps while the inside stays wet, and volatile terpenes evaporate with the water. Dry too slowly, too warm, or in still, wet air, and *Botrytis* and other moulds grow [6]. **Water activity (aw)** is the energy status of water in the bud (0–1.0): the equilibrium RH of the air around a sealed sample, divided by 100. It is what microbes "feel", unlike **moisture content** (% water by weight). A bud in a sealed jar **at equilibrium** at 62 % RH has aw ≈ 0.62; the room's RH, or a jar you just opened, tells you nothing about the bud. At aw 0.55–0.65, dried flower holds roughly 8–12 % water by weight [7]. **How to tell the bud is done:** small stems **snap**; a sample **sealed 12–24 h** reads a stable 58–65 %; and the flower has lost roughly three-quarters of its wet weight, ending at about **20–25 % of wet weight** (depends on cultivar, density and stem). Weigh a tagged branch at the chop and every day or two: a slow, even fall is a good dry. ## Numbers that matter | Parameter | Target | Evidence | |---|---|---| | Temperature | 15–21 °C (60–70 °F) | Grower practice; grower survey average ~65 °F [4] | | RH | 55–62 % | Grower practice; survey average ~53 % [4] | | Duration | 7–14 days | Grower practice | | Light | Dark | Light degrades THC ([long-term storage](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md)) | | Air | Gentle circulation in the room, not on the buds; exchange to remove moisture | | | End-point aw | ~0.60–0.65 to start cure; final 0.55–0.65 | Established standard [1] | | "Needs more drying" | aw > 0.68 | [2] | | Hygrometer in jar test | Stable 58–65 % RH after 12–24 h sealed (aw ≈ RH / 100 once equilibrated) | Grower practice | | Moisture content at end-point | ~8–12 % w/w | [7] | | Finished weight | ~20–25 % of wet weight | Grower practice | ## How to do it 1. Before the chop, clean the dry space, set the climate and check the hygrometer (salt test). 2. Cut whole plants or large branches and remove big fan leaves. Then **trim wet now or dry later**: it's grower preference (see below). Weigh and tag one branch so you can track weight loss. 3. Hang with space between branches; buds shouldn't touch. 4. Log RH/temperature; aim for slow, steady weight loss. 5. From day 5, test small stems: bend → wait; snap → nearly ready. 6. Buck, trim if you haven't, and jar to measure: seal a sample with a hygrometer or aw meter and leave it untouched; if it reads above ~65 % after 12–24 h, keep drying. ## Wet trim vs dry trim > **House position: grower preference.** Both work, and both make excellent flower. The founder has trimmed hundreds of pounds by hand and prefers to **dry trim**: brushing the sugar leaf off a dry bud is far easier on the hands than scissoring a wet, sticky one, even at the cost of a little trichome loss, and that loss doesn't matter much because it all gets used anyway (the trim and the shake go to hash or edibles). Plenty of skilled growers wet trim for good reasons. Pick the one that suits your room, your hands and your volume. | | Wet trim | Dry trim | |---|---|---| | Speed of drying | Faster (less leaf to buffer); good in a humid room where mould risk is high | Slower (sugar leaves act as a jacket); good in a dry room where buds would otherwise crisp | | Space | Trimmed buds take less hanging or rack space | Whole branches need more hanging space | | Hands and labour | Sticky resin gums scissors; slower, harder on the hands | Leaves are crisp and brush or snip off easily; far easier on the hands at volume | | Trichomes | Fewer heads knocked off while handling the wet, pliable bud | A little more trichome loss from handling dry flower; it ends up in the trim, which still gets used | | Look | Tight, precise manicure | Slightly looser look; handle gently | | Who prefers it | Humid climates, rack dryers, growers who want the finish done on day one | The founder; terpene-focused growers who want a slower dry; anyone trimming a lot by hand | ## Other drying methods - **Freeze drying and water curing:** *Contested*. Neither is proven to give better flower, and GenetixBay doesn't recommend either. A slow hang dry and a proper cure remain the standard. ## How to confirm it worked Buds feel dry outside but slightly springy; small stems snap; aroma is intact (not "hay" or "grass"); jarred aw settles at 0.58–0.65. ## Common mistakes - Drying in the grow tent with lights or heat running. - Fans blowing directly on buds. - 3-day "fast dries" in summer heat. Expect harsh smoke and a hay or grassy smell; **a cure will never fix a bad dry** (house position). Hay smell means bacteria, over-drying or drying too fast, and it never truly comes out. - Over-drying below aw 0.55 (brittle, terpenes lost, hay smell). - Ignoring mould: break open the largest colas; grey fuzz or brown inner tissue = discard that bud. ## Safety Mouldy cannabis can carry *Aspergillus* and other fungi that are a health risk, particularly for people with weakened immune systems. When in doubt, throw it out. ## Evidence Wet vs dry trim is grower preference (house position): we found no independent peer-reviewed comparison of terpene or trichome retention, which makes it an open GenetixBay trial. The rejection of freeze drying and water curing is a house position (*Contested*). One 2023 study compared freeze-drying with other drying methods for terpene content. The aw range is *Established* as an industry standard [1][2]. Terpene loss on air-drying is *Supported* [3][5]. The 60/60 recipe and 7–14 days are *Grower practice*; there's no published study that optimises cannabis drying rate for terpenes. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (D8196 water activity measurement; D8197 range). https://sn.astm.org/node/2445/printable/print 3. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 4. Cannabis Business Times. Special report: cannabis post-harvest benchmarks (grower survey; average drying ~53 % RH, ~65 °F). https://www.cannabisbusinesstimes.com/business-issues-benchmarks/cannabis-post-harvest-operations/article/15689633/post-harvest-benchmarks-with-room-to-experiment 5. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 6. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 7. Modern Canna Laboratories. 2025. Validation of moisture content and water activity methods in cannabis flower (method-validation white paper; cured flower typically 5-9 % moisture by water-specific methods at aw 0.45-0.60; 103 °C oven loss-on-drying overstates moisture). https://moderncanna.com/wp-content/uploads/2026/04/Method_Validation_Study_Moisture_Content_and_Water-Activity_in_Cannabis_Flower.pdf --- # Irradiated cannabis: gamma, e-beam, X-ray, ozone, RF and what they do to your weed > Much legal cannabis is decontaminated after harvest so it can pass microbial limits. That means ionising radiation (gamma from cobalt-60, electron beam, X-ray), or ozone, cold plasma, radio-frequency heating, UV or steam. Irradiation doesn't make flower radioactive. At typical doses (2.5–20 kGy) studies find no meaningful change in total THC or CBD. Effects on terpenes range from nothing measurable to 10–20 % losses of volatile monoterpenes, up to 38 % for one compound. Killing mould doesn't remove mycotoxins it has already made. Disclosure rules are patchy: Canada requires the irradiation symbol on edibles but not on dried flower, Washington discloses remediation to consumers only on request, and Nevada has a treatment-label rule. Most places tell the shopper nothing. Growing your own, where legal, with clean IPM and a proper dry avoids the issue. - Canonical: https://genetixbay.com/knowledge/harvest-cure/irradiated-cannabis.html - Category: Harvest and cure · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Harvest, Cure · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is legal weed irradiated?** Much legal cannabis is decontaminated after harvest, often by irradiation, so it can pass microbial limits, and in most places shoppers are never told. Producers may treat a lot after a failed test or routinely before testing, which Colorado calls a 'microbial control step'. Methods include gamma, electron beam and X-ray irradiation, plus ozone, cold plasma, radio-frequency heating, UV-C and steam. **Is irradiated weed radioactive?** Irradiated weed is not radioactive. Gamma rays from cobalt-60, electron beams up to 10 MeV and X-rays up to 5 MeV, or 7.5 MeV with gold or tantalum targets, do not make the product radioactive, just as irradiated spices aren't. US food law allows up to 30 kGy on dried spices, above typical cannabis doses. The real concerns are terpenes, mycotoxins and disclosure. **Does irradiation destroy terpenes?** Irradiation does not destroy terpenes, but it can reduce them. Two studies found no significant terpene change, while others measured 10–20% losses of volatile monoterpenes such as myrcene, ocimene and terpinolene, up to 38% for one compound, with sesquiterpenes barely changing. In one electron-beam study, 12 weeks of normal storage cost more terpenes than the treatment did. No blind sensory panel exists. **Does irradiation lower THC?** Irradiation does not meaningfully lower THC at typical doses of 2.5–20 kGy. Four studies across gamma, electron beam and X-ray found no consistent loss of total THC or CBD. At higher X-ray doses, Δ9-THC fell 3–7% and CBN rose 19–28% while THCA stayed unchanged, consistent with slightly faster oxidation. One study even measured higher cannabinoids after electron-beam treatment. **Why is cannabis irradiated?** Cannabis is irradiated to kill yeasts, moulds and bacteria so it passes regulatory microbial limits, such as total yeast and mould counts and 'not detected' rules for Aspergillus, toxin-producing E. coli and Salmonella. A failed lot must be destroyed or treated and retested, so treatment saves sales. The health case is strongest for immunocompromised patients, for whom inhaled Aspergillus can be fatal. **What is e-beam cannabis?** E-beam cannabis is flower treated with an electron beam from an accelerator, at up to 10 MeV, to kill microbes. Typical doses are 5–12 kGy and treatment takes minutes rather than the hours gamma needs, but penetration is shallow, so product passes through in thin layers. In one hemp study, about 5 kGy cut monoterpenes 10–11% while total cannabinoids stayed unchanged. **What is remediated cannabis?** Remediated cannabis is a lot that failed a required safety test, usually for microbes, and was then treated, for example by irradiation, ozone or heat, and retested so it could be sold instead of destroyed. Rules vary: Massachusetts allows two remediation attempts before disposal, Michigan requires mycotoxin testing and two consecutive passing retests after Aspergillus failures, and Washington bars remediating pesticide failures. **Do dispensaries have to tell you if weed is irradiated?** In most places dispensaries do not have to tell you if weed was irradiated or otherwise treated. Washington requires remediation methods to be disclosed to consumers on request, Nevada adopted a rule requiring an irradiation notice with the Radura symbol, and Colorado records methods only in state tracking. Food law requires irradiation labels, but cannabis law mostly doesn't, so ask the retailer directly. **Is irradiated cannabis labelled in Canada?** In Canada, irradiated edible cannabis must carry the Radura symbol and the words 'irradiated', 'treated with radiation' or 'treated by irradiation', but irradiated dried flower has no required label, according to media reporting of the federal regulator's position. So an irradiated gummy shows the symbol while an irradiated bag of flower may not. Ask the producer for treatment details and before-and-after test results. **Does ozone treatment ruin cannabis?** Nobody knows whether ozone treatment ruins cannabis, because no peer-reviewed study has measured its effect on cannabis chemistry. Ozone is a strong oxidising gas, used at about 200–400 ppm for 20 minutes to 48 hours, that diffuses into the bud, and terpenes and cannabinoids have bonds it can oxidise. Treating ozone as gentle because it isn't 'radiation' is a mistake. **What is RF decontamination of cannabis?** RF decontamination heats cannabis from the inside with non-ionising radio waves, a dielectric form of pasteurisation. Heating buds to 90–98 °C for one minute cut total yeast and mould from 23,000 to under 10 CFU/g in one study. That study did not measure terpenes or decarboxylation, though heat at that level threatens both volatile terpenes and cannabinoid acids. **What are the microbial limits for cannabis?** Cannabis microbial limits vary more than a thousandfold by jurisdiction. Colorado sets yeast and mould below 10,000 CFU/g, Dutch medical flower must reach 100 CFU/g or less, and Australia's limit for inhaled medical products is 20 CFU/g. California, Washington and Oregon set no total yeast and mould limit, testing instead for specific pathogens such as STEC and Salmonella, plus four Aspergillus species in California. **Does irradiation remove mycotoxins?** Irradiation does not reliably remove mycotoxins. Kill steps reduce living spores, but toxins the mould already made and dead spores can remain. In one small, industry-funded study, a gamma-treated sample still contained ochratoxin A, aflatoxins and viable Aspergillus and Penicillium, and a Canadian study found electron beam took counts to undetectable without eliminating mycotoxins. A clean microbial retest says nothing about toxins. **How can I tell if my cannabis was irradiated?** The surest way to tell whether cannabis was irradiated is to ask the retailer or producer whether the lot was treated, by which method and dose, and for before-and-after certificates of analysis, including mycotoxins. Labels rarely help, because most jurisdictions require no disclosure, though Nevada has a treatment-label rule and Washington must disclose remediation on request. Growing your own, where legal, avoids the question. **Is medical cannabis irradiated?** Much medical cannabis is irradiated, because medical programmes set near-sterile microbial targets to protect immunocompromised patients. All Dutch medical flower is gamma-irradiated at about 10 kGy after lab release to meet 100 CFU/g or less, and Australia's inhaled limit of 20 CFU/g more or less requires a kill step. Germany bans irradiated medicines unless specifically permitted under its radiation ordinance. **Short answer.** A lot of legal and medical cannabis is decontaminated after harvest so it can pass microbial limits. The main methods are ionising radiation (gamma rays from cobalt-60, electron beam, X-ray), ozone, cold plasma, radio-frequency heating, UV-C and steam. Irradiation **doesn't make flower radioactive** [29][30]. At typical doses of 2.5–20 kGy, studies find **no meaningful change in total THC or CBD** [1][2][5][6]. Terpene results range from no significant change [2][5] to **10–20 % losses of volatile monoterpenes, up to 38 % for one compound** [1][6]. Killing mould doesn't remove the **mycotoxins** it already made [8][10]. Disclosure is patchy, and in most places the shopper is never told. Grow your own where it's legal, keep the crop clean and dry it properly, and the question never comes up. > **House position.** The founder doesn't like irradiated weed, and they aren't alone. GenetixBay's view has two parts. First, **consumers deserve to be told**: which lot was treated, how, at what dose, with test results from before and after. Second, the cleanest answer is **not to need it**. Healthy plants, good integrated pest management (IPM), sanitation and a proper dry produce flower that passes on its own. That's the craft side of the craft-vs-industrial argument (see [craft vs industrial cannabis](https://genetixbay.com/knowledge/genetics-history/craft-vs-industrial-cannabis.md)). > > **Where the evidence pushes back, honestly:** the published chemistry shows smaller effects than many growers expect. Two studies found no significant terpene change. The ones that found losses measured roughly 10–20 % of the most volatile monoterpenes, about what a few months of normal storage costs [6]. The evidence doesn't prove irradiation is harmless to aroma. It also doesn't prove irradiation ruins it. Nobody has run a proper blind smell-and-smoke panel. That's a Bay Trial waiting to happen. ## Why legal cannabis gets decontaminated Cannabis is a dense, resinous flower grown in warm, humid rooms. It carries yeasts, moulds and bacteria from the field, the drying room and the trimming table. Regulators set limits on microbial counts, typically **total yeast and mould (TYM)** and **total aerobic count (TAMC)**, plus "not detected" rules for specific pathogens such as *Aspergillus*, Shiga-toxin *E. coli* and *Salmonella*. When a lot fails, the producer has two choices: destroy it, or treat it and retest. Colorado's rules spell this out: destroy, decontaminate, or remediate [22]. Massachusetts allows **two** remediation attempts, and anything that fails after the second must be disposed of [27]. That is the economics in one line. A failed lot that is destroyed earns nothing. A treated lot that passes can be sold. Many producers don't wait for a failure. They treat every lot as routine, before testing (Colorado calls this a "microbial control step") [21]. The health case is real but narrower than the marketing suggests: - Sequencing studies of dispensary flower found toxigenic *Penicillium* and *Aspergillus* [32], and bacteria and fungi in all 20 samples tested [31]. - In US insurance data, people who used cannabis were **3.5 times** more likely to have a fungal infection diagnosis. That figure is an association, not proof of cause [34]. - The case for sterilising is strongest for **immunocompromised** patients, where inhaled *Aspergillus* can be fatal [9]. That is why medical programmes demand very low counts. ## The methods Only gamma, e-beam and X-ray are "irradiation" in the food-law sense (ionising radiation). The rest are other decontamination methods, but labelling rules sometimes lump them together. | Method | How it works | Penetration | Typical treatment | Notes | |---|---|---|---|---| | **Gamma (cobalt-60)** | Photons of 1.17 and 1.33 MeV from a sealed source break microbial DNA | Deep: whole bags, drums and pallets | 7.5–20 kGy. Dutch medical product gets 10 kGy [1][17]. The US research biomass got 15–20.8 kGy [2] | Needs a nuclear facility; slow (hours) and the most expensive [3][11] | | **Electron beam (e-beam)** | Beam of electrons from an accelerator, up to 10 MeV for food [30] | Shallow: product goes through in thin layers. | 5–12 kGy [3][6] | Takes minutes, not hours [11]. ED50 for fungi is about 3.6 kGy and ED90 about 8.1 kGy [3] | | **X-ray** | Electrons hit a metal target and the resulting X-rays penetrate like gamma; up to 5 MeV, or 7.5 MeV with gold or tantalum targets [30] | Deep | 2.5 kGy killed all four regulated *Aspergillus* species in spiked flower [5] | Machine source, no isotope. Colorado approves it in a sealed enclosure [21] | | **UV-C** | Germicidal UV damages DNA on surfaces it reaches | Surface only; the folds of a bud shade most of it [11] | Varies | Colorado approves UV [21]. No cannabis-specific efficacy or chemistry data found | | **Ozone** | Oxidising gas that diffuses into the bud | Gas reaches inner surfaces | 200–400 ppm for 20 min to 48 h [11] | Strong oxidiser, and terpenes and cannabinoids have oxidisable bonds. No peer-reviewed cannabis chemistry data found [11] | | **Cold plasma** | Ionised gas (here low-pressure air plus hydrogen peroxide vapour) makes reactive species | Surface and gas phase | 2.5–10 min under vacuum gave about 3–4 log reductions [3] | Cheaper and simpler than gamma [3]; quality data are mostly from food studies [11] | | **Radio frequency (RF)** | Non-ionising radio waves heat the whole bud from inside (dielectric heating), a kind of pasteurisation | Whole volume | 90–98 °C for 1 min cut TYM from 23,000 to under 10 CFU/g [12] | Heat at that level threatens volatile terpenes and decarboxylation; the RF study didn't measure either [12] | | **Steam** | Short steam pulses | Surface | 10–20 s pulses cut fungi below detection [4] | Cannabinoids fell slightly with longer exposure, "insignificant" per the authors; terpenes changed little [4] | | **Other** (vaporised hydrogen peroxide, microwave, vacuum steam, dry heat) | Gas or heat | Varies | Varies | Colorado lists hydrogen peroxide vapour, microwave and pasteurisation as approved methods [21]. No published cannabis chemistry data found for vacuum steam or dry heat | A kilogray (kGy) is one joule of energy absorbed per gram. US law allows up to **30 kGy** on dried spices and herbs [30], so cannabis doses sit within the range used on food. ## What the studies found Here is every controlled study we could find that measured chemistry before and after treatment. | Study | Method, dose | Material | Cannabinoids | Terpenes and other | |---|---|---|---|---| | Hazekamp 2016 [1] | Gamma, ≥ 10 kGy | 4 Dutch medical varieties, 10 g samples | Total THC and CBD unchanged; no CBN or Δ8-THC formed | Losses mostly **10–20 %**, **up to 38 %**, in myrcene, cis-ocimene, terpinolene and a few sesquiterpenes. Profile kept its shape. Water content and trichome structure unchanged. The author works for the producer that supplied the product | | Majumdar et al. 2023 [2] | Gamma, 15.0–20.8 kGy | > 2,000 kg ground biomass (US research supply), 33 lots analysed | No significant change (p > 0.05) | No significant terpene change in the sample reported (p = 0.13); moisture unchanged. TYM fell from 13,000 to < 10 CFU/g | | Frink et al. 2022 [5] | X-ray, 0.5–5.0 kGy | Ground flower, lab scale | THCA unchanged (140 → 140 mg/g at 2.5 kGy). Δ9-THC down 3 % at 2.5 kGy and 7 % at 5 kGy. **CBN up 19 % and 28 %** | Slight downward trend in caryophyllene and a few others. GC-MS was qualitative and not statistically tested | | Goffman et al. 2025 [6] | E-beam, ~5 kGy | 2 high-CBD hemp cultivars, stored 12 weeks | Total cannabinoids and CBD unchanged | Total terpenes **−8.4 %** right after treatment. **Monoterpenes −10 to −11 %**, sesquiterpenes −2 to −3 %. After 12 weeks: −24.0 % irradiated vs −22.3 % untreated, so storage did most of the damage. Funded by a hemp flower seller | | Kovalchuk et al. 2020 [7] | E-beam, 5 kGy | 4 dry-flower cultivars | Measured cannabinoids **rose** in all four; THC significantly in three | Several terpenes shifted, some up. | | Jerushalmi et al. 2021 [4] | Steam, 10–20 s | Medical inflorescences | Small, non-significant drop with longer exposure | Minor; mostly some terpenes appearing that weren't in the control | | Jerushalmi et al. 2020 [3] | Gamma 7.5–8.4 kGy; e-beam 4–12 kGy; cold plasma 2.5–10 min | Medical inflorescences, some inoculated with *Botrytis* | Not measured | Not measured. Fungi down about 5–8 logs (gamma, e-beam) and up to about 6 logs (plasma) | | Hall & Rothmeier 2025 [13] | E-beam, 10 kGy | 1 cultivar, split sample, 6 months | Irradiated sample lost 9.7 % total THC vs 0.8 % for the control | Blind panel of 3 judges; mixed results (irradiated sample kept higher aroma scores). Industry white paper, not peer-reviewed. The two halves differed by about 3 points THC at day 0, which is larger than the effect it reports | What this adds up to: - **Cannabinoids:** across gamma, e-beam and X-ray at normal doses, there's no consistent loss of total THC or CBD [1][2][5][6]. Small Δ9-THC losses and a CBN rise at higher X-ray doses [5] fit radiation speeding up oxidation slightly. - **Terpenes:** the volatile **monoterpenes** (myrcene, ocimene, terpinolene) are what move, when anything moves [1][6]. Sesquiterpenes barely change [6]. The leading explanation is faster evaporation rather than chemical destruction [1]. The best-controlled storage study found that 12 weeks on the shelf cost more terpenes than the e-beam did [6]. - **Smell and smoke:** no peer-reviewed blind sensory panel exists. The only sensory data come from one 3-judge, non-peer-reviewed comparison [13]. Hazekamp noted users reporting a changed taste or smell, called "a subtle change" possible, and didn't test it [1]. - **Mycotoxins and dead spores:** irradiation kills living cells but doesn't reliably clear toxins already made. In one gamma-treated sample, ochratoxin A, aflatoxins and other toxins were still detectable, along with viable *Aspergillus* and *Penicillium*. That was a single sample with industry funding [8], so treat it as a warning, not a measurement of the whole market. A Canadian study makes the same point about e-beam: it takes counts to undetectable but doesn't eliminate mycotoxins [10]. ## Microbial limits by jurisdiction Limits vary by more than a thousandfold. That's why one market irradiates almost everything and another rarely bothers. | Jurisdiction | Yeast and mould limit (flower) | Other key rules | Source | |---|---|---|---| | **Netherlands (medical, Office of Medicinal Cannabis)** | ≤ 100 CFU/g of final product | All supplied flower is gamma-irradiated after lab release (10 kGy) | [1][17] | | **Australia (TGA, inhaled)** | TYM ≤ 20 CFU/g; TAMC ≤ 200 CFU/g | Alternative raw-material limits of 200 / 20,000 CFU/g where the competent authority accepts them. | [18] | | **EU, Ph. Eur. inhalation category** | TYM 10¹, TAMC 10² CFU/g | Germany: irradiated medicines are banned unless permitted under the AMRadV; per-strain licences reported at about €4,500 and up to a year | [11][19] | | **Israel (medical)** | 2,000 CFU/g TYM | All four farms surveyed in one study exceeded it before treatment. | [3] | | **Canada** | Health Canada accepts the Ph. Eur. 5.1.8 **oral** herbal limits for smoked and vaped dried cannabis. Reported as TYM 10⁴ / TAMC 10⁵ [11], but one study cites 50,000 CFU/g [10]. | Health Canada says it may revisit if oral limits prove insufficient for inhalation | [14] | | **Colorado** | < 10⁴ CFU/g | *Aspergillus* absent in 1 g. Decontamination allowed for microbial and water-activity failures, then retest | [22] | | **Michigan** | 10,000 CFU/g (as quoted in 2020 bulletin) | *Aspergillus* failures may be remediated after mycotoxin testing, then must pass two consecutive retests | [23][24] | | **California** | No total yeast and mould limit | Four pathogenic *Aspergillus* species (fumigatus, flavus, niger, terreus), STEC and *Salmonella* not detected in 1 g | [20] | | **Washington** | No total yeast and mould limit | Bile-tolerant gram-negative bacteria ≤ 10⁴ CFU/g (unprocessed), STEC and *Salmonella* < 1. Pesticide failures can't be remediated | [26] | | **Oregon** | No total yeast and mould limit | *Aspergillus* testing removed in 2023 after a court stay; STEC and *Salmonella* still required | [28] | | **Massachusetts** | Set in the regulator's testing protocol. | Max two remediation attempts | [27] | | **Nevada** | | Treatment-label rule (see below) | [25] | Two things stand out. Medical programmes with near-sterile targets (the Netherlands, Australia, Germany's imports) more or less require a kill step. Markets with pathogen-only rules (California, Washington, Oregon) give a clean grower a fair chance to pass without one. ## Who has to tell you | Jurisdiction | What the shopper sees | Source | |---|---|---| | **US food (comparison)** | Radura logo plus "Treated with radiation" or "Treated by irradiation" on retail packages. Irradiated *ingredients*, like spices, need no label | [29][30] | | **Canada, edibles** | Radura symbol plus "irradiated", "treated with radiation" or "treated by irradiation" | [15] | | **Canada, dried flower** | **Nothing required.** Health Canada allows irradiation and doesn't require a label, per media reporting. So an irradiated gummy carries the symbol and an irradiated flower doesn't | [16] | | **Nevada** | Rule 12.065 (adopted 2020) required "NOTICE: This product contains ingredients that have been treated with irradiation" in bold with the Radura. A 2022 revision proposed widening it to any treatment: "NOTICE: This product has undergone treatment using [method of treatment] to ensure compliance with testing standards." | [25] | | **Washington** | Remediation methods must be disclosed down the chain to processors and retailers, and to "the consumer upon request". So **ask** | [26] | | **Colorado** | The method must be recorded in the state tracking system. A consumer label for decontaminated product was proposed in 2023 and met industry resistance. Routine pre-test "microbial control steps" weren't covered by the proposal | [21] | | **Michigan** | Remediated packages are flagged in the tracking system; we found no consumer label rule. | [24] | | **Massachusetts, California, Oregon** | No remediation or irradiation label rule found in the testing regulations. | [20][27][28] | | **Netherlands** | The regulator says openly that its product is gamma-irradiated | [17] | | **Germany** | Irradiation needs an AMRadV permit; the ordinance itself doesn't require a patient-facing "irradiated" label | [19] | The pattern: food law tells you, and cannabis law mostly doesn't. The industry argued that "remediated" or "decontaminated" implies the product was unsafe beforehand [25]. That's a reasonable point about wording. It isn't a reason to tell people nothing. ## What to ask your retailer or producer 1. **Was this lot treated after harvest?** Ask about routine treatment as well as remediation after a failed test. 2. **Which method, and what dose or settings?** kGy for gamma, e-beam or X-ray; ppm and time for ozone; temperature and time for RF. 3. **Can I see the certificate of analysis from before and after treatment?** Look at yeast and mould, aerobic count and *Aspergillus*, and the terpene panel if there is one. 4. **Was it tested for mycotoxins?** A clean microbial retest says nothing about toxins already made [8]. 5. **What's the harvest date and the water activity?** Old, over-dry flower has lost its monoterpenes whether or not it was zapped [6][33]. In Washington you're entitled to an answer on request [26]. Elsewhere a good shop will answer anyway. If they won't, that tells you something too. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) for reading the rest of the label. ## Growing your own: why the question goes away Where home growing is legal (check your local rules), nobody irradiates your jar. Here's how to make flower that wouldn't need it: - **Start clean.** Sanitise between runs, quarantine incoming clones and keep a clean floor and clean tools (see [sanitation and prevention](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md)). - **Prevent bud rot rather than treat it.** Keep air moving through the canopy, keep RH in check in late flower and don't overcrowd dense colas (see [botrytis bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)). - **Genetics matter.** In a Canadian study, some cultivars consistently carried far lower yeast and mould counts than others under the same conditions [10]. Select for mould resistance. - **Dry properly.** Hang-dried flower had significantly lower yeast and mould than wet-trimmed, rack-dried flower in the same study [10]. Aim for a slow dry and a finished water activity of **0.55–0.65** [33] (see [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md)). - **Cure and store cool, dark and airtight**, so you don't hand microbes or oxidation a second chance (see [curing](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) and [long-term storage](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md)). - **Bin what's rotten.** At home there's no economic pressure to rescue a mouldy lot, which is the whole reason industrial remediation exists. ## Common mistakes - **Calling irradiated weed radioactive.** It isn't [29]. That claim discredits the real concerns. - **Assuming "passed testing" means "never had a problem".** In most markets a passing result can follow a treatment you're never told about. - **Blaming irradiation for every flat jar.** Age, a fast dry and heat cost more terpenes than an e-beam dose does [6]. Check the harvest date first. - **Treating ozone and RF as gentle because they're "not radiation".** Ozone is a strong oxidiser, and RF heats the bud to 90–98 °C [12]. Neither has better published chemistry data than gamma. - **Thinking a kill step fixes everything.** It doesn't remove mycotoxins [8][10], and it does nothing about pesticides or heavy metals. ## Evidence - Irradiation doesn't make product radioactive at permitted energies: *Established* [29][30]. - No meaningful change in total THC or CBD at typical doses: *Supported* by four studies across gamma, e-beam and X-ray [1][2][5][6]. One study found higher measured cannabinoids after 5 kGy e-beam [7]; one non-peer-reviewed white paper found faster THC loss over 6 months [13]. - Monoterpene losses of roughly 10–20 % (up to 38 %) after gamma or e-beam: *Supported* [1][6]. Other studies found no significant terpene change [2][5], so the size of the effect is *Contested*. - Effect on aroma and smoke quality: *Unknown*. There's no peer-reviewed blind sensory panel. Founder and consumer reports of a changed taste are *Grower practice* observations [1]. - Kill steps don't remove existing mycotoxins: *Supported* [8][10], from small studies. - Hang-drying and genotype lower yeast and mould: *Supported* in one large study [10]. - Ozone, UV-C, cold plasma and RF effects on cannabis chemistry: *Thin*. Efficacy data exist [3][12]; peer-reviewed chemistry data mostly don't [11]. - Disclosure rules: regulation texts cited [15][21][25][26][30]. Several state labelling positions are marked ## Sources 1. Hazekamp A. 2016. Evaluating the effects of gamma-irradiation for decontamination of medicinal cannabis. Frontiers in Pharmacology 7:108. https://doi.org/10.3389/fphar.2016.00108 2. Majumdar CG, ElSohly MA, Ibrahim EA, Elhendawy MA, Stanford D, Chandra S, Wanas AS, Radwan MM. 2023. Effect of gamma irradiation on cannabinoid, terpene, and moisture content of cannabis biomass. Molecules 28(23):7710. https://doi.org/10.3390/molecules28237710 3. Jerushalmi S, Maymon M, Dombrovsky A, Freeman S. 2020. Effects of cold plasma, gamma and e-beam irradiations on reduction of fungal colony forming unit levels in medical cannabis inflorescences. Journal of Cannabis Research 2:12. https://doi.org/10.1186/s42238-020-00020-6 4. Jerushalmi S, Maymon M, Dombrovsky A, Regev R, Schmilovitch Z, Namdar D, Shalev N, Koltai H, Freeman S. 2021. Effects of steam sterilization on reduction of fungal colony forming units, cannabinoids and terpene levels in medical cannabis inflorescences. Scientific Reports 11:13973. https://doi.org/10.1038/s41598-021-93264-y 5. Frink S, Marjanovic O, Tran P, Wang Y, Guo W, Encarnacion N, Alcantara D, Moezzi B, Vrdoljak G. 2022. Use of X-ray irradiation for inactivation of Aspergillus in cannabis flower. PLOS ONE 17(11):e0277649. https://doi.org/10.1371/journal.pone.0277649 6. Goffman FD, Carrera DÁ, Latino DARS, Cronje C, Katsir L. 2025. Impact of electron beam treatment and storage duration on microbial stability and phytochemical integrity in hemp flowers. Molecules 30(17):3601. https://doi.org/10.3390/molecules30173601 7. Kovalchuk O, Li D, Rodriguez-Juarez R, Golubov A, Hudson D, Kovalchuk I. 2020. The effect of cannabis dry flower irradiation on the level of cannabinoids, terpenes and anti-cancer properties of the extracts. Biocatalysis and Agricultural Biotechnology 29:101736. https://doi.org/10.1016/j.bcab.2020.101736 8. Rani M, Kaddoura MJ, Samsatly J, Chamberland G, Jabaji S, George S. 2025. Detection of mycotoxigenic fungi and residual mycotoxins in cannabis buds following gamma irradiation. Toxins 17(11):528. https://doi.org/10.3390/toxins17110528 9. Ruchlemer R, Amit-Kohn M, Raveh D, Hanuš L. 2015. Inhaled medicinal cannabis and the immunocompromised patient. Supportive Care in Cancer 23(3):819-822. https://doi.org/10.1007/s00520-014-2429-3 10. Punja ZK, Ni L, Lung S, Buirs L. 2023. Total yeast and mold levels in high THC-containing cannabis (Cannabis sativa L.) inflorescences are influenced by genotype, environment, and pre- and post-harvest handling practices. Frontiers in Microbiology 14:1192035. https://doi.org/10.3389/fmicb.2023.1192035 11. Nestel S, Hedtfeld C, Spilker U, Ehlbeck J, Guenther S, Schnabel U. 2026. Sanitation of medical cannabis flowers (Cannabis sativa L., flos): comparing current technologies and non-thermal plasma novelties from safety and quality perspectives. Journal of Cannabis Research 8:50. https://doi.org/10.1186/s42238-026-00417-9 12. Aleksandrov M, Ristovski B, Maksimova V. 2023. Development of a technological method for microbiological decontamination of dry cannabis flowers (poster abstract). Arhiv za farmaciju 73(Suppl. 4):S67-S68. https://asistent.ceon.rs/index.php/arhfarm/article/view/46337 13. Hall F, Rothmeier T. 2025. Impact of electron beam irradiation on cannabis quality over time: a chemical and sensory evaluation (industry white paper, not peer-reviewed). https://stratcann.com/wp-content/uploads/2025/09/Confidential-Pre-print-Impact-of-Electron-Beam-Irradiation-on-Cannabis-Quality-Over-Time.pdf 14. Health Canada. 2020. Heavy metal and microbial testing limits for dried cannabis (notice, 30 December 2020). https://www.canada.ca/en/health-canada/services/drugs-medication/cannabis/industry-licensees-applicants/updates-cannabis-industrial-hemp/2020-12-30-heavy-metal-microbial-testing-limits.html 15. Cannabis Regulations (SOR/2018-144), s. 132.18(1)(p): labelling of irradiated edible cannabis. Justice Laws Website. https://laws-lois.justice.gc.ca/eng/Regulations/SOR-2018-144/section-132.18-20250312.html 16. Leafly Canada. 2020. Irradiation 101 for Canadians (reports Health Canada does not require irradiated dried cannabis to be labelled; updated 17 Nov 2020). https://www.leafly.ca/news/cannabis-101/irradiation-101-canadians 17. Office of Medicinal Cannabis (Netherlands). Factsheet productieproces medicinale cannabis (batches are gamma-irradiated after laboratory release). https://www.cannabisbureau.nl/binaries/cannabisbureau/documenten/brochures/2018/02/22/factsheet-productieproces/Factsheet+productieproces+NL_31402.pdf 18. Therapeutic Goods Administration (Australia). 2020. Guidance: microbiological quality of medicinal cannabis products. https://www.tga.gov.au/resources/resource/guidance/microbiological-quality-medicinal-cannabis-products 19. Germany. Verordnung über radioaktive oder mit ionisierenden Strahlen behandelte Arzneimittel (AMRadV). https://www.gesetze-im-internet.de/amradv/BJNR005020987.html 20. California Code of Regulations, title 4, § 15720. Microbial impurities testing. https://www.law.cornell.edu/regulations/california/4-CCR-15720 21. Colorado Marijuana Rules, 1 CCR 212-3, Rule 3-320 (approved microbial decontamination and microbial control step methods). https://www.law.cornell.edu/regulations/colorado/1-CCR-212-3-3-320 22. Colorado Marijuana Rules, 1 CCR 212-3, Rule 4-240 (contaminated product and failed test results) and Rule 4-115 (sampling and testing program). https://www.law.cornell.edu/regulations/colorado/1-CCR-212-3-4-240 ; https://www.law.cornell.edu/regulations/colorado/1-CCR-212-3-4-115 23. Michigan Admin. Code R 420.306. Testing marihuana product after failed initial safety testing and remediation. https://www.law.cornell.edu/regulations/michigan/Mich-Admin-Code-R-420-306 24. Michigan LARA / Marijuana Regulatory Agency. 2019-2020. Retesting and remediation technical bulletins. https://www.michigan.gov/documents/lara/12-20._Retesting_and_Remediation_Technical_Bulletin_641821_7.pdf ; https://www.michigan.gov/documents/lara/12-12-2019_Remediation_of_Marijuana_from_Medical_to_Adult_Use_673814_7.pdf 25. Nevada Cannabis Compliance Board. 2022. Proposed changes to NCCR 12.065 (cannabis treatment and remediation; shows 2020 irradiation-label text with Radura). https://ccb.nv.gov/wp-content/uploads/2022/04/Proposed-Changes-to-NCCR-12.065.pdf 26. Washington Administrative Code 314-55-102. Quality assurance and quality control (as amended by WSR 25-09-167, effective 24 May 2025). https://app.leg.wa.gov/wac/default.aspx?cite=314-55-102 27. Massachusetts 935 CMR 500.160. Testing of marijuana and marijuana products. https://www.law.cornell.edu/regulations/massachusetts/935-CMR-500-160 28. Oregon Health Authority. 2023. PH 53-2023: permanent amendment removing Aspergillus testing (OAR 333-007). https://www.oregon.gov/oha/PH/RULESREGULATIONS/Documents/PH_53-2023TrackedChanges.pdf 29. US FDA. Food irradiation: what you need to know. https://www.fda.gov/food/buy-store-serve-safe-food/food-irradiation-what-you-need-know 30. US 21 CFR 179.26. Ionizing radiation for the treatment of food (sources, energy limits, 30 kGy for dried spices, Radura labelling). https://www.law.cornell.edu/cfr/text/21/179.26 31. Benedict K, Thompson GR, Jackson BR. 2020. Cannabis use and fungal infections in a commercially insured population, United States, 2016. Emerging Infectious Diseases 26(6):1308-1310. https://doi.org/10.3201/eid2606.191570 32. Thompson GR, Tuscano JM, Dennis M, et al. 2017. A microbiome assessment of medical marijuana. Clinical Microbiology and Infection 23(4):269-270. https://doi.org/10.1016/j.cmi.2016.12.001 33. McKernan K, Spangler J, Zhang L, et al. 2016. Cannabis microbiome sequencing reveals several mycotoxic fungi native to dispensary grade Cannabis flowers. F1000Research 4:1422. https://doi.org/10.12688/f1000research.7507.2 34. ASTM D8197. Standard specification for maintaining acceptable water activity (aw) range (0.55 to 0.65) for dry cannabis flower. ASTM International. https://store.astm.org/d8197-22.html --- # Long-term storage: keeping cured flower potent and aromatic > Light is the biggest single cause of cannabinoid loss in storage, air oxidation turns THC into CBN, and warmth and humidity speed both and invite mould. Store cured flower in full, airtight, opaque glass with the bud at aw 0.55–0.65 (an equilibrated jar reading), cool and dark; skip humidity packs, a marketing gimmick. Kept that way it is reasonably stable for one to two years; at room temperature over several years THC loss can be near total. Freezing is possible but makes trichomes brittle. - Canonical: https://genetixbay.com/knowledge/harvest-cure/long-term-storage.html - Category: Harvest and cure · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Cure · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should I store cannabis with humidity packs?** You don't need humidity packs to store cannabis; GenetixBay considers them a marketing gimmick. A well-cured bud in a full, airtight jar holds its own water activity of 0.55–0.65 for months without a sachet. The only data saying packs help is a pack maker's own test, and in the founder's experience they cost terpenes. If a jar goes too dry, add a fresh, slightly moister bud for a day. **How long does cured cannabis stay good?** Cured cannabis stays reasonably stable for about 1–2 years when stored dark at around 20 °C (68 °F), according to classic storage studies, after which losses build. One study recorded a mean THC loss of about 13% per year in coarse material, and a forensic study found near-total THC loss after four years at room temperature, even in the dark. Cooler, airtight, opaque storage helps. **Does cannabis lose potency over time?** Cannabis does lose potency over time. Light is the largest single cause of cannabinoid loss in storage, air oxidation converts THC to CBN, and heat speeds both. Research found a mean THC loss of about 13% per year, ranging from 5% to 26%, in coarse material. Aroma fades too, as volatile monoterpenes keep escaping and sesquiterpenes become a larger share. **Should I store cannabis in the freezer?** You can store cannabis in a freezer at −18 °C (0 °F), which slows chemical degradation, but frozen trichome heads become brittle and snap off when handled, according to grower practice. Use vacuum-sealed or fully sealed glass, don't move frozen packages around, and don't open them until fully thawed. No controlled study has compared freezer, fridge and cellar storage of cannabis flower. **Why does old weed turn into CBN?** Old weed turns into CBN because oxygen slowly oxidises THC in stored flower, even in the dark, as the classic 1976 storage study showed. Light also destroys THC but does not produce CBN, and warmth speeds oxidation. Half-empty jars hold more oxygen and age faster, so keep flower in full, airtight, opaque jars kept cool to slow CBN formation. **What is the best container for storing buds?** The best container for storing buds is a full, airtight glass jar that is opaque or UV-blocking, or clear glass kept in a dark box. Keep headspace minimal and move flower into smaller jars as you use it, since half-empty jars hold more oxygen. Avoid plastic bags, which are permeable and build static, and store at a stable 10–18 °C (50–65 °F). **Short answer.** **Dark, cool, airtight, and at the right humidity.** Light was the single biggest factor in cannabinoid loss in the classic storage study; THC lost to light didn't become CBN, while **air oxidation in the dark did** form CBN [1]. Carefully stored herbal cannabis was **reasonably stable for 1–2 years in the dark at ~20 °C (68 °F)** [1][2], with a mean THC loss in coarse material of about **13 % per year** (range 5–26 %) [2]. Over **four years at room temperature**, a forensic study found near-total THC loss even in the dark [3]. Keep the **bud** at **aw 0.55–0.65** [4], about 8–12 % moisture by weight (method dependent) [6]. A jar hygrometer only shows that once the jar has sat sealed long enough to equilibrate (aw ≈ RH / 100). > **House position: humidity packs are a marketing gimmick.** A well-cured bud in a full, airtight jar holds its own water activity for months; it doesn't need a sachet. The only data saying packs help comes from a pack maker's own test, and in the founder's experience they cost you terpenes. If a jar has gone too dry, put a fresh, slightly moister bud in it for a day. ## What degrades flower | Factor | Effect | Evidence | |---|---|---| | Light (including indoor light) | Largest single cause of cannabinoid loss; does not produce CBN | *Supported* [1] | | Oxygen | THC → CBN by oxidation | *Supported* [1] | | Heat | Speeds oxidation, decarboxylation and terpene evaporation; effect up to 20 °C small in [1] | *Supported* | | Humidity above aw 0.65 | Mould risk | *Established* [4] | | Humidity below aw 0.55 | Brittle buds, trichome loss, terpene loss | *Established* [4] | | Time | Monoterpenes keep escaping; sesquiterpene share rises [5] | *Supported* | ## Numbers that matter | Parameter | Target | |---|---| | Container | Full, airtight, opaque or UV-blocking glass (or glass in a dark box) | | Headspace | Minimal; downsize jars as you use flower | | Bud aw | 0.55–0.62 at the end of the cure, read from an equilibrated, sealed jar; no humidity packs (a marketing gimmick); add a fresh bud if a jar has gone too dry | | Weight check | Weigh full jars when you store them; a gain means moisture got in, a big loss means a leaky seal | | Temperature | 10–18 °C (50–65 °F), stable; avoid repeated warm/cold cycles | | Expected stability | ~1–2 years dark at room temperature; then progressive loss [1][2][3] | ## Freezer or fridge? - **Fridge:** cool, but door-opening cycles cause condensation and RH spikes. Only for sealed, untouched stock; let jars warm to room temperature before opening. - **Freezer (−18 °C / 0 °F):** slows chemistry, but trichome heads become brittle and snap off when handled frozen (*Grower practice*). Use vacuum-sealed or fully sealed glass, don't open until fully thawed, and don't move frozen bags around. - ## Common mistakes - Clear jars on a shelf in daylight. - Half-empty jars kept for months (lots of oxygen). - Plastic bags (permeable, static). - Storing next to heat sources (lamps, fridges' exhaust, cars). ## Evidence Light, oxygen and time effects are *Supported* by the classic and recent storage studies [1][2][3]. The aw range is *Established* [4]; moisture content at that aw depends on the measuring method [6]. Freezer advice is *Grower practice*. Humidity packs are a marketing gimmick (house position); the only pro-pack data is the manufacturer's own, and no independent study either way has been found. ## Sources 1. Fairbairn JW, Liebmann JA, Rowan MG, 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1–7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x 2. UNODC Bulletin on Narcotics, 1978. Stability of cannabis on storage (13 % mean THC loss per year in coarse powder; stable 1–2 years dark at 20 °C). https://unodc.org/unodc/en/data-and-analysis/bulletin/bulletin_1978-01-01_4_page007.html 3. Zamengo L, Bettin C, Badocco D, et al., 2019. The role of time and storage conditions on the composition of hashish and marijuana samples: a four-year study. Forensic Science International 298:131–137. https://doi.org/10.1016/j.forsciint.2019.02.058 4. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. https://store.astm.org/d8197-22.html 5. Modern Canna Laboratories. 2025. Validation of moisture content and water activity methods in cannabis flower (method-validation white paper; cured flower typically 5-9 % moisture by water-specific methods at aw 0.45-0.60; 103 °C oven loss-on-drying overstates moisture). https://moderncanna.com/wp-content/uploads/2026/04/Method_Validation_Study_Moisture_Content_and_Water-Activity_in_Cannabis_Flower.pdf 6. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf --- # Pre-harvest flushing: a myth that costs you yield and resin > Pre-harvest flushing is a myth, and a harmful one. Starving the plant of nutrients in its last weeks takes food away during the phase when it is packing on most of its final weight, trichomes and resin, so it costs yield and resin and gives nothing back: controlled studies found no gain in flower quality, minerals or cannabinoids, and longer nutrient withdrawal tended to cut dry mass and cannabinoid yield. Cannabis stores what it takes up in its tissue, and plain water at the end does not wash it out. Feed through to harvest at stage-appropriate strength; taste and ash are made by plant health, not overfeeding, and slow drying and proper curing. The one valid flush treats the medium, not the plant: a root-zone flush to wash out accumulated salts, at any stage. - Canonical: https://genetixbay.com/knowledge/harvest-cure/flush-debate.html - Category: Harvest and cure · Level: Intermediate - Evidence: Myth · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Ripening, Harvest · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should I flush my cannabis before harvest?** No, you should not flush cannabis before harvest. Pre-harvest flushing is a myth and actively harmful: the last weeks of flower are when the plant packs on most of its final weight, trichomes and resin, and plain water starves it then. Controlled studies found no gain in flower quality, minerals or cannabinoids. Feed through to harvest at stage strength, tapering only nitrogen. **Is flushing a myth?** Pre-harvest flushing is a myth. Cannabis is a bioaccumulator: nutrients it absorbs are built into proteins, chlorophyll, cell walls and cell contents, so a week or two of plain water cannot rinse them out of the flower. In Utah State research, leaf nitrogen fell during a flush but flower nitrogen did not change. The only valid flush is a root-zone salt flush of the medium. **Does flushing improve taste or make white ash?** Flushing does not improve taste or make white ash. No controlled study has shown a smoking-quality benefit, and in the one taste trial, tasters preferred unflushed flower. Black ash and harsh smoke almost always trace back to fast drying, rushed or wet curing, or how the joint burns. Taste comes from a healthy, never-overfed plant, a slow 7–14 day dry and a proper cure. **Does flushing reduce yield?** Flushing can reduce yield, and longer flushes cost more. Controlled studies found that longer nutrient withdrawal tended to cut dry mass and cannabinoid yield, and in Clemson trials flushes of 3 weeks or more reduced dried bud weight. Short flushes of 2 weeks or less showed no consistent yield change, but none showed any gain, so flushing is a cost with no return. **How long should I flush?** The right length for a pre-harvest flush is zero days, because flushing before harvest is a harmful myth. Research shows flushes of 2 weeks or less gave no consistent benefit, while flushes of 3 weeks or more cut dried bud weight. The only valid flush, a root-zone salt flush, is measured by volume rather than days: about 2–3 times the container volume, run through slowly. **Should I flush living soil?** You should not flush living soil. A living-soil bed has nothing to flush out, and pre-harvest flushing is a myth that costs yield and resin in any system. Keep watering living soil normally right up to harvest, let lower leaves fade naturally in the last 2–3 weeks, and judge harvest timing by the trichomes rather than by leaf colour. **When is flushing actually useful?** Flushing is useful only as a root-zone flush that washes accumulated salts out of the growing medium, at any stage when there is a real problem. Signs include runoff EC roughly 1.0 mS/cm or more above input in coco or soil, slab EC above input plus 1.5 in rockwool, salt crust, spreading burnt tips or lockout. It treats the medium, not the plant, and is not a pre-harvest ritual. **How do I flush salt build-up out of coco or soil?** To flush salt build-up, first record input and runoff pH and EC. Run about 2–3 times the container volume through slowly in several passes: pH-adjusted plain water at about 6.3–6.8 for soil, or a light solution at EC 0.4–0.8 mS/cm with calcium and magnesium at pH 5.8–6.0 for coco. Stop when runoff EC is within 0.3–0.5 of input, then resume normal feeding. **Does lower nitrogen at the end raise THC percentage?** Lower nitrogen at the end can raise THC and terpene percentage slightly while lowering total yield. Research by Saloner and Bernstein found cannabinoid and terpenoid concentrations were suppressed at higher nitrogen supply, while inflorescence yield rose with nitrogen up to about 160 mg/L. It is a trade-off set through the feed recipe, not a reason to flush, which starves the plant of everything. **What should I do instead of flushing?** Instead of flushing, feed through to harvest at stage strength and taper only nitrogen. Watch runoff EC and do a root-zone flush only if salts build up, let lower leaves fade naturally over the last 2–3 weeks, and judge harvest by trichomes. Then put your effort into a slow 7–14 day dry and a proper cure, which are what actually shape taste and smoothness. **Should I put my plants in darkness before harvest?** You should not put plants in darkness before harvest. Giving cannabis 24–72 hours of darkness before the chop is a myth, and GenetixBay's founder calls it complete and utter nonsense, because it cuts photosynthesis while the plant is still finishing its resin. For over 20 years they have offered 50 seeds to anyone who finds an unbiased, multi-plant peer-reviewed study showing a benefit. Nobody has claimed it. **How do I taper nitrogen before harvest?** To taper nitrogen before harvest, cut nitrogen in steps while feeding phosphorus, potassium, calcium, magnesium, sulphur and micronutrients at full strength: about 100–150 mg/L at 4 weeks out, roughly 75% of that at 3 weeks, 50% at 2 weeks, 25% in the last week and 0–20 mg/L in the final days. A diluted two-part bottle cannot do this; single salts or per-element dosing can. **Why does tissue nitrogen drop in late flower?** Tissue nitrogen drops in late flower because the plant remobilises nitrogen from its leaves into developing flowers, dilutes it as the flowers bulk up, and has fewer ions available at the roots. It is not water washing the plant clean. During a flush the leaves yellow as they are stripped, yet in Utah State research flower nitrogen stayed unchanged, and calcium, iron and zinc actually rose in other trials. **Short answer.** Don't flush before harvest. It doesn't clean the bud, and it does harm. The last weeks of flower are when the plant packs on most of its final weight and finishes its trichomes and resin. Cutting its food then starves it during the most important phase, for no return. Controlled studies found that flushing did **not** improve flower quality, minerals or cannabinoids [1][2][3]. Longer nutrient withdrawal **tended to cut dry mass and cannabinoid yield** [2][3][4]. In the one taste trial, tasters **preferred the unflushed** flower [7]. Feed through to harvest at the strength the stage calls for. Taste and ash come from a healthy plant that was never overfed, followed by slow [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) and proper [curing](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md). > **House position: Myth.** Pre-harvest flushing for taste or to "clean the plant" is a myth, and it's actively harmful: it starves the plant while it is building yield and resin. The only valid flush treats the medium, not the plant (see [When flushing IS useful](#when-flushing-is-useful)). *Greenleaf aside: flushing is for toilets.* ## What's happening: cannabis is a bioaccumulator A bioaccumulator is a plant that takes up minerals and holds on to them. Cannabis is a well-known one (that's why hemp is used to clean contaminated land). Nutrients it absorbs don't sit in the bud like dust on a shelf, waiting to be rinsed off. They are built into tissue: proteins, nucleic acids, chlorophyll, cell walls, and ions held inside cells. Giving the roots plain water for a week or two doesn't pull those back out of the flower. What plain water does do is force the plant to move mobile nutrients (N, P, K, Mg) out of its **leaves** to keep the flowers going. That's why fan leaves yellow fast during a flush. Growers see the yellowing and think "it worked". It didn't: in the Utah State work, leaf nitrogen fell but **flower nitrogen didn't change** [2]. The leaves were stripped; the bud was not cleaned. Meanwhile, the plant is short of food during the weeks when bracts are swelling and trichome heads are filling. That's the harm. ### Falling nitrogen isn't "cleaning", and some elements go up When tissue nitrogen does fall in late flower, that reflects how the plant uses and moves N (remobilising it from leaves into developing flowers, and diluting it as flowers bulk up), plus the roots having fewer ions to take up. It isn't water washing the plant clean. And flushing doesn't lower everything. Some elements **rise** in flower tissue after a flush, which is the opposite of what a "clean-out" would do: - In the Clemson and Cannabis Research Coalition trials, **calcium rose** in flower with flushes of 3 weeks or more, and those same flushes cut dried bud weight. The authors note that tissue calcium commonly rises as nitrogen falls [9]. - In the 0–14-day industry trial, **iron was at least 50 ppm higher** in flower flushed 10 or 14 days, and **zinc roughly 73 ppm higher** at 14 days, while P, K, Ca, Mg and S didn't change and N was 6.7 % lower [10]. The likely reasons are a **concentration effect** (less bud mass with the same or slightly more of an element gives a higher percentage) and micronutrients released from the medium when plain water goes through it [9][10]. ## The studies | Study | Design | Result | Evidence quality | |---|---|---|---| | Stemeroff, Guelph 2017 [1] | Plain water for the last ≤ 2 weeks | No change in flower minerals or cannabinoids; no consistent yield change | MSc thesis, controlled | | Hershkowitz, Utah State 2024 [2] | Pre-harvest nutrient deprivation | No gain in flower quality or total cannabinoid yield; deficiency symptoms within 1 week; leaf N fell, flower N unchanged; yield declined as flush length increased (as cited in [3]) | MS thesis, controlled (Bugbee lab) | | Alden & Faust 2025 [3]; Alden 2025 [4] | 0 up to 3–4 weeks of fertiliser restriction | Flushing "tended to decrease dry mass, cannabinoid yield, and mineral nutrient concentrations" [4] | Peer-reviewed paper and PhD dissertation | | Saloner et al. 2024 (as cited in [3]) | 2-week flush | No effect on inflorescence yield | Peer-reviewed | | Industry trial [7][10] | 0, 7, 10, 14 days | Most minerals unchanged; N 6.7 % lower, Fe and Zn higher after 10–14 days; tasters preferred unflushed | Single, industry-funded | The pattern: short flushes do nothing useful; longer ones cost you. No controlled study has shown a gain in quality, cannabinoids or yield. As the HortScience authors put it, no study to date has shown that flushing improves smoking quality [3]. ### Late-flower nutrition matters Cannabis yield responds to nutrient supply through flower. In Saloner and Bernstein's work, inflorescence yield and plant function rose with nitrogen supply up to about 160 mg/L N in flower [5]. You don't need luxury levels either: work from the Bugbee lab found that extra phosphorus and excess fertiliser did not raise yield or quality and just ended up in the runoff [2][6]. The target is "enough, all the way to the end", not "too much, then nothing". ### The nitrogen and potency trade-off Nitrogen also affects the *percentage* of cannabinoids. In the same work, cannabinoid and terpenoid concentrations were suppressed at higher N supply, while yield rose with N up to ~160 mg/L [5]. So lower N can raise cannabinoid and terpene **percentages** while lowering **total yield**: a smaller crop with a slightly higher number on the label. It's a trade-off you set with your feed recipe through flower (see [nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md) and [feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md)), not a reason to flush. Starving the plant at the end costs yield and resin without that being a controlled choice. ## What actually drives taste and ash - **Plant health through the whole grow.** A plant that was never hungry, never burnt, and never stalled. - **Not overfeeding in the first place.** Sensible EC and P in late flower (see [feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md)). Excess salt is a root-zone problem, fixed with a root-zone flush when it happens, not with a pre-harvest starve. - **Slow drying:** about 7–14 days in the dark at 15–21 °C (60–70 °F) and 55–62 % RH (see [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md)). - **Proper curing:** sealed jars at 58–65 % RH, burped, for 2–8 weeks (see [curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md)). Black ash and harsh smoke almost always trace back to fast drying, wet or rushed curing, or how the joint burns, not to nutrients left in the plant. ## Instead of flushing: taper nitrogen The GenetixBay approach is **taper nitrogen, don't flush**. In late flower, cut N back, towards zero near the finish, while keeping P, K, Ca, Mg, S and the micronutrients fed at normal strength. You get the controlled side of the N trade-off (lower N, a slightly higher cannabinoid and terpene percentage [5]) without starving the plant of everything else while it finishes its resin. Experienced growers widely recommend it; it's *Grower practice*, and no controlled trial has tested this exact ramp. | Weeks before harvest | N (mg/L) | Everything else | |---|---|---| | −4 | 100–150 (normal late flower) | Full late-flower feed | | −3 | ~75–110 (about 75 %) | P, K, Ca, Mg, S and micros unchanged | | −2 | ~50–75 (about 50 %) | Unchanged | | −1 | ~25–40 (about 25 %) | Unchanged | | Final days | 0–20 | Unchanged; keep normal runoff | A bottled 2-part can't do this: dilute it to cut N and you cut every other element with it. Single salts make this possible: drop calcium nitrate and potassium nitrate, take K from potassium sulfate and MKP, and switch the Ca source to an N-free salt such as calcium chloride (small doses only: 50 mg/L Cl brings just ~28 mg/L Ca, so keep Cl under ~50–70 mg/L; see [chloride](https://genetixbay.com/knowledge/nutrients/chlorine.md)) or calcium sulfate (gypsum) dissolved directly in the final solution. A per-element dosing controller does the same job automatically. Details in [nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md) and [feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md). ## What to do in the final weeks 1. **Feed through to harvest at the strength the stage calls for, tapering only N** (above). In coco, rockwool and hydro keep normal late-flower EC and normal runoff. In soil, keep your normal feeding schedule. 2. **Watch runoff EC.** If it climbs well above input, that's salt build-up. Do a root-zone flush (below) and go back to normal feeding. 3. **Let the plant fade on its own.** Some lower-leaf yellowing in the last 2–3 weeks is normal senescence. Don't force it. 4. **Judge harvest by trichomes** (see [trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md)), then put your effort into drying and curing. 5. **Living soil:** there's nothing to flush. Keep watering normally. ## When flushing IS useful There's one valid flush, and it treats the **medium**, not the plant. A **root-zone flush** washes accumulated salts out of the medium so you can start fresh. It can be done at any stage when there's a real problem. It isn't a pre-harvest ritual. **When to do it** - Runoff EC far above input (roughly input + 1.0 mS/cm or more in coco/soil; slab EC above input + 1.5 in rockwool) (see [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). - Salt crust on the medium surface, burnt tips spreading on fresh growth (see [brown or burnt tips](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md)). - Lockout: deficiency symptoms despite a full feed, with runoff pH or EC out of range (see [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)). **How to do it** 1. **Measure first.** Record input and runoff pH and EC so you can see the change. 2. **Choose the water:** - **Soil:** pH-adjusted plain water (pH ~6.3–6.8). - **Coco, rockwool, hydro media:** a **light nutrient solution** (about EC 0.4–0.8 mS/cm, with Ca and Mg) at pH ~5.8–6.0. Plain water in coco strips Ca and Mg from the exchange sites and can trigger the deficiency you were trying to fix. 3. **Volume:** run about **2–3 times the container volume** through slowly, in several passes, letting it drain between them. For an 11 L (3 gal) pot, that's ~20–30 L. 4. **Check runoff EC** on the last pass. Stop when it's close to your flush input (within ~0.3–0.5 mS/cm) and runoff pH is back in range. 5. **Resume normal feeding** at the next watering (soil: once the top few cm dry back). Don't leave the plant on plain water. 6. **Find the cause:** feed EC too high, too little runoff, or water too hard (see [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md)). ## Common mistakes - Stacking one myth on another: a flush followed by 24–72 h of darkness. Both cut the plant's resources in its final days. - Starving plants for 1–3 weeks before harvest and losing bulk and resin. - Reading yellow fan leaves as proof the flush "worked". - Blaming black ash on nutrients when the bud was dried in 3 days. - Flushing coco with plain water and causing Ca/Mg deficiency. - Drowning a soil pot that's already waterlogged. - Using a root-zone flush as a substitute for fixing feed EC or runoff volume. > **Greenleaf's standing challenge: darkness before harvest.** Putting plants in 24–72 h of darkness before the chop is a *Myth*, and the founder's verdict is "complete and utter nonsense": why cut photosynthesis in the most critical part of the life cycle, while the plant is still finishing its resin? For more than 20 years the founder has offered a standing challenge: find a peer-reviewed study showing a benefit (not a single-plant study, not biased or skewed) and a 50-pack of seeds is yours, no questions asked. Nobody has claimed it. ## Evidence - Pre-harvest flushing improves taste, ash or "cleanliness": **Myth** (house position). No controlled study has shown a quality benefit [1][2][3], and the one sensory trial favoured unflushed flower [7]. - Flushing does not raise cannabinoids or yield: *Supported* [1][2][3][4]. - Longer nutrient withdrawal costs dry mass and cannabinoid yield: *Supported* [2][3][4]. Short flushes (≤ 2 weeks) didn't consistently change yield in [1] or Saloner et al. (via [3]), so the size of the loss depends on how long and how hard you starve the plant. - Root-zone flushing to clear salt build-up: *Grower practice*, consistent with substrate-management guidance. - Some flower elements (Ca, Fe, Zn) rising after a flush, a concentration effect: *Supported* by trial reports [9][10], not yet by a journal paper. - Lower N raising cannabinoid and terpene percentages while lowering yield: *Supported* [5]. A trade-off, not a reason to flush. ## Sources 1. Stemeroff J. 2017. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 2. Hershkowitz JA. 2024. Nutrient management of cannabis in controlled environments. MS thesis, Utah State University (Bugbee lab). https://digitalcommons.usu.edu/etd2023/178 3. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 4. Alden MJ. 2025. Horticultural strategies to improve yield and efficiency for controlled-environment cannabis production. PhD dissertation, Clemson University. https://open.clemson.edu/all_dissertations/4161 5. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 6. Westmoreland FM, Bugbee B. 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 7. Cannabis Business Times. Cannabis cultivation flushing research and yield (industry trial: 0, 7, 10, 14 days; tasters preferred unflushed). https://www.cannabisbusinesstimes.com/article/cannabis-cultivation-flushing-research-yield/ 8. Cannabis Business Times. New experiments in flushing: let your cultivation goals dictate your plans. https://www.cannabisbusinesstimes.com/business-issues-benchmarks/cannabis-industry-research/article/15687664/new-experiments-in-flushing-let-your-cultivation-goals-dictate-your-plans 9. Alden M, Faust J, Justice A. 2023. New experiment in flushing. Cannabis Research Coalition. https://www.cannabisrc.org/post/new-experiment-in-flushing 10. Industry flushing trial report, 2019. https://www.rxgreentechnologies.com/rxgt_trials/flushing-trial/ --- # Trichome ripeness: clear, cloudy, amber, and what the evidence says > Trichome heads go from clear to cloudy (milky) to amber or brown as flowers mature; research confirms browning marks gland senescence and that trichomes on one bract mature unevenly and at genotype-specific rates. Cannabinoid concentration typically rises to a plateau and then falls as plants senesce. The popular claim that amber heads mean high CBN and couch-lock is a myth: CBN mainly forms by oxidation after harvest. A dark period before harvest is a myth too. Harvest when most heads are cloudy with some amber, and track it by date and lab tests for your cultivar. - Canonical: https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.html - Category: Harvest and cure · Level: Intermediate - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Ripening, Harvest · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Should I harvest at cloudy or amber trichomes?** Harvesting at cloudy or amber trichomes is a matter of preference, according to GenetixBay, but the ideal is a mix: a few clear, mostly cloudy and some amber, roughly 5–20%. Earlier harvests near 0–5% amber are chosen for brighter aroma and later ones for a heavier body effect, though that distinction rests on grower reports only, not controlled research. **When should I harvest based on trichomes?** Harvest based on trichomes by checking calyx heads under 60–100× magnification at the top cola, mid canopy and lower buds, and scoring the share of clear, cloudy and amber heads. Start at the early end of the cultivar's flowering window, remembering breeder times often exclude the 10–14 day post-flip transition. Combine trichomes with swollen calyxes, receded pistils and slowing water use. **Does amber trichome mean more CBN?** Amber trichomes do not mean more CBN; that is a myth. CBN forms mainly when THC oxidises after harvest and in storage, not on the living plant, and no study has shown that amber heads contain substantial CBN. Research confirms amber or brown heads mark gland senescence, but no peer-reviewed work has calibrated amber percentage against THC, CBN or terpene content. **Do amber trichomes make a couchlock high?** Amber trichomes do not reliably make a couch-lock high; the claim is a myth that has never been tested. Effects depend on dose, overall chemistry and the person, not on head colour. Amber marks ageing glands, and the CBN usually blamed for sedation forms mainly after harvest. Reports that amber-heavy harvests feel heavier are grower anecdotes, not evidence. **Should I put my plants in darkness before harvest?** Darkness before harvest is a myth, so do not give cannabis 24–72 hours of dark before the chop to 'boost trichomes'. Switching off photosynthesis in the final days takes energy away while the plant is still finishing its resin. GenetixBay's founder has offered a 50-pack of seeds for over 20 years to anyone producing an unbiased, multi-plant peer-reviewed study showing a benefit; nobody has. **What percentage of amber trichomes should I harvest at?** Most growers harvest when trichomes are mostly cloudy with about 5–20% amber, which is grower practice rather than a research-calibrated target, and a few clear heads at that point are fine. Leaving plants for more amber risks senescence, falling cannabinoid concentration and bud rot. Record your amber score, harvest date and any lab results to calibrate the window for each cultivar. **Should I look at trichomes on the sugar leaves or the calyx?** Check trichomes on the calyxes, not the sugar leaves. Sugar-leaf trichomes turn amber earlier than those on the calyx, so reading them makes flowers look riper than they are and pushes you to harvest too early. Sample calyxes at the top cola, mid canopy and lower buds, because top colas often ripen days before lower buds. **Are pistil colours a good harvest indicator?** Pistil colour alone is not a good harvest indicator, because it is affected by stress and genetics. Receded, coloured pistils and a halt in new white pistils are useful supporting signs, alongside swollen calyxes and slowing water use, but judging by pistils only is a common mistake. Use calyx trichome colour and the cultivar's flowering window as the main guides. **Short answer.** Use a 60–100× loupe or a clip-on phone microscope on **calyxes** (not sugar leaves). Heads move from **clear → cloudy (milky) → amber/brown**. Research confirms browning marks **gland senescence**, and that heads on the same bract mature at different rates, varying by genotype and plant age [1][2]. Cannabinoid concentration generally rises to a **plateau, then falls** as plants senesce [4][5]. Cloudy vs amber is a **matter of preference** (house position); the ideal is a nice mix: **a few clear, mostly cloudy, some amber (roughly 5–20 %)**, confirmed against flowering days for your cultivar and, if possible, lab results. The idea that **amber = lots of CBN = couch-lock** is a *Myth* (house position): CBN forms mainly by **oxidation of THC after harvest and in storage** [6], and the effect claims have not been tested. ## What's happening in the gland Stalked capitate trichomes are tiny glands whose head cells secrete resin (cannabinoid acids such as THCA, and terpenes) into a storage cavity under a cuticle. As flowers mature, gland morphology and metabolite content shift [3]. Late in maturation heads brown, lose UV autofluorescence, senesce and can detach; resin may pool and heads stick together or collapse [1]. Colour is a **proxy** for maturity, not a direct measure of chemistry. No peer-reviewed study we can cite has calibrated "% amber" against THC, CBN or terpene content in drug-type cannabis. Automated trichome-phenotype tracking was developed precisely because "clear/milky/brown" is a widely used heuristic with little scientific description [2]. ## What we know about timing and chemistry | Finding | Evidence | |---|---| | Cannabinoid acids and monoterpenes peak at different times by chemotype; CBD-dominant and mixed types peaked later than THC-dominant in one study | *Supported* [4] | | In hemp, total THC/CBD/CBG peaked ~6–7 weeks after anthesis, then declined with senescence; plateau length varied by variety | *Supported* (hemp) [5] | | Trichome development and maturation differ by genotype and plant age; heads on one bract are at mixed stages | *Supported* [1] | | Light exposure degrades THC without forming CBN; air oxidation in the dark forms CBN | *Supported* [6] | | Amber heads on the plant contain substantial CBN | *Myth*; not shown. CBN comes mainly from post-harvest oxidation [6] | | Amber-heavy harvests give couch-lock | *Myth*; effects depend on dose, chemistry, person | ## How to judge ripeness in practice While you watch the trichomes, keep feeding at stage strength. The final weeks are when the plant packs on most of its final weight and finishes its resin; a pre-harvest flush starves it then and is a *Myth* that costs you yield and resin (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). 1. **Know the cultivar's window** (breeder's stated flowering days ±1 week). Breeder times often count from first pistils, not the flip, so add the 10–14 day transition: a stated 8 weeks is about 9.5–10 weeks from the flip (see [the flip-to-flower transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md)). Start checking at the early end. 2. **Sample 3 sites:** top cola, mid canopy, lower bud. Look at calyx heads, not sugar leaves (sugar-leaf heads amber earlier). 3. **Score** roughly: % clear, % cloudy, % amber. 4. **Combine with other signs:** calyxes swollen, most pistils receded and coloured (pistil colour alone is unreliable; it's affected by stress and genetics), new white pistils stopped, slowing water use. 5. **Decide:** most growers harvest at mostly cloudy with 5–20 % amber. Earlier (≈0–5 % amber) tends to be chosen for "bright" aroma; later for heavier body, by grower report only. 6. **Record it.** Harvest date + trichome score + lab results = your own calibration. GenetixBay journals let you compare runs. ## Numbers that matter | Item | Typical | |---|---| | Magnification | 60–100× | | Harvest window | Mostly cloudy; ~5–20 % amber (*Grower practice*) | | Days of flower | Cultivar-specific; drug-type commonly 56–70 days from flip | | Variation across one plant | Top colas often ripen days before lower buds (*Grower practice*) | ## Common mistakes - Reading sugar leaves. - Judging by pistils only. - Leaving plants "for more amber" until senescence and bud rot set in. - A 24–72 h dark period before harvest to "boost trichomes". It's a *Myth*: it cuts photosynthesis in the final days (see the challenge below). > **Greenleaf's standing challenge: darkness before harvest.** Putting plants in 24–72 h of darkness before the chop is a *Myth*, and the founder's verdict is "complete and utter nonsense": why cut photosynthesis in the most critical part of the life cycle, while the plant is still finishing its resin? For more than 20 years the founder has offered a standing challenge: find a peer-reviewed study showing a benefit (not a single-plant study, not biased or skewed) and a 50-pack of seeds is yours, no questions asked. Nobody has claimed it. ## Evidence Morphological maturation and genotype effects are *Supported* [1][2][3]. Chemistry time courses are *Supported* in hemp and across chemotypes [4][5]. The amber→CBN→couch-lock chain is a *Myth* (house position); CBN formation mainly by post-harvest oxidation is *Supported* [6]. A pre-harvest dark period is a *Myth* (house position; no qualifying study). Overall the colour-based harvest heuristic is *Grower practice* with a plausible but uncalibrated basis. ## Sources 1. Punja ZK, Sutton DB, Kim T, 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 2. Sutton DB, Punja ZK, Hamarneh G, 2023. Characterization of trichome phenotypes to assess maturation and flower development in Cannabis sativa L. by automatic trichome gland analysis. Smart Agricultural Technology. https://www.limswiki.org/index.php/Journal:Characterization_of_trichome_phenotypes_to_assess_maturation_and_flower_development_in_Cannabis_sativa_L._by_automatic_trichome_gland_analysis 3. Livingston SJ, Quilichini TD, Booth JK, et al., 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37–56. https://doi.org/10.1111/tpj.14516 4. Aizpurua-Olaizola O, Soydaner U, Öztürk E, et al., 2016. Evolution of the cannabinoid and terpene content during the growth of Cannabis sativa plants from different chemotypes. Journal of Natural Products 79(2):324–331. https://pubmed.ncbi.nlm.nih.gov/26836472/ 5. Yang R, Berthold EC, McCurdy CR, et al., 2020. Development of cannabinoids in flowers of industrial hemp (Cannabis sativa L.): a pilot study. Journal of Agricultural and Food Chemistry. https://pubmed.ncbi.nlm.nih.gov/32392412/ 6. Fairbairn JW, Liebmann JA, Rowan MG, 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1–7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x --- # Backcrossing, IBLs and stabilisation > A backcross crosses offspring back to one parent (the recurrent parent) to recover that parent's genome while keeping a trait from the other: each backcross halves the donor's share (50%, 25%, 12.5%, 6.25%...). An IBL is a line inbred and selected over many generations until it breeds fairly true. 'Stable' should mean measured uniformity across a grow-out, not a generation count. - Canonical: https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.html - Category: Breeding · Level: Breeder - Evidence: Established · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is a backcross in cannabis breeding?** A backcross in cannabis breeding crosses an offspring back to one of its parents, called the recurrent parent, to recover that parent's genome while keeping a trait from the other parent, the donor. The first cross is donor x recurrent (F1); each following generation is a selected offspring crossed back to the recurrent parent again. **What does BX1, BX2, BX3 mean?** BX1, BX2 and BX3 count how many times offspring have been crossed back to the recurrent parent. On average a BX1 carries 75% of the recurrent parent's genome, a BX2 87.5% and a BX3 93.75%, so the donor share halves each time (25%, 12.5%, 6.25%). Real plants vary around these averages, and DNA near the target gene lingers longer. **What is cubing?** Cubing is grower jargon for backcrossing to the same clone three times, so a 'cubed' line is a BX3 with about 94% of that clone's genome on average. It recovers much of the clone's character, but the seeds still segregate and are inbred towards one individual. A cubed line is not a seed copy of the clone. **What is an IBL and how many generations does it take?** An IBL (inbred line) is a cannabis line inbred and selected over many generations until it breeds fairly true, but the term has no fixed definition or generation count. GenetixBay treats 'IBL' as a breeder claim unless backed by grow-out uniformity tables, tester rounds or genomic data showing low heterozygosity. An 'F6 IBL' label without data proves nothing. **How do I know if my line is stable?** A cannabis line is stable when grow-outs reproduce the target traits at a stated frequency, not when it reaches a certain generation. Count off-types in grow-outs of at least 50 plants; a suggested target is 5% or fewer off-types for key traits and 2% or fewer intersex plants, held for at least two generations and two environments. **How do I add one trait to my favourite strain?** To add one trait to a favourite cannabis line, cross it with a donor carrying the trait, then repeatedly backcross selected offspring to the favourite line. For a dominant trait, select carriers by eye; for a recessive trait such as autoflowering, add a self or sib-cross reveal generation or use a DNA marker. Prove the recurrent parent sex-stable first. **Short answer.** Backcrossing moves a trait into a line you already like: cross, then keep crossing selected offspring back to the line you want to recover. After three backcrosses the offspring average ~94% recurrent-parent genome. Stabilisation is different: it means narrowing a population, by inbreeding and selection, until it produces the same type reliably. Neither is finished until you measure uniformity in a real grow-out. ## Backcrossing ### The mechanics - **Donor** = carries the trait you want (e.g., autoflowering, CBD, mould resistance). - **Recurrent parent** = the line you want to end up with. - F1 = donor x recurrent. BX1 = F1 x recurrent. BX2 = selected BX1 x recurrent. And so on. | Generation | Average recurrent-parent genome | Donor genome | |---|---|---| | F1 | 50% | 50% | | BX1 | 75% | 25% | | BX2 | 87.5% | 12.5% | | BX3 | 93.75% | 6.25% | | BX4 | 96.9% | 3.1% | These are averages [1]. Real plants vary, and DNA from around the target gene ("linkage drag") stays longer, especially in low-recombination regions of the cannabis genome [6]. ### Dominant vs recessive targets - **Dominant trait:** select carriers each generation by eye, then backcross again. - **Recessive trait** (e.g., autoflowering [4]): BX offspring are carriers but don't show it. Either self or sib-cross a generation to reveal it, then continue, or use a DNA marker to pick carriers. - **Codominant trait** (chemotype [3]): visible by lab test in every generation. ### "Cubing" in cannabis Grower jargon for repeatedly backcrossing to one clone (the clone is used as the recurrent parent three times: "BX3" = "cubed"). It recovers a lot of the clone's genome, but the progeny are still segregating and inbred towards one individual; it is not a copy of the clone (*Grower practice* term; genetics *Established*). ## Stabilisation and IBLs ### What "stable" should mean A line is stable for a trait when grow-outs reproduce it at a stated frequency. The useful definitions come from variety testing: **Distinct, Uniform, Stable (DUS)**. Uniformity means off-types stay below a set threshold in a sample, and stability means the line still looks the same after repeated propagation [5]. ### How to get there 1. Start with a large selected population (not one pair). 2. Each generation, grow enough plants to see the variation (≥20-50 females where possible). 3. Select for the target traits; keep several parents (2-5 females, 2-5 males) to limit inbreeding depression [2]. 4. Track the **off-type rate** per trait per generation. 5. Stop calling it "stabilising" and start calling it stable when the off-type rate has stayed below your published threshold for at least two generations and two environments. ### IBL claims "IBL" has no fixed definition in cannabis. Treat it as a breeder claim (L2 on GenetixBay) unless supported by published grow-out data (uniformity tables, tester rounds) or genomic data showing low heterozygosity (L3-L4). ## Numbers that matter | Measure | Example target | How to measure | |---|---|---| | Off-type rate for a key trait | ≤5% (breeder-set; DUS uses formal statistical thresholds) | Count in a grow-out of ≥50 plants | | Intersex rate | ≤2% (breeder-set); intersex plants are culled, never used as parents | All plants observed to harvest | | Flowering time spread | ±7 days | Days flip to harvest | | Chemotype off-types (for a type III line) | 0 in ≥30 tested | Lab or marker test | Targets are suggested GenetixBay practice, not legal standards. ## Common mistakes - Backcrossing to a clone with a hidden intersex tendency: you concentrate it. Prove the recurrent parent sex-stable over at least two runs first (see [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md)). - Narrowing to one male and one female every generation, then blaming "bad luck" for weak plants. - Publishing "F6 IBL" with no uniformity data. - Forgetting linkage drag: an unwanted trait close to your target gene can ride along for many backcrosses. ## Evidence - Backcross genome recovery and linkage drag: *Established* [1]. - Inbreeding depression from narrow populations: *Established* [2]. - Trait-specific inheritance used above: *Established* / *Supported* [3][4]. - DUS concepts: *Established* (regulatory standard) [5]. - "Cubing" and "IBL" usage in cannabis: *Grower practice* terminology. ## Sources 1. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 3. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 4. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 5. UPOV. Test guidelines for hemp (Cannabis sativa L.), TG/276/1. https://www.upov.int/edocs/tgdocs/en/tg276_01.pdf 6. Laverty KU, Stout JM, Sullivan MJ, et al. 2019. A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci. Genome Research 29(1):146-156. https://doi.org/10.1101/gr.242594.118 --- # Breeder record-keeping and naming ethics > Keep a dated record of every plant, cross, batch and test, linked by permanent IDs, so any seed can be traced to its parents. Name lines honestly: a new, unique name for new genetics, the original name only for the original genetics, clear labels (F2, BX, S1, feminised), and never a famous name on something it isn't. Names are claims; records are the evidence. Sex stability is part of the ethics: cull herm-prone plants, never breed from them, and publish every batch's herm rate. - Canonical: https://genetixbay.com/knowledge/breeding/record-keeping-naming-ethics.html - Category: Breeding · Level: Breeder - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What records should a cannabis breeder keep?** A cannabis breeder should keep dated records for every plant (ID, source, sex, photos, scores), every selection decision, every pollination (female, male, date, branch, pollen batch), every seed batch (parents, seed count, feminised or regular, storage), every test (germination, sex, chemotype, HLVd), every release and every transfer. Undated notes not linked to plant IDs don't count. **How should I name my new strain?** Give a new cannabis cross a new, unique name that no one else has used for cannabis; search first. Following international cultivated-plant naming principles, avoid names that mislead about origin, effect or breeder, and avoid copying other brands. Publish the name together with its pedigree claim, generation and grow-out results. **Can I use someone else's strain name?** Use another breeder's strain name only for their original genetics. An S1 or cross of it should be labelled as such, for example 'Line A S1' with your breeder name, or given a new name with Line A shown in the pedigree. Adding a famous name to genetics that don't descend from it to help sales is misleading. **What should go on a seed pack label?** A cannabis seed pack label should show the line name and breeder, the pedigree claim with generation (F1, F2, BX, S1) and evidence level, feminised or regular, photoperiod or autoflower, batch and pack IDs, seed count, germination test result with date and sample size, the grow-out herm rate with plant count, the packing date and any legally required notice. **How do I write a pedigree?** Write a cannabis pedigree female first, as female x male, then add the generation and method, such as F2, BX2 to Line A, S1 or feminised by STS reversal. Name the specific individuals with their IDs, not just line names, for example 'Line A #3 x Line B male #7', and mark any uncertain link as reported or unverified. **Is it OK to rename a clone?** No, renaming a clone to claim ownership of it is not acceptable practice. A clone-only cannabis cut keeps its original name; add your selection or source as a qualifier instead. Renaming cuts is one reason same-named strains so often turn out genetically different in DNA studies, and it breaks the chain of records. **Should breeders disclose hermaphrodite rates?** Yes, breeders should disclose hermaphrodite rates. The GenetixBay breeder standard requires growing out a sample of every seed batch and publishing its herm rate with the number of plants, number of intersex plants, the week seen and the conditions. A herm rate without a plant count means little. Featuring needs a 10-plant screening grow with zero herms; the label Verified under 2% herm rate needs about 150 or more pooled community-grown plants, because 10 plants can't tell 2% from 10%. **Is it ethical to sell seed from a plant that hermed?** No, selling seed from a plant that hermed is not ethical under GenetixBay breeding standards. Herm pollen makes female-looking seed that carries the same intersex tendency into every pack. A plant that herms, along with its clones, should be culled and never selfed, reversed or crossed. Releasing untested or unstable seed is pollen chucking. **Short answer.** If it isn't written down, dated and linked to a plant ID, it didn't happen. Record every pollination, batch, test and selection. Name new work with a new, unique name; label generation and seed type plainly; and never reuse a famous name for genetics that aren't it. The strain-name mess documented in genetic studies [3][4] is largely a record-keeping and naming failure. ## What's happening Cannabis grew up outside formal plant variety systems. Names spread by word of mouth, cuts were renamed, and seed was sold under borrowed names. Genetic studies of dispensary samples found many same-named strains with genetic outliers [3], and lab data show some names are chemically consistent while others are not [4]. Good records are the fix the industry skipped. ## The minimum record set | Record | Contents | GenetixBay entity | |---|---|---| | Plant | ID, source (pack, cut, cross), germination date, sex, photos, scores | GB-IND / GB-CUT | | Selection | Rubric scores, notes, why kept or culled | Journal event on GB-IND | | Pollination | Female ID, male (or reversed female) ID, date, branch, pollen batch | `pollination` event | | Batch | Parents, dates, seed count, feminised/regular, storage | GB-BAT | | Test | Germination (n, %, date, method), sex check, chemotype, HLVd | GB-DOC on the batch or plant | | Release | Line name, pedigree claim, generation, description, grow-out data | GB-GEN with LIN claims | | Transfer | Who received seed or cuts, when | `transfer` event | ## Writing a pedigree - **Female first:** `(Line A x Line B)`, female x male. - **Generation and method:** `F2`, `BX2 to Line A`, `S1`, `Feminised (STS-reversed Line A #3)`. - **Specific individuals, not just names:** `Line A #3 (GB-CUT-...) x Line B male #7 (GB-IND-...)`. - **Mark uncertain links as uncertain:** "reported" or "unverified", with the evidence level. ## Naming rules (GenetixBay practice, drawn from the ICNCP) The International Code of Nomenclature for Cultivated Plants requires that a cultivar name be unique within its denomination class, not misleading, and established by publication [1]. Applied to cannabis: 1. **New genetics, new name.** A new cross gets a name no one else has used for cannabis. Search GenetixBay and the wider web first. 2. **Original name for original genetics only.** "Line A" means the line as released by its originator. Your S1 or cross of it is "Line A S1 (your breeder name)" or a new name with "Line A" in the pedigree. 3. **No borrowed fame.** Don't add a famous name to genetics that aren't descended from it to help sales. 4. **Don't rename a clone to own it.** A clone-only keeps its name; add your selection or source as a qualifier. 5. **Don't use names that mislead about origin or effect** (e.g., implying a region, a medical effect, or a breeder who wasn't involved) [1]. 6. **Not trademarks of others.** Avoid names that copy food, sweets or other brands. Besides being misleading, it creates legal risk. 7. **Publish the evidence with the name**: pedigree claim, generation, grow-out results. ## Ethics beyond names - **Credit sources.** Name the breeder or keeper of parent material where known. - **No undisclosed reversals.** Feminised status and method should be on the label. - **Report problems.** Intersex rates, off-types and low germination belong in the public record. ### Males first, selfing last > **House position: males are a necessity.** Real breeding needs real males, selected as carefully as the females. Males are encouraged and rewarded on GenetixBay, and a well-documented male line is a prized contribution. Selfing is mostly frowned upon: it was historically an emergency measure to save a line, not a shortcut. GenetixBay holds the best breeding standards: snobby, and proud of it. ### Sex stability is an ethics standard > **Breeder's standard.** Cannabis is dioecious and has been stable for millennia; herm-prone lines are mainly breeder error. A GenetixBay breeder (BRD-500) commits to: (1) using only mothers, reversal donors and males that ran sex-stable for at least two cycles; (2) culling every plant that herms, with its clones, and never selfing, reversing or crossing from it; (3) no repeated S1-on-S1 releases without grow-out and culling; (4) growing out a sample of every batch and publishing its herm rate (n plants, n intersex, week, conditions) on the GB-BAT; (5) not releasing a batch or line that herms under normal conditions. GenetixBay checks this in two tiers: a 10-plant screening grow (any herm fails the line for featuring), then pooled community grow reports, where a line needs about 150 plants or more (149 with zero herms, by a one-sided 95% bound) before it can be labelled "Verified under 2% herm rate". See [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md). Releasing untested, unstable seed is "pollen chucking", and it is how herm-prone genetics spread. See [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md), [S1s and selfing](https://genetixbay.com/knowledge/breeding/s1-selfing.md) and [feminised seed](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md). - **Don't claim effects.** Effects are "reported", never promised; no medical claims. - **Respect origins.** For landrace or collected material, credit the source region and community, record what you actually know about where and when it was collected (with its evidence level), and share value back where you can. See [landrace hunting and biopiracy](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md). ## Pack label checklist - Line name and breeder - Pedigree claim with generation (F1, F2, BX, S1) and evidence level - Feminised / regular; photoperiod / autoflower - Batch ID (GB-BAT) and pack ID (GB-PKG) - Seed count - Germination test result, date, n - Grow-out herm rate (n plants, n intersex), and "Verified under 2%" only once pooled reports reach the Tier 2 standard - Packing date - Local legal notice where required ## Common mistakes - Paper notes that never get matched to plants. - Writing "Line A x Line B" without saying which individuals. - Publishing a name before checking it's free. - Deleting bad results. On GenetixBay history is append-only; corrections are new events, not erasures. ## Evidence - Naming principles: *Established* (international code) [1]. - Strain-name inconsistency in markets: *Supported* [3][4]. - Record sets and label checklist: GenetixBay practice (*Grower practice*). ## Sources 1. Brickell CD, et al. (eds). 2016. International Code of Nomenclature for Cultivated Plants, 9th edition. Scripta Horticulturae 18. ISHS. https://www.ishs.org/scripta-horticulturae/international-code-nomenclature-cultivated-plants-ninth-edition 2. UPOV. Test guidelines for hemp (Cannabis sativa L.), TG/276/1. https://www.upov.int/edocs/tgdocs/en/tg276_01.pdf 3. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 4. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLoS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 5. McPartland JM, Small E. 2020. A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys 144:81-112. https://doi.org/10.3897/phytokeys.144.46700 --- # Breeders vs pollen chuckers: what real cannabis breeding looks like > A breeder sets a goal, grows large populations, selects both females and males, progeny-tests the parents, stabilises the line over generations (F2s, backcrosses, IBLs), test-grows every batch and discloses its herm rate. A pollen chucker crosses two popular cuts, or selfs one, and sells the first-generation seed untested. Plant-breeding science explains why the difference shows up in your tent: crosses of heterozygous clones segregate, selecting only one sex halves progress, and intersex expression is heritable and responds to selection. - Canonical: https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.html - Category: Breeding · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is a pollen chucker?** A pollen chucker is someone who crosses two popular clones, or selfs one, gives the seed a new name and sells it without growing it out. There is no written goal, no male selection, no progeny testing, no stabilisation and no published herm rate. It is seed production rather than plant breeding, and the result is a segregating lottery ticket. **What's the difference between a breeder and a pollen chucker?** The difference is process. A cannabis breeder writes a goal, grows dozens to hundreds of plants per generation, selects males as carefully as females, progeny-tests parents, stabilises over several generations, test-grows every batch and publishes the herm rate with a plant count. A pollen chucker releases the first F1 or S1 of trending cuts with none of that. **Is crossing two clones breeding?** Crossing two clones is only the first step of breeding, not the finished product. Elite cannabis clones are heterozygous, so a cross between two of them already segregates like an F2 and throws many different plants. Uniform F1 hybrids need inbred parent lines, which takes years of selection, stabilisation and test grows that a single clone cross skips. **Why do males matter in cannabis breeding?** Males matter because half of every seed's genes come from the father. Under the breeder's equation, response to selection equals heritability times the average selection differential of both sexes, so using a random male halves the gain each generation. With heritability 0.3 and females 4 units above average, a selected male gives 1.2 units of gain versus 0.6. **How many plants do you need to test a seed line?** Testing a cannabis seed line takes more plants than most packs hold. To have a 95% chance of seeing a type that occurs 1 in 16 in an F2 you need about 47 plants, and about 191 for a 1-in-64 type. Ten seeds is a peek, not a test, which is why GenetixBay pools tester grows across growers. **How many plants to prove a low herm rate?** Proving a cannabis line's herm rate is under 2% takes about 150 plants with zero herms. By the rule of three, zero herms in n plants puts the 95% upper bound on the true rate at about 3 divided by n, so zero in 10 plants only shows the rate is probably below roughly 26-30%. Always publish the plant count. **Why are some seed lines so inconsistent?** Many cannabis seed lines are inconsistent because they are crosses of two heterozygous elite clones, which segregate like an F2 instead of giving a uniform F1. Without large populations, male selection, several generations of stabilisation and test grows, each seed draws a different combination of genes. The 'F1' on the pack says nothing about uniformity. **How do I tell if a seed line was properly bred?** A properly bred cannabis seed line comes with evidence: a stated generation and male, breeder notes, independent test-grow reports, a uniformity or flowering-time range, and a herm rate with the plant count it came from. Warning signs are a pedigree of two famous cut names only, no herm data, huge yield or THC claims, and herms always blamed on light leaks. **What is progeny testing?** Progeny testing judges a candidate parent by its offspring rather than by its own looks. A breeder grows out families from each candidate male and female, then keeps the parents whose offspring are good and uniform. It is established plant-breeding practice and the main way to evaluate cannabis males, whose resin and flavour can't be seen directly. **Short answer.** A breeder sets a goal, grows big populations, selects **both** females and males, tests what the parents actually pass on, stabilises the line over several generations, test-grows every batch and publishes its herm rate. A pollen chucker crosses two popular cuts (or selfs one), gives the seed a new name and sells it without growing it out. The first is plant breeding as every textbook describes it [1][2][3]. The second is seed production. It isn't a matter of taste: the genetics explain why one gives you a line and the other gives you a lottery ticket. > **House position: we're snobby, and proud of it.** GenetixBay holds breeders to the standards of plant breeding, not of seed marketing. Males are a necessity, and they're encouraged and rewarded here. Selfing is mostly frowned upon. Every line publishes a herm rate from tester grows, and lines above **2 %** in tester grows don't qualify for Bay Lines, the Seed Club or featuring. We criticise practices, never named people: this article names no one, and neither should you when you quote it. ## What real breeding is Plant-breeding texts agree on the core loop: define objectives, build or choose variable populations, select, evaluate the selections' offspring, and repeat until the line breeds true for what you want [1][2][3]. In cannabis terms: 1. **A defined goal.** "A terpinolene-dominant, mould-tolerant, 9-week line that stays female under stress" is a goal. "Cross the two cuts everyone wants" is a marketing plan. 2. **Large populations.** Rare combinations only turn up if you grow enough plants. If a desirable type is 1 in 16 in an F2 (two recessive genes), you need about 47 plants for a 95 % chance of seeing even one; at 1 in 64 (three genes) you need about 191 [5]. A pack of ten seeds is a peek, not a hunt. See [selection and pheno hunting](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md). 3. **Selection of females and males.** Half of every seed's genes come from its father. You can't see a male's resin or flavour directly, so breeders judge males by vigour, structure, stem-rub aroma, sex stability, and above all by what their daughters turn out like. 4. **Progeny testing.** A plant's own looks are only part of the story; what counts is what it passes on. Breeders grow out the offspring of candidate parents and keep the parents whose families are good and uniform [1][3][4]. 5. **Stabilisation over generations.** F2s and later generations, backcrosses and inbred lines (IBLs) fix the wanted traits so the seed breeds true. That takes years. See [backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) and [F1, F2, F3 explained](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md). 6. **Test grows.** Every batch is grown out, by the breeder and by independent testers, before release. Germination, uniformity, flowering time and sex stability are measured, not assumed. 7. **Honest herm-rate disclosure.** The batch's herm rate goes on the record, with the number of plants it came from. Intersex plants are culled and never used as parents. See [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). 8. **Records and naming ethics.** Every plant, cross and batch is traceable to its parents; the name says what it is (F1, F2, BX, S1, feminised); a famous name is never put on something it isn't. On GenetixBay that means GB-IDs with evidence levels, and documented males in the **Stud Book**, the male showcase where each male's selection journal, keeper and sire credits are kept. See [record-keeping and naming ethics](https://genetixbay.com/knowledge/breeding/record-keeping-naming-ethics.md) and [documenting lineage evidence](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md). ## Breeder vs pollen chucker | | Breeder | Pollen chucker | |---|---|---| | Goal | Written down before the first cross | "Cross the two cuts that are trending" | | Population size | Dozens to hundreds per generation | Whatever fits in the tent | | Males | Selected, tested, kept; the father matters as much as the mother | Whatever male was around, or none (reversed female) | | Selfing | A last resort to save a line, labelled S1 | The default, because it needs no male | | Testing parents | Progeny tests: judged by what their offspring do | Judged by the parent cuts' reputation | | Generations before release | Several (F2+, backcrosses, IBL work) | One. The F1 (or S1) is the product | | Test grows | Every batch, in-house and independent testers | None, or "the customers are the testers" | | Herm rate | Measured, published with the plant count, culled from the line | Not measured; herms blamed on the grower's light leak | | Name | Unique, with generation and type on the label | A mash-up of the parents' famous names | | Records | Traceable pedigree and batch records | "Trust me" | | What you get | A line that grows the way the description says | A segregating lottery ticket | ## Why the difference shows in your tent ### Crossing two clones doesn't make a uniform F1 The uniform F1 hybrids of maize or tomatoes come from crossing two **inbred** (highly homozygous) parents: every seed gets the same pair of gametes, so every plant is the same [1][3]. Elite cannabis clones are not inbred; they're heterozygous selections, often from polyhybrid backgrounds. Each clone makes many different gametes, so a cross between two of them already segregates like an F2 [5]. That's why a pack of "Famous Cut × Other Famous Cut" throws a dozen different plants, and why the "F1" on the pack says nothing about uniformity. Making true F1 hybrids in cannabis needs inbred parent lines first, which is exactly the slow work Barcaccia and colleagues set out as a breeding scheme [6]. ### Selecting only females halves your progress The breeder's equation predicts the response to selection: **R = h² × S** R is the gain in the next generation, h² the narrow-sense heritability of the trait and S the selection differential (how far your chosen parents sit above the population average) [4][5]. When the two sexes are selected differently, S is the average of the two: **S = (S♀ + S♂) / 2** [4]. Worked example: a trait with h² = 0.3. You pick females 4 units above average. - Male also selected, 4 units above: S = 4, R = 1.2 units per generation. - Random male (S♂ = 0): S = 2, R = 0.6 units. **Half the progress**, every generation. That's the arithmetic behind "males are a necessity". A breeder who never selects a male is throwing away half the gain, and taking pot luck on half the genome. ### Selfing and reversal concentrate what's there, good and bad Selfing halves heterozygosity each generation (F rises from 0 to 0.5, 0.75, 0.875...), so recessive faults, including inbreeding depression, surface fast [13]. That can be a tool when a breeder does it deliberately and culls hard. Done casually, on a plant chosen because it's popular, it fixes whatever that plant carries. See [S1s and selfing](https://genetixbay.com/knowledge/breeding/s1-selfing.md). ### Intersex expression is heritable, and it responds to selection This is where pollen chucking does the most damage. - **Sex expression has a genetic basis.** In monoecious hemp, the degree of male and female flowering varies between cultivars and has a genetic basis [10]; genome-wide work has mapped loci associated with sex expression [11]. (Hemp, not drug-type cannabis: we're extrapolating, carefully.) - **It responds to selection, in both directions.** Monoecious hemp exists because 20th-century breeders selected *for* plants with both sexes [8][10]. If selection can push a dioecious species towards monoecy, careless selection can drift a line towards herming, and careful selection can hold it female. - **Herm pollen makes feminised seed.** Seed from hermaphroditic pollen in drug-type cannabis gave only female progeny [9]. A plant that herms in the room and seeds itself has made a new batch of "feminised" seed carrying the same tendency. Reversing an unproven female with silver does the same thing on purpose [12]. Put together: selling seed from a line no one has test-grown, or from a plant that hermed, spreads intersex tendency. The house position is that herm-prone lines are mainly a breeding failure; see [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). ### Small test grows can't prove sex stability How many plants does a test grow need? If a line's true herm rate is *p*, the chance of seeing zero herms in *n* plants is (1 − *p*)ⁿ. | True herm rate | Chance of zero herms in 10 plants | Plants for a 95 % chance of catching at least one | |---|---|---| | 20 % | 11 % | 14 | | 10 % | 35 % | 29 | | 5 % | 60 % | 59 | | 2 % | 82 % | 149 | And the reverse: if you see **zero** herms in *n* plants, the 95 % upper bound on the true rate is about 3/*n* (the "rule of three"). Zero in 10 plants only tells you the rate is probably below about 26–30 %. To back a claim of "under 2 %" with a clean test, you need about **150 plants** across testers. That's why GenetixBay asks for the plant count next to every herm rate, and why tester grows are pooled. ## How to spot a pollen-chucked line - The pedigree is two famous cut names and nothing else: no generation, no male, no breeder notes. - The first release is an F1 or S1 of popular clones, with no test-grow reports. - No herm rate, or a herm rate with no plant count. - Huge numbers on the pack (yield, THC) and nothing about uniformity or flowering-time range (see [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md)). - A new name every season for similar parents. - When herms are reported, the answer is always "light leak". None of this proves anything about a particular seller. It tells you what evidence to ask for. ## How to do it properly (the short version) 1. Write the goal down. 2. Grow enough plants to find what you're after; select males as carefully as females, and keep them (register them in the Stud Book). 3. Progeny-test your candidate parents before committing to them. 4. Stabilise across generations; label each one honestly. 5. Test-grow every batch with independent testers; cull intersex plants; publish the herm rate with the plant count. 6. Keep the records; name it honestly; let the line earn its reputation. ## Common mistakes - Treating the first cross as the finished product. - Using whichever male is available, or skipping males entirely. - Selecting on one plant's looks without testing what it passes on. - Quoting "no herms" from a handful of plants. - Keeping a herm because it's the best smoke in the room. ## Evidence - The breeding loop (objectives, variable populations, selection, progeny testing, stabilisation, testing): *Established* plant-breeding practice [1][2][3]. - Breeder's equation and the halving of response when one sex is unselected: *Established* quantitative genetics [4][5]. - Crosses of heterozygous parents segregate; uniform F1 hybrids need inbred parents: *Established* [1][3][5]; proposed for cannabis [6]. - Selfing raises homozygosity and exposes recessive load: *Established* [13]. - Sex expression has a genetic basis and responds to selection: *Supported* in hemp [10][11], and by the deliberate breeding of monoecious hemp [8]; a heritability estimate for intersex tendency in drug-type cannabis hasn't been published. - Herm pollen gives all-female, herm-carrying seed: *Supported* in drug-type cannabis [9][12]. - Strain names hiding genetically different plants: *Supported* [14]. - Herm-prone lines being mainly a product of poor breeding practice: GenetixBay house position, consistent with the above and with long breeder experience; drug-type cannabis has been dioecious through recorded history [7][8]. - Test-grow sample sizes: *Established* binomial arithmetic. ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 3. Fehr WR, Suza WP. 2025. Principles of Cultivar Development (open edition of Fehr WR 1987/1991, Vol. 1: Theory and Technique). Iowa State University Digital Press. https://doi.org/10.31274/isudp.2025.200 4. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 5. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 6. Barcaccia G, Palumbo F, Scariolo F, Vannozzi A, Borin M, Bona S. 2020. Potentials and challenges of genomics for breeding cannabis cultivars. Frontiers in Plant Science 11:573299. https://doi.org/10.3389/fpls.2020.573299 7. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 8. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 9. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 10. Faux AM, Berhin A, Dauguet N, Bertin P. 2014. Sex chromosomes and quantitative sex expression in monoecious hemp (Cannabis sativa L.). Euphytica 196(2):183-197. https://doi.org/10.1007/s10681-013-1023-y 11. Petit J, Salentijn EMJ, Paulo MJ, Denneboom C, Trindade LM. 2020. Genetic architecture of flowering time and sex determination in hemp (Cannabis sativa L.): a genome-wide association study. Frontiers in Plant Science 11:569958. https://doi.org/10.3389/fpls.2020.569958 12. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 13. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 14. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 --- # Breeding autoflowers: getting the trait into a photoperiod line > Because autoflowering is recessive in mapped populations, a photo x auto F1 is all photoperiod. You recover autos in the F2 (about 1 in 4) or by backcrossing the F1 to the auto parent (about 1 in 2). To make an auto version of a photoperiod line, alternate crossing to the photo parent with a generation that reveals autos, or use a DNA marker to keep carriers. - Canonical: https://genetixbay.com/knowledge/breeding/breeding-autoflowers.html - Category: Breeding · Level: Breeder - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I breed my own autoflower strain?** To breed an autoflower line, cross a photoperiod plant with a stable auto. The F1 will all be photoperiod; sib-cross the F1s to get an F2 with about 25% autos, or backcross an F1 to the auto for about 50%. Select autos with the traits you want, then backcross towards the photoperiod parent with reveal generations and stabilise. **Why are all my auto x photo seeds photoperiod?** Auto x photo seeds are all photoperiod because autoflowering is controlled by a recessive allele at the Autoflower1 locus in mapped populations. The F1 carries one auto and one photoperiod copy, so it flowers by day length, though heterozygotes may flower about two weeks earlier. Autos reappear in the F2 (about 25%) or in a backcross to the auto. **How many generations to make an autoflower version of a strain?** Making an autoflower version of a photoperiod cannabis line takes about five generations. The marker-free route (F1, BX1, a reveal F2, BX2, another reveal) recovers about 87.5% of the photoperiod parent's genome. With a validated DNA marker you can backcross three times picking carriers, then make an F2, recovering about 94%. Stabilisation testing follows. **Can I cross two autoflowers?** Crossing two autoflowers usually gives autoflowering offspring if both carry the same recessive auto allele. But not every auto source has been shown to share the Autoflower1 locus, so two auto lines of unknown origin can give photoperiod offspring if their mechanisms differ. Whether all autos share one locus is contested, so test-grow the offspring under long days. **How do I make sure my auto line is stable?** To check an autoflower line is stable, grow at least 50 seeds from the auto x auto line under long days, 18/6 or longer. Any plant that doesn't start flowering at the expected age, usually 3-5 weeks, is a photoperiod off-type. Aim for zero photoperiod off-types in a 50-plant test before release; any off-type means incomplete fixation. **Why are autoflowers less potent than photoperiods?** Early autoflowers were less potent because the auto trait came from wild, unselected ruderalis-type populations, and linkage drag carried donor DNA around the auto gene along with it. Repeated backcrossing into elite photoperiod lines with selection for resin has closed most of the gap. In the founder's experience autos now test slightly under photo sisters, with some matching them. **Are autos better than photoperiods?** Whether autos are better than photoperiods depends on what 'better' means. Per square foot per year, autoflowers are very hard to beat because more harvests fit in a year, except perhaps by a dialled-in sea of green or SCROG. Per plant, autos have a lower yield ceiling because they can't be vegged longer, and they usually test slightly under photo sisters. **Short answer.** Cross photo x auto, grow the F1 (all photoperiod), then either sib-cross the F1s (F2: ~25% autos) or backcross an F1 to the auto (~50% autos). To keep a photoperiod line's character while adding autoflowering, backcross towards the photo parent, using a "reveal" generation or a DNA marker each time to keep the hidden auto allele. ## What's happening In the populations mapped by Toth et al. (2022), autoflowering is controlled by a recessive allele at **Autoflower1** on chromosome 1; F2s fit 1:2:1 genotypes with about 25% autos [1]. Heterozygotes flowered about two weeks earlier in the field but did not autoflower [1]. Not all auto sources have been shown to share this locus, so crossing two different auto lines may not always give autos if they carry different mechanisms (*Contested*) [1]. ## Paths compared | Plan | Generations | Auto share | Photo-parent genome (avg) | |---|---|---|---| | F1 then F2 | 2 | ~25% of F2 | ~50% | | F1 x auto parent (backcross to auto) | 2 | ~50% | ~25% | | Backcross to photo with reveal steps (F1, BX1, BX1-F2 reveal, BX2, BX2-F2 reveal) | 5 | ~25% in each reveal generation | ~87.5% | | Backcross to photo with a marker (F1, BX1, BX2, BX3 picking carriers, then F2) | 5 | ~25% in final F2 | ~94% | Averages from standard backcross genetics [3]; actual recovery varies. ## Step by step: marker-free route 1. **P:** Photo line female x stable auto male (or reverse). Record IDs. 2. **F1:** All photoperiod. Pick the best F1s. 3. **F2:** Sib-cross F1s. Grow under 18/6 or longer; autos are the ones that flower at 3-5 weeks [1]. 4. **Select** autos with the photo parent's best traits. 5. **Backcross** chosen autos to the photo parent (BX1, all photoperiod, all carriers). 6. **Reveal:** sib-cross BX1s; select autos again. 7. **Repeat** 5-6 until the line looks like the photo parent in the traits you care about. 8. **Stabilise:** grow 50+ seeds from your auto x auto line under long days; any plant that doesn't flower at the expected age is an off-type. Aim for 0 photoperiod off-types in a 50-plant test before release. ## Step by step: marker-assisted route If a validated marker for your auto source exists (check the lab's validation in your germplasm), backcross F1 x photo parent each generation and test seedlings, keeping only carriers [1]. Reveal autos only in the final generation. This saves time but costs lab fees, and markers may not predict every auto source [1]. ## Growing tips for selection > **House position: autoflowers.** An auto runs on a strict countdown from germination, so any setback costs it time it can't get back. **Plant it straight into its final pot**: transplanting is almost a no-no, because of how the auto's taproot reacts (the founder's observation, compared with photoperiods). **Train with LST, don't top**: topping will never produce what proper low-stress training does on an auto. *Grower practice*, house-endorsed. - Sow selection plants **straight into their final pots** and train with LST only, so every plant gets the same clean run and setbacks don't mask differences. - Score autos on **days to flower** and **total cycle length** under the same long-day schedule (18/6 or 20/4). - Expect more variation in size and yield than in photoperiod hunts: you can't veg longer to equalise. - Clones of autos flower on the parent's age clock; select from seed populations. ## Numbers that matter | Test | Plants for 95% chance of ≥1 auto | |---|---| | F2 (p = 0.25) | 11 | | BX to auto (p = 0.5) | 5 | | Want ≥5 autos in an F2 | 34 | Binomial calculations [3][4]. ## Are autos better? Better how? Growers ask it as if there's one answer. There isn't: better at what? The grower's side (yield per area per year, finickiness, "good for beginners") is in [photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md). The short version: per square foot per year autos are very hard to beat, except perhaps by a dialled-in sea of green or SCROG with a dedicated nursery, because more harvests fit in a year [6]. Here's the breeder's side: why autos lagged on cannabinoids, and why the best have caught up. **The trait itself is one switch.** Day-neutral flowering maps to a major locus, Autoflower1, and behaves as a recessive in the populations studied [1]. It's not quite all-or-nothing: in triploid and diploid hybrids, the fewer photoperiod alleles a plant carried, the earlier it flowered, which points to incomplete dominance of the photoperiod allele [5]. One gene doesn't make a plant weak. What came with it did. **Why autos lagged: what came along with the gene.** The auto trait came into drug-type breeding from northern and Central Asian populations popularly called ruderalis [8], which were wild or weedy, small, and not selected for resin. When you bring one trait in from an unimproved donor, you also bring in the chromosome segments around it and, in the early crosses, half the donor's genome. Plant breeders call the first problem **linkage drag** [7]. Each backcross to an elite photoperiod parent halves the remaining donor genome on average (50 %, 25 %, 12.5 %...) [3], but the segment linked to Autoflower1 on chromosome 1 hangs on longest because you're selecting for it every generation. Early autos were a cross or two away from the donor, and tested like it. **Why the best have caught up.** Breeders kept backcrossing autos into elite photoperiod lines, selecting each generation for resin and potency as hard as for the auto trait, and kept recombining away the linked donor segment. A modern elite auto can be mostly elite photoperiod genome carrying a small piece of the donor. In the founder's experience autos still usually test slightly under their photoperiod sisters, but some give them a real run (no controlled matched-line comparison found). > **Founder's records.** The founder has had an elite autoflower lab-test at **30 %** and has pulled **3/4 lb (about 340 g) in under 80 days**. One grower, one elite line: the ceiling, not the average. **Why the yield ceiling is lower per plant.** An auto can't be vegged longer, so plant size is set by its genetic clock and how cleanly it's grown in the first weeks. Breeders select for vigour in that window and for a cycle length that suits the market (faster lines give more cycles a year; slower ones give bigger plants). A one-week difference in cycle length changes cycles per year by roughly 8–10 % at 10–12-week cycles, which is why days to harvest is a breeding target, not just a convenience. **What that means for breeding.** Treat potency and terpenes in an auto project as quantitative traits to select for every generation, not as something the elite photo parent will hand over by itself (see [quantitative traits and heritability](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md)). Grow big populations, select the males too, and test-grow before release; the same standards as any line (see [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md)). ## Common mistakes - Expecting F1 autos. - Releasing a "stable auto" that throws photoperiod plants (incomplete fixation or a second photoperiod source). - Crossing two auto lines of unknown origin and getting photoperiod offspring (possible if mechanisms differ) [1]. ## Evidence - Recessive single-locus inheritance in mapped populations: *Supported* [1][2]. - Universality across auto sources: *Contested* [1]. - Backcross arithmetic: *Established* [3]. - Incomplete dominance of the photoperiod allele (dosage affects flowering time): *Supported* [5]. - Linkage drag from an unimproved donor as the reason early autos lagged: *Supported* as general breeding principle [7]; not measured directly for Autoflower1. - Modern autos testing slightly under photo sisters, the best matching them: founder's observation; no controlled comparison found. ## Sources 1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 2. Genetic mapping of SNP markers and candidate genes associated with day-neutral flowering in Cannabis sativa L. (preprint). bioRxiv 2023.04.17.537043. https://www.biorxiv.org/content/10.1101/2023.04.17.537043 3. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 4. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 5. Kurtz LE, Brand MH, Lubell-Brand JD. 2023. Gene dosage at the autoflowering locus effects flowering timing and plant height in triploid cannabis. Journal of the American Society for Horticultural Science 148(2):83-88. https://doi.org/10.21273/JASHS05293-23 6. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 7. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 8. Hillig KW. 2005. Genetic evidence for speciation in Cannabis (Cannabaceae). Genetic Resources and Crop Evolution 52:161-180. https://doi.org/10.1007/s10722-003-4452-y --- # Chemotype inheritance: how THC and CBD synthase alleles pass on > Whether a plant is THC dominant, CBD dominant or mixed is controlled mainly by a single inheritance block carrying THCA synthase and CBDA synthase genes, which behaves close to codominant: THC x CBD gives mixed (type II) F1s and a 1:2:1 split in the F2. CBG-dominant and cannabinoid-free types come from non-functional synthase alleles. Total cannabinoid amount is a separate, quantitative trait. - Canonical: https://genetixbay.com/knowledge/breeding/chemotype-inheritance.html - Category: Breeding · Level: Breeder - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **If I cross a THC plant with a CBD plant what do I get?** Crossing a THC-dominant cannabis plant with a CBD-dominant one gives mixed chemotype II F1 offspring, roughly 1:1 to 1:2 THC:CBD, when both parents are homozygous. Any pure THC or pure CBD plant in the F1 means a parent wasn't homozygous. Intercrossing those mixed F1s gives about 1 THC : 2 mixed : 1 CBD in the F2. **How is the THC to CBD ratio inherited?** The THC to CBD ratio in cannabis is inherited as one block, close to codominant. The THCA synthase and CBDA synthase genes are separate but tightly linked in low-recombination regions, so they pass on together like a single locus with two alleles. Research models this as B_T and B_D: two copies of either give a pure type, one of each gives mixed. **What are chemotypes I, II, III, IV and V?** Cannabis chemotypes are classes by cannabinoid profile. Type I is THC-dominant (THC:CBD above about 10:1), type II is mixed (about 0.5:1 to 3:1), type III is CBD-dominant (CBD:THC above about 10:1), type IV is CBG-dominant from non-functional synthase alleles, and type V has only trace cannabinoids because the pathway is blocked upstream. Boundaries vary between studies. **Can a 1:1 THC:CBD plant breed true?** No, a 1:1 THC:CBD cannabis plant cannot breed true. Mixed chemotype II plants are heterozygous, carrying one THC synthase and one CBD synthase allele, so their seed segregates about 25% THC-dominant, 50% mixed and 25% CBD-dominant. Keep a 1:1 cultivar as a clone, or remake it each time by crossing pure THC and pure CBD parents. **How are CBG-dominant plants made?** CBG-dominant cannabis (chemotype IV) is made by breeding plants homozygous for non-functional THCA and CBDA synthase alleles. With neither enzyme working, the precursor CBGA builds up instead of being converted. Research shows these null alleles inherit predictably, so once a line is homozygous for them it breeds true for the CBG-dominant chemotype. **Can I predict THC percentage from genetics?** Genetics can predict a cannabis plant's chemotype class but not its THC percentage. Which synthase a plant carries sets the THC:CBD ratio, while total cannabinoid amount is a separate many-gene quantitative trait that is sensitive to environment and lab. Seedling DNA or leaf tests predict class well; select for potency only from repeated flower tests at the same stage and lab. **Short answer.** CBGA is the shared precursor; a THCA synthase turns it into THCA and a CBDA synthase into CBDA. Which functional synthase a plant carries is inherited as one block, close to codominant. THC-dominant x CBD-dominant gives mixed F1s (roughly 1:1 to 1:2 THC:CBD); intercross those and you get about 1 THC : 2 mixed : 1 CBD. Mixed plants never breed true. How *much* total cannabinoid a plant makes is a separate, many-gene trait. ## What's happening - **The pathway.** CBGA sits at a fork. THCAS, CBDAS and CBCAS compete for it. If neither THCAS nor CBDAS works, CBGA builds up (chemotype IV) [2]. If CBGA itself is barely made (or trichome development fails), the plant is near cannabinoid-free (chemotype V) [8]. - **The 2003 model.** de Meijer et al. crossed inbred pure-THC and pure-CBD plants and explained the results with one locus, B, with codominant alleles B_T and B_D [1]. The F1 was uniformly mixed; F2s segregated 1:2:1. - **The genomic picture.** THCAS and CBDAS are separate but closely linked genes, sitting in large (>250 kb), retrotransposon-rich, low-recombination regions that differ structurally between drug and hemp types [3][4]. In practice they still inherit together, so the one-locus model predicts well, but "B_T" and "B_D" are really haplotypes (gene blocks), not single genes. Non-functional copies and gene duplications exist [3]. - **CBD in drug-type lines** often traces to hemp introgressed into marijuana backgrounds [5] (*Supported*). ## Chemotypes | Chemotype | Typical ratio | Inferred synthase genotype | Breeds true? | |---|---|---|---| | I, THC dominant | THC:CBD > ~10:1 (often far higher) | B_T / B_T | Yes, for chemotype | | II, mixed | ~0.5:1 to 3:1 | B_T / B_D | No: segregates 1:2:1 | | III, CBD dominant | CBD:THC > ~10:1 (hemp lines often 20-30:1) | B_D / B_D | Yes, for chemotype | | IV, CBG dominant | High CBG, low THC and CBD | Null (non-functional) synthase alleles, homozygous [2] | Yes, once homozygous | | V, near zero | Trace cannabinoids | Pathway blocked upstream [8] | Yes | Ratio boundaries are approximate and vary between studies [1][6]. Note: "CBD dominant" plants still make some THC; even good hemp lines show THC:CBD ratios around 1:20 to 1:30 because CBDAS itself makes a little THCA. ## Punnett square: THC x CBD F1 (B_T/B_D) x F1 (B_T/B_D): | | B_T | B_D | |---|---|---| | **B_T** | I (THC) | II (mixed) | | **B_D** | II (mixed) | III (CBD) | Backcross F1 (B_T/B_D) to the CBD parent (B_D/B_D): 1 mixed : 1 CBD. Two backcrosses with selection for type III recover a CBD-dominant line with the THC parent's other traits partly kept. ## Step by step: breeding a stable CBD-dominant line 1. Cross your THC-dominant selection (female) with a stable CBD-dominant male. 2. Grow F1s; all should be type II. Any type I or III F1 means a parent wasn't homozygous. 3. Choose the best F1 (or backcross to the CBD parent). 4. In the F2 or BX1, **screen seedlings with a chemotype DNA marker** if available [7], or test a leaf or flower sample by chromatography. 5. Keep only type III plants; select among them for the traits you want. 6. Confirm the ratio with flower tests (same stage, same lab) on several plants of the final line. ## Numbers that matter | Population | Expected chemotype split | |---|---| | I x III (both homozygous) | 100% II | | II x II | 25% I : 50% II : 25% III | | II x III | 50% II : 50% III | | II x I | 50% I : 50% II | | Plants needed for 95% chance of ≥1 type III in an F2 | 11 (p = 0.25) | | ...of ≥5 type III in an F2 | 34 (binomial, p = 0.25) | ## Common mistakes - Expecting a 1:1 cultivar to breed true. It is heterozygous by definition. - Selecting "high THC" from small, single-run lab results. Total THC is quantitative and environment- and lab-sensitive. - Assuming a seedling leaf test predicts the final ratio exactly. It predicts chemotype class well; ratios shift through flowering (*Supported*). - Forgetting legal limits: in hemp jurisdictions, total THC limits apply to the crop, and type II segregants can exceed them. ## Evidence - Single inheritance unit, codominant model: *Established* [1], refined by genomics [3][4]. - CBG-dominant inheritance via null alleles: *Established* [2]. - Chemotype markers for seedling screening: *Supported* [7]; marker performance may vary by germplasm. - Hemp introgression as a CBD source in drug-type lines: *Supported* [5]. ## Sources 1. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 2. de Meijer EPM, Hammond KM. 2005. The inheritance of chemical phenotype in Cannabis sativa L. (II): Cannabigerol predominant plants. Euphytica 145:189-198. https://doi.org/10.1007/s10681-005-1164-8 3. Weiblen GD, Wenger JP, Craft KJ, et al. 2015. Gene duplication and divergence affecting drug content in Cannabis sativa. New Phytologist 208(4):1241-1250. https://doi.org/10.1111/nph.13562 4. Laverty KU, Stout JM, Sullivan MJ, et al. 2019. A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci. Genome Research 29(1):146-156. https://doi.org/10.1101/gr.242594.118 5. Grassa CJ, Weiblen GD, Wenger JP, et al. 2021. A new Cannabis genome assembly associates elevated cannabidiol (CBD) with hemp introgressed into marijuana. New Phytologist 230(4):1665-1679. https://doi.org/10.1111/nph.17243 6. Hillig KW, Mahlberg PG. 2004. A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae). American Journal of Botany 91(6):966-975. https://doi.org/10.3732/ajb.91.6.966 7. de Meijer EPM, Hammond KM, Sutton A. 2009. The inheritance of chemical phenotype in Cannabis sativa L. (IV): cannabinoid-free plants. Euphytica 168:95-112. https://doi.org/10.1007/s10681-009-9894-7 8. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 --- # Clone-only cuts and how to preserve them > A clone-only is one selected genotype kept alive by cuttings. It can be lost to pests, disease, hop latent viroid (HLVd) or accident, and it accumulates rare somatic mutations, which are not the same thing as a loss. Cuts from different parts of a plant can also behave differently (topophysis), so take them from consistent locations. Preserve it with clean, tested mothers in at least two locations, regular fresh cuttings, a tissue-culture backup where possible, and seed (S1s or crosses) as genetic insurance, not as a copy. - Canonical: https://genetixbay.com/knowledge/breeding/clone-only-preservation.html - Category: Breeding · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is a clone-only strain?** A clone-only strain is a single cannabis genotype that exists only as cuttings from one original selection, so losing the last plant loses it forever. Seed made from it preserves its alleles but not the plant itself. Copies passed between growers are supposed to be the same genotype, but mislabelled cuts are common and only a DNA comparison settles it. **How do I keep a mother plant long-term?** To keep a cannabis mother long-term, refresh it every 6-12 months from rooted cuttings of a healthy mother, keep at least two mothers in separate places, test for HLVd and quarantine anything new for 2-3 weeks. Grower practice also keeps a slow-growing backup clone line at about 18-22 °C under low light, around 100-200 µmol/m²/s PPFD. **Do clones degrade over time (genetic drift)?** No, cannabis clones don't degrade from genetic drift. The GenetixBay position is zero genetic drift in a well-kept cut apart from pathogens such as HLVd. Somatic mutations are measurable by sequencing, but no study links them to the decline growers describe. The founder keeps cuts over 40 years old with no decline. Test a 'weak' old cut for HLVd first. **Is clone decline real?** Clone decline is real as a symptom but not as ageing. When an old cannabis cut loses vigour, the cause is a pathogen, above all hop latent viroid, which reduces flower mass, trichomes, cannabinoids and terpenes, often without obvious symptoms. The idea that age wears out the genetics is a myth. Clean, tested stock shows no decline. **What is hop latent viroid and how do I keep it out?** Hop latent viroid (HLVd) is a pathogen that reduces cannabis flower mass, trichomes, cannabinoids and terpenes, often with no obvious symptoms. It spreads through infected cuttings, tools and sap. Keep it out with tested-clean stock, a 2-3 week quarantine with an RT-qPCR test, and strict tool hygiene: ethanol and peroxide disinfectants were reported ineffective, so use bleach-based products or single-use blades. **How can I back up a clone?** Back up a cannabis clone by keeping two clean mothers in two locations, holding a slow-growing clone line as a living spare, and banking the genotype in tissue culture, where meristem culture also helps clean infected stock. As extra insurance, make honestly labelled S1s or crosses, which preserve the clone's genes for breeding if the plant itself is lost. **Is a clone-only from two different people the same plant?** A clone-only from two different people is not necessarily the same plant. Same-named cuts are often mislabelled or swapped along the way, and only a DNA fingerprint comparison proves two cuts are one genotype. Ask for the cut's written history (who, when, from where) and record it with its evidence level so the chain of custody stays visible. **Why do clones from the same mother grow differently?** Clones from the same mother can grow differently because of position effects, called topophysis: a cutting can 'remember' whether it came from a vigorous leader or a shaded lower branch. This is a physiological carry-over and may or may not involve mutation. Pathogens such as HLVd, and differences in how cuts are rooted and grown, also cause differences. **Where on the mother should I take cuttings?** Take cannabis cuttings from consistent locations on the mother: healthy, vigorous upper-to-mid shoots of similar age. Avoid the oldest, most stressed or shaded lower branches. One cannabis study found apical versus basal origin barely changed rooting, but consistent sourcing means a clone that grows differently actually tells you something. Log where each cut came from. **Short answer.** A clone-only exists as one genotype, so losing the last plant loses it forever. Keep at least two clean mothers in two places, refresh mothers from young cuttings, test for HLVd, quarantine anything new, and bank the genotype in tissue culture if you can. Seed made from it preserves its alleles, not the plant itself. ## What's happening - **Identity.** A clone is genetically the same as its source, except for rare new mutations. "Clone-only" names refer to one original selection; copies passed between people are supposed to be that genotype. Often they are not: mislabelled cuts are common, and only a DNA comparison settles it (see [genotyping](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md)). - **"Clone decline".** Growers report old cuts losing vigour. The real cause is **pathogens**, above all **HLVd**, which reduces flower mass, trichomes, cannabinoids and terpenes, often without obvious symptoms [1][2][5]. Age "wearing out the genetics" is a *Myth*. - **Somatic mutations.** DNA studies do find small numbers of new mutations accumulating in different parts of a plant and its clones [3]. That is measurable at the sequence level, but **a mutation doesn't mean a loss**: most change nothing you can see, the odd one could even help (that's how bud sports are found), and no study has linked them to the performance decline growers describe. The founder's decades-old cuts show none. Keep refreshing mothers from good cuttings anyway; it's cheap insurance. - **Position effects (topophysis).** Cuts taken from different parts of the same plant can behave differently for a while: a cutting "remembers" whether it came from a vigorous leader or a shaded lower side branch. Horticulture calls this **topophysis**; it was described in conifer cuttings, where side-branch cuttings kept growing like branches [6]. It is a physiological carry-over, and it **may or may not be mutation**: the genomic study above found that somatic mutations differ between branches of one plant [3], so a cut can differ for either reason. In cannabis, one controlled study found that apical vs basal origin made little difference to *rooting* [7]; whether position affects later vigour, structure or chemistry hasn't been tested. The practical rule: **take cuts from consistent locations** (healthy, vigorous upper-to-mid shoots of similar age), so that a "different" clone actually means something. > **House position: no clone decline without a pathogen.** Apart from pathogens (HLVd and the like), there is zero genetic drift in a well-kept cut. The founder keeps cuts more than 40 years old, and seed stock from roughly 50–70 years ago, with no decline; cannabinoid content keeps improving as cultivation technique improves. If an old cut "got weak", test it for HLVd before you blame its age. ## Threats and controls | Threat | How it arrives | Prevention | Detection | |---|---|---|---| | HLVd | Infected cuttings, contaminated tools, sap; not shown to spread by sap-feeding insects [1] | Tested-clean stock; tool hygiene; quarantine | RT-qPCR test of roots/leaves | | Spider mites, broad/russet mites, thrips, aphids | Cuttings, clothing, other plants | Quarantine 2-3 weeks, dips, IPM | Weekly loupe inspection | | Powdery mildew | Spores on cuttings and air | Quarantine, airflow, RH control | Visual | | Root rot (Pythium, Fusarium) | Water, media | Clean water and media | Roots and wilt | | Somatic mutation | Rare, measurable by sequencing; not a loss as such; no shown effect on performance | Refresh mothers from the clone's best-performing cuttings; keep tissue culture backup | Performance records, sequencing | | Position effect (topophysis) | Cuts from shaded lower branches vs vigorous leaders | Take cuts from consistent locations; log where each came from | Side-by-side records | | Accident | Power, heat, people | Two locations | n/a | HLVd is hard to kill: ethanol, peroxide-based and some oxidising disinfectants were reported ineffective, and autoclaving did not inactivate it [1]. Use bleach-based or validated products and single-use blades for high-value work [2]. ## Step by step: a preservation plan 1. **Verify identity.** Get the cut's history in writing (who, when, from where) and, ideally, a genotype fingerprint. Record it as a GB-CUT with its claims and evidence level. 2. **Quarantine** in a separate space for 2-3 weeks: inspect, treat, and test for HLVd before it meets your mothers. 3. **Keep two mothers** in separate rooms or with a trusted partner where sharing is legal. 4. **Refresh mothers every 6-12 months** from rooted cuttings of a healthy mother (*Grower practice*). Take every cut from the same kind of location (vigorous upper-to-mid shoots) and note it in the log. 5. **Keep a small clone line** in a cool, low-light "slow" space (e.g., 18-22 °C, low PPFD ~100-200 µmol/m²/s) as a living backup (*Grower practice*). 6. **Tissue culture backup** for important cuts: meristem culture combined with testing is a route to clean stock and long-term storage [4]. See [tissue culture basics](https://genetixbay.com/knowledge/breeding/tissue-culture-basics.md). 7. **Seed insurance.** Make S1s or crosses; they preserve the genes for breeding if the clone is lost. Label them honestly. 8. **Log** every transfer and test as an event, so the chain of custody stays visible. ## Common mistakes - One mother, one room. - Trusting "it came from the original" without documentation. - Assuming a healthy-looking mother is viroid-free. - Taking cuttings from the most stressed, oldest branches. - Taking cuts from random spots, then blaming the genetics (or "decline") when they grow differently. - Treating every mutation as a loss: a sport can be neutral, or even a new selection. ## Evidence - HLVd impact and transmission through cuttings: *Established* [1][2][5]. - Clone decline without a pathogen: *Myth* (house position; founder's 40+-year cuts and 50–70-year seed stock). - Somatic mutations detectable within plants: *Supported* (one genomic study) [3]; effect on performance not shown, and a mutation is not a loss. - Topophysis (position effects in cuttings): *Established* in woody plants [6]; in cannabis, cutting position barely affected rooting [7] and later effects are untested. Taking cuts from consistent locations is *Grower practice* and house advice. - Tissue culture as backup and cleanup route: *Supported* [4]; protocol success is genotype dependent. - Mother refresh intervals and slow-growth backups: *Grower practice*. ## Sources 1. Adkar-Purushothama CR, Sano T, Perreault JP. 2023. Hop latent viroid: a hidden threat to the cannabis industry. Viruses 15(3):681. https://doi.org/10.3390/v15030681 2. Oregon State University Extension. Hop latent viroid in hemp (EM 9570). https://extension.oregonstate.edu/catalog/em-9570-hop-latent-viroid-hemp 3. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 4. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 5. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa): viroid diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases 6. Olesen PO. 1978. On cyclophysis and topophysis. Silvae Genetica 27(5):173-178. https://www.thuenen.de/media/institute/fg/PDF/Silvae_Genetica/1978/Vol._27_Heft_5/27_5_173.pdf 7. Caplan D, Stemeroff J, Dixon M, Zheng Y. 2018. Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science 98(5):1126-1132. https://doi.org/10.1139/cjps-2018-0038 --- # Collecting and storing cannabis pollen > Collect pollen from freshly opened sacs in still, clean air, sieve it, dry it briefly, and use it within days, or mix it with a dry carrier (baked flour), seal it with desiccant and freeze it. Cannabis pollen loses viability within about a week in a fridge; one study kept it viable for at least four months by mixing it 1:10 with baked flour, vacuum-drying and storing in liquid nitrogen. Home freezer storage is grower practice and should be germination tested. - Canonical: https://genetixbay.com/knowledge/breeding/pollen-collection-storage.html - Category: Breeding · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I collect cannabis pollen?** Collect cannabis pollen by isolating the male in a still, clean space and laying dry glossy paper under branches once the first sacs open, or standing cut branches in water over paper. After 12-24 hours, tap the branches and sieve through a fine mesh of about 100-150 µm. Surface-dry 1-3 hours without heat, then label it. **How long does cannabis pollen last?** Cannabis pollen lasts only hours to about 1-2 days in open air at room temperature, and days to about a week sealed and dry in a fridge at 2-6 °C, depending on the male's flowering stage. Research shows pollen dried with flour at 1:10 and held in liquid nitrogen kept viability for at least 4 months. **Can I freeze cannabis pollen?** Yes, cannabis pollen can be frozen if it is dried first. Mix it about 1:10 by weight with oven-dried flour, portion it into small sealed vials with silica gel, and freeze; never refreeze a portion. Home freezers weren't tested in the key study, so months-long survival is grower practice and variable. Always test before relying on it. **Why mix pollen with flour?** Mixing cannabis pollen with dry flour dilutes it for easier, more even application and helps buffer moisture during storage. In research, pollen mixed 1:10 with baked wheat flour, vacuum-dried and stored in liquid nitrogen showed no significant viability loss versus fresh-dried pollen after 4 months. Bake the flour at about 95-110 °C first and cool it fully. **How do I test if my pollen is still viable?** Test cannabis pollen viability by pollinating one tagged branch on a spare female and counting seeds 5-7 weeks later. For a faster lab check, dust pollen on a medium of 10% sucrose, 0.005% boric acid and 10 mM calcium chloride, keep it at about 22 °C in the dark, and look for pollen tubes under a microscope at 100-400x. **Short answer.** Fresh pollen is best. For use within a few days, keep it dry and cool in paper. For weeks to months, mix it with a dry carrier, seal it with desiccant and freeze it, then test a sample before you rely on it. Lab work shows cannabis pollen dies fast in a fridge and survives months only when dried and frozen properly [1]. > **House position.** Males are a necessity, and are encouraged and rewarded on GenetixBay; storing a selected male's pollen is how you keep his contribution. Selfing pollen from reversed females is mostly frowned upon (see [S1s and selfing](https://genetixbay.com/knowledge/breeding/s1-selfing.md)). ## What's happening Pollen is a living two-celled structure (cannabis pollen is bicellular) [1]. It dies from moisture, heat and time. Drying slows metabolism but drying too hard also kills it; freezing without drying ruptures cells. The carrier (flour) dilutes it for easier application and buffers moisture. ## What the research shows Gaudet et al. (2020) built a pollen germination assay for cannabis and tested storage [1]: | Finding | Detail | |---|---| | Developmental stage matters | Pollen from mid-flowering male stage (BBCH 64) kept viability longest | | Fridge storage (4 °C) | Most stages lost viability within 1 week; mid-stage pollen kept ~22% germination at 21 days | | Liquid nitrogen, untreated | Failed to germinate | | Liquid nitrogen with DMSO or glycerol | 0% after 24 h | | Flour 1:10 (pollen:flour, w/w), vacuum-dried 5 kPa for 40 min, then liquid nitrogen | No significant loss vs fresh-dried control after 4 months | | Drying alone | Cut germination by ~50% vs fresh | | Germination start | Within 30 minutes on medium | Home freezers (-18 to -20 °C) were **not** tested in that study. Grower reports of pollen surviving months to a year or more in a home freezer are *Grower practice*; results vary widely, so always test. ## Numbers that matter | Storage | Expected life | Evidence | |---|---|---| | Open air, room temperature | Hours to ~1-2 days | *Supported* [1] | | Sealed, dry, fridge 2-6 °C | Days to ~1 week, stage dependent | *Supported* [1] | | Dried, flour, desiccant, home freezer | Weeks to months, variable | *Grower practice* | | Dried, flour 1:10, liquid nitrogen | ≥4 months tested | *Supported* [1] | ## Step by step: collection 1. Isolate the male (or reversed female) in a still, clean space. 2. When the first sacs open, lay clean, dry glossy paper under the branches, or cut branches and stand them in water over paper. 3. After 12-24 h, tap the branches. Sieve through a fine mesh (about 100-150 µm, a tea strainer works) to remove anthers and debris (*Grower practice*). 4. Leave the pollen spread thin on paper for 1-3 hours at room temperature and low humidity to surface-dry. Avoid heat. 5. Label: source plant ID, date, stage. ## Step by step: home freezer storage 1. Bake plain flour at ~95-110 °C (200-230 °F) for about an hour to dry it; cool completely (*Grower practice*; the study used baked wheat flour [1]). 2. Mix pollen with flour about 1:10 by weight (the study ratio) [1]. 3. Put small portions in separate small vials or folded paper inside a sealed jar with a silica gel pack. 4. Freeze. Each portion is one use: **never refreeze**. 5. To use, let the sealed container reach room temperature before opening (about 30-60 min) so condensation doesn't wet the pollen. ## How to test viability - **Practical test:** pollinate one tagged branch on a spare female and count seeds 5-7 weeks later. - **Germination test:** dust pollen on a medium of 10% sucrose with 0.005% boric acid and 10 mM calcium chloride (simplified from [1]), incubate at ~22 °C in the dark, and look for pollen tubes under a microscope (100-400x). Germination began within 30 minutes and the study read results after 16 h [1]. ## Common mistakes - Collecting pollen near flowering females, or with fans running. - Storing pollen in plastic bags in the fridge for "later this season". - Thawing and refreezing the same vial. - Assuming pollen is good because it looks fine. Dead pollen looks the same. ## Evidence - Cannabis pollen storage and viability results: *Supported* (one well-designed lab study) [1]. - Home freezer protocols: *Grower practice*. - Pollen from reversed females behaves the same in use: *Supported* [3]. ## Sources 1. Gaudet D, Yadav NS, Sorokin A, Bilichak A, Kovalchuk I. 2020. Development and optimization of a germination assay and long-term storage for Cannabis sativa pollen. Plants 9(5):665. https://doi.org/10.3390/plants9050665 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 3. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 --- # Elite clone-only gatekeeping: why the classics live in a few hands > Many celebrated cultivars, from the Chem 91 and original OG Kush cuts to Pre-'98 Bubba Kush and old Skunk phenotypes, began as single plants and spread as cuttings through small circles. Published histories describe cuts passed only between friends, press reports put rare clone-only cuts at US$10,000 or more, and the classic Skunk aroma is described by veterans as gone from today's seed. The founder's view is that some holders keep cuts closed on purpose to control the gene pool. The public record documents the scarcity and the closed circles but can't show motive. A single garden is also a single point of failure: one HLVd infection or one bad summer can erase a cut. GenetixBay's answer is open preservation: GB-IDs, the Stud Book, preservation rewards and sharing in legal lanes. - Canonical: https://genetixbay.com/knowledge/breeding/elite-clone-gatekeeping.html - Category: Breeding · Level: Intermediate - Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is an elite clone-only cut?** An elite clone-only cut is one exceptional cannabis plant kept alive only as cuttings, so every copy is the same genotype. Because few drug-type lines breed true, growers keep a standout plant as a cut rather than trusting seed. Some 'clone-only' names also exist as seed crosses or S1s, so the label doesn't always mean truly seedless. **Why are some strains clone-only?** Some cannabis strains are clone-only because they began as one standout plant from a segregating seed batch, and seed from that plant would not reproduce it. Very few drug-type lines are true-breeding, so the only way to keep the exact plant is by cuttings. Many famous cultivars passed through a bottleneck of one plant or a few. **How much do elite cannabis clones cost?** Common cannabis clones sell for about US$5-10, and a 2025 survey of the hemp-legal clone market found most at US$20-100, with one breeder cut at US$600. Press reports put rare clone-only cuts at US$10,000 or more. Cut-for-cut trades are more common than sales; no checkable six-figure sale of a single cut has been published. **Is the original Skunk #1 lost?** The original Skunk phenotypes appear to be nearly lost, though Skunk #1 seed is still sold. Veteran breeders say the most pungent classic skunk aroma hasn't been seen in 15-20 years, and today's seed reportedly lacks the acidic, rotten smell. A revival hunt popped over 200 old seeds and kept 70 females and 20 males to try to recover it. **Where did the Chemdog and OG Kush cuts come from?** Published histories say the Chem 91 cut grew from a handful of seeds found in a bag in the early 1990s and spread when two growers swapped cuttings after meeting at a 1992 show. The original OG Kush was the one survivor of five small plants, shared first within a small circle of friends. Its link to Chem is less well substantiated. **Why won't people share rare cuts?** Rare cannabis cuts are often kept within small circles of trust, traded cut for cut rather than shared openly, and holders usually can't share without repercussions. The founder believes some hoard deliberately to control the gene pool; that is their view, and the public record documents scarcity and closed circles but cannot prove anyone's motive. **How can rare clones be preserved?** Rare cannabis clones are best preserved with copies in several places, HLVd testing and quarantine, tissue-culture backups and a documented record. Closed circles are a single point of failure: one viroid, fire or keeper quitting can end a line. GenetixBay gives each cut a GB-ID with history and tests, rewards preservation and encourages legal open sharing. **Can cannabis clones be frozen or stored in tissue culture?** Yes, cannabis clones can be held in tissue culture and frozen. Research shows shoot tips of elite cultivars can be stored in liquid nitrogen by droplet vitrification. A 2021 study froze nodal explants from 13 commercial genotypes; regrowth after thawing ranged from 26.7% to 66.7%, and regrown plants matched controls for most major traits. **Short answer.** A clone-only cut is one plant, kept alive as cuttings. Many of the most influential cuts in cannabis began as a single selection and spread hand to hand through small circles of growers [1][2][7]. The public record shows the scarcity: press reports put rare clone-only cuts at **US$10,000 or more** [5], published histories describe cuts shared only "within a small circle of friends" [2], and veterans say the classic Skunk aroma hasn't been seen in **15-20 years** [3]. Why holders keep cuts closed isn't something the record can show. The risk it creates is clear, though: one garden, one viroid, one bad summer, and a classic is gone. GenetixBay exists to change that. > **Founder's view (house position, round 7).** Elite clone-only gatekeeping is real, and it's part of why GenetixBay exists. Near-extinct classics, like the elusive original Skunk cuts, survive in very small elite circles as clone-only. They can cost five or six figures, or a cut traded the other way, and holders usually can't share without repercussions. The founder believes some do this deliberately: controlling the gene pool, hoarding the best and pushing out the poop. That last part is his view from decades inside the culture. The public accounts below document scarcity, closed circles and cut-for-cut trading. They don't, and can't, prove anyone's motive. We name plants here, never people. ## What "clone-only" means - **One genotype.** A seed is a new genetic individual; a cutting is a copy. A clone-only cultivar exists only as copies of one original plant (see [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md)). - **Why cuts beat seed for a keeper.** Very few drug-type lines are true-breeding, so seed from the same pack segregates. Growers keep the one exceptional plant as a cut: "cloning guarantees the preservation of your genetics" [14]. - **Not always truly seedless.** Some "clone-only" names also exist as seed (crosses, S1s), and forum histories argue about which cuts were ever really seedless [7]. The name says "only one plant"; the market sometimes says otherwise. ## The public record: famous cuts and how they spread | Cut | What published histories say | Source | |---|---|---| | **Chem 91** and its sisters | Grown from a handful of seeds out of a bag in the early 1990s. The "Chem 91" became "the most desirable cut". Cuttings were exchanged between two growers after they met at a 1992 show and found they "both had the fire". Its link to OG Kush is "less easily substantiated" | High Times 2016 [1] | | **Original OG Kush** | Of five small plants that travelled west, "only one survived". That cut was "the original, clone-only OG Kush plant", first shared within a small circle of friends; later OGs spread mainly through seeds found in bags | Leafly 2024 [2] | | **Pre-'98 Bubba Kush** | Enthusiasts use "Pre-'98" to mark the original clone apart from later, diluted versions; commercial growers say it's hard to justify commercially because it yields less | Westword 2016 [4] | | **Old Skunk phenotypes** | Breeders interviewed say they haven't had the original flavour in over 20 years, and the most pungent Afghan-type skunk hasn't been seen in 15-20 years. Today's Skunk #1 seed "doesn't have the acidic, rotten smell". A revival hunt popped over 200 old seeds and kept 70 females and 20 males for clone and breeding projects | High Times 2022 [3] | Two things stand out. First, each of these lines passed through a **bottleneck of one plant or a few**. Second, that one plant then lived in **a few gardens**, spread by personal trust, not by any public record. That is the gatekeeping pattern in its plainest form, whatever the motives. ## What elite cuts cost - A major strain directory notes common clones sell for about **US$5-10**, while "exotic, clone-only rarities can go for as much as **$10,000 or more**" [5]. - A 2025 magazine survey of the hemp-legal clone market found most clones at **US$20-100**; a breeder cut of one popular cultivar listed at **US$600**; and one listing at **US$420,000**, which the seller called "a little bit of a joke" [6]. Treat that last figure as a stunt, not a market price. - Forum histories describe four-figure prices for clone-only cuts and, more often, **cut-for-cut trades** rather than sales [7]. ## Why closed circles are dangerous for the gene pool Whatever the reason a cut is kept close, a closed circle is a single point of failure. - **HLVd moves with cuttings.** Hop latent viroid spreads mainly through infected cuttings and tools, often without obvious symptoms [9][10]. One commercial survey reported HLVd at about **90 %** of California facilities tested [9]; in Canada, about **26 %** of nearly 16,000 plant samples sent to a diagnostic lab from 2020 to 2022 tested positive [10]. A cut passed around a small network can carry the viroid to every copy that exists. See [HLVd](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). - **Fewer copies, fewer chances.** Fire, theft, power failure, a mite outbreak or the keeper simply quitting can end a line that has no backup outside the circle. - **Names drift when records don't exist.** Same-named cuts from different sources are often genetically different [8]. Without a documented chain of custody, a lost cut gets "replaced" by something else under the same name (see [same cut, a thousand names](https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.md)). That is one route to [everything tasting the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md). ## Preservation that doesn't depend on trust - **Tissue culture** lets a cut be held clean, small and slow-growing, and meristem culture is a recognised route to cleaning up infected stock [11]. See [tissue culture basics](https://genetixbay.com/knowledge/breeding/tissue-culture-basics.md). - **Cryopreservation works for cannabis.** Shoot tips of elite cultivars have been stored in liquid nitrogen by droplet vitrification [12]. A 2021 study froze nodal explants from **13 commercial genotypes**; regrowth after thawing ranged from **26.7 % to 66.7 %**, and regrown plants were similar to controls for most major traits [13]. The authors' stated reason: "it is important to develop methods to preserve the genetic integrity of elite genetics" [13]. - **Seed as insurance.** Crosses or S1s preserve alleles, not the plant itself, but they're far better than nothing once a cut is gone. ## GenetixBay's answer - **GB-ID for every cut.** A GB-CUT record holds the cut's claimed history, its evidence level, who holds it, and its HLVd and genotype tests. A cut with a record can be traced; a cut with only a name can't (see [documenting lineage](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md)). - **Preservation rewards.** Registering and custodian-verifying holdings of a Wanted line, germination-testing vault seed, and journalling a revival grow against the historic description all earn Pearls. Vault cuts and seeds are never sold for Pearls; they're gifted by merit through lawful lanes. - **The Stud Book.** Clone-only culture is almost all females. The Stud Book showcases documented males with selection journals and sire credits, so the next generation of classics isn't locked inside one female's garden. - **Open sharing, where legal.** Lines registered, described and shared in legal lanes stay in the commons. Sharing a cut is credited, not punished. ## Common mistakes - Paying a premium for a famous name with no chain of custody or genotype. - Bringing a "rare" cut straight into your mother room without quarantine and an HLVd test. - Keeping your only copy of an irreplaceable cut in one room. - Assuming a cut is lost because you can't buy it. Ask, document, and register a Wanted line. ## Evidence - Famous cultivars began as single plants and spread as cuttings through small circles: *Supported* by consistent published histories [1][2][4], though details are disputed in each. - Rare clone-only cuts selling for US$10,000 or more: *Supported* by press reports [5]; six-figure sales: not documented publicly. - Loss of the classic Skunk aroma from today's seed: *Grower practice* (veteran testimony) [3]. - Cut-for-cut trading and closed circles: *Grower practice*, documented in forum histories and press [1][2][7]. - Deliberate hoarding to control the gene pool: founder's view; *not measurable* from the public record. - HLVd spread through cuttings: *Established* [9][10]. Tissue culture and cryopreservation as backup: *Supported* [11][12][13]. ## Sources 1. High Times. 2016. 25 years of Chem Dog. https://hightimes.com/?p=160919 2. Leafly. 2024. An epoch of OG: the OG Kush family genealogy. https://www.leafly.com/news/strains-products/og-kush-marijuana-family-strains-appreciation 3. High Times. 2022. The great Skunk hunt. https://hightimes.com/?p=290983 4. Westword. 2016. Why Colorado tokers love Bubba Kush. https://www.westword.com/news/why-colorado-tokers-love-bubba-kush-8234691 5. Leafly. 2026. Where to buy weed clones online. https://www.leafly.ca/wp-home/?p=233048 6. Leaf Magazine. 2025. Fire follower: hemp legalization turbocharges the clone scene. https://leafmagazines.com/culture/fire-follower-hemp-legalization-turbocharges-the-clone-scene/ 7. THCFarmer forum. 2010-2011. Clone only strains thread. https://www.thcfarmer.com/threads/clone-only-strains-clones.24696/ 8. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 9. Adkar-Purushothama CR, Sano T, Perreault JP. 2023. Hop latent viroid: a hidden threat to the cannabis industry. Viruses 15(3):681. https://doi.org/10.3390/v15030681 10. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa): viroid diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases 11. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 12. Uchendu EE, Lata H, Chandra S, Khan IA, ElSohly MA. 2019. Cryopreservation of shoot tips of elite cultivars of Cannabis sativa L. by droplet vitrification. Medical Cannabis and Cannabinoids 2(1):29-34. https://doi.org/10.1159/000496869 13. Downey CD, Golenia G, Boudko EA, Jones AMP. 2021. Cryopreservation of 13 commercial Cannabis sativa genotypes using in vitro nodal explants. Plants 10(9):1794. https://doi.org/10.3390/plants10091794 14. PBS Independent Lens. 2017. Growing industry: why weed seeds are giving way to pot clones. https://www.pbs.org/independentlens/blog/growing-industry-weed-seeds-giving-way-pot-clones/ --- # F1, F2, F3 explained: what filial generations really mean > An F1 is the first generation from two parents; it is uniform only if both parents were true-breeding (inbred). An F2 comes from crossing F1 siblings and shows the most variation. Each later generation of sib-mating with selection increases uniformity slowly. In cannabis, most 'F1 hybrids' are crosses of heterozygous clones, so they behave like segregating F2s. - Canonical: https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.html - Category: Breeding · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What does F1 mean on a seed pack?** F1 on a cannabis seed pack means the first generation from crossing parent A with parent B. It says nothing about uniformity unless both parents were inbred. Most cannabis F1s are crosses of two heterozygous clones, which segregate like an F2 at many genes, so one pack can show several distinct phenotypes. **Why are my F1 plants not uniform?** Cannabis F1 plants are usually not uniform because the parents were heterozygous clones, not inbred lines. Uniform F1 hybrids, as in maize, come only from two homozygous parents that each pass on identical gametes. Elite cannabis clones are highly heterozygous polyhybrids, so each makes many different gametes and the F1 varies from the first generation. **Why are F2 seeds so variable?** F2 cannabis seeds are variable because every gene that differed between the original parents segregates 1:2:1 in the F2, so variation is at its maximum. With just 10 differing genes there are 3 to the power of 10, or 59,049, genotype combinations. That makes the F2 the worst generation for uniformity but the best for finding new combinations. **How many generations to make a stable strain?** Making a stable cannabis strain usually takes many generations, and the count alone proves nothing. With full-sib mating, heterozygosity falls by only about 19% per generation, leaving about 41% after four generations and 27% after six; selfing halves it each time. Judge stability by measured uniformity in grow-outs, and avoid bottlenecking to one pair each generation. **Is an F2 the same as an S1?** No, an F2 is not the same as an S1. An F2 crosses two F1 siblings, while an S1 is a single plant pollinated by itself, usually after reversal. Selfing halves heterozygosity in one generation, so an S1 reveals recessive traits faster and is more inbred, whereas a sib-mated F2 keeps more diversity and maximum segregation. **Short answer.** F1 = parent A x parent B. F2 = F1 x F1 (siblings, in cannabis). F3 = F2 x F2, and so on. The textbook promise ("F1s are uniform") holds only when both parents are inbred. Cross two heterozygous clones, which is what most cannabis "F1s" are, and you get variation from the first generation. ## What's happening ### The textbook case (inbred parents) - P1 is AA BB CC..., P2 is aa bb cc... (both homozygous). - **F1** is Aa Bb Cc... at every differing gene: genetically identical siblings, uniform, often vigorous (hybrid vigour) [2]. - **F2**: each gene segregates 1:2:1, so variation is maximal. With 10 differing genes there are 3^10 = 59,049 genotype combinations [1]. - **F3 and later**: with sibling mating and selection, heterozygosity falls and families become more uniform. ### The cannabis case (heterozygous parents) Most elite cannabis clones are highly heterozygous polyhybrids [5]. Crossing two of them is genetically like an F2 at many genes: the "F1" segregates. That's why one pack of "F1 hybrid" seed can show several distinct phenotypes. Calling it F1 is correct by definition (first generation of that cross) but misleading about uniformity. ## How fast does heterozygosity fall? | Mating system | Heterozygosity left after each generation | After 4 generations | After 6 generations | |---|---|---|---| | Selfing (S1, S2...) | x ½ | ~6% | ~1.6% | | Full-sib mating | H(t) = ½H(t-1) + ¼H(t-2); tends to x 0.81 per generation | ~41% | ~27% | | Random mating in a large population | ~no change | | | Values are single-locus expectations starting from unrelated parents [2]; selection and linkage change them in practice. The point: sib-mated cannabis lines take many generations to approach true breeding, and "F5 IBL" says more about effort than about measured uniformity. ## Worked example: chemotype in F1 and F2 THC-dominant inbred (B_T/B_T) x CBD-dominant inbred (B_D/B_D) [3]: - F1: all B_T/B_D, all mixed type II. Uniform for chemotype. - F2: 1 type I : 2 type II : 1 type III. - F3 from a type III F2 pair: all type III. Fixed for that trait. Note that being fixed for chemotype says nothing about the other few thousand genes. ## Naming conventions | Label | Meaning | Uniformity to expect | |---|---|---| | F1 (inbred parents) | Uniform hybrid | High | | F1 (clone x clone) | First cross of two heterozygous plants | Low to moderate | | F2 | F1 sibling cross | Lowest; best for finding new combinations | | F3-F6 | Further sib generations with selection | Rising | | BX1, BX2 | Backcrosses to one parent | Moving towards the recurrent parent | | S1 | Selfed | Variable; reveals recessives | | IBL | "Inbred line", undefined generation count | Claim; check data | ## Step by step: making F2s that mean something 1. Grow out at least 10-20 F1s (both sexes for regular seed). 2. Select the best female and the best 1-3 males (by progeny tests if you can). 3. Make the F2 cross and record parents as GB-IND IDs, not just the line name. 4. Grow a large F2 (see [pheno hunting](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) for numbers) and select. 5. Advance by crossing selected F2 siblings; to stabilise, keep the population from bottlenecking to a single pair every generation (inbreeding depression) [4]. ## Common mistakes - Expecting uniform F1s from two clone-only parents. - Selling F2s as if they were stable. They are the opposite. - Making every generation from one male and one female. That is close to selfing in its inbreeding effect, without the planning. ## Evidence - Segregation, F1 uniformity from inbred parents, F2 variability: *Established* [1][2]. - Heterozygosity of commercial cannabis: *Supported* [5]. - Chemotype example: *Established* [3]. - Inbreeding effects of narrow sib-mating: *Established* in general plant genetics [4]. ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 2. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 3. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 4. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 5. Lynch RC, Vergara D, Tittes S, et al. 2016. Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences 35(5-6):349-363. https://doi.org/10.1080/07352689.2016.1265363 --- # Feminised seed and sex reversal: methods, with safety notes > Feminised seed is made by forcing a genetic female to grow male flowers, then using that pollen on another (or the same) female. Silver ions block ethylene action; silver thiosulfate (STS) sprayed at about 3 mM silver was the most effective treatment in a controlled hemp study, and colloidal silver also works. Silver compounds are hazardous: wear gloves and eye protection, never consume treated plants, and dispose of waste as hazardous. Careless feminising (unproven donors, stress-herm pollen) is a main source of herm-prone seed; reverse only females proven stable over at least two runs. - Canonical: https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.html - Category: Breeding · Level: Breeder - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Transition, Flower · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How are feminised seeds made?** Feminised cannabis seeds are made by spraying a genetic female, or one branch, with silver thiosulfate or colloidal silver before and into early flower. Silver blocks ethylene, so the plant grows male flowers that shed fertile pollen carrying only X chromosomes. That pollen fertilises an untreated female, and nearly all the resulting seeds are female. **How do I make silver thiosulfate for reversing cannabis?** For 1 litre of about 3 mM silver STS at a 1:4 molar ratio, dissolve 0.51 g silver nitrate in 500 mL distilled water and 2.98 g sodium thiosulfate pentahydrate in another 500 mL. Pour the silver solution slowly into the thiosulfate while stirring; it should stay clear. Use gloves, goggles and a respirator, and dispose of waste as hazardous. **Colloidal silver or STS for feminised seeds?** STS is the more effective choice for feminised cannabis seed: a 3 mM silver thiosulfate spray applied three times, a week apart, worked best on all four hemp cultivars tested. Colloidal silver also produces fertile pollen but is less potent per spray and needs repeated, often daily, applications. Both are silver hazards; gibberellic acid is less consistent. **When should I spray STS?** Spray STS on cannabis to runoff three times, 7 days apart, starting a few days before or at the flip to 12/12, which is grower practice. Spraying too late fails because existing female flowers won't convert. Male flowers usually appear about 2-3 weeks after the flip and open about 4-6 weeks after it. **Is reversed pollen safe? Can I smoke a reversed plant?** Never smoke or consume a cannabis plant treated with silver, because silver accumulates in its tissue; destroy it once its pollen is collected. The pollen itself is used only to make seed, and the plants grown from that seed are never sprayed. Handle silver nitrate as a corrosive chemical and dispose of treated material as hazardous waste. **Why do some feminised seeds turn out hermaphrodite?** Feminised seeds turn out hermaphrodite mainly because of careless feminising, the GenetixBay breeder position. Reversing a female that wasn't proven sex-stable, or using pollen from a plant that hermed under stress, passes that intersex tendency into every seed. Reverse only females that ran fully female for at least two cycles, and grow out every batch to record its herm rate. **Short answer.** Spray a genetic female (or one branch of it) with silver thiosulfate or colloidal silver before and into early flower; it grows male flowers that shed fertile pollen. That pollen carries only X chromosomes, so seeds it makes are nearly all female [2][4]. Lubell and Brand found 3 mM STS, sprayed to runoff three times a week apart, the most effective treatment on four hemp cultivars [1]. Treat silver compounds as hazardous chemicals. Feminised seed is only as stable as the donor you reverse: careless feminising is one of the main ways herm-prone lines reach growers. > **Breeder's standard.** Reverse only a female that has run fully female for at least two cycles under normal conditions, using controlled reversal, never pollen from a plant that hermed by itself. Grow out a sample of every batch, cull and record intersex plants, disclose the herm rate, and don't release a batch from a line that herms. See [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). **Legal first.** Making seed may need a licence where you live, and chemical use on plants can be regulated. Check local rules. ## What's happening Ethylene promotes female flower development in cannabis. Silver ions (Ag⁺) block ethylene receptors, so new flowers develop as male [3]. Silver thiosulfate (STS) carries silver into the plant more effectively than silver nitrate, which is why STS outperformed silver nitrate in early work [3]. Gibberellic acid can also induce male flowers but is less consistent (*Supported*) [2]. The plant is still genetically XX. Its pollen is X-bearing, so any seed is XX (female), barring rare exceptions [4]. ## Method comparison | Method | Typical use | Effectiveness | Notes | |---|---|---|---| | STS foliar spray | 3 mM silver, 1:4 silver nitrate:sodium thiosulfate (molar) [1] | High; 3 mM best for all four cultivars tested, 0.3 mM variable [1] | Industry standard; hazardous chemicals | | Colloidal silver spray | Repeated sprays, often daily | Effective; up to 379 male flowers per plant in [2] | Less potent per spray, more applications; still a silver hazard | | Gibberellic acid (GA3) | Spray | Lower and inconsistent [2] | Not recommended as primary method | | Stress-induced "rodelization" (letting a female self late in flower) | None | Unreliable | Selects directly for intersex tendency; never use for seed lines | ## Preparing STS (illustrative, matches the published ratio) To make **1 L** of approximately **3 mM silver** STS at a **1:4 molar ratio** [1][5]: | Component | Amount | Notes | |---|---|---| | Silver nitrate (AgNO₃, 169.87 g/mol) | 0.51 g (3 mmol) | Dissolve in 500 mL distilled water | | Sodium thiosulfate pentahydrate (Na₂S₂O₃·5H₂O, 248.18 g/mol) | 2.98 g (12 mmol) | Dissolve in 500 mL distilled water. If anhydrous (158.11 g/mol): 1.90 g | | Mixing | Pour the silver nitrate solution **slowly into** the thiosulfate solution while stirring | Reverse order can precipitate silver; a clear solution is correct | | Wetting agent | A few drops of non-ionic surfactant per litre | Optional | Use distilled or RO water only; tap water chlorides precipitate silver. Make fresh; store any stock in a dark bottle in a fridge and use within weeks (*Grower practice*). ## Step by step 1. **Choose the donor female.** Stable across at least two runs: no intersex flowers. Take a clone and reverse the clone (or one branch), not your only mother. 2. **Separate it.** Move it to a separate space once treated; it will shed pollen. 3. **Spray** to runoff (about 20 mL per small plant in [1]) on three occasions, 7 days apart. Growers commonly start a few days before or at the flip to 12/12 (*Grower practice*). Cover the medium to limit runoff into the pot. 4. **Wait.** Male flowers usually appear about 2-3 weeks after flip and open about 4-6 weeks after flip (*Grower practice*). 5. **Collect pollen** on paper under still air, sieve and use or store (see [pollen collection](https://genetixbay.com/knowledge/breeding/pollen-collection-storage.md)). 6. **Pollinate** an untreated female (for a feminised cross) or a clone of the same plant (for an S1). 7. **Destroy** the treated plant after pollen collection. 8. **Record** the batch as feminised in the GB-BAT and note the reversal method. ## Safety (read this before buying anything) - **Silver nitrate is corrosive and an oxidiser.** It causes serious eye damage and stains skin black-grey. Wear nitrile gloves, wrap-around goggles and long sleeves. Work away from food. Keep away from children and pets. - **Spraying makes an inhalable mist.** Wear at least a particulate respirator (FFP2/N95 or better) and spray in a ventilated area away from other plants. - **Never consume** flowers, leaves or extracts from a treated plant. Silver accumulates. - **Disposal.** Silver compounds are toxic to aquatic life. Do not pour leftovers or runoff down the drain or onto soil. Collect waste in a labelled container and take it to a hazardous waste facility, following local rules. - **First aid.** Eyes: rinse with water for at least 15 minutes and seek medical help. Skin: wash with soap and water. - Read and keep the supplier's safety data sheet (SDS). ## Common mistakes - Reversing a plant that already hermaphrodites. You'll sell that tendency in every pack. - Collecting "free" pollen from a stress herm instead of a controlled reversal. That is the pollen-chucker route to unstable feminised lines. - Releasing a feminised batch without a grow-out and a recorded herm rate. - Spraying too late in flower. Existing female flowers won't convert. - Tap water in the mix: cloudy solution, weak effect. - Labelling feminised seed as regular, or vice versa. DNA sex markers can check a sample of seedlings [6]. ## Evidence - STS induction of fertile male flowers, 3 mM most effective: *Established* (controlled studies) [1][3]. - Colloidal silver and STS for feminised seed, fertile pollen confirmed: *Established* [2]. - Hermaphrodite and reversed-female pollen gives female progeny: *Established* [2][4]. - Spray timing details: *Grower practice*. - Herm-prone feminised seed comes mainly from careless feminising (unproven donors, stress-herm pollen, no grow-out): GenetixBay house position (breeder experience). Well-selected, controlled-reversal feminised lines need not herm more than regular seed; controlled cannabis comparisons are limited. ## Sources 1. Lubell JD, Brand MH. 2018. Foliar sprays of silver thiosulfate produce male flowers on female hemp plants. HortTechnology 28(6):743-747. https://doi.org/10.21273/HORTTECH04188-18 2. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 3. Ram HYM, Sett R. 1982. Induction of fertile male flowers in genetically female Cannabis sativa plants by silver nitrate and silver thiosulphate anionic complex. Theoretical and Applied Genetics 62:369-375. https://doi.org/10.1007/BF00275107 4. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 5. USDA ARS. Silver thiosulfate (STS) solution preparation sheet. https://www.ars.usda.gov/ARSUSERFILES/80600500/HDM_DATA/Silver%20thiosulfate_STS_solution.pdf 6. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 --- # Genotyping: what a DNA test can and can't prove > A DNA test can reliably show whether two samples are the same genotype, rule out a claimed parent (exclusion), support a parent-child relationship when both parents are sampled, predict sex and chemotype class from seedlings, and place a plant on a map of genetic groups. It cannot prove a 40-year-old pedigree from a name, measure THC %, tell you a plant's 'indica percentage', or guarantee how it will grow. - Canonical: https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.html - Category: Breeding · Level: Breeder - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Can a DNA test prove my strain's lineage?** A DNA test can support a cannabis strain's lineage only when the claimed mother, the claimed father and several offspring are all sampled, and close relatives are ruled out. Without the parents, DNA can exclude a claimed parent but not confirm one. It cannot prove an old story attached to a name unless there is a documented reference sample to compare. **Can genetics tests tell if two clones are the same?** Yes, genetic tests can tell whether two cannabis clones are the same genotype, provided the lab reads enough markers. Thousands of SNPs give far better resolution than a handful of microsatellites. Expect tiny differences from somatic mutation and genotyping error, and ask the lab for its error rate and replicate data before trusting a match. **What does a cannabis genotype report show?** A cannabis genotype report shows the plant's readings at many DNA positions (SNPs or microsatellites) and how they compare with other samples, ideally as identity-by-state or kinship values. It can also report validated trait markers for sex, chemotype class and some flowering genes. A 'match' is only as good as the reference database behind it. **Can DNA tell me the THC percentage?** No, DNA cannot tell you a cannabis plant's THC percentage. Validated markers can usually predict chemotype class, meaning THC-dominant or CBD-dominant, but total cannabinoid content is a quantitative, many-gene trait that depends heavily on environment and on the testing lab. DNA also doesn't measure flavour or effect. **Is a sativa/indica percentage from a DNA test real?** A sativa/indica percentage from a DNA test is not meaningful ancestry. Genome-wide research found samples labelled 'indica' and 'sativa' were genetically indistinct. Such percentages only describe similarity to the lab's reference panel, and reference panels are biased towards commercial material, so '62% sativa' should not be read as a measure of where the plant came from. **What do I need for an L4 lineage confirmation?** An L4 lineage confirmation needs young leaf samples from the claimed female, the claimed male or reversed female, and at least 5 offspring, each labelled with GB-IDs and photographed at sampling. Send them with a chain-of-custody note for parentage or kinship analysis, then attach the report as a GB-DOC for a staff archivist to check. **Short answer.** DNA is excellent at **identity** (same plant or not), **exclusion** (this can't be the parent) and **trait markers** with proven links (sex, chemotype class, some flowering genes). It is weaker at **inclusion** without both parents sampled, and useless for proving an old story attached to a name. It does not measure potency, flavour or effect. ## What's happening A genotype test reads many DNA positions (SNPs or microsatellites) in a sample. Comparing those readings across samples answers questions about relatedness. Parentage logic is simple [1]: a child must carry one allele from each parent at every position. One consistent mismatch across many markers (allowing for error) excludes a parent; consistent matches support but don't prove parentage, because relatives of the true parent may also match. ## Can and can't | Question | Can a test answer it? | Notes | |---|---|---| | Are these two clones the same genotype? | **Yes**, with enough markers | Expect tiny differences from somatic mutation and genotyping error [7] | | Is plant X a possible parent of seed lot Y? | **Yes, by exclusion** | Strongest when several offspring are tested | | Is plant X *the* parent? | **Supported** if both parents and offspring are sampled and close relatives are ruled out | This is the L4 standard | | Is this the "original" 1990s cut? | Only by comparison with a documented reference sample | Without a reference, no | | Will this seedling be male? | **Yes** with validated sex markers [3] | | | Is this seedling THC- or CBD-dominant? | **Usually**, chemotype class markers [3] | Markers can fail in some germplasm | | Is this an autoflower? | **Sometimes** [6] | Markers don't predict all auto sources | | What THC % will it test? | **No** | Total cannabinoids are quantitative and environment- and lab-dependent | | What does it taste like / feel like? | **No** | Terpene synthase variants are linked to labels [5], but aroma is multi-gene and environmental | | What % indica vs sativa is it? | **Not meaningfully** | Genome-wide, "indica" and "sativa" labelled samples were genetically indistinct in [5]; such percentages describe similarity to a reference panel, not ancestry | | Which landrace is it from? | Only roughly, if the reference panel contains relevant landraces | Reference panels are biased to commercial material [2] | ## What to ask a lab 1. **What markers and how many?** Thousands of SNPs give far better resolution than a few microsatellites. Schwabe and McGlaughlin used 10 microsatellites [4]; Henry et al. used 22 targeted SNPs chosen for ancestry and chemotype across 420 accessions [2]. Both are useful research panels; neither is a whole-genome fingerprint. 2. **What reference database?** Matches are only as good as the samples behind them. 3. **Error rate and repeatability?** Ask for replicate data. 4. **How do they report relatedness?** Look for identity-by-state or kinship values, not marketing labels. 5. **Can they run parentage with your own parents and offspring?** This is what L4 needs. 6. **Data ownership:** can you download raw genotypes, and who else can use them? ## Step by step: an L4 parentage test 1. Sample the claimed female, the claimed male (or reversed female) and at least 5 offspring. Use young leaf tissue, labelled with GB-IDs. 2. Record sampling with dated photos showing the label and plant. 3. Send to the lab with a chain-of-custody note. 4. Request a parentage or kinship analysis. 5. Attach the report as a GB-DOC to the LIN claim. A staff archivist checks consistency. ## Common mistakes - Taking "98% match to Strain X" as identity. Ask: match to what sample, from where? - Treating "62% sativa" as ancestry. - Assuming a DNA match means the same flower quality. Health (HLVd), environment and somatic changes still matter. ## Evidence - Parentage logic and exclusion vs inclusion: *Established* [1]. - Clone identity and population structure from SNP assays: *Supported* [2][4]. - Sex and chemotype markers: *Supported* [3]. - Indica/sativa labels not reflecting genome-wide ancestry: *Supported* [5]. - Autoflower markers: *Supported* in mapped germplasm [6]. ## Sources 1. Jones AG, Small CM, Paczolt KA, Ratterman NL. 2010. A practical guide to methods of parentage analysis. Molecular Ecology Resources 10(1):6-30. https://doi.org/10.1111/j.1755-0998.2009.02778.x 2. Henry P, et al. 2020. A single nucleotide polymorphism assay sheds light on the extent and distribution of genetic diversity, population structure and functional basis of key traits in cultivated north American cannabis. Journal of Cannabis Research 2:26. https://doi.org/10.1186/s42238-020-00036-y 3. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 4. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 5. Watts S, McElroy M, Migicovsky Z, et al. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y 6. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 7. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 --- # How to document lineage evidence (GB-ID evidence levels L0-L4) > On GenetixBay every parentage statement is a claim with an evidence level: L0 unverified, L1 community reported with a source, L2 breeder reported, L3 documented by an accepted GB-DOC, L4 lab-confirmed by a genomic report consistent with the parent-child relationship. Breeders raise the level by attaching dated, original evidence and, where possible, by recording crosses on the platform as they happen. - Canonical: https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.html - Category: Breeding · Level: Breeder - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I prove the lineage of my strain?** Prove a cannabis strain's lineage by treating 'A x B' as a claim and attaching the strongest evidence you have. For a new cross, register both parents as GenetixBay records and log the pollination event on the day. For an old line, collect dated first-hand sources. A genomic parentage report on parent and offspring samples is the strongest proof. **What are GenetixBay evidence levels?** GenetixBay evidence levels rate a lineage claim from L0 to L4. L0 is an unverified name, L1 a sourced community report, L2 the certified breeder's own statement, L3 an archivist-accepted document from the time such as a catalogue, patent or lab certificate, and L4 a genomic report consistent with the parent-child relationship. Records show the highest accepted level. **What documents count as lineage evidence?** Documents that count as cannabis lineage evidence include dated original forum posts by the breeder, photos of original packs or catalogues, breeder journals with dated photos, patents and plant breeders' rights filings, and genomic parentage reports. A lab certificate of analysis supports chemotype claims only, not parentage. A name on a menu or seed shop page is weak evidence. **How do I get my cross to L3 or L4?** To reach L3, submit a document from the time, such as an era catalogue, patent, breeders' rights filing or dated original post, as a GB-DOC for archivist review. To reach L4, send leaf samples from both parents and several offspring to a genotyping lab and attach a report showing the parent-child relationship is consistent for those specific samples. **What is a witnessed lineage?** A witnessed lineage is a GenetixBay flag for crosses recorded as they happen: both parents exist as individual or cut records and the pollination event was logged on the platform at the time. That makes parentage machine-verifiable within the platform's records. It is a separate flag alongside the evidence level and does not replace L4 DNA confirmation. **How are lineage disputes handled?** On GenetixBay, any member with reputation 25 or higher can dispute a lineage claim with a reason and evidence. The claimant has 14 days to respond, then a three-person panel rules the claim upheld, overturned or unresolved. Losing claims are marked disputed or superseded but never deleted, and there is one appeal. **Short answer.** Treat "A x B" as a claim and attach the strongest evidence you have. A name alone is L0. A sourced community report is L1. The certified breeder's own statement is L2. An archivist-accepted document from the time (catalogue, dated post, patent, lab certificate) is L3. A genomic report consistent with the parent-child relationship is L4. Crosses recorded on GenetixBay as they happen carry a separate "witnessed" flag. ## What's happening Cannabis lineage history is mostly oral. Genetic studies show names and reported ancestry often don't match the DNA [3]. GenetixBay doesn't try to declare one "true" story. It records each claim, who made it, the evidence attached and any conflicting claims, in an append-only history (platform spec §6) [1]. ## The evidence ladder | Level | Name | What it takes | Who can set it | |---|---|---|---| | L0 | Unverified | A name or anonymous assertion | Anyone | | L1 | Community reported | A member's claim with a source: dated forum post, photo of an old pack | Rep ≥25 | | L2 | Breeder reported | The certified breeder of the line asserts it | GB-BRD owner | | L3 | Documented | A GB-DOC accepted by an archivist: era catalogue, patent, plant breeders' rights filing, lab certificate (for chemotype claims) | Archivist (rep ≥500 or staff) | | L4 | Lab-confirmed | Genomic report attached, parent/child relationship consistent | Staff archivist with lab report as GB-DOC | Rules to know [1]: - A record shows the **highest accepted level**, with the **number of conflicting claims** beside it. - Levels change only through events; nothing is deleted. - A verified breeder account is shown separately from verified genetics. A certified breeder can still make an L2 claim that turns out wrong. - **Witnessed lineage** (`witnessed=true`): when both parents are GB-IND/GB-CUT records and the `pollination` event is logged on the platform at the time, parentage is machine-verifiable within the platform's records. It is a distinct flag, not a substitute for L4 DNA confirmation. ## What makes good evidence | Evidence | Strength | Notes | |---|---|---| | Name on a menu or seed shop page | Weak (L0-L1) | Copies spread errors | | Dated original forum post by the breeder, at the time | L1-L3 depending on acceptance | Archive the page (snapshot) and record the URL and date | | Photo of an original pack or catalogue | L1, L3 if accepted with provenance | Show date, batch, maker | | Breeder's own journal with dated photos | L2, stronger if logged live | Live GenetixBay journals carry server timestamps | | Patent or plant breeders' rights filing | L3 | Formal, dated public record | | Lab certificate of analysis | L3 for chemotype claims only | Not evidence of parentage; labs vary [5] | | Genomic parentage report | L4 | Must show consistency for the specific parent and child samples [2] | ## Step by step: documenting a new cross (BRD-510 practical) 1. **Before pollinating,** make sure both parents exist as GB-IND or GB-CUT records with photos. 2. **Log the `pollination` event** on the day: female ID, male ID, date, branch. 3. **Create the GB-BAT** at harvest: seed count, feminised/regular, storage. 4. **Attach tests** as GB-DOCs: germination, sex check, chemotype. 5. **Register the GB-GEN** with LIN claims to the parents (L2 as a certified breeder, plus the witnessed flag). 6. **Optional L4:** send leaf samples from the parents and several offspring to a genotyping lab; attach the report. ## Step by step: documenting an old (heritage) line 1. Collect every source: dated posts, catalogues, magazine articles, interviews, pack photos. 2. Separate **first-hand** (the breeder, at the time) from **second-hand** (later retellings). 3. Submit each as a separate claim with its own evidence. Conflicting claims sit side by side. 4. Request archivist review for L3. 5. If living material exists, compare its DNA to other samples sold under the same name (see [genotyping](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md)). ## Disputes Any member with rep ≥25 can dispute a claim with a reason and evidence. The claimant has 14 days to respond; a three-person panel rules upheld, overturned or unresolved. Losing claims are marked disputed or superseded, never deleted, and there is one appeal [1]. ## Common mistakes - Treating a lab THC certificate as proof of parentage. - Citing a seed shop's description of someone else's line. - Uploading screenshots without URL and date. - Raising your own line's level by repeating your own claim across accounts (this is a moderation offence). ## Evidence - Claims-and-evidence structure: GenetixBay policy [1]. - DNA parentage analysis principles: *Established* [2]. - Mismatch between names and DNA: *Supported* [3]. - Naming and publication principles: *Established* [4]. ## Sources 1. GenetixBay. GB-ID provenance model, 2026. https://genetixbay.com/how-it-works 2. Jones AG, Small CM, Paczolt KA, Ratterman NL. 2010. A practical guide to methods of parentage analysis. Molecular Ecology Resources 10(1):6-30. https://doi.org/10.1111/j.1755-0998.2009.02778.x 3. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 4. Brickell CD, et al. (eds). 2016. International Code of Nomenclature for Cultivated Plants, 9th edition. Scripta Horticulturae 18. ISHS. https://www.ishs.org/scripta-horticulturae/international-code-nomenclature-cultivated-plants-ninth-edition 5. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 --- # Inbreeding depression and hybrid vigour > Inbreeding makes hidden harmful recessive alleles homozygous, so inbred plants often lose vigour, yield and fertility (inbreeding depression). Crossing unrelated lines masks those alleles and can push F1s above both parents (hybrid vigour, or heterosis). The vigour fades in the F2 because the masking breaks down as genes segregate. - Canonical: https://genetixbay.com/knowledge/breeding/inbreeding-depression-hybrid-vigour.html - Category: Breeding · Level: Breeder - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is inbreeding depression in cannabis?** Inbreeding depression in cannabis is the loss of vigour, yield and fertility when related plants are mated. Selfing, sib-mating or repeated backcrossing to one clone makes hidden harmful recessive alleles homozygous. Symptoms include slower or deformed seedlings, lower germination, smaller plants, poorer seed set and odd mutants such as albino or variegated seedlings. **Why are my F2 or S1 plants weaker?** F2 and S1 cannabis plants are often weaker because inbreeding exposes harmful recessive alleles that the parents carried hidden. Selfing raises the inbreeding coefficient to 0.5 in one generation, and F2s also lose the F1's hybrid vigour as genes segregate. A line sib-mated from one pair for several generations will show it most. **What is hybrid vigour?** Hybrid vigour, or heterosis, is when offspring of two different, unrelated parents outperform either parent in growth and yield. It is the flip side of inbreeding depression: the F1 carries a working allele at most genes where either parent was weak. In cannabis it shows mostly in growth and yield, not necessarily in flower quality. **Why are F1 hybrids so vigorous?** F1 cannabis hybrids are vigorous mainly because crossing unrelated parents masks harmful recessive alleles, so each F1 carries a functional copy at most genes where a parent was weak. This dominance explanation is thought to be the main cause; heterozygote superiority at some genes may add a little. The finer mechanisms are still debated. **How do I avoid inbreeding depression when stabilising a line?** Avoid inbreeding depression by keeping the breeding population wide, with several females and several males each generation rather than one pair. Select hard for vigour and sex stability and cull every intersex plant, which purges harmful recessives over time. Track germination, seedling vigour and dry yield; a germination drop over 10 points signals a problem. **Does hybrid vigour carry on into the next generation?** No, hybrid vigour does not fully carry on into the next generation. Heterosis is strongest in the F1 and declines in the F2 and later generations as genes segregate and harmful recessives become homozygous again. Expecting F2s to keep the F1's vigour is a common mistake; production seed for vigour is remade from two different parent lines. **Short answer.** Every outbreeding plant carries hidden, mostly recessive, harmful alleles. Inbreeding (selfing, sib-mating, backcrossing to one clone) makes them homozygous and visible: weaker growth, lower yield, poorer seed set. Crossing unrelated parents hides them again and can give F1s more vigour than either parent. That vigour is strongest in the F1 and declines as later generations segregate [1][2]. ## What's happening Two main explanations, both supported [1][2]: 1. **Dominance (partial dominance) hypothesis.** Most of inbreeding depression comes from many mildly harmful recessive alleles. Inbreeding exposes them; crossing masks them. This is thought to be the main cause in most species [1]. 2. **Overdominance.** At some genes the heterozygote itself is superior. This is harder to prove and probably explains less [1]. Heterosis is the flip side: the F1 of two different inbred lines carries a functional allele at most genes where either parent was weak [2]. Real mechanisms also involve gene regulation and dosage effects that are still being worked out [2] (*Contested* in detail). Cannabis is naturally outcrossing and dioecious, so it is expected to carry a substantial load of hidden recessives (*Supported* by general theory; little cannabis-specific data) [1][4]. **Inbreeding and hermaphrodites.** Selfing a dioecious species is only possible by forcing or tolerating male flowers on females. The GenetixBay breeder position is that repeated, unselected selfing (S1 on S1) of plants that herm is a main source of herm-prone lines: inbreeding fixes the tendency along with everything else. Inbreed only from proven-stable females, cull every intersex plant in each inbred generation, and outcross rather than self again when a line starts throwing hermies. See [S1s and selfing](https://genetixbay.com/knowledge/breeding/s1-selfing.md) and [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). ## How much heterozygosity is lost | Mating | Inbreeding coefficient (F) after 1 / 2 / 3 generations | |---|---| | Selfing | 0.50 / 0.75 / 0.875 | | Full sibs | 0.25 / 0.375 / 0.50 | | Half sibs | 0.125 / ~0.22 / ~0.31 | | Backcross to same clone (offspring F) | 0.25 / 0.375 / 0.4375 (approx.) | Selfing and full-sib values are standard; half-sib and backcross values are approximations [3]. ## Symptoms of inbreeding depression - Slower seedlings, more weak or deformed seedlings, lower germination. - Smaller plants and lower yield. - Lower pollen production or seed set. - More unusual mutants (variegation, leaf deformities, albino seedlings). - More intersex plants, if the line was selfed from unstable parents (house position; see above). - Sometimes more variation in performance, not less. ## How to manage it 1. **Keep the breeding population wide.** Several females and several males each generation. Avoid single-pair bottlenecks every generation. 2. **Select hard for vigour and sex stability** in inbred generations; cull every plant that herms. This **purges** the worst recessives over time [1]. 3. **Use inbreeding on purpose, briefly.** S1 or sib generations reveal recessives; then outcross the best. 4. **Make F1s from two genuinely different, partially inbred lines** if you want uniform, vigorous production seed. This is how hybrid seed works in maize and vegetables [2][3]. 5. **Measure.** Germination rate, seedling vigour and dry yield per plant tracked across generations show inbreeding depression early. ## Numbers that matter | Signal | Possible inbreeding depression if... | |---|---| | Germination | falls by >10 percentage points vs earlier generations under the same test | | Seedling abnormalities | >2-5% of seedlings | | Yield | inbred family mean consistently below both outcrossed checks | Thresholds are GenetixBay practice suggestions, not research values. ## Common mistakes - Blaming "bad genetics" on a line you've sib-mated from one pair for five generations. - Expecting F2s to keep the F1's vigour. - Selfing again from a plant that hermed. You fix the defect along with the traits. - Assuming hybrid vigour means better flower quality. It mostly shows in growth and yield. ## Evidence - Inbreeding depression from recessive load and its purging: *Established* [1]. - Heterosis in crops: *Established* as a phenomenon; mechanisms partly *Contested* [2]. - Cannabis-specific inbreeding depression magnitudes: *Grower practice* (little published data). ## Sources 1. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 2. Schnable PS, Springer NM. 2013. Progress toward understanding heterosis in crop plants. Annual Review of Plant Biology 64:71-88. https://doi.org/10.1146/annurev-arplant-042110-103827 3. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 4. Lynch RC, Vergara D, Tittes S, et al. 2016. Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences 35(5-6):349-363. https://doi.org/10.1080/07352689.2016.1265363 --- # Mendelian genetics for growers, with Punnett squares > Traits controlled by one gene follow Mendel's rules: each parent passes one of its two alleles at random, so a cross of two heterozygotes gives a 1:2:1 genotype ratio and, for a dominant trait, a 3:1 look. In cannabis the clearest single-gene examples are autoflowering (recessive) and the THC/CBD chemotype switch (close to codominant). - Canonical: https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.html - Category: Breeding · Level: Intermediate - Evidence: Established · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do Punnett squares work for cannabis?** A Punnett square for cannabis lists one parent's possible gametes across the top and the other's down the side, then fills each box with the resulting offspring genotype. Crossing two autoflower carriers (Aa x Aa) gives 1 AA, 2 Aa and 1 aa, so about a quarter of the seedlings are autos. Each box is one equally likely outcome. **What does 3:1 ratio mean?** A 3:1 ratio means that in an F2 from two carriers of a recessive trait, about three offspring show the dominant trait for every one showing the recessive. For autoflowering, 100 F2 plants should give about 75 photoperiod and 25 autos. Check real counts with a chi-square test; small tents of 10-12 plants rarely show a clean 3:1. **What is dominant and recessive in cannabis?** In cannabis, a dominant allele shows its effect with one copy, while a recessive allele shows only when a plant has two copies. Autoflowering behaves as recessive in mapped populations, so carriers look photoperiod. Dominant does not mean common or better; it only describes how alleles interact. Chemotype alleles are codominant, so heterozygotes are visible. **How many plants do I need to find a recessive trait?** To have a 95% chance of finding at least one plant showing a single recessive trait in a cannabis F2, where it occurs in 25% of plants, grow 11 plants. Two unlinked recessives together (1 in 16) need 47 plants and three (1 in 64) need 191. The formula is n = ln(0.05) divided by ln(1 - p). **Why don't my F2 ratios match the textbook?** Cannabis F2 ratios often miss the textbook because samples are small, linked genes travel together, weak seedlings die before scoring and under-count recessive classes, many traits are controlled by multiple genes, and dominance is not always complete. Autoflower heterozygotes, for example, flower earlier than pure photoperiod plants. A chi-square test shows whether a deviation is just chance. **What is linkage?** Linkage is when genes sit close together on the same chromosome and are inherited together instead of independently. Cannabis has 10 chromosome pairs, and recombination is concentrated near chromosome ends, so large central regions pass on in blocks. The THC and CBD synthase genes sit in one such block, which is why chemotype inherits like a single gene. **Short answer.** Every plant carries two copies (alleles) of each gene and passes one, chosen at random, to each seed. Cross two plants that each carry one hidden recessive allele and about a quarter of the offspring will show the recessive trait. Most traits growers care about (yield, potency, flavour) are not single genes, but Mendel's rules are still the foundation: they explain why F1s look uniform and F2s scatter. ## What's happening Mendel's two laws [1]: 1. **Segregation.** The two alleles of a gene separate when pollen and ovules form, so each gamete carries one. 2. **Independent assortment.** Alleles of different genes are inherited independently, **unless the genes sit close together on the same chromosome** (linkage). Cannabis has 10 chromosome pairs, and recombination is concentrated near chromosome ends, so large central regions are inherited in blocks [5]. That matters: the THC and CBD synthase genes sit together in such a block [5]. ## Punnett square 1: a recessive trait (autoflowering) Autoflowering behaves as one recessive gene in the mapped populations [3]. **A** = photoperiod, **a** = auto. F1 (Aa) x F1 (Aa): | | A | a | |---|---|---| | **A** | AA (photo) | Aa (photo) | | **a** | Aa (photo) | aa (**auto**) | Genotypes 1 AA : 2 Aa : 1 aa. Phenotypes 3 photo : 1 auto. Two of every three photoperiod F2s still carry the auto allele, and you cannot see which by eye. ## Punnett square 2: a codominant trait (chemotype) de Meijer et al. (2003) modelled chemotype with one locus, **B**, and alleles **B_T** (THC synthase) and **B_D** (CBD synthase), behaving codominantly [4]. Later work shows it is really two tightly linked genes inherited as a unit, with complications (see [chemotype inheritance](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md)). THC:CBD F1 (B_T/B_D) x THC:CBD F1 (B_T/B_D): | | B_T | B_D | |---|---|---| | **B_T** | B_T/B_T (THC dominant, type I) | B_T/B_D (mixed, type II) | | **B_D** | B_T/B_D (mixed, type II) | B_D/B_D (CBD dominant, type III) | Expect 1 type I : 2 type II : 1 type III. Here you **can** see the heterozygote, because both alleles show. ## Punnett square 3: two genes at once Cross two plants that are heterozygous for both autoflowering (Aa) and chemotype (B_T/B_D). If the genes are unlinked, you get 16 combinations. The share that is **auto and CBD dominant** (aa and B_D/B_D) is ¼ x ¼ = **1/16**. Each extra fixed requirement multiplies the odds down. That is the core reason pheno hunts need big numbers. ## Numbers that matter | Situation | Expected share | Plants to grow for 95% chance of at least one | |---|---|---| | Recessive trait in an F2 (¼) | 25% | 11 | | Two unlinked recessives (1/16) | 6.25% | 47 | | Three unlinked recessives (1/64) | 1.6% | 191 | | Homozygous dominant you can't see (1/3 of dominant-looking F2s) | 33% of the dominant class | Needs a progeny test | Formula: n = ln(0.05) / ln(1 - p). With p = 0.25, n = 10.4, so 11 plants [2]. ## Checking a ratio Use a chi-square test. For 100 F2 plants with 70 photo and 30 auto against 75:25: χ² = (70-75)²/75 + (30-25)²/25 = 0.33 + 1.0 = 1.33, below 3.84 (1 degree of freedom, 5% level), so the data fit 3:1. Toth et al. used exactly this logic to call autoflowering recessive [3]. ## Why real ratios drift - **Small samples.** Ten plants rarely show a perfect 3:1. - **Linkage.** Genes near each other travel together. - **Selection before scoring.** If weak seedlings die first, recessive classes can be under-counted. - **Many genes.** Height, yield and terpene totals are quantitative; see [quantitative traits](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md). - **Dominance is not always complete.** Autoflower heterozygotes flower earlier than pure photoperiods even though they are not autos [3]. ## Common mistakes - Assuming "dominant" means "common" or "better". It only describes how alleles interact. - Reading 3:1 into a 12-plant tent. - Forgetting that a dominant-looking plant can be AA or Aa. Only a test cross (to aa) or a DNA marker tells you. ## Evidence - Mendel's laws and chi-square testing: *Established* [1][2]. - Autoflowering as a single recessive locus: *Supported* [3]. - Chemotype as a near-codominant single inheritance unit: *Established* as a working model, refined since [4][5]. ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 2. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 3. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 4. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 5. Laverty KU, Stout JM, Sullivan MJ, et al. 2019. A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci. Genome Research 29(1):146-156. https://doi.org/10.1101/gr.242594.118 --- # Pollination and seed production, step by step > Pollinate females about 2-4 weeks into flower when stigmas are white and receptive, using fresh or stored pollen applied with a brush or bag to marked branches; seeds mature in roughly 5-7 weeks. Isolation is everything: pollen travels on air, clothing and fans, so a planned cross needs a separate space or strict bagging, and every pollination gets a dated record. - Canonical: https://genetixbay.com/knowledge/breeding/pollination-seed-production.html - Category: Breeding · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Flower, Ripening, Harvest · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **When should I pollinate my cannabis plant?** Pollinate a cannabis plant when its stigmas are fresh, white and upright, typically around weeks 2-4 of flower, within a receptive window of about weeks 2-5. Grower practice favours early to mid flower; pollinating too late gives low seed set and immature seed at harvest. Repeat after 3-5 days if coverage looks poor. **How long do cannabis seeds take to mature after pollination?** Cannabis seeds take about 5-7 weeks to mature after pollination, based on grower practice. Keep the plant in flowering conditions throughout, and watch for bud rot because swelling seed pods hold moisture. Harvesting earlier tends to lower germination, so wait until the bracts split and the seeds are dark and hard. **How do I pollinate just one branch?** To pollinate one cannabis branch, dab pollen onto its stigmas with a clean, dry, lightly loaded watercolour brush, or slip a paper or fine-mesh pollination bag holding a pinch of pollen over the branch, tie it, shake gently and remove it after 24-48 hours. Tag the branch with the cross, date and pollen batch. **How do I stop pollen from getting everywhere?** Stop cannabis pollen spreading by keeping the male in a separate room or tent with its own air, turning fans off or low while pollinating, and changing clothes and washing hands and arms after handling males. Bag individual branches, then mist the plant lightly to knock down stray airborne pollen. Outdoors, parentage can't be guaranteed without bagging. **How do I know seeds are ripe?** Cannabis seeds are ripe when the bracts around them split and the seeds are dark, either mottled or uniformly dark, and hard when squeezed. Pale green or white seeds are immature and germinate poorly. Dry seeded branches for 1-2 weeks, rub out the seeds, discard tiny, pale or cracked ones, then dry them about another week. **How many seeds does one plant make?** How many seeds one cannabis plant makes depends on how much of it is pollinated and how well. Each female flower holds one ovule, so it can make one seed, and a single pollinated branch typically yields dozens to hundreds of seeds depending on its size and coverage. Whole-plant pollination gives far more seed but raises pollen risk. **Short answer.** Pollinate when the female's stigmas are fresh and white, typically weeks 2-4 of flower. Brush or bag pollen onto labelled branches, keep the room still for a few hours, then wait about 5-7 weeks until the seeds are dark, hard and the bracts split. Contain pollen ruthlessly and write down every pollination. **Legal first.** Producing seed may require a licence or be prohibited where you live, even where growing is legal. Check local rules before starting. > **House position: males are a necessity.** Real breeding needs real males, selected as carefully as the females. Males are encouraged and rewarded on GenetixBay, and a well-documented male line is a prized contribution. Selfing is mostly frowned upon: it was historically an emergency measure to save a line, not a shortcut. GenetixBay holds the best breeding standards: snobby, and proud of it. ## What's happening Cannabis is wind pollinated. A single male can shed enormous amounts of light, dry pollen that travels long distances outdoors (*Established*) [1]. Each female flower holds one ovule, so one pollen grain landing on a receptive stigma can make one seed. Pollen viability drops fast at room conditions [2], so fresh pollen or properly stored pollen matters. ## Numbers that matter | Parameter | Typical value | Notes | |---|---|---| | Female receptive window | ~weeks 2-5 of flower | White, upright stigmas; best early-mid flower (*Grower practice*) | | Male pollen shed | ~2-4 weeks after flip, cultivar dependent | Sacs open from the bottom up | | Pollen viability at room temp | Hours to a few days | [2] | | Pollen viability at 4 °C | Mostly lost within 1 week (stage dependent) | Mid-stage pollen kept ~22% germination at 21 days [2] | | Seed maturation | ~5-7 weeks from pollination | Earlier harvest lowers germination (*Grower practice*) | | Seeds per pollinated branch | dozens to hundreds | Depends on branch size and coverage | | Seed storage | Cool, dry, dark; ~5 °C maintained germination for years [5] | See [seed testing](https://genetixbay.com/knowledge/breeding/seed-germination-testing-qc.md) | ## Step by step ### 1. Plan the cross - Choose the female (seed parent) and male (pollen parent) and record both GB-IND or GB-CUT IDs. Convention: write **female x male**. - Decide **whole plant** (more seed, more pollen risk) or **branch** pollination (keeps the rest sinsemilla for evaluation). ### 2. Isolate - **Best:** a separate room or tent for the male, with its own air. Collect pollen there. - Keep fans off or low during pollination. Change clothes and wash hands and arms after handling males. - Outdoors, other growers' males (and hemp fields) can pollinate your plants. You cannot guarantee parentage outdoors without bagging. ### 3. Collect pollen - Cut a male branch with opening sacs, place it on clean, dry paper in still air for 12-24 h, then tap and sieve. See [pollen collection and storage](https://genetixbay.com/knowledge/breeding/pollen-collection-storage.md). ### 4. Pollinate - **Brush method:** a clean, dry watercolour brush, lightly loaded, dabbed onto stigmas of a tagged branch. - **Bag method:** slip a paper or fine-mesh pollination bag with a pinch of pollen over the branch, tie it, shake gently, remove after 24-48 h. - Mist the plant lightly afterwards to knock down stray pollen in the air (*Grower practice*). - **Tag the branch:** cross, date, pollen batch. - Repeat after 3-5 days for better coverage if needed. ### 5. Mature - Keep flowering conditions. Stigmas on fertilised flowers shrivel within a few days. - Watch for bud rot: swelling seed pods hold moisture. - Seeds are ready when the bracts split and seeds are dark, mottled (or uniformly dark) and hard when squeezed. Pale green or white seeds are immature. ### 6. Harvest and clean - Dry the seeded branches for 1-2 weeks, then rub buds over a screen. Discard tiny, pale or cracked seeds. - Dry seeds further at room temperature in a paper envelope for about a week, then store cool and dry. ### 7. Record and test - Record: parents, pollination dates, harvest date, seed count, viability test. On GenetixBay this is a **GB-BAT** batch record with a `pollination` event. - Run a germination test before you share or sell any seed. ## Common mistakes - Accidental pollination of the whole room from a single forgotten male or hermaphrodite. - Saving seed from an accidental herm pollination. It carries the herm tendency; discard it. - Pollinating too late in flower: low seed set and immature seed at harvest. - No tags. Six weeks later you won't remember which branch got which pollen. - Selling or gifting seed without a germination test. ## Evidence - Wind pollination and pollen dispersal: *Established* [1]. - Pollen viability decline at room and fridge temperature: *Established* (cannabis-specific assay) [2]. - Receptive window, maturation time, bag and brush methods: *Grower practice*. - Reversed-female pollen for feminised seed: *Established* [3][4]. - Seed storage at ~5 °C: *Supported* [5]. ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 2. Gaudet D, Yadav NS, Sorokin A, Bilichak A, Kovalchuk I. 2020. Development and optimization of a germination assay and long-term storage for Cannabis sativa pollen. Plants 9(5):665. https://doi.org/10.3390/plants9050665 3. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 4. Lubell JD, Brand MH. 2018. Foliar sprays of silver thiosulfate produce male flowers on female hemp plants. HortTechnology 28(6):743-747. https://doi.org/10.21273/HORTTECH04188-18 5. Small E, Brookes B. 2012. Temperature and moisture content for storage maintenance of germination capacity of seeds of industrial hemp, marijuana, and ditchweed forms of Cannabis sativa. Journal of Natural Fibers 9(4):240-255. https://doi.org/10.1080/15440478.2012.737179 --- # Polyhybrids vs landraces: what each gives a breeder > A landrace is a locally adapted, farmer-maintained population with a regional history; it is variable but coherent, and a reservoir of diversity. A polyhybrid is a modern line with many ancestors from different gene pools; it can be highly productive but is heterozygous and segregates unpredictably. Breeders use landraces as sources of new traits and polyhybrids as elite starting material. - Canonical: https://genetixbay.com/knowledge/breeding/polyhybrids-vs-landraces.html - Category: Breeding · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is a landrace strain?** A landrace cannabis strain is a regional population shaped over many generations by local farmers and climate. Plant-genetic-resources literature defines it by historical origin, distinct identity, local adaptation and links to traditional farming, usually without formal improvement. Landraces are variable but coherent, and many are now endangered by replacement with hybrids. **What is a polyhybrid?** A polyhybrid is a cannabis line whose pedigree combines many unrelated ancestors, which describes most commercial strains today. Polyhybrids are often productive indoors and bred for flowering in about 8-10 weeks, but each plant is highly heterozygous. Genetic studies show their reported ancestry and actual genetic structure only partly agree. **Are landraces more stable than hybrids?** Landraces are usually more uniform from seed than polyhybrids, though not perfectly uniform. A landrace in its region has moderate to high but coherent variation, while polyhybrid seed shows low uniformity because each parent is heterozygous at many genes. A landrace's variation is part of its value, not a defect, and imports often lose some through bottlenecks. **Why are my polyhybrid seeds so variable?** Polyhybrid cannabis seeds are variable because each parent clone is heterozygous at a large share of its genes. Crossing two such plants reshuffles many alleles at once, so the so-called F1 behaves like an F2 and throws many different phenotypes. Uniform seed would require more inbred, stabilised parent lines. **How should a landrace be preserved?** Preserve a cannabis landrace by keeping population size up, ideally 20-50 or more females and 10-20 or more males per generation, pooling pollen from many males, and isolating it from other cannabis. Avoid selecting for your own preferences; remove only diseased or off-type plants. Document its origin and regenerate stored seed before germination falls. **Is an heirloom the same as a landrace?** No, an heirloom is not the same as a landrace. An heirloom or heritage cannabis line has been kept for decades, often outside its origin, by growers or seed collectors. It may descend from a landrace but has been through new selection and founder bottlenecks, losing some adaptation. Many 1990s seed-bank 'pure landraces' are really heirlooms. **Short answer.** Landraces are regional populations shaped by local farmers and climate over many generations: variable, adapted, and genetically distinct from each other. Polyhybrids are modern mixes of many such sources: often more productive in indoor conditions, but heterozygous, so their seed scatters. Neither is "better". Landraces are where new traits live; polyhybrids are where most modern selection happens. ## Definitions - **Landrace:** a dynamic population with historical origin, distinct identity, local adaptation and association with traditional farming, usually lacking formal improvement [1]. - **Heirloom / heritage line:** a line kept for decades (often outside its origin) by growers or seed collectors. It may descend from a landrace but has been through new selection and bottlenecks. Not the same thing. - **Polyhybrid:** a line whose pedigree combines many unrelated ancestors. Most commercial "strains" today [3][6]. ## Comparison | Feature | Landrace (in origin) | Heirloom import | Polyhybrid | |---|---|---|---| | Genetic variation within | Moderate to high, but coherent | Often reduced (founder bottleneck) | High heterozygosity per plant | | Uniformity from seed | Moderate | Variable | Low | | Adaptation | Local climate, day length, pests | Partly lost outside origin | Indoor production | | Flowering time | Often long (tropical) or short (high latitude) | As origin | Bred for 8-10 weeks typically | | Value to breeders | Novel alleles, resistance, unusual chemistry | Historical reference | Elite combinations to select from | | Conservation status | Many endangered by hybrid replacement [2] | Small populations, drift | Abundant | McPartland and Small (2020) describe several high-THC landrace groups as critically endangered germplasm and note that widespread hybridisation over the past 50 years has blurred distinctions [2] (*Supported*). ## Why polyhybrid seed scatters A polyhybrid clone may be heterozygous at a large share of its genes. Crossing two such clones produces offspring that reshuffle many alleles at once, so the "F1" behaves like an F2 (see [F1, F2, F3](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md)). Genetic studies show commercial drug-type cannabis is a mixed gene pool in which reported ancestry and genetic structure only partly agree [6] (*Supported*). ## Preserving a landrace properly 1. **Keep population size up.** Grow and cross as many plants as you can, ideally ≥20-50 females and ≥10-20 males per generation; bottlenecks lose rare alleles (*Supported* by general conservation genetics) [5]. 2. **Avoid strong selection** for your own preferences; you are conserving, not improving. Remove only diseased or off-type plants (pollen contamination). 3. **Pool pollen** from many males, or do many pair crosses and bulk the seed. 4. **Isolate** from other cannabis. 5. **Document origin claims**: where collected, when, by whom, and how many seeds, as GB-DOCs. Unverified origin = L1 at best. 6. **Store seed** properly and regenerate before germination falls (see [seed testing](https://genetixbay.com/knowledge/breeding/seed-germination-testing-qc.md)). ## Using a landrace in breeding - Cross landrace x elite, then backcross to the elite while selecting for the landrace trait (see [backcrossing](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md)). - Expect long flowering, tall stretch or different chemistry in early generations. - Check legality and benefit-sharing rules for collected material from other countries. ## Common mistakes - Calling a 1990s seed-bank line a "pure landrace". Usually it is an heirloom with its own history. - "Preserving" a landrace by keeping one female and one male. - Treating a landrace's variation as a defect. It is the point. ## Evidence - Landrace definition: *Established* (plant genetic resources literature) [1]. - Endangered status of cannabis landraces: *Supported* [2]. - Commercial cannabis as a mixed, heterozygous gene pool: *Supported* [3][6]. - East Asian domestication origin: *Contested* [4]. - Population-size guidance: *Supported* by general genetics [5]; exact numbers are rules of thumb. ## Sources 1. Villa TCC, Maxted N, Scholten M, Ford-Lloyd B. 2005. Defining and identifying crop landraces. Plant Genetic Resources 3(3):373-384. https://doi.org/10.1079/PGR200591 2. McPartland JM, Small E. 2020. A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys 144:81-112. https://doi.org/10.3897/phytokeys.144.46700 3. Lynch RC, Vergara D, Tittes S, et al. 2016. Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences 35(5-6):349-363. https://doi.org/10.1080/07352689.2016.1265363 4. Ren G, Zhang X, Li Y, et al. 2021. Large-scale whole-genome resequencing unravels the domestication history of Cannabis sativa. Science Advances 7(29):eabg2286. https://doi.org/10.1126/sciadv.abg2286 5. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 6. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 --- # Quantitative traits and heritability: why most good traits are hard to fix > Yield, potency, terpene totals, vigour and flowering time are controlled by many genes plus environment. Heritability (the share of variation due to genes in a given population and setting) predicts how much of a selected plant's advantage passes to its offspring: response = heritability x selection differential. Cannabinoid ratios are highly heritable; absolute THC % and yield much less so. - Canonical: https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.html - Category: Breeding · Level: Breeder - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is heritability in plant breeding?** Heritability in plant breeding is the share of the variation you see in a trait that is genetic, in a specific population and environment. Broad-sense heritability (all genetic variance divided by total variance) matters for clone selection. Narrow-sense heritability (additive variance only) matters for seed breeding, because only additive effects reliably pass to offspring. **Why don't the offspring of my best plant perform as well?** Offspring of your best cannabis plant usually regress towards the average because much of that plant's edge came from environment, such as pot position or light, and from dominance and gene interactions that don't breed true. With a yield heritability of 0.3, picking plants 100 g/m² above a 400 g/m² average predicts offspring around 430 g/m², not 500. **Is THC percentage genetic or environmental?** THC percentage in cannabis is both genetic and environmental. The THC:CBD ratio is very highly heritable, but absolute THC percentage has only moderate heritability and is strongly affected by light, harvest timing and the testing lab. Research found absolute cannabinoid amounts varied much more than ratios, so a 2-point difference between two labs proves nothing. **What is the breeder's equation?** The breeder's equation is R = h² x S, where R is the response (how much the next generation's average moves), h² is narrow-sense heritability and S is the selection differential, meaning how far the chosen parents sit above the population average. It can also be written R = i x h² x σ_P, using selection intensity: about 1.75 for the top 10%. **How do I reduce environmental noise in a pheno hunt?** Reduce environmental noise in a cannabis pheno hunt by growing siblings side by side in identical pots, medium and feed, randomising positions because edge plants get different light. Score 2-4 clones of each candidate in a second run, use the same lab, harvest stage and top-cola sample for chemistry, and weigh and date every measurement. **What is genotype by environment interaction?** Genotype by environment interaction is when cultivars rank differently in different conditions, for example cultivar A beating cultivar B in coco but not in soil. It is a separate part of total trait variation from genetics and environment alone. It means a keeper selected in one setup may not stay the best in another, so test candidates across conditions. **Short answer.** A quantitative trait is one shaped by many genes of small effect plus the environment, so it varies continuously (grams, percent, days). Heritability tells you how much of the variation you see is genetic in *your* population and *your* room. When heritability is low, the best-looking plant is often just the luckiest, and its offspring regress towards the average. ## What's happening Observed variation splits into parts [1]: **V_P = V_G + V_E + V_GxE**, and **V_G = V_A + V_D + V_I** - V_A, **additive**: the part that reliably passes to offspring. - V_D, **dominance** and V_I, **epistasis** (gene interactions): show in an individual or F1 but do not breed true. - V_E, **environment**: pot position, light, watering, pests. - V_GxE, **genotype by environment**: cultivar A beats B in coco but not in soil. Two heritabilities: - **Broad-sense (H²) = V_G / V_P.** Useful for clone selection, because a clone copies the whole genotype. - **Narrow-sense (h²) = V_A / V_P.** Useful for seed breeding, because only additive effects reliably pass on. ## The breeder's equation **R = h² x S** [1] - S (selection differential) = mean of the plants you keep minus the mean of the population. - R (response) = how much the next generation's mean moves. Example: a population averages 400 g/m². You keep plants averaging 500 g/m² (S = 100). If h² for yield in that setting is 0.3, expect next generation's mean around 430 g/m², not 500. ## What we know for cannabis | Trait | Heritability (indicative) | Notes | |---|---|---| | THC:CBD ratio (chemotype) | Very high | Largely one inheritance unit; see [chemotype inheritance](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) | | Cannabinoid composition ratios | High; stable within a genotype | Absolute amounts varied much more than ratios [2] | | Absolute THC % | Moderate | Strongly affected by light, harvest timing and lab [2][4][5] | | Flowering time | Moderate to high, with major genes | Cultivar origin predicted flowering in hemp [4] | | Yield | Low to moderate | Strongly environment driven [5] | | Terpene profile (which terpenes) | Moderate to high | Tandem terpene synthase genes; see strain-name article | | Morphology and phenology | Lower than cannabinoid traits in [2] | | Naim-Feil et al. (2023) concluded that cannabinoid composition should respond more strongly to selection than morphological and phenological traits [2] (*Supported*). Published cannabis heritability values come from small, single-site studies; treat specific numbers as tentative. Lab numbers add noise too: THC results for similar products varied systematically between testing labs in Washington State [3]. A 2-point THC difference between two plants tested at two labs is not evidence of anything. ## How to raise your effective heritability You cannot change the genes' heritability by wishing, but you can cut V_E: 1. **Grow siblings side by side in the same pots, medium and feed.** Randomise positions; edge plants get different light. 2. **Replicate.** Score clones of each candidate (2-4 each) in a second run before choosing. 3. **Use the same lab, same harvest stage, same sample position** (top cola) for chemistry. 4. **Measure, don't guess.** Grams dry per plant, days to finish, weighed and dated in the journal. 5. **Progeny test.** The best evidence a plant is genetically superior is how its offspring perform. ## Numbers that matter | Concept | Formula | Use | |---|---|---| | Broad-sense heritability | H² = V_G / V_P | Clone selection | | Narrow-sense heritability | h² = V_A / V_P | Seed lines | | Response to selection | R = h² x S | Predict gain | | Selection intensity | i (e.g. top 10% ≈ 1.75; top 20% ≈ 1.40) | R = i x h² x σ_P | Selection intensities are standard normal-distribution values [1]. ## Common mistakes - Picking the "keeper" from one run of one plant per seed. You are partly selecting the luckiest pot. - Treating THC % as a fixed property of a cut. It isn't [2][3]. - Selecting on many traits at once with tiny populations. Gains per trait shrink fast. ## Evidence - Variance partitioning and the breeder's equation: *Established* [1]. - Cannabinoid ratios more heritable than absolute content and morphology: *Supported* [2]. - Lab-to-lab THC variation: *Supported* [3]. - Specific cannabis heritability values: *Contested* (small studies). ## Sources 1. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 2. Naim-Feil E, Elkins AC, Malmberg MM, et al. 2023. The Cannabis plant as a complex system: interrelationships between cannabinoid compositions, morphological, physiological and phenological traits. Plants 12(3):493. https://doi.org/10.3390/plants12030493 3. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 4. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 5. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # S1s and selfing: what happens when a plant pollinates itself > An S1 is seed from a plant pollinated by its own pollen, usually by reversing one female clone or branch. S1s are feminised, and they are not copies of the parent: each S1 seed is a new genotype. Selfing halves heterozygosity per generation, reveals hidden recessives (good and bad), and is a fast way to test what a clone carries. Done carelessly, especially S1 on S1 from plants that herm, it is one of the main ways herm-prone lines are made; only self proven-stable females and cull every intersex offspring. - Canonical: https://genetixbay.com/knowledge/breeding/s1-selfing.html - Category: Breeding · Level: Breeder - Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is an S1 seed?** An S1 seed comes from a female cannabis plant pollinated by itself: one branch or clone is reversed to make pollen, which is then used on the same genotype. S1 offspring reshuffle the parent's own alleles, segregating 1:2:1 at every heterozygous gene, so they relate to their parent much as F2s relate to an F1. **Is an S1 a copy of the mother plant?** No, an S1 is not a copy of the mother plant. Selfing reshuffles the mother's alleles, so S1s vary: some resemble the parent, while about 25% show each hidden recessive trait. Research found genetic variation among S1 progeny similar to that among cross-fertilised progeny. Selling S1s as 'the clone in seed form' is misleading. **Are S1 seeds feminised?** Yes, S1 seeds are feminised. The reversed female's pollen carries only X chromosomes, as do its ovules, so the S1 seeds are female, barring rare exceptions. Feminised is not the same as stable, though: S1s still segregate genetically and inherit any intersex tendency the parent carried, so only self a proven sex-stable female. **Why are my S1s weaker than the clone?** S1s are often weaker than the parent clone because selfing halves heterozygosity in one generation, raising the inbreeding coefficient to 0.5. That exposes harmful recessive alleles the clone carried hidden, which is inbreeding depression: weaker growth, poorer fertility and deformities. Selecting for vigour and fertility over several selfed generations can gradually purge the worst. **What is an S2?** An S2 is the next generation after an S1: a selected S1 plant pollinated by itself. Expected heterozygosity drops to about 25%, with an inbreeding coefficient of 0.75; an S3 drops to 12.5%. Stacking S1 on S1 without strict culling fixes everything the line carries, including any intersex tendency, which GenetixBay considers a main route to herm-prone lines. **Should I make S1s of my keeper?** Make S1s of a keeper only for a clear purpose, such as finding the recessives it carries or backing up its alleles in seed, and only if it stayed fully female for at least two runs. GenetixBay frowns on selfing as a shortcut; a proper cross with a selected male is preferred. S1s preserve the keeper's alleles, not its exact combination. **Do S1 seeds turn hermaphrodite?** S1 seeds turn hermaphrodite mainly when the parent was unstable or was selfed from stress-herm pollen. The GenetixBay breeder position is that careless and repeated selfing is a prime source of herm-prone lines, because the tendency passes into every female seed. One S1 from a proven-stable mother, grown out with intersex plants culled, is a legitimate tool. **Short answer.** You reverse one branch (or a clone) of a female so it makes pollen, then use that pollen on the same genotype. The seed is an S1. S1s are female (both gametes carry X) [1][2] and they are related to the parent like F2s are to an F1: they reshuffle the parent's own alleles. Expect variation, some plants close to the parent, and some recessive surprises. Used carelessly, selfing is also one of the main ways herm-prone lines get made. > **Breeder's standard.** Only self a female that has stayed fully female for at least two runs, reversed under control (never pollen from a stress herm). Grow out the S1s, cull every plant that shows intersex flowers, and don't self again from a line that throws hermies. Never stack S1 on S1 without that culling, and disclose the herm rate with any S1 seed you release. Cannabis is a dioecious species; keeping it that way is the breeder's job. > **House position: selfing is mostly frowned upon.** Real breeding needs real males, selected as carefully as the females. Males are encouraged and rewarded on GenetixBay, and a well-documented male line is a prized contribution. Selfing is mostly frowned upon: it was historically an emergency measure to save a line, not a shortcut. GenetixBay holds the best breeding standards: snobby, and proud of it. ## What's happening At every gene where the parent is heterozygous (Aa), S1 offspring segregate 1 AA : 2 Aa : 1 aa. On average half the heterozygosity is lost per generation of selfing [4]. That does two things: 1. **Reveals recessives.** Useful hidden traits (a colour, a terpene type, autoflowering) appear in ~25% of plants. So do harmful ones (weak growth, poor fertility, deformities): this is inbreeding depression [3]. 2. **Fixes faster.** A selfed line becomes uniform much faster than a sib-mated one, if you can live with the inbreeding. Punja and Holmes (2020) found the genetic variation among progeny after one generation of selfing was similar to that among cross-fertilised progeny in their markers [1]. That is a reminder: S1 seed is not a clone in a seed. ## Numbers that matter | Generation | Expected heterozygosity left (from a fully heterozygous start) | Inbreeding coefficient F | |---|---|---| | S0 (the parent) | 100% | 0 | | S1 | 50% | 0.5 | | S2 | 25% | 0.75 | | S3 | 12.5% | 0.875 | | S4 | 6.25% | 0.94 | Single-locus expectations [4]. Real clones are not 100% heterozygous, so start values are lower. ## When S1s make sense | Goal | S1 useful? | Why | |---|---|---| | Back up a clone in seed form | Partly | You preserve its alleles, not its exact combination | | Find what recessives a clone carries | Yes | ~25% of S1s show each recessive | | Make a feminised production line fast | Sometimes | Uniformity rises quickly; vigour may fall | | Create a breeding parent with fewer hidden recessives | Yes, with selection over S1-S3 | Purging by selection | | Sell "a seed version of clone X" | Only with honest labelling | Must say S1 and show grow-out variation | ## Why careless selfing makes hermies Historically, selfing was an emergency measure: a way to save a line when no male was left, not a trait to want or a shortcut to sell. Treat it the same way today. Cannabis has been dioecious and stable for millennia. The GenetixBay breeder position is that herm-prone lines are mainly made, not born, and repeated selfing is a prime route: - **Selfing a plant that has already hermed** puts its readiness to make male flowers into every seed, and with no male parent there is nothing to dilute it. - **S1 on S1 (S2, S3...)** without strict culling fixes whatever the line carries, the tendency included, at the same speed it fixes the traits you wanted. - **Hermaphrodite pollen gives female seed** [1], so the defect hides inside an "all-female" pack until the buyer's light leak exposes it. Punja and Holmes found one generation of selfing had no measurable effect on genetic diversity in their markers and said more sequential selfing would need study [1]. That supports the point that one S1 from a proven-stable mother is a tool; it is the unselected stacking and selfing of unstable plants that does the damage. ## Step by step 1. Choose a female with **no** intersex tendency across at least two runs. Selfing a plant that hermaphrodites readily concentrates the trait. Don't self it; cull it. 2. Reverse one clone or branch with silver thiosulfate (see [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) for method and safety). 3. Collect the pollen in a separate space. 4. Pollinate tagged branches on an untreated clone of the same plant. 5. Harvest seed 5-7 weeks later; record as an S1 batch with the parent's GB-IND/GB-CUT ID. 6. Grow out at least 20-30 S1s and record vigour, uniformity and any off-types or intersex plants. Cull intersex plants and never use them as parents. Publish those numbers, including the herm rate, with the seed. ## Common mistakes - Selling S1s as "the clone in seed form". - Selfing for several generations without selecting for vigour and fertility. - Using pollen from a stress-induced hermaphrodite rather than controlled reversal. You can't separate "the trait" from "the tendency". - Stacking S1 on S1 and releasing the result untested. That is how pollen chuckers spread herm-prone genetics. ## Evidence - S1 seed is female and genetically variable: *Established* [1][2]. - Loss of heterozygosity and inbreeding depression under selfing: *Established* [3][4]. - Careless and repeated selfing as a main source of herm-prone lines: GenetixBay house position (breeder experience). Risk depends mainly on the parent's own stability and on culling; one generation of selfing did not reduce marker diversity [1]. Controlled cannabis comparisons of intersex rates in S1 vs outcrossed lines are lacking. ## Sources 1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 3. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 4. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ --- # Seed germination testing and quality control for breeders > Before seed leaves your hands, test it: germinate a random sample of at least 100 seeds (400 in four replicates is the lab standard) and count normal seedlings, not just cracked seeds. Report the result with the date on the batch record. Store seed cool and dry; one study recommended about 5 °C to keep germination for years. - Canonical: https://genetixbay.com/knowledge/breeding/seed-germination-testing-qc.html - Category: Breeding · Level: Breeder - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Seedling · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How do I test cannabis seed germination rate?** Test cannabis seed germination by randomly counting out 4 x 25 seeds from the mixed batch, placing each replicate on two layers of moist paper towel with distilled water in a closed container, and incubating at about 24-26 °C (75-79 °F) in the dark. Count normal seedlings at days 3, 5 and 7, then report the percentage, date and sample size. **What is a good germination rate for cannabis seeds?** A good germination rate for fresh, well-made cannabis seed is 85-90% or higher, a grower practice target. Count only normal seedlings with a healthy root and intact cotyledons; a seed that cracks but produces a stunted or deformed seedling doesn't count. Always publish the rate with the test date and the number of seeds tested. **How many seeds should I test?** Test at least 100 cannabis seeds per batch, as 4 replicates of 25, the GenetixBay suggested minimum; official seed labs test 400. For batches under 200 seeds, test at least 10% or 20 seeds and state the number. Small tests are rough: at a 90% rate, 20 seeds gives about plus or minus 13 points, 100 seeds about 6. **How should I store cannabis seeds?** Store cannabis seeds cool, dry, dark and sealed, at about 5 °C. Dry them at room conditions for about a week before sealing so moisture stays low, and keep them in a sealed container, because a fridge without one exposes seeds to moisture cycles. Avoid warm drawers, and re-test germination every 12 months. **How long do cannabis seeds stay viable?** Cannabis seeds stored dry and sealed at about 5 °C were reported to maintain germination for roughly 6 years, though that figure comes from a secondary report. Germination falls over time, faster in warm or humid storage, so re-test stored batches every 12 months and regenerate seed before germination drops too far. **What is a tetrazolium test?** A tetrazolium (TZ) test is a quick seed viability test that stains living seed tissue red, usually within 24-48 hours. It estimates the percentage of seeds that are alive, which can be higher than the germination rate because some living seeds are dormant or weak. A germination test remains the measure of normal seedlings. **Short answer.** Count normal seedlings from a random sample, under controlled conditions, and report the percentage with the test date and sample size. Official labs test 400 seeds in replicates [2][3]; a small breeder should test at least 100 per batch (or 4 x 25). A seed that cracks but makes a deformed or weak seedling is not "germinated" for QC purposes. ## What's happening **Germination** (in seed-testing terms) is the percentage of seeds that produce normal seedlings under favourable conditions [1]. **Viability** is the percentage alive, which can be estimated quickly with a tetrazolium (TZ) stain that turns living tissue red, typically in 24-48 hours [1]. Germination ≤ viability, because some living seeds are dormant or weak. ## Numbers that matter | Item | Standard or target | Notes | |---|---|---| | Official test size | 400 seeds, in replicates | AOSA practice reported by state labs [2][3] | | Breeder in-house test | ≥100 seeds (4 x 25) per batch | GenetixBay suggested minimum | | Small batch (<200 seeds) | Test ≥10% or 20 seeds, state the n | Smaller tests are wide-error estimates | | Official hemp test timing | 7-day prechill then 7-14 days warm; up to 3 weeks total | As described by Oregon State seed lab [1] | | TZ test | 24-48 h | [1] | | Storage | ~5 °C, dry, sealed | Recommended to maintain germination about 6 years in [4] (secondary report) | | Seed moisture | Low; dry seeds at room conditions for a week before sealing | *Grower practice* | | Good fresh germination | ≥85-90% | *Grower practice* target for well-made seed | ## Error bars for small tests A germination percentage from a small sample is rough. Approximate 95% margin of error for an observed 90% rate [6]: | Seeds tested | ±margin (approx.) | |---|---| | 20 | ±13 points | | 50 | ±8 points | | 100 | ±6 points | | 400 | ±3 points | (Normal approximation, 1.96 x √(p(1-p)/n); less accurate at very small n.) ## Step by step: an in-house test 1. **Sample randomly.** Mix the whole batch, then count out 4 x 25 seeds without picking the nicest. 2. **Set up.** Two layers of moist paper towel (or germination paper) in a closed container, one replicate each. Use distilled water. Label each with batch ID and date. 3. **Incubate** at ~24-26 °C (75-79 °F) in the dark. 4. **Count at day 3, day 5 and day 7** (and day 10-14 if many are slow). Remove counted seedlings. 5. **Classify** each seed: normal seedling (healthy root, intact cotyledons emerging), abnormal (stunted, rotten root, no shoot), dead, or ungerminated firm (possibly dormant). 6. **Calculate** germination = normal seedlings / seeds tested x 100. Report per replicate and total. 7. **Optional sex check** for feminised batches: DNA-sex a sample of seedlings (e.g., 20-50) with validated markers [5]; one male in 50 suggests contamination worth investigating. 8. **Record** the result on the GB-BAT with date, method, n and the person who ran it. ## Quality control beyond germination | Check | Why | |---|---| | Seed count per pack (count, not weigh) | Customer trust | | Visual: cracked, immature (pale), insect damage | Removes poor seed before packing | | Off-type rate in a grow-out | Shows whether the line is what you say | | Sex ratio (regular) / male or intersex rate (feminised and regular) | Core product claim; a line that herms under normal conditions is not released (see [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md)) | | Chemotype (where claimed) | Legal and customer claim | | Re-test after storage (every 12 months) | Germination falls over time | ## Common mistakes - Testing the 10 best-looking seeds. - Counting a cracked shell as germination. - Storing seed in a warm drawer, or in a fridge without a sealed container (moisture cycles). - Publishing a germination rate with no date or sample size. ## Evidence - Germination and TZ definitions, lab sample sizes: *Established* (seed-testing standards) [1][2][3]. - Cool, dry storage of Cannabis seed: *Supported* [4]. - In-house sample sizes and thresholds: *Grower practice* / GenetixBay practice. ## Sources 1. Oregon State University Seed Laboratory. Industrial hemp seed testing. https://seedlab.oregonstate.edu/seed-testing/industrial-hemp 2. Minnesota Department of Agriculture. Cannabis seed testing. https://www.mda.state.mn.us/cannabis-seed-testing 3. Alaska Plant Materials Center, State Seed Laboratory. Seed testing. https://plants.alaska.gov/SeedTest.html 4. Small E, Brookes B. 2012. Temperature and moisture content for storage maintenance of germination capacity of seeds of industrial hemp, marijuana, and ditchweed forms of Cannabis sativa. Journal of Natural Fibers 9(4):240-255. https://doi.org/10.1080/15440478.2012.737179 5. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 6. Suza W, Lamkey K (eds). 2023. Quantitative Methods for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativeplantbreeding/ --- # Selection and pheno hunting: sample sizes and scoring rubrics > A pheno hunt is a selection experiment: grow enough seeds to have a real chance of finding what you want, clone every candidate before flowering, score each plant on a fixed weighted rubric, and re-grow the top few as clones before you call a keeper. The plants needed follow 1 - (1 - p)^n: a 1-in-10 type needs 29 plants for a 95% chance of seeing at least one. Sex stability is a gate: any plant that herms is culled, whatever else it scores. - Canonical: https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.html - Category: Breeding · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg, Flower, Harvest, Cure · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **How many seeds should I pop for a pheno hunt?** How many seeds to pop depends on how rare the target type is. For a 95% chance of finding at least one plant, a 1-in-4 type needs 11 females, 1 in 10 needs 29, 1 in 20 needs 59 and 1 in 100 needs 299. Double those for regular seed to allow for males, and add germination losses. Fewer than 10 females is a sampling. **How do I pick a keeper?** Pick a cannabis keeper by writing a brief before popping seeds, cloning every seedling, scoring all plants on the same weighted rubric, shortlisting the top 10-20%, then re-running 2-4 clones of each shortlisted plant together. Most 'keepers' fall out in that second run. Cull any plant showing pollen sacs or nanners, however good it smells. **What should I score in a pheno hunt?** Score cannabis plants 1-5 on vigour and health, structure, pest and mould resistance, flowering time, dry yield, resin and trim, blind-rated dry aroma, lab chemistry from the same lab and stage, and blind smoke reports, each multiplied by a weight fixed before scoring. Sex stability is a gate, not a score: any intersex plant is culled. **Should I clone before flowering?** Yes, clone every cannabis seedling before flipping to flower, taking two cuts each and labelling them with the parent's ID. Without clones you can lose the winner at harvest, since a flowered seed plant is hard to keep. Discard the clones of rejected plants later, and use the clones of shortlisted plants for the confirmation run. **How many times should I run a cut before deciding?** Run a cannabis cut at least twice before deciding it's a keeper: once in the seed hunt, then a second run with 2-4 clones of each shortlisted candidate grown side by side. A single run of one plant mostly selects the luckiest pot, because environmental noise can make a plant look better than its genes deserve. **Short answer.** Decide what you are looking for before you pop a seed, grow enough plants to have a fair chance of finding it, clone every candidate, score every plant the same way, and confirm the winners in a second run. One run of one plant is a lottery ticket, not a selection. > **Breeder's standard.** Sex stability is a gate, not a score. Any plant that shows pollen sacs or nanners during the hunt is out, along with its clones, however good it smells. Don't use it as a mother, a reversal donor or a pollen parent. Record the week and conditions, and report the line's herm rate. Cannabis is a dioecious species; a herm in a hunt is a defect in that seed lot, and the light leak that exposed it did you a favour. ## What's happening In a segregating seed lot (F2, polyhybrid, landrace), each seed is a different genotype. You are sampling a distribution. Two forces fight you: 1. **Rarity.** The combination you want may be 1 in 10 or 1 in 100. 2. **Environmental noise.** A plant in the best corner looks better than its genes deserve [1]. Good hunting raises your odds against the first and filters out the second. ## How many plants? Probability of finding at least one plant of a type with frequency p in n plants: **P = 1 - (1 - p)^n**, so **n = ln(1 - P) / ln(1 - p)** [1]. | Frequency of target type | 80% chance | 90% chance | 95% chance | 99% chance | |---|---|---|---|---| | 1 in 4 (25%) | 6 | 9 | 11 | 17 | | 1 in 10 (10%) | 16 | 22 | 29 | 44 | | 1 in 20 (5%) | 32 | 45 | 59 | 90 | | 1 in 50 (2%) | 80 | 114 | 149 | 228 | | 1 in 100 (1%) | 161 | 230 | 299 | 459 | Add germination losses and males (regular seed: double it). Practical rule: fewer than 10 females is a sampling, not a hunt. ## Before you start - **Write the brief.** Three to five must-have traits and the weighted score below. Changing criteria mid-hunt makes you pick favourites. - **Mint a GB-IND per seedling** and label pots with it. - **Uniform conditions.** Same pot size, medium, feed; rotate positions weekly. - **Clone everyone** before flipping (2 cuts each). Discard clones of rejected plants later. ## Scoring rubric (score 1-5 each, multiply by weight) | Trait | Weight | How to score | When | |---|---|---|---| | Vigour and health | 2 | Growth rate, leaf colour, no deficiencies under standard feed | Veg | | Structure | 1 | Internode spacing, branching, support needed | Late veg / week 3 flower | | Sex stability | 3 (gate) | Any pollen sacs or nanners = cull plant and clones; note week and any trigger | Whole flower | | Pest and mould resistance | 2 | Powdery mildew, botrytis incidence, mite tolerance | Whole run | | Flowering time | 1 | Days from flip to harvest-ready | Harvest | | Yield | 2 | Dry grams per plant (or per m²) | After dry | | Resin and trim | 1 | Trichome coverage, leaf-to-calyx ratio | Late flower | | Aroma (dry) | 2 | Intensity, distinctness; blind rated by 2-3 people | After cure | | Chemistry | 2 | Lab cannabinoid and terpene panel, same lab, same stage | After dry | | Smoke / effect report | 1 | Blind panel notes; reported, not promised | After cure | Gate traits (sex stability, serious mould) remove a plant regardless of score. Weights are a *Grower practice* template; adjust to your brief, but fix them before scoring. Structured descriptors in DUS test guidelines are a good model for consistent scoring language [5]. ## Step by step 1. **Germinate** the full lot together; record germination rate (it is QC data for the batch). 2. **Veg cull** only for gross faults (weak, deformed, sick). Don't cull on looks too early. 3. **Clone** all survivors, label clones with the parent GB-IND. 4. **Flower and score** using the rubric, with dated photos at weeks 3, 6 and harvest. 5. **Shortlist** the top 10-20% by total score. 6. **Re-run** shortlisted clones together (2-4 each). This is where most "keepers" fall out. 7. **Select** the keeper(s). Record why. For breeding, also keep the best males or note which females pass traits to offspring (progeny testing). ## Selecting males You can't smoke a male. Use: - vigour, structure, resistance and sex stability (no female flowers; a male that makes female flowers is intersex and is culled); - stem rub aroma (*Grower practice*, weak evidence); - **progeny testing**: cross each candidate to the same female and compare offspring. This is the only strong evidence of a male's breeding value. ## Common mistakes - Popping 5 seeds and calling the best one "the keeper". - Not cloning before flower, then losing the winner at harvest. - Scoring THC from one sample at one lab and treating it as fixed [4]. - Letting a strong-smelling but intersex plant through "because the herm was stress". Stress reveals susceptible genetics; sex stability is a gate, not a bonus. ## Evidence - Sample-size probability and selection theory: *Established* [1][2]. - Cannabinoid ratios more selectable than absolute amounts: *Supported* [3]. - Lab variability in potency: *Supported* [4]. - Rubric weights and male stem-rub: *Grower practice*. - Sex stability as a hard gate (cull herm-prone plants, never breed from them): GenetixBay breeder's standard; see [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). ## Sources 1. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 2. Suza W, Lamkey K (eds). 2023. Quantitative Methods for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativeplantbreeding/ 3. Naim-Feil E, Elkins AC, Malmberg MM, et al. 2023. The Cannabis plant as a complex system: interrelationships between cannabinoid compositions, morphological, physiological and phenological traits. Plants 12(3):493. https://doi.org/10.3390/plants12030493 4. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 5. UPOV. 2023. Test guidelines for hemp (Cannabis sativa L.), TG/276/1. https://www.upov.int/edocs/tgdocs/en/tg276_01.pdf --- # Tissue culture basics for cannabis growers and breeders > Tissue culture grows small pieces of a plant (usually nodes or shoot tips) on a sterile gel medium, giving clean, compact, long-lived backups of clones and a route to cleaning up infected stock. Cannabis tissue culture works but is genotype dependent and poorly replicated in the literature; contamination control is the main skill. - Canonical: https://genetixbay.com/knowledge/breeding/tissue-culture-basics.html - Category: Breeding · Level: Advanced - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Veg · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is cannabis tissue culture?** Cannabis tissue culture, or micropropagation, is growing small plant pieces such as nodal segments or shoot tips in sterile jars on a gel of nutrients, sugar and plant growth regulators. It runs through initiation, multiplication, rooting and acclimatisation. Its main uses are space-saving clean clone banks and producing pathogen-tested stock, since hundreds of genotypes fit on a shelf. **Can I do tissue culture at home?** Yes, cannabis tissue culture is learnable at home, but most failures come from contamination, often from internal bacteria in a dirty mother. Published protocols often work on only one or two cultivars, so expect to adjust. Handle pressure cookers, bleach and 70% ethanol safely, and never open a pressure vessel under pressure. **Does tissue culture remove viroids?** Tissue culture can help remove viroids such as HLVd, but it is not guaranteed. Meristem or shoot-tip culture combined with testing is a standard route to pathogen-free stock in many crops and is used for cannabis, yet viroids are hard to eliminate and cannabis elimination rates are poorly documented. Test every plantlet before release. **What medium is used for cannabis tissue culture?** Cannabis tissue culture typically uses MS or DKW basal salts, with DKW often reported to perform better for shoots depending on genotype, plus about 2-3% sucrose (20-30 g/L) and 6-8 g/L agar or gellan gum at pH 5.7-5.8. A cytokinin drives multiplication and an auxin such as IBA drives rooting. Exact concentrations vary by protocol. **How long can a cannabis clone be kept in tissue culture?** Published cannabis protocols set no firm maximum time a clone can be kept in tissue culture; it is maintained by repeated transfers, with active multiplication cycles of about 3-6 weeks. Culture is nearly but not perfectly a genetic freeze, so slow-growth storage at lower temperature with fewer transfers is used to reduce cell divisions and the variation they cause. **Short answer.** Tissue culture (micropropagation) means growing small plant pieces in sterile jars on a gel of nutrients, sugar and plant growth regulators. For cannabis its main uses are clean, space-saving clone banks and producing pathogen-tested stock. It is learnable at home, but most failures are contamination, and published protocols often work on only one or two cultivars [1]. ## What's happening Plant cells can regrow shoots and roots when given the right nutrients and hormone balance. In culture there are no pests and little space needed, so hundreds of genotypes fit on a shelf. Monthony et al. (2021) reviewed the field and found important gaps: many studies used hemp as a stand-in for drug-type cannabis, tested one cultivar, or were not independently replicated [1] (*Supported* as a caution). ## The stages | Stage | What happens | Typical duration | |---|---|---| | 0. Mother prep | Clean, pest-free, tested mother; spray-free for a while | 2-4 weeks | | I. Initiation | Surface-sterilise nodal segments or shoot tips; place on medium | 2-4 weeks | | II. Multiplication | Shoots grow and are subdivided | 3-6 weeks per cycle | | III. Rooting | Transfer to rooting medium (often auxin) | 2-4 weeks | | IV. Acclimatisation | Move to plugs under high humidity, then harden off | 1-3 weeks | Durations are indicative (*Grower practice* and [1][2]). ## Media and conditions | Factor | Common choice | Notes | |---|---|---| | Basal salts | MS (Murashige and Skoog) or DKW (Driver and Kuniyuki walnut) | DKW often reported to perform better for cannabis shoots (*Supported*, genotype dependent) [1] | | Sugar | Sucrose ~2-3% (20-30 g/L) | | | Gel | Agar ~6-8 g/L or gellan gum | | | pH | ~5.7-5.8 before autoclaving | | | Cytokinin (multiplication) | e.g., meta-topolin or BAP at low µM | Concentrations vary by protocol [1][2] | | Auxin (rooting) | e.g., IBA | | | Temperature | ~22-25 °C (72-77 °F) | | | Light | ~16 h, low intensity ~30-60 µmol/m²/s | | These are typical ranges across published protocols; check the protocol you follow for exact values. ## Does it clean up HLVd? Meristem (shoot-tip) culture combined with testing is a standard route for producing pathogen-free stock in many crops, and is used for cannabis. Viroids can be difficult to eliminate and success is not guaranteed; every plantlet must be tested before release [3] (*Supported* for the approach; elimination rates in cannabis are poorly documented). ## Is it a perfect genetic freeze? Nearly, but not perfectly. Somatic mutations occur in all dividing tissue [4], and culture can add some variation (somaclonal variation) depending on method. Slow-growth storage (lower temperature, fewer transfers) reduces the number of cell divisions (*Supported* in general plant TC) [1]. ## Safety - Autoclaves and pressure cookers: follow the manufacturer's instructions; never open under pressure. - Bleach (sodium hypochlorite) for surface sterilisation: gloves and eye protection; never mix with acids or ammonia. - Ethanol (70%) and flame or bead sterilisers near each other are a fire risk. Keep ethanol closed and away from flames. ## Common mistakes - Starting from a dirty mother. Internal bacteria show up weeks later. - Copying one paper's hormone recipe and expecting it to work on every cultivar. - Skipping acclimatisation humidity: plantlets lose water fast in normal air. - Calling tissue culture "virus free" without tests. ## Evidence - Feasibility and limitations of cannabis TC: *Supported* (reviews) [1][2]. - DKW vs MS for cannabis: *Supported*, genotype dependent [1]. - Viroid elimination through meristem culture: *Grower practice* / limited published data [3]. ## Sources 1. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 2. Adhikary D, Kulkarni M, El-Mezawy A, et al. 2021. Medical cannabis and industrial hemp tissue culture: present status and future potential. Frontiers in Plant Science 12:627240. https://doi.org/10.3389/fpls.2021.627240 3. Adkar-Purushothama CR, Sano T, Perreault JP. 2023. Hop latent viroid: a hidden threat to the cannabis industry. Viruses 15(3):681. https://doi.org/10.3390/v15030681 4. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 --- # Craft vs industrial cannabis: did legalisation's commercial model hurt quality? > The founder's opinion is that legalisation's commercial model hurt quality: small, careful growers were priced out by large facilities, and product is now grown to a price. The evidence supports parts of that. Wholesale prices fell by roughly 75-80 %, Oregon's flower is at its lowest price since legalisation, Washington lost about a third of its producer businesses from 2017 to 2023, California's licensed canopy is dominated by a few large farms, Canadian excise duty can take 30 % or more of a producer's gross revenue, and regulators have recalled legal product for mould and pesticides. But no data show the grey market was cleaner, and Health Canada's own testing found illegal flower far dirtier than legal flower. Craft vs industrial is the real fault line. Growing your own, where legal, is the surest way to control quality. - Canonical: https://genetixbay.com/knowledge/genetics-history/craft-vs-industrial-cannabis.html - Category: Genetics history · Level: Intermediate - Evidence: Contested · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Did legalisation make weed worse?** Legalisation made weed worse in the founder's opinion, and the evidence supports parts of that view: flower became a price-driven commodity, small producers left, and regulators recalled legal product for aspergillus and banned pesticides. But no data show the grey market was cleaner, and Health Canada's own testing found illegal flower far dirtier. The real fault line is craft versus industrial production. **Is craft cannabis better than commercial cannabis?** Craft cannabis being better than commercial cannabis is the founder's experience rather than a measured result: no controlled tasting or chemistry data compare small-batch with industrial flower. What is documented is that commodity prices reward growing the most grams for the least money, and that large facilities can irradiate flower to pass microbial limits. GenetixBay proposes blind Bay Trials to settle it. **Why are small cannabis farms going out of business?** Small cannabis farms are going out of business mainly because of price collapse, tax and compliance cost. Washington's producer businesses fell from 973 in 2017 to 666 in 2023, with 44% five-year survival. In California the largest 10% of farms held about 60% of permitted area, and permit costs topped farmers' reasons for not licensing. Oregon expects further consolidation. **Is legal cannabis contaminated?** Legal cannabis is sometimes contaminated, though testing lowers the risk. Regulators have recalled licensed flower for aspergillus, failed microbial limits and pesticides not allowed on cannabis, and a 2024 private investigation found 25 of 42 California products above limits. Still, Health Canada found trace pesticides in only 2 of 50 legal samples, against 94% of illegal samples carrying multiple pesticides. **Was grey-market weed better than legal weed?** No data show grey-market weed was better or cleaner than legal weed. Nobody systematically tested grey-market flower, and the only measured comparison, Health Canada's 2023 survey, found 94% of illegal samples carried multiple pesticides, averaging 3.4 compounds, plus more mycotoxins and microbes. The founder's view that small grey-era growers gave better care is their experience, labelled as contested. **Why is legal weed so cheap now?** Legal weed is cheap now because oversupply and commodity competition drove prices to the floor. Wholesale prices fell about 82% in California from 2010 to 2022 and about 77% in Washington from 2006 to 2022. Oregon's median retail flower reached US$3.75 per gram in 2024, its lowest since legalisation, when estimated demand was only 57% of the harvest. **How much does excise duty cost Canadian cannabis growers?** Canadian excise duty on dried cannabis is the greater of CA$1 per gram or 10% of the sale, and the Competition Bureau estimated it affects producers' gross revenue by 30% or more. As of September 2022, 66% of licensees remitting excise owed the tax agency money. The duty was designed when prices were much higher, and the federal expert panel asked for a review. **What are cannabis appellations of origin?** Cannabis appellations of origin are place-based standards that tie a label to where and how flower was grown, much like wine regions. California's Cannabis Appellations Program lets producers petition to define a region's standards, with labels enforced by the state cannabis regulator, and petitions were expected to open in 2026. They give small craft growers a legal way to prove origin. **Is legal cannabis irradiated?** Some legal cannabis is irradiated: large facilities can treat finished flower to meet microbial limits rather than growing it clean. In one controlled study, standard gamma irradiation left THC and CBD unchanged but cut some monoterpenes by a typical 10 to 20%, and terpinolene by 38% in one variety. Growing your own, where legal, avoids it entirely. **Short answer.** The founder thinks so, and parts of the record back them. Legal markets turned flower into a commodity: wholesale prices fell by roughly **75-82 %** [9], Oregon flower now sells at its **lowest median price since legalisation** [7], Washington lost **31.6 %** of its producer businesses between 2017 and 2023 [8], and regulators have recalled licensed product for **aspergillus, failed microbial limits and banned pesticides** [3][4][5]. What the data don't show is that the grey market was cleaner: Health Canada's own tests found illegal flower far dirtier than legal flower [1]. The fault line isn't legal vs illegal. It's **craft vs industrial**, and the surest craft is your own, grown where it's legal. > **Founder's view (house position, round 7).** In the founder's opinion, legalisation's commercial model was the worst thing that happened to cannabis quality. Better product and better care existed in the grey-market era and with small mom-and-pop growers, who've since been priced out by large facilities. This is his opinion, from decades of growing. Below is the evidence that supports it, and the evidence that cuts against it. GenetixBay never encourages buying from an illegal market; the answer we push is craft, documentation, and growing your own where your local rules allow it. ## The case for the founder's view ### 1. Flower became a commodity, priced to the floor | Market | What happened | Source | |---|---|---| | California | Wholesale sinsemilla about **US$5,500/lb in 2010**; spot index about **US$1,000/lb in September 2022** (−82 %, inflation-adjusted) | Caulkins 2022 [9] | | Washington | Wholesale about **US$4,085/lb (2006)** to about **US$950/lb (2022)**, −77 %; retail bud about **US$40/g (2006)** to about **US$10/g** | Caulkins 2022 [9] | | Washington, first 2.5 legal years | About 45 million priced items in the state's seed-to-sale data: prices fell steadily at both processor and retail level | Caulkins et al. 2018 [10] | | Oregon | Median retail flower **US$3.85/g (2023)** and **US$3.75/g (2024)**, "the lowest point the market has seen since legalization", blamed on oversupply. Estimated demand was **57 %** of the 2024 harvest | OLCC 2025 [7] | | Canada | Legal flower averaged about **CA$10.23/g** in Q3 2019 [18]; prices have fallen since, which is why excise now takes a larger share of each sale (see below) [14][15] | StatCan 2019; Competition Bureau 2023 | Caulkins, an economist who generally favours tight regulation, puts it bluntly: product differentiation is the "natural strategic response to commoditization" [9]. When a gram sells for a few dollars, the business that survives is the one that grows the most grams for the least money. That is a cost incentive, not a quality incentive. ### 2. The small farms are the ones leaving - **Washington:** producer and producer-processor businesses fell from **973 (2017) to 666 (2023)**. Producers' five-year survival rate is **44 %**, against **71 %** for retailers; annual turnover about **11 %** [8]. - **California:** in the first two years of state permits, the **largest 10 % of farms held about 60 % of permitted cultivation area** statewide. Growth in permitted area shifted towards larger, newer farms on flatter land, away from the small, older farms of the remote northern hills [12]. - **California compliance:** in a survey of 362 farmers, high cost (permits plus bringing a site up to standard) was the most-cited reason for not licensing. Among farms growing under about 100 lb, only **43 %** had applied [11]. The authors describe financial, administrative and psychological barriers that "disproportionately affect farmers with fewer resources" [11]. - **California tax:** a cultivation tax of **US$161.28 per pound of dried flower** applied regardless of the farm's selling price until it was repealed on **1 July 2022** [13]. - **Oregon:** low-fee open licensing produced massive oversupply, then a producer licence moratorium (2019), a near-total licence moratorium (2022) and per-capita caps (2024). The regulator expects no new producer licences "for many years" and warns of "additional market consolidation" [7]. ### 3. Canada's tax and compliance load falls hardest on small growers - Excise duty on dried cannabis is the greater of **CA$1 per gram or 10 %** of the sale. The Competition Bureau estimated excise affects producers' gross revenue by **30 % or more**, and found **66 %** of licensees remitting excise owed the Canada Revenue Agency money as of September 2022 [14]. - The Bureau called licensing and compliance costs "particularly burdensome for small and medium-sized businesses", with sites needing to be fully built before a licence is issued [14]. - The federal expert panel noted the duty was designed when prices were much higher, asked Finance Canada to review it, and recommended letting micro-cultivators sell direct to distributors [15]. - Micro-licences are now the most common new licence type: of roughly **900** federal licence holders in March 2024, about **396** were micros; 2024 saw **106** revocations against **101** new licences [16]. ### 4. Recalls and contamination in the legal supply Regulator actions are a matter of public record. We describe them without naming businesses. - **Michigan, November 2021:** the state regulator recalled flower, pre-rolls and other products tested by one laboratory over roughly three months, citing "inaccurate and/or unreliable" results after product that had failed for **aspergillus** was later passed. Reported scale: about **64,000 lb** of product [3]. - **Colorado, 2015-2017:** state and Denver health advisories, holds and recalls for licensed product with residues of pesticides not allowed on cannabis, including **myclobutanil**, avermectin and imidacloprid [4]. - **California, 2024:** a newspaper investigation had 42 licensed retail products tested privately; **25** showed pesticide levels above state limits or above federal tobacco standards. The state regulator later recalled at least one product it had been told about months earlier [5]. These are private tests, not regulator findings, and an industry review disputed the sample. - **Canada:** Health Canada publishes cannabis recalls in its public database; microbial (yeast, mould, bacteria) failures and products not tested for microbes appear regularly, though labelling errors are the most common reason overall [2]. Its random retail sampling has itself triggered a microbial recall [1]. - **Potency labels:** in Health Canada's sample of 50 legal flower products, **48 %** tested under **80 %** of their labelled THC [1] (see [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md)). ### 5. Irradiation: decontaminate the batch instead of growing it clean Large facilities can irradiate finished flower to meet microbial limits. In one study, standard gamma irradiation left THC and CBD unchanged but cut some monoterpenes by a typical **10-20 %**, and terpinolene by **38 %** in one variety [6]. A grower who controls mould in the room has no need for it. The full methods, rules and studies are in [irradiated cannabis](https://genetixbay.com/knowledge/harvest-cure/irradiated-cannabis.md). ## What the evidence doesn't show This section matters most if you're going to argue the point in public. - **No data show the grey market was cleaner.** Nobody systematically tested grey-market flower. The best modern comparison runs the other way: in Health Canada's 2023 survey, **94 %** of illegal samples had multiple pesticides (average **3.4**, 24 different compounds, myclobutanil and paclobutrazol most common), against trace levels in just **2** of 50 legal samples. Illegal samples also carried more mycotoxins and microbes, including opportunistic pathogens [1]. Today's seized illegal product isn't the same thing as a careful small grower of the 1990s, but it's the only measured comparison we have. - **"Better care" is the founder's experience, not a measurement.** We have no controlled tasting or chemistry data comparing grey-market craft with today's industrial flower. - **Concentration isn't uniform.** Canada's market is fragmented, not monopolised: the largest producer held "just over 10 %" in 2023 and the top firms' share has fallen since early legalisation [14]. The pressure on small growers there comes mainly from price, tax and compliance cost, not from one giant. - **Many recalls are about testing, not growing.** The Michigan recall was triggered by unreliable laboratory results [3]. That's a failure of the industrial testing chain, which supports scepticism about labels, but it doesn't prove the plants were grown carelessly. - **Oregon cuts both ways.** It had low fees and many small producers, and still saw prices collapse from oversupply [7]. Cheap licences alone don't save the craft grower. - **Consumers say they like craft more than they pay for it.** Surveys find many buyers would pay only a small premium for small-batch flower (the ones we found are commercial polls). ## Where craft is fighting back - **Appellations of origin.** California is building a Cannabis Appellations Program: producer-led petitions to define place-based standards, with labels enforced by the state's cannabis regulator. Petitions were expected to open in 2026 [17]. - **Micro-licences** in Canada and smaller tiers elsewhere give a legal route for small-batch growers, though the economics remain hard [14][15][16]. - **Home grow, where legal.** The only supply chain you fully control is your own: your genetics, your IPM, your dry and cure (see [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) and [curing](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md)), no irradiation, no lab shopping. Check your local rules first; start with the [first grow guide](https://genetixbay.com/knowledge/basics/first-grow-guide.md). ## What GenetixBay does about it - **Document the craft.** Every line gets a GB-ID with lineage, grow journals and test results, so quality is something you can show, not a word on a jar. - **Reward care, not volume.** On the Bay, yield and potency numbers never earn rewards by themselves; journals, males in the Stud Book, preservation of lost lines and open trials do. - **Settle it with data.** Bay Trials can compare small-batch and industrial practices side by side, with blind panels and lab tests, so the next round of this argument has better numbers. - **Keep the gene pool open.** See [why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) and [patents and the gene pool](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md). ## Evidence - Wholesale and retail price collapse after legalisation: *Supported* by regulator data and economic analysis [7][9][18]. - Small producers exiting and area concentrating in larger farms: *Supported* in Washington and California [8][11][12]; Canada's market is *fragmented*, with pressure from tax and compliance cost [14][15]. - Excise and compliance burden on small Canadian producers: *Supported* by the Competition Bureau and the expert panel [14][15]. - Contamination and recalls in legal supply: *Supported* as documented regulator actions [2][3][4] and one private-testing investigation [5]; rates relative to the old grey market are unknown. - Irradiation reduces some terpenes: *Supported* (one controlled study) [6]. - Grey-market or mom-and-pop product was better cared for: founder's view; *Contested*. The only measured legal-vs-illegal comparison favours legal product on contaminants [1]. ## Sources 1. Health Canada. 2025. Cannabis Data Gathering Program: a comparison of legal and illegal dried cannabis products (final report). https://www.canada.ca/content/dam/hc-sc/documents/services/publications/healthy-living/data-gathering-program-comparison-legal-illegal-dried-cannabis-products/data-gathering-program-comparison-legal-illegal-dried-cannabis-products.pdf 2. Government of Canada. Recalls and safety alerts database (cannabis product recalls). https://recalls-rappels.canada.ca/en 3. CBS News. 2021. Michigan marijuana regulators recall cannabis products from hundreds of stores, citing 'unreliable' test results. https://www.cbsnews.com/news/michigan-marijuana-recall-cannabis/ 4. Colorado Department of Agriculture. Pesticide use in cannabis production. https://ag.colorado.gov/plants/pesticides/pesticide-use-in-cannabis-production-information 5. Environmental Health News. 2024. Legal cannabis in California found contaminated with pesticides (summarising the Los Angeles Times/WeedWeek investigation). https://www.ehn.org/legal-cannabis-in-california-found-contaminated-with-pesticides-2668553310.html 6. Hazekamp A. 2016. Evaluating the effects of gamma-irradiation for decontamination of medicinal cannabis. Frontiers in Pharmacology 7:108. https://doi.org/10.3389/fphar.2016.00108 7. Oregon Liquor and Cannabis Commission. 2025. Recreational marijuana supply and demand report. https://www.oregonlegislature.gov/citizen_engagement/Reports/2025SupplyandDemand_Full%20Report_1-29-25.pdf 8. Washington Joint Legislative Audit and Review Committee. 2025. Cannabis market study. https://leg.wa.gov/jlarc/reports/2025/CannabisMarket/pf_ii/default.html 9. Caulkins JP. 2022. Market trends in high-potency cannabis products (presentation, UW ADAI symposium). https://adai.uw.edu/wordpress/wp-content/uploads/Caulkins2022.pdf 10. Caulkins JP, Bao Y, Davenport S, et al. 2018. Big data on a big new market: insights from Washington State's legal cannabis market. International Journal of Drug Policy. https://www.rand.org/pubs/external_publications/EP67961.html 11. Bodwitch H, Polson M, Biber E, Hickey G, Butsic V. 2021. Why comply? Farmer motivations and barriers in cannabis agriculture. Journal of Rural Studies 86:155-170. https://doi.org/10.1016/j.jrurstud.2021.05.006 12. Dillis C, Biber E, Bodwitch H, et al. 2021. Shifting geographies of legal cannabis production in California. Land Use Policy 105. https://crc.berkeley.edu/wp-content/uploads/2021/03/Dillis-et-al-2021.pdf 13. California Legislative Analyst's Office. 2022. Cannabis tax revenue update (cultivation tax eliminated by Chapter 56, Statutes of 2022). https://lao.ca.gov/LAOEconTax/article/Detail/762 14. Competition Bureau Canada. 2023. Planting the seeds for competition: submission to the Cannabis Act legislative review. https://competition-bureau.canada.ca/en/how-we-foster-competition/education-and-outreach/planting-seeds-competition 15. Health Canada. 2024. Legislative Review of the Cannabis Act: Final Report of the Expert Panel. https://www.canada.ca/en/health-canada/services/publications/drugs-medication/legislative-review-cannabis-act-final-report-expert-panel.html 16. StratCann. 2025. Micros again the most popular licence type in 2024. https://stratcann.com/news/micros-again-the-most-popular-licence-type-in-2024 17. California Department of Food and Agriculture. Cannabis Appellations Program. https://www.cdfa.ca.gov/oars/cap 18. Statistics Canada. 2019. StatsCannabis data availability: crowdsourced cannabis prices, third quarter 2019. https://www150.statcan.gc.ca/n1/daily-quotidien/191009/dq191009a-eng.htm --- # How hybrid 'strains' emerged > Modern drug-type cannabis is mostly a mix of South Asian-derived long-flowering types and Central Asian (Afghan) hashish types, crossed from the 1970s onwards in North America, then distributed by Dutch seed companies from the mid-1980s, and multiplied into thousands of names in clone-driven and legal markets since the 1990s. The broad story is supported by genetics; most specific pedigrees are oral claims with conflicting versions. - Canonical: https://genetixbay.com/knowledge/genetics-history/how-hybrid-strains-emerged.html - Category: Genetics history · Level: Intermediate - Evidence: Contested · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Where did modern cannabis strains come from?** Modern cannabis strains came mostly from crossing South Asian-derived long-flowering, narrow-leaflet types with Central Asian Afghan hashish types. North American growers did this from the 1970s, Dutch seed companies spread the hybrids from the mid-1980s, and clone trading and legal markets multiplied the names from the 1990s. Genetics supports this broad story; most specific pedigrees are claims. **When did indica and sativa get crossed?** Narrow-leaflet long-flowering types (grower 'sativa') and broad-leaflet Afghan types (grower 'indica') were crossed in earnest from the mid to late 1970s, after Afghan seed reached California. The hybrids finished earlier outdoors in temperate climates and suited indoor lights in the 1980s. Exact dates vary between popular accounts, and both labels describe plant shape, not separate species. **What is the history of Skunk #1?** The history of Skunk #1 is mostly oral claim. Popular accounts agree it came from a California seed operation, reached the Netherlands in the mid-1980s and won an early Amsterdam competition. They disagree on its pedigree, either (Afghani x Colombian Gold) x Acapulco Gold or an unordered Afghani, Colombian and Mexican three-way, on a 1976 or later release, and on a 1987 or 1988 award. **Why did Dutch seed banks matter?** Dutch seed banks mattered because, from the mid-1980s, they collected North American hybrid lines and sold seed internationally, turning regional selections into a global gene pool. Amsterdam cannabis competitions popularised the names. The broad history is supported, but company-level details come from popular accounts at the claim level, so specific founding stories and dates should be treated as unverified. **Where did CBD strains come from?** CBD-rich drug-type cannabis strains largely came from hemp introgression. A 2021 genome study found that high-CBD drug-type lines carry hemp-derived genome segments around the CBDAS region, the gene for the enzyme that makes CBD. These lines became prominent in legal markets in the 2010s and 2020s, alongside autoflower hybrids and brand-driven naming. **Are famous strain pedigrees true?** Famous strain pedigrees are mostly unverified claims, not documented facts. They usually rest on popular histories or breeder interviews given decades later, and versions often conflict. Repetition across seed shop pages is not evidence. On GenetixBay each version is recorded as a separate claim; none reaches L3 without period documents or L4 without DNA from documented reference material. **Short answer.** Until the 1960s, drug cannabis was mostly regional landraces. From the late 1960s and 1970s, North American growers imported seed from Mexico, Colombia, Thailand, India and, crucially, Afghanistan, and crossed the long-flowering narrow-leaflet types with early, resinous Afghan types to get plants that finished outdoors in temperate climates and indoors under lights. Dutch seed companies spread these hybrids worldwide from the mid-1980s. Clone trading and, later, legal markets multiplied the names [1][2]. The broad arc is *Supported*; nearly every specific pedigree is a claim. ## The arc, with evidence labels | Period | What happened | Evidence | |---|---|---| | 1960s-70s | Imported export-grade cannabis (Mexico, Colombia, Jamaica, Thailand) brings seed to North America; outdoor growing begins in earnest | *Supported* [1] | | Mid-late 1970s | Afghan seed reaches California; crosses with long-flowering types prove early and productive | *Supported* as history [1][2]; exact dates vary between accounts [6][7] | | Late 1970s-early 1980s | Named stabilised hybrids appear (e.g., Skunk #1, Haze family, Northern Lights family) | Lines' existence *Supported*; pedigrees L1 with conflicting versions [6][7] | | 1980s | Indoor growing under HID lights rewards short, early, Afghan-heavy hybrids | *Supported* [1] | | Mid-1980s | Dutch seed companies collect North American lines and sell seed internationally; Amsterdam cannabis competitions popularise names | *Supported* as history; company details L1 [6] | | 1990s-2000s | Clone-only selections spread hand to hand (the Kush and "OG" families, Chemdawg-related cuts, Diesel types) | Names *Supported*; origins mostly L0-L1 | | 2000s-2010s | Online seed trade and forums; feminised seed becomes common; explosion of crosses and names | *Supported* | | 2010s-2020s | Legal markets; CBD-rich drug-type lines, often traced to hemp introgression [4]; autoflower hybrids; brand-driven naming | CBD from hemp introgression *Supported* [4] | ## Conflicting claims: one worked example **Skunk #1** is a useful example of why GenetixBay records claims rather than "facts". Popular histories agree it came from a California seed operation (often named as Sacred Seeds) and reached the Netherlands in the 1980s, and that it won an early Amsterdam competition. They disagree on details [6][7]: | Claim | Version A | Version B | Level | |---|---|---|---| | Pedigree | (Afghani x Colombian Gold) x Acapulco Gold | Three-way of Afghani, Colombian and Mexican without order | L1 | | Release date | 1976 | Late 1970s / early 1980s | L1 | | Arrival in the Netherlands | 1985 | Mid-1980s, date varies | L1 | | First major award | 1987 | 1988 | L1 | On a GenetixBay record, each version is a separate claim with its source and level. None reaches L3 without period documents (catalogues, dated publications), and none reaches L4 without DNA from documented reference material. ## What genetics says about the big picture - Commercial drug-type cannabis forms a gene pool distinct from hemp, with internal structure that only partly matches reported "sativa/indica" ancestry [3] (*Supported*). - Widespread hybridisation over roughly the past 50 years has blurred historical distinctions [2] (*Supported*). - Modern drug-type lines are a mix of many landrace sources and are highly heterozygous [5] (*Supported*). - High-CBD drug-type lines carry hemp-derived genome segments around the CBDAS region [4] (*Supported*). - Even the US government's research supply was genetically unlike state-market cannabis [8], a reminder that "cannabis" in older studies may not represent today's plants. ## Common mistakes - Repeating a famous pedigree as fact because it is printed on many seed shop pages. Repetition is not evidence. - Assuming a modern seed line with a classic name is the original population. - Treating a single breeder interview, decades later, as documentation. It is a first-hand claim (valuable, L1-L2), not a period record. ## Evidence - Broad hybridisation history: *Supported* [1][2][3][5]. - CBD via hemp introgression: *Supported* [4]. - Specific strain pedigrees and dates: *Contested* / L0-L1 (popular histories [6][7] disagree). ## Sources 1. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://www.ucpress.edu/book/9780520292482/cannabis 2. McPartland JM, Small E. 2020. A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys 144:81-112. https://doi.org/10.3897/phytokeys.144.46700 3. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 4. Grassa CJ, Weiblen GD, Wenger JP, et al. 2021. A new Cannabis genome assembly associates elevated cannabidiol (CBD) with hemp introgressed into marijuana. New Phytologist 230(4):1665-1679. https://doi.org/10.1111/nph.17243 5. Lynch RC, Vergara D, Tittes S, et al. 2016. Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences 35(5-6):349-363. https://doi.org/10.1080/07352689.2016.1265363 6. Leafly. The history of Dutch marijuana seed banks (popular history). https://www.leafly.com/news/growing/history-dutch-marijuana-seed-banks 7. High Times. The history of hybrids: how breeding and selection led to modern marijuana (popular history). https://hightimes.com/?p=200428 8. Vergara D, Huscher EL, Keepers KG, et al. 2021. Genomic evidence that governmentally produced Cannabis sativa poorly represents genetic variation available in state markets. Frontiers in Plant Science 12:668315. https://doi.org/10.3389/fpls.2021.668315 --- # Indica, sativa and ruderalis: what the names really mean > Cannabis is one species, Cannabis sativa L., showing different phenotypes. Nearly everything grown today is a hybrid, with a few outlier landraces. Distinct groups, ruderalis included, may have existed long ago, but not today. As a guide to effects or species, indica vs sativa is nonsense: genetic and chemical studies show the labels don't match ancestry or predict chemistry. At most they describe plant shape: leaflet width, structure and flowering time. - Canonical: https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.html - Category: Genetics history · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is indica a different species from sativa?** Indica is not a different species from sativa. The taxonomic consensus and GenetixBay house position is one species, Cannabis sativa L., showing different phenotypes; any indica and sativa split sits at subspecies or variety level. A minority multi-species view rests on older data from geographically separated populations, which may have been distinct long ago but are not today. **What is Cannabis ruderalis?** Cannabis ruderalis is the name used for small, feral, northern populations that are often autoflowering. Most botanists treat it as a feral or wild-type form of Cannabis sativa, a variety at most, not a separate species. Autoflowering seed is commonly traced to these populations, and the autoflower trait has been mapped to a recessive locus in the populations studied. **Why do botanists say sativa and indica are mixed up?** Botanists say sativa and indica are mixed up because the popular labels run backwards relative to formal names. In a 2020 classification, var. indica is the South Asian narrow-leaflet type growers call 'sativa', and var. afghanica is the Central Asian broad-leaflet type growers call 'indica'. Linnaeus named European hemp sativa in 1753; Lamarck named Indian drug plants indica in 1785. **What is the difference between indica and sativa genetically?** Genetically, there is little consistent difference between plants labelled indica and sativa. A 2021 study found the labelled samples genetically indistinct genome-wide; the labels tracked only a handful of terpenes linked to terpene synthase gene regions. A 2015 study found genetic structure only moderately correlated with reported ancestry. The labels carry a sliver of aroma information, not ancestry. **Does indica mean sedating?** Indica does not reliably mean sedating; that rule of thumb is a myth. Effects depend on dose, cannabinoids, terpenes, the person and the setting. A survey of 89,923 US lab results found indica, hybrid and sativa labels did not reliably separate samples by chemistry, and no cited study shows the labels predict effects. Choose by lab-tested chemistry instead. **Does sativa give you energy?** Sativa does not reliably give you energy; 'sativa equals energy' is marketing shorthand, not botany. Labels tied to a few terpenes may explain why people perceive differences, but large chemical surveys show the labels do not consistently match chemistry. As a guide, 'sativa' describes plant shape at most: tall structure, narrow leaflets and long flowering. **Is everything a hybrid now?** Nearly everything grown and sold today is a hybrid, with only a few outlier landraces. Centuries of trade and roughly 50 years of intensive hybridising have blurred the old distinctions between regional groups, and taxonomists describe the remaining high-THC domesticates as endangered. Describe a plant by its shape, flowering time and lab-tested chemistry rather than a hybrid percentage. **Short answer.** It's **one species**, *Cannabis sativa* L., showing different phenotypes [1]. Nearly everything grown today is a **hybrid**, with a few outlier landraces. As a guide to effects or species, "indica vs sativa" is nonsense: the labels don't track genome-wide ancestry [5][6] and don't reliably predict cannabinoids or terpenes [5][8]. At most, "indica" and "sativa" describe **plant shape**: broad vs narrow leaflets, compact vs open structure, short vs long flowering. Three vocabularies get tangled here: formal botany, historical names (Linnaeus's *C. sativa* in 1753 for European hemp; Lamarck's *C. indica* in 1785 for Indian drug plants) and grower slang. > **House position: one species, different phenotypes.** Thousands of years ago there may well have been distinct, isolated groups, ruderalis included. Today there aren't: centuries of trade and decades of hybridising have mixed nearly everything. "This one's an indica, it'll put you on the couch" is marketing, not botany. Describe a plant by its shape, its flowering time and its lab-tested chemistry. ## What's happening ### Formal botany - **One species** is the consensus and the house position: Small and Cronquist (1976) classified all cannabis as *C. sativa*, dividing it by THC content and domestication status [3]; McPartland (2018) reviews the systematics and supports one species, with any indica/sativa split at subspecies or variety level [1]. - **More than one species** is a minority view: Hillig (2005) argued from allozyme data on older collections for *C. sativa*, *C. indica* and possibly *C. ruderalis* [4]. Those data describe historical, geographically separated populations, which fits the house view that distinct groups may have existed long ago, not that they exist in today's gene pool. - McPartland and Small (2020) name the high-THC domesticates *C. sativa* subsp. *indica*, with **var. *indica*** (South Asian, narrow leaflets, "Sativa" in grower use) and **var. *afghanica*** (Central Asian, broad leaflets, "Indica" in grower use) [2]. Hence "the names are backwards". ### Grower vocabulary | Grower term | Usually means | Botanical counterpart (approx.) | |---|---|---| | "Sativa" | Tall, narrow leaflets, long flowering, "uplifting" | South Asian drug type (var. *indica* in [2]) | | "Indica" | Short, broad leaflets, early, "relaxing" | Central Asian hashish type (var. *afghanica* in [2]) | | "Hybrid" | Everything in between, i.e., almost everything sold | Mixed | | "Ruderalis" | Small, feral, northern, often autoflowering | Feral / wild-type populations (var. *ruderalis* in some systems) [1][4] | | "Hemp" | Fibre or seed type, low THC | *C. sativa* subsp. *sativa* in [1][3] | ## What genetics says about modern labels - Sawler et al. (2015): genetic structure moderately correlated with reported sativa/indica ancestry; hemp was more similar to "indica" type marijuana than to "sativa" strains [6]. - Watts et al. (2021): "sativa" and "indica" labelled samples were **genetically indistinct genome-wide**; the labels tracked a handful of terpenes controlled by terpene synthase gene regions [5]. - Smith et al. (2022), 89,923 lab results from six US states: the indica/hybrid/sativa labels "did not reliably distinguish samples based on their chemical content" [8]. So the labels carry a sliver of information (a few aroma compounds), but not ancestry, not species, and not a predictable effect. ## Does indica mean sedating? No, not reliably: *Myth* as a rule of thumb. Effects are reported, not promised, and depend on dose, cannabinoids, terpenes, person and setting. The labels' link to a few terpenes [5] may explain why people perceive differences, but large chemical surveys found the labels don't reliably separate samples [8], and no study cited here shows they predict effects. GenetixBay articles describe chemistry instead of using effect labels. ## Ruderalis and autoflowering Autoflowering germplasm is commonly attributed to northern, feral "ruderalis" populations (*Supported* as history claim) [4]. The trait itself is mapped to a recessive locus in the populations studied [7]. See [photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md). ## Common mistakes - "This strain is 70% indica." That number is a breeder estimate or a similarity score, not measured ancestry. - Using leaf shape to predict effect. - Calling indica and sativa different species. - Assuming the botanical and grower meanings agree. ## Evidence - One species with different phenotypes: *Supported*, the taxonomic consensus and house position [1][3]; a minority multi-species view rests on older population data [4]. - Popular labels reversed relative to some formal names: *Supported* [2]. - Labels not reflecting genome-wide ancestry: *Supported* [5][6]. - Labels not predicting chemistry: *Supported* [5][8]. - Labels predicting effects ("indica = couch, sativa = energy"): *Myth* (house position). ## Sources 1. McPartland JM. 2018. Cannabis systematics at the levels of family, genus, and species. Cannabis and Cannabinoid Research 3(1):203-212. https://doi.org/10.1089/can.2018.0039 2. McPartland JM, Small E. 2020. A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys 144:81-112. https://doi.org/10.3897/phytokeys.144.46700 3. Small E, Cronquist A. 1976. A practical and natural taxonomy for Cannabis. Taxon 25(4):405-435. https://doi.org/10.2307/1220524 4. Hillig KW. 2005. Genetic evidence for speciation in Cannabis (Cannabaceae). Genetic Resources and Crop Evolution 52:161-180. https://doi.org/10.1007/s10722-003-4452-y 5. Watts S, McElroy M, Migicovsky Z, et al. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y 6. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 7. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 8. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Landrace hunting or biopiracy? Benefit-sharing, consent and cannabis > International law says a country owns rights over its genetic resources: under the Convention on Biological Diversity (1992) and the Nagoya Protocol (in force 2014), anyone taking plant material for breeding or research needs prior informed consent and mutually agreed terms, including benefit-sharing. Cannabis falls through the cracks: it isn't in the Plant Treaty's crop list, it's still a Schedule I drug under the 1961 Single Convention, most seed was collected before these rules existed, and the US and Canada aren't Nagoya parties. Turmeric, neem, hoodia and rooibos show what credit and compensation look like when they're taken seriously. GenetixBay's position: credit the source region and community on every record, document provenance honestly with evidence levels, encourage benefit-sharing and fair practice, and reward returning value to source communities. - Canonical: https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.html - Category: Genetics history · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What is biopiracy in cannabis?** Biopiracy in cannabis means taking seed or the traditional knowledge attached to it, then commercialising or patenting the result without consent from, credit to or benefit for the source community and country. It has no single legal definition. Two wrongs often travel together: taking without permission, an access problem, and claiming as new what farmers already bred, a patent and credit problem. **Is collecting landrace seed biopiracy?** Collecting landrace seed is not automatically biopiracy, but collecting it without the source country's permission, the community's informed consent or any share of the benefits is what the term describes. Drug law is a separate question: cannabis collection has been technically illegal in most source countries for decades, which covers nearly every landrace in circulation. GenetixBay's position is to credit the source region and community, document provenance honestly and reward returning value to them. **Does the Nagoya Protocol apply to cannabis?** The Nagoya Protocol applies only partly to cannabis in practice. It requires prior informed consent and benefit-sharing for genetic resources used in breeding or research, but most cannabis seed in circulation was collected before the Convention on Biological Diversity took effect in 1993, old widespread varieties are generally treated as out of scope, and the US and Canada are not parties. **What is prior informed consent and benefit-sharing?** Prior informed consent means getting permission from the provider country, and for traditional knowledge the community, before collecting, with full disclosure of how the material will be used. Benefit-sharing means returning a fair share of what results, such as payments, royalties or seed, on mutually agreed terms set in writing. Both come from the 1992 Convention on Biological Diversity and the Nagoya Protocol. **Is Canada or the US a party to the Nagoya Protocol?** Neither Canada nor the United States is a party to the Nagoya Protocol, so no user-country compliance checks apply there. Canada ratified the underlying Convention on Biological Diversity in 1992, while the US signed it in 1993 but never ratified. As of October 2026 the Protocol had 143 parties, including the EU, India, South Africa, Mexico and Morocco. **Is cannabis covered by the Plant Treaty (ITPGRFA)?** Cannabis is not covered by the Plant Treaty (ITPGRFA). The treaty's Multilateral System shares 64 food and forage crops listed in its Annex I under a standard transfer agreement, and cannabis is not on that list. That means its ready-made exchange and benefit-sharing system does not apply, leaving cannabis to national access laws and drug laws. **What is the Cali Fund?** The Cali Fund is a global fund, launched in February 2025 under a 2024 biodiversity convention decision, for sharing benefits from digital sequence information such as published genome data. Large users are expected to pay an indicative 1% of profits or 0.1% of revenue, with at least half going to Indigenous peoples and local communities. Payment is voluntary, and by August 2026 contributions totalled only US$6,000. **How should landrace seed be collected ethically?** Collect landrace seed ethically by getting any national access permit or licence that exists, then the community's prior informed consent in their language. Put mutually agreed terms in writing, credit the region, community and farmers by name, compensate them, share seed back, and document place, date, collector and seed numbers. Never patent what you collected. **Should source communities be paid for landrace genetics?** Source communities should be paid for landrace genetics, in GenetixBay's view, whether or not a treaty requires it. The farmers who selected landraces over centuries deserve credit and compensation. Precedents from other plants show it can work: a 2003 hoodia agreement gave San communities 6% of royalties, and a 2019 rooibos deal set a 1.5% farm-gate levy for Khoi and San communities. **Short answer.** Collecting seed from farmers and selling the descendants isn't automatically biopiracy, but doing it without the source country's permission, the community's consent or any share of the benefits is what the term means. Since the Convention on Biological Diversity (1992), countries hold sovereign rights over their genetic resources, and the Nagoya Protocol (in force 2014) spells out the rules: **prior informed consent**, **mutually agreed terms** and **fair benefit-sharing** [1][2]. Cannabis mostly slips past them: it isn't on the Plant Treaty's crop list [3], it remains a Schedule I drug [7][8], most seed in circulation was collected before these rules existed, and neither the US nor Canada is a Nagoya party [1][2]. The law hasn't caught up. Practice can. > **House position (founder's view): a strong yes on benefit-sharing.** The farmers who selected the world's landraces over centuries deserve credit and compensation, and anyone collecting from them should do it with consent. That's a value, not a legal summary: as below, the law often doesn't require it for cannabis. We think it should be done anyway. ## What "biopiracy" means There's no single legal definition. In policy use it means taking genetic resources or the traditional knowledge attached to them, then commercialising or patenting the result, without consent from, credit to or benefit for the people and country they came from. Two separate wrongs often travel together: **taking without permission** (an access problem) and **claiming as new what a community already knew or bred** (a patent and credit problem). ## The rules, in one table | Instrument | What it does | Who's in (as of October 2026) | |---|---|---| | **Convention on Biological Diversity** (1992; in force 29 December 1993) [1] | States have sovereign rights over their genetic resources. Access needs the provider country's **prior informed consent** (Art. 15(5)) on **mutually agreed terms** (Art. 15(4)), with fair sharing of benefits. Art. 8(j) protects Indigenous and local communities' traditional knowledge | **196 Parties.** The **US signed (1993) but never ratified.** Canada ratified in 1992 | | **Nagoya Protocol** (adopted 2010; in force 12 October 2014) [2] | Makes CBD access and benefit-sharing (ABS) operational: benefit-sharing (Art. 5), PIC (Art. 6), community consent for traditional knowledge (Art. 7), user-country compliance checks (Arts. 15-17). "Utilisation" means research and development on a resource's genetic or biochemical make-up; breeding counts | **143 Parties.** In: EU, India, South Africa, Mexico, Pakistan (2016), Lebanon (2018), Afghanistan (2018), Nepal (2019), Morocco (2022). **Not in: US, Canada, Jamaica.** Colombia and Thailand signed but haven't ratified | | **EU Regulation 511/2014** [6] | Users in the EU must exercise due diligence that genetic resources they use were accessed legally under the provider's ABS law | EU member states | | **Plant Treaty (ITPGRFA)** (2001; in force 2004) [3] | A shared pool for 64 food and forage crops (Annex I) under a standard transfer agreement | **Cannabis is not in Annex I**, so the Treaty's ready-made system doesn't cover it | | **CBD Decision 16/2 and the Cali Fund** (COP16, 2 November 2024; fund launched 25 February 2025) [4] | A global fund for benefits from **digital sequence information** (genome data). Large users are expected to pay an indicative **1 % of profits or 0.1 % of revenue**; **at least 50 %** goes to Indigenous peoples and local communities [4][5] | Voluntary. By August 2026 it had **two confirmed contributions totalling US$6,000**, against an expected US$1 billion a year [5] | | **WIPO treaty on IP, genetic resources and traditional knowledge** (adopted 24 May 2024) [16] | Patent applicants must disclose the origin of genetic resources or traditional knowledge an invention is based on | Not yet in force: it needs 15 ratifications. | ## Why cannabis falls through the cracks 1. **It's still a controlled drug.** Cannabis and cannabis resin remain in **Schedule I** of the 1961 Single Convention; the 2020 vote only removed them from Schedule IV (27 votes to 25, one abstention) [7][8]. An ABS permit doesn't make an export legal, and drug law doesn't grant access rights. Collecting and moving cannabis material lawfully needs both, and in most source countries the drug-law side has been closed for decades, so nearly every landrace in circulation was technically collected outside the law. The treaty definition of "cannabis" excludes seeds not accompanied by the tops [7], but national laws on seed vary widely. Check local rules before collecting, carrying or importing any plant material. 2. **Most seed was collected before the rules.** The bulk of "landrace" seed in Western catalogues was gathered on travels in the 1960s to 1980s, before the CBD's 1993 entry into force. ABS law is generally not applied retroactively, and the CBD's start date is commonly treated as the threshold [9]. Whether later breeding of old collections counts as new utilisation is debated. 3. **Widespread material may be out of scope.** Analysts of the coffee sector note that old, globally disseminated varieties are generally treated as outside Nagoya's reach [9]. Heirloom cannabis lines grown worldwide for decades are in the same position. 4. **Big user countries aren't bound.** The US isn't a CBD party and neither the US nor Canada has joined Nagoya [1][2], so no user-country compliance check applies there. 5. **Genome data moves freely.** Landrace sequences in public databases are digital sequence information. The Cali Fund exists for exactly this, but payment is voluntary and, so far, close to nil [4][5]. ## Source countries: a snapshot | Country | What applies | Notes | |---|---|---| | **Morocco** | Law 13-21 (2021) allows medical and industrial cannabis under a state regulator (ANRAC); non-medical products above 1 % THC barred [14]. Nagoya Party since 2022 [2] | In 2024 the regulator approved the local variety, **Beldia**, for licensed cooperatives; it made up **2,786 of 4,082 tonnes** of the 2024 legal harvest [15]. A source country putting its own landrace first | | **India** | Biological Diversity Act 2002 (amended 2023): foreign users need national approval to access biological resources and associated knowledge. Nagoya Party [2] | | | **South Africa** | Biodiversity Act 2004, Chapter 6, and the Bioprospecting, Access and Benefit-Sharing Regulations (2008). Nagoya Party [2] | The legal home of the hoodia and rooibos agreements below [12][13] | | **Afghanistan, Pakistan, Nepal, Lebanon** | Nagoya Parties since 2016-2019 [2] | Drug law makes lawful collection of cannabis material effectively impossible | | **Colombia, Jamaica, Thailand** | CBD Parties, not Nagoya Parties [1][2]; each has a licensed cannabis regime | | ## Precedents: what credit and compensation look like None of these are cannabis, but they are the public cases the field learned from. | Case | What happened | |---|---| | **Turmeric** | A 1995 US patent (5,401,504) claimed turmeric for wound healing. India's Council of Scientific and Industrial Research challenged it with prior art including a 1953 Indian medical journal paper; the US Patent Office rejected all claims in 1997 [10] | | **Neem** | A European patent on a neem-oil fungicide was revoked in 2000 after opposition; the Board of Appeal dismissed the appeal in 2005 for lack of inventive step [11] | | **Hoodia** | After an appetite-suppressant compound from hoodia, long used by San people, was patented and licensed without them, a 2003 agreement gave San communities **6 % of royalties and 8 % of milestone payments**, paid into a trust [12] | | **Rooibos** | A 2019 agreement under South Africa's ABS rules requires processors to pay a levy of **1.5 % of the farm-gate price** to Khoi and San communities for their traditional knowledge, estimated at about R12 million a year [13] | The lesson: patents on traditional knowledge can be beaten with documented prior art, and benefit-sharing works when it's written into law and contracts. ## The cannabis practices Described as practices, because that's what the record supports: - **Seed collected on travels and sold as "landrace"** decades later, after generations of selection and sometimes crossing elsewhere. That's an heirloom, not a landrace, and the farmers are rarely named (see [landraces of the world](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md), especially its *Credit where it's due* section). - **Country names as marketing.** A region in a name is a claim, not provenance. - **Protection filed on landrace-derived material.** Plant patents, utility patents and breeders' rights can cover lines and traits whose roots are farmer selections; all are public records (see [patents and the gene pool](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md)). - **Erosion at source.** While collected seed is sold abroad, the domesticates at home are endangered by hybrid replacement [17]. Taking without giving back speeds the loss. ## What fair practice looks like 1. **Know the law.** Where a national ABS permit or drug-law licence is available, get it. Because cannabis collection has been technically illegal almost everywhere, legality alone can't be the test of fair practice; consent, credit and returning value are. GenetixBay doesn't advise anyone to break the law where they live. 2. **Prior informed consent** from the community, in their language, before collecting, including what the material will be used for and whether it may be sold or protected. 3. **Mutually agreed terms in writing:** what is shared, how much, for how long. 4. **Credit by name:** region, community and, where they wish, the farmers. Not "Asian landrace", but the valley and the people. 5. **Compensation:** a share of seed sales, a fixed payment, or funding the community wants, such as a community seed bank. 6. **Share seed back.** Return seed and records to the community and to public gene banks where legal, so a collection doesn't become the only copy. 7. **Document everything:** collection place and date, collector, number of seeds or plants, permits, and how the line has been maintained since. 8. **Don't patent what you collected.** Prior art belongs to the people who bred it. ## GenetixBay's position We don't gatekeep the archive on how seed was collected decades ago: cannabis collection has been technically illegal almost everywhere for generations, so that test would erase nearly every landrace. What we ask for instead is credit and honesty. - **Credit the source on every record.** Landrace populations get their own record type (GB-LRC) with region of origin, keeper or custodian, collection history and evidence level, and every line descended from one carries the **source region and community credit** forward. - **Document provenance honestly.** Collection place and date, collector and maintenance history are evidence-graded claims (L0-L4; see [documenting lineage evidence](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md)). Unknown stays unknown; we label collected-and-maintained lines as heirloom, not landrace. - **Encourage benefit-sharing and fair practice.** Consent, written terms, compensation and sharing seed back are the standard we promote, whether or not a treaty forces it. - **Reward returning value.** Breeders and members who return seed, records or money to source communities earn recognition on the platform for it. ## Common mistakes - "It was legal to buy, so it's ethical." Access law, drug law and ethics are three different questions. - "Nagoya doesn't apply, so nothing is owed." The law is a floor. - "Old seed is fair game." It may be outside the law; the credit is still owed. - Encouraging anyone to smuggle seed. Never. ## Evidence - CBD and Nagoya obligations (PIC, MAT, benefit-sharing) and party status: *Established* (treaty texts and official lists) [1][2]. - Cannabis absent from Plant Treaty Annex I: *Established* [3]. - Cannabis in Schedule I of the 1961 Convention: *Established* [7][8]. - Cali Fund rates, voluntary status and low uptake: *Established* for the decision [4]; *Supported* for uptake (press report) [5]. - Pre-CBD and widespread material falling outside ABS: *Supported*, with legal debate [9]. - Turmeric, neem, hoodia and rooibos outcomes: *Established* (public decisions and agreements) [10]-[13]. - Morocco's Beldia programme: *Supported* (press reports of regulator data) [14][15]. - Source communities deserve credit and compensation beyond what the law requires: founder's view. ## Sources 1. Convention on Biological Diversity, 1992 (Articles 8(j) and 15), and list of Parties. Secretariat of the CBD. https://www.cbd.int/information/parties.shtml 2. Nagoya Protocol on Access to Genetic Resources and the Fair and Equitable Sharing of Benefits Arising from their Utilization, 2010 (in force 12 October 2014): text and signatories/Parties list. Secretariat of the CBD. https://www.cbd.int/abs/nagoya-protocol/signatories 3. International Treaty on Plant Genetic Resources for Food and Agriculture, 2001, Annex I (crops covered under the Multilateral System). FAO. https://www.fao.org/plant-treaty/en/ 4. UNDP Multi-Partner Trust Fund Office. 25 February 2025. Press release: The Cali Fund launches in the margins of the resumed session of COP16. https://mptf.undp.org/news/press-release-cali-fund-launches-margins-resumed-session-cop16 5. Mbenywe M. 1 September 2026. UN fund for sharing biodiversity benefits struggles for attention and money. Mongabay. https://news.mongabay.com/2026/09/un-fund-for-sharing-biodiversity-benefits-struggles-for-attention-and-money/ 6. Regulation (EU) No 511/2014 on compliance measures for users from the Nagoya Protocol in the Union. https://eur-lex.europa.eu/eli/reg/2014/511/oj 7. Single Convention on Narcotic Drugs, 1961, as amended by the 1972 Protocol (Article 1(1)(b), Articles 23 and 28). UNODC. https://www.unodc.org/pdf/convention_1961_en.pdf 8. UNODC. 3 December 2020. CND votes on recommendations for cannabis and cannabis-related substances. https://unodc.org/unodc/frontpage/2020/December/cnd-votes-on-recommendations-for-cannabis-and-cannabis-related-substances.html 9. Lachenmeier DW, Montagnon C. 2024. Convention on Biological Diversity (CBD) and the Nagoya Protocol: implications and compliance strategies for the global coffee community. Foods 13(2):254. https://doi.org/10.3390/foods13020254 10. Down To Earth. That's an old remedy (on the revocation of US Patent 5,401,504, turmeric for wound healing, after a CSIR challenge, 1997). https://www.downtoearth.org.in/news/thats-an-old-remedy-26452 11. European Patent Office, Technical Board of Appeal. Decision T 0416/01, 8 March 2005 (neem oil fungicide; appeal dismissed). https://www.epo.org/en/boards-of-appeal/decisions/t010416eu1 12. Bulletin of the World Health Organization. 2003. 81(5):382. San people and CSIR sign hoodia benefit-sharing agreement (news item). https://scielosp.org/article/bwho/2003.v81n5/382-382 13. TimesLive. 2 November 2019. Khoi and San sign deal that gives them a cut of rooibos riches. https://www.timeslive.co.za/news/south-africa/2019-11-02-khoi-and-san-sign-deal-that-gives-them-a-cut-of-rooibos-riches/ 14. CMS. Expert guide to a legal roadmap to cannabis: Morocco (Law No. 13-21 on the legal uses of cannabis). https://cms.law/en/int/expert-guides/cms-expert-guide-to-a-legal-roadmap-to-cannabis/morocco 15. North Africa Post. 27 December 2024. Morocco's 2024 legal cannabis harvest rises to over 4000 tons (ANRAC annual review). https://northafricapost.com/?p=83076 16. WIPO Treaty on Intellectual Property, Genetic Resources and Associated Traditional Knowledge (adopted 24 May 2024): notification of ratification by Peru. https://www.wipo.int/wipolex/en/treaties/notifications/details/treaty_gratk_4 17. McPartland JM, Small E. 2020. A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys 144:81-112. https://doi.org/10.3897/phytokeys.144.46700 --- # Landraces of the world: an overview > Drug-type cannabis landraces developed across South and Central Asia and were carried to Africa, the Middle East and the Americas, where local farmers adapted them over centuries. Genomic work points to an Asian origin of domestication (exact region contested). Many traditional landraces are now endangered by hybrid replacement, and most 'landrace' seed in commerce is better described as heirloom: collected at some point, then maintained elsewhere. Every origin story here is a claim; this article labels the evidence. - Canonical: https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.html - Category: Genetics history · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **What are the main cannabis landraces?** The main cannabis landraces fall into two broad drug-type groups. South Asian-derived narrow-leaflet, long-flowering types grow across India, Southeast Asia, Africa, the Caribbean and Latin America. Central Asian broad-leaflet hashish types come from Afghanistan, northwest Pakistan and parts of Central Asia. Regional lines such as Thai, Colombian, Mexican, Jamaican and Moroccan types sit within these groups. **Where did cannabis originate?** Cannabis originated in Asia, though the exact region is contested. A 2021 study resequencing 110 accessions concluded it was first domesticated in East Asia in the early Neolithic. Critics note most basal samples came from Xinjiang or Qinghai, often counted as Central Asia, and key regions went unsampled. The older view places the origin in Central Asia. **What is an Afghani landrace?** An Afghani landrace is a Central Asian broad-leaflet hashish type from Afghanistan, the Hindu Kush and northwest Pakistan. Farmers sieving resin for hashish selected short, compact, early (about 7 to 9 weeks) and resin-heavy plants, often with sesquiterpene alcohols such as guaiol. That selection is the root of every 'Afghani' and 'Kush' in modern hybrids. Botanists call it var. afghanica. **Are landraces still pure?** Landraces are not reliably pure today. Taxonomists describe traditional high-THC domesticates as endangered, with about 50 years of hybridising having obliterated differences between them, and in Morocco traditional kif has largely given way to introduced hybrids. Landraces were never uniform anyway; they vary a lot within a population, and mid-20th-century exports often mixed regions. **Which landraces are sativa and which are indica?** In grower terms, the South Asian-derived landraces of India, Thailand and Southeast Asia, Africa, Jamaica, Mexico and Colombia are the narrow-leaflet 'sativa' types, and Afghan and Hindu Kush hashish landraces are the broad-leaflet 'indica' types. Formal botany flips this, naming them var. indica and var. afghanica. Both labels describe plant shape and flowering time, not separate species. **Are landrace seeds sold online real landraces?** Most landrace seed sold online is better described as heirloom: collected at some point, then grown and selected for years in another country, with bottlenecks and sometimes cross-pollination. A true landrace is a farmer-maintained population in its home region. A country name in a strain name is not proof of origin; look for collection place, date, collector and maintenance history. **Short answer.** Cannabis was domesticated in Asia, then spread with people for fibre, seed and resin. Drug-type landraces fall into two broad historical groups: **South Asian-derived** narrow-leaflet types (India, Southeast Asia, Africa, the Caribbean and Latin America), and **Central Asian** broad-leaflet hashish types (Afghanistan, Pakistan's northwest, parts of Central Asia) [2][3]. Many are endangered, and most "landrace" seed sold today is heirloom material with a history of its own [2]. ## Where it began - **Ren et al. (2021)** resequenced 110 accessions and concluded cannabis was first domesticated in **East Asia** in the early Neolithic, with modern hemp and drug cultivars descending from an ancestral gene pool now represented by feral plants and landraces in China [1] (*Supported*, with criticism). - **Critique:** most "basal" samples came from Xinjiang or Qinghai, which many define as Central Asia, and key regions (Russia, Afghanistan) were unsampled [7]. The older view places origin in Central Asia [3][6]. Treat the exact region as *Contested*; an Asian origin is well supported. ## The two drug-type groups McPartland and Small (2020) classified high-THC domesticates using 1,100 herbarium specimens and literature meta-analysis [2]: | Group (common name) | Formal name proposed [2] | Typical traits | THC:CBD | |---|---|---|---| | South Asian ("Sativa" in popular use) | *C. sativa* subsp. *indica* var. *indica* | Narrow leaflets, tall, long flowering, little or no sesquiterpene alcohols | ≥7 | | Central Asian ("Indica" in popular use) | *C. sativa* subsp. *indica* var. *afghanica* | Broad leaflets, short, early, sesquiterpene alcohols (e.g., guaiol, eudesmols) present, hashish tradition | <7 | Yes, this flips the popular labels, which is part of why taxonomists and growers talk past each other. See [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md). ## A regional overview All lineage and origin statements below are **claims** at roughly L1 (community and ethnobotanical reports) unless a citation says otherwise. Dates are approximate. | Region | Traditional use | Commonly reported traits | Evidence notes | |---|---|---|---| | Afghanistan, Hindu Kush, northwest Pakistan | Sieved hashish (charas in some areas) | Broad leaflets, compact, early flowering (~7-9 weeks), resinous | Central Asian group *Supported* [2][3]; individual seed lines' origins L1 | | India and Nepal (Himalayan foothills) | Hand-rubbed charas, ganja | Mixed; foothill types narrow-leaflet, long flowering | Region-level *Supported* [2][3]; feral populations widespread | | Southeast Asia (Thailand, Laos, Cambodia, Vietnam) | Ganja | Very long flowering (12-16+ weeks), tall, narrow leaflets | *Supported* [3]; heavy loss from hybrid replacement reported [2] | | Africa (South Africa, Malawi, Congo, Ethiopia, Morocco) | Ganja and dagga; Moroccan hashish | Southern and central types narrow-leaflet, long flowering; modern Moroccan crop now largely hybrid | Arrival via Arab and Indian Ocean trade *Supported* [3]; Moroccan hybrid replacement L1 | | Middle East (Lebanon) | Sieved hashish | Variable | L1 | | Caribbean (Jamaica) | Ganja, introduced with indentured South Asian labour in the 19th century | Narrow leaflet, long flowering | Introduction route *Supported* [3] | | Mexico and Central America | Ganja (export era 1960s-70s) | Narrow leaflet, long flowering | Spread history *Supported* [3]; named regional lines (e.g., from specific states) L1 | | Colombia | Export ganja 1960s-70s | Narrow leaflet, long flowering | *Supported* as history [3] | | Brazil | Traditional use in the northeast | Narrow leaflet | L1 | | Northern and Central Asia, Eastern Europe (feral, "ruderalis") | Wild/feral; hemp | Small, early, often day-neutral | Source of autoflowering trait *Supported* as claim [4] | ## Credit where it's due Nearly every modern line, whatever its catalogue name, is built on plants selected over centuries by farmers who never got a seed-bank credit. GenetixBay's position is that they deserve far more of it. - **Afghanistan and the Hindu Kush** (Mazar-i-Sharif, Balkh and the northern provinces; the mountain valleys into northwest Pakistan, including Chitral): farmers who sieve dried plants for resin and press it into hashish selected short, early, broad-leaflet, resin-heavy plants. That selection is the root of every "Afghani" and "Kush" in modern hybrids [2][3][11]. - **The Himalaya: Nepal and the Indian hills** (Darchula, the Parvati Valley, Malana): smallholders hand-rub charas from living plants and keep their own seed, alongside fibre and seed uses [3][9][11]. - **India's ganja growers:** by the 1890s, where ganja was carefully managed, female plants "often receive special care and have the males removed" [8]. That is sinsemilla, practised and understood long before the word reached Western growers. - **Morocco's Rif and Lebanon's Bekaa:** kif and sieved hashish traditions that ran whole regional economies [3][10][11]. - **Thailand, Colombia, Mexico, Jamaica, central and southern Africa:** the long-flowering narrow-leaflet lines that gave modern hybrids their "sativa" side [2][3]. Credit isn't only history. McPartland and Small describe these domesticates as **endangered**, with 50 years of hybridising having "obliterated differences" between them [2]; in Morocco, traditional kif has largely given way to introduced high-yielding hybrids [10]. Preserving and documenting what's left is why GenetixBay exists. See [old cannabis wasn't weak](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md), [why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) and [patents and the gene pool](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md). ## Landrace vs heirloom in your seed catalogue A landrace is a farmer-maintained population in its region [5]. Seed collected decades ago and grown since in another country has been through new selection, bottlenecks and sometimes cross-pollination. GenetixBay records these as heritage lines with: - collection place and date (claim, with evidence level); - who collected it and how many seeds or plants; - how it has been maintained since (population size, isolation). ## Common mistakes - Treating a country name in a strain name as proof of origin. - Assuming landraces are uniform. They vary a lot within a population. - Assuming old means pure. Mid-20th-century exports often mixed regions. ## Evidence - Asian origin of domestication: *Supported*; exact region *Contested* [1][7]. - Two broad drug-type groups (South Asian and Central Asian): *Supported* [2][3][4]. - Endangered status of traditional landraces: *Supported* [2]. - Regional trait descriptions: *Grower practice* / ethnobotanical reports, labelled per row. ## Sources 1. Ren G, Zhang X, Li Y, et al. 2021. Large-scale whole-genome resequencing unravels the domestication history of Cannabis sativa. Science Advances 7(29):eabg2286. https://doi.org/10.1126/sciadv.abg2286 2. McPartland JM, Small E. 2020. A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys 144:81-112. https://doi.org/10.3897/phytokeys.144.46700 3. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://www.ucpress.edu/book/9780520292482/cannabis 4. Hillig KW. 2005. Genetic evidence for speciation in Cannabis (Cannabaceae). Genetic Resources and Crop Evolution 52:161-180. https://doi.org/10.1007/s10722-003-4452-y 5. Villa TCC, Maxted N, Scholten M, Ford-Lloyd B. 2005. Defining and identifying crop landraces. Plant Genetic Resources 3(3):373-384. https://doi.org/10.1079/PGR200591 6. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 7. McPartland J. Was cannabis first grown in eastern China? (commentary). BeyondTHC. https://beyondthc.com/was-cannabis-first-grown-in-eastern-china/ 8. Indian Hemp Drugs Commission. 1894. Report of the Indian Hemp Drugs Commission, 1893-94, chapter V (cultivation of ganja; removal of male plants). https://deriv.nls.uk/dcn9/7443/74434811.9.htm 9. Clarke RC. 2007. Traditional Cannabis cultivation in Darchula District, Nepal: seed, resin and textiles. Journal of Industrial Hemp 12(2):19-42. 10. Chouvy P-A, Afsahi K. 2014. Hashish revival in Morocco. International Journal of Drug Policy 25(3):416-423. https://doi.org/10.1016/j.drugpo.2014.01.001 11. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Old cannabis wasn't weak: the "so much stronger than 20 years ago" myth > "Cannabis is far stronger than it used to be" is false as a claim about the plant's genetics. Famous hashish, charas and sinsemilla traditions are centuries old and impossible with 5 % plants, and old seed grown well today still tests high. The 'weak old weed' numbers come from seized samples: mostly cheap compressed export brick of leaf, seed and stem, often stored for years before testing, measured with changing methods. The best of what source regions grew was rarely exported. What changed is the market and growing technique: fresh, seedless, indoor flower. - Canonical: https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.html - Category: Genetics history · Level: Beginner - Evidence: Myth · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Is weed stronger now than in the 1970s?** Weed is not stronger than in the 1970s as a matter of genetics; that claim is a myth. The average bag sold today tests higher than the average 1975 seized brick because today's product is fresh, seedless, indoor sinsemilla selected for THC, while 1970s seizures were mostly compressed leaf, seed and stem. Traditional resin and well-grown landrace flower were always strong. **Was old cannabis really only 3–5 % THC?** Old cannabis was not really only 3 to 5% THC; those figures describe the average seized sample. US monitoring found ordinary marijuana under 1.5% THC in 1980, but that was mostly kilobrick of pressed leaf, stem and seed, often tested years after seizure. UK customs found imported Indian resin sometimes above 20% THC, and hash oil ran 25 to 45%. **Why do studies say cannabis potency has increased?** Studies say cannabis potency increased because seized-sample averages rose, from about 4% THC in 1995 to about 12% in 2014 in US monitoring. But early seizures were dominated by brick, old samples degraded in storage, and methods and sampling changed. Correcting for sample age cuts the apparent 10.5-fold rise since 1970 to roughly 6 to 7-fold. **Are landrace strains weak?** Landrace strains are not weak. Afghan sieved hashish, Himalayan hand-rubbed charas and Indian seedless ganja were famous long before lab testing, and imported Indian resin in the early 1980s sometimes tested above 20% THC. Low results from grow-outs in England reflected outdoor conditions and harvest timing. The founder's roughly 70-year-old seed stock tests in the high 20s when grown well. **How strong was traditional hashish or charas?** Traditional hashish and charas could be very strong. In seized samples, Moroccan hashish averaged 9.2% THC (up to 13.4%) and Indian resin reached 20.9%, and some early-1980s imported Indian resin exceeded 20% even after smuggling. Lebanese hashish was typically low in THC but high in CBD, about 9%, showing that resin traditions differ in chemotype, not just strength. **Is today's cannabis a different plant from what my parents smoked?** Today's cannabis is not a fundamentally different plant from what earlier generations smoked; the genetics are broadly the same, while growing and the market changed. Sold product is fresher, seedless and indoor-grown, and selection for THC shifted chemistry: in US monitoring data the THC to CBD ratio rose from about 14 to about 80. That compositional change is real. **What was Mexican brick weed?** Mexican brick weed was compressed kilobrick, the cheap export cannabis US buyers mostly bought in the 1960s and 70s: leaf, stem, seed and flower pressed together for smuggling. US monitoring categories separated it from sinsemilla, and ordinary marijuana samples ran under 1.5% THC in 1980. It was built for weight and price, not quality, and often degraded before testing. **Why wasn't good sinsemilla exported in the 1970s?** Good sinsemilla was rarely exported in the 1970s because the US import market paid for volume, cheap compressed brick, so source regions had little incentive to send their best. This is the founder's reading of the market history, consistent with brick-dominated seizures. Seedless flower reached the US market at scale only through domestic growing, with sinsemilla 42% of eradicated plants by 1987. **Short answer.** No. As a claim about the **plant's genetics**, "cannabis is far stronger than it was 20 (or 50) years ago" is a *Myth*. Potent cannabis is old: the sieved hashish of Afghanistan and the Hindu Kush, the hand-rubbed charas of the Himalaya and the seedless ganja of India were famous long before anyone ran a lab test, and growers in British India were removing male plants to make sinsemilla in the 1890s [8][9][10]. The monitoring numbers that show "3 % in the 1970s" describe something else: the average **seized** sample, which for years was cheap compressed export brick of leaf, seed and stem, often stored for years before testing [2][3][5][7]. The best of what source regions grew was rarely what got exported. What changed is the market (fresh, seedless, indoor flower) and growing technique. > **House position: the genetics didn't change; the growing and the market did.** Quality has stayed broadly the same for thousands of years. Regional growers have grown sinsemilla for centuries and mastered it, and the landrace farmers who built the foundation of nearly every modern line deserve far more credit than they get. The founder keeps seed stock collected roughly 70 years ago that regularly tests in the **high 20s** when grown with modern technique (founder's records, unpublished) [23]. ## Credit where it's due Nearly every modern line, whatever its catalogue name, goes back to plants selected over centuries by farmers who never got a seed-bank credit. Their work is documented by ethnobotanists and travellers, and it deserves naming: | Region | People and tradition | What the record shows | |---|---|---| | **Afghanistan: Mazar-i-Sharif, Balkh and the north** | Farmers who sieve dried plants over fine cloth to collect resin heads and press them into hashish | A resin economy built on broad-leaflet Central Asian landraces, the source of the "Afghani" and "Kush" lines in almost every modern hybrid [9][10][13] | | **Hindu Kush and northwest Pakistan, including Chitral** | Mountain growers of short, early, resinous plants suited to a short season | The genetic root of "indica" (var. *afghanica* in formal botany), selected for resin and early finish [9][13] | | **Nepal (e.g. Darchula) and the Indian Himalaya: Parvati Valley, Malana** | Smallholders who hand-rub charas from living plants and keep their own seed | Documented resin, seed and fibre traditions in Darchula [11]; Himalayan hand-rubbed charas described across the region [9][10] | | **India: Bengal and elsewhere** | Licensed ganja cultivators who removed male plants so females stayed seedless | In the 1890s, where ganja was carefully managed, females "often receive special care and have the males removed" [8]: sinsemilla, a century before the word was fashionable | | **Morocco: the Rif (Ketama)** | Kif farmers and dry-sift hashish makers | A long kif and hashish tradition, now largely replaced by introduced high-yielding hybrids [12] | | **Lebanon: the Bekaa** | Sieved, pressed resin, graded by sieve | A resin tradition with a distinctive chemistry: seized Lebanese hash is typically CBD-rich [14] | | **Thailand, Colombia, Mexico, Jamaica, central and southern Africa** | Long-flowering narrow-leaflet landraces grown for ganja and export flower | The South Asian-derived lineages behind the "sativa" side of modern hybrids [9][13] | Taxonomists now describe these domesticates as **endangered**: 50 years of hybridising have "obliterated differences" between them [13], and in Morocco traditional kif has largely given way to introduced hybrids [12]. Credit isn't only a matter of history; it's a reason to preserve what's left (see [landraces of the world](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md)). ## Most of the best was never exported The weak numbers in the 1970s measured **what reached Western markets**, and that was mostly the cheap end. - **The import market wanted volume.** US buyers in the 1960s and 70s mostly bought compressed "kilobrick": leaf, stem, seed and flower pressed together for smuggling. The US monitoring programme's own categories for the 1980s separate kilobrick and loose material from sinsemilla, and ordinary marijuana in its samples ran **under 1.5 % THC in 1980**, about **3.3 % by 1983–84** [7]. - **Seedless flower reached the market at scale only later.** A domestic sinsemilla movement grew in northern California, Oregon and Hawaii from the mid-to-late 1970s [20]. By 1986–87, domestic production was estimated at roughly **18–25 %** of the US supply, and sinsemilla made up **42 %** of plants eradicated in 1987, up from 26 % in 1983 [19]. - **So the early series compares unlike things:** an export commodity built for weight and price in the 1970s, against seedless, fresh, indoor flower later on. Neither tells you what a skilled Afghan, Nepali or Indian farmer kept for local hashish, charas or ganja. That source regions had little incentive to export their best is the founder's reading of the market history, consistent with the brick-dominated seizures above; we haven't found a study that quantifies export grades directly. ## What the old data actually show | Data | What it found | What it means | |---|---|---| | UK customs seizures, 1975–1989 [2] | Mean about **4 % THC for herb and 8 % for resin**, with no clear trend; hash oil **25–45 %** throughout | Imported material wasn't getting stronger, and concentrates were always strong | | UK imported resin, early 1980s [15] | Indian resin had a high mean and a wide spread, with some samples **above 20 %** THC | Traditional resin could be very potent, even after smuggling | | Seized hashish, Israel and Czech Republic [14] | Moroccan mean **9.2 %** (up to 13.4 %); Indian up to **20.9 %**; Lebanese low in THC but high in CBD (mean ~9 %) | Old resin traditions differ in chemotype, not just strength | | Imported seed grown out in England [16][17] | Under 1 % to over 7 % THC; grow-outs at 0.9–2.2 % mean | English outdoor conditions and harvest timing, not genetics alone, set the number | | UK sinsemilla, 2008 [21] | Mean 16.2 %, median 15.0 %; resin median 5.0 %, "typical for many years" | Resin has been stable for decades | Honest reading: these figures support "traditional resin and good flower were never weak" and "the average import was low grade". They don't prove that old landraces matched today's best flower plant for plant; that's what a fair grow-out would test (see below). ## Why the monitoring numbers show a rise The best-known series is the US potency monitoring programme. ElSohly et al. (2016) report average THC in seized cannabis rising from about **4 % in 1995 to about 12 % in 2014** across nearly 39,000 samples, alongside a shift in seizures towards sinsemilla [1]. Mehmedic et al. (2010) found a similar rise from 1993 to 2008 [6]. The data are real; the question is what they measure. | Problem | What happened | Effect on the trend | |---|---|---| | **What was seized** | Early seizures were dominated by brick and loose material; sinsemilla was a small share [7] | Early averages describe cheap bulk material | | **Storage** | THC breaks down with air, light and time [18]; resin THC can halve in under a year and herb loses roughly 17 % a year at room temperature [2]. Early samples were often tested long after seizure | Old samples read lower than they were fresh | | **Freshness adjustment** | Correcting the US series for sample age cuts the apparent **10.5-fold** 1970–2010 rise to roughly **6–7-fold** [5] | A large share of the "rise" is a storage artefact | | **Methods and sampling** | Methods, sample sources and sample sizes changed over the decades; early years rest on few samples [3] | Years aren't strictly comparable | | **Selection bias** | Seizures follow enforcement priorities and smuggling routes, not what skilled growers produced [3] | The series tracks the bulk market | | **Market shift** | Later years contain far more sinsemilla and indoor flower [1][6] | The average rises even if the best plants didn't change | The European monitoring agency's review concluded that claims of a tenfold or greater rise were "not supported", that natural variation exceeded long-term change, and that THC oxidation in storage plus measurement error could mask changes [2]. A literature review reached the same verdict on 20- to 30-fold claims [3]. ## What the evidence against us says We don't hide the other side: - **Average measured THC did rise.** A meta-analysis of herbal cannabis found THC rising by about **0.29 percentage points a year** from 1970 to 2017, and resin by 0.57 points a year [4]. Reviews accept real rises over 10-year windows in several countries [3]. - **Chemistry shifted.** In the US series, CBD fell as THC rose, so the THC:CBD ratio went from about **14 to about 80** [1]. That's a real compositional change in what's sold. - **Some of it is breeding.** The European review attributes higher indoor potency partly to genetics (selected, female-only seed), alongside sinsemilla technique and freshness [2]. Our reading: the average bag sold today does test higher than the average 1975 brick, because of fresher product, sinsemilla, indoor growing, selection for THC over CBD, and a market that sells flower rather than compressed leaf. That isn't the same as "the plant used to be weak". Traditional resin and well-grown landrace flower were strong, and legal-market flower "approaching or exceeding 30 %" total THC is still very rare [22] (see [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md)). ## How to tell the difference - **Ask what was measured.** Seized, mixed, stored export material, or fresh, trimmed sinsemilla? - **Ask when it was tested.** A sample tested years after seizure has lost THC [2][18]. - **Compare like with like.** Heirloom seed grown with modern technique, side by side with a modern hybrid, tested by the same lab, is the fair test. It's an obvious GenetixBay trial. ## Common mistakes - Treating "average seized sample" as "the plant". - Calling landraces "weak" without growing them well. - Crediting modern breeders for resin that traditional farmers selected for centuries. - Assuming a modern label number is accurate (see [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md)). ## Evidence - Rise in average THC of seized samples: *Established* as a description of those datasets [1][6]; real increases in average measured THC: *Supported* [4]. - Reading that rise as a change in the plant's genetic potential: *Myth* (house position). The early data's limits (brick and mixed material, storage degradation, freshness, changing methods, selection bias) are *Supported* [2][3][5][7]. - Potent traditional resin and sinsemilla practice: *Established* historically [8][9][10]; high-THC traditional resin samples: *Supported* [14][15]. - "The best wasn't exported": *Supported* in part by seizure categories and the rise of domestic sinsemilla [7][19][20]; export economics not quantified. - Founder's heirloom seed stock testing in the high 20s: founder's records, not peer reviewed [23]. ## Sources 1. ElSohly MA, Mehmedic Z, Foster S, Gon C, Chandra S, Church JC. 2016. Changes in cannabis potency over the last 2 decades (1995-2014): analysis of current data in the United States. Biological Psychiatry 79(7):613-619. https://pmc.ncbi.nlm.nih.gov/articles/PMC4987131/ 2. King LA, Carpentier C, Griffiths P. 2004. An overview of cannabis potency in Europe. EMCDDA Insights 6. European Monitoring Centre for Drugs and Drug Addiction, Lisbon. https://www.euda.europa.eu/publications/insights/cannabis-potency_en 3. McLaren J, Swift W, Dillon P, Allsop S. 2008. Cannabis potency and contamination: a review of the literature. Addiction 103(7):1100-1109. https://doi.org/10.1111/j.1360-0443.2008.02230.x 4. Freeman TP, Craft S, Wilson J, et al. 2021. Changes in delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in cannabis over time: systematic review and meta-analysis. Addiction 116(5):1000-1010. https://doi.org/10.1111/add.15253 5. Sevigny EL. 2013. Is today's marijuana more potent simply because it's fresher? Drug Testing and Analysis 5(1):62-67. https://doi.org/10.1002/dta.1430 6. Mehmedic Z, et al. 2010. Potency trends of Δ9-THC and other cannabinoids in confiscated cannabis preparations from 1993 to 2008. Journal of Forensic Sciences 55(5):1209-1217. https://doi.org/10.1111/j.1556-4029.2010.01441.x 7. ElSohly MA, et al. 2000. Potency trends of Δ9-THC and other cannabinoids in confiscated marijuana from 1980-1997. Journal of Forensic Sciences 45(1):24-30. 8. Indian Hemp Drugs Commission. 1894. Report of the Indian Hemp Drugs Commission, 1893-94, chapter V (cultivation of ganja; removal of male plants). National Library of Scotland digital copy. https://deriv.nls.uk/dcn9/7443/74434811.9.htm 9. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 10. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). 11. Clarke RC. 2007. Traditional Cannabis cultivation in Darchula District, Nepal: seed, resin and textiles. Journal of Industrial Hemp 12(2):19-42. 12. Chouvy P-A, Afsahi K. 2014. Hashish revival in Morocco. International Journal of Drug Policy 25(3):416-423. https://doi.org/10.1016/j.drugpo.2014.01.001 13. McPartland JM, Small E. 2020. A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys 144:81-112. https://doi.org/10.3897/phytokeys.144.46700 14. Hanuš LO, et al. 2016. The main cannabinoids content in hashish samples seized in Israel and Czech Republic. Israel Journal of Plant Sciences 63(3):182-190. 15. Baker PB, et al. 1980. Variation in the THC content in illicitly imported Cannabis products. Bulletin on Narcotics 32(4):47-54 (part II: Bulletin on Narcotics 34(3/4):101-108, 1982). 16. Baker PB, Gough TA, Taylor BJ. 1983. The physical and chemical features of Cannabis plants grown in the United Kingdom of Great Britain and Northern Ireland from seeds of known origin, part II. Bulletin on Narcotics 35(1):51-62. https://www.ojp.gov/pdffiles1/Digitization/119769NCJRS.pdf 17. Fairbairn JW, Liebmann JA. 1974. Cannabinoid content of Cannabis sativa grown in England from imported seed. Journal of Pharmacy and Pharmacology 26:413-419. 18. Fairbairn JW, Liebmann JA, Rowan MG. 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1-7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x 19. National Narcotics Intelligence Consumers Committee (NNICC). 1988. The NNICC Report 1987: the supply of illicit drugs to the United States (domestic share of the marijuana supply; sinsemilla share of eradicated plants). NCJRS 111482. 20. Raphael R. 1985. Cash Crop: An American Dream. Ridge Times Press, Mendocino. 21. Hardwick S, King L. 2008. Home Office Cannabis Potency Study 2008. Home Office Scientific Development Branch, UK. 22. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 23. GenetixBay founder. Seed-stock records and lab certificates for heirloom lines kept from seed collected roughly 50-70 years ago (unpublished, held by GenetixBay). --- # Patents and the gene pool: who can own a cannabis plant? > Cannabis can be protected by US utility patents (covering plants, traits, extracts and methods), plant patents (for asexually reproduced varieties) and plant variety protection certificates (for seed-propagated hemp, since 2019), plus plant breeders' rights in Canada and the EU. Grants are public record. Legal commentators worry that thin prior art and broad claims could fence off parts of a shared gene pool. The open responses are public, dated documentation: prior-art databases, open-source seed pledges and genotype registries. GenetixBay's answer is preservation, GB-ID documentation and open sharing. - Canonical: https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.html - Category: Genetics history · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Can you patent a cannabis strain?** You can patent a cannabis strain in the US. A plant patent covers one distinct, asexually reproduced variety (a clone), a utility patent can cover a plant with defined traits, breeding methods or extracts, and plant variety protection covers seed-propagated varieties, with hemp accepted since 2019. Each runs about 20 years. Canada and the EU grant plant breeders' rights. **Are there cannabis patents?** Cannabis patents exist and are public record. Examples include a 2015 US utility patent claiming a hybrid plant with a defined terpene and CBD profile, a 2016 plant patent reported as the first US cannabis plant patent, and a 2003 US government patent on cannabinoids as antioxidants and neuroprotectants. Legal commentators report filings rose sharply once legal markets opened. **What is a plant patent vs a utility patent?** A plant patent protects one distinct variety reproduced asexually, essentially a single clone. A utility patent protects any new, useful and non-obvious invention, which for cannabis can include a plant defined by traits, a breeding method, an extract or a use. Both last 20 years from filing. Seed-propagated varieties are covered separately by plant variety protection certificates. **Can a patent stop me growing my own seeds?** Whether a patent could stop you growing your own seeds depends on the patent's exact claims, the jurisdiction and the facts. A patent can block making, using or selling what its claims cover during its term, but claims are read narrowly, and a patent on defined traits does not cover every plant with one trait. For anything specific, ask a patent attorney. **What is prior art for cannabis?** Prior art for cannabis is anything publicly known before a patent's filing date, such as dated publications, variety descriptions, chemistry or genotype records, that shows a claimed invention is not new. Prior art cannot validly be claimed. Decades of prohibition left little formal publication, and oral knowledge or private grow records are hard for patent examiners to find or cite. **How do I protect a landrace or heirloom from being patented?** Protect a landrace or heirloom from being patented by publishing a dated, findable record of it: its description, chemistry, genotype and history. That defensive publication becomes prior art that defeats later claims of novelty. GenetixBay GB-IDs give timestamped public records for lines, cuts and males. Keeping a line's history only in your head or a private chat does not count. **Short answer.** In the US, cannabis plants and what's made from them can be protected three ways: **utility patents** (plants, traits, extracts and methods), **plant patents** (a specific asexually reproduced variety) and **plant variety protection** certificates (seed-propagated varieties; hemp accepted since 2019) [1][5][6][11]. Canada and the EU grant plant breeders' rights too. All of these are public records. Legal commentators worry that thin documented prior art makes broad claims easier to obtain and harder to challenge [7][8]. The answer that doesn't need a lawyer is **public, dated documentation of what already exists**, which is what GB-IDs and open sharing provide. > **House position: preservation is why GenetixBay exists.** Patents plus consolidation can narrow the commons, and a narrower commons means a narrower gene pool. We don't speculate about anyone's motives, and we don't accuse companies. We document: every line, every cut, every male, with dates and evidence, in the open, so the shared heritage of cannabis stays shared. ## The three kinds of protection (US) | Type | Covers | Term | Example on public record | |---|---|---|---| | **Utility patent** | A new, useful, non-obvious invention: can include a plant with defined traits, a breeding method, an extract or a use | 20 years from filing | US 9,095,554 (2015): claims a hybrid cannabis plant with a defined genotype, terpene profile (myrcene not dominant), terpene oil content and CBD content, with deposited seed [1] | | **Plant patent** | One distinct, asexually reproduced variety (a clone) | 20 years from filing | US PP27,475 'Ecuadorian Sativa' (2016), reported as the first US cannabis plant patent [5] | | **Plant variety protection (PVP)** | A distinct, uniform, stable seed-propagated variety | 20 years | USDA began accepting hemp applications on 24 April 2019 [6] | A historical oddity: the US government itself holds a utility patent on cannabinoids as antioxidants and neuroprotectants (US 6,630,507, 2003) [4]. ## What a patent can and can't do - It **can** stop others making, using or selling what the claims cover, for the term of the patent, where it's in force. - It **can't** reach backwards: something publicly known before the filing date is prior art and can't validly be claimed. - Claims are read narrowly against their exact wording. A patent on a plant with a defined set of traits doesn't cover every plant with one of those traits. - Whether home growers could ever be affected depends on the claims, the jurisdiction and the facts. We're not lawyers; for anything specific, ask one. ## The court case people cite The best-known US dispute concerned **US 9,730,911**, a patent on cannabis extracts and formulations. In the district court (Colorado, filed 2018), the court in 2019 declined to throw out the claims as covering a natural phenomenon, reported as the first cannabis patent case decided in federal court. The infringement claims were later dismissed with prejudice by agreement. On appeal over attorney fees, the Federal Circuit in 2023 affirmed that the case wasn't "exceptional" enough to award fees [2][3]. That's the record; we draw no conclusions about any party. ## The worry about the commons Commentators make three documented points [7][8]: 1. **Thin prior art.** Decades of prohibition meant little formal publication on cannabis varieties, chemistry and breeding. Patent examiners search published literature; oral knowledge and unpublished grow records are hard to cite. 2. **Rising filings.** Patent and breeders'-rights filings on cannabis rose sharply once legal markets opened [7]. 3. **Breadth.** Claims framed around trait combinations (chemotype, terpene profile) could overlap with plants bred or kept long before, if nobody can prove it. ## The open responses | Response | What it is | Status | |---|---|---| | **Prior-art databases** | Public, dated genetic and chemical records of existing varieties, so examiners and challengers can find them | One prominent non-profit prior-art project announced its dissolution in 2019 [10]; commercial genotype registries also publish dated genotypes | | **Defensive publication** | Publishing a variety's description, chemistry and genotype openly, with a date, so it becomes prior art | Anyone can do it; the record has to be findable and dated | | **Open-source seed pledges** | Breeders pledge that a variety and its derivatives stay free to use, breed and share | The main open-source seed initiative accepts cannabis materials only up to 0.3 % THC [9] | | **Plant breeders' rights with breeder exemptions** | PVP-style protection usually lets other breeders use the variety for further breeding | Built into PVP law [11] | ## GenetixBay's answer: preserve, document, share - **GB-IDs are dated, public evidence.** Every registered line, cut and male carries a timestamped record: who, when, where from, photos, journals, lab results and, where available, genotype data (see [documenting lineage](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md)). That's exactly the kind of record prior-art searches need. - **Open by default.** Knowledge-base text and trial results are CC BY-SA. Members choose what to publish about their genetics; the archive keeps it permanently. - **Preservation before it's gone.** Wanted-line and revival programmes, clone backups and the Stud Book for males keep diversity alive (see [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) and [landraces of the world](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md)). - **No legal advice.** If you think a patent affects you, talk to a patent attorney in your jurisdiction. ## Common mistakes - "They patented Kush." Patents claim specific, defined things; read the claims before repeating a headline. - Assuming a variety is protected (or unprotected) without checking the patent and PVP databases. - Keeping your line's history only in your head or a private chat. Undated, unpublished knowledge can't serve as prior art. ## Evidence - The existence and content of the patents, certificates and case cited: public record [1]–[6][11]. - Legal commentary on prior art and the commons: *Supported* as commentary [7][8]; its practical effect on growers is *Contested*. - Documentation as a defence: *Supported* in principle (prior art defeats novelty); how often it has been used for cannabis isn't documented. ## Sources 1. US Patent 9,095,554. Breeding, production, processing and use of specialty cannabis. Granted 4 August 2015. https://patents.google.com/patent/US9095554 2. US Patent 9,730,911. Cannabis extracts and methods of preparing and using same. https://patents.google.com/patent/US9730911 3. United Cannabis Corp. v. Pure Hemp Collective Inc., No. 22-1363 (Fed. Cir. 8 May 2023) (precedential; attorney-fee appeal). https://caselaw.findlaw.com/court/us-federal-circuit/2199626.html 4. US Patent 6,630,507. Cannabinoids as antioxidants and neuroprotectants. Assignee: United States Department of Health and Human Services. Granted 7 October 2003. https://patents.google.com/patent/US6630507 5. US Plant Patent PP27,475. Cannabis plant named 'Ecuadorian Sativa'. Issued 20 December 2016. https://patents.google.com/patent/USPP27475 6. USDA Agricultural Marketing Service, Plant Variety Protection Office. 2019. Announcement: PVPO accepting applications for seed-propagated hemp (24 April 2019). Summary: https://www.cooley.com/news/insight/2019/2019-04-26-usda-announces-acceptance-of-pvp-applications-for-hemp 7. Wyse J, Luria G. 2021. Trends in intellectual property rights protection for medical cannabis and related products. Journal of Cannabis Research 3:1. https://doi.org/10.1186/s42238-020-00057-7 8. Kingsbury A. 2021. Patenting pot: the hazy uncertainty surrounding cannabis patents. Cornell Law Review 106(4). 9. Open Source Seed Initiative. Frequently asked questions (pledging Cannabis materials). https://osseeds.org/faq/ 10. Portland Mercury. 7 May 2019. Open Cannabis Project to dissolve (report on the prior-art database project's closure). 11. 35 U.S.C. §161 (plant patents) and 7 U.S.C. §2321 et seq. (Plant Variety Protection Act). https://www.law.cornell.edu/uscode/text/35/161 --- # Same cut, a thousand names: renaming, relabelling and the shrinking gene pool > Renaming clones, relabelling cuts and reusing famous names make the market look far more diverse than it is. Genetic studies find the same plant sold under different names and different plants sold under one name: in one study 35 % of comparisons put a sample closer to a differently named sample than to its namesakes, and in Nevada 637 recorded names (396 after cleaning) covered three chemical profiles. Hidden sameness makes breeders cross near-identical material while believing they're adding diversity. GenetixBay's answer is the GB-ID: a permanent record tied to the plant, its source and its evidence, not to its name. - Canonical: https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.html - Category: Genetics history · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Are different strain names really different plants?** Different strain names are often not different plants. In a 2015 genetic study, 35% of comparisons put a sample closer to a differently named sample than to its namesakes, and a 2019 study found two differently named samples from one outlet with identical genotypes. A name is a label, not a genotype; only lineage records or DNA comparison show plants differ. **Why do so many strains seem to be the same plant?** So many strains seem to be the same plant because many are. Cuts get renamed as they pass hand to hand, popular clones are rebranded as new, and unrelated crosses borrow famous names. In Nevada's medical market, 637 recorded names (396 after cleaning) covered just three chemical profiles. Breeders crossing renamed cuts are often working with the same few parents. **Do growers rename clones?** Growers do rename clones, sometimes by accident and sometimes deliberately. A cut passed on loses its label and gets a new name, a popular clone is rebranded to look exclusive, and tags fall off in mother rooms and nurseries. Renaming changes nothing in the plant but erases its history. Good practice is to keep the arriving name and add a qualifier. **Is the same cut sold under different names?** The same cut is sold under different names, and genetic studies have documented it. One 2019 study of 122 retail samples found two samples sold under different names from the same outlet with identical genotypes, and only 4 of 30 named strains assigned consistently. Small marker sets can call close relatives identical, so a match needs a reference sample to confirm. **What studies show cannabis strains are mislabelled?** Studies showing cannabis strains are mislabelled include Sawler 2015 (names often fail to reflect genetic identity), Schwabe and McGlaughlin 2019 (outliers in most of 30 retail strains), Watts 2021 (same-named pairs as distant as differently named ones), Reimann-Philipp 2020 (637 Nevada names, three chemical profiles) and Borin 2025 (European seed probably mislabeled). Most are small studies, but they agree. **How does renaming strains hurt cannabis genetic diversity?** Renaming hurts genetic diversity by hiding sameness, not by changing genes. Breeders who cross two 'different strains' that are actually one cut are inbreeding while believing they outcross, so the hybrid pool folds back on a few parents, and originals drop out of circulation when renamed cuts replace them. This dilution is the founder's view, consistent with the evidence but not directly measured. **How can I tell if two strains are the same cut?** To tell if two strains are the same cut, compare their documented sources and chain of custody first, then lab-tested chemistry, and for important plants a DNA comparison against a reference sample. A name or a THC number proves nothing. Even a small-marker genetic match can mistake close relatives for one plant, so treat it as strong evidence only alongside a reference. **What is a GB-ID?** A GB-ID is GenetixBay's permanent identifier for a cannabis line, cut, batch or plant. It never changes and is never reused, whatever the plant is later called. Aliases are recorded with who used them and when, same-named lines from different sources stay separate, lineage claims carry evidence levels, and lab-tested terpene profiles sit on the record. **Short answer.** A name costs nothing to change, and the plant doesn't change with it. Genetic studies keep finding the **same genotype under different names** and **different genotypes under one name** [1][2][3]. In Nevada's medical market, **637 recorded names** (396 after cleaning up spellings and obvious duplicates) sat on just **three** chemical profiles [4]. The shelf looks diverse; the gene pool underneath is narrower than the menu, and renaming hides how narrow. GenetixBay's answer is the GB-ID: a permanent record tied to the plant and its evidence, not to whatever it's called this year. > **House position (founder's view).** "Same cut, a thousand names" is out of hand, and it's part of why everything tastes the same: everything is being replaced or hybridised with similar material, and the gene pool is getting diluted. The studies below back the first half directly (names hide sameness). The dilution half is supported by evidence of narrow commercial chemistry and endangered landraces, but no one has yet measured commercial genetic diversity over time, so we label it carefully. ## How one cut becomes a thousand names These are practices, seen across markets. None needs bad intent; several often involve it. | Practice | What happens | What it does to the record | |---|---|---| | **Renaming a clone** | A cut is passed on, the label is lost or dropped, and it gets a new name at the next stop | One genotype, several names | | **Rebranding a popular cut** | A well-known clone is sold under a fresh name so it looks new or exclusive | One genotype, several names; the original's history disappears | | **Borrowing a famous name** | An unrelated cross or seedling is sold under a name buyers already want | Several genotypes, one name | | **Seed lines sold as one "strain"** | Every seed is a different genotype, but all share the name | Many genotypes, one name | | **"The original cut" claims** | A cut is called the original without a chain of custody | An unverifiable claim attached to a name | | **Menu relabelling** | Retail menus rename or regroup product to match demand or an "indica/sativa" slot | Names that track marketing, not plants | | **Mix-ups** | Tags fall off in mother rooms, nurseries and supply chains | Honest errors that look like everything above | The International Code of Nomenclature for Cultivated Plants says a cultivar name should be unique and not misleading [11]. Most cannabis naming has never been held to it, because for decades it couldn't be: under prohibition, a name passed by word of mouth was the only record there was. ## What the genetic studies found | Study | Material | Finding | |---|---|---| | Sawler et al. 2015 [1] | 81 drug-type and 43 hemp samples, 14,031 SNPs | In **6 of 17 comparisons (35 %)**, samples were genetically closer to samples with *different* names than to samples sharing their name. A sample sold as 100 % sativa was nearly identical (IBS = 0.98) to one sold as 100 % indica. The authors: genetic identity "cannot be reliably inferred by its name" | | Schwabe & McGlaughlin 2019 [2] | 122 retail samples of 30 named strains, three US states, 10 microsatellites | Only **4 of 30** strains gave a consistent genetic assignment across all their samples. Two samples sold under **different names** (Larry OG and Tahoe OG) from the same outlet had **identical** genotypes. The authors: inconsistency "is evident and is not limited to a single source" | | Watts et al. 2021 [3] | 297 samples with chemistry, 137 genotyped at 116,296 SNPs | Pairs of samples with the **same** cultivar name (e.g. OG Kush) were often as genetically and chemically distant as pairs with different names | | Reimann-Philipp et al. 2020 [4] | Nevada medical lab records, January 2016 to June 2017 | **637** names; **396** after merging misspellings and obvious duplicates; **three** terpene-defined chemical clusters. The authors: "many different names are assigned to basically the same products" | | Schwabe et al. 2022 [5] | 32 retail samples of four names from 21 Colorado outlets | Most samples within a name matched, but each name had outliers, and **55 untrained panellists could smell the difference** between an outlier and its namesakes | | Borin et al. 2025 [7] | 171 plants from 20 seed varieties bought from European distributors | Results "revealed doubts regarding the quality and identity" of some seed on the market, "probably mislabeled" or poorly produced | Two honest caveats. Most of these studies are small, and genotyping with a few markers can call two close relatives "identical" (see [what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md)). And some names hold up well: in [5], six of seven Blue Dream samples were one genotype. The pattern isn't "every name is false". It's that **a name alone tells you nothing you can check**. ## Why renaming dilutes the gene pool Renaming doesn't change a single gene. The damage is to what breeders *think* they're working with. 1. **False diversity.** A breeder who crosses "two different strains" that are the same cut, or parent and child under new names, is inbreeding while believing they're outcrossing. Multiply that across a market and the hybrid swarm keeps folding back on the same few parents (see [how hybrid strains emerged](https://genetixbay.com/knowledge/genetics-history/how-hybrid-strains-emerged.md)). 2. **The shelf converges.** Commercial THC-dominant flower in six US states fell into three terpene groups, two of them holding about 87 % of samples [6]; North American licensed-producer material clusters into a handful of chemotype-linked groups [8]; and the Nevada data show the same few profiles hiding behind hundreds of names [4]. That's the chemistry of a narrow pool wearing many labels (see [why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md)). 3. **Originals get lost.** When a renamed cut displaces the original name, the original's history, and sometimes the original plant, drops out of circulation. Nobody hunts for a line they think they already have. 4. **Distinct material is replaced, not added.** The traditional high-THC domesticates are endangered, with decades of hybridising having "obliterated differences" between them [9]. New names on old hybrids don't replace what's lost at source. ## The GB-ID answer A GB-ID is GenetixBay's **permanent identifier** for a line, a cut, a batch or a plant. It never changes and is never reused, whatever the plant is called. - **The record follows the plant, not the name.** A cut keeps one GB-ID however many names it picks up. Aliases are recorded, with who used them and when. - **Same name, different source, different record.** Two lines sharing a name are linked as `shares_name`, never merged on name alone (see [why strain names are unreliable](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md)). - **Claims carry evidence levels.** "The original cut" is an L0 claim until there's chain of custody, grow-out evidence or a DNA match to a reference sample (L4). See [documenting lineage evidence](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md). - **Chemistry, not hype.** Lab-tested terpene profiles sit on the record, so a genuinely different line can be found by what it is. - **Duplicates come out in the open.** When two GB-IDs turn out to be one genotype, the evidence is added and the records are linked as the same plant, with both names kept as aliases. ## For growers and breeders 1. Ask where a cut came from and who had it before. A name with no history is a claim. 2. Before crossing two "different" lines, compare their records and, for important parents, their genotypes. 3. If you rename nothing, you're already ahead: keep the name a cut arrived with and add your selection as a qualifier (see [naming ethics](https://genetixbay.com/knowledge/breeding/record-keeping-naming-ethics.md)). 4. Register cuts and males with full history, including the names they've carried. ## Common mistakes - Assuming two names are two plants because the vendors are different. - Assuming the same name is the same plant because the menu says so. - Treating a small-marker "match" as proof of identity without a reference sample. - Treating every name as a lie. Some are consistent; the point is to check. ## Evidence - Same name hiding different genotypes: *Supported* by several independent studies [1][2][3][5]. - Different names on the same genotype: *Supported* [1][2][4], with small samples. - Names overstating chemical diversity: *Supported* [4][6]. - Narrow commercial gene pool and endangered landraces: *Supported* [6][8][9][10]. - Renaming as a cause of gene-pool dilution: founder's view, consistent with the evidence above but *not directly measured*. ## Sources 1. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 2. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 3. Watts S, McElroy M, Migicovsky Z, Maassen H, van Velzen R, Myles S. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y 4. Reimann-Philipp U, Speck M, Orser C, et al. 2020. Cannabis chemovar nomenclature misrepresents chemical and genetic diversity; survey of variations in chemical profiles and genetic markers in Nevada medical cannabis samples. Cannabis and Cannabinoid Research 5(3):215-230. https://doi.org/10.1089/can.2018.0063 5. Schwabe AL, Naibauer SK, McGlaughlin ME, Gilbert AN. 2022. Human olfactory discrimination of genetic variation within Cannabis strains. Frontiers in Psychology 13:942694. https://doi.org/10.3389/fpsyg.2022.942694 6. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 7. Borin M, Scariolo F, Cappello Fusaro M, et al. 2025. Genotyping of commercial European Cannabis seeds based on multiple mapped marker loci: a comparative study of drug and hemp varieties. Plants 14(19):3050. https://doi.org/10.3390/plants14193050 8. Henry P, Khatodia S, Kapoor K, et al. 2020. A single nucleotide polymorphism assay sheds light on the extent and distribution of genetic diversity, population structure and functional basis of key traits in cultivated north American cannabis. Journal of Cannabis Research 2:26. https://doi.org/10.1186/s42238-020-00036-y 9. McPartland JM, Small E. 2020. A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys 144:81-112. https://doi.org/10.3897/phytokeys.144.46700 10. Lynch RC, Vergara D, Tittes S, et al. 2016. Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences 35(5-6):349-363. https://doi.org/10.1080/07352689.2016.1265363 11. Brickell CD, et al. (eds). 2016. International Code of Nomenclature for Cultivated Plants, 9th edition. Scripta Horticulturae 18. ISHS. https://www.ishs.org/scripta-horticulturae/international-code-nomenclature-cultivated-plants-ninth-edition --- # Why everything tastes the same: the evidence that commercial cannabis is converging > Growers keep saying modern weed all tastes the same, and the data back them up. A study of nearly 90,000 US lab results found THC-dominant flower falling into just three terpene groups, two of which held about 87 % of samples. Strain names and indica/sativa labels promise far more variety than the chemistry shows, traditional landraces in their home regions are being replaced by introduced hybrids, and retail prices rise with THC rather than aroma. GenetixBay's answer is preservation, documentation with GB-IDs, and open sharing of distinctive lines. - Canonical: https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.html - Category: Genetics history · Level: Intermediate - Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked) - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Why does all modern weed taste the same?** Modern weed tastes the same because commercial cannabis really is converging chemically. In nearly 90,000 lab results from six US states, THC-dominant flower fell into three terpene groups, and caryophyllene-limonene and myrcene-pinene held about 87% of samples. Breeders reuse the same few popular parents, the market pays for THC rather than aroma, and landraces are being hybridised away. **Are strains losing their diversity?** Commercial strains do appear to be losing diversity, though nobody has measured genetic diversity over time directly. Cross-sectional data show thousands of names on a few terpene groups and broad genetic clusters, and landraces are endangered by hybrid replacement at source. Diversity is not gone: terpinolene-led and rarer profiles and documented heirloom lines still circulate. **What are the main terpene profiles in cannabis?** The main terpene profiles in commercial THC-dominant cannabis are three groups found in a 2022 study of US lab data: caryophyllene-limonene, myrcene-pinene, and terpinolene-myrcene. The first two held 87.4% of samples, and terpinolene-led flower is the smallest group, around an eighth. Rarer dominants include ocimene and the sesquiterpene alcohols guaiol and eudesmols, linked to some Central Asian lines. **Are landrace strains disappearing?** Landrace strains are disappearing in their home regions. Taxonomists describe traditional high-THC domesticates as endangered, with 50 years of introgressive hybridisation having obliterated differences between them. In Morocco's Rif, traditional kif has largely been replaced by introduced high-yielding hybrids. Similar replacement is widely reported elsewhere, though less systematically documented. **Why does the market breed for THC instead of flavour?** The market breeds for THC instead of flavour because price follows THC. In about 30 million Washington State flower sales, price per gram rose with THC content, and labels, lab results and shelf placement lead with a THC number. When buyers pay for potency, breeders select for it. That is a price signal at work, not anyone's plan. **How can I find cannabis with a different terpene profile?** To find cannabis with a different terpene profile, read the terpene section of the certificate of analysis, not just THC, and look for less common dominants such as terpinolene, ocimene, or high guaiol and eudesmols. Grow heirloom and landrace seed with documented history and pheno-hunt for aroma, keeping odd incense or pine keepers even if they are not trending. **What makes cannabis smell like gas?** Cannabis smells like gas mostly because of prenylated volatile sulfur compounds, not terpenes. A 2021 study found seven across 13 cultivars; the key one, 3-methyl-2-butene-1-thiol, was most abundant in the most pungent samples and recreated the fuel-like smell when added to a base aroma mix. These compounds rise towards the end of flower, peak during curing, and are detected at tiny traces. **Why is every new strain gas or candy?** Every new strain seems to be gas or candy because the market rewards loud aromas, so breeders cross loud to loud. Consumers rated citrus-sweet-pungent samples as more potent and valuable, though perceived potency did not track measured THC. Those notes ride on trace sulfur compounds and esters over the same few terpene backbones, so popular cuts keep parenting the next wave. **Are the classic strains disappearing?** Classic profiles such as incense, hash, pine and old haze are losing ground, in GenetixBay's house view, because the gas and candy trend crowds them out. Nobody bans a classic; it simply stops being crossed and stocked. Terpinolene-led flower is already the smallest commercial group. Menu share by aroma has not been measured, so preserving and sharing classic cuts, seed and males matters. **Short answer.** It isn't just nostalgia. In nearly 90,000 lab results from six US states, THC-dominant flower fell into **three terpene groups**, and two of them (caryophyllene–limonene and myrcene–pinene) held about **87 %** of samples with terpene data [1]. Thousands of strain names sit on top of that narrow chemistry [1][3]. Meanwhile the traditional landraces that once supplied distinct profiles are being hybridised away in their home regions [6][7], and retail prices rise with THC, not aroma [9]. The evidence shows convergence. GenetixBay's answer is to preserve, document and share what's distinctive. > **House position, carefully framed.** The founder's view, after growing thousands of cultivars, is that modern commercial lines are converging, distinctive old profiles are being bred out, and the best is kept by a few. We don't claim a plot. The data below show convergence driven by ordinary forces: everyone breeding from the same few popular parents, the market paying for THC, and landraces disappearing at source. Those are things a community can do something about. ## What the data show | Study | What they measured | Finding | |---|---|---| | Smith et al. 2022 [1] | 89,923 flower lab results, six US states; 42,843 with terpenes | **96.5 %** THC-dominant. THC-dominant samples clustered into three terpene groups: I caryophyllene–limonene, II myrcene–pinene, III terpinolene–myrcene. Groups I and II held **87.4 %**. Commercial labels matched chemistry poorly | | Reimann-Philipp et al. 2020 [3] | Nevada medical cannabis, chemistry and genetic markers | Hundreds of strain names, but terpene profiles fell into a few clusters: names "misrepresent" the real diversity | | Watts et al. 2021 [2] | Genomes and chemistry of retail samples | "Indica" and "sativa" labels were genetically indistinct genome-wide; only a few terpenes tracked the labels | | Schwabe & McGlaughlin 2019 [11] | Same-named strains from dispensaries in three states | Most named strains had genetic outliers; names don't guarantee a distinct genotype | | Lynch et al. 2016; Sawler et al. 2015 [4][5] | Genotypes of hundreds of drug-type varieties | A few broad genetic groups underlie the drug-type market, and reported ancestry only partly matches genotype | (2020) from the full text; we haven't found a study that measures commercial genetic diversity directly over time. ## Why it's happening **1. Everyone breeds from the same parents.** Modern drug-type cannabis is a hybrid swarm built from a limited set of founders, and popular lines get crossed with each other repeatedly (see [how hybrid strains emerged](https://genetixbay.com/knowledge/genetics-history/how-hybrid-strains-emerged.md)). The genetic groups found in commercial samples are few and broad [4][5]. **2. The market pays for THC.** In about 30 million Washington State flower sales, price per gram rose with THC content [9]. Labels, lab results and shelf placement lead with a THC number. When buyers pay for THC, breeders select for it, and aroma diversity isn't what gets selected. **3. Landraces are disappearing at source.** McPartland and Small describe the high-THC domesticates as **endangered**: 50 years of introgressive hybridisation "obliterated differences" between them [6]. In Morocco's Rif, traditional kif has largely been replaced by introduced high-yielding hybrids [7]. Similar replacement is widely reported elsewhere [8], though documented less systematically. **4. Names hide the sameness.** With thousands of names and few chemotypes, the shelf looks diverse when it isn't [1][3][10]. A new name is easier to produce than a new terpene profile. ## What the data don't show - **Not that diversity is gone.** Cluster III (terpinolene-led) and rarer profiles exist [1]; heirloom and landrace lines still circulate. - **Not who is hoarding what.** "The best is kept by a few" is the founder's experience, not something these studies measure. We present it as their view. - **Not that THC selection is anyone's plan.** It's what a price signal does. ## The gas and candy trend > **House position: the gas and candy trend is killing the classics.** The founder's view, and GenetixBay's: market selection for "gas" and "candy" is crowding out the old profiles (incense, hash, pine, haze). Below is what the chemistry shows about those two trends and why they narrow the pool. How fast the classics are losing shelf space hasn't been measured; that part is the founder's experience. **What "gas" is, chemically.** The skunky, fuel-like note that buyers call gas comes mostly from a family of **prenylated volatile sulfur compounds**, not from terpenes. Oswald and colleagues found seven of them across 13 cultivars; the key one, 3-methyl-2-butene-1-thiol (labelled VSC3), was the most abundant sulfur compound in the samples a panel rated most pungent, and adding it to a mix of major cannabis aroma compounds recreated the characteristic smell [12]. These compounds rose sharply towards the end of flower, peaked during curing and then fell off in storage [12]. Sulfur compounds are smelled at tiny concentrations, so a trace of them dominates a jar. **What "candy" and "tropical" are.** A follow-up study of 31 rosin samples found that the sweet, fruity, "exotic" aromas track **minor, non-terpene compounds**: esters, and a class of tropical sulfur compounds built on a 3-mercaptohexyl group (3-mercaptohexanol, 3-mercaptohexyl acetate and 3-mercaptohexyl butyrate), the same family that gives some hops and tropical fruit their character [13]. Savoury "chemical" notes tracked skatole [13]. The key line: terpene profiles were "remarkably similar" across varieties whose aromas differed sharply, and terpenes contributed mainly to the generic cannabis smell, not to what made each variety distinctive [13]. **Why that narrows the pool.** 1. **The backbone stays the same.** If the "new" aromas ride on trace compounds, a menu of candy and gas cuts can sit on the same couple of terpene backbones the lab data already show: caryophyllene–limonene and myrcene–pinene, with 87 % of THC-dominant samples between them [1]. Different top notes; same underlying chemistry, often the same few parents (see [same cut, a thousand names](https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.md)). 2. **The market rewards loud.** When consumers rated strains by smell, citrus-sweet-pungent samples were judged more potent and worth more per gram than earthy-woody ones, yet perceived potency didn't correlate with measured THC at all [14]. Loud sells, so breeders cross loud to loud, and every popular gas or dessert cut becomes the parent of the next wave. 3. **The classics lose by default.** Incense, hash, pine and old haze profiles are mostly earthy, woody, spicy or terpinolene-led. Terpinolene-dominant flower is already the smallest of the three commercial groups, around an eighth of THC-dominant samples [1]. Nobody bans a classic; it just stops being crossed, stops being stocked, and survives only where someone keeps it. **What the data don't show.** No study we've found counts menu share by aroma type over time, so "dessert and candy crosses dominate menus" is a widely shared observation, including the founder's, not a measured trend. Nor does the chemistry say gas or candy is bad. They're real, interesting compounds. The problem is a market that selects for them at the expense of everything else. **What to do about it.** Keep and share the classic profiles (cuts, seed, males in the Stud Book), describe aroma on GB-ID records in words and chemistry, and when you hunt, keep the odd incense or pine keeper even if it isn't what's trending. ## What GenetixBay does about it - **Preserve.** Wanted-line and revival programmes, clone backups, males in the Stud Book, seed vaults (see [landraces of the world](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) and [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md)). - **Document chemistry, not names.** GB-IDs carry lab-tested terpene profiles, so a distinctive line can be found by what it is, not what it's called (see [chemotype inheritance](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md)). - **Reward aroma, not just THC.** On the Bay, potency numbers never earn rewards by themselves; documentation, males and preservation do. - **Share openly.** Distinctive lines registered, described and shared in legal lanes stay in the commons (see [patents and the gene pool](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md)). ## For growers: finding something different 1. Ask for the certificate of analysis and read the **terpene** section, not just THC. 2. Look for the less common dominants: terpinolene, ocimene, or high levels of guaiol and eudesmols (associated with some Central Asian lines [2][6]). 3. Grow heirloom and landrace seed with a documented history, and pheno-hunt for aroma (see [selection and pheno-hunting](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md)). ## Evidence - Commercial THC-dominant flower clustering into a few terpene groups: *Supported* by large lab datasets [1][3]. - Labels and names misrepresenting diversity: *Supported* [1][2][3][11]. - Landrace erosion by hybridisation: *Supported* [6][7]; extent outside Morocco less documented. - Price tracking THC: *Supported* in one large market [9]. - "The best is hoarded by a few": founder's view, not measured. - "Gas" aroma driven by prenylated volatile sulfur compounds (VSC3): *Supported* by one detailed study [12]. - Candy/tropical aromas driven by minor non-terpene compounds, with terpene profiles similar across divergent aromas: *Supported* by one study of 31 extracts [13]. - Consumers rating loud, sweet-pungent flower as more potent and valuable without any link to measured THC: *Supported* [14]. - The gas/candy trend crowding out classic profiles: house position (founder's view); menu share by aroma type not yet measured. ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Watts S, McElroy M, Migicovsky Z, et al. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y 3. Reimann-Philipp U, Speck M, Orser C, et al. 2020. Cannabis chemovar nomenclature misrepresents chemical and genetic diversity; survey of variations in chemical profiles and genetic markers in Nevada medical cannabis samples. Cannabis and Cannabinoid Research 5(3):215-230. https://doi.org/10.1089/can.2018.0063 4. Lynch RC, Vergara D, Tittes S, et al. 2016. Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences 35(5-6):349-363. https://doi.org/10.1080/07352689.2016.1265363 5. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 6. McPartland JM, Small E. 2020. A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives. PhytoKeys 144:81-112. https://doi.org/10.3897/phytokeys.144.46700 7. Chouvy P-A, Afsahi K. 2014. Hashish revival in Morocco. International Journal of Drug Policy 25(3):416-423. https://doi.org/10.1016/j.drugpo.2014.01.001 8. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 9. Smart R, Caulkins JP, Kilmer B, Davenport S, Midgette G. 2017. Variation in cannabis potency and prices in a newly legal market: evidence from 30 million cannabis sales in Washington state. Addiction 112(12):2167-2177. https://doi.org/10.1111/add.13886 10. Hazekamp A, Fischedick JT. 2012. Cannabis: from cultivar to chemovar. Drug Testing and Analysis 4(7-8):660-667. https://doi.org/10.1002/dta.407 11. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 12. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196 13. Oswald IWH, Paryani TR, Sosa ME, et al. 2023. Minor, nonterpenoid volatile compounds drive the aroma differences of exotic cannabis. ACS Omega 8(42):39203-39216. https://doi.org/10.1021/acsomega.3c04496 14. Gilbert AN, DiVerdi JA. 2018. Consumer perceptions of strain differences in Cannabis aroma. PLOS ONE 13(2):e0192247. https://doi.org/10.1371/journal.pone.0192247 --- # Why strain names are unreliable: what genetic studies show > Several genetic and chemical studies of retail cannabis show that the same strain name often hides different genotypes, that 'indica' and 'sativa' labels don't match genome-wide ancestry, and that potency labels vary by lab. Some names are reasonably consistent, many are not. A name is a claim; a documented source, a GB-ID with evidence and, ultimately, DNA are the evidence. - Canonical: https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.html - Category: Genetics history · Level: Beginner - Evidence: Supported · Status: Draft: awaiting expert review - Stage: Any stage · Systems: Any system - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Questions and answers **Are cannabis strain names accurate?** Cannabis strain names are often not accurate. Retail studies found genetic outliers within most same-named strains, and differently named samples that were genetically closer to each other than to their namesakes. Some names are reasonably consistent while others are 'consistently inconsistent'. Treat a name as a claim; a documented source, a lineage record and ultimately DNA are the evidence. **Is my Blue Dream the same as someone else's?** Your Blue Dream may or may not be the same as someone else's. A clone name should mean one genotype, but cuts get mixed up, renamed or borrowed, and seed sold under the name is a population of different genotypes. One study found six of seven retail Blue Dream samples were one genotype. Check the source and chain of custody, or compare DNA. **Do indica and sativa labels mean anything?** Indica and sativa labels mean very little on a menu. They do not match genome-wide ancestry and only loosely track a few terpenes: myrcene, guaiol and eudesmols for 'indica', bergamotene and farnesene for 'sativa'. Menus mostly use them for expected effect and aroma. Cannabis is one species, and the labels at most describe plant shape. **Why does the same strain test differently?** The same strain tests differently because the plants may differ and the labs certainly do. Seed lines segregate into varied genotypes, renamed or mixed-up cuts share names, and Washington State data showed reported THC varied systematically by testing lab. Same-named hemp cultivars from different suppliers even flowered differently. Flower labelled above about 35% total cannabinoids is not credible. **What studies show strain names are unreliable?** Key studies showing strain names are unreliable are Sawler 2015 (14,031 SNPs, names often lacking genetic identity), Schwabe and McGlaughlin 2019 (outliers in most retail strains across three US states), Watts 2021 (indica and sativa genetically indistinct), Smith 2022 (89,923 lab results, labels poorly aligned with chemotype) and Jikomes and Zoorob 2018 (THC varying by lab). **How can I trust a strain name?** You can trust a strain name only as far as the evidence behind it. For seed, prefer lines with a GenetixBay record at L2 or higher from a certified breeder, batch records and grower journals. For a clone, ask for documented chain of custody and, for important cuts, a genotype comparison with a reference sample. Choose by lab-tested chemistry, not the name. **Short answer.** Because names travel more easily than plants. And the "indica", "sativa" or "hybrid" tag beside the name is no better: it's one species, nearly everything sold is a hybrid, and the tag doesn't predict chemistry or effects (see [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md)). Studies sampling retail cannabis found genetic outliers within most same-named strains [2], genome-wide similarity between "indica" and "sativa" labelled samples [3], and labels that only loosely track chemistry [4]. Some names are consistent; many are not. Trust sources and evidence, not names. ## What the studies found | Study | What they did | Key finding | Evidence | |---|---|---|---| | Sawler et al. 2015 [1] | 14,031 SNPs in 81 marijuana and 43 hemp samples | Genetic structure only moderately correlated with reported sativa/indica ancestry; strain names often did not reflect a meaningful genetic identity | *Supported* | | Schwabe & McGlaughlin 2019 [2] | 10 microsatellites; same-named strains from dispensaries in three US states | Most strains had at least one genetic outlier; after removing outliers many strains were fairly stable; type labels did not match genetic groups | *Supported* (limited sample, 3 states) | | Watts et al. 2021 [3] | >100,000 SNPs and chemical profiles of hundreds of samples | "Sativa" and "indica" labelled samples were genetically indistinct genome-wide; labels associated with a few terpenes (myrcene, guaiol, β- and γ-eudesmol for "indica"; bergamotene, farnesene for "sativa") linked to terpene synthase gene regions | *Supported* | | Smith et al. 2022 [4] | Lab data from 89,923 samples in six US states | Distinct chemotypes exist, but commercial labels don't consistently align with them; some strain names were consistent, others "consistently inconsistent" | *Supported* | | Jikomes & Zoorob 2018 [5] | Washington State lab data | Reported THC varied systematically by testing lab | *Supported* | | Henry et al. 2020 [6] | 22-SNP assay on 420 accessions from licensed producers | Clear population structure linked to chemotype; genetic identity relates to chemical composition | *Supported* | | Zhang et al. 2021 [7] | Hemp cultivars from different suppliers | Same-named cultivars from different sources flowered differently | *Supported* (hemp) | ## Why it happens 1. **Seed vs clone.** A name sold as seed is a population of different genotypes; a clone name is one genotype. Both get the same name. 2. **Renaming and borrowing.** Cuts renamed to sound new; popular names reused on unrelated genetics. 3. **Segregation.** Even honest seed lines vary, especially F1s of heterozygous clones and F2s. 4. **Mix-ups.** Labels lost in nurseries, mother rooms and supply chains. 5. **Marketing labels.** "Indica" and "sativa" on menus mostly track expected effect and aroma, not ancestry [3]. 6. **Lab variation.** Potency differences partly reflect the lab, not the plant [5]. Flower labelled above ~35 % total cannabinoids isn't credible; see [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## What this means for you | You want to... | Do this | |---|---| | Buy seed you can trust | Prefer lines with a GenetixBay record at L2+ from a certified breeder, batch records and grower journals | | Trust a clone | Ask for documented chain of custody and, for important cuts, a genotype comparison with a reference sample | | Compare two "same" strains | Compare sources and, if needed, DNA; don't rely on name or THC number | | Choose by effect | Use chemistry (cannabinoids and dominant terpenes) as a rough guide; effects are reported, not promised | ## How GenetixBay handles names - A **GB-GEN** is "this name as released by this breeder or source". Two lines with the same name from different sources are separate records linked as `shares_name`, never merged on name alone. - Aliases and misspellings are recorded with sources. - Every lineage claim carries an evidence level (L0-L4). See [documenting lineage evidence](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md). ## Common mistakes - "It says Blue Dream, so it's the Blue Dream." Maybe. Check the source. - Treating "indica = sedating, sativa = energising" as genetics. It's marketing shorthand loosely tied to a few terpenes (*Contested* as an effect predictor) [3]. - Dismissing all names. Some are consistent, and a well-documented line is meaningful. ## Evidence - Within-name genetic inconsistency: *Supported* by multiple independent studies [1][2]. - Indica/sativa labels not reflecting genome-wide ancestry: *Supported* [1][3]. - Weak alignment between labels and chemotype: *Supported* [4]. - Lab effects on potency: *Supported* [5]. ## Sources 1. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 2. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 3. Watts S, McElroy M, Migicovsky Z, et al. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y 4. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLoS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 5. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 6. Henry P, et al. 2020. A single nucleotide polymorphism assay sheds light on the extent and distribution of genetic diversity, population structure and functional basis of key traits in cultivated north American cannabis. Journal of Cannabis Research 2:26. https://doi.org/10.1186/s42238-020-00036-y 7. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 --- # GenetixBay cannabis glossary: every term > 759 terms. Index: https://genetixbay.com/knowledge/glossary/ --- # 12/12 > 12/12 is the classic flowering schedule for photoperiod cannabis: 12 hours of light and 12 hours of uninterrupted darkness, which triggers and sustains flowering. - Canonical: https://genetixbay.com/knowledge/glossary/12-12.html - Also written: 12-12, 12/12 light cycle, twelve twelve, 12 on 12 off, flip to 12/12, the flip - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" 12/12 is 12 hours of light and 12 hours of darkness per day. Most [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis has a critical day length somewhere around 12–14 hours: shorter days (longer nights) trigger flowering. 12/12 sits safely on the short side for nearly every drug-type cultivar, so it became the default. "Flipping" means switching from a veg schedule to 12/12. ## In practice Because the light period is fixed, flower [DLI](https://genetixbay.com/knowledge/glossary/dli.md) depends entirely on intensity. At 900 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), 12/12 gives about 39 mol/m²/day. Darkness must be truly dark: Eckels and Bugbee (2024) reported that even low-level night light can delay cannabis flowering. 12/12 is the safe choice, not the only one. Zhang and colleagues (2021) showed critical photoperiods vary widely between [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md), and Peterswald and colleagues (2023) tested longer flowering photoperiods in [medicinal cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md), finding some cultivars flowered and yielded well on more than 12 hours. ## Units and formula DLI = PPFD × 12 × 0.0036. ## Don't confuse with - **13/11**: a longer flowering day, endorsed by GenetixBay for many cultivars. - **Photoperiod**: the general term for day length. ## Myth check "Flower must be exactly 12/12" is a *Myth*. GenetixBay's position: [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) works, and some cultivars flower at 14–15 hours. Test your cultivar; that is what [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md) trials are for. ## Related terms [13/11](https://genetixbay.com/knowledge/glossary/13-11.md), [18/6](https://genetixbay.com/knowledge/glossary/18-6.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [Light leak](https://genetixbay.com/knowledge/glossary/light-leak.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md) ## Read more - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Peterswald TJ, Mieog JC, Azman Halimi R, et al., 2023. Moving away from 12:12; the effect of different photoperiods on biomass yield and cannabinoids in medicinal cannabis. Plants 12(5):1061. https://doi.org/10.3390/plants12051061 3. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis --- # 13/11 > 13/11 is a flowering schedule of 13 hours light and 11 hours dark; GenetixBay endorses it, as most cultivars still flower while gaining extra daily light. - Canonical: https://genetixbay.com/knowledge/glossary/13-11.html - Also written: 13-11, 13/11 light cycle, 13 hours light, 13 on 11 off, extended flower photoperiod - Glossary category: Environment and light · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" 13/11 means 13 hours of light and 11 hours of darkness. For most drug-type cultivars, 11 hours of uninterrupted darkness is still long enough to trigger and hold flowering, and the extra hour adds about 8% more daily light than [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) at the same [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md). ## In practice At 900 µmol/m²/s, 13/11 gives about 42 [mol/m²/day](https://genetixbay.com/knowledge/glossary/dli.md) against 39 on 12/12. Many growers run it as roughly 12 hours at full intensity plus ramps at each end: a 30-minute sunrise and 30-minute sunset add time without adding much DLI, but ease the transition and match the founder's practice. Peterswald and colleagues (2023) tested [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md) longer than 12 hours in [medicinal cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md) and found that some cultivars yielded well on them; Zhang and colleagues (2021) showed critical day length differs between cultivars. Long-flowering, equatorial-type lines may delay or stall on longer days, so watch the first two weeks: if [pistils](https://genetixbay.com/knowledge/glossary/pistil.md) are slow to appear, drop to 12/12. ## Units and formula DLI = PPFD × 13 × 0.0036. ## Don't confuse with - **12/12**: the conservative default. - **Light leak**: unplanned light in the dark period; 13/11 is planned and dark periods must stay dark. ## Myth check GenetixBay house position: **flower does not have to be exactly 12/12.** 13/11 is endorsed, and some cultivars flower at 14–15 hours. *Supported* by cultivar-variation studies; the house says "test your cultivar" and members can log results through [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), [Sunrise/sunset ramp](https://genetixbay.com/knowledge/glossary/sunrise-sunset-ramp.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) ## Read more - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ## Sources 1. Peterswald TJ, Mieog JC, Azman Halimi R, et al., 2023. Moving away from 12:12; the effect of different photoperiods on biomass yield and cannabinoids in medicinal cannabis. Plants 12(5):1061. https://doi.org/10.3390/plants12051061 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 --- # 18/6 > 18/6 is the standard vegetative light schedule: 18 hours of light and 6 hours of darkness each day, keeping photoperiod cannabis from flowering. - Canonical: https://genetixbay.com/knowledge/glossary/18-6.html - Also written: 18-6, 18/6 light cycle, 18 on 6 off, eighteen six, 18 hours light - Glossary category: Environment and light · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" 18/6 means 18 hours of light followed by 6 hours of uninterrupted darkness every 24 hours. It is the most common vegetative schedule for [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis: the long day keeps plants in veg, and the dark period gives a natural break that some growers use to lower room temperature and electricity costs at off-peak times. ## In practice At 600 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), 18/6 delivers about 39 [mol/m²/day](https://genetixbay.com/knowledge/glossary/dli.md) (600 × 18 × 0.0036). Many growers also run [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) on 18/6 or 20/4; autoflowers flower on age, not day length, so the schedule there is a trade-off between DLI and power cost. 18/6 is a convention, not a biological requirement. Cannabis grows fine on [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) in veg, and the GenetixBay house position endorses it. Some growers simply prefer 18/6 for cheaper power, cooler nights or a fixed maintenance window. Either works if the DLI is adequate. [Light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) during the 6 dark hours do not matter much in veg. They matter in flower. ## Units and formula DLI = PPFD × 18 × 0.0036 on 18/6. ## Don't confuse with - **12/12**: the flowering schedule. - **20/4**: a common alternative for autoflowers and veg, giving more DLI. ## Myth check "Plants need 6 hours of sleep in veg" is a *Myth* for cannabis; see the 24/0 entry and [the photoperiod article](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md). ## Related terms [24/0](https://genetixbay.com/knowledge/glossary/24-0.md), [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md) ## Read more - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 --- # 24/0 > 24/0 means lights on 24 hours a day with no dark period; GenetixBay endorses it for veg, as cannabis does not need a sleep period before flowering. - Canonical: https://genetixbay.com/knowledge/glossary/24-0.html - Also written: 24-0, 24/0 light cycle, 24 hours light, lights on 24/7, continuous light - Glossary category: Environment and light · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" 24/0 is a schedule with continuous light and no dark period. [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis stays vegetative under it, because long uninterrupted darkness is what triggers flowering. It is used in veg and for clones, and by some growers for [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md). ## In practice 24/0 gives the highest [DLI](https://genetixbay.com/knowledge/glossary/dli.md) for a given [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md): 400 µmol/m²/s on 24/0 delivers about 35 mol/m²/day, the same as 540 µmol/m²/s on [18/6](https://genetixbay.com/knowledge/glossary/18-6.md). That lets growers run a fixture dimmer, closer and more evenly for the same daily light, which can suit [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and clones. Costs: higher electricity use and no cool night to drop room temperature or humidity. Watch for interveinal leaf mottling or [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md) in some cultivars under continuous light, a response documented in several other crops. If a cultivar shows it, switch to 20/4 or 18/6. ## Don't confuse with - **18/6**: the conventional veg schedule. - **24/0 in flower**: photoperiod plants will not flower under it; autoflowers will, but results vary. ## Myth check GenetixBay house position: **24/0 in veg is endorsed.** Cannabis does not need a "sleep period" in veg. The claim that plants must have darkness every day to grow well is a *Myth* for vegetative cannabis. Grower experience is broad (*Grower practice*); controlled cannabis data are limited, and members are welcome to run a [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md) trial of 24/0 vs 18/6 on their own cultivars. ## Related terms [18/6](https://genetixbay.com/knowledge/glossary/18-6.md), [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md) ## Read more - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 --- # 420 > 420 is cannabis culture shorthand for cannabis itself and for April 20, celebrated as an unofficial cannabis day. - Canonical: https://genetixbay.com/knowledge/glossary/420.html - Also written: 4/20, four-twenty, 4:20, April 20, 420 friendly - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" 420 (four-twenty) is a code word for cannabis and for the date 20 April (4/20 in US date format), observed in many countries as an informal cannabis holiday. "420 friendly" in a listing means cannabis use is accepted. ## In practice The most widely cited origin is a group of California high-school students in the early 1970s who met at 4:20 pm to smoke, with the phrase spread later through music and fan culture. Other popular explanations, such as a police code or the number of chemicals in cannabis, are myths. For growers, the date is also a calendar marker: in the Northern Hemisphere, mid to late April is a common time to start seeds for an outdoor season. GenetixBay itself launches its community on 20 April 2027. ## Don't confuse with - **Croptober**: harvest season for outdoor growers in the Northern Hemisphere, around October. ## Related terms [Marijuana](https://genetixbay.com/knowledge/glossary/marijuana.md), [Heady](https://genetixbay.com/knowledge/glossary/heady.md), [Connoisseur](https://genetixbay.com/knowledge/glossary/connoisseur.md) --- # 60/60 rule > A drying rule of thumb: dry cannabis at about 60 °F (15.5 °C) and 60% relative humidity so buds dry slowly over roughly 10-14 days. - Canonical: https://genetixbay.com/knowledge/glossary/60-60-rule.html - Also written: 60-60 rule, 60 60 rule, 60/60, sixty sixty, 60F 60% rule - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The 60/60 rule is a popular drying guideline: hold the [drying room](https://genetixbay.com/knowledge/glossary/drying-room.md) around 60 °F (about 15.5 °C) and 60% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). At those settings, buds lose water slowly and evenly, usually reaching jar-ready in roughly 10-14 days, depending on bud density and how much stem and leaf is left on. ## In practice The rule works because it slows evaporation from the bud surface to match the rate water can move out from inside. That avoids [case hardening](https://genetixbay.com/knowledge/glossary/case-hardening.md), helps [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) break down, and keeps more of the volatile [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) that are lost fastest in warm, fast dries. It is a target, not a law. Many growers run 60-68 °F (15-20 °C) and 55-62% RH with good results. What matters is a slow, even dry with no mould. Adjust for your material: - **Wet trimmed, small buds**: stay at the cooler, more humid end. - **Whole-plant hang, dense colas**: watch mould risk; a little lower RH or more air movement may be needed. Measure at bud level with a calibrated hygrometer. Room-corner readings can be several points off. ## Don't confuse with - **Jar RH targets for curing**: a proxy for [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), a separate measure. - **Water activity**: the bud's own measure of available water. - **VPD**: a growing metric, not a drying rule. ## Related terms [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md), [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # A/B nutrient > An A/B nutrient is a mineral feed split into two concentrates so that calcium (part A) is kept apart from sulfate and phosphate (part B), which would precipitate together. - Canonical: https://genetixbay.com/knowledge/glossary/a-b-nutrient.html - Also written: two-part nutrient, 2-part nutrient, A and B, part A part B, A+B, two-part feed - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An A/B nutrient is a complete mineral feed sold or mixed as two separate concentrates. Part A usually contains [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), often with [potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md) and [iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md). Part B contains the [phosphates](https://genetixbay.com/knowledge/glossary/phosphate.md), sulfates and the remaining [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md). Kept apart in concentrated form, they stay clear; mixed together at concentrate strength, calcium phosphate and calcium sulfate drop out as sludge. ## In practice Add part A to the water, stir, then add part B, never pouring one concentrate straight into the other. Equal doses of A and B are typical, but check the label. The limitation is that both parts scale together: cutting the dose to reduce nitrogen also reduces everything else. That is why [per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md) exists, and why a late-flower [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) is hard to run with a bottled two-part alone. ## Don't confuse with - **One-part nutrient**: a single concentrate that avoids the precipitation problem by formulation. - **Bloom and grow bottles**: a stage split, which may or may not also be an A/B split. - **A/B testing**: a trial method, not a feed. ## Related terms [One-part nutrient](https://genetixbay.com/knowledge/glossary/one-part-nutrient.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Per-element feeding tricks: what growers adjust, stage by stage](https://genetixbay.com/knowledge/nutrients/per-element-tricks.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Abscisic acid > A plant hormone (ABA) that signals water stress, closes stomata and maintains seed dormancy. - Canonical: https://genetixbay.com/knowledge/glossary/abscisic-acid.html - Also written: ABA, abscisin, dormin, stress hormone - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Abscisic acid (ABA) is the plant's main drought and stress hormone. When roots dry out or leaves lose water, ABA levels rise within minutes and [guard cells](https://genetixbay.com/knowledge/glossary/stomata.md) close stomata to cut water loss. ABA also keeps seeds dormant, slows growth under stress and helps leaves cope with cold and salinity. Despite the name, its role in abscission (leaf drop) is minor; [ethylene](https://genetixbay.com/knowledge/glossary/ethylene.md) does most of that. ## In practice ABA is why plants stop drinking and growing when the medium gets [too dry](https://genetixbay.com/knowledge/glossary/over-drying.md) or the air too harsh. With stomata shut, CO₂ uptake falls and growth stalls, even with perfect light. It's also part of the story behind controlled late drought. Caplan et al. (2019) reported that a moderate drought stress in late flower raised [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) concentration and yield per area in their trial. GenetixBay endorses mild late [dry-backs](https://genetixbay.com/knowledge/glossary/dryback.md) where a cultivar tolerates it (Supported, house-endorsed), and notes every cultivar responds differently. Push too hard and you lose yield. ## Don't confuse with - **Ethylene**: the ripening and [senescence](https://genetixbay.com/knowledge/glossary/senescence.md) gas. - **Cytokinin**: a growth hormone that ABA broadly opposes. - **Wilting**: the visible result of water loss, which ABA tries to prevent. ## Related terms [Stomata](https://genetixbay.com/knowledge/glossary/stomata.md), [Transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md), [Ethylene](https://genetixbay.com/knowledge/glossary/ethylene.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md) ## Read more - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) - [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. 2. Caplan D, Dixon M, Zheng Y. 2019. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience 54(5):964-969. https://doi.org/10.21273/HORTSCI13510-18 --- # Absolute humidity > Absolute humidity is the actual mass of water vapour in a volume of air, in grams per cubic metre, independent of temperature. - Canonical: https://genetixbay.com/knowledge/glossary/absolute-humidity.html - Also written: AH, water vapour density, water vapor density, g/m³ humidity, humidity ratio - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Absolute humidity (AH) is the mass of water vapour per unit volume of air, usually in grams per cubic metre (g/m³). Unlike [relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), it does not change when the air warms or cools (ignoring the small expansion of air), so it tells you how much water is actually in the room. Engineers often use the related humidity ratio (grams of water per kilogram of dry air), which is what [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) and HVAC sizing charts are based on. ## In practice Air at 26 °C (79 °F) and 60% RH holds about 14.6 g/m³. Cool that same air to 20 °C (68 °F) at lights-off without removing any water and RH jumps to about 84%, because 20 °C air can hold only about 17.3 g/m³. That is the reason night-time humidity spikes in flower rooms, and why dehumidifiers must keep running after lights-off. To lower humidity you must physically remove water: [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) to drier air outside, or dehumidify. Heating only lowers RH, not AH. ## Units and formula AH (g/m³) ≈ 2,165 × e ÷ (T + 273.15), where e is actual vapour pressure in kPa and T is air temperature in °C. ## Don't confuse with - **Relative humidity**: a percentage of saturation, which shifts with temperature. - **Dew point**: the temperature at which the current AH would saturate the air. ## Related terms [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Dew point](https://genetixbay.com/knowledge/glossary/dew-point.md), [Dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) ## Read more - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) - [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Sources 1. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm --- # Accession > An accession is a distinct sample of plant material (seed, tissue or cuttings) entered into a collection or gene bank under its own ID with records of origin. - Canonical: https://genetixbay.com/knowledge/glossary/accession.html - Also written: accessions, germplasm accession, seed accession, accession number - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An accession is a sample of plant material added to a [gene](https://genetixbay.com/knowledge/glossary/gene.md) bank or collection and given its own identifier. Its record (passport data) includes where and when it was collected, by whom, the population it came from, and how it has been maintained or regenerated since. ## In practice Gene banks for crops such as maize or wheat hold accessions as seed, [tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md) or field collections. For cannabis the same idea applies to private and community collections. A seed line with a passport record (collection region, year, number of parent plants, every [regeneration](https://genetixbay.com/knowledge/glossary/re-veg.md) since) is far more useful to breeders and preservationists than a named pack with no history. GenetixBay applies accession thinking to member material: each plant or seed line gets an ID, and its origin, lineage and test results are recorded, so a cut or a line can be traced and compared over time. ## Don't confuse with - **Cultivar**: a variety; one cultivar may be held as several accessions from different sources. - **Strain name**: a label without a record. - **Germplasm**: the [genetic material](https://genetixbay.com/knowledge/glossary/germplasm.md) in general; an accession is one recorded sample of it. ## Related terms [Germplasm](https://genetixbay.com/knowledge/glossary/germplasm.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Heirloom](https://genetixbay.com/knowledge/glossary/heirloom.md), [Genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md) ## Read more - [How to document lineage evidence (GB-ID evidence levels L0-L4)](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md) - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) ## Sources 1. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 --- # Achene > The dry, single-seeded fruit of cannabis that growers call a seed; a hard shell (pericarp plus seed coat) encloses one embryo and does not split open. - Canonical: https://genetixbay.com/knowledge/glossary/achene.html - Also written: cannabis seed, seed (botanical), achenes, fruit - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An achene is a small, dry, one-seeded fruit that stays closed at maturity. What growers buy as a cannabis "seed" is botanically an achene: the hard outer [shell](https://genetixbay.com/knowledge/glossary/seed-coat.md) is the fruit wall (pericarp) fused tightly over the true seed coat, with a single embryo and a little endosperm inside. Each develops from one [pollinated](https://genetixbay.com/knowledge/glossary/pollination.md) [pistillate flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md), wrapped in its [bract](https://genetixbay.com/knowledge/glossary/bract.md). ## In practice Mature achenes are typically 2-5 mm long, grey to brown, often mottled or "tiger-striped", and they rattle out of the bract when ripe, usually around 4-6 weeks after pollination. Pale, green or soft seeds are usually immature and [germinate](https://genetixbay.com/knowledge/glossary/germination.md) poorly. A breeder checks ripeness by the colour, a firm shell that resists a gentle squeeze, and bracts starting to split. Storage is about the embryo inside: cool, dark and dry. Seeds kept at low moisture and low temperature hold germination for years (Small & Brookes 2012). ## Don't confuse with - **Seed coat (testa)**: the thin layer of the true seed, inside the achene shell. - **Bract**: the leafy sheath that wraps the developing achene, not part of the fruit. - **Calyx**: the reduced [perianth](https://genetixbay.com/knowledge/glossary/calyx.md) on the ovary; often misused for the bract. ## Related terms [Seed coat](https://genetixbay.com/knowledge/glossary/seed-coat.md), [Cotyledon](https://genetixbay.com/knowledge/glossary/cotyledon.md), [Radicle](https://genetixbay.com/knowledge/glossary/radicle.md), [Bract](https://genetixbay.com/knowledge/glossary/bract.md) ## Read more - [Seed viability and storage: keeping cannabis seeds alive](https://genetixbay.com/knowledge/germination/seed-viability-storage.md) - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 2. Small E, Brookes B. 2012. Temperature and moisture content for storage maintenance of germination capacity of seeds of industrial hemp, marijuana, and ditchweed forms of Cannabis sativa. Journal of Natural Fibers 9(4):240-255. https://doi.org/10.1080/15440478.2012.737179 --- # Acid vs neutral cannabinoids > Acid cannabinoids (THCA, CBDA, CBGA) are the carboxylated forms the plant makes; neutral cannabinoids (THC, CBD, CBG) form when heat or time removes the carboxyl group. - Canonical: https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.html - Also written: acidic cannabinoids, neutral cannabinoids, acid cannabinoids, carboxylated cannabinoids, decarboxylated cannabinoids, acid forms - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cannabis makes its cannabinoids as carboxylic acids, marked with an "A" ([THCA](https://genetixbay.com/knowledge/glossary/thca.md), CBDA, [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), CBCA, [THCVA](https://genetixbay.com/knowledge/glossary/thcva.md)). The acids are the biosynthetic products of the trichome enzymes. Their neutral forms ([THC](https://genetixbay.com/knowledge/glossary/thc.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), [CBG](https://genetixbay.com/knowledge/glossary/cbg.md), CBC, [THCV](https://genetixbay.com/knowledge/glossary/thcv.md)) appear when the carboxyl group leaves as CO2 during [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), mostly through heat, slowly through storage. ## In practice Raw and cured flower is mostly acids; smoke, vapour and cooked products are mostly neutrals. That's why a flower COA lists both and why labels report calculated "total THC". The distinction also drives lab method choice: HPLC measures the acids and neutrals separately at room temperature, while GC heats the sample, converts most acids in the inlet and reports neutrals unless the sample is derivatised first. ## Units and formula Neutral = acid × conversion factor: about 0.877 for THCA to THC and CBDA to CBD, 0.878 for CBGA to CBG and 0.867 for THCVA to THCV (molecular weight ratios). ## Don't confuse with - **Total THC**: a calculated combination of acid and neutral. - **Degradation products** (CBN, CBL): formed by oxidation or light, not by decarboxylation alone. ## Related terms [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [THC](https://genetixbay.com/knowledge/glossary/thc.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md), [HPLC](https://genetixbay.com/knowledge/glossary/hplc.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. 2. ElSohly MA, Slade D. 2005. Chemical constituents of marijuana: the complex mixture of natural cannabinoids. Life Sciences 78(5):539-548. 3. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. --- # Action threshold > The pest or disease level, set in advance, at which a grower takes a specific control action because waiting longer would cost more than acting. - Canonical: https://genetixbay.com/knowledge/glossary/action-threshold.html - Also written: economic threshold, treatment threshold, intervention threshold, action level, economic injury level - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An action threshold is the level of pest or disease, measured by scouting, at which a defined control step is triggered. In field crops it is tied to the economic injury level, the point where damage costs more than control. For high-value cannabis, thresholds are set low because the tolerance for damage or contamination in flowers is close to zero. ## In practice Thresholds turn vague worry into a rule. Examples a grower might write down: more than 10 [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) per yellow card per week in veg triggers an extra predator release; any confirmed [broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md) or [russet mite](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md) on a clone triggers destruction of that batch; any [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) colony in late veg triggers removal of affected leaves and an environment check. The numbers are grower-set, not universal; record counts weekly and adjust thresholds as you learn what your room tolerates. Stage matters: the same count that is tolerable in early veg can be unacceptable two weeks into flower, when options run out. ## Don't confuse with - **Economic injury level**: the damage break-even point; the action threshold sits below it to leave time to act. - **Zero tolerance**: a threshold of one, used for pests such as russet mites and for pathogens such as [HLVd](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md). - **Spray schedule**: action by calendar, not by count. ## Related terms [IPM](https://genetixbay.com/knowledge/glossary/ipm.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Preventive release](https://genetixbay.com/knowledge/glossary/preventive-release.md) ## Read more - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) ## Sources 1. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects --- # Aerial dispersal > Pests spreading on air currents; spider mites gather at plant tops and drop on silk threads to be carried by wind or fans. - Canonical: https://genetixbay.com/knowledge/glossary/aerial-dispersal.html - Also written: ballooning, silk ballooning, wind dispersal - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Aerial dispersal is movement on air currents rather than by walking. [Spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) in crowded colonies move to the highest leaf tips, mass on webbing and let themselves be blown off, a behaviour often called ballooning; UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) notes mites are spread by wind as well as on clothing and plants. [Eriophyid](https://genetixbay.com/knowledge/glossary/eriophyid-mite.md) [russet mites](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md) and [winged aphids](https://genetixbay.com/knowledge/glossary/alate.md) also travel on air. ## In practice Indoors, strong [oscillating fans](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) and exhaust airflow move dispersing mites from plant to plant. That is a reason to treat a whole room, not only the visible hot spot, and to work and move air from clean areas toward infested ones, never the reverse. ## Don't confuse with - **Phoresy**: riding on another animal, e.g. [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md) on [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md). - **Ambulatory dispersal**: walking along touching leaves. ## Related terms [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [Airflow](https://genetixbay.com/knowledge/glossary/airflow.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) - [Integrated pest management (IPM) for cannabis: a complete programme for home and small commercial growers](https://genetixbay.com/knowledge/pests/integrated-pest-management-program.md) ## Sources 1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # Aeroponics > Aeroponics grows plants with roots hanging in air inside a dark chamber, wetted by sprayed nutrient solution; low-pressure (LPA) systems use ordinary pumps and spray heads. - Canonical: https://genetixbay.com/knowledge/glossary/aeroponics.html - Also written: aero, aeroponic, LPA, low-pressure aeroponics, low pressure aeroponics, spray hydroponics - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Aeroponics is a hydroponic method in which roots are suspended in an enclosed, dark chamber and periodically or continuously sprayed with nutrient solution. Roots sit in air, so oxygen supply is excellent. Low-pressure aeroponics (LPA) uses a standard submersible or inline pump and sprinkler-style heads, producing coarse droplets; [high-pressure aeroponics](https://genetixbay.com/knowledge/glossary/hpa.md) (HPA) uses a high-pressure pump and fine-mist nozzles. ## In practice LPA is common in home cloners and some vegetative systems: cuttings root quickly in a box of misted air. For full grows, LPA behaves much like a well-aerated [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) with a spray, and most units keep a pool of solution at the bottom. Keep solution cool, around 18-21 °C (64-70 °F), and use a timer or run continuously depending on the design. A pump failure dries exposed roots far faster than in DWC, so alarms and backup matter. Research on aeroponic indoor farming highlights excellent root aeration and harvestable root mass, but also the system's sensitivity to failures. ## Don't confuse with - **HPA**: true fine-mist aeroponics at high pressure, with no standing solution. - **Fogponics**: ultrasonic fog, even smaller droplets. ## Related terms [HPA](https://genetixbay.com/knowledge/glossary/hpa.md), [Fogponics](https://genetixbay.com/knowledge/glossary/fogponics.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [Root zone](https://genetixbay.com/knowledge/glossary/root-zone.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md) ## Read more - [Low-pressure aeroponics (LPA)](https://genetixbay.com/knowledge/systems/lpa-aeroponics.md) - [High-pressure aeroponics (HPA)](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) ## Sources 1. Eldridge BM, Manzoni LR, Graham CA, et al., 2020. Getting to the roots of aeroponic indoor farming. New Phytologist 228:1183–1192. https://doi.org/10.1111/nph.16780 2. Lakhiar IA, Gao J, Syed TN, Chandio FA, Buttar NA, 2018. Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics. Journal of Plant Interactions 13(1):338–352. https://doi.org/10.1080/17429145.2018.1472308 --- # Air pot > An air pot is a rigid container with cone-shaped holes in its walls that air-prune roots, preventing circling and drying the medium faster than a solid pot. - Canonical: https://genetixbay.com/knowledge/glossary/air-pot.html - Also written: air pots, air-pruning pot, air pruning pot, root pruning pot - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An air pot is a rigid plastic container whose wall is covered in outward-pointing cones, each with a hole at the tip. Roots growing towards the wall are guided into the cones, meet air, dry at the tip and stop, which causes the root to branch. The result is a fibrous root system without the dense circling seen in solid pots. ## In practice Air pots dry quickly, especially at the edges, so watering frequency goes up and the edges of the medium can stay dry if the grower only waters the centre. Water slowly and all over, or run [drip emitters](https://genetixbay.com/knowledge/glossary/drip-irrigation.md) around the perimeter. They suit soil and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md); they are rarely used with pure inert hydro media. Like [fabric pots](https://genetixbay.com/knowledge/glossary/fabric-pot.md), they are most useful when a plant will stay in the same container for a long time, such as a [mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md) or a big outdoor plant. ## Don't confuse with - **Fabric pot**: soft and breathable over its whole surface; an air pot breathes only through its holes. - **Air pruning (outdoor beds)**: the same effect, from raised mesh-bottomed beds. ## Related terms [Fabric pot](https://genetixbay.com/knowledge/glossary/fabric-pot.md), [Root-bound](https://genetixbay.com/knowledge/glossary/root-bound.md), [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) ## Read more - [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Air stone > An air stone is a porous diffuser connected to an air pump that breaks air into fine bubbles in a nutrient solution, mixing it and helping maintain dissolved oxygen. - Canonical: https://genetixbay.com/knowledge/glossary/air-stone.html - Also written: airstone, air stones, bubbler, air diffuser, diffuser stone, air pump and stone - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An air stone is a porous block or disc, made of mineral, ceramic or sintered material, fed by an air pump through tubing. Air forced through it emerges as many fine bubbles. The bubbles themselves add some oxygen, but their main effect is circulation: they keep the solution moving, bring water to the surface where it exchanges gases with the air, and prevent stagnant zones. ## In practice In [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) and [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), air stones run 24 hours a day. A rough rule many growers use is about 1 L/min of air per 4 L of solution, or more. Clean or replace stones when bubbles become coarse or uneven, since mineral and biofilm build-up clogs them. Place the pump above the water line, or fit a check valve, so water can't siphon back into the pump if it stops. Aeration only works well in cool water; warm solution can't hold much oxygen however hard it is bubbled. ## Don't confuse with - **Water pump**: moves solution; an air pump moves air. - **Venturi or oxygen injector**: other ways of raising dissolved oxygen. ## Related terms [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [Chiller](https://genetixbay.com/knowledge/glossary/chiller.md) ## Read more - [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 --- # Air-filled porosity > Air-filled porosity is the share of a container's volume that holds air rather than water after it has drained, a key factor in root oxygen and overwatering risk. - Canonical: https://genetixbay.com/knowledge/glossary/air-filled-porosity.html - Also written: AFP, air porosity, air space, aeration porosity, air-filled pore space - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Air-filled porosity is the percentage of a medium's total volume occupied by air at [container capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md), after free [drainage](https://genetixbay.com/knowledge/glossary/runoff.md). It sits alongside water-holding capacity: the pores in a pot are shared between water and air, and roots need both. Coarse materials such as [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), bark, [coco chips](https://genetixbay.com/knowledge/glossary/coco-coir.md) and [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md) raise it; fine peat and fine coco lower it. ## In practice Container media for most crops perform well at roughly 10-30% air-filled porosity after drainage. Below about 10% roots are prone to oxygen shortage and [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md); very high values dry quickly and need frequent irrigation. Pot height matters too: a short, wide pot holds a deeper saturated layer at its base relative to its volume, so the same mix has less air in a shallow pot than a tall one. This is why adding perlite helps [overwatered](https://genetixbay.com/knowledge/glossary/overwatering.md) soil grows and why coco and [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) can be irrigated many times a day. ## Don't confuse with - **Total porosity**: all pore space, air plus water. - **Water-holding capacity**: the water side of the same split. ## Related terms [Field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md), [Perlite](https://genetixbay.com/knowledge/glossary/perlite.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) ## Read more - [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Airflow > Airflow is the movement of air through and around the canopy; it thins the still boundary layer on leaves, evens out temperature and humidity, and lowers mould risk. - Canonical: https://genetixbay.com/knowledge/glossary/airflow.html - Also written: air flow, air movement, air circulation, canopy airflow, air exchange - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Airflow covers two jobs. Circulation stirs air inside the grow space so there are no hot, humid or CO2-depleted pockets. Exchange replaces room air with fresh air to remove heat and moisture and bring in [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md). Both work by reducing the boundary layer, the thin film of still air around each leaf that slows gas and heat exchange. ## In practice Kitaya and colleagues (2003) showed that leaf gas exchange improves sharply as air speed rises from still air to around 0.5–1 m/s, with little extra benefit beyond that. A practical target is canopy leaves that flutter gently, not whip. Constant strong wind dries leaves, can cause [windburn](https://genetixbay.com/knowledge/glossary/wind-burn.md) (clawed, papery leaves on the fan side) and wastes energy. Good airflow means air moving above the canopy, through it and below it. Dense flower rooms need [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) under the canopy too, because the inside of a [cola](https://genetixbay.com/knowledge/glossary/cola.md) is where [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) starts. If leaves at the back of the tent are still while the front ones dance, add or reposition a fan. ## Don't confuse with - **Exhaust (ventilation)**: removes air from the space; [circulation fans](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) only mix it. - **CFM**: a fan rating, not a measure of air speed at the leaf. ## Related terms [Oscillating fan](https://genetixbay.com/knowledge/glossary/oscillating-fan.md), [Exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md), [Microclimate](https://genetixbay.com/knowledge/glossary/microclimate.md), [CFM](https://genetixbay.com/knowledge/glossary/cfm.md) ## Read more - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) ## Sources 1. Kitaya Y, Tsuruyama J, Shibuya T, Yoshida M, Kiyota M, 2003. Effects of air current speed on gas exchange in plant leaves and plant canopies. Advances in Space Research 31(1):177–182. --- # Alate > The winged form of an aphid, produced mainly when colonies crowd or plants decline; alates fly to new plants and are caught on sticky cards. - Canonical: https://genetixbay.com/knowledge/glossary/alate.html - Also written: alates, winged aphid, winged morph, alatae - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An alate is a winged aphid. Most [aphids](https://genetixbay.com/knowledge/glossary/aphid.md) on a plant are wingless (apterous); winged forms develop when colonies become crowded, when the host plant deteriorates, or seasonally, and they fly or drift on air to found new colonies. UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) notes that winged aphids appear when populations are high or plants are stressed. ## In practice Alates on a yellow [sticky card](https://genetixbay.com/knowledge/glossary/sticky-trap.md) are often the first sign of aphids, including [root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md) that are otherwise hidden below ground. One alate on a card means a colony somewhere; inspect nearby plants and root balls. Alates arriving through intakes are a reason to screen air inlets. ## Don't confuse with - **Apterous aphid**: the wingless form. - **Whitefly**: also white and winged, but powdery and not an aphid. ## Related terms [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Holocyclic and anholocyclic](https://genetixbay.com/knowledge/glossary/holocyclic.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) - [Root aphids (rice root aphid) on indoor cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/root-aphids.md) - [Cannabis aphid (Phorodon cannabis): ID, life table, overwintering and control](https://genetixbay.com/knowledge/pests/cannabis-aphid.md) ## Sources 1. UC IPM. Pest Notes: Aphids (Publication 7404). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html --- # Alkalinity > Alkalinity is water's capacity to neutralise acid, mainly from dissolved bicarbonate and carbonate, reported in mg/L as CaCO3; it decides how much pH Down you need. - Canonical: https://genetixbay.com/knowledge/glossary/alkalinity.html - Also written: total alkalinity, water alkalinity, bicarbonate alkalinity, mg/L CaCO3, ppm as CaCO3 - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Alkalinity is the [acid-neutralising capacity](https://genetixbay.com/knowledge/glossary/buffering-capacity.md) of water. In irrigation water it comes almost entirely from bicarbonate (HCO₃⁻) and carbonate (CO₃²⁻), with small contributions from hydroxide and other weak bases. It is reported as mg/L (ppm) of calcium carbonate equivalent. Alkalinity is not the same as high [pH](https://genetixbay.com/knowledge/glossary/ph.md): water can be at pH 7.5 with low alkalinity and move easily, or at pH 7.5 with high alkalinity and resist acid stubbornly. ## In practice Rough guide for container growing: | Alkalinity (mg/L as CaCO3) | Effect | |---|---| | Below 40 | Little buffering; pH moves easily ([RO](https://genetixbay.com/knowledge/glossary/ro-water.md), rain) | | 40–100 | Comfortable for most container growing | | 100–200 | Needs acid; media pH tends to creep up | | Above 200 | Needs significant acidification or RO blending | Water utilities publish alkalinity in annual water-quality reports, and inexpensive aquarium [KH](https://genetixbay.com/knowledge/glossary/carbonate-hardness.md) test kits give a usable estimate. Acid dosing to neutralise most of the bicarbonate, rather than simply chasing pH, gives a stable result. ## Units and formula 1 dKH = 17.86 mg/L as CaCO3. Bicarbonate (mg/L) ≈ alkalinity as CaCO3 × 1.22. ## Don't confuse with - **pH**: the acidity level, not the reserve. - **Hardness**: calcium and magnesium content; often related, but not the same thing. ## Related terms [Buffering capacity](https://genetixbay.com/knowledge/glossary/buffering-capacity.md), [Carbonate hardness](https://genetixbay.com/knowledge/glossary/carbonate-hardness.md), [pH Down](https://genetixbay.com/knowledge/glossary/ph-down.md), [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md), [General hardness](https://genetixbay.com/knowledge/glossary/general-hardness.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Sources 1. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Allele > An allele is one version of a gene; a diploid cannabis plant carries two alleles at each locus, one from each parent, which may be the same or different. - Canonical: https://genetixbay.com/knowledge/glossary/allele.html - Also written: alleles, gene variant, allelic variant - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An allele is one version of a [gene](https://genetixbay.com/knowledge/glossary/gene.md). Cannabis is diploid, so every plant carries two alleles at each [locus](https://genetixbay.com/knowledge/glossary/locus.md), one inherited through the pollen and one through the ovule. If the two are the same the plant is homozygous at that locus; if they differ it is [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md). ## In practice The best-known cannabis example is the cannabinoid synthase locus. One allele (often written B_T) makes a functional [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md); another (B_D) makes [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md). A plant carrying B_T/B_T is THC-dominant, B_D/B_D is CBD-dominant, and B_T/B_D produces both in a roughly balanced ratio (de Meijer et al. 2003). Breeders who want a stable 1:1 [THC](https://genetixbay.com/knowledge/glossary/thc.md):[CBD](https://genetixbay.com/knowledge/glossary/cbd.md) seed line learn quickly why it cannot breed true: the balanced plants are heterozygous and their offspring segregate. Alleles are written with letters (A and a) for teaching. Real cannabis loci can have more than two alleles in the population, and some regions contain duplicated, non-functional copies of synthase genes (Laverty et al. 2019). ## Don't confuse with - **Gene**: the position and function; the allele is the variant at that position. - **Mutation**: the event that creates a new allele. Most alleles in a population are old, not new. - **Phenotype**: what you see. Two different allele pairs can produce the same visible result when one is [dominant](https://genetixbay.com/knowledge/glossary/dominant.md). ## Related terms [Gene](https://genetixbay.com/knowledge/glossary/gene.md), [Locus](https://genetixbay.com/knowledge/glossary/locus.md), [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md), [Dominant](https://genetixbay.com/knowledge/glossary/dominant.md), [Recessive](https://genetixbay.com/knowledge/glossary/recessive.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 2. Laverty KU, Stout JM, Sullivan MJ, et al. 2019. A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci. Genome Research 29(1):146-156. https://doi.org/10.1101/gr.242594.118 3. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 --- # Alpha-pinene > Alpha-pinene is a bicyclic monoterpene with a sharp pine-resin aroma, the main terpene of conifer needles and a common, usually secondary, terpene in cannabis. - Canonical: https://genetixbay.com/knowledge/glossary/alpha-pinene.html - Also written: α-pinene, a-pinene, pinene, alpha pinene - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Alpha-pinene is the most widespread [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) in nature, giving pine needles and turpentine their smell. It is a bicyclic [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), an isomer of [beta-pinene](https://genetixbay.com/knowledge/glossary/beta-pinene.md), with the double bond in a different position. In cannabis it is usually present at modest levels and is rarely the single [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) terpene, though some cultivars are notably pine-forward. ## In practice Many COAs list "pinene" or show alpha- and beta-pinene separately; alpha is usually the larger of the two. Typical flower readings run 0.05-0.3% w/w. Like other monoterpenes it is volatile and lost during fast, warm drying. If a [lab reports](https://genetixbay.com/knowledge/glossary/coa.md) "total pinene", ask whether it's the sum of both isomers. ## Don't confuse with - **Beta-pinene**: the isomer, with a more herbal, green note. - **Pine-sol / pine-cleaner smells**: often a blend of compounds, not pinene alone. ## Myth check Claims that pinene "counteracts short-term memory effects of [THC](https://genetixbay.com/knowledge/glossary/thc.md)" circulate widely. They rest on early lab and hypothesis papers, not established human trials; treat them as unproven. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Beta-pinene](https://genetixbay.com/knowledge/glossary/beta-pinene.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Terpinolene](https://genetixbay.com/knowledge/glossary/terpinolene.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # Amblyseius swirskii > A warmth-loving generalist predatory mite that eats thrips larvae, whitefly eggs and nymphs and broad mites, and can persist on pollen. - Canonical: https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.html - Also written: swirskii, A. swirskii, swirski mite - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Amblyseius swirskii* is a generalist [predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) of the family Phytoseiidae, originally from the eastern Mediterranean. It feeds on young [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) larvae, [whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md) eggs and young nymphs, [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md) and other small [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), and can live on pollen when prey is scarce. That diet makes it one of the most widely used preventive predators in greenhouse crops. ## In practice Growers release *swirskii* in veg, loose on leaves or in sachets, to keep thrips and whitefly from building. It needs warmth: it performs best above roughly 20 °C (68 °F) and does poorly in cool rooms. Low humidity limits egg survival. Because it does not eat spider mites well, it is often combined with *[Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md)* or *[Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md)*. It is also used against broad mites on tips. Rooms with heavy trichome coverage can slow movement on some cultivars, which is one reason releases go in early. ## Don't confuse with - **Neoseiulus cucumeris**: the cooler-tolerant thrips predator, usually cheaper and less persistent. - **Orius**: a predatory bug that eats adult thrips as well as larvae. - **Spider mite predators**: *persimilis* and *californicus*. ## Related terms [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md), [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md), [Predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) ## Read more - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) - [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) ## Sources 1. UConn IPM. Biological Control of Western Flower Thrips. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-western-flower-thrips/ 2. UConn IPM. Biological Control of Whiteflies. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-whiteflies --- # Amino acid chelate > An amino acid chelate is a metal bound to amino acids such as glycine; it is a gentler, biodegradable alternative to synthetic chelates, often sold for foliar sprays. - Canonical: https://genetixbay.com/knowledge/glossary/amino-acid-chelate.html - Also written: amino acid chelates, amino chelate, glycinate, chelated amino acids - Glossary category: Nutrients · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An amino acid chelate is a metal ion, such as iron, zinc, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md), copper, calcium or magnesium, complexed with one or more amino acids, glycine being the most common. The bonds are weaker than those of [EDTA](https://genetixbay.com/knowledge/glossary/edta.md) or [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md), and the amino acids are biodegradable. ## In practice These products are marketed mainly for [foliar feeding](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) and organic-leaning programmes, with claims of better uptake through the leaf. Evidence for their superiority over synthetic [chelates](https://genetixbay.com/knowledge/glossary/chelate.md) or simple salts in cannabis is thin (Evidence: Contested). In a [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) reservoir, microbes break down the amino acids, so stability over days is lower than with synthetic chelates. Labels may also count the amino acids as nitrogen, which is small but real. ## Don't confuse with - **Synthetic chelates (EDTA, DTPA, EDDHA)**: stronger, more predictable in solution. - **Amino acid biostimulants**: free amino acids sold for growth claims, without a metal. - **Protein hydrolysate**: a crude source of amino acids, often from fish or plant protein. ## Related terms [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md), [EDTA](https://genetixbay.com/knowledge/glossary/edta.md), [Foliar feeding](https://genetixbay.com/knowledge/glossary/foliar-feeding.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Ammonium > Ammonium (NH4+) is the positively charged form of nitrogen; a small share stabilises root-zone pH, but too much reduces cannabis yield and quality. - Canonical: https://genetixbay.com/knowledge/glossary/ammonium.html - Also written: NH4+, NH4, ammoniacal nitrogen, NH4-N, ammonium nitrogen - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Ammonium is the cation NH4+, a form of nitrogen plants can absorb directly and use without first reducing it. Its uptake releases hydrogen ions from the root, so it acidifies the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). Inside the plant it must be assimilated quickly, because free ammonium is toxic at high levels. ## In practice Mineral feeds usually keep ammonium to a small fraction of total N, often around 10-20% or less. That share offsets the upward [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md) caused by [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) uptake. Saloner and Bernstein found that high NH4/NO3 ratios reduced [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), terpenoids and yield in [medical cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md). Ammonium excess shows as dark, cupped or [clawed leaves](https://genetixbay.com/knowledge/glossary/leaf-clawing.md) and poor root growth, and it competes with calcium, magnesium and potassium uptake. ## Units and formula [Lab reports](https://genetixbay.com/knowledge/glossary/coa.md) may give NH4-N (nitrogen only): 1 mg/L NH4-N = 1.29 mg/L NH4+. ## Don't confuse with - **Ammonia (NH3)**: the uncharged gas, more toxic, favoured at high [pH](https://genetixbay.com/knowledge/glossary/ph.md). - **Nitrate**: the main hydro N form, which pushes pH up. - **Urea**: an organic N compound converted to ammonium by an enzyme. ## Related terms [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [Monoammonium phosphate](https://genetixbay.com/knowledge/glossary/monoammonium-phosphate.md), [Ammonium nitrate](https://genetixbay.com/knowledge/glossary/ammonium-nitrate.md), [Urea](https://genetixbay.com/knowledge/glossary/urea.md) ## Read more - [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) ## Sources 1. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 2. Langenfeld NJ, Bugbee B. 2025. pH control in recirculating hydroponics with nitric acid and ammonium nitrate. HortScience 60(9):1555. https://journals.ashs.org/view/journals/hortsci/60/9/article-p1555.xml --- # Ammonium nitrate > Ammonium nitrate (NH4NO3) is a 34-35% nitrogen salt, half ammonium and half nitrate, used in small amounts to steer root-zone pH in hydro. - Canonical: https://genetixbay.com/knowledge/glossary/ammonium-nitrate.html - Also written: NH4NO3, 34-0-0 - Glossary category: Nutrients · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Ammonium nitrate is a salt containing nitrogen in both its main plant-available forms: about 17% as [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) and 17% as [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), for 34-35% total N. It is very soluble and strongly hygroscopic. ## In practice In mineral hydro it is used sparingly to add an ammonium fraction, which offsets the [pH](https://genetixbay.com/knowledge/glossary/ph.md) rise caused by nitrate uptake. Langenfeld and Bugbee examined [nitric acid](https://genetixbay.com/knowledge/glossary/nitric-acid.md) and ammonium nitrate as tools for pH control in [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md). Too much shifts the NH4/NO3 balance and harms cannabis yield and quality. Pure ammonium nitrate is restricted or regulated in many places because it is an oxidiser with explosive potential; many growers use calcium ammonium nitrate or the ammonium in fertiliser-grade [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md) instead. Check local rules. ## Units and formula 1 g/L gives about 340-350 mg/L (ppm) N, half as NH4-N and half as NO3-N. ## Don't confuse with - **Calcium ammonium nitrate (CAN)**: ammonium nitrate blended with limestone or dolomite. - **Ammonium sulfate**: ammonium with [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), more acidifying. - **Urea**: an organic N compound needing enzymatic conversion. ## Related terms [Ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Nitric acid](https://genetixbay.com/knowledge/glossary/nitric-acid.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) ## Sources 1. Langenfeld NJ, Bugbee B. 2025. pH control in recirculating hydroponics with nitric acid and ammonium nitrate. HortScience 60(9):1555. https://journals.ashs.org/view/journals/hortsci/60/9/article-p1555.xml 2. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 --- # Anther > The pollen-producing part of a stamen; in cannabis each male flower has five anthers that split to shed wind-blown pollen. - Canonical: https://genetixbay.com/knowledge/glossary/anther.html - Also written: anthers, pollen sac, pollen sacs, stamen, pollen pod - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An anther is the pollen-bearing head of a stamen, held up on a thin filament. Inside, pollen sacs produce [pollen grains](https://genetixbay.com/knowledge/glossary/pollen.md); when ripe, the anther wall splits lengthwise (dehisces) and releases them. Cannabis is wind-pollinated, so anthers shed large volumes of light, dry pollen that can travel a long way on air. ## In practice Breeders collect pollen by isolating a flowering male and tapping open flowers over paper. Pollen kept dry and cold lasts weeks in a fridge and much longer frozen. On a female, anthers matter as a warning sign. Single yellow-green anthers poking out of a bud ("[bananas](https://genetixbay.com/knowledge/glossary/nanners.md)") are exposed stamens from an [intersex plant](https://genetixbay.com/knowledge/glossary/hermaphrodite.md). They can shed pollen without the plant ever forming a full [male flower](https://genetixbay.com/knowledge/glossary/staminate-flower.md). Remove the plant or the affected parts quickly, and don't breed from it. Growers sometimes call a closed male flower a "pollen sac". Botanically the sacs are inside the anther. ## Don't confuse with - **Staminate flower**: the whole male flower containing the anthers. - **Stigma**: the female pollen-receiving hair. - **Seed pod**: a [pollinated](https://genetixbay.com/knowledge/glossary/pollination.md) [bract](https://genetixbay.com/knowledge/glossary/bract.md) holding a developing seed. ## Related terms [Staminate flower](https://genetixbay.com/knowledge/glossary/staminate-flower.md), [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), [Stigma](https://genetixbay.com/knowledge/glossary/stigma.md), [Dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md) ## Read more - [Collecting and storing cannabis pollen](https://genetixbay.com/knowledge/breeding/pollen-collection-storage.md) - [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Gaudet D, Yadav NS, Sorokin A, Bilichak A, Kovalchuk I. 2020. Development and optimization of a germination assay and long-term storage for Cannabis sativa pollen. Plants 9(5):665. https://doi.org/10.3390/plants9050665 --- # Anthocyanin > A water-soluble flavonoid pigment stored in cell vacuoles that colours leaves, stems and flowers red, purple or blue, set by genetics and enhanced by cool temperatures. - Canonical: https://genetixbay.com/knowledge/glossary/anthocyanin.html - Also written: anthocyanins, purple pigment, purple colour, purple color, purpling - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Anthocyanins are flavonoid pigments made through the phenylpropanoid pathway and stored in the vacuole. Depending on the molecule and the vacuole's [pH](https://genetixbay.com/knowledge/glossary/ph.md) they appear red, purple or blue. In cannabis, whether a plant can turn purple is mainly genetic; cool temperatures, high light and late-season [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) breakdown bring it out (Bassolino et al. 2023). ## In practice Purple bracts, [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) and stems in late flower are usually anthocyanin expression in a cultivar that carries it, often triggered by nights a good 5-10 °C (9-18 °F) cooler than days. A cultivar without the genetics won't purple however cold you run it. Purple stems or petioles in veg are frequently genetic and harmless. They point to a problem only alongside other symptoms, such as dull, dark leaves with spotting (possible phosphorus or cold-root issues). ## Don't confuse with - **Chlorophyll**: the green [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) pigment. - **Carotenoids**: yellow and orange pigments revealed as chlorophyll fades. - **Phosphorus deficiency**: may cause purpling, but with other leaf symptoms. ## Myth check Cold for colour is real (Established). Claims that [cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) add [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), flavour or resin are unsupported unless peer-reviewed data shows otherwise; anthocyanin and yield have different temperature optima (Kim et al. 2025). Purple is [bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md), not potency. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md), [Phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md) ## Read more - [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) ## Sources 1. Bassolino L, Fulvio F, Pastore C, et al. 2023. When Cannabis sativa L. turns purple: biosynthesis and accumulation of anthocyanins. Antioxidants 12(7):1393. https://doi.org/10.3390/antiox12071393 2. Kim SR, Basnet P, Kovaleski AP, Ellison SL. 2025. Anthocyanin accumulation, inflorescence dry weight and total cannabidiol content have different temperature optima in Cannabis sativa. Journal of Cannabis Research 7:51. https://doi.org/10.1186/s42238-025-00311-w --- # Aphid > Small soft-bodied sap-sucking insects of the family Aphididae that cluster on stems and leaf undersides, excrete sticky honeydew and multiply rapidly by live birth. - Canonical: https://genetixbay.com/knowledge/glossary/aphid.html - Also written: aphids, greenfly, blackfly, plant lice, green peach aphid, Myzus persicae - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Aphids are small, soft-bodied insects of the family Aphididae, about 1-3 mm long, that feed on [phloem sap](https://genetixbay.com/knowledge/glossary/phloem.md) through a needle-like stylet. Most have two tube-like cornicles at the rear. Indoors, females give birth to live young without mating, so a colony can double in days. Several species use cannabis, including the [cannabis aphid](https://genetixbay.com/knowledge/glossary/cannabis-aphid.md) (*Phorodon cannabis*) and the generalist green peach aphid (*Myzus persicae*). ## In practice Signs are colonies on leaf undersides and stems, white cast skins, sticky [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md), and the black [sooty mould](https://genetixbay.com/knowledge/glossary/sooty-mould.md) that grows on it. Ants farming honeydew are a strong clue outdoors. Heavy feeding curls and yellows leaves, and some aphids carry [plant viruses](https://genetixbay.com/knowledge/glossary/plant-virus.md). Standard tools are [parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md) such as *Aphidius colemani*, predators such as lacewing larvae and ladybirds, and soft contact sprays such as [insecticidal soap](https://genetixbay.com/knowledge/glossary/insecticidal-soap.md) in veg only. Honeydew and cast skins on buds are a quality problem, so act early. Check what is registered for cannabis locally. ## Don't confuse with - **Whitefly nymphs**: flat, scale-like and fixed in place on the leaf underside. - **Root aphid**: lives on roots, rarely seen on foliage until late. - **Mealybugs**: covered in white waxy fluff. ## Related terms [Cannabis aphid](https://genetixbay.com/knowledge/glossary/cannabis-aphid.md), [Root aphid](https://genetixbay.com/knowledge/glossary/root-aphid.md), [Aphidius](https://genetixbay.com/knowledge/glossary/aphidius.md), [Ladybird](https://genetixbay.com/knowledge/glossary/ladybird.md), [Lacewing](https://genetixbay.com/knowledge/glossary/lacewing.md), [Insecticidal soap](https://genetixbay.com/knowledge/glossary/insecticidal-soap.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. UC IPM. Pest Notes: Aphids (Publication 7404). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html 2. UConn IPM. Biological Control of Aphids. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-aphids/ --- # Aphidius > Tiny parasitic wasps of the genus Aphidius that lay eggs inside aphids; the larva kills the host from inside, leaving a swollen tan mummy. - Canonical: https://genetixbay.com/knowledge/glossary/aphidius.html - Also written: Aphidius colemani, Aphidius ervi, aphid parasitoid, parasitic wasp, parasitoid wasp, aphid mummy - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Aphidius* is a genus of tiny parasitic wasps (family Braconidae), about 2-3 mm long, that develop inside [aphids](https://genetixbay.com/knowledge/glossary/aphid.md). A female stabs an aphid with her ovipositor and lays one egg; the larva eats the aphid from inside, turning it into a bloated, papery, tan or golden "mummy". A new wasp chews a round exit hole and flies off to parasitise more aphids. They do not sting people. ## In practice *Aphidius colemani* targets smaller aphids such as green peach and melon aphids; *Aphidius ervi* handles larger species such as potato aphid. Matching the wasp to the aphid matters, so identify the species first. Growers release them preventively or at first sight of colonies, and some keep [banker plants](https://genetixbay.com/knowledge/glossary/banker-plant.md) with grain aphids to breed wasps continuously. Mummies on leaves are the proof they are working. Wasps fly well and find scattered colonies that predators miss. Avoid broad-spectrum sprays and very high temperatures during releases. ## Don't confuse with - **Aphid cast skins**: white and flat, left after moulting; mummies are swollen and tan. - **Fungus-killed aphids**: fuzzy and grey-white. - **Encarsia and Eretmocerus**: parasitic wasps for [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md), not aphids. ## Related terms [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Cannabis aphid](https://genetixbay.com/knowledge/glossary/cannabis-aphid.md), [Ladybird](https://genetixbay.com/knowledge/glossary/ladybird.md), [Banker plant](https://genetixbay.com/knowledge/glossary/banker-plant.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. UConn IPM. Biological Control of Aphids. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-aphids/ 2. UConn IPM. Aphid Banker Plants. https://ipm-cahnr.media.uconn.edu/wp-content/uploads/sites/3216/2024/08/aphidbankerplants.pdf --- # Apical dominance > The suppression of side-shoot growth by the main growing tip, driven mainly by auxin flowing down the stem from the apex. - Canonical: https://genetixbay.com/knowledge/glossary/apical-dominance.html - Also written: apical control, top dominance, leader dominance - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Apical dominance is the tendency of the main [shoot tip](https://genetixbay.com/knowledge/glossary/apical-meristem.md) to grow fastest while holding back the buds and branches below it. [Auxin](https://genetixbay.com/knowledge/glossary/auxin.md) made in the apex moves down the stem and, together with cytokinin and strigolactone signalling, keeps [axillary buds](https://genetixbay.com/knowledge/glossary/axillary-bud.md) dormant or slow. The result is a single-leader, "Christmas tree" shape. ## In practice Almost every training method is a way of breaking or redirecting apical dominance: - **Topping** and **FIM** remove the apex, releasing the buds below. - **[LST](https://genetixbay.com/knowledge/glossary/lst.md)** bends the leader down so that side branches sit as high and receive as much auxin relief and light as the top. - **Mainlining** and **manifolding** combine topping with symmetrical shaping. - **[SCROG](https://genetixbay.com/knowledge/glossary/scrog.md)** spreads every tip level under a net. Cultivars differ a lot. Some have strong apical dominance and grow one fat [main cola](https://genetixbay.com/knowledge/glossary/cola.md); others branch freely on their own. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md), which can't spare recovery time, are better shaped by LST than by topping (house position). ## Don't confuse with - **Apical meristem**: the tissue; apical dominance is its effect. - **Phototropism**: bending toward light, a separate auxin response. - **Stretch**: elongation in early flower, not branch suppression. ## Related terms [Apical meristem](https://genetixbay.com/knowledge/glossary/apical-meristem.md), [Auxin](https://genetixbay.com/knowledge/glossary/auxin.md), [Cytokinin](https://genetixbay.com/knowledge/glossary/cytokinin.md), [Axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md), [Cola](https://genetixbay.com/knowledge/glossary/cola.md) ## Read more - [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md) - [LST: low-stress training](https://genetixbay.com/knowledge/training/lst.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Apical meristem > The zone of dividing cells at the very tip of a shoot (or root) that produces new leaves, nodes and stem; removing it is what topping does. - Canonical: https://genetixbay.com/knowledge/glossary/apical-meristem.html - Also written: shoot apical meristem, SAM, growing tip, growth tip, shoot tip - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An apical meristem is a small region of undifferentiated, actively dividing cells at the tip of a shoot or root. The shoot apical meristem builds the plant upward: it lays down each new node, leaf primordium and [axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md). The root apical meristem, protected by the root cap, drives root growth downward. ## In practice Topping removes the shoot apical meristem of the main stem. With the tip gone, two axillary buds below take over, giving two main shoots. [FIM](https://genetixbay.com/knowledge/glossary/fim.md) removes most of the young tip but leaves some meristem tissue, which often produces three or more shoots, less predictably. The meristem is fragile. [Heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md) close to a lamp, [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md), and some calcium or [boron](https://genetixbay.com/knowledge/glossary/boron.md) problems show up first as twisted, stunted or dead growing tips, because that is where new tissue forms. When the newest growth [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) wrong, look at the tip first. In flowering, the apical meristem of each shoot converts to producing flowers and forms the top of the [cola](https://genetixbay.com/knowledge/glossary/cola.md). ## Don't confuse with - **Axillary bud**: a dormant meristem at a node, held back by the apex. - **Apical dominance**: the control the tip exerts, not the tissue itself. - **Cambium**: the lateral meristem that thickens stems. ## Related terms [Apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), [Axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md), [Node](https://genetixbay.com/knowledge/glossary/node.md), [Auxin](https://genetixbay.com/knowledge/glossary/auxin.md) ## Read more - [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md) - [FIM: pinching most of the tip for multiple tops](https://genetixbay.com/knowledge/training/fim.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Arrhenotoky > Reproduction in which unmated females lay unfertilised eggs that become males, while mated females make both sexes. Typical of spider mites and thrips. - Canonical: https://genetixbay.com/knowledge/glossary/arrhenotoky.html - Also written: arrhenotokous parthenogenesis, arrhenotokous - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Arrhenotoky is a type of [parthenogenesis](https://genetixbay.com/knowledge/glossary/parthenogenesis.md) in which unfertilised eggs develop into males. A [spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) or [western flower thrips](https://genetixbay.com/knowledge/glossary/thrips.md) female that has never mated still lays eggs, but all become sons; once she mates she lays mostly daughters. It is the reproductive face of [haplodiploidy](https://genetixbay.com/knowledge/glossary/haplodiploidy.md). ## In practice For growers, arrhenotoky means a single female that survives a spray or arrives on a clone can found a population on her own, by producing sons and then mating with them. It is one reason quarantine and zero-tolerance clone policies matter: one survivor is enough. ## Don't confuse with - **Thelytoky**: unfertilised eggs become females (some thrips; [aphids](https://genetixbay.com/knowledge/glossary/aphid.md) by live birth). - **Haplodiploidy**: the genetic system behind it. ## Related terms [Haplodiploidy](https://genetixbay.com/knowledge/glossary/haplodiploidy.md), [Parthenogenesis](https://genetixbay.com/knowledge/glossary/parthenogenesis.md), [Sex ratio](https://genetixbay.com/knowledge/glossary/sex-ratio.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Sources 1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 2. Grbic, M. et al., 2011. The genome of Tetranychus urticae reveals herbivorous pest adaptations. Nature 479:487-492. https://doi.org/10.1038/nature10640 --- # ATC > ATC (automatic temperature compensation) is a meter feature that corrects pH or EC readings for sample temperature, usually referencing EC to 25 °C. - Canonical: https://genetixbay.com/knowledge/glossary/atc.html - Also written: automatic temperature compensation, temperature compensation, temp compensation, temperature-compensated - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" ATC (automatic temperature compensation) uses a built-in temperature sensor to correct readings. It works differently for [EC](https://genetixbay.com/knowledge/glossary/ec.md) and [pH](https://genetixbay.com/knowledge/glossary/ph.md), and growers often misunderstand the pH part. ## In practice **EC:** conductivity rises roughly 2% per °C. An uncompensated reading of a 1.40 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) solution would read about 1.54 at 30 °C and 1.26 at 20 °C. With ATC, the meter converts readings to the 25 °C reference so numbers are comparable. This matters a lot for EC; without ATC, cold reservoirs look weak and warm ones look strong. **pH:** ATC corrects for how the electrode's response (its slope, about 59 mV per pH unit at 25 °C) changes with temperature. It does not correct for the real pH change of the solution itself with temperature, which is small for nutrient solutions. So a compensated [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) reports the true pH at the sample's current temperature. Best practice: let probe and sample reach the same temperature, and calibrate near the temperature you measure at. Large gaps (cold reservoir, warm buffer) still cause errors and slow readings. ## Units and formula EC₂₅ ≈ EC_T ÷ (1 + 0.02 × (T − 25)), T in °C. Some meters let you set the coefficient (1.9–2.1% per °C). ## Don't confuse with - **Calibration**: corrects the electrode against standards; ATC corrects for temperature. ## Related terms [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md), [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), [Two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md) ## Read more - [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) ## Sources 1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality --- # Autoflower > A day-neutral cannabis plant that starts flowering by age, usually a few weeks after germination, regardless of light schedule; the trait is mainly recessive. - Canonical: https://genetixbay.com/knowledge/glossary/autoflower.html - Also written: autoflowering, auto, autos, day-neutral, day neutral, autoflowering cannabis, autoflowering seeds - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An autoflower is a day-neutral cannabis plant: it switches to flowering at a set developmental age, typically 3-5 weeks from [germination](https://genetixbay.com/knowledge/glossary/germination.md), rather than in response to long nights. Seed to harvest is often about 9-12 weeks. The trait comes from northern, short-season populations (often labelled [ruderalis](https://genetixbay.com/knowledge/glossary/ruderalis.md)) and is controlled mainly by a [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) locus mapped as *Autoflower1* (Toth et al. 2022), so both parents must carry it for true-breeding autos. ## In practice Autos can run under [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) or 20/4 from seed to harvest, and growers stagger them for [continuous harvests](https://genetixbay.com/knowledge/glossary/perpetual-harvest.md). House positions: - **Any setback costs time**: an auto runs on a fixed countdown from germination and can't recover lost days. - **Transplanting is almost a no-no**: plant in the final container (founder observation on taproot reaction). - **Train, don't top**: topping never matches proper LST on an auto. - **"Good for beginners"** is true only because autos quickly show who has a green thumb, not because they forgive mistakes. Yield per square metre per year is very hard to beat with autos. [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) levels usually sit slightly under [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) sisters, though elite autos can match them. ## Don't confuse with - **Photoperiod**: flowers in response to long nights. - **Fast version**: a photoperiod hybrid bred for short flowering, not day-neutral. - **Ruderalis**: the source populations, not a synonym for every auto. ## Related terms [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [Ruderalis](https://genetixbay.com/knowledge/glossary/ruderalis.md), [Taproot](https://genetixbay.com/knowledge/glossary/taproot.md), [Short-day plant](https://genetixbay.com/knowledge/glossary/short-day-plant.md) ## Read more - [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - [Breeding autoflowers: getting the trait into a photoperiod line](https://genetixbay.com/knowledge/breeding/breeding-autoflowers.md) ## Sources 1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 2. Kurtz LE, Brand MH, Lubell-Brand JD. 2023. Gene dosage at the autoflowering locus effects flowering timing and plant height in triploid cannabis. Journal of the American Society for Horticultural Science 148(2):83-88. https://doi.org/10.21273/JASHS05293-23 --- # Auxin > A class of plant hormones, chiefly indole-3-acetic acid (IAA), that drives cell elongation, apical dominance, bending toward light and root formation. - Canonical: https://genetixbay.com/knowledge/glossary/auxin.html - Also written: auxins, IAA, indole-3-acetic acid, IBA, indole-3-butyric acid, NAA - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Auxins are plant hormones that regulate growth and shape. The main natural auxin is indole-3-acetic acid (IAA), made mostly in young leaves and [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) and moved down the stem by polar transport. Auxin promotes cell elongation, maintains [apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), causes phototropism and gravitropism, and triggers adventitious and lateral root formation. ## In practice Two everyday uses for growers: - **Training**: topping removes the main auxin source, so side buds wake up. Bending a stem changes auxin flow, which is part of why [LST](https://genetixbay.com/knowledge/glossary/lst.md) evens out a canopy. - **Cloning**: rooting products use synthetic or related auxins, mainly indole-3-butyric acid (IBA) and sometimes NAA, as gels, powders or dips. In cannabis, IBA treatment improved rooting of cuttings in controlled trials (Caplan et al. 2018). Auxin works in balance with [cytokinin](https://genetixbay.com/knowledge/glossary/cytokinin.md): high auxin relative to cytokinin favours roots; high cytokinin favours shoots. That ratio is the core of tissue-culture media. Rooting products are concentrates of plant-growth regulators. Follow label rates and wear gloves. ## Don't confuse with - **Cytokinin**: promotes shoot and bud growth, opposing apical dominance. - **Gibberellin**: drives [internode](https://genetixbay.com/knowledge/glossary/internode.md) elongation and [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). - **Fertiliser**: supplies nutrients; hormones are signals, not food. ## Related terms [Apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), [Cytokinin](https://genetixbay.com/knowledge/glossary/cytokinin.md), [Gibberellin](https://genetixbay.com/knowledge/glossary/gibberellin.md), [Apical meristem](https://genetixbay.com/knowledge/glossary/apical-meristem.md) ## Read more - [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. 2. Caplan D, Stemeroff J, Dixon M, Zheng Y. 2018. Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science 98(5):1126-1132. https://doi.org/10.1139/cjps-2018-0038 --- # Axillary bud > A dormant shoot bud in the angle (axil) between a leaf and the stem at each node, able to grow into a branch or a flower cluster. - Canonical: https://genetixbay.com/knowledge/glossary/axillary-bud.html - Also written: lateral bud, auxiliary bud, axil bud, side shoot bud - Glossary category: Plant biology - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An axillary bud is a small meristem in the axil, the upper angle where a leaf [petiole](https://genetixbay.com/knowledge/glossary/petiole.md) meets the stem. Every node has one (or a pair on opposite-leaved growth). Under [apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md) most stay small; released, each can grow into a full branch. In flower, axillary buds produce the clusters of [pistillate flowers](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) that make up [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md) along each branch. ## In practice When you top a plant, the two axillary buds just below the cut become the new main shoots. When you [lollipop](https://genetixbay.com/knowledge/glossary/lollipopping.md), you remove low axillary shoots that would only make small, airy buds in shade. When you take a clone, you want a node with healthy axillary buds above the cut. Many growers write "auxiliary bud". The botanical term is axillary, from axil. A strong axillary bud next to a weak petiole can be damaged by tearing leaves off rather than cutting them; that is one practical reason for "tuck, don't pluck". ## Don't confuse with - **Apical meristem**: the bud at the tip of a shoot, not in a leaf axil. - **Pre-flower**: the first flower that forms at a node, not the bud itself. - **Bud (flower)**: a mature cluster of flowers; slang reuse of the word. ## Related terms [Node](https://genetixbay.com/knowledge/glossary/node.md), [Apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), [Apical meristem](https://genetixbay.com/knowledge/glossary/apical-meristem.md), [Cola](https://genetixbay.com/knowledge/glossary/cola.md) ## Read more - [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md) - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Bacillus thuringiensis > A soil bacterium whose crystal proteins kill caterpillars after they eat treated leaves; subspecies kurstaki and aizawai are the strains used against budworms. - Canonical: https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.html - Also written: Bt, B.t., Btk, Bacillus thuringiensis kurstaki, Bt aizawai - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Bacillus thuringiensis* (Bt) is a soil bacterium that forms crystal proteins toxic to specific insect groups. Once eaten, the [crystals](https://genetixbay.com/knowledge/glossary/trichome.md) dissolve in the alkaline gut of the larva, bind to gut receptors and punch holes in the gut wall; the larva stops feeding within hours and dies over a few days. Subspecies *kurstaki* (Btk) and *aizawai* target caterpillars; subspecies *israelensis* (Bti) targets fly larvae. ## In practice Outdoor growers spray Btk or *aizawai* products against [corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md), loopers and other caterpillars. Timing is everything: it must be on the leaf or flower when young larvae feed, before they bore into [colas](https://genetixbay.com/knowledge/glossary/cola.md), and sunlight breaks it down within days, so repeat applications follow egg-laying. It has no contact action and does not harm bees, [predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md) or people at label rates. Whether and how late it may go on flowers depends on the product label and local rules; check what is registered for cannabis locally and respect the [pre-harvest interval](https://genetixbay.com/knowledge/glossary/pre-harvest-interval.md). ## Don't confuse with - **Bti**: the mosquito and [fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) strain, used as a soil drench. - **Bt crops**: plants engineered to make Bt proteins; no such cannabis exists commercially. - **Beauveria bassiana**: a fungus that infects on contact. ## Related terms [Bti](https://genetixbay.com/knowledge/glossary/bti.md), [Caterpillar](https://genetixbay.com/knowledge/glossary/caterpillar.md), [Corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Pre-harvest interval](https://genetixbay.com/knowledge/glossary/pre-harvest-interval.md) ## Read more - [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Sources 1. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 2. Utah State University Extension. Corn Earworm (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-corn-earworm --- # Backcross > A backcross is a cross of a hybrid back to one of its parents (or that parent's line), repeated to recover the parent's traits while keeping one introduced trait. - Canonical: https://genetixbay.com/knowledge/glossary/backcross.html - Also written: BX, BC, backcrossing, BX1, BX2, BX3, back cross, cubing, cubed - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A backcross (BX or BC) crosses an offspring back to one of its parents, called the recurrent parent. Each round raises the expected share of the recurrent parent's genome. Breeders use repeated backcrossing to move one trait from a donor into an [elite](https://genetixbay.com/knowledge/glossary/elite-cut.md) line while keeping the elite line's type. ## In practice Example: an elite female clone is crossed to a male carrying the [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) trait. A male from the offspring is crossed back to the same female (BX1), then a selected BX1 male back to her again (BX2), then BX3. Each time the breeder selects offspring that carry the wanted trait and otherwise look like the clone. "Cubing" is cannabis slang for three backcrosses to a female clone, from the idea of raising her share to the third power. It approaches the clone's [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) but never reproduces her exactly, and [linkage drag](https://genetixbay.com/knowledge/glossary/linkage.md) means some donor DNA around the selected trait comes along. ## Units and formula Expected recurrent-parent share after n backcrosses (starting from an [F1](https://genetixbay.com/knowledge/glossary/f1.md) at 50%): 1 - (1/2)^(n+1). BX1: 75%; BX2: 87.5%; BX3: 93.75%; BX4: about 96.9%. ## Don't confuse with - **Selfing**: [pollinating](https://genetixbay.com/knowledge/glossary/pollination.md) a plant with its own pollen. A backcross uses a different plant (the offspring) as the other parent. - **Outcross**: crossing to an unrelated plant. - **Clone**: a backcross line is never identical to the recurrent parent; only a cutting is. ## Related terms [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Introgression](https://genetixbay.com/knowledge/glossary/introgression.md), [P1](https://genetixbay.com/knowledge/glossary/p1.md), [Stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md) ## Read more - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 --- # Badder > Badder is a soft, cake-batter-textured concentrate formed by whipping an extract so its cannabinoids crystallise finely; it can be solvent-based or, as rosin badder, solventless. - Canonical: https://genetixbay.com/knowledge/glossary/badder.html - Also written: batter, cake batter, badder concentrate, whipped badder - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Badder (also "batter") is a concentrate texture: thick, opaque and smooth, like cake batter or frosting. It is produced by inducing fine crystallisation of the [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) acids through agitation and controlled conditions after extraction. The result holds more of its [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) in a creamy matrix than brittle forms do. Badder can come from [hydrocarbon extracts](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md) or from [rosin](https://genetixbay.com/knowledge/glossary/rosin.md), where it is often called rosin badder or whipped rosin. ## In practice On a menu, "badder" tells you about texture and, roughly, about processing style; it doesn't tell you potency, starting material or whether solvents were used. For that you need the product type (live or [cured](https://genetixbay.com/knowledge/glossary/curing.md), rosin or resin) and the [COA](https://genetixbay.com/knowledge/glossary/coa.md). Badder is generally wetter and looser than budder, though the terms overlap. GenetixBay defines the product only and gives no processing information. ## Don't confuse with - **Budder**: similar but typically stiffer and smoother. - **Sauce**: [crystals](https://genetixbay.com/knowledge/glossary/trichome.md) in a liquid terpene-rich fraction; separated rather than whipped. - **Shatter**: glassy, non-crystallised. ## Related terms [Wax](https://genetixbay.com/knowledge/glossary/wax.md), [Shatter](https://genetixbay.com/knowledge/glossary/shatter.md), [Sauce](https://genetixbay.com/knowledge/glossary/sauce.md), [Rosin](https://genetixbay.com/knowledge/glossary/rosin.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md) --- # Bag appeal > Bag appeal is how good flower looks in the bag or jar, frost, colour, density and trim, which sells cannabis but does not measure its quality. - Canonical: https://genetixbay.com/knowledge/glossary/bag-appeal.html - Also written: bag-appeal, jar appeal, eye appeal, looks - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Bag appeal is the visual impression of [cured](https://genetixbay.com/knowledge/glossary/curing.md) flower: [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) coverage ("frost"), colour, bud density and shape, and how neatly it is trimmed. It is the single biggest driver of retail price. ## In practice Breeders select for bag appeal because it photographs well and sells. A grower can raise it with a careful dry and cure, gentle handling and a good trim. It says little about aroma after grinding, smoke quality, [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) content, or how the flower was dried. ## Don't confuse with - **Quality**: aroma, flavour, smoke, cure, freshness and reported effects. A plain-looking jar can beat a beautiful one. - **Potency**: frost is suggestive but not a reliable predictor of [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md). ## Myth check "Frosty and purple means better." GenetixBay position: bag appeal is not quality. [Purple colour](https://genetixbay.com/knowledge/glossary/anthocyanin.md) comes from anthocyanins, which depend on genetics and cool temperatures and do not add potency or terpenes. The founder admits they are "a sucker for any red strain", which proves the point: looks are a preference, not a measurement. See [purple stems and leaves](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md). ## Related terms [Frosty](https://genetixbay.com/knowledge/glossary/frosty.md), [Purp](https://genetixbay.com/knowledge/glossary/purp.md), [Top shelf](https://genetixbay.com/knowledge/glossary/top-shelf.md), [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md), [Dank](https://genetixbay.com/knowledge/glossary/dank.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) - [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) --- # Bagseed > Bagseed is a seed found in purchased flower, of unknown parentage and often the product of accidental pollination, including by intersex plants. - Canonical: https://genetixbay.com/knowledge/glossary/bagseed.html - Also written: bag seed, bag seeds, bagseeds, mystery seed - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Bagseed is any seed found in a bag of purchased flower. Its mother is unknown in practice, its father is completely unknown, and in modern [sinsemilla](https://genetixbay.com/knowledge/glossary/sinsemilla.md) it very often comes from [self-pollination](https://genetixbay.com/knowledge/glossary/selfing.md) by a plant that threw [pollen sacs](https://genetixbay.com/knowledge/glossary/anther.md) or bananas late in flower. ## In practice Many growers' first plant is bagseed, and some turn out well. The risk is genetic: if the seed came from an [intersex plant](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), the offspring are more likely to carry the same tendency. Expect a mix of sexes, a wide spread of types and a higher-than-normal chance of intersex flowers. If you grow bagseed, treat it as a test: watch closely for pollen sacs from week 3 of flower onward, keep it away from any plants you care about, and do not breed from it unless you have grown out enough offspring to rule out [herm tendency](https://genetixbay.com/knowledge/glossary/herm-prone.md). ## Don't confuse with - **Regular seed**: deliberately made from a chosen male and female, with known parents. - **Feminised seed**: made deliberately by sex-reversing a selected female. Bagseed from a herm is accidental and untested. - **Landrace seed**: [open-pollinated seed](https://genetixbay.com/knowledge/glossary/open-pollinated.md) from a known population and region. ## Myth check "Seeds in good weed are normal." In well-grown sinsemilla they are not. Seeds mean pollen reached the flowers, either from a male or from an intersex plant. See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). ## Related terms [Nanners](https://genetixbay.com/knowledge/glossary/nanners.md), [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md), [Regular seed](https://genetixbay.com/knowledge/glossary/regular-seed.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md) ## Read more - [Regular, feminised, autoflower or clone: choosing your starting material](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md) - [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) --- # Banker plant > A non-crop plant kept in the grow to host harmless alternative prey or pollen, breeding beneficial insects continuously so they are ready when pests arrive. - Canonical: https://genetixbay.com/knowledge/glossary/banker-plant.html - Also written: banker plants, banker plant system, open rearing system - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A banker plant is a non-crop plant placed among or near the crop to support a breeding population of beneficial organisms. The classic system is cereal plants such as barley or wheat infested with bird cherry-oat [aphid](https://genetixbay.com/knowledge/glossary/aphid.md) (*Rhopalosiphum padi*), which feeds only on grasses and cannot attack the crop. [Parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md) such as *Aphidius colemani* breed on those aphids and then hunt crop aphids. Flowering plants that provide pollen support predators such as [Orius](https://genetixbay.com/knowledge/glossary/orius.md). ## In practice Banker plants make [biocontrol](https://genetixbay.com/knowledge/glossary/biological-control.md) self-sustaining rather than relying on repeated purchases. In cannabis they suit greenhouses and long-running mother rooms more than short sealed indoor runs. They need replacing every few weeks as the cereal ages, and they must be scouted like any crop so they do not become a source of pests. Choose host aphids that cannot use cannabis; the [rice root aphid](https://genetixbay.com/knowledge/glossary/root-aphid.md), for example, also uses grasses and cannabis roots, so not every grass aphid is safe. ## Don't confuse with - **Trap crop**: a plant that lures pests away from the crop. - **Companion planting**: a broader garden practice with weaker evidence. ## Related terms [Aphidius](https://genetixbay.com/knowledge/glossary/aphidius.md), [Orius](https://genetixbay.com/knowledge/glossary/orius.md), [Preventive release](https://genetixbay.com/knowledge/glossary/preventive-release.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. UConn IPM. Aphid Banker Plants. https://ipm-cahnr.media.uconn.edu/wp-content/uploads/sites/3216/2024/08/aphidbankerplants.pdf --- # Batch > A batch (or lot) is a defined quantity of product from the same plants, harvest and processing run that is sampled and tested as one unit and carries one ID. - Canonical: https://genetixbay.com/knowledge/glossary/batch.html - Also written: lot, batch number, lot number, harvest batch, production batch, batch ID - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A batch is a quantity of cannabis or cannabis product that is treated as uniform for testing and tracking. For flower it usually means one cultivar from one harvest, dried and [cured](https://genetixbay.com/knowledge/glossary/curing.md) together, up to a maximum size set by regulation. For extracts it means one production run. The batch ID ties the physical product to its [COA](https://genetixbay.com/knowledge/glossary/coa.md). ## In practice Check that the batch number on the package matches the COA. A COA for batch A says nothing about batch B, even of the same cultivar from the same producer. Regulators commonly cap batch size (for flower, often a few kilograms to tens of kilograms; check local rules) and set how many sample increments must be drawn. Mixing material from different harvests into one batch undermines the meaning of the test. For home growers, "batch" simply means the harvest you're describing, a useful habit when keeping records or sending samples. ## Don't confuse with - **Cultivar**: genetics; one cultivar [yields](https://genetixbay.com/knowledge/glossary/yield.md) many batches. - **Sample**: the portion taken from a batch for testing. - **Run**: a grower's word for a grow cycle, which may produce several batches. ## Related terms [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Homogenisation (sampling)](https://genetixbay.com/knowledge/glossary/homogenisation.md), [Microbial testing](https://genetixbay.com/knowledge/glossary/microbial-testing.md), [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md) --- # Bay Lines > Bay Lines are GenetixBay's community breeding programme: lines bred from member-nominated keepers and documented males, tested and released with full records. - Canonical: https://genetixbay.com/knowledge/glossary/bay-lines.html - Also written: Bay Line, GenetixBay lines, community lines, community breeding programme - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Bay Lines is the community breeding programme on GenetixBay. Members nominate keepers from their documented grows; selected keepers and [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md) males become parents, and the resulting lines are tester-grown, documented and released with complete [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) records. ## In practice A member's keeper, with a good journal, is nominated; if it is picked as a Bay Lines parent the member receives Wild Pearls and a permanent credit on the line record. Each line publishes its tester data, including [germination](https://genetixbay.com/knowledge/glossary/germination.md), [sex ratio](https://genetixbay.com/knowledge/glossary/sex-ratio.md) and [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md). A line must pass a 10-plant screening grow with zero [herms](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) to qualify, and loses its place if pooled community reports show a herm rate above 2% (see [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md)). Seed is handled only through licensed channels where the law requires it. The aim is the opposite of chucking: chosen parents, real numbers grown out, open records, and credit to the people who found the plants. ## Don't confuse with - **Seed Club**: the licensed partner programme through which some seed reaches members. - **Hype drops**: Bay Lines are released on evidence, not countdowns. ## Related terms [Keeper](https://genetixbay.com/knowledge/glossary/keeper.md), [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md), [Herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md), [Seed Club](https://genetixbay.com/knowledge/glossary/seed-club.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) ## Read more - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) --- # Bay Trials > Bay Trials are GenetixBay's member-run controlled grow experiments that test growing claims side by side and publish the results openly. - Canonical: https://genetixbay.com/knowledge/glossary/bay-trials.html - Also written: Bay Trial, GenetixBay trials, member trials, open trials - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Bay Trials are [open research](https://genetixbay.com/knowledge/glossary/open-research.md) on GenetixBay: members run controlled, side-by-side grows to test claims that the literature has not settled for indoor drug-type cannabis, and the results move those claims up or down the evidence ladder. ## In practice A trial defines its question, protocol and minimum enrolment in advance. A typical design uses matched clones, a split tent or paired rooms, one variable changed (tuck vs strip [defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md), [LED vs HPS](https://genetixbay.com/knowledge/glossary/led-vs-hps.md), hydro vs [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md)), [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) recorded on both sides, lab COAs, and blind taste panels where flavour is the question. Each trial card shows the question, the founder's hunch where there is one (labelled as a hunch), enrolment progress and, once signed off, a verdict of Busted, Confirmed or Inconclusive. Open questions include whether tucking beats stripping for [dry yield](https://genetixbay.com/knowledge/glossary/yield.md), whether defoliation raises [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) content, LED vs HPS, and whether a living-soil run beats a well-grown hydro run in a blind taste test. ## Don't confuse with - **Tester grows**: report how a line performs; they do not test a growing claim. - **Single grow journals**: useful evidence, but uncontrolled. ## Related terms [Open research](https://genetixbay.com/knowledge/glossary/open-research.md), [Mythbusters](https://genetixbay.com/knowledge/glossary/mythbusters.md), [Evidence ladder](https://genetixbay.com/knowledge/glossary/evidence-ladder.md), [Grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md), [Smoke report](https://genetixbay.com/knowledge/glossary/smoke-report.md) ## Read more - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) - [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) --- # Beans > Beans is slang for cannabis seeds; "popping beans" means germinating them. - Canonical: https://genetixbay.com/knowledge/glossary/beans.html - Also written: bean, seeds (slang), pop beans, popping beans - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Beans is common slang for [cannabis seeds](https://genetixbay.com/knowledge/glossary/achene.md). "Popping beans" means [germinating](https://genetixbay.com/knowledge/glossary/germination.md) them, and "bean count" is how many seeds are in a pack. ## In practice "I popped 12 beans of that line and got 11 up" means 12 seeds were germinated and 11 emerged, a germination rate of about 92%. Growers swap and trade beans, store them cool and dry, and rate [seed lots](https://genetixbay.com/knowledge/glossary/seed-run.md) by germination, vigour and uniformity. A healthy seed is fully formed, hard, and usually grey to brown with a darker pattern; pale, soft or crushed seeds often fail. Storage matters more than age alone: seed kept dry and cold, sealed against moisture, can stay viable for many years, while seed kept warm and humid can fail within a couple of years. See [seed viability and storage](https://genetixbay.com/knowledge/germination/seed-viability-storage.md). ## Don't confuse with - **Achene**: the botanical name for what growers call a seed (seed plus fruit wall). - **Bagseed**: one source of beans, but a specific, untrusted one. - **Clones**: plants started from cuttings, not seed. ## Related terms [Regs](https://genetixbay.com/knowledge/glossary/regs.md), [Fems](https://genetixbay.com/knowledge/glossary/fems.md), [Seed bank](https://genetixbay.com/knowledge/glossary/seed-bank.md), [Germination](https://genetixbay.com/knowledge/glossary/germination.md) ## Read more - [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md) --- # Beauveria bassiana > An insect-killing fungus whose spores germinate on contact, penetrate the cuticle and kill soft-bodied pests such as whiteflies, thrips, aphids and root aphids. - Canonical: https://genetixbay.com/knowledge/glossary/beauveria-bassiana.html - Also written: Beauveria, B. bassiana, white muscardine fungus, entomopathogenic fungus - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Beauveria bassiana* is an entomopathogenic fungus: it infects and kills insects. Spores that land on an insect [germinate](https://genetixbay.com/knowledge/glossary/germination.md), grow through the cuticle and multiply inside the body. Dead insects turn stiff and become covered in white fungal growth, which is why the disease is called white muscardine. It is found naturally in soils worldwide. ## In practice Growers apply spore formulations as [foliar sprays](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) against [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md), thrips and [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), or as drenches against [root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md) and other soil pests. Spores need direct contact with the pest and benefit from high humidity for the first hours after application; very dry air and some fungicides reduce [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md). It works over days, not hours, so it is used early and repeated. Because it adds live fungal spores, growers generally keep it off flowering buds, where it could raise microbial counts on lab tests. Check what is registered for cannabis locally and what the label allows by growth stage. ## Don't confuse with - **Botrytis**: a plant pathogen that rots buds; *Beauveria* attacks insects, not plants. - **Bacillus thuringiensis**: a bacterium that must be eaten. - **Metarhizium**: a related insect-killing fungus with green spores. ## Related terms [Whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md), [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Root aphid](https://genetixbay.com/knowledge/glossary/root-aphid.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md) ## Read more - [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) - [Root aphids (rice root aphid) on indoor cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/root-aphids.md) ## Sources 1. UConn IPM. Biological Control of Whiteflies. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-whiteflies 2. Cranshaw, W. and Wainwright-Evans, S., 2020. Cannabis sativa as a host of rice root aphid (Hemiptera: Aphididae) in North America. Journal of Integrated Pest Management 11(1):15. --- # Beet curly top virus > BCTV, a leafhopper-spread curtovirus that stunts outdoor hemp and cannabis, curling and yellowing new leaves; there is no cure once a plant is infected. - Canonical: https://genetixbay.com/knowledge/glossary/beet-curly-top-virus.html - Also written: BCTV, curly top, curly top virus, Curtovirus - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Beet curly top virus (BCTV) is a single-stranded DNA [virus](https://genetixbay.com/knowledge/glossary/plant-virus.md) in the genus *Curtovirus* (family Geminiviridae) with a very wide host range, including sugar beet, tomato, pepper, beans and [hemp](https://genetixbay.com/knowledge/glossary/hemp.md). It is transmitted almost entirely by the [beet leafhopper](https://genetixbay.com/knowledge/glossary/leafhopper.md) (*Circulifer tenellus*). It is one of the most damaging viral diseases of outdoor hemp in the arid western United States. ## In practice Infected plants show cupped, curled and mottled new leaves, yellowing that starts at the tips, stunting and a general "witches' broom" look, sometimes with twisted stems. Early infection can stop a plant flowering properly; late infection does less harm. Indoor grows rarely see it because the vector is an outdoor insect. Management is avoiding hot spots near weedy rangeland, using row covers on young plants, controlling host weeds and pulling infected plants. Testing by PCR confirms it, since symptoms mimic herbicide drift and nutrient problems. ## Don't confuse with - **Hop latent viroid**: an RNA [viroid](https://genetixbay.com/knowledge/glossary/viroid.md) spread by tools and clones, not insects. - **Herbicide drift**: distorted growth on many species at once along a field edge. - **Broad mite damage**: twisted tips, but [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) are visible under 40x. ## Related terms [Leafhopper](https://genetixbay.com/knowledge/glossary/leafhopper.md), [Plant virus](https://genetixbay.com/knowledge/glossary/plant-virus.md), [Viroid](https://genetixbay.com/knowledge/glossary/viroid.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md) ## Read more - [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ## Sources 1. Colorado State University (Mountain Scholar). Beet curly top virus - beet leafhopper dynamics in hemp in Colorado. https://mountainscholar.org/items/690318d0-f830-4090-b0a5-c1e18581d7b5/full 2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Curly Top. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-curly-top --- # Beneficial element > A beneficial element is one that improves growth or stress tolerance in some plants without being strictly essential, such as silicon, sodium, cobalt and selenium. - Canonical: https://genetixbay.com/knowledge/glossary/beneficial-element.html - Also written: beneficial elements, beneficial nutrient, quasi-essential element - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A beneficial element is a mineral element that is not required for every plant to complete its life cycle, but which stimulates growth or improves resilience in some species or conditions. The usual examples are [silicon](https://genetixbay.com/knowledge/glossary/silicon.md), [sodium](https://genetixbay.com/knowledge/glossary/sodium.md), [cobalt](https://genetixbay.com/knowledge/glossary/cobalt.md), selenium and aluminium. An element is "essential" only if the plant cannot complete its life cycle without it and its role cannot be replaced by another. ## In practice For cannabis, silicon is the only beneficial element growers commonly add, mainly as [potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md) for stiffer stems and some stress tolerance. Sodium is a functional nutrient for certain salt-loving and C4 plants but is a contaminant for cannabis. Cobalt matters to nitrogen-fixing legumes. Epstein argued that silicon deserved more attention in plant biology because it is so abundant in tissue despite not being essential. ## Don't confuse with - **Micronutrient**: an essential element needed in trace amounts. - **Biostimulant**: a product category, often organic, not an element. ## Related terms [Silicon](https://genetixbay.com/knowledge/glossary/silicon.md), [Sodium](https://genetixbay.com/knowledge/glossary/sodium.md), [Cobalt](https://genetixbay.com/knowledge/glossary/cobalt.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) ## Read more - [Silicon (Si) for cannabis: beneficial, not essential, and how to dose it](https://genetixbay.com/knowledge/nutrients/silicon.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Epstein E. 1994. The anomaly of silicon in plant biology. PNAS 91(1):11-17. https://doi.org/10.1073/pnas.91.1.11 --- # Beneficial-microbe reservoir > A beneficial-microbe reservoir deliberately inoculates hydroponic solution with helpful bacteria and fungi so they occupy the root zone before pathogens can; GenetixBay prefers this approach. - Canonical: https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.html - Also written: bio reservoir, biological reservoir, beneficial reservoir, microbe-dosed reservoir, living reservoir, bio-buckets - Glossary category: Systems and media · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A beneficial-microbe reservoir is a hydroponic strategy in which the solution is regularly dosed with live, beneficial organisms, typically *Bacillus* species, sometimes *Trichoderma* or mixed consortia, and is kept free of sanitisers that would kill them. The [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md) colonise roots and surfaces, compete with pathogens such as *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)* for space and nutrients, and can form a protective biofilm on healthy white roots. ## In practice Dose according to the product, usually weekly or with every reservoir change, and avoid chlorine, [peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) and other oxidisers that wipe them out. Keep the solution cool (about 18-21 °C, 64-70 °F) and well aerated; beneficials do not replace good temperature and oxygen management. Roots in a healthy bio reservoir are often tan-tinged or slightly fuzzy-white; slime and a sour smell indicate trouble. ## Myth check House position: a beneficial-microbe reservoir is preferred. Bacteria will show up in any reservoir regardless, so you may as well have the good ones. A [sterile reservoir](https://genetixbay.com/knowledge/glossary/sterile-reservoir.md) is valid too, but you must commit to it fully; it's a personal choice. Evidence: Supported for biological control of root pathogens in hydroponics; product results vary. See [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md). ## Don't confuse with - **Sterile reservoir**: the opposite strategy. - **Compost tea**: a brewed soil drench, not a hydro inoculant. ## Related terms [Sterile reservoir](https://genetixbay.com/knowledge/glossary/sterile-reservoir.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [Compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) ## Read more - [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) - [Recirculating deep water culture (RDWC)](https://genetixbay.com/knowledge/systems/rdwc.md) ## Sources 1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 2. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 --- # Benefit-sharing > Benefit-sharing is returning a fair share of the benefits from using genetic resources or traditional knowledge, money, credit, access or support, to the people who provided them. - Canonical: https://genetixbay.com/knowledge/glossary/benefit-sharing.html - Also written: benefit sharing, access and benefit-sharing, ABS, fair and equitable benefit-sharing - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Benefit-sharing is the principle that when [genetic resources](https://genetixbay.com/knowledge/glossary/germplasm.md) or associated traditional knowledge are used, for research, breeding or commercial products, the providers receive a fair and equitable share of the resulting benefits. Under the [Nagoya Protocol](https://genetixbay.com/knowledge/glossary/nagoya-protocol.md) it is agreed on mutually agreed terms before access. ## In practice Benefits can be monetary (royalties, licence fees, a share of sales) or non-monetary (credit and naming, sharing research results, training, returning improved seed, supporting local seed conservation). For cannabis [landraces](https://genetixbay.com/knowledge/glossary/landrace.md), even the simplest step, naming the region and community on every record and pack instead of relabelling the material, is rarely done. GenetixBay's position: landrace growers built the foundation of nearly every modern line and deserve far more credit and compensation. Recording source communities on [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) records is one practical step. See [landrace hunting and biopiracy](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md). Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Charity**: benefit-sharing is an obligation agreed in advance, not a donation. ## Related terms [Nagoya Protocol](https://genetixbay.com/knowledge/glossary/nagoya-protocol.md), [Prior informed consent](https://genetixbay.com/knowledge/glossary/prior-informed-consent.md), [Biopiracy](https://genetixbay.com/knowledge/glossary/biopiracy.md), [Landrace hunter](https://genetixbay.com/knowledge/glossary/landrace-hunter.md) ## Read more - [Landrace hunting or biopiracy? Benefit-sharing, consent and cannabis](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md) ## Sources 1. Secretariat of the Convention on Biological Diversity. 2011. Nagoya Protocol on Access to Genetic Resources and the Fair and Equitable Sharing of Benefits Arising from their Utilization. https://www.cbd.int/abs/ --- # Beta-caryophyllene > Beta-caryophyllene is a spicy, peppery sesquiterpene common in cannabis, notable as a dietary terpene that also binds the CB2 receptor in laboratory studies. - Canonical: https://genetixbay.com/knowledge/glossary/beta-caryophyllene.html - Also written: β-caryophyllene, caryophyllene, BCP, trans-caryophyllene, carophyllene - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Beta-caryophyllene (BCP) is a bicyclic [sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) found in black pepper, cloves, hops and many cannabis cultivars. It smells spicy, woody and peppery. It is one of the most common [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) in commercial flower and usually travels with [alpha-humulene](https://genetixbay.com/knowledge/glossary/humulene.md), which is made by the same family of enzymes. ## In practice Readings of 0.2-0.8% w/w are common in flower. As a sesquiterpene it is less volatile than the [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md), so its share of the total often rises in stored material. In air it slowly oxidises to [caryophyllene oxide](https://genetixbay.com/knowledge/glossary/caryophyllene-oxide.md). Lab studies have shown it binds CB2 receptors, which made it famous. That's a pharmacology finding, not a promise of any effect from smoking a flower, and GenetixBay makes no health claims. ## Don't confuse with - **Caryophyllene oxide**: the oxidised derivative, less aromatic. - **Humulene**: its isomeric partner, woodier and earthier. - **Alpha-caryophyllene**: an older name for humulene, a source of confusion. ## Related terms [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Humulene](https://genetixbay.com/knowledge/glossary/humulene.md), [Caryophyllene oxide](https://genetixbay.com/knowledge/glossary/caryophyllene-oxide.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. 2. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 3. Russo EB. 2011. Taming THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects. British Journal of Pharmacology 163(7):1344-1364. https://doi.org/10.1111/j.1476-5381.2011.01238.x --- # Beta-pinene > Beta-pinene is a bicyclic monoterpene and isomer of alpha-pinene with a green, woody, herbal aroma, common in cannabis at low levels. - Canonical: https://genetixbay.com/knowledge/glossary/beta-pinene.html - Also written: β-pinene, b-pinene, beta pinene, nopinene - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Beta-pinene is a bicyclic [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md) with the same formula as [alpha-pinene](https://genetixbay.com/knowledge/glossary/alpha-pinene.md) but an exocyclic double bond. It smells woody and green, more like fresh-cut herbs, rosemary or dill than like pine needles. It is found in hops, rosemary, parsley, basil and many cannabis cultivars, where it usually sits below alpha-pinene. ## In practice Lab [terpene panels](https://genetixbay.com/knowledge/glossary/terpene-test.md) often report it separately at roughly 0.02-0.2% w/w in flower. Because both pinenes come from related synthase enzymes, they tend to rise and fall together across cultivars, and a "pine" [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) usually shows both. As a monoterpene it's volatile and sensitive to drying conditions. ## Don't confuse with - **Alpha-pinene**: the more abundant isomer, with a sharper pine smell. - **Camphene**: another bicyclic monoterpene with a camphor-pine smell, often listed nearby on panels. - **Pinene (unspecified)**: some labels sum both isomers; check the method. ## Related terms [Alpha-pinene](https://genetixbay.com/knowledge/glossary/alpha-pinene.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Biofilm > A slimy community of microbes stuck to surfaces in a matrix they secrete; in hydro, it coats lines, reservoirs and roots and can shelter pathogens. - Canonical: https://genetixbay.com/knowledge/glossary/biofilm.html - Also written: root slime, slime, brown slime, reservoir slime, slimy roots - Glossary category: Pests and diseases · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A biofilm is a community of bacteria, fungi or algae that attach to a surface and wrap themselves in a sticky matrix of their own polymers. In irrigation and hydroponic systems biofilms coat tubing, emitters, [chillers](https://genetixbay.com/knowledge/glossary/chiller.md), reservoir walls and roots. They are more resistant to disinfectants than free-floating microbes, and can protect pathogens such as *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)*. ## In practice Growers meet biofilm as "root slime": brown or tan gel on roots in [deep water culture](https://genetixbay.com/knowledge/glossary/dwc.md) and [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md), often with a sour smell, or as clogged [drippers](https://genetixbay.com/knowledge/glossary/drip-irrigation.md) and slick lines. Not every biofilm is harmful; beneficial bacteria also form films on healthy roots. Trouble begins when warm, low-oxygen water lets harmful organisms dominate. [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) is light-tight reservoirs, cool well-aerated solution, regular cleaning of lines between runs, and a consistent strategy: either a deliberate [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) or a fully committed sterile one. GenetixBay prefers the beneficial route, since bacteria arrive regardless. ## Don't confuse with - **Pythium root rot**: a specific pathogen; slime is often a symptom of it, not the same thing. - **Algae**: green growth where light reaches the water. - **Additive staining**: brown colour without slime. ## Related terms [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Shore fly](https://genetixbay.com/knowledge/glossary/shore-fly.md) ## Read more - [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) - [Recirculating deep water culture (RDWC)](https://genetixbay.com/knowledge/systems/rdwc.md) ## Sources 1. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic production (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 2. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 --- # Biological control > Using living natural enemies, such as predators, parasitoids, nematodes and microbes, to suppress pests and diseases instead of, or before, chemical sprays. - Canonical: https://genetixbay.com/knowledge/glossary/biological-control.html - Also written: biocontrol, biological pest control, beneficial insects, beneficials, natural enemies, bugs on bugs - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Biological control is the use of living organisms to reduce pest or disease populations. In cannabis it includes predators ([predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md), Orius, lacewings, ladybirds), parasitoids (wasps such as *Aphidius*), [entomopathogenic nematodes](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md) (*Steinernema feltiae*), insect-killing microbes (*[Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md)*, *[Beauveria bassiana](https://genetixbay.com/knowledge/glossary/beauveria-bassiana.md)*) and antagonistic microbes in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). It is a core pillar of [IPM](https://genetixbay.com/knowledge/glossary/ipm.md), especially because so few chemical options are permitted on cannabis. ## In practice Biocontrol works best preventively: release in veg while pests are scarce, match each organism to the pest and the room's temperature and humidity, and keep incompatible sprays away. It is slow compared with a knock-down spray and needs scouting to check establishment. Indoor rooms suit it because the agents cannot fly away easily. Microbial products are pesticides in many jurisdictions and must be registered; check what is registered for cannabis locally. Order from suppliers who guarantee live counts and ship quickly; dead beneficials fix nothing. ## Don't confuse with - **Cultural control**: changing how the crop is grown. - **Biostimulants**: products aimed at plant growth, not pest suppression. - **Organic pesticides**: plant- or mineral-derived chemicals, not living organisms. ## Related terms [Predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md), [Aphidius](https://genetixbay.com/knowledge/glossary/aphidius.md), [Steinernema feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md), [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md), [Preventive release](https://genetixbay.com/knowledge/glossary/preventive-release.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Sources 1. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf 2. UConn IPM. Biological Control of Western Flower Thrips. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-western-flower-thrips/ 3. UC IPM. Natural Enemies Gallery: Phytoseiulus predatory mites. https://ipm.ucanr.edu/natural-enemies/phytoseiulus-predatory-mites/ --- # Biopiracy > Biopiracy is taking genetic resources or traditional knowledge from a country or community without consent or benefit-sharing, especially to patent or profit from them. - Canonical: https://genetixbay.com/knowledge/glossary/biopiracy.html - Also written: bio-piracy, biopirates, genetic resource misappropriation, biological piracy - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Biopiracy is the appropriation of [genetic resources](https://genetixbay.com/knowledge/glossary/germplasm.md) or traditional knowledge without the providers' [prior informed consent](https://genetixbay.com/knowledge/glossary/prior-informed-consent.md) or fair [benefit-sharing](https://genetixbay.com/knowledge/glossary/benefit-sharing.md), often followed by patenting or commercial use that excludes the people who developed or kept the resource. ## In practice The term is used both legally, where a country's access rules or the [Nagoya Protocol](https://genetixbay.com/knowledge/glossary/nagoya-protocol.md) were breached, and ethically, for practices that are technically legal but unfair. In cannabis, critics point to [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) seed collected without permission, renamed and sold with no credit to its origin, and to patents built on traits that traditional growers had selected for generations. GenetixBay's view is firm: responsible [landrace hunting](https://genetixbay.com/knowledge/glossary/landrace-hunter.md) and biopiracy are different things. Consent, documentation, credit and compensation make the difference. See [landrace hunting and biopiracy](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md). Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Bioprospecting**: searching for useful genetic resources; it becomes biopiracy when consent and benefit-sharing are missing. - **Landrace hunting**: can be done responsibly. ## Related terms [Benefit-sharing](https://genetixbay.com/knowledge/glossary/benefit-sharing.md), [Prior informed consent](https://genetixbay.com/knowledge/glossary/prior-informed-consent.md), [Nagoya Protocol](https://genetixbay.com/knowledge/glossary/nagoya-protocol.md), [Landrace hunter](https://genetixbay.com/knowledge/glossary/landrace-hunter.md), [Utility patent](https://genetixbay.com/knowledge/glossary/utility-patent.md) ## Read more - [Landrace hunting or biopiracy? Benefit-sharing, consent and cannabis](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md) ## Sources 1. Secretariat of the Convention on Biological Diversity. 2011. Nagoya Protocol on Access to Genetic Resources and the Fair and Equitable Sharing of Benefits Arising from their Utilization. https://www.cbd.int/abs/ --- # Biostimulant > A biostimulant is a product claimed to improve plant growth, uptake or stress tolerance by means other than supplying nutrients, such as seaweed extract, humics, amino acids or microbes. - Canonical: https://genetixbay.com/knowledge/glossary/biostimulant.html - Also written: biostimulants, bio-stimulant, plant biostimulant, growth enhancer - Glossary category: Nutrients · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A biostimulant is a substance or microorganism applied to plants or the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) to improve nutrient uptake, efficiency, stress tolerance or quality, independently of its own nutrient content. Common categories are humic and [fulvic](https://genetixbay.com/knowledge/glossary/fulvic-acid.md) substances, seaweed and plant extracts, protein hydrolysates and amino acids, chitosan, and beneficial bacteria and fungi. Regulatory definitions differ by jurisdiction. ## In practice Some categories have reasonable evidence in some crops, such as [mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md) in low-phosphorus soils and certain seaweed extracts under stress. In cannabis, controlled data are sparse, and effects found so far are small or inconsistent (Evidence: Contested). Results depend heavily on product, dose, medium and cultivar. Growers who want to know should run a side-by-side with an untreated control of the same cultivar. ## Don't confuse with - **Fertiliser**: supplies nutrients by definition. - **Plant growth regulator**: hormone-like substances that directly alter growth, regulated differently. ## Myth check Label claims for biostimulants often run ahead of the evidence. See [buyer beware: label claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Humic acid](https://genetixbay.com/knowledge/glossary/humic-acid.md), [Fulvic acid](https://genetixbay.com/knowledge/glossary/fulvic-acid.md), [Amino acid chelate](https://genetixbay.com/knowledge/glossary/amino-acid-chelate.md), [Molasses](https://genetixbay.com/knowledge/glossary/molasses.md), [Organic fertiliser](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) - [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) ## Sources 1. Bernstein N, Gorelick J, Zerahia R, Koch S. 2019. Impact of N, P, K, and humic acid supplementation on the chemical profile of medical cannabis (Cannabis sativa L). Frontiers in Plant Science 10:736. https://doi.org/10.3389/fpls.2019.00736 --- # Bisabolol > Bisabolol (alpha-bisabolol) is a mild, floral, chamomile-like sesquiterpene alcohol found as a minor terpene in some cannabis cultivars. - Canonical: https://genetixbay.com/knowledge/glossary/bisabolol.html - Also written: alpha-bisabolol, α-bisabolol, levomenol, bisabolol oxide - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Alpha-bisabolol, also called levomenol, is a monocyclic [sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) alcohol. It is the main aroma compound of German chamomile and a common ingredient in cosmetics because it is gentle on skin. In cannabis it is a minor [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) with a soft, sweet, floral smell, more noticeable in a few cultivar families than in most. ## In practice Readings from [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md) to roughly 0.1-0.2% w/w are typical It isn't on every lab's [terpene panel](https://genetixbay.com/knowledge/glossary/terpene-test.md), so its absence on a [COA](https://genetixbay.com/knowledge/glossary/coa.md) may simply mean it wasn't tested. As a heavier sesquiterpenoid, it survives drying and storage better than the [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md). GenetixBay makes no claims about its effects in cannabis. ## Don't confuse with - **Bisabolene**: the related hydrocarbon, spicier and less floral. - **Linalool**: a monoterpene alcohol with a lavender note. - **Chamomile extract**: a mix of many compounds, not bisabolol alone. ## Related terms [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), [Linalool](https://genetixbay.com/knowledge/glossary/linalool.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Nerolidol](https://genetixbay.com/knowledge/glossary/nerolidol.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Bloom booster > A bloom booster is a high-phosphorus, high-potassium additive sold for flowering; cannabis trials show a P plateau, so past moderate levels it adds cost and runoff, not yield. - Canonical: https://genetixbay.com/knowledge/glossary/bloom-booster.html - Also written: bloom boosters, PK booster, PK boost, flower booster, bud booster, high-P booster - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A bloom booster is a supplement, usually high in phosphorus and potassium and often based on [monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md), sold to be added to a base feed during flowering. Labels such as 0-50-30 or "PK 13-14" are typical. Some products also contain sugars, amino acids or plant extracts. ## In practice A complete base feed already supplies enough phosphorus for flowering cannabis. Independent trials by Shiponi and Bernstein, Westmoreland and Bugbee, and Hershkowitz, Westmoreland and Bugbee found yield and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) plateau at moderate root-zone P, roughly 25-60 mg/L (ppm). Above that, extra P mostly leaves in the [runoff](https://genetixbay.com/knowledge/glossary/runoff.md), and can tie up [zinc](https://genetixbay.com/knowledge/glossary/zinc.md), iron and [copper](https://genetixbay.com/knowledge/glossary/copper.md). Excess K from the same bottle can suppress calcium and magnesium. ## Don't confuse with - **Bloom base**: a complete flowering feed, not an add-on. - **Plant growth regulators**: some historic "boosters" contained them; a separate concern. ## Myth check "More phosphorus in flower means bigger buds" is not supported: there is a plateau (Evidence: Established; GenetixBay house position agrees with the trials). See [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md), [N-P-K ratio](https://genetixbay.com/knowledge/glossary/npk-ratio.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), [Feed chart](https://genetixbay.com/knowledge/glossary/feed-chart.md) ## Read more - ["Bloom boosters" for cannabis: what's real and what's marketing](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) - [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) ## Sources 1. Westmoreland FM, Bugbee B. 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 2. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 3. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323 --- # Blue light > Blue light is the 400–500 nm band; it keeps plants compact with shorter internodes and thicker leaves, but a high blue fraction slightly lowers cannabis yield. - Canonical: https://genetixbay.com/knowledge/glossary/blue-light.html - Also written: blue photons, blue spectrum, 400-500 nm, blue fraction, blue LEDs - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Blue light covers roughly 400–500 nm. Plants detect it with cryptochromes and phototropins, which control stomatal opening, phototropism (bending towards light) and stem elongation. More blue generally means shorter [internodes](https://genetixbay.com/knowledge/glossary/internode.md), smaller and thicker leaves and more compact plants. Blue photons drive [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) a little less efficiently than red ones per photon, and blue diodes are typically less efficient to produce. ## In practice Westmoreland, Kusuma and Bugbee (2021) grew cannabis under fixtures with blue fractions from about 4% to 20% of photons. Lower blue gave slightly higher yield and slightly taller plants, while [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) concentration barely changed. They concluded fixture [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) matters more than the blue fraction. *Established*. Use more blue (around 15–20% of photons) when height is your problem, for example in a short tent or with stretchy cultivars, and in veg if you want tight plants. Most white [LEDs](https://genetixbay.com/knowledge/glossary/led.md) already give 10–20% blue, which is fine for the whole run. ## Units and formula Blue fraction (%) = photons 400–500 nm ÷ total [PAR](https://genetixbay.com/knowledge/glossary/par.md) photons × 100. A spectroradiometer or the fixture's spectral datasheet gives this. ## Don't confuse with - **Colour temperature**: "cool" 5,000–6,500 K white has more blue than "warm" 3,000 K white, but kelvin is not a blue percentage. - **UV-A**: 315–400 nm, sensed partly by the same receptors. ## Myth check "Veg needs a blue lamp and flower needs a red lamp" is outdated HPS-era advice. A single broad white spectrum works for both. *Supported*. ## Related terms [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md), [UV-A](https://genetixbay.com/knowledge/glossary/uv-a.md), [Red:far-red ratio](https://genetixbay.com/knowledge/glossary/red-far-red-ratio.md), [Photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988 --- # Boric acid > Boric acid (H3BO3) is the usual boron source in micronutrient mixes, about 17.5% boron; plants absorb boron in this same uncharged form. - Canonical: https://genetixbay.com/knowledge/glossary/boric-acid.html - Also written: H3BO3, boracic acid, orthoboric acid - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Boric acid is a weak acid of [boron](https://genetixbay.com/knowledge/glossary/boron.md), about 17.5% B. In normal nutrient solutions most boron exists as uncharged boric acid, which is the main form roots absorb. It dissolves slowly in cold water; warm water helps when making stock. ## In practice Boron has a narrow window between enough and too much, so boric acid is dosed from a concentrated [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) stock, not by the pinch. Final feeds usually aim for about 0.2-0.5 mg/L (ppm) B. Check the water report first: some tap and [well waters](https://genetixbay.com/knowledge/glossary/tap-water.md) already supply a meaningful share. Borax ([sodium](https://genetixbay.com/knowledge/glossary/sodium.md) borate, about 11% B) and solubor-type sodium borates are alternatives but add sodium. ## Units and formula 1 mg/L of boric acid gives about 0.175 mg/L (ppm) B. To reach 0.3 ppm B, add about 1.7 mg/L. ## Don't confuse with - **Borax**: sodium tetraborate, a different boron salt with sodium. - **Boric acid as an insecticide**: same chemical, different purpose and dose; never dose a feed from pest-bait products. ## Related terms [Boron](https://genetixbay.com/knowledge/glossary/boron.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) ## Read more - [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Boron > Boron (B) is a micronutrient needed for cell-wall structure and growing tips; the gap between deficient and toxic levels is narrow. - Canonical: https://genetixbay.com/knowledge/glossary/boron.html - Also written: B, borate, boron deficiency, boron toxicity - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Boron is a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) taken up mainly as uncharged [boric acid](https://genetixbay.com/knowledge/glossary/boric-acid.md). It cross-links pectins in cell walls and is needed wherever cells are dividing and expanding: [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md), root tips and developing flowers. In cannabis it is largely immobile. ## In practice [Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) kills or deforms growing points: brittle, thickened or hollow stems, distorted new leaves and dying tips. It can look like [calcium deficiency](https://genetixbay.com/knowledge/glossary/calcium.md). Toxicity shows as yellowing and burning of older leaf margins. The safe window is narrow, so hydro feeds use small amounts, usually about 0.2-0.5 mg/L (ppm) B, typically from boric acid or a borate. Some tap and [well waters](https://genetixbay.com/knowledge/glossary/tap-water.md) carry enough boron to matter; check the water report. ## Don't confuse with - **Calcium deficiency**: similar new-growth symptoms; check [pH](https://genetixbay.com/knowledge/glossary/ph.md), humidity and the feed for both. - **Borax or boric acid as insecticide**: a different use at very different concentrations. - **Potassium deficiency**: margin burn on older leaves but with a different pattern and history. ## Myth check "A pinch of borax" is a risky home fix. With a narrow margin, measure grams per litre, not pinches. See [boron](https://genetixbay.com/knowledge/nutrients/boron.md). ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), [Boric acid](https://genetixbay.com/knowledge/glossary/boric-acid.md), [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) ## Read more - [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Botrytis > Botrytis cinerea, the fungus behind bud rot or grey mould, which rots dense colas from the inside in cool, humid conditions late in flower. - Canonical: https://genetixbay.com/knowledge/glossary/botrytis.html - Also written: bud rot, grey mould, gray mold, grey mold, Botrytis cinerea, botrytis bud rot, BBR - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Botrytis cinerea* is a fungus that causes grey mould, called bud rot on cannabis. It attacks dense flowers from the inside, usually starting near the stem of a [cola](https://genetixbay.com/knowledge/glossary/cola.md) where moisture is trapped. Infected tissue turns brown and mushy; [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) wilt and yellow; grey, fuzzy spores appear as it progresses. It also causes stem cankers and damping-off. ## In practice The classic sign is a single dried, discoloured leaf sticking out of an otherwise healthy cola. Pulling it reveals brown rot inside. Botrytis loves cool nights, high humidity, dew, poor airflow and wounds such as caterpillar damage. Indoors, controlling humidity and night-time [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) late in flower is the main [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md); outdoors, open-structured cultivars and early harvest before autumn rain help. Infected buds should be cut out with a margin, bagged in the room and removed; do not shake spores onto the rest of the crop. Mouldy buds should never be consumed. ## Don't confuse with - **Powdery mildew**: white surface powder on leaves first, not internal rot. - **Corn earworm damage**: holes and [frass](https://genetixbay.com/knowledge/glossary/frass.md), often with botrytis following. - **Natural senescence**: yellowing fan leaves late in flower, with healthy bud tissue. ## Related terms [Powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), [Corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [White mould](https://genetixbay.com/knowledge/glossary/white-mould.md), [Mold](https://genetixbay.com/knowledge/glossary/mold.md) ## Read more - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Sources 1. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker 2. Utah State University Extension. Hemp bud rot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot 3. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full --- # Bottom watering > Bottom watering lets a pot absorb water or solution from a tray beneath it, so the medium wets from the base upward by capillary action. - Canonical: https://genetixbay.com/knowledge/glossary/bottom-watering.html - Also written: bottom-watering, bottom feeding, sub-irrigation, subirrigation, watering from below, tray watering - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Bottom watering (sub-irrigation) means standing a container in a shallow tray of water or nutrient solution and letting it soak up through the [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) holes. Water moves upward by capillarity until the medium is moist, and the excess is then removed. [Ebb-and-flow](https://genetixbay.com/knowledge/glossary/ebb-and-flow.md) tables automate the same process. ## In practice It wets dry [peat](https://genetixbay.com/knowledge/glossary/peat.md) and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) that repel water from above, keeps the surface drier (which discourages [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md)), and avoids splashing. Leave the pot in the tray for about 15-30 minutes, then empty what remains; leaving a pot standing in water for hours waterlogs the base. Because water moves only upward and does not drain through, salts build up near the surface over time, so top-water to runoff now and then to clear them. Commercial nurseries use sub-irrigation widely for potted plants. ## Don't confuse with - **Wick system**: continuous capillary feed through a cord. - **Ebb and flow**: automated, [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) flood-and-drain. ## Related terms [Wick system](https://genetixbay.com/knowledge/glossary/wick-system.md), [Ebb and flow](https://genetixbay.com/knowledge/glossary/ebb-and-flow.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), [Ceramic sensor watering](https://genetixbay.com/knowledge/glossary/ceramic-sensor-watering.md) ## Read more - [Bottom-watering, soak trays and wick (self-watering) systems](https://genetixbay.com/knowledge/systems/bottom-watering-wick.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Bract > In cannabis, the small leaf-like sheath (perigonal bract) that wraps each female flower's ovary and carries the densest capitate-stalked trichomes. - Canonical: https://genetixbay.com/knowledge/glossary/bract.html - Also written: perigonal bract, bracts, floral bract, pistillate bract, seed bract - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A bract is a modified leaf associated with a flower. In female cannabis, each [pistillate flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) is enclosed by a perigonal bract: a small, cupped, green structure that wraps the ovary and from which the [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md) protrude. The bract swells as the flower matures and, if pollinated, encloses the developing seed. Bracts carry the highest density of [capitate-stalked](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md) glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) on the plant. ## In practice What growers call "calyxes" or "calyx-to-leaf ratio" are, botanically, bracts. A "high calyx-to-leaf ratio" means many swollen bracts and few [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md), which makes trimming easy and puts more resin into the bud. Bract swelling in late flower is one of the visual ripeness signs, alongside [trichome colour](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md). Because bracts are where most resin sits, the share of a dried bud's mass that is bract (and trichome) rather than stem and leaf sets a hard ceiling on what flower can test. ## Don't confuse with - **Calyx**: the true calyx is a thin, reduced perianth on the ovary, barely visible; growers use the word for the bract. - **Sugar leaf**: a small [true leaf](https://genetixbay.com/knowledge/glossary/true-leaves.md) among the flowers. - **Pistil**: the female reproductive organ inside the bract. ## Related terms [Calyx](https://genetixbay.com/knowledge/glossary/calyx.md), [Pistil](https://genetixbay.com/knowledge/glossary/pistil.md), [Capitate-stalked trichome](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md), [Cola](https://genetixbay.com/knowledge/glossary/cola.md), [Achene](https://genetixbay.com/knowledge/glossary/achene.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 3. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Breeder > A breeder develops lines over generations with clear goals, large grow-outs, selection of both sexes, stability and herm testing, and honest lineage records. - Canonical: https://genetixbay.com/knowledge/glossary/breeder.html - Also written: breeders, plant breeder, cannabis breeder, seed breeder - Glossary category: Grower slang and culture · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A breeder, in the sense GenetixBay uses, is someone who develops a line over several generations toward a stated goal, rather than releasing a single cross. The work is mostly numbers and patience: grow many plants, select hard, keep and evaluate males, test for stability and [intersex](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) tendency, and record everything. ## In practice A breeder working a line might grow 100-300 plants per generation, keep the top 2-5% of females and a few carefully chosen males, cross or [backcross](https://genetixbay.com/knowledge/glossary/backcross.md) them, and repeat until the offspring are uniform enough to describe honestly. Before release, tester grows report [germination](https://genetixbay.com/knowledge/glossary/germination.md), [sex ratio](https://genetixbay.com/knowledge/glossary/sex-ratio.md), [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md) and spread of types. A breeder publishes what the line is and is not, including the faults. Good breeders value males as much as females, because half the genetics of every seed comes from the father. ## Don't confuse with - **Pollen chucker**: crosses and sells without the selection and testing. - **Seed bank**: a vendor that sells seed, often from many breeders. Selling is not breeding. - **Grower**: growing well and breeding well are different skills; many great growers never breed. ## Myth check "Herms are just cannabis being cannabis." GenetixBay position: [herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) lines mostly come from breeding shortcuts (repeated selfing, careless feminising, untested crosses). A breeder culls for it. See [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Pollen chucker](https://genetixbay.com/knowledge/glossary/pollen-chucker.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md), [Test grow](https://genetixbay.com/knowledge/glossary/test-grow.md) ## Read more - [Breeders vs pollen chuckers: what real cannabis breeding looks like](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) --- # Brick weed > Brick weed is seeded, lower-grade cannabis pressed into dense blocks for smuggling and cheap sale, historically the bulk of imported cannabis. - Canonical: https://genetixbay.com/knowledge/glossary/brick-weed.html - Also written: brick, brickweed, compressed, compressed weed, brick schwag, pressed weed - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Brick weed is cannabis compressed into hard blocks, typically including leaf, stem and seed, and dried and stored with little care. It was the standard form of imported cannabis in North America for decades. ## In practice Brick [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) flat, brown and crushed, often smells of hay or must, and is full of seeds and stems. Compression ruptures [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), and long, warm, poorly sealed storage oxidises [THC](https://genetixbay.com/knowledge/glossary/thc.md) toward [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) and evaporates [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md). By the time it was sold, brick had lost much of whatever it started with. ## Don't confuse with - **Sinsemilla**: seedless, carefully dried flower. - **Pressed hash**: compressed resin, a deliberate concentrate rather than a smuggling shortcut. - **Mids**: middle-grade loose flower. ## Myth check "Old weed was weak, so modern genetics must be much stronger." GenetixBay position (*Supported*): the numbers mislead. Government monitoring series tested largely seized commercial brick and mixed material (leaf, seed, stem) rather than [sinsemilla](https://genetixbay.com/knowledge/glossary/sinsemilla.md). Old samples sat degrading in storage, methods and [sampling](https://genetixbay.com/knowledge/glossary/homogenisation.md) changed, and the seizures were not representative (ElSohly et al. 2016 discusses the series). Source regions also had little reason to export their best sensi when the import market paid for cheap brick. The genetics did not suddenly change; growing technique and the material sampled did. See [old cannabis was not weak](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md). ## Related terms [Sinsemilla](https://genetixbay.com/knowledge/glossary/sinsemilla.md), [Mids](https://genetixbay.com/knowledge/glossary/mids.md), [Shake](https://genetixbay.com/knowledge/glossary/shake.md), [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md) ## Read more - [Old cannabis wasn't weak: the "so much stronger than 20 years ago" myth](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md) ## Sources 1. ElSohly MA, Mehmedic Z, Foster S, Gon C, Chandra S, Church JC. 2016. Changes in cannabis potency over the last 2 decades (1995-2014): analysis of current data in the United States. Biological Psychiatry 79(7):613-619. https://doi.org/10.1016/j.biopsych.2016.01.004 2. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. --- # Broad mite > Polyphagotarsonemus latus, a microscopic tarsonemid mite whose toxic feeding twists, glazes and stunts new growth; often mistaken for calcium deficiency or heat stress. - Canonical: https://genetixbay.com/knowledge/glossary/broad-mite.html - Also written: broad mites, Polyphagotarsonemus latus, tropical mite - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The broad mite (*Polyphagotarsonemus latus*) is a tarsonemid mite about 0.2 mm long, too small to see with the naked eye or a 10x loupe. It feeds on the youngest leaves and [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md). Its saliva is toxic to the plant, so even a modest population distorts growth far out of proportion to its size. ## In practice The classic picture is new growth that is twisted, narrow, shiny or glassy, with leaf edges curling down and tips that stall. Growers often chase it as a calcium or boron problem first. Confirming it takes a 40-60x scope or a digital microscope on a growing tip: look for clear oval adults and eggs dotted with white bumps. Broad mites travel on clones, clothing and air currents, so quarantine of incoming cuts is the main defence. [Predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md) such as *[Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md)* and *[Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md)* are used against them. In flower, options shrink sharply; check what is registered for cannabis locally. ## Don't confuse with - **Hemp russet mite**: an [eriophyid mite](https://genetixbay.com/knowledge/glossary/eriophyid-mite.md) that bronzes and curls leaves upward, usually starting lower on the plant. - **Calcium or boron deficiency**: no [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) under magnification, and the damage tracks [root-zone conditions](https://genetixbay.com/knowledge/glossary/root-zone.md). - **Heat or light stress**: improves when the stress is removed. ## Related terms [Hemp russet mite](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md), [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [Cyclamen mite](https://genetixbay.com/knowledge/glossary/cyclamen-mite.md), [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) ## Read more - [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ## Sources 1. UConn IPM. Managing Broad Mites on Greenhouse Crops. https://ipm.cahnr.uconn.edu/ipm-managing-broad-mites-on-greenhouse-crops 2. Virginia Cooperative Extension. Broad mite (ENTO-587). https://pubs.ext.vt.edu/content/pubs_ext_vt_edu/en/ENTO/ento-587/ento-587.html --- # Bti > Bacillus thuringiensis subsp. israelensis, a bacterial strain whose toxins kill fly larvae, including fungus gnats, after ingestion; applied as a medium drench. - Canonical: https://genetixbay.com/knowledge/glossary/bti.html - Also written: Bacillus thuringiensis israelensis, B.t.i., Bt israelensis, Bt for fungus gnats - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Bti is *[Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md)* subspecies *israelensis*, a strain whose crystal toxins are active against the larvae of certain flies: mosquitoes, black flies and [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md). Larvae must eat the bacterium for it to work. It has no effect on adult flies, caterpillars, beetles, [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) or plants. ## In practice Growers drench the medium with a Bti solution, or soak granules in water and use the liquid, to cut fungus gnat larvae in the top few centimetres of soil or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md). Results show as fewer adults on [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) one to two weeks later, since existing adults are untouched. It breaks down within days, so repeated drenches at roughly weekly intervals during heavy pressure are typical. It pairs well with drying the medium surface and with [nematodes](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md) or [soil predatory mites](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md). Check what is registered for cannabis locally. ## Don't confuse with - **Btk**: the caterpillar strain, sprayed on foliage. - **Steinernema feltiae**: living nematodes, not a bacterial toxin. - **Hydrogen peroxide drenches**: oxidisers that also harm beneficial root life. ## Related terms [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md), [Fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [Steinernema feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) ## Read more - [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ## Sources 1. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf 2. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ --- # Bubble hash > Bubble hash, or ice water hash, is a solventless concentrate made by separating trichome heads from cannabis in cold water and collecting them on graded mesh bags. - Canonical: https://genetixbay.com/knowledge/glossary/bubble-hash.html - Also written: ice water hash, ice hash, water hash, ice-water hash, IWH, ice water extraction - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Bubble hash is [hash](https://genetixbay.com/knowledge/glossary/hash.md) made with ice water. Cold makes [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) brittle so they snap off the plant under gentle agitation; the heads, being denser, separate from plant matter in the water, and the slurry is filtered through a series of mesh bags graded in microns. Each bag catches a size fraction of heads, which is then dried. The name comes from the way high-grade material bubbles when heated. ## In practice Hash makers describe grades by micron fraction and by melt quality, often on an informal one-to-six-star scale. The middle fractions usually hold the cleanest, most intact heads; the finest and coarsest fractions carry more debris. Starting material can be dried flower, trim or [fresh frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) plants; fresh frozen gives "live" products. Russo et al. (2021) studied a fresh-frozen ice water method and reported that it preserved [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene profiles](https://genetixbay.com/knowledge/glossary/terpene-profile.md) well. GenetixBay defines the product but doesn't provide processing steps. ## Don't confuse with - **Dry sift**: separated with dry screens, no water. - **Full melt**: the top grade of bubble hash (or [dry sift](https://genetixbay.com/knowledge/glossary/kief.md)), not a separate method. - **Rosin**: may be pressed from bubble hash, but is a further product. ## Related terms [Micron bags](https://genetixbay.com/knowledge/glossary/micron-bags.md), [Full melt](https://genetixbay.com/knowledge/glossary/full-melt.md), [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), [Live rosin](https://genetixbay.com/knowledge/glossary/live-rosin.md), [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md), [Fresh frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) ## Sources 1. Russo EB, Plumb J, Whiteley VL. 2021. Novel solventless extraction technique to preserve cannabinoid and terpenoid profiles of fresh cannabis inflorescence. Molecules 26(18):5496. https://doi.org/10.3390/molecules26185496 2. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Bucking > Removing buds from their branches and stems, either before drying (wet bucking) or after (dry bucking), ready for trimming or jarring. - Canonical: https://genetixbay.com/knowledge/glossary/bucking.html - Also written: bucked, de-stemming, destemming, bucking buds, debudding - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Bucking is taking the buds off the stems. Done by hand with fingers or snips, or by machines with sized holes that strip buds from pulled-through branches, it separates the flower from the woody stem so it can be trimmed, dried on racks, or [jarred](https://genetixbay.com/knowledge/glossary/curing-jar.md). ## In practice When to buck depends on the trim and dry approach: - **Wet bucking**: after chop, before rack-drying [wet-trimmed](https://genetixbay.com/knowledge/glossary/wet-trim.md) buds. Saves [drying space](https://genetixbay.com/knowledge/glossary/drying-room.md) but speeds the dry; slow the room to compensate. - **Dry bucking**: after hang-drying, once small stems snap. Usual with [dry trimming](https://genetixbay.com/knowledge/glossary/dry-trim.md). Good practice: - buck gently and cool, since dry [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) shatter with rough handling; - leave a small stem stub on large buds if you'll jar untrimmed and trim later; - keep sizes sorted: big buds, smalls and larf dry and cure at different rates. Stems stripped out at bucking still hold water. Leaving larger [colas](https://genetixbay.com/knowledge/glossary/cola.md) on a short stem during the dry slows it and helps evenness. ## Don't confuse with - **Trimming**: removing [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) from buds. - **Chop**: cutting the plant down. - **Defoliation**: leaf removal while growing. ## Related terms [Wet trim](https://genetixbay.com/knowledge/glossary/wet-trim.md), [Dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md), [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), [Curing](https://genetixbay.com/knowledge/glossary/curing.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) --- # Bud rot check > Routine inspection of dense colas in late flower, at harvest and during drying and curing for signs of grey mould (Botrytis cinerea) and other rots. - Canonical: https://genetixbay.com/knowledge/glossary/bud-rot-check.html - Also written: mold check, mould check, checking for bud rot, checking for mold, rot check, botrytis check - Glossary category: Harvest, drying and curing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A bud rot check is a deliberate inspection of buds for mould, mainly [grey mould](https://genetixbay.com/knowledge/glossary/botrytis.md) caused by *Botrytis cinerea*, which rots dense flowers from the inside out. It belongs in late flower, at harvest, during the dry and in the first weeks of the cure, because the fungus thrives in humid, still air and tightly packed buds. ## In practice What to look for: - a single [sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) or bract cluster turning dry, brown or grey while the rest is green; - soft, mushy, brown tissue inside a [cola](https://genetixbay.com/knowledge/glossary/cola.md) near the stem; - grey, fuzzy growth, sometimes with dusty spores; - a musty or damp smell in the room or a jar. How to check: gently part the largest colas, especially top colas and buds near the stem, and look in at the core. Use a loupe on suspicious spots. In jars, empty a sample of buds onto a tray rather than looking through the glass. If you find it, cut the affected bud out with a margin, bag it inside the room to avoid spreading spores, and don't smoke or process mouldy material. Then fix the cause: [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) in late flower around 40-50%, air through the canopy, a [drying room](https://genetixbay.com/knowledge/glossary/drying-room.md) at about 55-62% RH, not higher. ## Don't confuse with - **Powdery mildew**: white powder on leaf surfaces. - **Natural senescence**: yellowing leaves, not brown, mushy buds. - **Pistil browning**: normal ageing of stigmas. ## Related terms [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md), [Cola](https://genetixbay.com/knowledge/glossary/cola.md), [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md), [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Jeweler's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) ## Read more - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. Punja ZK. 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857-3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Bud site > A bud site is a node where flowers form, where leaf meets stem, or a branch tip; training aims to put more of them in strong light. - Canonical: https://genetixbay.com/knowledge/glossary/bud-site.html - Also written: bud sites, flowering site, budsite, flower site, bud node - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A bud site is any place on the plant where flowers develop: each node, where a leaf and side shoot meet the stem, and every branch tip. In flower, the tips become [colas](https://genetixbay.com/knowledge/glossary/cola.md) and the nodes along each branch produce smaller clusters. Large, dense buds form only where there is strong light and good supply from nearby leaves. ## In practice Training techniques are judged by what they do to bud sites. Topping and mainlining multiply main [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md). [LST](https://genetixbay.com/knowledge/glossary/lst.md) and [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md) lift many sites into the same strong light. [Lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md) removes the weak sites below the canopy, which would otherwise make small, airy "[popcorn](https://genetixbay.com/knowledge/glossary/popcorn-buds.md)" buds. The goal is not the maximum number of sites, but the maximum number of well-lit ones. ## Don't confuse with - **Cola**: the main terminal cluster of flowers on a stem; a cola is made of many fused bud sites. - **Pre-flower**: the first flowers that appear at nodes, used to sex plants. ## Related terms [Node](https://genetixbay.com/knowledge/glossary/node.md), [Cola](https://genetixbay.com/knowledge/glossary/cola.md), [Lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md) --- # Budtender > A budtender is a retail worker in a cannabis store who helps customers choose products; training and product knowledge vary widely. - Canonical: https://genetixbay.com/knowledge/glossary/budtender.html - Also written: budtenders, bud tender, dispensary staff, cannabis retail staff - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A budtender (from bartender) is a staff member at a cannabis store or dispensary who serves customers, explains products and processes sales. ## In practice Budtenders are often the main source of product information customers get, so their advice is only as good as their training and the product data they have. Some are deeply knowledgeable growers; others have a short training course and a menu. Advice framed around "indica for sleep, sativa for energy" reflects the labels, not the chemistry. Useful questions for any budtender: what is the harvest or packaging date, who grew it, was it irradiated or otherwise decontaminated, what do the lab results show for [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) and [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), and is the result from more than one lab. Laws in many places restrict what retail staff may say about effects; check local rules. ## Don't confuse with - **Pharmacist**: a regulated health professional; budtenders generally cannot give medical advice. ## Related terms [Top shelf](https://genetixbay.com/knowledge/glossary/top-shelf.md), [Smoke report](https://genetixbay.com/knowledge/glossary/smoke-report.md), [Licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md), [Labelling requirements](https://genetixbay.com/knowledge/glossary/labelling-requirements.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) --- # Buffering capacity > Buffering capacity is how strongly a water, solution or medium resists pH change when acid or base is added; high capacity means stable but hard-to-move pH. - Canonical: https://genetixbay.com/knowledge/glossary/buffering-capacity.html - Also written: buffer capacity, pH buffering capacity, buffering power, acid-neutralising capacity, acid neutralizing capacity - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Buffering capacity is the amount of acid or base needed to change the [pH](https://genetixbay.com/knowledge/glossary/ph.md) of a solution or medium by a given amount. In water it comes mostly from bicarbonate and carbonate, measured as [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md). In growing media it comes from organic matter, clay, lime and [cation exchange](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md) sites: peat and soil buffer strongly, [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) moderately, [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) and [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md) hardly at all. ## In practice High buffering capacity is a mixed blessing. Soil rich in organic matter keeps root-zone pH steady even when input pH is off, which is why soil growers need to adjust less. But water with high alkalinity takes a lot of acid to bring down and, over weeks, can push container media pH upwards. Low buffering capacity is the RO-water and hydro problem: pH moves easily, so small additions overshoot and drift is fast. A small reservoir of [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) with nutrients may drift 0.3–0.5 pH units in a day. ## Units and formula For water, buffering capacity is usually reported as alkalinity in mg/L (ppm) as CaCO3, or as [carbonate hardness](https://genetixbay.com/knowledge/glossary/carbonate-hardness.md) in dKH. ## Don't confuse with - **pH**: where the solution is; buffering capacity is how firmly it stays there. - **Cation exchange capacity (CEC)**: a medium's ability to hold cations; related but not the same. ## Related terms [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [pH buffer](https://genetixbay.com/knowledge/glossary/ph-buffer.md), [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md), [Carbonate hardness](https://genetixbay.com/knowledge/glossary/carbonate-hardness.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) ## Sources 1. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 2. Abad M, Noguera P, Puchades R, Maquieira A, Noguera V. 2002. Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology 82(3):241-245. https://doi.org/10.1016/S0960-8524(01)00189-4 --- # Bulbous trichome > The smallest glandular trichome on cannabis, a few cells with a tiny head (about 10-30 µm), scattered over leaves and stems. - Canonical: https://genetixbay.com/knowledge/glossary/bulbous-trichome.html - Also written: bulbous trichomes, bulbous gland, bulbous glandular trichome - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A bulbous trichome is a minute glandular [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) made of a few cells: a one- or two-celled base and a small secretory head, often only 10-30 µm across. They occur widely on leaves, stems and [bracts](https://genetixbay.com/knowledge/glossary/bract.md) of cannabis plants of both sexes. Their contribution to total resin is small because each holds so little. ## In practice Most growers never notice bulbous trichomes; even with a 60x [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) they appear as faint specks among larger glands. They are mainly of interest in botanical descriptions, in microscopy of trichome development, and when explaining why some resin is found even on leaves that carry few visible glands. When people grade frost or count glands for harvest, they are looking at [capitate-stalked](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md) heads, not bulbous ones. The three-way classification (bulbous, [capitate-sessile](https://genetixbay.com/knowledge/glossary/capitate-sessile-trichome.md), capitate-stalked) comes from classic microscopy of cannabis epidermis and is still used in current research. ## Don't confuse with - **Capitate-sessile trichome**: larger head, sits on the surface without a tall stalk. - **Capitate-stalked trichome**: the big mushroom gland on bracts. - **Cystolith trichome**: non-glandular hair with a calcium carbonate crystal. ## Related terms [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md), [Capitate-sessile trichome](https://genetixbay.com/knowledge/glossary/capitate-sessile-trichome.md), [Capitate-stalked trichome](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Burping > Briefly opening sealed curing jars to release moist air and let fresh air in, so moisture keeps declining slowly during the cure. - Canonical: https://genetixbay.com/knowledge/glossary/burping.html - Also written: burp, burping jars, burp the jars, jar burping, airing jars - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Burping is opening [curing jars](https://genetixbay.com/knowledge/glossary/curing-jar.md) for a short time, typically a few minutes to tens of minutes, to swap the humid air in the headspace for room air. It lets moisture that has migrated from the bud cores to the surface escape, so the cure moves gradually toward the target [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) without the jar staying too wet. ## In practice A common schedule (Grower practice): - **Week 1**: once or twice a day, guided by equilibrated [jar RH](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md). - **Week 2**: every day or two. - **Weeks 3-4**: once or twice a week, then mostly sealed. Let the hygrometer guide you rather than the calendar. If a jar equilibrates above about 65% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), burp longer or take the buds out to air on a tray for an hour or so. If it drops below about 55%, keep it closed. House approach: if you need to add moisture back, put a fresh bud in the jar rather than a [humidity pack](https://genetixbay.com/knowledge/glossary/humidity-pack.md). When opening, smell the jar. A sharp ammonia or musty smell means too wet and possible microbial growth; spread the buds out and inspect for mould. ## Don't confuse with - **Curing**: the whole process; burping is one step in it. - **Venting a grow room**: air exchange in cultivation. - **Humidity packs**: try to hold RH fixed, which is the opposite of a slow decline. ## Related terms [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Equilibrium relative humidity](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md), [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Humidity pack](https://genetixbay.com/knowledge/glossary/humidity-pack.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html --- # Cal-Mag > Cal-Mag is a supplement supplying calcium and magnesium, usually as nitrates; need depends on cultivar, water source (RO vs tap) and medium (coco), not on LED lighting. - Canonical: https://genetixbay.com/knowledge/glossary/cal-mag.html - Also written: CalMag, Cal Mag, calcium magnesium supplement, Ca-Mg supplement - Glossary category: Nutrients · Evidence: Myth - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cal-Mag is a class of supplement providing calcium and magnesium, typically [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md) and [magnesium nitrate](https://genetixbay.com/knowledge/glossary/magnesium-nitrate.md) in liquid form, sometimes with iron. It also adds nitrogen, which counts towards the feed total. ## In practice Growers use it to make up for calcium and magnesium missing from [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) or very soft water, to buffer [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) before planting, and with cultivars that genuinely demand more Ca and Mg. With hard tap water, a complete base often already supplies enough. Too much raises [EC](https://genetixbay.com/knowledge/glossary/ec.md), pushes nitrogen up and can suppress potassium. Dose to a target in mg/L (ppm) of Ca and Mg, not by habit. ## Don't confuse with - **Epsom salt**: magnesium and sulfur only, no calcium. - **Calcium nitrate**: calcium only. - **Coco buffer**: a Cal-Mag use, not the product itself. ## Myth check "[LEDs](https://genetixbay.com/knowledge/glossary/led.md) need more Cal-Mag" is a Myth (GenetixBay house position). LEDs do not create a Ca or Mg requirement. Demand is driven by cultivar, water source and coco [cation exchange](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md); [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) differences under LED (Nelson and Bugbee) affect transpiration and environment settings, not nutrient need in themselves. See [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [Magnesium](https://genetixbay.com/knowledge/glossary/magnesium.md), [Magnesium nitrate](https://genetixbay.com/knowledge/glossary/magnesium-nitrate.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Secondary nutrient](https://genetixbay.com/knowledge/glossary/secondary-nutrient.md) ## Read more - [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) - [Buffering coco coir: why it matters and how to do it](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md) ## Sources 1. Morad D, Bernstein N. 2023. Response of medical cannabis to magnesium (Mg) supply at the vegetative growth phase. Plants 12(14):2676. https://doi.org/10.3390/plants12142676 2. Nelson JA, Bugbee B. 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10):e0138930. https://doi.org/10.1371/journal.pone.0138930 3. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Calcium > Calcium (Ca) is an immobile secondary nutrient that builds cell walls and membranes; it travels only in the transpiration stream, so deficiency appears in new growth. - Canonical: https://genetixbay.com/knowledge/glossary/calcium.html - Also written: Ca, Ca2+, calcium deficiency, Ca deficiency - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Calcium is a secondary macronutrient absorbed as Ca2+. It cross-links pectins in cell walls, stabilises membranes and acts as a signalling ion. Calcium moves only upward with water in the xylem and cannot be moved from old leaves to new ones, so it is immobile. ## In practice Deficiency shows on new and fast-growing tissue: distorted or crinkled young leaves, brown [necrotic spots](https://genetixbay.com/knowledge/glossary/necrosis.md), weak stems and dying [growing tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md). Because Ca rides the [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) stream, low transpiration (very high humidity, poor airflow) can cause local shortage even when the feed is fine. Hydro feeds usually carry about 120-200 mg/L (ppm) Ca, most often from [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md). [Coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) binds calcium on its exchange sites, which is why coco needs buffering. ## Don't confuse with - **Cal-Mag**: a product class that supplies Ca and Mg, not the element. - **pH lockout**: low root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) reduces Ca uptake; check pH before adding more. - **Rust spots from pathogens or light stress**: see the rust-spot article before blaming Ca. ## Myth check Calcium demand varies mainly by cultivar, water source and medium, not by light type (Evidence: house position, Myth for "LEDs need [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md)"). See [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md). ## Related terms [Secondary nutrient](https://genetixbay.com/knowledge/glossary/secondary-nutrient.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md) ## Read more - [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) - [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Calcium chloride > Calcium chloride (CaCl2) adds calcium without nitrogen, useful for late-flower nitrogen tapering, but it adds chloride, so doses must stay modest. - Canonical: https://genetixbay.com/knowledge/glossary/calcium-chloride.html - Also written: CaCl2, CaCl2·2H2O, calcium chloride dihydrate - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Calcium chloride is a very soluble salt of calcium and [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md). The anhydrous form is about 36% Ca; the more common dihydrate (CaCl2·2H2O) is about 27% Ca and 48% Cl. It is strongly hygroscopic and releases heat as it dissolves. ## In practice Its main use in cannabis feeds is supplying calcium when the grower wants to cut nitrogen, such as during a late-flower [N taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md), since [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md) brings N along. The trade-off is chloride. Small amounts are harmless, but heavy use raises chloride enough to burn leaf margins. Many growers split the job: calcium chloride for part of the Ca, gypsum or reduced calcium nitrate for the rest. Food-grade or reagent grade avoids the contaminants in de-icing salt. ## Units and formula 1 g/L of the dihydrate gives about 273 mg/L (ppm) Ca and 482 mg/L Cl. ## Don't confuse with - **Calcium nitrate**: the standard calcium source, with nitrogen. - **Road de-icing salt**: may be calcium chloride but contains impurities. - **Calcium sulfate (gypsum)**: low solubility, adds [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) instead of chloride. ## Related terms [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [Chlorine (nutrient)](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) - [Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add](https://genetixbay.com/knowledge/nutrients/chlorine.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. White PJ, Broadley MR. 2001. Chloride in soils and its uptake and movement within the plant: a review. Annals of Botany 88(6):967-988. https://doi.org/10.1006/anbo.2001.1540 --- # Calcium nitrate > Calcium nitrate is the standard hydroponic calcium source, supplying about 19% calcium and 15.5% nitrogen, mostly as nitrate. - Canonical: https://genetixbay.com/knowledge/glossary/calcium-nitrate.html - Also written: CaNO3, Ca(NO3)2, calcium nitrate tetrahydrate, cal nit, 15.5-0-0 - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Calcium nitrate is a highly soluble salt that supplies both calcium and [nitrate nitrogen](https://genetixbay.com/knowledge/glossary/nitrate.md). The fertiliser grade most growers buy is a double salt with a little [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), analysed at about 15.5% N (roughly 14.4% nitrate-N and 1.1% ammonium-N) and 19% Ca. ## In practice It is the backbone of the A part in almost every two-part mineral feed. Because it reacts with [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md) and phosphate to form insoluble precipitates, it must never be mixed with [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), MKP or [potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md) in concentrated form. In the final dilute tank, they coexist without trouble. It is hygroscopic: keep the bag sealed or it turns to slush. ## Units and formula 1 g/L gives about 155 mg/L (ppm) N and 190 mg/L Ca. A feed of 0.8 g/L therefore adds roughly 150 ppm Ca and 125 ppm N. ## Don't confuse with - **Calcium chloride**: supplies calcium without nitrogen but adds [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md). - **Calcium carbonate (lime)**: insoluble, used to raise soil [pH](https://genetixbay.com/knowledge/glossary/ph.md), not a hydro calcium source. - **Cal-Mag**: a blended product, often based on calcium nitrate plus a magnesium salt. ## Related terms [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Calibration solution > A calibration solution is a standard liquid of known pH or EC used to calibrate meters, such as pH 4.01, 7.00 and 10.01 buffers or 1.413 mS/cm EC standard. - Canonical: https://genetixbay.com/knowledge/glossary/calibration-solution.html - Also written: calibration fluid, buffer solution pH 7, pH 4 buffer, 1413 solution, EC standard, cal solution - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A calibration solution is a reference liquid with a certified value at a stated temperature, usually 25 °C. [pH](https://genetixbay.com/knowledge/glossary/ph.md) buffers are commonly 4.01, 7.00 and 10.01. [EC](https://genetixbay.com/knowledge/glossary/ec.md) standards include 1,413 µS/cm (1.413 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md)), a potassium [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) solution that sits in the range of most nutrient solutions, plus lower and higher standards for water and strong solutions. ## In practice Use fresh solution for each calibration: pour a small amount into a clean cup, calibrate, then discard it. Never dip the probe into the stock bottle or pour used solution back. Check the expiry date; once opened, buffers drift as they absorb CO2 (the pH 10 buffer is most sensitive) and as dirty probes contaminate them. Single-use sachets avoid this. Rinse the probe with distilled or [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) between solutions and blot, do not wipe, the glass bulb. Let solution and probe reach room temperature before calibrating, or use a meter with [automatic temperature compensation](https://genetixbay.com/knowledge/glossary/atc.md). ## Don't confuse with - **Storage solution**: usually 3 M potassium chloride, used to keep pH probes hydrated; it is not a calibration standard. - **pH Up and pH Down**: adjust solutions; they are not references. ## Related terms [Two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md), [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md), [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md), [pH buffer](https://genetixbay.com/knowledge/glossary/ph-buffer.md) ## Read more - [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) --- # Calyx > Botanically, the sepals of a flower; in female cannabis a thin, reduced perianth on the ovary, though growers use the word for the resinous bract. - Canonical: https://genetixbay.com/knowledge/glossary/calyx.html - Also written: calyxes, calyces, perianth, calyx-to-leaf ratio - Glossary category: Plant biology - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In botany the calyx is the outer whorl of a flower, made of its sepals. In female cannabis the true calyx (perianth) is reduced to a thin, translucent membrane hugging the ovary, hard to see without magnification. The plump, resin-covered green pod growers point at and call a "calyx" is in fact the [perigonal bract](https://genetixbay.com/knowledge/glossary/bract.md) that surrounds it. ## In practice The grower usage is everywhere and isn't going anywhere: "calyx-to-leaf ratio", "[foxtailing](https://genetixbay.com/knowledge/glossary/foxtailing.md) calyxes", "stacked calyxes". Read it as "bract". A high ratio means buds built mostly of swollen bracts with little leaf, which trims fast and carries more resin per gram. Being precise matters in breeding notes and plant descriptions. A [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) record or a test guideline should say "bract" for the structure that carries the resin. Botanical papers on cannabis flower development (e.g. Spitzer-Rimon et al. 2019) use the correct terms, which makes them easier to read once you know. ## Don't confuse with - **Bract**: the leafy sheath around the flower that growers usually mean. - **Pistil**: the ovary, style and [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md); the calyx surrounds the ovary. - **Sugar leaf**: a small [true leaf](https://genetixbay.com/knowledge/glossary/true-leaves.md), not part of the flower. ## Related terms [Bract](https://genetixbay.com/knowledge/glossary/bract.md), [Pistil](https://genetixbay.com/knowledge/glossary/pistil.md), [Stigma](https://genetixbay.com/knowledge/glossary/stigma.md), [Sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Candy terps > Candy terps is slang for the sweet, fruity, dessert-like aroma profile fashionable in modern cannabis, often paired with gas as the dominant market trend. - Canonical: https://genetixbay.com/knowledge/glossary/candy-terps.html - Also written: candy, candy strains, dessert terps, dessert strains, fruity terps, gas and candy - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Candy terps describes flower that smells and tastes like sweets: [fruit](https://genetixbay.com/knowledge/glossary/achene.md), sugar, cream, bakery. Together with gas, it is the profile modern breeding and marketing chase most. ## In practice Menus are full of dessert-named cultivars, many sharing a handful of parents. A grower looking for something different, such as incense, pine, [hash](https://genetixbay.com/knowledge/glossary/hash.md) spice, sharp citrus or old-school [skunk](https://genetixbay.com/knowledge/glossary/skunk.md), often has to search out older lines or preservation projects. ## Don't confuse with - **Terpene names**: candy is a perception, produced by mixtures of [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), esters and other volatiles, not one compound. - **Exotic**: the price tier candy cultivars usually occupy. ## Myth check "The market just wants what's best." GenetixBay position (*Supported*): the gas/candy trend is killing the classics. Studies of commercial cannabis show products cluster into a few chemical groups regardless of name (Smith et al. 2022), and market selection for [THC](https://genetixbay.com/knowledge/glossary/thc.md) % and fashion squeezes out aroma diversity. GenetixBay's answer is not to complain but to preserve: keep and share classic profiles, record aroma in words and chemistry on [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) records, and keep the odd incense or pine keeper even if it is not trending. See [why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md). ## Related terms [Gas](https://genetixbay.com/knowledge/glossary/gas.md), [Terps](https://genetixbay.com/knowledge/glossary/terps.md), [Hype strain](https://genetixbay.com/knowledge/glossary/hype-strain.md), [Renamed cut](https://genetixbay.com/knowledge/glossary/renamed-cut.md), [Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Cannabinoid > A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA. - Canonical: https://genetixbay.com/knowledge/glossary/cannabinoid.html - Also written: cannabinoids, cannabanoid, cannabinoid compounds - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A cannabinoid is a compound that either acts on the cannabinoid receptors (CB1, CB2) or belongs to the chemical family the cannabis plant makes in its [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md). The word covers three groups: [phytocannabinoids](https://genetixbay.com/knowledge/glossary/phytocannabinoid.md) (made by plants), endocannabinoids (made by animals, such as anandamide) and synthetic cannabinoids (made in a lab). More than 100 phytocannabinoids have been described from cannabis, though only a handful occur at more than trace levels. ## In practice Growers and labs mostly mean the plant's major cannabinoids: [THCA](https://genetixbay.com/knowledge/glossary/thca.md), CBDA, [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) and their neutral forms [THC](https://genetixbay.com/knowledge/glossary/thc.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) and [CBG](https://genetixbay.com/knowledge/glossary/cbg.md). On a typical drug-type flower COA, THCA makes up well over 90% of the cannabinoid total, with the rest split between Δ9-THC, CBGA and minor compounds. A "high cannabinoid" plant is one with a high total across all of them, not only THC. ## Don't confuse with - **Terpene**: aroma compounds made in the same trichome heads; they are not cannabinoids, even though both share a precursor pathway. - **Phytocannabinoid**: the narrower, plant-only subset of cannabinoids. - **Synthetic cannabinoid**: lab-made receptor agonists, often unrelated in structure and not found in the plant. ## Related terms [Phytocannabinoid](https://genetixbay.com/knowledge/glossary/phytocannabinoid.md), [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [Acid vs neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. 2. ElSohly MA, Slade D. 2005. Chemical constituents of marijuana: the complex mixture of natural cannabinoids. Life Sciences 78(5):539-548. --- # Cannabis aphid > Phorodon cannabis, an aphid that feeds mainly on cannabis and hemp, colonising leaf undersides and buds and leaving honeydew and cast skins in flower. - Canonical: https://genetixbay.com/knowledge/glossary/cannabis-aphid.html - Also written: hemp aphid, Phorodon cannabis, cannabis aphids - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The cannabis aphid (*Phorodon cannabis*) is an [aphid](https://genetixbay.com/knowledge/glossary/aphid.md) that specialises on *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)*. Wingless forms are pale green to yellow, often with faint darker stripes, and about 1-2 mm long. It became a widespread [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) pest in North America after hemp production expanded in the late 2010s. Like other aphids it reproduces rapidly by live birth. ## In practice Colonies form on leaf undersides and stems and, by late season, inside flowers. Damage is mostly contamination rather than yield loss: [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md), [sooty mould](https://genetixbay.com/knowledge/glossary/sooty-mould.md) and white cast skins stuck in buds make the crop look and test poorly. Outdoors it can overwinter as eggs on plant debris; indoors it rides in on clones. Scout leaf undersides weekly, and use [parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md) (*Aphidius* species), lacewings and ladybirds as the backbone. Soap or oil sprays are for veg only. Check what is registered for cannabis locally. ## Don't confuse with - **Green peach aphid**: a generalist with many hosts; [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) similar and needs a closer look at the head tubercles to tell apart. - **Rice root aphid**: lives on roots, not foliage. - **Thrips larvae**: slender and fast, with no cornicles. ## Related terms [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Root aphid](https://genetixbay.com/knowledge/glossary/root-aphid.md), [Aphidius](https://genetixbay.com/knowledge/glossary/aphidius.md), [Ladybird](https://genetixbay.com/knowledge/glossary/ladybird.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. NC State Extension. Cannabis Aphid in Industrial Hemp. https://content.ces.ncsu.edu/cannabis-aphid-in-industrial-hemp 2. Utah State University Extension. Cannabis Aphids. https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-cannabis-aphid.php --- # Cannabis irradiation > Cannabis irradiation is treating harvested flower with ionising radiation, gamma, electron beam or X-ray, to cut microbial counts; permission and labelling rules vary. - Canonical: https://genetixbay.com/knowledge/glossary/irradiation.html - Also written: irradiation, irradiated cannabis, irradiated weed, gamma irradiation, e-beam treatment, x-ray treatment - Glossary category: Legal and regulatory · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cannabis irradiation is the use of ionising radiation to reduce bacteria, yeasts and moulds on harvested flower so it passes microbial limits. The main methods are gamma rays (usually from cobalt-60), electron beam (e-beam) and X-ray. Other decontamination methods include ozone, radio-frequency heating and UV, which are not ionising radiation. Irradiation does not make the flower radioactive. ## In practice Some regulated markets allow irradiation of cannabis, and it is widely used in some medical supply chains; others restrict it. Whether it must be disclosed on the label varies, so consumers often cannot tell. Studies report modest changes: [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) content largely unchanged, with some loss of [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) reported (Hazekamp 2016). Irradiation does not remove [mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md) or pesticide residues already present, and it can mask poor drying or hygiene that caused the contamination. GenetixBay's view: growing your own, where legal, is the surest way to know your flower was dried well rather than rescued by decontamination. [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) (clean rooms, airflow, a proper dry) beats a kill step. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **UV treatment**: non-ionising, mainly surface-acting. - **Pasteurisation**: heat-based, a different process. ## Related terms [Compliance testing](https://genetixbay.com/knowledge/glossary/compliance-testing.md), [Labelling requirements](https://genetixbay.com/knowledge/glossary/labelling-requirements.md), [Licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) ## Read more - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) ## Sources 1. Hazekamp A. 2016. Evaluating the effects of gamma-irradiation for decontamination of medicinal cannabis. Frontiers in Pharmacology 7:108. https://doi.org/10.3389/fphar.2016.00108 --- # Cannabis sativa L. > The single botanical species, in the family Cannabaceae, that covers all hemp and drug-type cannabis; "L." credits Linnaeus, who named it in 1753. - Canonical: https://genetixbay.com/knowledge/glossary/cannabis-sativa.html - Also written: Cannabis sativa, C. sativa, cannabis species, Cannabaceae - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Cannabis sativa* L. is the botanical name for cannabis: one species in the family Cannabaceae, alongside hops (*Humulus*). The "L." is the author citation for Carl Linnaeus, who published the name in 1753. Most current taxonomists treat all cultivated and wild cannabis, [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) and drug-type alike, as this one species, with variation expressed as subspecies, varieties or simply [phenotypes](https://genetixbay.com/knowledge/glossary/phenotype.md). ## In practice Growers use "sativa" in two [senses](https://genetixbay.com/knowledge/glossary/sinsemilla.md), and that causes endless muddle. Botanically, every plant in your tent is *Cannabis sativa*. In shop talk, "sativa" means a tall, narrow-leaflet, long-flowering plant. A breeder writing a [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) record should use the species name for the species and describe shape plainly ("narrow leaflets, 11-week flower") rather than lean on the label. The species is normally [dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md) (separate male and female plants), wind-pollinated, an annual, and with an XY sex-chromosome system ([2n](https://genetixbay.com/knowledge/glossary/diploid.md) = 20). ## Don't confuse with - **"Sativa" (shop label)**: a plant-shape description, not a species. - **Ruderalis**: a name for wild, [day-neutral](https://genetixbay.com/knowledge/glossary/autoflower.md) northern populations, not a separate species in the house view. - **Hemp**: a use and legal category within the same species. ## Myth check "Indica, sativa and [ruderalis](https://genetixbay.com/knowledge/glossary/ruderalis.md) are three species" is not the consensus. GenetixBay's position (Established, one-species taxonomy): one species, many phenotypes, and nearly everything grown today is a hybrid. Indica/sativa describes plant shape at most and does not predict effects. See [indica, sativa, ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Ruderalis](https://genetixbay.com/knowledge/glossary/ruderalis.md), [Dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [Achene](https://genetixbay.com/knowledge/glossary/achene.md) ## Read more - [Indica, sativa and ruderalis: what the names really mean](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. McPartland JM. 2018. Cannabis systematics at the levels of family, genus, and species. Cannabis and Cannabinoid Research 3(1):203-212. https://doi.org/10.1089/can.2018.0039 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 3. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 --- # Cannflavin > Cannflavins are prenylated flavones (A, B and C) that are characteristic of cannabis, first isolated in 1985 and found mainly in leaves and bracts at low levels. - Canonical: https://genetixbay.com/knowledge/glossary/cannflavin.html - Also written: cannflavins, cannflavin A, cannflavin B, cannflavin C - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cannflavins are [flavones](https://genetixbay.com/knowledge/glossary/flavonoid.md) (based on luteolin's skeleton) that carry an extra prenyl or geranyl side chain. Cannflavin A carries a geranyl group, cannflavin B a prenyl group, and cannflavin C a geranyl group at a different position. Barrett and colleagues first isolated cannflavins [A and B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) in 1985 during laboratory work on enzyme inhibition. The plant [genes](https://genetixbay.com/knowledge/glossary/gene.md) for their final steps were described more recently. ## In practice Cannflavins are present in small amounts, mostly in leaf and [bract](https://genetixbay.com/knowledge/glossary/bract.md) tissue rather than in the [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) resin, and almost never appear on commercial COAs. Their main interest is in research. GenetixBay makes no therapeutic claims: laboratory activity is not evidence of any effect from consuming cannabis. ## Don't confuse with - **Cannabinoids**: different class, although both use a geranyl group from the same precursor pool. - **Generic flavonoids**: apigenin, quercetin and others occur widely in plants; cannflavins are characteristic of cannabis. - **Anthocyanins**: pigment flavonoids responsible for [purple colour](https://genetixbay.com/knowledge/glossary/anthocyanin.md). ## Related terms [Flavonoid](https://genetixbay.com/knowledge/glossary/flavonoid.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md), [Geranyl pyrophosphate](https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.md) ## Sources 1. Barrett ML, Gordon D, Evans FJ. 1985. Isolation from Cannabis sativa L. of cannflavin, a novel inhibitor of prostaglandin production. Biochemical Pharmacology 34(11):2019-2024. 2. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. --- # Canopy > The canopy is the top layer of foliage and buds across a grow, the surface that intercepts most of the light and where yield is mostly made. - Canonical: https://genetixbay.com/knowledge/glossary/canopy.html - Also written: plant canopy, the canopy, canopy level, canopy area - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The canopy is the upper surface of foliage formed by all the plants in a space. Light from overhead fixtures is measured at canopy level, and most of the plant's [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) and most of its large buds happen within the top 30-45 cm (12-18 in) or so. Canopy area, the floor area the canopy covers, is also how commercial [yields](https://genetixbay.com/knowledge/glossary/yield.md) and licences are measured. ## In practice Growers manage the canopy by training (topping, [LST](https://genetixbay.com/knowledge/glossary/lst.md), [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md)), by pruning what sits below it, and by setting the light height so [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) is right at the top: typically about 600-1,000 µmol/m²/s in flower without added CO₂. A dense canopy blocks light from lower branches, which is why the growth beneath it is often [lollipopped](https://genetixbay.com/knowledge/glossary/lollipopping.md). "[Canopy temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md)" or "leaf temperature" readings come from this layer. ## Don't confuse with - **Even canopy**: a canopy where all tops sit at the same height. - **Grow area**: the tent or room floor; canopy area can be smaller if plants don't fill it. ## Related terms [Even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md), [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md), [Plant density](https://genetixbay.com/knowledge/glossary/plant-density.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) ## Sources 1. Westmoreland FM, Kusuma P, Bugbee B., 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLOS ONE 16(3):e0248988. https://doi.org/10.1371/journal.pone.0248988 --- # Capitate-sessile trichome > A glandular trichome with a resin head but little or no stalk, sitting close to the surface of leaves and young bracts. - Canonical: https://genetixbay.com/knowledge/glossary/capitate-sessile-trichome.html - Also written: capitate sessile trichome, sessile trichome, sessile glandular trichome, capitate-sessile - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A capitate-sessile trichome is a glandular [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) whose secretory head sits almost directly on the epidermis, with a very short stalk or none visible. Heads are smaller than stalked glands, roughly 25-70 µm across. They occur on leaves, [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md), stems and early-developing [bracts](https://genetixbay.com/knowledge/glossary/bract.md). Livingston et al. (2020) found that, on cannabis flowers, many sessile-looking glands are an early developmental stage of [capitate-stalked](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md) glands, and that the two differ in metabolism: stalked glands make relatively more [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) and fluoresce differently. Sessile glands on leaves stay sessile. ## In practice On a loupe they look like tiny beads stuck to the leaf surface. Their presence on sugar leaves is why trim from close to the bud carries resin and gets kept for processing, while large [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) carry far less. They matter less for [harvest timing](https://genetixbay.com/knowledge/glossary/harvest-window.md) than stalked glands, because the flower's bulk resin sits in stalked heads. ## Don't confuse with - **Capitate-stalked trichome**: tall stalk, large head, dominant on bracts. - **Bulbous trichome**: much smaller, a few cells. - **Cystolith hair**: non-glandular, no resin. ## Related terms [Capitate-stalked trichome](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md), [Bulbous trichome](https://genetixbay.com/knowledge/glossary/bulbous-trichome.md), [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md), [Sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) ## Read more - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) ## Sources 1. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 --- # Capitate-stalked trichome > The large mushroom-shaped glandular trichome on cannabis bracts, with a multicellular stalk and a resin-filled head; it holds most of the flower's cannabinoids and terpenes. - Canonical: https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.html - Also written: capitate stalked trichome, stalked glandular trichome, capitate-stalked, stalked trichome, mushroom trichome - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The capitate-stalked trichome is the [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) resin gland on mature female cannabis flowers. It has a multicellular stalk, often 150-500 µm long, topped by a globular head about 60-100 µm across. In the head, a disc of secretory cells pumps resin into a storage cavity under a waxy cuticle. Livingston et al. (2020) showed these stalked glands develop from sessile-like precursors as flowers mature, and produce more [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) than sessile glands. ## In practice These are the glands you inspect for [harvest timing](https://genetixbay.com/knowledge/glossary/harvest-window.md). Heads go from clear to cloudy as resin fills and changes, then some turn amber as they age and oxidise. Cloudy heads are often described as peak-full; amber means ageing. They are also the ones lost to rough handling. Trimming, bagging and warm, dry handling shear heads off their stalks. That is a big part of why buds should be handled cold and gently, and why trim method is a trade-off. Gland density varies widely by [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) and plant age (Punja et al. 2023). ## Don't confuse with - **Capitate-sessile trichome**: a smaller head with no tall stalk, sitting flat on the surface. - **Bulbous trichome**: the smallest glandular type. - **Cystolith trichome**: a non-glandular, claw-shaped hair. ## Related terms [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md), [Capitate-sessile trichome](https://genetixbay.com/knowledge/glossary/capitate-sessile-trichome.md), [Bract](https://genetixbay.com/knowledge/glossary/bract.md), [Trichome ripeness](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md) ## Read more - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) ## Sources 1. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 2. Punja ZK, Sutton DB, Kim T. 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 --- # Carbon filter > A carbon filter scrubs odour from exhaust air by passing it through activated carbon, which adsorbs aroma compounds such as terpenes. - Canonical: https://genetixbay.com/knowledge/glossary/carbon-filter.html - Also written: charcoal filter, activated carbon filter, odour filter, odor filter, scrubber, can filter - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A carbon filter is a cylinder or panel packed with activated carbon, mounted on the [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) line so all air leaving the grow space passes through it. Activated carbon has an enormous internal surface area that adsorbs volatile organic compounds, including the [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) compounds that make cannabis smell. It does not remove humidity or heat. ## In practice Typical setup: filter in the tent, fan pulling air through the filter, then ducting outside. Match the filter's rated airflow to the fan's real [CFM](https://genetixbay.com/knowledge/glossary/cfm.md). Bed depth matters; deeper carbon beds give air more contact time and last longer. Filters saturate over time. Lifespan is roughly 12–24 months in normal use. High humidity, above about 70% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), shortens it because water occupies adsorption sites, and dust clogs it, so keep the pre-filter sleeve clean and replace it when grey. When odour starts leaking with [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md) confirmed, the carbon is spent. Some growers lose aroma control in late flower when terpene output peaks. Lower fan speed slightly to increase contact time rather than running full blast. ## Don't confuse with - **Ozone generators**: oxidise odours; harmful to people and plants at effective concentrations. - **HEPA filter**: removes particles, not odour. ## Related terms [Exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md), [Negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md), [CFM](https://genetixbay.com/knowledge/glossary/cfm.md), [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) ## Read more - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) --- # Carbonate hardness > Carbonate hardness (KH) is the bicarbonate and carbonate content of water, often given in German degrees (dKH); in practice it is a measure of alkalinity. - Canonical: https://genetixbay.com/knowledge/glossary/carbonate-hardness.html - Also written: KH, dKH, carbonate hardness (KH), temporary hardness, German degrees KH - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Carbonate hardness (KH, from the German *Karbonathärte*) measures the bicarbonate and carbonate in water. Despite the name, it is really a measure of [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), not of calcium or magnesium. It is also called temporary hardness because boiling drives off [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) and precipitates part of it as limescale. Aquarium test kits report it in degrees of carbonate hardness (dKH). ## In practice KH is what makes [hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) resist [pH Down](https://genetixbay.com/knowledge/glossary/ph-down.md). A grower with water at 8 dKH (about 143 mg/L as CaCO3) needs considerably more acid per litre than one at 2 dKH (about 36 mg/L), even if both waters start at [pH](https://genetixbay.com/knowledge/glossary/ph.md) 7.8. An aquarium KH drop-test kit is a cheap way to know your water. Above about 6 dKH, plan for regular acid dosing or blending with [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md). ## Units and formula - 1 dKH = 17.86 mg/L as CaCO3 ≈ 0.357 meq/L - 1 mg/L as CaCO3 = 0.056 dKH ## Don't confuse with - **General hardness (GH)**: calcium and magnesium content. - **Alkalinity**: KH is a way of expressing it. - **Potassium (K)**: the "K" in KH is German, not the element. ## Related terms [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [General hardness](https://genetixbay.com/knowledge/glossary/general-hardness.md), [Buffering capacity](https://genetixbay.com/knowledge/glossary/buffering-capacity.md), [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Caryophyllene oxide > Caryophyllene oxide is the oxidation product of beta-caryophyllene, a less aromatic sesquiterpene epoxide that tends to increase as cannabis ages in air. - Canonical: https://genetixbay.com/knowledge/glossary/caryophyllene-oxide.html - Also written: beta-caryophyllene oxide, β-caryophyllene oxide, caryophyllene epoxide, BCPO - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Caryophyllene oxide is an epoxide formed when [beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md) reacts with oxygen. The plant makes some, but much of what a lab finds in dried flower forms during drying and storage. Its smell is faint, woody and dry compared with the spicy parent compound. ## In practice Read it as an age and handling marker. Fresh, well-stored flower usually shows little caryophyllene oxide relative to beta-caryophyllene; flower that has been dried warm, stored in air or kept for a long time tends to show a higher ratio. Comparing the oxide-to-parent ratio between two COAs of the same cultivar is a quick, rough way to see which sample was handled more gently, provided both labs report both compounds. ## Don't confuse with - **Beta-caryophyllene**: the aromatic parent compound. - **Humulene epoxides**: related oxidation products of [humulene](https://genetixbay.com/knowledge/glossary/humulene.md). - **CBN**: also an age marker, but from [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) oxidation. ## Related terms [Beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md), [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) ## Read more - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # Case hardening > A drying fault where a bud's surface dries too fast and seals, leaving the core wet; buds feel dry, then rehydrate and risk mould in the jar. - Canonical: https://genetixbay.com/knowledge/glossary/case-hardening.html - Also written: case hardened, case-hardened buds, crispy outside wet inside, outer dry inner wet - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Case hardening is a term borrowed from timber and food drying. When the surface of a bud loses water faster than the core can supply it, the outer tissue dries and tightens into a shell that slows further drying. The bud feels crisp outside while the centre is still moist. ## In practice Symptoms: buds that feel jar-ready after only a few days, then go spongy and damp once sealed; jars whose [equilibrated RH](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md) climbs far above 65% overnight; dense [colas](https://genetixbay.com/knowledge/glossary/cola.md) with a damp core when cut open. Causes: warm, dry [drying rooms](https://genetixbay.com/knowledge/glossary/drying-room.md); fans blowing directly on buds; wet-trimmed small buds on racks in low humidity; dry periods of only 3-5 days. [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md): slow the dry, about 15-21 °C (60-70 °F) and 55-62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), with gentle indirect airflow, aiming for roughly 7-14 days. Leave more leaf and stem on ([dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md), [whole-plant hang](https://genetixbay.com/knowledge/glossary/whole-plant-hang.md)) in dry climates. If it happens: jar the buds and burp often, or spread them on a tray in a humid room for short sessions, letting the moisture even out. Check closely for mould. ## Don't confuse with - **Over-drying**: dry all the way through. - **Sweat**: moisture moving outward in a jar, part of a normal cure. - **Mould**: a possible consequence of case hardening, not the same thing. ## Related terms [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md), [60/60 rule](https://genetixbay.com/knowledge/glossary/60-60-rule.md), [Over-drying](https://genetixbay.com/knowledge/glossary/over-drying.md), [Sweat](https://genetixbay.com/knowledge/glossary/sweat.md), [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 --- # Caterpillar > The larval stage of moths and butterflies (order Lepidoptera); on cannabis, leaf-chewers, stem borers and bud-boring species whose frass seeds bud rot. - Canonical: https://genetixbay.com/knowledge/glossary/caterpillar.html - Also written: caterpillars, worms, larvae, European corn borer, Ostrinia nubilalis, hemp borer - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A caterpillar is the larva of a moth or butterfly (order Lepidoptera). Several groups attack cannabis: leaf chewers such as loopers and armyworms, stem borers such as the European corn borer (*Ostrinia nubilalis*) and the [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) borer (*Grapholita delineata*), and bud feeders such as the [corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md) (*Helicoverpa zea*). Outdoor and greenhouse crops carry most of the risk; sealed indoor rooms rarely see them. ## In practice Signs are ragged holes in leaves, wilting branch tips above a borer's entry hole, and above all [frass](https://genetixbay.com/knowledge/glossary/frass.md) (droppings) inside buds. Wet frass and chewed tissue give *Botrytis* an easy entry, so one caterpillar can rot a whole [cola](https://genetixbay.com/knowledge/glossary/cola.md). Growers scout for moths at dusk, eggs on leaf surfaces and fresh frass. *[Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md)* products, which must be eaten to work, are the standard biological option and work best on young larvae before they bore into buds. Netting and [pheromone traps](https://genetixbay.com/knowledge/glossary/pheromone-trap.md) help outdoors. Check what is registered for cannabis locally. ## Don't confuse with - **Fungus gnat larvae**: tiny clear maggots in the medium, not on the plant. - **Cutworms**: a caterpillar group that hides in soil by day and severs [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) at the base. - **Slug damage**: holes plus slime trails, usually low on the plant. ## Related terms [Corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md), [Cutworm](https://genetixbay.com/knowledge/glossary/cutworm.md), [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md), [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md) ## Read more - [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Sources 1. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 2. Cranshaw, W. Hemp pests (CSU, 2020). https://webdoc.agsci.colostate.edu/bspm/InsectInformation/Talks2020/HempPests.pdf --- # Cation exchange capacity > Cation exchange capacity (CEC) is a medium's ability to hold positively charged nutrients such as calcium, magnesium and potassium on its surfaces and release them later. - Canonical: https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.html - Also written: CEC, cation exchange, exchange capacity, cation-exchange capacity - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cation exchange capacity is the total amount of exchangeable positive ions (cations) that a medium can hold on negatively charged sites on clay, organic matter and organic fibres. Held cations, such as Ca²⁺, Mg²⁺, K⁺, NH₄⁺ and Na⁺, are not washed straight out; they swap with others in the soil solution, giving a nutrient reserve and buffering against sudden change. ## In practice High-CEC media (clay soils, compost-rich soil, peat, [vermiculite](https://genetixbay.com/knowledge/glossary/vermiculite.md)) are forgiving: they hold nutrients between feeds and resist [pH](https://genetixbay.com/knowledge/glossary/ph.md) swings. Low-CEC media ([rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md), sand) hold almost nothing, so the plant sees exactly what is in the solution. [Coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) sits in between and has a characteristic preference: its sites load with potassium and [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) during processing and tend to grab calcium and magnesium from feed, which is why coco is buffered with calcium before use. ## Units and formula CEC is measured in centimoles of charge per kilogram (cmol(+)/kg), equivalent to milliequivalents per 100 g (meq/100 g). Sandy soils are often under 10; clay- and humus-rich soils 20-40 or more. ## Don't confuse with - **Buffering (pH)**: resistance to pH change; related but not the same quantity. - **EC**: dissolved salts in solution; CEC is nutrients held on solids. ## Related terms [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [Buffering capacity](https://genetixbay.com/knowledge/glossary/buffering-capacity.md), [Peat](https://genetixbay.com/knowledge/glossary/peat.md), [Soil](https://genetixbay.com/knowledge/glossary/soil.md), [Vermiculite](https://genetixbay.com/knowledge/glossary/vermiculite.md) ## Read more - [Buffering coco coir: why it matters and how to do it](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md) - [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) ## Sources 1. Brady NC, Weil RR, 2017. The Nature and Properties of Soils, 15th ed. Pearson. 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # CBC > CBC (cannabichromene) is a minor neutral cannabinoid formed when CBCA decarboxylates; it is usually present at well under 1% w/w in mature drug-type flower. - Canonical: https://genetixbay.com/knowledge/glossary/cbc.html - Also written: cannabichromene, neutral CBC - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CBC, cannabichromene, is the neutral form of [CBCA](https://genetixbay.com/knowledge/glossary/cbca.md), one of the three main products the plant can make from [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md). It is a minor [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) in nearly all modern drug-type and hemp-type material, though some reports find relatively higher CBCA in young plants and in certain lines. Light exposure can slowly convert CBC into [CBL](https://genetixbay.com/knowledge/glossary/cbl.md) during storage. ## In practice Many potency panels report CBC or CBCA alongside the main cannabinoids. A reading of 0.1-0.5% w/w is typical for flower. It counts toward [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) but rarely changes a plant's classification. GenetixBay makes no claims about CBC's effects; human evidence is thin. ## Don't confuse with - **CBCA**: the acid form the plant makes. - **CBN**: a [THC](https://genetixbay.com/knowledge/glossary/thc.md) oxidation product with a similar abbreviation. - **CBL**: a light-induced breakdown product of CBC. ## Related terms [CBCA](https://genetixbay.com/knowledge/glossary/cbca.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [CBL](https://genetixbay.com/knowledge/glossary/cbl.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md) ## Sources 1. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. 2. ElSohly MA, Slade D. 2005. Chemical constituents of marijuana: the complex mixture of natural cannabinoids. Life Sciences 78(5):539-548. --- # CBCA > CBCA (cannabichromenic acid) is the acid cannabinoid that CBCA synthase makes from CBGA; it decarboxylates to CBC and is usually a minor component of the profile. - Canonical: https://genetixbay.com/knowledge/glossary/cbca.html - Also written: CBC-A, cannabichromenic acid - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CBCA, cannabichromenic acid, is the third major product of the [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) branch point, alongside [THCA](https://genetixbay.com/knowledge/glossary/thca.md) and [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md). A dedicated oxidocyclase, CBCA synthase, converts CBGA to CBCA. In most plants this enzyme loses the competition for CBGA, so CBCA stays at low levels in mature flower. Heat or time [decarboxylates](https://genetixbay.com/knowledge/glossary/decarboxylation.md) it to [CBC](https://genetixbay.com/knowledge/glossary/cbc.md). ## In practice On a full [COA](https://genetixbay.com/knowledge/glossary/coa.md), CBCA is typically a fraction of a percent of flower weight. Breeders interested in unusual chemotypes look for it, but there are few CBCA-dominant lines. Because [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) can itself produce small amounts of CBCA as a side product, some CBCA appears in THC-type plants even without a highly active CBCA synthase. ## Units and formula Total CBC ≈ CBC + [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) × CBCA (CBCA and THCA are isomers, so the factor is the same). ## Don't confuse with - **CBC**: the neutral form. - **CBGA**: the precursor. - **CBDA**: an isomer made by a different synthase. ## Related terms [CBC](https://genetixbay.com/knowledge/glossary/cbc.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md), [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), [Acid vs neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md) ## Sources 1. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004. 2. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. --- # CBD > CBD (cannabidiol) is a non-intoxicating neutral cannabinoid formed when CBDA decarboxylates; hemp-type and CBD-dominant cannabis make it mainly as CBDA in their trichomes. - Canonical: https://genetixbay.com/knowledge/glossary/cbd.html - Also written: cannabidiol, C.B.D., neutral CBD - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CBD, cannabidiol, is the neutral [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) formed when [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md) loses its carboxyl group. It does not produce the intoxication associated with [THC](https://genetixbay.com/knowledge/glossary/thc.md). Like THC, it barely exists in the living plant; the plant makes CBDA through the enzyme [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), and the conversion to CBD happens with heat and time. ## In practice Growers classify plants by their THC:CBD balance: THC-dominant, balanced (roughly 1:1) or CBD-dominant. A CBD-dominant flower [COA](https://genetixbay.com/knowledge/glossary/coa.md) might show CBDA at 12% w/w, CBD at 0.5% w/w and total THC under 0.5% w/w. That ratio is set mainly by genetics at the synthase locus, so it is fixed for a given plant and reliable across clones. GenetixBay makes no health or therapeutic claims about CBD. Effects are reported, not promised. ## Units and formula [Total CBD](https://genetixbay.com/knowledge/glossary/total-cbd.md) = CBD + [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) × CBDA, in % w/w. ## Don't confuse with - **CBDA**: the acid form the plant actually makes. - **CBN**: an oxidation product of THC, not related to CBD despite the similar name. - **Hemp**: a legal category based on THC, not a chemical definition of "CBD plant". ## Related terms [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md), [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [Total CBD](https://genetixbay.com/knowledge/glossary/total-cbd.md), [THC](https://genetixbay.com/knowledge/glossary/thc.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. Taura F, Sirikantaramas S, Shoyama Y, et al. 2007. Cannabidiolic-acid synthase, the chemotype-determining enzyme in the fiber-type Cannabis sativa. FEBS Letters 581(16):2929-2934. 2. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. --- # CBDA > CBDA (cannabidiolic acid) is the acid cannabinoid made by CBDA synthase from CBGA; it dominates hemp-type and CBD-type cannabis and decarboxylates to CBD. - Canonical: https://genetixbay.com/knowledge/glossary/cbda.html - Also written: CBD-A, cannabidiolic acid - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CBDA, cannabidiolic acid, is the form in which the plant stores [CBD](https://genetixbay.com/knowledge/glossary/cbd.md). [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) cyclises [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) into CBDA in the [trichome head](https://genetixbay.com/knowledge/glossary/trichome-heads.md), competing with [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) for the same CBGA supply. [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md) by heat or time turns CBDA into CBD. ## In practice Plants with two functional CBDA synthase alleles and no functional THCA synthase make mostly CBDA; plants with one of each tend toward a balanced 1:1 profile. A breeder crossing a THCA-type with a CBDA-type parent typically sees a mix of THC-type, balanced and CBD-type offspring in the F2, roughly following simple Mendelian ratios at that locus, though real data are messier. Feeding, light or stress do not switch a plant from [THCA](https://genetixbay.com/knowledge/glossary/thca.md) to CBDA. ## Units and formula 1 g of CBDA can yield at most [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) g of CBD. Total CBD = CBD + 0.877 × CBDA. ## Don't confuse with - **CBD**: the neutral product of decarboxylation. - **CBGA**: the shared precursor of both CBDA and THCA. - **THCA**: the alternative product of the same precursor, from a different enzyme. ## Related terms [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [Total CBD](https://genetixbay.com/knowledge/glossary/total-cbd.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. Taura F, Sirikantaramas S, Shoyama Y, et al. 2007. Cannabidiolic-acid synthase, the chemotype-determining enzyme in the fiber-type Cannabis sativa. FEBS Letters 581(16):2929-2934. 2. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. --- # CBDA synthase > CBDA synthase is the trichome enzyme that converts CBGA into CBDA; it competes with THCA synthase, and its alleles largely decide whether a plant is CBD-dominant. - Canonical: https://genetixbay.com/knowledge/glossary/cbda-synthase.html - Also written: CBDAS, CBDA synthase gene, cannabidiolic acid synthase, CBD synthase - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CBDA synthase (CBDAS) is the oxidocyclase enzyme that converts [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) into [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md). Taura and colleagues characterised it in 2007 and described it as the chemotype-determining enzyme in fibre-type cannabis. It sits in the same genomic region as [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) and competes for the same CBGA pool. ## In practice Hemp-type and CBD-type plants carry functional CBDAS and typically non-functional or absent THCAS. Crossing a THC-type plant with a CBD-type plant produces [F1](https://genetixbay.com/knowledge/glossary/f1.md) offspring that are usually balanced (roughly 1:1), and an F2 that segregates into THC-type, balanced and CBD-type plants. Real ratios drift from textbook Mendelian numbers because the synthase region contains several linked gene copies and some partially active alleles. Even CBD-dominant plants produce a little [THCA](https://genetixbay.com/knowledge/glossary/thca.md), because CBDAS isn't perfectly specific; that matters for anyone growing [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) under a [THC](https://genetixbay.com/knowledge/glossary/thc.md) limit. ## Don't confuse with - **THCA synthase**: the competing enzyme. - **CBD**: the neutral form, made later by decarboxylation. - **CBGA**: the substrate, not the enzyme. ## Related terms [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) - [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md) ## Sources 1. Taura F, Sirikantaramas S, Shoyama Y, et al. 2007. Cannabidiolic-acid synthase, the chemotype-determining enzyme in the fiber-type Cannabis sativa. FEBS Letters 581(16):2929-2934. 2. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004. --- # CBG > CBG (cannabigerol) is the neutral, decarboxylated form of CBGA, the cannabinoid precursor; most plants convert nearly all of it onward, but some cultivars are bred to accumulate it. - Canonical: https://genetixbay.com/knowledge/glossary/cbg.html - Also written: cannabigerol, neutral CBG - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CBG, cannabigerol, is the neutral [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) formed when [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) decarboxylates. In most plants it is a minor compound, typically under 1% w/w, because the synthases convert CBGA into [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md) or CBCA as fast as it is made. Plants that lack functional synthase activity can't do that conversion, so CBGA builds up instead. ## In practice "CBG cultivars" are plants bred for non-functional THCA and CBDA synthases, which leaves CBGA as the dominant cannabinoid; COAs from such plants can show CBGA well into double figures with near-zero THCA. In ordinary THC-type flower, a modest CBGA reading is normal and is sometimes higher in earlier-harvested material, since conversion is still underway. GenetixBay makes no claims about CBG's effects. ## Units and formula Total CBG ≈ CBG + 0.878 × CBGA (the factor differs slightly from [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) because CBGA has a slightly higher molecular weight). ## Don't confuse with - **CBGA**: the acid form and the actual biosynthetic precursor. - **CBD**: a different neutral cannabinoid, from CBDA. - **CBN**: a [THC](https://genetixbay.com/knowledge/glossary/thc.md) breakdown product. ## Related terms [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md), [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. 2. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004. --- # CBGA > CBGA (cannabigerolic acid) is the precursor cannabinoid that the plant converts into THCA, CBDA or CBCA, formed by joining olivetolic acid to geranyl pyrophosphate. - Canonical: https://genetixbay.com/knowledge/glossary/cbga.html - Also written: CBG-A, cannabigerolic acid, mother cannabinoid, precursor cannabinoid - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CBGA, cannabigerolic acid, is the branch point of [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) biosynthesis. A prenyltransferase enzyme attaches a ten-carbon geranyl group (from geranyl pyrophosphate) to olivetolic acid, producing CBGA in the [trichome head](https://genetixbay.com/knowledge/glossary/trichome-heads.md). Three oxidocyclase enzymes then compete for it: [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) makes [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) makes CBDA and CBCA synthase makes CBCA. Whatever isn't converted stays as CBGA. ## In practice That competition is why the [THC:CBD ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md) is mostly a genetic trait. A plant's synthase alleles decide where the CBGA goes. Growers sometimes call CBGA the "mother cannabinoid", a convenient image but chemically it is simply the shared precursor. [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md) turns any remaining CBGA into [CBG](https://genetixbay.com/knowledge/glossary/cbg.md). ## Don't confuse with - **CBG**: the neutral form, after decarboxylation. - **Olivetolic acid**: one of CBGA's two building blocks, not a cannabinoid itself. - **CBGVA**: the propyl (C3) analogue, made from divarinic acid, which leads to THCVA and CBDVA. ## Related terms [CBG](https://genetixbay.com/knowledge/glossary/cbg.md), [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md), [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), [Olivetolic acid](https://genetixbay.com/knowledge/glossary/olivetolic-acid.md), [Geranyl pyrophosphate](https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004. 2. Sirikantaramas S, Morimoto S, Shoyama Y, et al. 2004. The gene controlling marijuana psychoactivity: molecular cloning and heterologous expression of Δ1-tetrahydrocannabinolic acid synthase from Cannabis sativa L. Journal of Biological Chemistry 279(38):39767-39774. 3. Taura F, Sirikantaramas S, Shoyama Y, et al. 2007. Cannabidiolic-acid synthase, the chemotype-determining enzyme in the fiber-type Cannabis sativa. FEBS Letters 581(16):2929-2934. --- # CBL > CBL (cannabicyclol) is a minor cannabinoid formed when CBC is exposed to light; it is a degradation product rather than something the plant makes by enzyme. - Canonical: https://genetixbay.com/knowledge/glossary/cbl.html - Also written: cannabicyclol, CBLA, cannabicyclolic acid - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CBL, cannabicyclol, is a non-enzymatic degradation product. UV and visible light drive an internal ring-closing reaction in [CBC](https://genetixbay.com/knowledge/glossary/cbc.md) (or [CBCA](https://genetixbay.com/knowledge/glossary/cbca.md), giving CBLA), converting it to CBL. It is usually found only at trace levels and mainly in aged or light-exposed material. It was first described in the 1960s and its structure was revised shortly after. ## In practice Most potency panels don't report CBL at all. When it does appear, it tells you about storage history, much as [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) does: material kept in clear containers or bright conditions. For growers, the practical point is the same as for every [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md): store [cured](https://genetixbay.com/knowledge/glossary/curing.md) flower cool, dark and with minimal air. No meaningful effects are reported for CBL at the levels found in flower. ## Don't confuse with - **CBC**: the parent compound that light converts into CBL. - **CBN**: also a degradation product, but from [THC](https://genetixbay.com/knowledge/glossary/thc.md) by oxidation. - **CBG**: a precursor-derived cannabinoid with a similar abbreviation. ## Related terms [CBC](https://genetixbay.com/knowledge/glossary/cbc.md), [CBCA](https://genetixbay.com/knowledge/glossary/cbca.md), [CBN](https://genetixbay.com/knowledge/glossary/cbn.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) ## Read more - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) ## Sources 1. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. 2. ElSohly MA, Slade D. 2005. Chemical constituents of marijuana: the complex mixture of natural cannabinoids. Life Sciences 78(5):539-548. --- # CBN > CBN (cannabinol) is a cannabinoid formed mainly when THC or THCA oxidises after harvest, so high CBN readings usually signal age, heat, light or air exposure, not plant ripeness. - Canonical: https://genetixbay.com/knowledge/glossary/cbn.html - Also written: cannabinol, CBNA, cannabinolic acid - Glossary category: Cannabinoids and terpenes · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CBN, cannabinol, is a [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) that the plant does not make by enzyme. It forms mainly when [THC](https://genetixbay.com/knowledge/glossary/thc.md) (or [THCA](https://genetixbay.com/knowledge/glossary/thca.md), which yields CBNA) oxidises and aromatises, a reaction driven by oxygen, heat, light and time. That is why CBN is the classic marker of old or poorly stored cannabis and of old [hashish](https://genetixbay.com/knowledge/glossary/hashish.md). ## In practice Fresh, well-cured flower usually shows CBN under 0.2% w/w or not detected. Material stored warm, in light or with lots of air for months shows rising CBN and falling THC. A high CBN line on a [COA](https://genetixbay.com/knowledge/glossary/coa.md) is a storage story, not a cultivar trait. ## Don't confuse with - **CBD**: unrelated in origin; CBN comes from THC. - **Amber trichomes**: a visual change in the head, not a measurement of CBN. ## Myth check House position: the idea that letting [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) go amber on the plant fills the bud with CBN and produces "couch-lock" is unsupported. CBN is mainly a post-harvest oxidation product; amber colour on the plant does not mean meaningful CBN. [Harvest timing](https://genetixbay.com/knowledge/glossary/harvest-window.md) is a matter of preference: a few clear, mostly cloudy, some amber. See [trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [THC](https://genetixbay.com/knowledge/glossary/thc.md), [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [CBL](https://genetixbay.com/knowledge/glossary/cbl.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) ## Read more - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) ## Sources 1. ElSohly MA, Slade D. 2005. Chemical constituents of marijuana: the complex mixture of natural cannabinoids. Life Sciences 78(5):539-548. 2. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. --- # Ceramic sensor watering > Ceramic sensor watering uses a porous ceramic cone in the medium that opens a small valve when the soil dries, feeding water from a gravity-fed reservoir on demand. - Canonical: https://genetixbay.com/knowledge/glossary/ceramic-sensor-watering.html - Also written: ceramic probe watering, ceramic cone watering, tensiometer valve watering, gravity-fed auto watering, auto-watering spikes - Glossary category: Systems and media · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Ceramic sensor watering is a generic class of passive auto-watering device. A porous ceramic cone filled with water is pushed into the medium. As the medium dries, it pulls water out through the ceramic, creating suction that opens a small valve on a supply line from a raised reservoir. When the medium is moist again, suction drops and the valve closes. It works like a tensiometer controlling a tap. ## In practice These devices are popular in living-soil and organic grows, where they keep the soil evenly moist without pumps or timers. Set the sensitivity and placement so the medium stays moist but not saturated; most kits have an adjustment for this. Use plain water or very light teas rather than strong mineral solutions, which can clog the ceramic and valve. Clean ceramics between runs. The trade-off: they hold soil at one [moisture level](https://genetixbay.com/knowledge/glossary/moisture-content.md), so there is no real [wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md); that suits [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) better than [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) or crop steering. ## Don't confuse with - **Drip irrigation on a timer**: time-based rather than moisture-based. - **Self-watering pot**: a wick or reservoir in the pot base. ## Related terms [Bottom watering](https://genetixbay.com/knowledge/glossary/bottom-watering.md), [Wick system](https://genetixbay.com/knowledge/glossary/wick-system.md), [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), [Wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md) ## Read more - [Bottom-watering, soak trays and wick (self-watering) systems](https://genetixbay.com/knowledge/systems/bottom-watering-wick.md) - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) --- # CF > CF (conductivity factor) is an EC scale used mainly in Australia, New Zealand and the UK, where 1 CF equals 0.1 mS/cm (100 µS/cm). - Canonical: https://genetixbay.com/knowledge/glossary/cf.html - Also written: conductivity factor, CF units, CF reading, CF scale - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CF (conductivity factor) is a unit of [electrical conductivity](https://genetixbay.com/knowledge/glossary/ec.md) common in Australian, New Zealand and some UK hydroponic literature and meters. It is EC scaled by ten to avoid decimals: 1 CF = 0.1 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) = 100 [µS/cm](https://genetixbay.com/knowledge/glossary/us-cm.md). So a solution of 1.6 mS/cm is CF 16. ## In practice CF is a straight multiplication, with no conversion-factor ambiguity, unlike ppm. If a nutrient chart from Australia says "CF 12–16 in veg", that is EC 1.2–1.6 mS/cm. Some older Australian charts quote even higher flower values (CF 20–25); treat those as upper limits, since controlled cannabis trials do not show yield gains from pushing nutrient concentration hard. When sharing numbers on GenetixBay, use mS/cm so everyone reads the same scale. ## Units and formula - CF = EC (mS/cm) × 10 - EC (mS/cm) = CF ÷ 10 - CF 10 ≈ 500 ppm ([500 scale](https://genetixbay.com/knowledge/glossary/ppm500.md)) ≈ 700 ppm ([700 scale](https://genetixbay.com/knowledge/glossary/ppm700.md)) ## Don't confuse with - **Conversion factor**: the multiplier that turns EC into ppm (0.5 or 0.7); despite similar words, it is a different thing from CF. - **ppm**: a calculated estimate that depends on meter scale. ## Related terms [EC](https://genetixbay.com/knowledge/glossary/ec.md), [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md), [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md) ## Read more - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) ## Sources 1. University of California Cooperative Extension, Ventura County. Salinity units and conversions (640 ppm = 1 dS/m). https://ucanr.edu/node/125832 --- # CFM > CFM (cubic feet per minute) is the volume of air a fan moves per minute; growers use it to size exhaust fans to their grow space volume. - Canonical: https://genetixbay.com/knowledge/glossary/cfm.html - Also written: cubic feet per minute, ft³/min, cfm rating, m³/h, airflow rating - Glossary category: Environment and light · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CFM (cubic feet per minute) is a volumetric airflow rate. Fan manufacturers quote it at zero static pressure, meaning free air with no ducting or filter, so real-world airflow in a grow setup is always lower. The metric equivalent is cubic metres per hour (m³/h). ## In practice Basic sizing: calculate the grow space volume, choose an exchange rate, then add for restrictions. Example: a 1.5 × 1.5 × 2 m (5 × 5 × 6.5 ft) tent is 4.5 m³, about 160 ft³. One exchange per minute needs 160 CFM. Add about 25% for a [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) and 10–20% for each long run or tight bend, giving a fan rated around 220–250 CFM. Run it on a controller at partial speed most of the time; headroom matters on hot days. Match the carbon filter's rated CFM to the fan. A filter too small for the fan restricts flow, lets air pass too fast to scrub odour, and saturates quickly. A slightly oversized filter is fine; it just costs more. ## Units and formula - 1 CFM = 1.699 m³/h - 1 m³/h = 0.589 CFM - Required CFM ≈ volume (ft³) × exchanges per minute × restriction factor (about 1.25–1.5) ## Don't confuse with - **Air speed (m/s or ft/min)**: how fast air moves at the leaf, not total volume. - **Static pressure**: the resistance the fan works against; it reduces actual CFM. ## Related terms [Exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md), [Carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md), [Negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md), [Airflow](https://genetixbay.com/knowledge/glossary/airflow.md) ## Read more - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) --- # Charas > Charas is hashish made by rubbing the resin off living cannabis flowers by hand and rolling it into balls or sticks, a traditional method of the Himalayan regions. - Canonical: https://genetixbay.com/knowledge/glossary/charas.html - Also written: hand-rubbed hash, hand rubbed hash, finger hash, rubbed hash, Himalayan charas - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Charas is the hand-rubbed form of [hashish](https://genetixbay.com/knowledge/glossary/hashish.md). Instead of drying and sieving the plant, the maker rubs living, resinous flower [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) between the palms so that sticky resin accumulates on the hands, then scrapes and rolls it into balls, sticks or small slabs. The method is traditional in the Himalayan foothills of India and Nepal and nearby regions. Clarke documented it in Nepal and in *Hashish!*. ## In practice Because it is collected from fresh plants, charas tends to be soft, dark and aromatic, and it often includes plant fragments and moisture, making quality highly variable. It is labour-intensive: a long day of rubbing [yields](https://genetixbay.com/knowledge/glossary/yield.md) a small amount per person. Collected from local [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) populations, charas reflects regional plant genetics and tradition, and it's one of the oldest living concentrate cultures. GenetixBay defines the product only. ## Don't confuse with - **Sieved hashish**: made from dried plants, not live ones. - **Temple ball**: a shaping and curing style, traditionally associated with Nepalese [hash](https://genetixbay.com/knowledge/glossary/hash.md). - **Live rosin**: also made from fresh material, but by ice water separation and pressing. ## Myth check House position: the landrace growers behind charas traditions deserve far more credit. See [landraces of the world](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md). ## Related terms [Hashish](https://genetixbay.com/knowledge/glossary/hashish.md), [Hash](https://genetixbay.com/knowledge/glossary/hash.md), [Temple ball](https://genetixbay.com/knowledge/glossary/temple-ball.md), [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md) ## Read more - [Landraces of the world: an overview](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) - [Old cannabis wasn't weak: the "so much stronger than 20 years ago" myth](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md) ## Sources 1. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Chelate > A chelate is a metal ion held by an organic molecule at several points, keeping micronutrients such as iron, zinc and manganese dissolved and available across a wider pH range. - Canonical: https://genetixbay.com/knowledge/glossary/chelate.html - Also written: chelated, chelation, chelating agent, chelated micronutrients, chelates - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A chelate is a complex in which an organic molecule, the chelating agent, grips a metal ion at two or more points, like a claw (the word comes from the Greek for claw). The grip protects the metal from reacting with hydroxide, [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) or carbonate and dropping out of solution. Iron, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md), zinc and copper are the metals most often chelated in fertilisers. ## In practice Without chelation, iron in particular precipitates within hours once [pH](https://genetixbay.com/knowledge/glossary/ph.md) rises above about 6. Synthetic chelates differ in stability: [EDTA](https://genetixbay.com/knowledge/glossary/edta.md) is fine for typical hydro pH, [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md) holds higher, and [EDDHA](https://genetixbay.com/knowledge/glossary/eddha.md) survives alkaline conditions. Natural compounds such as amino acids, humic and [fulvic acids](https://genetixbay.com/knowledge/glossary/fulvic-acid.md) and citrate also bind metals, but more loosely and less predictably. Labels list which elements are chelated and with what agent. ## Don't confuse with - **Complexing agents**: a broader class; not all complexes are true chelates. - **Biostimulant**: a marketing category; a chelate is a defined chemical form. - **Sequestered**: often used loosely on labels to mean chelated or complexed. ## Myth check "Chelated" on a label does not make a product better in itself. The chelate type has to match the root-zone pH. See [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md). ## Related terms [Iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md), [EDTA](https://genetixbay.com/knowledge/glossary/edta.md), [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md), [EDDHA](https://genetixbay.com/knowledge/glossary/eddha.md), [Amino acid chelate](https://genetixbay.com/knowledge/glossary/amino-acid-chelate.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) ## Read more - [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. HortScience. 2025. Iron chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA) in high-pH soilless media. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Chemotype > A chemotype is a plant's chemical phenotype, in cannabis usually its dominant cannabinoid class: THC-dominant (I), mixed (II), CBD-dominant (III), CBG-dominant (IV) or cannabinoid-free (V). - Canonical: https://genetixbay.com/knowledge/glossary/chemotype.html - Also written: chemotypes, chemical phenotype, cannabinoid chemotype, chemotype I, chemotype III - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A chemotype is the chemical phenotype of a plant. In cannabis research it normally means the [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) class, set largely by the [alleles](https://genetixbay.com/knowledge/glossary/allele.md) at the cannabinoid synthase locus. The usual scheme: chemotype I is THC-dominant, II is mixed [THC](https://genetixbay.com/knowledge/glossary/thc.md) and [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), III is CBD-dominant, IV is CBG-dominant, and V has almost no cannabinoids (de Meijer et al. 2003; de Meijer et al. 2009). ## In practice Chemotype is the first thing to fix in a medicinal or hemp line and the easiest to test early. Breeders can screen seedlings with a DNA marker for the synthase alleles (Toth et al. 2020) and keep only the wanted chemotype before flowering. A THC-dominant × CBD-dominant cross gives uniform type II [F1s](https://genetixbay.com/knowledge/glossary/f1.md); their [F2s](https://genetixbay.com/knowledge/glossary/f2.md) segregate back into I, II and III. Some writers extend "chemotype" to [terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) ("a limonene chemotype"). That use is looser and less standardised; terpene profiles are controlled by many genes and shift with growing conditions. ## Don't confuse with - **Chemovar**: a named cultivar defined by its chemistry. A chemotype is a class; a [chemovar](https://genetixbay.com/knowledge/glossary/chemovar.md) is a variety. - **Potency**: chemotype is the type of cannabinoid, not how much. Two type I plants can test 12% or 25%. - **Indica or sativa**: these labels do not predict chemotype (Smith et al. 2022). ## Related terms [Chemovar](https://genetixbay.com/knowledge/glossary/chemovar.md), [Codominant](https://genetixbay.com/knowledge/glossary/codominant.md), [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 2. de Meijer EPM, Hammond KM, Sutton A. 2009. The inheritance of chemical phenotype in Cannabis sativa L. (IV): cannabinoid-free plants. Euphytica 168:95-112. https://doi.org/10.1007/s10681-009-9894-7 3. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 --- # Chemotype ratio > The chemotype ratio is the balance of a plant's main cannabinoids, usually THC to CBD, classing plants as type I (THC-dominant), II (mixed), III (CBD-dominant), IV (CBG) or V (near-zero). - Canonical: https://genetixbay.com/knowledge/glossary/chemotype-ratio.html - Also written: THC:CBD ratio, THC to CBD ratio, cannabinoid ratio, chemotype I II III, type I/II/III, CBD:THC ratio - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The chemotype ratio describes how a plant's [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) output is split, almost always expressed as total [THC](https://genetixbay.com/knowledge/glossary/thc.md) to total [CBD](https://genetixbay.com/knowledge/glossary/cbd.md). Researchers use five broad classes: type I, THC-dominant; type II, mixed THC and CBD; type III, CBD-dominant; type IV, CBG-dominant; type V, almost no cannabinoids. The ratio is set mainly by the synthase genes, so it is highly heritable and stable within a clone. ## In practice A COA showing total THC 21% and total CBD 0.05% is type I (ratio over 100:1). One showing 7% THC and 9% CBD is type II (about 1:1.3). Breeders crossing types I and III expect type II [F1s](https://genetixbay.com/knowledge/glossary/f1.md) and a [segregating](https://genetixbay.com/knowledge/glossary/segregation.md) [F2](https://genetixbay.com/knowledge/glossary/f2.md). Seedling genotyping can predict the class early; the absolute percentage still depends on many other genes and the grow. ## Don't confuse with - **[Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md)** (genetics term): the overall chemical phenotype or class; the ratio is how it's measured. - **Terpene profile**: aroma chemistry, separate from the cannabinoid ratio. - **Potency**: total amount, independent of the ratio. ## Myth check Indica/sativa labels don't predict the chemotype ratio or [terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) (house position, supported by Smith et al. 2022 and others). See [chemotype inheritance](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md). ## Related terms [Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md), [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md), [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. Hillig KW, Mahlberg PG. 2004. A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae). American Journal of Botany 91(6):966-975. https://doi.org/10.3732/ajb.91.6.966 2. Hazekamp A, Fischedick JT. 2012. Cannabis: from cultivar to chemovar. Drug Testing and Analysis 4(7-8):660-667. https://doi.org/10.1002/dta.407 3. Lynch RC, Vergara D, Tittes S, et al. 2016. Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences 35(5-6):349-363. https://doi.org/10.1080/07352689.2016.1265363 --- # Chemovar > A chemovar is a cultivar defined and named by its chemical profile, chiefly cannabinoids and terpenes, rather than by its appearance or a market strain name. - Canonical: https://genetixbay.com/knowledge/glossary/chemovar.html - Also written: chemovars, chemical variety, chemical cultivar - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A chemovar (chemical variety) is a cultivar characterised by its chemistry: its [cannabinoid ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md) and its [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md). The term is used by researchers and some regulators who want a label that means something measurable, instead of a market strain name. ## In practice The push for chemovars comes from the evidence that strain names and indica/sativa labels are poor guides. Large datasets of lab results show that commercial cannabis falls into a few chemical clusters, and that the label on the jar often does not match its cluster (Smith et al. 2022). Describing a product as "THC-dominant, high [myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md) and [beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md)" tells a buyer more than a name. For a breeder, describing a selection as a chemovar means reporting a lab profile with the clone: [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md), major terpenes and their percentages, grown and tested more than once. Chemistry shifts with environment, [harvest timing](https://genetixbay.com/knowledge/glossary/harvest-window.md) and drying, so one test is a snapshot. ## Don't confuse with - **Chemotype**: a broad class (I to V); a chemovar is a specific cultivar within that class. - **Strain**: a name that may or may not match the chemistry. - **Cultivar**: the formal term for a cultivated variety selected for any trait; a chemovar is one defined by chemistry. ## Myth check Indica/sativa does not predict chemistry or effect; see [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md). ## Related terms [Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md), [Cultivar](https://genetixbay.com/knowledge/glossary/cultivar.md), [Strain](https://genetixbay.com/knowledge/glossary/strain.md), [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) - [Why strain names are unreliable: what genetic studies show](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Watts S, McElroy M, Migicovsky Z, Maassen H, van Velzen R, Myles S. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y --- # Child-resistant packaging > Child-resistant packaging is a container that most young children cannot open in a standard test while most adults can, required for cannabis in many markets. - Canonical: https://genetixbay.com/knowledge/glossary/child-resistant-packaging.html - Also written: CR packaging, child-proof packaging, child resistant, CR container, child-resistant - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Child-resistant (CR) packaging is a container designed and tested so that most young children cannot open it within a set time, while most adults, including older adults, can. Testing follows formal protocols, for example the US poison [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) packaging test method (16 CFR 1700.20) or ISO 8317 for reclosable packages. ## In practice Many cannabis regulations require CR packaging for retail products, sometimes for the outer package and sometimes for the immediate container, along with opaque or plain packaging rules. For home growers, the same logic applies at home: store jars of flower and any edibles locked or out of reach and clearly labelled, since accidental ingestion by children is the main documented harm in this area. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Tamper-evident**: shows if a package was opened; not the same as child-resistant. - **Airtight**: about freshness; a [mason jar](https://genetixbay.com/knowledge/glossary/curing-jar.md) is airtight but not child-resistant. ## Related terms [Labelling requirements](https://genetixbay.com/knowledge/glossary/labelling-requirements.md), [Licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md), [Home grow](https://genetixbay.com/knowledge/glossary/home-grow.md) --- # Chiller > A chiller is a refrigeration unit that cools hydroponic nutrient solution, keeping it around 18-21 °C so it holds more oxygen and root pathogens are discouraged. - Canonical: https://genetixbay.com/knowledge/glossary/chiller.html - Also written: water chiller, reservoir chiller, aquarium chiller, res chiller, inline chiller - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A chiller is a compressor-based refrigeration unit, like a small air conditioner for water, that pulls heat out of a reservoir. Solution is pumped through the chiller's heat exchanger and back, or a coil is placed in the tank. Units are rated by cooling capacity (watts, BTU/h or horsepower fractions) and by the volume they can handle. ## In practice Chillers matter most in [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md) and [aeroponics](https://genetixbay.com/knowledge/glossary/aeroponics.md), where roots live in solution. Cool water holds more dissolved oxygen, and warm solution above roughly 22-24 °C (72-75 °F) is strongly linked to *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)* [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md). Size the chiller for the room's heat, not just the reservoir volume: lights, pumps and warm air all add heat. Place the unit where it can [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) its own heat outside the grow, and insulate lines and buckets. Frozen water bottles are a short-term emergency fix, not a substitute. ## Don't confuse with - **Air conditioner**: cools air; may help, but solution can still warm from pumps and lights. - **Heat exchanger coil**: one part of a chiller setup. ## Related terms [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) ## Read more - [Recirculating deep water culture (RDWC)](https://genetixbay.com/knowledge/systems/rdwc.md) - [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ## Sources 1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 2. Cornell CEA. Hydroponic lettuce handbook. https://cea.cals.cornell.edu/ --- # Chloramine > Chloramine (monochloramine) is a long-lasting water disinfectant made from chlorine and ammonia; unlike chlorine, it does not leave water by standing or aerating. - Canonical: https://genetixbay.com/knowledge/glossary/chloramine.html - Also written: monochloramine, chloramines, NH2Cl, chloraminated water, combined chlorine - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Chloramine is a disinfectant formed by combining chlorine with ammonia, mainly as monochloramine (NH₂Cl). Many [municipal water](https://genetixbay.com/knowledge/glossary/tap-water.md) systems use it because it lasts longer in pipes than [free chlorine](https://genetixbay.com/knowledge/glossary/free-chlorine.md) and forms fewer disinfection by-products. US regulators set a maximum residual disinfectant level of 4 mg/L (as Cl₂) for both chlorine and chloramine in drinking water; typical levels are lower. ## In practice Chloramine is stable. Letting water stand overnight or bubbling it does not remove it meaningfully, which is the key difference from free chlorine. At drinking-water levels its direct effect on cannabis roots is probably small, but growers running [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) or [beneficial-microbe reservoirs](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) worry about effects on microbes. Evidence in cannabis is thin (*Grower practice* concern). Removal options: - Ascorbic acid (vitamin C) neutralises chloramine quickly; about 2.5 parts ascorbic acid per part chlorine is a commonly cited ratio (USDA Forest Service), so a pinch per large reservoir is enough. - Catalytic [activated carbon filters](https://genetixbay.com/knowledge/glossary/carbon-filter.md). - [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) systems with a catalytic carbon pre-stage. Find out what your supplier uses from its water-quality report. ## Don't confuse with - **Free chlorine**: evaporates from standing water within a day or so. - **Chloride**: the ion Cl⁻, a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), not a disinfectant. ## Myth check "Leave tap water out for 24 hours to remove chlorine" does not work for chloramine. *Established*. ## Related terms [Free chlorine](https://genetixbay.com/knowledge/glossary/free-chlorine.md), [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Sources 1. Water Quality Association. 2014. Chloramine fact sheet. https://wqa.org/wp-content/uploads/2022/09/2014_Chloramine.pdf 2. USDA Forest Service. Vitamin C dechlorination. https://www.fs.usda.gov/t-d/pubs/html/05231301/05231301.html --- # Chlorine (nutrient) > As a plant nutrient, chlorine is used as the chloride ion (Cl-) in tiny amounts for photosynthesis and osmotic balance; excess from water or salts is the usual problem. - Canonical: https://genetixbay.com/knowledge/glossary/chloride-nutrient.html - Also written: Cl, Cl-, chloride, chloride nutrient, chloride toxicity - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Chlorine is an essential [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), taken up and used as the chloride ion (Cl-). It helps the water-splitting step of [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), balances charge and osmotic pressure in cells and supports stomatal movement. Chloride is highly mobile and is present almost everywhere, so true [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) is rare. ## In practice The practical issue is excess. Tap water, coco that was not washed, [calcium chloride](https://genetixbay.com/knowledge/glossary/calcium-chloride.md) or potassium chloride, and some organic inputs can push chloride high enough to burn leaf margins and tips, starting on older leaves. Moderate chloride is tolerated; problems tend to appear when it climbs into the low hundreds of mg/L (ppm). A water report or runoff test shows where it comes from. ## Don't confuse with - **Chlorine as water treatment**: dissolved chlorine gas or [hypochlorite](https://genetixbay.com/knowledge/glossary/free-chlorine.md) used as a disinfectant, a separate topic covered in [pH](https://genetixbay.com/knowledge/glossary/ph.md) and water quality. - **Chloramine**: a longer-lasting disinfectant in many municipal supplies. - **Nutrient burn**: [tip burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) from total [EC](https://genetixbay.com/knowledge/glossary/ec.md) rather than chloride specifically. ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Calcium chloride](https://genetixbay.com/knowledge/glossary/calcium-chloride.md), [Sodium](https://genetixbay.com/knowledge/glossary/sodium.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md) ## Read more - [Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add](https://genetixbay.com/knowledge/nutrients/chlorine.md) - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Sources 1. White PJ, Broadley MR. 2001. Chloride in soils and its uptake and movement within the plant: a review. Annals of Botany 88(6):967-988. https://doi.org/10.1006/anbo.2001.1540 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Chlorophyll > The green pigment in chloroplasts that absorbs mainly blue and red light to drive photosynthesis; chlorophyll a and b are the main forms in plants. - Canonical: https://genetixbay.com/knowledge/glossary/chlorophyll.html - Also written: chlorophyll a, chlorophyll b, chlorophylls, green pigment - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Chlorophyll is the pigment that captures light for [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md). Plants carry chlorophyll a and b, which absorb strongly in the blue (around 430-450 nm) and red (around 640-680 nm) and reflect green. Each molecule has a magnesium atom at its centre, and building it needs nitrogen, magnesium and iron, among other things. ## In practice Leaf colour is largely chlorophyll status: - **Pale or yellow older leaves**: often nitrogen or magnesium moving to new growth, or natural late-flower [senescence](https://genetixbay.com/knowledge/glossary/senescence.md). - **Pale new growth**: often iron, [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) or root-zone/[pH](https://genetixbay.com/knowledge/glossary/ph.md) issues. - **Dark, glossy green**: frequently excess nitrogen. Chlorophyll breakdown in late flower reveals other pigments (carotenoids, anthocyanins) and is normal, especially with a [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md). After harvest, chlorophyll still in the material breaks down during a slow dry and cure. Material dried too fast keeps a green, grassy, [hay-like smell](https://genetixbay.com/knowledge/glossary/hay-smell.md). Drying and curing, not [flushing](https://genetixbay.com/knowledge/glossary/flushing.md), decide that. ## Don't confuse with - **Anthocyanin**: purple/red pigment in the vacuole, not photosynthetic. - **Carotenoids**: yellow-orange accessory pigments. - **Chlorosis**: the symptom of losing chlorophyll. ## Myth check "Flushing removes chlorophyll" is a Myth. Chlorophyll is broken down by the plant's own senescence and by a proper dry, not by plain water at the roots. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Related terms [Photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), [Anthocyanin](https://genetixbay.com/knowledge/glossary/anthocyanin.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md), [Hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) ## Read more - [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. 2. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 --- # Chlorosis > Yellowing of normally green plant tissue caused by too little chlorophyll, from nutrient shortage, poor root uptake, pH lockout, light damage, pests or normal ageing. - Canonical: https://genetixbay.com/knowledge/glossary/chlorosis.html - Also written: chlorotic, leaf chlorosis, yellowing of leaves - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Chlorosis is yellowing of tissue that should be green, because the leaf is making or keeping too little chlorophyll. It is a symptom, not a diagnosis: nitrogen, magnesium, iron, manganese, sulfur and zinc shortages all cause it, and so do [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) or [rotting roots](https://genetixbay.com/knowledge/glossary/root-rot.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md) out of range, cold [root zones](https://genetixbay.com/knowledge/glossary/root-zone.md) and excess light (Marschner 2012). ## In practice Where the chlorosis starts is the first clue. On old, lower leaves it usually means a [mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md) (N, Mg, K) is being moved out to feed new growth; on new growth it points to an immobile one (Fe, Mn, Zn, S, Ca, B) or to high root-zone pH (Cockson et al. 2019). Uniform chlorosis of the whole leaf, veins included, differs from [interveinal chlorosis](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md), where the veins stay green. Chlorotic tissue can green up again if the cause is fixed early; once it turns brown it will not. ## Don't confuse with - **Necrosis**: dead, brown or black tissue, which follows severe chlorosis. - **Senescence**: normal ageing and [fade](https://genetixbay.com/knowledge/glossary/senescence.md) of old leaves, especially in late flower. - **Light bleaching**: white or pale tops nearest the lamp, caused by light and heat rather than nutrition. ## Related terms [Interveinal chlorosis](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md), [Necrosis](https://genetixbay.com/knowledge/glossary/necrosis.md), [Chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md), [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md) ## Read more - [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) - [Yellow new growth on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.md) - [Cannabis lookalike problems: how to tell them apart](https://genetixbay.com/knowledge/diagnosis/lookalikes.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Chop > Chop is grower slang for harvesting, cutting down plants at the end of flower; "chop day" is harvest day. - Canonical: https://genetixbay.com/knowledge/glossary/chop.html - Also written: chop day, chopped, chopping, the chop, harvest day - Glossary category: Grower slang and culture · Evidence: Myth - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Chop means harvest: cutting the plant, or its branches, at the end of flowering so drying can begin. "Chop day" is the day it happens. ## In practice Growers decide when to chop by looking at [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) under a [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md). GenetixBay suggests a mix: a few clear, mostly cloudy, some amber; the exact balance is personal preference. Plants are often cut as whole plants or large branches and hung, or broken down for [wet trimming](https://genetixbay.com/knowledge/glossary/wet-trim.md), depending on whether the grower prefers wet or [dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md). Two pre-chop rituals are not recommended here. Pre-harvest [flushing](https://genetixbay.com/knowledge/glossary/flushing.md) starves the plant during the weeks it is packing on its final weight and resin, and 24-72 hours of darkness before chop has no credible evidence of benefit. ## Myth check GenetixBay positions: flushing before chop is a *Myth* and actively harmful; [taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) instead and keep feeding the rest. [Darkness before harvest](https://genetixbay.com/knowledge/glossary/darkness-before-harvest.md) is a *Myth*; the founder has offered a 50-pack of seeds for 20+ years to anyone who finds a sound peer-reviewed study showing a benefit, and nobody has claimed it. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Trichome ripeness](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md), [Wet trim](https://genetixbay.com/knowledge/glossary/wet-trim.md), [Dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md), [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), [Flushing](https://genetixbay.com/knowledge/glossary/flushing.md) ## Read more - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) --- # Chromosome > A chromosome is one long DNA molecule packaged with proteins that carries many genes; cannabis normally has 10 pairs, nine autosome pairs plus an X/Y sex pair. - Canonical: https://genetixbay.com/knowledge/glossary/chromosome.html - Also written: chromosomes, chromosome pair, autosome, autosomes, karyotype - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A chromosome is a single long DNA molecule, wrapped around proteins, carrying hundreds to thousands of [genes](https://genetixbay.com/knowledge/glossary/gene.md) in a fixed order. Cannabis is [diploid](https://genetixbay.com/knowledge/glossary/diploid.md) with 2n = 20: nine pairs of autosomes plus one pair of [sex chromosomes](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md), XX in females and XY in males (Divashuk et al. 2014). ## In practice Chromosomes are why genes travel in groups. During meiosis each pair separates, so every pollen grain and ovule receives one copy of each of the ten chromosomes, with some segments swapped between the pair by crossing over. Genes on different chromosomes assort independently; genes close together on one chromosome are linked. Growers meet chromosomes most directly through sex. A female (XX) reversed to make pollen still only carries X chromosomes, so its pollen gives all-female (XX) seed. That is the basis of [feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md). Some cultivated plants have extra whole sets of chromosomes ([polyploids](https://genetixbay.com/knowledge/glossary/polyploid.md)). Triploid and tetraploid cannabis exist, mostly from deliberate breeding. ## Don't confuse with - **Genome**: the full DNA content of a cell across all chromosomes. - **Gene**: a small part of one chromosome. - **Chromatid**: one of the two copies of a chromosome after it has duplicated before cell division. ## Related terms [Gene](https://genetixbay.com/knowledge/glossary/gene.md), [Locus](https://genetixbay.com/knowledge/glossary/locus.md), [Diploid](https://genetixbay.com/knowledge/glossary/diploid.md), [XY sex determination](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 2. Prentout D, Razumova O, Rhone B, et al. 2020. An efficient RNA-seq-based segregation analysis identifies the sex chromosomes of Cannabis sativa. Genome Research 30(2):164-172. https://doi.org/10.1101/gr.251207.119 --- # Chuck > To chuck is to pollinate plants loosely, usually an open or one-off cross, often implying little selection or record keeping. - Canonical: https://genetixbay.com/knowledge/glossary/chuck.html - Also written: chucking, chucked, chuck pollen, chuck a cross - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" To chuck (or "chuck pollen") is slang for [pollinating](https://genetixbay.com/knowledge/glossary/pollination.md) a plant or a whole room, usually as a quick one-off cross. The word is neutral among friends ("I chucked my male at the whole tent") and critical when applied to someone selling the result. ## In practice A home grower might keep one male, collect a few hundred milligrams of pollen and dust a single lower branch of each female, which is a controlled way to get seed without seeding the whole crop. "Chucking the room" means letting a male open freely among the females, so every plant sets seed and parentage of each seed is unknown. That is [open pollination](https://genetixbay.com/knowledge/glossary/open-pollinated.md). What separates a useful chuck from a careless one is records: which female, which male, which branch, the date, and how many seeds came back. Without those, the seed cannot be traced and a later problem ([herms](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), off-types) cannot be tracked to its source. ## Don't confuse with - **Pollen chucker**: the person, and the criticism. Chucking once for your own garden does not make you one. - **Selfing**: pollinating a plant with its own pollen ([S1](https://genetixbay.com/knowledge/glossary/s1.md)). Chucking implies a second parent. - **Breeding**: a programme of selection over generations, not a single pollination. ## Related terms [Pollen chucker](https://genetixbay.com/knowledge/glossary/pollen-chucker.md), [Cross](https://genetixbay.com/knowledge/glossary/cross.md), [Open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md), [Breeder](https://genetixbay.com/knowledge/glossary/breeder.md) ## Read more - [Pollination and seed production, step by step](https://genetixbay.com/knowledge/breeding/pollination-seed-production.md) --- # Clay pebbles > Clay pebbles (LECA) are fired, expanded clay balls used as an inert hydroponic medium that drains freely, holds a little water and anchors roots. - Canonical: https://genetixbay.com/knowledge/glossary/clay-pebbles.html - Also written: LECA, expanded clay, clay balls, expanded clay aggregate, hydro pebbles - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Clay pebbles, or LECA (lightweight expanded clay aggregate), are small balls of clay fired in a kiln so they expand and become porous. They are pH-neutral once rinsed, hold almost no nutrients and only a little water inside their pores, and leave large air gaps between the balls. That makes them a classic support medium for hydroponic systems. ## In practice Clay pebbles fill [net pots](https://genetixbay.com/knowledge/glossary/net-pot.md) in [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) and [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), fill trays in [ebb and flow](https://genetixbay.com/knowledge/glossary/ebb-and-flow.md), and line the base of containers. Rinse new pebbles well to remove dust that can clog pumps, and soak them before use. Because they dry quickly, plants grown purely in clay need frequent irrigation or roots that reach the solution. They can be washed, sterilised and reused for many cycles. ## Don't confuse with - **Perlite**: much lighter and finer; usually mixed into a medium rather than used alone. - **Pumice**: natural volcanic rock with a similar role; irregular shape. ## Related terms [Net pot](https://genetixbay.com/knowledge/glossary/net-pot.md), [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [Ebb and flow](https://genetixbay.com/knowledge/glossary/ebb-and-flow.md), [Growing medium](https://genetixbay.com/knowledge/glossary/growing-medium.md), [Hydroponics](https://genetixbay.com/knowledge/glossary/hydroponics.md) ## Read more - [Ebb and flow (flood and drain)](https://genetixbay.com/knowledge/systems/ebb-and-flow.md) - [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 --- # Clone-only > A clone-only is a cultivar that exists only as cuttings from one original plant, with no seed line that reliably reproduces it. - Canonical: https://genetixbay.com/knowledge/glossary/clone-only.html - Also written: clone only, clone-only cut, clone-only strain, cut-only - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A clone-only is a single [genotype](https://genetixbay.com/knowledge/glossary/genotype.md), usually one exceptional plant selected from seed long ago, that survives only as cuttings passed from grower to grower. There is no seed that reproduces it: its seed, or seed from crosses using it, segregates into new genotypes. Many famous classic cultivars are clone-only. ## In practice Keeping a clone-only alive means keeping mothers healthy and free of pathogens, rooting backups, and ideally storing it in tissue culture. Its identity can be confirmed by [DNA fingerprinting](https://genetixbay.com/knowledge/glossary/genotyping.md), which matters because names drift and the same name often travels with different cuts. House view: [elite clone-only](https://genetixbay.com/knowledge/glossary/elite-cut.md) gatekeeping is real. Some near-extinct classics survive only in small private circles, can change hands for very high prices or trades, and holders often cannot share them without repercussions. The founder believes some of this is deliberate control of the [gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md). GenetixBay's answer is [the Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) documentation, preservation rewards and open sharing. ## Don't confuse with - **Elite cut (slang)**: the hype term; a clone-only is the factual status. - **Seed line**: breeds from seed, with variation. - **S1 of a clone-only**: seed, not the clone; each seed is a new genotype. ## Myth check Clones do not "drift" or wear out genetically. Old cuts that decline almost always carry a pathogen such as [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), or a care problem. House position: zero [genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md) apart from pathogens. See [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) and [hop latent viroid](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). ## Related terms [Cultivar](https://genetixbay.com/knowledge/glossary/cultivar.md), [Genotype](https://genetixbay.com/knowledge/glossary/genotype.md), [Tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md), [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) ## Sources 1. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 2. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 --- # Cloning > Cloning is propagating a plant by rooting cuttings from it, producing new plants that are genetically identical to the donor. - Canonical: https://genetixbay.com/knowledge/glossary/cloning.html - Also written: clone, clones, taking clones, taking cuttings, vegetative propagation, asexual propagation - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cloning in horticulture means vegetative (asexual) propagation: a piece of the plant, usually a [shoot tip](https://genetixbay.com/knowledge/glossary/apical-meristem.md), is cut off and encouraged to grow roots. The rooted cutting is a genetic copy of the donor, including its sex, so every clone of a female is female. ## In practice A typical cannabis cut is 8-15 cm (3-6 in) with 2-3 nodes, taken from a healthy vegetative plant, trimmed of lower leaves, dipped in a [rooting hormone](https://genetixbay.com/knowledge/glossary/rooting-hormone.md) and set in a plug of rockwool, peat, [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) or an [aeroponic](https://genetixbay.com/knowledge/glossary/aeroponics.md) cloner. Roots usually appear in 7-14 days at about 22-26 °C (72-79 °F) medium temperature, high humidity and gentle light (about 100-200 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md)). Cloning is how growers keep a selected keeper, run uniform [sea-of-green](https://genetixbay.com/knowledge/glossary/sog.md) crops and preserve cultivars. [Genotype](https://genetixbay.com/knowledge/glossary/genotype.md) carries over; pathogens such as viroids carry over too. ## Don't confuse with - **Cutting**: the piece of plant itself; cloning is the whole process. - **Tissue culture**: cloning from tiny explants in sterile culture; can clean up pathogens. - **Reproductive cloning (animals)**: unrelated technology. ## Myth check House position: clones do not drift genetically. Apparent decline is pathogens or care. Cuts from different parts of a plant can behave differently (topophysis), so take them from consistent locations. ## Related terms [Cutting](https://genetixbay.com/knowledge/glossary/cutting.md), [Mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md), [Rooting hormone](https://genetixbay.com/knowledge/glossary/rooting-hormone.md), [Cloning dome](https://genetixbay.com/knowledge/glossary/cloning-dome.md), [Tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Tissue culture basics for cannabis growers and breeders](https://genetixbay.com/knowledge/breeding/tissue-culture-basics.md) ## Sources 1. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 --- # Cloning dome > A cloning dome is a clear lid over a tray that keeps humidity high around unrooted cuttings or seedlings, reducing water loss until roots form. - Canonical: https://genetixbay.com/knowledge/glossary/cloning-dome.html - Also written: humidity dome, propagator, propagation dome, clone dome, propagator lid - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A [cloning](https://genetixbay.com/knowledge/glossary/cloning.md) (humidity) dome is a clear plastic cover over a seed or propagation tray. Cuttings have no roots, so they can only replace water lost through their leaves by drawing it up the cut stem; a dome keeps the surrounding air near saturation, typically 80-95% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), so they lose very little. ## In practice Mist the inside, keep the medium damp rather than wet, and keep the tray warm (about 22-26 °C, 72-79 °F) under gentle light. Most domes have vents. Open them gradually once roots show, usually after a week or so, then remove the lid over a few days so the clones adjust to room humidity. Wipe condensation and remove dead leaves daily; stagnant, saturated air favours mould. A heat mat under the tray speeds rooting by warming the medium more than the air. ## Don't confuse with - **Aeroponic cloner**: roots cuttings in mist, often without a dome. - **Hardening off**: gradually lowering humidity is a form of it, but the term usually refers to moving plants outdoors. ## Related terms [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md), [Cutting](https://genetixbay.com/knowledge/glossary/cutting.md), [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [Hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) ## Read more - [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) --- # CMH > CMH (ceramic metal halide) is a discharge lamp with a ceramic arc tube giving a broad, sun-like spectrum and better efficacy than standard metal halide. - Canonical: https://genetixbay.com/knowledge/glossary/cmh.html - Also written: ceramic metal halide, LEC, light emitting ceramic, CDM, ceramic MH, 315 W CMH - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Ceramic metal halide (CMH) lamps use a ceramic arc tube, like [HPS](https://genetixbay.com/knowledge/glossary/hps.md), filled with [metal halide](https://genetixbay.com/knowledge/glossary/metal-halide.md) salts, like MH. The ceramic tolerates higher temperatures, so the lamp runs hotter and more efficiently with a broader and more stable spectrum than quartz MH. "LEC" (light emitting ceramic) is a marketing name for the same lamp class. The common grow sizes are 315 W and 630 W (two lamps), on low-frequency square-wave ballasts. ## In practice CMH was popular in the 2010s as a single lamp for both veg and flower, valued for its [broad spectrum](https://genetixbay.com/knowledge/glossary/full-spectrum.md), good colour rendering for inspecting plants and a small amount of UV. [Efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) is roughly 1.5–1.9 µmol/J, better than MH and similar to or below DE HPS, and well below modern [LEDs](https://genetixbay.com/knowledge/glossary/led.md). A 315 W CMH typically covers about 0.9 × 0.9 m (3 × 3 ft) for flower. Like other HID lamps, it emits radiant heat and contains mercury. Some CMH lamps emit enough UV that the fixture glass matters; follow the lamp's rated fixture type. ## Don't confuse with - **Metal halide (MH)**: quartz arc tube, bluer, less efficient. - **HPS**: ceramic tube too, but [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) fill and orange-yellow light. - **LED**: solid-state; higher efficacy and dimmable over a wide range. ## Related terms [Metal halide](https://genetixbay.com/knowledge/glossary/metal-halide.md), [HPS](https://genetixbay.com/knowledge/glossary/hps.md), [LED](https://genetixbay.com/knowledge/glossary/led.md), [UV-A](https://genetixbay.com/knowledge/glossary/uv-a.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # CO2 enrichment > CO2 enrichment raises carbon dioxide in a sealed grow space from about 420 ppm to roughly 800–1,500 ppm, letting plants use higher light intensities productively. - Canonical: https://genetixbay.com/knowledge/glossary/co2-enrichment.html - Also written: CO2, carbon dioxide enrichment, CO2 supplementation, CO2 ppm, enriched CO2, carbon dioxide - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" CO2 enrichment means adding carbon dioxide to the growing air above ambient, which is now about 420 ppm outdoors. CO2 is the raw material for [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), and at high light levels it becomes the limiting factor. Enrichment raises the [light saturation point](https://genetixbay.com/knowledge/glossary/light-saturation-point.md) and the optimum temperature, so plants can turn more light into growth. Chandra and colleagues (2011) found cannabis photosynthesis increased substantially at elevated CO2. ## In practice Enrichment pays only when light is already high, roughly above 800–1,000 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), and the room is sealed or [exhausts](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) rarely; venting enriched air wastes it. Common targets are 800–1,200 ppm in veg and early flower, sometimes to 1,500 ppm at high PPFD, with a slightly higher temperature, about 26–30 °C (79–86 °F). Most growers stop enrichment in the last week or two of flower. Safety first. CO2 is odourless and displaces oxygen. NIOSH sets an exposure limit of 5,000 ppm averaged over a working day, with 40,000 ppm immediately dangerous to life. Use a monitor with an alarm, never enter a heavily enriched room for long, and keep burners and tanks away from living areas. ## Units and formula CO2 in ppm (parts per million by volume). 1,000 ppm = 0.1%. ## Don't confuse with - **ppm (nutrients)**: [TDS](https://genetixbay.com/knowledge/glossary/tds.md) readings for solutions, an unrelated scale. - **Ventilation**: brings CO2 back to ambient but cannot exceed it. ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Light saturation point](https://genetixbay.com/knowledge/glossary/light-saturation-point.md), [Temperature](https://genetixbay.com/knowledge/glossary/temperature.md), [Exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) ## Read more - [CO₂ enrichment: when it pays, how much, and how to stay safe](https://genetixbay.com/knowledge/environment/co2-enrichment.md) ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2011. Photosynthetic response of Cannabis sativa L., an important medicinal plant, to elevated levels of CO2. Physiology and Molecular Biology of Plants 17:291–295. https://doi.org/10.1007/s12298-011-0066-6 2. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 3. NIOSH Pocket Guide to Chemical Hazards: Carbon dioxide (REL 5,000 ppm TWA; ST 30,000 ppm; IDLH 40,000 ppm). https://www.cdc.gov/niosh/npg/npgd0103.html --- # COA > A COA (certificate of analysis) is a lab's signed report of what it measured in a specific sample, such as cannabinoids, terpenes, moisture and contaminants, with methods and limits. - Canonical: https://genetixbay.com/knowledge/glossary/coa.html - Also written: certificate of analysis, C of A, lab certificate, lab report, test results sheet - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A certificate of analysis is the formal report a testing laboratory issues for a sample. A complete COA identifies the lab and its accreditation, the client, the sample and batch ID, [sampling](https://genetixbay.com/knowledge/glossary/homogenisation.md) and receipt dates, the methods used, each result with units, the [LOD](https://genetixbay.com/knowledge/glossary/lod.md) or LOQ, pass/fail against any limits, and a signature from an authorised analyst. ## In practice Read a COA from the top: is it the right product and batch, from a lab accredited for that method, dated recently? Then check the basis ([dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) or [as received](https://genetixbay.com/knowledge/glossary/dry-weight-basis.md)), the moisture figure, and whether "total [THC](https://genetixbay.com/knowledge/glossary/thc.md)" was calculated with the [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) factor. A flower COA reading 20.4% total THC at 11% moisture as received is a coherent document. One reading 38% with no moisture data and no method reference deserves suspicion. A COA describes only the sample the lab received. It does not prove that every jar from the batch matches, and it says nothing about samples the lab never saw. ## Don't confuse with - **Label**: the number printed on retail packaging, which may be rounded or taken from a different test. - **Spec sheet**: a seller's description, not an independent measurement. ## Myth check A COA is only as good as the sample and the lab. House position: [inflated labels](https://genetixbay.com/knowledge/glossary/label-inflation.md) and [lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md) are well documented (Jikomes & Zoorob 2018; Schwabe et al. 2023). See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [LOQ](https://genetixbay.com/knowledge/glossary/loq.md), [Batch](https://genetixbay.com/knowledge/glossary/batch.md), [ISO/IEC 17025](https://genetixbay.com/knowledge/glossary/iso-17025.md), [Lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. ISO/IEC 17025:2017. General requirements for the competence of testing and calibration laboratories. International Organization for Standardization, Geneva. 2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 --- # Cobalt > Cobalt (Co) is not essential for cannabis; it is needed by nitrogen-fixing bacteria in legume nodules, so it appears only as a trace in some feeds. - Canonical: https://genetixbay.com/knowledge/glossary/cobalt.html - Also written: Co, Co2+, cobalt nutrient - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cobalt is not an essential element for higher plants. It is required for vitamin B12 and by the bacteria that fix nitrogen in legume root nodules, which is why it is sometimes listed as "beneficial". Cannabis does not form those nodules and has no known requirement for cobalt. ## In practice Some fertiliser blends and [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) premixes contain trace cobalt, mostly as a carry-over from formulas designed for legumes and other crops. Growers should neither add it nor worry about its absence. At higher concentrations cobalt is toxic and can interfere with iron uptake, causing [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md) on new growth. If a label lists cobalt, the amount should be tiny, well below 0.1 mg/L (ppm) in the final solution. ## Don't confuse with - **Copper (Cu)**: an essential micronutrient; easy to confuse by symbol. - **Molybdenum**: essential for [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) reduction; also needed by nitrogen-fixing bacteria. - **Nickel**: essential in trace amounts for urease. ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Beneficial element](https://genetixbay.com/knowledge/glossary/beneficial-element.md), [Nickel](https://genetixbay.com/knowledge/glossary/nickel.md), [Molybdenum](https://genetixbay.com/knowledge/glossary/molybdenum.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Coco coir > Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered. - Canonical: https://genetixbay.com/knowledge/glossary/coco-coir.html - Also written: coco, coir, coconut coir, coco peat, cocopeat, coco fibre, coco chips - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Coco coir is the fibrous material from coconut husks, processed into fine pith (coco peat), fibre and chips. It holds a lot of water while still leaving plenty of [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), rewets easily, resists compaction and breaks down slowly. It carries a natural [cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), holding potassium and [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) from processing. ## In practice Raw coco can carry salts from washing in brackish water; quality products are washed to low [EC](https://genetixbay.com/knowledge/glossary/ec.md). Its exchange sites also tend to take up calcium and magnesium and release potassium and sodium, which is why coco is pre-treated ("buffered") with a calcium solution and why coco feeds carry more calcium and magnesium. Run it like hydro: feed with every watering at about pH 5.8-6.2, water to [10-20% runoff](https://genetixbay.com/knowledge/glossary/watering-to-runoff.md), and never let it dry completely. Coco rewards frequent [fertigation](https://genetixbay.com/knowledge/glossary/fertigation.md); small pots fed several times a day perform strongly. ## Don't confuse with - **Peat**: also a fine organic medium, but more acidic and harder to rewet. - **Coco (food)**: coconut flesh and water; unrelated. ## Myth check [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) needs in coco come from its cation exchange, [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) and cultivar, not from LED lighting (GenetixBay: Myth). See [buffering coco](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md). ## Related terms [Buffering capacity](https://genetixbay.com/knowledge/glossary/buffering-capacity.md), [Cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), [Drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), [High-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md), [Perlite](https://genetixbay.com/knowledge/glossary/perlite.md) ## Read more - [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) - [Buffering coco coir: why it matters and how to do it](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md) ## Sources 1. Abad M, Noguera P, Puchades R, Maquieira A, Noguera V, 2002. Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology 82(3):241–245. https://doi.org/10.1016/S0960-8524(01)00189-4 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 3. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17 --- # Codominant > Codominance is when both alleles at a locus show in a heterozygous plant, as with THCA and CBDA synthase, so a B_T/B_D plant makes both THC and CBD. - Canonical: https://genetixbay.com/knowledge/glossary/codominant.html - Also written: codominance, co-dominant, co-dominance, incomplete dominance - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Two [alleles](https://genetixbay.com/knowledge/glossary/allele.md) are codominant when a heterozygous plant expresses both of them rather than one masking the other. Incomplete dominance is a close relative: the heterozygote is intermediate between the two [homozygotes](https://genetixbay.com/knowledge/glossary/homozygous.md). Growers usually lump the two together. ## In practice The cannabinoid synthase locus is the standard cannabis case. In de Meijer's model, B_T codes for [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) and B_D for [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md). B_T/B_T plants are THC-dominant ([chemotype I](https://genetixbay.com/knowledge/glossary/chemotype.md)), B_D/B_D plants CBD-dominant (chemotype III), and B_T/B_D plants make both, typically in a ratio near 1:1 (chemotype II) (de Meijer et al. 2003). This has a direct breeding consequence. Cross two balanced 1:1 plants and the offspring segregate about 1 THC-dominant : 2 balanced : 1 CBD-dominant. A "1:1 seed line" cannot be fixed by selection alone, because the balanced type is the heterozygote. The stable route is to cross a THC-dominant and a CBD-dominant parent, which gives uniform balanced [F1s](https://genetixbay.com/knowledge/glossary/f1.md). ## Units and formula Expected offspring of B_T/B_D × B_T/B_D: 25% B_T/B_T, 50% B_T/B_D, 25% B_D/B_D. Real ratios vary because the region also contains duplicated and non-functional synthase copies (Laverty et al. 2019). ## Don't confuse with - **Dominant**: one allele masks the other; in codominance neither is hidden. - **Ratio inheritance**: the exact [THC:CBD ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md) within balanced plants still varies with other genes and environment. ## Related terms [Dominant](https://genetixbay.com/knowledge/glossary/dominant.md), [Recessive](https://genetixbay.com/knowledge/glossary/recessive.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md), [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 2. Laverty KU, Stout JM, Sullivan MJ, et al. 2019. A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci. Genome Research 29(1):146-156. https://doi.org/10.1101/gr.242594.118 --- # Cola > The dense, elongated cluster of flowers that forms at the end of a stem or branch; the main cola tops the leader. - Canonical: https://genetixbay.com/knowledge/glossary/cola.html - Also written: colas, main cola, top cola, terminal bud, apical bud cluster - Glossary category: Plant biology - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A cola is the terminal inflorescence of a cannabis branch: many tightly packed [pistillate flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) clusters stacked along the top of a stem, with small [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) among them. The largest, on the main stem, is the main or top cola. The word is Spanish for "tail". ## In practice Training decides how many colas a plant makes. An untrained plant with strong [apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md) puts most of its weight into one main cola. Topping, [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md) and manifolding make many even colas, which share light better. Big colas carry risk. A dense top cola can hold moisture inside, and *[Botrytis cinerea](https://genetixbay.com/knowledge/glossary/botrytis.md)* (bud rot) usually starts inside such colas near the stem, out of sight. In late flower, check the biggest colas first by gently parting them and looking for brown, mushy flowers or grey fuzz. Keep [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) in late flower around 40-50% and air moving through the canopy. [Foxtailing](https://genetixbay.com/knowledge/glossary/foxtailing.md) (spires of new flowers growing out from a finished cola) is usually heat or [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md), sometimes genetic. ## Don't confuse with - **Bud**: a general word for any flower cluster; a cola is a large terminal one. - **Popcorn bud**: small, loose buds low on the plant. - **Calyx**: an individual flower structure within the cola. ## Related terms [Apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), [Bract](https://genetixbay.com/knowledge/glossary/bract.md), [Calyx](https://genetixbay.com/knowledge/glossary/calyx.md), [Node](https://genetixbay.com/knowledge/glossary/node.md), [Sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) ## Read more - [SCROG: screen of green](https://genetixbay.com/knowledge/training/scrog.md) - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 --- # Cold nights > Cold nights are deliberately low night temperatures in late flower; they can bring out purple colour in cultivars that carry it, but don't raise terpenes or resin. - Canonical: https://genetixbay.com/knowledge/glossary/cold-nights.html - Also written: cold night temperatures, night temperature drop, cold snap, cooling for colour, temperature drop for purple - Glossary category: Environment and light · Evidence: Myth - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" "Cold nights" refers to dropping night temperatures well below day temperatures in the last weeks of flower, often to 12–16 °C (54–61 °F) against days in the mid-20s °C. Growers do it to bring out purple, red or blue colour. The colour comes from [anthocyanins](https://genetixbay.com/knowledge/glossary/anthocyanin.md), pigments whose production rises in low temperatures in plants that have the genes for them. ## In practice It only works on cultivars that carry the colour genetics. A green line will not turn purple in the cold, and some purple lines colour up at normal temperatures anyway. Keep it to late flower, avoid going much below about 10 °C (50 °F), and manage humidity carefully: cold nights push [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) up and dense buds near the [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) are an open invitation to botrytis. The founder admits to being "a sucker for any red strain", but [bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md) is not quality. Colour says nothing about potency or aroma. ## Don't confuse with - **Purple stems from deficiency**: purple [petioles](https://genetixbay.com/knowledge/glossary/petiole.md) in veg often point to cold roots, phosphorus uptake problems or genetics, not a desired colour. - **DIF**: the general concept of [day-night temperature difference](https://genetixbay.com/knowledge/glossary/dif.md). ## Myth check GenetixBay house position: **colour from cold is real** (anthocyanins; *Established*). Claims that cold nights increase **[terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), flavour or resin are a Myth** unless peer-reviewed data show otherwise, and none do so far. Members can test it in a [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md) side-by-side. ## Related terms [DIF](https://genetixbay.com/knowledge/glossary/dif.md), [Temperature](https://genetixbay.com/knowledge/glossary/temperature.md), [Anthocyanin](https://genetixbay.com/knowledge/glossary/anthocyanin.md), [Dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) ## Read more - [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) --- # Companion planting > Companion planting grows other plant species alongside cannabis to attract beneficial insects, repel or trap pests, cover soil or support soil life. - Canonical: https://genetixbay.com/knowledge/glossary/companion-planting.html - Also written: companion plants, companion plant, interplanting, polyculture, intercropping - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Companion planting is placing other species near or among cannabis plants for a benefit. Common goals are attracting predators and pollinators (flowering plants such as yarrow, alyssum, dill), trapping pests away from the crop (trap crops), covering bare soil (clover and other cover crops) and fixing nitrogen (legumes) in living-soil beds. ## In practice Outdoors and in living-soil beds, low-growing cover crops reduce evaporation and keep soil life active. Flowering herbs can support populations of [beneficial insects](https://genetixbay.com/knowledge/glossary/biological-control.md) such as hoverflies, [lacewings](https://genetixbay.com/knowledge/glossary/lacewing.md) and predatory wasps, which is a recognised [integrated pest management](https://genetixbay.com/knowledge/glossary/ipm.md) tactic in other crops. Specific claims, such as basil repelling [spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), are mostly anecdotal for cannabis. Companions can compete for light, water and nutrients if crowded, and some, such as clover, can host pests too. Keep them low and away from stems. ## Don't confuse with - **Cover crop**: one kind of companion, grown mainly to protect and feed soil. - **Beneficial insects**: the predators companions help attract; covered under pests. ## Related terms [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), [Outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) ## Read more - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) --- # Compliance testing > Compliance testing is mandatory lab analysis of cannabis or hemp for potency (often total THC) and contaminants, required before sale or to prove legal status. - Canonical: https://genetixbay.com/knowledge/glossary/compliance-testing.html - Also written: total THC compliance testing, regulatory testing, mandatory testing, state testing, potency compliance test - Glossary category: Legal and regulatory · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Compliance testing is the lab analysis a regulator requires before cannabis or [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) can be sold, or to confirm a hemp crop is under the [THC](https://genetixbay.com/knowledge/glossary/thc.md) limit. Typical panels cover [cannabinoid potency](https://genetixbay.com/knowledge/glossary/potency-testing.md), moisture or [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), microbial contaminants, [mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md), pesticides, heavy metals and residual solvents for extracts. ## In practice For potency, many systems report total THC, calculated as THC + [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) x [THCA](https://genetixbay.com/knowledge/glossary/thca.md), so that acidic THCA (which converts to THC on heating) is counted. Hemp rules may require sampling within a set number of days before harvest. A failed microbial test can lead to destruction, remediation, or decontamination such as irradiation where permitted. Compliance numbers are only as good as the lab and the sampling. Studies of legal markets show results vary systematically between labs and labels often overstate potency (Jikomes & Zoorob 2018; Schwabe et al. 2023). GenetixBay criticises the practice of lab shopping and inflated results, not named businesses. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **R&D testing**: voluntary testing for a breeder or grower's own information. - **Certificate of analysis (COA)**: the report a test produces. ## Related terms [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md), [Cannabis irradiation](https://genetixbay.com/knowledge/glossary/irradiation.md), [Lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: testing reveals inflated THC potency on retail cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 --- # Compost tea > Compost tea is a liquid made by steeping compost or worm castings in water, often aerated with food sources, to extract and multiply microbes for the root zone. - Canonical: https://genetixbay.com/knowledge/glossary/compost-tea.html - Also written: aerated compost tea, ACT, AACT, actively aerated compost tea, worm tea, compost extract - Glossary category: Systems and media · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Compost tea is a brewed liquid in which compost or worm castings are steeped in water. Actively aerated compost tea (AACT) bubbles air through the brew for roughly 24-36 hours, often with a small amount of sugar source or kelp, to multiply aerobic microbes. It is applied as a soil drench or sometimes a [foliar spray](https://genetixbay.com/knowledge/glossary/foliar-feeding.md). ## In practice Growers use teas to inoculate fresh soil with microbes, to support [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) between [top dressings](https://genetixbay.com/knowledge/glossary/top-dressing.md), and as a mild nutrient source. Use within hours of brewing, while the microbes are active. Brew in clean equipment; anaerobic, sour-smelling brews or teas made with molasses-heavy recipes can culture unwanted organisms, and there are food-safety concerns about foliar use on crops near harvest. Evidence: research shows compost teas can suppress some plant diseases in some crops, but results are inconsistent and depend heavily on the compost and method. For cannabis yield, evidence is thin. Sugars in a brew feed microbes, not the plant. ## Don't confuse with - **Compost leachate**: liquid drained from a compost heap; not a brewed tea. - **Herbal teas (fermented plant extracts)**: different recipes and aims. ## Related terms [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), [Beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md), [Top dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md), [Mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md) ## Read more - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) - [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) --- # Concentrate > A concentrate is any cannabis product in which the trichome resin has been separated from plant material, giving far higher cannabinoid and terpene content than flower. - Canonical: https://genetixbay.com/knowledge/glossary/concentrate.html - Also written: concentrates, cannabis concentrate, cannabis extract, extracts, extract - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A concentrate is a product made by separating the resin, meaning the [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) produced in [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), from the leaf, [bract](https://genetixbay.com/knowledge/glossary/bract.md) and stem of the plant. Concentrates divide into [solventless](https://genetixbay.com/knowledge/glossary/solventless.md) types (kief, [hash](https://genetixbay.com/knowledge/glossary/hash.md), rosin) and solvent-based types (shatter, wax, badder, [live resin](https://genetixbay.com/knowledge/glossary/live-resin.md), [distillate](https://genetixbay.com/knowledge/glossary/distillate.md), isolate). Separation removes most of the plant mass, so cannabinoid content rises sharply. ## In practice Solventless hash commonly tests far above flower, and refined solvent products such as distillate can exceed 80-90% THC. That is the main reason extremely high numbers appear in the market: they belong to concentrates, not flower. Giordano et al. (2025) found concentrate labels in one state's retail market were generally closer to measured values than flower labels. Legal categories, testing rules and limits vary; check local rules. ## Don't confuse with - **Flower**: dried buds; even the best flower can't approach concentrate potency. - **Edible**: a product made with a concentrate or infused fat, not the concentrate itself. - **Infusion**: cannabinoids dissolved into a carrier (oil, butter), not separated resin. ## Myth check House position: 40%+ figures belong to concentrates, not to flower. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md), [Hash](https://genetixbay.com/knowledge/glossary/hash.md), [Rosin](https://genetixbay.com/knowledge/glossary/rosin.md), [Distillate](https://genetixbay.com/knowledge/glossary/distillate.md), [Potency ceiling](https://genetixbay.com/knowledge/glossary/potency-ceiling.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Giordano G, et al. 2025. Label accuracy of retail cannabis flower and concentrates in Colorado. Scientific Reports. https://www.nature.com/articles/s41598-025-03854-3 --- # Connoisseur > A cannabis connoisseur judges flower and hash on aroma, flavour, cure, smoke and genetics history rather than THC percentage or looks. - Canonical: https://genetixbay.com/knowledge/glossary/connoisseur.html - Also written: connoisseurs, connoisseur grade, cannasseur, head - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A connoisseur is someone with trained judgement for cannabis quality: aroma and flavour, how the flower was dried and [cured](https://genetixbay.com/knowledge/glossary/curing.md), how it burns and smokes, and where the genetics come from. The word also labels a market tier ("connoisseur grade"). ## In practice A connoisseur tasting session [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) like a wine flight: several samples, small amounts, notes on aroma intact and ground, first draw and later draws, ash colour, harshness, and any hay, grass or musty notes from a poor dry. Knowing that a [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) means bacteria, drying too fast or [over-drying](https://genetixbay.com/knowledge/glossary/over-drying.md), and never fully cures out, is the kind of knowledge connoisseurs bring. Connoisseurs are often the first to say that [THC](https://genetixbay.com/knowledge/glossary/thc.md) percentage and quality are different things, and that classic profiles are being lost. ## Don't confuse with - **Heady**: describes craft and culture; a connoisseur is the judge. - **Budtender**: a retail role; some are connoisseurs, many are not. ## Related terms [Heady](https://genetixbay.com/knowledge/glossary/heady.md), [Smoke report](https://genetixbay.com/knowledge/glossary/smoke-report.md), [Terps](https://genetixbay.com/knowledge/glossary/terps.md), [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) --- # Contact vs systemic > Contact products act only where the spray touches the pest; systemic products are absorbed and move inside the plant, which raises residue concerns in cannabis. - Canonical: https://genetixbay.com/knowledge/glossary/contact-vs-systemic.html - Also written: contact pesticide, systemic pesticide, systemic insecticide, systemic fungicide, translaminar, contact insecticide - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A contact pesticide works only on pests or pathogens it physically touches, and usually has little or no residual action. A systemic pesticide is absorbed by leaves or roots and carried through the plant's vascular tissue, protecting new growth and reaching pests that feed on sap. Translaminar products sit in between: they move from one leaf surface to the other, but not throughout the plant. ## In practice Soaps, oils, many botanical extracts and some microbials are contact products, so coverage, especially of leaf undersides, decides whether they work, and repeat applications are needed. Systemic products persist in plant tissue, and with a crop that is smoked or concentrated that means a real risk of residues in the final product. Many jurisdictions permit very few or no systemic actives on cannabis, and test for residues; the conazole fungicide myclobutanil, which forms toxic combustion products, has been behind well-publicised cannabis recalls. Check what is registered for cannabis locally, and never assume a product legal on vegetables is legal on cannabis. ## Don't confuse with - **Residual activity**: how long a product keeps working; contact products can still have some. - **Biological control**: living agents, not chemicals. - **Pre-harvest interval**: the waiting time before harvest set on a label. ## Related terms [Insecticidal soap](https://genetixbay.com/knowledge/glossary/insecticidal-soap.md), [Horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md), [Pre-harvest interval](https://genetixbay.com/knowledge/glossary/pre-harvest-interval.md), [Pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) ## Read more - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) ## Sources 1. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Conversion factor > The conversion factor is the multiplier a TDS meter applies to EC to report ppm, commonly 0.5, 0.64 or 0.7; it is why ppm readings differ between meters. - Canonical: https://genetixbay.com/knowledge/glossary/conversion-factor.html - Also written: EC to ppm conversion, TDS factor, ppm conversion factor, k factor, EC conversion - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A conversion factor, in this context, is the number used to estimate [total dissolved solids](https://genetixbay.com/knowledge/glossary/tds.md) (ppm or mg/L) from measured [electrical conductivity](https://genetixbay.com/knowledge/glossary/ec.md). True TDS depends on which ions are present, so the factor is an approximation. Meters use fixed values: 0.5 (NaCl, the [500 scale](https://genetixbay.com/knowledge/glossary/ppm500.md)), 0.7 (the 442 natural-water scale) or 0.64 (a common agronomy figure). ## In practice The factor is the reason two growers with identical reservoirs post different ppm numbers. To compare, convert both back to EC: divide ppm by the factor and then by 1,000 to get [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md). Example: 900 ppm on a 0.5 meter is 1.8 mS/cm; 900 ppm on a 0.7 meter is 1.29 mS/cm. Following a 700-scale chart on a 500-scale meter therefore feeds about 40% stronger than intended. Some meters let you set the factor. Choose one, label it, and keep it for the life of your logs. ## Units and formula - ppm = EC ([µS/cm](https://genetixbay.com/knowledge/glossary/us-cm.md)) × factor - EC (µS/cm) = ppm ÷ factor - Common factors: 0.5, 0.64, 0.7 ## Don't confuse with - **CF (conductivity factor)**: an EC unit (EC × 10), not a ppm multiplier. - **Temperature compensation coefficient**: the about 2% per °C correction for EC. ## Related terms [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md), [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md), [TDS](https://genetixbay.com/knowledge/glossary/tds.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), [CF](https://genetixbay.com/knowledge/glossary/cf.md) ## Read more - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) ## Sources 1. University of California Cooperative Extension, Ventura County. Salinity units and conversions (640 ppm = 1 dS/m). https://ucanr.edu/node/125832 2. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality --- # Copper > Copper (Cu) is a micronutrient used in photosynthetic electron transport and lignin formation; plants need only traces, and excess is toxic to roots. - Canonical: https://genetixbay.com/knowledge/glossary/copper.html - Also written: Cu, Cu2+, copper deficiency, copper toxicity - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Copper is a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) absorbed as Cu2+. It is part of plastocyanin, which carries electrons in [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), and of enzymes involved in lignin synthesis and oxidative defence. Plants need very little, and it is largely immobile. ## In practice [Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) is rare in mineral feeds. When it occurs, new leaves may be dark or bluish, twisted, with wilting or dying tips and weak stems. [Toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) is the more realistic risk: copper pipes, copper-based ionisers, copper fungicide residues or overdosing can damage roots and induce [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md). Hydro feeds usually carry only about 0.03-0.1 mg/L (ppm) Cu. ## Don't confuse with - **Copper fungicides**: a pest-control use, not a nutrition strategy. - **Zinc deficiency**: also twists new growth, but with [short internodes](https://genetixbay.com/knowledge/glossary/node-stacking.md). - **Heat stress**: tip curl without a nutrient cause. ## Myth check Copper is sometimes added to reservoirs as a "root protectant". At the doses that suppress pathogens it can also injure roots; treat claims with caution. See [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md). ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Copper sulfate](https://genetixbay.com/knowledge/glossary/copper-sulfate.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md) ## Read more - [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Copper sulfate > Copper sulfate pentahydrate (CuSO4·5H2O), about 25.5% copper, supplies trace copper in micronutrient mixes and is toxic to roots in excess. - Canonical: https://genetixbay.com/knowledge/glossary/copper-sulfate.html - Also written: CuSO4, copper sulphate, blue vitriol, bluestone, CuSO4·5H2O - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Copper sulfate is the bright blue salt of [copper](https://genetixbay.com/knowledge/glossary/copper.md) and [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), normally sold as the pentahydrate (CuSO4·5H2O) at about 25.5% Cu. It is soluble and also widely used as a fungicide and algicide. ## In practice In a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) stock, copper is needed at very low levels, about 0.03-0.1 mg/L (ppm) in the final feed. That is only a fraction of a milligram of salt per litre, so it is always dosed from a concentrated stock. Overdosing damages roots and can induce [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md). Garden-store copper sulfate sold for algae control may not be pure enough for nutrition; check the grade. ## Units and formula 1 mg/L of the pentahydrate gives about 0.255 mg/L (ppm) Cu. ## Don't confuse with - **Bordeaux mixture**: copper sulfate plus lime, a fungicide spray. - **Copper chelate (Cu-EDTA)**: more stable at higher [pH](https://genetixbay.com/knowledge/glossary/ph.md). - **Copper ionisers**: devices that release copper into water, a contamination risk in hydro. ## Related terms [Copper](https://genetixbay.com/knowledge/glossary/copper.md), [Sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) ## Read more - [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Corn earworm > Helicoverpa zea, a moth caterpillar that bores into developing cannabis flowers outdoors, leaving frass that triggers bud rot; growers call it budworm. - Canonical: https://genetixbay.com/knowledge/glossary/corn-earworm.html - Also written: budworm, budworms, bud worm, Helicoverpa zea, cotton bollworm, tomato fruitworm, CEW - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The corn earworm (*Helicoverpa zea*), also called cotton bollworm or tomato fruitworm, is a noctuid moth whose larvae feed in flowers and [fruits](https://genetixbay.com/knowledge/glossary/achene.md). On outdoor [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) and cannabis it is the main "budworm": larvae tunnel into [colas](https://genetixbay.com/knowledge/glossary/cola.md) during flowering. Mature larvae are up to about 4 cm long and vary from green to brown or pink, with light and dark stripes along the body. ## In practice Moths migrate and lay eggs singly on flowers from mid to late summer, so damage peaks just as buds are bulking. Look for small holes, browning patches inside colas and pellets of [frass](https://genetixbay.com/knowledge/glossary/frass.md); pull apart any bud with a brown spot. The bigger loss is often secondary *[Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md)* that starts in the frass. *[Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md)* sprays aimed at newly hatched larvae, before they bore in, are the usual biological option. [Pheromone traps](https://genetixbay.com/knowledge/glossary/pheromone-trap.md) show when moth flights begin. Check what is registered for cannabis locally, including the [pre-harvest interval](https://genetixbay.com/knowledge/glossary/pre-harvest-interval.md). ## Don't confuse with - **European corn borer**: bores into stems and branches rather than buds. - **Bud rot alone**: grey fuzz and brown tissue with no frass or tunnels. - **Tobacco budworm**: *Chloridea virescens*, a close relative with similar habits. ## Related terms [Caterpillar](https://genetixbay.com/knowledge/glossary/caterpillar.md), [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md), [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md) ## Read more - [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Sources 1. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 2. Utah State University Extension. Corn Earworm (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-corn-earworm --- # Cotyledon > One of the two rounded seed leaves packed in the embryo that open first after germination and feed the seedling until the true leaves take over. - Canonical: https://genetixbay.com/knowledge/glossary/cotyledon.html - Also written: cotyledons, seed leaf, seed leaves, cotys - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cotyledons are the embryonic leaves formed inside the seed. Cannabis is a dicot, so each [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) opens two smooth, oval, unserrated cotyledons on top of the [hypocotyl](https://genetixbay.com/knowledge/glossary/hypocotyl.md). They hold stored reserves and start photosynthesising as soon as they turn green, carrying the seedling until the [first true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) expand. ## In practice Healthy cotyledons are firm, even and green. Pale or stretched seedlings with cotyledons held high on a long, thin stem usually need more light, not more feed. Yellowing cotyledons after two or three weeks are normal as their reserves run out. Early yellowing combined with pale new growth points to the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) or too little light. Seedlings need little or no fertiliser while the cotyledons and the first one or two pairs of true leaves are still working. Damaged or missing cotyledons slow a seedling but rarely kill it. Occasionally a seedling shows three cotyledons (tricot). It is a developmental quirk and says nothing reliable about vigour or sex. ## Don't confuse with - **True leaves**: the first serrated, compound-type leaves that follow the cotyledons. - **Hypocotyl**: the stem section below the cotyledons. - **Fan leaves**: the large mature leaves of an established plant. ## Related terms [True leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md), [Hypocotyl](https://genetixbay.com/knowledge/glossary/hypocotyl.md), [Radicle](https://genetixbay.com/knowledge/glossary/radicle.md), [Achene](https://genetixbay.com/knowledge/glossary/achene.md) ## Read more - [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Crawler > The mobile first-instar nymph of a mealybug or scale insect; the only stage without protective wax, so the stage contact sprays hit best. - Canonical: https://genetixbay.com/knowledge/glossary/crawler.html - Also written: crawlers, mealybug crawler - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A crawler is the newly hatched first-instar nymph of a [mealybug](https://genetixbay.com/knowledge/glossary/mealybug.md) or scale insect. Crawlers are tiny, mobile and largely free of the wax that later protects the insect; they walk or are carried by wind, people and ants to new feeding sites. UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) describes crawlers as the stage that disperses. ## In practice Timing matters: contact classes such as soaps and oils work far better on crawlers than on waxy adults and egg sacs. Because mealybug generations take about four weeks at 25 C, crawler emergence comes in waves, and treatments are aimed at each wave rather than on a fixed weekly calendar. Follow the label and local law. ## Don't confuse with - **Ovisac**: the cottony egg sac that crawlers hatch from. - **Instar**: any stage between moults, not only the first. ## Related terms [Mealybug](https://genetixbay.com/knowledge/glossary/mealybug.md), [Instar](https://genetixbay.com/knowledge/glossary/instar.md), [Honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md) ## Read more - [Mealybugs and root mealybugs on cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/mealybugs.md) ## Sources 1. Flint, M.L. Pest Notes: Mealybugs. UC ANR Publication 74174. https://ipm.ucanr.edu/PMG/PESTNOTES/pn74174.html --- # Crop steering > Crop steering adjusts irrigation timing, volume and dryback, along with climate, to push plants towards vegetative growth or generative (flowering) growth. - Canonical: https://genetixbay.com/knowledge/glossary/crop-steering.html - Also written: crop-steering, plant steering, generative steering, vegetative steering, steering - Glossary category: Systems and media · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Crop steering is an irrigation and climate strategy, developed in greenhouse tomato and adopted widely in commercial cannabis, that uses the plant's root-zone water status as a lever. Vegetative steering keeps the substrate wetter, with smaller [drybacks](https://genetixbay.com/knowledge/glossary/dryback.md) and frequent small irrigations, to encourage leaf and stem growth. Generative steering uses larger drybacks, higher substrate [EC](https://genetixbay.com/knowledge/glossary/ec.md) and fewer, later irrigations to push flower development. ## In practice Growers measure substrate [water content](https://genetixbay.com/knowledge/glossary/moisture-content.md) and EC with sensors or by weighing a pot, set a first irrigation time after lights-on, deliver small "shots" until the medium is near [container capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md), then let it dry back overnight by a target percentage. Typical guides quote overnight drybacks of a few percent for vegetative steering and larger ones for generative, but numbers depend on the substrate and sensor. It works best in [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), which have fast, predictable water dynamics. Evidence: grower and industry practice, with limited peer-reviewed cannabis trials. ## Don't confuse with - **Drought stress**: an uncontrolled or extended dry-down; steering is precise and daily. - **Training**: physical shaping; steering is irrigation-based. ## Related terms [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md), [Field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md), [Drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), [High-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md), [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) ## Read more - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) ## Sources 1. Stemeroff J, 2018. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 --- # Cross > A cross is the offspring of mating two different plants, written female x male, as "A x B"; one cross starts a line but is not one. - Canonical: https://genetixbay.com/knowledge/glossary/cross.html - Also written: crosses, crossed, x (as in A x B), crossing - Glossary category: Grower slang and culture · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A cross is the result of [pollinating](https://genetixbay.com/knowledge/glossary/pollination.md) a plant of one [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) with pollen from another, and also the act itself. By convention it is written female first: "A x B" means A was the mother and B supplied the pollen. ## In practice Crossing two unrelated, fairly uniform parents gives an [F1](https://genetixbay.com/knowledge/glossary/f1.md) that can be vigorous and fairly even. Crossing two [polyhybrid](https://genetixbay.com/knowledge/glossary/polyhybrid.md) [clone-only cuts](https://genetixbay.com/knowledge/glossary/clone-only.md), which is what most modern crosses are, gives an F1 that [segregates](https://genetixbay.com/knowledge/glossary/segregation.md) a lot, so packs of the same "strain" can look like several different plants. That is why one cross with a new name is not a stable cultivar. Record the cross properly: which plant, which male or pollen batch, the date, how many seeds, and the identity of both parents. A cross registered with its parents on GenetixBay starts life with a traceable lineage claim instead of a name alone. ## Don't confuse with - **Line**: a population carried over generations; a cross is one generation. - **Backcross**: crossing offspring back to a parent. - **Hybrid**: any cross between distinct parents; nearly all modern cannabis is hybrid. ## Related terms [F1](https://genetixbay.com/knowledge/glossary/f1.md), [Line](https://genetixbay.com/knowledge/glossary/line.md), [Pollen chucker](https://genetixbay.com/knowledge/glossary/pollen-chucker.md), [Breeder](https://genetixbay.com/knowledge/glossary/breeder.md), [Backcross](https://genetixbay.com/knowledge/glossary/backcross.md) ## Read more - [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md) - [Pollination and seed production, step by step](https://genetixbay.com/knowledge/breeding/pollination-seed-production.md) --- # Cultivar > A cultivar (cultivated variety) is a group of cultivated plants selected for distinct, uniform and stable traits that are kept when propagated, by seed or by cuttings. - Canonical: https://genetixbay.com/knowledge/glossary/cultivar.html - Also written: cultivars, cultivated variety, cv., variety, varietal - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A cultivar is the formal botanical term for a cultivated variety: a population of plants selected for particular traits that is distinct from others, sufficiently uniform, and stable when propagated. The rules for naming cultivars are set by the International Code of Nomenclature for Cultivated Plants (ICNCP). A cultivar can be a seed line or a clonal line. ## In practice GenetixBay uses "cultivar" in place of "strain" where precision matters. A [clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) is a clonal cultivar. A seed line that [breeds true](https://genetixbay.com/knowledge/glossary/true-breeding.md) for its key traits is a seed cultivar. A pack of seed from a one-off cross of two [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) is, strictly, not yet a cultivar: its plants are not uniform or stable. Formal cultivar names under the ICNCP are written in single quotes after the species, for example *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)* 'Name'. [Plant variety protection](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md) systems use similar tests of distinctness, uniformity and stability. ## Don't confuse with - **Strain**: the popular cannabis word; used loosely for anything from a clone to a brand name. - **Chemovar**: a cultivar defined by its chemistry. - **Landrace**: a traditional, locally adapted population, often more variable than a modern cultivar. - **Variety (botanical rank)**: "var." is a formal taxonomic rank below species, different from a cultivar. ## Related terms [Strain](https://genetixbay.com/knowledge/glossary/strain.md), [Chemovar](https://genetixbay.com/knowledge/glossary/chemovar.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Accession](https://genetixbay.com/knowledge/glossary/accession.md) ## Read more - [Why strain names are unreliable: what genetic studies show](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) - [Breeder record-keeping and naming ethics](https://genetixbay.com/knowledge/breeding/record-keeping-naming-ethics.md) ## Sources 1. Brickell CD, et al. (eds). 2016. International Code of Nomenclature for Cultivated Plants, 9th edition. Scripta Horticulturae 18. ISHS. https://www.ishs.org/scripta-horticulturae/international-code-nomenclature-cultivated-plants-ninth-edition --- # Cultural control > Pest and disease prevention by changing how the crop is grown, such as humidity, airflow, spacing, watering and cultivar choice, so pests and pathogens struggle to establish. - Canonical: https://genetixbay.com/knowledge/glossary/cultural-control.html - Also written: cultural controls, cultural practices, prevention, preventive measures, environmental control of pests - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cultural control means using growing practices to make the crop a poor home for pests and disease. It covers the environment, [plant spacing](https://genetixbay.com/knowledge/glossary/plant-density.md), watering, media, crop timing and cultivar choice. It is the foundation layer of [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) and usually the least expensive. ## In practice Examples on cannabis: keeping humidity and [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) in check late in flower to deny *[Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md)*; moving air through and under the canopy against [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md); letting the top of the medium dry between waterings to cut [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md); cool, oxygenated nutrient solution against *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)*; spacing plants and thinning crowded interior growth; avoiding overhead watering outdoors; and choosing cultivars with known tolerance, such as those carrying mapped mildew resistance. Removing weeds and host plants near outdoor grows reduces insects that carry viruses. None of these act fast, but together they lower pressure so other tools work. ## Don't confuse with - **Biological control**: living [natural enemies](https://genetixbay.com/knowledge/glossary/biological-control.md), not growing practices. - **Sanitation**: hygiene; overlaps, but focuses on cleaning rather than how plants are grown. - **Chemical control**: pesticides and fungicides, the last layer. ## Related terms [IPM](https://genetixbay.com/knowledge/glossary/ipm.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) ## Read more - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) ## Sources 1. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew 2. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Cultured Pearls > Cultured Pearls are GenetixBay Pearls bought with money, usable only as store credit in the GenetixBay store; they never transfer between members. - Canonical: https://genetixbay.com/knowledge/glossary/cultured-pearls.html - Also written: Cultured Pearl, purchased Pearls, store credit Pearls - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cultured Pearls are the purchased kind of Pearl. They work as store credit in the GenetixBay store, for things such as digital items, memberships and merchandise. ## In practice Cultured Pearls stay with the member who bought them: they cannot be sent, tipped or used in the Swap. This keeps money-linked value out of the peer layer. A seed pack is never priced in or paid with Cultured Pearls. If a purchase is reversed (for example by a chargeback), the Cultured Pearls from it and anything bought with them are reversed too. The separation exists for legal reasons as well as fairness: points bought with cash are treated differently from points earned by contribution in many places' consumer and cannabis law. ## Don't confuse with - **Wild Pearls**: earned by contribution and transferable between members. - **Gift card**: Cultured Pearls have no cash value and are not redeemable for cash. ## Related terms [Pearls](https://genetixbay.com/knowledge/glossary/pearls.md), [Wild Pearls](https://genetixbay.com/knowledge/glossary/wild-pearls.md), [Founding Member](https://genetixbay.com/knowledge/glossary/founding-member.md) --- # Cured resin > Cured resin is a solvent-based extract made from dried and cured cannabis rather than fresh frozen material, typically with a more aged, less bright aroma than live resin. - Canonical: https://genetixbay.com/knowledge/glossary/cured-resin.html - Also written: cured extract, cured BHO, cured-resin, dried-material extract - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cured resin is a concentrate extracted with solvents from material that has been dried and [cured](https://genetixbay.com/knowledge/glossary/curing.md), the way flower is prepared for smoking. Drying and curing change aroma chemistry, mainly by losing [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) and oxidising some compounds, so cured resin tends to smell more like cured flower and less like the living plant. Most traditional solvent concentrates, such as shatter and many waxes, were made from cured material. ## In practice On a menu, "cured" versus "live" mainly signals the starting material and aroma style; it doesn't on its own say anything about potency or safety. Cured material is easier to store and process than [fresh frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md), so cured resin is usually cheaper. Solvent extraction is an industrial process for licensed facilities only; never attempt it at home. GenetixBay provides definitions only. ## Don't confuse with - **Live resin**: from fresh frozen material. - **Curing (flower)**: the post-harvest moisture-decline process; cured resin simply starts from cured flower. - **Hash rosin**: [solventless](https://genetixbay.com/knowledge/glossary/solventless.md), from [hash](https://genetixbay.com/knowledge/glossary/hash.md). ## Related terms [Live resin](https://genetixbay.com/knowledge/glossary/live-resin.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md), [Shatter](https://genetixbay.com/knowledge/glossary/shatter.md), [Wax](https://genetixbay.com/knowledge/glossary/wax.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md) --- # Curing > Holding dried cannabis in sealed containers so its moisture declines slowly and evenly over weeks, improving smoothness and aroma. - Canonical: https://genetixbay.com/knowledge/glossary/curing.html - Also written: cure, the cure, jar curing, curing cannabis, cured, long cure - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Curing is the final post-harvest step: dried buds are sealed in containers (usually [glass jars](https://genetixbay.com/knowledge/glossary/curing-jar.md)) and opened periodically while moisture redistributes from the core to the surface and slowly declines. Over weeks, residual chlorophyll and starch break down, and harshness and grassy notes fade. ## In practice House position: curing is slowly reducing [moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md) over time, not holding it constant. A steady, slow decline gives the best product. Targets are about the bud: [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) around 0.55-0.65 and a moisture content of roughly 10-12% w/w, checked by equilibrated jar RH, [stem snap](https://genetixbay.com/knowledge/glossary/stem-snap-test.md) and weight loss. A typical approach: 1. Jar when small stems snap. Fill jars about three-quarters, loosely. 2. First week: check daily. Burp if equilibrated RH sits above about 65%; take buds out to air if far above. 3. Weeks 2-4: open less often as [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) steadies in range. 4. Keep jars dark and cool, about 15-21 °C (60-70 °F). Two to four weeks is a solid cure. Longer helps within reason. ## Don't confuse with - **Drying**: removing most of the water, before the cure. - **Storage**: keeping a finished cure stable. - **Water curing**: a soaking method (Contested, not recommended). ## Myth check A cure will never fix a bad dry (house position). [Hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) from bacteria, over-drying or drying too fast never truly comes out. [Humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md) rob [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md); they are a marketing gimmick. See [curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md). ## Related terms [Burping](https://genetixbay.com/knowledge/glossary/burping.md), [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Equilibrium relative humidity](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md), [Humidity pack](https://genetixbay.com/knowledge/glossary/humidity-pack.md), [Hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. 3. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 --- # Curing jar > An airtight container, usually wide-mouth glass, used to cure and store dried cannabis; ideally filled about three-quarters and kept dark and cool. - Canonical: https://genetixbay.com/knowledge/glossary/curing-jar.html - Also written: cure jar, curing jars, mason jar, glass jar, jarring, jarred - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A curing jar is the sealed container in which dried buds cure. Glass is the standard: it is inert, gas-tight with a good lid, holds no odour and lets you see the buds. Wide-mouth jars are easiest to load and inspect. Other options include food-grade stainless or ceramic containers with airtight seals; thin plastic bags and porous containers lose aroma. ## In practice How to use them: - **Fill to about three-quarters**, loosely, so air can circulate and you can roll the buds when [burping](https://genetixbay.com/knowledge/glossary/burping.md). - **Add a small calibrated hygrometer**, and read it only once the jar has equilibrated (several hours to overnight). - **Label** cultivar, harvest date and jarring date, and in trials the wet and [dry weights](https://genetixbay.com/knowledge/glossary/dry-weight.md). - **Store dark and cool**, about 15-21 °C (60-70 °F). Clear glass in light degrades [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md); keep jars in a cupboard or use amber or opaque glass. For [long-term storage](https://genetixbay.com/knowledge/glossary/long-term-storage.md), once the cure is done, fill jars more fully to cut headspace and oxygen. House position: no [humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md). If a jar needs moisture, add a fresh bud. ## Don't confuse with - **Humidity pack**: a sachet sold for jars; GenetixBay doesn't recommend them. - **Turkey bag**: a plastic oven bag used for bulk storage. - **Vacuum container**: removes air but can crush buds. ## Related terms [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Burping](https://genetixbay.com/knowledge/glossary/burping.md), [Equilibrium relative humidity](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md), [Long-term storage](https://genetixbay.com/knowledge/glossary/long-term-storage.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) ## Sources 1. Fairbairn JW, Liebmann JA, Rowan MG. 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1-7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x 2. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html --- # Cut > A cut is slang for a clone of one specific plant, used to mean that individual genotype, as in "the original cut". - Canonical: https://genetixbay.com/knowledge/glossary/cut.html - Also written: cuts, a cut, the cut, cutting (slang) - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A cut is a rooted clone taken from a specific plant, and by extension that plant's [genotype](https://genetixbay.com/knowledge/glossary/genotype.md). Saying "I have the cut" means having a living copy of one selected individual, not seed of the line. ## In practice Growers trade, keep and argue about cuts. A famous [clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) is passed from garden to garden as cuts for decades. Because every cut of one plant is genetically identical (barring rare mutations), a cut is the only way to grow exactly the same plant again; seed from it, even [selfed](https://genetixbay.com/knowledge/glossary/selfing.md), gives new individuals. The claim "this is the original cut" is only as good as its chain of custody. Two cuts with the same name may be different plants, and the same plant may circulate under many names. On GenetixBay a cut's identity is a claim with an evidence level until grow-outs or a DNA match back it up. Take cuts from consistent positions on the plant: cuttings from different branches can behave a little differently ([position effects](https://genetixbay.com/knowledge/glossary/topophysis.md)), which is not the same as the genetics changing. ## Don't confuse with - **Clone**: the horticultural term; "cut" is the slang, with a strong sense of "this specific individual". - **Pheno**: one plant from a [seed lot](https://genetixbay.com/knowledge/glossary/seed-run.md). A [pheno](https://genetixbay.com/knowledge/glossary/pheno.md) becomes a cut once it is kept and cloned. ## Myth check "Cuts drift and get weaker over time." GenetixBay position: no [genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md) beyond pathogens such as [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md). Decline in an old cut is almost always disease or care. See [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md). ## Related terms [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md), [Elite cut](https://genetixbay.com/knowledge/glossary/elite-cut.md), [Keeper](https://genetixbay.com/knowledge/glossary/keeper.md), [Renamed cut](https://genetixbay.com/knowledge/glossary/renamed-cut.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) --- # Cut trading > Cut trading is growers exchanging clones of selected plants with each other, a traditional way rare genetics spread and are kept alive. - Canonical: https://genetixbay.com/knowledge/glossary/cut-trading.html - Also written: trading cuts, clone trading, cut trade, clone swap - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cut trading is the exchange of rooted clones (cuts) between growers, usually one keeper for another. It is how many [clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) cultivars spread and survived before any formal archive existed. ## In practice Trading carries two big risks. First, pests and pathogens: [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md), [russet mites](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md) and [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md) travel inside cuts, so a new clone should be quarantined, inspected and, ideally, viroid-tested before it joins the garden. Second, identity: a traded cut's name is a claim, and the same plant circulates under many names while different plants share one name. Record where each cut came from and when. The legality of giving or trading cannabis plants varies widely, including whether a trade counts as a sale. Check local rules. On GenetixBay, member-to-member exchange runs through the Swap only in the lanes the law allows where both members live. ## Don't confuse with - **Clone sales**: commercial supply of clones by a licensed nursery. - **Seed trading**: lower pest risk, but offspring are new individuals rather than copies. ## Related terms [Cut](https://genetixbay.com/knowledge/glossary/cut.md), [Elite cut](https://genetixbay.com/knowledge/glossary/elite-cut.md), [The Swap](https://genetixbay.com/knowledge/glossary/the-swap.md), [Hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) --- # Cutting > A cutting is a piece of shoot, usually a tip with two or three nodes, removed from a plant so it can be rooted into a new, genetically identical plant. - Canonical: https://genetixbay.com/knowledge/glossary/cutting.html - Also written: cuttings, clipping, slip, unrooted cutting, shoot cutting - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A cutting is a section of stem removed from a [donor plant](https://genetixbay.com/knowledge/glossary/mother-plant.md) for rooting. In cannabis it is almost always a softwood tip cutting: the [growing tip](https://genetixbay.com/knowledge/glossary/apical-meristem.md) plus two or three nodes, 8-15 cm (3-6 in) long. Once rooted, it is a clone. ## In practice Take cuttings from firm, vegetative, well-fed shoots, ideally from the lower and middle canopy at a consistent position on the plant. Cut at a 45° angle just below a node with a sterile blade, drop it straight into clean water or onto a damp surface so air does not enter the stem, then remove the lowest leaves and trim large [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) by about half to cut water loss. Cuttings from flowering plants root slowly and often [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) with odd, single-blade leaves. Unrooted cuttings carry pests and pathogens from the donor. Inspect and quarantine anything brought in. ## Don't confuse with - **Clone**: a rooted cutting; growers use both words loosely. - **Cut (slang)**: shorthand for a specific clonal line ("the original cut"), covered as slang. ## Related terms [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md), [Mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md), [Rooting hormone](https://genetixbay.com/knowledge/glossary/rooting-hormone.md), [Cloning dome](https://genetixbay.com/knowledge/glossary/cloning-dome.md), [Node](https://genetixbay.com/knowledge/glossary/node.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) --- # Cutworm > Moth caterpillars of the family Noctuidae, such as the black cutworm (Agrotis ipsilon), that hide in soil by day and chew through seedling stems at night. - Canonical: https://genetixbay.com/knowledge/glossary/cutworm.html - Also written: cutworms, black cutworm, Agrotis ipsilon, Agrotis - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cutworms are the larvae of several noctuid moths, notably the black cutworm (*Agrotis ipsilon*). They are plump, greasy-looking grey to brown caterpillars, up to about 4-5 cm long, that curl into a C-shape when disturbed. They hide in the top layer of soil by day and feed at night. ## In practice The giveaway is a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) or young [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) cut clean through at or just below the soil line overnight, often with the top lying beside it. Digging gently around the stem usually turns up the culprit. They are an outdoor and greenhouse problem, worst in fields that were weedy or grassy the season before. Simple stem collars of card or plastic pushed into the soil around transplants stop most damage. Hand-picking at night with a torch works in small gardens. [Entomopathogenic nematodes](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md) and *[Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md)* are biological options. Check what is registered for cannabis locally. ## Don't confuse with - **Damping-off**: the stem rots and pinches at the base; it is not chewed through. - **Slugs**: slime trails and ragged leaf holes. - **Corn earworm**: feeds in buds later in the season. ## Related terms [Caterpillar](https://genetixbay.com/knowledge/glossary/caterpillar.md), [Corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md), [Damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md), [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md), [Steinernema feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md) ## Read more - [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Sources 1. Cranshaw, W. Hemp pests (CSU, 2020). https://webdoc.agsci.colostate.edu/bspm/InsectInformation/Talks2020/HempPests.pdf --- # Cyclamen mite > Phytonemus pallidus, a tarsonemid mite related to the broad mite that distorts new growth on many ornamentals; rarely reported on cannabis and often confused with broad mite. - Canonical: https://genetixbay.com/knowledge/glossary/cyclamen-mite.html - Also written: cyclamen mites, Phytonemus pallidus, strawberry mite - Glossary category: Pests and diseases · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The cyclamen mite (*Phytonemus pallidus*) is a microscopic [tarsonemid mite](https://genetixbay.com/knowledge/glossary/tarsonemid-mite.md), a close relative of the [broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md). It prefers cool, humid conditions and feeds inside folded buds and [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) of crops such as cyclamen, African violet and strawberry. Feeding leaves new leaves crinkled, thickened and stunted. ## In practice Growers sometimes say "cyclamen mites" for any invisible mite that twists cannabis tips. In most cannabis cases the culprit turns out to be the broad mite or the [hemp russet mite](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md); cyclamen mite on cannabis is rarely documented. The distinction matters for scouting more than control, since both tarsonemids are handled the same way: quarantine new plants, inspect growing tips under 40x or more, and use [predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md) such as *[Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md)* or *[Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md)*. Keep ornamental houseplants, especially cyclamen and strawberries, out of the grow room. ## Don't confuse with - **Broad mite**: favours warmer rooms and is the documented tarsonemid on cannabis. - **Hemp russet mite**: eriophyid, four legs, carrot-shaped, bronzes leaves. - **Genetic leaf mutations**: show on one plant or one cut, with no [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) present. ## Related terms [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Hemp russet mite](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md), [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) ## Read more - [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ## Sources 1. UConn IPM. Managing Broad Mites on Greenhouse Crops. https://ipm.cahnr.uconn.edu/ipm-managing-broad-mites-on-greenhouse-crops --- # Cystolith trichome > A non-glandular, claw-shaped hair on cannabis leaves that contains a calcium carbonate crystal (cystolith); it makes no resin. - Canonical: https://genetixbay.com/knowledge/glossary/cystolith-trichome.html - Also written: cystolith, cystolithic hair, non-glandular trichome, non-glandular trichomes, unicellular trichome, covering trichome - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A cystolith trichome is a non-glandular, single-celled hair, typically short and curved like a claw, with a deposit of calcium carbonate (a cystolith) at its base. These [hairs](https://genetixbay.com/knowledge/glossary/pistil.md) cover the upper surface of cannabis leaves and give them a slightly rough feel. Longer, thinner non-glandular hairs are found on the undersides and on stems. Neither type produces resin. ## In practice Under a [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md), cystolith hairs are clear, pointed and stalk-only, with no ball head. New growers sometimes mistake them for "[clear trichomes](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md)" on [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) and decide a plant isn't ripe. Look for the resin head: no head, not a glandular [trichome](https://genetixbay.com/knowledge/glossary/trichome.md). Cystolith hairs are a botanical identification feature of the cannabis and hop family and were long used in forensic microscopy to recognise plant material. ## Don't confuse with - **Glandular trichomes**: the resin-producing types with heads. - **Clear trichome**: a glandular head that hasn't clouded yet; it still has a head. - **Powdery mildew**: white fungal spots that rub off, not hairs. ## Related terms [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md), [Bulbous trichome](https://genetixbay.com/knowledge/glossary/bulbous-trichome.md), [Leaflet](https://genetixbay.com/knowledge/glossary/leaflet.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Cytokinin > A class of plant hormones made mainly in roots that promote cell division, shoot and side-bud growth, and delay leaf ageing. - Canonical: https://genetixbay.com/knowledge/glossary/cytokinin.html - Also written: cytokinins, kinetin, zeatin, BAP, 6-benzylaminopurine - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cytokinins are adenine-derived hormones, such as zeatin, made largely in root tips and carried up the xylem. They promote cell division, release [axillary buds](https://genetixbay.com/knowledge/glossary/axillary-bud.md) from [apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), delay [leaf senescence](https://genetixbay.com/knowledge/glossary/senescence.md), and with [auxin](https://genetixbay.com/knowledge/glossary/auxin.md) set whether tissue makes shoots or roots. Synthetic forms such as kinetin and 6-benzylaminopurine (BAP) are widely used in [tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md). ## In practice Growers rarely apply cytokinins directly, but the hormone links root health and shoot growth. A big, active root system supplies more cytokinin, which supports leafy, branchy growth and keeps leaves green longer. Root damage, cold or [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) roots cut cytokinin supply, and part of the slowdown you see is hormonal. In micropropagation, a high cytokinin-to-auxin ratio in the medium drives shoot multiplication; reversing the ratio drives rooting. Seaweed extracts are often marketed as "cytokinin-rich". Concentrations and effects in cannabis are not well documented. Treat claims cautiously. ## Don't confuse with - **Auxin**: promotes roots and apical dominance; often the counterweight. - **Gibberellin**: drives elongation rather than division. - **Abscisic acid**: a stress and dormancy hormone, broadly opposite in effect. ## Related terms [Auxin](https://genetixbay.com/knowledge/glossary/auxin.md), [Apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md), [Axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md) ## Read more - [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. 2. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 --- # Damping-off > The collapse of seedlings or cuttings when soil-borne pathogens such as Pythium, Rhizoctonia solani and Fusarium rot the stem at the soil line. - Canonical: https://genetixbay.com/knowledge/glossary/damping-off.html - Also written: damping off, dampening off, seedling rot, pre-emergence damping-off, Rhizoctonia solani - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Damping-off is a disease syndrome, not one pathogen. [Seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) either rot before they emerge, or they emerge and then collapse as the stem at the soil line turns brown, thin and water-soaked. The usual culprits are *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)* species, *Rhizoctonia solani*, *[Fusarium](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md)* species and sometimes *[Botrytis cinerea](https://genetixbay.com/knowledge/glossary/botrytis.md)*. Fresh cuttings can suffer the same rot at the base. ## In practice The textbook sign is a seedling that [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) fine in the morning and has toppled by evening, with a pinched "wire stem" at the base. Cold, [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) media, high humidity under domes, reused trays and unsterilised compost all raise the risk. [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) is clean or new starter media, washed trays, warm (around 22-25 °C / 72-77 °F) but not soggy conditions, a gentle fan once seedlings are up, and no heavy feeding before [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md). A collapsed seedling cannot be saved, so remove it and its plug to protect its neighbours. ## Don't confuse with - **Cutworms**: chew stems clean through at night. - **Stretching**: tall, thin stems from low light, but firm and green. - **Drowning**: limp but not pinched or brown at the base. ## Related terms [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md), [Fusarium wilt](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md), [Cutworm](https://genetixbay.com/knowledge/glossary/cutworm.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) ## Read more - [Damping-off: why seedlings collapse at the soil line](https://genetixbay.com/knowledge/germination/damping-off.md) ## Sources 1. NC State Extension. Damping-off in flower and vegetable seedlings. https://content.ces.ncsu.edu/damping-off-in-flower-and-vegetable-seedlings 2. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping --- # Dank > Dank is slang for strong-smelling, high-quality flower; originally it meant damp and musty, which in real cannabis is a warning sign. - Canonical: https://genetixbay.com/knowledge/glossary/dank.html - Also written: danky, dankness, the dank, dank weed - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Dank is slang for good cannabis, especially flower with a strong, pungent aroma. The everyday English meaning is damp, cold and musty. ## In practice When a grower calls a jar dank, they mean pungent and well made. The original meaning is worth remembering, because a genuinely damp or musty smell in flower is a defect: it can mean the buds were dried too slowly, sealed too wet, or have mould. A good cure smells clean and sharp, not like a cellar. ## Don't confuse with - **Loud**: strong aroma; near-synonym. - **Musty or hay smell**: musty points to excess moisture or mould; hay points to drying too fast or bacterial breakdown. Neither is dank in the slang sense, and a cure will never fully fix a bad dry. ## Related terms [Loud](https://genetixbay.com/knowledge/glossary/loud.md), [Fire](https://genetixbay.com/knowledge/glossary/fire.md), [Gas](https://genetixbay.com/knowledge/glossary/gas.md), [Terps](https://genetixbay.com/knowledge/glossary/terps.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) --- # Darkness before harvest > The practice of keeping plants in total darkness for 24-72 hours before cutting to boost resin; GenetixBay rates it a Myth and runs a standing challenge against it. - Canonical: https://genetixbay.com/knowledge/glossary/darkness-before-harvest.html - Also written: dark period before harvest, 48 hours of darkness, 72 hours dark, pre-harvest darkness, dark treatment, lights off before harvest, 24-72 hours darkness - Glossary category: Harvest, drying and curing · Evidence: Myth - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Darkness before harvest means switching the lights off, or covering outdoor plants, for 24-72 hours before the chop. Proponents say the stress makes the plant pump out more resin or [THC](https://genetixbay.com/knowledge/glossary/thc.md). There is no credible evidence that it does. ## In practice GenetixBay's advice is simple: keep the normal light schedule right up to harvest, and cut when the [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) say so. If a dark period helps with logistics (planning a lights-off harvest day, for example), treat it as logistics, not quality. Why it makes no sense physiologically: - the last weeks are when the plant packs on most of its final weight and resin; - trichome resin is built from [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), so switching it off takes away the supply; - a day or two of darkness can't build meaningful new gland mass; - lab-measured [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) increases from short dark periods haven't held up in controlled work. ## Don't confuse with - **The flowering dark period**: the nightly 11-12 h dark that triggers and maintains flower. - **Light deprivation**: covering outdoor plants to force early flowering. - **Harvest window**: the right time to cut, judged by trichomes. ## Myth check Myth, "complete and utter nonsense" in the founder's words. Why cut photosynthesis in the most critical part of the life cycle? The founder's standing challenge, open for 20+ years: find a peer-reviewed study (not a single-plant study, not biased or skewed) showing a benefit, and a 50-pack of seeds is yours, no questions asked. Nobody has claimed it. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md), [Flushing](https://genetixbay.com/knowledge/glossary/flushing.md), [Photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), [Trichome ripeness](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md) ## Read more - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # Decarboxylation > Decarboxylation is the loss of a carboxyl group as CO2 that turns acid cannabinoids such as THCA and CBDA into neutral THC and CBD, quickly with heat, slowly with time. - Canonical: https://genetixbay.com/knowledge/glossary/decarboxylation.html - Also written: decarb, decarbing, decarboxylate, decarboxylated, decarbed - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Decarboxylation is a chemical reaction in which a carboxylic acid group (-COOH) leaves a molecule as carbon dioxide. In cannabis it converts the [acid cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md) the plant makes ([THCA](https://genetixbay.com/knowledge/glossary/thca.md), [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md), CBGA and others) into their neutral counterparts ([THC](https://genetixbay.com/knowledge/glossary/thc.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), [CBG](https://genetixbay.com/knowledge/glossary/cbg.md)). The reaction is driven mainly by heat; it also happens slowly at room temperature during drying, curing and storage. ## In practice Smoking and vaporising decarboxylate THCA almost instantly. Raw, cured flower is still mostly THCA, which is why a COA shows THCA high and Δ9-THC low. Over long storage, slow decarboxylation raises the Δ9-THC line a little while oxidation pushes some THC on toward [CBN](https://genetixbay.com/knowledge/glossary/cbn.md). Gas chromatography decarboxylates samples in its hot inlet, which is why GC cannot measure the acids directly. GenetixBay doesn't publish processing temperatures or times. ## Units and formula Mass is lost as CO2: 1 g THCA gives at most [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) g THC; 1 g CBDA gives at most 0.877 g CBD. Real conversions fall short of that because of side reactions and degradation. ## Don't confuse with - **Oxidation**: a different reaction that degrades THC to CBN. - **Curing**: a controlled moisture decline; any decarboxylation during it is minor. ## Related terms [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [THC](https://genetixbay.com/knowledge/glossary/thc.md), [Acid vs neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md) ## Read more - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) ## Sources 1. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. 2. ElSohly MA, Slade D. 2005. Chemical constituents of marijuana: the complex mixture of natural cannabinoids. Life Sciences 78(5):539-548. --- # Decriminalisation vs legalisation > Decriminalisation removes or reduces criminal penalties for some cannabis offences; legalisation creates a lawful framework for production, sale and use. - Canonical: https://genetixbay.com/knowledge/glossary/decriminalisation.html - Also written: decriminalisation, decriminalization, legalisation, legalization, decrim - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Decriminalisation and legalisation are different legal changes. Decriminalisation (US "decriminalization") keeps cannabis prohibited but stops treating some offences, usually possession of small amounts, as crimes: they become civil violations with fines, or are simply not prosecuted. Legalisation creates a lawful system: licensed growing and retail, rules on possession and [home grow](https://genetixbay.com/knowledge/glossary/home-grow.md), taxes, testing and labelling. ## In practice Under decriminalisation there is usually still no legal way to buy, and cultivation or sale can remain serious crimes. Under legalisation, activity outside the licensed system, such as unlicensed sale or growing beyond limits, is still illegal. Some places combine the two, or legalise only medical access. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Depenalisation**: reducing penalties without changing the law's classification; often used loosely. - **Tolerance policy**: authorities choosing not to enforce, without changing the law. ## Related terms [Possession limit](https://genetixbay.com/knowledge/glossary/possession-limit.md), [Home grow](https://genetixbay.com/knowledge/glossary/home-grow.md), [Licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md), [Grey market](https://genetixbay.com/knowledge/glossary/grey-market.md), [Scheduling](https://genetixbay.com/knowledge/glossary/scheduling.md) --- # Defensive publication > Defensive publication is publicly disclosing a plant, trait or method so it becomes prior art, preventing others from later patenting it as new. - Canonical: https://genetixbay.com/knowledge/glossary/defensive-publication.html - Also written: defensive disclosure, prior art publication, publish to protect, defensive publishing - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Defensive publication means deliberately making an invention, variety or trait public, with enough detail and a reliable date, so that it counts as prior art. Patent offices cannot validly grant a patent on something already publicly disclosed, so publication keeps it in the public domain. ## In practice For cannabis, a defensive publication might be a dated, public record of a line's lineage, [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md), growth habit and lab-measured [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md), or a written description of a breeding or processing technique. To work, the record must be accessible, dated in a way that can be proven, and specific enough that a skilled person could recognise or reproduce it. GenetixBay's public [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) records, dated journals and open trial results can serve this role as a side effect of good documentation. Whether a specific record defeats a specific patent claim is a legal question for patent professionals. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Open-source seed pledge**: a promise about how seed may be used, not a disclosure for prior art. - **Trade secret**: the opposite strategy, keeping it private. ## Related terms [Utility patent](https://genetixbay.com/knowledge/glossary/utility-patent.md), [Open-source seed](https://genetixbay.com/knowledge/glossary/open-source-seed.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Open research](https://genetixbay.com/knowledge/glossary/open-research.md) ## Read more - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) - [How to document lineage evidence (GB-ID evidence levels L0-L4)](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md) ## Sources 1. Kloppenburg J. 2014. Re-purposing the master's tools: the open source seed initiative and the struggle for seed sovereignty. Journal of Peasant Studies 41(6):1225-1246. https://doi.org/10.1080/03066150.2013.875897 --- # Defoliation > Defoliation is removing fan leaves from a plant to open the canopy to light and air; GenetixBay's house view is to tuck leaves rather than strip them. - Canonical: https://genetixbay.com/knowledge/glossary/defoliation.html - Also written: defoliating, defol, defoliate, leaf stripping, stripping fan leaves - Glossary category: Cultivation and training · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Defoliation is the deliberate removal of leaves, usually large [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md), to expose [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md), improve airflow and reduce humidity within the canopy. It ranges from removing a few leaves that shade a bud to near-total stripping at set points in flower ([schwazzing](https://genetixbay.com/knowledge/glossary/schwazzing.md)). ## In practice Leaves are the plant's solar panels: they capture light and supply sugars to the developing flowers. Removing a shading leaf can help a bud underneath; removing too many cuts [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md). Responses vary sharply by cultivar. Most growers who defoliate do so lightly before the flip and again around week 3 of flower. ## Myth check House position: "tuck, don't pluck". Maximise leaf surface area, like a solar farm for the buds. Stripping within reason doesn't appear to hurt yield, and some clones grow just as fast or faster after losing most leaves, while others suffer; in the founder's experience tucking helps more. Whether defoliation raises yield or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) is an open question for GenetixBay [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md). Evidence: Contested. See [defoliation and lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Don't confuse with - **Tucking**: moving leaves aside instead of removing them. - **Leaf drop (senescence)**: natural yellowing and loss of leaves late in flower. ## Related terms [Lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md), [Schwazzing](https://genetixbay.com/knowledge/glossary/schwazzing.md), [Tucking](https://genetixbay.com/knowledge/glossary/tucking.md), [Fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md) ## Read more - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) --- # Degree-day > A unit of accumulated heat above a pest's lower developmental threshold; development finishes when a stage's degree-day total is reached, whatever the calendar says. - Canonical: https://genetixbay.com/knowledge/glossary/degree-day.html - Also written: degree-days, growing degree-day, GDD, heat units, thermal time - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A degree-day is one day spent one degree above an organism's [lower developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md). A pest needing 150 degree-days (C) per generation with a threshold of 10 C finishes in 15 days at a steady 20 C (10 degrees above threshold) and in 10 days at 25 C. UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) describes degree-days as physiological time: heat, not days, drives insect and mite development. ## In practice Outdoors, degree-day models time scouting and treatment, for example predicting moth egg-laying from trap catches. Indoors the temperature is near constant, so you can turn degree-days straight into days: divide the requirement by (room temperature minus threshold). Use the leaf or [canopy temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md), not the thermostat. Above the upper threshold the sum stops adding up, because development slows or stops. ## Don't confuse with - **Calendar spray schedule**: ignores temperature, so it drifts out of step with the pest. - **Growing degree-days for crops**: same idea, different thresholds. ## Related terms [Developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md), [Life table](https://genetixbay.com/knowledge/glossary/life-table.md), [Generation time](https://genetixbay.com/knowledge/glossary/generation-time.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) - [Budworms on cannabis: corn earworm and tobacco budworm in numbers](https://genetixbay.com/knowledge/pests/budworms-corn-earworm.md) - [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Sources 1. UC IPM. Degree-Days: About Degree-Days. University of California ANR. https://ipm.ucanr.edu/WEATHER/ddconcepts.html --- # Dehumidifier > A dehumidifier removes water vapour from grow-room air, usually by condensing it on a cold coil; it is the main tool for controlling humidity in flower. - Canonical: https://genetixbay.com/knowledge/glossary/dehumidifier.html - Also written: dehumidifiers, dehu, dehumidification, desiccant dehumidifier, refrigerant dehumidifier - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A dehumidifier pulls water vapour out of the air. Refrigerant (compressor) units blow air over a cold coil where water condenses, then reheat the air slightly over the hot coil; they work best above about 18 °C (64 °F). Desiccant units absorb water on a drying wheel and work better in cold spaces. Both add heat to the room: refrigerant units release the latent heat of the water they condense plus their own power. ## In practice Plants [transpire](https://genetixbay.com/knowledge/glossary/transpiration.md) most of the water you give them. A flower tent watered with 10 L (2.6 US gal) a day releases close to that into the air, so the dehumidifier must remove a similar amount when the [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) cannot. Capacity is rated in litres or pints per day at specific test conditions (often 30 °C / 80% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) or 27 °C / 60% RH); real capacity at 25 °C and 50% RH is much lower. Size with margin. The critical time is lights-off, when temperature drops and RH climbs towards the [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md). Run the dehumidifier on a humidistat through the night in flower. Empty or [drain](https://genetixbay.com/knowledge/glossary/runoff.md) it continuously; a full tank stops it. ## Don't confuse with - **Exhaust fan**: removes humidity only if outside air is drier. - **Air conditioner**: dehumidifies as a side effect while cooling, often not enough on its own. ## Related terms [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Dew point](https://genetixbay.com/knowledge/glossary/dew-point.md), [Humidifier](https://genetixbay.com/knowledge/glossary/humidifier.md), [Absolute humidity](https://genetixbay.com/knowledge/glossary/absolute-humidity.md) ## Read more - [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Sources 1. Corredor-Perilla IC, Kwon H, Park J, 2025. High relative humidity in cannabis cultivation (effects on flowering, biomass and cannabinoids). Frontiers in Plant Science 16:1678142. https://doi.org/10.3389/fpls.2025.1678142 --- # Delta-8 THC > Delta-8 THC is an isomer of THC with the double bond shifted one position; the plant makes only traces, so commercial delta-8 is semi-synthetic, usually converted from CBD. - Canonical: https://genetixbay.com/knowledge/glossary/delta-8-thc.html - Also written: Δ8-THC, delta 8, d8, delta-8, delta-8-tetrahydrocannabinol - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Delta-8 THC (Δ8-THC) is an isomer of [Δ9-THC](https://genetixbay.com/knowledge/glossary/thc.md): the same atoms, with the ring double bond in a different position. It is chemically more stable than Δ9-THC and forms naturally only in trace amounts in cannabis. Its reported effects are described as similar to but milder than Δ9-THC; human data are limited. ## In practice Almost all delta-8 sold today is semi-synthetic: [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) (often from [hemp](https://genetixbay.com/knowledge/glossary/hemp.md)) is chemically converted with acids and solvents. That process can leave by-products, other isomers and residues that a standard potency panel does not identify, which is why independent testing of these products often finds unlabeled compounds. GenetixBay is about growing plants; it gives no conversion methods. Legal status varies widely and changes often; check local rules. ## Don't confuse with - **Δ9-THC**: the main THC isomer the plant (via [THCA](https://genetixbay.com/knowledge/glossary/thca.md)) actually produces. - **HHC**: a hydrogenated derivative, also semi-synthetic. - **THCV**: a natural varin [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md), not a THC isomer. ## Related terms [THC](https://genetixbay.com/knowledge/glossary/thc.md), [HHC](https://genetixbay.com/knowledge/glossary/hhc.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md), [Isolate](https://genetixbay.com/knowledge/glossary/isolate.md) ## Sources 1. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. 2. ElSohly MA, Slade D. 2005. Chemical constituents of marijuana: the complex mixture of natural cannabinoids. Life Sciences 78(5):539-548. --- # Developmental threshold > The temperatures below which (lower) and above which (upper) a pest's development stops or slows; they bound degree-day models. - Canonical: https://genetixbay.com/knowledge/glossary/developmental-threshold.html - Also written: lower developmental threshold, upper developmental threshold, base temperature, lower threshold, upper threshold, thermal threshold - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The lower developmental threshold is the temperature at which development halts; the upper threshold is where it slows or stops because heat becomes harmful. Lower thresholds are usually estimated by extrapolating a straight line of development rate against temperature down to zero. For many greenhouse [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) and insects the lower threshold sits around 8-12 C and the upper around 32-40 C, but each species and stage differs. ## In practice Between the thresholds, warmer means faster generations. Near the upper threshold, mortality and egg failure rise, so the fastest growth (highest r_m) usually sits a few degrees below it. Grow rooms at 24-30 C sit right in the fast zone for spider mites, [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) and [aphids](https://genetixbay.com/knowledge/glossary/aphid.md). Indoor nights rarely drop below a pest's lower threshold, which is why indoor populations never pause. ## Don't confuse with - **Critical thermal limit**: the temperature that kills, not just stops development. - **Diapause**: a programmed dormancy, triggered by [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md) as well as temperature. ## Related terms [Degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [Life table](https://genetixbay.com/knowledge/glossary/life-table.md), [Diapause](https://genetixbay.com/knowledge/glossary/diapause.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) ## Sources 1. UC IPM. Degree-Days: About Degree-Days. University of California ANR. https://ipm.ucanr.edu/WEATHER/ddconcepts.html --- # Dew point > Dew point is the temperature at which air becomes saturated and water starts condensing; when leaves or buds cool to it, free water forms and mould risk jumps. - Canonical: https://genetixbay.com/knowledge/glossary/dew-point.html - Also written: dewpoint, dew-point temperature, Td, condensation point - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The dew point is the temperature to which air must be cooled, at constant [water content](https://genetixbay.com/knowledge/glossary/moisture-content.md), to reach 100% [relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md). Any surface at or below the dew point collects condensation. Because it depends only on how much water the air holds, it is a more stable measure of moisture than RH. ## In practice Air at 26 °C (79 °F) and 60% RH has a dew point of about 17.6 °C (64 °F). If lights go off and the room or the inside of a dense [cola](https://genetixbay.com/knowledge/glossary/cola.md) drops to that temperature, water condenses on tissue. Leaves radiating heat to a cool ceiling or wall can sit a degree or two below air temperature, so trouble can start even when the air itself is above the dew point. Rule of thumb for flower: keep the coldest surface in the canopy at least 3–5 °C (5–9 °F) above the dew point, especially in the first hour after lights-off. Run [dehumidification](https://genetixbay.com/knowledge/glossary/dehumidifier.md) and airflow through the dark period and ramp temperature down slowly. Free water on buds for a few hours is enough for [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) spores to [germinate](https://genetixbay.com/knowledge/glossary/germination.md). ## Units and formula Magnus approximation (°C): Td = 243.04 × γ ÷ (17.625 − γ), where γ = ln(RH ÷ 100) + 17.625 × T ÷ (243.04 + T). ## Don't confuse with - **Relative humidity**: changes with temperature; dew point does not. - **Frost point**: the equivalent below 0 °C, where ice forms. ## Related terms [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [Absolute humidity](https://genetixbay.com/knowledge/glossary/absolute-humidity.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [DIF](https://genetixbay.com/knowledge/glossary/dif.md), [Dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) ## Read more - [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Sources 1. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm --- # Dialled in > Dialled in describes a grow, room or recipe tuned until results are consistent and near the plant's potential, run after run. - Canonical: https://genetixbay.com/knowledge/glossary/dialled-in.html - Also written: dialed in, dialled-in, dialed-in, dial in, dialling in - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Dialled in (US "dialed in") means a grow has been tuned until it performs consistently: environment, light, feeding and irrigation are matched to the cultivar and the room, and results repeat. ## In practice Getting dialled in is a cycle of measuring and adjusting: logging temperature, [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) and [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) through the day, measuring [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) across the canopy, tracking feed and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md) and [pH](https://genetixbay.com/knowledge/glossary/ph.md), and recording dry weight and quality at the end. A dialled-in room hits its targets, for example about 1.2-1.5 kPa VPD in mid flower and an [even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md) at the planned PPFD, without daily firefighting. A setup is dialled in for one cultivar at a time. Cultivars differ in nutrient demand, Ca/Mg use, [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) and light tolerance, so a new cut usually needs a few runs. "Test your cultivar" is the GenetixBay approach: record what you change and what it does. ## Don't confuse with - **Maxed out**: pushing every input to the limit. Dialled in is about consistency, not extremes. ## Related terms [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Crop steering](https://genetixbay.com/knowledge/glossary/crop-steering.md), [Grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) ## Read more - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) --- # Diamonds > Diamonds are large crystals of THCA, typically grown out of a solvent extract and sold alone or in terpene-rich sauce; they are nearly pure THCA. - Canonical: https://genetixbay.com/knowledge/glossary/diamonds.html - Also written: THCA diamonds, THC diamonds, THCA crystals, diamonds and sauce, crystalline THCA - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Diamonds are crystalline [THCA](https://genetixbay.com/knowledge/glossary/thca.md), grown in coarse [crystals](https://genetixbay.com/knowledge/glossary/trichome.md) rather than powder. In typical production a [fresh-frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) or cured [solvent extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md) is left under controlled conditions so THCA crystallises out of solution, separating from a liquid fraction rich in [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) (the "sauce"). The crystals can be cleaned and sold alone or recombined with sauce as "diamonds and sauce". ## In practice Pure diamonds can test well above 90% THCA because they're essentially one compound. Like all THCA, they convert to [THC](https://genetixbay.com/knowledge/glossary/thc.md) with heat; a lab's [total THC calculation](https://genetixbay.com/knowledge/glossary/total-thc.md) applies the 0.877 factor, so 98% THCA corresponds to about 86% total THC. The crystals themselves have little smell; aroma comes from the sauce. Diamonds made from rosin also exist and are solventless. GenetixBay defines the product only; no crystallisation methods. ## Don't confuse with - **Isolate**: also near-pure, but usually a fine powder and usually [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) or THCA refined to a standard grade. - **Sugar**: small crystals in a wet matrix. - **Gemstones**: obviously unrelated; "diamonds" is purely a product nickname. ## Related terms [Sauce](https://genetixbay.com/knowledge/glossary/sauce.md), [Isolate](https://genetixbay.com/knowledge/glossary/isolate.md), [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [Live resin](https://genetixbay.com/knowledge/glossary/live-resin.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md) --- # Diapause > A programmed, hormone-controlled dormancy that a pest enters in response to cues such as short days and cool temperatures, ahead of bad conditions. - Canonical: https://genetixbay.com/knowledge/glossary/diapause.html - Also written: overwintering diapause, reproductive diapause, diapausing females - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Diapause is a genetically programmed pause in development or reproduction, triggered in advance by cues rather than by the bad conditions themselves. In the [two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) only adult females diapause; the cue is short [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md) experienced by the immature stages, strengthened by cool temperatures, and diapausing females turn orange-red and stop laying. Reviews of spider mite photoperiodism describe this response in detail. ## In practice Diapause matters indoors in two ways. A 12-hour flowering photoperiod and cool nights can push some mite strains toward diapause, so orange mites hiding in cracks and canopy debris survive between runs. Several [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md) also diapause under short days, notably some strains of [Orius](https://genetixbay.com/knowledge/glossary/orius.md) bugs and the [aphid](https://genetixbay.com/knowledge/glossary/aphid.md) midge, so they can fail in flower rooms unless a non-diapausing strain is used. ## Don't confuse with - **Quiescence**: an immediate slowdown when conditions turn bad, reversed as soon as they improve. - **Carmine mite colour**: red mites are not necessarily diapausing; some forms are red all year. ## Related terms [Developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md), [Degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ## Sources 1. Goto, S.G., 2016. Physiological and molecular mechanisms underlying photoperiodism in the spider mite: comparisons with insects. Journal of Comparative Physiology B 186:969-984. https://doi.org/10.1007/s00360-016-1018-9 2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # DIF > DIF is day temperature minus night temperature; a larger positive DIF lengthens stems, while zero or negative DIF tends to keep plants shorter. - Canonical: https://genetixbay.com/knowledge/glossary/dif.html - Also written: day-night temperature difference, temperature differential, positive DIF, negative DIF, temperature DIF, day/night differential - Glossary category: Environment and light · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" DIF (from "difference") is the day temperature minus the night temperature. A day of 26 °C and a night of 20 °C is a DIF of +6 °C (about +11 °F). Research on greenhouse ornamentals showed that stem elongation responds to DIF more than to average temperature: positive DIF increases [internode length](https://genetixbay.com/knowledge/glossary/internode.md), zero DIF reduces it, and negative DIF (cooler days than nights) reduces it further. A short temperature drop at dawn gives part of the effect. ## In practice Growers use DIF mainly to manage [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) in early flower. Keeping the gap small, around 0–4 °C (0–7 °F), may help restrain height in stretchy cultivars; a larger gap of 6–10 °C (11–18 °F) late in flower is often used for colour. Evidence in cannabis specifically is thin; the effect is well documented in other crops. *Supported* by extrapolation. Watch the humidity side. When lights go off and the room cools quickly, [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) climbs and may approach the [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) on leaves and buds, inviting [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md). Ramp temperature down, run [dehumidification](https://genetixbay.com/knowledge/glossary/dehumidifier.md) at lights-off, and keep air moving. ## Units and formula DIF = day temperature − night temperature (°C or °F). ## Don't confuse with - **Cold nights**: a large positive DIF used for colour; see that entry for what it does and does not do. - **VPD**: humidity-driven, though DIF changes [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) at night. ## Related terms [Temperature](https://genetixbay.com/knowledge/glossary/temperature.md), [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md), [Cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md), [Dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) ## Read more - [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) --- # Differential diagnosis > The method of listing every cause that could produce a symptom, then ruling causes out with cheap checks and tests until one or two remain. - Canonical: https://genetixbay.com/knowledge/glossary/differential-diagnosis.html - Also written: diagnostic differential, rule-out list - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A differential diagnosis is the clinician's way of thinking applied to plants: list all the causes that fit the symptom, then eliminate them in order of likelihood and cost of checking. Plant nutrition texts stress that visual symptoms alone are often ambiguous and need confirmation by analysis or by the plant's response to correction (Marschner 2012). ## In practice GenetixBay's order is: where on the plant it started, the pattern, then [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) and watering, [pH](https://genetixbay.com/knowledge/glossary/ph.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), climate, light, pests and disease, and only then a nutrient. The diagnosis graph behind the symptom checker scores each cause this way and asks the question that best separates the leading candidates. ## Don't confuse with - **A guess from one photo**: one answer with no ruled-out alternatives. - **A tissue test**: one of the tests used within a differential, not the method itself. ## Related terms [Chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md), [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md) ## Read more - [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) - [Cannabis lookalike problems: how to tell them apart](https://genetixbay.com/knowledge/diagnosis/lookalikes.md) - [How to describe your plant's problem so it can be diagnosed](https://genetixbay.com/knowledge/diagnosis/how-to-describe-your-plants-problem.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Dioecious > Having male and female flowers on separate individual plants; drug-type cannabis is naturally dioecious with an XY sex-chromosome system. - Canonical: https://genetixbay.com/knowledge/glossary/dioecious.html - Also written: dioecy, dioecism, separate sexes, two-house plant - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A dioecious species has separate male and female individuals: each plant carries only staminate (male) or only pistillate (female) flowers. Cannabis is naturally dioecious. Females are XX and males XY, with [sex chromosomes](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md) confirmed by cytogenetics and genome studies (Divashuk et al. 2014; Prentout et al. 2020). Seed populations normally come out roughly half male, half female. ## In practice Dioecy is why growers sex plants and why seedless flower is possible: remove the males, keep the females unpollinated. It is also why regular seed matters for breeders. Every true cross needs a male, which is why GenetixBay encourages keeping and documenting good males in [the Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md). [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md) is made by inducing pollen on a female; the offspring are XX and almost all female. ## Don't confuse with - **Monoecious**: male and [female flowers](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) on the same plant, as in some bred [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md). - **Hermaphrodite (intersex)**: an abnormal dioecious individual showing both sexes. - **Feminised**: a seed-production method, not a change to the species' biology. ## Myth check GenetixBay position: drug-type cannabis has been recorded as dioecious and stable throughout history. [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) lines are mainly the result of breeder error (repeated selfing, careless feminising, unstable "[pollen chucker](https://genetixbay.com/knowledge/glossary/pollen-chucker.md)" releases), not a natural tendency. Stress reveals susceptible genetics; it doesn't make [intersex](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) normal. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Monoecious](https://genetixbay.com/knowledge/glossary/monoecious.md), [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), [Staminate flower](https://genetixbay.com/knowledge/glossary/staminate-flower.md), [Pistillate flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) ## Read more - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) ## Sources 1. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 2. Prentout D, Razumova O, Rhone B, et al. 2020. An efficient RNA-seq-based segregation analysis identifies the sex chromosomes of Cannabis sativa. Genome Research 30(2):164-172. https://doi.org/10.1101/gr.251207.119 3. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 --- # Diploid > A diploid organism carries two complete sets of chromosomes, one from each parent; normal cannabis is diploid with 2n = 20. - Canonical: https://genetixbay.com/knowledge/glossary/diploid.html - Also written: diploidy, 2n, diploid plant - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A diploid plant carries two full sets of [chromosomes](https://genetixbay.com/knowledge/glossary/chromosome.md) in its body cells, one set from the pollen parent and one from the seed parent. Normal cannabis is diploid with 2n = 20 chromosomes. Its pollen and ovules are haploid (n = 10), so fertilisation restores the diploid number. ## In practice Diploidy is why every gene comes in two copies and why simple [Mendelian ratios](https://genetixbay.com/knowledge/glossary/mendelian-inheritance.md) work. With two [alleles](https://genetixbay.com/knowledge/glossary/allele.md) per [locus](https://genetixbay.com/knowledge/glossary/locus.md) a plant is either [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) or [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md), and a heterozygote passes each allele to half its gametes. Almost all cannabis grown today is diploid. [Polyploid](https://genetixbay.com/knowledge/glossary/polyploid.md) plants (triploids with three sets, tetraploids with four) are made deliberately, for example to produce mostly seedless triploid crops, and they do not follow diploid ratios. ## Units and formula Cannabis: haploid n = 10; diploid 2n = 20; triploid 3n = 30; tetraploid 4n = 40. ## Don't confuse with - **Polyploid**: more than two chromosome sets. - **Haploid**: one set, as in pollen and egg cells. - **Dioecious**: separate male and female plants. Cannabis is both diploid and [dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md), but the two words describe different things. ## Related terms [Polyploid](https://genetixbay.com/knowledge/glossary/polyploid.md), [Chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 2. Kurtz LE, Brand MH, Lubell-Brand JD. 2023. Gene dosage at the autoflowering locus effects flowering timing and plant height in triploid cannabis. Journal of the American Society for Horticultural Science 148(2):83-88. https://doi.org/10.21273/JASHS05293-23 --- # Dissolved oxygen > Dissolved oxygen (DO) is the amount of oxygen gas held in water or nutrient solution, measured in mg/L, and roots need it to respire and take up nutrients. - Canonical: https://genetixbay.com/knowledge/glossary/dissolved-oxygen.html - Also written: DO, DO levels, oxygen in solution, O2 in water, mg/L oxygen - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Dissolved oxygen is the concentration of O₂ gas held in a liquid. Roots respire, using oxygen to power growth and active nutrient uptake. In soil and [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) media they get it from air in the pores; in water culture they depend entirely on what is dissolved. How much the solution can hold depends mainly on temperature: cold water holds more. ## In practice Hydroponic guidance for leafy crops recommends keeping DO at about 7-8 mg/L or more, with stress and failure as levels drop below about 3-4 mg/L. Saturated fresh water holds roughly 9 mg/L at 20 °C (68 °F) and about 8 mg/L at 25 °C (77 °F). Low DO shows as brown, slimy roots, wilting and sudden [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md). Raise DO with cooler solution, more aeration and circulation, and fewer dead spots; keep root mass healthy, since rotting roots and microbes consume oxygen. ## Units and formula mg/L (equal to ppm for oxygen in water) or % saturation. A handheld optical DO meter is the most reliable test. ## Don't confuse with - **Hydrogen peroxide**: releases oxygen briefly as it breaks down; not a sustained DO source. - **Aeration**: the process; DO is the measured result. ## Related terms [Air stone](https://genetixbay.com/knowledge/glossary/air-stone.md), [Chiller](https://genetixbay.com/knowledge/glossary/chiller.md), [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md) ## Read more - [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) - [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ## Sources 1. Cornell CEA. Hydroponic lettuce handbook. https://cea.cals.cornell.edu/ 2. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 --- # Distillate > Distillate is a highly refined cannabis oil in which cannabinoids, usually THC or CBD, have been separated from most other compounds by distillation, leaving a clear, almost odourless oil. - Canonical: https://genetixbay.com/knowledge/glossary/distillate.html - Also written: THC distillate, cannabis distillate, distilled oil, distillate oil - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Distillate is the product of refining a crude cannabis extract by distillation under vacuum, a step that separates compounds by boiling point. The process [decarboxylates](https://genetixbay.com/knowledge/glossary/decarboxylation.md) the acids along the way, so finished distillate is mostly neutral [THC](https://genetixbay.com/knowledge/glossary/thc.md) (or [CBD](https://genetixbay.com/knowledge/glossary/cbd.md)), commonly reported above 80-90% of a single [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md). [Terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), waxes, lipids and [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) are largely removed, leaving a viscous, pale gold to clear oil. ## In practice Distillate is the base of many vape cartridges, edibles and infused products because it is consistent and has little flavour. Terpenes are often added back for taste, from cannabis or other plant sources, so a cartridge's aroma may say little about its starting material. Some products marketed as cannabis distillate contain semi-synthetic cannabinoids; only a full lab panel tells you. Distillation is an industrial process; GenetixBay gives no methods. ## Don't confuse with - **Isolate**: a crystalline, single-compound product, purer than distillate. - **Full-spectrum extract**: retains more of the plant's compound range. - **Crude oil (extract)**: the unrefined starting point. ## Related terms [Isolate](https://genetixbay.com/knowledge/glossary/isolate.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md), [Entourage effect](https://genetixbay.com/knowledge/glossary/entourage-effect.md) --- # DLI > Daily light integral: the total number of PAR photons a square metre of canopy receives in one day, in mol/m²/day; PPFD multiplied by hours of light. - Canonical: https://genetixbay.com/knowledge/glossary/dli.html - Also written: daily light integral, daily light sum, mol/m²/day, mol/m2/d - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" DLI (daily light integral) is the total [PAR](https://genetixbay.com/knowledge/glossary/par.md) light delivered to a surface over 24 hours, in moles of photons per square metre per day (mol/m²/day). It joins intensity and duration into one number, which matters because plants respond to both. Growth tracks DLI more closely than it tracks [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) alone. ## In practice A canopy at 900 µmol/m²/s for 12 hours receives 900 × 12 × 0.0036 ≈ 39 mol/m²/day. The same canopy in veg at 600 µmol/m²/s for 18 hours gets about 39 mol/m²/day too. Outdoors, clear summer days at mid-latitudes reach roughly 50–60 mol/m²/day. Rough indoor targets: [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and clones 6–15, veg 25–40, flower 35–55 mol/m²/day (higher only with [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md), good heat removal and strong genetics). DLI is why flower intensity matters so much: the [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) is fixed near 12 hours, so the only way to add light is to raise PPFD. It is also why sunrise and sunset ramps add little to the daily total: low PPFD for an hour contributes little to DLI. ## Units and formula - DLI (mol/m²/day) = PPFD (µmol/m²/s) × hours × 3,600 ÷ 1,000,000 - Shortcut: DLI = PPFD × hours × 0.0036 - Required PPFD = DLI ÷ (hours × 0.0036) ## Don't confuse with - **PPFD**: an instantaneous rate, not a daily total. - **Photoperiod**: hours of light only, with no intensity. ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [Light intensity](https://genetixbay.com/knowledge/glossary/light-intensity.md), [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 --- # Dominant > A dominant allele is one whose effect shows in the phenotype even when only one copy is present, masking the other (recessive) allele at that locus. - Canonical: https://genetixbay.com/knowledge/glossary/dominant.html - Also written: dominance, dominant allele, complete dominance - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An [allele](https://genetixbay.com/knowledge/glossary/allele.md) is dominant when one copy is enough for its trait to show. In a heterozygous plant (Aa), the dominant allele A sets the phenotype and the [recessive allele](https://genetixbay.com/knowledge/glossary/recessive.md) a is hidden. Dominance describes how two alleles at one [locus](https://genetixbay.com/knowledge/glossary/locus.md) interact; it says nothing about whether the trait is good, common or strong. ## In practice Dominance is why a cross can hide traits. Cross a plant carrying a dominant trait with one lacking it and every [F1](https://genetixbay.com/knowledge/glossary/f1.md) may show the dominant version. The recessive allele is still there, carried silently, and returns in about a quarter of [F2](https://genetixbay.com/knowledge/glossary/f2.md) plants (the 3:1 ratio). [Autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) is the classic cannabis example of the reverse case: the autoflowering trait at the Autoflower1 locus behaves as recessive, so an auto crossed to a [photoperiod plant](https://genetixbay.com/knowledge/glossary/photoperiod.md) gives photoperiod F1s (Toth et al. 2022). Breeders then need an F2 or a backcross to recover autos. ## Don't confuse with - **Codominant**: both alleles show (THC and [CBD synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) at the B locus). Not a case of one masking the other. - **Prevalent**: a dominant allele can be rare in a population; dominance is not frequency. - **"Dominant" in strain marketing**: "indica-dominant" is a shape label, not a genetic statement. ## Related terms [Recessive](https://genetixbay.com/knowledge/glossary/recessive.md), [Codominant](https://genetixbay.com/knowledge/glossary/codominant.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md), [Punnett square](https://genetixbay.com/knowledge/glossary/punnett-square.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 2. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 --- # Doubling time > The days an unchecked pest population needs to double, equal to ln 2 divided by r_m (0.693 / r_m). - Canonical: https://genetixbay.com/knowledge/glossary/doubling-time.html - Also written: population doubling time - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Doubling time is the time a population growing at its intrinsic rate of increase takes to double: 0.693 divided by r_m. An r_m of 0.2 per day gives 3.5 days; 0.35 per day gives 2 days. It is the most intuitive way to explain why a week of inaction matters. ## In practice Doubling time is an upper bound from lab conditions; real rooms with predators or poor food run slower. Even so, a pest that doubles every 3 days goes up about 128-fold in 3 weeks (seven doublings), which is why weekly scouting is the minimum. ## Don't confuse with - **Generation time**: birth to next birth, several doublings long. ## Related terms [Intrinsic rate of increase (r_m)](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [Generation time](https://genetixbay.com/knowledge/glossary/generation-time.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) ## Sources 1. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605 --- # Downy mildew > An oomycete leaf disease of cannabis, historically attributed to Pseudoperonospora cannabina, causing yellow patches above and grey-purple fuzz under leaves in cool, wet weather. - Canonical: https://genetixbay.com/knowledge/glossary/downy-mildew.html - Also written: Pseudoperonospora cannabina, Pseudoperonospora humuli, downy mold, DM - Glossary category: Pests and diseases · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Downy mildew is a disease caused by oomycetes, water moulds rather than true fungi. On cannabis it has historically been attributed to *Pseudoperonospora cannabina*; the hop downy mildew pathogen, *Pseudoperonospora humuli*, has also been reported on [hemp](https://genetixbay.com/knowledge/glossary/hemp.md). Infected leaves show pale yellow, angular patches on the upper surface and greyish to purplish downy growth underneath, where spores form. ## In practice Downy mildew needs free water and cool temperatures, so it is chiefly an outdoor and greenhouse problem in wet spells, not a common indoor one. Spores spread by wind and splash, and infected leaves curl, brown and drop. Growers manage it with airflow, wider spacing, watering at the base, removing infected leaves and keeping hop yards and cannabis apart where both are grown. Diagnosis is easier with a hand lens on the leaf underside early in the morning, when sporulation is visible. Check what is registered for cannabis locally. ## Don't confuse with - **Powdery mildew**: white powder on upper surfaces, grows without leaf wetness. - **Septoria leaf spot**: tan lesions with dark margins and pycnidia. - **Magnesium deficiency**: [interveinal yellowing](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) with no growth underneath. ## Related terms [Powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md), [Leaf spot](https://genetixbay.com/knowledge/glossary/leaf-spot.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md) ## Read more - [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) ## Sources 1. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 2. BC Ministry of Agriculture. Diseases of cannabis in British Columbia (factsheet). https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/agriculture-and-seafood/animal-and-crops/plant-health/disease-factsheets/specialty-crops/diseases_of_cannabis_in_british_columbia.pdf --- # Drain-to-waste > Drain-to-waste fertigation feeds each plant fresh nutrient solution and lets the runoff leave the system rather than returning it to the reservoir. - Canonical: https://genetixbay.com/knowledge/glossary/drain-to-waste.html - Also written: drain to waste, DTW, run to waste, open system, free-draining fertigation - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Drain-to-waste (an open system) is a [fertigation](https://genetixbay.com/knowledge/glossary/fertigation.md) method in which every irrigation is fresh, [pH-](https://genetixbay.com/knowledge/glossary/ph-down.md) and EC-adjusted solution, and whatever [drains](https://genetixbay.com/knowledge/glossary/runoff.md) from the pot goes to a drain or collection tank and is not reused. It is the standard method for [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and rockwool, both commercially and in many home grows. ## In practice Because the plant always sees a known solution, drain-to-waste is stable and easy to diagnose. Growers monitor runoff volume (often 10-20% of input), runoff [EC](https://genetixbay.com/knowledge/glossary/ec.md) and runoff [pH](https://genetixbay.com/knowledge/glossary/ph.md) to see what is happening in the medium. It pairs naturally with crop steering, where the size and timing of irrigations are adjusted to push vegetative or generative growth. The cost is more water and nutrient use than a [recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md) and the need to dispose of runoff responsibly. ## Don't confuse with - **Recirculating (closed)**: solution returns to the reservoir and is reused. - **Hand watering to runoff**: the same principle done manually in soil or coco. ## Related terms [Recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [Drip irrigation](https://genetixbay.com/knowledge/glossary/drip-irrigation.md), [Crop steering](https://genetixbay.com/knowledge/glossary/crop-steering.md), [Watering to runoff](https://genetixbay.com/knowledge/glossary/watering-to-runoff.md), [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md) ## Read more - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 2. Stemeroff J, 2018. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 --- # Drip irrigation > Drip irrigation delivers water or nutrient solution through tubing and emitters directly to each plant's medium, in measured amounts on a timer or controller. - Canonical: https://genetixbay.com/knowledge/glossary/drip-irrigation.html - Also written: drip system, drip feed, drip emitters, dripper, drippers, top-feed drip - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Drip irrigation is a system of pipes, small-bore tubing and emitters that places water or nutrient solution right at the base of each plant. A pump or pressurised line and a timer or controller decide when and how much. It is the delivery method behind most [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) [fertigation](https://genetixbay.com/knowledge/glossary/fertigation.md) and many automated soil grows. ## In practice Emitters are rated by flow, commonly 1-4 L/h; pressure-compensating types give equal flow along long lines. Use one to four emitters per pot depending on [pot size](https://genetixbay.com/knowledge/glossary/pot-size.md), spread so the whole medium wets, and add a stake so they stay put. Filters before the emitters prevent clogging from sediment and precipitated salts. The solution can be used once ([drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md)) or collected and returned ([recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md)). Measure each irrigation: collect output from a test emitter and a test pot's [runoff](https://genetixbay.com/knowledge/glossary/runoff.md). ## Don't confuse with - **Fertigation**: feeding nutrients through irrigation; drip is the hardware that usually does it. - **Ebb and flow**: floods a whole tray instead of feeding each pot. ## Related terms [Fertigation](https://genetixbay.com/knowledge/glossary/fertigation.md), [Drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), [Recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [High-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md), [Crop steering](https://genetixbay.com/knowledge/glossary/crop-steering.md) ## Read more - [Recirculating drip (top-feed, runoff returns)](https://genetixbay.com/knowledge/systems/recirculating-drip.md) - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 2. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 --- # Drop > A drop is a seed or clone release, often limited and announced in advance, especially from popular breeders or seed vendors. - Canonical: https://genetixbay.com/knowledge/glossary/drop.html - Also written: seed drop, drops, new drop, limited drop - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A drop is a release of new seed, clones or product, usually limited in quantity and announced ahead of time to build demand. "The drop sold out in four minutes" is a typical boast. ## In practice Drops borrow from streetwear marketing: scarcity, countdowns and exclusive names. For buyers, the useful questions are the same as for any seed: what are the parents, how many generations has it been worked, how many tester grows reported, what [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md), what [germination](https://genetixbay.com/knowledge/glossary/germination.md) rate on this batch? A limited drop of an untested cross is still an untested cross. Seed sales and shipping are regulated differently in different places. Check local rules before buying or importing seed. ## Don't confuse with - **Restock**: bringing back an existing product, possibly from a new [seed batch](https://genetixbay.com/knowledge/glossary/seed-run.md) with different parents. - **Release**: the neutral term; a drop implies hype and limited stock. ## Related terms [Restock](https://genetixbay.com/knowledge/glossary/restock.md), [Hype strain](https://genetixbay.com/knowledge/glossary/hype-strain.md), [Seed bank](https://genetixbay.com/knowledge/glossary/seed-bank.md), [Test grow](https://genetixbay.com/knowledge/glossary/test-grow.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) --- # Dry trim > Trimming sugar leaves after buds have dried, leaving the leaves on during the dry to slow it and protect the bud. - Canonical: https://genetixbay.com/knowledge/glossary/dry-trim.html - Also written: dry trimming, trimming dry, dry-trimmed, trim after drying, brush trim - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Dry trimming means hanging branches or whole plants with their [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) (and sometimes [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md)) still attached, drying them, and trimming once the buds are dry enough to jar. The leaves curl around the buds as they dry, acting as a slow-release humidity shield. ## In practice Wet versus dry trim is grower preference in the GenetixBay view. The founder has trimmed hundreds of pounds and prefers dry trimming: they brush dry buds free of their dried leaves rather than scissoring wet ones, even at the cost of a little [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) loss. It all gets used anyway, because the trim goes to processing. Reasons growers dry trim: - slower, more even dry, especially in dry climates; - much less sticky, faster work per gram; - leaves crumble off easily once dry. The costs: - more [drying space](https://genetixbay.com/knowledge/glossary/drying-room.md); - more mould risk in humid rooms; - dry heads break off more readily with handling, so work gently and cool. Trim once the small stems snap rather than bend. ## Don't confuse with - **Wet trim**: trimming fresh, before the dry. - **Machine trim**: mechanical tumbling or cutting, wet or dry. - **Curing**: after trimming, not instead of it. ## Related terms [Wet trim](https://genetixbay.com/knowledge/glossary/wet-trim.md), [Sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md), [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), [Whole-plant hang](https://genetixbay.com/knowledge/glossary/whole-plant-hang.md), [Stem snap test](https://genetixbay.com/knowledge/glossary/stem-snap-test.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 --- # Dry weight > The weight of cannabis after drying (and usually trimming), the basis growers use for yield; it is typically about 20-25% of trimmed wet weight. - Canonical: https://genetixbay.com/knowledge/glossary/dry-weight.html - Also written: dried weight, final dry weight, cured weight, dry bud weight, dry mass - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Dry weight is the mass of harvested flower once it has been dried to a stable, jar-ready moisture, generally around 0.55-0.65 [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md). When growers quote yield in grams per plant, [grams per square metre](https://genetixbay.com/knowledge/glossary/yield.md) or [grams per watt](https://genetixbay.com/knowledge/glossary/grams-per-watt.md), they mean dry, trimmed bud. ## In practice Dry weight keeps falling a little during the cure, because curing is a slow decline in moisture, not holding it constant. A few percent loss over the first weeks in the jar is normal. That's why weights are most comparable when taken at the same stage (at jarring, or after a set cure time) and at a checked water activity. Watch out for false gains. Buds jarred too wet weigh more but risk mould, and they lose the weight anyway. Buds over-dried weigh less and smoke harsh. Neither is a better yield. Precision matters in trials. GenetixBay [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) should record dry weight with the water activity or equilibrated [jar RH](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md) at weighing, so comparisons between growers are fair. ## Units and formula Typical dry ≈ trimmed wet × 0.20-0.25. Yield per area = dry weight / [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md) (g/m²). ## Don't confuse with - **Wet weight**: fresh weight at harvest. - **Dry-weight basis**: lab correction for [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) % at 0% moisture. - **Bone-dry weight**: oven-dried with all water removed, a lab figure. ## Related terms [Wet weight](https://genetixbay.com/knowledge/glossary/wet-weight.md), [Moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md), [Yield](https://genetixbay.com/knowledge/glossary/yield.md), [Curing](https://genetixbay.com/knowledge/glossary/curing.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html --- # Dry-weight basis > Dry-weight basis reports a result per gram of sample with its water removed, while as-received basis reports it per gram as delivered, water included; dry-weight figures are always higher. - Canonical: https://genetixbay.com/knowledge/glossary/dry-weight-basis.html - Also written: dry weight basis, dry-weight vs as-received, as-received basis, as received, dry basis, DW basis, wet weight basis - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) result can be expressed in two ways. As-received (wet basis) divides by the weight of the sample as it arrived, water and all. Dry-weight basis divides by the weight after the water is mathematically removed. Because [cured](https://genetixbay.com/knowledge/glossary/curing.md) flower holds roughly 8-13% water, the same sample reads 9-15% higher on a dry-weight basis. ## In practice A flower sample at 12% moisture tests 20.0% total [THC](https://genetixbay.com/knowledge/glossary/thc.md) as received. On dry-weight basis: 20.0 / (1 - 0.12) = 22.7%. Neither number is wrong, but comparing one lab's dry-weight figure with another's as-received figure is comparing different things. Some jurisdictions require one basis or the other; a good [COA](https://genetixbay.com/knowledge/glossary/coa.md) always states which, and prints the moisture. ## Units and formula Dry-weight result = as-received result / (1 - moisture fraction). Moisture fraction is from a loss-on-drying test, e.g. 0.12 for 12%. ## Don't confuse with - **Water activity**: a measure of how available the water is, not how much there is. - **Wet (fresh) weight of a harvest**: plant weight before drying, a different context. ## Myth check Reporting on [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) is legitimate when disclosed. Swapping bases without saying so inflates labels. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [Moisture correction](https://genetixbay.com/knowledge/glossary/moisture-correction.md), [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Label inflation](https://genetixbay.com/knowledge/glossary/label-inflation.md), [Water activity test](https://genetixbay.com/knowledge/glossary/water-activity-test.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 --- # Dryback > Dryback is the drop in a substrate's water content between irrigations, usually expressed as a percentage of its content at full saturation. - Canonical: https://genetixbay.com/knowledge/glossary/dryback.html - Also written: dry-back, dry back, drybacks, substrate dryback, overnight dryback - Glossary category: Systems and media · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Dryback is how much a growing medium dries between one irrigation and the next. It is measured as the fall in volumetric [water content](https://genetixbay.com/knowledge/glossary/moisture-content.md) (from a substrate sensor) or in pot weight (from a scale), and expressed as a percentage. It is the core control variable in crop steering. ## In practice A [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) block or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) pot is brought to near [container capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md) in the morning, then allowed to dry during the day and overnight. If a sensor reads 65% water content after the last irrigation and 52% before the first one next morning, the overnight dryback is 13 percentage points, or 20% of the starting value. Smaller drybacks favour vegetative growth; larger drybacks favour generative growth and can concentrate root-zone [EC](https://genetixbay.com/knowledge/glossary/ec.md). Too large a dryback stresses the plant and can damage roots on rewetting. Always state which way you're calculating it: percentage points of water content, or percentage of the starting value. ## Units and formula Dryback (%) = (WC_max − WC_min) / WC_max × 100, or simply WC_max − WC_min in points. ## Don't confuse with - **Runoff**: water draining out; dryback is water lost by uptake and evaporation. ## Related terms [Crop steering](https://genetixbay.com/knowledge/glossary/crop-steering.md), [Field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md), [Wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md), [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md) ## Read more - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) - [Growing in rockwool (stonewool cubes and slabs)](https://genetixbay.com/knowledge/systems/rockwool.md) ## Sources 1. Stemeroff J, 2018. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 --- # Drying room > A dark, ventilated space where freshly harvested cannabis is dried under controlled temperature, humidity and gentle airflow, usually for 7-14 days. - Canonical: https://genetixbay.com/knowledge/glossary/drying-room.html - Also written: dry room, drying space, drying tent, dry tent, drying area - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A drying room (or drying tent) is any space set aside to dry harvested cannabis. The goal is to remove water slowly and evenly, without mould and without driving off volatile [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), before the buds go into curing containers. ## In practice Common targets (Grower practice, aligned with post-harvest benchmarks and drying research): | Factor | Target | |---|---| | Temperature | about 15-21 °C (60-70 °F) | | [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) | about 55-62% | | Light | darkness | | Air | gentle circulation around, not onto, the buds; slow exchange | | Duration | about 7-14 days | Equipment is usually a small [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) or [humidifier](https://genetixbay.com/knowledge/glossary/humidifier.md), a fan aimed at a wall or the floor, a [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) for odour, and a calibrated hygrometer at bud level. Warm, dry rooms dry too fast and give a grassy, [hay-like smell](https://genetixbay.com/knowledge/glossary/hay-smell.md), harsh smoke and [terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md). Cold, damp rooms risk mould. The dry is where quality is kept or lost; a cure can't fix a bad dry. ## Don't confuse with - **Curing**: the finishing phase in sealed containers. - **Grow room**: different climate targets and lights on. - **Freeze dryer**: a machine, not a room (Contested method). ## Related terms [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), [60/60 rule](https://genetixbay.com/knowledge/glossary/60-60-rule.md), [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Case hardening](https://genetixbay.com/knowledge/glossary/case-hardening.md), [Terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Sources 1. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. 3. Cannabis Business Times. Special report: cannabis post-harvest benchmarks (grower survey; average drying ~53 % RH, ~65 °F). https://www.cannabisbusinesstimes.com/business-issues-benchmarks/cannabis-post-harvest-operations/article/15689633/post-harvest-benchmarks-with-room-to-experiment --- # DTPA > DTPA (diethylenetriaminepentaacetic acid) is a synthetic chelating agent that keeps iron available up to about pH 7.0-7.5, a common choice for coco and hydro. - Canonical: https://genetixbay.com/knowledge/glossary/dtpa.html - Also written: diethylenetriaminepentaacetic acid, DTPA chelate, pentetic acid - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" DTPA, diethylenetriaminepentaacetic acid, is a synthetic [chelating agent](https://genetixbay.com/knowledge/glossary/chelate.md) with eight binding points, gripping metals more strongly than [EDTA](https://genetixbay.com/knowledge/glossary/edta.md). [Fe-DTPA](https://genetixbay.com/knowledge/glossary/iron-chelate.md), about 10-11% Fe, is the most common form in horticulture. ## In practice Fe-DTPA holds iron in solution up to roughly [pH](https://genetixbay.com/knowledge/glossary/ph.md) 7.0-7.5, giving a safety margin when root-zone pH drifts high in [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), rockwool or [recirculating hydro](https://genetixbay.com/knowledge/glossary/recirculating-system.md). Many professional greenhouse recipes use it as the default iron source for that reason. It is also used in soil testing as an extractant for [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md), which is why "DTPA-extractable" appears on soil reports. Like EDTA, it degrades under strong light. ## Don't confuse with - **EDTA**: less stable above pH 6.5. - **EDDHA**: stable to pH 9 or more. - **DTPA soil test**: a lab extraction method, not a fertiliser recommendation. ## Related terms [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md), [Iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md), [EDTA](https://genetixbay.com/knowledge/glossary/edta.md), [EDDHA](https://genetixbay.com/knowledge/glossary/eddha.md), [Iron](https://genetixbay.com/knowledge/glossary/iron.md) ## Read more - [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. HortScience. 2025. Iron chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA) in high-pH soilless media. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # DWC > DWC (deep water culture) suspends a plant's roots in an aerated nutrient solution, typically in a bucket with a net pot lid and an air stone. - Canonical: https://genetixbay.com/knowledge/glossary/dwc.html - Also written: deep water culture, deep-water culture, bubble bucket, DWC bucket - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Deep water culture is a hydroponic system in which roots hang directly in a container of nutrient solution, kept oxygenated by an air pump and [air stone](https://genetixbay.com/knowledge/glossary/air-stone.md). The plant sits in a [net pot](https://genetixbay.com/knowledge/glossary/net-pot.md) filled with [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md) or rockwool in the lid. It is simple, has few moving parts, and grows plants very fast when solution conditions are right. ## In practice A typical home DWC is a 15-25 L (4-6 gal) bucket per plant. Key targets: solution temperature about 18-21 °C (64-70 °F), dissolved oxygen well above 5 mg/L, [pH](https://genetixbay.com/knowledge/glossary/ph.md) about 5.6-6.2, and [EC](https://genetixbay.com/knowledge/glossary/ec.md) rising from about 0.6-1.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) for young plants to 1.6-2.2 mS/cm in flower. Top up with water or weak solution as the plant drinks, and change or refresh the solution every 1-2 weeks. Warm, poorly aerated solution is the main cause of [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) (*[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)*). ## Don't confuse with - **RDWC**: several DWC sites linked to recirculate through a shared control bucket. - **Kratky**: passive, unaerated water culture with an air gap. ## Related terms [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [Air stone](https://genetixbay.com/knowledge/glossary/air-stone.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [Net pot](https://genetixbay.com/knowledge/glossary/net-pot.md), [Chiller](https://genetixbay.com/knowledge/glossary/chiller.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md) ## Read more - [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) - [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 2. Cornell CEA. Hydroponic lettuce handbook. https://cea.cals.cornell.edu/ 3. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 --- # Ebb and flow > Ebb and flow (flood and drain) periodically floods a tray of potted plants with nutrient solution, then drains it back to a reservoir, pulling fresh air into the medium. - Canonical: https://genetixbay.com/knowledge/glossary/ebb-and-flow.html - Also written: flood and drain, flood-and-drain, ebb & flow, ebb-and-flow, flood table, flood tray - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Ebb and flow is a [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) hydroponic system. A timer-controlled pump fills a tray or bed with nutrient solution to a set depth, holds it briefly, and then lets it [drain](https://genetixbay.com/knowledge/glossary/runoff.md) back to the reservoir under gravity. As the solution drains, air is drawn into the medium, so roots get both water and oxygen each cycle. ## In practice Plants sit in containers of [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md) or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) on a flood table. Floods typically last about 10-20 minutes, and the number per day rises from one or two for young plants to several in peak flower, depending on medium and [container size](https://genetixbay.com/knowledge/glossary/pot-size.md). An overflow fitting sets the maximum level and prevents spills if a timer fails. Reservoirs need to be large enough to flood the tray without running dry, and solution is changed regularly because returning runoff carries salts and root exudates. ## Don't confuse with - **Drip irrigation**: delivers solution to each pot rather than flooding the whole tray. - **Bottom watering**: a manual version of the same idea, without recirculation. ## Related terms [Recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [Clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md), [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [Wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md) ## Read more - [Ebb and flow (flood and drain)](https://genetixbay.com/knowledge/systems/ebb-and-flow.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 --- # EC > EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength. - Canonical: https://genetixbay.com/knowledge/glossary/ec.html - Also written: electrical conductivity, conductivity, EC reading, nutrient strength, electroconductivity - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" EC (electrical conductivity) is the ability of a solution to carry an electric current, which rises with the concentration of dissolved ions. Pure water conducts almost nothing; nutrient salts dissociate into charged ions that conduct. EC tells you the total salt strength of a solution, not which ions are present: a solution of table salt and a balanced nutrient mix can share the same EC. ## In practice Typical working ranges for the input solution: | Stage | EC ([mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md)) | |---|---| | Seedlings, clones | 0.4–0.8 | | Early veg | 0.8–1.2 | | Late veg | 1.2–1.6 | | Flower | 1.4–2.2 | More is not better. Hershkowitz, Westmoreland and Bugbee (2025) found elevated root-zone nutrient concentration did not increase yield or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) in medical cannabis, while Baas and Wijnen (2023) tested cannabis across EC 1.8–12 mS/cm in rockwool. Too high an EC causes [osmotic stress](https://genetixbay.com/knowledge/glossary/osmotic-stress.md) and tip burn. Always note your base water EC; tap water often starts at 0.2–0.8 mS/cm. ## Units and formula 1 mS/cm = 1,000 µS/cm = 1 dS/m = 10 CF ≈ 500 ppm ([500 scale](https://genetixbay.com/knowledge/glossary/ppm500.md)) ≈ 700 ppm ([700 scale](https://genetixbay.com/knowledge/glossary/ppm700.md)). EC rises about 2% per °C, so meters report at 25 °C. ## Don't confuse with - **TDS/ppm**: a number calculated from EC with a [conversion factor](https://genetixbay.com/knowledge/glossary/conversion-factor.md); EC is the actual measurement. - **Runoff EC**: what leaves the pot, not what goes in. ## Related terms [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md), [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md), [TDS](https://genetixbay.com/knowledge/glossary/tds.md), [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) ## Read more - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ## Sources 1. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 2. Baas R, Wijnen D. 2023. Effects of EC on cannabis in rockwool (1.8 to 12 mS/cm). Acta Horticulturae 1377. https://www.ishs.org/ishs-article/1377_97 3. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality --- # EC meter > An EC meter measures how well a solution conducts electricity, giving nutrient strength in mS/cm or as ppm via a conversion factor. - Canonical: https://genetixbay.com/knowledge/glossary/ec-meter.html - Also written: EC pen, conductivity meter, TDS pen, ppm meter, EC tester, truncheon meter - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An EC meter applies an alternating voltage across two or four electrodes and measures the current, giving [electrical conductivity](https://genetixbay.com/knowledge/glossary/ec.md). Most include a temperature sensor and report EC at 25 °C. "[TDS](https://genetixbay.com/knowledge/glossary/tds.md)" or "ppm" meters are EC meters that multiply the result by a [conversion factor](https://genetixbay.com/knowledge/glossary/conversion-factor.md). Fixed "truncheon" style meters show EC on a scale of lights or markings. ## In practice EC sensors are far more robust than [pH](https://genetixbay.com/knowledge/glossary/ph.md) probes: no glass bulb, no storage solution, and they hold calibration much longer. Calibrate every few weeks or after cleaning with a standard such as 1.413 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), and check against it if readings look odd. Keep the electrodes clean. Rinse after use, and occasionally clean with mild soapy water or a dilute acid to remove [nutrient films](https://genetixbay.com/knowledge/glossary/nft.md). Make sure no air bubbles sit on the sensor face when reading, and stir gently. Pick a meter that shows mS/cm, not only ppm, so your numbers translate to research and charts. ## Don't confuse with - **pH meter**: measures acidity; different sensor, different care. - **Substrate EC sensor**: inserted into the medium to read pore-water EC, often with moisture; values differ from [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) EC. ## Related terms [EC](https://genetixbay.com/knowledge/glossary/ec.md), [TDS](https://genetixbay.com/knowledge/glossary/tds.md), [Calibration solution](https://genetixbay.com/knowledge/glossary/calibration-solution.md), [ATC](https://genetixbay.com/knowledge/glossary/atc.md), [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) ## Read more - [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) ## Sources 1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality --- # EDDHA > EDDHA is a strong iron chelate that stays effective up to pH 9 or more, used for alkaline soils and hard water; it colours solutions dark red. - Canonical: https://genetixbay.com/knowledge/glossary/eddha.html - Also written: EDDHA chelate, ethylenediamine di(o-hydroxyphenylacetic) acid, EDDHA iron, red iron chelate - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" EDDHA, ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid), is a synthetic [chelating agent](https://genetixbay.com/knowledge/glossary/chelate.md) used almost entirely for iron. [Fe-EDDHA](https://genetixbay.com/knowledge/glossary/iron-chelate.md) products typically contain about 6% Fe. The quality of EDDHA products depends on the share of iron held in the more stable ortho-ortho form, which labels may state. ## In practice Fe-EDDHA is the fix for iron [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md) in alkaline soils and with high-pH, [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md), where [EDTA](https://genetixbay.com/knowledge/glossary/edta.md) and [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md) fail. It costs more per gram of iron. It stains water, reservoirs and runoff a deep wine-red, which alarms growers the first time. For hydro kept in the usual [pH](https://genetixbay.com/knowledge/glossary/ph.md) 5.5-6.5 range, it is rarely necessary; DTPA usually covers drift. Using it as a short-term rescue for [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md) in high-pH soil is a common practice. ## Don't confuse with - **EDTA**: cheaper, works only below about pH 6.5. - **DTPA**: middle ground, good to about pH 7.5. - **Red runoff from organic matter**: tannins or humics, not EDDHA. ## Related terms [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md), [Iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md), [EDTA](https://genetixbay.com/knowledge/glossary/edta.md), [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md), [Iron](https://genetixbay.com/knowledge/glossary/iron.md) ## Read more - [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. HortScience. 2025. Iron chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA) in high-pH soilless media. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Edible > An edible is a food or drink containing cannabinoids from an infused fat, tincture or concentrate; effects are reported to start later and last longer than inhaled cannabis. - Canonical: https://genetixbay.com/knowledge/glossary/edible.html - Also written: edibles, cannabis edible, cannabis edibles, infused food, infused edibles, gummies - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An edible is any cannabis product meant to be eaten or drunk: baked goods, gummies, chocolates, drinks and capsules among them. [Cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) are added as [decarboxylated](https://genetixbay.com/knowledge/glossary/decarboxylation.md) extract, [distillate](https://genetixbay.com/knowledge/glossary/distillate.md), isolate or an infused fat such as butter or oil. Because cannabinoids are taken through the digestive system and metabolised by the liver, the reported onset is slower and the reported duration longer than inhalation, which is a common cause of over-consumption. ## In practice Regulated edibles are labelled in milligrams per serving and per package rather than %, and many markets cap the dose per serving and package; check local rules. [Label accuracy](https://genetixbay.com/knowledge/glossary/label-inflation.md) for edibles has been mixed in published testing. Edibles look like ordinary food, so storing them securely away from children and pets matters. GenetixBay gives no recipes, dosing advice or medical claims; effects are reported only. ## Don't confuse with - **Tincture**: a liquid preparation, usually taken by dropper. - **Raw cannabis**: uncooked flower is mostly [THCA](https://genetixbay.com/knowledge/glossary/thca.md), not [THC](https://genetixbay.com/knowledge/glossary/thc.md). - **Concentrate**: an ingredient for edibles, not an edible itself. ## Related terms [Tincture](https://genetixbay.com/knowledge/glossary/tincture.md), [Distillate](https://genetixbay.com/knowledge/glossary/distillate.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md), [Isolate](https://genetixbay.com/knowledge/glossary/isolate.md) --- # EDTA > EDTA (ethylenediaminetetraacetic acid) is the most common synthetic chelating agent in fertilisers, effective for iron up to about pH 6.0-6.5. - Canonical: https://genetixbay.com/knowledge/glossary/edta.html - Also written: ethylenediaminetetraacetic acid, EDTA chelate, Na2EDTA, edetate - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" EDTA, ethylenediaminetetraacetic acid, is a synthetic [chelating agent](https://genetixbay.com/knowledge/glossary/chelate.md) that binds metal ions at six points. In fertilisers it carries iron ([Fe-EDTA](https://genetixbay.com/knowledge/glossary/iron-chelate.md), about 13% Fe), and often zinc, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md) and copper. It is cheap and widely used. ## In practice Fe-EDTA works well in hydro and [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) media kept around [pH](https://genetixbay.com/knowledge/glossary/ph.md) 5.5-6.2. Above about 6.5 its iron becomes progressively less available, so it is a weak choice for alkaline water, high-pH soil or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) run high. Fe-EDTA also breaks down under strong light, so clear reservoirs and lines exposed to light lose iron faster. At high pH, EDTA can also pick up calcium, displacing the iron it carries. EDTA is not readily biodegradable, which has raised environmental questions about its heavy use in agriculture. ## Don't confuse with - **DTPA**: a related chelate, stable to a higher pH. - **EDDHA**: much more stable at high pH, used for alkaline soils. - **HEDTA**: a related chelate with intermediate properties. ## Related terms [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md), [Iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md), [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md), [EDDHA](https://genetixbay.com/knowledge/glossary/eddha.md), [Iron](https://genetixbay.com/knowledge/glossary/iron.md) ## Read more - [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. HortScience. 2025. Iron chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA) in high-pH soilless media. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Eighth > An eighth is one-eighth of an ounce of cannabis, sold as 3.5 grams; it is the standard retail unit for flower in North America. - Canonical: https://genetixbay.com/knowledge/glossary/eighth.html - Also written: 8th, an eighth, eighths, 3.5, 3.5 g - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An eighth is 1/8 of an avoirdupois ounce, 3.54 g, rounded to 3.5 g in retail. It is the most common retail size for flower in North America, and prices are often quoted "per eighth". ## In practice Because flower keeps losing moisture after packaging, an eighth sealed at the right moisture can weigh slightly less weeks later, and one packed too wet will dry in the jar. Regulated markets set tolerances for net weight; check local rules. For a home grower, an eighth is a handy unit for sample jars and for comparing cure results between batches. ## Units and formula | Slang | Nominal weight | Metric | |---|---|---| | Gram | 1 g | 1 g | | Eighth | 1/8 oz | 3.5 g (exact: 3.54 g) | | Quarter | 1/4 oz | 7 g | | Half | 1/2 oz | 14 g | | Ounce (zip, O) | 1 oz | 28 g (exact: 28.35 g) | | QP | 1/4 lb (4 oz) | 113 g | | Pound (elbow, LB) | 1 lb (16 oz) | 454 g (exact: 453.6 g) | Retail rounds an eighth to 3.5 g and an ounce to 28 g. ## Don't confuse with - **Quarter**: 7 g, two eighths. - **Metric 5 g packs**: some markets sell in round metric units instead. ## Related terms [Gram](https://genetixbay.com/knowledge/glossary/gram.md), [Ounce](https://genetixbay.com/knowledge/glossary/ounce.md), [QP](https://genetixbay.com/knowledge/glossary/qp.md), [Elbow](https://genetixbay.com/knowledge/glossary/elbow.md) --- # Elbow > Elbow is slang for a pound of cannabis, 16 ounces or about 454 grams, from the spoken abbreviation "L-B". - Canonical: https://genetixbay.com/knowledge/glossary/elbow.html - Also written: pound, lb, elbows, a pound - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Elbow is slang for a pound (lb) of cannabis: 16 oz, about 454 g. The word comes from saying the abbreviation "LB" out loud. ## In practice Growers measure big [yields](https://genetixbay.com/knowledge/glossary/yield.md) in pounds: "a pound per light" means about 454 g dry from one fixture, a common benchmark for a well-run room with a high-output light. Commercial growers price and trade wholesale flower by the pound. Possessing or transporting a pound without a licence is a serious offence in most places, even where personal use is legal. Check local rules. ## Units and formula | Slang | Nominal weight | Metric | |---|---|---| | Gram | 1 g | 1 g | | Eighth | 1/8 oz | 3.5 g (exact: 3.54 g) | | Quarter | 1/4 oz | 7 g | | Half | 1/2 oz | 14 g | | Ounce (zip, O) | 1 oz | 28 g (exact: 28.35 g) | | QP | 1/4 lb (4 oz) | 113 g | | Pound (elbow, LB) | 1 lb (16 oz) | 454 g (exact: 453.6 g) | Retail rounds an eighth to 3.5 g and an ounce to 28 g. ## Don't confuse with - **Kilo**: 1,000 g, about 2.2 lb. - **Wet weight**: a pound of freshly cut flower dries down to roughly a fifth of that. ## Related terms [QP](https://genetixbay.com/knowledge/glossary/qp.md), [Ounce](https://genetixbay.com/knowledge/glossary/ounce.md), [Gram](https://genetixbay.com/knowledge/glossary/gram.md), [Yield](https://genetixbay.com/knowledge/glossary/yield.md) --- # Elite cut > An elite cut is a famous, proven clone-only plant, often held by a few growers and traded rather than sold openly. - Canonical: https://genetixbay.com/knowledge/glossary/elite-cut.html - Also written: elite cuts, elite clone, elite clone-only, clone-only elite, elite - Glossary category: Grower slang and culture · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An elite cut is a selected individual plant, kept only as clones, with a reputation that makes it highly sought after. Many classics, including some original Skunk-era selections, survive only this way. ## In practice Elite cuts move through small circles of trusted growers. Public accounts describe cuts changing hands for very large sums or only in trade for another elite, and holders often cannot share without consequences from the circle that gave it to them. The result is that some near-extinct classics depend on a handful of gardens, and a pest outbreak or a [viroid](https://genetixbay.com/knowledge/glossary/viroid.md) infection can wipe out a lineage. ## Don't confuse with - **Clone-only**: any cultivar kept only as clones. Elite adds reputation and scarcity. - **Keeper**: any selected plant; most keepers never become elite. ## Myth check GenetixBay position (the founder's view, *Grower practice*): elite clone-only gatekeeping is real, and part of why GenetixBay exists. Some holders hoard the best and control access to the [gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md). The answer is preservation in the open: [GB-IDs](https://genetixbay.com/knowledge/glossary/gb-id.md), [the Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md), rewards for preservation and sharing within legal lanes. "The original cut" stays an unverified claim until chain of custody or a DNA match backs it. See [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md). ## Related terms [Cut](https://genetixbay.com/knowledge/glossary/cut.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md), [Cut trading](https://genetixbay.com/knowledge/glossary/cut-trading.md), [Keeper](https://genetixbay.com/knowledge/glossary/keeper.md), [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Same cut, a thousand names: renaming, relabelling and the shrinking gene pool](https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.md) --- # Emerson effect > The Emerson effect is the jump in photosynthesis when far-red light (above 680 nm) is combined with shorter red light, exceeding the sum of each alone. - Canonical: https://genetixbay.com/knowledge/glossary/emerson-effect.html - Also written: Emerson enhancement effect, Emerson enhancement, red drop, Emerson red drop - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The Emerson effect, described by Robert Emerson in the 1950s, has two parts. The "red drop" is the sharp fall in [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) efficiency for light beyond about 680 nm on its own. The "enhancement effect" is the finding that adding shorter-wavelength light restores and boosts that efficiency, so the combined rate exceeds the sum of the two lights separately. It was key evidence that photosynthesis runs two photosystems in series: photosystem I absorbs [far-red](https://genetixbay.com/knowledge/glossary/far-red.md) well, photosystem II does not. ## In practice For growers, the Emerson effect is the reason far-red photons are not wasted when a fixture also delivers plenty of 400–700 nm light. Zhen and Bugbee (2020) measured far-red photons up to about 750 nm contributing to canopy photosynthesis at near-equal efficiency when mixed with [PAR](https://genetixbay.com/knowledge/glossary/par.md). This supports counting ePAR (400–750 nm) for whole-canopy work. *Established* in model crops; cannabis-specific canopy measurements remain few. It does not mean you can replace PAR with far-red. A far-red-only source gives very little photosynthesis and a lot of [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). Typical fixtures with far-red keep it to a minority of total photons, often under 10–15%. ## Don't confuse with - **Red:far-red ratio**: a developmental signal via [phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md), separate from the photosynthetic enhancement. - **Far-red**: the waveband; the Emerson effect is how it interacts with other light. ## Related terms [Far-red](https://genetixbay.com/knowledge/glossary/far-red.md), [PAR](https://genetixbay.com/knowledge/glossary/par.md), [Red:far-red ratio](https://genetixbay.com/knowledge/glossary/red-far-red-ratio.md), [Photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Zhen S, Bugbee B, 2020. Far-red photons have equivalent efficiency to traditional photosynthetic photons: implications for redefining photosynthetically active radiation. Plant, Cell & Environment 43(5):1259–1272. https://doi.org/10.1111/pce.13730 --- # Entomopathogenic fungi > Fungi that infect and kill insects and mites through the cuticle; their spores need high humidity at the leaf surface to germinate. - Canonical: https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.html - Also written: insect-killing fungi, mycoinsecticide, fungal biopesticide, Metarhizium, Isaria fumosorosea, Lecanicillium - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Entomopathogenic fungi are fungi whose spores land on an insect or mite, [germinate](https://genetixbay.com/knowledge/glossary/germination.md), penetrate the cuticle and kill it from inside within days. [Beauveria bassiana](https://genetixbay.com/knowledge/glossary/beauveria-bassiana.md), Metarhizium species, Cordyceps (Isaria) fumosorosea and Lecanicillium are the main greenhouse examples, and extension [biocontrol](https://genetixbay.com/knowledge/glossary/biological-control.md) guides for [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) list several of them. ## In practice Spores need moisture to germinate, so these products work best when leaf-surface humidity stays high for hours, which conflicts with flower rooms kept at 40-55% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) to prevent [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md). They are mainly a veg-stage and media-drench tool. Many fungicides kill them, so do not tank-mix. Follow the label and local law. ## Don't confuse with - **Plant pathogens**: fungi that attack the crop, such as botrytis. - **Bt**: a bacterium, not a fungus, that works only when eaten. ## Related terms [Beauveria bassiana](https://genetixbay.com/knowledge/glossary/beauveria-bassiana.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) - [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) ## Sources 1. UConn IPM. Biological Control of Whiteflies. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-whiteflies --- # Entourage effect > The entourage effect is the hypothesis that cannabis compounds, especially cannabinoids and terpenes together, produce effects different from any single compound; human evidence remains contested. - Canonical: https://genetixbay.com/knowledge/glossary/entourage-effect.html - Also written: entourage, ensemble effect, whole-plant synergy, full-spectrum effect, cannabis synergy - Glossary category: Cannabinoids and terpenes · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The entourage effect is a hypothesis that the many compounds in cannabis interact so that the whole plant acts differently from purified [THC](https://genetixbay.com/knowledge/glossary/thc.md) or [CBD](https://genetixbay.com/knowledge/glossary/cbd.md). The term comes from endocannabinoid research by Ben-Shabat, Mechoulam and colleagues in 1998; Russo (2011) extended it to cannabinoid-terpene interactions. Critics such as Cogan (2020) argue that much of it is marketing, and controlled human tests of specific terpene-cannabinoid combinations have so far been limited and mixed. ## In practice The phrase is used to sell "full-spectrum" products and to argue against isolates and [distillates](https://genetixbay.com/knowledge/glossary/distillate.md). For growers, there is a firmer, separate point: people consistently report that aroma matters to their experience, and one survey study (Plumb et al. 2022) found that aroma predicted reported subjective effects better than THC percentage. That supports caring about [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and [VSCs](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) without endorsing specific synergy claims. GenetixBay makes no medical claims; effects are only reported. ## Don't confuse with - **Terpene profile**: a measurement; the entourage effect is a hypothesis about what the measurement means. - **Full-spectrum**: a product label, not a tested outcome. ## Myth check Evidence: Contested. Claims that a particular terpene "steers" effects are not established. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Isolate](https://genetixbay.com/knowledge/glossary/isolate.md), [Distillate](https://genetixbay.com/knowledge/glossary/distillate.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Russo EB. 2011. Taming THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects. British Journal of Pharmacology 163(7):1344-1364. https://doi.org/10.1111/j.1476-5381.2011.01238.x 2. Cogan PS. 2020. The 'entourage effect' or 'hodge-podge hashish': the questionable rebranding, marketing, and expectations of cannabis polypharmacy. Expert Review of Clinical Pharmacology 13(8):835-845. 3. Plumb J, Demirel S, Sackett J, Russo EB, Wilson-Poe AR. 2022. The nose knows: aroma, but not THC mediates the subjective effects of smoked and vaporized cannabis flower. Psychoactives 1(2):70-86. https://doi.org/10.3390/psychoactives1020008 --- # Epistasis > Epistasis is an interaction between genes in which the effect of one gene depends on, or is masked by, alleles at another gene. - Canonical: https://genetixbay.com/knowledge/glossary/epistasis.html - Also written: epistatic, epistatic interaction, gene interaction, gene-gene interaction - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Epistasis is when the effect of one [gene](https://genetixbay.com/knowledge/glossary/gene.md) depends on which [alleles](https://genetixbay.com/knowledge/glossary/allele.md) are present at another gene. One gene can mask another, enhance it, or only matter in combination with it. [Dominance](https://genetixbay.com/knowledge/glossary/dominant.md) is an interaction between alleles at one locus; epistasis is between loci. ## In practice Pathway genes give the cleanest examples. A [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase allele cannot do anything if the plant lacks enough of the precursor CBGA upstream; that is part of how [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) IV (CBG-dominant) and chemotype V (cannabinoid-free) plants arise (de Meijer et al. 2009). The synthase genotype only shows when the upstream genes work. For breeders, epistasis explains why a great combination sometimes vanishes in the next generation: the good result depended on alleles at two or more genes being together, and [segregation](https://genetixbay.com/knowledge/glossary/segregation.md) split them. It is also one reason an [elite clone](https://genetixbay.com/knowledge/glossary/elite-cut.md) can be easier to keep than to recreate from seed. ## Units and formula Classic modified F2 ratios signal epistasis: 9:3:4 ([recessive](https://genetixbay.com/knowledge/glossary/recessive.md) epistasis), 12:3:1 (dominant epistasis), 9:7 (complementary genes), instead of the 9:3:3:1 of two independent genes. ## Don't confuse with - **Dominance**: within one gene. - **Pleiotropy**: one gene affecting several traits. - **Linkage**: two genes inherited together because of their position, not because they interact. ## Related terms [Dominant](https://genetixbay.com/knowledge/glossary/dominant.md), [Quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.md), [Heterosis](https://genetixbay.com/knowledge/glossary/heterosis.md), [Gene](https://genetixbay.com/knowledge/glossary/gene.md), [Pleiotropy](https://genetixbay.com/knowledge/glossary/pleiotropy.md) ## Read more - [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md) ## Sources 1. de Meijer EPM, Hammond KM, Sutton A. 2009. The inheritance of chemical phenotype in Cannabis sativa L. (IV): cannabinoid-free plants. Euphytica 168:95-112. https://doi.org/10.1007/s10681-009-9894-7 2. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 --- # Equilibrium relative humidity > The relative humidity of the air in a sealed container once it has stopped exchanging moisture with the material inside; ERH / 100 equals the material's water activity. - Canonical: https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.html - Also written: ERH, equilibrium RH, equilibrated RH, jar RH, sealed-jar RH - Glossary category: Harvest, drying and curing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Equilibrium relative humidity (ERH) is the [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) that the headspace of a closed container settles at when the product inside neither gains nor loses water. At that point, the air's RH reflects the product's [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md): ERH (%) = aw × 100. ERH depends on temperature, so readings are compared at a stable room temperature. ## In practice ERH is what a hygrometer in a [curing jar](https://genetixbay.com/knowledge/glossary/curing-jar.md) actually tells you, but only after equilibration. Right after you seal or open a jar, the reading is the room's air, not the bud's. Wait several hours, ideally overnight, at stable temperature before trusting it. House position: jar RH is a proxy. The target is the bud's water activity (about 0.55-0.65) and [moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md), and equilibrated jar RH is a practical stand-in for aw. A jar that settles above about 65% needs more air; one under about 55% is over-dried. Calibrate cheap hygrometers before trusting them; errors of 3-5 points are common. A salt test (a sealed bag with damp table salt gives about 75% RH) is the usual home check. ## Units and formula aw = ERH / 100 (at equilibrium, same temperature). ## Don't confuse with - **Room RH**: the air in the drying or storage room. - **Moisture content**: water by weight, not humidity. - **Humidity pack setting**: what a sachet tries to impose. ## Related terms [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md), [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Burping](https://genetixbay.com/knowledge/glossary/burping.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (D8196 water activity measurement; D8197 range). https://sn.astm.org/node/2445/printable/print --- # Eriophyid mite > A family of microscopic, carrot-shaped mites with only two pairs of legs; includes the hemp russet mite, invisible without about 40-60x magnification. - Canonical: https://genetixbay.com/knowledge/glossary/eriophyid-mite.html - Also written: eriophyid, eriophyid mites, Eriophyidae - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Eriophyid mites (family Eriophyidae) are the smallest plant-feeding [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), roughly 0.2 mm long, worm- or carrot-shaped, with two pairs of legs at the front end instead of four. They include rust, russet, gall and bud mites. The [hemp russet mite](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md), Aculops cannabicola, is the [cannabis species](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md); Colorado State notes it cannot be seen without magnification. ## In practice Eriophyids are found by their damage (bronzing, upward curling, brittle leaves) and confirmed with a 40-60x [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) or microscope, often by lifting mites onto clear tape. They spread on clones and air currents. Their size and speed of increase make them a zero-tolerance pest in mother rooms. ## Don't confuse with - **Spider mites**: much larger, four pairs of legs, visible at 10x. - **Tarsonemid mites**: broad and [cyclamen mites](https://genetixbay.com/knowledge/glossary/cyclamen-mite.md), also tiny but with four pairs of legs. ## Related terms [Hemp russet mite](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md), [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) ## Read more - [Hemp russet mite (Aculops cannabicola): life cycle, detection and control](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md) - [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ## Sources 1. Colorado State University. Hemp russet mite (hemp IPM). https://agsci.colostate.edu/agbio/ipm-pests/29895-2/ --- # Ethylene > A gaseous plant hormone that regulates ripening, senescence, stress responses and, in cannabis, female flower expression; blocking it makes females produce pollen. - Canonical: https://genetixbay.com/knowledge/glossary/ethylene.html - Also written: ethene, C2H4, ripening hormone, ethylene gas - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Ethylene (C₂H₄) is a simple gas that acts as a plant hormone. It promotes [fruit](https://genetixbay.com/knowledge/glossary/achene.md) ripening, leaf and flower senescence, abscission, and responses to wounding, flooding and other stress. In cannabis it also promotes [female flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) development; blocking ethylene signalling pushes female plants to form [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md). ## In practice That last point is the basis of [feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md). Silver ions block ethylene receptors, so sprays of [silver thiosulfate](https://genetixbay.com/knowledge/glossary/sts.md) (STS) or silver nitrate on a female plant induce fertile male flowers (Ram & Sett 1982; Lubell & Brand 2018). Pollen from that [reversed female](https://genetixbay.com/knowledge/glossary/sex-reversal.md) carries no Y chromosome, so the seeds are female. Ethylene also builds up around stressed or damaged tissue and in closed spaces. Ripening fruit stored with cut material, or [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) roots producing ethylene precursors, can speed yellowing and leaf drop. Ethylene-releasing products are sometimes promoted for "ripening" cannabis faster. Evidence of a quality benefit in cannabis is thin. Treat as Contested and keep it off consumable crops unless the data improves. ## Don't confuse with - **Ethanol**: an alcohol, not a hormone. - **Gibberellin**: tends to push toward male expression. - **Abscisic acid**: the main drought-stress hormone. ## Related terms [Gibberellin](https://genetixbay.com/knowledge/glossary/gibberellin.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md), [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), [Abscisic acid](https://genetixbay.com/knowledge/glossary/abscisic-acid.md) ## Read more - [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) ## Sources 1. Ram HYM, Sett R. 1982. Induction of fertile male flowers in genetically female Cannabis sativa plants by silver nitrate and silver thiosulphate anionic complex. Theoretical and Applied Genetics 62:369-375. https://doi.org/10.1007/BF00275107 2. Lubell JD, Brand MH. 2018. Foliar sprays of silver thiosulfate produce male flowers on female hemp plants. HortTechnology 28(6):743-747. https://doi.org/10.21273/HORTTECH04188-18 3. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Eucalyptol > Eucalyptol (1,8-cineole) is a monoterpenoid ether with a cool, minty, camphor-like smell, the main compound in eucalyptus oil and a minor terpene in cannabis. - Canonical: https://genetixbay.com/knowledge/glossary/eucalyptol.html - Also written: 1,8-cineole, cineole, cineol, 1,8-cineol, eucalyptole - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Eucalyptol, also called 1,8-cineole, is a cyclic [monoterpenoid](https://genetixbay.com/knowledge/glossary/monoterpene.md) ether. It dominates eucalyptus oil and is present in rosemary, sage, bay laurel and cardamom. Its smell is fresh, cool, medicinal and camphorous. In cannabis it is usually a trace-to-minor component of the profile. ## In practice Readings in flower are typically low, often [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md) to below 0.1% w/w. A few cultivars carry a recognisable "menthol" or eucalyptus note in which eucalyptol plays a part, though other compounds such as fenchol or borneol can contribute similar cool notes. Not every [terpene panel](https://genetixbay.com/knowledge/glossary/terpene-test.md) includes it. ## Don't confuse with - **Menthol**: a different monoterpenoid alcohol from mint; not typical in cannabis. - **Camphor**: a ketone with a related smell, sometimes on extended panels. - **Eucalyptus oil**: a mixture; eucalyptol is its main but not only component. ## Related terms [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Alpha-pinene](https://genetixbay.com/knowledge/glossary/alpha-pinene.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Even canopy > An even canopy is one where all main tops sit at roughly the same height, so each receives similar light intensity and buds develop more uniformly. - Canonical: https://genetixbay.com/knowledge/glossary/even-canopy.html - Also written: flat canopy, level canopy, uniform canopy, canopy uniformity - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An even canopy is a flat, level layer of tops. Light intensity falls off with distance from the fixture and varies across the footprint, so a top 30 cm (12 in) below its neighbours can receive a fraction of their light. Flattening the canopy brings every bud site into the same light band. ## In practice Growers level a canopy with [LST](https://genetixbay.com/knowledge/glossary/lst.md), topping, mainlining, [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md) and [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md) the tallest tops in early flower. The aim is usually a spread of no more than about 10-15 cm (4-6 in) between the highest and lowest [main colas](https://genetixbay.com/knowledge/glossary/cola.md). Research on large [medicinal cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md) plants found that plant architecture affected how uniform [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) content was between top and lower buds, which supports the logic of training for evenness. A [PAR](https://genetixbay.com/knowledge/glossary/par.md) meter reading at several points across the canopy shows how even it really is. ## Don't confuse with - **Uniform PPFD**: even light from the fixture; you need both an even light map and an even canopy. - **Uniform plants**: same genetics and size; helps, but is not the same as a level canopy. ## Related terms [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [Supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md), [Mainlining](https://genetixbay.com/knowledge/glossary/mainlining.md) ## Read more - [LST: low-stress training](https://genetixbay.com/knowledge/training/lst.md) - [SCROG: screen of green](https://genetixbay.com/knowledge/training/scrog.md) ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ --- # Evidence ladder > The GenetixBay evidence ladder labels every growing claim as Established, Supported, Grower practice, Contested or Myth, according to how strong the evidence is. - Canonical: https://genetixbay.com/knowledge/glossary/evidence-ladder.html - Also written: Established, Supported, Grower practice, Contested, Myth, evidence labels - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The evidence ladder is the set of five labels GenetixBay uses on knowledge-base articles, glossary entries and Greenleaf answers to show how well a claim is supported. ## In practice A reader can see at a glance whether advice is settled science or lore. Pre-harvest [flushing](https://genetixbay.com/knowledge/glossary/flushing.md) is labelled *Myth*; [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md) for better buds is *Grower practice*, house-endorsed; mild late drought is *Supported*. [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) exist to move claims up or down the ladder with controlled member grows, and Mythbusters shows the verdicts. Some topics carry a GenetixBay house position set by the founder. Those are stated plainly with their label rather than presented as evenly balanced. ## Units and formula | Label | Meaning | |---|---| | Established | Multiple studies or extension consensus | | Supported | Some research, or strong grower consensus consistent with research | | Grower practice | Widely used, little formal research | | Contested | Evidence conflicts or is thin on both sides | | Myth | Evidence contradicts the claim | ## Don't confuse with - **Evidence levels L0-L4**: for lineage claims on [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) records, not growing advice. - **Peer review**: one input to a label, not a label itself. ## Related terms [Evidence levels L0-L4](https://genetixbay.com/knowledge/glossary/evidence-levels-l0-l4.md), [Mythbusters](https://genetixbay.com/knowledge/glossary/mythbusters.md), [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md), [Open research](https://genetixbay.com/knowledge/glossary/open-research.md) ## Read more - [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) --- # Evidence levels L0-L4 > GenetixBay evidence levels rate lineage claims from L0 (unverified) through L1 community reported, L2 breeder reported and L3 documented to L4 lab-confirmed. - Canonical: https://genetixbay.com/knowledge/glossary/evidence-levels-l0-l4.html - Also written: L0, L1, L2, L3, L4, lineage evidence levels, GB-ID evidence levels - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" On GenetixBay every parentage statement ("A x B", "the original cut") is treated as a claim with an evidence level. The levels run from L0 to L4. ## In practice Breeders raise a claim's level by attaching dated, original evidence and, ideally, by recording crosses on the platform as they happen. A certified breeder can still make an L2 claim that turns out wrong, so a verified breeder account is shown separately from verified genetics. Witnessed lineage (both parents on record and the pollination logged at the time) is a separate flag, not a substitute for L4. ## Units and formula | Level | Name | Typical evidence | |---|---|---| | L0 | Unverified | A name or anonymous assertion | | L1 | Community reported | A member's claim with a source, such as a dated forum post or a [photo](https://genetixbay.com/knowledge/glossary/photoperiod.md) of an old pack | | L2 | Breeder reported | The line's certified breeder asserts it | | L3 | Documented | A period document accepted by an archivist: catalogue, patent, [breeders' rights](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md) filing, [lab certificate](https://genetixbay.com/knowledge/glossary/coa.md) ([chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) only) | | L4 | Lab-confirmed | A genomic report consistent with the specific parent-child relationship | ## Don't confuse with - **Evidence ladder**: the Established-to-Myth labels for growing claims in articles. - **Lab COA**: proves chemistry, not parentage. ## Related terms [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Evidence ladder](https://genetixbay.com/knowledge/glossary/evidence-ladder.md), [Renamed cut](https://genetixbay.com/knowledge/glossary/renamed-cut.md), [Genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md), [Elite cut](https://genetixbay.com/knowledge/glossary/elite-cut.md) ## Read more - [How to document lineage evidence (GB-ID evidence levels L0-L4)](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md) - [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md) --- # Exhaust fan > An exhaust fan pulls air out of the grow space through ducting, removing heat, humidity and odour and drawing in fresh air. - Canonical: https://genetixbay.com/knowledge/glossary/exhaust-fan.html - Also written: inline fan, extraction fan, extractor fan, duct fan, exhaust, inline duct fan - Glossary category: Environment and light · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An exhaust fan is a ducted fan, usually an inline type mounted in the duct, that pulls air out of the grow space and sends it outside the room or building. It is the main tool for removing heat from lights and water vapour from [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md). When the space is sealed apart from passive intake vents, the exhaust also creates [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md), so odour leaves only through the [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md). ## In practice Size the fan from the volume of the space and the restrictions in the line. A 1.2 × 1.2 × 2 m (4 × 4 × 6.5 ft) tent holds about 2.9 m³ (about 102 ft³). A common rule is one full air exchange every 1–3 minutes, then add 25–50% for a carbon filter, bends and long ducts. That gives roughly 100–200 [CFM](https://genetixbay.com/knowledge/glossary/cfm.md) (170–340 m³/h) for this tent, more under hot HID lights. Use a speed controller or a climate controller rather than running at full speed all the time. Keep ducting as straight and short as possible; each sharp bend costs airflow. Mount the fan with vibration isolation to reduce noise. ## Don't confuse with - **Oscillating fan**: circulates air inside the space without removing any. - **Intake fan**: pushes air in; running it stronger than the exhaust loses negative pressure. ## Related terms [CFM](https://genetixbay.com/knowledge/glossary/cfm.md), [Negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md), [Carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md), [Airflow](https://genetixbay.com/knowledge/glossary/airflow.md) ## Read more - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) --- # Exotic > Exotic is retail slang for fashionable, high-priced cultivars with unusual flavours or colours; it describes marketing, not origin or proven genetics. - Canonical: https://genetixbay.com/knowledge/glossary/exotic.html - Also written: exotics, exotic strain, exotic flower, exotic genetics - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Exotic, in cannabis retail, means a fashionable, expensive cultivar, usually a recent [polyhybrid](https://genetixbay.com/knowledge/glossary/polyhybrid.md) with a dessert, [candy](https://genetixbay.com/knowledge/glossary/candy-terps.md) or gas profile and striking [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md). Despite the word, "exotic" flower rarely has anything to do with foreign origins. ## In practice A menu might sort flower into "exotics", "premium" and "value". The exotic label is a price tier. Some exotic flower is superb, some is ordinary flower in good packaging. The useful questions are the same as for any jar: who grew it, when it was harvested, how it was dried and [cured](https://genetixbay.com/knowledge/glossary/curing.md), and whether the lab results are believable. ## Don't confuse with - **Landrace**: a genuinely regional, farmer-maintained population, often from the places "exotic" seems to imply. - **Zaza**: near-synonym with stronger street flavour. - **Rare**: scarce in supply. Exotics are often widely available under one name. ## Related terms [Zaza](https://genetixbay.com/knowledge/glossary/zaza.md), [Hype strain](https://genetixbay.com/knowledge/glossary/hype-strain.md), [Top shelf](https://genetixbay.com/knowledge/glossary/top-shelf.md), [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) --- # F1 > F1 is the first generation of offspring from crossing two parents; if the parents are inbred and different, F1 plants are uniform and often show hybrid vigour. - Canonical: https://genetixbay.com/knowledge/glossary/f1.html - Also written: F1 hybrid, first filial generation, F1 seed, F1 hybrid seed, F1s - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" F1 is the first filial generation: the seed of a cross between two P1 parents. In classic plant breeding the parents are two different [inbred lines](https://genetixbay.com/knowledge/glossary/inbred-line.md), so every F1 seed gets the same set of [alleles](https://genetixbay.com/knowledge/glossary/allele.md) from each parent. The result is a uniform, highly heterozygous crop that often shows [hybrid vigour](https://genetixbay.com/knowledge/glossary/heterosis.md). ## In practice That uniformity is why maize and vegetable growers buy F1 hybrid seed every year. Cannabis is mostly different. Few cannabis parents are inbred, so a cross of two hybrid clones produces "F1" seed that varies a lot. Growers still call it F1 because it is the first cross, but genetically it [segregates](https://genetixbay.com/knowledge/glossary/segregation.md) more like an [F2](https://genetixbay.com/knowledge/glossary/f2.md). True uniform cannabis F1 seed requires two inbred parents ([IBLs](https://genetixbay.com/knowledge/glossary/ibl.md) or highly inbred lines). It exists, but it is a significant breeding investment. Saving seed from F1 plants and growing it out gives F2s, which segregate widely. That is expected, not a fault of the seed. ## Don't confuse with - **F2**: offspring of F1 × F1. Wide variation. - **Feminised F1**: an F1 made with [reversed female](https://genetixbay.com/knowledge/glossary/sex-reversal.md) pollen; still an F1, but with all-female seed. - **Hybrid**: any cross between different parents. Every F1 is a hybrid; not every hybrid is a uniform F1. ## Myth check "F1 hybrid" on a pack does not guarantee uniformity unless the parents were inbred; see [F1, F2, F3 explained](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md). ## Related terms [P1](https://genetixbay.com/knowledge/glossary/p1.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md), [Hybrid](https://genetixbay.com/knowledge/glossary/hybrid.md), [Heterosis](https://genetixbay.com/knowledge/glossary/heterosis.md), [Filial generation](https://genetixbay.com/knowledge/glossary/filial-generation.md), [Inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md) ## Read more - [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md) - [Inbreeding depression and hybrid vigour](https://genetixbay.com/knowledge/breeding/inbreeding-depression-hybrid-vigour.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Schnable PS, Springer NM. 2013. Progress toward understanding heterosis in crop plants. Annual Review of Plant Biology 64:71-88. https://doi.org/10.1146/annurev-arplant-042110-103827 --- # F2 > F2 is the second filial generation, made by crossing or selfing F1 plants; it shows the widest segregation, bringing back hidden recessives and new combinations. - Canonical: https://genetixbay.com/knowledge/glossary/f2.html - Also written: second filial generation, F2 generation, F2s, F2 seed - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" F2 is the generation produced by crossing [F1](https://genetixbay.com/knowledge/glossary/f1.md) plants with each other (or selfing an F1). Each F1 parent passes one of its two [alleles](https://genetixbay.com/knowledge/glossary/allele.md) at random, so the F2 contains every combination of the original parents' alleles in [Mendelian ratios](https://genetixbay.com/knowledge/glossary/mendelian-inheritance.md): 1:2:1 genotypes at each locus, 3:1 visible ratio for a dominant trait. ## In practice The F2 is the breeder's hunting ground. [Recessive traits](https://genetixbay.com/knowledge/glossary/recessive.md) hidden in the F1 reappear, and new combinations show up that neither grandparent had. That is why [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md), specific colours or rare aromas from one grandparent are often recovered in an F2 rather than an F1. The trade-off is variation. An F2 pack can range from tall to short, fast to slow, and fuel to fruit. Expect to grow more plants: for a wanted combination of two recessive traits, about 1 in 16; for three, about 1 in 64. ## Don't confuse with - **F1**: the uniform (or less variable) first cross. - **F3 and later**: produced by crossing selected F2s; [segregation](https://genetixbay.com/knowledge/glossary/segregation.md) narrows as selection continues. - **S1**: selfed seed from one plant; similar segregation to an F2 of that plant's genotype, but every seed is female and [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) is higher. ## Related terms [F1](https://genetixbay.com/knowledge/glossary/f1.md), [Filial generation](https://genetixbay.com/knowledge/glossary/filial-generation.md), [Segregation](https://genetixbay.com/knowledge/glossary/segregation.md), [Pheno hunt](https://genetixbay.com/knowledge/glossary/pheno-hunt.md), [Recessive](https://genetixbay.com/knowledge/glossary/recessive.md) ## Read more - [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md) - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ --- # Fabric pot > A fabric pot is a breathable, sewn felt or non-woven container that lets air and water through its walls, drying the medium faster and air-pruning roots. - Canonical: https://genetixbay.com/knowledge/glossary/fabric-pot.html - Also written: fabric pots, grow bag, grow bags, smart pot, cloth pot, felt pot - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A fabric pot is a soft container made of non-woven polypropylene or felt. Water evaporates through the walls, which raises air in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md), cools the medium by evaporation, and air-prunes roots: tips that reach the wall dry out and stop, prompting branching instead of circling. ## In practice Fabric pots are forgiving of heavy-handed watering and are popular in soil and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md). The flip side is that they dry faster and unevenly, so in hot, [dry rooms](https://genetixbay.com/knowledge/glossary/drying-room.md) they need water more often, and the outer layer of medium can dry out before the core. Stand them on a raised tray or crate so the base [drains](https://genetixbay.com/knowledge/glossary/runoff.md) and does not wick runoff back. Sizes are usually sold in US gallons (a "5 gal" bag holds about 19 L when full, often less in practice). ## Don't confuse with - **Air pot**: a rigid plastic pot with cones and holes; also air-prunes, but holds its shape and dries differently. - **Plastic nursery pot**: solid walls; holds water longer and roots circle at the wall. ## Related terms [Air pot](https://genetixbay.com/knowledge/glossary/air-pot.md), [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md), [Root-bound](https://genetixbay.com/knowledge/glossary/root-bound.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) ## Read more - [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Fan leaf > A large palmate cannabis leaf with several long leaflets on a long petiole; fan leaves do most of the plant's photosynthesis and carry few trichomes. - Canonical: https://genetixbay.com/knowledge/glossary/fan-leaf.html - Also written: fan leaves, fans, water leaves, shade leaves, big leaves - Glossary category: Plant biology · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fan leaves are the big, iconic palmate leaves of cannabis: usually five to eleven serrated leaflets radiating from a long [petiole](https://genetixbay.com/knowledge/glossary/petiole.md), growing from the main stem and branches. They are the plant's solar panels, doing most of the [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) and storing [mobile nutrients](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md) that the plant can draw on later in flower. They carry far fewer glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) than [bracts](https://genetixbay.com/knowledge/glossary/bract.md) and [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md). ## In practice Fan leaves are central to the [defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md) argument. House approach: "tuck, don't pluck". Maximise leaf surface like a solar farm for the buds, and tuck leaves out of the way of bud sites rather than strip them. Cultivars respond differently: some clones lost most of their fans with no effect or even grew faster, while others suffered. Stripping within reason doesn't seem to hurt yield, but in the founder's experience tucking helps more. It remains an open question for [GenetixBay trials](https://genetixbay.com/knowledge/glossary/bay-trials.md). Fan leaves are also the main diagnostic surface. Where and how a fan yellows tells you much more than new growth alone. At harvest, fans are usually removed first; they make poor smoking material. ## Don't confuse with - **Sugar leaf**: small, resin-coated leaf within the bud. - **Leaflet**: one blade of a fan leaf. - **Cotyledon**: the seed leaf of a seedling. ## Related terms [Sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md), [Leaflet](https://genetixbay.com/knowledge/glossary/leaflet.md), [Petiole](https://genetixbay.com/knowledge/glossary/petiole.md), [Photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) ## Read more - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 --- # Far-red > Far-red is light from about 700 to 750 nm, just beyond visible red; it adds to canopy photosynthesis when mixed with other light and triggers shade responses like stretch. - Canonical: https://genetixbay.com/knowledge/glossary/far-red.html - Also written: far red, FR, far-red light, 730 nm, 730nm - Glossary category: Environment and light · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Far-red is the waveband from roughly 700 to 750 nm (some definitions run to 800 nm). It sits outside classical [PAR](https://genetixbay.com/knowledge/glossary/par.md), and the eye barely sees it. On its own it drives little [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), but mixed with shorter wavelengths it boosts photosynthesis through the [Emerson enhancement effect](https://genetixbay.com/knowledge/glossary/emerson-effect.md). Zhen and Bugbee (2020) showed far-red photons up to 750 nm were about as effective as PAR photons for whole-canopy photosynthesis in several crops. *Established* outside cannabis. ## In practice Far-red is also a signal. A low [red:far-red ratio](https://genetixbay.com/knowledge/glossary/red-far-red-ratio.md) reads as shade and promotes stem elongation and leaf expansion. Some growers use a short burst of far-red at lights-off (end-of-day far-red) to speed the switch to darkness signalling; cannabis-specific evidence for meaningful gains is limited. Peterswald and colleagues (2025) reviewed and tested far-red in [medicinal cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md) with mixed outcomes on yield and quality. Add far-red if you want faster canopy closure and can tolerate [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). Skip it if you are short on height. Fixtures with far-red are often rated in ePAR (400–750 nm), which inflates the headline number compared with PAR-only ratings. ## Don't confuse with - **Infrared (heat)**: thermal infrared is far longer wavelength (above about 3,000 nm); 730 nm far-red [LEDs](https://genetixbay.com/knowledge/glossary/led.md) do not heat plants meaningfully. - **Red (660 nm)**: the most efficient photosynthetic band; far-red balances it. ## Related terms [Red:far-red ratio](https://genetixbay.com/knowledge/glossary/red-far-red-ratio.md), [Emerson effect](https://genetixbay.com/knowledge/glossary/emerson-effect.md), [PAR](https://genetixbay.com/knowledge/glossary/par.md), [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Zhen S, Bugbee B, 2020. Far-red photons have equivalent efficiency to traditional photosynthetic photons: implications for redefining photosynthetically active radiation. Plant, Cell & Environment 43(5):1259–1272. https://doi.org/10.1111/pce.13730 2. Peterswald TJ et al., 2025. The effects of far-red light on medicinal Cannabis. Scientific Reports. https://pmc.ncbi.nlm.nih.gov/articles/PMC12092679/ 3. Kotiranta S et al., 2024. (Low R:FR increased height and reduced inflorescence yield.) Industrial Crops and Products. https://doi.org/10.1016/j.indcrop.2023.117772 --- # Fecundity > The number of eggs or live young a female produces, per day or in her lifetime; a key life-table input. - Canonical: https://genetixbay.com/knowledge/glossary/fecundity.html - Also written: lifetime fecundity, eggs per female, oviposition rate - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fecundity is the reproductive output of a female, given per day (oviposition rate) or over her life. Small [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) lay a few eggs a day for one to three weeks, while a single noctuid moth such as the [corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md) can lay hundreds to a few thousand eggs. Temperature and host quality change fecundity strongly. ## In practice Fecundity alone misleads. What matters is how early the eggs come: a female laying most of her eggs in her first days pushes r_m much higher than one spreading the same total over weeks. Over-fertilised, nitrogen-rich soft growth tends to raise fecundity in sap and cell feeders (Grower practice, supported in other crops). ## Don't confuse with - **Fertility**: eggs that hatch, not just eggs laid. - **R0**: daughters that survive, after mortality. ## Related terms [Life table](https://genetixbay.com/knowledge/glossary/life-table.md), [Intrinsic rate of increase (r_m)](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [Net reproductive rate (R0)](https://genetixbay.com/knowledge/glossary/net-reproductive-rate.md), [Sex ratio](https://genetixbay.com/knowledge/glossary/sex-ratio.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) ## Sources 1. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605 --- # Feed chart > A feed chart is a manufacturer's or grower's schedule of nutrient doses by week or stage; treat it as a ceiling to test against, not a rule. - Canonical: https://genetixbay.com/knowledge/glossary/feed-chart.html - Also written: feeding chart, feeding schedule, nutrient schedule, feed schedule, nute schedule - Glossary category: Nutrients · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A feed chart is a table giving how much of each product to add per litre, and the expected [EC](https://genetixbay.com/knowledge/glossary/ec.md), for each week or stage of growth. Manufacturers publish them for their product lines; experienced growers keep their own. ## In practice Manufacturer charts are often written for maximum product use and fast-feeding cultivars, and they frequently stack several additives on a base. Many growers start at half to three-quarters of chart strength and adjust by watching the plants and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) EC. Charts are also system-specific: [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) and [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) need different strengths and frequencies than soil. Translating a chart into [elemental ppm](https://genetixbay.com/knowledge/glossary/elemental-ppm.md) shows what it really delivers and makes comparisons possible. ## Don't confuse with - **Recipe**: a formula in grams of salt or mg/L of each element, independent of a product line. - **Feed by stage guide**: general targets, not tied to a bottle. ## Myth check A feed chart is not evidence that every additive on it is needed. Trials show cannabis yield plateaus with moderate nutrient strength and phosphorus (Evidence: Established). Test your cultivar. See [feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md). ## Related terms [ppm of an element](https://genetixbay.com/knowledge/glossary/elemental-ppm.md), [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md), [Nutrient burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md), [Bloom booster](https://genetixbay.com/knowledge/glossary/bloom-booster.md) ## Read more - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ## Sources 1. Bevan L, Jones M, Zheng Y. 2021. Optimisation of nitrogen, phosphorus, and potassium for soilless production of Cannabis sativa in the flowering stage using response surface analysis. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 2. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 --- # Feminised seed > Feminised seed is seed made by pollinating a female with pollen from another female (or itself) that was chemically reversed, so nearly every seed grows into a female. - Canonical: https://genetixbay.com/knowledge/glossary/feminised-seed.html - Also written: feminized seed, feminised seeds, feminized seeds, feminised, feminized - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Feminised seed is produced by crossing two females, or a female with herself. One of them is treated so that it grows [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) and makes pollen ([sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md)), most often with [silver thiosulfate](https://genetixbay.com/knowledge/glossary/sts.md) (Ram and Sett 1982; Lubell and Brand 2018). Because that pollen carries only X [chromosomes](https://genetixbay.com/knowledge/glossary/chromosome.md), the seed is genetically female (XX). ## In practice Feminised seed saves space and time: no males to find and remove, nearly every plant flowers into usable bud. That is why most seed sold for home growers is feminised. Its quality depends entirely on the breeder's discipline. Good practice is to reverse only females that have stayed fully female over several runs, under controlled conditions, and to grow out and check the seed before release. Poor practice (reversing a plant that already [herms](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), or using pollen from stress herms) spreads unstable sex expression into the seed. Feminised seed cannot be used to select males, so lines bred only by feminising lose half of what breeding normally samples. ## Don't confuse with - **S1**: feminised seed from a female [selfed](https://genetixbay.com/knowledge/glossary/selfing.md) with her own reversed pollen. All [S1s](https://genetixbay.com/knowledge/glossary/s1.md) are feminised; most feminised seed is a cross of two different females. - **Regular seed**: male × female, about half males. - **Autoflower**: a flowering trait, independent of feminisation. ## Myth check Herms in feminised seed are mainly breeder error, not "what fem seed does". See [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Regular seed](https://genetixbay.com/knowledge/glossary/regular-seed.md), [Sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md), [STS](https://genetixbay.com/knowledge/glossary/sts.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md), [XY sex determination](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md) ## Read more - [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) - [Regular, feminised, autoflower or clone: choosing your starting material](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md) ## Sources 1. Ram HYM, Sett R. 1982. Induction of fertile male flowers in genetically female Cannabis sativa plants by silver nitrate and silver thiosulphate anionic complex. Theoretical and Applied Genetics 62:369-375. https://doi.org/10.1007/BF00275107 2. Lubell JD, Brand MH. 2018. Foliar sprays of silver thiosulfate produce male flowers on female hemp plants. HortTechnology 28(6):743-747. https://doi.org/10.21273/HORTTECH04188-18 3. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 --- # Fems > Fems is slang for feminised seed, made with pollen from a chemically sex-reversed female so nearly every plant grows female. - Canonical: https://genetixbay.com/knowledge/glossary/fems.html - Also written: femmed seed, fem seeds, femmies, fem, femmed - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fems is slang for [feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md). A female plant (or branch) is treated so it makes pollen, usually with [silver thiosulfate](https://genetixbay.com/knowledge/glossary/sts.md) or [colloidal silver](https://genetixbay.com/knowledge/glossary/sex-reversal.md), and that pollen fertilises another female, or the same one in an [S1](https://genetixbay.com/knowledge/glossary/s1.md). The seed carries no Y chromosome, so nearly every plant is female. ## In practice Fems suit growers with limited space who want every plant to flower. A 5-pack of fems should give 5 females. The quality of fems depends on the breeder's choice of which female to reverse: reversing a plant that never showed [intersex](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) flowers, over a large test, is careful work; reversing whatever is popular is not. ## Don't confuse with - **Regs**: regular seed with males and females. - **Herm pollen seed**: seed from a plant that threw [bananas](https://genetixbay.com/knowledge/glossary/nanners.md) on its own. It is also "feminised" in a sense, but it is accidental and selects for intersex tendency. - **Clones**: identical copies; fems are new individuals. ## Myth check "Fems always herm." Not inherently. [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) fems come mainly from careless feminising and repeated selfing, not from the method itself. Ask for the line's tester [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md). See [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md). ## Related terms [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [Regs](https://genetixbay.com/knowledge/glossary/regs.md), [Sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md), [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md) ## Read more - [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) - [Regular, feminised, autoflower or clone: choosing your starting material](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md) --- # Fertigation > Fertigation is delivering fertiliser dissolved in irrigation water, so plants are fed every time they are watered rather than through solid amendments. - Canonical: https://genetixbay.com/knowledge/glossary/fertigation.html - Also written: fertigate, fertigating, feed and water, nutrient irrigation - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fertigation (fertiliser plus irrigation) means supplying nutrients in the water. It covers hand-watering with a nutrient solution and automated [drip systems](https://genetixbay.com/knowledge/glossary/drip-irrigation.md) using a dosing pump or [stock tanks](https://genetixbay.com/knowledge/glossary/stock-solution.md). It is the default method in soilless media such as [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), rockwool and peat mixes, where the medium itself holds little nutrition. ## In practice The grower mixes or injects a solution to a target [EC](https://genetixbay.com/knowledge/glossary/ec.md) (for example 1.2-2.4 mS/cm depending on stage and cultivar) and pH (about 5.8-6.2 in coco), and applies it with each irrigation. Automated systems use one or more concentrated stock solutions and an injector or dosing pump at a set ratio. Fertigation gives precise, fast control of what the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) sees, and enables crop steering and [per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md). GenetixBay's Jardin uses per-element dosing so nitrogen can be tapered in late flower without cutting P, K, Ca, Mg and the micros. ## Don't confuse with - **Foliar feeding**: spraying nutrients on leaves. - **Top dressing**: solid amendments on the surface. ## Related terms [Drip irrigation](https://genetixbay.com/knowledge/glossary/drip-irrigation.md), [Drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), [High-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md), [Hydroponics](https://genetixbay.com/knowledge/glossary/hydroponics.md), [Crop steering](https://genetixbay.com/knowledge/glossary/crop-steering.md) ## Read more - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Field capacity > Field capacity is the amount of water a medium holds after it has been saturated and allowed to drain freely; in pots it is called container capacity. - Canonical: https://genetixbay.com/knowledge/glossary/field-capacity.html - Also written: container capacity, pot capacity, water holding capacity, drained upper limit - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Field capacity is the [water content](https://genetixbay.com/knowledge/glossary/moisture-content.md) of a soil once gravity [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) has stopped after saturation, usually a day or two after heavy rain in the field. In containers the equivalent is container capacity: the water a pot holds once it stops dripping after a full watering. Because a pot is shallow and has a perched water table at the bottom, container capacity is wetter than field capacity of the same material in the ground. ## In practice Growers treat container capacity as "100% full". In crop steering, substrate water content is read with sensors or pot weight, and the first irrigations of the day bring the medium back up to near field or container capacity. The [dryback](https://genetixbay.com/knowledge/glossary/dryback.md) is then measured from that point. A pot that holds 6 kg of water at container capacity and is down to 4.8 kg has lost 20%. Taller containers drain better and hold proportionally more air at container capacity. ## Don't confuse with - **Saturation**: every pore full of water, before drainage; roots can't breathe for long. - **Permanent wilting point**: the dry end of the range, where the plant can no longer extract water. ## Related terms [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md), [Wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md), [Air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), [Crop steering](https://genetixbay.com/knowledge/glossary/crop-steering.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) ## Read more - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 2. Brady NC, Weil RR, 2017. The Nature and Properties of Soils, 15th ed. Pearson. --- # Filial generation > Filial generations (F1, F2, F3 and on) count generations of offspring from an original cross, each made by crossing plants of the previous generation together. - Canonical: https://genetixbay.com/knowledge/glossary/filial-generation.html - Also written: filial, F-generation, F3, F4, F5, Fn, F-number - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A filial generation is one step of offspring counted from an original cross. The parents are P1, their seed is the [F1](https://genetixbay.com/knowledge/glossary/f1.md), F1 × F1 gives the [F2](https://genetixbay.com/knowledge/glossary/f2.md), F2 × F2 gives the F3, and so on. The number tells you how many generations of crossing within the line have happened since the founders. ## In practice The F-number signals how far a line is towards [breeding true](https://genetixbay.com/knowledge/glossary/true-breeding.md), but only if the breeder selected along the way. A line taken to F5 or F6 with strict selection in every generation can be close to stable for its key traits. A line taken to F5 by sowing whatever came out, with no selection, is mostly just older. [Cannabis labels](https://genetixbay.com/knowledge/glossary/labelling-requirements.md) sometimes misuse the numbers: "F1" on a cross of two [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md), or "F5" with no records. Ask for the generation history, the number of plants grown at each step and what was selected. ## Units and formula For a single [gene](https://genetixbay.com/knowledge/glossary/gene.md) starting [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) in the F1: the F2 is 1 AA : 2 Aa : 1 aa, so 50% heterozygous. With random mating in a large population and no selection it stays near 50% in later generations; only selection and [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) fix the trait. With selfing every generation it halves: 50% in F2, 25% in F3, 12.5% in F4. ## Don't confuse with - **Backcross (BX)**: crossing back to a parent, a different route. - **S-generation**: selfed generations (S1, S2), counted separately. - **IBL**: an inbred line, often the end point of many filial generations with selection. ## Related terms [P1](https://genetixbay.com/knowledge/glossary/p1.md), [F1](https://genetixbay.com/knowledge/glossary/f1.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md), [Segregation](https://genetixbay.com/knowledge/glossary/segregation.md) ## Read more - [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md) - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # FIM > FIM is a training cut that pinches off most, but not all, of a plant's newest growing tip, often producing three or four new main shoots instead of one. - Canonical: https://genetixbay.com/knowledge/glossary/fim.html - Also written: FIMing, FIM'ing, fimming, F.I.M., f*** I missed - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" FIM (named from the grower joke "f*** I missed", from an attempt at topping that left part of the tip) is a technique where roughly 70-80% of the newest shoot at the very top is pinched or cut off, leaving a small part of the [growing tip](https://genetixbay.com/knowledge/glossary/apical-meristem.md). The damaged tip often regrows as three or four shoots rather than the two from a clean top. ## In practice FIM is done on the newest, still-folded growth, not the stem below it. Results are inconsistent: sometimes four [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md), sometimes one or two, sometimes a stunted cluster. It recovers faster than topping because less tissue is removed, and the plant keeps more height. Many growers combine FIM with [LST](https://genetixbay.com/knowledge/glossary/lst.md) to spread the new tops out. Evidence for FIM is almost entirely grower experience; there are no controlled cannabis trials comparing it with topping. ## Don't confuse with - **Topping**: a clean cut through the stem above a node; reliably gives two tops. - **Pinching (other crops)**: a general term; in cannabis it usually means topping or FIM. ## Related terms [Topping](https://genetixbay.com/knowledge/glossary/topping.md), [Apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md) ## Read more - [FIM: pinching most of the tip for multiple tops](https://genetixbay.com/knowledge/training/fim.md) --- # Fire > Fire is slang for excellent cannabis; it is enthusiasm, not a description of any measurable trait. - Canonical: https://genetixbay.com/knowledge/glossary/fire.html - Also written: fire weed, straight fire, flames, heat - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fire is general slang for very good cannabis, or anything good. "That's fire" carries no specific information about aroma, potency or growing. ## In practice Fire is the most common word in reviews and social posts, which makes it the least useful. A [smoke report](https://genetixbay.com/knowledge/glossary/smoke-report.md) that says "fire" has told you that the reviewer liked it. Useful reports describe the aroma when broken and ground, the flavour on the first and later draws, smoothness, ash and burn, how the cure smells, and reported effects, plus how it was grown and stored. On GenetixBay, a smoke report is most useful when it is tied to a journal and a batch record, so readers can see what grow and cure produced the flower being called fire. ## Don't confuse with - **Fire as a fault**: harsh, hot, coughing smoke, usually from poor drying or curing or a dirty pipe, is the opposite of the slang meaning. ## Related terms [Dank](https://genetixbay.com/knowledge/glossary/dank.md), [Loud](https://genetixbay.com/knowledge/glossary/loud.md), [Zaza](https://genetixbay.com/knowledge/glossary/zaza.md), [Smoke report](https://genetixbay.com/knowledge/glossary/smoke-report.md) --- # Flavonoid > Flavonoids are polyphenolic plant compounds, including flavones, flavonols and anthocyanins, that colour and protect plant tissue; cannabis contains common ones plus cannabis-specific cannflavins. - Canonical: https://genetixbay.com/knowledge/glossary/flavonoid.html - Also written: flavonoids, flavonols, flavones, plant flavonoids - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Flavonoids are a large family of polyphenols built on a C6-C3-C6 skeleton. Plants use them as pigments, UV screens and defence compounds. In cannabis the main ones are flavones and flavonols (apigenin, luteolin, kaempferol, quercetin glycosides), the prenylated cannflavins, and [anthocyanins](https://genetixbay.com/knowledge/glossary/anthocyanin.md), which give purple and red colour. ## In practice Flavonoids sit mostly in leaves and [bracts](https://genetixbay.com/knowledge/glossary/bract.md) rather than [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), typically in the region of 1% of dry leaf weight or less. They are rarely tested on commercial COAs. Growers meet them as colour: purple bud is anthocyanin expression, set by genetics and brought out by cool temperatures. ## Don't confuse with - **Terpenes**: aroma compounds; flavonoids add little aroma. - **Anthocyanins**: one flavonoid subclass, responsible for purple. - **Cannabinoids**: a separate class made in [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md). ## Myth check House position: [bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md) is not quality. Purple and frost don't mean potency, and [cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) bring out colour in cultivars that carry it but have no proven effect on [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) or resin. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Cannflavin](https://genetixbay.com/knowledge/glossary/cannflavin.md), [Anthocyanin](https://genetixbay.com/knowledge/glossary/anthocyanin.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. 2. Barrett ML, Gordon D, Evans FJ. 1985. Isolation from Cannabis sativa L. of cannflavin, a novel inhibitor of prostaglandin production. Biochemical Pharmacology 34(11):2019-2024. --- # Flip > The flip is switching a photoperiod plant from long vegetative days to a flowering light schedule, usually around 12 hours of light, to start flowering. - Canonical: https://genetixbay.com/knowledge/glossary/flip.html - Also written: flipping, flip to flower, flipping to 12/12, switch to flower, flowering switch - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The flip is the moment a grower changes the light schedule from veg (typically [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) or 24/0) to flower (typically [12/12](https://genetixbay.com/knowledge/glossary/12-12.md)) to trigger flowering in [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis. The plant responds to the long, uninterrupted dark period, not to the light hours as such. Visible [pistils](https://genetixbay.com/knowledge/glossary/pistil.md) usually appear within one to two weeks, followed by the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). ## In practice Growers flip once the plant has filled about half to two-thirds of the space it should occupy at harvest, allowing for the stretch. The dark period must be truly dark; [light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) can delay flowering or contribute to stress. House position: flower doesn't have to be exactly 12/12. A [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) schedule is endorsed, and some cultivars flower with 14-15 h of light. In practice that means around 12 h at high intensity, with sunrise and sunset ramps adding the rest. Test your cultivar. ## Don't confuse with - **Autoflowering**: flowers by age, so there is no flip. - **Flip (slang, selling)**: unrelated. ## Related terms [Veg time](https://genetixbay.com/knowledge/glossary/veg-time.md), [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), [Re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) ## Read more - [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) --- # Flowering stage > The reproductive phase of the cannabis life cycle, from the switch to flowering until harvest, during which the plant stretches, builds buds and ripens resin. - Canonical: https://genetixbay.com/knowledge/glossary/flowering-stage.html - Also written: flowering phase, flower stage, bloom, bloom phase, flowering period, in flower - Glossary category: Plant biology - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The flowering stage is the period when a cannabis plant produces its inflorescences. In [photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md) it begins when the night becomes long enough; in [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) it begins at a set age. It ends at harvest, or, for seed crops, at seed maturity. ## In practice Indoors, a typical photoperiod flower runs 7-10 weeks for most [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) and 11-16 weeks or more for some long-flowering equatorial types. It falls into rough phases: - **Transition and stretch (weeks 1-3)**: rapid elongation, often 50-200% height gain, first clusters of stigmas. - **Bulking (weeks 3-6 or so)**: bud mass and [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) density build fast. - **Ripening (final 2-3 weeks)**: bracts swell, [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) turn cloudy then partly amber, fan leaves may yellow. Climate shifts with it: [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) typically drops from about 50-60% early to 40-50% late to protect dense colas from botrytis. House position: the last weeks are when the plant packs on most of its final weight and resin. Keep feeding ([taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) rather than starving the plant) and keep the lights on. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Don't confuse with - **Pre-flowering**: early single flowers at nodes during veg. - **Flip**: the act of changing the light schedule. - **Senescence**: the ageing at the end of flower, not the whole stage. ## Related terms [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [Autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md), [Pre-flower](https://genetixbay.com/knowledge/glossary/pre-flower.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md), [Harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md) ## Read more - [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Aizpurua-Olaizola O, Soydaner U, Öztürk E, et al. 2016. Evolution of the cannabinoid and terpene content during the growth of Cannabis sativa plants from different chemotypes. Journal of Natural Products 79(2):324-331. https://pubmed.ncbi.nlm.nih.gov/26836472/ --- # Flushing > Feeding only plain water for days or weeks before harvest to "clean" the plant; GenetixBay rates it a Myth that harms yield, unlike a root-zone salt flush. - Canonical: https://genetixbay.com/knowledge/glossary/flushing.html - Also written: flush, pre-harvest flush, preharvest flush, flushing before harvest, final flush, plain water flush, flushed - Glossary category: Harvest, drying and curing · Evidence: Myth - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Flushing, in cannabis lore, means stopping all nutrients and giving only plain water (often large volumes) for the last one to three weeks before harvest. The claim is that it removes stored nutrients, improves taste and gives white ash. The plant doesn't work that way. Cannabis is a bioaccumulator: what it takes up is built into tissue, and plain water in the final days doesn't wash it out. ## In practice House position (Myth): flushing is for toilets. Pre-harvest flushing is actively harmful, not just useless. It starves the plant in its most critical phase, when it's packing on most of its final weight, [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) and resin. Controlled studies found no taste or quality benefit (Alden & Faust 2025; Hershkowitz 2024). Losses grow with how long and hard the plant is starved; some elements even rise in flower tissue after a flush, a concentration effect. What to do instead: - **Taper nitrogen**: cut N back toward zero near the finish while feeding P, K, Ca, Mg, S and [micros](https://genetixbay.com/knowledge/glossary/micronutrient.md). - **Dry and cure properly**: that's where taste and smooth smoke come from. - **Root-zone flush only for salts**: that treats the medium, at any stage. ## Don't confuse with - **Root-zone flush**: washing [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) out of the medium, valid at any stage. - **Nitrogen taper**: the GenetixBay alternative. - **Leaching**: routine [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) in [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md). ## Myth check Myth, and harmful. Full evidence in [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md); see also [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md), [Nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md), [Harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md) ## Read more - [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) - [Flushing before harvest: myth (summary)](https://genetixbay.com/knowledge/nutrients/flushing.md) ## Sources 1. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 2. Hershkowitz JA. 2024. Nutrient management of cannabis in controlled environments. MS thesis, Utah State University (Bugbee lab). https://digitalcommons.usu.edu/etd2023/178 3. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 --- # Fogponics > Fogponics is a form of aeroponics that bathes roots in a fog of nutrient solution made by ultrasonic foggers, with droplets far smaller than spray systems. - Canonical: https://genetixbay.com/knowledge/glossary/fogponics.html - Also written: fog-ponics, fogponic, ultrasonic aeroponics, fogger system, mist culture - Glossary category: Systems and media · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fogponics uses ultrasonic transducers ([foggers](https://genetixbay.com/knowledge/glossary/humidifier.md)) to turn nutrient solution into a cold fog of very fine droplets, typically under about 10 µm, which fills a closed root chamber. In theory, tiny droplets give roots both oxygen and nutrients with almost no water barrier. ## In practice In practice, fogponics is mostly used for [cloning](https://genetixbay.com/knowledge/glossary/cloning.md) and small experimental systems. Common problems: transducers heat the solution, salts build up and crust on the discs, units wear out and need regular replacement, and fog alone may deliver [too little water](https://genetixbay.com/knowledge/glossary/underwatering.md) and nutrients to large flowering plants. Many builds combine fog with a spray or a shallow pool. Evidence for full-cycle cannabis production in fogponics is limited to grower reports; treat it as experimental. ## Don't confuse with - **HPA**: pressure-driven mist with larger droplets. - **Humidifier fog**: the same hardware, used for air humidity, not root feeding. ## Related terms [Aeroponics](https://genetixbay.com/knowledge/glossary/aeroponics.md), [HPA](https://genetixbay.com/knowledge/glossary/hpa.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [Root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) ## Read more - [Fogponics: ultrasonic fog for roots (a supplement, not a system)](https://genetixbay.com/knowledge/systems/fogponics.md) ## Sources 1. Lakhiar IA, Gao J, Syed TN, Chandio FA, Buttar NA, 2018. Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics. Journal of Plant Interactions 13(1):338–352. https://doi.org/10.1080/17429145.2018.1472308 --- # Foliar feeding > Foliar feeding is spraying a dilute nutrient solution onto leaves for quick uptake through the leaf surface; it suits micronutrient fixes but cannot replace root feeding. - Canonical: https://genetixbay.com/knowledge/glossary/foliar-feeding.html - Also written: foliar feed, foliar spray, foliar application, foliar, spraying leaves - Glossary category: Nutrients · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Foliar feeding is applying nutrients in dilute solution directly to leaves. Ions enter through the cuticle, [stomata](https://genetixbay.com/knowledge/glossary/stomata.md) and small pores, and are used locally or moved on through the phloem. Uptake works best for elements needed in small amounts, such as iron, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md), zinc, boron and magnesium, and for [urea](https://genetixbay.com/knowledge/glossary/urea.md). ## In practice Growers use foliar sprays as a quick, temporary fix for a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) shortage while correcting the root-zone cause, usually [pH](https://genetixbay.com/knowledge/glossary/ph.md). [Macronutrients](https://genetixbay.com/knowledge/glossary/macronutrient.md) cannot be supplied in meaningful amounts this way: leaves cannot absorb enough without burning. Spray at low strength, with lights off or low, covering leaf undersides, and stop once flowers form. Wet buds invite [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md), and residues can end up in the harvested flower. ## Don't confuse with - **Root feeding (fertigation)**: the main route for all nutrients. - **Foliar pest sprays**: pesticides, a separate topic with their own rules. - **Misting for humidity**: plain water, no nutrients. ## Myth check Foliar feeding in flower is not a shortcut to quality, and it adds disease risk. See [botrytis bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md). ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), [Iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md), [Amino acid chelate](https://genetixbay.com/knowledge/glossary/amino-acid-chelate.md), [Urea](https://genetixbay.com/knowledge/glossary/urea.md) ## Read more - [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Foot-candle > A foot-candle is an imperial unit of illuminance (one lumen per square foot, about 10.76 lux); like lux, it measures eye brightness, not plant-usable light. - Canonical: https://genetixbay.com/knowledge/glossary/foot-candle.html - Also written: fc, foot candle, footcandle, ft-c, foot-candles - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A foot-candle (fc) is one lumen per square foot, equal to 10.764 lux. It is the [illuminance](https://genetixbay.com/knowledge/glossary/lux.md) unit used in older North American horticulture texts and building lighting codes. It shares the flaw of lux: it is weighted to the human eye, which sees green and yellow best and undervalues the red and [blue light](https://genetixbay.com/knowledge/glossary/blue-light.md) plants rely on. ## In practice Older grow guides quote targets such as "5,000–10,000 fc for flowering". These numbers date from the [HPS](https://genetixbay.com/knowledge/glossary/hps.md) era, when nearly everyone used the same spectrum, so a rough conversion held. They do not transfer to [LED](https://genetixbay.com/knowledge/glossary/led.md) fixtures, whose spectra vary widely. A red-heavy LED can deliver more usable light at a lower foot-candle reading than an HPS. If you only have a foot-candle meter, use it to check uniformity under one fixture type: walk it across the canopy and look for weak corners. For anything else, use a quantum sensor and work in [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md). ## Units and formula - 1 fc = 1 lm/ft² = 10.764 lux - 1,000 fc ≈ 10,760 lux ≈ 200 µmol/m²/s in sunlight (sunlight factor about 54 lux per µmol/m²/s; varies by source) ## Don't confuse with - **Lux**: the same quantity in metric units. - **PPFD**: the plant-relevant photon count, in µmol/m²/s. - **Foot-lambert**: a unit of luminance (light leaving a surface), not illuminance. ## Myth check "Lux and foot-candles are fine for grow lights" is a *Myth* once you mix lamp types. Brightness to your eye is not [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) value. ## Related terms [Lux](https://genetixbay.com/knowledge/glossary/lux.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [PAR](https://genetixbay.com/knowledge/glossary/par.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) --- # Founder effect > The founder effect is the loss of genetic diversity when a new population is started from a few individuals, so it carries only a sample of the source population's alleles. - Canonical: https://genetixbay.com/knowledge/glossary/founder-effect.html - Also written: founder population, founder effects, founder event - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The founder effect is reduced and shifted [genetic diversity](https://genetixbay.com/knowledge/glossary/gene-pool.md) in a population started by a small number of individuals. The founders carry only part of the source population's [alleles](https://genetixbay.com/knowledge/glossary/allele.md), and by chance some rare alleles become common in the new population while others disappear. ## In practice Many [cannabis seed](https://genetixbay.com/knowledge/glossary/achene.md) lines began as founder events. A traveller brought back seed from a few plants of a [landrace](https://genetixbay.com/knowledge/glossary/landrace.md); a breeder started a line from one exceptional female and one male; a [heirloom](https://genetixbay.com/knowledge/glossary/heirloom.md) was passed on as a single packet. Each of these new populations reflects its few founders, not the full landrace. That is why two "Afghan" lines from different collections can differ markedly, and why a line kept outside its source region may drift away from the original type. Records of how many plants founded a line, and from where, help breeders judge how representative it is. ## Don't confuse with - **Genetic bottleneck**: a crash in numbers within an existing population; the founder effect is the start of a new one. - **Selection**: founders chosen for traits are both a selection and a founder event. - **Landrace**: the source population, typically far more diverse than lines founded from it. ## Related terms [Genetic bottleneck](https://genetixbay.com/knowledge/glossary/genetic-bottleneck.md), [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Heirloom](https://genetixbay.com/knowledge/glossary/heirloom.md) ## Read more - [How hybrid 'strains' emerged](https://genetixbay.com/knowledge/genetics-history/how-hybrid-strains-emerged.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 --- # Founding Member > A Founding Member is an early backer of GenetixBay who joins before launch, getting first access, a permanent badge and among the lowest numbers in the archive. - Canonical: https://genetixbay.com/knowledge/glossary/founding-member.html - Also written: Founding Members, founding membership, founding cohort, Founding Member badge - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Founding Members are GenetixBay's first supporters: people who buy a founding membership before the public launch. Their money funds the first phase of the project alongside hardware deposits. ## In practice Founding Members get first access to the community, the archive and the journal, then early access to the Jardin beta and closed beta features. They carry a permanent Founding Member badge and receive some of the lowest member numbers in the archive, a small thing that matters in a community that values history. Backer tiers grant earlier access, never a higher evidence level or special standing in trials. Founding Breeders, a parallel programme for breeders, get founding terms for their storefronts and verification. ## Don't confuse with - **Member / Pro tiers**: regular paid memberships after launch. - **Investor**: Founding Members buy a membership, not a share of the company. ## Related terms [Pearls](https://genetixbay.com/knowledge/glossary/pearls.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Jardin](https://genetixbay.com/knowledge/glossary/jardin.md), [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) --- # Foxtailing > Foxtailing is the growth of new, elongated calyx spires on top of existing buds; it can be genetic, or a stress response to excess heat or light. - Canonical: https://genetixbay.com/knowledge/glossary/foxtailing.html - Also written: foxtails, foxtail, foxtailed buds, spiky buds, calyx stacking - Glossary category: Environment and light · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Foxtailing is when buds keep stacking new [calyxes](https://genetixbay.com/knowledge/glossary/calyx.md) upwards and outwards in thin spires, rather than swelling into dense colas. The result looks like a fox's tail or a spiky tower. It has two broad causes. Some cultivars foxtail naturally, especially long-flowering, narrow-leaflet lines, and that is a heritable trait. Others foxtail only under stress, most often heat or excess light at the tops nearest the fixture. ## In practice Telling them apart: genetic foxtailing appears throughout the plant, including lower buds that never got hot. Environmental foxtailing concentrates at the canopy top, often alongside [bleaching](https://genetixbay.com/knowledge/glossary/light-stress.md), and appears after a run of high [leaf temperatures](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) (above about 30 °C / 86 °F) or [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) above about 1,200 µmol/m²/s without matching CO2. Fixes for the environmental form: raise or dim the light, lower canopy temperature, improve airflow over the tops, and keep [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) in range. Late in flower, some cultivars push a [final flush](https://genetixbay.com/knowledge/glossary/flushing.md) of foxtails as they ripen; check [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) before blaming the room. Foxtailed buds are not necessarily lower quality, but stress foxtailing usually comes with reduced density and bag appeal. ## Don't confuse with - **Light stress (bleaching)**: loss of pigment; often happens alongside environmental foxtailing. - **Re-veg**: new leafy growth from buds after a [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) disruption, not stacked calyxes. ## Related terms [Heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md), [Light stress](https://genetixbay.com/knowledge/glossary/light-stress.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Temperature](https://genetixbay.com/knowledge/glossary/temperature.md) ## Read more - [Foxtailing buds on cannabis: genetics or stress?](https://genetixbay.com/knowledge/diagnosis/foxtails.md) - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) --- # Frass > Insect excrement: the dark pellets left by caterpillars, the tiny black specks left by thrips, and the fine debris left by other feeders; finding it is a key sign of a hidden pest. - Canonical: https://genetixbay.com/knowledge/glossary/frass.html - Also written: insect frass, caterpillar droppings, insect droppings - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Frass is the excrement and feeding debris left by insects. On cannabis the two kinds that matter most are the dark green to black pellets of caterpillars, often found on leaves below a damaged bud, and the tiny black specks of thrips on silvered leaf surfaces (Oregon State University Extension, EM 9626). ## In practice Frass on a leaf below a [cola](https://genetixbay.com/knowledge/glossary/cola.md) means look inside the bud: [budworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md) caterpillars tunnel in, and their feeding wounds are a common entry point for [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md). Check daily in flower, gently parting dense colas. Fresh caterpillar frass is moist and green; old frass is dry and dark. ## Don't confuse with - **Soil or perlite specks**: no pattern, and no feeding damage nearby. - **Sooty mould**: a black film growing on [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md), not pellets. - **Septoria fruiting bodies**: tiny black dots inside [leaf spots](https://genetixbay.com/knowledge/glossary/leaf-spot.md). ## Related terms [Caterpillar](https://genetixbay.com/knowledge/glossary/caterpillar.md), [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Bud rot check](https://genetixbay.com/knowledge/glossary/bud-rot-check.md) ## Read more - [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Sources 1. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp --- # Free chlorine > Free chlorine is the disinfectant (hypochlorous acid and hypochlorite) added to many tap waters; it dissipates from standing or aerated water within about a day. - Canonical: https://genetixbay.com/knowledge/glossary/free-chlorine.html - Also written: chlorine (water treatment), residual chlorine, hypochlorite, hypochlorous acid, chlorinated water - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Free chlorine is the chlorine in water present as hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻), the active forms produced when chlorine gas or sodium hypochlorite is added for disinfection. Drinking water usually carries a residual well under the 4 mg/L US limit. The balance between HOCl and OCl⁻ depends on [pH](https://genetixbay.com/knowledge/glossary/ph.md); HOCl, the stronger disinfectant, dominates below about pH 7.5. ## In practice Free chlorine is volatile. Standing water in an open container loses much of it within 24 hours, faster with aeration or stirring. [Carbon filters](https://genetixbay.com/knowledge/glossary/carbon-filter.md) remove it efficiently, and [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) pre-filters are designed to strip it to protect the membrane. Ascorbic acid also neutralises it. Growers dechlorinate mainly to protect microbes in [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), [compost teas](https://genetixbay.com/knowledge/glossary/compost-tea.md) or [beneficial reservoirs](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md). Direct harm to cannabis at tap-water levels is not well documented. Some hydro growers deliberately add low doses of hypochlorite to [sterile reservoirs](https://genetixbay.com/knowledge/glossary/sterile-reservoir.md); that is a separate, deliberate strategy that needs commitment. ## Don't confuse with - **Chloramine**: chlorine bound to ammonia; stable, does not evaporate. - **Chloride (Cl⁻)**: the plant [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), harmless at normal levels. - **Chlorine (nutrient)**: the element as a plant nutrient, a separate entry. ## Related terms [Chloramine](https://genetixbay.com/knowledge/glossary/chloramine.md), [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - [Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add](https://genetixbay.com/knowledge/nutrients/chlorine.md) ## Sources 1. Water Quality Association. 2014. Chloramine fact sheet. https://wqa.org/wp-content/uploads/2022/09/2014_Chloramine.pdf 2. USDA Forest Service. Vitamin C dechlorination. https://www.fs.usda.gov/t-d/pubs/html/05231301/05231301.html --- # Freeze drying > Drying fresh cannabis by freezing it and then removing ice under vacuum (sublimation) in hours or days; GenetixBay labels it Contested and does not recommend it. - Canonical: https://genetixbay.com/knowledge/glossary/freeze-drying.html - Also written: freeze-dried, freeze dried cannabis, lyophilisation, lyophilization, freeze dryer - Glossary category: Harvest, drying and curing · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Freeze drying (lyophilisation) freezes plant material and then lowers the pressure so that ice turns directly into vapour, skipping the liquid phase. Home and commercial freeze dryers can take fresh buds to jar-ready dryness in about a day or two instead of the usual one to two weeks. ## In practice Claims made for it: faster turnaround, less mould risk, better [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) retention and colour. Evidence specific to cannabis is limited, and results reported by growers are mixed. Some like the look and aroma; others report brittle [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md), a different texture, and flavour that doesn't develop as a slow dry and cure does. GenetixBay house position (Contested): not proven, and the founder isn't sold on it. We don't recommend it over a slow, controlled [hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md) and cure. If you try it, treat it as an experiment: split a harvest, freeze-dry half, hang-dry the other half, and compare blind. That's exactly the kind of [Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md) GenetixBay exists to run. ## Don't confuse with - **Freezing fresh material**: frozen, not dried, used as a processing input. - **Hang drying**: slow air-drying in a controlled room. - **Water curing**: a soaking method, also Contested. ## Myth check Contested. No solid cannabis data shows it beats a proper slow dry. See [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md), [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 --- # Fresh frozen > Fresh frozen is cannabis frozen immediately after harvest without drying or curing, used as starting material for live resin and live rosin to keep more volatile aroma. - Canonical: https://genetixbay.com/knowledge/glossary/fresh-frozen.html - Also written: fresh-frozen, FF, fresh frozen material, frozen whole plant, FFWP, fresh frozen flower - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fresh frozen describes harvested cannabis, typically whole flowers or whole plants with large [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) removed, that is frozen promptly and kept frozen until processing. Skipping the drying and curing stage preserves a larger share of the volatile [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md), which Ross and ElSohly (1996) showed are lost in significant amounts during air-drying. "Live" products are made from fresh frozen material. ## In practice Fresh frozen is sold or processed by [wet weight](https://genetixbay.com/knowledge/glossary/wet-weight.md), which is much heavier than [dried weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) because it's still mostly water; a fresh plant loses most of its mass on drying. Material must stay frozen; thawing and refreezing damages [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) and invites microbial problems. For hash makers, cold makes heads brittle and easier to separate in ice water. Russo et al. (2021) examined a fresh-frozen solventless process and reported good preservation of the chemical profile. GenetixBay gives no processing procedures. ## Don't confuse with - **Freeze-dried flower**: frozen then dried under vacuum; a different, contested curing alternative. - **Wet trim**: trimming before drying, not freezing. - **Cured material**: dried and [cured](https://genetixbay.com/knowledge/glossary/curing.md) before processing. ## Related terms [Live rosin](https://genetixbay.com/knowledge/glossary/live-rosin.md), [Live resin](https://genetixbay.com/knowledge/glossary/live-resin.md), [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. Russo EB, Plumb J, Whiteley VL. 2021. Novel solventless extraction technique to preserve cannabinoid and terpenoid profiles of fresh cannabis inflorescence. Molecules 26(18):5496. https://doi.org/10.3390/molecules26185496 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # Frosty > Frosty describes flower densely covered in glandular trichomes, so it looks sugared or snow-dusted; it signals resin coverage, not exact potency. - Canonical: https://genetixbay.com/knowledge/glossary/frosty.html - Also written: frost, frosted, frosty buds, caked, covered - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Frosty (or "frost") describes buds so densely coated in glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) that they look white, sugared or dusted with snow. The visible "frost" is mostly [capitate-stalked trichome](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md) heads, where [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) are made and stored. ## In practice Frost is genetic first, then growing conditions, then handling. Good light, healthy late-flower feeding and gentle handling at harvest keep it on the bud; rough trimming, compression and warm storage knock it off or degrade it. Growers inspect trichomes with a 60x loupe to judge ripeness by head colour (clear, cloudy, amber), not by how frosty the bud [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) from a distance. [Sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) can be frostier than the buds look, which is why they are often kept for hash rather than discarded. ## Don't confuse with - **Potency**: frosty flower is not always strong; trichome density, head size and resin chemistry all vary. - **Mould**: white fuzzy or powdery patches ([powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md)) are not frost. Look with a loupe: trichomes are glassy stalks with round heads. ## Related terms [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md), [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md), [Sticky](https://genetixbay.com/knowledge/glossary/sticky.md) ## Read more - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) --- # Full melt > Full melt is the highest grade of solventless hash, so pure in trichome heads that it melts almost completely with little or no residue when heated. - Canonical: https://genetixbay.com/knowledge/glossary/full-melt.html - Also written: full-melt, full melt hash, FMH, six-star hash, 6-star - Glossary category: Processing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Full melt is a quality grade, not a method. It describes [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), and occasionally exceptional [dry sift](https://genetixbay.com/knowledge/glossary/kief.md), consisting almost entirely of intact [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) with very little stalk, leaf or other plant matter. Heated, it liquefies and vaporises leaving minimal ash or char. Growers often grade [hash](https://genetixbay.com/knowledge/glossary/hash.md) on an informal star scale, and full melt corresponds to the top, five- to six-star end. ## In practice Only a small share of any wash reaches full-melt quality, and some cultivars almost never produce it, because their heads are small, fragile or stick tightly to plant tissue. Hash makers therefore talk about "washers": cultivars that release large, sturdy heads in ice water. Full melt is commonly consumed as is, rather than pressed into [rosin](https://genetixbay.com/knowledge/glossary/rosin.md). The grading scale is informal and not standardised; two makers' "six stars" may differ. ## Don't confuse with - **Melt (half melt)**: lower grades that partly melt and leave residue. - **Rosin**: a pressed oil, not a hash grade. - **Full spectrum**: a marketing label for extracts with broad compound profiles, unrelated. ## Related terms [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Kief](https://genetixbay.com/knowledge/glossary/kief.md), [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), [Micron bags](https://genetixbay.com/knowledge/glossary/micron-bags.md), [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md) ## Sources 1. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Full spectrum > Full spectrum is a marketing term for a grow light with broad output across the visible range, usually a white LED, sometimes with added red, far-red or UV. - Canonical: https://genetixbay.com/knowledge/glossary/full-spectrum.html - Also written: full-spectrum LED, full spectrum light, broad spectrum, white LED spectrum, sunlike spectrum - Glossary category: Environment and light · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" "Full spectrum" has no agreed technical definition. On a grow light it usually means white [LEDs](https://genetixbay.com/knowledge/glossary/led.md) (blue chips coated with phosphor) that emit continuously from about 420 to 700 nm, often with extra red diodes near 660 nm, and sometimes [far-red](https://genetixbay.com/knowledge/glossary/far-red.md) (730 nm) or UV-A (385–405 nm) channels. It is used to contrast with older "blurple" fixtures that had only narrow red and blue peaks. ## In practice White-dominant fixtures are easier to work under: you can see [true leaf](https://genetixbay.com/knowledge/glossary/true-leaves.md) colour, spot [deficiencies](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) and pests, and judge [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) without guessing. That alone is a good reason to choose one. Spectrally, broad white light also includes green photons, which penetrate deeper into the canopy than red or blue because leaves absorb them less strongly. What "full spectrum" does not guarantee: high [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), a useful far-red fraction, or any UV at all. Read the spectral graph and the µmol/J figure on the datasheet. No fixture reproduces sunlight exactly, and none needs to. ## Don't confuse with - **Spectrum**: the general concept; every lamp has one. - **Blurple**: red and blue only fixtures; efficient for [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) but poor for inspecting plants. - **Colour temperature**: a 3,000 K or 4,000 K label describes appearance, not plant response. ## Myth check "Full spectrum means more [THC](https://genetixbay.com/knowledge/glossary/thc.md)" is unsupported. Controlled trials find intensity and efficacy drive yield; spectrum tweaks mostly change shape. *Myth* as a potency claim. ## Related terms [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md), [LED](https://genetixbay.com/knowledge/glossary/led.md), [Far-red](https://genetixbay.com/knowledge/glossary/far-red.md), [UV-A](https://genetixbay.com/knowledge/glossary/uv-a.md), [Blue light](https://genetixbay.com/knowledge/glossary/blue-light.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988 --- # Fulvic acid > Fulvic acid is the small, soluble fraction of humic substances that stays dissolved at any pH and binds metal ions; its benefit in cannabis is largely unproven. - Canonical: https://genetixbay.com/knowledge/glossary/fulvic-acid.html - Also written: fulvic acids, fulvates, fulvic - Glossary category: Nutrients · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fulvic acid is the fraction of [humic substances](https://genetixbay.com/knowledge/glossary/humic-acid.md) that remains soluble at all [pH](https://genetixbay.com/knowledge/glossary/ph.md) values. Its molecules are smaller and richer in oxygen-containing acid groups than humic acid, so it binds metal ions and moves more freely in water. It is usually yellow to golden brown. ## In practice It is sold as a nutrient carrier, [foliar](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) additive and "uptake enhancer". It does complex [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md), which may help keep them soluble. Claims that it dramatically improves uptake, yield or quality in cannabis lack controlled trials (Evidence: Contested). Products vary widely in source and concentration, and the analytical methods for "fulvic content" are not standardised, so labels are hard to compare. Small doses are generally harmless; treat any large claims with suspicion. ## Don't confuse with - **Humic acid**: the larger fraction that precipitates at low pH. - **Synthetic chelates**: defined chemicals with known stability. - **Shilajit or similar supplements**: human products marketed with fulvic claims, unrelated to plant feeding. ## Myth check Label claims for fulvic products often outrun the evidence. See [buyer beware: label claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [Humic acid](https://genetixbay.com/knowledge/glossary/humic-acid.md), [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md), [Foliar feeding](https://genetixbay.com/knowledge/glossary/foliar-feeding.md), [Biostimulant](https://genetixbay.com/knowledge/glossary/biostimulant.md) ## Read more - [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Fungus gnat > Small dark flies of the genus Bradysia (family Sciaridae) whose larvae live in wet growing media, feeding on fungi, organic matter and young roots. - Canonical: https://genetixbay.com/knowledge/glossary/fungus-gnat.html - Also written: fungus gnats, Bradysia, sciarid fly, sciarid, soil gnats, dark-winged fungus gnat - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fungus gnats are small, delicate, dark grey flies, about 2-4 mm long, mainly *Bradysia* species in the family Sciaridae. Adults are weak fliers with long legs and a Y-shaped wing vein. The larvae are clear to white legless maggots with a shiny black head, living in the top few centimetres of moist media. ## In practice Adults are a nuisance; larvae do the damage. They chew [root hairs](https://genetixbay.com/knowledge/glossary/root-hair.md) and can spread root pathogens such as *Pythium*, which is why they matter most for seedlings and fresh clones. Constantly wet media and organic-rich mixes breed them. Growers monitor with [yellow sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) near the medium surface and with potato slices pressed into the top layer, checked after a couple of days for larvae. Letting the top layer dry between waterings, [bottom watering](https://genetixbay.com/knowledge/glossary/bottom-watering.md) and top-dressing with coarse sand help. [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) uses *[Steinernema feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md)* nematodes, the soil mite *[Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md)*, and *[Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md)* subsp. *israelensis* (Bti) drenches. ## Don't confuse with - **Shore fly**: stockier, with dark wings marked by pale spots, feeding on algae. - **Root aphid**: winged forms on traps look gnat-like but have [aphid](https://genetixbay.com/knowledge/glossary/aphid.md) bodies. - **Whitefly**: white wings, lives on leaf undersides. ## Related terms [Shore fly](https://genetixbay.com/knowledge/glossary/shore-fly.md), [Steinernema feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md), [Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md), [Bti](https://genetixbay.com/knowledge/glossary/bti.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) ## Read more - [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ## Sources 1. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf 2. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ 3. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ --- # Fusarium wilt > A soil-borne fungal disease, chiefly Fusarium oxysporum, that blocks water-conducting tissue, causing one-sided yellowing, wilting and brown streaks inside the stem. - Canonical: https://genetixbay.com/knowledge/glossary/fusarium-wilt.html - Also written: Fusarium, Fusarium oxysporum, fusarium root rot, Fusarium crown rot, Fusarium solani - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fusarium wilt is a vascular disease caused by *Fusarium oxysporum*, a soil-borne fungus that enters through roots and grows into the [xylem](https://genetixbay.com/knowledge/glossary/xylem.md), the water-conducting tissue. As it blocks the vessels, the plant cannot move water. Other *Fusarium* species, such as *F. solani*, cause crown and [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), and several species also infect buds. ## In practice Symptoms often start on one side of a plant or one branch: leaves yellow and wilt, then the whole plant collapses even in moist media. Cutting the lower stem lengthwise shows brown or reddish streaks in the wood. The fungus survives in soil for years as resting spores and spreads on media, tools, water and clones. There is no cure for an infected plant; remove it with its medium, sanitise containers and tools, and do not reuse that soil. In hydroponics it often appears alongside *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)*. Clean propagation material and fresh media are the [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md). ## Don't confuse with - **Pythium**: a water mould causing slimy root rot rather than vascular streaks. - **Underwatering**: plants recover after watering; fusarium wilt does not. - **Septoria leaf spot**: spots on leaves, no wilt. ## Related terms [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), [Damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) ## Read more - [Fusarium in cannabis: wilt, crown rot and bud rot](https://genetixbay.com/knowledge/diseases/fusarium.md) ## Sources 1. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 2. Utah State University Extension. Hemp Fusarium wilt (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-fusarium-wilt 3. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Gas > Gas is slang for a sharp fuel, diesel or solvent-like aroma in cannabis, and by extension for any flower people rate highly. - Canonical: https://genetixbay.com/knowledge/glossary/gas.html - Also written: gassy, gas terps, fuel, fuely, diesel funk - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Gas describes a pungent fuel-, diesel- or solvent-like aroma, often with sour, [skunky](https://genetixbay.com/knowledge/glossary/skunk.md) or garlicky notes. Through overuse it has also become general praise: "that's gas" means "that's good". ## In practice The aroma itself is real and complex. Research points to more than the classic [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md): minor [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) compounds, including prenylated [volatile sulfur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md), contribute strongly to the skunky, "gassy" edge of some cultivars even at very low concentrations. Terpene percentages on a label do not capture it well. Because gas is fashionable, many modern lines are bred toward it, and many crosses share the same few gas-heavy parents. ## Don't confuse with - **Loud**: strong aroma of any kind; gas is one flavour of loud. - **Skunk**: an older word for a related pungent profile, and also a lineage name. - **Candy terps**: the sweet, fruity end of the modern market. ## Myth check "Gas means potent." Aroma and [THC](https://genetixbay.com/knowledge/glossary/thc.md) content are separate traits; the nose does not measure [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). GenetixBay also agrees that the gas/[candy](https://genetixbay.com/knowledge/glossary/candy-terps.md) trend is crowding out classic profiles. See [why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md). ## Related terms [Terps](https://genetixbay.com/knowledge/glossary/terps.md), [Candy terps](https://genetixbay.com/knowledge/glossary/candy-terps.md), [Loud](https://genetixbay.com/knowledge/glossary/loud.md), [Zaza](https://genetixbay.com/knowledge/glossary/zaza.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) --- # Gas chromatography > Gas chromatography (GC) separates volatile compounds in a heated gas stream; it is used for terpenes and residual solvents and decarboxylates acid cannabinoids in its hot inlet. - Canonical: https://genetixbay.com/knowledge/glossary/gas-chromatography.html - Also written: GC, GC-FID, GC-MS, gas chromatograph, GC testing - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In gas chromatography the sample is vaporised in a heated inlet and carried by an inert gas through a long, thin column. Compounds separate by volatility and their interaction with the column coating, then reach a detector: a flame ionisation detector (GC-FID) for quantification, or a mass spectrometer (GC-MS) for identification. ## In practice GC is the standard for [terpene profiles](https://genetixbay.com/knowledge/glossary/terpene-profile.md) and residual solvent testing, often with headspace [sampling](https://genetixbay.com/knowledge/glossary/homogenisation.md) (analysing the vapour above a sealed sample). Specialised setups, such as two-dimensional GC with sulfur detection, found the prenylated [thiols](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) behind skunk aroma. For [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), GC has a built-in problem: the hot inlet [decarboxylates](https://genetixbay.com/knowledge/glossary/decarboxylation.md) [THCA](https://genetixbay.com/knowledge/glossary/thca.md) to [THC](https://genetixbay.com/knowledge/glossary/thc.md), and the conversion is not always complete or consistent. Without a derivatisation step, a GC potency result reports mostly neutral THC and cannot separate the original THCA and THC. That's why potency is normally done by [HPLC](https://genetixbay.com/knowledge/glossary/hplc.md). ## Don't confuse with - **HPLC**: liquid-phase, room temperature, measures acids directly. - **GC-MS for pesticides**: the same technique family, but a different method and panel. ## Related terms [HPLC](https://genetixbay.com/knowledge/glossary/hplc.md), [Terpene test](https://genetixbay.com/knowledge/glossary/terpene-test.md), [Residual solvents](https://genetixbay.com/knowledge/glossary/residual-solvents.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [Acid vs neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md) ## Sources 1. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. 2. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196 --- # GB-ID > A GB-ID is GenetixBay's permanent identifier, such as GB-GEN-0001842-6, for a genetic line, landrace, seed batch, plant, cut, grow, harvest, trial or document, so records never get lost or renamed. - Canonical: https://genetixbay.com/knowledge/glossary/gb-id.html - Also written: GB ID, GBID, GenetixBay ID, GB-IDs, GenetixBay identifier - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A GB-ID is the permanent identifier GenetixBay assigns to every record in its genetics archive: lines, [seed batches](https://genetixbay.com/knowledge/glossary/seed-run.md), individual plants and cuts, grows, harvests and supporting documents. Once issued, a GB-ID is never reused or reassigned, so the record keeps its identity even if a name changes or is disputed. ## In practice A breeder registers a new cross as a line, links it to the GB-IDs of its mother and father, and gives each seed batch its own ID, so a restock made from different parents is visibly a different batch. A grower's plant from that batch gets its own ID, and its journal, harvest and lab results attach to it. Lineage statements on the record are claims with evidence levels (L0-L4), and crosses logged on the platform as they happen carry a "witnessed" flag. QR batch IDs on packs help growers check that a pack is genuine. The point is provenance and preservation: when the same cut circulates under a thousand names, a permanent ID with an evidence trail is how the genetics stay traceable. ## How to read one A GB-ID [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) like `GB-GEN-0001842-6`: - **GB** marks it as a GenetixBay ID. - **GEN** is the record type. Common ones: GEN (genetic line), LRC ([landrace](https://genetixbay.com/knowledge/glossary/landrace.md) population), BAT (seed batch), PKG (seed pack), IND (individual plant, including the males in [the Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md)), CUT (cutting), GRW (grow journal), HRV (harvest), DOC (document), TRL ([Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md)), CRT (certificate) and USR (member). - **0001842** is the serial, seven digits. - **6** is a check digit. Mistype one digit or swap two neighbours and the ID won't validate, so the search box can tell you "did you mean" instead of opening the wrong record. IDs carry no country, year or owner: those live on the record, where they can be corrected openly. Most serials count up, so a low number shows a record is old. Serials 0000001 to 0041999 are reserved for records recovered from the original 2009 exchange and the beta years; new records start at 0042000. Member IDs are the exception: they're random, so nobody can work out how many members there are from one. Paste any GB-ID into search to open its record. ## Don't confuse with - **Strain name**: a label anyone can attach. A GB-ID identifies a specific record. - **Seed-to-sale tag**: a regulator's compliance tracking for licensed businesses. - **Evidence level**: how well a claim on a GB-ID record is supported, not the ID itself. ## Related terms [Evidence levels L0-L4](https://genetixbay.com/knowledge/glossary/evidence-levels-l0-l4.md), [Renamed cut](https://genetixbay.com/knowledge/glossary/renamed-cut.md), [Seed-to-sale tracking](https://genetixbay.com/knowledge/glossary/seed-to-sale-tracking.md), [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md), [Grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md) ## Read more - [How to document lineage evidence (GB-ID evidence levels L0-L4)](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md) - [Breeder record-keeping and naming ethics](https://genetixbay.com/knowledge/breeding/record-keeping-naming-ethics.md) --- # Gene > A gene is a stretch of DNA that carries the instructions for one functional product, usually a protein such as an enzyme, and is the basic unit of inheritance. - Canonical: https://genetixbay.com/knowledge/glossary/gene.html - Also written: genes, genetic factor, hereditary unit - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A gene is a [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) of DNA that codes for one functional product, usually a protein. In cannabis many of the genes breeders care about code for enzymes: [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md), [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) and the [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) synthases that set aroma. Each gene sits at a fixed position on a chromosome, and a [diploid plant](https://genetixbay.com/knowledge/glossary/diploid.md) carries two copies of it, one from each parent. ## In practice Growers use "gene" loosely to mean "the genetics" of a plant. Breeders use it precisely. When a breeder says "the [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) gene is codominant", they mean the CBDA synthase gene at one locus, whose two versions ([alleles](https://genetixbay.com/knowledge/glossary/allele.md)) both show in the plant. Most traits growers select for (yield, vigour, resin density, flowering time) are not one gene but many genes acting together, plus the environment. ## Don't confuse with - **Allele**: a version of a gene. "Gene" is the slot; "allele" is what fills it. - **Genetics**: the whole inherited make-up of a plant, or the science. "Good genetics" means a good [genotype](https://genetixbay.com/knowledge/glossary/genotype.md), not one gene. - **Strain**: a market name. It says nothing reliable about which genes a plant carries. ## Related terms [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Locus](https://genetixbay.com/knowledge/glossary/locus.md), [Chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md), [Genotype](https://genetixbay.com/knowledge/glossary/genotype.md), [Mutation](https://genetixbay.com/knowledge/glossary/mutation.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 2. Laverty KU, Stout JM, Sullivan MJ, et al. 2019. A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci. Genome Research 29(1):146-156. https://doi.org/10.1101/gr.242594.118 --- # Gene pool > The gene pool is the total set of alleles present in a population, cultivar group or species; a narrow gene pool limits what breeders can select from. - Canonical: https://genetixbay.com/knowledge/glossary/gene-pool.html - Also written: gene pools, genetic diversity, allelic diversity, shrinking gene pool, narrowing gene pool - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The gene pool is all the [alleles](https://genetixbay.com/knowledge/glossary/allele.md) present in a population, at all loci. A large, diverse gene pool holds many versions of each [gene](https://genetixbay.com/knowledge/glossary/gene.md); a narrow one holds few. Breeders can only select from what is there. ## In practice The evidence suggests the commercial cannabis gene pool is narrowing. Large chemical datasets show commercial products cluster into a few chemotype and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) groups (Smith et al. 2022). [Landraces](https://genetixbay.com/knowledge/glossary/landrace.md) in source regions have been mixed with imported [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md). Popular lines are crossed again and again with similar material, and one cut can travel under many names, so the number of truly different [genotypes](https://genetixbay.com/knowledge/glossary/genotype.md) behind the market is smaller than the number of names suggests. Patents on plants, traits and methods add another pressure: they can restrict how some material is used. The facts are public records; the concern is the effect on the commons. The response is preservation: keeping landraces, [heirlooms](https://genetixbay.com/knowledge/glossary/heirloom.md), old cuts and males alive, documenting them, and sharing them openly. ## Don't confuse with - **Germplasm**: the physical seeds, plants and tissue. - **Genome**: the DNA of one individual; a gene pool spans many. - **Number of strains**: names are not genetic diversity. ## Myth check "Everything tastes the same now" has evidence behind it; see [why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md). ## Related terms [Germplasm](https://genetixbay.com/knowledge/glossary/germplasm.md), [Genetic bottleneck](https://genetixbay.com/knowledge/glossary/genetic-bottleneck.md), [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Founder effect](https://genetixbay.com/knowledge/glossary/founder-effect.md) ## Read more - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Lynch RC, Vergara D, Tittes S, et al. 2016. Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences 35(5-6):349-363. https://doi.org/10.1080/07352689.2016.1265363 --- # General hardness > General hardness (GH) is the calcium and magnesium dissolved in water, expressed as mg/L CaCO3 or German degrees (dGH); hard water supplies some Ca and Mg. - Canonical: https://genetixbay.com/knowledge/glossary/general-hardness.html - Also written: GH, dGH, total hardness, water hardness, hard water, permanent hardness - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" General hardness (GH), also called total hardness, is the concentration of divalent cations in water, mainly calcium (Ca²⁺) and magnesium (Mg²⁺). It is reported as mg/L (ppm) of calcium carbonate equivalent or in German degrees (dGH). Common classification for drinking water (US Geological Survey): soft below 60 mg/L, moderately hard 61–120, hard 121–180, very hard above 180 mg/L as CaCO3. ## In practice Hard water brings free calcium and magnesium. Water at 200 mg/L as CaCO3 from mostly calcium supplies roughly 60–80 mg/L of Ca. Growers on [hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) may need little or no added [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md); growers on [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) need all of it from the nutrient. Hardness usually comes with high [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), so hard water also needs acid. Find GH in the utility's water report, test with an aquarium GH kit, or get a lab analysis that lists Ca and Mg separately. ## Units and formula - 1 dGH = 17.86 mg/L as CaCO3 (equivalent to 10 mg/L CaO) - Hardness (mg/L as CaCO3) = 2.497 × Ca (mg/L) + 4.118 × Mg (mg/L) ## Don't confuse with - **Carbonate hardness (KH)**: bicarbonate and carbonate, which is alkalinity. - **EC**: total dissolved ions, including sodium, [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) and sulfate, not just Ca and Mg. ## Myth check Cal-Mag need is driven by water source, medium and **cultivar**, not by [LED](https://genetixbay.com/knowledge/glossary/led.md) lighting. The LED claim is a *Myth*; see [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md). ## Related terms [Carbonate hardness](https://genetixbay.com/knowledge/glossary/carbonate-hardness.md), [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Generation time > The average time from a female's birth to the birth of her offspring; at a set temperature it fixes how often a pest population multiplies. - Canonical: https://genetixbay.com/knowledge/glossary/generation-time.html - Also written: mean generation time, generation length - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Generation time is the mean age at which females produce their offspring, from a [life table](https://genetixbay.com/knowledge/glossary/life-table.md). It is longer than egg-to-adult development, because females need a pre-oviposition period and lay over many days. For [two-spotted spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) it is roughly one to two weeks at 25 C in lab studies, shorter in heat. ## In practice Generation time drives control intervals. A spray or release that misses eggs must be repeated before the survivors mature and lay, which means within one egg-plus-immature period at your temperature. [Degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md) thresholds let you convert one temperature's generation time to another's. ## Don't confuse with - **Doubling time**: how long numbers take to double, much shorter than a generation. ## Related terms [Intrinsic rate of increase (r_m)](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [Degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [Life table](https://genetixbay.com/knowledge/glossary/life-table.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) ## Sources 1. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605 2. UC IPM. Degree-Days: About Degree-Days. University of California ANR. https://ipm.ucanr.edu/WEATHER/ddconcepts.html --- # Genetic bottleneck > A genetic bottleneck is a sharp drop in the number of breeding plants, after which the population carries only a fraction of its former genetic diversity. - Canonical: https://genetixbay.com/knowledge/glossary/genetic-bottleneck.html - Also written: bottleneck, population bottleneck, bottlenecked, bottleneck effect - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A genetic bottleneck happens when a population is reduced to very few breeding individuals. Only the [alleles](https://genetixbay.com/knowledge/glossary/allele.md) carried by the survivors pass on; rare alleles are often lost, and the population afterwards is more inbred and less variable, even if it later grows large again. ## In practice Cannabis has passed through many bottlenecks. [Landraces](https://genetixbay.com/knowledge/glossary/landrace.md) carried out of source regions in a single seed packet; a whole line rebuilt from three plants after a raid or crop loss; a modern cultivar group descended mostly from a handful of famous clones. Each step narrows what breeders have to work with. Breeders create bottlenecks themselves by making each generation from one female and one male. The cure is [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md): use many parents, keep backup seed, and preserve material from different sources. ## Don't confuse with - **Founder effect**: a special case, when a new population is started by a few individuals. - **Genetic drift**: random change in allele frequency; it is strongest during and after a bottleneck. - **Selection**: keeping plants on purpose for traits; a bottleneck is a loss in numbers, chosen or not. ## Related terms [Founder effect](https://genetixbay.com/knowledge/glossary/founder-effect.md), [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [Germplasm](https://genetixbay.com/knowledge/glossary/germplasm.md) ## Read more - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 --- # Genetic drift > Genetic drift is random change in allele frequencies between generations of a seed population, strongest in small populations; clones do not drift this way. - Canonical: https://genetixbay.com/knowledge/glossary/genetic-drift.html - Also written: clone drift, random genetic drift, allele drift, clone decline - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In population genetics, genetic drift is the random change in how common [alleles](https://genetixbay.com/knowledge/glossary/allele.md) are from one generation of seed to the next, caused by which plants happen to reproduce. In small populations it can lose alleles entirely or fix them by chance, regardless of whether they are useful. ## In practice Drift matters for seed lines. Keep a line going with two or three parents per generation and it drifts quickly: alleles vanish, variation shrinks, and the line can change type without any selection. [Open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md) and [heirloom lines](https://genetixbay.com/knowledge/glossary/heirloom.md) stay true to their character only with enough parents each generation. Growers also say "clone drift" for an old cut that seems to have changed. That is a different claim, and it is wrong. ## Don't confuse with - **Selection**: non-random change, driven by the breeder's choices. - **Somatic mutation**: rare changes in a plant's own cells. They happen (Adamek et al. 2022), but a mutation does not mean a loss, and it is not drift. - **Topophysis**: cuts from different parts of a plant behaving differently. ## Myth check House position: clones show zero genetic drift apart from pathogens. A cut that declines over years almost always carries a pathogen such as [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), or suffers poor mother care. The GenetixBay founder keeps cuts 40+ years old and seed stock 50 to 70 years old with no decline. See [hop latent viroid and viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Genetic bottleneck](https://genetixbay.com/knowledge/glossary/genetic-bottleneck.md), [Founder effect](https://genetixbay.com/knowledge/glossary/founder-effect.md), [Somaclonal variation](https://genetixbay.com/knowledge/glossary/somaclonal-variation.md), [Mutation](https://genetixbay.com/knowledge/glossary/mutation.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 --- # Genotype > The genotype is the set of alleles a plant actually carries, either at one locus or across its whole genome, as opposed to the traits you can see. - Canonical: https://genetixbay.com/knowledge/glossary/genotype.html - Also written: genotypes, genetic make-up, genetic makeup, genome type - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The genotype is the genetic make-up of a plant: the [alleles](https://genetixbay.com/knowledge/glossary/allele.md) it carries at one [locus](https://genetixbay.com/knowledge/glossary/locus.md) (for example B_T/B_D at the [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase locus) or across the whole genome. Each seed is a new genotype. Every clone cut from one plant shares that plant's genotype. ## In practice "Same genotype" is the honest way to say "same plant". A mother kept for ten years and a cut passed to a friend are the same genotype, even if one grows better because of its care or a virus-free status. A pack of seeds from one cross holds many genotypes, which is why you [pheno](https://genetixbay.com/knowledge/glossary/pheno.md) hunt. A [DNA test](https://genetixbay.com/knowledge/glossary/genotyping.md) reads part of the genotype. It can tell whether two cuts are the same plant and give a rough idea of ancestry. It cannot read [THC](https://genetixbay.com/knowledge/glossary/thc.md) percentage or flavour off the label, because those also depend on many genes and on how the plant was grown. ## Don't confuse with - **Phenotype**: what the genotype produces in a given environment. Same genotype, different room, different [phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md). - **Strain**: a name. Studies of retail cannabis show the same name often hides different genotypes (Sawler et al. 2015). - **Chemotype**: the [chemical phenotype](https://genetixbay.com/knowledge/glossary/chemotype.md), partly set by genotype. ## Related terms [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md), [Genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md), [Genotype by environment interaction](https://genetixbay.com/knowledge/glossary/genotype-by-environment.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) - [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md) ## Sources 1. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 2. Henry P, Khatodia S, Kapoor K, et al. 2020. A single nucleotide polymorphism assay sheds light on the extent and distribution of genetic diversity, population structure and functional basis of key traits in cultivated north American cannabis. Journal of Cannabis Research 2:26. --- # Genotype by environment interaction > Genotype by environment interaction (GxE) is when different genotypes respond differently to the same change in conditions, so the best cultivar in one room may not be best in another. - Canonical: https://genetixbay.com/knowledge/glossary/genotype-by-environment.html - Also written: GxE, G×E, GxE interaction, genotype-environment interaction, phenotypic plasticity - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Genotype by environment interaction (GxE) means the effect of the environment depends on the [genotype](https://genetixbay.com/knowledge/glossary/genotype.md). Two cultivars may rank one way under one light, feed or climate and the other way under another. Phenotypic plasticity is the related idea that one genotype can produce different [phenotypes](https://genetixbay.com/knowledge/glossary/phenotype.md) in different conditions. ## In practice GxE is why "test your cultivar" is GenetixBay's stance. One clone may love [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) veg and [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) flower; another stalls. Some cultivars thrive with a mild late [dry-back](https://genetixbay.com/knowledge/glossary/dryback.md); others lose yield. One mother handles [heavy defoliation](https://genetixbay.com/knowledge/glossary/schwazzing.md); her sister sulks. Ca and Mg demand also varies by cultivar, more than by light type. For breeders, GxE means selections should be tested in more than one environment before release. A keeper selected under one grower's lights in one climate may disappoint in a cooler, more humid room. Tester grows across many members are a practical way to see GxE. ## Don't confuse with - **Genotype**: the DNA, which does not change between rooms. - **Environmental effect**: when every genotype shifts the same way (all plants yield less in a cold room), that is not GxE. - **Genetic drift**: clones do not drift genetically because they are moved to a new room. ## Related terms [Genotype](https://genetixbay.com/knowledge/glossary/genotype.md), [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md), [Heritability](https://genetixbay.com/knowledge/glossary/heritability.md), [Test grow](https://genetixbay.com/knowledge/glossary/test-grow.md), [Quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.md) ## Read more - [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 --- # Genotyping > Genotyping is reading a plant's DNA at selected markers to identify it, compare it with other plants, check sex or chemotype, or estimate its ancestry. - Canonical: https://genetixbay.com/knowledge/glossary/genotyping.html - Also written: DNA test, DNA testing, genetic testing, DNA fingerprinting, genetic fingerprint, genotype test - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Genotyping is determining which [alleles](https://genetixbay.com/knowledge/glossary/allele.md) a plant carries at a set of DNA markers, usually [SNPs](https://genetixbay.com/knowledge/glossary/snp.md) or short repeats, from a small tissue sample. The result is a genetic fingerprint that can be compared between plants. ## In practice What genotyping can show: - whether two cuts are the same [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) (identity) or close relatives; - likely parentage, if the candidate parents were also tested; - [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) sex and [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase type, with dedicated markers (Toth et al. 2020); - broad ancestry and population structure (Sawler et al. 2015; Henry et al. 2020). What it cannot show: a cultivar's name, its exact [THC](https://genetixbay.com/knowledge/glossary/thc.md) percentage, its flavour or its yield. Those depend on many genes plus how it is grown. A DNA report saying "70% indica" reflects the reference panel used, not a species. Results are only as good as the database. Comparing a cut to a reference only proves something if the reference itself came from a documented source. ## Don't confuse with - **Potency testing**: chemistry of the dried flower, not DNA. - **Genome sequencing**: reads almost the whole genome; genotyping reads chosen markers. - **Strain ID apps**: guesses from [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md) or names, not DNA. ## Related terms [SNP](https://genetixbay.com/knowledge/glossary/snp.md), [Marker-assisted selection](https://genetixbay.com/knowledge/glossary/marker-assisted-selection.md), [Genotype](https://genetixbay.com/knowledge/glossary/genotype.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md), [Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) ## Read more - [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md) - [How to document lineage evidence (GB-ID evidence levels L0-L4)](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md) ## Sources 1. Henry P, Khatodia S, Kapoor K, et al. 2020. A single nucleotide polymorphism assay sheds light on the extent and distribution of genetic diversity, population structure and functional basis of key traits in cultivated north American cannabis. Journal of Cannabis Research 2:26. 2. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 3. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 --- # Geraniol > Geraniol is a rosy, floral monoterpene alcohol made from geranyl pyrophosphate, found in rose and geranium oils and as a minor terpene in cannabis. - Canonical: https://genetixbay.com/knowledge/glossary/geraniol.html - Also written: geranyl alcohol, trans-geraniol, lemonol - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Geraniol is an acyclic [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md) alcohol, the main scent of rose and palmarosa oils and a component of geranium and citronella. Its smell is rosy, sweet and floral with a citrus edge. It forms when the [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) group is removed from [geranyl pyrophosphate](https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.md), the same C10 precursor that feeds both monoterpenes and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). ## In practice In cannabis it is generally minor, [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md) to roughly 0.1% w/w. It often appears together with [linalool](https://genetixbay.com/knowledge/glossary/linalool.md) in floral-leaning profiles. Labs sometimes report geranyl acetate, its ester, separately. Geraniol is moderately volatile and can oxidise to citral-type aldehydes during storage. ## Don't confuse with - **Geranyl pyrophosphate**: the phosphorylated precursor, not an aroma compound. - **Geranial**: an aldehyde (part of citral), lemon-scented. - **Nerol**: the cis isomer of geraniol, with a sweeter rose note. ## Related terms [Geranyl pyrophosphate](https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.md), [Linalool](https://genetixbay.com/knowledge/glossary/linalool.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Geranyl pyrophosphate > Geranyl pyrophosphate (GPP) is a ten-carbon terpene precursor that cannabis uses both to build monoterpenes and, joined to olivetolic acid, to make the cannabinoid precursor CBGA. - Canonical: https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.html - Also written: GPP, geranyl diphosphate, GDP (geranyl diphosphate), geranyl-PP - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Geranyl pyrophosphate (GPP, also called geranyl diphosphate) is a C10 isoprenoid made by joining two five-carbon isoprene units. In the [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) it sits at a fork: [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) synthases turn GPP into [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) such as myrcene, limonene and pinene, while an aromatic prenyltransferase attaches its geranyl group to [olivetolic acid](https://genetixbay.com/knowledge/glossary/olivetolic-acid.md) to form [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md). One more isoprene unit turns GPP into farnesyl pyrophosphate (FPP, C15), the start of the [sesquiterpenes](https://genetixbay.com/knowledge/glossary/sesquiterpene.md). ## In practice GPP links [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and terpene chemistry. Both compete for the same precursor supply in the same glands, which is one reason heavy-resin plants tend to be both potent and aromatic: they simply have more gland capacity. Whether pushing one pathway costs the other in a living plant is not well established. Growers never measure GPP; it is a concept for understanding the pathway. ## Don't confuse with - **Geraniol**: a monoterpene alcohol made from GPP, which can be measured on a [terpene panel](https://genetixbay.com/knowledge/glossary/terpene-test.md). - **Farnesyl pyrophosphate**: the C15 precursor of sesquiterpenes. - **Pyrophosphate** in fertilisers: unrelated. ## Related terms [Olivetolic acid](https://genetixbay.com/knowledge/glossary/olivetolic-acid.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md) ## Sources 1. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004. 2. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Germination > Germination is the stage where a viable seed absorbs water, splits its shell and pushes out a root (radicle), usually within 1-7 days at 20-30 °C. - Canonical: https://genetixbay.com/knowledge/glossary/germination.html - Also written: germinate, germinating, germ, popping seeds, sprouting - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Germination is the process by which a dormant seed takes up water (imbibition), restarts its metabolism and emerges a [radicle](https://genetixbay.com/knowledge/glossary/radicle.md), the first root. In cannabis the radicle normally appears within 24-72 hours of soaking at warm temperatures, with stragglers out to about a week. The [seedling stage](https://genetixbay.com/knowledge/glossary/seedling.md) begins once the [cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) open above the surface. ## In practice Growers "germ" or "pop" seeds by soaking them, starting them between damp paper towels, or sowing straight into a plug or the final medium about 5-10 mm (0.2-0.4 in) deep. Warmth matters more than method: around 22-28 °C (72-82 °F) is the comfortable band, and germination slows sharply below about 15 °C (59 °F). Keep the seed moist, not [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md); a seed sitting in standing water can run short of oxygen. A germination rate is a percentage: 48 of 50 seeds showing a radicle is 96%. ## Don't confuse with - **Seed viability**: whether a seed is alive and able to germinate; germination is the event itself. - **Emergence**: the shoot breaking the surface, which comes after germination. - **Sprouting (food)**: same biology, different purpose; seeds sold for eating are not selected for growing. ## Related terms [Paper towel method](https://genetixbay.com/knowledge/glossary/paper-towel-method.md), [Seedling](https://genetixbay.com/knowledge/glossary/seedling.md), [Taproot](https://genetixbay.com/knowledge/glossary/taproot.md), [Damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) ## Read more - [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md) - [Seed viability and storage: keeping cannabis seeds alive](https://genetixbay.com/knowledge/germination/seed-viability-storage.md) ## Sources 1. Geneve RL, et al., 2022. Temperature limits for seed germination in industrial hemp (Cannabis sativa L.). Crops 2(4):415–427. https://doi.org/10.3390/crops2040029 2. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 --- # Germplasm > Germplasm is living genetic material (seeds, pollen, tissue or plants) kept for breeding, research or conservation, representing the genetic diversity of a crop. - Canonical: https://genetixbay.com/knowledge/glossary/germplasm.html - Also written: germ plasm, genetic resources, plant genetic resources, breeding material, genetic material - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Germplasm is the living genetic material of a crop held for future use: seed, pollen, [tissue cultures](https://genetixbay.com/knowledge/glossary/tissue-culture.md), cuttings and whole plants. The term covers both a single sample and the collective diversity breeders can draw on. ## In practice Germplasm conservation keeps options open. A disease resistance, a rare [terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) or an early-finishing trait may sit in an old [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) or an obscure [heirloom](https://genetixbay.com/knowledge/glossary/heirloom.md) for decades before a breeder needs it. Losing that material loses the option. Cannabis germplasm has been poorly conserved compared with other crops, partly because of prohibition. Much of it lives in private collections: [clone-only cuts](https://genetixbay.com/knowledge/glossary/clone-only.md), heirloom seed, individual breeders' stock. Each storage form has limits. Seed lasts years if dry and cold; pollen can be frozen; clones need constant upkeep; tissue culture slows growth but needs lab skill. Preservation and documentation of germplasm is why GenetixBay exists. ## Don't confuse with - **Gene pool**: the total set of alleles in a population or species; germplasm is the physical material that carries it. - **Seed bank (shop)**: a company selling seed, not a conservation collection; "[gene](https://genetixbay.com/knowledge/glossary/gene.md) bank" is the conservation term. ## Related terms [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Accession](https://genetixbay.com/knowledge/glossary/accession.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md), [Genetic bottleneck](https://genetixbay.com/knowledge/glossary/genetic-bottleneck.md) ## Read more - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) ## Sources 1. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 2. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 --- # Gibberellin > A family of plant hormones (gibberellins, GA) that promote stem elongation, seed germination and, in cannabis, can shift sex expression toward male flowers. - Canonical: https://genetixbay.com/knowledge/glossary/gibberellin.html - Also written: gibberellins, GA, GA3, gibberellic acid - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Gibberellins are diterpenoid plant hormones; more than a hundred are known, a few of which (such as GA1, GA3, GA4) are biologically active. They promote stem and [internode](https://genetixbay.com/knowledge/glossary/internode.md) elongation, break seed dormancy by triggering enzymes that mobilise seed reserves, and influence flowering and sex expression. ## In practice Gibberellin activity sits behind much of the early-flower [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) and shade-avoidance elongation. Many plant growth regulators sold to keep plants short work by blocking gibberellin synthesis. These are best avoided on a consumable crop. In cannabis sex expression, gibberellic acid (GA3) applied to female plants can induce [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md). Historically it was one of the methods for producing pollen from females, though silver compounds ([silver thiosulfate](https://genetixbay.com/knowledge/glossary/sts.md), silver [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md)), which block [ethylene](https://genetixbay.com/knowledge/glossary/ethylene.md) action, are far more reliable for feminised-seed work. Gibberellin seed soaks are used on dormant seed of some crops. Fresh, healthy [cannabis seed](https://genetixbay.com/knowledge/glossary/achene.md) rarely needs them. ## Don't confuse with - **Auxin**: drives elongation and rooting through a different pathway. - **Ethylene**: in cannabis, promotes female flowering and ripening. - **Stretch**: the growth response; gibberellin is one of its drivers. ## Related terms [Auxin](https://genetixbay.com/knowledge/glossary/auxin.md), [Internode](https://genetixbay.com/knowledge/glossary/internode.md), [Ethylene](https://genetixbay.com/knowledge/glossary/ethylene.md), [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) ## Read more - [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) - [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. 2. Ram HYM, Sett R. 1982. Induction of fertile male flowers in genetically female Cannabis sativa plants by silver nitrate and silver thiosulphate anionic complex. Theoretical and Applied Genetics 62:369-375. https://doi.org/10.1007/BF00275107 --- # Gram > A gram (g) is the base metric unit for weighing cannabis flower and concentrates; 28 g make a retail ounce and 3.5 g an eighth. - Canonical: https://genetixbay.com/knowledge/glossary/gram.html - Also written: g, grams, a g, gs - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A gram (g) is the basic unit used to weigh cannabis for sale, dosing and yield records. Grow [yields](https://genetixbay.com/knowledge/glossary/yield.md) are reported in grams of dry flower, for example "450 g per m²" or "1.2 g per watt". ## In practice Growers compare runs using [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) in grams after drying and trimming, not [wet weight](https://genetixbay.com/knowledge/glossary/wet-weight.md): fresh flower loses roughly 75-80% of its weight as it dries. A plant weighing 500 g wet at chop might give 100-125 g dry. Weigh on a calibrated scale with 0.1 g or 0.01 g resolution for small amounts, and record yield per plant and per square metre so results can be compared between rooms and grows. ## Units and formula | Slang | Nominal weight | Metric | |---|---|---| | Gram | 1 g | 1 g | | Eighth | 1/8 oz | 3.5 g (exact: 3.54 g) | | Quarter | 1/4 oz | 7 g | | Half | 1/2 oz | 14 g | | Ounce (zip, O) | 1 oz | 28 g (exact: 28.35 g) | | QP | 1/4 lb (4 oz) | 113 g | | Pound (elbow, LB) | 1 lb (16 oz) | 454 g (exact: 453.6 g) | Retail rounds an eighth to 3.5 g and an ounce to 28 g. ## Don't confuse with - **Gram of concentrate**: same weight unit, very different amount of [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md). - **Gram per watt**: a lighting efficiency yardstick for yield, not a sales unit. ## Related terms [Eighth](https://genetixbay.com/knowledge/glossary/eighth.md), [Ounce](https://genetixbay.com/knowledge/glossary/ounce.md), [QP](https://genetixbay.com/knowledge/glossary/qp.md), [Elbow](https://genetixbay.com/knowledge/glossary/elbow.md), [Dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) --- # Grams per watt > Grams per watt (g/W) is dry flower yield divided by the electrical wattage of the grow lights, a rough measure of how efficiently a grow turns power into product. - Canonical: https://genetixbay.com/knowledge/glossary/grams-per-watt.html - Also written: g/w, gpw, grams/watt, gram per watt, yield per watt - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Grams per watt is a yield efficiency figure: dry grams harvested divided by the wattage the lights draw. A 480 W light producing 480 g is "1 g/W". It is popular because it is easy to calculate, but it mixes two things: how efficient the light fixture is and how well the grower uses the light. ## In practice Home growers commonly report around 0.5-1.0 g/W; efficient [LED](https://genetixbay.com/knowledge/glossary/led.md) rooms with good genetics and environment report more. Be careful comparing numbers: use wall wattage, not the "equivalent" wattage marketed on fixtures, and state the run time, since a longer flower adds weight. A more physical measure is grams per mole of photons (g/mol), which removes [fixture efficiency](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) from the equation. Research shows yield rises with photon delivery, and that fixture efficacy (µmol/J) matters more to cost than fine spectrum tweaks. ## Units and formula g/W = dry flower (g) / fixture power draw (W). Example: 600 g / 720 W = 0.83 g/W. ## Don't confuse with - **g/m²**: yield per area; the better comparison between grows. - **Photon efficacy (µmol/J)**: a property of the light, not the grow. ## Related terms [Yield](https://genetixbay.com/knowledge/glossary/yield.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) ## Sources 1. Westmoreland FM, Kusuma P, Bugbee B., 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLOS ONE 16(3):e0248988. https://doi.org/10.1371/journal.pone.0248988 --- # Grasshopper > Plant-chewing insects of the family Acrididae, often Melanoplus species in North America, that strip leaves of outdoor cannabis in dry summers. - Canonical: https://genetixbay.com/knowledge/glossary/grasshopper.html - Also written: grasshoppers, Melanoplus, Acrididae, locust - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Grasshoppers are chewing insects of the family Acrididae with large hind legs for jumping. In North America the damaging species are mostly *Melanoplus* spp. They hatch in spring from egg pods laid in undisturbed soil and feed through summer. Outbreaks follow warm, dry years. ## In practice Damage on outdoor cannabis is ragged holes and missing leaf margins, sometimes stripped [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md). Grasshoppers move in from field edges, ditches and rangeland, so the edge rows suffer first. For a small grow, hand-picking in cool mornings when they are sluggish, fine netting, and keeping grass mowed near the garden are practical. Poultry and wild birds take many. On large areas, baits based on the microsporidian *Nosema locustae* (now often named *Paranosema locustae*) are a biological option aimed at young nymphs. Indoor growers can ignore them. Check what is registered for cannabis locally. ## Don't confuse with - **Caterpillar damage**: similar holes, but look for [frass](https://genetixbay.com/knowledge/glossary/frass.md) and larvae on the plant. - **Leafhoppers**: tiny sap feeders that jump but do not chew holes. - **Hail damage**: shredded leaves across the whole crop at once. ## Related terms [Caterpillar](https://genetixbay.com/knowledge/glossary/caterpillar.md), [Leafhopper](https://genetixbay.com/knowledge/glossary/leafhopper.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md) ## Sources 1. Cranshaw, W. Hemp pests (CSU, 2020). https://webdoc.agsci.colostate.edu/bspm/InsectInformation/Talks2020/HempPests.pdf --- # Greenhouse growing > Greenhouse growing uses sunlight under a covered structure, adding varying degrees of control over temperature, humidity, light deprivation and supplemental lighting. - Canonical: https://genetixbay.com/knowledge/glossary/greenhouse-growing.html - Also written: greenhouse, greenhouse grow, hoop house, polytunnel, mixed-light - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Greenhouse growing places plants under glass or plastic film, so they receive sunlight but are protected from rain, wind and some pests. Structures range from simple unheated hoop houses (polytunnels) to fully climate-controlled glasshouses with heating, cooling, [dehumidification](https://genetixbay.com/knowledge/glossary/dehumidifier.md), [blackout](https://genetixbay.com/knowledge/glossary/light-deprivation.md) curtains and supplemental lamps ("mixed-light"). ## In practice Glazing and frames block some light; a typical greenhouse transmits roughly 60-80% of outdoor light depending on the covering and its age. The structure extends the season at both ends and keeps late-flower buds dry, the biggest advantage over open outdoor growing. Blackout systems allow light deprivation for several harvests per year, and supplemental lighting raises [DLI](https://genetixbay.com/knowledge/glossary/dli.md) in winter. Greenhouses heat up fast on sunny days; ventilation and shading are essential, and humidity spikes at dawn and dusk are a common mould trigger. ## Don't confuse with - **Light dep**: a technique often used in greenhouses, not the structure itself. - **Indoor**: no sunlight at all. ## Related terms [Indoor growing](https://genetixbay.com/knowledge/glossary/indoor-growing.md), [Outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md), [Light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md) --- # Grey market > The grey market is cannabis supply outside the licensed system where use is legal or tolerated, or in a legal gap; it carries legal risk and no product oversight. - Canonical: https://genetixbay.com/knowledge/glossary/grey-market.html - Also written: gray market, grey-market, gray-market, unregulated market, legacy market - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The grey market is cannabis supply that sits between the fully legal and fully illegal: unlicensed sellers operating where possession or use is legal or tolerated, businesses exploiting gaps between laws, or channels whose legal status is unclear. The term "legacy market" is often used for growers and sellers who predate legal licensing. ## In practice Grey-market products have no [mandatory testing](https://genetixbay.com/knowledge/glossary/compliance-testing.md), labelling or recalls, so contamination, potency and identity are unknown, and buying or selling them can be an offence depending on where you are. GenetixBay never encourages buying from illegal or unlicensed sources. The founder's opinion is that the craft standards of many small, pre-legalisation growers were higher than those of today's industrial model. The constructive response is to support craft production within the law and to grow your own where [home grow](https://genetixbay.com/knowledge/glossary/home-grow.md) is legal. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Black market**: clearly illegal supply. - **Licensed craft**: small-batch production inside the legal system. ## Related terms [Decriminalisation vs legalisation](https://genetixbay.com/knowledge/glossary/decriminalisation.md), [Licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md), [Compliance testing](https://genetixbay.com/knowledge/glossary/compliance-testing.md), [Home grow](https://genetixbay.com/knowledge/glossary/home-grow.md) --- # Grow journal > A grow journal is a dated record of a grow, with photos, environment, feeding, problems and results, used to learn, share and prove what happened. - Canonical: https://genetixbay.com/knowledge/glossary/grow-journal.html - Also written: grow diary, grow log, grow journals, grow diaries, journal - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A grow journal (grow diary, grow log) is a running record of one grow: what was planted, when, in what medium and system, under what light and climate, what was fed, what went wrong, and what came out at harvest. ## In practice A useful entry has a date, a photo, the stage, and numbers: air temperature and [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) (or [VPD](https://genetixbay.com/knowledge/glossary/vpd.md)), light intensity in [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), [feed EC](https://genetixbay.com/knowledge/glossary/input-ec.md) in [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) and [pH](https://genetixbay.com/knowledge/glossary/ph.md), any runoff readings, and actions taken. The final entries record dry weight, cure notes and, ideally, lab results. Journals from many growers on the same line are the closest thing to field-trial data most cultivars ever get. On GenetixBay the journal is central: entries are timestamped and tied to the plant's and batch's [GB-IDs](https://genetixbay.com/knowledge/glossary/gb-id.md), documented grows earn rewards, and a member's keeper with a strong journal can be nominated for community breeding. Yield and potency numbers by themselves never earn rewards; documentation does. ## Don't confuse with - **Smoke report**: the tasting write-up at the end, one part of a journal. - **Breeding records**: pollination dates and parent IDs; a breeder's journal includes them. ## Related terms [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Smoke report](https://genetixbay.com/knowledge/glossary/smoke-report.md), [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md), [Dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) ## Read more - [How to document lineage evidence (GB-ID evidence levels L0-L4)](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md) - [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) --- # Growing medium > A growing medium (plural media) is the material roots grow in, such as soil, coco, rockwool or clay pebbles, which anchors the plant and holds water, air and sometimes nutrients. - Canonical: https://genetixbay.com/knowledge/glossary/growing-medium.html - Also written: media, medium, substrate, grow media, growing media, growing substrate - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A growing medium, or substrate, is whatever the roots grow in. It anchors the plant and holds a balance of water and air; some media (soil, compost, peat, coco) also hold and supply nutrients, while others (rockwool, perlite, [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md)) are nearly inert. "Media" is the plural. ## In practice Media are judged by a few properties: water-holding capacity, [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), [cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), salt content (starting [EC](https://genetixbay.com/knowledge/glossary/ec.md)), stability over time and cleanliness. These decide how often to water, how to feed, and how forgiving the system is. Soil and amended mixes buffer mistakes; inert media give fast, precise control but punish errors quickly. Choosing a medium is the first and most important systems decision: see [choosing a system](https://genetixbay.com/knowledge/systems/choosing-a-system.md). ## Don't confuse with - **Root zone**: the environment around the roots, including solution and microbes. - **Medium (DWC)**: in water culture the "medium" in the [net pot](https://genetixbay.com/knowledge/glossary/net-pot.md) only anchors the plant; roots live in solution. ## Related terms [Soil](https://genetixbay.com/knowledge/glossary/soil.md), [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [Soilless](https://genetixbay.com/knowledge/glossary/soilless.md), [Air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), [Cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md) ## Read more - [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Guaiol > Guaiol is a sesquiterpene alcohol with a woody, piney, slightly rosy smell, named for guaiacum wood and present as a minor terpene in some cannabis cultivars. - Canonical: https://genetixbay.com/knowledge/glossary/guaiol.html - Also written: guaiac alcohol, champacol, guajol - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Guaiol is a bicyclic [sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) alcohol found in guaiacum wood oil and cypress pine, where it can crystallise out of the oil. Its smell is woody, piney and faintly rosy. In cannabis it is a minor [terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), more common in some cultivar families, and often reported on larger panels alongside other sesquiterpene alcohols such as eudesmols. ## In practice Typical flower readings run from [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md) to roughly 0.2% w/w. Guaiol is one of the terpenoids that, with eudesmols and bulnesol, has been associated with certain landrace-derived [chemotypes](https://genetixbay.com/knowledge/glossary/chemotype.md) in some studies, but the pattern is not strong enough to use as a cultivar fingerprint. Low volatility means it holds up through drying and storage. ## Don't confuse with - **Guaiacol**: a smoky phenol from wood smoke; a different compound. - **Guaiacum**: the tree genus that gives the name. - **Eudesmol**: a related sesquiterpene alcohol that often co-occurs. ## Related terms [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Nerolidol](https://genetixbay.com/knowledge/glossary/nerolidol.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Guaranteed analysis > The guaranteed analysis is the legally required label statement of minimum nutrient content, giving P as P2O5 and K as K2O; multiply by 0.436 and 0.830 for elements. - Canonical: https://genetixbay.com/knowledge/glossary/guaranteed-analysis.html - Also written: guaranteed minimum analysis, label analysis, fertiliser label, oxide analysis - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The guaranteed analysis is the section of a fertiliser label listing the minimum percentage of each nutrient the manufacturer guarantees, by weight. By long convention, phosphorus is stated as P2O5 and potassium as K2O, a legacy of nineteenth-century analysis methods. Other nutrients (Ca, Mg, S, [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md)) are usually stated as elements, and the label may break nitrogen into [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), ammoniacal and [urea](https://genetixbay.com/knowledge/glossary/urea.md) forms. Exact rules vary by jurisdiction. ## In practice To compare products or build a recipe, convert to elements and to the final solution. A label showing [0-52-34](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) means 52% P2O5 and 34% K2O, which is about 22.7% P and 28.2% K. At 1 g/L, that gives about 227 mg/L (ppm) P and 282 mg/L K. ## Units and formula | From | To element | Multiply by | |---|---|---| | P2O5 | P | 0.436 | | K2O | K | 0.830 | | P | P2O5 | 2.291 | | K | K2O | 1.205 | ## Don't confuse with - **Ingredient list**: names the salts or materials used, not their nutrient content. - **N-P-K ratio**: the three headline numbers only. ## Related terms [N-P-K ratio](https://genetixbay.com/knowledge/glossary/npk-ratio.md), [ppm of an element](https://genetixbay.com/knowledge/glossary/elemental-ppm.md), [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Feed chart](https://genetixbay.com/knowledge/glossary/feed-chart.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Guerrilla grow > A guerrilla grow is cannabis planted on land the grower does not own or control, typically wild or remote ground, a practice that is illegal in most places. - Canonical: https://genetixbay.com/knowledge/glossary/guerrilla-grow.html - Also written: guerilla grow, guerrilla growing, guerilla growing, guerrilla grower - Glossary category: Cultivation and training - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A guerrilla grow is an outdoor planting on land the grower does not own, lease or have permission to use, such as woodland, field margins or public land. The term comes from the unofficial, hidden nature of the plot. Historically it was common where any cultivation was prohibited. ## In practice Even where [home growing](https://genetixbay.com/knowledge/glossary/home-grow.md) is legal, planting on someone else's land usually is not: it can involve trespass, damage to protected land, and breaches of rules that require plants to be grown at the grower's own residence. Guerrilla plots also cause real environmental harm in some regions, from water diversion, rodenticides, fertiliser [run-off](https://genetixbay.com/knowledge/glossary/runoff.md) and litter. GenetixBay does not advise on guerrilla growing; grow legally where you have permission, and check local rules. The word turns up in older grow literature and in forum discussions about hardy, mould-resistant outdoor cultivars. ## Don't confuse with - **Outdoor growing**: planting in your own garden or land, legal in some places. - **Guerrilla gardening**: unrelated activism planting flowers or vegetables in neglected public spaces. ## Related terms [Outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md), [Companion planting](https://genetixbay.com/knowledge/glossary/companion-planting.md), [Hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) --- # Hang dry > Drying harvested cannabis by hanging branches upside down in a dark, controlled room so buds dry slowly with even airflow around them. - Canonical: https://genetixbay.com/knowledge/glossary/hang-dry.html - Also written: hang drying, hanging to dry, branch hang, hanging buds, drying line - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hang drying is the traditional drying method: cut branches are hung upside down from lines or hangers in a dark room with controlled temperature, humidity and gentle air movement. Buds dry in open air without being crushed, and the stem slows moisture loss from the buds. ## In practice A good target is a dry of about 7-14 days at around 15-21 °C (60-70 °F) and 55-62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), the zone the "[60/60](https://genetixbay.com/knowledge/glossary/60-60-rule.md)" rule aims for. Keep fans off the buds directly; air should move around them, not through them. Darkness protects [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) from light degradation. Practical tips: - space branches so they don't touch; - hang thick, dense [colas](https://genetixbay.com/knowledge/glossary/cola.md) with more room than airy branches; - check daily for musty smells or soft spots in dense buds; - check stems from about day 5-7 on; when small stems snap rather than bend, it's time to trim or jar. Rack drying (buds on mesh shelves) is the main alternative, common after [wet trim](https://genetixbay.com/knowledge/glossary/wet-trim.md). It suits limited space but is more prone to flat spots and uneven drying. ## Don't confuse with - **Whole-plant hang**: hanging the entire plant uncut. - **Curing**: the slow finish in sealed containers after drying. - **Freeze drying**: rapid vacuum drying (Contested, not recommended). ## Related terms [Whole-plant hang](https://genetixbay.com/knowledge/glossary/whole-plant-hang.md), [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md), [60/60 rule](https://genetixbay.com/knowledge/glossary/60-60-rule.md), [Dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md), [Case hardening](https://genetixbay.com/knowledge/glossary/case-hardening.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # Haplodiploidy > A sex-determination system where males develop from unfertilised eggs with one chromosome set and females from fertilised eggs with two; found in mites, thrips and whiteflies. - Canonical: https://genetixbay.com/knowledge/glossary/haplodiploidy.html - Also written: haplodiploid, haplo-diploid - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Haplodiploidy is the sex system in which males are haploid (one chromosome set, from an unfertilised egg) and females [diploid](https://genetixbay.com/knowledge/glossary/diploid.md). [Two-spotted spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [western flower thrips](https://genetixbay.com/knowledge/glossary/thrips.md) and whiteflies all use it. The spider mite genome paper discusses it as part of the biology that makes the species such an adaptable pest. ## In practice Haplodiploidy speeds up pesticide resistance. In haploid males every [gene](https://genetixbay.com/knowledge/glossary/gene.md) is exposed to selection, so a [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) resistance gene cannot hide in carriers the way it does in diploid species; resistant males survive and pass it to all their daughters. Combine that with a generation of about a week at 25-30 C and resistance can appear within one season of repeating one [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md). ## Don't confuse with - **Arrhenotoky**: the reproduction mode that follows from haplodiploidy (unmated females make sons). - **Parthenogenesis in aphids**: females make daughters without males, a different system. ## Related terms [Arrhenotoky](https://genetixbay.com/knowledge/glossary/arrhenotoky.md), [Sex ratio](https://genetixbay.com/knowledge/glossary/sex-ratio.md), [Pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Sources 1. Grbic, M. et al., 2011. The genome of Tetranychus urticae reveals herbivorous pest adaptations. Nature 479:487-492. https://doi.org/10.1038/nature10640 2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # Hardening off > Hardening off is gradually exposing plants raised indoors or under a dome to harsher conditions, such as sun, wind and lower humidity, so they adapt without shock. - Canonical: https://genetixbay.com/knowledge/glossary/hardening-off.html - Also written: harden off, hardening, acclimatising, acclimatizing, acclimation - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hardening off is the gradual acclimatisation of a plant to a tougher environment. Indoor-raised plants have thinner cuticles and leaves adapted to low light and still air; put straight into full sun and wind they can bleach, wilt or stall. Over one to two weeks they thicken their leaves and cuticles and adjust [stomata](https://genetixbay.com/knowledge/glossary/stomata.md). ## In practice For outdoor planting, start with an hour or two of morning sun or shade outdoors, increase daily, and bring plants in on [cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) until they spend full days and nights outside. Night temperatures should be reliably above about 10 °C (50 °F) before planting out. For clones coming out of a dome, the same idea applies to humidity: vents opened over several days. Note that full sun can exceed 1,500-2,000 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) PPFD at midday, several times what most indoor plants have seen. ## Don't confuse with - **Transplant shock**: damage from root disturbance; hardening off addresses the above-ground environment. - **Stress training**: deliberate bending or damage to shape plants, unrelated. ## Related terms [Cloning dome](https://genetixbay.com/knowledge/glossary/cloning-dome.md), [Transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md), [Outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md), [Light stress](https://genetixbay.com/knowledge/glossary/light-stress.md) ## Read more - [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) --- # Harvest window > The span of days, often one to two weeks, in which a cannabis plant is ripe enough to cut, judged mainly by trichome head colour and bud development. - Canonical: https://genetixbay.com/knowledge/glossary/harvest-window.html - Also written: harvest time, harvest timing, when to harvest, ripeness window, harvest point - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The harvest window is the period during which a crop is ready to cut. For cannabis it opens once most [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) have turned cloudy and [bracts](https://genetixbay.com/knowledge/glossary/bract.md) have swollen, and closes as heads go increasingly amber and the plant starts to decline. On many cultivars that window lasts about one to two weeks; breeder flowering times are only a starting estimate. ## In practice GenetixBay's guidance (Grower practice, house position): harvest timing is a matter of preference. Aim for a nice mix: a few clear heads, mostly cloudy, some amber. Check heads on bracts, not [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md), and sample several buds, top and lower, over several days. Other signs that support the call: - bracts visibly swollen and tight; - most stigmas darkened and receded; - new [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) production slowed; - natural fade in fan leaves. Large plants often ripen top-down. Some growers take the [top colas](https://genetixbay.com/knowledge/glossary/cola.md) first and give lower buds a few extra days. Don't change the feed or lights to "finish" the plant. Keep feeding ([taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md)) and keep the lights on until you chop. ## Don't confuse with - **Flowering time**: a breeder estimate in weeks; the window is what the plant shows. - **Trichome ripeness**: the main indicator of the window, not the window itself. - **Chop**: the act of cutting. ## Myth check [Darkness before harvest](https://genetixbay.com/knowledge/glossary/darkness-before-harvest.md) and pre-harvest flushing do not improve the crop (Myth). See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Trichome ripeness](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md), [Jeweler's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md), [Pistil](https://genetixbay.com/knowledge/glossary/pistil.md), [Chop](https://genetixbay.com/knowledge/glossary/chop.md), [Flowering stage](https://genetixbay.com/knowledge/glossary/flowering-stage.md) ## Read more - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) ## Sources 1. Punja ZK, Sutton DB, Kim T. 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 2. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 --- # Hash > Hash is any concentrate made by separating trichome heads from cannabis and collecting or pressing them, from dry sift and ice water hash to hand-rubbed charas. - Canonical: https://genetixbay.com/knowledge/glossary/hash.html - Also written: hash concentrate, trichome concentrate, resin concentrate, hasj, hashes - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hash is the modern grower's catch-all term for concentrated cannabis resin obtained by physically separating [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md): by dry sieving, by agitation in ice water, or by hand-rubbing live plants. The collected resin may be used loose, pressed into a solid, or processed further (pressed into rosin, for example). It is a solventless product unless stated otherwise. ## In practice Growers describe hash by method and quality: [dry sift](https://genetixbay.com/knowledge/glossary/kief.md), [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md) (bubble), full melt, [temple balls](https://genetixbay.com/knowledge/glossary/temple-ball.md), pressed hash. Quality depends on the starting material, how cleanly the heads were separated, and how the hash was cured and stored. Colour runs from pale blond to dark brown; darkness can come from plant matter, oxidation, pressing or heat, so colour alone is a poor guide. GenetixBay defines hash types but doesn't give processing instructions. ## Don't confuse with - **Hashish**: the traditional pressed resin of historic hash-making regions; often used interchangeably. - **Solvent extracts**: shatter, wax and [live resin](https://genetixbay.com/knowledge/glossary/live-resin.md) use solvents and are not hash. - **Kief**: loose heads, unpressed. ## Myth check House position: [traditional hash](https://genetixbay.com/knowledge/glossary/hashish.md) and [charas](https://genetixbay.com/knowledge/glossary/charas.md) cultures would have been impossible with weak plants; "old weed was weak" is wrong about the genetics. See [old cannabis was not weak](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md). ## Related terms [Hashish](https://genetixbay.com/knowledge/glossary/hashish.md), [Kief](https://genetixbay.com/knowledge/glossary/kief.md), [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Charas](https://genetixbay.com/knowledge/glossary/charas.md), [Pressed hash](https://genetixbay.com/knowledge/glossary/pressed-hash.md), [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md) ## Read more - [Old cannabis wasn't weak: the "so much stronger than 20 years ago" myth](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md) ## Sources 1. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). 2. Chouvy P-A, Afsahi K. 2014. Hashish revival in Morocco. International Journal of Drug Policy 25(3):416-423. https://doi.org/10.1016/j.drugpo.2014.01.001 --- # Hash rosin > Hash rosin is rosin pressed from hash, usually ice water hash, rather than from flower; it is cleaner and typically higher in quality than flower rosin. - Canonical: https://genetixbay.com/knowledge/glossary/hash-rosin.html - Also written: flower rosin vs hash rosin, flower rosin, bubble hash rosin, ice water hash rosin, hash-rosin - Glossary category: Processing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" [Rosin](https://genetixbay.com/knowledge/glossary/rosin.md) can be pressed from two kinds of starting material. Flower rosin is pressed directly from dried flower: simpler, but it carries more plant lipids, [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) and other compounds from the plant tissue into the oil, and it usually has a lower yield per gram of resin present. Hash rosin is pressed from [hash](https://genetixbay.com/knowledge/glossary/hash.md), most often [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md) or [dry sift](https://genetixbay.com/knowledge/glossary/kief.md), which has already had most plant matter removed. Hash rosin made from [fresh frozen material](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) is [live rosin](https://genetixbay.com/knowledge/glossary/live-rosin.md). ## In practice Among solventless makers, hash rosin is widely considered the higher-grade product: cleaner, more consistent texture and better flavour. Flower rosin remains popular with home consumers because it needs only the flower. In both cases the outcome depends mainly on the starting material: rosin can't improve poor hash or poorly grown flower. GenetixBay defines the products only and gives no pressing settings. ## Don't confuse with - **Live rosin**: hash rosin made from fresh frozen material. - **Pressed hash**: compressed solid hash, not an extracted oil. - **Resin (live or cured)**: [solvent-based extracts](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md). ## Related terms [Rosin](https://genetixbay.com/knowledge/glossary/rosin.md), [Live rosin](https://genetixbay.com/knowledge/glossary/live-rosin.md), [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md), [Kief](https://genetixbay.com/knowledge/glossary/kief.md) ## Sources 1. Russo EB, Plumb J, Whiteley VL. 2021. Novel solventless extraction technique to preserve cannabinoid and terpenoid profiles of fresh cannabis inflorescence. Molecules 26(18):5496. https://doi.org/10.3390/molecules26185496 --- # Hashish > Hashish is the traditional pressed resin concentrate of cannabis, made for centuries by sieving or rubbing trichome heads from plants and compressing them into blocks or balls. - Canonical: https://genetixbay.com/knowledge/glossary/hashish.html - Also written: haschisch, haschich, traditional hashish, traditional hash, hachís - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hashish is the historic name, from Arabic, for compressed cannabis resin. Traditional production falls into two families. Sieved hashish, from regions spanning North Africa, the Levant and Central Asia, is made by beating or sieving dried plants over fabric screens and pressing the collected powder. Rubbed hashish ([charas](https://genetixbay.com/knowledge/glossary/charas.md)), from the Himalayan regions, is made by hand-rubbing live flowers. Clarke's *Hashish!* (1998, updated 2010) documents these traditions in detail. ## In practice "Hashish" today usually means the traditional styles and their modern descendants: pressed blocks, slabs and balls with a firm or pliable texture and dark exterior from oxidation. Seized hashish analysed in modern studies has ranged widely in potency, depending on the source and method. The existence of these traditions, often valued highly in their regions, is part of the evidence that potent cannabis isn't new. ## Don't confuse with - **Hash**: the broader modern grower term, including [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md) and [dry sift](https://genetixbay.com/knowledge/glossary/kief.md). - **Charas**: the hand-rubbed subtype of hashish. - **Brick weed**: compressed flower, not resin. ## Myth check House position: the "weak old weed" story ignores centuries of hashish and charas. See [old cannabis was not weak](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Hash](https://genetixbay.com/knowledge/glossary/hash.md), [Charas](https://genetixbay.com/knowledge/glossary/charas.md), [Temple ball](https://genetixbay.com/knowledge/glossary/temple-ball.md), [Pressed hash](https://genetixbay.com/knowledge/glossary/pressed-hash.md), [Kief](https://genetixbay.com/knowledge/glossary/kief.md) ## Read more - [Old cannabis wasn't weak: the "so much stronger than 20 years ago" myth](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md) - [Landraces of the world: an overview](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) ## Sources 1. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). 2. Chouvy P-A, Afsahi K. 2014. Hashish revival in Morocco. International Journal of Drug Policy 25(3):416-423. https://doi.org/10.1016/j.drugpo.2014.01.001 --- # Hay smell > A grassy, hay-like aroma in dried cannabis caused by drying too fast, over-drying or bacterial activity; in GenetixBay's view it never fully cures out. - Canonical: https://genetixbay.com/knowledge/glossary/hay-smell.html - Also written: smells like hay, grassy smell, hay-like smell, smells like cut grass, green smell - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hay smell is the flat, grassy or hay-like aroma of badly dried cannabis, often with a harsh, green taste on smoking. It replaces or masks the cultivar's normal [terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md). The usual causes are drying too fast (warm, [dry rooms](https://genetixbay.com/knowledge/glossary/drying-room.md) or [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) blowing on buds), [over-drying](https://genetixbay.com/knowledge/glossary/over-drying.md), or bacterial and microbial activity in material that sat too wet, too warm, or packed too tightly. ## In practice [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) is the cure: - Dry slowly, about 7-14 days at around 15-21 °C (60-70 °F) and 55-62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). - Keep air moving around, not onto, the buds. - Don't pack wet buds into bags or bins. - Jar at the [stem snap](https://genetixbay.com/knowledge/glossary/stem-snap-test.md), then cure as a slow decline in moisture. If a batch smells of hay, a long, careful cure may soften it a little, but it won't bring back what was lost. ## Don't confuse with - **Ammonia smell**: wet material with microbial growth; check for mould. - **Musty smell**: mould; inspect and discard affected buds. - **Fresh "green" smell at chop**: normal before the dry. ## Myth check House position: a cure will never fix a bad dry. Hay smell means bacteria, over-drying or drying too fast, and it never truly comes out. Nor does it come from "not [flushing](https://genetixbay.com/knowledge/glossary/flushing.md)": taste and ash come from drying, curing and plant health (Myth). See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Related terms [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md), [Over-drying](https://genetixbay.com/knowledge/glossary/over-drying.md), [Chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md), [Terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) ## Sources 1. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. 2. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 --- # Haze > Haze is a generic name for a family of long-flowering, narrow-leaflet hybrids built from tropical landrace material, known for sharp, spicy, incense-like aroma. - Canonical: https://genetixbay.com/knowledge/glossary/haze.html - Also written: hazes, haze strains, hazy, haze family - Glossary category: Grower slang and culture · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Haze names a family of cannabis lines descended from crosses of tropical [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) material, built by growers in coastal California in the late 1960s and 1970s. It is now a generic lineage word for tall, slow-flowering, aromatic plants. ## In practice Haze-type plants are tall and stretchy, with long flowering times, often 12-16 weeks or more from flip, and airy, resinous buds. The aroma is typically spicy, incense, citrus or sharp. Their length makes them demanding indoors: heavy [stretch](https://genetixbay.com/knowledge/glossary/stretch.md), a long run and late-season mould risk outdoors in temperate climates. Many modern "hazes" are [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) that keep some of the aroma and shorten flowering. The exact landrace components of the original haze are told in several versions; treat specific claims as low-evidence. ## Don't confuse with - **Sativa**: haze is the textbook "sativa" shape, but the label describes structure at most, not effect. - **Hazy appearance**: unrelated. ## Related terms [Kush](https://genetixbay.com/knowledge/glossary/kush.md), [Skunk](https://genetixbay.com/knowledge/glossary/skunk.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md) ## Read more - [How hybrid 'strains' emerged](https://genetixbay.com/knowledge/genetics-history/how-hybrid-strains-emerged.md) - [Landraces of the world: an overview](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) ## Sources 1. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. --- # Heady > Heady is slang for things made with exceptional craft and care, from hand-blown glass to small-batch flower; it signals artisan quality and insider culture. - Canonical: https://genetixbay.com/knowledge/glossary/heady.html - Also written: heady glass, heady culture, heady weed, heady shit, heady scene - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Heady describes something made with unusual skill, care or artistry, and the community that values it. It began with intricate hand-blown glass pipes and spread to flower, [hash](https://genetixbay.com/knowledge/glossary/hash.md) and growers who work in small batches. ## In practice "Heady flower" means carefully grown, slow-dried, well-cured small-batch cannabis, often from a named grower rather than a large facility. "Heady hash" means top-grade resin. The word also marks belonging: heads know the growers, the history and the lineages. The word carries no specification. A heady label, like a [top-shelf](https://genetixbay.com/knowledge/glossary/top-shelf.md) one, is a claim; the proof is in the dry, the cure, the smoke and the records. ## Don't confuse with - **Exotic**: fashionable and expensive; heady implies craft and care. - **Head**: a dedicated cannabis enthusiast, the person heady things are made for. ## Related terms [Connoisseur](https://genetixbay.com/knowledge/glossary/connoisseur.md), [Fire](https://genetixbay.com/knowledge/glossary/fire.md), [Zaza](https://genetixbay.com/knowledge/glossary/zaza.md) --- # Heat stress > Heat stress is damage or slowed growth when leaf or canopy temperature rises above what the plant can handle, typically above about 30–32 °C (86–90 °F) in cannabis. - Canonical: https://genetixbay.com/knowledge/glossary/heat-stress.html - Also written: heat stressed, heat damage, high temperature stress, heat burn, too hot - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Heat stress is the set of responses and damage that follow when plant tissue gets too hot. [Photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) slows as enzymes and membranes lose efficiency, respiration rises, and the plant spends energy protecting itself. Chandra and colleagues (2008) found cannabis leaf photosynthesis peaked around 25–30 °C (77–86 °F) and declined above that range at ambient [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md). ## In practice Common signs: leaves cupping upwards ([tacoing](https://genetixbay.com/knowledge/glossary/taco-leaf.md)) to reduce exposure, edges curling, leaf tips crisping on top growth, wilting at midday despite moist roots, airy or [foxtailed buds](https://genetixbay.com/knowledge/glossary/foxtailing.md) at the canopy top, and fading aroma late in flower. Sustained [canopy temperatures](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) above about 30–32 °C (86–90 °F) are a warning. With CO2 enrichment, the optimum shifts a couple of degrees higher. Fix the cause in order: measure leaf temperature (not just air), raise or dim the light, increase exhaust and air movement over the tops, cool the intake air, and check root-zone temperature, especially in hydro where warm water loses dissolved oxygen. ## Don't confuse with - **Light stress**: damage from excess light; often occurs alongside heat stress. - **Nutrient burn**: crisp tips across the plant from high [EC](https://genetixbay.com/knowledge/glossary/ec.md), not concentrated at the top. ## Myth check "Heat makes plants [herm](https://genetixbay.com/knowledge/glossary/hermaphrodite.md)" needs framing. GenetixBay position: intersex flowers mainly reflect genetics from poor breeding. Heat stress can *reveal* susceptible lines; it is not normal for stable cannabis. See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). ## Related terms [Temperature](https://genetixbay.com/knowledge/glossary/temperature.md), [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md), [Light stress](https://genetixbay.com/knowledge/glossary/light-stress.md), [Foxtailing](https://genetixbay.com/knowledge/glossary/foxtailing.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) ## Read more - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) - [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # Heavy metals panel > A heavy metals panel measures toxic elements, usually lead, arsenic, cadmium and mercury, in a cannabis sample, typically by ICP-MS, against regulatory action limits. - Canonical: https://genetixbay.com/knowledge/glossary/heavy-metals-panel.html - Also written: heavy metals test, heavy metal testing, metals panel, ICP-MS, lead arsenic cadmium mercury, heavy metals - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A heavy metals panel quantifies the toxic [trace elements](https://genetixbay.com/knowledge/glossary/micronutrient.md) most regulators require: lead (Pb), arsenic (As), cadmium (Cd) and mercury (Hg), sometimes with others such as chromium. The usual method digests the sample in acid and measures it by inductively coupled plasma mass spectrometry (ICP-MS), which detects elements at parts-per-billion levels. ## In practice Cannabis takes up metals readily from its [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md), which is why [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) has been studied for cleaning contaminated soils. That same trait makes metals a real risk in flower. Sources include contaminated soil, some fertilisers and amendments, poor water and equipment. A [COA](https://genetixbay.com/knowledge/glossary/coa.md) reports each element in µg/g (ppm) or µg/kg (ppb) against action limits that vary by jurisdiction and product type; check local rules. If a crop fails, test inputs, not just the flower. ## Units and formula µg/g = ppm; µg/kg = ppb. 0.5 µg/g lead = 500 µg/kg. ## Don't confuse with - **Plant nutrients**: iron, [zinc](https://genetixbay.com/knowledge/glossary/zinc.md), [copper](https://genetixbay.com/knowledge/glossary/copper.md) and [manganese](https://genetixbay.com/knowledge/glossary/manganese.md) are essential micronutrients, not "heavy metals" in this regulatory sense, though they can be toxic in excess. - **Pesticide panel**: organic chemical residues, a separate test. ## Related terms [Pesticide panel](https://genetixbay.com/knowledge/glossary/pesticide-panel.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [LOD](https://genetixbay.com/knowledge/glossary/lod.md), [Batch](https://genetixbay.com/knowledge/glossary/batch.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) --- # Heirloom > An heirloom is a seed line kept and passed down by growers for decades, usually outside its region of origin, preserving an older type rather than a recent hybrid. - Canonical: https://genetixbay.com/knowledge/glossary/heirloom.html - Also written: heirloom line, heirloom seed, heritage line, heritage seed, heirloom strain - Glossary category: Genetics and breeding · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An heirloom (or heritage line) is a seed line that has been maintained and passed on by growers over many generations, typically decades, without being crossed into new [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md). In cannabis it usually means [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) or early-hybrid material that left its source region, often in the 1960s to 1980s, and has been kept going by successive growers since. ## In practice Heirlooms are a key reservoir of older genetics. Seed stock of 50 to 70 years old, kept and regrown carefully, can still test in the high 20s for [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md), which is direct evidence that the genetics were never weak. Keeping an heirloom honest means [open pollination](https://genetixbay.com/knowledge/glossary/open-pollinated.md) with enough plants each generation, isolation from other pollen, and records of who kept it and when. Seed from a handful of parents each time narrows the line through [genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md); crossing it to a modern hybrid ends it as an heirloom, whatever the label says. ## Don't confuse with - **Landrace**: maintained in its region of origin by local farmers; an heirloom may descend from one. - **Clone-only**: a single [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) kept by cuttings; an heirloom is a seed population. - **"Classic" or "OG" (marketing)**: often hybrids under an old name. ## Related terms [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md), [Accession](https://genetixbay.com/knowledge/glossary/accession.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Seed run](https://genetixbay.com/knowledge/glossary/seed-run.md) ## Read more - [Polyhybrids vs landraces: what each gives a breeder](https://genetixbay.com/knowledge/breeding/polyhybrids-vs-landraces.md) - [Landraces of the world: an overview](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) ## Sources 1. Villa TCC, Maxted N, Scholten M, Ford-Lloyd B. 2005. Defining and identifying crop landraces. Plant Genetic Resources 3(3):373-384. https://doi.org/10.1079/PGR200591 --- # Hemp > Hemp is cannabis grown for fibre, seed or other uses and, in many laws, defined as Cannabis sativa with no more than 0.3% THC by dry weight. - Canonical: https://genetixbay.com/knowledge/glossary/hemp.html - Also written: industrial hemp, hemp plant, hemp cultivar, fibre hemp, fiber hemp - Glossary category: Legal and regulatory · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hemp is *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)* L. grown for fibre, grain, oil or low-THC flower and extracts. Botanically it is the same species as drug-type cannabis. The legal difference is chemistry: many jurisdictions define hemp as cannabis with no more than 0.3% [THC](https://genetixbay.com/knowledge/glossary/thc.md) on a [dry-weight basis](https://genetixbay.com/knowledge/glossary/dry-weight-basis.md), though they differ on which THC counts (delta-9 THC only, or total THC including [THCA](https://genetixbay.com/knowledge/glossary/thca.md)) and which plant parts are sampled. ## In practice The US federal definition since 2018 used 0.3% delta-9 THC on a dry-weight basis, with pre-harvest testing rules later moving toward total THC; Congress has since changed the federal definition again with effect around late 2026. Canada and the EU also use a 0.3% THC threshold for hemp cultivation under their own rules. A crop that tests "hot" above the limit may have to be destroyed. Many fibre and grain hemp cultivars are [monoecious](https://genetixbay.com/knowledge/glossary/monoecious.md), bred on purpose to carry male and [female flowers](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) on one plant. That is a deliberate agricultural trait, not the norm for drug-type cannabis. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Drug-type cannabis**: same species, high-THC [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md). - **CBD flower**: often legally hemp, but grown and sold as smokable flower. ## Related terms [Marijuana](https://genetixbay.com/knowledge/glossary/marijuana.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [Compliance testing](https://genetixbay.com/knowledge/glossary/compliance-testing.md), [Monoecious](https://genetixbay.com/knowledge/glossary/monoecious.md), [Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) ## Read more - [Indica, sativa and ruderalis: what the names really mean](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Agriculture Improvement Act of 2018, Pub. L. 115-334, sec. 10113 (definition of hemp, 7 U.S.C. 1639o). 2. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLOS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 --- # Hemp russet mite > Aculops cannabicola, a microscopic eriophyid mite specific to cannabis that causes upward leaf curl, bronzing and dull, greasy-looking trichomes. - Canonical: https://genetixbay.com/knowledge/glossary/hemp-russet-mite.html - Also written: russet mite, russet mites, Aculops cannabicola, HRM, rust mite - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The hemp russet mite (*Aculops cannabicola*) is an [eriophyid mite](https://genetixbay.com/knowledge/glossary/eriophyid-mite.md) about 0.2 mm long, carrot-shaped, with only four legs near the head. It feeds only on cannabis and hops relatives, which makes it a [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) and cannabis specialist. It is invisible without strong magnification. ## In practice Damage usually starts low and works up. Leaf edges curl upward, surfaces turn dull, bronze or russet, and [petioles](https://genetixbay.com/knowledge/glossary/petiole.md) can become brittle. In flower the [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) crowd into buds and onto [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) stalks, leaving heads that look matted or greasy. By the time a grower notices, populations can number in the thousands per leaf. Confirm with a 40x or stronger scope; the mites look like moving beige dust. Most infestations arrive on clones, so quarantine and inspection of incoming material matter more than any spray. Clean [mother stock](https://genetixbay.com/knowledge/glossary/mother-plant.md) is the long-term fix. Check what is registered for cannabis locally before treating. ## Don't confuse with - **Broad mite**: distorts new growth from the top; russet mites start lower and bronze leaves. - **Two-spotted spider mite**: visible with a 10x loupe, makes [stippling](https://genetixbay.com/knowledge/glossary/stippling.md) and webbing. - **Rust fungi or nutrient bronzing**: no mites under the scope. ## Related terms [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Sulfur burner](https://genetixbay.com/knowledge/glossary/sulfur-burner.md) ## Read more - [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ## Sources 1. Colorado State University. Hemp russet mite, Aculops cannabicola. https://agsci.colostate.edu/agbio/ipm-pests/29895-2/ 2. NC State Extension. Hemp Russet Mite in Industrial Hemp. https://content.ces.ncsu.edu/hemp-russet-mite-in-industrial-hemp --- # Heritability > Heritability is the share of a trait's variation within a population that is due to genetic differences rather than environment, on a scale from 0 to 1. - Canonical: https://genetixbay.com/knowledge/glossary/heritability.html - Also written: heritable, h2, broad-sense heritability, narrow-sense heritability - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Heritability is the proportion of the observed variation in a trait, in one population and one set of conditions, that is explained by genetic differences. It runs from 0 (all differences are environmental) to 1 (all are genetic). Broad-sense heritability (H²) counts all genetic effects; narrow-sense (h²) counts only the additive part, which is what predicts response to selection. ## In practice High-heritability traits respond quickly to selection: pick the best parents and the offspring follow. Flowering time and the [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase type behave like this. Low-heritability traits (yield per plant is the classic) are dominated by environment and plant position, so selecting the biggest plant in a tent often picks the luckiest spot, not the best [genes](https://genetixbay.com/knowledge/glossary/gene.md). That is why good breeders grow candidates in uniform conditions, repeat them as clones, and judge parents by their offspring. ## Units and formula H² = VG / VP and h² = VA / VP, where VP is total phenotypic variance, VG genetic variance and VA additive genetic variance. Response to selection: R = h² × S (the breeder's equation), where S is how far the selected parents are above the population mean. ## Don't confuse with - **Inherited**: a trait can be fully genetic yet show zero heritability in a uniform population, because there is no variation left. - **Fixed number**: heritability belongs to a population and an environment; change either and it changes. ## Related terms [Quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md), [Genotype by environment interaction](https://genetixbay.com/knowledge/glossary/genotype-by-environment.md), [Progeny test](https://genetixbay.com/knowledge/glossary/progeny-test.md) ## Read more - [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 --- # Herm threshold > The herm threshold is GenetixBay's two-tier herm standard: a 10-plant screening grow with zero herms to be featured, then about 150 or more community-grown plants before a line can be Verified under 2% herm rate. - Canonical: https://genetixbay.com/knowledge/glossary/herm-threshold.html - Also written: 2% herm threshold, Verified under 2% herm rate, herm screening, herm rate threshold, hermaphrodite threshold, 2 percent herm rule, herm rate - Glossary category: GenetixBay terms · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The herm threshold is GenetixBay's standard for sex stability. It has two tiers, because a small test grow can catch a bad line but can't prove a good one. ## In practice - **Tier 1, screening.** The breeder (or the Bay's testers) flowers a test grow of at least 10 plants. Any [herm](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), meaning any plant that shows [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) or bare [anthers](https://genetixbay.com/knowledge/glossary/anther.md) ([nanners](https://genetixbay.com/knowledge/glossary/nanners.md)), fails the line for [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md), [the Seed Club](https://genetixbay.com/knowledge/glossary/seed-club.md) and featuring. A line can be reworked and screened again. - **Tier 2, verified.** Community grow reports on the line are pooled against its batch [GB-IDs](https://genetixbay.com/knowledge/glossary/gb-id.md). Only when they add up to about 150 plants or more, with few enough herms, can the line earn the label **"Verified under 2% herm rate"**. If the pooled rate rises above 2%, the line loses featuring until it's reworked. Testers record each herm against the batch GB-ID with [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md) and the week of flower, so the rate is data, not hearsay. ## Why two tiers Ten plants can't tell 2% from 10%. A line that herms 2% of the time shows zero herms in 10 plants about 82% of the time; a line that herms 10% of the time still shows zero about 35% of the time. So a clean 10-plant grow is a screen: it fails obvious problems, and it can't certify a low rate. To certify, GenetixBay uses a one-sided 95% upper bound on the true herm rate (exact binomial, Clopper-Pearson). "Verified under 2%" means that bound is below 2%: | Herms seen | Plants needed | |---|---| | 0 | 149 | | 1 | 236 | | 2 | 313 | With zero herms the rule of thumb is the "rule of three": the 95% upper bound is about 3/n, so 3/150 = 2%. With one or more herms you need more plants. ## Units and formula Herm rate (%) = intersex plants / plants flowered x 100. Verified when the one-sided 95% upper bound is under 2%; with zero herms in n plants that bound is 1 - 0.05^(1/n), which drops below 2% at n = 149. ## Myth check "Some herms are just normal." GenetixBay position: intersex plants are mainly a breeding fault, revealed by stress, not normal behaviour. 5-10% herms in a commercial room means poor genetics. GenetixBay holds best breeding standards, "snobby, and proud of it". See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md), [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md), [Nanners](https://genetixbay.com/knowledge/glossary/nanners.md), [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md), [Seed Club](https://genetixbay.com/knowledge/glossary/seed-club.md), [Test grow](https://genetixbay.com/knowledge/glossary/test-grow.md) ## Read more - [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - [Seed germination testing and quality control for breeders](https://genetixbay.com/knowledge/breeding/seed-germination-testing-qc.md) ## Sources 1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 --- # Herm-prone > Herm-prone describes a line whose plants often produce intersex flowers; GenetixBay treats this as a breeding fault and a reason not to breed from it. - Canonical: https://genetixbay.com/knowledge/glossary/herm-prone.html - Also written: herm prone, hermy, hermie-prone, herm tendency, herm-y - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Herm-prone describes a cultivar or seed line in which a noticeable share of plants develop [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) or bare anthers alongside [female flowers](https://genetixbay.com/knowledge/glossary/pistillate-flower.md). It is a property of the genetics, revealed more often under stress such as [light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md), heat or late harvest. ## In practice A grower who sees [nanners](https://genetixbay.com/knowledge/glossary/nanners.md) on 3 of 10 plants from one pack, in a tent where another line stayed clean, has good reason to call that pack herm-prone. On GenetixBay every line publishes a [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md) from tester grows; any [herm](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) in the 10-plant screening grow, or a pooled rate above 2%, keeps a line out of featuring and the community programmes (see [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md)). Log every intersex plant against its batch record so the rate is real data, not anecdote. ## Don't confuse with - **Stress-induced herm**: an argument, not a separate category. Almost any plant can be forced with extreme stress; the question is how easily. Lines that herm under ordinary indoor conditions are herm-prone. - **Monoecious hemp**: bred on purpose to carry both flower types; not the norm for cannabis. ## Myth check "All cannabis herms under stress, so it doesn't matter." GenetixBay house position: herm-prone lines are **mainly breeder error**: repeated selfing ([S1](https://genetixbay.com/knowledge/glossary/s1.md) on S1), careless feminising, and [pollen chuckers](https://genetixbay.com/knowledge/glossary/pollen-chucker.md) spreading unstable genetics. 5-10% herms in a commercial room means poor genetics, not normal cannabis. Cull, don't breed. See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Nanners](https://genetixbay.com/knowledge/glossary/nanners.md), [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), [Herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md), [Pollen chucker](https://genetixbay.com/knowledge/glossary/pollen-chucker.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md) ## Read more - [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - [S1s and selfing: what happens when a plant pollinates itself](https://genetixbay.com/knowledge/breeding/s1-selfing.md) ## Sources 1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 --- # Hermaphrodite > In cannabis growing, a plant (usually female) that develops both pistillate and staminate flowers or anthers; botanists call it intersex or monoecious expression. - Canonical: https://genetixbay.com/knowledge/glossary/hermaphrodite.html - Also written: hermie, herm, hermaphroditic, intersex, intersex plant, hermaphroditism - Glossary category: Plant biology · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A hermaphrodite, in cannabis growing, is a plant expressing both sexes, usually a female that produces [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) or exposed [anthers](https://genetixbay.com/knowledge/glossary/anther.md) among its buds. Botanists prefer "intersex" or "monoecious expression", because cannabis flowers are normally single-sexed. The self-pollen these plants shed is fertile, so they can seed themselves and everything nearby. ## In practice Look from mid-flower onward for male flower clusters at nodes, or single yellow-green anthers protruding from buds. Check again in late flower. Act on what you find: - Remove the plant, or at least the affected parts, before anthers open. - Never use it as a parent. - Note the cultivar and source; a pattern across seeds from one source is a genetics problem. GenetixBay standard: zero herms in a 10-plant screening grow for [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md), [Seed Club](https://genetixbay.com/knowledge/glossary/seed-club.md) and featuring; "[Verified under 2% herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md)" (the founder's threshold) only after about 150 or more pooled community-grown plants. See [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md). ## Don't confuse with - **Monoecious hemp**: a deliberately bred, stable trait in some [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md). - **Foxtailing**: spires of new [pistillate flowers](https://genetixbay.com/knowledge/glossary/pistillate-flower.md), not male. - **Male plant**: an XY plant with only staminate flowers. ## Myth check "[Late-flower bananas](https://genetixbay.com/knowledge/glossary/nanners.md) are normal" is wrong. House position: intersex expression is mainly breeder error (repeated selfing, careless feminising, unstable releases), not a natural cannabis trait. Stress reveals susceptible genetics rather than causing healthy ones to switch. 5-10% herms in a commercial operation means poor genetics (Punja & Holmes 2020 observed it; GenetixBay interprets it this way). See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). ## Related terms [Dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md), [Monoecious](https://genetixbay.com/knowledge/glossary/monoecious.md), [Anther](https://genetixbay.com/knowledge/glossary/anther.md), [Staminate flower](https://genetixbay.com/knowledge/glossary/staminate-flower.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md) ## Read more - [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) ## Sources 1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Faux AM, Berhin A, Dauguet N, Bertin P. 2014. Sex chromosomes and quantitative sex expression in monoecious hemp (Cannabis sativa L.). Euphytica 196(2):183-197. https://doi.org/10.1007/s10681-013-1023-y --- # Heterosis > Heterosis (hybrid vigour) is the tendency of offspring from genetically different parents to outgrow or outperform both parents in traits such as vigour and yield. - Canonical: https://genetixbay.com/knowledge/glossary/heterosis.html - Also written: hybrid vigour, hybrid vigor, heterotic, F1 vigour, hybrid vitality - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Heterosis, or hybrid vigour, is when the offspring of two genetically different parents performs better than the average of the parents, or better than the best parent, for traits like growth rate, size, yield or stress tolerance. It is the mirror image of [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md). ## In practice Heterosis is strongest when two distinct, inbred parents are crossed: the [F1](https://genetixbay.com/knowledge/glossary/f1.md) is uniform and vigorous. Maize breeding is built on it. In cannabis, growers notice it as F1 seedlings that race away compared with either parent, or a fresh [outcross](https://genetixbay.com/knowledge/glossary/outcross.md) that rescues a tired line. It fades in the [F2](https://genetixbay.com/knowledge/glossary/f2.md). Crossing F1 plants with each other reshuffles the [alleles](https://genetixbay.com/knowledge/glossary/allele.md), so part of the vigour is lost and the population becomes variable again. That is why F1 seed is normally remade each time from the parents. The causes are still debated: masking of deleterious [recessives](https://genetixbay.com/knowledge/glossary/recessive.md) (dominance), favourable allele interactions, and gene-regulation effects all contribute (Schnable and Springer 2013). ## Don't confuse with - **Heterozygosity**: a genetic state; heterosis is a performance outcome. [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) plants are not automatically vigorous. - **Stretch**: fast vertical growth from light or temperature, not hybrid vigour. - **Quality**: a vigorous F1 is not necessarily higher in [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) or flavour. ## Related terms [F1](https://genetixbay.com/knowledge/glossary/f1.md), [Hybrid](https://genetixbay.com/knowledge/glossary/hybrid.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [Outcross](https://genetixbay.com/knowledge/glossary/outcross.md), [Inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md) ## Read more - [Inbreeding depression and hybrid vigour](https://genetixbay.com/knowledge/breeding/inbreeding-depression-hybrid-vigour.md) ## Sources 1. Schnable PS, Springer NM. 2013. Progress toward understanding heterosis in crop plants. Annual Review of Plant Biology 64:71-88. https://doi.org/10.1146/annurev-arplant-042110-103827 2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 --- # Heterozygous > A plant is heterozygous at a locus when it carries two different alleles there (Aa), so its offspring can inherit either one and segregate. - Canonical: https://genetixbay.com/knowledge/glossary/heterozygous.html - Also written: heterozygote, heterozygosity, heterozygotes, het - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A plant is heterozygous at a locus when its two [alleles](https://genetixbay.com/knowledge/glossary/allele.md) differ, for example Aa. Half its gametes carry A and half carry a. When heterozygous plants are crossed or selfed, their offspring segregate into different genotypes, which is why seed from a heterozygous plant varies. ## In practice Most cannabis cultivars on the market are highly heterozygous: they are [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) of hybrids. That is why a seed pack from two famous parents throws a spread of plants and why an [elite clone](https://genetixbay.com/knowledge/glossary/elite-cut.md)'s seed rarely reproduces the clone. The clone holds its heterozygous combination intact only because it is propagated vegetatively. "Het" is breeder shorthand for a plant known to carry one copy of a [recessive allele](https://genetixbay.com/knowledge/glossary/recessive.md), as in "het for the auto trait". A test cross or a DNA marker can confirm it. Heterozygosity is not a defect. High heterozygosity in [F1](https://genetixbay.com/knowledge/glossary/f1.md) hybrids is associated with [hybrid vigour](https://genetixbay.com/knowledge/glossary/heterosis.md), and wild or [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) populations keep plenty of it. ## Don't confuse with - **Homozygous**: two identical alleles. - **Hybrid**: a cross between different parents; hybrids are usually heterozygous at many loci, but a hybrid between two different [inbred lines](https://genetixbay.com/knowledge/glossary/inbred-line.md) is uniform even so. - **Unstable**: heterozygous plants are genetically normal; "unstable" in breeder talk means the seed line does not breed true. ## Related terms [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Segregation](https://genetixbay.com/knowledge/glossary/segregation.md), [F1](https://genetixbay.com/knowledge/glossary/f1.md), [Heterosis](https://genetixbay.com/knowledge/glossary/heterosis.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 --- # HHC > HHC (hexahydrocannabinol) is a hydrogenated derivative of THC, found only in traces in the plant; products sold as HHC are semi-synthetic, made by chemically converting other cannabinoids. - Canonical: https://genetixbay.com/knowledge/glossary/hhc.html - Also written: hexahydrocannabinol, hydrogenated THC, HHC-O - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" HHC, hexahydrocannabinol, is a [THC](https://genetixbay.com/knowledge/glossary/thc.md) molecule with its ring double bond saturated with hydrogen. Traces have been reported in cannabis and pollen, but nothing near commercial quantities. Products labelled HHC are semi-synthetic: a [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) starting material, typically derived from [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), is converted through intermediates and then hydrogenated over a metal catalyst. ## In practice Commercial HHC is a mixture of two forms (9R and 9S epimers) whose ratio varies by batch, so two HHC products can differ even at the same labelled strength. Possible by-products and catalyst residues are not covered by an ordinary potency panel. GenetixBay gives no synthesis or conversion information. Reported effects are described as THC-like; human data are scarce. Legal status differs widely between jurisdictions and is changing; check local rules. ## Don't confuse with - **Delta-8 THC**: an isomer of THC, not a hydrogenated form. - **THC**: the natural plant-derived cannabinoid (as [THCA](https://genetixbay.com/knowledge/glossary/thca.md)). - **Distillate**: a concentrate format, which may or may not contain semi-synthetics. ## Related terms [Delta-8 THC](https://genetixbay.com/knowledge/glossary/delta-8-thc.md), [THC](https://genetixbay.com/knowledge/glossary/thc.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md), [Distillate](https://genetixbay.com/knowledge/glossary/distillate.md) ## Sources 1. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. --- # High-frequency fertigation > High-frequency fertigation feeds small volumes of nutrient solution many times a day, keeping the root zone consistently moist and fed so small pots can produce large plants. - Canonical: https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.html - Also written: HFF, high frequency fertigation, high-frequency feeding, pulse feeding - Glossary category: Systems and media · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" High-frequency fertigation (HFF) means irrigating with nutrient solution several to many times per day, often from 4 to 20 or more small events in the light period, instead of watering thoroughly every few days. The [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) stays close to [container capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md) with a steady nutrient concentration, so water and nutrient stress never build up. ## In practice HFF is used mostly with [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) on [drip systems](https://genetixbay.com/knowledge/glossary/drip-irrigation.md), because they [drain](https://genetixbay.com/knowledge/glossary/runoff.md) fast and hold plenty of air even when wet. Each event is small, sized so that runoff accumulates to the target fraction over the day. The approach lets growers use smaller containers: the medium no longer has to store days of water. ## Myth check House position on [pot size](https://genetixbay.com/knowledge/glossary/pot-size.md): big things come in small packages if you push nutrients and water hard enough. The founder has harvested more than 4 oz (113 g) dry from a 16 oz (about 0.5 L) cup with high-frequency fertigation. Pot size is a trade-off against feeding frequency, not a fixed rule. Evidence: Grower practice, house-endorsed. See [drain-to-waste and crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md). ## Don't confuse with - **Crop steering**: may use HFF in its schedules, but deliberately varies [dryback](https://genetixbay.com/knowledge/glossary/dryback.md). ## Related terms [Fertigation](https://genetixbay.com/knowledge/glossary/fertigation.md), [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md), [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [Drip irrigation](https://genetixbay.com/knowledge/glossary/drip-irrigation.md), [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md) ## Read more - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) - [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 2. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # Hoagland solution > Hoagland solution is a classic 1950 hydroponic recipe by Hoagland and Arnon, still used as a research baseline: about 210 ppm N, 31 P, 235 K and 200 Ca. - Canonical: https://genetixbay.com/knowledge/glossary/hoagland-solution.html - Also written: Hoagland's solution, Hoagland nutrient solution, Hoagland and Arnon solution, half-strength Hoagland - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hoagland solution is a complete nutrient solution described by Dennis Hoagland and Daniel Arnon in their 1950 University of California circular, "The water-culture method for growing plants without soil". It is one of the most cited recipes in plant science and is often used at half strength as a research control. ## In practice Solution 1 uses [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md), [monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) and [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), plus iron and a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) mix. It works out to roughly 210 mg/L (ppm) N, 31 P, 235 K, 200 Ca, 48 Mg and 64 S. Solution 2 replaces part of the [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) with ammonium [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md). For cannabis, it is a sound educational starting point. Most modern cannabis recipes run more phosphorus and magnesium, and replace the original iron source with a modern [chelate](https://genetixbay.com/knowledge/glossary/chelate.md). ## Units and formula Solution 1 macros in mmol/L: 15 N, 1 P, 6 K, 5 Ca, 2 Mg, 2 S. ## Don't confuse with - **Commercial "Hoagland" powders**: may differ from the original in micronutrients or iron form. - **Feed chart**: a product schedule, not a defined recipe. ## Related terms [ppm of an element](https://genetixbay.com/knowledge/glossary/elemental-ppm.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ## Sources 1. Hoagland DR, Arnon DI. 1950. The water-culture method for growing plants without soil. California Agricultural Experiment Station Circular 347. https://archive.org/details/watercultureme3450hoag/ --- # Holocyclic and anholocyclic > Aphid life cycles with (holocyclic) or without (anholocyclic) a yearly sexual generation that lays overwintering eggs. - Canonical: https://genetixbay.com/knowledge/glossary/holocyclic.html - Also written: holocyclic, anholocyclic, holocycle, anholocycle - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A holocyclic [aphid](https://genetixbay.com/knowledge/glossary/aphid.md) has one sexual generation a year, usually in autumn, in which males and egg-laying females mate and lay eggs that overwinter; the rest of the year females reproduce by [parthenogenesis](https://genetixbay.com/knowledge/glossary/parthenogenesis.md). An anholocyclic aphid skips the sexual stage entirely and reproduces asexually all year. UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) describes both patterns among pest aphids. ## In practice Indoors, the distinction matters for two reasons. Anholocyclic populations, such as [rice root aphid](https://genetixbay.com/knowledge/glossary/root-aphid.md) in cannabis rooms, never pause. Holocyclic species such as the [cannabis aphid](https://genetixbay.com/knowledge/glossary/cannabis-aphid.md) can produce sexual forms and eggs after the flip to short days, so a room that seems clean can carry overwintering eggs into the next run. ## Don't confuse with - **Parthenogenesis**: the asexual reproduction both cycles use most of the year. - **Diapause**: dormancy; overwintering aphid eggs are in [diapause](https://genetixbay.com/knowledge/glossary/diapause.md). ## Related terms [Parthenogenesis](https://genetixbay.com/knowledge/glossary/parthenogenesis.md), [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Alate](https://genetixbay.com/knowledge/glossary/alate.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) - [Cannabis aphid (Phorodon cannabis): ID, life table, overwintering and control](https://genetixbay.com/knowledge/pests/cannabis-aphid.md) - [Root aphids (rice root aphid) on indoor cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/root-aphids.md) ## Sources 1. UC IPM. Pest Notes: Aphids (Publication 7404). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html --- # Home grow > Home grow is growing cannabis for personal use at your residence, permitted in some jurisdictions within plant-count, location and security limits. - Canonical: https://genetixbay.com/knowledge/glossary/home-grow.html - Also written: home cultivation, homegrow, growing at home, home growing, personal grow - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Home grow means cultivating cannabis at a private residence for your own use, not for sale. Where it is legal, it usually comes with conditions: a maximum number of plants per person or household, rules on where plants may be (indoors, outdoors, visible from the street), security and child-access requirements, a minimum age, and sometimes landlord or local consent. ## In practice A household in a place allowing four plants per residence can grow four, whether they are [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) or in flower, unless the rule distinguishes stages. Some places allow home grow for registered medical patients only, or set different limits for adult use. Others ban it completely even where retail sales are legal. Growing more than the limit, selling home-grown cannabis, or giving it away in exchange for anything of value can turn a legal hobby into a serious offence. GenetixBay's position is that growing your own is the most direct way to know what you are consuming: how it was grown, dried and [cured](https://genetixbay.com/knowledge/glossary/curing.md), and that it was not irradiated. That is an argument for legal home grow, never for breaking local law. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Personal cultivation limit**: the specific numeric cap that defines a legal home grow. - **Licensed production**: commercial growing under a licence, with tracking and testing. - **Decriminalisation**: reduced penalties, which may not make growing legal. ## Related terms [Personal cultivation limit](https://genetixbay.com/knowledge/glossary/personal-cultivation-limit.md), [Plant count limit](https://genetixbay.com/knowledge/glossary/plant-count-limit.md), [Possession limit](https://genetixbay.com/knowledge/glossary/possession-limit.md), [Decriminalisation vs legalisation](https://genetixbay.com/knowledge/glossary/decriminalisation.md) ## Read more - [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) --- # Homogenisation (sampling) > Homogenisation is grinding and mixing a sample so every portion the lab tests represents the whole; together with representative sampling it often matters more than the instrument. - Canonical: https://genetixbay.com/knowledge/glossary/homogenisation.html - Also written: homogenization, sample homogenisation, sample homogenization, sampling, representative sampling, sample prep, composite sample - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cannabis is not uniform. [Top colas](https://genetixbay.com/knowledge/glossary/cola.md), lower buds, larger and smaller flowers, and the outside versus the inside of a bud all differ in [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) density and moisture. Representative sampling means taking increments from across the batch according to a plan. Homogenisation means grinding and mixing those increments so that the few hundred milligrams actually weighed for analysis stand for the whole. ## In practice A single top bud can read several points higher than a composite of buds from the whole plant. Testing only the best-looking material is one route to [inflated labels](https://genetixbay.com/knowledge/glossary/label-inflation.md). Good practice for a home grower sending a sample: take several buds from the top, middle and lower canopy, grind them together, mix thoroughly and send a portion. Labs grind again and often run replicates. Regulators specify sample increment numbers per batch size; check local rules. ## Don't confuse with - **Homogeniser** (dairy/food): a device for emulsifying liquids. - **Batch**: the lot being represented; homogenisation is how a sample represents it. - **Measurement uncertainty**: lab estimates often exclude sampling error, which can be larger. ## Myth check A single "hero bud" test is not a batch result. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [Batch](https://genetixbay.com/knowledge/glossary/batch.md), [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md), [Measurement uncertainty](https://genetixbay.com/knowledge/glossary/measurement-uncertainty.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Ellison SLR, Williams A (eds). 2012. Eurachem/CITAC Guide: Quantifying Uncertainty in Analytical Measurement, 3rd edition. --- # Homozygous > A plant is homozygous at a locus when it carries two identical alleles there (AA or aa), so it passes the same allele to every offspring. - Canonical: https://genetixbay.com/knowledge/glossary/homozygous.html - Also written: homozygote, homozygosity, homozygotes - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A plant is homozygous at a [locus](https://genetixbay.com/knowledge/glossary/locus.md) when both copies of the [gene](https://genetixbay.com/knowledge/glossary/gene.md) are the same [allele](https://genetixbay.com/knowledge/glossary/allele.md), for example AA or aa. Every gamete it makes carries that allele, so for that trait it breeds true. A line can be homozygous at one locus and [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) at thousands of others. ## In practice "Stable" in breeder talk means "homozygous for the traits that matter". [Inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) (sib crossing, backcrossing, [selfing](https://genetixbay.com/knowledge/glossary/selfing.md)) raises homozygosity generation by generation. One generation of selfing removes, on average, half of the remaining heterozygosity; full-sib mating removes it more slowly. A plant that is homozygous for its key traits is valuable as a parent: cross it to anything and it donates the same alleles every time, which makes its offspring predictable. That is the logic behind IBLs and inbred parents for [F1 seed](https://genetixbay.com/knowledge/glossary/f1.md). The price is that high homozygosity across the whole genome also exposes deleterious recessives, which is [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md). ## Units and formula Expected heterozygosity after n generations of selfing, starting from a fully heterozygous locus: (1/2)^n. After S1: 50%; after S3: 12.5%; after S6: about 1.6%. ## Don't confuse with - **Heterozygous**: two different alleles at the locus. - **Uniform**: a line can look uniform while carrying hidden heterozygosity at many loci. ## Related terms [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [True breeding](https://genetixbay.com/knowledge/glossary/true-breeding.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md) ## Read more - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 --- # Honeydew > The sugary liquid excreted by sap-feeding insects such as aphids, whiteflies, mealybugs and soft scales; it makes leaves sticky and feeds sooty mould. - Canonical: https://genetixbay.com/knowledge/glossary/honeydew.html - Also written: honey dew - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Honeydew is the excess sugary sap that phloem-feeding insects excrete. UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) lists [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), [leafhoppers](https://genetixbay.com/knowledge/glossary/leafhopper.md), [mealybugs](https://genetixbay.com/knowledge/glossary/mealybug.md), soft scales and [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) as common producers, with both immatures and adults producing it. On cannabis it shows as shiny, sticky leaf [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) beneath a colony. ## In practice Honeydew is a diagnostic clue: sticky leaves point to a sap feeder above, not to a mite. It grows black [sooty mould](https://genetixbay.com/knowledge/glossary/sooty-mould.md) that cuts light, and ants that farm honeydew defend aphids and mealybugs from their [natural enemies](https://genetixbay.com/knowledge/glossary/biological-control.md). Washing it off treats the symptom; the colony is the problem. ## Don't confuse with - **Sticky (slang)**: resinous buds, nothing to do with pests. - **Guttation droplets**: water from leaf margins, not sugar. ## Related terms [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md), [Mealybug](https://genetixbay.com/knowledge/glossary/mealybug.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) - [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) - [Mealybugs and root mealybugs on cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/mealybugs.md) ## Sources 1. UC IPM. Sooty Mold. https://ipm.ucanr.edu/home-and-landscape/sooty-mold/ --- # Hop latent viroid > HLVd, a small infectious RNA that spreads through sap and tools, causing stunting, brittle stems, small loose buds and reduced resin in cannabis; called dudding. - Canonical: https://genetixbay.com/knowledge/glossary/hop-latent-viroid.html - Also written: HLVd, hop latent viroid disease, dudding, dudding disease, duds, dudded plants - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hop latent viroid (HLVd) is a [viroid](https://genetixbay.com/knowledge/glossary/viroid.md), a tiny circular RNA of about 256 nucleotides with no protein coat, that infects hops and cannabis. In cannabis it causes "dudding": plants that grow slowly, with shorter [internodes](https://genetixbay.com/knowledge/glossary/internode.md), brittle stems, smaller and looser flowers, and less resin. Many infected plants show few or no symptoms for long periods, especially [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md) in veg, which is how it spreads unnoticed. ## In practice HLVd moves in sap: on scissors, razors, hands and clones taken from infected mothers. It is also found in roots and [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) solution, and seed transmission has been reported at low rates. Detection needs a lab test, typically RT-qPCR on root or leaf tissue. There is no cure for an infected plant. Clean-up relies on testing mothers, discarding positives, sterilising tools between plants, and recovering clean stock by [meristem tip culture](https://genetixbay.com/knowledge/glossary/meristem-culture.md). ## Myth check "[Clone decline](https://genetixbay.com/knowledge/glossary/genetic-drift.md)" or "genetic drift" in old cuts is a pathogen story, not a genetics story. GenetixBay's house position is that there is zero genetic drift in kept cuts apart from pathogens such as HLVd; the founder keeps cuts more than 40 years old with no decline. Label: Supported. See [HLVd and viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Don't confuse with - **Nutrient lockout**: responds to root-zone fixes; HLVd does not. - **Hermaphrodite traits**: genetic; HLVd is infectious. ## Related terms [Viroid](https://genetixbay.com/knowledge/glossary/viroid.md), [Plant virus](https://genetixbay.com/knowledge/glossary/plant-virus.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) ## Read more - [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ## Sources 1. Adkar-Purushothama CR, Sano T, Perreault J-P, 2023. Hop latent viroid: a hidden threat to the cannabis industry. Viruses 15(3):681. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10053334/ 2. Punja ZK et al., 2025. Hop latent viroid transmission, spread and longevity in cannabis; meristem tip culture. Plants 14(5):830. https://www.mdpi.com/2223-7747/14/5/830 3. Oregon State University Extension. Hop latent viroid in hemp (EM 9570). https://extension.oregonstate.edu/catalog/em-9570-hop-latent-viroid-hemp --- # Hopperburn > Yellowing and browning that starts at leaf tips and margins in a V shape, caused by potato leafhopper feeding blocking leaf veins. - Canonical: https://genetixbay.com/knowledge/glossary/hopperburn.html - Also written: hopper burn, leafhopper burn - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hopperburn is the injury caused by potato [leafhopper](https://genetixbay.com/knowledge/glossary/leafhopper.md) (Empoasca fabae) feeding. The insect's saliva disrupts the leaf's vascular tissue, so the leaf yellows, then browns, starting at the tip and margins in a V-shaped pattern, and may curl. UConn Extension and Utah State [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) notes describe it. ## In practice Hopperburn is easily mistaken for nutrient [tip burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) or [heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md). Check leaf undersides for small, wedge-shaped green leafhoppers that run sideways, and use yellow [sticky cards](https://genetixbay.com/knowledge/glossary/sticky-trap.md) outdoors. On cannabis it is usually a minor, outdoor problem; beet leafhopper and [curly top virus](https://genetixbay.com/knowledge/glossary/beet-curly-top-virus.md) matter far more. ## Don't confuse with - **Nutrient burn**: tip burn from high [EC](https://genetixbay.com/knowledge/glossary/ec.md), no insects present. - **Curly top**: a [virus](https://genetixbay.com/knowledge/glossary/plant-virus.md) spread by the beet leafhopper, with curling and stunting. ## Related terms [Leafhopper](https://genetixbay.com/knowledge/glossary/leafhopper.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md) ## Read more - [Leafhoppers on cannabis: beet leafhopper, curly top and hopperburn](https://genetixbay.com/knowledge/pests/leafhoppers.md) ## Sources 1. Legrand, A., 2023. Beware of hopperburn. UConn Extension. https://extension.uconn.edu/publication/beware-of-hopperburn-2 2. Utah State University Extension. Potato leafhopper (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-potato-leafhopper --- # Horticultural oil > A refined petroleum or plant oil sprayed to smother soft-bodied pests and eggs and suppress powdery mildew on contact; used only on foliage, never on flowers. - Canonical: https://genetixbay.com/knowledge/glossary/horticultural-oil.html - Also written: horticultural oils, mineral oil, paraffinic oil, summer oil, dormant oil, plant oil spray - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Horticultural oil is a highly refined oil, either paraffinic mineral oil or a plant oil such as canola, cottonseed or soybean, mixed with an emulsifier so it spreads in water. It kills mites, [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), [whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md) nymphs, scale crawlers and eggs by smothering them and disrupting their membranes, and it can suppress [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md). It has no residual action once dry. ## In practice Oils are contact tools for veg and [mother plants](https://genetixbay.com/knowledge/glossary/mother-plant.md). Coverage of leaf undersides decides success, and repeat sprays are needed to catch hatching eggs. Risks: oils can burn leaves when applied in heat (above about 30 °C / 86 °F), under strong lights, on drought-stressed plants or close to [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) applications. They should never touch flowers, where they coat [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) and leave residue. Many oil products are registered pesticides; check what is registered for cannabis locally, and test on a few leaves first. ## Don't confuse with - **Neem oil**: may contain [azadirachtin](https://genetixbay.com/knowledge/glossary/neem-oil.md), an insect growth disruptor. - **Insecticidal soap**: fatty-acid salts that break down cell membranes. - **Essential oil sprays**: aromatic plant extracts; separate actives with their own rules. ## Related terms [Neem oil](https://genetixbay.com/knowledge/glossary/neem-oil.md), [Insecticidal soap](https://genetixbay.com/knowledge/glossary/insecticidal-soap.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md), [Sulfur burner](https://genetixbay.com/knowledge/glossary/sulfur-burner.md), [Scale insect](https://genetixbay.com/knowledge/glossary/scale-insect.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ## Sources 1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 2. UC IPM. Pest Notes: Aphids (Publication 7404). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html --- # HPA > HPA (high-pressure aeroponics) mists roots with very fine droplets from a high-pressure pump and accumulator, giving maximum aeration but little margin for failure. - Canonical: https://genetixbay.com/knowledge/glossary/hpa.html - Also written: high-pressure aeroponics, high pressure aeroponics, HP aero, true aeroponics, HPA aeroponics - Glossary category: Systems and media · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" High-pressure aeroponics delivers nutrient solution to suspended roots as a fine mist, produced by forcing solution through small nozzles at high pressure. A typical system has a high-pressure pump filling a pressurised accumulator tank, a solenoid valve and a cycle timer that fires bursts of a few seconds every few minutes. Commonly quoted targets are droplets of about 20-50 µm at roughly 5.5-8 bar (80-120 psi). ## In practice HPA gives roots unmatched oxygen access and very fast growth when everything works. But the margin is tiny: with no reservoir of water around the roots, a stuck solenoid, clogged nozzle or power cut can dry and kill roots within minutes. Successful growers use fine filtration, redundant nozzles, alarms and battery backup, and keep root chambers dark and cool. It is an advanced system; GenetixBay suggests mastering [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) first. ## Don't confuse with - **LPA**: low-pressure spray with large droplets and often a pool of solution. - **Fogponics**: ultrasonic fog, not pressure-driven. ## Related terms [Aeroponics](https://genetixbay.com/knowledge/glossary/aeroponics.md), [Fogponics](https://genetixbay.com/knowledge/glossary/fogponics.md), [Root zone](https://genetixbay.com/knowledge/glossary/root-zone.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md) ## Read more - [High-pressure aeroponics (HPA)](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) ## Sources 1. Lakhiar IA, Gao J, Syed TN, Chandio FA, Buttar NA, 2018. Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics. Journal of Plant Interactions 13(1):338–352. https://doi.org/10.1080/17429145.2018.1472308 2. Eldridge BM, Manzoni LR, Graham CA, et al., 2020. Getting to the roots of aeroponic indoor farming. New Phytologist 228:1183–1192. https://doi.org/10.1111/nph.16780 --- # HPLC > HPLC (high-performance liquid chromatography) separates compounds dissolved in a liquid under pressure; it is the standard cannabis potency method because it measures acid cannabinoids without heating them. - Canonical: https://genetixbay.com/knowledge/glossary/hplc.html - Also written: high-performance liquid chromatography, high pressure liquid chromatography, HPLC-UV, HPLC-DAD, UHPLC, liquid chromatography - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" HPLC pumps a liquid (the mobile phase) carrying the dissolved sample through a column packed with fine particles. Compounds interact with the packing differently and leave the column at different times. A detector, usually UV or diode-array (DAD), measures each compound as it exits, and comparison with reference standards turns peak size into concentration. ## In practice HPLC runs at or near room temperature, so [THCA](https://genetixbay.com/knowledge/glossary/thca.md) and [THC](https://genetixbay.com/knowledge/glossary/thc.md), CBDA and [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) appear as separate peaks. That's why it's the default potency method for flower and concentrates. A typical cannabis method resolves around 10-17 [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). Its weaknesses: compounds without a reference standard, or that co-elute (come out together), can be misidentified or missed, and results still depend on [sample prep](https://genetixbay.com/knowledge/glossary/homogenisation.md) and calibration. UHPLC is a faster, higher-pressure variant. ## Don't confuse with - **GC**: heats the sample and decarboxylates acids unless derivatised; used for [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and [residual solvents](https://genetixbay.com/knowledge/glossary/residual-solvents.md). - **LC-MS**: liquid chromatography coupled to mass spectrometry; more specific, used for pesticides and [mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md). - **HPLC grade**: a purity grade for solvents, not a test. ## Related terms [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md), [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md), [LC-MS](https://genetixbay.com/knowledge/glossary/lc-ms.md), [Acid vs neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md), [LOQ](https://genetixbay.com/knowledge/glossary/loq.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Berman P, Futoran K, Lewitus GM, Mukha D, Benami M, Shlomi T, Meiri D. 2018. A new ESI-LC/MS approach for comprehensive metabolic profiling of phytocannabinoids in Cannabis. Scientific Reports 8:14280. https://doi.org/10.1038/s41598-018-32651-4 2. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. --- # HPS > HPS (high-pressure sodium) is a gas-discharge lamp with orange-yellow light peaking near 589 nm; it was the standard flowering light before LEDs. - Canonical: https://genetixbay.com/knowledge/glossary/hps.html - Also written: high-pressure sodium, high pressure sodium, sodium lamp, DE HPS, double-ended HPS, SE HPS - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A high-pressure sodium (HPS) lamp produces light by passing an arc through [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) vapour (with mercury and xenon) inside a ceramic tube. Its spectrum is concentrated in yellow and orange around 589 nm, with little blue. It needs a ballast to start and run. Single-ended (SE) lamps screw into a socket; double-ended (DE) lamps are held at both ends and are more efficient. ## In practice For decades a 600 W or 1,000 W HPS over a 1.2 × 1.2 m (4 × 4 ft) area was the flowering standard. Modern DE HPS fixtures reach about 1.7–2.1 [µmol/J](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), well below good [LEDs](https://genetixbay.com/knowledge/glossary/led.md). HPS also emits a lot of radiant (infrared) heat that warms leaf surfaces directly. Nelson and Bugbee (2015) showed leaves under HPS run warmer than under LED at the same air temperature and [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), which changes ideal room settings: HPS rooms are often run cooler in air temperature. Bulbs lose output with age; many growers replace them every 2–4 cycles. Handle with care: lamps contain mercury and get extremely hot. ## Don't confuse with - **Metal halide (MH)**: a related discharge lamp with bluer light, traditionally for veg. - **CMH**: [ceramic metal halide](https://genetixbay.com/knowledge/glossary/cmh.md), a broader-spectrum discharge lamp. - **LED**: solid-state, more efficient, less radiant heat at the canopy. ## Myth check [LED vs HPS](https://genetixbay.com/knowledge/glossary/led-vs-hps.md) for final quality is an open question at GenetixBay: an open [Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md). See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [LED](https://genetixbay.com/knowledge/glossary/led.md), [Metal halide](https://genetixbay.com/knowledge/glossary/metal-halide.md), [CMH](https://genetixbay.com/knowledge/glossary/cmh.md), [LED vs HPS](https://genetixbay.com/knowledge/glossary/led-vs-hps.md), [Photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Sources 1. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # HST > HST (high-stress training) covers training methods that deliberately cut, crush or break plant tissue, such as topping, FIM and supercropping, to reshape growth. - Canonical: https://genetixbay.com/knowledge/glossary/hst.html - Also written: high-stress training, high stress training, high stress techniques - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" High-stress training is an umbrella term for techniques that wound the plant on purpose: removing [growing tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) (topping, [FIM](https://genetixbay.com/knowledge/glossary/fim.md)), crushing and bending stems ([supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md)), or heavy pruning. The wound redirects hormones and growth, but the plant needs time to recover, usually a few days to a week per event. ## In practice HST is done in veg, or in the first week or two of flower for supercropping, on healthy, well-rooted plants. Space events out and never stack several at once on a stressed plant. [Photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md) tolerate HST well because veg can simply be extended. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) do not, because they cannot buy back lost days; [LST](https://genetixbay.com/knowledge/glossary/lst.md) is the better tool for them. ## Myth check House position: stem snapping (supercropping) gives better buds, and the founder does it all the time. This is grower practice, house-endorsed; controlled trials are lacking. Stress does not reliably raise potency, and stress beyond what the plant can recover from costs yield. See [HST and supercropping](https://genetixbay.com/knowledge/training/hst-supercropping.md). ## Don't confuse with - **LST**: bending without wounding. - **Stress (environmental)**: heat, drought or [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md); HST is mechanical. ## Related terms [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Topping](https://genetixbay.com/knowledge/glossary/topping.md), [FIM](https://genetixbay.com/knowledge/glossary/fim.md), [Supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md), [Monster cropping](https://genetixbay.com/knowledge/glossary/monster-cropping.md) ## Read more - [HST and supercropping: controlled stem crushing](https://genetixbay.com/knowledge/training/hst-supercropping.md) --- # Humic acid > Humic acid is a large, dark organic fraction of decomposed matter that binds nutrients and may modestly aid root growth; effects in cannabis are small and inconsistent. - Canonical: https://genetixbay.com/knowledge/glossary/humic-acid.html - Also written: humic acids, humates, humic substances, potassium humate, leonardite extract - Glossary category: Nutrients · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Humic acid is the part of humic substances that dissolves in alkaline solution but precipitates when acidified. It is a mix of large, complex organic molecules from decomposed plant matter, usually extracted from leonardite, [peat](https://genetixbay.com/knowledge/glossary/peat.md) or lignite. It binds metal ions and adds [cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md). ## In practice Growers add humic products to soil and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) as a "root stimulant". In soil it can improve structure, water holding and [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) availability. Bernstein and colleagues tested humic acid supplementation on [medical cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md) and found effects on the plant's chemical profile were limited compared with N, P and K changes. In hydro, humic acid can stain reservoirs, foam and precipitate at low [pH](https://genetixbay.com/knowledge/glossary/ph.md), and may feed biofilm. Expect modest effects at best (Evidence: Contested). ## Don't confuse with - **Fulvic acid**: the smaller fraction that stays soluble at any pH. - **Compost tea**: a microbial brew, not an extract. - **Humus**: the stable organic matter in soil as a whole. ## Related terms [Fulvic acid](https://genetixbay.com/knowledge/glossary/fulvic-acid.md), [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md), [Organic fertiliser](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md), [Biostimulant](https://genetixbay.com/knowledge/glossary/biostimulant.md) ## Read more - [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) ## Sources 1. Bernstein N, Gorelick J, Zerahia R, Koch S. 2019. Impact of N, P, K, and humic acid supplementation on the chemical profile of medical cannabis (Cannabis sativa L). Frontiers in Plant Science 10:736. https://doi.org/10.3389/fpls.2019.00736 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Humidifier > A humidifier adds water vapour to the air to raise relative humidity, used mostly for clones, seedlings and veg, or dry climates. - Canonical: https://genetixbay.com/knowledge/glossary/humidifier.html - Also written: humidifiers, ultrasonic humidifier, evaporative humidifier, mister, fogger - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A humidifier raises humidity by adding water to the air. Ultrasonic units vibrate water into a fine mist that evaporates; evaporative units pass air over a wet wick; steam units boil water. Each evaporating litre also cools the air slightly, because evaporation absorbs heat. ## In practice Humidifiers matter most early on: clones like about 70–85% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and early veg 60–70%, which can be hard to hold in dry winter air or under strong [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md). Put the unit on a humidistat or controller and keep it out of the direct line of the canopy so droplets do not settle on leaves. Ultrasonic humidifiers spray out whatever is dissolved in the water. With [hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md), that means white mineral dust on leaves, fans and fixtures. Use [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) or distilled water in ultrasonics. Clean the tank weekly; stagnant water grows bacteria and fungi that get misted straight into the room. In flower, needing a humidifier usually means the exhaust is running too hard or the room is [too hot](https://genetixbay.com/knowledge/glossary/heat-stress.md); adjust those first. ## Don't confuse with - **Dehumidifier**: does the opposite. - **Fogponics fogger**: mists nutrient solution onto roots, a growing system rather than room humidification. ## Related terms [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) ## Read more - [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) --- # Humidity pack > A salt-solution sachet sold to hold a sealed container at a fixed relative humidity; GenetixBay regards them as a marketing gimmick that robs terpenes. - Canonical: https://genetixbay.com/knowledge/glossary/humidity-pack.html - Also written: humidity packs, two-way humidity pack, two-way humidity control, humidity sachet, 62% pack, 58% pack, humidity control pack - Glossary category: Harvest, drying and curing · Evidence: Myth - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A humidity pack is a sealed pouch of saturated salt solution behind a vapour-permeable membrane. It absorbs or releases water to pull a closed container's air toward a set [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), commonly 58% or 62%. "Two-way" means it can both add and remove moisture. ## In practice They are widely sold for jars and storage. GenetixBay doesn't recommend them. House position (Myth for the quality claims): - They are a marketing gimmick. The pro-pack data is essentially the manufacturer's own. - They rob [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md): the pack and its membrane give the jar's volatiles somewhere else to go. - Curing is a slow decline in moisture, not holding moisture constant, which is exactly what a pack is designed to do. If buds are [too dry](https://genetixbay.com/knowledge/glossary/over-drying.md) and you need to add moisture, put a fresh bud in the jar instead. To keep stock in range, start with a good dry, fill airtight [glass jars](https://genetixbay.com/knowledge/glossary/curing-jar.md) well, and store them dark and cool. ## Don't confuse with - **Desiccant**: removes moisture only, for seeds and electronics. - **Hygrometer**: measures RH, doesn't control it. - **Water activity target**: the goal (0.55-0.65 aw), not a product. ## Myth check "Humidity packs keep your stash fresher" is a Myth in the house view. A well-dried, well-cured bud in a full, airtight, dark jar does the job. See [curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Burping](https://genetixbay.com/knowledge/glossary/burping.md), [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (salt-based humidity control sachets for aw below 0.68). https://sn.astm.org/node/2445/printable/print --- # Humulene > Humulene (alpha-humulene) is a woody, earthy, hop-like sesquiterpene, an isomer of beta-caryophyllene that usually appears alongside it in cannabis profiles. - Canonical: https://genetixbay.com/knowledge/glossary/humulene.html - Also written: alpha-humulene, α-humulene, alpha-caryophyllene, α-caryophyllene - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Humulene, properly alpha-humulene, is a monocyclic [sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) first identified in hops (*Humulus lupulus*), cannabis's closest cultivated relative. It smells woody, earthy and herbal, the "noble hop" note in beer. Its older name, alpha-caryophyllene, reflects that it is an isomer of [beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md); the two are often produced by the same [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) synthase. ## In practice On a [terpene panel](https://genetixbay.com/knowledge/glossary/terpene-test.md), humulene typically reads at roughly a third of the beta-caryophyllene figure, around 0.05-0.3% w/w in flower. If a [COA](https://genetixbay.com/knowledge/glossary/coa.md) shows high caryophyllene with no humulene at all, it's worth asking whether humulene was in the lab's method. As a sesquiterpene it is fairly persistent through drying and storage. ## Don't confuse with - **Humulone**: a bitter acid from hops, not a terpene and not in cannabis. - **Beta-caryophyllene**: its isomer, spicier and peppery. - **Caryophyllene oxide**: an oxidation product of beta-caryophyllene, not of humulene (humulene epoxides exist but are seldom reported). ## Related terms [Beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md), [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Hybrid > A hybrid is the offspring of two genetically different parents; almost all modern cannabis is hybrid, built from crosses between landrace-derived and other lines. - Canonical: https://genetixbay.com/knowledge/glossary/hybrid.html - Also written: hybrids, hybrid strain, hybridisation, hybridization, crossbred - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A hybrid is the offspring of a cross between genetically different parents. In crop breeding it often means a specific [F1](https://genetixbay.com/knowledge/glossary/f1.md) between two [inbred lines](https://genetixbay.com/knowledge/glossary/inbred-line.md); in cannabis it usually just means any cultivar with mixed ancestry. ## In practice Almost everything on the cannabis market today is a hybrid, often many generations of hybrids crossed together. Modern lines trace back to crosses made from the 1960s on, between [landraces](https://genetixbay.com/knowledge/glossary/landrace.md) from Afghanistan, Thailand, Mexico, Colombia, India and elsewhere, and later between the hybrids themselves. Only a few outlier landraces remain unmixed. So "hybrid" on a dispensary label is not a meaningful third category beside indica and sativa. It is the default state of the plant. What matters is documented lineage, selection and test results. ## Don't confuse with - **F1 hybrid**: a specific cross, usually of inbred parents, with uniform offspring. - **Polyhybrid**: a hybrid with many different lines in its recent ancestry. - **Landrace**: a locally adapted traditional population, not a recent cross. ## Myth check Indica, sativa and "hybrid" describe plant shape at most, not species or effect. Cannabis is one species, *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)* L. (McPartland 2018). See [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md). ## Related terms [F1](https://genetixbay.com/knowledge/glossary/f1.md), [Polyhybrid](https://genetixbay.com/knowledge/glossary/polyhybrid.md), [Heterosis](https://genetixbay.com/knowledge/glossary/heterosis.md), [Cross](https://genetixbay.com/knowledge/glossary/cross.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Indica](https://genetixbay.com/knowledge/glossary/indica.md) ## Read more - [How hybrid 'strains' emerged](https://genetixbay.com/knowledge/genetics-history/how-hybrid-strains-emerged.md) - [Polyhybrids vs landraces: what each gives a breeder](https://genetixbay.com/knowledge/breeding/polyhybrids-vs-landraces.md) ## Sources 1. McPartland JM. 2018. Cannabis systematics at the levels of family, genus, and species. Cannabis and Cannabinoid Research 3(1):203-212. https://doi.org/10.1089/can.2018.0039 2. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 --- # Hydrogen peroxide > Hydrogen peroxide (H₂O₂) is an oxidising sanitiser used to clean hydroponic equipment and reservoirs; it breaks down quickly into water and oxygen and kills beneficial microbes too. - Canonical: https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.html - Also written: H2O2, H₂O₂, peroxide, food-grade peroxide, hydrogen peroxide reservoir - Glossary category: Systems and media · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hydrogen peroxide is a reactive oxygen compound that kills microbes by oxidation, then decomposes into water and oxygen. In growing it is used to sanitise reservoirs, tubing, trays and tools between runs, and sometimes dosed into a reservoir to suppress pathogens in a sterile-style system. ## In practice Retail peroxide is commonly 3%; stronger 12-35% grades are corrosive and need gloves and eye protection. In a running reservoir, peroxide breaks down within hours to a day or so, faster in warm, organic-rich solution, so it gives no lasting protection unless re-dosed. It does not distinguish good from bad microbes: it will wipe out a beneficial programme, and high doses damage root tips. Dosing guidance varies widely. The oxygen it releases is brief and small; it is not a substitute for aeration and cool water. ## Don't confuse with - **Dissolved oxygen**: oxygen gas held in solution; peroxide is a separate oxidiser. - **Hypochlorous acid / chlorine**: other oxidising sanitisers with longer-lasting residuals. ## Myth check "Peroxide oxygenates roots" overstates it; oxygen release is brief. Using it to rescue [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) can help clean the system but does not fix warm, stagnant conditions that caused it. ## Related terms [Sterile reservoir](https://genetixbay.com/knowledge/glossary/sterile-reservoir.md), [Beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) ## Read more - [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) ## Sources 1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ --- # Hydroponics > Hydroponics is growing plants without soil, feeding roots a complete mineral nutrient solution either directly in water or through an inert medium. - Canonical: https://genetixbay.com/knowledge/glossary/hydroponics.html - Also written: hydro, hydroponic, hydroponic growing, water culture, hydroponically - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Hydroponics is the cultivation of plants with their roots in a nutrient solution rather than soil. All mineral nutrients come from dissolved salts. Roots sit either directly in water ([deep water culture](https://genetixbay.com/knowledge/glossary/dwc.md), NFT, aeroponics) or in an inert support medium such as rockwool, [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md) or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) that holds little or no nutrition of its own. ## In practice Because the grower supplies every element, hydro gives fast growth and precise control, and mistakes show quickly. The key numbers to manage are [EC](https://genetixbay.com/knowledge/glossary/ec.md) (often about 1.0-2.4 mS/cm depending on stage), pH (about 5.5-6.5), solution temperature (about 18-22 °C, 64-72 °F) and dissolved oxygen. Systems are either [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) (solution returns to a reservoir) or [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md) (each feed is used once). Many growers count coco and rockwool [fertigation](https://genetixbay.com/knowledge/glossary/fertigation.md) as hydroponics; purists reserve the word for systems with roots in water. ## Don't confuse with - **Soilless**: any medium without mineral soil, including peat mixes; not always fed like hydro. - **Aquaponics**: hydroponics fed by fish waste via a bacterial biofilter. ## Myth check House position: a well-grown hydro run gives a well-grown living-soil run a run for its money, even on taste. Plants mostly don't care where ions come from. Whether soil biology adds something extra is an open question for a blind [Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md). ## Related terms [Soilless](https://genetixbay.com/knowledge/glossary/soilless.md), [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [NFT](https://genetixbay.com/knowledge/glossary/nft.md), [Drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), [Recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md) ## Read more - [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Hype strain > A hype strain is a cultivar name in heavy demand because of marketing or social media, regardless of how stable or distinctive the genetics are. - Canonical: https://genetixbay.com/knowledge/glossary/hype-strain.html - Also written: hype strains, hyped strain, flavour of the month, fotm strain, hype cut - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A hype strain is a name that everyone wants this season. Demand comes from [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md), influencer posts, competition wins and scarcity, not necessarily from tested genetics. ## In practice Hype strains are typically crossed into everything within a year: every vendor offers "[hype name] x something". The original may be a single [clone-only cut](https://genetixbay.com/knowledge/glossary/clone-only.md); much of what is sold under the name is unrelated or a one-generation cross. Expect wide variation between packs and between dispensary jars carrying the same label. To judge one, ignore the name and ask for the evidence: parents, generations, tester reports, [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md), lab results from more than one source. Treat potency numbers on the label with suspicion. ## Don't confuse with - **Elite cut**: a proven individual, which may or may not be hyped. - **Classic**: a line or cut with a long, documented track record. ## Myth check "Everything tastes the same now." GenetixBay position: the evidence shows commercial cannabis converging on a few chemical profiles (Smith et al. 2022), driven partly by hype cycles that cross the same few cuts into everything. See [why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md). ## Related terms [Drop](https://genetixbay.com/knowledge/glossary/drop.md), [Renamed cut](https://genetixbay.com/knowledge/glossary/renamed-cut.md), [Pollen chucker](https://genetixbay.com/knowledge/glossary/pollen-chucker.md), [Candy terps](https://genetixbay.com/knowledge/glossary/candy-terps.md), [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md) ## Read more - [Why strain names are unreliable: what genetic studies show](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Hypocotyl > The section of seedling stem between the root and the cotyledons; it elongates to lift the seed leaves above the medium. - Canonical: https://genetixbay.com/knowledge/glossary/hypocotyl.html - Also written: seedling stem, hypocotyl stem, stem below the cotyledons - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The hypocotyl is the part of the embryonic axis below the [cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) and above the root. After the [radicle](https://genetixbay.com/knowledge/glossary/radicle.md) emerges, the hypocotyl lengthens in a hook shape, pushes up through the medium, then straightens to raise the cotyledons into the light. Its length is controlled largely by light signals perceived by [phytochromes](https://genetixbay.com/knowledge/glossary/phytochrome.md) and cryptochromes. ## In practice A long, thin, floppy hypocotyl is the classic "stretched [seedling](https://genetixbay.com/knowledge/glossary/seedling.md)". It means too little light (or too little blue, or a lamp much too far away), sometimes combined with heat. Seedlings typically do fine around 100-300 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) at canopy; very dim windowsills give leggy hypocotyls. Growers often bury a stretched hypocotyl deeper at transplant. Cannabis can root along a buried stem, and the plant gains support. Keep the cotyledons above the surface. The hypocotyl is also the tissue most attacked by [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) fungi, which pinch it at the soil line. ## Don't confuse with - **Epicotyl**: the stem above the cotyledons, carrying the [first true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md). - **Internode**: the stem length between two nodes on an established plant. - **Radicle**: the embryonic root below it. ## Related terms [Cotyledon](https://genetixbay.com/knowledge/glossary/cotyledon.md), [Radicle](https://genetixbay.com/knowledge/glossary/radicle.md), [True leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md), [Phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md) ## Read more - [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # IBL > An IBL (inbred line) is a seed line that has been inbred and selected over many generations until it breeds true for its main traits, giving uniform offspring. - Canonical: https://genetixbay.com/knowledge/glossary/ibl.html - Also written: IBLs, in-bred line, stabilised line, stabilized line, stable line - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" IBL stands for [inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md). In cannabis it means a seed line taken through many generations of closely related crosses (sib crosses, backcrosses or selfing) with selection each generation, until it breeds true: its seed reliably produces plants of the same type. An IBL is [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) at most of the loci that define its traits. ## In practice A real IBL is slow, expensive work: typically six or more generations, large populations at each step, and strict culling for herms, weak vigour and off-types. The pay-off is a line you can rely on, and an ideal parent for making uniform [F1](https://genetixbay.com/knowledge/glossary/f1.md) [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md), because it passes the same alleles every time. IBLs also preserve a type. Many classic lines and some [landraces](https://genetixbay.com/knowledge/glossary/landrace.md) survive only because someone kept them going as [open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md) or inbred seed lines rather than chasing new crosses. Ask for proof. A line called "IBL" should come with its generation history, population sizes and [herm rates](https://genetixbay.com/knowledge/glossary/herm-threshold.md) from tester grows. ## Don't confuse with - **Landrace**: a traditional, locally adapted population, often more variable than an IBL. - **Clone-only**: a single genotype kept by cuttings, not a seed line. - **Polyhybrid**: a recent mix of many lines, the opposite of an IBL. - **Inbreeding depression**: the risk inbreeding carries; good IBL work culls it. ## Related terms [Inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md), [True breeding](https://genetixbay.com/knowledge/glossary/true-breeding.md), [Stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md), [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [F1](https://genetixbay.com/knowledge/glossary/f1.md), [Line breeding](https://genetixbay.com/knowledge/glossary/line-breeding.md) ## Read more - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 --- # Immobile nutrient > An immobile nutrient stays where it is first deposited, so its deficiency shows on young leaves and growing tips first: Ca, S, Fe, Mn, B, Cu. - Canonical: https://genetixbay.com/knowledge/glossary/immobile-nutrient.html - Also written: immobile nutrients, immobile elements, non-mobile nutrient, phloem-immobile nutrient - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An immobile nutrient is an element that, once built into a leaf, cannot be readily moved through the phloem to other tissue. New growth depends entirely on current supply from the roots. Calcium, [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md), iron, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md), [boron](https://genetixbay.com/knowledge/glossary/boron.md) and copper are usually classed as immobile or poorly mobile. ## In practice When new growth is pale, distorted or dying while old leaves look fine, suspect an immobile nutrient. [Interveinal yellowing](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) on the newest leaves points to iron; distorted, spotted new leaves to calcium or boron; even pale new growth to sulfur. Calcium is a special case: it moves only with water in the xylem, so low [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) under high humidity can starve new growth even when the feed holds plenty. Because these elements depend on root uptake, [pH](https://genetixbay.com/knowledge/glossary/ph.md) problems often show up here first. ## Don't confuse with - **Mobile nutrient**: remobilised from old leaves; symptoms start low. - **Unavailable**: a nutrient can be present but [locked out](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md) by pH; mobility is about movement inside the plant. ## Related terms [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md), [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [Iron](https://genetixbay.com/knowledge/glossary/iron.md), [Boron](https://genetixbay.com/knowledge/glossary/boron.md), [Nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) ## Read more - [Mobile vs immobile nutrients: reading old vs new leaves](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) - [Yellow new growth on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Inbred line > Inbreeding is mating between related plants, which raises homozygosity; an inbred line is the resulting population, measured by the inbreeding coefficient F. - Canonical: https://genetixbay.com/knowledge/glossary/inbred-line.html - Also written: inbred lines, inbreeding, inbred population, inbreeding coefficient - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Inbreeding is mating between relatives: siblings, parent and offspring, or a plant with itself. It makes offspring more [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) because relatives share [alleles](https://genetixbay.com/knowledge/glossary/allele.md) inherited from common ancestors. A population produced this way is an inbred line. The degree of inbreeding is measured by the inbreeding coefficient F, the probability that both alleles at a locus are identical by descent. ## In practice Breeders inbreed on purpose to fix traits and to make parents that pass predictable alleles. The same process exposes [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) defects, so every generation needs culling. Some species tolerate inbreeding well; cannabis, an [outcrossing](https://genetixbay.com/knowledge/glossary/outcross.md) species, often shows [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md) after several generations if selection is weak. The cannabis term [IBL](https://genetixbay.com/knowledge/glossary/ibl.md) (inbred line) usually implies a finished, stable product. "Inbred line" in general plant breeding just means any population made by inbreeding. ## Units and formula Starting from non-inbred parents, F after one generation of: [selfing](https://genetixbay.com/knowledge/glossary/selfing.md) = 0.5; full-sib mating = 0.25; half-sib mating = 0.125. Repeated selfing: F = 1 - (1/2)^n. ## Don't confuse with - **IBL**: the cannabis-market label for a stabilised inbred line. - **Line breeding**: a milder form of inbreeding around a superior ancestor. - **Clone**: copying a plant does not inbreed it; inbreeding needs sexual reproduction. ## Related terms [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md), [Sib cross](https://genetixbay.com/knowledge/glossary/sib-cross.md), [Line breeding](https://genetixbay.com/knowledge/glossary/line-breeding.md) ## Read more - [Inbreeding depression and hybrid vigour](https://genetixbay.com/knowledge/breeding/inbreeding-depression-hybrid-vigour.md) - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 --- # Inbreeding depression > Inbreeding depression is the loss of vigour, fertility, yield or survival that follows mating between relatives, mainly because harmful recessive alleles become homozygous. - Canonical: https://genetixbay.com/knowledge/glossary/inbreeding-depression.html - Also written: inbreeding decline, inbred depression, loss of vigour from inbreeding - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Inbreeding depression is reduced fitness in offspring of related parents: slower growth, smaller plants, poorer seed set, weak [germination](https://genetixbay.com/knowledge/glossary/germination.md), deformities or more susceptibility to stress. The main cause is that [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) makes harmful [recessive alleles](https://genetixbay.com/knowledge/glossary/recessive.md) homozygous, so their effects show; loss of heterozygote advantage adds to it (Charlesworth and Willis 2009). ## In practice Cannabis is naturally [outcrossing](https://genetixbay.com/knowledge/glossary/outcross.md), so it carries a load of hidden recessives and can suffer when inbred hard. Breeders see it after repeated selfing ([S1](https://genetixbay.com/knowledge/glossary/s1.md) on S1) or several sib generations with small populations. Signs: falling germination rates, runts, twisted leaves, lower yields, and in some lines unstable sex expression. The defence is selection and population size. Cull hard each generation, keep many parents, and outcross when a line weakens. A good IBL is one where the breeder purged the defects along the way rather than inbreeding past them. ## Don't confuse with - **Clone decline**: clones are not inbred and do not inbreed. A cut that weakens over years almost always has a pathogen (such as [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md)) or a care problem. - **Genetic drift**: random loss of [alleles](https://genetixbay.com/knowledge/glossary/allele.md) in small populations; it often accompanies inbreeding but is a separate process. - **Heterosis**: the opposite effect, from crossing unrelated lines. ## Related terms [Inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md), [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md), [Heterosis](https://genetixbay.com/knowledge/glossary/heterosis.md), [Outcross](https://genetixbay.com/knowledge/glossary/outcross.md), [Recessive](https://genetixbay.com/knowledge/glossary/recessive.md), [Genetic bottleneck](https://genetixbay.com/knowledge/glossary/genetic-bottleneck.md) ## Read more - [Inbreeding depression and hybrid vigour](https://genetixbay.com/knowledge/breeding/inbreeding-depression-hybrid-vigour.md) - [S1s and selfing: what happens when a plant pollinates itself](https://genetixbay.com/knowledge/breeding/s1-selfing.md) ## Sources 1. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 2. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 --- # Independent assortment > Independent assortment is Mendel's rule that alleles of genes on different chromosomes are passed to gametes independently of each other, creating new trait combinations. - Canonical: https://genetixbay.com/knowledge/glossary/independent-assortment.html - Also written: law of independent assortment, Mendel's second law, free assortment - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Independent assortment is Mendel's second law: [genes](https://genetixbay.com/knowledge/glossary/gene.md) on different [chromosomes](https://genetixbay.com/knowledge/glossary/chromosome.md) (or far apart on one) are inherited independently. Which [allele](https://genetixbay.com/knowledge/glossary/allele.md) a gamete gets at one gene tells you nothing about which allele it gets at another. That is how a cross produces combinations neither parent had. ## In practice It is the reason breeders can combine traits. Cross a plant with dense resin but late flowering to an early plant with thin resin; if the genes involved are on different chromosomes, some [F2](https://genetixbay.com/knowledge/glossary/f2.md) plants will be early and resinous. The expected two-gene F2 ratio is 9:3:3:1, so the wanted double combination may be only 1 in 16, or rarer if both traits are [recessive](https://genetixbay.com/knowledge/glossary/recessive.md). Cannabis has 10 chromosome pairs, so many genes do assort independently. Genes close together on one chromosome do not: they tend to travel together, which is [linkage](https://genetixbay.com/knowledge/glossary/linkage.md). ## Don't confuse with - **Segregation**: separation of two alleles of one gene; assortment is about how different genes combine. - **Linkage**: the exception, when genes sit near each other and are inherited as a block. - **Recombination**: crossing over within a chromosome, which is what eventually breaks linkage. ## Related terms [Segregation](https://genetixbay.com/knowledge/glossary/segregation.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md), [Mendelian inheritance](https://genetixbay.com/knowledge/glossary/mendelian-inheritance.md), [Punnett square](https://genetixbay.com/knowledge/glossary/punnett-square.md), [Chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ --- # Indica > Indica is a popular label for broad-leaflet, compact, faster-flowering cannabis plants; it describes plant shape at most, not a separate species or a predictable effect. - Canonical: https://genetixbay.com/knowledge/glossary/indica.html - Also written: Cannabis indica, C. indica, indica-dominant, indicas, broad-leaf - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" "Indica" is used for cannabis plants with broad [leaflets](https://genetixbay.com/knowledge/glossary/leaflet.md), short stature, dense structure and relatively quick flowering. Historically some botanists named a separate species, *Cannabis indica*, and modern taxonomists still debate subspecies names. The current consensus treats cannabis as one species, *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)* L. (McPartland 2018; Small 2015). ## In practice On a label, "indica" is meant to promise relaxing, body-heavy effects. The evidence does not support that. Genetic studies show indica/sativa labels match measured ancestry poorly (Sawler et al. 2015), and chemical studies show labels do not predict [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) or [terpene profiles](https://genetixbay.com/knowledge/glossary/terpene-profile.md) (Smith et al. 2022; Watts et al. 2021). Almost everything sold today is a hybrid, with a few outlier [landraces](https://genetixbay.com/knowledge/glossary/landrace.md). Use the word, if at all, to describe shape: broad leaflets, compact build, shorter flowering. For effects, look at the lab profile and grow reports. ## Don't confuse with - **Afghan or Hindu Kush landraces**: real traditional populations often described as indica; the label is a later Western shorthand. - **Chemotype**: the chemical class, which an indica label does not predict. ## Myth check House position: indica versus sativa is nonsense as a guide to effects or species. It is one species showing different [phenotypes](https://genetixbay.com/knowledge/glossary/phenotype.md). See [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Sativa](https://genetixbay.com/knowledge/glossary/sativa.md), [Hybrid](https://genetixbay.com/knowledge/glossary/hybrid.md), [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Chemovar](https://genetixbay.com/knowledge/glossary/chemovar.md) ## Read more - [Indica, sativa and ruderalis: what the names really mean](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) ## Sources 1. McPartland JM. 2018. Cannabis systematics at the levels of family, genus, and species. Cannabis and Cannabinoid Research 3(1):203-212. https://doi.org/10.1089/can.2018.0039 2. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 3. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Indoor growing > Indoor growing is cultivating cannabis entirely under artificial light in a tent or room, giving full control over light, climate and photoperiod. - Canonical: https://genetixbay.com/knowledge/glossary/indoor-growing.html - Also written: indoor, indoor grow, grow room, indoors - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Indoor growing means raising plants in an enclosed space where all light comes from lamps and the climate is managed with fans, extraction, heaters, [dehumidifiers](https://genetixbay.com/knowledge/glossary/dehumidifier.md) and air conditioning. The grower decides the [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), so photoperiod plants can be held in veg or flowered at any time of year. ## In practice Indoor grows range from a 60 × 60 cm (2 × 2 ft) tent to commercial rooms. The main controlled variables are light intensity ([PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) and [DLI](https://genetixbay.com/knowledge/glossary/dli.md)), photoperiod, temperature, humidity and [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), airflow, CO₂ and [root-zone conditions](https://genetixbay.com/knowledge/glossary/root-zone.md). Control comes at a price: electricity, equipment, and responsibility for every condition the sun and weather would otherwise supply. Benefits are year-round harvests, consistent results and protection from weather and many outdoor pests. Typical problems are heat, humidity in late flower, [light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) and pests that thrive in still, warm air, such as [spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md). ## Don't confuse with - **Greenhouse**: sunlight plus some control; often with supplemental lights. - **Indoor (slang, quality)**: "indoor" on a menu means indoor-grown flower, often sold as a quality marker; that is a market claim, not a guarantee. ## Related terms [Outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md), [Greenhouse growing](https://genetixbay.com/knowledge/glossary/greenhouse-growing.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Perpetual harvest](https://genetixbay.com/knowledge/glossary/perpetual-harvest.md) ## Read more - [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) --- # Input EC > Input EC is the electrical conductivity of the nutrient solution going into the pot or system, in mS/cm, including the base EC of the source water. - Canonical: https://genetixbay.com/knowledge/glossary/input-ec.html - Also written: feed EC, EC in, inflow EC, reservoir EC, feed strength - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Input EC (feed EC) is the [conductivity](https://genetixbay.com/knowledge/glossary/ec.md) of the solution you actually apply: source water plus nutrients plus any [pH](https://genetixbay.com/knowledge/glossary/ph.md) adjusters. It is the dose. It is measured after mixing and pH adjustment, at 25 °C or with [temperature compensation](https://genetixbay.com/knowledge/glossary/atc.md). ## In practice Always know your base water EC. Tap water at 0.5 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) plus 1.2 mS/cm of nutrients gives an input EC of about 1.7 mS/cm, but 0.5 of that may be sodium, chloride and bicarbonate that are not useful to the plant. With [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) at 0.02 mS/cm, nearly all the EC is nutrient. Two growers following the same chart can therefore deliver quite different nutrition. Track input and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) EC together. Input EC is what you control; runoff EC tells you how the plant and medium responded. Hershkowitz, Westmoreland and Bugbee (2025) found that raising nutrient concentration beyond moderate levels did not improve yield or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), so a stable, moderate input EC with steady runoff is a sound default. ## Don't confuse with - **Runoff EC**: what drains out. - **Additive EC**: the EC added by nutrients alone (input minus base water), which some charts quote. ## Related terms [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) ## Read more - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ## Sources 1. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 2. Cavins TJ, Whipker BE, Fonteno WC, Harden B, McCall I, Gibson JL. Monitoring and managing pH and EC using the PourThru extraction method. NC State University Horticulture Information Leaflet 590. Cited via MSU Extension: https://www.canr.msu.edu/uploads/resources/pdfs/measuring_ph_and_ec_of_crops_grown_in_large_containers.pdf --- # Insecticidal soap > Potassium salts of fatty acids sprayed to kill soft-bodied pests such as aphids, mites and whitefly nymphs on contact by disrupting their cell membranes. - Canonical: https://genetixbay.com/knowledge/glossary/insecticidal-soap.html - Also written: insecticidal soaps, potassium salts of fatty acids, soap spray, potassium soap, fatty acid soap - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Insecticidal soap is a spray of potassium salts of fatty acids. It kills soft-bodied insects and [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) that it wets directly, by disrupting the cell membranes of the outer body and removing protective waxes. Once dry it has no residual activity, and it is relatively low in [toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) to people and mammals. ## In practice Growers use soap in veg against [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), spider mites, whitefly nymphs, thrips larvae and [mealybug crawlers](https://genetixbay.com/knowledge/glossary/crawler.md). It only works where it touches, so leaf undersides must be soaked, and repeat sprays every few days catch hatching eggs. [Hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md) reduces [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md); soft or [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) helps. It can scorch leaves of some cultivars, in heat or under strong light, so test on a few leaves first. Dish detergents are not the same product: they are formulated differently and can damage leaves. Keep soap off flowers. Check what is registered for cannabis locally. ## Don't confuse with - **Horticultural oil**: smothers pests; can be combined, but phytotoxicity risk rises. - **Surfactant or wetting agent**: improves spreading, not a pesticide by itself. - **Dish soap**: a cleaning product, not a registered insecticide. ## Related terms [Horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md), [Neem oil](https://genetixbay.com/knowledge/glossary/neem-oil.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md), [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. UC IPM. Pest Notes: Aphids (Publication 7404). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html 2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # Instar > A developmental stage between two moults of an insect larva or nymph; control tactics often work only on early instars. - Canonical: https://genetixbay.com/knowledge/glossary/instar.html - Also written: instars, larval instar, nymphal instar, first instar, early instar - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An instar is the stage of an insect between one moult and the next. A caterpillar typically passes through five or six larval instars before pupating; an [aphid](https://genetixbay.com/knowledge/glossary/aphid.md) has four nymphal instars. Each instar is larger and, often, harder to kill. Oregon State Extension advises targeting [corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md) while larvae are small, before they bore into [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) buds. ## In practice Instar matters for timing. Bt-class sprays act when eaten and work best on first and second instars still feeding on the surface; late instars inside [colas](https://genetixbay.com/knowledge/glossary/cola.md) are out of reach. Scout for eggs and tiny larvae after moth flights, not for damage. ## Don't confuse with - **Generation**: egg to egg, several instars long. - **Pupa**: the non-feeding stage after the last larval instar. ## Related terms [Crawler](https://genetixbay.com/knowledge/glossary/crawler.md), [Life table](https://genetixbay.com/knowledge/glossary/life-table.md), [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md) ## Read more - [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) - [Budworms on cannabis: corn earworm and tobacco budworm in numbers](https://genetixbay.com/knowledge/pests/budworms-corn-earworm.md) ## Sources 1. Shrestha, G., 2022. Corn earworm management in hemp (EM 9626). Oregon State University Extension. https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp --- # Internode > The length of stem between two adjacent nodes; short internodes mean compact plants and tight bud stacking, long ones mean stretch. - Canonical: https://genetixbay.com/knowledge/glossary/internode.html - Also written: internodes, internodal spacing, internode length, node spacing - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An internode is the segment of stem between two nodes. Internode length is set by genetics and strongly modified by light, temperature and hormones (mainly [gibberellins](https://genetixbay.com/knowledge/glossary/gibberellin.md) and auxin). It is the main component of plant height. ## In practice Growers talk about "tight internodal spacing" as a desirable trait: more nodes, more bud sites, denser [colas](https://genetixbay.com/knowledge/glossary/cola.md). Typical indoor spacing in veg runs from about 2-5 cm (1-2 in) on compact plants to 10 cm (4 in) or more on stretchy ones. What lengthens internodes: - low light intensity or a lamp too far away; - a high far-red to red ratio (shade-avoidance signal read by [phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md)); - warmer days than nights ([positive DIF](https://genetixbay.com/knowledge/glossary/dif.md)); - the first two to three weeks of flower, when most cultivars "[stretch](https://genetixbay.com/knowledge/glossary/stretch.md)" 50-200%. What shortens them: higher [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), more [blue light](https://genetixbay.com/knowledge/glossary/blue-light.md), cooler days relative to nights, and training. A tall, gappy plant under a dim light is a light problem before it is a genetic one. ## Don't confuse with - **Node**: the attachment point; the internode is the space between. - **Stretch**: the flowering-phase surge in internode length. - **Petiole length**: [leaf stalk](https://genetixbay.com/knowledge/glossary/petiole.md) length, separate from stem spacing. ## Related terms [Node](https://genetixbay.com/knowledge/glossary/node.md), [Gibberellin](https://genetixbay.com/knowledge/glossary/gibberellin.md), [Phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md), [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md) ## Read more - [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. 2. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 --- # Interveinal chlorosis > Yellowing of the leaf tissue between the veins while the veins themselves stay green; on old leaves it points to magnesium, on new leaves to iron or manganese. - Canonical: https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.html - Also written: interveinal yellowing, green veins yellow leaf, yellow between the veins - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Interveinal chlorosis is a yellowing pattern in which the blade between the veins loses colour while the veins stay green, leaving a green skeleton. In cannabis trials, magnesium shortage produced it on lower, older leaves, and iron and [manganese](https://genetixbay.com/knowledge/glossary/manganese.md) shortages produced it on new and upper leaves (Cockson et al. 2019; Llewellyn et al. 2023). ## In practice Use location to split it. Old leaves with interveinal chlorosis: think magnesium, often induced by low root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) or excess potassium or calcium. New leaves: iron (smooth, pale, newest leaves) or manganese (netted, upper-middle leaves with small tan spots), usually from high root-zone pH. Check pH before adding any supplement. Early [light bleaching](https://genetixbay.com/knowledge/glossary/light-stress.md) can also leave veins green at the canopy top, so check light intensity too. ## Don't confuse with - **[Chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md)** in general: any yellowing, including uniform yellowing where the veins [fade](https://genetixbay.com/knowledge/glossary/senescence.md) too. - **Marginal scorch**: yellow then brown leaf edges, typical of potassium shortage or [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md). - **Light bleaching**: pale [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) nearest the fixture only. ## Related terms [Chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md), [Magnesium](https://genetixbay.com/knowledge/glossary/magnesium.md), [Iron](https://genetixbay.com/knowledge/glossary/iron.md), [Manganese](https://genetixbay.com/knowledge/glossary/manganese.md), [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md) ## Read more - [Magnesium (Mg) in cannabis: interveinal yellowing, targets and the K-Ca competition](https://genetixbay.com/knowledge/nutrients/magnesium.md) - [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) - [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) - [Cannabis lookalike problems: how to tell them apart](https://genetixbay.com/knowledge/diagnosis/lookalikes.md) ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Intrinsic rate of increase (r_m) > The per-day rate at which an unchecked pest population multiplies under set conditions, from a life table; N(t) = N0 x e^(r_m x t). - Canonical: https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.html - Also written: r_m, rm, intrinsic rate of natural increase, per-capita growth rate - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The intrinsic rate of increase, written r_m, is the exponential growth rate a population reaches when food is unlimited and nothing eats it, at one temperature and host. Birch set out the modern method in 1948: combine age-specific survival and egg-laying from a [life table](https://genetixbay.com/knowledge/glossary/life-table.md) and solve for r. It is the best single number for comparing how fast pests explode. ## In practice An r_m of 0.25 per day means the population grows by e^0.25, about 28%, every day and doubles in ln 2 / 0.25 = 2.8 days. Ten [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) become 10 x e^(0.25 x 21), about 1,900, in three weeks. Values come from lab leaf discs or single host plants, so treat them as an upper bound for a cannabis room with predators, crowding and plant defences. Temperature changes r_m more than anything else a grower controls. ## Don't confuse with - **Net reproductive rate (R0)**: offspring per female per generation, not per day. - **Finite rate of increase (lambda)**: e^r_m, the daily multiplication factor. - **Fecundity**: [eggs per female](https://genetixbay.com/knowledge/glossary/fecundity.md), one input to r_m. ## Related terms [Life table](https://genetixbay.com/knowledge/glossary/life-table.md), [Net reproductive rate (R0)](https://genetixbay.com/knowledge/glossary/net-reproductive-rate.md), [Generation time](https://genetixbay.com/knowledge/glossary/generation-time.md), [Doubling time](https://genetixbay.com/knowledge/glossary/doubling-time.md), [Fecundity](https://genetixbay.com/knowledge/glossary/fecundity.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605 2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # Introgression > Introgression is the movement of genes from one population or type into another through hybridisation followed by repeated backcrossing. - Canonical: https://genetixbay.com/knowledge/glossary/introgression.html - Also written: introgressed, introgressive hybridisation, introgressive hybridization, gene flow, trait introgression - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Introgression is the transfer of [genetic material](https://genetixbay.com/knowledge/glossary/germplasm.md) from one population into another, through a cross followed by repeated [backcrossing](https://genetixbay.com/knowledge/glossary/backcross.md) to the receiving population. The result is a population that is mostly the recipient but carries segments of the donor's DNA. ## In practice Breeders introgress traits on purpose: move the [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) [allele](https://genetixbay.com/knowledge/glossary/allele.md), a disease resistance or a chemotype into an [elite](https://genetixbay.com/knowledge/glossary/elite-cut.md) line by crossing then backcrossing several times. The CBD-producing alleles in many drug-type cannabis lines appear to come from [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) introgressed into marijuana (Grassa et al. 2021). Introgression also happens unintentionally. When imported hybrid seed is grown near traditional fields, its pollen enters the local [landrace](https://genetixbay.com/knowledge/glossary/landrace.md). Over generations the landrace carries more and more foreign DNA and loses its distinct type. That is one documented route by which source-region landraces are being diluted. ## Don't confuse with - **Backcross**: the breeding step; introgression is the overall movement of genes. - **Hybrid**: the first cross; introgression requires further generations. - **Contamination (seed purity)**: stray pollen in a [seed run](https://genetixbay.com/knowledge/glossary/seed-run.md); it can start introgression if the seed is kept. ## Related terms [Backcross](https://genetixbay.com/knowledge/glossary/backcross.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Outcross](https://genetixbay.com/knowledge/glossary/outcross.md) ## Read more - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Grassa CJ, Weiblen GD, Wenger JP, et al. 2021. A new Cannabis genome assembly associates elevated cannabidiol (CBD) with hemp introgressed into marijuana. New Phytologist 230(4):1665-1679. https://doi.org/10.1111/nph.17243 2. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 --- # Inverse square law > The inverse square law says light from a point source falls with the square of distance; grow fixtures are not point sources, so it only roughly predicts PPFD. - Canonical: https://genetixbay.com/knowledge/glossary/inverse-square-law.html - Also written: inverse-square law, inverse square rule, 1/r² law, light distance rule - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The inverse square law states that intensity from a point source falls in proportion to 1 ÷ distance². Double the distance and you get a quarter of the light. It is exact for a true point source radiating into empty space, and that is the catch: grow rooms have neither. ## In practice A large [LED](https://genetixbay.com/knowledge/glossary/led.md) board or bar fixture is closer to an extended source, and tent walls reflect much of the stray light back. Near a wide fixture, [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) falls much more slowly than the law predicts; far from it, the fixture starts to behave more like a point. A bare [HPS](https://genetixbay.com/knowledge/glossary/hps.md) bulb with a reflector sits in between. Example: the law predicts that raising a light from 30 cm to 60 cm (12 to 24 in) cuts PPFD by 75%. Under a 1.2 m wide LED in a reflective tent, a meter might show a drop of only 25–40% at canopy centre. Height also changes spread: a higher fixture gives a more [even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md) at a lower peak. The only reliable answer is to measure PPFD at canopy height in a grid and adjust height or dimmer. ## Units and formula I₂ = I₁ × (d₁ ÷ d₂)² (point source only). ## Don't confuse with - **Light spread (beam angle)**: how widely a fixture distributes light; a separate property from fall-off. ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Light intensity](https://genetixbay.com/knowledge/glossary/light-intensity.md), [LED](https://genetixbay.com/knowledge/glossary/led.md), [HPS](https://genetixbay.com/knowledge/glossary/hps.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) --- # IPM > Integrated pest management: preventing and controlling pests by combining monitoring, prevention, cultural, biological and, as a last resort, chemical tools against set action thresholds. - Canonical: https://genetixbay.com/knowledge/glossary/ipm.html - Also written: integrated pest management, integrated pest and disease management, IPDM, integrated pest control - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" IPM, integrated pest management, is a decision-making system for keeping pests and diseases below damaging levels with the least risk to people, the crop and beneficial organisms. It is not a product or a single tactic. It layers [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md), monitoring, thresholds and a ranked set of controls, with chemical options used last and chosen for selectivity. ## In practice A cannabis IPM programme usually [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) like this: quarantine and inspect incoming clones; sanitise rooms and tools between runs; set the environment to discourage pests and disease; scout weekly with a hand lens and [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) and keep records; release beneficial organisms preventively in veg; and decide in advance what level of pest triggers each action. Any spray happens in veg, is chosen for its [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md) and compatibility with the [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md) in use, and follows its label. In flower the toolkit narrows sharply, which is why IPM in cannabis is mostly about what happens before week one of flower. Check what is registered for cannabis locally. ## Don't confuse with - **Spray schedule**: calendar spraying without monitoring; the opposite of IPM. - **Organic growing**: a source-of-inputs standard; organic growers still need IPM. - **Biological control**: one component of IPM, not the whole system. ## Related terms [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Cultural control](https://genetixbay.com/knowledge/glossary/cultural-control.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md) ## Read more - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) ## Sources 1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 2. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects --- # IR thermometer > An IR (infrared) thermometer reads surface temperature from emitted infrared radiation; growers use it to measure leaf temperature for leaf VPD. - Canonical: https://genetixbay.com/knowledge/glossary/ir-thermometer.html - Also written: infrared thermometer, IR gun, temp gun, laser thermometer, thermal camera - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An infrared (IR) thermometer measures the thermal infrared radiation a surface emits and converts it to a temperature. It does not touch the surface and reads in under a second. The red laser on many units only shows where you are aiming; it does not measure anything. Thermal cameras do the same job across a whole image. ## In practice Set emissivity to about 0.95–0.98 for leaves. Check the distance-to-spot ratio: a 12:1 gun held 30 cm (12 in) away reads a circle about 2.5 cm (1 in) wide, so get close enough to fill the spot with one leaf. Aim at leaves on the canopy top that face the light, read several, and average. Common errors: reading the pot or the floor through gaps in the canopy, reading a shiny surface (low emissivity) and reading leaves in the fixture's direct radiant output under [HPS](https://genetixbay.com/knowledge/glossary/hps.md) right after moving them. Use the [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) with room [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) and air temperature to calculate leaf [VPD](https://genetixbay.com/knowledge/glossary/vpd.md). ## Don't confuse with - **Probe thermometer**: measures air or liquid temperature by contact. - **PAR meter**: measures light, not heat. - **Thermal imaging of root zones**: shows only surface temperature, not inside the medium. ## Related terms [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md), [Leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Temperature](https://genetixbay.com/knowledge/glossary/temperature.md) ## Read more - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ## Sources 1. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # Iron > Iron (Fe) is an immobile micronutrient needed to make chlorophyll and run electron transport; deficiency yellows new leaves between green veins. - Canonical: https://genetixbay.com/knowledge/glossary/iron.html - Also written: Fe, Fe2+, Fe3+, iron deficiency, Fe deficiency - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Iron is a micronutrient required for chlorophyll synthesis and for the cytochromes and iron-sulfur proteins that carry electrons in photosynthesis and respiration. It is immobile, so the plant cannot move it from old leaves to new ones. In solution, iron precipitates as insoluble hydroxides as [pH](https://genetixbay.com/knowledge/glossary/ph.md) rises, so feeds supply it as a [chelate](https://genetixbay.com/knowledge/glossary/chelate.md). ## In practice [Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) appears as [interveinal chlorosis](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) on the newest leaves: bright yellow tissue with fine green veins, in severe cases nearly white. The usual cause is high root-zone pH, not a lack of iron in the bottle. Hydro feeds typically carry about 1-3 mg/L (ppm) Fe. Which chelate is used matters: EDTA-iron loses effectiveness above about pH 6.5, DTPA holds to about 7.5, and EDDHA well beyond. ## Don't confuse with - **Magnesium deficiency**: interveinal too, but on older leaves. - **Manganese deficiency**: interveinal mottling with less contrast, often on middle leaves. - **Nitrogen deficiency**: uniform yellowing of old leaves. ## Myth check Adding more iron rarely fixes iron [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md) when pH is the problem. Correct the root-zone pH first. See [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md). ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), [Iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md), [EDTA](https://genetixbay.com/knowledge/glossary/edta.md), [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md), [EDDHA](https://genetixbay.com/knowledge/glossary/eddha.md) ## Read more - [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) - [Yellow new growth on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. HortScience. 2025. Iron chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA) in high-pH soilless media. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml --- # Iron chelate > An iron chelate is iron bound to an organic molecule (EDTA, DTPA or EDDHA) that keeps it dissolved and available; each type holds up to a different pH. - Canonical: https://genetixbay.com/knowledge/glossary/iron-chelate.html - Also written: chelated iron, Fe chelate, Fe-EDTA, Fe-DTPA, Fe-EDDHA, iron EDTA - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An iron chelate is ferric iron held in a ring-like organic molecule, the [chelating agent](https://genetixbay.com/knowledge/glossary/chelate.md), which stops it from forming insoluble hydroxides. The three common types are Fe-EDTA (about 13% Fe), Fe-DTPA (about 10-11% Fe) and Fe-EDDHA (about 6% Fe). They differ mainly in how high a [pH](https://genetixbay.com/knowledge/glossary/ph.md) they survive. ## In practice Fe-EDTA works well up to about pH 6.0-6.5, fine for most hydro but weak in high-pH soil or water. Fe-DTPA holds to about pH 7.0-7.5 and is the usual choice for [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and hydro. Fe-EDDHA stays effective to pH 9 or more and is used for alkaline soils; it stains solutions dark red. [EDTA](https://genetixbay.com/knowledge/glossary/edta.md) iron also breaks down in strong light, so opaque reservoirs help. Feeds typically target about 1-3 mg/L (ppm) Fe. ## Don't confuse with - **Iron sulfate**: unchelated iron, precipitates quickly above pH 6. - **Iron oxide or rust**: insoluble and unavailable to roots. - **Amino acid chelates**: weaker, less stable bonding, different behaviour in solution. ## Related terms [Iron](https://genetixbay.com/knowledge/glossary/iron.md), [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md), [EDTA](https://genetixbay.com/knowledge/glossary/edta.md), [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md), [EDDHA](https://genetixbay.com/knowledge/glossary/eddha.md) ## Read more - [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. HortScience. 2025. Iron chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA) in high-pH soilless media. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # ISO/IEC 17025 > ISO/IEC 17025 is the international standard for the competence of testing and calibration laboratories; accreditation to it shows a lab's specific methods have been independently assessed. - Canonical: https://genetixbay.com/knowledge/glossary/iso-17025.html - Also written: ISO 17025, ISO/IEC 17025:2017, 17025 accreditation, lab accreditation, accredited lab, ISO accreditation - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" ISO/IEC 17025, "General requirements for the competence of testing and calibration laboratories", sets out how a lab must manage its methods, staff, equipment, [traceability](https://genetixbay.com/knowledge/glossary/track-and-trace.md), [measurement uncertainty](https://genetixbay.com/knowledge/glossary/measurement-uncertainty.md), quality control and reporting. An independent accreditation body assesses the lab and grants accreditation for a defined scope: specific tests on specific sample types. ## In practice Check the scope, not just the logo. A lab can be accredited for potency in flower by [HPLC](https://genetixbay.com/knowledge/glossary/hplc.md) but not for pesticides or for concentrates. A [COA](https://genetixbay.com/knowledge/glossary/coa.md) from an accredited lab should name the accreditation body and certificate number; most bodies publish searchable scopes. Accreditation shows the lab has a working quality system and has been assessed; it doesn't guarantee every number, and documented lab-to-lab bias has occurred among accredited labs. Many regulated markets require it; check local rules. ## Don't confuse with - **ISO 9001**: a general quality-management standard, not specific to testing competence. - **State licence**: permission to operate as a cannabis lab, separate from accreditation. - **Proficiency testing**: one ongoing requirement within 17025. ## Related terms [Proficiency testing](https://genetixbay.com/knowledge/glossary/proficiency-testing.md), [Measurement uncertainty](https://genetixbay.com/knowledge/glossary/measurement-uncertainty.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md), [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. ISO/IEC 17025:2017. General requirements for the competence of testing and calibration laboratories. International Organization for Standardization, Geneva. --- # Isolate > An isolate is a concentrate refined to one cannabinoid at very high purity, often 99% or more, usually a white crystalline powder such as CBD or THCA isolate. - Canonical: https://genetixbay.com/knowledge/glossary/isolate.html - Also written: CBD isolate, THCA isolate, cannabinoid isolate, crystalline isolate, crystalline, 99% isolate - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An isolate is a single [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) separated from every other compound in the plant, typically by crystallisation from a refined extract. [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) isolate and [THCA](https://genetixbay.com/knowledge/glossary/thca.md) isolate are the common forms; both are white or off-white crystalline solids when pure. Isolates have essentially no [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), flavonoids or minor cannabinoids, so they have little smell or taste. ## In practice Manufacturers use isolates where exact dosing and no flavour are wanted, or as a starting material for other products. A [COA](https://genetixbay.com/knowledge/glossary/coa.md) for a good isolate reads 98-99%+ of the target compound with little else. THCA isolate is also the basis of some "diamonds" products. Semi-synthetic cannabinoids such as [delta-8](https://genetixbay.com/knowledge/glossary/delta-8-thc.md) [THC](https://genetixbay.com/knowledge/glossary/thc.md) and HHC are commonly made by chemically converting CBD isolate. GenetixBay defines the product only; no processing details. ## Don't confuse with - **Distillate**: an oil, usually 80-95% of the target cannabinoid with other compounds present. - **Diamonds**: large THCA [crystals](https://genetixbay.com/knowledge/glossary/trichome.md) grown in terpene-rich sauce; chemically similar, different product style. - **Full-spectrum**: retains much of the plant's chemistry. ## Related terms [Distillate](https://genetixbay.com/knowledge/glossary/distillate.md), [Diamonds](https://genetixbay.com/knowledge/glossary/diamonds.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [Entourage effect](https://genetixbay.com/knowledge/glossary/entourage-effect.md) --- # Jardin > Jardin is GenetixBay's grow system in development: a controller and sensor kit for logging and climate control, with per-element custom nutrient dosing. - Canonical: https://genetixbay.com/knowledge/glossary/jardin.html - Also written: Jardin grow system, GenetixBay Jardin, Jardin controller, Jardin hub - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Jardin is the grow system GenetixBay is developing: a hub with climate sensors, camera and plug-in modules that logs a grow, controls the environment and, in its dosing form, mixes nutrients element by element instead of from a fixed bottled ratio. It is in development, not a shipping product. ## In practice The headline idea is per-element [custom dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md). A bottled [two-part nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) fixes the ratio between nitrogen, phosphorus, potassium and everything else, so cutting nitrogen in late flower means cutting the rest too. Dosing from separate element stocks lets a grower follow the GenetixBay approach: [taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) toward zero near the finish while keeping P, K, Ca, Mg, S and the [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md) fed, instead of [flushing](https://genetixbay.com/knowledge/glossary/flushing.md). Jardin keeps a running estimate of each element in the reservoir from what it dosed, what the plants drank and what drained, and a lab test resets that estimate. On the climate side it handles light dimming with sunrise and sunset ramps and VPD-driven fan control, and everything is logged to the grower's journal with who or what made each change. ## Don't confuse with - **Professor Greenleaf**: the knowledge assistant, which can read Jardin's data but is a separate thing. - **A nutrient brand**: Jardin doses from whatever element stocks the grower uses. ## Related terms [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md), [Grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md), [Professor Greenleaf](https://genetixbay.com/knowledge/glossary/professor-greenleaf.md) ## Read more - [Per-element feeding tricks: what growers adjust, stage by stage](https://genetixbay.com/knowledge/nutrients/per-element-tricks.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) --- # Jeweler's loupe > A small handheld magnifier, typically 30-60x for cannabis use, used to inspect trichome heads and spot pests and male flowers. - Canonical: https://genetixbay.com/knowledge/glossary/jewelers-loupe.html - Also written: jewellers loupe, jeweller's loupe, loupe, jewelers loupe, pocket microscope, trichome scope - Glossary category: Harvest, drying and curing - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A jeweler's loupe is a small folding magnifying lens built for close inspection of gems. Growers use loupes, and increasingly cheap pocket digital microscopes, to look at [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), early [pre-flowers](https://genetixbay.com/knowledge/glossary/pre-flower.md), anthers on suspected [intersex plants](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), and tiny pests such as [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) and thrips. ## In practice Magnification matters: - **10-20x**: enough for sexing pre-flowers and spotting spider mites. - **30x**: borderline for [trichome colour](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md); you see heads but not reliably cloudy versus clear. - **60-100x**: comfortable for judging clear, cloudy and amber heads, and for broad and [russet mites](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md), which are near-invisible below this. Tips: steady your hand against the plant or use a clip-on stand; use daylight or a neutral white torch rather than the grow light, because purple-pink [LED](https://genetixbay.com/knowledge/glossary/led.md) light makes heads look misleadingly amber; check bract [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md), not sugar leaves. A phone-attached clip lens or USB microscope lets you photograph heads for a grow journal and compare day to day, which makes the call far more objective. ## Don't confuse with - **Magnifying glass**: usually 2-5x, too weak for trichomes. - **Microscope**: higher magnification, normally bench-mounted. - **Trichome ripeness**: what you judge with the loupe. ## Related terms [Trichome ripeness](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md), [Harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md), [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md) ## Read more - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) --- # Keeper > A keeper is a plant from a seed hunt good enough to be kept alive as a clone or mother for future runs or breeding. - Canonical: https://genetixbay.com/knowledge/glossary/keeper.html - Also written: keepers, keeper pheno, keeper plant, keeper cut - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A keeper is an individual plant judged good enough to keep: it is cloned before or during flower and maintained as a mother after the rest of the [seed lot](https://genetixbay.com/knowledge/glossary/seed-run.md) is harvested and discarded. ## In practice A grower pops 20 seeds, clones each [seedling](https://genetixbay.com/knowledge/glossary/seedling.md), flowers the originals, and judges vigour, structure, yield, resin, aroma, cure quality and pest resistance. One or two plants make the cut and become keepers; the clones of the rest go in the bin. Experienced hunters judge after drying and curing, not only on the plant, because aroma and smoke change a great deal through the cure. A keeper can be female or male. Keeper males, chosen on vigour, structure, aroma when stems are rubbed and, ideally, the quality of their daughters, are just as important for breeding. On GenetixBay, a member's keeper can be nominated with its journal and, if selected, become a parent in a community line, with credit on the record. ## Don't confuse with - **Pheno**: any one plant in the hunt. A keeper is the [pheno](https://genetixbay.com/knowledge/glossary/pheno.md) that survives selection. - **Elite cut**: a keeper that has become widely known and sought after. - **Mother plant**: the horticultural role; a keeper is usually kept as one. ## Related terms [Pheno](https://genetixbay.com/knowledge/glossary/pheno.md), [Pheno hunt](https://genetixbay.com/knowledge/glossary/pheno-hunt.md), [Cut](https://genetixbay.com/knowledge/glossary/cut.md), [Mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md) ## Read more - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) --- # Kief > Kief is the loose, powdery collection of trichome heads that falls or is sifted off dried cannabis through fine screens; it is the simplest solventless concentrate. - Canonical: https://genetixbay.com/knowledge/glossary/kief.html - Also written: dry sift, keef, kif, dry-sift, crystals (kief) - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Kief is the accumulated [resin glands](https://genetixbay.com/knowledge/glossary/trichome.md), mainly the heads of [capitate stalked trichomes](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md), separated from dried flower and trim by mechanical sieving. The name comes from the North African *kif*, a term once used for prepared cannabis. "Dry sift" is the modern grower term for kief made deliberately and carefully through graded screens, as opposed to whatever settles in the bottom of a grinder. ## In practice Quality depends on how much plant material comes through with the heads. Grinder kief is usually greenish and contaminated with leaf and stalk fragments. Carefully sifted dry sift is pale tan and mostly intact heads, and the finest grades approach the purity of [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md). Kief can be used loose or pressed into [hash](https://genetixbay.com/knowledge/glossary/hash.md). GenetixBay defines the product only and doesn't give processing instructions. ## Don't confuse with - **Hash**: kief that has been pressed or otherwise consolidated into a mass. - **Pollen**: male [cannabis pollen](https://genetixbay.com/knowledge/glossary/pollen.md), unrelated; "pollen" is also a slang name for kief, which causes confusion. - **Bubble hash**: [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) separated with ice water rather than dry screening. ## Related terms [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), [Hash](https://genetixbay.com/knowledge/glossary/hash.md), [Pressed hash](https://genetixbay.com/knowledge/glossary/pressed-hash.md), [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md), [Micron bags](https://genetixbay.com/knowledge/glossary/micron-bags.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Kratky method > The Kratky method is a passive hydroponic system with no pumps: plants sit above a container of solution, and a growing air gap forms as the level drops. - Canonical: https://genetixbay.com/knowledge/glossary/kratky.html - Also written: kratky, Kratky hydroponics, passive hydroponics, non-circulating hydroponics, set and forget hydro - Glossary category: Systems and media · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The Kratky method, developed by B. A. Kratky at the University of Hawaii, is a non-circulating hydroponic technique. A plant in a [net pot](https://genetixbay.com/knowledge/glossary/net-pot.md) sits in a lid over a tank filled with nutrient solution. As the plant drinks, the level falls, leaving an [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md); the upper roots adapt to breathe in that humid air while lower roots keep drinking. No pump, [air stone](https://genetixbay.com/knowledge/glossary/air-stone.md) or electricity is needed. ## In practice Kratky works very well for lettuce and herbs. For cannabis, which drinks large volumes and is grown for months, it needs a big container (tens of litres per plant), a starting [EC](https://genetixbay.com/knowledge/glossary/ec.md) and [pH](https://genetixbay.com/knowledge/glossary/ph.md) set carefully, and top-ups with weak solution rather than refilling to the top, which would drown the air-adapted roots. Warm solution and stagnation make [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) more likely. Some growers use it for seedlings or small autos, or as a learning tool. ## Don't confuse with - **DWC**: actively aerated with an air pump. - **Wick system**: passive, but feeds a medium through a wick. ## Related terms [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [Hydroponics](https://genetixbay.com/knowledge/glossary/hydroponics.md), [Net pot](https://genetixbay.com/knowledge/glossary/net-pot.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md) ## Read more - [Kratky (passive, non-circulating hydroponics)](https://genetixbay.com/knowledge/systems/kratky.md) ## Sources 1. Kratky BA, 2004. A suspended pot, non-circulating hydroponic method. Acta Horticulturae 648:83–89. https://www.ctahr.hawaii.edu/hawaii/downloads/A_Suspended_Pot_Non-circulating_Hydroponic_Method.pdf --- # Kush > Kush is a generic name for cannabis tied to landrace material from the Hindu Kush region of Afghanistan and Pakistan, and now for its many hybrid descendants. - Canonical: https://genetixbay.com/knowledge/glossary/kush.html - Also written: kushes, Hindu Kush, kush strains, kushy - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Kush refers to cannabis from, or descended from, the Hindu Kush mountain region spanning Afghanistan and Pakistan. [Landraces](https://genetixbay.com/knowledge/glossary/landrace.md) there were grown for [hashish](https://genetixbay.com/knowledge/glossary/hashish.md), and the name now covers a wide family of [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md). ## In practice Hindu Kush-type plants are typically short, stocky and broad-leafleted, with fast flowering and heavy resin, adapted to a short mountain season and selected over generations for sieved and hand-pressed [hash](https://genetixbay.com/knowledge/glossary/hash.md). Seed brought out in the 1970s became foundation stock for many indoor lines. Today "kush" on a label is mostly a family tag: it may mean real kush ancestry, a generic earthy-pine-hash aroma, or nothing. ## Don't confuse with - **Indica**: kush plants are the textbook "indica" shape, but the indica/sativa split is not a reliable guide to effects or species. - **OG**: a modern family often grouped with kush. ## Myth check "Kush means indica means sedating." GenetixBay position: indica vs sativa is nonsense as a guide to effects or species. Nearly everything today is a hybrid of one species, *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)* L., and labels do not predict chemistry (McPartland 2018; Watts et al. 2021). See [indica, sativa, ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md). ## Related terms [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [OG](https://genetixbay.com/knowledge/glossary/og.md), [Haze](https://genetixbay.com/knowledge/glossary/haze.md), [Skunk](https://genetixbay.com/knowledge/glossary/skunk.md) ## Read more - [Landraces of the world: an overview](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) - [Indica, sativa and ruderalis: what the names really mean](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) ## Sources 1. McPartland JM. 2018. Cannabis systematics at the levels of family, genus, and species. Cannabis and Cannabinoid Research 3(1):203-212. https://doi.org/10.1089/can.2018.0039 2. Watts S, McElroy M, Migicovsky Z, et al. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y 3. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. --- # Lab shopping > Lab shopping is the practice of choosing testing labs because they report higher potency or more passing results, rather than because they are most accurate. - Canonical: https://genetixbay.com/knowledge/glossary/lab-shopping.html - Also written: lab-shopping, shopping for labs, potency shopping, lab hopping, testing shopping - Glossary category: Lab testing · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Lab shopping happens when producers send samples to the labs that return the highest [THC](https://genetixbay.com/knowledge/glossary/thc.md) numbers or the fewest contaminant failures. Labs compete for clients, and in a market where higher THC sells for more, there is pressure to deliver "good" numbers. The practice, not any individual lab, is the problem GenetixBay calls out. ## In practice Jikomes and Zoorob (2018) analysed Washington State's regulatory data and found that reported THC differed systematically between testing facilities, consistent with some labs reporting higher potency than others. Schwabe et al. (2023) bought retail flower and found that most samples tested below their label claims, many by a wide margin. A Colorado study (Giordano et al. 2025) found [label accuracy](https://genetixbay.com/knowledge/glossary/label-inflation.md) varied with product type. Regulators in several states have responded with standardised methods, audits and recalls. ## Don't confuse with - **Measurement uncertainty**: honest random variation of a point or two, not a consistent upward bias. - **Getting a second opinion**: retesting at an independent [accredited lab](https://genetixbay.com/knowledge/glossary/iso-17025.md) to check a result is good practice. ## Myth check House position: lab shopping and label inflation are real and documented. Criticise the practice, never named businesses. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Label inflation](https://genetixbay.com/knowledge/glossary/label-inflation.md), [Potency ceiling](https://genetixbay.com/knowledge/glossary/potency-ceiling.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Proficiency testing](https://genetixbay.com/knowledge/glossary/proficiency-testing.md), [Measurement uncertainty](https://genetixbay.com/knowledge/glossary/measurement-uncertainty.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 3. Giordano G, et al. 2025. Label accuracy of retail cannabis flower and concentrates in Colorado. Scientific Reports. https://www.nature.com/articles/s41598-025-03854-3 --- # Label inflation > Label inflation is the gap between the potency printed on cannabis packaging and what independent testing finds, a documented, mostly upward bias in retail THC claims. - Canonical: https://genetixbay.com/knowledge/glossary/label-inflation.html - Also written: inflated labels, THC inflation, potency inflation, inflated THC, label accuracy, juiced numbers - Glossary category: Lab testing · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Label inflation describes retail cannabis whose stated [THC](https://genetixbay.com/knowledge/glossary/thc.md) or [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) is higher than what the product actually contains. Causes include [lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md), favourable [sampling](https://genetixbay.com/knowledge/glossary/homogenisation.md) (testing the best buds), undisclosed basis changes, calculation errors, and degradation between test and sale. ## In practice Schwabe et al. (2023) bought flower from retail stores and retested it: most samples fell below their labels, many by more than the allowed variance. Jikomes and Zoorob (2018) found systematic differences between labs in state regulatory data. Giordano et al. (2025) found flower labels in one state were more often inaccurate than concentrate labels. House position: most flower people believe is mid-20s to 30s really tests mid-teens to low 20s at best. Growing a plant to even 30% total cannabinoids is a real feat, yet those numbers appear on labels far too often. ## Don't confuse with - **Measurement uncertainty**: normal random variation of a point or two either way. - **Degradation**: THC loss over long storage, real but slower and smaller than typical inflation gaps. ## Myth check "Today's weed is 30%+" is a label story, not a lab-verified average. Criticise the practice, not named businesses. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) and [old cannabis was not weak](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md). ## Related terms [Lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md), [Potency ceiling](https://genetixbay.com/knowledge/glossary/potency-ceiling.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Dry-weight basis](https://genetixbay.com/knowledge/glossary/dry-weight-basis.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) - [Old cannabis wasn't weak: the "so much stronger than 20 years ago" myth](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md) ## Sources 1. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 2. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 3. Giordano G, et al. 2025. Label accuracy of retail cannabis flower and concentrates in Colorado. Scientific Reports. https://www.nature.com/articles/s41598-025-03854-3 --- # Labelling requirements > Labelling requirements are the legal rules on what cannabis packages must and must not show, such as potency, warnings, lot number and dates. - Canonical: https://genetixbay.com/knowledge/glossary/labelling-requirements.html - Also written: labeling requirements, cannabis labels, label rules, product labelling, packaging labels - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Labelling requirements specify what a regulated cannabis package must carry and what it must not. Typical mandatory items: product type, net weight, [THC](https://genetixbay.com/knowledge/glossary/thc.md) and [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) (often as total THC and total CBD), lot or batch number, producer licence, packaging date, health warnings and a standard cannabis symbol. Common prohibitions: health claims, appeal to young people, false or misleading statements. ## In practice Read the label for what it actually states. A packaging date is not a harvest date. Potency is a single lab result, which can be inflated or not representative of the whole lot. Whether [irradiation](https://genetixbay.com/knowledge/glossary/irradiation.md) must be disclosed varies by place. [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md) data is often voluntary. GenetixBay's buyer-beware position: flower labelled above about 35% [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) is not credible, and most flower labelled mid-20s to 30s really tests lower. See [buyer beware: label claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Child-resistant packaging**: the container standard, separate from the label. - **COA**: the [lab report](https://genetixbay.com/knowledge/glossary/coa.md) behind the label figures. ## Related terms [Child-resistant packaging](https://genetixbay.com/knowledge/glossary/child-resistant-packaging.md), [Compliance testing](https://genetixbay.com/knowledge/glossary/compliance-testing.md), [Cannabis irradiation](https://genetixbay.com/knowledge/glossary/irradiation.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: testing reveals inflated THC potency on retail cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 --- # Lacewing > Insects of the family Chrysopidae, mainly Chrysoperla species, whose larvae are general predators of aphids, thrips, mite eggs and young caterpillars. - Canonical: https://genetixbay.com/knowledge/glossary/lacewing.html - Also written: lacewings, green lacewing, Chrysoperla, Chrysoperla carnea, Chrysoperla rufilabris, aphid lion - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Green lacewings are delicate green insects of the family Chrysopidae with large, net-veined wings. The adults of the commonly sold *Chrysoperla* species feed on nectar, pollen and [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md). Their larvae, often called aphid lions, are voracious generalist predators with sickle-shaped jaws that eat [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), [thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md) nymphs, mite eggs and small caterpillars. ## In practice Growers buy lacewings as eggs on cards or as young larvae in a carrier and distribute them near pest colonies. Larvae hunt for two to three weeks before pupating. Because they eat almost anything small, including each other and other [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md), they are best used as a strike force on aphid hot spots rather than as the only programme. Eggs sit on hair-like stalks, which is how growers recognise wild lacewings outdoors. Avoid broad-spectrum sprays where they are active. ## Don't confuse with - **Ladybird larvae**: stockier, spiny, usually dark with orange marks. - **Brown lacewings**: a related family with similar predatory larvae. - **Syrphid fly larvae**: legless maggots that also eat aphids. ## Related terms [Ladybird](https://genetixbay.com/knowledge/glossary/ladybird.md), [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Aphidius](https://genetixbay.com/knowledge/glossary/aphidius.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. UC IPM. Pest Notes: Aphids (Publication 7404). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html 2. UConn IPM. Biological Control of Aphids. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-aphids/ --- # Ladybird > Predatory beetles of the family Coccinellidae, such as Hippodamia convergens, whose adults and larvae eat aphids and other soft-bodied pests. - Canonical: https://genetixbay.com/knowledge/glossary/ladybird.html - Also written: ladybug, ladybugs, ladybirds, lady beetle, convergent lady beetle, Hippodamia convergens, Coccinellidae, mealybug destroyer - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Ladybirds, called ladybugs or lady beetles in North America, are beetles of the family Coccinellidae. Most species are predators. Both adults and the alligator-shaped larvae eat [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), and the larvae usually eat more. The convergent lady beetle (*Hippodamia convergens*) is the species most often sold; the mealybug destroyer (*Cryptolaemus montrouzieri*) is a specialist used against [mealybugs](https://genetixbay.com/knowledge/glossary/mealybug.md). ## In practice Many commercially sold convergent lady beetles are collected from wild overwintering sites, and released adults tend to fly away within days, especially outdoors. Indoors, releasing them at dusk after misting plants, and closing vents, keeps more of them on the crop. Their best role is as a supplement on visible aphid colonies, alongside [parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md) and [lacewings](https://genetixbay.com/knowledge/glossary/lacewing.md). Wild ladybirds arriving outdoors are a good sign; avoid broad-spectrum sprays that kill them. Larvae look nothing like adults, so learn to recognise them before squashing "pests". ## Don't confuse with - **Lacewing larvae**: also called aphid lions, with sickle-shaped jaws. - **Asian lady beetle**: *Harmonia axyridis*, a predator that can become a nuisance indoors. - **Mexican bean beetle**: a plant-eating coccinellid, not a beneficial. ## Related terms [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Lacewing](https://genetixbay.com/knowledge/glossary/lacewing.md), [Aphidius](https://genetixbay.com/knowledge/glossary/aphidius.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Mealybug](https://genetixbay.com/knowledge/glossary/mealybug.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. UC IPM. Pest Notes: Aphids (Publication 7404). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html 2. UConn IPM. Biological Control of Aphids. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-aphids/ --- # Landrace > A landrace is a traditional, locally adapted cannabis population kept by farmers in one region over many generations, with its own type and plenty of internal variation. - Canonical: https://genetixbay.com/knowledge/glossary/landrace.html - Also written: landraces, land race, landrace strain, landrace variety, traditional variety - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A landrace is a population of a crop shaped by farmers and local conditions in one region over a long time. It has a recognisable type, local adaptation (to climate, [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md), pests and use) and more internal variation than a modern cultivar. It is maintained by saving seed from the best plants each season (Villa et al. 2005). ## In practice Cannabis landraces from Afghanistan, Pakistan, India, Nepal, Thailand, Mexico, Colombia, Jamaica, Lebanon, Morocco and other regions are the foundation of almost every modern line. [Hashish](https://genetixbay.com/knowledge/glossary/hashish.md), [charas](https://genetixbay.com/knowledge/glossary/charas.md) and [sinsemilla](https://genetixbay.com/knowledge/glossary/sinsemilla.md) traditions show those farmers mastered high-quality cannabis long before modern breeding. True landraces are under pressure. Imported hybrid seed has been crossed into many source populations, and modern genomic work shows how much mixing has occurred. Seed sold online as "landrace" may be a recent collection, a reselection or a hybrid. Ask when and where it was collected, how many parents were used and how it was maintained. ## Don't confuse with - **Heirloom**: a line kept outside its source region, often for decades; a landrace is kept where it evolved. - **IBL**: inbred and [stabilised](https://genetixbay.com/knowledge/glossary/stabilisation.md); a landrace is [open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md) and variable. - **Wild cannabis (feral)**: escaped populations, not farmer-maintained. ## Myth check Old landrace cannabis was not weak. See [old cannabis was not weak](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md) and, on collection ethics, [landrace hunting and biopiracy](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md). ## Related terms [Heirloom](https://genetixbay.com/knowledge/glossary/heirloom.md), [Open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Accession](https://genetixbay.com/knowledge/glossary/accession.md), [Introgression](https://genetixbay.com/knowledge/glossary/introgression.md), [Hybrid](https://genetixbay.com/knowledge/glossary/hybrid.md) ## Read more - [Landraces of the world: an overview](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) - [Polyhybrids vs landraces: what each gives a breeder](https://genetixbay.com/knowledge/breeding/polyhybrids-vs-landraces.md) ## Sources 1. Villa TCC, Maxted N, Scholten M, Ford-Lloyd B. 2005. Defining and identifying crop landraces. Plant Genetic Resources 3(3):373-384. https://doi.org/10.1079/PGR200591 2. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 3. Ren G, Zhang X, Li Y, et al. 2021. Large-scale whole-genome resequencing unravels the domestication history of Cannabis sativa. Science Advances 7(29):eabg2286. https://doi.org/10.1126/sciadv.abg2286 --- # Landrace hunter > A landrace hunter travels to cannabis-growing regions to collect seed from local farmer populations, ideally with consent, credit and benefit-sharing for source communities. - Canonical: https://genetixbay.com/knowledge/glossary/landrace-hunter.html - Also written: landrace hunting, landrace hunters, seed hunter, genetics hunter - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A landrace hunter is someone who travels to regions with traditional cannabis farming to find and collect seed from local populations, usually to preserve them, breed with them or sell them. ## In practice Landrace hunting has saved material that would otherwise have vanished, and it has also taken farmers' work without credit or payment. A responsible collection [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) like this: farmers know what is being collected and why, they agree to it, the collector records the village or region, date, local name and growing practice, and the source community receives credit and a fair share of any benefit. Collected seed should be grown out openly, documented and shared, not reduced to a brand name. Taking [cannabis seed](https://genetixbay.com/knowledge/glossary/achene.md) across borders is illegal in many places, and access to [genetic resources](https://genetixbay.com/knowledge/glossary/germplasm.md) is regulated by national law in many countries. Check local and national rules. ## Don't confuse with - **Seed bank (vendor)**: may sell "[landrace](https://genetixbay.com/knowledge/glossary/landrace.md)" seed that was collected long ago, remade, or hybridised. - **Biopiracy**: taking genetic resources or traditional knowledge without consent or [benefit-sharing](https://genetixbay.com/knowledge/glossary/benefit-sharing.md). ## Myth check GenetixBay position: landrace growers built the foundation of nearly every modern line and deserve far more credit. Landrace hunting vs [biopiracy](https://genetixbay.com/knowledge/glossary/biopiracy.md) is a real distinction: consent, credit and compensation make the difference. See [landrace hunting and biopiracy](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md). ## Related terms [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Biopiracy](https://genetixbay.com/knowledge/glossary/biopiracy.md), [Benefit-sharing](https://genetixbay.com/knowledge/glossary/benefit-sharing.md), [Nagoya Protocol](https://genetixbay.com/knowledge/glossary/nagoya-protocol.md), [Prior informed consent](https://genetixbay.com/knowledge/glossary/prior-informed-consent.md) ## Read more - [Landrace hunting or biopiracy? Benefit-sharing, consent and cannabis](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md) - [Landraces of the world: an overview](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) ## Sources 1. Secretariat of the Convention on Biological Diversity. 2011. Nagoya Protocol on Access to Genetic Resources and the Fair and Equitable Sharing of Benefits Arising from their Utilization. https://www.cbd.int/abs/ 2. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. --- # Larf > Larf is small, airy, underdeveloped buds from the lower, shaded parts of a plant, usually low in density and weight. - Canonical: https://genetixbay.com/knowledge/glossary/larf.html - Also written: larfy, larf buds, lurf, fluff - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Larf is the wispy, loose, undersized bud growth that forms deep in the canopy, where light intensity is too low for flowers to fill out. ## In practice Larf forms where light drops off: indoors, light intensity falls fast below the top of the canopy, and lower sites receive a fraction of the top's [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md). A plant with many low branches spends resources on sites that will never fill. Growers reduce larf by training for an [even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md) ([SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), manifolding) and by removing the lowest growth before or in early flower ([lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md)). GenetixBay's "tuck, don't pluck" approach favours moving leaves and branches into light over stripping where possible. Larf is still usable: it is often set aside for hash, edibles or personal use. ## Don't confuse with - **Popcorn buds**: small but dense buds; larf is small and airy. - **Foxtailing**: spiky regrowth on mature buds from heat or [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md). ## Related terms [Popcorn buds](https://genetixbay.com/knowledge/glossary/popcorn-buds.md), [Lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md), [Nugs](https://genetixbay.com/knowledge/glossary/nugs.md) ## Read more - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) - [SCROG: screen of green](https://genetixbay.com/knowledge/training/scrog.md) --- # LC-MS > LC-MS couples liquid chromatography with mass spectrometry, identifying compounds by mass as well as retention time; it is used for pesticides, mycotoxins and detailed cannabinoid profiling. - Canonical: https://genetixbay.com/knowledge/glossary/lc-ms.html - Also written: LC-MS/MS, LCMS, liquid chromatography-mass spectrometry, LC-QQQ, tandem mass spectrometry - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" LC-MS separates compounds by [liquid chromatography](https://genetixbay.com/knowledge/glossary/hplc.md), as in HPLC, then ionises them and measures their mass-to-charge ratio. Tandem instruments (LC-MS/MS, triple quadrupole) fragment each ion and monitor specific fragments, which makes them highly selective and able to quantify trace contaminants in a complex plant matrix. ## In practice Testing labs mainly use LC-MS/MS for [pesticide panels](https://genetixbay.com/knowledge/glossary/pesticide-panel.md) and [mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md), because it reaches parts-per-billion levels and separates target compounds from cannabis's crowded background. Research groups use high-resolution LC-MS for wide [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) profiling: Berman et al. (2018), from Dr. Dedi Meiri's lab, used ESI-LC/MS to profile scores of [phytocannabinoids](https://genetixbay.com/knowledge/glossary/phytocannabinoid.md), far beyond a routine panel. It's more expensive than HPLC-UV and needs careful calibration and matrix-matched standards. ## Don't confuse with - **HPLC-UV**: same separation, but a UV detector; cheaper, standard for potency. - **GC-MS**: gas-phase separation with mass detection; used for volatiles and some pesticides. - **MS (alone)**: the detector, not the full method. ## Related terms [HPLC](https://genetixbay.com/knowledge/glossary/hplc.md), [Pesticide panel](https://genetixbay.com/knowledge/glossary/pesticide-panel.md), [Mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md), [LOD](https://genetixbay.com/knowledge/glossary/lod.md), [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md) ## Sources 1. Berman P, Futoran K, Lewitus GM, Mukha D, Benami M, Shlomi T, Meiri D. 2018. A new ESI-LC/MS approach for comprehensive metabolic profiling of phytocannabinoids in Cannabis. Scientific Reports 8:14280. https://doi.org/10.1038/s41598-018-32651-4 --- # Leaf clawing > Leaves whose tips hook sharply downward like a claw, usually on dark green leaves; a classic sign of excess nitrogen, and also seen with waterlogged roots. - Canonical: https://genetixbay.com/knowledge/glossary/leaf-clawing.html - Also written: the claw, claw leaves, clawed leaves, eagle claw - Glossary category: Plant biology · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Leaf clawing is a downward hooking of the [leaflet](https://genetixbay.com/knowledge/glossary/leaflet.md) tips, so the leaf [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) like a bird's claw. On cannabis it is most often linked to excess nitrogen, especially a high [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) share, where leaves also turn very dark and glossy; a high ammonium share has been shown to harm cannabis growth and yield (Saloner and Bernstein 2022). The link between the claw shape itself and nitrogen is *Grower practice*. ## In practice Separate it from [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) by lifting the pot: a heavy, wet pot with whole leaves drooping and curling down suggests root oxygen, not nitrogen. Read [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md) and check the feed record. Twisted, glassy, clawed new growth with no other cause points to [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md). ## Don't confuse with - **Overwatering droop**: the whole leaf hangs and curls down, and recovers as the pot dries. - **Taco leaf**: edges fold up, not down. - **Praying leaves**: healthy leaves angled upward toward the light. ## Related terms [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) ## Read more - [Clawing leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/clawing-leaves.md) - [Cannabis lookalike problems: how to tell them apart](https://genetixbay.com/knowledge/diagnosis/lookalikes.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 --- # Leaf spot > Any disease that causes discrete dead spots on leaves; on cannabis, mainly fungi such as Septoria cannabis and Alternaria, plus some bacteria. - Canonical: https://genetixbay.com/knowledge/glossary/leaf-spot.html - Also written: leaf spots, leaf spot disease, Alternaria, brown leaf spot, fungal leaf spot - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Leaf spot is a descriptive term for any disease that produces distinct [necrotic spots](https://genetixbay.com/knowledge/glossary/necrosis.md) on leaves. On cannabis the commonest cause is *[Septoria cannabis](https://genetixbay.com/knowledge/glossary/septoria-leaf-spot.md)* (Septoria leaf spot); *Alternaria* species, *Cercospora* species and some bacteria also cause leaf spots, mostly outdoors. Spots often have a darker margin, a yellow halo, or concentric rings, depending on the organism. ## In practice Most leaf spot pathogens need wet leaves, so they appear after rain, heavy dew or overhead watering, and on lower leaves first where splash and humidity are highest. Growers check spots with a hand lens for tiny black fruiting bodies, which point to a fungus, and send samples to a plant diagnostic lab when unsure. Management is the same across most types: remove infected leaves, clear debris, water at the base, improve airflow, and rotate outdoor sites. Many "spots" turn out to be nutrient or [pH](https://genetixbay.com/knowledge/glossary/ph.md) problems, so check the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) before blaming a pathogen. ## Don't confuse with - **Calcium or potassium deficiency**: patterns linked to feeding and pH, no fruiting bodies. - **Light or spray burn**: spots where droplets or hot spots hit, not spreading. - **Spider mite stippling**: many tiny pale dots. ## Related terms [Septoria leaf spot](https://genetixbay.com/knowledge/glossary/septoria-leaf-spot.md), [Downy mildew](https://genetixbay.com/knowledge/glossary/downy-mildew.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md) ## Read more - [Septoria leaf spot (yellow leaf spot) in cannabis](https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.md) - [Rust-coloured spots on cannabis leaves: a differential](https://genetixbay.com/knowledge/diagnosis/rust-spots.md) ## Sources 1. Utah State University Extension. Hemp leaf spot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-leaf-spot 2. University of Kentucky Plant Pathology. Septoria leaf spot of hemp (PPFS-AG-H-01). https://plantpathology.mgcafe.uky.edu/files/ppfs-ag-h-01.pdf --- # Leaf temperature > Leaf temperature is the actual surface temperature of a leaf, which often differs from air temperature by 1–3 °C depending on light source and transpiration. - Canonical: https://genetixbay.com/knowledge/glossary/leaf-temperature.html - Also written: leaf temp, leaf surface temperature, canopy temperature, leaf temperature offset - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Leaf temperature is the temperature of the leaf tissue itself. It is set by a balance of energy gained (absorbed light and radiant heat) and lost ([transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) cooling, convection to air, radiation to cooler surfaces). It is the temperature that governs [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) rate and leaf [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), so it matters more than the room thermometer. ## In practice Under [LED](https://genetixbay.com/knowledge/glossary/led.md), which emits little radiant heat, a well-watered, transpiring leaf often sits 1–3 °C (2–5 °F) below air temperature. Under [HPS](https://genetixbay.com/knowledge/glossary/hps.md), the extra infrared often pushes leaves to or above air temperature. Nelson and Bugbee (2015) quantified this. It is the main reason a grower who switches from HPS to LED should raise room temperature: the goal is a similar leaf temperature, typically 24–28 °C (75–82 °F) in flower. Leaf temperature rising towards or above air temperature under LED can mean [stomata](https://genetixbay.com/knowledge/glossary/stomata.md) are closing, a sign of root problems, drought or VPD set too high. ## Don't confuse with - **Air temperature**: what the room thermometer reads. - **Canopy-top temperature near the fixture**: can be hotter than leaves lower down. - **Low-stress training (LST)**: an unrelated training method sharing the abbreviation; prefer "leaf temp" to avoid confusion. ## Related terms [Leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md), [IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md), [Temperature](https://genetixbay.com/knowledge/glossary/temperature.md), [LED vs HPS](https://genetixbay.com/knowledge/glossary/led-vs-hps.md), [Heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md) ## Read more - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) - [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) ## Sources 1. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # Leaf VPD > Leaf VPD is the vapour pressure deficit between the inside of a leaf, at leaf temperature, and the surrounding air; it is what actually drives transpiration. - Canonical: https://genetixbay.com/knowledge/glossary/leaf-vpd.html - Also written: LVPD, leaf vapor pressure deficit, leaf vapour pressure deficit, leaf-to-air VPD, leaf-air VPD - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Leaf VPD (leaf-to-air [vapour pressure deficit](https://genetixbay.com/knowledge/glossary/vpd.md)) is the difference between the saturation vapour pressure inside the leaf, assumed saturated at [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md), and the actual vapour pressure of the surrounding air. Because water moves from the wet leaf interior to the air, leaf VPD is the true driving force for [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md). Air VPD only equals leaf VPD when the leaf is at air temperature. ## In practice Leaf temperature differs from air temperature by light source and transpiration. Under [LED](https://genetixbay.com/knowledge/glossary/led.md), leaves commonly run about 1–3 °C below air; under [HPS](https://genetixbay.com/knowledge/glossary/hps.md) they can be near or above air temperature (Nelson and Bugbee 2015). Using air VPD alone can mislead you by several tenths of a kPa. Example: a grower at 26 °C air and 60% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) reads an air VPD of 1.35 kPa and thinks the room is dry. An [infrared thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md) shows the leaf at 24 °C. Leaf VPD is about 1.0 kPa, comfortably in the flower range. Raising humidity here would have been the wrong call. Measure leaf temperature on top-canopy leaves facing the light, several leaves, with an IR thermometer or thermal camera. ## Units and formula Leaf VPD (kPa) = es(T_leaf) − es(T_air) × RH ÷ 100, with es = 0.6108 × exp(17.27 × T ÷ (T + 237.3)). ## Don't confuse with - **Air VPD**: uses air temperature for both terms. - **Leaf temperature offset**: the input; leaf VPD is the result. ## Related terms [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md), [IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md), [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) ## Read more - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ## Sources 1. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 2. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm --- # Leafhopper > Small wedge-shaped jumping insects of the family Cicadellidae that suck plant sap; the beet leafhopper (Circulifer tenellus) spreads beet curly top virus to hemp. - Canonical: https://genetixbay.com/knowledge/glossary/leafhopper.html - Also written: leafhoppers, Cicadellidae, beet leafhopper, Circulifer tenellus, hoppers - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Leafhoppers are sap-feeding insects of the family Cicadellidae, usually 3-10 mm long, wedge-shaped and quick to jump sideways or fly when disturbed. Most cause little direct harm to cannabis. The species that matters is the beet leafhopper (*Circulifer tenellus*), which carries [beet curly top virus](https://genetixbay.com/knowledge/glossary/beet-curly-top-virus.md) into [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) and cannabis crops in the dry western United States. ## In practice Direct feeding shows as pale flecks on leaves. The real concern is [virus](https://genetixbay.com/knowledge/glossary/plant-virus.md) spread: one feeding visit from an infected beet leafhopper can transmit curly top, which then stunts and curls the plant with no cure. Outdoor growers in curly-top regions watch for leafhopper flights from weedy rangeland in spring and early summer. [Yellow sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) help monitor. Row covers on young plants, reducing nearby host weeds and removing infected plants promptly are the main tools. Sprays rarely stop virus spread, because the insect transmits before it dies. Check what is registered for cannabis locally. ## Don't confuse with - **Aphids**: slow-moving, soft-bodied colonies; they do not jump. - **Thrips**: tiny, slender and leave silvery scars. - **Planthoppers**: a related group with different antennae placement. ## Related terms [Beet curly top virus](https://genetixbay.com/knowledge/glossary/beet-curly-top-virus.md), [Plant virus](https://genetixbay.com/knowledge/glossary/plant-virus.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md) ## Sources 1. Colorado State University (Mountain Scholar). Beet curly top virus - beet leafhopper dynamics in hemp in Colorado. https://mountainscholar.org/items/690318d0-f830-4090-b0a5-c1e18581d7b5/full 2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Curly Top. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-curly-top --- # Leaflet > One of the separate serrated blades that make up a palmate cannabis leaf; a mature fan leaf typically has five to eleven leaflets. - Canonical: https://genetixbay.com/knowledge/glossary/leaflet.html - Also written: leaflets, leaf blade, finger, fingers, leaf fingers - Glossary category: Plant biology · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A leaflet is one blade of a compound leaf. Cannabis leaves are palmately compound: several leaflets radiate from the tip of a single [petiole](https://genetixbay.com/knowledge/glossary/petiole.md) like fingers from a palm. Leaflet count rises with maturity (one, three, five, seven, nine, eleven, occasionally thirteen) and then drops again as leaves get smaller toward the flowers. ## In practice Leaflet shape is the main thing people mean when they say a plant "[looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) indica" (broad, short leaflets) or "looks sativa" (long, narrow leaflets). That is a description of shape and nothing more. Leaflet width varies even across one plant and with light and nutrition. Leaflets are also where most diagnosis happens: where on the leaflet a symptom starts (tip, margin, between veins) and whether it is on old or new growth narrows the cause fast. Unusual leaflet forms (fused, webbed or single-blade "duckfoot") are genetic leaf-shape variants. ## Don't confuse with - **Leaf**: the whole compound organ including petiole and all leaflets. - **Fan leaf**: a large mature leaf; it is made of leaflets. - **Serration**: the saw-tooth edge of a leaflet. ## Myth check Broad leaflets do not mean a sedating effect, and narrow ones do not mean an energetic one. Leaf shape does not predict chemistry (Supported: Smith et al. 2022; Watts et al. 2021). See [indica, sativa, ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md). ## Related terms [Fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md), [Petiole](https://genetixbay.com/knowledge/glossary/petiole.md), [Serration](https://genetixbay.com/knowledge/glossary/serration.md), [True leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 2. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Leafminer > Insect larvae, on cannabis mainly Liriomyza fly maggots (family Agromyzidae), that tunnel between the leaf surfaces, leaving pale winding trails. - Canonical: https://genetixbay.com/knowledge/glossary/leafminer.html - Also written: leafminers, leaf miner, leaf miners, Liriomyza, agromyzid fly - Glossary category: Pests and diseases · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A leafminer is any insect larva that feeds inside a leaf, between the upper and lower surfaces. On cannabis the usual culprits are small agromyzid flies, mainly *Liriomyza* species. The adult female punctures the leaf to lay eggs; the larva then eats a pale, winding tunnel that widens as it grows, and finally drops out to pupate in the medium. ## In practice Leafminer trails are distinctive: serpentine white or tan lines, often with a dark thread of [frass](https://genetixbay.com/knowledge/glossary/frass.md) down the middle. Damage on cannabis is usually cosmetic and limited to [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md), mostly outdoors or in greenhouses. Picking off mined leaves and destroying them breaks the cycle. [Yellow sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) catch adults. In greenhouse crops, [parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md) such as *Diglyphus isaea* are used against them. Because larvae are protected inside the leaf, contact sprays do little. Check what is registered for cannabis locally. ## Don't confuse with - **Thrips**: surface scraping with silvery patches, not tunnels. - **Spider mite stippling**: tiny dots, no trails. - **Septoria leaf spot**: round spots with dark margins, not winding lines. ## Related terms [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md) ## Sources 1. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects --- # LED > An LED (light-emitting diode) grow light uses solid-state diodes to produce light; modern fixtures are the most efficient grow lights, at roughly 2.5–3 µmol/J. - Canonical: https://genetixbay.com/knowledge/glossary/led.html - Also written: LEDs, light-emitting diode, LED grow light, LED fixture, quantum board, LED bars - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A light-emitting diode (LED) is a semiconductor that emits light when current passes through it. Horticultural LED fixtures combine many diodes, usually phosphor-coated white chips plus deep red (around 660 nm) and sometimes far-red or UV, on boards or bars driven by a power supply. The spectrum is set by the diode mix and can be tuned freely. ## In practice Kusuma, Pattison and Bugbee (2020) placed the best horticultural LEDs near 3 [µmol/J](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), well above [HPS](https://genetixbay.com/knowledge/glossary/hps.md). More of the electricity becomes light and less becomes heat, and the heat that remains leaves through heatsinks rather than as radiant heat on the canopy. Leaves under LED tend to run cooler than under HPS at the same air temperature (Nelson and Bugbee 2015), so LED rooms are often run 1–3 °C (2–5 °F) warmer in air temperature to keep [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) in range. Practical notes: LEDs can be hung closer and dimmed, which makes it easy to overshoot [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) and bleach tops. Use a quantum meter, not the "equivalent watts" on the box. Diodes slowly lose output over thousands of hours; drivers are the usual failure point. ## Don't confuse with - **Blurple**: older red and blue-only LEDs. - **Full spectrum**: a marketing label, not a guarantee of efficacy. ## Myth check "LEDs need more [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md)" is a *Myth*. GenetixBay's position: calcium and magnesium demand depends mainly on **cultivar**, water source ([RO](https://genetixbay.com/knowledge/glossary/ro-water.md) vs tap) and medium ([coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) buffering), not on the light type. See [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md). ## Related terms [Photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), [HPS](https://genetixbay.com/knowledge/glossary/hps.md), [LED vs HPS](https://genetixbay.com/knowledge/glossary/led-vs-hps.md), [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md), [Full spectrum](https://genetixbay.com/knowledge/glossary/full-spectrum.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) ## Sources 1. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 3. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988 --- # LED vs HPS > LED vs HPS is the debate over whether LED or high-pressure sodium lights grow better cannabis; LEDs are clearly more efficient, while final-quality differences remain an open question. - Canonical: https://genetixbay.com/knowledge/glossary/led-vs-hps.html - Also written: LED versus HPS, HPS vs LED, LED or HPS, LED vs HID - Glossary category: Environment and light · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" "LED vs HPS" is the long-running grower argument over which light type produces the best cannabis. Two questions get mixed together. Efficiency is settled: modern [LEDs](https://genetixbay.com/knowledge/glossary/led.md) deliver about 2.5–3 [µmol/J](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) against roughly 1.7–2.1 for [HPS](https://genetixbay.com/knowledge/glossary/hps.md), so they give the same photons for less power and heat (Kusuma, Pattison and Bugbee 2020). *Established*. Final quality (aroma, resin, density, taste) at the same light level is not settled. ## In practice Switching from HPS to LED is not a like-for-like swap. LED canopies receive less radiant heat, so [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) runs lower at the same air temperature (Nelson and Bugbee 2015). Growers who keep their HPS room settings often see slower growth and blame the light. Raise air temperature 1–3 °C (2–5 °F) and re-check leaf [VPD](https://genetixbay.com/knowledge/glossary/vpd.md). Irrigation needs also change because [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) falls. Many reports of "HPS buds are better" come from comparisons that changed several things at once: intensity, temperature, cultivar or grower experience. ## Don't confuse with - **Spectrum differences**: part of the comparison, but intensity and leaf temperature usually matter more. - **Wattage**: compare µmol/s and µmol/J, not watts. ## Myth check GenetixBay's house position: **"perhaps".** Quality differences between LED and HPS are an **open [Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md)**. The plan is a proper controlled study (same cultivar and clone source, matched [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) and leaf VPD, blind evaluation) to settle it. Until then it is *Contested*. Follow the trial in [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [LED](https://genetixbay.com/knowledge/glossary/led.md), [HPS](https://genetixbay.com/knowledge/glossary/hps.md), [Photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Sources 1. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 3. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988 --- # Licensed producer > A licensed producer is a business authorised by a regulator to grow, process or sell cannabis commercially, subject to security, tracking, testing and labelling rules. - Canonical: https://genetixbay.com/knowledge/glossary/licensed-producer.html - Also written: LP, LPs, licensed grower, licensed cultivator, licensed producers, commercial licence holder - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A licensed producer (LP) is a business holding a government licence to cultivate and often process or sell cannabis. Licence classes vary: large-scale cultivation, micro-cultivation, nursery, processing, testing, retail. ## In practice Licensed production comes with obligations: site security, plant and batch tracking, mandatory lab testing for potency and contaminants, product recalls, record keeping, packaging and labelling rules. These costs weigh heavily on small growers. GenetixBay's founder holds the opinion that the commercial model of [legalisation](https://genetixbay.com/knowledge/glossary/decriminalisation.md) has been bad for quality: scale economics, contamination controls met by decontamination (including [irradiation](https://genetixbay.com/knowledge/glossary/irradiation.md)), and regulatory costs have pushed out many small, careful growers. That is presented as opinion, backed by the documented costs and practices, not as a claim about any particular licence holder. The constructive answer is craft production where licences allow it, and growing your own where that is legal. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Licensed retailer**: sells to the public, does not usually grow. - **Hemp licence**: a separate regime in many places. ## Related terms [Seed-to-sale tracking](https://genetixbay.com/knowledge/glossary/seed-to-sale-tracking.md), [Compliance testing](https://genetixbay.com/knowledge/glossary/compliance-testing.md), [Labelling requirements](https://genetixbay.com/knowledge/glossary/labelling-requirements.md), [Cannabis irradiation](https://genetixbay.com/knowledge/glossary/irradiation.md), [Home grow](https://genetixbay.com/knowledge/glossary/home-grow.md) --- # Life table > A record of survival and egg-laying at each age for a cohort of pests at set conditions, from which development time, fecundity and r_m are calculated. - Canonical: https://genetixbay.com/knowledge/glossary/life-table.html - Also written: life tables, fertility life table, age-stage life table, demographic parameters - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A life table follows a group of eggs at one temperature, humidity and host through to the death of the last adult, recording how many survive each day and how many eggs each female lays. From it come the development time of each stage, adult longevity, [fecundity](https://genetixbay.com/knowledge/glossary/fecundity.md), [sex ratio](https://genetixbay.com/knowledge/glossary/sex-ratio.md), the net reproductive rate ([R0](https://genetixbay.com/knowledge/glossary/net-reproductive-rate.md)), [generation time](https://genetixbay.com/knowledge/glossary/generation-time.md) and the [intrinsic rate of increase (r_m)](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), using the method Birch set out in 1948. ## In practice Almost all pest life tables are lab studies on leaf discs or a standard host such as bean, cucumber or rose, not cannabis. They are still the best numbers available. Use them for comparisons and for timing re-applications at your room temperature, and expect real cannabis rooms to run somewhat slower because of predators, plant chemistry and crowding. ## Don't confuse with - **Degree-day model**: uses only development time, not reproduction. - **Field population count**: what is there now, not what could grow. ## Related terms [Intrinsic rate of increase (r_m)](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [Net reproductive rate (R0)](https://genetixbay.com/knowledge/glossary/net-reproductive-rate.md), [Generation time](https://genetixbay.com/knowledge/glossary/generation-time.md), [Fecundity](https://genetixbay.com/knowledge/glossary/fecundity.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) ## Sources 1. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605 --- # Light compensation point > The light compensation point is the PPFD at which a leaf's photosynthesis exactly balances its respiration, so net carbon gain is zero. - Canonical: https://genetixbay.com/knowledge/glossary/light-compensation-point.html - Also written: compensation point, LCP, light compensation - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The light compensation point is the light intensity at which a leaf fixes exactly as much [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) through [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) as it releases through respiration. Below it the leaf is a net consumer of sugars; above it the leaf is a net exporter. For sun-adapted crops it typically sits in the tens of [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md). It rises with temperature, because respiration speeds up faster than photosynthesis. ## In practice The idea explains why deep, shaded lower growth contributes little. Leaves and [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md) sitting in heavy shade at the bottom of a dense canopy may be near or below their compensation point for much of the day, so they consume more than they produce. That is the logic behind [lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md) and removing the lowest larf. It is also a reason not to over-strip. A leaf receiving moderate light is still a net producer feeding nearby buds. GenetixBay's preference is "tuck, don't pluck": train and tuck leaves to open light paths before removing working leaves. ## Don't confuse with - **Light saturation point**: the high end, where extra light stops helping. - **CO2 compensation point**: the CO2 concentration at which photosynthesis balances respiration at a given light level. ## Related terms [Light saturation point](https://genetixbay.com/knowledge/glossary/light-saturation-point.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x --- # Light deprivation > Light deprivation (light dep) covers greenhouse or outdoor plants with blackout material to give long nights, forcing photoperiod plants to flower earlier than the natural season. - Canonical: https://genetixbay.com/knowledge/glossary/light-deprivation.html - Also written: light dep, light-dep, dep, blackout, forced flowering - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Light deprivation is the practice of shortening the day artificially for sun-grown plants by pulling an opaque cover over them each evening and removing it in the morning, so they get roughly 12 hours of uninterrupted darkness. [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis responds by flowering, even in midsummer when natural nights are short. ## In practice Light dep lets greenhouse and outdoor growers harvest in summer, before autumn rain and mould, and run two or more crops per year. Covers must be truly lightproof and pulled at the same time every day; inconsistency or leaks can cause [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) or stress. Under covers, heat and humidity build quickly in warm weather, so ventilation and [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) are important. Automated blackout curtains do this on a timer in commercial greenhouses; small growers use tarps on frames. ## Don't confuse with - **Darkness before harvest**: a separate idea (24-72 h of dark before chopping) that GenetixBay classes as a myth. - **Indoor flip**: the same switch done with a light timer. ## Related terms [Greenhouse growing](https://genetixbay.com/knowledge/glossary/greenhouse-growing.md), [Outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md), [Flip](https://genetixbay.com/knowledge/glossary/flip.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) ## Read more - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) --- # Light intensity > Light intensity is how much photosynthetic light reaches the plants per unit area and time, measured as PPFD in µmol/m²/s; it is the biggest light lever on yield. - Canonical: https://genetixbay.com/knowledge/glossary/light-intensity.html - Also written: intensity, light level, light strength, how much light - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Light intensity, in horticulture, means the photon flux density at the plant: [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) in µmol/m²/s. It is the single biggest lighting factor in cannabis yield. Spectrum and [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) matter, but within sensible ranges neither moves yield as much as giving the canopy more photons. ## In practice Llewellyn and colleagues (2022) found indoor cannabis yield rose in proportion to light intensity across the range they tested, and Rodriguez-Morrison and colleagues (2021) saw gains up to about 1,800 µmol/m²/s in flower. *Established*. The practical ceiling is set by everything else: heat removal, [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md), water and nutrient supply, and the cultivar. Typical progression: [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) 100–300, veg 400–700, flower 700–1,100 µmol/m²/s without CO2 enrichment. Raise intensity over a week or so rather than in one jump; leaves acclimate. Signs you have outrun the rest of the environment: upward-cupping ([tacoing](https://genetixbay.com/knowledge/glossary/taco-leaf.md)) top leaves, bleached tips, and slower rather than faster growth. "Intensity" in casual talk often means fixture wattage or "how bright it [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md)". Neither is a measurement of what the plant receives; distance, reflectors and spectrum change everything. ## Don't confuse with - **DLI**: intensity accumulated over the day. - **Wattage**: electrical input, not light output. - **Brightness (lux)**: eye-weighted, misleading under grow lights. ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md), [Light saturation point](https://genetixbay.com/knowledge/glossary/light-saturation-point.md), [Inverse square law](https://genetixbay.com/knowledge/glossary/inverse-square-law.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) ## Sources 1. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # Light leak > A light leak is unwanted light entering the grow space during the dark period; in flower it can delay or disrupt flowering in photoperiod cannabis. - Canonical: https://genetixbay.com/knowledge/glossary/light-leak.html - Also written: light leaks, light pollution, dark period interruption, night interruption, light leaking - Glossary category: Environment and light · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A light leak is any light reaching flowering plants during their scheduled night: gaps in tent zips, indicator [LEDs](https://genetixbay.com/knowledge/glossary/led.md) on equipment, a hallway light under the door, a streetlamp through a window. [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis measures the length of uninterrupted darkness through [phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md), and even a brief or dim interruption can reset that clock. ## In practice Eckels and Bugbee (2024) reported that low-level night light pollution delayed flowering in cannabis. Other short-day crops respond to remarkably low levels. A practical test: sit inside the tent with lights off for five minutes until your eyes adjust. If you can see your hand, find the leak. Cover equipment LEDs with tape, seal zip ends and use a green headlamp only for brief checks. In veg, leaks are harmless. In flower they show as delayed [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) formation, a return to vegetative growth ([re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md)) or uneven ripening. ## Don't confuse with - **Sunrise/sunset ramp**: planned dim light; it counts as day. - **Night break**: a deliberate interruption used to hold plants in veg on short days. ## Myth check "Light leaks cause [hermaphrodites](https://genetixbay.com/knowledge/glossary/hermaphrodite.md)" needs care. GenetixBay's house position: herms are mainly a sign of **genetics from poor breeding**, not normal cannabis. Stress such as light interruption can *reveal* a susceptible line; it does not make a stable one herm. Fix the leak, but cull plants that throw intersex flowers and don't breed from them. See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md). ## Related terms [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) ## Read more - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) ## Sources 1. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis --- # Light saturation point > The light saturation point is the PPFD above which photosynthesis stops rising; for cannabis it is unusually high and moves upwards with CO2 and temperature. - Canonical: https://genetixbay.com/knowledge/glossary/light-saturation-point.html - Also written: saturation point, LSP, light saturation, photosynthetic saturation - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The light saturation point is the light level at which a leaf's [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) rate plateaus: more photons no longer raise carbon gain. It is read from a light-response curve. It is not a fixed number. It rises with [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) concentration and with temperature up to the optimum, and it differs between single leaves and whole canopies, where lower leaves are shaded. ## In practice Chandra and colleagues (2008) measured cannabis leaf photosynthesis rising to around 1,500 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) at 25–30 °C (77–86 °F) and ambient CO2. Whole-plant trials go further: Rodriguez-Morrison and colleagues (2021) saw flower yield keep rising up to about 1,800 µmol/m²/s, because a canopy saturates later than any one leaf. *Established*. For growers, the useful idea is diminishing returns. Each extra 100 µmol/m²/s above about 1,000 buys less, costs the same in power and heat, and needs more CO2 and tighter [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) to pay off. Many rooms without CO2 enrichment stop at 900–1,100 µmol/m²/s for that reason. ## Don't confuse with - **Light compensation point**: the low end, where photosynthesis just balances respiration. - **Light stress**: damage when absorbed light exceeds what the leaf can use or dissipate; it can happen below the saturation point if heat or VPD is wrong. ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Light compensation point](https://genetixbay.com/knowledge/glossary/light-compensation-point.md), [CO2 enrichment](https://genetixbay.com/knowledge/glossary/co2-enrichment.md), [Light stress](https://genetixbay.com/knowledge/glossary/light-stress.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [CO₂ enrichment: when it pays, how much, and how to stay safe](https://genetixbay.com/knowledge/environment/co2-enrichment.md) ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # Light stress > Light stress is damage when leaves or buds absorb more light than they can use or dissipate, showing as bleached white or yellow tops nearest the fixture. - Canonical: https://genetixbay.com/knowledge/glossary/light-stress.html - Also written: light burn, light bleaching, bleaching, photobleaching, white tops, light damage - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Light stress (light burn, bleaching) happens when the light a tissue absorbs outpaces its capacity to use the energy in [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) or shed it safely as heat. Excess energy forms reactive oxygen species that destroy chlorophyll and other pigments. The classic sign is bleaching: top leaves and bud [bracts](https://genetixbay.com/knowledge/glossary/bract.md) closest to the light turn pale yellow, then white, while lower growth stays green. ## In practice Bleaching shows up most often under high-output [LEDs](https://genetixbay.com/knowledge/glossary/led.md) hung too close, because LEDs emit less radiant heat and growers do not feel the warning on their hand the way they would under HPS. It is more likely when [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) is high (above about 1,200 µmol/m²/s at the tops), CO2 is ambient, [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) is wrong or [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) is very high, and late in flower when leaves are senescing. Signs in order: upward cupping (tacoing) of top leaves, yellowing between veins at the top only, then bleached white bracts. Fix by raising or dimming the fixture to bring top PPFD back to 900–1,100 µmol/m²/s, and check leaf temperature and VPD. Bleached buds do not regreen; they are usually lower in potency and aroma. ## Don't confuse with - **Nutrient deficiency**: yellowing that follows mobility patterns (old vs new leaves), not distance from the light. - **Heat stress**: driven by temperature; often occurs alongside light stress. - **Foxtailing**: a growth form change, which can be a response to light or [heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md). ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md), [Light saturation point](https://genetixbay.com/knowledge/glossary/light-saturation-point.md), [Foxtailing](https://genetixbay.com/knowledge/glossary/foxtailing.md) ## Read more - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x --- # Limonene > Limonene is a monoterpene with a citrus aroma, found in citrus peel and many cannabis cultivars, where it is often among the top three terpenes. - Canonical: https://genetixbay.com/knowledge/glossary/limonene.html - Also written: d-limonene, (+)-limonene, limonine, lemonene - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Limonene is a cyclic [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md). The (+)-form, d-limonene, dominates citrus peel oil and smells of orange and lemon; cannabis produces mainly the (-)-form, which smells more pine-lemon. It is one of the most frequent [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) in commercial flower, often paired with [beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md) in the "sweet, gassy, citrus" profile that dominates many markets. ## In practice Typical flower readings run 0.1-0.8% w/w. Limonene is volatile and oxidises in air; oxidation products are part of the stale smell of old buds. Note that a lemony aroma isn't proof of limonene: some citrus-like notes come from other compounds such as [terpinolene](https://genetixbay.com/knowledge/glossary/terpinolene.md), [valencene](https://genetixbay.com/knowledge/glossary/valencene.md) or esters. Only a [terpene test](https://genetixbay.com/knowledge/glossary/terpene-test.md) tells you. ## Don't confuse with - **Valencene**: a citrus-smelling [sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), much less volatile. - **Linalool**: floral, not citrus. - **Citral/lemon aldehydes**: other citrus compounds, minor in cannabis. ## Myth check Claims that limonene makes a cultivar "uplifting" are not established by controlled human data; effects are only reported. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md), [Beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md), [Valencene](https://genetixbay.com/knowledge/glossary/valencene.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Linalool > Linalool is a floral, lavender-scented monoterpene alcohol found in lavender and some cannabis cultivars, usually at low levels below 0.3% w/w. - Canonical: https://genetixbay.com/knowledge/glossary/linalool.html - Also written: linalol, linolool, beta-linalool, linalyl alcohol - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Linalool is an acyclic [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md) alcohol, strictly a monoterpenoid. It is the [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) aroma compound of lavender and occurs in coriander, basil, birch and many flowers. In cannabis it is a floral, sweet, slightly spicy note that is usually a secondary [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) rather than the dominant one. ## In practice Typical flower readings run from [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md) to about 0.3% w/w. A few cultivar families are notably linalool-rich, and breeders who chase floral profiles select for it with [terpene tests](https://genetixbay.com/knowledge/glossary/terpene-test.md). As an alcohol, linalool is a little less volatile than the hydrocarbon monoterpenes but still sensitive to warm, fast drying. ## Don't confuse with - **Linalyl acetate**: the ester partner in lavender oil, rarely reported in cannabis. - **Geraniol**: another floral monoterpene alcohol, rosier in scent. - **Linoleic acid**: a fatty acid, unrelated despite the similar name. ## Myth check Linalool is often marketed as "calming". Animal and inhalation studies exist, but there is no established human evidence that the amount in cannabis produces such an effect; effects are only reported. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Geraniol](https://genetixbay.com/knowledge/glossary/geraniol.md), [Bisabolol](https://genetixbay.com/knowledge/glossary/bisabolol.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. 2. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Line > A line is a population of plants descended from chosen parents and maintained over generations under one name, with recorded lineage. - Canonical: https://genetixbay.com/knowledge/glossary/line.html - Also written: lines, seed line, genetic line, breeding line - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A line is a breeding population carried on over generations from defined parents, under one name. It implies continuity: you can make more of it, and the next batch should resemble the last. ## In practice A breeder "working a line" grows each generation, selects parents for the next, and records which plants went into which batch. "Is it a line or a cross?" is a fair question to ask a seller: a single cross of two clones is one generation with no track record, while a line has been grown out, selected and tested several times. Lines are tracked on GenetixBay by [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), with each batch of seed recorded separately, because the same name can cover very different batches if the parents changed. ## Don't confuse with - **Strain**: a popular name that may refer to a line, a cut or just a label. - **IBL**: a line inbred until it breeds fairly true; a stricter claim. - **Cut**: one individual kept by [cloning](https://genetixbay.com/knowledge/glossary/cloning.md). ## Related terms [Cross](https://genetixbay.com/knowledge/glossary/cross.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Breeder](https://genetixbay.com/knowledge/glossary/breeder.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md) ## Read more - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) - [How to document lineage evidence (GB-ID evidence levels L0-L4)](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md) --- # Line breeding > Line breeding is a mild form of inbreeding in which plants are mated within a family, often back towards one outstanding ancestor, to concentrate its traits while limiting inbreeding. - Canonical: https://genetixbay.com/knowledge/glossary/line-breeding.html - Also written: linebreeding, line-bred, line breed, line work - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Line breeding means keeping matings within one family or line, usually so that offspring stay closely related to one superior ancestor, without the full intensity of [selfing](https://genetixbay.com/knowledge/glossary/selfing.md) or repeated [full-sib crosses](https://genetixbay.com/knowledge/glossary/sib-cross.md). The aim is to concentrate that ancestor's good [alleles](https://genetixbay.com/knowledge/glossary/allele.md) while keeping [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) moderate. ## In practice A cannabis breeder might have one exceptional female. Instead of selfing her, the breeder crosses her to a selected male, picks the best sons and daughters, crosses them with each other and occasionally back to her (if she is kept as a clone), and keeps several family branches going in parallel. Branches can later be crossed together to restore vigour. Line breeding is the patient middle path between [outcrossing](https://genetixbay.com/knowledge/glossary/outcross.md) everything and inbreeding hard. It depends on keeping enough families and records: which plant came from which cross, and how each branch performed. ## Don't confuse with - **Backcross**: a specific, repeated cross to one recurrent parent; line breeding is broader. - **Selfing**: the most intense inbreeding. - **Line (market use)**: "a line" can mean any seed family; line breeding is a method. ## Related terms [Inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md), [Backcross](https://genetixbay.com/knowledge/glossary/backcross.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Sib cross](https://genetixbay.com/knowledge/glossary/sib-cross.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md) ## Read more - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Linkage > Linkage is the tendency of genes that sit close together on the same chromosome to be inherited together, rather than independently. - Canonical: https://genetixbay.com/knowledge/glossary/linkage.html - Also written: genetic linkage, linked genes, linkage drag, linked traits - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Linkage is the tendency of [genes](https://genetixbay.com/knowledge/glossary/gene.md) that are close together on a [chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md) to be inherited as a unit. They break apart only when crossing over (recombination) happens between them during meiosis, and the closer they are, the rarer that is. ## In practice Linkage helps and hurts. It helps [marker-assisted selection](https://genetixbay.com/knowledge/glossary/marker-assisted-selection.md): a DNA marker tightly linked to a trait gene predicts the trait in seedlings. It hurts when an unwanted trait rides along with a wanted one. Breeders call that linkage drag: you backcross a trait into a line and a chunk of the donor chromosome comes with it, sometimes carrying poorer vigour or an off aroma. In cannabis the region around the [THCA](https://genetixbay.com/knowledge/glossary/thca.md) and [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) genes is a well-studied case. It is a [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) of repeats and duplicated synthase copies with little recombination, so it tends to move as a block (Laverty et al. 2019; Grassa et al. 2021). ## Units and formula Distance is measured in centimorgans (cM): 1 cM ≈ 1% recombination per generation between two loci. ## Don't confuse with - **Independent assortment**: the default for genes on different chromosomes. - **Sex linkage**: genes on the X or Y chromosome, inherited with sex. - **Pleiotropy**: one gene affecting several traits; linkage is two genes travelling together. ## Related terms [Independent assortment](https://genetixbay.com/knowledge/glossary/independent-assortment.md), [Locus](https://genetixbay.com/knowledge/glossary/locus.md), [Chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md), [QTL](https://genetixbay.com/knowledge/glossary/qtl.md), [Marker-assisted selection](https://genetixbay.com/knowledge/glossary/marker-assisted-selection.md), [Introgression](https://genetixbay.com/knowledge/glossary/introgression.md) ## Read more - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. Laverty KU, Stout JM, Sullivan MJ, et al. 2019. A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci. Genome Research 29(1):146-156. https://doi.org/10.1101/gr.242594.118 2. Grassa CJ, Weiblen GD, Wenger JP, et al. 2021. A new Cannabis genome assembly associates elevated cannabidiol (CBD) with hemp introgressed into marijuana. New Phytologist 230(4):1665-1679. https://doi.org/10.1111/nph.17243 3. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 --- # Live resin > Live resin is a solvent-based cannabis extract made from fresh frozen plant material instead of dried and cured flower, to retain more volatile aroma compounds. - Canonical: https://genetixbay.com/knowledge/glossary/live-resin.html - Also written: live extract, live hydrocarbon extract, live BHO, live-resin - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Live resin is a concentrate extracted with a solvent, most commonly a hydrocarbon such as butane or propane, from plants frozen right after harvest. Because the material skips drying and curing, a larger share of the volatile [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) survives into the extract than when dried flower is used. The finished product often has a sauce, [badder](https://genetixbay.com/knowledge/glossary/badder.md) or sugar consistency. ## In practice Live resin is a product category on dispensary menus, and it is usually priced above [cured resin](https://genetixbay.com/knowledge/glossary/cured-resin.md). "Live" describes the starting material, not a method or a purity level. Extraction with solvents is a regulated industrial process that requires licensed, engineered equipment; it should never be attempted at home. GenetixBay defines the product and gives no extraction information. ## Don't confuse with - **Live rosin**: from the same type of starting material, but [solventless](https://genetixbay.com/knowledge/glossary/solventless.md). - **Cured resin**: extracted from dried and [cured](https://genetixbay.com/knowledge/glossary/curing.md) material. - **Rosin**: solventless; resin (as in live resin) is a [solvent extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md). ## Related terms [Live rosin](https://genetixbay.com/knowledge/glossary/live-rosin.md), [Cured resin](https://genetixbay.com/knowledge/glossary/cured-resin.md), [Fresh frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md), [Sauce](https://genetixbay.com/knowledge/glossary/sauce.md), [Diamonds](https://genetixbay.com/knowledge/glossary/diamonds.md) --- # Live rosin > Live rosin is rosin pressed from ice water hash made from fresh frozen plants, preserving more of the volatile aroma of the living plant; it is solventless. - Canonical: https://genetixbay.com/knowledge/glossary/live-rosin.html - Also written: live hash rosin, LHR, fresh frozen rosin, live-rosin - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Live rosin is made in three stages: whole plants or flowers are frozen soon after harvest ([fresh frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md)), washed in ice water to separate [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) (bubble hash), and the dried [hash](https://genetixbay.com/knowledge/glossary/hash.md) is pressed into [rosin](https://genetixbay.com/knowledge/glossary/rosin.md). "Live" means the starting material was never dried and cured, so more [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) survive. No solvent is used at any stage. ## In practice Live rosin is often considered the top tier of [solventless concentrates](https://genetixbay.com/knowledge/glossary/solventless.md), and it commands a premium because it needs good washing cultivars, careful freezing, cold handling and skilled processing. Russo et al. (2021) reported that a fresh-frozen ice water method preserved [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene profiles](https://genetixbay.com/knowledge/glossary/terpene-profile.md) closely. Textures include badder, jam and sauce-like forms. GenetixBay defines the product only; no processing parameters. ## Don't confuse with - **Live resin**: also from fresh frozen material, but extracted with solvents. - **Flower rosin**: pressed from dried flower, not from hash. - **Hash rosin**: may be live or cured, depending on the starting material. ## Related terms [Rosin](https://genetixbay.com/knowledge/glossary/rosin.md), [Hash rosin](https://genetixbay.com/knowledge/glossary/hash-rosin.md), [Fresh frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md), [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Live resin](https://genetixbay.com/knowledge/glossary/live-resin.md), [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md) ## Sources 1. Russo EB, Plumb J, Whiteley VL. 2021. Novel solventless extraction technique to preserve cannabinoid and terpenoid profiles of fresh cannabis inflorescence. Molecules 26(18):5496. https://doi.org/10.3390/molecules26185496 --- # Living soil > Living soil is an organic growing medium managed to sustain an active soil food web, so microbes and invertebrates release nutrients and the soil is reused across cycles. - Canonical: https://genetixbay.com/knowledge/glossary/living-soil.html - Also written: living organic soil, LOS, living soil bed, soil food web, beneficial soil biology - Glossary category: Systems and media · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Living soil is a soil or soil-like mix built from compost, aeration, minerals and [organic amendments](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md), managed so that bacteria, fungi, protozoa, [nematodes](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md) and worms remain active. The organisms break down organic matter and release nutrients, so the grower feeds the soil rather than the plant, usually with top-dressed amendments and water rather than bottled fertiliser. ## In practice Living soil works best in larger volumes: beds or containers of 40-100 L or more, often reused for many cycles with [no-till](https://genetixbay.com/knowledge/glossary/no-till.md) methods. Water quality matters (chlorine-free is often recommended), mulch keeps the surface moist, and cover crops can keep roots in the soil between plants. It is forgiving and low-input once established, but slower to correct: [deficiencies](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) are fixed with amendments that take days to weeks to release. ## Myth check House position: a well-grown hydro run gives a well-grown living-soil run a run for its money, even on taste; plants mostly don't care where their ions come from. Whether a symbiotic soil-plant effect adds flavour is an open question and a candidate [Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md) (blind taste panel). See [living soil](https://genetixbay.com/knowledge/systems/living-soil.md). ## Don't confuse with - **Super soil**: heavily amended, but not necessarily managed for biology or reuse. ## Related terms [No-till](https://genetixbay.com/knowledge/glossary/no-till.md), [Super soil](https://genetixbay.com/knowledge/glossary/super-soil.md), [Top dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md), [Mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md), [Compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) ## Read more - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) ## Sources 1. Brady NC, Weil RR, 2017. The Nature and Properties of Soils, 15th ed. Pearson. --- # Locus > A locus is the fixed position on a chromosome where a particular gene or DNA marker sits; the plural is loci. - Canonical: https://genetixbay.com/knowledge/glossary/locus.html - Also written: loci, gene locus, genetic locus - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A locus is the fixed physical position on a [chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md) where a [gene](https://genetixbay.com/knowledge/glossary/gene.md) or a DNA marker sits. The plural is loci. Every plant of the species has the same loci in the same order (barring rearrangements); what differs between plants is which [alleles](https://genetixbay.com/knowledge/glossary/allele.md) occupy them. ## In practice Breeders talk about loci when one position controls a clear trait. The [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase region is often called the B locus, after de Meijer's model of [THC](https://genetixbay.com/knowledge/glossary/thc.md)/CBD inheritance. [Autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) behaviour maps to a major locus named Autoflower1 (Toth et al. 2022). DNA tests report results locus by locus: a [genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md) panel might read a few thousand SNP loci and compare them between two cuts. When a trait is controlled by many loci of small effect, the regions are called [quantitative trait loci](https://genetixbay.com/knowledge/glossary/qtl.md) (QTL). Most yield and vigour traits fall in that group. ## Don't confuse with - **Gene**: a gene occupies a locus, but a locus can also be a marker with no known function. - **Allele**: the variant found at the locus. - **Chromosome**: the whole DNA molecule that carries thousands of loci. Cannabis has 10 chromosome pairs. ## Related terms [Gene](https://genetixbay.com/knowledge/glossary/gene.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md), [QTL](https://genetixbay.com/knowledge/glossary/qtl.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 2. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 --- # LOD > The LOD (limit of detection) is the lowest amount of a compound a method can reliably tell apart from zero, but not necessarily measure accurately. - Canonical: https://genetixbay.com/knowledge/glossary/lod.html - Also written: limit of detection, detection limit, MDL, method detection limit - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The limit of detection is the smallest concentration at which a method can say "this compound is present" with stated confidence. Below the LOD, the signal can't be separated from instrument noise and blank variation. It is often estimated as about three times the standard deviation of blank measurements, though methods differ. ## In practice A [COA](https://genetixbay.com/knowledge/glossary/coa.md) might list myclobutanil with LOD 0.01 µg/g and result "[ND](https://genetixbay.com/knowledge/glossary/non-detect.md)". That means the lab saw nothing at or above 0.01 µg/g, not that the sample contains zero. A result between the LOD and the [LOQ](https://genetixbay.com/knowledge/glossary/loq.md) shows the compound is probably present but the number isn't reliable; many labs report those as " Lollipopping removes the lower branches and small shoots on a plant, usually around the flip, so energy goes to the top buds and airflow improves underneath. - Canonical: https://genetixbay.com/knowledge/glossary/lollipopping.html - Also written: lollipop, lollipopped, lolli-popping, under-canopy pruning, bottom stripping - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Lollipopping is pruning the lower third or so of a plant, removing small branches, weak [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md) and lower leaves that sit in the shade beneath the canopy. What remains [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) like a lollipop: bare stem below, dense foliage and [colas](https://genetixbay.com/knowledge/glossary/cola.md) on top. ## In practice Most growers lollipop just before or within about the first two to three weeks of flower, when it is clear which shoots will reach the canopy. The aims are fewer small, airy "[popcorn](https://genetixbay.com/knowledge/glossary/popcorn-buds.md)" buds, better airflow under the canopy (lower humidity pockets, less risk of mould), and easier watering access. Work in stages on a sensitive plant rather than all at once. The evidence is grower practice. It removes tissue that receives little light, so yield losses should be small, but light-hungry lower leaves can still contribute. ## Don't confuse with - **Defoliation**: removing [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md), often throughout the canopy. - **Schwazzing**: aggressive whole-plant [defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md) at set points in flower. ## Myth check House position: "tuck, don't pluck". Remove what is truly shaded and useless; keep productive leaves. See [defoliation and lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md). ## Related terms [Defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md), [Schwazzing](https://genetixbay.com/knowledge/glossary/schwazzing.md), [Bud site](https://genetixbay.com/knowledge/glossary/bud-site.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md), [Tucking](https://genetixbay.com/knowledge/glossary/tucking.md) ## Read more - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) --- # Long-term storage > Keeping cured cannabis for months or years with minimal loss, by holding it cool, dark, airtight and at a stable water activity of about 0.55-0.65. - Canonical: https://genetixbay.com/knowledge/glossary/long-term-storage.html - Also written: cannabis storage, storing cannabis, stash storage, storing buds, long term storage - Glossary category: Harvest, drying and curing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Long-term storage covers what happens after the cure. The enemies are light, heat, oxygen and moisture swings. [THC](https://genetixbay.com/knowledge/glossary/thc.md) degrades slowly to [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) mostly through oxidation, and [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) evaporate. Stored dark at room temperature, cannabis keeps reasonably well for one to two years; in light and warmth the loss is much faster (Fairbairn et al. 1976; Zamengo et al. 2019). ## In practice The basics: - **Container**: airtight glass, filled well to limit headspace; opaque or kept in a dark cupboard. - **Temperature**: cool and stable, roughly 15-21 °C (60-70 °F) or cooler; avoid heat swings. - **Moisture**: stable around 0.55-0.65 aw, set by a proper cure. - **Light**: none. UV and visible light speed THC breakdown. - **Handling**: open as little as possible. Freezing [cured](https://genetixbay.com/knowledge/glossary/curing.md) flower is debated. Frozen [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) become brittle and break off with handling. If you freeze, seal airtight first and let jars warm fully before opening to avoid condensation. House position: [humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md) are not needed, a marketing gimmick that robs terpenes. ## Don't confuse with - **Curing**: the active finishing phase, with [burping](https://genetixbay.com/knowledge/glossary/burping.md). - **Seed storage**: seeds need drier conditions and cold. - **Vacuum sealing**: can crush buds; it's one storage option, not a must. ## Related terms [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md), [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Humidity pack](https://genetixbay.com/knowledge/glossary/humidity-pack.md) ## Read more - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) ## Sources 1. Fairbairn JW, Liebmann JA, Rowan MG. 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1-7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x 2. Zamengo L, Bettin C, Badocco D, et al. 2019. The role of time and storage conditions on the composition of hashish and marijuana samples: a four-year study. Forensic Science International 298:131-137. https://doi.org/10.1016/j.forsciint.2019.02.058 3. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html --- # LOQ > The LOQ (limit of quantitation) is the lowest concentration a method can measure with acceptable accuracy and precision; below it a result is reported as Loud is slang for flower with a very strong, room-filling aroma, often implying high quality. - Canonical: https://genetixbay.com/knowledge/glossary/loud.html - Also written: loud pack, loudpack, so loud, loud weed - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Loud describes flower whose aroma is so strong it fills a room when the jar opens. It is praise for intensity of smell, and often stands in for quality in general. ## In practice Loudness comes from volatile compounds ([terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and minor [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) compounds among them) and from how well those were preserved after harvest. Slow drying in a cool, dark room, a cure that lowers moisture gradually, and airtight, cool storage keep flower loud. Heat, light, open air and [over-drying](https://genetixbay.com/knowledge/glossary/over-drying.md) make it quiet quickly. Grinding releases far more aroma than smelling an intact bud. ## Don't confuse with - **Gas**: one specific loud profile (fuel, diesel). - **Strong**: smell is not potency. A loud jar can test modestly and a quiet one high. ## Related terms [Dank](https://genetixbay.com/knowledge/glossary/dank.md), [Gas](https://genetixbay.com/knowledge/glossary/gas.md), [Terps](https://genetixbay.com/knowledge/glossary/terps.md), [Fire](https://genetixbay.com/knowledge/glossary/fire.md) ## Read more - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) --- # LST > LST (low-stress training) bends and ties stems so the plant grows wide and flat, exposing more bud sites to light without cutting or breaking tissue. - Canonical: https://genetixbay.com/knowledge/glossary/lst.html - Also written: low-stress training, low stress training, tie-down, tying down, bending branches - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Low-stress training is the gradual bending and tying of stems so the main top is pulled down and sideways and lower branches rise to the same height. The plant does not lose any tissue, so recovery time is minimal. The goal is an even, [flat canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md) where many [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) share the same light. ## In practice Start once the plant has 4-5 nodes and the stem is flexible. Bend the main stem over and anchor it to the pot rim with [soft ties](https://genetixbay.com/knowledge/glossary/plant-ties.md), then keep pulling up-turning tips outward every day or two. Stems bend best in the warm part of the light period, and a turgid plant snaps more easily than a slightly dry one. Keep LST going into the first two to three weeks of flower, while the plant [stretches](https://genetixbay.com/knowledge/glossary/stretch.md). LST is the preferred technique for [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md): it adds yield without the recovery pause of cutting. ## Don't confuse with - **HST**: [high-stress training](https://genetixbay.com/knowledge/glossary/hst.md), which deliberately damages tissue (topping, [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md)). - **SCROG**: a screen-based system that uses LST-style tucking as its method. ## Related terms [HST](https://genetixbay.com/knowledge/glossary/hst.md), [Topping](https://genetixbay.com/knowledge/glossary/topping.md), [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [Plant ties](https://genetixbay.com/knowledge/glossary/plant-ties.md), [Even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md) ## Read more - [LST: low-stress training](https://genetixbay.com/knowledge/training/lst.md) ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ --- # Lux > Lux is illuminance weighted to human eye sensitivity (lumens per square metre); it misreads grow lights because plants use red and blue light the eye underweights. - Canonical: https://genetixbay.com/knowledge/glossary/lux.html - Also written: lx, lux meter, lux reading, illuminance - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Lux (lx) is a photometric unit: lumens per square metre. Photometric units weight light by the human eye's sensitivity, which peaks in green-yellow at 555 nm and falls steeply towards deep red and blue. Plants use exactly those red and blue wavelengths heavily, so lux is the wrong instrument for [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md). ## In practice A cheap lux meter can be useful for one thing: comparing the same lamp type at different heights or positions. It cannot compare an [HPS](https://genetixbay.com/knowledge/glossary/hps.md) with a red-heavy [LED](https://genetixbay.com/knowledge/glossary/led.md), or a white LED with a blurple one, because their lux-to-PPFD ratios differ. Rough [conversion factors](https://genetixbay.com/knowledge/glossary/conversion-factor.md) (lux per 1 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md)): sunlight about 54, cool white LED about 65–75, HPS about 80–85. A deep red and blue fixture can read low in lux while delivering plenty of PPFD. Phone apps that use the camera to estimate PPFD apply one of these factors and can be badly wrong under a different spectrum. ## Units and formula - 1 lux = 1 lumen/m² - 1 [foot-candle](https://genetixbay.com/knowledge/glossary/foot-candle.md) = 10.764 lux - PPFD ≈ lux ÷ factor for that light source (approximate only) ## Don't confuse with - **PPFD**: counts photons from 400 to 700 nm equally, regardless of how bright they look. - **Lumens**: total eye-weighted output of a lamp; lux is lumens per square metre. ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Foot-candle](https://genetixbay.com/knowledge/glossary/foot-candle.md), [PAR](https://genetixbay.com/knowledge/glossary/par.md), [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) ## Sources 1. McCree KJ, 1972. The action spectrum, absorptance and quantum yield of photosynthesis in crop plants. Agricultural Meteorology 9:191–216. --- # Macronutrient > A macronutrient is an essential element plants need in large amounts, measured in tens to hundreds of mg/L: nitrogen, phosphorus and potassium, plus calcium, magnesium and sulfur. - Canonical: https://genetixbay.com/knowledge/glossary/macronutrient.html - Also written: macronutrients, macro nutrients, macros, primary nutrients, major nutrients - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Macronutrients are the essential mineral elements a plant needs in the largest quantities, typically present in dry leaf tissue at 0.1% to several percent. The primary macronutrients are nitrogen (N), phosphorus (P) and potassium (K). Calcium (Ca), magnesium (Mg) and [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) (S) are also macronutrients, often called [secondary nutrients](https://genetixbay.com/knowledge/glossary/secondary-nutrient.md). Carbon, hydrogen and oxygen come from air and water and are not counted as fertiliser nutrients. ## In practice A typical cannabis hydro feed carries macronutrients in the tens to hundreds of mg/L (ppm): roughly 150-200 N, 30-60 P, 150-300 K, 120-200 Ca, 40-70 Mg and 50-100 S, varying with stage and system. [Fertiliser labels](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md) highlight [N-P-K](https://genetixbay.com/knowledge/glossary/npk-ratio.md), but Ca, Mg and S shortages cause just as many problems, especially with [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md). ## Don't confuse with - **Micronutrient**: needed in far smaller amounts, but just as essential. - **Macros in diet slang**: protein, fat and carbohydrate, unrelated. - **Importance**: "macro" refers to quantity, not to how essential an element is. ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Secondary nutrient](https://genetixbay.com/knowledge/glossary/secondary-nutrient.md), [N-P-K ratio](https://genetixbay.com/knowledge/glossary/npk-ratio.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md) ## Read more - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Magnesium > Magnesium (Mg) is a mobile secondary nutrient at the centre of every chlorophyll molecule; deficiency causes interveinal yellowing on older leaves. - Canonical: https://genetixbay.com/knowledge/glossary/magnesium.html - Also written: Mg, Mg2+, magnesium deficiency, Mg deficiency - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Magnesium is a secondary macronutrient absorbed as Mg2+. It sits at the centre of the chlorophyll molecule, activates the enzymes that fix carbon and handle ATP, and helps load sugars into the phloem. It is mobile, so the plant strips it from older leaves when supply runs short. ## In practice Classic [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) is [interveinal chlorosis](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) on lower and middle leaves: green veins with yellow tissue between, later turning brown. Hydro feeds usually run about 40-70 mg/L (ppm) Mg, most often from [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md). High potassium, calcium or ammonium competes with Mg at the root, so a deficiency can appear even with Mg in the tank. Morad and Bernstein found cannabis responds to Mg supply across a range before plateauing. ## Don't confuse with - **Iron deficiency**: also interveinal, but on new growth. - **Potassium deficiency**: starts at leaf margins rather than between the veins. - **Epsom salt**: a common Mg source, not a synonym for magnesium. ## Myth check [LEDs](https://genetixbay.com/knowledge/glossary/led.md) do not create a magnesium need (Evidence: house position, Myth). Mg demand is driven by cultivar, [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) and coco [cation exchange](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md). See [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Secondary nutrient](https://genetixbay.com/knowledge/glossary/secondary-nutrient.md), [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md), [Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md) ## Read more - [Magnesium (Mg) in cannabis: interveinal yellowing, targets and the K-Ca competition](https://genetixbay.com/knowledge/nutrients/magnesium.md) - [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) ## Sources 1. Morad D, Bernstein N. 2023. Response of medical cannabis to magnesium (Mg) supply at the vegetative growth phase. Plants 12(14):2676. https://doi.org/10.3390/plants12142676 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Magnesium nitrate > Magnesium nitrate supplies about 9.5% magnesium and 11% nitrogen as nitrate, and unlike Epsom salt it can share a concentrated stock with calcium nitrate. - Canonical: https://genetixbay.com/knowledge/glossary/magnesium-nitrate.html - Also written: Mg(NO3)2, magnesium nitrate hexahydrate, 11-0-0 magnesium, mag nitrate - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Magnesium nitrate is a soluble salt of magnesium and [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), sold as the hexahydrate Mg(NO3)2·6H2O. It contains about 9.5% Mg and 10.9% N, all as nitrate. It carries no [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), so it does not precipitate with calcium. ## In practice It is used to add magnesium where sulfate is already high, or to build a one-part or [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) concentrate where calcium and magnesium must share a bottle. It also adds nitrogen, so it is less suitable than [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md) when tapering N in late flower. Liquid Cal-Mag supplements are often [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md) plus magnesium nitrate. ## Units and formula 1 g/L gives about 95 mg/L (ppm) Mg and 109 mg/L N. ## Don't confuse with - **Magnesium sulfate (Epsom salt)**: Mg with [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md), no nitrogen, must stay apart from concentrated calcium. - **Calcium nitrate**: the calcium counterpart. - **Cal-Mag**: a finished product that may contain magnesium nitrate. ## Related terms [Magnesium](https://genetixbay.com/knowledge/glossary/magnesium.md), [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md), [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Magnesium (Mg) in cannabis: interveinal yellowing, targets and the K-Ca competition](https://genetixbay.com/knowledge/nutrients/magnesium.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Magnesium sulfate > Magnesium sulfate heptahydrate, sold as Epsom salt, is the common hydro magnesium source, supplying about 9.9% magnesium and 13% sulfur. - Canonical: https://genetixbay.com/knowledge/glossary/magnesium-sulfate.html - Also written: Epsom salt, Epsom salts, MgSO4, magnesium sulphate, MgSO4·7H2O, epsom - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Magnesium sulfate is the salt of magnesium and [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md). The form used in growing is the heptahydrate (MgSO4·7H2O), the same chemical as pharmacy Epsom salt, at about 9.9% Mg and 13% S. Anhydrous and monohydrate forms are stronger per gram, so check which you have. ## In practice It belongs in the B stock, away from concentrated [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), because calcium and sulfate form gypsum. Growers using [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) or coco often add it to bring Mg into the 40-70 mg/L (ppm) range. Pharmacy grade works, but avoid scented bath products, which carry oils and dyes. It is sometimes used as a [foliar spray](https://genetixbay.com/knowledge/glossary/foliar-feeding.md), though root feeding is more reliable. ## Units and formula 1 g/L of the heptahydrate gives about 99 mg/L (ppm) Mg and 130 mg/L S. ## Don't confuse with - **Magnesium nitrate**: Mg plus nitrogen, can share a stock with calcium. - **Cal-Mag**: a blend, not the same as Epsom salt. - **Table salt**: [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md), harmful in a feed. ## Related terms [Magnesium](https://genetixbay.com/knowledge/glossary/magnesium.md), [Sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md), [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md), [Foliar feeding](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Magnesium (Mg) in cannabis: interveinal yellowing, targets and the K-Ca competition](https://genetixbay.com/knowledge/nutrients/magnesium.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Morad D, Bernstein N. 2023. Response of medical cannabis to magnesium (Mg) supply at the vegetative growth phase. Plants 12(14):2676. https://doi.org/10.3390/plants12142676 --- # Mainlining > Mainlining is a training method that tops a plant low, removes lower growth and splits it symmetrically into a set number of evenly sized main colas. - Canonical: https://genetixbay.com/knowledge/glossary/mainlining.html - Also written: main-lining, main lining, mainline - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mainlining is a structured training system that combines low topping, removal of all growth below the topping point, and repeated symmetrical topping so that every main stem is fed from a single central "hub". The result is a plant with 4, 8 or 16 identical [colas](https://genetixbay.com/knowledge/glossary/cola.md) sitting at the same height. ## In practice Top above the third node, strip everything below, tie the two remaining shoots horizontally, then top each again to make four, then eight. Each branch draws evenly from the hub, so buds tend to be uniform. The cost is time: mainlining typically adds about two to four weeks of veg compared with an untrained plant. It suits [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md) and [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md); it is a poor fit for [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md). Evidence is grower practice. Cannabis research does show that plant architecture affects how uniform [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) content is across the canopy, which supports the logic of even colas. ## Don't confuse with - **Manifolding**: often used as a synonym; some growers reserve it for the hub-and-arms shape specifically. - **Mainline (drugs)**: unrelated. ## Related terms [Manifolding](https://genetixbay.com/knowledge/glossary/manifolding.md), [Topping](https://genetixbay.com/knowledge/glossary/topping.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md) ## Read more - [Mainlining and manifolding: building a symmetrical plant](https://genetixbay.com/knowledge/training/mainlining-manifolding.md) ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ --- # Male selection > Male selection is the choice of which male plants become parents, judged by their vigour, structure, early aroma and above all by the quality of their offspring. - Canonical: https://genetixbay.com/knowledge/glossary/male-selection.html - Also written: selecting males, male choice, picking a male, male hunting, stud male selection - Glossary category: Genetics and breeding · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Male selection is choosing which males to breed from. A male contributes half the [genes](https://genetixbay.com/knowledge/glossary/gene.md) of every seed he sires, so his choice matters as much as the female's. Because males do not produce bud, breeders judge them on indirect traits and, best of all, on their offspring. ## In practice Breeders start with many regular [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and keep the males that show vigour, good branching, strong stems, resistance, sensible flowering time and good aroma when stems are rubbed or early flowers open. Some males also show resin on [calyxes](https://genetixbay.com/knowledge/glossary/calyx.md) and leaves. Unwanted males are culled before they shed pollen. The real test is a [progeny test](https://genetixbay.com/knowledge/glossary/progeny-test.md): cross the candidate males to the same female, grow out the seed from each, and see which male's offspring are best. Keep the winners as clones or store their pollen, so a proven male can be used again. ## Don't confuse with - **Pheno hunt**: usually means selecting females for flower. - **Feminised breeding**: skips males entirely, and with them half of selection. ## Myth check House position: males are a necessity and are encouraged and rewarded on GenetixBay. The [male showcase](https://genetixbay.com/knowledge/glossary/stud-book.md) is the Stud Book. Selecting males carefully is one of the clearest differences between breeders and [pollen chuckers](https://genetixbay.com/knowledge/glossary/pollen-chucker.md); see [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md). ## Related terms [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Progeny test](https://genetixbay.com/knowledge/glossary/progeny-test.md), [Regular seed](https://genetixbay.com/knowledge/glossary/regular-seed.md), [Pollen](https://genetixbay.com/knowledge/glossary/pollen.md), [Test cross](https://genetixbay.com/knowledge/glossary/test-cross.md) ## Read more - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) - [Breeders vs pollen chuckers: what real cannabis breeding looks like](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 --- # Manganese > Manganese (Mn) is a micronutrient that splits water in photosynthesis and activates many enzymes; low pH can raise it to toxic levels. - Canonical: https://genetixbay.com/knowledge/glossary/manganese.html - Also written: Mn, Mn2+, manganese deficiency, manganese toxicity - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Manganese is a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) absorbed as Mn2+. It is essential to the water-splitting complex of photosystem II and activates a range of enzymes. It is largely immobile in the plant. Its availability rises sharply as root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) falls. ## In practice [Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) shows as interveinal mottling on young and middle leaves, with less contrast than iron [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md) and sometimes small dead spots. It is most common at high pH. Toxicity is the more frequent problem in acidic soil or hydro run too low: brown speckling on older leaves and induced [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md), because Mn competes with Fe. Hydro feeds usually carry roughly 0.5-1 mg/L (ppm) Mn, typically from [manganese sulfate](https://genetixbay.com/knowledge/glossary/manganese-sulfate.md) or a chelate. ## Don't confuse with - **Iron deficiency**: brighter yellow with sharper green veins on the newest leaves. - **Magnesium deficiency**: older leaves, broad [interveinal yellowing](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md). - **Rust-coloured spots from light or pathogens**: check pH and history before blaming Mn. ## Myth check When Mn toxicity appears, the fix is usually raising root-zone pH back into range, not cutting the micronutrient blend. See [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md). ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), [Manganese sulfate](https://genetixbay.com/knowledge/glossary/manganese-sulfate.md), [Iron](https://genetixbay.com/knowledge/glossary/iron.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) ## Read more - [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Manganese sulfate > Manganese sulfate (MnSO4) is the common soluble manganese source for DIY micronutrient mixes, about 32% Mn in the monohydrate form. - Canonical: https://genetixbay.com/knowledge/glossary/manganese-sulfate.html - Also written: MnSO4, manganese sulphate, MnSO4·H2O, manganous sulfate - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Manganese sulfate is the salt of [manganese](https://genetixbay.com/knowledge/glossary/manganese.md) and [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), usually sold as the monohydrate (MnSO4·H2O) at about 32% Mn. A tetrahydrate form also exists, with less Mn per gram (about 24.6%). It is soluble and pale pink. ## In practice It is the usual Mn source in home-made micronutrient stocks, often alongside zinc sulfate, [copper sulfate](https://genetixbay.com/knowledge/glossary/copper-sulfate.md), boric acid and [sodium molybdate](https://genetixbay.com/knowledge/glossary/sodium-molybdate.md), with [chelated iron](https://genetixbay.com/knowledge/glossary/iron-chelate.md) added separately. The final solution typically needs only about 0.5-1 mg/L (ppm) Mn, so the salt is dosed in milligrams per litre, ideally from a concentrated stock rather than weighed fresh each time. In high-pH conditions, [chelated](https://genetixbay.com/knowledge/glossary/chelate.md) manganese is more reliable than the sulfate. ## Units and formula 1 mg of the monohydrate per litre gives about 0.32 mg/L (ppm) Mn. To reach 0.5 ppm Mn, add about 1.6 mg/L. ## Don't confuse with - **Magnesium sulfate**: [Epsom salt](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md); Mg, not Mn. - **Manganese chelate (Mn-EDTA)**: stays available at higher [pH](https://genetixbay.com/knowledge/glossary/ph.md). ## Related terms [Manganese](https://genetixbay.com/knowledge/glossary/manganese.md), [Sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md) ## Read more - [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Manifolding > Manifolding builds a plant's structure as a central hub with symmetrical horizontal arms, so every top receives equal sap flow and grows to similar size. - Canonical: https://genetixbay.com/knowledge/glossary/manifolding.html - Also written: manifold, manifold training, building a manifold, hub training - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Manifolding is the hub-and-arms structure at the heart of mainlining. The plant is topped low, and the two remaining branches are tied out flat to form the manifold. Each arm is then topped again, and the new shoots are trained out to form the next tier, so every final [cola](https://genetixbay.com/knowledge/glossary/cola.md) is the same number of branch points from the root. ## In practice Growers use "manifold" and "mainline" almost interchangeably. Where they differ, manifolding describes building the hub (often 8 arms off a flat base), and mainlining describes the overall method including stripping lower growth. Symmetry is the point: an uneven manifold produces uneven colas. Allow extra [veg time](https://genetixbay.com/knowledge/glossary/veg-time.md), typically two to four weeks. Like mainlining, this is grower practice without controlled cannabis yield trials. ## Don't confuse with - **Irrigation manifold**: the pipe that splits water to many drip lines; same word, a systems term. - **SCROG**: a screen used to spread [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md); can be combined with a manifold. ## Related terms [Mainlining](https://genetixbay.com/knowledge/glossary/mainlining.md), [Topping](https://genetixbay.com/knowledge/glossary/topping.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md) ## Read more - [Mainlining and manifolding: building a symmetrical plant](https://genetixbay.com/knowledge/training/mainlining-manifolding.md) --- # Marijuana > Marijuana is a common name for drug-type cannabis flower; the word entered US English from Mexican Spanish and became the standard term in 20th-century law. - Canonical: https://genetixbay.com/knowledge/glossary/marijuana.html - Also written: marihuana, weed, pot, ganja, herb, grass - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Marijuana (also spelled marihuana) is a popular name for the dried flowering [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) of drug-type cannabis. Weed, pot, ganja, herb and grass are other common names. Botanically, all of these are *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)* L. ## In practice The word comes from Mexican Spanish and spread in US English in the early 20th century. It was written into US federal law in the 1937 Marihuana Tax Act and later statutes, and many laws still use it. Some people now avoid the word because of how it was used in early prohibition campaigns; regulators and industry increasingly prefer "cannabis". Ganja comes from Sanskrit and Hindi and entered English through South Asian and Caribbean use. GenetixBay uses "cannabis" in technical writing and does not police other words. ## Don't confuse with - **Hemp**: cannabis grown for fibre, seed or low-THC flower, often defined in law by a [THC](https://genetixbay.com/knowledge/glossary/thc.md) limit. - **Hashish**: compressed resin, not flower. - **Cannabis**: the genus name, and the neutral modern term for both. ## Related terms [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md), [Sinsemilla](https://genetixbay.com/knowledge/glossary/sinsemilla.md), [Scheduling](https://genetixbay.com/knowledge/glossary/scheduling.md), [420](https://genetixbay.com/knowledge/glossary/420.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) --- # Marker-assisted selection > Marker-assisted selection is choosing seedlings or parents by testing DNA markers linked to wanted traits, so plants can be selected before they flower. - Canonical: https://genetixbay.com/knowledge/glossary/marker-assisted-selection.html - Also written: MAS, marker assisted selection, marker-assisted breeding, molecular breeding, genomic selection - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Marker-assisted selection (MAS) uses DNA markers tightly linked to a trait to decide which plants to keep, rather than waiting for the trait to show. A leaf punch from a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) is tested, and only plants carrying the wanted marker [alleles](https://genetixbay.com/knowledge/glossary/allele.md) are grown on. Genomic selection extends the idea to many markers at once for [quantitative traits](https://genetixbay.com/knowledge/glossary/quantitative-trait.md). ## In practice The most useful cannabis markers so far are for traits with simple genetics: sex (a Y-linked marker), [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase type, and major flowering-time loci such as Autoflower1 (Toth et al. 2020; Toth et al. 2022). Screening 200 seedlings for sex and chemotype in week two saves months of space compared with growing them all to flower. MAS is weaker for complex traits like yield, [terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) or [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md), where many genes each contribute a little and the environment adds noise. It also depends on [linkage](https://genetixbay.com/knowledge/glossary/linkage.md): if the marker is not inside the gene, recombination can break the association in some offspring. ## Don't confuse with - **Genetic engineering**: MAS selects among natural variation; it does not change DNA. - **Genotyping for identity**: the same tools, used to compare plants rather than to select. ## Related terms [Genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md), [SNP](https://genetixbay.com/knowledge/glossary/snp.md), [QTL](https://genetixbay.com/knowledge/glossary/qtl.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md) ## Read more - [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md) ## Sources 1. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 2. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 3. Barcaccia G, Palumbo F, Scariolo F, Vannozzi A, Borin M, Bona S. 2020. Potentials and challenges of genomics for breeding cannabis cultivars. Frontiers in Plant Science 11:573299. https://doi.org/10.3389/fpls.2020.573299 --- # Mealybug > Soft-bodied sap-sucking insects of the family Pseudococcidae, covered in white waxy filaments, that hide in stem joints and roots and excrete honeydew. - Canonical: https://genetixbay.com/knowledge/glossary/mealybug.html - Also written: mealybugs, mealy bug, Pseudococcidae, citrus mealybug, Planococcus citri, root mealybug - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mealybugs are scale insects of the family Pseudococcidae, about 2-4 mm long, whose oval bodies are coated in white, mealy wax. They feed on sap through a stylet and excrete [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md). [Foliar](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) species such as the citrus mealybug (*Planococcus citri*) cluster in leaf axils and stem joints; root mealybugs (*Rhizoecus* species) live in the root ball. ## In practice Mealybugs are an uncommon cannabis pest and nearly always come in on houseplants or clones from a mixed collection. Look for cottony tufts in branch crotches, egg sacs, honeydew and [sooty mould](https://genetixbay.com/knowledge/glossary/sooty-mould.md). Root mealybugs show as white waxy patches on the root ball and the inside of the pot. The wax repels water-based sprays, so contact products struggle. [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) in greenhouses uses the [mealybug destroyer](https://genetixbay.com/knowledge/glossary/ladybird.md) beetle (*Cryptolaemus montrouzieri*) and [parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md). Quarantine incoming plants and keep ornamentals out of the grow. Check what is registered for cannabis locally. ## Don't confuse with - **Aphids**: no wax coat, faster breeding, cornicles on the rear. - **Powdery mildew**: white patches on leaf surfaces that wipe off and have no insects. - **Scale insects**: fixed under a hard or waxy shell, not mobile. ## Related terms [Scale insect](https://genetixbay.com/knowledge/glossary/scale-insect.md), [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Ladybird](https://genetixbay.com/knowledge/glossary/ladybird.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md), [Root aphid](https://genetixbay.com/knowledge/glossary/root-aphid.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects --- # Measurement uncertainty > Measurement uncertainty is the quantified range around a lab result within which the true value is expected to lie, typically stated as ± a value at about 95% confidence. - Canonical: https://genetixbay.com/knowledge/glossary/measurement-uncertainty.html - Also written: uncertainty of measurement, MU, measurement error, ± uncertainty, expanded uncertainty, error bars - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Every measurement carries uncertainty from weighing, extraction, calibration, instrument response, the analyst and, above all, [sampling](https://genetixbay.com/knowledge/glossary/homogenisation.md). Laboratories accredited to [ISO/IEC 17025](https://genetixbay.com/knowledge/glossary/iso-17025.md) must estimate it. It is commonly reported as an expanded uncertainty (coverage factor k = 2, roughly 95% confidence), for example "total [THC](https://genetixbay.com/knowledge/glossary/thc.md) 21.0% ± 1.5% w/w". ## In practice That ±1.5% means a reading of 21.0% is consistent with a true value anywhere from about 19.5% to 22.5% for that sample. Two COAs of 20.1% and 21.7% from the same batch may not disagree at all. Uncertainty usually grows with heterogeneous samples: a single bud from the top of a plant can differ by several points from a lower one, which the lab's own uncertainty doesn't capture. ## Units and formula Same units as the result; also expressed as relative %. Expanded uncertainty U = k × combined standard uncertainty, with k = 2 for about 95% coverage. ## Don't confuse with - **LOD/LOQ**: thresholds at the low end, not the spread of a result. - **Lab-to-lab bias**: a systematic offset, which uncertainty estimates may not include. ## Myth check Uncertainty explains small differences, not 10-point gaps. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md), [Homogenisation (sampling)](https://genetixbay.com/knowledge/glossary/homogenisation.md), [Proficiency testing](https://genetixbay.com/knowledge/glossary/proficiency-testing.md), [ISO/IEC 17025](https://genetixbay.com/knowledge/glossary/iso-17025.md), [Label inflation](https://genetixbay.com/knowledge/glossary/label-inflation.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Ellison SLR, Williams A (eds). 2012. Eurachem/CITAC Guide: Quantifying Uncertainty in Analytical Measurement, 3rd edition. 2. ISO/IEC 17025:2017. General requirements for the competence of testing and calibration laboratories. International Organization for Standardization, Geneva. --- # Medical vs adult-use > Medical and adult-use cannabis are separate legal channels: medical access depends on authorisation by a health professional, adult-use on age alone. - Canonical: https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.html - Also written: medical cannabis, adult-use cannabis, recreational cannabis, rec vs med, medicinal cannabis - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Medical and adult-use (recreational) cannabis are two legal routes to the same plant. Medical access requires a patient authorisation, registration or prescription, and may allow larger possession or [cultivation limits](https://genetixbay.com/knowledge/glossary/personal-cultivation-limit.md), different taxes or products. Adult-use access is open to adults above a minimum age, through licensed retail or [home grow](https://genetixbay.com/knowledge/glossary/home-grow.md), without any health justification. ## In practice Some places have only a medical programme, some only adult-use, and some both in parallel with different rules for each channel. The product in a medical and an adult-use jar may come from the same facility. Advertising and product claims are tightly limited in many places, especially any claim of health benefit. GenetixBay does not make medical claims. Effects people report are reported, not promised, and nothing here is advice about treating any condition. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Decriminalisation**: reduced penalties; not a legal supply channel. - **Hemp-derived products**: often regulated under separate [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) law. ## Related terms [Licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md), [Home grow](https://genetixbay.com/knowledge/glossary/home-grow.md), [Possession limit](https://genetixbay.com/knowledge/glossary/possession-limit.md), [Labelling requirements](https://genetixbay.com/knowledge/glossary/labelling-requirements.md) --- # Mendelian inheritance > Mendelian inheritance is the pattern in which single genes pass from parents to offspring in predictable ratios, following Mendel's laws of segregation and independent assortment. - Canonical: https://genetixbay.com/knowledge/glossary/mendelian-inheritance.html - Also written: Mendelian genetics, Mendel's laws, Mendelian ratios, Mendelism, simple inheritance - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mendelian inheritance is the pattern by which single [genes](https://genetixbay.com/knowledge/glossary/gene.md) pass to offspring in predictable ratios. Gregor Mendel described it from pea crosses in 1866: each parent passes one of its two alleles per gene at random ([segregation](https://genetixbay.com/knowledge/glossary/segregation.md)), and genes on different chromosomes are inherited independently ([independent assortment](https://genetixbay.com/knowledge/glossary/independent-assortment.md)). ## In practice Mendelian ratios are the breeder's first tool. A single-gene trait with a [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) and a [recessive allele](https://genetixbay.com/knowledge/glossary/recessive.md) gives a 3:1 visible ratio in the F2 and 1:1 in a [test cross](https://genetixbay.com/knowledge/glossary/test-cross.md). Cannabis traits that behave roughly this way include the [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase type (codominant, de Meijer et al. 2003), autoflowering (recessive) and some leaf and colour traits. Most traits growers care about are not Mendelian. Yield, vigour, resin coverage, total cannabinoid percentage and flowering time are quantitative: many genes of small effect plus the environment. For those, [Punnett squares](https://genetixbay.com/knowledge/glossary/punnett-square.md) mislead and breeders work with heritability, large populations and repeated selection. ## Units and formula One gene (Aa × Aa): 1 AA : 2 Aa : 1 aa, visible 3:1 if A is dominant. Two independent genes (AaBb × AaBb): visible 9:3:3:1. Test cross (Aa × aa): 1:1. ## Don't confuse with - **Quantitative inheritance**: continuous variation from many genes. - **Linkage**: genes close together on one chromosome break the independent-assortment rule. ## Related terms [Segregation](https://genetixbay.com/knowledge/glossary/segregation.md), [Independent assortment](https://genetixbay.com/knowledge/glossary/independent-assortment.md), [Punnett square](https://genetixbay.com/knowledge/glossary/punnett-square.md), [Dominant](https://genetixbay.com/knowledge/glossary/dominant.md), [Recessive](https://genetixbay.com/knowledge/glossary/recessive.md), [Quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 2. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 --- # Meristem culture > Meristem culture is tissue culture from the tiny dome of dividing cells at a shoot tip, used to regenerate plants free of viroids and viruses. - Canonical: https://genetixbay.com/knowledge/glossary/meristem-culture.html - Also written: meristem tip culture, shoot tip culture, meristem cleaning, meristem propagation - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Meristem culture is a [tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md) technique that starts from the [apical meristem](https://genetixbay.com/knowledge/glossary/apical-meristem.md): the dome of actively dividing cells at the very tip of a shoot, often under 0.5 mm with one or two leaf [primordia](https://genetixbay.com/knowledge/glossary/pre-flower.md). Because many [viroids](https://genetixbay.com/knowledge/glossary/viroid.md) and [viruses](https://genetixbay.com/knowledge/glossary/plant-virus.md) are absent or scarce in this tissue, plants regenerated from it can be free of an infection that the mother carries. ## In practice It is the main method of cleaning cannabis clones infected with [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md). The meristem is excised under magnification in sterile conditions, grown on gel into a plantlet, multiplied, then tested. Success is not guaranteed: some plantlets still carry the pathogen, so each line must be tested (often more than once) before it is called clean. Combining meristem culture with heat or cold treatment can improve elimination rates in other crops. Meristem culture keeps organised tissue, so the risk of [somaclonal variation](https://genetixbay.com/knowledge/glossary/somaclonal-variation.md) is lower than with callus-based methods. ## Don't confuse with - **Tissue culture (general)**: can use nodes, leaves or callus, not just the meristem. - **Meristem (anatomy)**: the growing tissue itself; meristem culture is the lab technique. ## Myth check A tired old cut is usually sick, not mutated or drifted. Cleaning it through meristem culture and testing often restores its vigour. See [hop latent viroid and viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). ## Related terms [Tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md), [Somaclonal variation](https://genetixbay.com/knowledge/glossary/somaclonal-variation.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md), [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md) ## Read more - [Tissue culture basics for cannabis growers and breeders](https://genetixbay.com/knowledge/breeding/tissue-culture-basics.md) - [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ## Sources 1. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 --- # Metal halide > A metal halide (MH) lamp is a gas-discharge grow light with a bluish-white spectrum, traditionally used in the vegetative stage before switching to HPS. - Canonical: https://genetixbay.com/knowledge/glossary/metal-halide.html - Also written: MH, MH lamp, metal-halide lamp, halide, MH bulb - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A metal halide (MH) lamp makes light from an arc through mercury vapour and metal halide salts in a quartz arc tube. The salts broaden the output into a bluish-white spectrum with more blue than [HPS](https://genetixbay.com/knowledge/glossary/hps.md). MH lamps run on ballasts, often the same ones that drive HPS lamps of matching wattage (check compatibility; many digital ballasts are rated for both). ## In practice The classic HID setup was MH for veg (compact, tight [internodes](https://genetixbay.com/knowledge/glossary/internode.md) from the extra blue) and HPS for flower (more output per watt and more red-orange). [Efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) of MH is lower than HPS, typically around 1.2–1.5 µmol/J, and output falls faster with age. Today MH is mostly found in older rooms or used as a supplementary spectrum. Like HPS, MH lamps emit substantial radiant heat and contain mercury. Quartz-tube MH lamps also emit some UV; use the protective glass the fixture was designed for, and do not run a lamp with a cracked outer bulb. ## Don't confuse with - **CMH (ceramic metal halide)**: uses a ceramic arc tube; more efficient and broader spectrum. - **HPS**: orange-yellow, higher efficacy, the old flower standard. - **LED**: far more efficient, with a spectrum that can match any of these. ## Related terms [HPS](https://genetixbay.com/knowledge/glossary/hps.md), [CMH](https://genetixbay.com/knowledge/glossary/cmh.md), [LED](https://genetixbay.com/knowledge/glossary/led.md), [Photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # Microbial testing > Microbial testing counts or detects bacteria and fungi in a cannabis sample, including total aerobic count (TAMC), total yeast and mould count (TYMC) and specific pathogens. - Canonical: https://genetixbay.com/knowledge/glossary/microbial-testing.html - Also written: micro testing, microbial panel, TYMC, TAMC, total yeast and mould count, total aerobic microbial count, total yeast and mold count - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Microbial testing checks how many living microorganisms a sample carries and whether specific harmful ones are present. Count-based tests include total aerobic microbial count (TAMC) and total yeast and mould count (TYMC), reported in colony-forming units per gram (CFU/g). Pathogen tests look for organisms such as *Salmonella*, Shiga-toxin-producing *E. coli* and pathogenic *Aspergillus* species, usually reported as detected or [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md) in a set sample mass. ## In practice A [COA](https://genetixbay.com/knowledge/glossary/coa.md) might show TYMC 2,000 CFU/g against a limit of 10,000 CFU/g: pass. Mould counts rise with slow, humid drying, dense buds, poor airflow and storage at high [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md). Labs use either culture plating or DNA-based (qPCR) methods; the two can give different counts on the same sample, so check the method. Limits vary by jurisdiction; check local rules. ## Units and formula CFU/g (colony-forming units per gram), often written as powers of ten, e.g. 10^4 CFU/g = 10,000 CFU/g. ## Don't confuse with - **Mycotoxins**: toxic chemicals some moulds leave behind, which can persist after the mould is killed. - **Visible mould**: a lab count can fail before anything is visible. - **Water activity**: a risk indicator for growth, not a microbe count. ## Related terms [Mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md), [Water activity test](https://genetixbay.com/knowledge/glossary/water-activity-test.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Batch](https://genetixbay.com/knowledge/glossary/batch.md), [Homogenisation (sampling)](https://genetixbay.com/knowledge/glossary/homogenisation.md) ## Read more - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. United States Pharmacopeia. General Chapter <61> Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests. --- # Microclimate > A microclimate is a small zone within the grow space whose temperature, humidity or airflow differs from the room average, such as inside a dense cola or a corner. - Canonical: https://genetixbay.com/knowledge/glossary/microclimate.html - Also written: micro-climate, micro climate, canopy microclimate, hot spots, dead air pockets - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A microclimate is the local environment in one small part of the grow space, which can be very different from what the room sensor reports. Common examples: the humid, still air inside a dense canopy, a hot spot directly under the centre of a fixture, a cold corner near an intake, or the air right next to the medium surface. ## In practice A sensor at mid-height in an open spot might read 24 °C (75 °F) and 50% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), while the air inside a thick [cola](https://genetixbay.com/knowledge/glossary/cola.md) near the bottom of the canopy sits several percent higher in RH with almost no air movement. That is where [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) start. Dense, unpruned lower canopies are the classic problem. How to manage microclimates: move the sensor to canopy height and check several locations; run [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) above and below the canopy; thin lower larf that will never ripen; space plants so air can pass between them. Check the coldest surfaces after lights-off for condensation. ## Don't confuse with - **Boundary layer**: the still air film directly on a leaf surface, millimetres thick. - **Room average**: what the controller sees; microclimates are why it can mislead. ## Related terms [Airflow](https://genetixbay.com/knowledge/glossary/airflow.md), [Oscillating fan](https://genetixbay.com/knowledge/glossary/oscillating-fan.md), [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [Dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) ## Read more - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Sources 1. Kitaya Y, Tsuruyama J, Shibuya T, Yoshida M, Kiyota M, 2003. Effects of air current speed on gas exchange in plant leaves and plant canopies. Advances in Space Research 31(1):177–182. 2. Corredor-Perilla IC, Kwon H, Park J, 2025. High relative humidity in cannabis cultivation (effects on flowering, biomass and cannabinoids). Frontiers in Plant Science 16:1678142. https://doi.org/10.3389/fpls.2025.1678142 --- # Micron bags > Micron bags are fine-mesh filter bags graded by opening size in microns, used to separate and size trichome heads in ice water hash making and to filter rosin. - Canonical: https://genetixbay.com/knowledge/glossary/micron-bags.html - Also written: bubble bags, wash bags, hash bags, ice water bags, micron screens, filter bags - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Micron bags are filter bags made of mesh with a precisely rated opening size, measured in microns (µm; 1 µm = 0.001 mm). In [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md) making they are used in a nested set of different grades so that each bag retains a different size fraction of [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) while plant debris and water pass or are held back. Similar but smaller bags are used to contain material in a [rosin](https://genetixbay.com/knowledge/glossary/rosin.md) press and filter the oil. [Dry sift](https://genetixbay.com/knowledge/glossary/kief.md) uses flat, framed screens on the same principle. ## In practice [Hash](https://genetixbay.com/knowledge/glossary/hash.md) makers label each collected fraction by the bag it came from, for example "90 µm" or "120 µm", because the fraction indicates head size and usually quality. The best fractions vary by cultivar, since head size is partly genetic. Mesh quality matters: inconsistent weave mixes grades. GenetixBay defines the equipment and gives no wash procedures. ## Units and formula Micron (µm) = one millionth of a metre. A 73 µm screen has openings 0.073 mm across. ## Don't confuse with - **Mesh count (lines per inch)**: an older sieve rating that doesn't convert simply to microns. - **Rosin bags**: the same principle, used for pressing rather than washing. ## Related terms [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Full melt](https://genetixbay.com/knowledge/glossary/full-melt.md), [Kief](https://genetixbay.com/knowledge/glossary/kief.md), [Rosin](https://genetixbay.com/knowledge/glossary/rosin.md), [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) ## Sources 1. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Micronutrient > A micronutrient is an essential element plants need only in trace amounts, below a few mg/L: iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel. - Canonical: https://genetixbay.com/knowledge/glossary/micronutrient.html - Also written: micronutrients, micros, trace elements, trace minerals, minor nutrients - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Micronutrients are essential elements required in very small amounts, usually under 0.01% of dry tissue. The accepted list for higher plants is iron (Fe), [manganese](https://genetixbay.com/knowledge/glossary/manganese.md) (Mn), zinc (Zn), [copper](https://genetixbay.com/knowledge/glossary/copper.md) (Cu), [boron](https://genetixbay.com/knowledge/glossary/boron.md) (B), [molybdenum](https://genetixbay.com/knowledge/glossary/molybdenum.md) (Mo), chlorine (Cl) and nickel (Ni). Most work as parts of enzymes or electron carriers, so a shortage halts specific processes rather than general growth. ## In practice In a hydro feed they are dosed in fractions of a mg/L (ppm) to a few mg/L: iron around 1-3, manganese around 0.5-1, and molybdenum as little as 0.03-0.05. Because the windows between [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) and [toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) are narrow, especially for boron and copper, growers dose micros from a concentrated stock or premix rather than weighing tiny amounts of salt. [pH](https://genetixbay.com/knowledge/glossary/ph.md) governs micronutrient availability more than anything else: most become less available as pH rises, while molybdenum becomes more available. ## Don't confuse with - **Beneficial elements**: silicon, sodium, cobalt and selenium help some plants but are not essential. - **Macronutrient**: needed in hundreds of times larger amounts. - **Micronised**: a particle size, not a nutrient class. ## Related terms [Macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md), [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md), [Iron](https://genetixbay.com/knowledge/glossary/iron.md), [Boron](https://genetixbay.com/knowledge/glossary/boron.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) ## Read more - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Mids > Mids is slang for middle-grade flower: not bad, not great, priced between budget and top-shelf, and often used as a put-down. - Canonical: https://genetixbay.com/knowledge/glossary/mids.html - Also written: mid, mid-grade, middies, midgrade, mid weed - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mids is slang for middle-quality flower: decent, cheaper than premium, unremarkable in aroma and [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md). Calling something "mid" is now general slang for mediocre. ## In practice The tiers are loosely defined and vary by region and decade. Flower usually lands in the mids tier for reasons of growing and handling rather than genetics: harvested early or late, dried too fast, [cured](https://genetixbay.com/knowledge/glossary/curing.md) badly, stored warm, or handled roughly so [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) fell off. The same cultivar grown and cured well can be [top-shelf](https://genetixbay.com/knowledge/glossary/top-shelf.md). Mids can also be honest value: plain-looking flower with a good dry and cure often smokes better than flashy flower with a rushed one. ## Don't confuse with - **Brick weed**: compressed, seeded, usually below mids. - **Shake**: loose fragments, a form rather than a grade. - **Larf**: small, airy lower buds, often sold as mids. ## Related terms [Top shelf](https://genetixbay.com/knowledge/glossary/top-shelf.md), [Brick weed](https://genetixbay.com/knowledge/glossary/brick-weed.md), [Zaza](https://genetixbay.com/knowledge/glossary/zaza.md), [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) --- # Mineral fertiliser > A mineral (synthetic) fertiliser supplies nutrients as soluble salts that dissolve straight into plant-available ions; chemically, the plant takes up the same ions as from organic sources. - Canonical: https://genetixbay.com/knowledge/glossary/mineral-fertiliser.html - Also written: synthetic fertiliser, synthetic fertilizer, mineral fertilizer, synthetic nutrients, salt-based nutrients, chemical fertiliser - Glossary category: Nutrients · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A mineral fertiliser, often called synthetic, is a manufactured or refined inorganic salt such as [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md), [monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) or [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md). It dissolves directly into ions such as [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), ammonium, [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md), potassium, calcium, magnesium and sulfate, the same ions microbes release from organic matter. ## In practice Mineral feeds are the standard for hydroponics, coco and rockwool because they are precise, fully soluble, measurable by [EC](https://genetixbay.com/knowledge/glossary/ec.md) and do not foul lines. They give fast response but no buffer: mistakes show quickly, and the root zone does not hold reserves the way amended soil does. Their quality depends on recipe and management rather than on origin. ## Don't confuse with - **"Chemical" as a scare word**: everything in a feed is a chemical, organic or not. - **Organic fertiliser**: nutrients released slowly by microbes. - **Plant growth regulators**: synthetic hormones, a different category entirely. ## Myth check "Synthetic nutrients make harsh smoke" is not supported by controlled trials; harshness comes mainly from drying and curing. The plant mostly doesn't care where the ions come from (GenetixBay house position). See [organic vs mineral](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Organic fertiliser](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md), [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md) ## Read more - [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Massuela DC, Munz S, Hartung J, Nkebiwe PM, Graeff-Honninger S. 2023. Cannabis Hunger Games: nutrient stress induction in flowering stage - impact of organic and mineral fertilizer levels on biomass, cannabidiol (CBD) yield and nutrient use efficiency. Frontiers in Plant Science 14:1233232. https://doi.org/10.3389/fpls.2023.1233232 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Mobile nutrient > A mobile nutrient is one the plant can move from older leaves to new growth, so its deficiency shows first on lower, older leaves: N, P, K, Mg, Cl, Mo. - Canonical: https://genetixbay.com/knowledge/glossary/mobile-nutrient.html - Also written: mobile nutrients, mobile elements, phloem-mobile nutrient - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A mobile nutrient is an element that can be withdrawn from existing tissue and moved through the [phloem](https://genetixbay.com/knowledge/glossary/phloem.md) to where it is needed. When supply runs short, the plant sacrifices old leaves to feed new ones, so symptoms appear on the lower canopy first. Nitrogen, phosphorus, potassium and magnesium are the classic mobile nutrients; chlorine and [molybdenum](https://genetixbay.com/knowledge/glossary/molybdenum.md) are also mobile, and [zinc](https://genetixbay.com/knowledge/glossary/zinc.md) moderately so. ## In practice Where a symptom starts is the first clue in diagnosis. Yellowing that begins at the bottom of the plant and works upward points to a mobile nutrient: even yellowing suggests nitrogen, [interveinal yellowing](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) suggests magnesium, and scorched margins suggest potassium. Some lower-leaf yellowing in late flower is normal remobilisation as the plant moves nutrients to the buds. ## Don't confuse with - **Immobile nutrient**: stays where it is first deposited; symptoms appear in new growth. - **Available**: whether a nutrient can be taken up from the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) is a separate question, governed mostly by [pH](https://genetixbay.com/knowledge/glossary/ph.md). ## Related terms [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Magnesium](https://genetixbay.com/knowledge/glossary/magnesium.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) ## Read more - [Mobile vs immobile nutrients: reading old vs new leaves](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) - [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Mode of action > How a pesticide kills its target, grouped by IRAC into numbered classes; rotating between groups across pest generations slows resistance. - Canonical: https://genetixbay.com/knowledge/glossary/mode-of-action.html - Also written: MoA, IRAC group, mode of action group - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mode of action is the biochemical target a pesticide hits, such as a nerve receptor, a growth process or energy production. The Insecticide Resistance Action Committee (IRAC) sorts insecticides and miticides into numbered groups by mode of action, and recommends that the same group not be used on successive pest generations. ## In practice For growers, the useful rule is: count generations, not sprays. At 27 C a [spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) generation is about a week, so one group used for three weekly sprays has selected three generations. Rotate by group number, not by product name, because different brands often share one group. Always follow the label and local law; many groups are not legal on cannabis. ## Don't confuse with - **Active ingredient**: the chemical, one of possibly many in a group. - **Contact vs systemic**: how it reaches the pest, not how it kills. ## Related terms [Pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) ## Read more - [Integrated pest management (IPM) for cannabis: a complete programme for home and small commercial growers](https://genetixbay.com/knowledge/pests/integrated-pest-management-program.md) - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) ## Sources 1. Insecticide Resistance Action Committee. Mode of Action classification. https://irac-online.org/modes-of-action/ --- # Moisture content > The amount of water in a material as a percentage of its weight; cured cannabis flower usually sits around 10-12% w/w, though measurement method matters. - Canonical: https://genetixbay.com/knowledge/glossary/moisture-content.html - Also written: MC, water content, moisture percentage, % moisture, moisture level - Glossary category: Harvest, drying and curing · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Moisture content (MC) is the mass of water in a sample as a percentage of its total (wet-basis) mass. Fresh cannabis is around 75-80% water; well-dried and [cured](https://genetixbay.com/knowledge/glossary/curing.md) flower is commonly cited at about 10-12% w/w. ## In practice Growers estimate it from weight. A plant typically loses about 70-80% of its [wet weight](https://genetixbay.com/knowledge/glossary/wet-weight.md) in drying, so [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) is commonly about 20-25% of fresh weight. Weighing a marked jar or test bud through the dry shows how fast you're going. House position: what matters during the cure is the bud's moisture content and [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), not [jar RH](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md) as such. Curing is a slow, steady decline in moisture, not holding it constant. MC and aw are related but not identical: two cultivars at the same MC can sit at different aw. ## Units and formula MC (wet basis, %) = (wet mass - dry mass) / wet mass × 100. ## Don't confuse with - **Water activity**: how available the water is, 0-1. - **Dry-weight basis**: lab reporting convention for [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). - **Relative humidity**: water vapour in air. ## Related terms [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Equilibrium relative humidity](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md), [Wet weight](https://genetixbay.com/knowledge/glossary/wet-weight.md), [Dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (D8196 water activity measurement; D8197 range). https://sn.astm.org/node/2445/printable/print --- # Moisture correction > Moisture correction converts a lab result from as-received to dry-weight basis using the sample's measured water content, usually from a loss-on-drying test. - Canonical: https://genetixbay.com/knowledge/glossary/moisture-correction.html - Also written: moisture-corrected, moisture adjustment, loss on drying, LOD (loss on drying), moisture content test, moisture analysis - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Moisture correction is the arithmetic step that removes water from the denominator of a result. The lab first measures [moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md), most often by loss on drying: a weighed portion is dried under controlled conditions until its weight stops falling, and the loss is taken as water (plus some volatile [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), a known small bias). The as-received result is then divided by (1 - moisture fraction). ## In practice [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md) 18.6% [as received](https://genetixbay.com/knowledge/glossary/dry-weight-basis.md), moisture 10.5%: corrected = 18.6 / 0.895 = 20.8% dry weight. The higher the moisture, the bigger the correction. A wet sample tested as received [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) weaker; the same sample moisture-corrected looks stronger. Moisture is also a quality signal: [cured](https://genetixbay.com/knowledge/glossary/curing.md) flower around 10-12% w/w moisture with [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) about 0.55-0.65 is in the safe, well-cured range. ## Units and formula Corrected (% w/w dry) = as-received (% w/w) / (1 - moisture %/100). ## Don't confuse with - **Water activity test**: measures free water availability (aw), not total water mass. - **LOD (limit of detection)**: same abbreviation as loss on drying, different meaning. ## Myth check Always check whether moisture correction was applied before comparing numbers. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [Dry-weight basis](https://genetixbay.com/knowledge/glossary/dry-weight-basis.md), [Water activity test](https://genetixbay.com/knowledge/glossary/water-activity-test.md), [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) --- # Molasses > Molasses is a sugar-rich by-product of sugar refining added to soil feeds; its sugars feed soil microbes, not the plant, and do not sweeten buds. - Canonical: https://genetixbay.com/knowledge/glossary/molasses.html - Also written: blackstrap molasses, unsulphured molasses, carbs (additive), carbohydrate additive, sugar additive - Glossary category: Nutrients · Evidence: Myth - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Molasses is the thick syrup left after sugar is crystallised from sugar cane or beet. Blackstrap molasses is the most concentrated grade, containing sugars plus some potassium, calcium, magnesium, iron and [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md). Gardeners often add it to soil drenches and [compost teas](https://genetixbay.com/knowledge/glossary/compost-tea.md). ## In practice In soil and compost teas, molasses is a quick food for bacteria and fungi, which can boost microbial activity for a while. That is its real role. Plants make their own sugars by [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) and do not take up meaningful sugar through the roots to use as food. In hydro and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), sugar feeds unwanted biofilm and can lead to root problems, so keep it out of reservoirs. Use unsulphured grades in soil; sulphured molasses contains a preservative. ## Don't confuse with - **Carbohydrate "bloom" additives**: often similar sugars in a branded bottle. - **Humic and fulvic acids**: organic acids, not sugars. ## Myth check Molasses and sugars feed soil microbes only, not the plant (GenetixBay house position, Evidence: Myth for "molasses sweetens buds" or "feeds the plant"). Flavour comes from genetics, overall health, drying and curing. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Organic fertiliser](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md), [Biostimulant](https://genetixbay.com/knowledge/glossary/biostimulant.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Humic acid](https://genetixbay.com/knowledge/glossary/humic-acid.md) ## Read more - [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Mold > The everyday word for visible fungal growth; on cannabis it covers several distinct diseases, mainly bud rot (Botrytis cinerea) and powdery mildew (Golovinomyces ambrosiae). - Canonical: https://genetixbay.com/knowledge/glossary/mold.html - Also written: mould, moldy buds, mouldy, mildew, mold and mildew, fungal growth - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mold (mould in British and Canadian English) is a loose word for fungi that grow as visible threads and spores. Growers use "mold" and "mildew" for very different problems, so the first step is naming the organism. On living cannabis the main ones are [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md) (*Botrytis cinerea*), [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) (*Golovinomyces ambrosiae*), [white mould](https://genetixbay.com/knowledge/glossary/white-mould.md) (*Sclerotinia sclerotiorum*) and, outdoors, [downy mildew](https://genetixbay.com/knowledge/glossary/downy-mildew.md). After harvest, *Penicillium* and *Aspergillus* species can grow on buds that are dried or stored too wet. ## In practice Each has a different cause and fix: bud rot follows cool, humid, stagnant conditions inside dense [colas](https://genetixbay.com/knowledge/glossary/cola.md); powdery mildew spreads in moderate humidity without leaf wetness; storage moulds follow high [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) in the jar. Some *Aspergillus* species are a health concern for people with weakened immunity, which is one reason many markets test for them. Mouldy flower should be discarded, not trimmed and smoked. [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) beats every cure: humidity control, airflow and a proper dry. ## Don't confuse with - **Trichomes**: glittering [resin heads](https://genetixbay.com/knowledge/glossary/trichome.md), not fuzzy growth. - **Total yeast and mold (TYM)**: a lab count, not a single organism. ## Related terms [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md), [Powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), [White mould](https://genetixbay.com/knowledge/glossary/white-mould.md), [Downy mildew](https://genetixbay.com/knowledge/glossary/downy-mildew.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md) ## Read more - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) - [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) ## Sources 1. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker --- # Molybdenum > Molybdenum (Mo) is the micronutrient needed in the smallest amount; plants need it to convert nitrate into usable nitrogen. - Canonical: https://genetixbay.com/knowledge/glossary/molybdenum.html - Also written: Mo, molybdate, MoO4 2-, molybdenum deficiency - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Molybdenum is a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) absorbed as the molybdate anion (MoO4 2-). It is the metal centre of [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) reductase, the enzyme that turns nitrate into nitrite on the way to amino acids. Without it, a nitrate-fed plant can starve for nitrogen while nitrate builds up in its tissue. Unlike most micronutrients, molybdenum becomes more available as [pH](https://genetixbay.com/knowledge/glossary/ph.md) rises. ## In practice [Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) is uncommon. It shows as pale, yellowing middle and older leaves with cupped or scorched margins, resembling [nitrogen deficiency](https://genetixbay.com/knowledge/glossary/nitrogen.md). Low pH makes it more likely. Hydro feeds carry tiny amounts, often around 0.03-0.05 mg/L (ppm) Mo, usually from [sodium molybdate](https://genetixbay.com/knowledge/glossary/sodium-molybdate.md) or [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) molybdate. ## Don't confuse with - **Nitrogen deficiency**: very similar look; Mo deficiency can occur with plenty of nitrate in the feed. - **Manganese**: different element; the symbols Mn and Mo are easy to mix up. - **Magnesium (Mg)**: also easy to confuse by symbol. ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Sodium molybdate](https://genetixbay.com/knowledge/glossary/sodium-molybdate.md), [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md) ## Read more - [Molybdenum (Mo) in cannabis: the trace element nitrate depends on](https://genetixbay.com/knowledge/nutrients/molybdenum.md) ## Sources 1. Kaiser BN, Gridley KL, Brady JN, Phillips T, Tyerman SD. 2005. The role of molybdenum in agricultural plant production. Annals of Botany 96(5):745-754. https://doi.org/10.1093/aob/mci226 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Mom > Mom is grower slang for a plant kept in vegetative growth only to supply clones, as in "I keep a mom of every keeper". - Canonical: https://genetixbay.com/knowledge/glossary/mom.html - Also written: moms, mum, momma, mommy plant - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mom (UK "mum") is everyday grower slang for a [mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md): a plant held in vegetative growth under long days so it can be cut repeatedly for clones and never flowers. ## In practice "Moms" live in a corner of the veg space, are kept small by regular cutting and root pruning, and are refreshed periodically by rooting a new cut to replace the old plant. A grower with five keepers might run five moms, each labelled, while a backup cut of each sits in a second location or in [tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md). Moms are the most valuable plants in a clone-based garden, so sanitation matters most here: pests, [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) and especially [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md) spread from a mom to every clone taken from it. Testing moms for [viroid](https://genetixbay.com/knowledge/glossary/viroid.md) and quarantining incoming cuts protects everything downstream. ## Don't confuse with - **Mother plant**: the horticultural term for the same thing; "mom" is the slang. - **Female plant**: every mom is female (unless it is a kept male, sometimes called a "dad"), but not every female is a mom. - **Keeper**: describes the selected [genotype](https://genetixbay.com/knowledge/glossary/genotype.md); mom describes its role. ## Myth check "Old moms run out of steam." GenetixBay position: there is no [genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md) apart from pathogens. A tired mom is usually [root-bound](https://genetixbay.com/knowledge/glossary/root-bound.md), underfed, infected or overcut. Start a fresh one from a cut. See [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md). ## Related terms [Mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md), [Cut](https://genetixbay.com/knowledge/glossary/cut.md), [Keeper](https://genetixbay.com/knowledge/glossary/keeper.md), [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) --- # Monoammonium phosphate > Monoammonium phosphate (MAP, NH4H2PO4) supplies about 12% nitrogen as ammonium and 26.6% phosphorus, adding P while gently acidifying the root zone. - Canonical: https://genetixbay.com/knowledge/glossary/monoammonium-phosphate.html - Also written: MAP, NH4H2PO4, ammonium dihydrogen phosphate, 12-61-0, mono ammonium phosphate - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Monoammonium phosphate is the salt NH4H2PO4. Soluble technical grade is sold as 12-61-0, which works out to about 12% N, all [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), and 26.6% elemental P. Cheaper granular agricultural MAP often contains insoluble impurities and is not suitable for hydro. ## In practice MAP is used where a grower wants phosphorus plus a little ammonium to steady [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md) in [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md). It also adds nitrogen, so it does not suit a late-flower feed where N is being tapered; [MKP](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) is the better P source there. Keep total ammonium to a small share of total N, as high NH4/[NO3](https://genetixbay.com/knowledge/glossary/nitrate.md) ratios cut cannabis yield and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). ## Units and formula 1 g/L gives about 120 mg/L (ppm) N and 266 mg/L P. ## Don't confuse with - **Diammonium phosphate (DAP)**: (NH4)2HPO4, more ammonium and more alkaline. - **Monopotassium phosphate (MKP)**: P with potassium instead of ammonium. - **MAP as a shipping acronym**: modified-atmosphere packaging is unrelated. ## Related terms [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), [Phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md), [Monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 --- # Monoecious > Having both male and female flowers on the same individual plant; in cannabis, a trait deliberately bred into some hemp cultivars, not the natural norm. - Canonical: https://genetixbay.com/knowledge/glossary/monoecious.html - Also written: monoecy, monoecism, monoecious hemp, co-sexual - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A monoecious plant carries separate male and [female flowers](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) on the same individual. Maize is the textbook example. In cannabis, monoecy is a trait selected deliberately in some [industrial hemp](https://genetixbay.com/knowledge/glossary/hemp.md) cultivars for uniform seed and fibre crops; those plants are genetically female (XX) with stable expression of [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) (Faux et al. 2014). ## In practice For drug-type growers, monoecious is mainly a word to read precisely: - A **monoecious hemp cultivar** is a bred, [stable line](https://genetixbay.com/knowledge/glossary/ibl.md), managed for grain or fibre. - A **drug-type plant** that suddenly shows male flowers on a female is [intersex](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) (hermaphrodite), not "naturally monoecious". Monoecious hemp pollen can seed nearby drug-type crops, just like a male. Outdoor growers near hemp fields should know that. ## Don't confuse with - **Dioecious**: separate male and female plants, the natural state of cannabis. - **Hermaphrodite**: in grower usage an intersex female, an unwanted abnormality. - **Perfect flower**: a single flower with both [stamens](https://genetixbay.com/knowledge/glossary/anther.md) and [pistil](https://genetixbay.com/knowledge/glossary/pistil.md), rare in cannabis. ## Myth check House position: monoecious hemp was bred on purpose and is not the norm for cannabis. Its existence does not make [herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) drug lines acceptable. Those reflect poor breeding. See [the sex guide](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md). ## Related terms [Dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md), [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), [Staminate flower](https://genetixbay.com/knowledge/glossary/staminate-flower.md) ## Read more - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) ## Sources 1. Faux AM, Berhin A, Dauguet N, Bertin P. 2014. Sex chromosomes and quantitative sex expression in monoecious hemp (Cannabis sativa L.). Euphytica 196(2):183-197. https://doi.org/10.1007/s10681-013-1023-y 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Monopotassium phosphate > Monopotassium phosphate (MKP, KH2PO4) supplies about 22.7% phosphorus and 28.7% potassium with no nitrogen, and is the base of most PK boosters. - Canonical: https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.html - Also written: MKP, KH2PO4, mono potassium phosphate, potassium dihydrogen phosphate, 0-52-34 - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Monopotassium phosphate is the salt KH2PO4, sold as 0-52-34. That analysis is in oxides; the elemental content is about 22.7% P and 28.7% K. It is soluble, slightly acidic and free of nitrogen, [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) and [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md). ## In practice MKP is the usual phosphorus source in mineral feeds and goes in the B stock, apart from concentrated calcium. Many "PK boosters" are mostly MKP. Because cannabis trials show a phosphorus plateau at moderate levels, a small dose is enough. Doubling it adds [runoff](https://genetixbay.com/knowledge/glossary/runoff.md), not buds. ## Units and formula 1 g/L gives about 227 mg/L (ppm) P and 287 mg/L K. Reaching 50 ppm P needs only about 0.22 g/L. ## Don't confuse with - **Monoammonium phosphate (MAP)**: P with [ammonium nitrogen](https://genetixbay.com/knowledge/glossary/ammonium.md) instead of potassium. - **Dipotassium phosphate**: K2HPO4, more alkaline and with a different ratio. - **Phosphoric acid**: a liquid acid that supplies P while lowering [pH](https://genetixbay.com/knowledge/glossary/ph.md). ## Myth check MKP is useful, but extra PK in flower does not raise yield past the plateau (Evidence: Established). See [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md). ## Related terms [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md), [Bloom booster](https://genetixbay.com/knowledge/glossary/bloom-booster.md), [Guaranteed analysis](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - ["Bloom boosters" for cannabis: what's real and what's marketing](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 --- # Monoterpene > A monoterpene is a ten-carbon terpene made from geranyl pyrophosphate, such as myrcene, limonene, pinene or terpinolene; they are the most volatile terpenes and the first lost in drying. - Canonical: https://genetixbay.com/knowledge/glossary/monoterpene.html - Also written: monoterpenes, C10 terpene, monoterpenoid, monoterpenoids - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A monoterpene contains ten carbons, two isoprene units, and is made from [geranyl pyrophosphate](https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.md) by [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) synthase enzymes. Monoterpenes dominate the bright top notes of cannabis aroma: myrcene (musky, earthy), [limonene](https://genetixbay.com/knowledge/glossary/limonene.md) (citrus), alpha- and beta-pinene (pine), [terpinolene](https://genetixbay.com/knowledge/glossary/terpinolene.md) (fresh, herbal), ocimene (sweet, green) and [linalool](https://genetixbay.com/knowledge/glossary/linalool.md) (floral, a monoterpenoid alcohol). ## In practice Because they are small and volatile, monoterpenes evaporate and oxidise more readily than [sesquiterpenes](https://genetixbay.com/knowledge/glossary/sesquiterpene.md). Ross and ElSohly (1996) reported large monoterpene losses after air-drying, with the sesquiterpene share rising in comparison. That is the chemistry behind the grower rule: dry slowly and cool, cure gently and keep jars cool and dark. Flower that smelled loud on the plant and dull after a fast, warm dry has lost monoterpenes. ## Don't confuse with - **Sesquiterpene**: C15, heavier and less volatile ([beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md), humulene). - **Monoterpenoid**: an oxygenated monoterpene such as linalool or eucalyptol; often lumped in. - **Terpene profile**: the mix measured in a given sample. ## Related terms [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Geranyl pyrophosphate](https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.md), [Myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md), [Limonene](https://genetixbay.com/knowledge/glossary/limonene.md), [Alpha-pinene](https://genetixbay.com/knowledge/glossary/alpha-pinene.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # Monster cropping > Monster cropping is taking cuttings from a plant in flower and re-vegging them, which tends to produce bushy plants with many tops after an initial slow phase. - Canonical: https://genetixbay.com/knowledge/glossary/monster-cropping.html - Also written: monster crop, monstercropping, cloning from flower, flowering clones - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Monster cropping means [taking cuttings](https://genetixbay.com/knowledge/glossary/cloning.md) from a flowering plant, usually in the first few weeks of flower, rooting them and keeping them under long days. The cuttings slowly revert to vegetative growth, and many throw out unusual, bushy growth with lots of branching shoots, which some growers like for a wide canopy. ## In practice Rooting from flowering tissue is slower than from vegetative cuttings, often 2-4 weeks, and the first new leaves are frequently small, round or single-bladed while the shoot reverts. Success varies by cultivar. Growers use it to rescue a [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) they forgot to clone before flipping, or to build [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md) with many cut sites. Evidence is anecdotal. Treat the "monster" growth as a side effect of [re-vegging](https://genetixbay.com/knowledge/glossary/re-veg.md), not a guaranteed yield gain. ## Don't confuse with - **Re-veg**: reverting a whole plant after harvest; monster cropping uses cuttings. - **Supercropping**: crushing and bending stems; unrelated despite the name. ## Related terms [Re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md), [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md), [Cutting](https://genetixbay.com/knowledge/glossary/cutting.md), [HST](https://genetixbay.com/knowledge/glossary/hst.md) ## Read more - [HST and supercropping: controlled stem crushing](https://genetixbay.com/knowledge/training/hst-supercropping.md) --- # Mother plant > A mother plant is a female kept permanently in vegetative growth to supply cuttings, so a selected genotype can be propagated as clones indefinitely. - Canonical: https://genetixbay.com/knowledge/glossary/mother-plant.html - Also written: mother, mothers, stock plant, donor plant, mother stock - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A mother plant (stock plant) is a plant held in vegetative growth, usually under 18 h or more of light, so it never flowers and can be cut repeatedly for clones. Every cutting from it carries the same [genotype](https://genetixbay.com/knowledge/glossary/genotype.md), which is how a selected individual is kept and shared. ## In practice Mothers are kept healthy rather than huge: moderate light (about 300-600 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md)), steady feeding with enough calcium and nitrogen, and regular pruning to keep many cuttable shoots. Many growers replace a mother every 6-12 months by rooting one of her own cuttings, simply because an old plant in a pot becomes woody, [root-bound](https://genetixbay.com/knowledge/glossary/root-bound.md) and hard to manage. Pathogens, especially [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), are the real threat to a mother line; test and keep a clean source. ## Myth check House position: there is no [genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md) in clones apart from pathogens. The founder keeps cuts over 40 years old with no decline. "Tired mother" symptoms are pathogens, poor care or cutting position, not the genotype wearing out. Take cuts from consistent positions on the plant. See [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md). ## Don't confuse with - **Mom (slang)**: the same idea in casual speech; this file covers the horticultural practice. ## Related terms [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md), [Cutting](https://genetixbay.com/knowledge/glossary/cutting.md), [Keeper](https://genetixbay.com/knowledge/glossary/keeper.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md), [Veg time](https://genetixbay.com/knowledge/glossary/veg-time.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) ## Sources 1. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 --- # mS/cm > mS/cm (millisiemens per centimetre) is the standard unit of EC for nutrient solutions; 1 mS/cm equals 1 dS/m and 1,000 µS/cm. - Canonical: https://genetixbay.com/knowledge/glossary/ms-cm.html - Also written: millisiemens per centimetre, millisiemens per centimeter, mS, millisiemens, dS/m - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" mS/cm (millisiemens per centimetre) is the unit used for [electrical conductivity](https://genetixbay.com/knowledge/glossary/ec.md) of nutrient solutions. The siemens is the unit of electrical conductance; dividing by the centimetre spacing of the probe gives conductivity. 1 mS/cm is numerically identical to 1 dS/m (decisiemens per metre), the unit preferred in soil science and irrigation papers. ## In practice mS/cm is the unit to use when comparing numbers across meters, nutrient charts and research, because it is a real measurement, while ppm depends on which [conversion factor](https://genetixbay.com/knowledge/glossary/conversion-factor.md) your meter uses. A grower whose pen reads "1.6" in EC mode is at 1.6 mS/cm; the same solution might read 800 on a 500-scale [ppm meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) or 1,120 on a 700-scale meter. Some meters display EC without a unit, and some older ones read in mmho/cm, an old name for the same thing (1 mmho/cm = 1 mS/cm). ## Units and formula | mS/cm | [µS/cm](https://genetixbay.com/knowledge/glossary/us-cm.md) | dS/m | [CF](https://genetixbay.com/knowledge/glossary/cf.md) | [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md) | [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md) | |---|---|---|---|---|---| | 1.0 | 1,000 | 1.0 | 10 | 500 | 700 | | 1.5 | 1,500 | 1.5 | 15 | 750 | 1,050 | | 2.0 | 2,000 | 2.0 | 20 | 1,000 | 1,400 | ## Don't confuse with - **µS/cm**: a thousand times smaller unit, used for low-EC water. - **ppm**: a calculated estimate, not a measured unit of conductivity. ## Related terms [EC](https://genetixbay.com/knowledge/glossary/ec.md), [µS/cm](https://genetixbay.com/knowledge/glossary/us-cm.md), [CF](https://genetixbay.com/knowledge/glossary/cf.md), [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md), [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md) ## Read more - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) ## Sources 1. University of California Cooperative Extension, Ventura County. Salinity units and conversions (640 ppm = 1 dS/m). https://ucanr.edu/node/125832 2. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality --- # Mulder's chart > Mulder's chart is a diagram showing antagonistic and synergistic interactions between plant nutrients, used as a rough guide to which excesses cause which deficiencies. - Canonical: https://genetixbay.com/knowledge/glossary/mulders-chart.html - Also written: Mulders chart, Mulder chart, nutrient interaction chart, Mulder's wheel - Glossary category: Nutrients · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mulder's chart is a circular diagram of the mineral nutrients, with lines connecting pairs that interact. One set of lines marks [antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), where an excess of one element reduces another; another marks synergism, where one aids another. It is named after the Dutch agronomist D. Mulder, who compiled such interactions in the mid-twentieth century. ## In practice Growers use it as a checklist when a [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) appears despite adequate feeding: if magnesium is low, check whether potassium, calcium or [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) is high; if [zinc](https://genetixbay.com/knowledge/glossary/zinc.md) is low, check phosphorus. It is a starting point rather than a law. Many interactions depend on concentration, [pH](https://genetixbay.com/knowledge/glossary/ph.md), medium and crop, and some lines on popular versions are drawn from soil studies with little support in hydro or in cannabis specifically. Reviews such as Fageria and Rietra and colleagues give a more nuanced picture. ## Don't confuse with - **Nutrient availability chart (pH chart)**: shows availability by pH, not element interactions. - **Feed chart**: a dosing schedule. ## Related terms [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), [Nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md) ## Read more - [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md) ## Sources 1. Fageria VD. 2001. Nutrient interactions in crop plants. Journal of Plant Nutrition 24(8):1269-1290. https://doi.org/10.1081/PLN-100106981 2. Rietra RPJJ, Heinen M, Dimkpa CO, Bindraban PS. 2017. Effects of nutrient antagonism and synergism on yield and fertilizer use efficiency. Communications in Soil Science and Plant Analysis 48(16):1895-1920. https://hub.ifdc.org/handle/20.500.14297/2410 --- # Mutation > A mutation is a change in a plant's DNA sequence, arising in seed or in one branch (a somatic mutation); mutations are rare and usually neutral. - Canonical: https://genetixbay.com/knowledge/glossary/mutation.html - Also written: mutations, mutant, somatic mutation, bud sport, genetic mutation - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A mutation is a change in DNA: a single base change, an insertion or deletion, or a larger rearrangement. Mutations in reproductive cells can pass to seed. Somatic mutations arise in body cells and stay in the branch where they occur, so a cut from that branch carries them. A visibly different branch is called a sport (bud sport). ## In practice Somatic mutations do accumulate in long-lived cannabis plants. Adamek et al. (2022) found them across different parts of a single plant, producing genetic mosaicism. Most such changes are neutral; they sit in DNA that does not affect traits growers notice. House position: a mutation does not mean a loss. Cuts from different parts of a plant can behave differently, which may or may not be mutation. Old cuts that decline are almost always carrying pathogens, not mutations. Occasionally a sport is an improvement, such as a variegated or differently coloured branch that some growers keep and propagate. ## Don't confuse with - **Genetic drift**: change in [allele](https://genetixbay.com/knowledge/glossary/allele.md) frequencies across seed generations. - **Somaclonal variation**: changes from [tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md) [regeneration](https://genetixbay.com/knowledge/glossary/re-veg.md). - **Epigenetic change**: altered [gene](https://genetixbay.com/knowledge/glossary/gene.md) activity without a sequence change. - **Herm expression**: a sex-expression failure, not a mutation in the plant. ## Myth check "Clones mutate and wear out" is not supported as an explanation for [clone decline](https://genetixbay.com/knowledge/glossary/genetic-drift.md); see [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md). ## Related terms [Somaclonal variation](https://genetixbay.com/knowledge/glossary/somaclonal-variation.md), [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md), [Topophysis](https://genetixbay.com/knowledge/glossary/topophysis.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) ## Sources 1. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 --- # Mycorrhizae > Mycorrhizae are symbioses in which fungi colonise plant roots and extend hyphae into the soil, trading water and nutrients such as phosphorus for the plant's sugars. - Canonical: https://genetixbay.com/knowledge/glossary/mycorrhizae.html - Also written: mycorrhiza, mycorrhizal fungi, myco, AMF, arbuscular mycorrhizal fungi, mycorrhizal inoculant - Glossary category: Systems and media · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A mycorrhiza is a mutualistic association between a fungus and a plant root. Cannabis forms arbuscular mycorrhizae (AM), in which fungi of the Glomeromycota grow inside root cortex cells and spread fine hyphae far into the soil. The hyphae explore a much larger volume than roots alone, improving uptake of phosphorus and other [immobile nutrients](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md) and water, in return for carbon from the plant. ## In practice Growers add mycorrhizal inoculants at planting or [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md), dusting powder or granules where roots will contact them. Benefits are clearest in low-phosphorus soils and living-soil systems. High phosphorus fertilisation suppresses colonisation, so in heavily fed hydro or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) the fungi have little to offer and often fail to establish. Many products contain few viable propagules; quality varies. Evidence: established for many crops; for cannabis, studies are limited and results mixed. ## Don't confuse with - **Trichoderma**: a beneficial root-zone fungus, but not mycorrhizal. - **Mycelium (mushrooms)**: fungal threads in general; not all form symbioses with plants. ## Related terms [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), [Root zone](https://genetixbay.com/knowledge/glossary/root-zone.md), [No-till](https://genetixbay.com/knowledge/glossary/no-till.md), [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) ## Read more - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) ## Sources 1. Smith SE, Read DJ, 2008. Mycorrhizal Symbiosis, 3rd ed. Academic Press. --- # Mycotoxins > Mycotoxins are toxic compounds made by certain moulds, such as aflatoxins and ochratoxin A from Aspergillus and Penicillium species; cannabis labs test for them at parts-per-billion levels. - Canonical: https://genetixbay.com/knowledge/glossary/mycotoxins.html - Also written: mycotoxin, aflatoxins, aflatoxin, ochratoxin A, aflatoxin B1, mycotoxin panel - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mycotoxins are secondary metabolites produced by some fungi. The ones cannabis labs usually test for are the aflatoxins (B1, B2, G1, G2), made mainly by *Aspergillus flavus* and *A. parasiticus*, and ochratoxin A, made by some *Aspergillus* and *Penicillium* species. They are heat-stable chemicals, so killing the mould, by heat or [irradiation](https://genetixbay.com/knowledge/glossary/irradiation.md), doesn't destroy toxin already made. ## In practice Testing is by [LC-MS/MS](https://genetixbay.com/knowledge/glossary/lc-ms.md), reported in µg/kg (ppb). A typical panel lists each aflatoxin plus a total and ochratoxin A, with action limits in the low tens of µg/kg (limits vary; check local rules). Risk rises with warm, humid drying and storage above safe [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), and with damp, compressed material. The best [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) is upstream: good airflow, controlled drying, cure to a stable moisture and store cool. ## Units and formula µg/kg = ppb (parts per billion). 20 µg/kg = 0.02 µg/g. ## Don't confuse with - **Microbial count (TYMC)**: counts live mould; mycotoxins are its chemical residue. - **Botrytis bud rot**: *[Botrytis cinerea](https://genetixbay.com/knowledge/glossary/botrytis.md)* is the common grey mould, not a major aflatoxin producer. - **Endotoxins**: bacterial cell-wall compounds, a separate category. ## Related terms [Microbial testing](https://genetixbay.com/knowledge/glossary/microbial-testing.md), [LC-MS](https://genetixbay.com/knowledge/glossary/lc-ms.md), [Water activity test](https://genetixbay.com/knowledge/glossary/water-activity-test.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [LOD](https://genetixbay.com/knowledge/glossary/lod.md) ## Read more - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) --- # Myrcene > Myrcene (beta-myrcene) is a monoterpene with a musky, earthy, ripe-fruit aroma and is the most common dominant terpene in commercial cannabis flower. - Canonical: https://genetixbay.com/knowledge/glossary/myrcene.html - Also written: beta-myrcene, β-myrcene, mercene, myrcine - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Myrcene, usually beta-myrcene, is an acyclic [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md) found in hops, mango, bay and many other plants. In cannabis it smells musky, earthy, herbal and a little like ripe fruit. Survey data from US retail flower (Smith et al. 2022) show myrcene as one of the most frequent [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), alongside [beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md) and [limonene](https://genetixbay.com/knowledge/glossary/limonene.md). ## In practice A [COA](https://genetixbay.com/knowledge/glossary/coa.md) might show myrcene at 0.3-1.0% w/w in a myrcene-dominant flower. It is volatile, so [fresh-frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) material and carefully cured flower read higher than fast-dried or old material. ## Don't confuse with - **Ocimene**: an isomeric monoterpene with a sweeter, greener smell. - **Terpinolene**: another monoterpene that dominates a different, less common chemotype. ## Myth check A popular claim says myrcene above 0.5% makes a cultivar "indica" and sedating. There is no controlled evidence for that threshold; it is a marketing rule of thumb. House position: indica/sativa labels don't predict chemistry or effects, and terpene percentages don't predict effects either. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md) and [why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md). ## Related terms [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Limonene](https://genetixbay.com/knowledge/glossary/limonene.md), [Beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Mythbusters > Mythbusters is GenetixBay's page of growing myths and their verdicts, with open Bay Trials and finished results marked Busted, Confirmed or Inconclusive. - Canonical: https://genetixbay.com/knowledge/glossary/mythbusters.html - Also written: GenetixBay Mythbusters, Mythbusters page, myth busting, busted myths - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Mythbusters is the GenetixBay knowledge-base section where common growing claims are tested against evidence. It lists open [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) and verdict cards for finished ones, and links to the article that covers each topic in depth. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## In practice Each entry states the claim, the current evidence label, the house position where there is one, and what a trial would need to settle it. Examples: pre-harvest [flushing](https://genetixbay.com/knowledge/glossary/flushing.md) (*Myth*, and actively harmful), 24-72 h of [darkness before harvest](https://genetixbay.com/knowledge/glossary/darkness-before-harvest.md) (*Myth*; the founder's 20-year standing offer of a 50-pack of seeds for a sound peer-reviewed study showing a benefit is unclaimed), [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) being needed because of [LEDs](https://genetixbay.com/knowledge/glossary/led.md) (*Myth*), [late-flower bananas](https://genetixbay.com/knowledge/glossary/nanners.md) being normal (*Myth*), tuck vs strip [defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md) (open). When a trial finishes, its card moves from "Open trials" to the verdicts, labelled Busted, Confirmed or Inconclusive. ## Don't confuse with - **The evidence ladder**: the labelling system Mythbusters uses. - **Opinion pieces**: house positions are labelled as such, with their evidence. ## Related terms [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md), [Evidence ladder](https://genetixbay.com/knowledge/glossary/evidence-ladder.md), [Open research](https://genetixbay.com/knowledge/glossary/open-research.md), [Flushing](https://genetixbay.com/knowledge/glossary/flushing.md) ## Read more - [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) --- # N-P-K ratio > The N-P-K ratio is the three numbers on a fertiliser label giving percent nitrogen, phosphate (P2O5) and potash (K2O) by weight, not elemental P and K. - Canonical: https://genetixbay.com/knowledge/glossary/npk-ratio.html - Also written: NPK, N-P-K, NPK ratio, fertiliser ratio, fertilizer grade - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The N-P-K ratio, or fertiliser grade, is the three numbers printed on a fertiliser: percent total nitrogen (N), percent available [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) expressed as P2O5, and percent soluble potash expressed as K2O, all by weight. A 10-5-20 product contains 10% N, 5% P2O5 and 20% K2O. ## In practice Because P and K are given as oxides, the numbers overstate the elements: 5% P2O5 is only about 2.2% P, and 20% K2O about 16.6% K. Comparing bottles by their N-P-K says little without knowing the dose and dilution. A liquid concentrate at 2-1-3 used at 5 mL/L can deliver more than a 20-20-20 powder at 0.2 g/L. The numbers also leave out calcium, magnesium, [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) and the [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md). ## Units and formula P = P2O5 × 0.436. K = K2O × 0.830. [mg/L of an element](https://genetixbay.com/knowledge/glossary/elemental-ppm.md) = (element % ÷ 100) × dose in mg/L. ## Don't confuse with - **Elemental analysis**: P and K as elements, used in hydro recipes and research. - **Ratio vs grade**: 10-10-10 and 20-20-20 have the same ratio but different strength. ## Related terms [Guaranteed analysis](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md), [Macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md) ## Read more - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Nagoya Protocol > The Nagoya Protocol is a 2010 international treaty under the Convention on Biological Diversity governing access to genetic resources and fair sharing of their benefits. - Canonical: https://genetixbay.com/knowledge/glossary/nagoya-protocol.html - Also written: Nagoya Protocol on Access and Benefit-sharing, ABS protocol, Nagoya - Glossary category: Legal and regulatory · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The Nagoya Protocol on Access to [Genetic Resources](https://genetixbay.com/knowledge/glossary/germplasm.md) and the Fair and Equitable Sharing of Benefits Arising from their Utilization is a supplementary agreement to the Convention on Biological Diversity. Adopted in 2010 and in force since October 2014, it requires parties to set rules so that genetic resources and associated traditional knowledge are accessed only with [prior informed consent](https://genetixbay.com/knowledge/glossary/prior-informed-consent.md) and on mutually agreed terms, including [benefit-sharing](https://genetixbay.com/knowledge/glossary/benefit-sharing.md). ## In practice For plant genetics, Nagoya means that collecting seed from a country for breeding or research can require permission from that country's authorities, and from local or indigenous communities where their knowledge or resources are involved, plus an agreement on how benefits will be shared. Not every country is a party, and cannabis's controlled status adds separate legal barriers to collection and export. The protocol is the legal backbone of the distinction between responsible [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) collection and [biopiracy](https://genetixbay.com/knowledge/glossary/biopiracy.md). See [landrace hunting and biopiracy](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md). Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **UPOV**: [breeders' rights](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md), not access and benefit-sharing. - **The International Treaty on Plant Genetic Resources for Food and Agriculture**: a related system for listed food and forage crops. ## Related terms [Benefit-sharing](https://genetixbay.com/knowledge/glossary/benefit-sharing.md), [Prior informed consent](https://genetixbay.com/knowledge/glossary/prior-informed-consent.md), [Biopiracy](https://genetixbay.com/knowledge/glossary/biopiracy.md), [Landrace hunter](https://genetixbay.com/knowledge/glossary/landrace-hunter.md), [UPOV](https://genetixbay.com/knowledge/glossary/upov.md) ## Read more - [Landrace hunting or biopiracy? Benefit-sharing, consent and cannabis](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md) ## Sources 1. Secretariat of the Convention on Biological Diversity. 2011. Nagoya Protocol on Access to Genetic Resources and the Fair and Equitable Sharing of Benefits Arising from their Utilization. https://www.cbd.int/abs/ --- # Nanners > Nanners (bananas) are exposed, banana-shaped anthers on a female flower: a hermaphrodite trait, not a normal part of late flowering, and a reason to cull. - Canonical: https://genetixbay.com/knowledge/glossary/nanners.html - Also written: bananas, nanner, banana, late-flower bananas - Glossary category: Grower slang and culture · Evidence: Myth - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nanners (bananas) are bare, yellow or pale-green [anthers](https://genetixbay.com/knowledge/glossary/anther.md) that grow directly out of a [female flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) cluster, usually late in flower. They shed pollen, often without an obvious pollen sac, and can seed the plant and anything nearby. They are a form of [intersex](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) (hermaphrodite) flowering. ## In practice A grower in week 7 of flower spots small yellow curved structures poking out of the buds. That is a nanner. Remove the plant from the room if possible, or at minimum pluck visible anthers carefully, bag the plant at harvest, and record the event against the cultivar. If several plants of one line do it, the line is the problem, not the room. ## Don't confuse with - **Pistils/stigmas**: the white to orange "[hairs](https://genetixbay.com/knowledge/glossary/pistil.md)" of a normal female flower. - **Pollen sacs (balls)**: closed [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) at nodes. Nanners are naked anthers. - **Foxtailing**: new calyx growth stacking on old buds, often from heat or [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md). ## Myth check "A few bananas at the end are normal; it means the plant is finishing." GenetixBay house position (*Myth*): nanners are **not normal**. Drug-type cannabis has been dioecious and stable for thousands of years. Late bananas mean poor genetics, usually from repeated selfing, careless feminising or untested crosses; stress only reveals the weakness. Even the best gas you ever grew is a herm if it throws them. Cull it and don't breed from it. Research on intersex flowering (Punja & Holmes 2020) documents the trait; GenetixBay reads it as a breeding fault. See [hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md), [Herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md) ## Read more - [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) ## Sources 1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 --- # ND (non-detect) > ND (non-detect) on a COA means the compound was not found at or above the method's limit of detection; it does not mean the amount is zero. - Canonical: https://genetixbay.com/knowledge/glossary/non-detect.html - Also written: ND, non-detect, not detected, nondetect, N.D., below detection - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" ND, "not detected", means that the lab's method saw no signal for that compound at or above its [limit of detection](https://genetixbay.com/knowledge/glossary/lod.md). It is a statement about the method's sensitivity as much as about the sample. A lab with an LOD of 0.1 µg/g and another with 0.005 µg/g can both report ND honestly on samples that contain very different trace levels. ## In practice When a [COA](https://genetixbay.com/knowledge/glossary/coa.md) shows ND for a pesticide, look for the LOD or [LOQ](https://genetixbay.com/knowledge/glossary/loq.md) printed beside it and the action limit that applies. "ND (LOD 0.01 µg/g)" is informative; a bare "ND" on a page with no limits or methods is not. In potency results, ND for a minor [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) such as [THCV](https://genetixbay.com/knowledge/glossary/thcv.md) usually just means it's below the panel's limit. It doesn't prove the plant can't make any. ## Don't confuse with - ** Death of plant tissue, seen as brown, tan or black patches, spots, tips or margins; it is permanent and the end point of many nutrient, salt, pest, disease and environmental problems. - Canonical: https://genetixbay.com/knowledge/glossary/necrosis.html - Also written: necrotic, necrotic spots, dead tissue, leaf necrosis - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Necrosis is dead plant tissue. On leaves it shows as dry brown or tan tips, margins or spots, or as black, water-soaked patches when disease is involved. It usually follows [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md): the tissue first yellows, then dies (Marschner 2012). ## In practice The position and shape of the necrosis help the diagnosis: brown tips on newest mature leaves suggest [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md); tan margins on old leaves suggest potassium; spots with yellow halos on new or middle leaves suggest calcium; spots with dark margins and tiny black specks suggest [septoria](https://genetixbay.com/knowledge/glossary/septoria-leaf-spot.md). Necrotic tissue never recovers, so judge any fix by the new growth that follows it (Cockson et al. 2019). ## Don't confuse with - **Chlorosis**: yellowing that can still recover. - **Senescence**: programmed ageing of old leaves. - **Light bleaching**: white rather than brown tissue at the canopy top. ## Related terms [Chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md), [Interveinal chlorosis](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md), [Nutrient burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md), [Leaf spot](https://genetixbay.com/knowledge/glossary/leaf-spot.md) ## Read more - [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) - [Rust-coloured spots on cannabis leaves: a differential](https://genetixbay.com/knowledge/diagnosis/rust-spots.md) - [Cannabis lookalike problems: how to tell them apart](https://genetixbay.com/knowledge/diagnosis/lookalikes.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Neem oil > An oil pressed from seeds of the neem tree (Azadirachta indica) that smothers soft-bodied pests and, in crude forms, contains azadirachtin, an insect growth disruptor. - Canonical: https://genetixbay.com/knowledge/glossary/neem-oil.html - Also written: neem, azadirachtin, cold-pressed neem oil, clarified hydrophobic neem oil, Azadirachta indica - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Neem oil is extracted from the seeds of the neem tree (*Azadirachta indica*). Crude or cold-pressed oil contains azadirachtin and related limonoids, which repel insects, reduce feeding and disrupt moulting. Clarified hydrophobic neem oil has most azadirachtin removed and acts mainly as a [horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md), smothering soft-bodied pests and some fungal growth on contact. ## In practice Growers use neem products in veg against [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), with thorough coverage of leaf undersides. It must never go on flowers: it leaves a strong odour and taste and oily residue on resin. It can burn leaves in heat or under strong light, and should not be combined with [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) within a couple of weeks. Products vary widely in composition, and in many places only registered formulations may be used on cannabis, whatever their natural origin. Check what is registered for cannabis locally. ## Myth check "Natural" does not mean harmless or legal. Azadirachtin is a pesticide active ingredient and is regulated as one. Label: Established. ## Don't confuse with - **Horticultural oil**: refined mineral or plant oil without azadirachtin. - **Neem cake or meal**: a soil amendment from pressed seed residue. ## Related terms [Horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md), [Insecticidal soap](https://genetixbay.com/knowledge/glossary/insecticidal-soap.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md), [Pre-harvest interval](https://genetixbay.com/knowledge/glossary/pre-harvest-interval.md), [Sulfur burner](https://genetixbay.com/knowledge/glossary/sulfur-burner.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) --- # Negative pressure > Negative pressure means the grow space is held slightly below surrounding air pressure by exhausting more air than comes in, so air and odour leak inwards, not out. - Canonical: https://genetixbay.com/knowledge/glossary/negative-pressure.html - Also written: negative air pressure, neg pressure, sucked-in tent, slight vacuum, negative pressure grow room - Glossary category: Environment and light · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Negative pressure is the state where air pressure inside a grow space is a little lower than outside it. It is created by running the [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) harder than the intake (or using only passive intake vents). Any gaps then let air in rather than out, so all exhaust air leaves through the [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md). That controls odour and helps keep dust and pests from blowing out into the home. ## In practice The visual test in a tent is simple: the walls bow slightly inwards. Aim for a gentle concave, not walls sucked tight against the frame; too much negative pressure starves the space of fresh air, strains the fan and can make the tent leak light through stressed seams. To set it up: size passive intake openings large enough (often 2–4 times the exhaust duct area), or run an intake fan at roughly 70–80% of the exhaust fan's real airflow. Close unused ports and flaps. Negative pressure is not a substitute for a filter: it ensures the filter handles everything. ## Don't confuse with - **Positive pressure**: used in clean rooms and some propagation areas to keep contaminants out; air leaks outwards. - **Sealed room**: no air exchange at all; climate is controlled by HVAC and [dehumidifiers](https://genetixbay.com/knowledge/glossary/dehumidifier.md), often with [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md). ## Related terms [Exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md), [Carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md), [CFM](https://genetixbay.com/knowledge/glossary/cfm.md), [Tent](https://genetixbay.com/knowledge/glossary/tent.md) ## Read more - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) --- # Neoseiulus californicus > A generalist-leaning predatory mite that eats spider mites and broad mites, survives on low prey or pollen, and tolerates warmer, drier rooms than Phytoseiulus. - Canonical: https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.html - Also written: californicus, N. californicus, Amblyseius californicus - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Neoseiulus californicus*, formerly *Amblyseius californicus*, is a phytoseiid [predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) that prefers [spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) but will also feed on [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md), other small mites and pollen. It is pale and translucent, about 0.3-0.5 mm, and slower than *[Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md)*. Its broader diet lets it survive when prey is scarce. ## In practice Growers use *californicus* as a preventive, standing army: released across the canopy in veg, often in sachets, before spider mites are seen. It copes with warmer temperatures and lower humidity better than *persimilis*, which suits many indoor rooms. It eats fewer mites per day, so on a heavy outbreak it is paired with *persimilis* on hot spots. It is also one of the predators used against broad mites. Releasing it well before flower gives populations time to establish. Keep incompatible sprays out of the release window. ## Don't confuse with - **Phytoseiulus persimilis**: a fast specialist that crashes without spider mites. - **Amblyseius swirskii**: better on [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) and [whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md); needs warmth. - **Neoseiulus fallacis**: a related species used mainly outdoors and in cooler climates. ## Related terms [Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md), [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Preventive release](https://genetixbay.com/knowledge/glossary/preventive-release.md), [Predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ## Sources 1. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf 2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # Neoseiulus cucumeris > A predatory mite that eats first-stage thrips larvae and some broad and cyclamen mites; tolerant of cooler rooms and widely used in sachets as a preventive. - Canonical: https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.html - Also written: cucumeris, N. cucumeris, Amblyseius cucumeris - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Neoseiulus cucumeris*, formerly *Amblyseius cucumeris*, is a phytoseiid [predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) that feeds mainly on first-instar [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) larvae. It also takes [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md), [cyclamen mites](https://genetixbay.com/knowledge/glossary/cyclamen-mite.md) and pollen. It cannot overpower older thrips larvae or adults, so it works as [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md), not as rescue. ## In practice Growers hang slow-release sachets, which breed [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) on a food source and release them for several weeks, or sprinkle loose material across the canopy from veg onward. It works at cooler temperatures than *[Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md)*, which makes it the usual choice in rooms that run below about 20 °C (68 °F). It is less persistent without prey, so sachets are replaced every few weeks. Pair it with a soil-dwelling predator or nematodes to catch thrips at the pupal stage in the medium. Avoid incompatible sprays near release dates. ## Don't confuse with - **Amblyseius swirskii**: stronger and longer-lasting, but needs warmth. - **Orius**: eats adult thrips too and flies between plants. - **Stratiolaelaps scimitus**: a soil mite, not a foliage predator. ## Related terms [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md), [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Preventive release](https://genetixbay.com/knowledge/glossary/preventive-release.md), [Predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) ## Read more - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Sources 1. UConn IPM. Biological Control of Western Flower Thrips. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-western-flower-thrips/ 2. UC IPM. Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html --- # Nerolidol > Nerolidol is a woody, floral, slightly citrus sesquiterpene alcohol found in neroli, jasmine and tea, and as a minor terpene in some cannabis cultivars. - Canonical: https://genetixbay.com/knowledge/glossary/nerolidol.html - Also written: trans-nerolidol, cis-nerolidol, peruviol, nerolidal - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nerolidol is an acyclic [sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) alcohol occurring as cis and trans isomers. It contributes woody, floral, fresh-bark and faintly citrus notes to neroli (bitter orange blossom) oil, jasmine, tea and ginger. In cannabis it is a minor [terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), more prominent in some cultivars than others, and often listed as "trans-nerolidol" on lab panels. ## In practice Readings range from [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md) to about 0.1-0.3% w/w in flower It is one of the less volatile terpenoids on a typical panel, so its relative share holds up in stored material. Because aroma depends on threshold as much as amount, a modest nerolidol figure can still be noticeable in the background of a profile. ## Don't confuse with - **Neral / geranial**: citral components, lemon-scented aldehydes. - **Linalool**: the [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md) alcohol analogue, smaller and more floral. - **Farnesol**: a related sesquiterpene alcohol with a different structure. ## Related terms [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), [Bisabolol](https://genetixbay.com/knowledge/glossary/bisabolol.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Net pot > A net pot is a plastic cup with slotted or mesh walls that holds a plant and its medium in a hydroponic lid, letting roots grow through into solution. - Canonical: https://genetixbay.com/knowledge/glossary/net-pot.html - Also written: net pots, net cup, mesh pot, netpot, hydro basket - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A net pot is a rigid plastic container with large openings in its sides and base. It sits in a hole in the lid of a hydroponic bucket, tray or channel, holding a [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) cube, [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md) or other support medium. Roots grow out through the openings and down into the solution or spray chamber. ## In practice Common sizes for cannabis [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) are 10-15 cm (4-6 in) diameter for each plant. Start a rooted cube or [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) in the net pot, surround it with rinsed clay pebbles, and keep the solution level just touching the base until roots have grown through; then lower the level to leave an air gap. Keep the top surface dry and covered where possible to reduce algae and gnats. Net pots are cleaned and reused between grows. ## Don't confuse with - **Fabric pot**: a breathable container for soil or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md). - **Air pot**: a rigid container with air-pruning holes, filled with a full medium. ## Related terms [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [Clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md), [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [Kratky method](https://genetixbay.com/knowledge/glossary/kratky.md) ## Read more - [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) - [Kratky (passive, non-circulating hydroponics)](https://genetixbay.com/knowledge/systems/kratky.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 --- # Net reproductive rate (R0) > The average number of female offspring a female produces in her lifetime after mortality: the population's multiplication per generation. - Canonical: https://genetixbay.com/knowledge/glossary/net-reproductive-rate.html - Also written: R0, net reproduction rate - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The net reproductive rate, R0, is how many daughters an average newborn female will leave, accounting for the chance she dies first. If R0 is 40, the population multiplies 40-fold each generation. It is calculated from a [life table](https://genetixbay.com/knowledge/glossary/life-table.md) by summing survival times daughters at each age. ## In practice R0 and r_m are linked through [generation time](https://genetixbay.com/knowledge/glossary/generation-time.md): r_m is approximately ln(R0) divided by the mean generation time T. A pest with modest R0 but very short generations, like a [spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) at 30 C, can outgrow one with a higher R0 and slow generations, like a [mealybug](https://genetixbay.com/knowledge/glossary/mealybug.md). ## Don't confuse with - **r_m**: per day, not per generation. - **Fecundity**: eggs laid, before mortality and [sex ratio](https://genetixbay.com/knowledge/glossary/sex-ratio.md). ## Related terms [Intrinsic rate of increase (r_m)](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md), [Life table](https://genetixbay.com/knowledge/glossary/life-table.md), [Generation time](https://genetixbay.com/knowledge/glossary/generation-time.md), [Fecundity](https://genetixbay.com/knowledge/glossary/fecundity.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) ## Sources 1. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605 --- # NFT > NFT (nutrient film technique) runs a thin, continuous film of nutrient solution along sloped channels, with roots resting in the stream and exposed to air above. - Canonical: https://genetixbay.com/knowledge/glossary/nft.html - Also written: nutrient film technique, nutrient film, NFT channel, NFT gully, gully system - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The nutrient film technique is a [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) hydroponic system in which plants sit in channels (gullies) set at a slight slope. A pump delivers solution to the high end, a shallow film flows past the roots and [drains](https://genetixbay.com/knowledge/glossary/runoff.md) back to a reservoir. Roots form a mat on the channel floor, wetted below and in air above. ## In practice NFT is the standard for lettuce and herbs and is used for tomatoes commercially, but it is less forgiving with cannabis. A large cannabis root mass can dam the channel, and if the pump stops, the thin film offers almost no buffer, so roots can dry within minutes. Growers who use it run wider channels, steeper slopes, short runs and backup power or alarms. Typical slopes in vegetable NFT are around 1:30 to 1:100. ## Don't confuse with - **Ebb and flow**: floods and drains periodically rather than flowing continuously. - **DWC**: roots fully submerged in deep, aerated solution. ## Related terms [Recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [Root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) ## Read more - [Nutrient film technique (NFT)](https://genetixbay.com/knowledge/systems/nft.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 --- # Nickel > Nickel (Ni) is a micronutrient required for urease, the enzyme that breaks down urea; plants need only traces, which most feeds and waters already contain. - Canonical: https://genetixbay.com/knowledge/glossary/nickel.html - Also written: Ni, Ni2+, nickel deficiency - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nickel is a trace [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), the most recent element accepted as essential for higher plants (Brown, Welch and Cary, 1987). Its best-known role is as the metal centre of urease, which splits [urea](https://genetixbay.com/knowledge/glossary/urea.md) into ammonia and [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md). Plants need it in amounts so small that impurities in salts and water usually cover the requirement. ## In practice [Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) is very rare in cannabis. Where it has been seen in other crops, it shows as urea accumulating to toxic levels in leaf tips, causing tip [necrosis](https://genetixbay.com/knowledge/glossary/necrosis.md), especially when urea is the nitrogen source. Most hydro recipes do not add nickel deliberately. Excess nickel is toxic and can induce iron or [zinc deficiency](https://genetixbay.com/knowledge/glossary/zinc.md), so supplements are not recommended without a reason. ## Don't confuse with - **Nutrient burn**: tip necrosis from high [EC](https://genetixbay.com/knowledge/glossary/ec.md), far more common than Ni-related urea burn. - **Nickel-plated fittings**: a possible contamination source rather than a feed. ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Urea](https://genetixbay.com/knowledge/glossary/urea.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) ## Read more - [Nickel (Ni) in cannabis: essential, needed in traces, almost never worth adding](https://genetixbay.com/knowledge/nutrients/nickel.md) ## Sources 1. Brown PH, Welch RM, Cary EE. 1987. Nickel: a micronutrient essential for higher plants. Plant Physiology 85(3):801-803. https://doi.org/10.1104/pp.85.3.801 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Nitrate > Nitrate (NO3-) is the main form of nitrogen in hydroponic and soilless feeds; its uptake tends to push root-zone pH upward. - Canonical: https://genetixbay.com/knowledge/glossary/nitrate.html - Also written: NO3-, NO3, nitrate nitrogen, NO3-N - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nitrate is the negatively charged ion NO3-, the dominant nitrogen form in mineral feeds and in aerated soil. Roots absorb it actively, store it in vacuoles and reduce it to [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) inside the plant before building amino acids, a step that needs [molybdenum](https://genetixbay.com/knowledge/glossary/molybdenum.md). ## In practice Most cannabis feeds supply 80-100% of their nitrogen as nitrate, from [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md) and [magnesium nitrate](https://genetixbay.com/knowledge/glossary/magnesium-nitrate.md). When roots take up nitrate they release hydroxide or bicarbonate to stay balanced, so a nitrate-heavy [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) reservoir drifts up in [pH](https://genetixbay.com/knowledge/glossary/ph.md) over days. Growers counter that with a small ammonium fraction or acid. ## Units and formula Labels and [lab reports](https://genetixbay.com/knowledge/glossary/coa.md) may quote "nitrate" or "NO3-N". NO3-N counts only the nitrogen: 1 mg/L NO3-N = 4.43 mg/L NO3-. Always check which one a report means. ## Don't confuse with - **Nitrite (NO2-)**: an intermediate, toxic at higher levels, not a feed form. - **Ammonium**: the positively charged nitrogen form, which pushes pH down. - **Nitrogen**: the element, counted the same whichever ion carries it. ## Related terms [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md), [Nitric acid](https://genetixbay.com/knowledge/glossary/nitric-acid.md) ## Read more - [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) ## Sources 1. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Nitric acid > Nitric acid (HNO3) lowers pH while adding nitrate nitrogen; growers use it to neutralise hard-water alkalinity, often alongside or instead of phosphoric acid. - Canonical: https://genetixbay.com/knowledge/glossary/nitric-acid.html - Also written: HNO3, nitric pH down, pH down (nitric) - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nitric acid is a strong mineral acid that supplies [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) when it neutralises [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md). Pure HNO3 is about 22% N by weight; commercial strengths are lower. It is the main pH-down acid in commercial greenhouse hydroponics. ## In practice Growers with hard, high-bicarbonate water often use nitric acid so that acidification adds nitrogen rather than too much phosphorus. The nitrogen it adds must be counted in the feed total, which matters during a late-flower [N taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md). Langenfeld and Bugbee studied nitric acid with [ammonium nitrate](https://genetixbay.com/knowledge/glossary/ammonium-nitrate.md) for [pH](https://genetixbay.com/knowledge/glossary/ph.md) control in [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) hydroponics. Concentrated nitric acid is highly corrosive, gives off toxic fumes and is an oxidiser. Most home growers buy it pre-diluted as a pH-down product, and should keep to that. It may be regulated in some places; check local rules. ## Don't confuse with - **Phosphoric acid**: lowers pH while adding phosphorus. - **Sulfuric acid**: lowers pH while adding [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md). - **Nitrate salts**: supply nitrate without lowering pH. ## Related terms [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [Phosphoric acid](https://genetixbay.com/knowledge/glossary/phosphoric-acid.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Ammonium nitrate](https://genetixbay.com/knowledge/glossary/ammonium-nitrate.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) ## Sources 1. Langenfeld NJ, Bugbee B. 2025. pH control in recirculating hydroponics with nitric acid and ammonium nitrate. HortScience 60(9):1555. https://journals.ashs.org/view/journals/hortsci/60/9/article-p1555.xml 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Nitrogen > Nitrogen (N) is the macronutrient plants use most, built into proteins, chlorophyll and nucleic acids; it drives leaf and stem growth and is fully mobile. - Canonical: https://genetixbay.com/knowledge/glossary/nitrogen.html - Also written: N, nitrogen deficiency, N deficiency, nitrogen toxicity - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nitrogen is the element plants take up in the largest amount after carbon, hydrogen and oxygen. It is part of every amino acid, protein, [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) molecule and strand of DNA. Plants absorb it mainly as [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) (NO3-) and [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) (NH4+), and they move it freely from old leaves to new growth. ## In practice A deficient plant yellows from the bottom up, evenly across the leaf, while new growth stays green. Excess gives very dark, glossy leaves, clawed tips and soft, leafy growth. Hydro and coco feeds typically run about 150-200 mg/L (ppm) N in veg and somewhat less in late flower. Saloner and Bernstein found that lower N supply in flower can raise [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) percentage while reducing total yield, a trade-off rather than a free win. ## Don't confuse with - **Nitrate**: one ionic form of nitrogen, not the element itself. - **Iron or sulfur deficiency**: those yellow the new growth first; nitrogen yellows the old growth first. - **Natural late-flower fade**: some lower-leaf yellowing near harvest is normal remobilisation. ## Myth check The GenetixBay approach is to [taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) in late flower, not to [flush](https://genetixbay.com/knowledge/glossary/flushing.md). Cut N back towards zero near the finish while keeping P, K, Ca, Mg, S and the micros fed. A plain-water flush starves the plant of everything at its most productive stage. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [Ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), [Macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md), [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md), [Urea](https://genetixbay.com/knowledge/glossary/urea.md), [N-P-K ratio](https://genetixbay.com/knowledge/glossary/npk-ratio.md) ## Read more - [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) - [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Saloner A, Bernstein N. 2020. Response of medical cannabis (Cannabis sativa L.) to nitrogen supply under long photoperiod. Frontiers in Plant Science 11:572293. https://doi.org/10.3389/fpls.2020.572293 3. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 --- # Nitrogen taper > Gradually cutting nitrogen in late flower, toward zero near the finish, while still feeding phosphorus, potassium, calcium, magnesium, sulfur and micronutrients; GenetixBay's alternative to flushing. - Canonical: https://genetixbay.com/knowledge/glossary/nitrogen-taper.html - Also written: N taper, tapering nitrogen, taper nitrogen, late-flower nitrogen reduction, nitrogen ramp-down, N ramp down - Glossary category: Harvest, drying and curing · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A nitrogen taper is a late-flower feeding strategy: reduce nitrogen step by step over the final weeks, approaching zero near harvest, while keeping every other nutrient supplied. The plant draws on its own stored nitrogen, older leaves [fade](https://genetixbay.com/knowledge/glossary/senescence.md) naturally, and buds keep the potassium, phosphorus, calcium, magnesium, sulfur and [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md) they need to finish. ## In practice The GenetixBay approach (house position, Supported): taper nitrogen, don't [flush](https://genetixbay.com/knowledge/glossary/flushing.md). Research shows that lower nitrogen can raise [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) percentages while lowering total yield (Saloner & Bernstein 2021). It's a trade-off you manage, not a reason to starve the plant. A typical outline: hold normal N through the bulking weeks, then cut it back over roughly the final 2-3 weeks, while holding K, Ca, Mg, P, S and micros steady. Watch the [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md): a gradual fade from the bottom is the goal; a sudden mid-canopy yellowing means you cut too hard or too early. This is why Jardin uses [per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md). A bottled two-part can't drop N without dropping everything else. ## Don't confuse with - **Pre-harvest flushing**: removes all feed (Myth, harmful). - **Feed reduction**: cutting all nutrients equally, which also starves K and Ca. - **Nitrogen deficiency**: an unwanted problem, not a managed finish. ## Related terms [Flushing](https://genetixbay.com/knowledge/glossary/flushing.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md), [Harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md) ## Read more - [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) - [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ## Sources 1. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 2. Hershkowitz JA. 2024. Nutrient management of cannabis in controlled environments. MS thesis, Utah State University (Bugbee lab). https://digitalcommons.usu.edu/etd2023/178 3. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 --- # No-till > No-till growing reuses living soil from cycle to cycle without turning or replacing it, cutting out the old root ball and replenishing with top-dressed amendments. - Canonical: https://genetixbay.com/knowledge/glossary/no-till.html - Also written: no till, notill, no-till growing, no-till bed, no-till pots - Glossary category: Systems and media · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" No-till is a soil-management approach borrowed from regenerative farming: the soil is not dug, mixed or replaced between crops. Old roots are left to decompose in place (or the stem is cut at the surface), fresh amendments are top-dressed and mulched, and the [soil food web](https://genetixbay.com/knowledge/glossary/living-soil.md), including fungal networks, stays intact. ## In practice Indoor no-till usually uses large fabric beds or containers, often 100 L or more per plant, with mulch, cover crops and sometimes worms. Between crops, the grower cuts the stem, [top-dresses](https://genetixbay.com/knowledge/glossary/top-dressing.md) compost and amendments, and replants into the same soil. Benefits claimed are improving structure and biology over time, less labour and less waste. The risk is building up pests ([fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md)) or pathogens, which a fresh medium would remove. Evidence for no-till benefits is strong in field agriculture; for indoor cannabis it is mostly grower practice. ## Don't confuse with - **Reusing soil**: recycling old mix by remixing and amending it; tilling counts as disturbance. - **Living soil**: no-till is a way of managing living soil. ## Related terms [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), [Top dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md), [Mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md), [Companion planting](https://genetixbay.com/knowledge/glossary/companion-planting.md) ## Read more - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) ## Sources 1. Brady NC, Weil RR, 2017. The Nature and Properties of Soils, 15th ed. Pearson. --- # Node > The point on a stem where a leaf (petiole) and its axillary bud attach; branches, flowers and clone roots all originate at nodes. - Canonical: https://genetixbay.com/knowledge/glossary/node.html - Also written: nodes, nodal site, leaf node, growth node - Glossary category: Plant biology - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A node is the place on a stem where one or more leaves attach. In cannabis each node carries a leaf on its [petiole](https://genetixbay.com/knowledge/glossary/petiole.md), an [axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md) in the angle between leaf and stem, and often a pair of small stipules. The stem between two nodes is the [internode](https://genetixbay.com/knowledge/glossary/internode.md). ## In practice Nodes are the grower's counting unit. Topping is usually done above the third to fifth node; mainlining builds a plant from a chosen node; clones root best when a node is buried or sits just above the cut. In flower, every node on a productive branch becomes a bud site, which is why [short internodes](https://genetixbay.com/knowledge/glossary/node-stacking.md) (many nodes per centimetre) give dense [colas](https://genetixbay.com/knowledge/glossary/cola.md). Nodes are also where you look first for sex. [Pre-flowers](https://genetixbay.com/knowledge/glossary/pre-flower.md) appear at the nodes, typically from the fourth to sixth node upward, a few weeks into vegetative growth on [photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md). Young cannabis has opposite nodes (two leaves per node). Older plants and flowering shoots switch to alternate nodes, one leaf per node. That switch signals maturity. ## Don't confuse with - **Internode**: the stem between nodes. - **Axillary bud**: the bud sitting at the node, not the node itself. - **Knuckle**: grower slang for a healed [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md) callus, often between nodes. ## Related terms [Internode](https://genetixbay.com/knowledge/glossary/internode.md), [Axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md), [Petiole](https://genetixbay.com/knowledge/glossary/petiole.md), [Apical meristem](https://genetixbay.com/knowledge/glossary/apical-meristem.md) ## Read more - [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md) - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Node stacking > Node stacking describes short internodes, so nodes and bud sites sit close together along a stem, giving dense colas and a compact plant. - Canonical: https://genetixbay.com/knowledge/glossary/node-stacking.html - Also written: tight node spacing, short internodes, stacked nodes, tight nodes - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Node stacking is grower shorthand for short spacing between nodes. The [internode](https://genetixbay.com/knowledge/glossary/internode.md), the length of stem between two nodes, is shaped by genetics, light intensity and spectrum, temperature (especially the day-night difference) and [plant density](https://genetixbay.com/knowledge/glossary/plant-density.md). Tight stacking puts more [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md) per centimetre of stem, which helps produce long, solid [colas](https://genetixbay.com/knowledge/glossary/cola.md). ## In practice Growers praise a cultivar for "stacking well" when its flowers join into one continuous cola in flower. To encourage tight nodes: enough light (low light makes plants reach), modest [day-night temperature differences](https://genetixbay.com/knowledge/glossary/dif.md), adequate [blue light](https://genetixbay.com/knowledge/glossary/blue-light.md) in veg, and not crowding plants so they compete upwards. Internode spacing of about 2-5 cm (1-2 in) in veg is typical of compact plants; long-flowering, narrow-leaflet types often space wider. Very dense colas can also hold more moisture inside, raising bud-rot risk in humid rooms. ## Don't confuse with - **Stretch**: a temporary increase in internode length after the flip. - **Foxtailing**: new calyx spires growing on top of finished buds. ## Related terms [Internode](https://genetixbay.com/knowledge/glossary/internode.md), [Node](https://genetixbay.com/knowledge/glossary/node.md), [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md), [Bud site](https://genetixbay.com/knowledge/glossary/bud-site.md) ## Read more - [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) --- # Nugs > Nugs is slang for whole, trimmed buds of dried cannabis flower, as opposed to shake or trim. - Canonical: https://genetixbay.com/knowledge/glossary/nugs.html - Also written: nug, nuggets, buds, nuggs - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nugs (from "nuggets") are whole, dried and trimmed buds. Saying "nice nugs" means the buds are intact, dense and well formed. ## In practice A "nug shot" is a close-up [photo](https://genetixbay.com/knowledge/glossary/photoperiod.md) of one bud, the standard way flower is shown off. Nug size depends on how the plant was trained and on how the [cola](https://genetixbay.com/knowledge/glossary/cola.md) was broken down: big nugs look impressive, but over-large ones dry unevenly and carry a higher risk of internal mould. Many growers break colas into medium-sized nugs before the cure for a more even moisture decline. Store nugs whole and grind just before use: an intact bud keeps its aroma far longer than ground flower. ## Don't confuse with - **Cola**: the whole terminal flower cluster on the plant, before it is cut into nugs. - **Shake**: loose fragments. ## Related terms [Popcorn buds](https://genetixbay.com/knowledge/glossary/popcorn-buds.md), [Shake](https://genetixbay.com/knowledge/glossary/shake.md), [Larf](https://genetixbay.com/knowledge/glossary/larf.md), [Cola](https://genetixbay.com/knowledge/glossary/cola.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) --- # Nutrient antagonism > Nutrient antagonism is when an excess of one element reduces the uptake or use of another, such as high potassium suppressing magnesium and calcium. - Canonical: https://genetixbay.com/knowledge/glossary/nutrient-antagonism.html - Also written: antagonism, ion antagonism, nutrient interaction, ion competition, antagonistic nutrients - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nutrient antagonism is a negative interaction in which one nutrient reduces the uptake, transport or function of another. It arises from competition for the same uptake sites, from precipitation in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md), or from internal effects on metabolism. The opposite, synergism, is when one element enhances another. Rietra and colleagues reviewed these interactions across crops. ## In practice Well-documented examples include potassium suppressing magnesium and calcium uptake, [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) competing with calcium, magnesium and potassium, phosphorus reducing zinc and iron availability, and manganese and iron competing with each other. In cannabis feeds, the usual trigger is an additive pushed to excess, such as a [PK booster](https://genetixbay.com/knowledge/glossary/bloom-booster.md) or extra [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md), that throws the ratio out. The fix is restoring balance, not adding the "missing" element on top. ## Don't confuse with - **Lockout from pH**: availability problems caused by root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) rather than another nutrient. - **Mulder's chart**: a diagram of interactions; useful but simplified. - **Nutrient toxicity**: direct damage from one element. ## Related terms [Mulder's chart](https://genetixbay.com/knowledge/glossary/mulders-chart.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Magnesium](https://genetixbay.com/knowledge/glossary/magnesium.md) ## Read more - [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md) ## Sources 1. Rietra RPJJ, Heinen M, Dimkpa CO, Bindraban PS. 2017. Effects of nutrient antagonism and synergism on yield and fertilizer use efficiency. Communications in Soil Science and Plant Analysis 48(16):1895-1920. https://hub.ifdc.org/handle/20.500.14297/2410 2. Fageria VD. 2001. Nutrient interactions in crop plants. Journal of Plant Nutrition 24(8):1269-1290. https://doi.org/10.1081/PLN-100106981 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Nutrient burn > Nutrient burn is browning and crisping of leaf tips, then margins, caused by a root-zone salt concentration (EC) higher than the plant can handle. - Canonical: https://genetixbay.com/knowledge/glossary/nutrient-burn.html - Also written: nute burn, nute-burn, tip burn, burnt tips, fertiliser burn, fertilizer burn, overfert - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nutrient burn is leaf damage from excess total salts in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). As [EC](https://genetixbay.com/knowledge/glossary/ec.md) climbs, water uptake slows, and salts build up at the leaf tips and edges where water evaporates. The tips yellow, then turn brown and crisp, and the damage creeps inward along the margins. It is a general salt effect, not a single-element [toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md). ## In practice Typical triggers are feeding above the plant's tolerance, letting a coco or rockwool slab dry back hard so EC concentrates, skipping [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) in containers, or stacking additives on a full-strength base. Check runoff EC against input EC: runoff much higher than input means salts are accumulating. Lower the [feed strength](https://genetixbay.com/knowledge/glossary/input-ec.md) or [water to runoff](https://genetixbay.com/knowledge/glossary/watering-to-runoff.md). In serious build-up, a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) to wash salts out of the medium is the valid fix. A slight tip burn in late flower on heavily fed plants is common and usually harmless. ## Don't confuse with - **Heat or light burn**: bleaching or crisping at the top of the canopy closest to the lamp. - **Potassium deficiency**: margin burn on older leaves with yellowing first. - **Chloride or boron toxicity**: specific elements, often from water. ## Myth check A root-zone flush treats the medium, not the plant, and is not a pre-harvest ritual. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Related terms [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Feed chart](https://genetixbay.com/knowledge/glossary/feed-chart.md), [ppm of an element](https://genetixbay.com/knowledge/glossary/elemental-ppm.md), [Nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) ## Read more - [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Nutrient deficiency > A nutrient deficiency is a shortage of an essential element in the plant tissue, causing characteristic symptoms; the cause is often pH or uptake rather than an empty feed. - Canonical: https://genetixbay.com/knowledge/glossary/nutrient-deficiency.html - Also written: deficiency, deficiencies, nutrient deficiencies, def, hunger sign - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A nutrient deficiency is a condition in which the plant contains too little of an essential element to function normally. It shows as specific symptoms: [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md), [necrosis](https://genetixbay.com/knowledge/glossary/necrosis.md), distortion, colour change or stunting, in a pattern that depends on the element and its mobility. Cockson and colleagues, and Llewellyn and colleagues, documented deficiency symptoms specifically in cannabis. ## In practice Diagnose by location first: old leaves suggest a [mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md), new growth an immobile one. Then by pattern: uniform, interveinal, marginal or spotted. Before adding anything, check root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md) and runoff, because most "deficiencies" in practice come from [pH lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md), root damage, cold or [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) media, or antagonism from an excess of another element. A tissue test confirms what symptoms only suggest. ## Don't confuse with - **Nutrient toxicity**: too much of an element, which can mimic a deficiency of another. - **Pest damage**: mites, thrips and pathogens can cause spotting or distortion with no nutrient cause. - **Natural senescence**: late-flower fade is expected. ## Myth check "Add more nutrients" is rarely the first fix. Check pH and roots first. See [how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md). ## Related terms [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), [Tissue test](https://genetixbay.com/knowledge/glossary/tissue-test.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md) ## Read more - [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) - [Mobile vs immobile nutrients: reading old vs new leaves](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) ## Sources 1. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y. 2023. Foliar symptomology, nutrient content, yield, and secondary metabolite variability of cannabis grown hydroponically with different single-element nutrient deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 --- # Nutrient lockout > Nutrient lockout is when plants show deficiency symptoms although nutrients are present, because pH, salt build-up, ion antagonism or damaged roots stop uptake. - Canonical: https://genetixbay.com/knowledge/glossary/nutrient-lockout.html - Also written: lockout, locked out, nutrient lock, pH lockout, nutrient lock-out - Glossary category: pH, EC and water · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nutrient lockout is grower shorthand for a plant that cannot take up nutrients that are present in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). It is not one mechanism. The common causes are root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) outside the working range (iron and manganese become insoluble at high pH, calcium and magnesium less available at low pH), [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) and [osmotic stress](https://genetixbay.com/knowledge/glossary/osmotic-stress.md), antagonism between ions (excess potassium suppressing magnesium and calcium, for example) and roots damaged by rot, overwatering, heat or low oxygen. ## In practice The classic error is to add more of the "missing" nutrient, raising [EC](https://genetixbay.com/knowledge/glossary/ec.md) and making things worse. Diagnose first, cheapest checks first: 1. Measure root-zone pH ([runoff](https://genetixbay.com/knowledge/glossary/runoff.md) or PourThru), not just input pH. 2. Compare runoff EC with input EC. 3. Inspect roots: white and firm is good; brown, slimy or smelly is a root problem, not a nutrient one. 4. Review the feed recipe for extreme ratios. Then fix the cause: correct pH, do a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) if runoff EC is high, and restore root health. New growth should come in clean within one to two weeks; damaged leaves will not recover. ## Don't confuse with - **True deficiency**: the element is genuinely short in the feed. - **Nutrient antagonism**: one specific cause of lockout. ## Myth check GenetixBay house position: a **root-zone flush** to wash accumulated salts out of the medium is the one valid [flush](https://genetixbay.com/knowledge/glossary/flushing.md). It treats the medium, not the plant, and can be done at any stage. A **pre-harvest flush** is a *Myth* and actively harmful: it starves the plant while it is packing on its final weight and resin. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Related terms [pH](https://genetixbay.com/knowledge/glossary/ph.md), [Salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), [Osmotic stress](https://genetixbay.com/knowledge/glossary/osmotic-stress.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md) ## Read more - [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) - [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md) - [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 2. Cavins TJ, Whipker BE, Fonteno WC, Harden B, McCall I, Gibson JL. Monitoring and managing pH and EC using the PourThru extraction method. NC State University Horticulture Information Leaflet 590. Cited via MSU Extension: https://www.canr.msu.edu/uploads/resources/pdfs/measuring_ph_and_ec_of_crops_grown_in_large_containers.pdf --- # Nutrient toxicity > Nutrient toxicity is damage from an excess of an element in the plant, either directly or by blocking uptake of others; boron, manganese, copper and chloride are common culprits. - Canonical: https://genetixbay.com/knowledge/glossary/nutrient-toxicity.html - Also written: toxicity, nutrient excess, element toxicity, overfeeding - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Nutrient toxicity is injury caused by too much of a particular element in the plant tissue. Some elements are directly toxic at high levels: [boron](https://genetixbay.com/knowledge/glossary/boron.md), [manganese](https://genetixbay.com/knowledge/glossary/manganese.md), copper, [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md), sodium and ammonium. Others, such as potassium or phosphorus in excess, do harm mainly by suppressing the uptake of other nutrients and inducing a [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md). ## In practice Toxicity symptoms often look like deficiencies of a different element: excess manganese induces iron [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md), excess phosphorus induces zinc deficiency, excess potassium induces magnesium or [calcium deficiency](https://genetixbay.com/knowledge/glossary/calcium.md). Direct toxicity often appears as burning of older leaf margins (boron, chloride) or brown speckling (manganese at low [pH](https://genetixbay.com/knowledge/glossary/ph.md)). Causes include overdosing micronutrients, water with high boron, sodium or chloride, pH drift that frees metals, and copper or zinc from plumbing. ## Don't confuse with - **Nutrient burn**: tip burn from high total [EC](https://genetixbay.com/knowledge/glossary/ec.md) rather than a single element. - **Nutrient deficiency**: too little rather than too much, though toxicity can cause one. - **Pesticide phytotoxicity**: damage from a spray, not from nutrition. ## Related terms [Nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md), [Nutrient burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), [Boron](https://genetixbay.com/knowledge/glossary/boron.md), [Manganese](https://genetixbay.com/knowledge/glossary/manganese.md) ## Read more - [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md) - [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Ocimene > Ocimene is a sweet, green, herbal monoterpene, usually reported as beta-ocimene isomers, that often accompanies terpinolene in cannabis profiles. - Canonical: https://genetixbay.com/knowledge/glossary/ocimene.html - Also written: beta-ocimene, β-ocimene, trans-ocimene, cis-ocimene, ocimine - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Ocimene is an acyclic [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), a structural isomer of [myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md), existing as several isomers (cis- and trans-beta-ocimene, alpha-ocimene). It smells sweet, green, herbal and slightly woody, and is found in basil (*Ocimum*, the source of the name), mint, orchids and mango. Plants release it readily; in many species it's a signalling volatile that attracts pollinators or responds to insect feeding. ## In practice Cannabis panels often report "ocimene" as one figure summing the isomers, or list them separately. Typical readings run from [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md) to about 0.3% w/w; higher values tend to appear in [terpinolene-dominant](https://genetixbay.com/knowledge/glossary/terpinolene.md) [chemotypes](https://genetixbay.com/knowledge/glossary/chemotype.md). It is very volatile, so it falls sharply in fast-dried or old flower and is often higher in [fresh-frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) material. ## Don't confuse with - **Myrcene**: an isomer with a muskier, earthier smell. - **Terpinolene**: a co-occurring monoterpene with a fresher, piney-floral note. - **Ocimum**: the basil genus, not a compound. ## Related terms [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpinolene](https://genetixbay.com/knowledge/glossary/terpinolene.md), [Myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. 2. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Oedema > Small blisters or corky bumps on leaf undersides caused by cells swelling with water and bursting when roots take up more water than the leaves can transpire, typically in cool, humid, wet conditions. - Canonical: https://genetixbay.com/knowledge/glossary/oedema.html - Also written: edema, leaf edema, leaf oedema, intumescence, intumescences - Glossary category: Plant biology · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Oedema (edema, or intumescence) is a physiological disorder, not a disease. When the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) is wet but the air is cool and humid, roots push in water faster than the leaves can lose it, and some leaf cells swell and rupture, leaving blisters that turn corky and tan. It is documented in many greenhouse crops (UMass Extension); cannabis-specific reports are anecdotal. ## In practice Look on the leaf underside for raised, water-soaked bumps that later turn brown and scabby, often on lower leaves. Fix the conditions: water less often, raise air temperature, lower [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) and increase airflow so [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) rises toward 0.8-1.2 kPa. Damaged leaves stay marked; new growth will be clean. ## Don't confuse with - **Mite or thrips damage**: flat [stipples](https://genetixbay.com/knowledge/glossary/stippling.md) or streaks, with pests visible under a lens. - **Septoria leaf spot**: flat spots with dark margins and black fruiting bodies. - **Spray burn**: spots where droplets dried in light. ## Related terms [Transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) ## Read more - [Spots, brown patches and dead edges on cannabis leaves: the master decision tree](https://genetixbay.com/knowledge/diagnosis/spots-necrosis-decision-tree.md) - [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Sources 1. University of Massachusetts Extension. Edema (oedema) of greenhouse crops, fact sheet. https://www.umass.edu/agriculture-food-environment/greenhouse-floriculture/fact-sheets/edema --- # OG > OG is a cannabis family name tied to a group of influential clone-only cultivars from the 1990s, and general slang for "original" or long-established. - Canonical: https://genetixbay.com/knowledge/glossary/og.html - Also written: OGs, OG Kush family, O.G. - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" OG has two meanings. In general slang it means original, veteran or authentic. In cannabis naming it refers to a family of influential [clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) cultivars that emerged in the 1990s and became the parents of a huge share of modern lines. ## In practice The origin of the OG family is disputed, including what the letters stand for; stories conflict and documentation is thin. Many cuts circulate under OG names, some genuinely related, some not, and "OG" is attached to new crosses as a marketing tag. Treat any specific OG lineage claim as low-evidence unless there is a documented chain of custody or DNA match. ## Don't confuse with - **Kush**: a broader name tied to [Hindu Kush](https://genetixbay.com/knowledge/glossary/kush.md) [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) material; OGs are often grouped with kush but the relationship is a claim. - **Original cut**: a claim about one specific clone, not a property of the name. ## Myth check "Everything with OG in the name is related." Names are unreliable as genetic evidence (Sawler et al. 2015). See [why strain names are unreliable](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md). ## Related terms [Kush](https://genetixbay.com/knowledge/glossary/kush.md), [Elite cut](https://genetixbay.com/knowledge/glossary/elite-cut.md), [Renamed cut](https://genetixbay.com/knowledge/glossary/renamed-cut.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) ## Read more - [Why strain names are unreliable: what genetic studies show](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) - [Same cut, a thousand names: renaming, relabelling and the shrinking gene pool](https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.md) ## Sources 1. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLOS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 --- # Olivetolic acid > Olivetolic acid is the phenolic building block of cannabinoids; joined to geranyl pyrophosphate it forms CBGA, and its five-carbon chain becomes the pentyl tail of THC and CBD. - Canonical: https://genetixbay.com/knowledge/glossary/olivetolic-acid.html - Also written: OA, olivetolate, olivetolic - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Olivetolic acid is a polyketide made in [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) secretory cells from hexanoyl-CoA and three malonyl-CoA units. Two enzymes do the work: a polyketide synthase (often called olivetol synthase or tetraketide synthase) and olivetolic acid cyclase. The product is the aromatic ring and five-carbon (pentyl) side chain that every "regular" [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) carries. ## In practice Growers never see olivetolic acid on a [COA](https://genetixbay.com/knowledge/glossary/coa.md); it is consumed as fast as it is made. Its relevance is conceptual. The side-chain length is set here: when the plant starts from a shorter precursor it makes divarinic acid instead, and the whole downstream chain shifts to the propyl "varin" cannabinoids (CBGVA, [THCVA](https://genetixbay.com/knowledge/glossary/thcva.md), CBDVA). That is why THCV-rich plants tend to be lower in [THC](https://genetixbay.com/knowledge/glossary/thc.md), not higher. Researchers producing cannabinoids in yeast also have to rebuild this step. ## Don't confuse with - **Olivetol**: the [decarboxylated](https://genetixbay.com/knowledge/glossary/decarboxylation.md) form, used in chemical synthesis; not the natural plant substrate. - **Geranyl pyrophosphate**: the terpene-derived partner that joins olivetolic acid to make [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md). - **CBGA**: the product, the first true cannabinoid in the pathway. ## Related terms [Geranyl pyrophosphate](https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [Phytocannabinoid](https://genetixbay.com/knowledge/glossary/phytocannabinoid.md), [THCVA](https://genetixbay.com/knowledge/glossary/thcva.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) ## Sources 1. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004. --- # One-part nutrient > A one-part nutrient is a complete mineral feed in a single concentrate or powder, formulated to avoid the calcium-sulfate and calcium-phosphate precipitation that forces most feeds into two parts. - Canonical: https://genetixbay.com/knowledge/glossary/one-part-nutrient.html - Also written: single-part nutrient, 1-part nutrient, one-part feed, complete one-part - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A one-part nutrient is a complete feed supplied as a single product. Liquid one-parts avoid precipitation by using calcium and [magnesium nitrates](https://genetixbay.com/knowledge/glossary/magnesium-nitrate.md) with little or no [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), or by leaving out calcium altogether and expecting it from the water or a separate supplement. Dry one-part powders can contain all salts because they only react once dissolved at feeding strength. ## In practice They are convenient: one measurement, less chance of mixing errors. The trade-offs are less flexibility and, for liquids, compromises in the recipe, such as low phosphorus or sulfate, or calcium supplied separately. Read the [guaranteed analysis](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md) to see what is missing. Dry one-part powders should be dissolved in the full volume of water, not made into a strong stock, or they will precipitate. ## Don't confuse with - **A/B nutrient**: two concentrates kept separate. - **Base plus additives**: a one-part base often still needs supplements in practice. - **Organic all-in-one**: slow-release amendments, a different approach. ## Related terms [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Magnesium nitrate](https://genetixbay.com/knowledge/glossary/magnesium-nitrate.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Open research > Open research is GenetixBay's approach of settling growing questions with member-run controlled trials and publishing protocols, data and verdicts for anyone to see. - Canonical: https://genetixbay.com/knowledge/glossary/open-research.html - Also written: open science, GenetixBay open research, citizen science, community research - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Open research means that GenetixBay tests growing and breeding claims in the open: protocols are published before trials start, members run the grows, data and lab results are shared, and verdicts are shown alongside the evidence. The aim is to replace forum arguments with numbers. ## In practice Questions come from the community and from house positions that deserve testing: [LED vs HPS](https://genetixbay.com/knowledge/glossary/led-vs-hps.md), tucking vs stripping leaves, hydro vs [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) taste, whether [defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md) raises [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), how individual cultivars respond to light hours. "Test your cultivar" is the GenetixBay way: run it, record it, share it. Results feed the evidence ladder and Mythbusters, and dated public records also serve preservation, since documented genetics and methods are harder to lock away. ## Don't confuse with - **Peer-reviewed research**: open research is citizen science with controls; it complements academic studies and cites them, but does not replace them. - **Anecdote**: one grow, uncontrolled. Open research needs matched comparisons and enough repeats. ## Related terms [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md), [Mythbusters](https://genetixbay.com/knowledge/glossary/mythbusters.md), [Evidence ladder](https://genetixbay.com/knowledge/glossary/evidence-ladder.md), [Defensive publication](https://genetixbay.com/knowledge/glossary/defensive-publication.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) ## Read more - [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) --- # Open-pollinated > Open-pollinated seed comes from a population left to cross freely among its own plants, without controlled pairs, which keeps a line's variation and type over generations. - Canonical: https://genetixbay.com/knowledge/glossary/open-pollinated.html - Also written: OP, open pollination, open-pollinated seed, OP seed, open pollinated - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Open-pollinated (OP) seed is produced by letting many plants of one population cross freely among themselves, by wind or by hand pollen mixes, instead of crossing one chosen female with one chosen male. Grown in isolation from other types, an OP population keeps its character from generation to generation while holding plenty of internal variation. ## In practice Most [landraces](https://genetixbay.com/knowledge/glossary/landrace.md) were maintained this way for centuries: a farmer saved seed from the best plants of a field each year. OP lines are resilient and adaptable because they carry many [alleles](https://genetixbay.com/knowledge/glossary/allele.md). They are also the practical way to preserve a population, as opposed to a single clone. Doing it well means a large enough population. Seed saved from two or three plants each year narrows the [gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md) fast through [genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md) and [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md). [Seed banks](https://genetixbay.com/knowledge/glossary/seed-bank.md) maintaining OP [accessions](https://genetixbay.com/knowledge/glossary/accession.md) aim for dozens of parents or more per regeneration. ## Don't confuse with - **F1 hybrid**: a controlled cross between two parents, usually uniform; its seed does not stay true. - **Landrace**: a type of OP population with local adaptation and history; not every OP line is a landrace. - **Uncontrolled pollination**: a room with a stray herm is accidental pollination, not an OP programme. ## Related terms [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Heirloom](https://genetixbay.com/knowledge/glossary/heirloom.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md) ## Read more - [Polyhybrids vs landraces: what each gives a breeder](https://genetixbay.com/knowledge/breeding/polyhybrids-vs-landraces.md) - [Landraces of the world: an overview](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Villa TCC, Maxted N, Scholten M, Ford-Lloyd B. 2005. Defining and identifying crop landraces. Plant Genetic Resources 3(3):373-384. https://doi.org/10.1079/PGR200591 --- # Open-source seed > Open-source seed is seed shared under a pledge that anyone may use, breed and share it, provided they do not restrict others' use through patents or licences. - Canonical: https://genetixbay.com/knowledge/glossary/open-source-seed.html - Also written: open source seed, OSSI pledge, open-source seed pledge, free seed, open seed - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Open-source seed is a model in which breeders release varieties with a pledge attached: you are free to use, save, breed and share this seed and its derivatives, but you may not patent it or otherwise restrict others from doing the same. The idea, borrowed from open-source software, was popularised for food crops by the Open Source Seed Initiative from the early 2010s (Kloppenburg 2014). ## In practice An open-source pledge is usually a short statement printed on the packet. Its legal strength is debated, since it relies on the recipient's agreement, but it signals intent and builds a shared pool of genetics. Combined with dated public records ([defensive publication](https://genetixbay.com/knowledge/glossary/defensive-publication.md)), it makes it harder for anyone to claim the material as their own invention later. The approach fits GenetixBay's purpose: preservation, documentation and open sharing of genetics, within the lanes the law allows. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Public domain**: no rights claimed at all, and no pledge binding later users. - **Open-pollinated**: a breeding description (seed that [breeds true](https://genetixbay.com/knowledge/glossary/true-breeding.md) from [open pollination](https://genetixbay.com/knowledge/glossary/open-pollinated.md)), not a licence. ## Related terms [Defensive publication](https://genetixbay.com/knowledge/glossary/defensive-publication.md), [Plant variety protection](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md), [Utility patent](https://genetixbay.com/knowledge/glossary/utility-patent.md), [Seed Club](https://genetixbay.com/knowledge/glossary/seed-club.md) ## Read more - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) ## Sources 1. Kloppenburg J. 2014. Re-purposing the master's tools: the open source seed initiative and the struggle for seed sovereignty. Journal of Peasant Studies 41(6):1225-1246. https://doi.org/10.1080/03066150.2013.875897 --- # Organic fertiliser > An organic fertiliser supplies nutrients from plant, animal or mineral-rock sources that soil microbes must break down into ions before roots can absorb them. - Canonical: https://genetixbay.com/knowledge/glossary/organic-fertiliser.html - Also written: organic fertilizer, organic nutrients, organic nutes, organic amendments, natural fertiliser - Glossary category: Nutrients · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An organic fertiliser is a nutrient source derived from living or once-living material, such as manures, composts, meals (blood, bone, fish, feather, kelp, seed), or from minimally processed mined minerals. Most of its nutrients are held in organic compounds that microbes mineralise into the same ions found in mineral feeds, so release depends on temperature, moisture and microbial activity. ## In practice Organic feeding suits soil and living-soil systems, where microbial life does the conversion. Release is slower and harder to measure, so [EC](https://genetixbay.com/knowledge/glossary/ec.md) readings mean little. Caplan, Dixon and Zheng found cannabis in [coir](https://genetixbay.com/knowledge/glossary/coco-coir.md) responded well to a liquid organic fertiliser at the right rate; Massuela and colleagues compared organic and [mineral fertiliser](https://genetixbay.com/knowledge/glossary/mineral-fertiliser.md) levels in flowering cannabis. In [recirculating hydro](https://genetixbay.com/knowledge/glossary/recirculating-system.md), raw organics tend to clog lines and feed biofilm. Certification rules for "organic" differ by jurisdiction. ## Don't confuse with - **Mineral (synthetic) fertiliser**: soluble salts delivering ions directly. - **Living soil**: a whole system, not a single product. ## Myth check Plants mostly don't care where the ions come from (GenetixBay house position). Organic feeding may bring slight [flavonoid](https://genetixbay.com/knowledge/glossary/flavonoid.md) or [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) differences, but that is unproven. See [organic vs mineral](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md). ## Related terms [Mineral fertiliser](https://genetixbay.com/knowledge/glossary/mineral-fertiliser.md), [Molasses](https://genetixbay.com/knowledge/glossary/molasses.md), [Humic acid](https://genetixbay.com/knowledge/glossary/humic-acid.md), [Biostimulant](https://genetixbay.com/knowledge/glossary/biostimulant.md), [N-P-K ratio](https://genetixbay.com/knowledge/glossary/npk-ratio.md) ## Read more - [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) ## Sources 1. Caplan D, Dixon M, Zheng Y. 2017. Optimal rate of organic fertilizer during the flowering stage for cannabis grown in two coir-based substrates. HortScience 52(12):1796-1803. https://doi.org/10.21273/HORTSCI12401-17 2. Massuela DC, Munz S, Hartung J, Nkebiwe PM, Graeff-Honninger S. 2023. Cannabis Hunger Games: nutrient stress induction in flowering stage - impact of organic and mineral fertilizer levels on biomass, cannabidiol (CBD) yield and nutrient use efficiency. Frontiers in Plant Science 14:1233232. https://doi.org/10.3389/fpls.2023.1233232 --- # Orius > Minute pirate bugs of the genus Orius, such as Orius insidiosus, that hunt adult and larval thrips plus mites and aphids; some strains pause breeding under short days. - Canonical: https://genetixbay.com/knowledge/glossary/orius.html - Also written: minute pirate bug, minute pirate bugs, Orius insidiosus, Orius laevigatus, pirate bug - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Orius* is a genus of minute pirate bugs (family Anthocoridae), small black-and-white predatory bugs about 2-3 mm long. They pierce prey with a beak and suck it dry. They are among the few released predators that eat adult [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) as well as larvae, and they also take [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), aphids and insect eggs. They can survive on pollen when prey is scarce. ## In practice Growers release *Orius insidiosus* or *Orius laevigatus* in veg to build a population ahead of thrips pressure, often with pollen supplements or flowering [banker plants](https://genetixbay.com/knowledge/glossary/banker-plant.md). They establish slowly and cost more than [predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md), so they suit longer crops and [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md). A key point for cannabis: some *Orius* populations enter [reproductive diapause](https://genetixbay.com/knowledge/glossary/diapause.md) under short days, which affects 12-hour flowering rooms; ask the supplier for a non-diapausing strain. They are frequently combined with *[Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md)* or *[Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md)*. ## Don't confuse with - **Predatory mites**: much smaller and only take young thrips larvae. - **Thrips**: slender, straw-coloured or brown, with fringed wings. - **Bed bugs**: a different, blood-feeding family. ## Related terms [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md), [Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Banker plant](https://genetixbay.com/knowledge/glossary/banker-plant.md) ## Read more - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Sources 1. UConn IPM. Biological Control of Western Flower Thrips. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-western-flower-thrips/ 2. UC IPM. Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html --- # Oscillating fan > An oscillating fan sweeps back and forth to circulate air over and through the canopy, mixing the room and preventing still, humid pockets. - Canonical: https://genetixbay.com/knowledge/glossary/oscillating-fan.html - Also written: clip fan, circulation fan, wall fan, oscillating clip fan, canopy fan - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An oscillating fan is a circulation fan that rotates side to side, sweeping its airflow across an arc. In grow tents and rooms, small clip-on or wall-mounted oscillating fans are the standard way to keep air moving inside the space. They do not remove heat or humidity; they spread it so the [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) and [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) can deal with it. ## In practice A 1.2 × 1.2 m (4 × 4 ft) tent typically runs two small oscillating fans: one above the canopy and one below it, aimed in a loop so air travels around the space rather than straight into a wall. Larger rooms use horizontal airflow [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) in a racetrack pattern. Aim for gentle, constant movement at the leaves (around 0.5–1 m/s), not a gale on one plant. Signs of too much: leaves on the windward side curling, clawing, or turning papery and pale. Signs of too little: soft growth, condensation at lights-off, [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) in the back corners. Clean the blades each cycle; dusty fans move less air and spread spores. ## Don't confuse with - **Exhaust fan**: an inline fan that moves air out of the space through ducting. - **Intake fan**: brings fresh air in, usually through a filter. ## Related terms [Airflow](https://genetixbay.com/knowledge/glossary/airflow.md), [Exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md), [Microclimate](https://genetixbay.com/knowledge/glossary/microclimate.md), [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) ## Read more - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) ## Sources 1. Kitaya Y, Tsuruyama J, Shibuya T, Yoshida M, Kiyota M, 2003. Effects of air current speed on gas exchange in plant leaves and plant canopies. Advances in Space Research 31(1):177–182. --- # Osmotic stress > Osmotic stress occurs when root-zone salt concentration is so high that roots struggle to draw in water, slowing growth and burning leaf tips even in wet media. - Canonical: https://genetixbay.com/knowledge/glossary/osmotic-stress.html - Also written: salinity stress, osmotic shock, high EC stress, physiological drought - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Osmotic stress is the water-uptake problem caused by high solute concentration around the roots. Water moves from higher to lower water potential; dissolved salts lower the water potential of the root-zone solution. When it falls close to the plant's own, roots take up water slowly, as if the medium were drier than it is. High sodium and [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) add specific ion [toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) on top. ## In practice Signs: dull, dark leaves, crisped tips and margins, wilting in moist medium, slowing growth, and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md) well above input. Seedlings and fresh clones show it at EC levels that established plants tolerate. A sudden jump in [feed strength](https://genetixbay.com/knowledge/glossary/input-ec.md) or a medium left to dry hard (concentrating salts) are common triggers. Cannabis tolerates a fairly wide EC window, but more is not better. Baas and Wijnen (2023) tested cannabis in rockwool from 1.8 to 12 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), and Yep, Gale and Zheng (2020) examined NaCl-induced stress in drug-type cannabis. Hershkowitz and colleagues (2025) found no yield benefit from elevated nutrient concentration. Fix: lower input EC, increase runoff, and run a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) if runoff EC is far above input. ## Don't confuse with - **Nutrient burn**: the visible tip damage, often one symptom of osmotic stress. - **Underwatering**: also wilting, but medium is dry and EC normal. ## Related terms [EC](https://genetixbay.com/knowledge/glossary/ec.md), [Salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), [Nutrient lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md) ## Read more - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) - [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ## Sources 1. Baas R, Wijnen D. 2023. Effects of EC on cannabis in rockwool (1.8 to 12 mS/cm). Acta Horticulturae 1377. https://www.ishs.org/ishs-article/1377_97 2. Yep B, Gale NV, Zheng Y. 2020. Frontiers in Plant Science 11:1169. https://doi.org/10.3389/fpls.2020.01169 3. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 --- # Ounce > An ounce of cannabis is 28.35 grams, rounded to 28 g in retail; slang includes zip, O and onion. - Canonical: https://genetixbay.com/knowledge/glossary/ounce.html - Also written: oz, zip, an O, onion, zips - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An ounce (oz) is 28.35 g (avoirdupois), rounded to 28 g when cannabis is sold. Slang names include "zip" (from zip-lock bags), "O" and "onion". ## In practice Many personal possession limits are written in ounces or in grams close to an ounce, for example 30 g in some places and 1 oz in others. The exact limit, and whether it covers dried flower only or equivalents, depends on the jurisdiction; check local rules. For yield, growers often talk in ounces per plant or per light. "Two zips off one plant" means about 56 g dry. ## Units and formula | Slang | Nominal weight | Metric | |---|---|---| | Gram | 1 g | 1 g | | Eighth | 1/8 oz | 3.5 g (exact: 3.54 g) | | Quarter | 1/4 oz | 7 g | | Half | 1/2 oz | 14 g | | Ounce (zip, O) | 1 oz | 28 g (exact: 28.35 g) | | QP | 1/4 lb (4 oz) | 113 g | | Pound (elbow, LB) | 1 lb (16 oz) | 454 g (exact: 453.6 g) | Retail rounds an eighth to 3.5 g and an ounce to 28 g. ## Don't confuse with - **Troy ounce**: 31.1 g, used for precious metals, not cannabis. - **Fluid ounce**: a volume, not a weight. ## Related terms [Gram](https://genetixbay.com/knowledge/glossary/gram.md), [Eighth](https://genetixbay.com/knowledge/glossary/eighth.md), [QP](https://genetixbay.com/knowledge/glossary/qp.md), [Elbow](https://genetixbay.com/knowledge/glossary/elbow.md), [Possession limit](https://genetixbay.com/knowledge/glossary/possession-limit.md) --- # Outcross > An outcross is a cross to an unrelated plant from outside the line, used to bring in new traits or vigour, or to rescue a line suffering inbreeding depression. - Canonical: https://genetixbay.com/knowledge/glossary/outcross.html - Also written: outcrossing, outcrossed, out-cross, wide cross - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" An outcross is a mating between a plant in a breeding line and an unrelated plant from outside it. The aim is to bring in [alleles](https://genetixbay.com/knowledge/glossary/allele.md) the line lacks: a resistance, a flavour, earlier finishing, or simply fresh [heterozygosity](https://genetixbay.com/knowledge/glossary/heterozygous.md). ## In practice Outcrossing is the standard cure for [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md). A line that has been sib crossed or selfed for several generations and has lost vigour, seed set or [germination](https://genetixbay.com/knowledge/glossary/germination.md) often bounces back in a single outcross. The cost is uniformity: the outcross reshuffles everything, so the breeder usually follows it with backcrosses to the original line to recover its type while keeping the new trait. Breeders also use "outcross" for crossing to a different population or type, for example a [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) into a modern hybrid line. That can dilute the landrace if the seed is then sold or released under the landrace's name, which is one way source-region [gene pools](https://genetixbay.com/knowledge/glossary/gene-pool.md) get contaminated. ## Don't confuse with - **Backcross**: crossing back to a parent or the original line, the opposite direction. - **Line breeding**: crossing within related plants; outcrossing goes outside. - **Hybrid**: the product of any cross between different parents. An outcross produces [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) by definition. ## Related terms [Cross](https://genetixbay.com/knowledge/glossary/cross.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [Heterosis](https://genetixbay.com/knowledge/glossary/heterosis.md), [Line breeding](https://genetixbay.com/knowledge/glossary/line-breeding.md), [Introgression](https://genetixbay.com/knowledge/glossary/introgression.md) ## Read more - [Inbreeding depression and hybrid vigour](https://genetixbay.com/knowledge/breeding/inbreeding-depression-hybrid-vigour.md) - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 --- # Outdoor growing > Outdoor growing is cultivating cannabis in the ground or containers under natural sunlight, where the season's day length controls when photoperiod plants flower. - Canonical: https://genetixbay.com/knowledge/glossary/outdoor-growing.html - Also written: outdoor, outdoor grow, growing outdoors, full sun, full-term outdoor - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Outdoor growing uses natural sunlight in open ground or containers. [Photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md) grow vegetatively through the long days of late spring and early summer and start flowering as nights lengthen in late summer, finishing from early autumn to late autumn depending on cultivar and latitude. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) ignore day length and can be planted on a rolling basis in warm months. ## In practice Sunlight is free and intense: a clear midsummer day can deliver a [DLI](https://genetixbay.com/knowledge/glossary/dli.md) of 50-60 mol/m²/day or more, well above typical indoor levels. Plants grown in large beds or the ground can become very large. Key decisions are cultivar choice (finishing before the autumn rains and frosts at your latitude), site (6-8 h or more of direct sun, airflow), soil preparation, and pest and mould management. Late-flower rain and humidity are the biggest risk to the crop through [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md). [Home growing](https://genetixbay.com/knowledge/glossary/home-grow.md) outdoors is legal only in some places, and rules often cover visibility and plant numbers. Check local rules. ## Don't confuse with - **Greenhouse**: under cover, often with [light-dep](https://genetixbay.com/knowledge/glossary/light-deprivation.md) and climate control. - **Guerrilla grow**: growing on land you do not own or control. ## Related terms [Indoor growing](https://genetixbay.com/knowledge/glossary/indoor-growing.md), [Greenhouse growing](https://genetixbay.com/knowledge/glossary/greenhouse-growing.md), [Light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md), [Hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md), [Companion planting](https://genetixbay.com/knowledge/glossary/companion-planting.md) ## Read more - [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) --- # Over-drying > Drying cannabis below the target water activity (under about 0.55), leaving buds brittle and harsh, with lost terpenes; rehydrating does not restore them. - Canonical: https://genetixbay.com/knowledge/glossary/over-drying.html - Also written: overdried, over dried, too dry, bone dry, crispy buds, overdrying - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Over-drying is taking buds past the point where they're jar-ready. Typical signs: buds crumble rather than spring back, big stems shatter, equilibrated [jar RH](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md) sits below about 55% (aw under about 0.55), and the smoke is harsh with a dull, flat aroma. It usually comes from warm, [dry rooms](https://genetixbay.com/knowledge/glossary/drying-room.md), too much airflow on the buds, or leaving material hanging too long. ## In practice [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md): dry slowly, about 15-21 °C (60-70 °F) and 55-62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) for 7-14 days. Check stems from about day 5-7 and jar when small stems snap but larger ones still bend. If buds are a little too dry: jar them and let moisture even out from the core first. If still under range, the GenetixBay approach is to put a fresh bud in the jar to bring moisture back, rather than a [humidity pack](https://genetixbay.com/knowledge/glossary/humidity-pack.md) or other wet items. Expect only partial recovery. Texture and burn improve, but lost [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) are gone and hay notes from a too-fast dry stay. ## Don't confuse with - **Case hardening**: dry outside, wet inside; feels over-dry but isn't. - **Long cure**: a slow, healthy moisture decline, not over-drying. - **Hay smell**: often caused by over-drying or drying too fast. ## Myth check House position: a cure will never fix a bad dry. See [curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md). ## Related terms [Case hardening](https://genetixbay.com/knowledge/glossary/case-hardening.md), [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md), [Terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # Overwatering > Overwatering is watering so often that the medium stays saturated, starving roots of oxygen, which causes drooping, slow growth and root disease. - Canonical: https://genetixbay.com/knowledge/glossary/overwatering.html - Also written: over-watering, overwatered, drowning, too much water, waterlogged - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Overwatering is less about the volume of a single watering and more about frequency: watering again before the medium has dried enough to let air back into its pores. Roots need oxygen for respiration. In saturated medium they suffocate, take up less water and nutrients, and become vulnerable to pathogens such as *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)*. ## In practice Typical signs are leaves that droop while firm and swollen (curled down from stem to tip, not limp and papery), a heavy pot, slow growth, yellowing, and [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) breeding in wet surfaces. [Seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) in large pots are the classic case. The fix is to wait until the pot is noticeably lighter before watering again, improve [drainage](https://genetixbay.com/knowledge/glossary/runoff.md), add [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) to dense mixes, or move to a smaller container or more air-porous pot. Note that [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and rockwool can be watered many times a day without overwatering, because they drain freely and hold plenty of air. ## Don't confuse with - **Underwatering**: limp, papery droop from [too little water](https://genetixbay.com/knowledge/glossary/underwatering.md); the pot feels light. - **Root rot**: often the consequence of chronic overwatering, but a disease in its own right. ## Related terms [Underwatering](https://genetixbay.com/knowledge/glossary/underwatering.md), [Wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), [Air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), [Field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md) ## Read more - [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - [Slow or stunted cannabis growth: a differential](https://genetixbay.com/knowledge/diagnosis/slow-growth.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # P1 > P1 is the parental generation: the two original plants crossed to start a breeding project, whose offspring are the F1. - Canonical: https://genetixbay.com/knowledge/glossary/p1.html - Also written: P1 generation, parental generation, P generation, parental line - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" P1 (the parental generation) is the pair of plants crossed to start a breeding programme. Their seed is the [F1](https://genetixbay.com/knowledge/glossary/f1.md), the F1 crossed among itself gives the [F2](https://genetixbay.com/knowledge/glossary/f2.md), and so on. In some texts the parents are written simply as P. ## In practice In cannabis the P1 pair is usually one selected female (often a clone) and one selected male. Documenting them properly is the foundation of any honest lineage: name or GB-style ID of each parent, where they came from, [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md), test results and the date of the cross. Without that, every later generation inherits a guess. The P1 parents do not have to be inbred. When they are [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) themselves, as most modern cannabis is, the "F1" is already variable. Breeders then talk about F1s loosely, but genetically that seed behaves more like an F2. ## Don't confuse with - **F1**: the offspring of P1, not the parents. - **Recurrent parent**: in a [backcross](https://genetixbay.com/knowledge/glossary/backcross.md) programme, the P1 plant crossed back into again and again. - **Mother plant**: a horticultural term for a plant kept for cuttings. A mother can be a P1, but not every P1 is kept as a mother. ## Related terms [F1](https://genetixbay.com/knowledge/glossary/f1.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md), [Filial generation](https://genetixbay.com/knowledge/glossary/filial-generation.md), [Hybrid](https://genetixbay.com/knowledge/glossary/hybrid.md), [Backcross](https://genetixbay.com/knowledge/glossary/backcross.md) ## Read more - [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Paper towel method > The paper towel method germinates seeds between damp paper towels in a covered container until the root shows, then moves them to a medium. - Canonical: https://genetixbay.com/knowledge/glossary/paper-towel-method.html - Also written: paper towel germination, paper towel method germination, towel method, wet paper towel - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The paper towel method is a [germination](https://genetixbay.com/knowledge/glossary/germination.md) technique in which seeds are placed between two damp (not dripping) paper towels, usually on a plate or in a sealed box, and kept warm and dark until the [radicle](https://genetixbay.com/knowledge/glossary/radicle.md) emerges. It lets the grower see exactly which seeds have popped and count a germination rate. ## In practice Fold seeds into a damp towel, cover to hold humidity, and keep at about 22-28 °C (72-82 °F). Check twice a day. Move each seed to its plug or pot once the root is about 5-10 mm (0.2-0.4 in) long, root pointing down, handling it by the [shell](https://genetixbay.com/knowledge/glossary/seed-coat.md) rather than the root. Waiting until the root is several centimetres long invites [root hairs](https://genetixbay.com/knowledge/glossary/root-hair.md) growing into the towel and damage during transfer. The trade-off: it adds a handling step. For [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md), sowing straight into the final pot avoids both that step and a later [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md), which GenetixBay prefers. ## Don't confuse with - **Soaking**: seeds in a glass of water for 12-24 h; often done before the towel step, but long soaks risk oxygen starvation. - **Direct sowing**: seed goes straight into the medium with no pre-germination. ## Related terms [Germination](https://genetixbay.com/knowledge/glossary/germination.md), [Seedling](https://genetixbay.com/knowledge/glossary/seedling.md), [Taproot](https://genetixbay.com/knowledge/glossary/taproot.md), [Transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md) ## Read more - [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md) ## Sources 1. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 --- # PAR > Photosynthetically active radiation: light in the 400–700 nm waveband that plants use for photosynthesis, counted in photons rather than brightness. - Canonical: https://genetixbay.com/knowledge/glossary/par.html - Also written: photosynthetically active radiation, PAR range, ePAR, extended PAR - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" PAR (photosynthetically active radiation) is the band of light from 400 to 700 nm that drives [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md). It is a waveband, not a measurement: the numbers growers quote ([PPF](https://genetixbay.com/knowledge/glossary/ppf.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md)) are all counts of PAR photons. Plant scientists count photons because photosynthesis is a photon-driven reaction; energy or perceived brightness is the wrong currency. ## In practice "PAR" is often used loosely to mean "the reading on my quantum meter". Strictly, a quantum sensor measures PPFD within the PAR band. When a fixture sheet says "PAR output", look for the unit: µmol/s is PPF (fixture total), µmol/m²/s is PPFD (at a point on the canopy). Research since 2020 shows [far-red](https://genetixbay.com/knowledge/glossary/far-red.md) photons from 700 to 750 nm drive canopy photosynthesis about as well as PAR photons when they are mixed with shorter wavelengths. That is why some specifications now report ePAR (extended PAR, 400–750 nm). A fixture rated in ePAR will look better on paper than the same fixture rated in PAR, so compare like with like. *Established* for the far-red finding in lettuce and other crops; cannabis-specific canopy data are thinner. ## Units and formula | Quantity | Band | Unit | |---|---|---| | PAR | 400–700 nm | (waveband, no unit) | | ePAR | 400–750 nm | (waveband, no unit) | | PPF | PAR | µmol/s | | PPFD | PAR | µmol/m²/s | ## Don't confuse with - **Lux**: weighted to the human eye, not to plants. - **PPFD**: a measured flux of PAR photons at a surface; PAR itself is only the band. ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [PPF](https://genetixbay.com/knowledge/glossary/ppf.md), [YPFD](https://genetixbay.com/knowledge/glossary/ypfd.md), [Far-red](https://genetixbay.com/knowledge/glossary/far-red.md), [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) ## Sources 1. McCree KJ, 1972. The action spectrum, absorptance and quantum yield of photosynthesis in crop plants. Agricultural Meteorology 9:191–216. 2. Zhen S, Bugbee B, 2020. Far-red photons have equivalent efficiency to traditional photosynthetic photons: implications for redefining photosynthetically active radiation. Plant, Cell & Environment 43(5):1259–1272. https://doi.org/10.1111/pce.13730 --- # Parasitoid > An insect, usually a tiny wasp, whose larva develops inside or on a single host pest and kills it, often leaving a 'mummy'. - Canonical: https://genetixbay.com/knowledge/glossary/parasitoid.html - Also written: parasitoids - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A parasitoid is an insect whose young develop in or on one host and kill it. UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) explains they are called parasitoids rather than parasites because they kill the host. Most used in greenhouses are small wasps, for example [Aphidius](https://genetixbay.com/knowledge/glossary/aphidius.md) on [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), Encarsia and Eretmocerus on [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md), Leptomastix and Anagyrus on [mealybugs](https://genetixbay.com/knowledge/glossary/mealybug.md) and Trichogramma on moth eggs. ## In practice Parasitoids are often host-specific, so the species must match the pest; the wrong Aphidius for the aphid present does little. Their own development time sets how long control takes, often two to three weeks before mummies appear. Most are harmed by broad-spectrum sprays and some are caught on [sticky cards](https://genetixbay.com/knowledge/glossary/sticky-trap.md), so plan both around releases. ## Don't confuse with - **Predator**: eats many prey, e.g. [predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md) and [lacewing](https://genetixbay.com/knowledge/glossary/lacewing.md) larvae. - **Parasite**: lives on a host without necessarily killing it. ## Related terms [Aphidius](https://genetixbay.com/knowledge/glossary/aphidius.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Banker plant](https://genetixbay.com/knowledge/glossary/banker-plant.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) - [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) - [Mealybugs and root mealybugs on cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/mealybugs.md) ## Sources 1. UC IPM. Parasitic Wasps and Flies. https://ipm.ucanr.edu/home-and-landscape/parasitic-wasps-and-flies/ --- # Parthenogenesis > Reproduction without mating. Indoor aphids are all-female and give live birth to daughters that already carry developing embryos. - Canonical: https://genetixbay.com/knowledge/glossary/parthenogenesis.html - Also written: asexual reproduction, viviparous parthenogenesis, thelytoky, telescoping generations - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Parthenogenesis is reproduction from unfertilised eggs or embryos. [Aphids](https://genetixbay.com/knowledge/glossary/aphid.md) indoors are almost always females that give birth to live nymphs without males (viviparous parthenogenesis); UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) notes that most aphids reproduce this way for much of the year. Embryos inside a mother can already contain the next generation, the so-called telescoping of generations. ## In practice Parthenogenesis is why aphids are among the fastest-multiplying cannabis pests: no males to feed, no eggs to hatch, and newborns that start reproducing within about a week in warm rooms. One aphid on a clone is a colony. Sexual forms and overwintering eggs appear only outdoors in autumn in species with a sexual stage. ## Don't confuse with - **Arrhenotoky**: unmated females make only males ([mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [thrips](https://genetixbay.com/knowledge/glossary/thrips.md)). - **Holocyclic life cycle**: includes a yearly sexual generation, usually outdoors. ## Related terms [Arrhenotoky](https://genetixbay.com/knowledge/glossary/arrhenotoky.md), [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Intrinsic rate of increase (r_m)](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) - [Cannabis aphid (Phorodon cannabis): ID, life table, overwintering and control](https://genetixbay.com/knowledge/pests/cannabis-aphid.md) ## Sources 1. UC IPM. Pest Notes: Aphids (Publication 7404). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html --- # Pearls > Pearls are GenetixBay's community points, in two kinds: Wild Pearls earned by contributing, and Cultured Pearls bought as store credit; neither has cash value. - Canonical: https://genetixbay.com/knowledge/glossary/pearls.html - Also written: Pearl, GenetixBay Pearls, Bay Pearls, Pearl balance - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Pearls are the points system on GenetixBay. They reward the work that keeps genetics alive and knowledge honest, and they come in two kinds that are kept strictly apart. ## In practice **Wild Pearls** are earned by doing: documented grow journals, keeper nominations, males registered in [the Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md), preservation of lost lines, joining trials, reviews after a completed swap. **Cultured Pearls** are purchased store credit for the GenetixBay store. Every Pearl movement is recorded in a ledger, so balances can be audited. Pearls never reward a yield or potency number by itself; documentation does. Where [cannabis seed](https://genetixbay.com/knowledge/glossary/achene.md) is concerned, Pearl use follows the law in each region, and a seed pack is never priced in or paid with Cultured Pearls. ## Don't confuse with - **Money**: Pearls have no cash value and cannot be cashed out. - **Reputation**: a separate measure of standing; Pearls are spendable, reputation is not. ## Related terms [Wild Pearls](https://genetixbay.com/knowledge/glossary/wild-pearls.md), [Cultured Pearls](https://genetixbay.com/knowledge/glossary/cultured-pearls.md), [The Swap](https://genetixbay.com/knowledge/glossary/the-swap.md), [Grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md), [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md) --- # Peat > Peat is partially decomposed sphagnum moss from bogs, the base of most potting mixes; it holds water and nutrients well but is acidic and needs lime. - Canonical: https://genetixbay.com/knowledge/glossary/peat.html - Also written: peat moss, sphagnum peat, sphagnum peat moss, peat-based mix, peat-lite - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Peat (sphagnum peat moss) is the slowly decomposed remains of bog mosses, harvested from peatlands. It is light, very water-retentive, has a useful [cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md) and is naturally acidic (raw [pH](https://genetixbay.com/knowledge/glossary/ph.md) about 3.5-4.5). Mixed with lime to raise the pH, plus [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) and fertiliser, it forms the base of most commercial [potting mixes](https://genetixbay.com/knowledge/glossary/potting-mix.md), including many sold as "soil". ## In practice Peat mixes work well for cannabis at a pH of about 6.0-6.5 in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). When very dry, peat becomes hydrophobic and sheds water; rewet it slowly or with a wetting agent, and avoid [letting it dry out](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md) fully. Mixes typically lose their starter fertiliser after two to four weeks. Peat extraction releases stored carbon and destroys bog habitat; [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and composted bark are common alternatives where growers want to reduce peat use. ## Don't confuse with - **Coco peat**: coconut pith, sometimes called peat but a different material. - **Peat pellets**: compressed peat discs for seeds and clones. ## Related terms [Potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [Perlite](https://genetixbay.com/knowledge/glossary/perlite.md), [Cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), [Soilless](https://genetixbay.com/knowledge/glossary/soilless.md) ## Read more - [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Per-element dosing > Per-element dosing builds a feed from individual salts or single-element stocks so each nutrient can be set independently, such as cutting nitrogen without cutting potassium. - Canonical: https://genetixbay.com/knowledge/glossary/per-element-dosing.html - Also written: single-element dosing, per-element feeding, custom dosing, salt-based dosing, DIY nutrients - Glossary category: Nutrients · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Per-element dosing means mixing the nutrient solution from separate salts or single-element stocks, with each element's mg/L (ppm) set on its own, instead of dosing a pre-blended product. It is standard in commercial greenhouse hydroponics and increasingly used by home growers. ## In practice Its main advantage is control. A bottled two-part scales everything together; per-element dosing can lower one element and hold the rest. The GenetixBay approach in late flower is to [taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) towards zero near the finish while keeping P, K, Ca, Mg, S and the micros fed, which means swapping [potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md) for [potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md) and part of [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md) for [calcium chloride](https://genetixbay.com/knowledge/glossary/calcium-chloride.md) or another N-free calcium source. Saloner and Bernstein found lower N in flower can raise cannabinoid and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) percentage while lowering total yield, a trade-off growers can now choose deliberately. It also lets growers correct for their water report. The cost is more maths and more containers. ## Don't confuse with - **A/B nutrient**: two fixed blends dosed together. - **Additives**: products stacked on a base, which add rather than adjust. ## Myth check Taper nitrogen, don't [flush](https://genetixbay.com/knowledge/glossary/flushing.md) (GenetixBay house position). See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) and [per-element tricks](https://genetixbay.com/knowledge/nutrients/per-element-tricks.md). ## Related terms [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md), [ppm of an element](https://genetixbay.com/knowledge/glossary/elemental-ppm.md), [Potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md), [Calcium chloride](https://genetixbay.com/knowledge/glossary/calcium-chloride.md) ## Read more - [Per-element feeding tricks: what growers adjust, stage by stage](https://genetixbay.com/knowledge/nutrients/per-element-tricks.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 3. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 --- # Perlite > Perlite is a light, white, puffed volcanic glass added to growing mixes to increase drainage and air space; it is chemically inert and holds no nutrients. - Canonical: https://genetixbay.com/knowledge/glossary/perlite.html - Also written: perlite rock, expanded perlite, sponge rock - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Perlite is volcanic glass heated rapidly until trapped water flashes to steam and the grains pop like [popcorn](https://genetixbay.com/knowledge/glossary/popcorn-buds.md) into light, porous white granules. In a mix it creates large pores that [drain](https://genetixbay.com/knowledge/glossary/runoff.md) quickly and fill with air, raising the [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) of the medium. It is essentially inert, near neutral [pH](https://genetixbay.com/knowledge/glossary/ph.md), and supplies no nutrients. ## In practice Common blends are 10-30% perlite in soil or [peat](https://genetixbay.com/knowledge/glossary/peat.md) mixes and 20-40% in [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md). More perlite means faster drainage and more frequent watering. It floats to the surface over time and can be blown about when dry; wet it before mixing and wear a dust mask, since the fine dust is an irritant. It does not break down, so it can be reused after cleaning. Pumice does a similar job, is heavier and does not float. ## Don't confuse with - **Vermiculite**: also expanded mineral, but it holds water and nutrients; the opposite job. - **Clay pebbles**: larger aggregate used as a hydro medium on its own. ## Related terms [Vermiculite](https://genetixbay.com/knowledge/glossary/vermiculite.md), [Air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), [Potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) ## Read more - [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Perpetual harvest > A perpetual harvest staggers plants at different stages, usually with separate veg and flower spaces, so that harvests come every few weeks instead of once per cycle. - Canonical: https://genetixbay.com/knowledge/glossary/perpetual-harvest.html - Also written: perpetual grow, perpetual, staggered harvest, continuous harvest, rolling harvest - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A perpetual harvest (perpetual grow) is a schedule in which plants of different ages run side by side. Typically a mother or seed nursery supplies new plants, a veg area holds the next batch, and the flower room is refilled each time part of it is harvested. The grower harvests on a regular interval, for example every two to three weeks, rather than everything at once. ## In practice The usual setup is two spaces with separate light schedules: one for [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md), clones and veg under 18 h or more of light, and one for flower under about 12 h. Each time a batch in flower is harvested, the next batch from veg moves in. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) make a single-room perpetual possible, since they flower regardless of light schedule. Benefits are steady supply and continuous use of the flower space. Costs are more equipment, more pest and pathogen risk from always having plants present, and less chance to deep-clean. ## Don't confuse with - **Perpetual flowering (autos)**: autos still finish once; perpetual refers to the schedule, not the plant. - **SOG**: often run perpetually, but [SOG](https://genetixbay.com/knowledge/glossary/sog.md) is a planting method. ## Related terms [Mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md), [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md), [SOG](https://genetixbay.com/knowledge/glossary/sog.md), [Veg time](https://genetixbay.com/knowledge/glossary/veg-time.md) ## Read more - [SOG: sea of green](https://genetixbay.com/knowledge/training/sog.md) --- # Personal cultivation limit > A personal cultivation limit is the legal maximum a person or household may grow for personal use, usually counted in plants, sometimes in canopy area. - Canonical: https://genetixbay.com/knowledge/glossary/personal-cultivation-limit.html - Also written: personal grow limit, cultivation limit, home grow limit, personal cultivation allowance - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A personal cultivation limit is the rule that sets how much cannabis a person or household may grow without a commercial licence. It is usually a number of plants, sometimes split into flowering and non-flowering plants, and sometimes a [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md). Some laws cap per person, others per residence regardless of how many adults live there. ## In practice The details matter. A limit per residence means two adults sharing a home do not get double. A limit on "flowering" plants may allow extra [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) or [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md) in veg, or may not. Clones in a propagation tray usually count once rooted. The harvest from a legal [home grow](https://genetixbay.com/knowledge/glossary/home-grow.md) can also run into the separate possession limit, especially where the limit for storage at home differs from public possession. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Plant count limit**: the plant-number form of a cultivation limit; also used in commercial and medical licences. - **Possession limit**: how much dried cannabis you may hold, a separate rule. ## Related terms [Home grow](https://genetixbay.com/knowledge/glossary/home-grow.md), [Plant count limit](https://genetixbay.com/knowledge/glossary/plant-count-limit.md), [Possession limit](https://genetixbay.com/knowledge/glossary/possession-limit.md), [Licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md) --- # Pesticide panel > A pesticide panel screens a cannabis sample for a defined list of pesticide residues, typically by LC-MS/MS and GC-MS/MS, reporting each against its action limit. - Canonical: https://genetixbay.com/knowledge/glossary/pesticide-panel.html - Also written: pesticide test, pesticide testing, pesticide screen, pesticide residue test, residue panel - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A pesticide panel is a multi-residue test for a fixed list of insecticides, fungicides, miticides, plant growth regulators and herbicides. Regulated markets publish their own lists, often 60-100 or more compounds, each with an action limit. Labs run the panel by [LC-MS/MS](https://genetixbay.com/knowledge/glossary/lc-ms.md) and [GC-MS](https://genetixbay.com/knowledge/glossary/gas-chromatography.md)/MS because no single technique covers all the chemistries. ## In practice A [COA](https://genetixbay.com/knowledge/glossary/coa.md) lists each compound with a result (often [ND](https://genetixbay.com/knowledge/glossary/non-detect.md)), the [LOD](https://genetixbay.com/knowledge/glossary/lod.md) or LOQ and the limit. A pass means none exceeded its limit, not that none were present. The panel only finds what's on the list: a compound outside the list isn't tested. Contamination can come from direct sprays, drift, contaminated inputs, or reused equipment. Limits and lists differ by jurisdiction; check local rules. For home growers, the safest route is an [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) approach that avoids residues on flowering plants in the first place. ## Units and formula µg/g (ppm) or µg/kg (ppb). Many action limits sit at 0.1 µg/g or lower. ## Don't confuse with - **Residual solvents**: leftover extraction solvents, a separate test. - **Heavy metals panel**: elements, not organic residues. - **Organic certification**: a production standard, not a residue test. ## Related terms [LC-MS](https://genetixbay.com/knowledge/glossary/lc-ms.md), [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md), [LOD](https://genetixbay.com/knowledge/glossary/lod.md), [ND (non-detect)](https://genetixbay.com/knowledge/glossary/non-detect.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md) ## Read more - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) --- # Pesticide resistance > The inherited ability of a pest population to survive doses of a pesticide that once controlled it, selected by repeated use of one mode of action. - Canonical: https://genetixbay.com/knowledge/glossary/pesticide-resistance.html - Also written: resistance, insecticide resistance, miticide resistance, fungicide resistance, mode of action rotation, IRAC, FRAC - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Pesticide resistance is a genetic change in a pest or pathogen population that lets it survive a product that used to work. It is selected, not created: every application kills susceptible individuals and leaves the few resistant ones to breed. Pests with short generations and huge populations, such as [two-spotted spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [western flower thrips](https://genetixbay.com/knowledge/glossary/thrips.md), *Bemisia* [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), develop resistance fastest. ## In practice Growers slow resistance by rotating products with different modes of action rather than different brand names, since many products share an active ingredient. Industry groups classify actives by [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md): the Insecticide Resistance Action Committee (IRAC) for insecticides and miticides, and the Fungicide Resistance Action Committee (FRAC) for fungicides. Other habits: use full label rates, do not spray when scouting says it is unnecessary, and lean on biological and [cultural controls](https://genetixbay.com/knowledge/glossary/cultural-control.md), which pests cannot easily evolve around. "It stopped working" after a few applications usually means poor coverage, wrong identification or resistance. ## Don't confuse with - **Plant disease resistance**: a crop trait, such as mildew-resistance [genes](https://genetixbay.com/knowledge/glossary/gene.md). - **Tolerance**: a plant coping with damage without losing yield. ## Related terms [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ## Sources 1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 2. UC IPM. Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html --- # Petiole > The stalk that attaches a leaf to the stem at a node; in cannabis it carries all the leaflets of a palmate leaf. - Canonical: https://genetixbay.com/knowledge/glossary/petiole.html - Also written: leaf stalk, leaf stem, petioles, leafstalk - Glossary category: Plant biology - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The petiole is the stalk between a [leaf blade](https://genetixbay.com/knowledge/glossary/leaflet.md) and the stem. On cannabis, each palmate leaf sits on one petiole that joins the stem at a node; the leaflets fan out from its far end. The petiole contains vascular bundles ([xylem](https://genetixbay.com/knowledge/glossary/xylem.md) and [phloem](https://genetixbay.com/knowledge/glossary/phloem.md)) that carry water in and sugars out. ## In practice Petioles feature in two everyday jobs. In diagnosis, colour and stiffness matter: red or purple petioles are common and often genetic or cold-related, and only mean much when combined with other symptoms such as dark, dull leaves (possible phosphorus issues) or poor growth. Drooping, soft petioles with turgid-looking leaves point to watering or root issues. In leaf management, growers who remove leaves cut the petiole a few millimetres from the stem rather than tearing it, which avoids ripping the stem skin and the [bud site](https://genetixbay.com/knowledge/glossary/bud-site.md) in the axil. The GenetixBay approach is "tuck, don't pluck": tuck a [fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md) under a neighbouring branch by its petiole rather than remove it, where possible. ## Don't confuse with - **Node**: the point on the stem where the petiole attaches. - **Stem (branch)**: carries nodes and buds; a petiole carries only a leaf. - **Midrib**: the central vein inside a leaflet. ## Related terms [Leaflet](https://genetixbay.com/knowledge/glossary/leaflet.md), [Node](https://genetixbay.com/knowledge/glossary/node.md), [Fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md), [Axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md) ## Read more - [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # pH > pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5. - Canonical: https://genetixbay.com/knowledge/glossary/ph.html - Also written: ph level, potential of hydrogen, acidity, pH value - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" pH is the negative base-10 logarithm of the hydrogen ion activity in a solution. Low pH is acidic, high pH is alkaline, and 7 is neutral at 25 °C. In the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md), pH controls nutrient solubility and uptake: iron, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md) and zinc become less available as pH rises, while calcium, magnesium and [molybdenum](https://genetixbay.com/knowledge/glossary/molybdenum.md) are less available when pH falls too low. ## In practice Accepted ranges, which GenetixBay treats as settled practice: | Medium | pH | |---|---| | Soil | about 6.0–7.0 | | [Coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) and hydro | about 5.5–6.5 | Drift within the range is normal and even helpful: a solution that wanders from 5.6 to 6.2 over a few days exposes roots to the best uptake window for different elements. Correct only when it leaves the range. *Established*. Measure pH of your input solution after adding nutrients, because fertilisers shift it. In soil, the medium buffers pH strongly, so the input matters less than in hydro. Check [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) occasionally to see what the root zone is doing. ## Units and formula pH = −log₁₀[H⁺]. A change of 1 unit means a 10-fold change in hydrogen ion concentration. ## Don't confuse with - **Alkalinity**: the water's capacity to resist pH change, not the pH itself. - **EC**: total dissolved salts; unrelated to acidity. ## Myth check "pH must be held at exactly 5.8" is a *Myth*. A range is the target; see [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md). ## Related terms [pH scale](https://genetixbay.com/knowledge/glossary/ph-scale.md), [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md), [Nutrient lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md), [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md), [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) ## Read more - [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 2. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 --- # pH buffer > A pH buffer is a solution containing a weak acid and its conjugate base that resists pH change; in growing it means calibration buffers or water chemistry that stabilises pH. - Canonical: https://genetixbay.com/knowledge/glossary/ph-buffer.html - Also written: buffer solution, buffer, pH buffering agent, pH stabiliser, pH stabilizer - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In chemistry, a buffer is a mixture of a weak acid and its conjugate base (or a weak base and its conjugate acid) that holds [pH](https://genetixbay.com/knowledge/glossary/ph.md) nearly constant when small amounts of acid or base are added. Growers use the word in two ways. Calibration buffers are standard solutions at pH 4.01, 7.00 and 10.01 used to calibrate meters. Root-zone or water buffers are chemical systems, chiefly bicarbonate and carbonate in water and [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) in some nutrient mixes, that keep a solution from swinging. ## In practice Bicarbonate is the main natural buffer in [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md). Some is helpful: around 30–60 ppm (mg/L) as CaCO3 [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) steadies pH in hydro. Too much forces constant acid dosing and pushes pH up in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) over time. Commercial "pH stabiliser" products are usually buffer blends. They can reduce drift but add their own ions; know what is in them. Calibration buffers degrade once opened and absorb [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) (the pH 10 buffer especially); replace them regularly and never pour used buffer back into the bottle. ## Don't confuse with - **Coco buffering**: pre-treating [coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md) with calcium and magnesium to load its exchange sites; a different meaning. - **Buffering capacity**: how much buffer is present. ## Related terms [Buffering capacity](https://genetixbay.com/knowledge/glossary/buffering-capacity.md), [Calibration solution](https://genetixbay.com/knowledge/glossary/calibration-solution.md), [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md) ## Read more - [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) ## Sources 1. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 --- # pH Down > pH Down is any acid used to lower solution pH, commonly phosphoric, nitric or sulfuric acid; each adds a nutrient, and all need gloves and eye protection. - Canonical: https://genetixbay.com/knowledge/glossary/ph-down.html - Also written: pH decreaser, pH minus, pH-, acid adjuster, pH down solution - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" pH Down is the generic name for acids used to lower the [pH](https://genetixbay.com/knowledge/glossary/ph.md) of water or nutrient solutions. Common choices: [phosphoric acid](https://genetixbay.com/knowledge/glossary/phosphoric-acid.md) (adds phosphorus; the usual hobby product), [nitric acid](https://genetixbay.com/knowledge/glossary/nitric-acid.md) (adds [nitrate nitrogen](https://genetixbay.com/knowledge/glossary/nitrate.md); common in commercial hydro and favoured in flower when P is already high) and sulfuric acid (adds sulfur). Citric acid is sometimes used in organic setups, but microbes consume it, so pH drifts back quickly. ## In practice How much you need depends mostly on the water's alkalinity, not its pH. Hard tap water with high bicarbonate needs far more acid than [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) at the same starting pH, because the acid first neutralises the bicarbonate. Langenfeld and Bugbee (2025) examined pH control in [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) hydroponics using nitric acid and [ammonium nitrate](https://genetixbay.com/knowledge/glossary/ammonium-nitrate.md). Add after nutrients, in small doses, mix well, wait, re-measure. Keep a log of millilitres per litre so the next mix is quick. **Safety:** concentrated acids burn skin and eyes. Wear gloves and eye protection, always add acid to water, never water to acid, store away from bases and keep out of reach of children. ## Don't confuse with - **Vinegar**: weak acetic acid; unstable and a poor choice in hydro. - **Reducing alkalinity**: the real job of acid in [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md); pH follows. ## Related terms [pH Up](https://genetixbay.com/knowledge/glossary/ph-up.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [Carbonate hardness](https://genetixbay.com/knowledge/glossary/carbonate-hardness.md) ## Read more - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Sources 1. Langenfeld NJ, Bugbee B. 2025. pH control in recirculating hydroponics with nitric acid and ammonium nitrate. HortScience 60(9):1555. https://journals.ashs.org/view/journals/hortsci/60/9/article-p1555.xml 2. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 --- # pH drift > pH drift is the gradual rise or fall of a nutrient solution's pH between adjustments, driven mainly by which ions the roots take up. - Canonical: https://genetixbay.com/knowledge/glossary/ph-drift.html - Also written: pH swing, pH creep, drifting pH, pH rising, pH falling, pH fluctuation - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" pH drift is the change in [pH](https://genetixbay.com/knowledge/glossary/ph.md) of a reservoir or [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) over time. Roots keep their internal charge balanced: when they take up more anions (especially [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), NO₃⁻) they release hydroxide or bicarbonate and the solution pH rises; when they take up more cations (especially [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), NH₄⁺) they release hydrogen ions and pH falls. Most hydro solutions are nitrate-dominant, so upward drift is the common pattern. ## In practice Other contributors: aeration strips dissolved [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) and nudges pH up, organic additives and microbes can push it either way, and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) or rockwool can release or absorb ions early in a run. Small reservoirs with [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) drift fastest because there is little buffering. GenetixBay's view matches the accepted practice: drift within about 5.5–6.5 in hydro is normal and not worth chasing. Adjust when it leaves the range. A rising pH that keeps climbing quickly can point to root problems; a steadily falling pH may mean too much ammonium or microbial activity. Langenfeld and Bugbee (2025) showed that balancing nitrate and ammonium can control drift in [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md). ## Don't confuse with - **Meter drift**: a probe losing calibration; check with a buffer solution. - **pH buffer**: a solution or chemical system that resists drift. ## Related terms [pH](https://genetixbay.com/knowledge/glossary/ph.md), [Buffering capacity](https://genetixbay.com/knowledge/glossary/buffering-capacity.md), [pH Up](https://genetixbay.com/knowledge/glossary/ph-up.md), [pH Down](https://genetixbay.com/knowledge/glossary/ph-down.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) ## Read more - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) ## Sources 1. Langenfeld NJ, Bugbee B. 2025. pH control in recirculating hydroponics with nitric acid and ammonium nitrate. HortScience 60(9):1555. https://journals.ashs.org/view/journals/hortsci/60/9/article-p1555.xml 2. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 3. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 --- # pH meter > A pH meter measures solution pH with a glass electrode whose voltage changes with hydrogen ion activity; it needs regular calibration and a moist probe. - Canonical: https://genetixbay.com/knowledge/glossary/ph-meter.html - Also written: pH pen, pH probe, pH tester, pH electrode, digital pH meter, pH meter probe - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A pH meter measures the voltage between a glass sensing electrode and a reference electrode, usually combined in one probe, and converts it to [pH](https://genetixbay.com/knowledge/glossary/ph.md). The thin glass bulb develops a voltage proportional to the hydrogen ion activity in the sample. Pens put the probe and meter in one body; benchtop and portable meters use replaceable probes on a cable. ## In practice Care rules that matter: - Keep the bulb wet. Store it in storage solution (usually 3 M KCl), never in distilled or [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), which draws ions out of the reference. - Calibrate with fresh buffers, at least weekly for hydro and before important readings. - Rinse after use; nutrient and organic residues coat the glass and slow response. - Probes age. Typical life is around one to two years with good care. Slow, drifting readings and low slope mean replacement. Liquid drop tests and paper strips work for rough checks but are hard to read precisely in coloured nutrient solutions. ## Don't confuse with - **EC meter**: measures salt strength, not acidity; many combo meters do both, with separate probes or sensors. - **Soil pH probe (two-metal type)**: inexpensive analogue probes are unreliable for growing decisions. ## Related terms [Two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md), [Calibration solution](https://genetixbay.com/knowledge/glossary/calibration-solution.md), [ATC](https://genetixbay.com/knowledge/glossary/atc.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) ## Read more - [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) --- # pH scale > The pH scale runs from 0 (strongly acidic) to 14 (strongly alkaline) with 7 neutral; it is logarithmic, so each whole unit is a tenfold change in acidity. - Canonical: https://genetixbay.com/knowledge/glossary/ph-scale.html - Also written: pH range, 0-14 scale, acid-base scale, logarithmic pH scale - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The pH scale expresses [acidity](https://genetixbay.com/knowledge/glossary/ph.md) and [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) of water-based solutions, usually from 0 to 14 at 25 °C. Values below 7 are acidic, 7 is neutral and above 7 is alkaline. The scale is logarithmic: pH 5 has ten times the hydrogen ion activity of pH 6, and a hundred times that of pH 7. ## In practice The logarithm is why small numbers matter. Moving a hydro reservoir from 6.0 to 7.0 is not a small nudge; it is a tenfold drop in hydrogen ions, enough to make iron and [manganese](https://genetixbay.com/knowledge/glossary/manganese.md) markedly less available. It is also why "a little" pH down can overshoot in unbuffered water: [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) has almost nothing to resist the change. Reference points: lemon juice about 2, rainwater about 5.6, pure water at 25 °C 7.0, many [tap waters](https://genetixbay.com/knowledge/glossary/tap-water.md) 7–8.5, baking soda solution about 8.3, household ammonia about 11. Cannabis [root zones](https://genetixbay.com/knowledge/glossary/root-zone.md) are kept at roughly 5.5–7.0 depending on medium. ## Units and formula pH = −log₁₀[H⁺]; [H⁺] = 10^(−pH) mol/L. ## Don't confuse with - **pH**: the measured value; the scale is the system. - **Buffering capacity**: how hard it is to move along the scale. ## Related terms [pH](https://genetixbay.com/knowledge/glossary/ph.md), [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md), [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [pH buffer](https://genetixbay.com/knowledge/glossary/ph-buffer.md) ## Read more - [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9 --- # pH Up > pH Up is any alkaline additive used to raise solution pH, commonly potassium hydroxide or potassium carbonate; it is caustic and needs gloves and eye protection. - Canonical: https://genetixbay.com/knowledge/glossary/ph-up.html - Also written: pH increaser, pH plus, pH+, alkaline adjuster, pH up solution - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" pH Up is the generic name for alkaline products that raise the [pH](https://genetixbay.com/knowledge/glossary/ph.md) of a nutrient solution or water. The usual active ingredients are potassium hydroxide (KOH, strong and fast), potassium carbonate (K₂CO₃) or potassium bicarbonate (KHCO₃), which also add a little buffering. All of them add some potassium. ## In practice Most growers need pH Up less often than [pH Down](https://genetixbay.com/knowledge/glossary/ph-down.md), because [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) and many fertiliser mixes tend to be alkaline or drift upwards. It is most common with [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) and acidic nutrient blends, or in [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and hydro when a new mix lands below about 5.5. Add small amounts, stir or circulate for several minutes, and re-measure; RO water has little buffering, so a few drops can overshoot. Adjust after adding nutrients, never before. Dilute concentrated pH Up in water first for small reservoirs. **Safety:** strong bases cause serious chemical burns to skin and eyes, often without immediate pain. Wear gloves and eye protection, store away from acids and out of reach of children and pets, and never mix pH Up and pH Down directly. ## Don't confuse with - **Buffer additives**: carbonate-based products raise both pH and [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md). - **Cal-Mag**: raises calcium and magnesium; it does not reliably raise pH. ## Related terms [pH Down](https://genetixbay.com/knowledge/glossary/ph-down.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md), [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) ## Read more - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) ## Sources 1. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 --- # Pheno > In grower slang, a pheno is one individual plant from a seed lot, usually numbered during a hunt, as in "the #4 pheno". - Canonical: https://genetixbay.com/knowledge/glossary/pheno.html - Also written: phenos, the #4 pheno, pheno #, keeper pheno number - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In grower slang, a pheno is one individual plant grown from a [seed lot](https://genetixbay.com/knowledge/glossary/seed-run.md) and evaluated as a candidate keeper. Hunters number them ("#1" to "#20") so each can be tracked through veg, flower, dry and cure, and the winner is then known by that number. ## In practice "The #4 pheno was the gassy one, #11 had the [fruit](https://genetixbay.com/knowledge/glossary/achene.md)" means plant 4 and plant 11 of the hunt. Each is a different [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) from the same parents. Once a pheno is kept and cloned it is often called a cut, and famous ones keep their number as part of the name. The slang [stretches](https://genetixbay.com/knowledge/glossary/stretch.md) the scientific word. Strictly, [phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md) means what you observe: genotype plus environment. Two clones of the #4 grown in different rooms share a genotype but can show different phenotypes. Growers usually mean "this genotype" when they say pheno. ## Don't confuse with - **Phenotype**: the scientific term, covering any observable trait under a given environment. - **Genotype**: the genetic make-up, which a clone shares exactly. - **Strain**: a name for a line or cut, not one individual from a seed hunt. ## Related terms [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md), [Pheno hunt](https://genetixbay.com/knowledge/glossary/pheno-hunt.md), [Keeper](https://genetixbay.com/knowledge/glossary/keeper.md), [Cut](https://genetixbay.com/knowledge/glossary/cut.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md) ## Read more - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) --- # Pheno hunt > A pheno hunt is growing many seeds of one line side by side and evaluating them to select the best individual plants, which are then kept as clones. - Canonical: https://genetixbay.com/knowledge/glossary/pheno-hunt.html - Also written: pheno hunting, phenotype hunt, phenotype hunting, pheno-hunting - Glossary category: Genetics and breeding · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A [pheno](https://genetixbay.com/knowledge/glossary/pheno.md) hunt is the process of growing a population of seeds from one cross or line and choosing the best individuals. Each [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) is a different [genotype](https://genetixbay.com/knowledge/glossary/genotype.md), so the hunt is a search for the rare plant that combines the traits you want. Winners are kept as clones ([mother plants](https://genetixbay.com/knowledge/glossary/mother-plant.md)) and grown again. ## In practice A useful hunt starts with enough seeds for the trait you want. For a trait in 1 in 10 plants, 30 seeds gives you about a 96% chance of at least one hit; for 1 in 50 you need well over 100. Take a cutting from every candidate before flowering so you can keep the winner. Grow everything in the same conditions, number each plant, and score traits with notes and [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md): vigour, structure, pest resistance, flowering time, aroma in late flower and after cure, yield, and lab results if possible. Then rerun the finalists as clones. A plant that won the first round because it sat in the best spot often loses the second. Cull any plant that shows [intersex](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) flowers, however good it smells. ## Don't confuse with - **Pheno (slang)**: the individual plant, "the gas pheno"; the hunt is the process. - **Breeding**: a hunt selects from what is there. Breeding makes new combinations and stabilises them. ## Related terms [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md), [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md), [Test grow](https://genetixbay.com/knowledge/glossary/test-grow.md), [Selection pressure](https://genetixbay.com/knowledge/glossary/selection-pressure.md) ## Read more - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Phenotype > The phenotype is what a plant visibly and measurably is (shape, colour, smell, chemistry, timing), the result of its genotype acting in a particular environment. - Canonical: https://genetixbay.com/knowledge/glossary/phenotype.html - Also written: phenotypes, phenotypic expression, observable traits - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The phenotype is the set of observable traits of a plant: height, leaf shape, flowering time, aroma, resin, [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) profile, pest resistance. It is produced by the [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) interacting with the environment. Phenotype = genotype + environment + their interaction. ## In practice Growers say "this [pheno](https://genetixbay.com/knowledge/glossary/pheno.md)" to mean one individual plant out of a seed pack, as in "the third pheno smelled like fuel". Strictly, that plant is a genotype that showed a particular phenotype in that room. Run the same clone under a different light, feed or [pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) and parts of the phenotype shift; the genotype does not. That is why serious selection means growing candidates side by side, in the same conditions, and ideally repeating the best ones as clones before deciding. A plant that stood out because it sat in the hot spot has a good phenotype but may not have a good genotype. ## Don't confuse with - **Genotype**: the DNA. The phenotype is what you see from it. - **Pheno (slang)**: shorthand for one [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) or selection; same root, looser use. - **Chemotype**: the chemical part of the phenotype. ## Myth check "Indica phenotype" and "sativa phenotype" describe plant shape at most (broad or narrow [leaflets](https://genetixbay.com/knowledge/glossary/leaflet.md), structure, flowering time). They do not predict chemistry or effect (Watts et al. 2021). See [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md). ## Related terms [Genotype](https://genetixbay.com/knowledge/glossary/genotype.md), [Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md), [Pheno hunt](https://genetixbay.com/knowledge/glossary/pheno-hunt.md), [Genotype by environment interaction](https://genetixbay.com/knowledge/glossary/genotype-by-environment.md), [Heritability](https://genetixbay.com/knowledge/glossary/heritability.md) ## Read more - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) - [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Watts S, McElroy M, Migicovsky Z, Maassen H, van Velzen R, Myles S. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y --- # Pheromone trap > A trap baited with a synthetic sex pheromone that catches males of one moth species; used to time scouting and sprays, not to control the pest. - Canonical: https://genetixbay.com/knowledge/glossary/pheromone-trap.html - Also written: pheromone traps, sex pheromone trap, moth trap, lure trap - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A pheromone trap uses a lure that imitates the sex attractant a female moth releases, so it catches males of one target species, such as [corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md) or European corn borer. Extension guides for [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) use trap catches to show when moths are flying and egg-laying is imminent. ## In practice Trap catches start the clock: combine them with a [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md) model to predict egg hatch, then scout flowers for eggs and young larvae. Traps catch too few moths to reduce a population, and catches reflect males only. Change lures on the schedule given by the lure maker. ## Don't confuse with - **Sticky card**: catches any small flying insect by colour. - **Light trap**: attracts many night-flying insects, including [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md). ## Related terms [Degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md) ## Read more - [Budworms on cannabis: corn earworm and tobacco budworm in numbers](https://genetixbay.com/knowledge/pests/budworms-corn-earworm.md) - [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Sources 1. Shrestha, G., 2022. Corn earworm management in hemp (EM 9626). Oregon State University Extension. https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 2. Pacific Northwest Insect Management Handbook. Hemp: caterpillars. https://pnwhandbooks.org/insect/agronomic/hemp/hemp-caterpillars --- # Phloem > The plant's living transport tissue that carries sugars, amino acids, hormones and mobile nutrients from leaves to roots, buds and other growing parts. - Canonical: https://genetixbay.com/knowledge/glossary/phloem.html - Also written: phloem tissue, sieve tubes, sugar transport tissue, phloem sap - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Phloem is the vascular tissue that moves the products of [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md). Living sieve-tube cells, supported by companion cells, carry a sugar-rich sap (mostly sucrose) from "sources" such as mature leaves to "sinks" such as roots, new shoots and developing flowers. Flow runs whichever way supply and demand dictate, so phloem moves material both up and down. ## In practice Phloem is the reason nutrients are called mobile or immobile. Nitrogen, phosphorus, potassium and magnesium move readily in phloem, so a plant short of them strips old leaves to feed new growth, and [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) shows low on the plant first. Calcium, boron and largely iron are poorly phloem-mobile, so their shortages show on new growth. In late flower, buds are the main sink. [Leaf senescence](https://genetixbay.com/knowledge/glossary/senescence.md) and nutrient remobilisation into flowers run through phloem, which is the biology behind both the natural fade and the GenetixBay [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md). Sap-sucking pests such as [aphids](https://genetixbay.com/knowledge/glossary/aphid.md) and [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) feed directly on phloem sap; their [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md) is excess sugar. ## Don't confuse with - **Xylem**: moves water and ions up from roots. - **Bark**: outer tissue that, on woody plants, contains phloem. - **Resin**: made in [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md), not carried in phloem. ## Related terms [Xylem](https://genetixbay.com/knowledge/glossary/xylem.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md), [Photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), [Nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) ## Read more - [Mobile vs immobile nutrients: reading old vs new leaves](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Phoresy > One animal riding on another to disperse without feeding on it, as broad mites do on whiteflies and aphids. - Canonical: https://genetixbay.com/knowledge/glossary/phoresy.html - Also written: phoretic, phoretic dispersal, hitchhiking mites - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Phoresy is dispersal by hitching a ride on another animal. The [broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md) is the classic cannabis-relevant example: UF/IFAS describes it clinging to the legs of [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) and some [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), which carry it to new plants. ## In practice Phoresy explains broad mite outbreaks on plants nobody touched, and is one reason whitefly and aphid control matters in rooms with a broad mite history. [Sticky cards](https://genetixbay.com/knowledge/glossary/sticky-trap.md) can carry hitchhikers too, so dispose of old cards outside the room. ## Don't confuse with - **Aerial dispersal**: riding air currents, not animals. - **Parasitism**: feeding on the host, which phoresy does not. ## Related terms [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Aerial dispersal](https://genetixbay.com/knowledge/glossary/aerial-dispersal.md), [Whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md) ## Read more - [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ## Sources 1. Fasulo, T.R. Broad mite, Polyphagotarsonemus latus. UF/IFAS EENY-183. https://doi.org/10.32473/edis-in340-2005 --- # Phosphate > Phosphate is the ionic form in which plants absorb phosphorus, mainly H2PO4- at the normal root-zone pH of 5.5-6.5. - Canonical: https://genetixbay.com/knowledge/glossary/phosphate.html - Also written: H2PO4-, HPO4 2-, PO4, orthophosphate, phosphate ion - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Phosphate is phosphorus combined with oxygen, present in solution as H2PO4- or HPO4 2- depending on [pH](https://genetixbay.com/knowledge/glossary/ph.md). Below about pH 7 the H2PO4- form dominates, and that is the form roots take up most readily. Phosphate is also a buffer: it resists pH change somewhat in nutrient solutions. ## In practice Phosphate comes from [monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md), [monoammonium phosphate](https://genetixbay.com/knowledge/glossary/monoammonium-phosphate.md) or [phosphoric acid](https://genetixbay.com/knowledge/glossary/phosphoric-acid.md). It reacts with calcium to form insoluble calcium phosphate when both are concentrated, or when pH rises well above 6.5. That is why phosphate and calcium sit in separate [A and B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) stocks, and why a cloudy reservoir after a pH spike can mean phosphate has dropped out. ## Units and formula Reports may quote PO4, P or P2O5. P = PO4 × 0.326; P = P2O5 × 0.436. Compare like with like. ## Don't confuse with - **Phosphite (phosphonate)**: a related ion sold as a fungicide or "[biostimulant](https://genetixbay.com/knowledge/glossary/biostimulant.md)"; plants cannot use it as a phosphorus source. - **Phosphorus**: the element itself, counted the same whichever ion carries it. ## Related terms [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md), [Monoammonium phosphate](https://genetixbay.com/knowledge/glossary/monoammonium-phosphate.md), [Phosphoric acid](https://genetixbay.com/knowledge/glossary/phosphoric-acid.md), [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md) ## Read more - [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) - [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Phosphoric acid > Phosphoric acid (H3PO4) is the most common pH-down acid; it lowers pH while adding phosphorus, about 27% P in the usual 85% grade. - Canonical: https://genetixbay.com/knowledge/glossary/phosphoric-acid.html - Also written: H3PO4, orthophosphoric acid, pH down (phosphoric) - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Phosphoric acid is a mineral acid of phosphorus. The 85% technical grade contains roughly 27% P by weight. Diluted retail pH-down products are usually phosphoric acid at a much lower strength. Adding it lowers [pH](https://genetixbay.com/knowledge/glossary/ph.md) and supplies [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) at the same time. ## In practice For most growers with soft or [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), the phosphorus from pH-down is small. With hard, high-alkalinity water, the acid needed to neutralise bicarbonate can add a meaningful amount of P, sometimes tens of mg/L (ppm). Count it towards the feed's P total, or split acidification with nitric or sulfuric acid. Concentrated acid is corrosive: wear eye and skin protection, add acid to water and never the reverse. ## Don't confuse with - **Nitric acid**: lowers pH and adds nitrogen instead. - **Citric acid**: an organic acid that microbes break down, so pH drifts back up. - **Phosphorous acid (phosphite)**: a fungicidal compound, not a P nutrient. ## Related terms [Phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md), [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Nitric acid](https://genetixbay.com/knowledge/glossary/nitric-acid.md), [pH Down](https://genetixbay.com/knowledge/glossary/ph-down.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Phosphorus > Phosphorus (P) is a mobile macronutrient used in energy transfer (ATP), DNA and cell membranes; cannabis needs moderate amounts and gains nothing from excess. - Canonical: https://genetixbay.com/knowledge/glossary/phosphorus.html - Also written: P, phosphorous, phosphorus deficiency, P deficiency - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Phosphorus is the [macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md) at the heart of energy transfer: it forms ATP, nucleic acids and the phospholipids in every cell membrane. Plants take it up as [phosphate ions](https://genetixbay.com/knowledge/glossary/phosphate.md) (mainly H2PO4- in the usual root-zone [pH range](https://genetixbay.com/knowledge/glossary/ph-scale.md)). It is mobile, so [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) shows on older leaves first. ## In practice Deficient plants grow slowly, with dark, dull or purplish older leaves and sometimes red [petioles](https://genetixbay.com/knowledge/glossary/petiole.md). Cannabis trials put the useful range roughly at 25-60 mg/L (ppm) P in solution; above that, yield and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) plateau and the extra simply leaves in the [runoff](https://genetixbay.com/knowledge/glossary/runoff.md). Excess P can also tie up zinc, iron and copper. ## Units and formula Labels state phosphorus as P2O5. Elemental P = P2O5 × 0.436. A "[0-52-34](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md)" salt contains about 22.7% P. ## Don't confuse with - **Phosphate**: the ionic form the plant absorbs, not the element. - **Purple stems from genetics or cold**: anthocyanin colour is not proof of P deficiency. ## Myth check "More phosphorus in flower means bigger buds" is not supported. Independent cannabis trials found a plateau past moderate P (Evidence: Established for the plateau). See [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md), [Macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md), [Bloom booster](https://genetixbay.com/knowledge/glossary/bloom-booster.md), [Guaranteed analysis](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md), [Monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) ## Read more - [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) - ["Bloom boosters" for cannabis: what's real and what's marketing](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) ## Sources 1. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323 2. Westmoreland FM, Bugbee B. 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 3. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 --- # Photon efficacy > Photon efficacy is how many micromoles of PAR photons a fixture produces per joule of electricity (µmol/J); higher means more light for the same power bill and heat. - Canonical: https://genetixbay.com/knowledge/glossary/photon-efficacy.html - Also written: PPE, photosynthetic photon efficacy, µmol/J, umol/J, fixture efficiency, efficacy - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Photon efficacy (photosynthetic photon efficacy, PPE) is a fixture's [PAR](https://genetixbay.com/knowledge/glossary/par.md) output divided by its electrical input, in micromoles per joule (µmol/J). One watt is one joule per second, so it is also µmol/s per watt. It is the best single number for comparing running cost, because every watt not turned into light becomes heat you also pay to remove. ## In practice Approximate fixture-level ranges: | Fixture class | µmol/J | |---|---| | [T5 fluorescent](https://genetixbay.com/knowledge/glossary/t5-fluorescent.md) | about 1.0–1.2 | | [Metal halide](https://genetixbay.com/knowledge/glossary/metal-halide.md) | about 1.2–1.5 | | [Ceramic metal halide](https://genetixbay.com/knowledge/glossary/cmh.md) | about 1.5–1.9 | | Double-ended [HPS](https://genetixbay.com/knowledge/glossary/hps.md) | about 1.7–2.1 | | Modern horticultural [LED](https://genetixbay.com/knowledge/glossary/led.md) | about 2.5–3.2 | Kusuma, Pattison and Bugbee (2020) reviewed the physics and put the best LEDs near 3 µmol/J, with a practical ceiling around 4. Westmoreland and colleagues (2021) concluded that efficacy matters more than fine spectrum tuning for cost-effective cannabis production. *Established*. A grower switching from a 1,000 W HPS at 1.9 µmol/J to a 700 W LED at 2.7 µmol/J gets about the same photons (1,900 vs 1,890 µmol/s) for 30% less power and much less heat. ## Units and formula Efficacy (µmol/J) = [PPF](https://genetixbay.com/knowledge/glossary/ppf.md) (µmol/s) ÷ wall power (W). Use measured wall power, not the "equivalent" wattage on the box. ## Don't confuse with - **Luminous efficacy (lm/W)**: eye-weighted; irrelevant to plants. - **PPFD**: light at the canopy, which also depends on height and reflectors. ## Related terms [PPF](https://genetixbay.com/knowledge/glossary/ppf.md), [LED](https://genetixbay.com/knowledge/glossary/led.md), [HPS](https://genetixbay.com/knowledge/glossary/hps.md), [LED vs HPS](https://genetixbay.com/knowledge/glossary/led-vs-hps.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) ## Sources 1. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 2. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988 --- # Photoperiod > The daily length of light versus dark; photoperiod cannabis flowers when nights grow long enough, rather than at a fixed age. - Canonical: https://genetixbay.com/knowledge/glossary/photoperiod.html - Also written: photoperiodism, photoperiodic, day length, photoperiod plant, photoperiod strain, photo, photos - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Photoperiod is the number of hours of light (and, crucially, uninterrupted dark) in a 24-hour cycle. Photoperiodism is a plant's flowering response to it. Most cannabis is photoperiodic: a [short-day plant](https://genetixbay.com/knowledge/glossary/short-day-plant.md) that stays vegetative under long days and switches to flowering once the dark period passes a cultivar-specific threshold. The plant measures the night through [phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md), so the length of uninterrupted darkness is what counts. ## In practice "Photoperiod" or "photo" also names the plant type, as opposed to an [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md). Indoors, growers hold photos in veg with [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) or [24/0](https://genetixbay.com/knowledge/glossary/24-0.md), then flip to a long-night schedule to flower. House positions: - **24/0 in veg is fine**: cannabis doesn't need a dark sleep period in veg. - **Flower doesn't have to be exactly 12/12**: 13/11 works for many cultivars, and some flower at 14-15 h of light. In practice that is about 12 h of high intensity with sunrise and sunset ramps adding the rest. - **Test your cultivar**: critical day length varies, which is exactly what [GenetixBay trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) are for. [Light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) during the dark period can delay flowering or contribute to stress in sensitive cultivars. ## Don't confuse with - **Autoflower**: flowers by age, largely ignoring day length. - **DLI**: total light dose per day, separate from day-length signalling. - **Light schedule (18/6, 12/12)**: the setting; photoperiod is the biology. ## Related terms [Short-day plant](https://genetixbay.com/knowledge/glossary/short-day-plant.md), [Autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md), [Phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md), [Flowering stage](https://genetixbay.com/knowledge/glossary/flowering-stage.md), [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) ## Read more - [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Petit J, Salentijn EMJ, Paulo MJ, Denneboom C, Trindade LM. 2020. Genetic architecture of flowering time and sex determination in hemp (Cannabis sativa L.): a genome-wide association study. Frontiers in Plant Science 11:569958. https://doi.org/10.3389/fpls.2020.569958 --- # Photosynthesis > The process in chloroplasts that uses light energy to turn carbon dioxide and water into sugars and oxygen; cannabis uses the C3 pathway. - Canonical: https://genetixbay.com/knowledge/glossary/photosynthesis.html - Also written: photosynthetic, carbon fixation, C3 photosynthesis, light reactions - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Photosynthesis is the conversion of light energy into chemical energy. In the chloroplast, [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) absorbs light, splits water and makes energy carriers (light reactions); the Calvin cycle then uses them to fix CO₂ into sugars. Cannabis is a C3 plant, so its rate responds strongly to CO₂ concentration as well as light. ## In practice Every gram of dry bud is mostly fixed carbon. In cannabis, yield rises roughly in line with light up to very high canopy intensities: Rodriguez-Morrison et al. (2021) saw yield keep climbing up to about 1,800 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) with ambient CO₂. Growers usually target about 600-900 µmol/m²/s in flower without added CO₂ and up to 1,200-1,500 with enrichment, provided temperature, [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), water and nutrients keep up. [Daily light integral](https://genetixbay.com/knowledge/glossary/dli.md) (DLI, mol/m²/day) is the useful total: intensity times hours. House position: the last weeks of flower are when the plant packs on most of its final weight and resin. That's why cutting light ([darkness before harvest](https://genetixbay.com/knowledge/glossary/darkness-before-harvest.md)) or starving the plant (pre-harvest [flushing](https://genetixbay.com/knowledge/glossary/flushing.md)) works against you. ## Don't confuse with - **Respiration**: burning sugars for energy, day and night. - **Photoperiod**: day-length signalling, not energy capture. - **Photomorphogenesis**: light shaping growth via photoreceptors. ## Related terms [Chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md), [Stomata](https://genetixbay.com/knowledge/glossary/stomata.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md), [CO2 enrichment](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [CO₂ enrichment: when it pays, how much, and how to stay safe](https://genetixbay.com/knowledge/environment/co2-enrichment.md) ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Chandra S, Lata H, Khan IA, ElSohly MA. 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14:299-306. https://doi.org/10.1007/s12298-008-0027-x 3. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Phytocannabinoid > A phytocannabinoid is a cannabinoid made by a plant, chiefly the terpenophenolic compounds cannabis builds in its glandular trichomes, such as THCA, CBDA and CBGA. - Canonical: https://genetixbay.com/knowledge/glossary/phytocannabinoid.html - Also written: phytocannabinoids, plant cannabinoid, plant cannabinoids - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A phytocannabinoid is a [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) of plant origin. In cannabis they are terpenophenolics: a phenolic ring from olivetolic acid joined to a [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) chain from [geranyl pyrophosphate](https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.md), forming [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), which enzymes then convert into [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md) or CBCA. The plant makes them almost entirely as carboxylic acids in the secretory cells of capitate glandular trichomes and stores them in the resin head. ## In practice When a COA lists THCA, CBDA, CBGA, THCVA and CBCA, every one of those is a phytocannabinoid. Hanuš and colleagues catalogued well over 100 from cannabis, but most growers will only ever see five to eight on a standard panel. A few plants outside the genus (some liverworts, some *Helichrysum* species) also make cannabinoid-like compounds, which is why the term is broader than "cannabis compound". ## Don't confuse with - **Endocannabinoid**: made by animals, including humans, not by plants. - **Semi-synthetic cannabinoid**: such as delta-8 [THC](https://genetixbay.com/knowledge/glossary/thc.md) or HHC as sold, produced by chemically converting plant [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) or THC rather than by the plant itself. - **Terpene**: a different compound class, though it supplies part of the cannabinoid skeleton. ## Related terms [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), [Olivetolic acid](https://genetixbay.com/knowledge/glossary/olivetolic-acid.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. 2. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004. --- # Phytochrome > A family of plant photoreceptors that sense red and far-red light, measuring night length for flowering and shade for stem elongation. - Canonical: https://genetixbay.com/knowledge/glossary/phytochrome.html - Also written: phytochromes, Pr, Pfr, red/far-red receptor, phyB - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Phytochromes are light-sensing proteins that switch between two forms. Red light (about 660 nm) converts the inactive form (Pr) to the active form (Pfr); [far-red light](https://genetixbay.com/knowledge/glossary/far-red.md) (about 730 nm) and darkness convert it back. The balance tells the plant about [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md) and shading. ## In practice Phytochrome is how cannabis measures the night. During a long dark period, Pfr drops; if the dark lasts long enough, flowering is triggered in photoperiod cultivars. A [light leak](https://genetixbay.com/knowledge/glossary/light-leak.md) or a brief light break during the night can reset the clock. That is why light-tight flower rooms matter, and why green work lights are used: phytochrome responds weakly to green. Far-red affects shape: a high far-red-to-red ratio (as under a canopy) signals shade and drives stretching. Some [LED](https://genetixbay.com/knowledge/glossary/led.md) fixtures add far-red to speed growth and canopy expansion; brief far-red at the end of the day is used by some growers to nudge flowering. Results vary by cultivar. ## Don't confuse with - **Chlorophyll**: captures light energy; phytochrome only [senses](https://genetixbay.com/knowledge/glossary/sinsemilla.md) it. - **Cryptochrome**: blue-light receptor shaping stem length and leaf form. - **Photoperiod**: the day-length response phytochrome helps measure. ## Related terms [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [Short-day plant](https://genetixbay.com/knowledge/glossary/short-day-plant.md), [Internode](https://genetixbay.com/knowledge/glossary/internode.md), [Hypocotyl](https://genetixbay.com/knowledge/glossary/hypocotyl.md) ## Read more - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 --- # Phytoseiulus persimilis > A specialist predatory mite that eats almost only Tetranychus spider mites, eggs to adults; fast-acting on hot spots but starves once prey runs out. - Canonical: https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.html - Also written: persimilis, P. persimilis, Chilean predatory mite - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Phytoseiulus persimilis* is a [predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) of the family Phytoseiidae that feeds almost only on [spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) in the genus *Tetranychus*, including the two-spotted spider mite. Adults are bright orange-red, pear-shaped, longer-legged and faster than their prey. They eat all stages of spider mites and reproduce quickly when food is plentiful. ## In practice Growers use *persimilis* as the knock-down predator for established spider mite patches, released directly on the stippled leaves. It works best in moderate temperatures and at [relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) above about 60%; hot, [dry rooms](https://genetixbay.com/knowledge/glossary/drying-room.md) over roughly 30 °C (86 °F) hurt it. Because it is a specialist, the population crashes once spider mites are gone, so it is not a preventive choice. A common pairing is *persimilis* for hot spots plus *[Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md)* across the room for staying power. Avoid broad-spectrum sprays before and after release. ## Don't confuse with - **Neoseiulus californicus**: a pale, slower generalist that persists at low prey and tolerates heat. - **Spider mites**: plant feeders with two dark body spots; *persimilis* is uniformly orange-red. - **Red velvet mites**: larger soil mites, not a [biocontrol](https://genetixbay.com/knowledge/glossary/biological-control.md) product. ## Related terms [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md), [Predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ## Sources 1. UC IPM. Natural Enemies Gallery: Phytoseiulus predatory mites. https://ipm.ucanr.edu/natural-enemies/phytoseiulus-predatory-mites/ 2. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf --- # Pistil > The female reproductive organ of a flower (ovary, style and stigmas); in cannabis growers loosely call the visible white stigmas "pistils". - Canonical: https://genetixbay.com/knowledge/glossary/pistil.html - Also written: pistils, hairs, pistillate organ, gynoecium, female hairs - Glossary category: Plant biology · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A pistil is the female part of a flower: the ovary holding the ovule, a short style, and [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md) that catch pollen. Each female cannabis flower has a single ovary inside its [bract](https://genetixbay.com/knowledge/glossary/bract.md), topped by two long, hair-like stigmas. Strictly, the white or orange "hairs" growers see are the stigmas, not the whole pistil. ## In practice "Pistils" is how growers spot a female. The first paired white hairs at a node mark a pistillate [pre-flower](https://genetixbay.com/knowledge/glossary/pre-flower.md). In flower, masses of fresh white stigmas mean active growth; as flowers age the stigmas darken through orange, red or brown and curl back. Pistil colour is a weak harvest guide. Stigmas also brown from heat, handling, low humidity or pollination, and cultivars differ. [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) are the better clock. ## Don't confuse with - **Stigma**: the pollen-receiving tip, the hair itself. - **Bract**: the sheath around the ovary, often miscalled the [calyx](https://genetixbay.com/knowledge/glossary/calyx.md). - **Stamen**: the male organ ([anther](https://genetixbay.com/knowledge/glossary/anther.md) on a filament). ## Myth check "Harvest when 70-90% of pistils are brown" is a rough rule, not a reliable indicator (Grower practice). GenetixBay uses [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md): a few clear, mostly cloudy, some amber, to taste. See [trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md). ## Related terms [Stigma](https://genetixbay.com/knowledge/glossary/stigma.md), [Bract](https://genetixbay.com/knowledge/glossary/bract.md), [Calyx](https://genetixbay.com/knowledge/glossary/calyx.md), [Pistillate flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md), [Pre-flower](https://genetixbay.com/knowledge/glossary/pre-flower.md) ## Read more - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 --- # Pistillate flower > A female flower with a pistil but no functional stamens; in cannabis, a bract-wrapped ovary topped by two stigmas. - Canonical: https://genetixbay.com/knowledge/glossary/pistillate-flower.html - Also written: female flower, female flowers, pistillate flowers, carpellate flower - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A pistillate flower is a female flower: it has a [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) (ovary, style, [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md)) and no functional stamens. In cannabis each one is tiny, a single ovary in a cupped [perigonal bract](https://genetixbay.com/knowledge/glossary/bract.md) with two protruding stigmas. They form in clusters at nodes and pack densely at [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) into colas. ## In practice Unpollinated female flowers are what drug-type growers harvest. When they are kept seedless ([sinsemilla](https://genetixbay.com/knowledge/glossary/sinsemilla.md)), the plant keeps producing new flowers and resin for weeks rather than diverting resources to seed. One stray pollen source can seed a room, so growers remove males and [intersex plants](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) early. Spotting them: a pistillate [pre-flower](https://genetixbay.com/knowledge/glossary/pre-flower.md) shows a teardrop bract with one or two white stigmas at a node, usually from the fourth to sixth node up, behind the stipule. ## Don't confuse with - **Staminate flower**: the [male flower](https://genetixbay.com/knowledge/glossary/staminate-flower.md) with anthers and pollen. - **Bud**: a cluster of many pistillate flowers, not a single flower. - **Intersex flower**: a pistillate plant producing some staminate flowers or anthers. ## Related terms [Pistil](https://genetixbay.com/knowledge/glossary/pistil.md), [Stigma](https://genetixbay.com/knowledge/glossary/stigma.md), [Bract](https://genetixbay.com/knowledge/glossary/bract.md), [Staminate flower](https://genetixbay.com/knowledge/glossary/staminate-flower.md), [Dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md) ## Read more - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 --- # Plant count limit > A plant count limit caps how many cannabis plants a person, household, patient or licence holder may have, and defines what counts as a plant. - Canonical: https://genetixbay.com/knowledge/glossary/plant-count-limit.html - Also written: plant count, plant limit, plant-count rule, plant numbers limit - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A plant count limit is a legal cap on the number of cannabis plants. It appears in [home grow](https://genetixbay.com/knowledge/glossary/home-grow.md) rules, medical patient and caregiver rules, and some commercial licences, and it usually comes with a definition of what a "plant" is. ## In practice Definitions vary: some count any rooted cutting or germinated [seedling](https://genetixbay.com/knowledge/glossary/seedling.md), some count only plants above a size, and some count only flowering plants. That definition shapes how people grow. Under a strict plant count, growers favour fewer, larger plants trained wide ([SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), mainlining, long veg) rather than many small plants ([SOG](https://genetixbay.com/knowledge/glossary/sog.md)). Under a canopy-area limit, the opposite can make sense. Commercial licences often use [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md) instead of plant count, and track individual plants or batches through [seed-to-sale systems](https://genetixbay.com/knowledge/glossary/seed-to-sale-tracking.md). Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Canopy limit**: a cap on square metres or feet of flowering area. - **Possession limit**: a weight limit on harvested cannabis. ## Related terms [Personal cultivation limit](https://genetixbay.com/knowledge/glossary/personal-cultivation-limit.md), [Home grow](https://genetixbay.com/knowledge/glossary/home-grow.md), [Track-and-trace](https://genetixbay.com/knowledge/glossary/track-and-trace.md), [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md) ## Read more - [SOG: sea of green](https://genetixbay.com/knowledge/training/sog.md) - [SCROG: screen of green](https://genetixbay.com/knowledge/training/scrog.md) --- # Plant density > Plant density is the number of plants per unit of canopy area; more plants raise yield per area up to a point but shorten veg and reduce uniformity. - Canonical: https://genetixbay.com/knowledge/glossary/plant-density.html - Also written: planting density, plants per square metre, plants per square meter, plants per m², stocking density, plant spacing - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Plant density is how many plants occupy a given area, usually given as plants per square metre (1 m² = 10.76 ft²). It interacts with [veg time](https://genetixbay.com/knowledge/glossary/veg-time.md): few large plants and many small plants can fill the same canopy, the first by growing longer, the second by numbers. ## In practice Typical ranges: one to four plants per m² for trained [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md) or mainlined plants; about 9-20 per m² for [sea of green](https://genetixbay.com/knowledge/glossary/sog.md) clones. In a study of drug-type [medical cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md), higher density increased yield per area while reducing yield per plant and lowering the uniformity of [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) content between plants. Higher density also means more clones, more stems, and denser air under the canopy, which raises humidity and mould risk. For home growers the deciding factor is often the law: many places cap plant numbers, so fewer, larger, well-trained plants make sense. Check local rules. ## Don't confuse with - **Plant count limits**: a legal cap on the number of plants; covered as a legal term. - **Canopy area**: the area itself; density divides [plant count](https://genetixbay.com/knowledge/glossary/plant-count-limit.md) by it. ## Related terms [SOG](https://genetixbay.com/knowledge/glossary/sog.md), [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [Yield](https://genetixbay.com/knowledge/glossary/yield.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md), [Veg time](https://genetixbay.com/knowledge/glossary/veg-time.md) ## Read more - [SOG: sea of green](https://genetixbay.com/knowledge/training/sog.md) ## Sources 1. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 2. Backer R, Schwinghamer T, Rosenbaum P, et al., 2019. Closing the yield gap for cannabis: a meta-analysis of factors determining cannabis yield. Frontiers in Plant Science 10:495. https://doi.org/10.3389/fpls.2019.00495 --- # Plant patent > A plant patent, in the US, protects a new and distinct asexually reproduced plant variety, such as a clone, for about 20 years from filing. - Canonical: https://genetixbay.com/knowledge/glossary/plant-patent.html - Also written: plant patents, PP, US plant patent - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A plant patent is a US form of patent that protects a new and distinct plant variety that has been asexually reproduced, for example propagated by cuttings, grafting or [tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md). It gives the owner the right to exclude others from asexually reproducing, selling or using the plant, for 20 years from filing. Tuber-propagated plants and plants found in an uncultivated state are excluded. ## In practice In cannabis, plant patents cover specific clones: one [genotype](https://genetixbay.com/knowledge/glossary/genotype.md), described by its distinguishing traits. A plant patent does not cover seed-grown offspring of the plant, which is where [utility patents](https://genetixbay.com/knowledge/glossary/utility-patent.md) and [plant variety protection](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md) differ. Patents on cannabis plants are public records and can be searched in patent databases. GenetixBay presents patents as documented facts. The concern is structural: patents plus consolidation can restrict the commons and narrow the [gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), which is why open preservation and documentation matter. See [patents and the gene pool](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md). Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Utility patent**: can cover plants, traits, seeds and methods. - **Plant variety protection**: a separate breeders' rights system. ## Related terms [Utility patent](https://genetixbay.com/knowledge/glossary/utility-patent.md), [Plant variety protection](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md), [Defensive publication](https://genetixbay.com/knowledge/glossary/defensive-publication.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) ## Read more - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) ## Sources 1. United States Code, Title 35, sections 161-164 (Plant Patents). --- # Plant ties > Plant ties are soft wire, rubber-coated twist ties or clips used to bend stems and anchor them during low-stress training or support. - Canonical: https://genetixbay.com/knowledge/glossary/plant-ties.html - Also written: training wire, plant tie, soft ties, garden wire, twist ties, tie-downs - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Plant ties are any soft fastener used to hold a stem in a new position: rubber- or foam-coated garden wire, plastic-coated twist ties, soft cord or purpose-made plant clips. They anchor branches to the pot rim, stakes or a net during [LST](https://genetixbay.com/knowledge/glossary/lst.md) and keep heavy [colas](https://genetixbay.com/knowledge/glossary/cola.md) upright in late flower. ## In practice Choose something that grips without cutting. Thin bare wire, fishing line and string can girdle a stem as it thickens, cutting off sap flow; check ties weekly and loosen or move them. Anchor points are often holes punched in the pot rim, or hooks clipped onto it. In [fabric pots](https://genetixbay.com/knowledge/glossary/fabric-pot.md), ties can be tied through the fabric itself. When bending, tie at a node or just below one, and move the tie further out along the stem as the branch grows. Re-adjust every day or two in fast veg. ## Don't confuse with - **Trellis**: the net or frame plants are tied to; ties are the fasteners. - **Stakes**: vertical supports, used with ties for tall or heavy plants. ## Related terms [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Trellis](https://genetixbay.com/knowledge/glossary/trellis.md), [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [Supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md) ## Read more - [LST: low-stress training](https://genetixbay.com/knowledge/training/lst.md) --- # Plant variety protection > Plant variety protection (plant breeders' rights) is an intellectual property right for a new plant variety that is distinct, uniform and stable, typically 20-25 years. - Canonical: https://genetixbay.com/knowledge/glossary/plant-variety-protection.html - Also written: PVP, plant breeders' rights, PBR, PVP certificate, breeders' rights - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Plant variety protection (PVP), called plant breeders' rights (PBR) in many countries, grants a breeder exclusive rights to produce and sell propagating material of a new variety. To qualify, the variety must be new (not sold too early), distinct from known varieties, uniform, and stable over generations, tested in what is called DUS testing. ## In practice Most national PVP systems follow the [UPOV Convention](https://genetixbay.com/knowledge/glossary/upov.md). Typical protection is 20-25 years, longer for trees and vines. PVP usually includes a breeder's exemption, so others may use a protected variety to breed new ones, and many systems allow farmers to save seed for their own use within limits. In the US, the Plant Variety Protection Act covers seed-reproduced and, since 2018, asexually reproduced varieties, and [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) varieties have received certificates. The uniformity and stability requirements make PVP a high bar for many cannabis "strains", which are often one-generation crosses. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Plant patent / utility patent**: patent law, generally without a breeder's exemption. - **Trademark**: protects a name or brand, not the genetics. ## Related terms [UPOV](https://genetixbay.com/knowledge/glossary/upov.md), [Plant patent](https://genetixbay.com/knowledge/glossary/plant-patent.md), [Utility patent](https://genetixbay.com/knowledge/glossary/utility-patent.md), [Cultivar](https://genetixbay.com/knowledge/glossary/cultivar.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md) ## Read more - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. UPOV. 1991. International Convention for the Protection of New Varieties of Plants (1991 Act). https://www.upov.int/upovlex/en/conventions/1991/content.html 2. Plant Variety Protection Act, 7 U.S.C. 2321 et seq. --- # Plant virus > An infectious particle of nucleic acid in a protein coat that replicates inside plant cells; on cannabis, often insect-spread and incurable once infected. - Canonical: https://genetixbay.com/knowledge/glossary/plant-virus.html - Also written: plant viruses, virus, viral disease, mosaic virus, tobacco mosaic virus, TMV, alfalfa mosaic virus, lettuce chlorosis virus - Glossary category: Pests and diseases · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A plant virus is a submicroscopic pathogen made of RNA or DNA in a protein coat, which can only multiply inside living plant cells. Viruses reported on cannabis and [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) include [beet curly top virus](https://genetixbay.com/knowledge/glossary/beet-curly-top-virus.md) (spread by [leafhoppers](https://genetixbay.com/knowledge/glossary/leafhopper.md)), lettuce chlorosis virus (spread by *Bemisia* [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md)), alfalfa mosaic virus and cucumber mosaic virus (spread by [aphids](https://genetixbay.com/knowledge/glossary/aphid.md)), among others. Symptoms include mottling, mosaic patterns, leaf curl, yellowing and stunting. ## In practice There is no cure for a virus-infected plant. Management is [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md): clean propagation material, controlling the insect vectors, removing weeds that host viruses, and roguing infected plants early. Diagnosis needs a lab test such as ELISA or PCR, because symptoms overlap heavily with nutrient problems, genetic leaf variegation and [viroid](https://genetixbay.com/knowledge/glossary/viroid.md) infection. ## Myth check Tobacco mosaic virus (TMV) gets blamed for nearly any mottled cannabis leaf, and smokers' hands are often named as the source. TMV can infect cannabis experimentally, but confirmed natural cases on cannabis are rare. Mottled leaves usually have another cause. Label: Contested. See [HLVd and viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md). ## Don't confuse with - **Viroid**: no protein coat, no [genes](https://genetixbay.com/knowledge/glossary/gene.md). - **Genetic variegation**: stable in a cut, not spreading. ## Related terms [Viroid](https://genetixbay.com/knowledge/glossary/viroid.md), [Hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), [Beet curly top virus](https://genetixbay.com/knowledge/glossary/beet-curly-top-virus.md), [Leafhopper](https://genetixbay.com/knowledge/glossary/leafhopper.md), [Whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md) ## Read more - [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ## Sources 1. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 2. Hadad L, Luria N, Smith E, et al., 2019. Lettuce chlorosis virus disease: a new threat to cannabis production. Viruses 11(9):802. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6784094/ 3. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full --- # Pleiotropy > Pleiotropy is when a single gene affects two or more apparently unrelated traits, so selecting on one trait changes the others too. - Canonical: https://genetixbay.com/knowledge/glossary/pleiotropy.html - Also written: pleiotropic, pleiotropic gene, pleiotropic effect - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Pleiotropy is when one [gene](https://genetixbay.com/knowledge/glossary/gene.md) influences several traits. Change the [allele](https://genetixbay.com/knowledge/glossary/allele.md) and you change all of them at once, whether you wanted to or not. ## In practice Flowering-time genes are a good cannabis example. Kurtz et al. (2023) showed that the dose of the [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) allele in [triploid](https://genetixbay.com/knowledge/glossary/polyploid.md) plants changed both flowering timing and plant height. Breeders working autos therefore see height and timing move together, and cannot fully separate them by selection. Pleiotropy is one cause of correlated responses in breeding. Push hard for one trait and another drifts: a line selected only for fast finishing may lose yield; one selected only for potency may lose vigour. Good breeders track several traits at once for this reason and record what else changed. ## Don't confuse with - **Linkage**: two separate genes near each other, inherited together. Recombination can eventually break [linkage](https://genetixbay.com/knowledge/glossary/linkage.md); it cannot separate two effects of one gene. - **Epistasis**: two genes interacting on one trait. - **Environment**: a correlation between traits can also come from the room, such as a hot spot that speeds finishing and cuts yield. ## Related terms [Epistasis](https://genetixbay.com/knowledge/glossary/epistasis.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md), [Gene](https://genetixbay.com/knowledge/glossary/gene.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.md) ## Read more - [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md) ## Sources 1. Kurtz LE, Brand MH, Lubell-Brand JD. 2023. Gene dosage at the autoflowering locus effects flowering timing and plant height in triploid cannabis. Journal of the American Society for Horticultural Science 148(2):83-88. https://doi.org/10.21273/JASHS05293-23 2. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 --- # Pollen > Pollen is the fine powder released by male flowers that carries the male gametes; when it lands on a female's stigmas it fertilises the ovules and produces seed. - Canonical: https://genetixbay.com/knowledge/glossary/pollen.html - Also written: pollen grains, cannabis pollen, male pollen, pollen dust - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Pollen is the dust-like material shed by [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) (or [reversed female](https://genetixbay.com/knowledge/glossary/sex-reversal.md) flowers). Each grain carries a haploid nucleus that, on landing on a stigma, grows a tube to an ovule and fertilises it, producing a seed. Cannabis pollen is wind-dispersed, light and produced in huge quantities. ## In practice One male can seed a whole room. Breeders isolate males, collect pollen on paper or in a bag over the flowers, and apply it to chosen branches with a brush. Collected pollen stays viable for days at room temperature; drying it and storing it cold or frozen extends that substantially (Gaudet et al. 2020). [Germination](https://genetixbay.com/knowledge/glossary/germination.md) tests tell you whether stored pollen is still worth using. Outdoors, cannabis and [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) pollen can travel long distances on wind, which is why seed producers and flower growers near hemp fields worry about stray pollination. ## Don't confuse with - **Trichome resin**: the sticky, aromatic heads on [female flowers](https://genetixbay.com/knowledge/glossary/pistillate-flower.md). Pollen is dusty, yellowish and odourless by comparison. - **Pollen from a herm**: genetically from the same female, it spreads sex instability. - **Nanners**: slang for exposed male anthers on a female plant; the source of [herm](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) pollen, covered in the slang entry. ## Related terms [Pollination](https://genetixbay.com/knowledge/glossary/pollination.md), [Male selection](https://genetixbay.com/knowledge/glossary/male-selection.md), [STS](https://genetixbay.com/knowledge/glossary/sts.md), [Cross](https://genetixbay.com/knowledge/glossary/cross.md), [Regular seed](https://genetixbay.com/knowledge/glossary/regular-seed.md) ## Read more - [Collecting and storing cannabis pollen](https://genetixbay.com/knowledge/breeding/pollen-collection-storage.md) - [Pollination and seed production, step by step](https://genetixbay.com/knowledge/breeding/pollination-seed-production.md) ## Sources 1. Gaudet D, Yadav NS, Sorokin A, Bilichak A, Kovalchuk I. 2020. Development and optimization of a germination assay and long-term storage for Cannabis sativa pollen. Plants 9(5):665. https://doi.org/10.3390/plants9050665 --- # Pollen chucker > A pollen chucker is someone who crosses two popular plants, skips selection and testing, and sells or spreads the seed as a new line. - Canonical: https://genetixbay.com/knowledge/glossary/pollen-chucker.html - Also written: pollen chuckers, chucker, pollen-chucker, chuckers - Glossary category: Grower slang and culture · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A pollen chucker is someone who dusts one plant with another's pollen, collects the seed and releases it as a "new strain" without the work that makes a line: choosing parents for a goal, growing out large numbers, culling, testing for stability and [herm tendency](https://genetixbay.com/knowledge/glossary/herm-prone.md), and recording the lineage. The term describes a practice, not a person, and it is meant as criticism. ## In practice The typical pattern: two hyped [clone-only cuts](https://genetixbay.com/knowledge/glossary/clone-only.md), one cross, one tester round or none, a fancy name, and a drop. The resulting [F1 seed](https://genetixbay.com/knowledge/glossary/f1.md) can be spectacular in a few packs and a lottery in the rest, because nobody grew 100+ plants to see the spread. Pollen from a [reversed female](https://genetixbay.com/knowledge/glossary/sex-reversal.md) or a stressed plant that threw [bananas](https://genetixbay.com/knowledge/glossary/nanners.md) makes it worse, since the herm tendency goes straight into the seed. ## Don't confuse with - **Breeder**: works a population over generations with defined goals, large grow-outs, selection of males as well as females, and published records. - **Hobby cross**: a home grower making seed for their own garden and saying so honestly is not chucking. The problem is marketing an untested cross as a finished line. ## Myth check "Any cross is breeding." GenetixBay position (*Grower practice*, house standard): a cross is the first step, not the product. Herm-prone and unstable lines are mainly the result of chucking-style shortcuts, not natural cannabis behaviour. See [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Breeder](https://genetixbay.com/knowledge/glossary/breeder.md), [Chuck](https://genetixbay.com/knowledge/glossary/chuck.md), [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md), [Hype strain](https://genetixbay.com/knowledge/glossary/hype-strain.md), [F1](https://genetixbay.com/knowledge/glossary/f1.md) ## Read more - [Breeders vs pollen chuckers: what real cannabis breeding looks like](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) --- # Pollination > Pollination is the transfer of pollen onto a female flower's stigmas; in cannabis it is usually by wind, or by hand when breeders pollinate chosen branches to make seed. - Canonical: https://genetixbay.com/knowledge/glossary/pollination.html - Also written: pollinating, pollinate, pollinated, hand pollination, seeding a branch, branch pollination - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Pollination is moving pollen onto the [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md) of a [female flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md). Fertilisation follows when the pollen tube reaches the ovule, and a seed develops inside the [calyx](https://genetixbay.com/knowledge/glossary/calyx.md) over the following weeks. Cannabis is naturally wind-pollinated. ## In practice Breeders pollinate deliberately and selectively. A common approach is to brush pollen onto one or two lower branches of a female a few weeks into flower, then mist the room and plant to kill stray pollen. The rest of the plant gives seedless flower, and the pollinated branch matures seed. Each pollinated branch is labelled with the cross and the date. Unplanned pollination is the grower's nightmare: one male or one [herm](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) can seed a room, lowering flower yield and quality as the plant puts energy into seed. It also gives seed with an unknown, often unstable, father. ## Don't confuse with - **Fertilisation**: the fusion after pollination; pollination can happen without fertilisation if the pollen is dead. - **Open pollination**: letting a population pollinate freely, as a breeding method. - **Selfing**: pollinating a plant with its own pollen. ## Related terms [Pollen](https://genetixbay.com/knowledge/glossary/pollen.md), [Cross](https://genetixbay.com/knowledge/glossary/cross.md), [Open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md), [Seed run](https://genetixbay.com/knowledge/glossary/seed-run.md), [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md) ## Read more - [Pollination and seed production, step by step](https://genetixbay.com/knowledge/breeding/pollination-seed-production.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Gaudet D, Yadav NS, Sorokin A, Bilichak A, Kovalchuk I. 2020. Development and optimization of a germination assay and long-term storage for Cannabis sativa pollen. Plants 9(5):665. https://doi.org/10.3390/plants9050665 --- # Polyhybrid > A polyhybrid is a cultivar whose recent ancestry mixes many different lines, so its seed segregates widely and rarely breeds true. - Canonical: https://genetixbay.com/knowledge/glossary/polyhybrid.html - Also written: polyhybrids, poly-hybrid, multi-hybrid, complex hybrid - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A polyhybrid is a cultivar built from many different parent lines in recent generations: a hybrid crossed with another hybrid crossed with a third. Its genome is a patchwork, [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) at many loci, and its seed [segregates](https://genetixbay.com/knowledge/glossary/segregation.md) widely. ## In practice Most current market cultivars are polyhybrids. That explains common grower experiences: a pack of seed from a famous cross produces plants that look and smell very different from each other; seed saved from a great polyhybrid clone throws a scatter of types; and "the same name" from two sources behaves differently. Polyhybrids are not bad. They can be vigorous, productive and full of variation to select from. But they are poor material for anyone who wants a predictable seed line, and they are part of why commercial cannabis is converging on similar profiles. Breeding polyhybrids from polyhybrids, with little [stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md), multiplies the problem. ## Don't confuse with - **Polyploid**: extra [chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md) sets; unrelated, despite the similar word. - **F1 hybrid**: a single cross, possibly uniform if the parents were inbred. - **Landrace**: a population with a long local history and coherent type. - **IBL**: stabilised by [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) and selection, the opposite end of the scale. ## Related terms [Hybrid](https://genetixbay.com/knowledge/glossary/hybrid.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Segregation](https://genetixbay.com/knowledge/glossary/segregation.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md) ## Read more - [Polyhybrids vs landraces: what each gives a breeder](https://genetixbay.com/knowledge/breeding/polyhybrids-vs-landraces.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Henry P, Khatodia S, Kapoor K, et al. 2020. A single nucleotide polymorphism assay sheds light on the extent and distribution of genetic diversity, population structure and functional basis of key traits in cultivated north American cannabis. Journal of Cannabis Research 2:26. --- # Polyploid > A polyploid plant carries more than two full sets of chromosomes, such as a triploid (three) or tetraploid (four); in cannabis these are almost always bred deliberately. - Canonical: https://genetixbay.com/knowledge/glossary/polyploid.html - Also written: polyploidy, triploid, tetraploid, polyploids, chromosome doubling - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A polyploid has more than two complete [chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md) sets. In cannabis the relevant types are tetraploids (4n = 40), usually made by treating seedlings or tissue-culture shoots with chemicals that block cell division and double the chromosomes, and triploids (3n = 30), produced by crossing a tetraploid with a [diploid](https://genetixbay.com/knowledge/glossary/diploid.md). ## In practice Triploids are the main commercial interest. Their uneven chromosome number makes meiosis fail, so they are largely sterile and set very little seed even when pollen drifts in. That makes them attractive for outdoor and [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) crops near pollen sources. Kurtz et al. (2023) used triploids to show that the dose of the [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) [allele](https://genetixbay.com/knowledge/glossary/allele.md) changes flowering time and plant height. Tetraploids are larger-celled and sometimes larger-flowered, but bigger plants do not automatically mean more [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). Claims of higher potency from polyploidy are not consistently supported. Polyploid lines also inherit in more complex ratios, so [stabilising](https://genetixbay.com/knowledge/glossary/stabilisation.md) them is slower. ## Don't confuse with - **Diploid**: the normal two sets. - **Polyhybrid**: a hybrid with many ancestors. Unrelated to chromosome number, despite the similar word. - **Mutation**: polyploidy changes whole chromosome sets, not single genes. ## Related terms [Diploid](https://genetixbay.com/knowledge/glossary/diploid.md), [Chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md), [Mutation](https://genetixbay.com/knowledge/glossary/mutation.md), [Tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md) ## Read more - [Tissue culture basics for cannabis growers and breeders](https://genetixbay.com/knowledge/breeding/tissue-culture-basics.md) ## Sources 1. Kurtz LE, Brand MH, Lubell-Brand JD. 2023. Gene dosage at the autoflowering locus effects flowering timing and plant height in triploid cannabis. Journal of the American Society for Horticultural Science 148(2):83-88. https://doi.org/10.21273/JASHS05293-23 2. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 --- # Popcorn buds > Popcorn buds are small, separate buds, usually from lower branches, often sold cheaper as "smalls" though they can be the same quality as the tops. - Canonical: https://genetixbay.com/knowledge/glossary/popcorn-buds.html - Also written: popcorn, popcorn nugs, popcorns, smalls - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Popcorn buds are small, round buds about the size of a popcorn kernel to a thumbnail, usually from lower branches or side shoots. Retail calls them "smalls". ## In practice Because they are small, popcorn buds sell for less than large [colas](https://genetixbay.com/knowledge/glossary/cola.md) from the same plant. Chemically they can be close to the [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) if they had decent light, though buds deep in the shade usually test somewhat lower. They dry faster than big colas, so a mixed batch needs attention to avoid [over-drying](https://genetixbay.com/knowledge/glossary/over-drying.md) the small ones. Many growers reduce popcorn by removing the weakest lower sites early, or by training so more sites reach the top of the canopy, where light is strongest. Others keep them on purpose as a personal stash of good flower at no extra cost. ## Don't confuse with - **Larf**: airy and underdeveloped; popcorn can be dense. - **Shake**: broken fragments, not whole small buds. ## Related terms [Larf](https://genetixbay.com/knowledge/glossary/larf.md), [Nugs](https://genetixbay.com/knowledge/glossary/nugs.md), [Shake](https://genetixbay.com/knowledge/glossary/shake.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md) ## Read more - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) --- # Possession limit > A possession limit is the maximum amount of cannabis a person may legally carry or keep, usually set by weight of dried flower or an equivalent. - Canonical: https://genetixbay.com/knowledge/glossary/possession-limit.html - Also written: possession limits, possession cap, public possession limit, legal limit (possession) - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A possession limit is the legal maximum quantity of cannabis an individual may have. Laws often set different limits for public possession and for storage at home, and convert other products (edibles, concentrates, seeds, plants) into "dried flower equivalents". ## In practice Common limits are written in grams (for example around 30 g of dried flower in some places) or in ounces (1 oz in others), but the figures, the equivalences and the treatment of home-grown harvest differ widely. A legal [home grow](https://genetixbay.com/knowledge/glossary/home-grow.md) can produce more than the possession limit allows you to keep, so some laws carve out an exception for cannabis stored where it was grown; others do not. Exceeding the limit can be treated as intent to supply. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Personal cultivation limit**: how many plants you may grow. - **Purchase limit**: how much a store may sell you in one transaction. ## Related terms [Ounce](https://genetixbay.com/knowledge/glossary/ounce.md), [Gram](https://genetixbay.com/knowledge/glossary/gram.md), [Home grow](https://genetixbay.com/knowledge/glossary/home-grow.md), [Decriminalisation vs legalisation](https://genetixbay.com/knowledge/glossary/decriminalisation.md) --- # Pot size > Pot size is the volume of medium a plant roots into; bigger pots give bigger plants within reason, but feeding frequency can let small pots punch well above their size. - Canonical: https://genetixbay.com/knowledge/glossary/pot-size.html - Also written: container size, pot volume, root volume, rooting volume, what size pot - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Pot size is the volume of growing medium available to one plant, usually given in litres or US gallons (1 US gal = 3.785 L). Across many crops, plant biomass rises with rooting volume: a meta-analysis found that doubling pot volume increased plant size by roughly 43% on average. ## In practice Common indoor sizes are 11-25 L (3-7 gal) for [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md) and 11-15 L (3-4 gal) for [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md). Larger pots buffer water and nutrients, so they forgive missed waterings. Smaller pots dry faster, which allows more frequent feeding and tighter control. ## Myth check House position: bigger pots give bigger [yields](https://genetixbay.com/knowledge/glossary/yield.md), within reason, but root volume is not the whole story. It is a trade-off against feeding frequency. The founder has grown more than 4 oz (113 g) dry from a 16 oz (about 0.5 L) cup by pushing water and nutrients hard with [high-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md). A small pot fed many times a day can match a big pot watered every few days; a small pot watered like a big one will starve. See [drain-to-waste and crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md). ## Don't confuse with - **Root-bound**: a symptom of a pot being too small for the watering regime, not a fixed property of pot size. ## Related terms [Root-bound](https://genetixbay.com/knowledge/glossary/root-bound.md), [High-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md), [Fabric pot](https://genetixbay.com/knowledge/glossary/fabric-pot.md), [Up-potting](https://genetixbay.com/knowledge/glossary/up-potting.md), [Yield](https://genetixbay.com/knowledge/glossary/yield.md) ## Read more - [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.md) - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) ## Sources 1. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Potassium > Potassium (K) is a mobile macronutrient that controls water balance, stomata and enzyme activity; deficiency scorches the edges of older leaves. - Canonical: https://genetixbay.com/knowledge/glossary/potassium.html - Also written: K, K+, kalium, potassium deficiency, K deficiency - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Potassium is a [macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md) taken up as the K+ ion. It is not built into structures; it stays dissolved in the cell sap, where it regulates osmotic pressure, opens and closes stomata, activates dozens of enzymes and moves sugars through the phloem. It is highly mobile. ## In practice [Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) starts on older and middle leaves as yellowing and then brown, crispy margins and tips, sometimes with rust-like spotting. Hydro feeds commonly carry about 150-300 mg/L (ppm) K. Saloner and colleagues found cannabis needs less K than many bottle labels suggest, and that very high K mostly crowds out calcium and magnesium uptake rather than adding yield. ## Units and formula Labels state potassium as K2O. Elemental K = K2O × 0.830. [Potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md) (13-0-46) is about 38% K; [monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) is about 28.7% K. ## Don't confuse with - **Nutrient burn**: [tip burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) from overall high [EC](https://genetixbay.com/knowledge/glossary/ec.md), not specifically low K. - **Magnesium deficiency**: [interveinal yellowing](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) on older leaves; K deficiency hits the leaf edges first. - **Potash**: a trade word for potassium salts, not a separate nutrient. ## Related terms [Macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md), [Potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md), [Potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), [Guaranteed analysis](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md) ## Read more - [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md) ## Sources 1. Saloner A, Sacks MM, Bernstein N. 2019. Response of medical cannabis (Cannabis sativa L.) genotypes to K supply under long photoperiod. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Potassium nitrate > Potassium nitrate (KNO3) is a soluble fertiliser salt supplying about 13% nitrogen as nitrate and 38% potassium, used in both veg and flower feeds. - Canonical: https://genetixbay.com/knowledge/glossary/potassium-nitrate.html - Also written: KNO3, saltpetre, saltpeter, 13-0-46, nitrate of potash - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Potassium nitrate is a salt of potassium and [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), sold as fertiliser grade 13-0-46. That means 13% N and 46% K2O, which is about 38% elemental K. It is fully soluble and contains no [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) or [sodium](https://genetixbay.com/knowledge/glossary/sodium.md). ## In practice It is the main way to add potassium while also adding nitrogen. It is compatible with [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), so it can sit in either the A or the B stock. Shifting part of the potassium from potassium nitrate to [potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md) or [MKP](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) lowers nitrogen while keeping K steady, which is one way per-element feeds taper N in late flower. Store it away from heat and combustibles, as it is an oxidiser. ## Units and formula 1 g/L gives about 130 mg/L (ppm) N and 380 mg/L K. ## Don't confuse with - **Potassium sulfate**: supplies K and S, no nitrogen. - **Sodium nitrate (Chile saltpetre)**: brings sodium, not wanted in cannabis feeds. - **Potassium chloride (muriate of potash)**: brings chloride; avoided in hydro. ## Related terms [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Guaranteed analysis](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Potassium silicate > Potassium silicate is a strongly alkaline liquid or powder used to add silicon (and some potassium) to feeds; it goes into the water first, before other nutrients. - Canonical: https://genetixbay.com/knowledge/glossary/potassium-silicate.html - Also written: K2SiO3, liquid silica, potassium silicate solution, water glass (potassium) - Glossary category: Nutrients · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Potassium silicate is a salt of potassium and silicate, sold as a viscous liquid or soluble powder. Analysis varies by product, so read the label for [SiO2](https://genetixbay.com/knowledge/glossary/silica.md) and K2O content. In water it forms [silicic acid](https://genetixbay.com/knowledge/glossary/silicon.md), the form roots absorb. Its solutions are strongly alkaline. ## In practice Add it to plain water first, stir, then add the other nutrients, then adjust [pH](https://genetixbay.com/knowledge/glossary/ph.md). Adding it to a finished feed, or mixing it with concentrates, can make the silicate polymerise into a gel or precipitate, and it can drag calcium and [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md) out with it. Expect it to raise pH noticeably; dose before the pH-down step. Typical use aims for tens of mg/L (ppm) of Si in the final solution. It also contributes potassium, which counts towards the feed's K total. ## Don't confuse with - **Silica**: silicon dioxide; the word is used loosely for any silicon supplement. - **Monosilicic acid products**: [stabilised](https://genetixbay.com/knowledge/glossary/stabilisation.md) silicic acid, a different formulation. - **Sodium silicate (water glass)**: brings [sodium](https://genetixbay.com/knowledge/glossary/sodium.md), unsuitable for cannabis. ## Related terms [Silicon](https://genetixbay.com/knowledge/glossary/silicon.md), [Silica](https://genetixbay.com/knowledge/glossary/silica.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md) ## Read more - [Silicon (Si) for cannabis: beneficial, not essential, and how to dose it](https://genetixbay.com/knowledge/nutrients/silicon.md) ## Sources 1. Epstein E. 1994. The anomaly of silicon in plant biology. PNAS 91(1):11-17. https://doi.org/10.1073/pnas.91.1.11 2. Guerriero G, Deshmukh R, Sonah H, Sergeant K, Hausman JF, Lentzen E, Valle N, Siddiqui KS, Exley C. 2019. Identification of the aquaporin gene family in Cannabis sativa and evidence for the accumulation of silicon in its tissues. Plant Science 287:110167. https://doi.org/10.1016/j.plantsci.2019.110167 --- # Potassium sulfate > Potassium sulfate (K2SO4) supplies roughly 41-45% potassium and 17-18% sulfur with no nitrogen, useful for adding K while tapering N in late flower. - Canonical: https://genetixbay.com/knowledge/glossary/potassium-sulfate.html - Also written: K2SO4, sulfate of potash, SOP, potassium sulphate, 0-0-50 - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Potassium sulfate is the salt of potassium and [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md). Pure K2SO4 is about 44.9% K and 18.4% S; fertiliser grades are commonly sold as 0-0-50 or 0-0-52 (K2O), roughly 41-43% K. Solubility is lower than most hydro salts, around 110 g/L at room temperature, so concentrated stocks are limited. ## In practice It is the go-to salt for raising potassium without raising nitrogen. In [per-element feeding](https://genetixbay.com/knowledge/glossary/per-element-dosing.md), swapping some [potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md) for potassium sulfate is how growers taper N in late flower while holding K steady. It belongs in the B stock, away from concentrated calcium, because calcium sulfate precipitates. Use soluble or "greenhouse" grade; agricultural granules can contain insoluble residue. ## Units and formula 1 g/L of pure salt gives about 449 mg/L (ppm) K and 184 mg/L S. ## Don't confuse with - **Potassium chloride (muriate of potash, MOP)**: cheaper but adds [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md). - **Potassium nitrate**: supplies nitrogen with the potassium. - **Potassium magnesium sulfate (langbeinite)**: a mixed mineral with Mg too. ## Related terms [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), [Potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md), [Sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Potency ceiling > The potency ceiling is the practical upper limit of cannabinoid content in dried flower; GenetixBay holds that flower labelled above about 35% total cannabinoids is not credible. - Canonical: https://genetixbay.com/knowledge/glossary/potency-ceiling.html - Also written: THC ceiling, potency limit, max THC flower, 35% limit, flower potency ceiling, how high can THC go - Glossary category: Lab testing · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The potency ceiling is the idea that dried cannabis flower can only contain so much [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md), because cannabinoids are made only in the heads of capitate glandular trichomes and the rest of the bud is bract, leaf, stem and water. GenetixBay's house position is that flower above about 35% [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) is not credible. The founder credits Dr. Dedi Meiri with stating this limit at a seminar (publication pending). ## In practice Build it from first principles. Separated [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), the purest form of the resin, typically test around 50-70% total cannabinoids. For flower to hit 40%, well over half its [dry mass](https://genetixbay.com/knowledge/glossary/dry-weight.md) would have to be pure gland heads, while a dried bud is mostly plant tissue by weight. Add water: at 10-12% moisture, part of the weight is water. Add the [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) conversion: a raw [THCA](https://genetixbay.com/knowledge/glossary/thca.md) total overstates real [THC](https://genetixbay.com/knowledge/glossary/thc.md). Numbers of 40%+ come from concentrates, [lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md), basis tricks or inflated testing. ## Units and formula Rough check: flower % ≈ (share of dry mass that is gland heads) × (cannabinoid % of head material) × (1 - moisture). Total THC = Δ9-THC + 0.877 × THCA. ## Myth check Buyer beware: "our seeds will hit 42%" is marketing, not chemistry. Even 30% is a real feat. Evidence: Supported (label studies; Meiri seminar remarks). See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Label inflation](https://genetixbay.com/knowledge/glossary/label-inflation.md), [Lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md), [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), [Total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Meiri D. Seminar remarks (personal attendance by the GenetixBay founder); publication pending. 2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 3. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 --- # Potency testing > Potency testing is laboratory measurement of a sample's cannabinoid content, normally by HPLC, reported as % w/w or mg/g for each cannabinoid plus calculated totals. - Canonical: https://genetixbay.com/knowledge/glossary/potency-testing.html - Also written: potency test, cannabinoid testing, cannabinoid profile test, THC test, potency analysis, cannabinoid potency - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Potency testing quantifies the [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) in a sample. The standard approach is [high-performance liquid chromatography](https://genetixbay.com/knowledge/glossary/hplc.md) with UV detection (HPLC-UV), which measures acid and [neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md) separately without heating them. The lab weighs a homogenised portion, extracts it with solvent, runs it against calibrated reference standards and reports each compound and the calculated totals. ## In practice Results depend heavily on steps before the instrument: which buds were sampled, how well they were ground and mixed, whether moisture was corrected, and how the lab calibrates. Jikomes and Zoorob (2018) showed that results in a regulated market differed systematically between labs, and Schwabe et al. (2023) found many retail labels well above independently measured values. For a home grower, one test of a well-mixed sample of several buds is far more useful than a single [top cola](https://genetixbay.com/knowledge/glossary/cola.md). ## Don't confuse with - **Terpene test**: measures aroma compounds, usually by [GC](https://genetixbay.com/knowledge/glossary/gas-chromatography.md). - **Genotyping**: reads DNA, can predict [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) class but not percentage. - **Home test kits**: colour or thin-layer kits give rough estimates, not COA-grade numbers. ## Myth check A higher number from a different lab is not proof of a better plant. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [HPLC](https://genetixbay.com/knowledge/glossary/hplc.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Homogenisation (sampling)](https://genetixbay.com/knowledge/glossary/homogenisation.md), [Measurement uncertainty](https://genetixbay.com/knowledge/glossary/measurement-uncertainty.md), [Label inflation](https://genetixbay.com/knowledge/glossary/label-inflation.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 3. Berman P, Futoran K, Lewitus GM, Mukha D, Benami M, Shlomi T, Meiri D. 2018. A new ESI-LC/MS approach for comprehensive metabolic profiling of phytocannabinoids in Cannabis. Scientific Reports 8:14280. https://doi.org/10.1038/s41598-018-32651-4 --- # Potting mix > Potting mix is a manufactured container medium, usually peat or coco with perlite, lime and starter fertiliser, designed to drain and hold air better than garden soil. - Canonical: https://genetixbay.com/knowledge/glossary/potting-mix.html - Also written: potting soil, potting compost, container mix, bagged soil, growing mix - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A potting mix is a blended container medium. Most are [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) despite the name "potting soil": a base of peat, coco or composted bark, an aerating component such as [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) or pumice, lime to set the [pH](https://genetixbay.com/knowledge/glossary/ph.md), often a wetting agent, and a starter charge of nutrients. Some add compost, worm castings or slow-release fertiliser. They are designed for containers, where native soil would compact and waterlog. ## In practice A good cannabis mix [drains](https://genetixbay.com/knowledge/glossary/runoff.md) freely, has visible perlite or bark, smells earthy rather than sour, and is not heavy or sticky. "Lightly amended" mixes feed [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and young plants for about two to four weeks before liquid feeding is needed; "hot" mixes rich in [organic nutrients](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md) can burn seedlings. Check the pH is roughly 6.0-7.0. Mixes for seed starting are finer and lower in fertiliser. Many growers add extra perlite (20-30%) to standard bags to increase [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md). ## Don't confuse with - **Garden soil**: native mineral soil; poor in containers on its own. - **Super soil**: a heavily amended organic mix designed to feed through most of the grow. ## Related terms [Soil](https://genetixbay.com/knowledge/glossary/soil.md), [Peat](https://genetixbay.com/knowledge/glossary/peat.md), [Perlite](https://genetixbay.com/knowledge/glossary/perlite.md), [Soilless](https://genetixbay.com/knowledge/glossary/soilless.md), [Super soil](https://genetixbay.com/knowledge/glossary/super-soil.md) ## Read more - [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Pour-through > A standard way to sample root-zone pH and EC: water the pot to saturation, wait 30 minutes to 2 hours, then pour a set volume of distilled water on top and measure the first liquid that drains out. - Canonical: https://genetixbay.com/knowledge/glossary/pour-through.html - Also written: pour-through test, pour-through method, pourthru, leachate test - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The pour-through method is an extension-standard way to read the [pH](https://genetixbay.com/knowledge/glossary/ph.md) and [EC](https://genetixbay.com/knowledge/glossary/ec.md) of the solution around the roots without disturbing them. The medium is saturated, allowed to settle, then enough water is poured on to push out about 50 mL of [leachate](https://genetixbay.com/knowledge/glossary/watering-to-runoff.md), which is measured (NC State / NCDA&CS). ## In practice Do it the same way every time, at the same time after feeding, and track the trend. [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md) well above input EC means salts are building up; much lower means the plant is hungry or over-leached. [Runoff](https://genetixbay.com/knowledge/glossary/runoff.md) pH far from input pH means the medium is drifting. ## Don't confuse with - **Slurry test**: measures a sample of medium mixed with water. - **Root-zone flush**: heavy watering to wash salts out, not a measurement. ## Related terms [Slurry test](https://genetixbay.com/knowledge/glossary/slurry-test.md), [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), [Runoff](https://genetixbay.com/knowledge/glossary/runoff.md), [Watering to runoff](https://genetixbay.com/knowledge/glossary/watering-to-runoff.md) ## Read more - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) - [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ## Sources 1. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction --- # Powdery mildew > A fungal disease, on cannabis caused mainly by Golovinomyces ambrosiae, that grows as white powdery patches on leaves and buds and thrives in moderate humidity. - Canonical: https://genetixbay.com/knowledge/glossary/powdery-mildew.html - Also written: PM, WPM, white powdery mildew, Golovinomyces ambrosiae, Golovinomyces cichoracearum, Erysiphales - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Powdery mildew is a fungal disease caused by obligate parasites in the order Erysiphales that live on the plant surface. On cannabis the main species is *Golovinomyces ambrosiae*, which was previously reported as *G. cichoracearum*. It forms white, flour-like patches of mycelium and spores on leaves, stems and, later, buds. Infected tissue yellows, [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) drops and buds become unsellable. ## In practice Unlike most fungi, powdery mildew does not need free water on the leaf, and moderate humidity, still air and low light within the canopy favour it. It is spread by airborne spores and on clones; the fungus has also been reported to persist inside some infected plant material. [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) is airflow, sensible humidity, [plant spacing](https://genetixbay.com/knowledge/glossary/plant-density.md) and clean starting material. Resistance [genes](https://genetixbay.com/knowledge/glossary/gene.md) such as *PM1* have been mapped, so cultivar choice matters. Once it reaches flowers, options are very limited; check what is registered for cannabis locally. ## Don't confuse with - **Trichomes**: [resin glands](https://genetixbay.com/knowledge/glossary/trichome.md) on buds and [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md); mildew spreads across [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) too and wipes off as dust. - **Downy mildew**: a water mould with grey-purple growth under leaves and yellow patches above. - **Spray residue or hard-water spots**: no spreading growth. ## Related terms [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md), [Sulfur burner](https://genetixbay.com/knowledge/glossary/sulfur-burner.md), [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Downy mildew](https://genetixbay.com/knowledge/glossary/downy-mildew.md) ## Read more - [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) - [White powder or white spots on cannabis leaves: a differential](https://genetixbay.com/knowledge/diagnosis/white-powder-on-leaves.md) ## Sources 1. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew 2. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 3. Mihalyov PD, Garfinkel AR, 2021. Discovery and genetic mapping of PM1, a powdery mildew resistance gene in Cannabis sativa L. Frontiers in Agronomy 3:720215. https://www.frontiersin.org/articles/10.3389/fagro.2021.720215/full --- # PPF > Photosynthetic photon flux: the total number of PAR photons a light fixture emits each second, in µmol/s, regardless of where they land. - Canonical: https://genetixbay.com/knowledge/glossary/ppf.html - Also written: photosynthetic photon flux, fixture PPF, total PPF, µmol/s output - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" PPF (photosynthetic photon flux) is the total output of [PAR](https://genetixbay.com/knowledge/glossary/par.md) photons from a fixture, in micromoles per second (µmol/s). It is measured in an integrating sphere, so it describes the lamp, not your canopy. Divide PPF by the fixture's wattage and you get [photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) (µmol/J), the single most useful number for comparing fixtures on running cost. ## In practice A 600 W [LED fixture](https://genetixbay.com/knowledge/glossary/led.md) rated at 1,620 µmol/s has an efficacy of 2.7 µmol/J. If every photon landed evenly on a 1.2 × 1.2 m (4 × 4 ft) canopy of 1.44 m², the average [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) would be about 1,125 µmol/m²/s. In reality some photons hit the walls or miss the canopy, so expect a lower average; reflective tent walls recover part of the loss. PPF tells you how much light you bought. PPFD tells you how much light the plants get. You need both: a high-PPF fixture hung badly can still leave the corners dim. ## Units and formula - PPF in µmol/s. - Average PPFD (ideal) ≈ PPF ÷ [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md) (m²). - Efficacy (µmol/J) = PPF (µmol/s) ÷ input power (W). ## Don't confuse with - **PPFD**: photons per square metre per second at the canopy, measured with a quantum sensor. - **Wattage**: power drawn from the wall, which says nothing about light output on its own. - **Lumens**: the human-eye version of output, irrelevant to [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md). ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), [PAR](https://genetixbay.com/knowledge/glossary/par.md), [LED](https://genetixbay.com/knowledge/glossary/led.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # PPFD > Photosynthetic photon flux density: the number of PAR photons landing on one square metre each second, in µmol/m²/s; the standard measure of light intensity at the canopy. - Canonical: https://genetixbay.com/knowledge/glossary/ppfd.html - Also written: photosynthetic photon flux density, PAR reading, µmol/m²/s, umol/m2/s, light density - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" PPFD (photosynthetic photon flux density) is the rate at which [PAR](https://genetixbay.com/knowledge/glossary/par.md) photons strike a surface, in micromoles per square metre per second (µmol/m²/s). It is what a quantum (PAR) meter reads, and it is the number to use when setting light height and dimmer levels. Full summer sun at noon is roughly 2,000 µmol/m²/s. ## In practice Typical indoor targets without added [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md): | Stage | PPFD (µmol/m²/s) | |---|---| | Clones and [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) | 100–300 | | Veg | 400–700 | | Flower | 700–1,100 | | Flower with CO2 at 800–1,200 ppm | up to about 1,500 | Cannabis keeps converting extra light into yield further than most crops. Rodriguez-Morrison and colleagues (2021) saw flower yield rise roughly linearly up to about 1,800 µmol/m²/s, and Llewellyn and colleagues (2022) found yield proportional to intensity. Past about 1,000 µmol/m²/s, though, heat, [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), CO2 and nutrition must keep up or the extra light shows up as [bleaching](https://genetixbay.com/knowledge/glossary/light-stress.md) instead of weight. *Established*. Measure a grid of points (centre, corners, edges) at canopy height, not one reading under the middle of the fixture. ## Units and formula [DLI](https://genetixbay.com/knowledge/glossary/dli.md) (mol/m²/day) = PPFD × hours of light × 0.0036. ## Don't confuse with - **PPF**: total fixture output in µmol/s, not per area. - **DLI**: the daily total; the same PPFD gives a higher DLI on longer days. - **Lux**: an eye-weighted brightness unit that misleads under grow lights. ## Related terms [DLI](https://genetixbay.com/knowledge/glossary/dli.md), [PPF](https://genetixbay.com/knowledge/glossary/ppf.md), [PAR](https://genetixbay.com/knowledge/glossary/par.md), [Light saturation point](https://genetixbay.com/knowledge/glossary/light-saturation-point.md), [Light intensity](https://genetixbay.com/knowledge/glossary/light-intensity.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 3. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x --- # ppm of an element > Ppm of an element means milligrams of that element per litre of solution (mg/L), the unit nutrient recipes use; it is not the ppm shown on an EC meter. - Canonical: https://genetixbay.com/knowledge/glossary/elemental-ppm.html - Also written: elemental ppm, mg/L of an element, ppm N, ppm per element, parts per million (nutrient) - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In nutrient recipes, "ppm" of an element means parts per million by mass, which in water equals milligrams of that element per litre (mg/L). "150 ppm N" means 150 mg of nitrogen per litre, whatever salt it came from. Research papers often use mmol/L instead. ## In practice A recipe written in elemental ppm lets growers compare feeds and build their own. To find how much of a salt delivers a target, use its percentage: 1 g/L of a salt supplies (percent × 10) mg/L of each element. [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md) at 19% Ca gives 190 ppm Ca per g/L, so 150 ppm Ca needs about 0.79 g/L. ## Units and formula - mg/L of element = g/L of salt × element % × 10 - mmol/L × atomic mass = mg/L (N 14.0, P 31.0, K 39.1, Ca 40.1, Mg 24.3, S 32.1) ## Don't confuse with - **EC meter ppm (ppm500 / ppm700)**: an estimate of total dissolved salts converted from [electrical conductivity](https://genetixbay.com/knowledge/glossary/ec.md), not a count of any element. 1.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) reads about 500 or 700 "ppm" depending on scale. - **Oxide ppm**: some charts quote P2O5 or K2O instead of P or K; convert first. ## Related terms [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md), [Guaranteed analysis](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Feed chart](https://genetixbay.com/knowledge/glossary/feed-chart.md) ## Read more - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # ppm500 > ppm500 is the TDS scale that converts EC to ppm with a factor of 0.5 (based on sodium chloride), so 1.0 mS/cm reads 500 ppm. - Canonical: https://genetixbay.com/knowledge/glossary/ppm500.html - Also written: 500 scale, ppm 500, NaCl scale, TDS 500, 0.5 conversion, NaCl ppm - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" ppm500 (the 500 scale, NaCl scale) is the most common ppm scale on handheld [TDS](https://genetixbay.com/knowledge/glossary/tds.md) meters. The meter measures [EC](https://genetixbay.com/knowledge/glossary/ec.md) and multiplies by 0.5, a factor that approximates the relationship between conductivity and dissolved mass for a [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) solution. It is the usual default on meters sold in North America. ## In practice A reservoir at 1.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) reads 800 ppm on a 500-scale meter. The same reservoir reads 1,120 ppm on a 700-scale meter. Neither is wrong; they are different conversions of the same EC. Trouble starts when growers copy a chart written for one scale with a meter set to the other, and over- or under-feed by 40%. If your meter's manual says "NaCl" or "0.5", you are on ppm500. When in doubt, switch to EC mode and work in mS/cm. ## Units and formula - ppm500 = EC (mS/cm) × 500 - EC (mS/cm) = ppm500 ÷ 500 - [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md) = ppm500 × 1.4 ## Don't confuse with - **ppm700**: the 442 scale, which reads 40% higher for the same solution. - **ppm of an element in a recipe**: a true concentration, not a meter scale. ## Related terms [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), [TDS](https://genetixbay.com/knowledge/glossary/tds.md), [Conversion factor](https://genetixbay.com/knowledge/glossary/conversion-factor.md) ## Read more - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) ## Sources 1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality 2. University of California Cooperative Extension, Ventura County. Salinity units and conversions (640 ppm = 1 dS/m). https://ucanr.edu/node/125832 --- # ppm700 > ppm700 is the TDS scale that converts EC to ppm with a factor of 0.7 (the 442 natural-water standard), so 1.0 mS/cm reads 700 ppm. - Canonical: https://genetixbay.com/knowledge/glossary/ppm700.html - Also written: 700 scale, ppm 700, 442 scale, TDS 700, 0.7 conversion, natural water scale - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" ppm700 (the 700 scale) converts [EC](https://genetixbay.com/knowledge/glossary/ec.md) to ppm by multiplying by about 0.7. It is based on the "442" natural-water reference, a mixture of 40% [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), 40% sodium bicarbonate and 20% sodium [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) meant to mimic the ions in fresh water. It is common on meters sold in Europe and Australia and in some nutrient charts. ## In practice A solution at 1.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) reads 1,120 ppm on a 700-scale meter and 800 ppm on a 500-scale meter. If a [feeding chart](https://genetixbay.com/knowledge/glossary/feed-chart.md) says "1,000 ppm in flower" and does not say which scale, it could mean 1.43 mS/cm (700 scale) or 2.0 mS/cm ([500 scale](https://genetixbay.com/knowledge/glossary/ppm500.md)). That is a big gap at the plant. Check your meter's manual or settings for "442" or "0.7". When sharing numbers, give [EC in](https://genetixbay.com/knowledge/glossary/input-ec.md) mS/cm, or at least label ppm as ppm500 or ppm700. ## Units and formula - ppm700 = EC (mS/cm) × 700 - EC (mS/cm) = ppm700 ÷ 700 - ppm500 = ppm700 ÷ 1.4 ## Don't confuse with - **ppm500**: the NaCl scale; 40% lower readings for the same solution. - **ppm640**: a factor used in some agronomy references (640 ppm per dS/m). ## Related terms [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), [TDS](https://genetixbay.com/knowledge/glossary/tds.md), [Conversion factor](https://genetixbay.com/knowledge/glossary/conversion-factor.md) ## Read more - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) ## Sources 1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality 2. University of California Cooperative Extension, Ventura County. Salinity units and conversions (640 ppm = 1 dS/m). https://ucanr.edu/node/125832 --- # Pre-flower > The first individual flowers that form at stem nodes during late vegetative growth, letting a grower tell male from female before full flowering. - Canonical: https://genetixbay.com/knowledge/glossary/pre-flower.html - Also written: preflower, pre-flowers, preflowers, pre flower, primordia, sex primordia - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Pre-flowers are solitary flowers that develop at the nodes of a maturing cannabis plant, usually behind the stipules, before the plant switches to full flowering. They appear because the plant has reached sexual maturity, not because of a change in [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md), so photoperiod plants show them in veg. ## In practice On photoperiod [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md), pre-flowers usually show about 4-6 weeks from [germination](https://genetixbay.com/knowledge/glossary/germination.md), around the fourth to sixth node. Use a 10-30x loupe: - **Female**: a small teardrop [bract](https://genetixbay.com/knowledge/glossary/bract.md), soon with one or two white [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md). - **Male**: a small round bud on a short stalk, no stigmas, often in a little cluster. Wait for stigmas before calling a female. A male pre-flower can look like an unformed female for a few days. Clones carry the sex of their mother; there is no need to sex them. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) simply show pre-flowers and roll into flowering a few weeks from germination. ## Don't confuse with - **Stipule**: a small pointed leaf-like spur at the node, present on both sexes. - **Axillary bud**: a shoot bud, not a flower. - **Flowering stage**: full inflorescence formation, triggered by photoperiod or age. ## Related terms [Node](https://genetixbay.com/knowledge/glossary/node.md), [Pistillate flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md), [Staminate flower](https://genetixbay.com/knowledge/glossary/staminate-flower.md), [Dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) ## Read more - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) - [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 --- # Pre-harvest interval > The minimum time, set on a pesticide label, that must pass between the last application and harvest so residues fall to permitted levels. - Canonical: https://genetixbay.com/knowledge/glossary/pre-harvest-interval.html - Also written: PHI, pre harvest interval, preharvest interval, days to harvest, withdrawal period - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The pre-harvest interval (PHI) is the minimum number of days, stated on a registered pesticide label, between the last application and harvest of the crop. It exists so that residues break down to levels the regulator considers acceptable. A PHI of zero days means the product may be applied up to harvest day if the label allows; it does not mean the product leaves no residue. ## In practice For cannabis the PHI is only meaningful when a product is actually registered for cannabis in that jurisdiction; a PHI written for lettuce or tomatoes does not transfer. Harvested cannabis is often tested for residues against strict limits, and flowers are smoked or concentrated, which magnifies any residue. Many growers therefore stop all sprays well before flower, regardless of label PHI. Record every application with date, product, active ingredient and rate, so the interval can be shown. Check what is registered for cannabis locally. ## Don't confuse with - **Re-entry interval (REI)**: how long workers must wait before entering a treated area. - **Residual activity**: how long a product keeps working. - **Flushing**: unrelated; plain water does not remove pesticide residues from plant tissue. ## Related terms [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md), [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md), [Sulfur burner](https://genetixbay.com/knowledge/glossary/sulfur-burner.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) ## Read more - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) --- # Predator:prey ratio > The number of predators per pest at release or on scouting, used to judge whether biological control will catch up; spider mite guides often cite 1:10 to 1:20. - Canonical: https://genetixbay.com/knowledge/glossary/predator-prey-ratio.html - Also written: predator to prey ratio, predator-prey ratio, release ratio - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A predator:prey ratio compares predator numbers with pest numbers on the same leaves or plants, and is the practical test of whether a [biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) release is winning. Biocontrol guides for [spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) commonly give ratios in the region of one [Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md) to 10-20 spider mites as the point where control usually follows; supplier technical sheets give similar figures (exact ratios vary by source). ## In practice The ratio only works with the climate in the predator's window. A 1:10 ratio can still fail above about 30 C or below 60% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) for persimilis, because the pest's r_m then outruns the predator. Count both on the same marked leaves weekly and record them in your grow journal; a rising predator share means the predators are winning. ## Don't confuse with - **Release rate**: predators per m2 or per plant, set before a ratio can be measured. - **Action threshold**: the pest level that triggers a step, with or without predators. ## Related terms [Predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md), [Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md) ## Read more - [Integrated pest management (IPM) for cannabis: a complete programme for home and small commercial growers](https://genetixbay.com/knowledge/pests/integrated-pest-management-program.md) - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ## Sources 1. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf 2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # Predatory mite > Mites, mostly of the family Phytoseiidae, released as biological control to eat pest mites, thrips larvae, whitefly eggs or fungus gnat larvae. - Canonical: https://genetixbay.com/knowledge/glossary/predatory-mite.html - Also written: predatory mites, predator mites, phytoseiid mites, Phytoseiidae, beneficial mites - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A predatory mite is a mite that hunts other small arthropods instead of feeding on plants. Most species used on crops belong to the family Phytoseiidae and live on foliage; *[Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md)* (family Laelapidae) works in the growing medium. They are bred commercially and shipped as loose material in a carrier such as bran or vermiculite, or in slow-release sachets hung on plants. ## In practice The species has to match the pest and the room. *[Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md)* is a specialist [spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) eater; *[Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md)* tolerates heat and low prey; *[Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md)* targets thrips larvae, whitefly and broad mites in warm rooms; *[Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md)* covers thrips larvae in cooler rooms. Releases work best early, while pests are scarce, and they fail when growers spray incompatible products in the same window. Check temperature and humidity ranges for each species, since many slow down below about 50% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). ## Don't confuse with - **Spider mites**: pests; predatory mites are faster, pear-shaped and usually lack the two dark spots. - **Parasitic wasps**: insects that lay eggs inside pests rather than eating them. - **Nematodes**: microscopic worms, applied as a drench. ## Related terms [Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md), [Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md), [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md), [Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md), [Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Sources 1. UC IPM. Natural Enemies Gallery: Phytoseiulus predatory mites. https://ipm.ucanr.edu/natural-enemies/phytoseiulus-predatory-mites/ 2. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf --- # Prenylthiol > Prenylthiol (3-methyl-2-butene-1-thiol) is the volatile sulfur compound identified as the main source of cannabis's skunky aroma, potent at trace concentrations. - Canonical: https://genetixbay.com/knowledge/glossary/prenylthiol.html - Also written: 3-methyl-2-butene-1-thiol, 3MBT, 321MBT, 3-MBT, prenyl mercaptan, skunk thiol - Glossary category: Cannabinoids and terpenes · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Prenylthiol, chemically 3-methyl-2-butene-1-thiol (often abbreviated 321MBT), is a small prenylated thiol. Oswald et al. (2021, *ACS Omega*) identified it as the key compound behind the classic [skunk](https://genetixbay.com/knowledge/glossary/skunk.md) smell of cannabis, ending the long assumption that the smell came from [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md). It is the same compound responsible for "lightstruck" or skunky beer. ## In practice Concentrations are tiny, too low for a standard [terpene panel](https://genetixbay.com/knowledge/glossary/terpene-test.md) to see, yet enough to dominate aroma because the human nose detects [thiols](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) at extremely low levels. Detecting it takes specialised sulfur-selective [gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md), so it doesn't appear on routine COAs. In the 2021 study, related prenylated [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) compounds were found across many cultivars, at different levels. That supports the grower observation that "skunk" is a genetic trait, not a product of feeding or curing tricks. ## Don't confuse with - **Skunk (the animal)**: its spray uses different thiols, though the smell overlaps. - **Terpenes**: present at much higher amounts, but not the skunk source. - **Skunk (cultivar name)**: a lineage name, not a chemical measurement. ## Related terms [Volatile sulfur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196 --- # Pressed hash > Pressed hash is loose trichome resin, such as kief or ice water hash, compressed into a solid cake or slab so it holds together and keeps better. - Canonical: https://genetixbay.com/knowledge/glossary/pressed-hash.html - Also written: pressed hashish, compressed hash, press hash, hash slab, slab hash, pressed kief - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Pressed hash is resin powder consolidated by pressure, and in traditional practice often by warmth and hand-working too. Compression bursts some heads and fuses the resin into a cohesive mass. A pressed mass exposes less surface to air than loose powder, which is one reason [traditional hash](https://genetixbay.com/knowledge/glossary/hashish.md) makers pressed their product for storage and transport. ## In practice Pressed hash is typically darker on the outside than inside, because the surface oxidises. Texture ranges from hard and crumbly (more plant matter, lower resin content) to soft and pliable (high resin content). Traditional sieved hashish was commonly sold pressed. Pressed hash is a solid resin product; [rosin](https://genetixbay.com/knowledge/glossary/rosin.md) is resin squeezed out as an oil. GenetixBay defines the product and gives no pressing settings or steps. ## Don't confuse with - **Rosin**: oil extracted under heat and pressure, then separated from the residue. - **Kief**: the same material before pressing. - **Brick weed**: compressed flower, not compressed resin. ## Related terms [Hash](https://genetixbay.com/knowledge/glossary/hash.md), [Kief](https://genetixbay.com/knowledge/glossary/kief.md), [Hashish](https://genetixbay.com/knowledge/glossary/hashish.md), [Temple ball](https://genetixbay.com/knowledge/glossary/temple-ball.md), [Rosin](https://genetixbay.com/knowledge/glossary/rosin.md) ## Sources 1. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Preventive release > Releasing beneficial organisms before a pest is found, so a standing population is ready to catch the first arrivals rather than chase an outbreak. - Canonical: https://genetixbay.com/knowledge/glossary/preventive-release.html - Also written: preventative release, prophylactic release, inoculative release, preventive biocontrol, sachet release - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A preventive release is the introduction of [biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) agents before a pest has been detected, or at very low levels. The goal is a resident population of predators or [parasitoids](https://genetixbay.com/knowledge/glossary/parasitoid.md) that can establish, breed on pollen or alternative prey, and suppress pests as they arrive. It contrasts with curative or inundative releases, which flood an existing outbreak. ## In practice Common preventive programmes on cannabis: slow-release sachets of *[Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md)* or *[Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md)* hung in veg; *[Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md)* across [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md); *[Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md)* sprinkled on the medium of new clones; periodic *Aphidius* releases or [banker plants](https://genetixbay.com/knowledge/glossary/banker-plant.md). Preventive releases are usually timed from clone or early veg until a few weeks into flower, because getting predators established before flower is far easier than rescuing a flowering crop. They only work if the room's environment suits the species and no incompatible sprays follow. ## Don't confuse with - **Curative release**: large numbers aimed at a known outbreak. - **Banker plant**: a support system that breeds beneficials in place. - **Spray schedule**: preventive chemistry by calendar. ## Related terms [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md), [Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md), [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md), [Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md), [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md) ## Read more - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Sources 1. UConn IPM. Biological Control of Western Flower Thrips. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-western-flower-thrips/ 2. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf --- # Prior informed consent > Prior informed consent is permission given in advance, with full information about intended use, by a country or community before its genetic resources or knowledge are accessed. - Canonical: https://genetixbay.com/knowledge/glossary/prior-informed-consent.html - Also written: PIC, free, prior and informed consent, FPIC, informed consent (genetic resources) - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Prior informed consent (PIC) is the principle that [genetic resources](https://genetixbay.com/knowledge/glossary/germplasm.md), and the traditional knowledge associated with them, may only be accessed after the provider has agreed, in advance, with a clear understanding of what will be done with them. Under the [Nagoya Protocol](https://genetixbay.com/knowledge/glossary/nagoya-protocol.md), PIC is required from the providing country and, where national law says so, from indigenous and local communities. ## In practice For a [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) collector, PIC means explaining to the farmers and relevant authorities who you are, what you want to collect, what you intend to do with it (preservation, breeding, sale), and what the community will receive, then getting their agreement before collecting. Consent obtained by misleading people, or after the fact, does not count. Documentation of consent, alongside mutually agreed terms, is what separates collection from taking. Free, prior and informed consent (FPIC) is a related standard in indigenous rights law that stresses the absence of coercion. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Benefit-sharing**: what the provider receives; PIC is the agreement to proceed. - **Medical informed consent**: the same idea in a different field. ## Related terms [Nagoya Protocol](https://genetixbay.com/knowledge/glossary/nagoya-protocol.md), [Benefit-sharing](https://genetixbay.com/knowledge/glossary/benefit-sharing.md), [Biopiracy](https://genetixbay.com/knowledge/glossary/biopiracy.md), [Landrace hunter](https://genetixbay.com/knowledge/glossary/landrace-hunter.md) ## Read more - [Landrace hunting or biopiracy? Benefit-sharing, consent and cannabis](https://genetixbay.com/knowledge/genetics-history/landrace-hunting-and-biopiracy.md) ## Sources 1. Secretariat of the Convention on Biological Diversity. 2011. Nagoya Protocol on Access to Genetic Resources and the Fair and Equitable Sharing of Benefits Arising from their Utilization. https://www.cbd.int/abs/ --- # Professor Greenleaf > Professor Greenleaf is GenetixBay's character and botanical knowledge assistant, who answers growing and breeding questions from the cited knowledge base and the grower's own records. - Canonical: https://genetixbay.com/knowledge/glossary/professor-greenleaf.html - Also written: Greenleaf, the Professor, Prof Greenleaf, Professor - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Professor Greenleaf is the face of GenetixBay: a cartoon professor, joint in hand, and the name of the platform's botanical knowledge assistant. In articles and courses he is the voice: clear, precise, dry, answer first. ## In practice Ask Greenleaf why lower leaves are yellowing and he works from the knowledge base and, if you allow it, your journal and sensor records, citing the articles behind the answer and labelling claims with the evidence ladder. Where an answer is his own interpretation of your data, it is marked as such. He prompts growers at useful moments, such as recording [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) at harvest, and proposals that would change a grow are queued for the grower's approval rather than applied silently. Greenleaf never appears near anything for sale. His job is knowledge, not selling. ## Don't confuse with - **A human expert review**: articles are written in Greenleaf's voice and reviewed; an automated answer is not a site visit. - **Jardin**: the hardware; Greenleaf is the knowledge side. ## Related terms [Evidence ladder](https://genetixbay.com/knowledge/glossary/evidence-ladder.md), [Jardin](https://genetixbay.com/knowledge/glossary/jardin.md), [Grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md), [Mythbusters](https://genetixbay.com/knowledge/glossary/mythbusters.md) ## Read more - [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) --- # Proficiency testing > Proficiency testing sends identical blind samples to many labs and compares their results with an assigned value, checking each lab's accuracy against its peers. - Canonical: https://genetixbay.com/knowledge/glossary/proficiency-testing.html - Also written: PT, proficiency test, PT scheme, interlaboratory comparison, round-robin testing, ring test - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In proficiency testing (PT), a provider prepares a homogeneous material, often [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) or cannabis flower, an oil, or a spiked matrix, splits it and sends identical blind portions to participating labs. Each lab analyses it with its routine method. The provider compares the results with an assigned value and scores each lab, commonly with a z-score. ## In practice A z-score between -2 and +2 is usually satisfactory; beyond ±3 is unsatisfactory and requires corrective action. [ISO/IEC 17025](https://genetixbay.com/knowledge/glossary/iso-17025.md) labs are expected to take part regularly. PT is one of the best tools against lab-to-lab bias: if one lab reads consistently high in PT rounds, that shows up. Some regulators publish PT outcomes or use them in audits. For consumers, asking a lab about its PT record is reasonable. ## Units and formula z = (lab result - assigned value) / standard deviation for proficiency assessment. |z| ≤ 2 satisfactory, 2 < |z| < 3 questionable, |z| ≥ 3 unsatisfactory. ## Don't confuse with - **Accreditation**: the overall assessment; PT is one input. - **Split sample retest**: an informal check between two labs, useful but not scored. ## Related terms [ISO/IEC 17025](https://genetixbay.com/knowledge/glossary/iso-17025.md), [Measurement uncertainty](https://genetixbay.com/knowledge/glossary/measurement-uncertainty.md), [Lab shopping](https://genetixbay.com/knowledge/glossary/lab-shopping.md), [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md), [Label inflation](https://genetixbay.com/knowledge/glossary/label-inflation.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. ISO/IEC 17025:2017. General requirements for the competence of testing and calibration laboratories. International Organization for Standardization, Geneva. --- # Progeny test > A progeny test judges a parent by growing out and measuring its offspring, the most reliable way to know what a plant, especially a male, actually passes on. - Canonical: https://genetixbay.com/knowledge/glossary/progeny-test.html - Also written: progeny testing, offspring test, progeny trial, breeding value test - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A progeny test evaluates a parent by its offspring rather than its own appearance. The candidate is crossed (to one standard tester or to several partners), the seed is grown in uniform conditions, and the offspring are scored. The parent's breeding value is the average performance of its offspring. ## In practice Progeny testing is how breeders choose males with confidence. Three candidate males are crossed to the same female; the offspring of each are grown side by side. Male B's [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) are the most vigorous and uniform with the best aroma: male B is kept, the others dropped. It also checks females. A gorgeous clone may pass on her traits poorly if they come from a [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) combination; her offspring will show it. For low-heritability traits such as yield, progeny testing is far more reliable than looking at the parent itself, because averaging many offspring cancels out environmental noise. ## Don't confuse with - **Test cross**: a specific cross to a [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) to diagnose one [locus](https://genetixbay.com/knowledge/glossary/locus.md). - **Test grow (tester grow)**: grow-outs of released or candidate seed to evaluate a line, often by several growers. - **Pheno hunt**: selecting individuals, not testing parents by offspring. ## Related terms [Male selection](https://genetixbay.com/knowledge/glossary/male-selection.md), [Test cross](https://genetixbay.com/knowledge/glossary/test-cross.md), [Test grow](https://genetixbay.com/knowledge/glossary/test-grow.md), [Heritability](https://genetixbay.com/knowledge/glossary/heritability.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md) ## Read more - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) - [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Punnett square > A Punnett square is a grid that lists each parent's possible gametes along two sides to predict the expected genotype ratios among offspring of a cross. - Canonical: https://genetixbay.com/knowledge/glossary/punnett-square.html - Also written: Punnett squares, Punnett grid, Punnet square, cross diagram - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A Punnett square is a simple grid for predicting offspring of a cross. One parent's possible gametes go across the top, the other's down the side, and each cell shows the [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) from that combination. The proportions of cells are the expected proportions of offspring. ## In practice For one [gene](https://genetixbay.com/knowledge/glossary/gene.md), Aa × Aa gives a 2 × 2 square: one AA, two Aa, one aa. If A is dominant, three of four plants look the same. For two independent genes the square is 4 × 4 and gives the 9:3:3:1 ratio. Breeders use it to plan how many seeds to pop. If you want a plant [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) for two [recessive traits](https://genetixbay.com/knowledge/glossary/recessive.md) from an [F2](https://genetixbay.com/knowledge/glossary/f2.md), only 1 in 16 is expected; to be about 95% sure of getting at least one, you need roughly 47 plants. For three recessives it is 1 in 64 and a few hundred seeds. ## Units and formula Chance of at least one hit in n plants = 1 - (1 - p)^n, where p is the expected fraction from the square. Solve for n to size a grow-out. ## Don't confuse with - **Actual results**: the square gives expected ratios; small grows deviate by chance. - **Quantitative traits**: yield or potency do not fit a Punnett square; they need [heritability](https://genetixbay.com/knowledge/glossary/heritability.md) and population thinking. - **Linked genes**: genes near each other on a chromosome do not assort freely, so the 9:3:3:1 square overstates recombinants. ## Related terms [Mendelian inheritance](https://genetixbay.com/knowledge/glossary/mendelian-inheritance.md), [Segregation](https://genetixbay.com/knowledge/glossary/segregation.md), [Dominant](https://genetixbay.com/knowledge/glossary/dominant.md), [Recessive](https://genetixbay.com/knowledge/glossary/recessive.md), [Test cross](https://genetixbay.com/knowledge/glossary/test-cross.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ --- # Purp > Purp is slang for purple-coloured cannabis; the colour comes from anthocyanins and depends on genetics and cool temperatures, not on potency. - Canonical: https://genetixbay.com/knowledge/glossary/purp.html - Also written: purple, purps, purple weed, purple buds, purpz - Glossary category: Grower slang and culture · Evidence: Myth - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Purp is slang for purple flower, or a cultivar known for turning purple. The colour comes from anthocyanins, water-soluble pigments that some [genotypes](https://genetixbay.com/knowledge/glossary/genotype.md) produce in leaves, [bracts](https://genetixbay.com/knowledge/glossary/bract.md) and [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md). ## In practice Genetics decide whether a plant can turn purple. Cool night temperatures in late flower, often a drop to about 15-18 °C (59-64 °F) or below, increase anthocyanin expression in plants that carry the trait. A plant without the genetics stays green however cold it gets. Purple stems and leaves in veg can also mean other things, including phosphorus or cold stress. See [purple stems and leaves](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md). ## Don't confuse with - **Purple as a strain family**: many names contain "purple"; the name does not guarantee the colour. - **Deficiency purpling**: dull purple [petioles](https://genetixbay.com/knowledge/glossary/petiole.md) with other symptoms, not glossy coloured bracts. ## Myth check "Purple weed is stronger" or "[cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) boost terps and resin". GenetixBay position: colour from cold is real; claims of more [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), flavour or resin are a myth unless peer-reviewed data shows otherwise. [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md) is not quality, though the founder admits they are "a sucker for any red strain". See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Anthocyanin](https://genetixbay.com/knowledge/glossary/anthocyanin.md), [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md), [Cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) ## Read more - [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) --- # Pythium > A genus of oomycete water moulds, such as Pythium myriotylum and P. aphanidermatum, that cause brown, slimy root rot, especially in warm hydroponic systems. - Canonical: https://genetixbay.com/knowledge/glossary/pythium.html - Also written: Pythium root rot, Pythium spp., pythium rot, Pythium myriotylum, Pythium dissotocum, Pythium aphanidermatum - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Pythium* is a genus of oomycetes, water moulds that look like fungi but are more closely related to brown algae. Several species infect cannabis roots, including *P. myriotylum*, *P. dissotocum* and *P. aphanidermatum*. They spread by swimming zoospores, so they thrive wherever roots sit in water: [deep water culture](https://genetixbay.com/knowledge/glossary/dwc.md), [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md) and [overwatered](https://genetixbay.com/knowledge/glossary/overwatering.md) pots. They also cause [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) of [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and cuttings. ## In practice Infected roots turn brown, soft and slimy, and the outer root tissue slips off, leaving the inner strand. Above ground the plant wilts in the heat of the day, yellows and stalls, despite a full reservoir. Warm nutrient solution above roughly 24-26 °C (75-79 °F), low dissolved oxygen and stagnant water favour it. [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) is cool, well-oxygenated solution, clean equipment, and either a dedicated [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) or a fully committed sterile one. [Fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) larvae can carry it in media. ## Don't confuse with - **Fusarium**: a true fungus that often causes wilt and brown vascular streaks in the stem. - **Tea-stained roots**: brown from additives but firm, with white tips. - **Overwatering in soil**: low oxygen without slime or root sloughing. ## Related terms [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), [Damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md), [Fusarium wilt](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md), [Biofilm](https://genetixbay.com/knowledge/glossary/biofilm.md), [Fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) ## Read more - [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) - [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ## Sources 1. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 2. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic production (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 3. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Root and Crown Rot. https://pnwhandbooks.org/node/12931 --- # QP > A QP is a quarter pound of cannabis: 4 ounces, about 113 grams. - Canonical: https://genetixbay.com/knowledge/glossary/qp.html - Also written: quarter pound, quarter-pound, qps, QP+, 4 oz - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A QP is a quarter pound: 4 oz, about 113 g of dried flower. It is a common unit in grower talk for a strong single-plant yield. ## In practice "A QP off one plant" is a good result indoors. The founder of GenetixBay has pulled a QP+ (4 oz+) from a plant in a 16 oz cup, which shows that [root volume](https://genetixbay.com/knowledge/glossary/pot-size.md) is not the whole story: with [high-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md), nutrients and water reach the roots often enough that a small container can support a large plant. Bigger pots still generally mean bigger [yields](https://genetixbay.com/knowledge/glossary/yield.md), within reason; pot size is a trade-off against how often you feed. Possession and transport limits are usually far below a QP for unlicensed people. Check local rules. ## Units and formula | Slang | Nominal weight | Metric | |---|---|---| | Gram | 1 g | 1 g | | Eighth | 1/8 oz | 3.5 g (exact: 3.54 g) | | Quarter | 1/4 oz | 7 g | | Half | 1/2 oz | 14 g | | Ounce (zip, O) | 1 oz | 28 g (exact: 28.35 g) | | QP | 1/4 lb (4 oz) | 113 g | | Pound (elbow, LB) | 1 lb (16 oz) | 454 g (exact: 453.6 g) | Retail rounds an eighth to 3.5 g and an ounce to 28 g. ## Don't confuse with - **Quarter**: a quarter ounce, 7 g. "Quarter" alone usually means this, not a QP. ## Related terms [Ounce](https://genetixbay.com/knowledge/glossary/ounce.md), [Elbow](https://genetixbay.com/knowledge/glossary/elbow.md), [Gram](https://genetixbay.com/knowledge/glossary/gram.md), [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) ## Read more - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) --- # QTL > A QTL (quantitative trait locus) is a region of the genome statistically linked to variation in a quantitative trait such as yield or flowering time. - Canonical: https://genetixbay.com/knowledge/glossary/qtl.html - Also written: quantitative trait locus, quantitative trait loci, QTLs, QTL mapping - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A QTL (quantitative trait locus) is a [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) of the genome whose variants are associated with differences in a [quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.md). A QTL may contain one causal [gene](https://genetixbay.com/knowledge/glossary/gene.md) or several; mapping often narrows the location long before anyone knows which gene is responsible. ## In practice QTL are found by growing a [segregating](https://genetixbay.com/knowledge/glossary/segregation.md) population (an [F2](https://genetixbay.com/knowledge/glossary/f2.md) or similar), measuring the trait, [genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md) each plant at many markers, and testing which markers track the trait. Genome-wide association studies (GWAS) do the same across unrelated plants. In cannabis, studies have mapped regions for flowering time and sex expression in hemp (Petit et al. 2020) and major flowering-time loci such as Autoflower1 and Early1 (Toth et al. 2022). For breeders the payoff is [marker-assisted selection](https://genetixbay.com/knowledge/glossary/marker-assisted-selection.md): screen seedlings for the markers and keep only those likely to carry the good [allele](https://genetixbay.com/knowledge/glossary/allele.md), before flowering. ## Don't confuse with - **Gene**: a QTL is a region; the gene inside it may still be unknown. - **Major gene**: a QTL with a large effect (like Autoflower1) behaves almost like a Mendelian gene; most QTL are small. - **Proof of a trait**: a QTL shifts probabilities. Plants carrying the good allele still vary. ## Related terms [Quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.md), [Locus](https://genetixbay.com/knowledge/glossary/locus.md), [Marker-assisted selection](https://genetixbay.com/knowledge/glossary/marker-assisted-selection.md), [SNP](https://genetixbay.com/knowledge/glossary/snp.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md) ## Read more - [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md) - [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md) ## Sources 1. Petit J, Salentijn EMJ, Paulo MJ, Denneboom C, Trindade LM. 2020. Genetic architecture of flowering time and sex determination in hemp (Cannabis sativa L.): a genome-wide association study. Frontiers in Plant Science 11:569958. https://doi.org/10.3389/fpls.2020.569958 2. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 3. Barcaccia G, Palumbo F, Scariolo F, Vannozzi A, Borin M, Bona S. 2020. Potentials and challenges of genomics for breeding cannabis cultivars. Frontiers in Plant Science 11:573299. https://doi.org/10.3389/fpls.2020.573299 --- # Quantitative trait > A quantitative trait varies continuously (yield, height, flowering time, cannabinoid content) because it is controlled by many genes of small effect plus the environment. - Canonical: https://genetixbay.com/knowledge/glossary/quantitative-trait.html - Also written: quantitative traits, polygenic trait, complex trait, continuous trait, polygenic - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A quantitative trait is one that varies on a continuous scale rather than in a few clear classes. It is shaped by many genes, each with a small effect, and by the environment. In cannabis, yield, height, [internode length](https://genetixbay.com/knowledge/glossary/internode.md), total [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) percentage, [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) content and most of flowering time are quantitative. ## In practice Quantitative traits do not fit [Punnett squares](https://genetixbay.com/knowledge/glossary/punnett-square.md). You cannot "fix 25% THC" the way you fix a [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) leaf trait. Instead breeders measure many plants under the same conditions, estimate heritability, and shift the population average a little each generation by selecting the best parents. Progress is steady but slow, and selecting on one trait can drag others with it. Grow-out size matters. A dozen plants tell you little about a trait whose variation is mostly environmental. Repeat measurements on clones of each candidate separate genotype from luck. ## Don't confuse with - **Qualitative (Mendelian) trait**: falls into distinct classes controlled by one or a few genes, such as [cannabinoid chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) or autoflowering. - **QTL**: the genomic regions that contribute to a quantitative trait. ## Myth check [Total cannabinoid content](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) is quantitative and has a biological ceiling. Seed sold as "will hit 40%" is a marketing claim, not genetics; see [buyer beware: label claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [QTL](https://genetixbay.com/knowledge/glossary/qtl.md), [Heritability](https://genetixbay.com/knowledge/glossary/heritability.md), [Mendelian inheritance](https://genetixbay.com/knowledge/glossary/mendelian-inheritance.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Genotype by environment interaction](https://genetixbay.com/knowledge/glossary/genotype-by-environment.md) ## Read more - [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 --- # Quarantine > Holding incoming plants, clones or seeds apart from the main grow, under observation and sometimes treatment, until they are shown to be free of pests and disease. - Canonical: https://genetixbay.com/knowledge/glossary/quarantine.html - Also written: quarantine room, isolation, clone quarantine, quarantine period - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Quarantine is isolating new plant material from the rest of a grow until it has been inspected, observed and, where needed, treated or tested. Most serious cannabis pests and pathogens, including [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md), [hemp russet mites](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md), [root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md), [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) and [HLVd](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), arrive on clones rather than through the air. ## In practice A workable quarantine is a separate tent or room with its own tools, visited last in the day or after a clothing change. New cuts stay there for long enough to see a full pest generation hatch and develop, commonly two to four weeks. During that time growers inspect tips under a 40x or stronger scope, check roots, hang [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) and send leaf or root samples for HLVd testing before cuts go near mothers. Some apply a preventive dip or release [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md) during quarantine; check what is registered for cannabis locally. Anything that fails is destroyed, not "treated and moved in". ## Don't confuse with - **Sanitation**: cleaning rooms and tools; quarantine controls what comes in. - **Tissue culture**: a lab method to clean infected stock; quarantine only catches problems. ## Related terms [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Hemp russet mite](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md), [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md) ## Read more - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) ## Sources 1. Punja ZK et al., 2025. Hop latent viroid transmission, spread and longevity in cannabis; meristem tip culture. Plants 14(5):830. https://www.mdpi.com/2223-7747/14/5/830 2. Colorado State University. Hemp russet mite, Aculops cannabicola. https://agsci.colostate.edu/agbio/ipm-pests/29895-2/ --- # Radicle > The embryonic root, the first structure to emerge from a germinating seed, which grows down to become the primary root or taproot. - Canonical: https://genetixbay.com/knowledge/glossary/radicle.html - Also written: embryonic root, seed root, first root, taproot tip - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The radicle is the embryonic root. It is the first organ to break out of the [seed coat](https://genetixbay.com/knowledge/glossary/seed-coat.md) during [germination](https://genetixbay.com/knowledge/glossary/germination.md), and it grows straight down under gravity to become the [primary root](https://genetixbay.com/knowledge/glossary/taproot.md) (the taproot). [Root hairs](https://genetixbay.com/knowledge/glossary/root-hair.md) form just behind its tip within a day or two. ## In practice When growers say a seed has "popped" or "tailed", they mean the radicle is out. Plant it once it is about 5-20 mm (0.2-0.8 in) long, tip down, roughly 5-10 mm deep. Longer tails are fragile and easily snapped; a broken radicle tip often stops or badly delays the [seedling](https://genetixbay.com/knowledge/glossary/seedling.md). Handle by the shell, never the root. The radicle and its fine root hairs dry out in minutes in open air. Move quickly from paper towel or water to medium, and keep the medium moist, not [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md). ## Don't confuse with - **Taproot**: the mature primary root that the radicle becomes. - **Hypocotyl**: the shoot-side stem segment that lifts the [cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md); it emerges after the radicle. - **Root hairs**: tiny single-cell outgrowths on the radicle, not separate roots. ## Related terms [Taproot](https://genetixbay.com/knowledge/glossary/taproot.md), [Hypocotyl](https://genetixbay.com/knowledge/glossary/hypocotyl.md), [Seed coat](https://genetixbay.com/knowledge/glossary/seed-coat.md), [Root hair](https://genetixbay.com/knowledge/glossary/root-hair.md) ## Read more - [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md) - [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # RDWC > RDWC (recirculating deep water culture) links several aerated buckets to a central control reservoir, pumping solution through all of them to keep conditions uniform. - Canonical: https://genetixbay.com/knowledge/glossary/rdwc.html - Also written: recirculating deep water culture, recirculating DWC, re-circulating DWC, under current, undercurrent - Glossary category: Systems and media · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Recirculating deep water culture is a hydroponic system in which several [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) sites are connected by pipes to a control bucket or reservoir, and a pump moves solution continuously through the whole loop. Each site is aerated, and adjustments to [pH](https://genetixbay.com/knowledge/glossary/ph.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md) and temperature are made in the control bucket only. ## In practice The larger shared volume is more stable than single buckets, and one [chiller](https://genetixbay.com/knowledge/glossary/chiller.md) can cool the whole system. Growers typically size the pump to turn over the full system volume several times per hour. Keep the control bucket accessible, insulate and lightproof all buckets and lines to stop algae and heat gain, and keep the solution around 18-21 °C (64-70 °F). The trade-off is shared risk: a [root disease](https://genetixbay.com/knowledge/glossary/root-rot.md) or pump failure affects every plant at once. Most growers run either a [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) or a fully sterile one. ## Don't confuse with - **DWC**: one standalone bucket. - **Ebb and flow**: also recirculates, but floods and [drains](https://genetixbay.com/knowledge/glossary/runoff.md) a tray instead of holding roots in solution. ## Related terms [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [Chiller](https://genetixbay.com/knowledge/glossary/chiller.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [Recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md) ## Read more - [Recirculating deep water culture (RDWC)](https://genetixbay.com/knowledge/systems/rdwc.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 2. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ --- # Re-veg > Re-veg is returning a flowering or harvested plant to vegetative growth by putting it back under long days, often to save a genotype after harvest. - Canonical: https://genetixbay.com/knowledge/glossary/re-veg.html - Also written: reveg, re-vegging, revegging, re-vegetation, regeneration - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Re-veg (re-vegetation) is reversing flowering in a [photoperiod plant](https://genetixbay.com/knowledge/glossary/photoperiod.md) by restoring long days, usually 18 h or more of light. Left with some buds and leaves after harvest, the plant gradually stops flowering and produces new vegetative shoots, which can then be cloned or grown on. ## In practice Breeders and [pheno](https://genetixbay.com/knowledge/glossary/pheno.md) hunters use re-veg to keep a plant they only identified as a keeper after smoking it. Leave the lower branches with some green leaves and small buds, keep the plant under [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) or [18/6](https://genetixbay.com/knowledge/glossary/18-6.md), feed lightly, and wait. Expect 2-6 weeks of odd growth: rounded, single-blade or smooth-edged leaves before normal leaves return. Success varies; old, heavily stripped or very late plants often fail. Accidental re-veg outdoors happens when a plant that started flowering early in spring sees lengthening days. ## Don't confuse with - **Monster cropping**: rooting cuttings from a flowering plant; the cuttings re-veg. - **Cloning before flower**: the easier route; keeping cuts of every candidate avoids needing re-veg. ## Related terms [Monster cropping](https://genetixbay.com/knowledge/glossary/monster-cropping.md), [Flip](https://genetixbay.com/knowledge/glossary/flip.md), [Mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md), [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) --- # Recessive > A recessive allele only shows its effect when a plant carries two copies of it; in a single copy it is masked by a dominant allele and carried silently. - Canonical: https://genetixbay.com/knowledge/glossary/recessive.html - Also written: recessive allele, recessive trait, recessives - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A recessive allele shows in the [phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md) only when the plant is [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) for it (aa). A plant with one copy (Aa) looks like the [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) type but passes the recessive allele to about half its offspring. ## In practice Recessives are why seed lines surprise people. Two vigorous parents can both carry a hidden recessive for weak growth, odd leaves or a missing trait; about one in four of their offspring will show it. Selfing and close [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) bring recessives out fast because they push loci towards homozygosity. That works both ways: it can reveal a rare recessive aroma a breeder wants to fix, or a defect that has to be culled. The [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) trait is recessive. So is the expression of many deleterious [alleles](https://genetixbay.com/knowledge/glossary/allele.md) that cause [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md). A breeder who wants to know whether a plant carries a recessive does a [test cross](https://genetixbay.com/knowledge/glossary/test-cross.md) with a known aa plant: any aa offspring prove the carrier. ## Don't confuse with - **Rare**: a recessive allele can be common in a population and still be hidden in most plants. - **Weak or bad**: recessive describes inheritance, not value. Many desirable traits are recessive. - **Codominant**: in codominance both alleles show; nothing is hidden. ## Related terms [Dominant](https://genetixbay.com/knowledge/glossary/dominant.md), [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) - [S1s and selfing: what happens when a plant pollinates itself](https://genetixbay.com/knowledge/breeding/s1-selfing.md) ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 --- # Reciprocal cross > A reciprocal cross repeats a cross with the parents' roles swapped (A × B, then B × A) to test whether the seed parent affects the offspring. - Canonical: https://genetixbay.com/knowledge/glossary/reciprocal-cross.html - Also written: reciprocal crosses, reverse cross, reversed cross - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A reciprocal cross repeats a cross with the sexes reversed: if the first cross was plant A (female) × plant B (male), the reciprocal is B (female) × A (male). For ordinary nuclear [genes](https://genetixbay.com/knowledge/glossary/gene.md) the two should give the same offspring. Differences point to maternal effects, organelle (chloroplast or mitochondrial) inheritance, or sex-linked genes. ## In practice In cannabis, a reciprocal requires a female and a male of each "side", or reversing a female to supply pollen. Breeders sometimes note that a cross made one way round grew differently from the reverse. Organelles are inherited mainly through the seed parent in most flowering plants, and genes on the [X and Y chromosomes](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md) are inherited differently by sons and daughters, so differences are possible. Claims of large differences in cannabis are mostly anecdotal; few controlled comparisons have been published. Breeders also say "reversed cross" or "the reverse" when naming. Good records state which parent was the seed parent, because the reciprocal is not automatically the same seed. ## Don't confuse with - **Sex reversal**: chemically inducing pollen on a female; a different meaning of "reversed". - **Backcross**: crossing back to a parent. ## Related terms [Cross](https://genetixbay.com/knowledge/glossary/cross.md), [P1](https://genetixbay.com/knowledge/glossary/p1.md), [XY sex determination](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md) ## Read more - [Pollination and seed production, step by step](https://genetixbay.com/knowledge/breeding/pollination-seed-production.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Recirculating system > A recirculating (closed) system returns drained nutrient solution to the reservoir to be reused, saving water and nutrients but needing more monitoring and sanitation. - Canonical: https://genetixbay.com/knowledge/glossary/recirculating-system.html - Also written: recirculating, recirculating hydro, closed system, closed-loop hydroponics, recirc - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A recirculating hydroponic system collects the solution that passes through or around the roots and returns it to the reservoir. [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), NFT, [ebb and flow](https://genetixbay.com/knowledge/glossary/ebb-and-flow.md) and recirculating drip are all closed systems. Only what the plants take up or evaporate is lost, so water and fertiliser use falls sharply compared with [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md). ## In practice Because solution is reused, its composition drifts: the plant takes some elements faster than others, [pH](https://genetixbay.com/knowledge/glossary/ph.md) moves, and root exudates and microbes accumulate. Growers top up between full changes, check pH and [EC](https://genetixbay.com/knowledge/glossary/ec.md) daily, and change or refresh the reservoir every one to two weeks. Recirculation can spread root pathogens such as *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)* to every plant, so sanitation, cool temperatures and a deliberate microbial strategy (beneficial or sterile) matter. ## Don't confuse with - **Drain-to-waste**: each feed used once. - **Recirculating drip**: one kind of closed system using [drippers](https://genetixbay.com/knowledge/glossary/drip-irrigation.md). ## Related terms [Drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [NFT](https://genetixbay.com/knowledge/glossary/nft.md), [Ebb and flow](https://genetixbay.com/knowledge/glossary/ebb-and-flow.md) ## Read more - [Recirculating drip (top-feed, runoff returns)](https://genetixbay.com/knowledge/systems/recirculating-drip.md) - [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 2. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ --- # Red:far-red ratio > The red:far-red ratio compares photons near 660 nm with those near 730 nm; plants read a low ratio as shade and respond by stretching. - Canonical: https://genetixbay.com/knowledge/glossary/red-far-red-ratio.html - Also written: R:FR, R/FR, red to far-red ratio, R:FR ratio, red/far-red - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The red:far-red ratio (R:FR) is the photon flux in a red band (usually 655–665 nm) divided by that in a [far-red](https://genetixbay.com/knowledge/glossary/far-red.md) band (usually 725–735 nm). Plants sense it through [phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md), which flips between a red-absorbing and a far-red-absorbing form. Daylight has an R:FR of roughly 1.1–1.2; under a leafy canopy it drops well below 1, because leaves absorb red and pass far-red. A low ratio tells the plant it is shaded. ## In practice Lower R:FR triggers shade-avoidance responses: longer [internodes](https://genetixbay.com/knowledge/glossary/internode.md), taller plants, thinner leaves, more [apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md). Kotiranta and colleagues (2024) found low R:FR increased cannabis height and reduced inflorescence yield in their setup, while a later trial by the same group (2025) reported higher yield but lower specialised-metabolite concentrations with a decreasing ratio. The direction depends on intensity, cultivar and how the far-red is added. *Contested* for yield; *Established* for [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). Most white [LEDs](https://genetixbay.com/knowledge/glossary/led.md) without a far-red channel have a high R:FR, giving compact plants. [HPS](https://genetixbay.com/knowledge/glossary/hps.md) has a moderate ratio. Growers who add far-red usually want faster canopy fill or a stronger end-of-day signal; those fighting stretch avoid it. ## Units and formula R:FR = photon flux (655–665 nm) ÷ photon flux (725–735 nm). Band definitions vary between papers; check which one a datasheet uses. ## Don't confuse with - **Far-red**: the waveband itself; the ratio is about balance. - **Red light**: drives [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) strongly; it is only one half of the ratio. ## Related terms [Far-red](https://genetixbay.com/knowledge/glossary/far-red.md), [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md), [Emerson effect](https://genetixbay.com/knowledge/glossary/emerson-effect.md), [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) - [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ## Sources 1. Kotiranta S et al., 2024. (Low R:FR increased height and reduced inflorescence yield.) Industrial Crops and Products. https://doi.org/10.1016/j.indcrop.2023.117772 2. Peterswald TJ et al., 2025. The effects of far-red light on medicinal Cannabis. Scientific Reports. https://pmc.ncbi.nlm.nih.gov/articles/PMC12092679/ --- # Regs > Regs is slang for regular seed: seed from a true male and female cross that gives roughly half male and half female plants. - Canonical: https://genetixbay.com/knowledge/glossary/regs.html - Also written: regulars, reg seeds, reg, regular beans - Glossary category: Grower slang and culture · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Regs (regulars) is slang for regular seed: seed made by [pollinating](https://genetixbay.com/knowledge/glossary/pollination.md) a female with pollen from a genuine male plant. Expect roughly a 1:1 ratio of males to females, though any single pack can vary. ## In practice Breeders and preservationists prefer regs because they carry the full genetics of a line, including the males needed to make the next generation. A grower who pops 10 regs and gets 6 females and 4 males has a normal result; the males can be culled, or kept, assessed and used for breeding. Sexing happens at [pre-flower](https://genetixbay.com/knowledge/glossary/pre-flower.md), from about 4-6 weeks of veg from seed, or earlier by forcing a clone into flower. ## Don't confuse with - **Fems**: [feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), made with pollen from a sex-reversed female, almost all female. - **Autos**: [day-neutral](https://genetixbay.com/knowledge/glossary/autoflower.md) plants; they can be regular or feminised. - **Bagseed**: unknown, often accidental seed. ## Myth check "Regs are worse than [fems](https://genetixbay.com/knowledge/glossary/fems.md)." Not on genetics. Regular seed is how cannabis has always reproduced, and males are half of every line. GenetixBay encourages and rewards keeping males (see [the Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md)). Fems save space, not quality. See [seed types](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md). ## Related terms [Regular seed](https://genetixbay.com/knowledge/glossary/regular-seed.md), [Fems](https://genetixbay.com/knowledge/glossary/fems.md), [Beans](https://genetixbay.com/knowledge/glossary/beans.md), [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md) ## Read more - [Regular, feminised, autoflower or clone: choosing your starting material](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md) --- # Regular seed > Regular seed comes from a normal cross of a female and a male, so it produces roughly half female and half male plants. - Canonical: https://genetixbay.com/knowledge/glossary/regular-seed.html - Also written: regular seeds, non-feminised seed, non-feminized seed - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Regular seed is seed from a female [pollinated](https://genetixbay.com/knowledge/glossary/pollination.md) by a real male. Each seed inherits an X from the mother and either an X or a Y from the father, so the crop comes out close to 50:50 female to male. ## In practice For flower-only growers, [regulars](https://genetixbay.com/knowledge/glossary/regs.md) mean more seeds to start and males to identify and remove before they shed pollen, typically when the first flowers show at the nodes or earlier with a DNA sex test. For breeders, regulars are the raw material. They contain males, and males carry half the genetics of the next generation. A selected male is how traits are combined, lines are [stabilised](https://genetixbay.com/knowledge/glossary/stabilisation.md), and diversity is kept. Many breeders and preservationists prefer regular seed for these reasons. Lines bred only through feminising skip [male selection](https://genetixbay.com/knowledge/glossary/male-selection.md) entirely. Expect the ratio to vary in small batches. Ten seeds might give three or seven females by chance. ## Don't confuse with - **Feminised seed**: female × [reversed female](https://genetixbay.com/knowledge/glossary/sex-reversal.md); nearly all females. - **Bagseed**: seed found in purchased flower; often from an accidental pollination of unknown origin. - **Landrace seed**: usually regular, but "regular" says nothing about origin. ## Myth check House position: males are a necessity in breeding and are encouraged and rewarded on GenetixBay. Regular seed is not "old-fashioned"; it is how breeding works. ## Related terms [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [Male selection](https://genetixbay.com/knowledge/glossary/male-selection.md), [XY sex determination](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md), [Cross](https://genetixbay.com/knowledge/glossary/cross.md), [F1](https://genetixbay.com/knowledge/glossary/f1.md) ## Read more - [Regular, feminised, autoflower or clone: choosing your starting material](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md) ## Sources 1. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Relative humidity > Relative humidity is the water vapour in air as a percentage of what it could hold at that temperature, so the same RH dries plants differently at different temperatures. - Canonical: https://genetixbay.com/knowledge/glossary/relative-humidity.html - Also written: RH, humidity, relative humidity %, %RH, humidity level - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Relative humidity (RH) is the ratio of the actual water vapour pressure in the air to the saturation vapour pressure at the same temperature, as a percentage. Because warm air can hold far more water than cold air, RH depends on temperature: warm a room without adding water and RH falls; cool it and RH rises, reaching 100% at the [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md). ## In practice Common ranges by stage: | Stage | RH | |---|---| | Clones | 70–85% | | [Seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and early veg | 60–70% | | Late veg | 50–65% | | Flower | 40–55% | | Late flower | 40–50% | High RH in flower raises the risk of [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md); Corredor-Perilla and colleagues (2025) reviewed the effects of high humidity in cannabis. Low RH with high temperature drives water loss faster than roots can supply. RH alone is an incomplete target. 60% RH at 20 °C and 60% RH at 30 °C produce very different [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), so experienced growers set RH from a VPD target and the current temperature. Cheap hygrometers can be off by 5% or more; check them against a calibrated reference or a two-salt test. ## Units and formula RH (%) = actual vapour pressure ÷ saturation vapour pressure × 100. ## Don't confuse with - **Absolute humidity**: grams of water per cubic metre of air. - **VPD**: the drying power, in kPa. - **Jar RH in curing**: a proxy for [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), covered under harvest and cure. ## Related terms [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Absolute humidity](https://genetixbay.com/knowledge/glossary/absolute-humidity.md), [Dew point](https://genetixbay.com/knowledge/glossary/dew-point.md), [Dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md), [Humidifier](https://genetixbay.com/knowledge/glossary/humidifier.md) ## Read more - [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ## Sources 1. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm 2. Corredor-Perilla IC, Kwon H, Park J, 2025. High relative humidity in cannabis cultivation (effects on flowering, biomass and cannabinoids). Frontiers in Plant Science 16:1678142. https://doi.org/10.3389/fpls.2025.1678142 --- # Renamed cut > A renamed cut is a known clone sold or shared under a new name, so one genotype circulates under many labels and lineage records get muddied. - Canonical: https://genetixbay.com/knowledge/glossary/renamed-cut.html - Also written: same cut 1,000 names, same cut, a thousand names, rebranded cut, renamed strain, rename - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A renamed cut is a clone of an existing cultivar given a new name, whether by accident (a lost label), to hide its source, or to market it as something new. "Same cut, a thousand names" describes how far this has gone. ## In practice Genetic studies of retail cannabis show that samples with the same name are often genetically different, and samples with different names can be near-identical (Sawler et al. 2015). For a grower, it means buying a "new" cut may get you a plant you already have, and a "rare" cut may be a common one with a story attached. ## Don't confuse with - **Phenotype names**: "#4" or "pink [pheno](https://genetixbay.com/knowledge/glossary/pheno.md)" marks one individual from a [seed lot](https://genetixbay.com/knowledge/glossary/seed-run.md), which is legitimate if the source is stated. - **Remake**: a new cross openly reusing an old name. ## Myth check GenetixBay position (*Supported*): renaming is out of hand and part of why "everything tastes the same". The same narrow pool of material is being relabelled and hybridised into everything, diluting the [gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md). A name alone is the weakest evidence level. [GB-IDs](https://genetixbay.com/knowledge/glossary/gb-id.md), recorded chains of custody and DNA matches are the fix. See [same cut, a thousand names](https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.md). ## Related terms [Cut](https://genetixbay.com/knowledge/glossary/cut.md), [Hype strain](https://genetixbay.com/knowledge/glossary/hype-strain.md), [Elite cut](https://genetixbay.com/knowledge/glossary/elite-cut.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Strain](https://genetixbay.com/knowledge/glossary/strain.md) ## Read more - [Same cut, a thousand names: renaming, relabelling and the shrinking gene pool](https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.md) - [Why strain names are unreliable: what genetic studies show](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) ## Sources 1. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLOS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 2. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Reservoir > A reservoir is the tank that holds a system's water or nutrient solution, the place where pH, EC, temperature and oxygen are measured and adjusted. - Canonical: https://genetixbay.com/knowledge/glossary/reservoir.html - Also written: res, nutrient reservoir, nutrient tank, feed tank, rez, sump - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A reservoir is the container that stores the solution used to water or feed plants. In [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md), solution returns to it after passing the roots; in [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md) it is a fresh-mix tank. It is the control point for the system: [pH](https://genetixbay.com/knowledge/glossary/ph.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), temperature, dissolved oxygen and the microbial state of the solution are all managed here. ## In practice Bigger is more stable: a large volume changes pH, EC and temperature more slowly. A common home guide is several litres of reservoir per plant, with recirculating systems sized so that a day's uptake is a small fraction of volume. Keep it lightproof to prevent algae, covered to keep debris and pests out, cool (about 18-21 °C, 64-70 °F) and well mixed. Log readings daily, top up as the level drops, and change or refresh it every one to two weeks in recirculating systems. ## Don't confuse with - **Control bucket**: the mixing and adjustment bucket in [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md); part of the reservoir function. - **Stock tank**: concentrate tank for injectors, not the working solution. ## Related terms [Chiller](https://genetixbay.com/knowledge/glossary/chiller.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [Recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [Beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md), [Sterile reservoir](https://genetixbay.com/knowledge/glossary/sterile-reservoir.md) ## Read more - [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) - [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.md) ## Sources 1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254 --- # Residual solvents > A residual solvents test measures leftover solvents such as butane, propane, ethanol or hexane in an extract, usually by headspace GC, against safety limits. - Canonical: https://genetixbay.com/knowledge/glossary/residual-solvents.html - Also written: residual solvent test, residual solvents test, solvent residue, residual solvent panel, RS test - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Residual solvents testing checks how much of the solvents used in, or contaminating, an extract remain in the finished product. The standard method is headspace [gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md): the sample is warmed in a sealed vial and the vapour above it is analysed, typically with FID or MS detection. Panels cover common extraction solvents (butane, propane, ethanol, hexane, heptane, acetone, isopropanol) and sometimes contaminants such as benzene. ## In practice This test applies mainly to solvent-based concentrates, though some markets require it for any extract. A [COA](https://genetixbay.com/knowledge/glossary/coa.md) lists each solvent in ppm (µg/g) against a limit; limits vary widely by solvent and jurisdiction, with lower-toxicity solvents generally allowed at higher levels. [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md) products such as [rosin](https://genetixbay.com/knowledge/glossary/rosin.md) and [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md) should read [ND](https://genetixbay.com/knowledge/glossary/non-detect.md), though some markets still test them. GenetixBay doesn't cover extraction methods; this entry defines the test only. ## Units and formula ppm = µg/g. Results are compared with solvent-specific action limits. ## Don't confuse with - **Terpene test**: also GC, but measuring aroma compounds rather than solvents. - **Solventless**: describes a production method; the test confirms the outcome. ## Related terms [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [LOD](https://genetixbay.com/knowledge/glossary/lod.md) --- # Restock > A restock is a new batch of a previously sold seed line; it may come from different parent plants than the original batch. - Canonical: https://genetixbay.com/knowledge/glossary/restock.html - Also written: restocks, restocked, back in stock, remake - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A restock is new stock of something that sold out. With seed, that means a new batch was made, and a new batch is a new set of pollinations. ## In practice If the breeder used the same mother and the same father (kept as clones or stored pollen), a restock can match the original closely. If a new male was chosen, or the line was remade from different plants, the restock is effectively a different population under the same name. Growers who loved the first batch and hated the second are often seeing exactly that. Ask whether a restock used the same parents and when the seed was made. Batch-level records, such as a separate GenetixBay batch ID for each production run, let growers compare batches instead of arguing about names. ## Don't confuse with - **Remake**: an openly new version of an old cross; at least it admits the change. - **Drop**: the first release. ## Related terms [Drop](https://genetixbay.com/knowledge/glossary/drop.md), [Line](https://genetixbay.com/knowledge/glossary/line.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Batch](https://genetixbay.com/knowledge/glossary/batch.md) ## Read more - [How to document lineage evidence (GB-ID evidence levels L0-L4)](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md) --- # Rhizosphere > The narrow zone of medium immediately around living roots, shaped by root exudates and densely populated by microbes that influence nutrient uptake and root health. - Canonical: https://genetixbay.com/knowledge/glossary/rhizosphere.html - Also written: root zone biology, rhizosphere microbiome, root microbiome, rhizo - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The rhizosphere is the thin layer of soil or medium, roughly a few millimetres, that is directly influenced by roots. Roots release sugars, organic acids and other exudates, and this feeds a microbial community far denser and more active than in the bulk medium. Those microbes help mineralise nutrients, compete with or suppress pathogens, and change local [pH](https://genetixbay.com/knowledge/glossary/ph.md). ## In practice Living-soil growers build the rhizosphere deliberately with compost, cover crops and minimal disturbance. In hydro, a "biological" reservoir with beneficial bacteria or fungi aims at the same idea. GenetixBay's preference for hydro is a [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md): bacteria will show up anyway, so you may as well have good ones. A fully sterile system is valid too, but only if you commit to it. What hurts it: [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) and low oxygen, very high salt [EC](https://genetixbay.com/knowledge/glossary/ec.md), broad-spectrum sterilants used half-heartedly, and warm stagnant solution, which favours *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)* species. [Molasses](https://genetixbay.com/knowledge/glossary/molasses.md) and sugars fed to the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) feed these microbes, not the plant. ## Don't confuse with - **Root zone**: the whole volume of medium roots occupy. - **Mycorrhizae**: one specific root-fungus partnership within the rhizosphere. - **Medium**: the physical substrate itself. ## Related terms [Mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md), [Root hair](https://genetixbay.com/knowledge/glossary/root-hair.md), [Root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) ## Read more - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) - [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # RO water > RO water is water stripped of most dissolved salts by reverse osmosis; it has near-zero EC and little buffering, so pH moves easily and Ca and Mg must be added. - Canonical: https://genetixbay.com/knowledge/glossary/ro-water.html - Also written: reverse osmosis water, reverse osmosis, RO, RO filter, RO system, purified water - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Reverse osmosis (RO) forces water under pressure through a semi-permeable membrane that rejects most dissolved ions and many organic compounds. Typical rejection is around 90–99% of [dissolved solids](https://genetixbay.com/knowledge/glossary/tds.md), depending on membrane condition and pressure. Systems usually include sediment and carbon pre-filters; the carbon stage protects the membrane from chlorine, and catalytic carbon is needed for chloramine. ## In practice RO gives a clean, predictable base, typically below about 0.02–0.05 mS/cm (20–50 µS/cm). That is ideal for hydro and for growers with hard, high-sodium or high-alkalinity [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md). Trade-offs: no calcium or magnesium, so the nutrient (or a [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) supplement) must supply all of it; almost no [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), so [pH](https://genetixbay.com/knowledge/glossary/ph.md) drifts more and [pH Down](https://genetixbay.com/knowledge/glossary/ph-down.md) overshoots easily; and a wastewater stream, often 1–4 litres per litre produced. Some growers blend RO with tap water to keep a little buffering. Replace pre-filters on schedule and watch [output EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md): a rising reading means a worn membrane. ## Don't confuse with - **Distilled water**: purified by boiling and condensing; similar result. - **Filtered tap water**: carbon or sediment filters do not remove dissolved salts. ## Myth check RO water is a genuine reason a grow needs Cal-Mag. [LED](https://genetixbay.com/knowledge/glossary/led.md) lighting is not: the LED claim is a *Myth*. See [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md). ## Related terms [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md), [General hardness](https://genetixbay.com/knowledge/glossary/general-hardness.md), [Buffering capacity](https://genetixbay.com/knowledge/glossary/buffering-capacity.md), [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md), [µS/cm](https://genetixbay.com/knowledge/glossary/us-cm.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) ## Sources 1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Rockwool > Rockwool is an inert growing medium spun from melted basalt rock into fibres, sold as plugs, cubes and slabs, that holds water and air in fixed proportions. - Canonical: https://genetixbay.com/knowledge/glossary/rockwool.html - Also written: rock wool, stonewool, stone wool, mineral wool, rockwool cubes - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Rockwool (stone wool) is made by melting basalt and chalk and spinning the melt into fine fibres, bound and formed into plugs, starter cubes, blocks and slabs. It is sterile when new, holds no nutrients, and has a very high pore volume, so it can be saturated and still hold a good fraction of air. That makes [water content](https://genetixbay.com/knowledge/glossary/moisture-content.md) highly controllable, which is why it dominates commercial crop steering. ## In practice New rockwool tends to be alkaline. Pre-soak it in pH-adjusted nutrient solution (about [pH](https://genetixbay.com/knowledge/glossary/ph.md) 5.5-5.8 is common) before use. Plants start in small plugs, move to 10 cm (4 in) blocks, and finish on slabs. Feed with every irrigation, watch [dryback](https://genetixbay.com/knowledge/glossary/dryback.md) by weight or sensor, and avoid letting it dry right out, as rewetting unevenly creates dry pockets. Fibres irritate skin and lungs; wear gloves and a dust mask when handling dry material. ## Don't confuse with - **Slab**: the large rockwool bag a mature plant finishes on; one product format. - **Insulation wool**: similar material, different density and binders; not for growing. ## Related terms [Rockwool slab](https://genetixbay.com/knowledge/glossary/rockwool-slab.md), [Crop steering](https://genetixbay.com/knowledge/glossary/crop-steering.md), [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md), [Drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), [Soilless](https://genetixbay.com/knowledge/glossary/soilless.md) ## Read more - [Growing in rockwool (stonewool cubes and slabs)](https://genetixbay.com/knowledge/systems/rockwool.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Rockwool slab > A rockwool slab is a large, plastic-wrapped block of stone wool on which several rockwool blocks sit and finish their roots, the standard format for commercial drain-to-waste. - Canonical: https://genetixbay.com/knowledge/glossary/rockwool-slab.html - Also written: slab, slabs, rockwool block, rockwool blocks, stonewool slab, grow slab - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) comes in a standard set of formats. Plugs and small cubes start seeds and cuttings; blocks, often about 10 × 10 cm (4 × 4 in) or larger, hold the young plant; and slabs, long plastic-wrapped bags of stone wool typically around 90-100 cm long, are what the blocks are set on to finish. Roots grow down from the block into the slab. ## In practice Slabs are soaked in nutrient solution before planting, then [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) slits are cut in the wrap. [Dripper](https://genetixbay.com/knowledge/glossary/drip-irrigation.md) stakes feed each block. The grower tracks slab weight or water-content sensors to control [dryback](https://genetixbay.com/knowledge/glossary/dryback.md), and slab [EC](https://genetixbay.com/knowledge/glossary/ec.md) to steer growth. Slabs differ in density and fibre orientation, which changes how they hold and release water; pick one designed for the crop and keep the type consistent run to run. Used slabs can be recycled through specialist schemes in some areas. ## Don't confuse with - **Rockwool cube or plug**: smaller starting formats. - **Coco slab (grow bag)**: similar shape and use, but [coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md). ## Related terms [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [Crop steering](https://genetixbay.com/knowledge/glossary/crop-steering.md), [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md), [Drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), [Field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md) ## Read more - [Growing in rockwool (stonewool cubes and slabs)](https://genetixbay.com/knowledge/systems/rockwool.md) - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Root aphid > Aphids that colonise roots and the crown below the medium surface, on cannabis chiefly the rice root aphid (Rhopalosiphum rufiabdominale), causing slow, unexplained decline. - Canonical: https://genetixbay.com/knowledge/glossary/root-aphid.html - Also written: root aphids, rice root aphid, Rhopalosiphum rufiabdominale, RRA - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Root aphids are [aphids](https://genetixbay.com/knowledge/glossary/aphid.md) that feed on roots instead of foliage. On indoor cannabis the main species is the rice root aphid (*Rhopalosiphum rufiabdominale*), first documented on North American cannabis in 2020. They are olive to dark green, about 1-2 mm long, and often coated with a fine white wax on the roots. ## In practice Root aphids are hard to spot because they live out of sight. Symptoms look like a feeding or watering problem: slow growth, yellowing, wilting between waterings and poor response to feed. Growers find them by tipping a plant out of its pot and inspecting roots and the root ball edge, or by seeing winged adults on [yellow sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md), often mistaken for [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md). They move between rooms on clones and in reused media. Management combines quarantine, fresh media between runs, and root-zone biologicals such as [entomopathogenic fungi](https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.md) and soil predators. Check what is registered for cannabis locally. ## Don't confuse with - **Fungus gnat**: flies with dangling legs; larvae are clear-bodied maggots, not aphids. - **Root mealybugs**: white, cottony, slow-moving and lacking cornicles. - **Root rot**: brown, slimy roots with no insects. ## Related terms [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [Steinernema feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md), [Beauveria bassiana](https://genetixbay.com/knowledge/glossary/beauveria-bassiana.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) ## Read more - [Root aphids (rice root aphid) on indoor cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/root-aphids.md) ## Sources 1. Cranshaw, W. and Wainwright-Evans, S., 2020. Cannabis sativa as a host of rice root aphid (Hemiptera: Aphididae) in North America. Journal of Integrated Pest Management 11(1):15. 2. Utah State University Extension. Rice Root Aphids (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-rice-root-aphid --- # Root hair > A microscopic tube-like outgrowth of a single root epidermal cell near the root tip that greatly increases surface area for water and nutrient uptake. - Canonical: https://genetixbay.com/knowledge/glossary/root-hair.html - Also written: root hairs, root fuzz, absorbing hairs - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A root hair is a fine extension of one epidermal cell, formed in a zone just behind the growing root tip. Root hairs are short-lived, usually days to a few weeks, and are constantly replaced as roots extend. Together they multiply the absorbing surface of a root many times over and are where most water and ion uptake happens in young roots. ## In practice The white fuzz on a new [radicle](https://genetixbay.com/knowledge/glossary/radicle.md) or on fresh hydro roots is root hairs. They are a health signal: clean, white, fuzzy roots mean oxygen and temperature are right. Brown, slimy roots with no fuzz point to oxygen starvation or [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md). Root hairs are destroyed by drying (seconds to minutes in open air), rough handling and very high [EC](https://genetixbay.com/knowledge/glossary/ec.md). That is why a rough [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) causes a short stall even when the [main roots](https://genetixbay.com/knowledge/glossary/taproot.md) look fine: the plant has to regrow its absorbing surface. In [deep water culture](https://genetixbay.com/knowledge/glossary/dwc.md), keeping solution near 18-21 °C (64-70 °F) with good aeration protects them. ## Don't confuse with - **Lateral roots**: true multicellular branch roots, not single cells. - **Mycorrhizal hyphae**: fungal threads that extend the root's reach, not plant tissue. - **Root rot**: browning disease, often first seen as loss of root hairs. ## Related terms [Radicle](https://genetixbay.com/knowledge/glossary/radicle.md), [Taproot](https://genetixbay.com/knowledge/glossary/taproot.md), [Rhizosphere](https://genetixbay.com/knowledge/glossary/rhizosphere.md), [Mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md) ## Read more - [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) - [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Root rot > Decay of roots by pathogens such as Pythium, Fusarium, Rhizoctonia or Phytophthora, usually triggered by low oxygen, heat and waterlogging around the roots. - Canonical: https://genetixbay.com/knowledge/glossary/root-rot.html - Also written: root disease, brown roots, rotting roots, crown rot, root and crown rot - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Root rot is the umbrella term for decay of a plant's roots by soil-borne or water-borne pathogens. On cannabis the main agents are the water mould *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)*, *[Fusarium](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md)* species, *[Rhizoctonia solani](https://genetixbay.com/knowledge/glossary/damping-off.md)* and occasionally *Phytophthora*. Healthy roots are white to cream and firm; rotting roots turn brown, soft and hollow, and the outer layer slides off. Rot at the base of the stem is called crown rot. ## In practice Root rot usually follows a weakness: warm water, little dissolved oxygen, [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) pots, compacted media or salt damage. In hydroponics, solution held above roughly 24-26 °C (75-79 °F) with poor aeration is the classic setup. Plants droop in the heat of the day, yellow, stall and do not respond to feed. Growers diagnose by pulling a plant and smelling and pressing the roots: a sour or rotten smell and slime mean pathogens. Fixing the cause, removing badly hit plants, cleaning the system and restoring oxygen come before any product. ## Don't confuse with - **Tea-coloured roots**: stained by additives or organic inputs but still firm. - **Overwatering**: low oxygen alone, reversible before pathogens take hold. - **Root aphids**: insects on roots, not decay. ## Related terms [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md), [Fusarium wilt](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md), [Biofilm](https://genetixbay.com/knowledge/glossary/biofilm.md), [Damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md) ## Read more - [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) - [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ## Sources 1. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Root and Crown Rot. https://pnwhandbooks.org/node/12931 3. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic production (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf --- # Root zone > The root zone is the volume of medium or solution where a plant's roots live, including its water, air, temperature, pH, EC and microbes. - Canonical: https://genetixbay.com/knowledge/glossary/root-zone.html - Also written: root environment, rootzone, root-zone conditions, below-ground - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The root zone is everything around the roots: the medium or solution, its moisture and air, its temperature, its [pH](https://genetixbay.com/knowledge/glossary/ph.md) and nutrient concentration ([EC](https://genetixbay.com/knowledge/glossary/ec.md)), and the microbes living on and around the roots. The [rhizosphere](https://genetixbay.com/knowledge/glossary/rhizosphere.md), strictly, is the thin layer of soil directly influenced by root secretions, where microbial activity is highest. ## In practice Most "nutrient" problems start in the root zone. The diagnostic order GenetixBay teaches is: check root-zone pH and EC, moisture and oxygen, and root health before blaming a [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md). Typical targets: pH about 6.0-7.0 in soil and 5.5-6.5 in [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) and hydro; root-zone temperature about 18-24 °C (64-75 °F); a medium that is moist with plenty of air, or a solution with high dissolved oxygen. Healthy roots are white to cream and smell earthy; brown, slimy or sour-smelling roots point to rot. ## Don't confuse with - **Growing medium**: the material; the root zone is the whole environment. - **Canopy**: the above-ground environment of leaves and buds. ## Related terms [Growing medium](https://genetixbay.com/knowledge/glossary/growing-medium.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [Air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), [Mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) ## Read more - [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) - [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Root-bound > A root-bound plant has filled its container so densely that roots circle the walls, water runs straight through, and growth slows or the plant wilts fast. - Canonical: https://genetixbay.com/knowledge/glossary/root-bound.html - Also written: rootbound, pot-bound, potbound, root bound, circling roots - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Root-bound (or pot-bound) describes a plant whose roots have filled the container and begun circling the walls and base, leaving little medium to hold water and air. The plant may wilt within hours of watering, need water far more often, show slowed growth, and stall after a flip because it cannot support the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). ## In practice Signs: roots poking from [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) holes, a root ball that lifts out as a solid white or brown mat, runoff appearing almost instantly. Fixes are to up-pot, or in flower to increase watering frequency rather than disturb roots. Fabric and [air-pruning pots](https://genetixbay.com/knowledge/glossary/air-pot.md) reduce circling because root tips that reach air stop elongating and branch instead. Being "full" is not automatically bad. A pot that is fully rooted at harvest is using its volume efficiently, and with frequent [fertigation](https://genetixbay.com/knowledge/glossary/fertigation.md) a small, full pot can still produce a large plant. ## Don't confuse with - **Overwatering**: drooping from saturated, airless medium; a root-bound plant droops from running out of water. - **Root rot**: brown, slimy, smelly roots from pathogens such as *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)*; a different problem. ## Related terms [Up-potting](https://genetixbay.com/knowledge/glossary/up-potting.md), [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md), [Air pot](https://genetixbay.com/knowledge/glossary/air-pot.md), [Fabric pot](https://genetixbay.com/knowledge/glossary/fabric-pot.md), [Transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md) ## Read more - [Slow or stunted cannabis growth: a differential](https://genetixbay.com/knowledge/diagnosis/slow-growth.md) - [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) ## Sources 1. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # Root-zone flush > Running a large volume of low-EC water or mild solution through the medium to wash out accumulated salts; it treats the medium, not the plant, and suits any stage. - Canonical: https://genetixbay.com/knowledge/glossary/root-zone-flush.html - Also written: root zone flush, salt flush, medium flush, leach, flush the medium, salt build-up flush, reset flush - Glossary category: Harvest, drying and curing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A root-zone flush is a corrective leach: you pass several times the container volume of low-EC, pH-adjusted water (or a dilute nutrient solution) through the medium to dissolve and wash out salts that have built up. It resets [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md) and [pH](https://genetixbay.com/knowledge/glossary/ph.md) so the roots see a predictable solution again. ## In practice When it's justified: - runoff EC well above input, for example 1.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) or more higher, and rising; - suspected lockout or salt burn with pH and root health checked; - after a feeding error or a switch of nutrient line. How growers usually do it: run about 2-3 times the [pot volume](https://genetixbay.com/knowledge/glossary/pot-size.md), pH-adjusted to the medium. In coco, [flush](https://genetixbay.com/knowledge/glossary/flushing.md) with a mild, balanced solution (around 0.5-1.0 mS/cm) rather than pure [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) to keep the buffer stable. Then check runoff EC and pH and resume normal feeding. House position: this is the one valid use of "flushing". It treats the medium, not the plant, and can be done at any stage. It is not a pre-harvest ritual. ## Don't confuse with - **Pre-harvest flushing**: plain water before harvest to "clean" the plant (Myth, harmful). - **Watering to runoff**: routine practice, not a reset. - **Reservoir change**: swapping hydro solution, not leaching a medium. ## Related terms [Flushing](https://genetixbay.com/knowledge/glossary/flushing.md), [Runoff](https://genetixbay.com/knowledge/glossary/runoff.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), [Nutrient lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md) ## Read more - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) - [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) ## Sources 1. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 2. Hershkowitz JA. 2024. Nutrient management of cannabis in controlled environments. MS thesis, Utah State University (Bugbee lab). https://digitalcommons.usu.edu/etd2023/178 --- # Rooting hormone > Rooting hormone is an auxin preparation, usually indole-3-butyric acid (IBA), applied to a cutting's base to speed and increase root formation. - Canonical: https://genetixbay.com/knowledge/glossary/rooting-hormone.html - Also written: rooting gel, rooting powder, cloning gel, auxin dip, rooting compound - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Rooting hormone is a product containing a synthetic [auxin](https://genetixbay.com/knowledge/glossary/auxin.md), most often indole-3-butyric acid (IBA) and sometimes naphthaleneacetic acid (NAA), in a gel, powder or liquid. Auxin applied to a fresh wound stimulates the formation of adventitious roots, so treated cuttings root sooner and more evenly. ## In practice Dip the freshly cut stem base into a small portion of product (never back into the stock container, which spreads pathogens), tap off excess and set it into the rooting medium. Cannabis is not a hard-to-root species; many cuttings root in plain water or [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) without hormone, but hormone usually shortens the time and evens out the batch. Concentrations for softwood cuttings are commonly in the low thousands of ppm for quick dips and lower for gels. Willow water and honey are folk alternatives; evidence for them in cannabis is thin. ## Don't confuse with - **Root stimulator (feed)**: a nutrient or [biostimulant](https://genetixbay.com/knowledge/glossary/biostimulant.md) product for rooted plants, not an auxin for cuttings. - **Cloning solution**: often a mild nutrient plus sanitiser for [aeroponic](https://genetixbay.com/knowledge/glossary/aeroponics.md) cloners. ## Related terms [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md), [Cutting](https://genetixbay.com/knowledge/glossary/cutting.md), [Auxin](https://genetixbay.com/knowledge/glossary/auxin.md), [Cloning dome](https://genetixbay.com/knowledge/glossary/cloning-dome.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) --- # Rosin > Rosin is a solventless concentrate: resin squeezed out of flower, kief or hash using heat and pressure, then collected as an oil free of plant material. - Canonical: https://genetixbay.com/knowledge/glossary/rosin.html - Also written: cannabis rosin, rosin oil, pressed rosin, rosin extract, rosin dab - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Rosin is cannabis resin extracted mechanically. The starting material is warmed and squeezed between plates so the resin flows out, usually through a fine mesh filter bag that holds back plant matter. No solvent is used, so it is a solventless product. The result ranges from a translucent sap to an opaque, buttery texture, depending on starting material, processing and any post-press handling. ## In practice What goes into the press largely decides what comes out. Rosin pressed from flower, called [flower rosin](https://genetixbay.com/knowledge/glossary/hash-rosin.md), carries more plant lipids and is usually lower in quality and yield than rosin pressed from [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md) (hash rosin). Rosin made from [fresh frozen material](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) via ice water hash is called [live rosin](https://genetixbay.com/knowledge/glossary/live-rosin.md). Post-press, rosin may be left to "jam" or "butter" as the [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) acids crystallise. GenetixBay defines rosin but doesn't provide temperatures, pressures or methods. ## Don't confuse with - **Pine rosin (colophony)**: the resin used on violin bows, unrelated. - **Resin (extract)**: [live resin](https://genetixbay.com/knowledge/glossary/live-resin.md) and [cured resin](https://genetixbay.com/knowledge/glossary/cured-resin.md) are solvent-based. - **Pressed hash**: resin compressed as a solid, not squeezed out as oil. ## Related terms [Hash rosin](https://genetixbay.com/knowledge/glossary/hash-rosin.md), [Live rosin](https://genetixbay.com/knowledge/glossary/live-rosin.md), [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md), [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md) ## Sources 1. Russo EB, Plumb J, Whiteley VL. 2021. Novel solventless extraction technique to preserve cannabinoid and terpenoid profiles of fresh cannabis inflorescence. Molecules 26(18):5496. https://doi.org/10.3390/molecules26185496 --- # Ruderalis > A name for wild or feral, short, early-flowering northern cannabis populations, the historic source of the autoflowering trait; not a separate species in GenetixBay's view. - Canonical: https://genetixbay.com/knowledge/glossary/ruderalis.html - Also written: Cannabis ruderalis, C. ruderalis, ruderalis genetics, ruderal cannabis - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Ruderalis refers to short, sparsely branched, early-maturing cannabis found growing wild or feral in Central and Eastern Europe and Central Asia. It was described as *Cannabis ruderalis* Janisch. in 1924. "Ruderal" means a plant of disturbed ground, such as roadsides and field edges. These populations often flower by age rather than night length and usually have low [THC](https://genetixbay.com/knowledge/glossary/thc.md). ## In practice For growers, "ruderalis" mostly means "where the [auto](https://genetixbay.com/knowledge/glossary/autoflower.md) [gene](https://genetixbay.com/knowledge/glossary/gene.md) came from". Modern autoflowers carry the day-neutral trait [introgressed](https://genetixbay.com/knowledge/glossary/introgression.md) into drug-type backgrounds over many generations, so a modern auto is overwhelmingly drug-type genetics plus the autoflowering [locus](https://genetixbay.com/knowledge/glossary/locus.md). Its quality says nothing about wild ruderalis. Calling an auto "a ruderalis hybrid" is fine as history. As taxonomy it is outdated. ## Don't confuse with - **Autoflower**: a trait and plant type; ruderalis is a population label. - **Hemp**: a use category within the same species. - **Landrace**: a farmer-selected local population, not a wild ruderal. ## Myth check "Indica, sativa and ruderalis are three species" is not the consensus. GenetixBay house position (Established): there is one species, *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)* L. Thousands of years ago there may have been more distinct groups, ruderalis included, but not today. See [indica, sativa, ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md). ## Related terms [Autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md), [Cannabis sativa L.](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md), [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) ## Read more - [Indica, sativa and ruderalis: what the names really mean](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) - [Breeding autoflowers: getting the trait into a photoperiod line](https://genetixbay.com/knowledge/breeding/breeding-autoflowers.md) ## Sources 1. McPartland JM. 2018. Cannabis systematics at the levels of family, genus, and species. Cannabis and Cannabinoid Research 3(1):203-212. https://doi.org/10.1089/can.2018.0039 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 3. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 --- # Runoff > Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone. - Canonical: https://genetixbay.com/knowledge/glossary/runoff.html - Also written: run-off, drain, drainage, runoff water, drain-to-waste runoff - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Runoff (drainage, [leachate](https://genetixbay.com/knowledge/glossary/watering-to-runoff.md)) is the solution that leaves a container after watering. Its [pH](https://genetixbay.com/knowledge/glossary/ph.md) and [EC](https://genetixbay.com/knowledge/glossary/ec.md) reflect the conditions in the medium more than the input solution does, because it has passed through the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) and picked up or lost ions. Runoff fraction is the share of applied water that drains, for example 1 L out of 5 L applied is 20% runoff. ## In practice In coco and rockwool [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), growers usually aim for about 10–20% runoff per day to stop salts accumulating. In soil and [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), many growers water to little or no runoff and test it only occasionally. How to test: water as normal, collect the first runoff in a clean container, and measure EC and pH promptly. For more consistent numbers, use the PourThru method developed for containers by NC State: wait about an hour after irrigation, then pour just enough distilled water on top to collect roughly 50 mL of leachate (Cavins and colleagues). Compare trends, not single readings. ## Don't confuse with - **Root-zone flush**: deliberately running large volumes through to strip salts; runoff is the normal drainage from routine watering. - **Input solution**: what goes into the pot. ## Myth check GenetixBay house position: a **[root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md)** to wash accumulated salts out of the medium is the one valid [flush](https://genetixbay.com/knowledge/glossary/flushing.md). It treats the medium, not the plant, and can be done at any stage. A **pre-harvest flush** is a *Myth* and actively harmful: it starves the plant while it is packing on its final weight and resin. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Related terms [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), [Input EC](https://genetixbay.com/knowledge/glossary/input-ec.md), [Salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), [Pour-through](https://genetixbay.com/knowledge/glossary/pour-through.md) ## Read more - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) ## Sources 1. Cavins TJ, Whipker BE, Fonteno WC, Harden B, McCall I, Gibson JL. Monitoring and managing pH and EC using the PourThru extraction method. NC State University Horticulture Information Leaflet 590. Cited via MSU Extension: https://www.canr.msu.edu/uploads/resources/pdfs/measuring_ph_and_ec_of_crops_grown_in_large_containers.pdf --- # Runoff EC > Runoff EC is the conductivity of solution draining from the pot; compared with input EC, it shows whether salts are building up or being used up in the root zone. - Canonical: https://genetixbay.com/knowledge/glossary/runoff-ec.html - Also written: drain EC, EC of runoff, runoff ppm, leachate EC, output EC - Glossary category: pH, EC and water · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Runoff EC is the [electrical conductivity](https://genetixbay.com/knowledge/glossary/ec.md) of the [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) from a container, in [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md). On its own it says little; its value is the comparison with what went in. It reflects the salt concentration in the medium's pore water, which is what the roots actually sit in. ## In practice Rules of thumb for coco and [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) media: | Runoff vs input | Meaning | |---|---| | Within about ±0.3 mS/cm | Balanced feeding | | Runoff higher by 0.5–1.0+ mS/cm | Salts accumulating; increase runoff or lower input EC | | Runoff lower | Plant is using nutrients faster than supplied; feed slightly stronger | Example: input 1.6 mS/cm, runoff 2.8 mS/cm. Salts are building up in the medium. Increase runoff fraction for a few irrigations or do a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) with a mild nutrient solution, then check that runoff returns towards input. In [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md) crop steering, growers sometimes let substrate EC climb on purpose to steer generative growth; that is a managed strategy, not neglect. ## Don't confuse with - **Input EC**: the strength of the solution you apply. - **Substrate EC**: measured in the medium by a probe; related but read differently. ## Myth check GenetixBay house position: a **root-zone flush** to wash accumulated salts out of the medium is the one valid [flush](https://genetixbay.com/knowledge/glossary/flushing.md). It treats the medium, not the plant, and can be done at any stage. A **pre-harvest flush** is a *Myth* and actively harmful: it starves the plant while it is packing on its final weight and resin. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Related terms [Input EC](https://genetixbay.com/knowledge/glossary/input-ec.md), [Runoff](https://genetixbay.com/knowledge/glossary/runoff.md), [Salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), [Osmotic stress](https://genetixbay.com/knowledge/glossary/osmotic-stress.md) ## Read more - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ## Sources 1. Cavins TJ, Whipker BE, Fonteno WC, Harden B, McCall I, Gibson JL. Monitoring and managing pH and EC using the PourThru extraction method. NC State University Horticulture Information Leaflet 590. Cited via MSU Extension: https://www.canr.msu.edu/uploads/resources/pdfs/measuring_ph_and_ec_of_crops_grown_in_large_containers.pdf 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # µS/cm > µS/cm (microsiemens per centimetre) is a unit of EC one thousandth of mS/cm, used mostly for low-conductivity water such as RO and rainwater. - Canonical: https://genetixbay.com/knowledge/glossary/us-cm.html - Also written: microsiemens per centimetre, microsiemens per centimeter, uS/cm, µS, microsiemens - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" µS/cm (microsiemens per centimetre) is a unit of [electrical conductivity](https://genetixbay.com/knowledge/glossary/ec.md). 1,000 µS/cm = 1 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md). Water-quality reports and lab analyses often use it because source waters have low conductivity and whole numbers are easier to read. Many meters switch automatically between µS/cm and mS/cm, which causes misreadings if you miss the unit on the display. ## In practice Typical values: distilled water about 0.5–3 µS/cm (rises as it absorbs CO2 from air), good [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) below about 20–50 µS/cm, rainwater roughly 5–50 µS/cm, many [tap waters](https://genetixbay.com/knowledge/glossary/tap-water.md) 200–800 µS/cm, and a flowering nutrient solution 1,400–2,200 µS/cm (1.4–2.2 mS/cm). A rising RO output reading is the first sign of worn membranes: if your RO water creeps from 15 to 60 µS/cm, it is time to service the system. The standard [calibration solution](https://genetixbay.com/knowledge/glossary/calibration-solution.md) for EC meters is 1,413 µS/cm (1.413 mS/cm), a potassium [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) solution at 25 °C. ## Units and formula µS/cm ÷ 1,000 = mS/cm. On a [500 scale](https://genetixbay.com/knowledge/glossary/ppm500.md), ppm ≈ µS/cm × 0.5; on a [700 scale](https://genetixbay.com/knowledge/glossary/ppm700.md), ppm ≈ µS/cm × 0.7. ## Don't confuse with - **mS/cm**: a thousand times larger; "1.4" and "1,400" can be the same solution. ## Related terms [EC](https://genetixbay.com/knowledge/glossary/ec.md), [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), [TDS](https://genetixbay.com/knowledge/glossary/tds.md) ## Read more - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Sources 1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality 2. University of California Cooperative Extension, Ventura County. Salinity units and conversions (640 ppm = 1 dS/m). https://ucanr.edu/node/125832 --- # S1 > S1 is seed from a plant pollinated with its own pollen; every S1 seed is female and a new genotype, not a copy of the parent. - Canonical: https://genetixbay.com/knowledge/glossary/s1.html - Also written: S1 seed, S1s, S2, S2 seed, selfed seed, first selfed generation, S1 generation - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" S1 is the first selfed generation: seed from a plant fertilised by its own pollen. In cannabis it is made by reversing a branch or clone of a female and using that pollen on the same genotype. S1s are female, because both gametes carry X. S2 is the next generation, S1 × S1 of the same line ([selfed](https://genetixbay.com/knowledge/glossary/selfing.md) again or crossed between two S1 sisters). ## In practice S1s are not clones of the parent. They reshuffle the parent's own [alleles](https://genetixbay.com/knowledge/glossary/allele.md) the way an F2 reshuffles an [F1](https://genetixbay.com/knowledge/glossary/f1.md)'s, so a pack of S1s varies: some plants close to the parent, some missing key traits, some showing [recessives](https://genetixbay.com/knowledge/glossary/recessive.md) the parent hid. At each heterozygous locus, about half the S1s become homozygous. People make S1s to preserve something of a clone in seed form, to test what a clone carries, or to start an [inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md) quickly. Each further S generation pushes inbreeding harder and raises the risk of [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md) and unstable sex expression. ## Units and formula Inbreeding coefficient: S1 F = 0.5, S2 F = 0.75, S3 F = 0.875 (starting from a non-inbred parent). ## Don't confuse with - **Clone**: an exact copy, made by cuttings. S1 is seed. - **Feminised cross**: female × different [reversed female](https://genetixbay.com/knowledge/glossary/sex-reversal.md); also all-female but not selfed. ## Myth check S1 on S1 from plants that [herm](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) is a main route to herm-prone lines. House position: selfing is mostly frowned upon; self only proven-stable females and cull every intersex offspring. See [S1s and selfing](https://genetixbay.com/knowledge/breeding/s1-selfing.md). ## Related terms [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [Sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md) ## Read more - [S1s and selfing: what happens when a plant pollinates itself](https://genetixbay.com/knowledge/breeding/s1-selfing.md) - [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) ## Sources 1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 --- # Salt build-up > Salt build-up is the accumulation of unused fertiliser and water salts in the growing medium, raising root-zone EC and causing osmotic stress and lockout-type symptoms. - Canonical: https://genetixbay.com/knowledge/glossary/salt-build-up.html - Also written: salt buildup, salt accumulation, salt build up, fertiliser salt build-up, fertilizer salt buildup, salt crust - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Salt build-up happens when more dissolved ions go into the medium than the plant takes up or the [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) carries away. Water evaporates and is transpired, salts stay behind, and the concentration in the pore water climbs. Sodium, chloride, sulfate and bicarbonate from [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md) accumulate especially, because plants use little of them. ## In practice Signs: runoff [EC](https://genetixbay.com/knowledge/glossary/ec.md) well above input EC (often by 1 mS/cm or more), white crust on the medium surface or pot edges, crisped leaf tips and margins, slowing growth, drooping despite moist medium, and deficiency-like symptoms because high salinity and imbalanced ions block uptake. Causes: low or no runoff in coco and soilless media, high-EC feeding, [hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) and infrequent large waterings that let the medium dry hard between them. Fix: a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) with enough volume (often two to three times the [pot volume](https://genetixbay.com/knowledge/glossary/pot-size.md)) of a mild, pH-adjusted nutrient solution or plain water, then resume feeding at a moderate EC with regular runoff of about 10–20%. Check that runoff EC falls back towards input. ## Don't confuse with - **Nutrient burn**: [tip burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) from a single over-strong feed. - **Pre-harvest flush**: an unrelated ritual GenetixBay rejects. ## Myth check GenetixBay house position: a **root-zone flush** to wash accumulated salts out of the medium is the one valid [flush](https://genetixbay.com/knowledge/glossary/flushing.md). It treats the medium, not the plant, and can be done at any stage. A **pre-harvest flush** is a *Myth* and actively harmful: it starves the plant while it is packing on its final weight and resin. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Related terms [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), [Osmotic stress](https://genetixbay.com/knowledge/glossary/osmotic-stress.md), [Nutrient lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md), [Runoff](https://genetixbay.com/knowledge/glossary/runoff.md), [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) ## Read more - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) - [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Cavins TJ, Whipker BE, Fonteno WC, Harden B, McCall I, Gibson JL. Monitoring and managing pH and EC using the PourThru extraction method. NC State University Horticulture Information Leaflet 590. Cited via MSU Extension: https://www.canr.msu.edu/uploads/resources/pdfs/measuring_ph_and_ec_of_crops_grown_in_large_containers.pdf --- # Sanitation > Cleaning and disinfecting rooms, tools, containers, irrigation and people's clothing so that pests and pathogens are not carried from plant to plant or crop to crop. - Canonical: https://genetixbay.com/knowledge/glossary/sanitation.html - Also written: hygiene, grow room hygiene, room sanitation, tool sterilisation, tool sterilization, disinfection - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sanitation is the set of hygiene practices that removes or kills pests and pathogens on surfaces, tools, equipment, water and people. It is the cheapest and most effective part of [IPM](https://genetixbay.com/knowledge/glossary/ipm.md), because it stops problems before they start rather than fighting them later. ## In practice Core habits: clean and disinfect rooms, walls, floors, trays, pots and irrigation lines between runs; clear plant debris and dead leaves; change or wash clothes before entering the grow, and visit the cleanest room first and quarantine last; sterilise cutting tools between plants when [taking clones](https://genetixbay.com/knowledge/glossary/cloning.md), using a disinfectant with documented [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) against [viroids](https://genetixbay.com/knowledge/glossary/viroid.md), since alcohol alone is not reliable against [HLVd](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md). Dirty surfaces must be cleaned before disinfecting, because organic matter neutralises many disinfectants. Never mix bleach with acids or ammonia-based cleaners: toxic gases form. Follow each disinfectant's label for dilution and contact time. ## Don't confuse with - **Sterilisation**: killing all microbes; most grow-room sanitation is disinfection, not true sterilisation. - **Quarantine**: controls what plants come in; sanitation controls what surfaces and people carry. - **Sterile reservoir**: a hydroponic strategy, one specific use of sanitation. ## Related terms [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md), [IPM](https://genetixbay.com/knowledge/glossary/ipm.md), [Hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), [Biofilm](https://genetixbay.com/knowledge/glossary/biofilm.md), [Cultural control](https://genetixbay.com/knowledge/glossary/cultural-control.md) ## Read more - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) ## Sources 1. Punja ZK et al., 2025. Hop latent viroid transmission, spread and longevity in cannabis; meristem tip culture. Plants 14(5):830. https://www.mdpi.com/2223-7747/14/5/830 2. BC Ministry of Agriculture. Diseases of cannabis in British Columbia (factsheet). https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/agriculture-and-seafood/animal-and-crops/plant-health/disease-factsheets/specialty-crops/diseases_of_cannabis_in_british_columbia.pdf --- # Sativa > Sativa is a popular label for tall, narrow-leaflet, slower-flowering cannabis plants; it describes plant shape at most, and all cannabis belongs to one species, Cannabis sativa. - Canonical: https://genetixbay.com/knowledge/glossary/sativa.html - Also written: sativa-dominant, sativas, narrow-leaf, sativa type - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In grower and retail use, "sativa" means a cannabis plant with narrow [leaflets](https://genetixbay.com/knowledge/glossary/leaflet.md), tall, open structure and long flowering, typical of many equatorial [landraces](https://genetixbay.com/knowledge/glossary/landrace.md). Botanically, *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)* L. is the name of the whole species, which includes every drug-type and [hemp plant](https://genetixbay.com/knowledge/glossary/hemp.md) (McPartland 2018). The two uses are easily confused. ## In practice Labels use "sativa" to promise uplifting, energetic effects. The evidence does not support that. Indica/sativa labels match measured genetic ancestry poorly (Sawler et al. 2015) and do not predict [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) or [terpene profiles](https://genetixbay.com/knowledge/glossary/terpene-profile.md) (Smith et al. 2022; Watts et al. 2021). Reported effects vary between individuals and depend on chemistry and dose, not leaf width. Today nearly every plant is a hybrid, with a few outlier landraces. As a shape description (narrow leaflets, [stretch](https://genetixbay.com/knowledge/glossary/stretch.md), long flowering) the word still has some use for growers planning space and time. ## Don't confuse with - ***Cannabis sativa* L.**: the species, which covers all cannabis. - **Hemp**: low-THC cannabis grown for fibre or seed; also *Cannabis sativa*, unrelated to the "sativa" label. - **Haze or Thai types**: real lineages often called sativa; the label adds nothing the lineage does not say better. ## Myth check House position: indica versus sativa is nonsense as a guide to effects or species. See [indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Indica](https://genetixbay.com/knowledge/glossary/indica.md), [Hybrid](https://genetixbay.com/knowledge/glossary/hybrid.md), [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Chemovar](https://genetixbay.com/knowledge/glossary/chemovar.md) ## Read more - [Indica, sativa and ruderalis: what the names really mean](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) ## Sources 1. McPartland JM. 2018. Cannabis systematics at the levels of family, genus, and species. Cannabis and Cannabinoid Research 3(1):203-212. https://doi.org/10.1089/can.2018.0039 2. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 3. Watts S, McElroy M, Migicovsky Z, Maassen H, van Velzen R, Myles S. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y --- # Sauce > Sauce is a runny, terpene-rich cannabis concentrate, usually the liquid fraction that separates when THCA crystallises out of an extract, often sold with diamonds. - Canonical: https://genetixbay.com/knowledge/glossary/sauce.html - Also written: terp sauce, terpene sauce, HTFSE, high-terpene full-spectrum extract, HTE, high terpene extract - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sauce is a liquid to syrupy concentrate high in [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and other volatile compounds. It most often forms when [THCA](https://genetixbay.com/knowledge/glossary/thca.md) crystallises out of an extract: the [crystals](https://genetixbay.com/knowledge/glossary/trichome.md) (diamonds) separate from a liquid fraction that holds most of the aroma and a share of the [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). That fraction, known in the industry as a high-terpene full-spectrum extract (HTFSE), is sold alone or with the crystals. ## In practice Sauce is usually made from [fresh frozen material](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) ([live resin](https://genetixbay.com/knowledge/glossary/live-resin.md) sauce), though [cured](https://genetixbay.com/knowledge/glossary/curing.md) sauce exists. Because it holds most of the volatile chemistry, it's chosen for flavour. Its cannabinoid percentage is lower than diamonds, while its terpene percentage on a [terpene test](https://genetixbay.com/knowledge/glossary/terpene-test.md) can be far higher than flower's. Rosin can produce a sauce-like texture as well. GenetixBay defines the product only and gives no processing information. ## Don't confuse with - **Diamonds**: the crystalline THCA fraction. - **Terpene isolates**: single terpenes, often not cannabis-derived, sold for flavouring. - **Badder**: whipped and opaque, not runny. ## Related terms [Diamonds](https://genetixbay.com/knowledge/glossary/diamonds.md), [Live resin](https://genetixbay.com/knowledge/glossary/live-resin.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Badder](https://genetixbay.com/knowledge/glossary/badder.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md) --- # Scale insect > Sap-sucking insects of the superfamily Coccoidea that settle on stems and leaves under a protective waxy or hard cover; rare on cannabis and usually introduced on other plants. - Canonical: https://genetixbay.com/knowledge/glossary/scale-insect.html - Also written: scale, scales, soft scale, armoured scale, armored scale, Coccoidea, brown soft scale - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Scale insects are sap feeders of the superfamily Coccoidea. After a short mobile [crawler](https://genetixbay.com/knowledge/glossary/crawler.md) stage, most settle in one spot and grow a cover: soft scales (family Coccidae, such as brown soft scale, *Coccus hesperidum*) produce a waxy dome and [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md), while armoured scales (Diaspididae) build a hard, detachable shield and do not make honeydew. ## In practice Scale is unusual on cannabis because the crop cycle is short, but long-lived [mother plants](https://genetixbay.com/knowledge/glossary/mother-plant.md) kept beside houseplants can pick it up. Signs are small brown or grey bumps along stems and leaf veins that do not move, plus sticky honeydew and [sooty mould](https://genetixbay.com/knowledge/glossary/sooty-mould.md) for soft scales. Crawlers are the vulnerable stage; adults under their covers shrug off most contact sprays. [Horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md) in veg, physical removal and [parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md) are the usual tools. Badly infested mothers are often easier to replace from a clean cut. Check what is registered for cannabis locally. ## Don't confuse with - **Mealybugs**: white and fluffy, still mobile as adults. - **Aphids**: soft, mobile, breed fast. - **Leaf spot lesions**: part of the leaf tissue; scales can be lifted off. ## Related terms [Mealybug](https://genetixbay.com/knowledge/glossary/mealybug.md), [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Sources 1. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects --- # Scheduling > Scheduling is placing a substance in a legal category of a drug-control law or treaty, which sets how strictly it is controlled and whether medical use is recognised. - Canonical: https://genetixbay.com/knowledge/glossary/scheduling.html - Also written: drug scheduling, drug schedule, schedule I, Schedule 1, controlled substance schedule, rescheduling - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Scheduling is the classification of drugs into numbered or lettered categories (schedules) under national law or international treaties. Each schedule carries a level of control: who may produce, prescribe, possess or research the substance, and with what licences and penalties. ## In practice Cannabis is scheduled at the international level under the [1961 Single Convention](https://genetixbay.com/knowledge/glossary/single-convention-1961.md) and, separately, in national laws. The same plant can be in different schedules in different countries, and countries reschedule over time. In the US, federal scheduling of cannabis has been under formal review. Some laws schedule "marihuana" while excluding [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) below a [THC](https://genetixbay.com/knowledge/glossary/thc.md) threshold, seeds, or mature stalks. Scheduling does not by itself make something legal or illegal for an individual; it sets the framework that other rules build on. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Legalisation**: creating a lawful supply and use system. - **Decriminalisation**: changing penalties, not schedules. ## Related terms [Single Convention on Narcotic Drugs, 1961](https://genetixbay.com/knowledge/glossary/single-convention-1961.md), [Decriminalisation vs legalisation](https://genetixbay.com/knowledge/glossary/decriminalisation.md), [Medical vs adult-use](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md), [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md) ## Sources 1. United Nations. 1961. Single Convention on Narcotic Drugs, 1961, as amended by the 1972 Protocol. https://www.unodc.org/unodc/en/treaties/single-convention.html --- # Schwazzing > Schwazzing is an aggressive defoliation method that strips almost all fan leaves on day 1 and again around day 21 of flower. - Canonical: https://genetixbay.com/knowledge/glossary/schwazzing.html - Also written: schwazz, schwaz, the schwazz, heavy defoliation - Glossary category: Cultivation and training · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Schwazzing is a named, very heavy defoliation schedule: nearly every [fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md) is removed at the start of flower, the plant regrows foliage over the next three weeks, and it is stripped again around day 21. Proponents say it pushes more light and energy into bud sites and improves airflow; critics say it simply removes [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) capacity. ## In practice It is used mainly on vigorous, healthy [photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md) with dense foliage in high-light rooms. Plants that are stressed, under-fed, slow or [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) are poor candidates. Responses vary widely by cultivar. ## Myth check House position: "tuck, don't pluck". Stripping within reason does not appear to hurt yield, and some cultivars tolerate even heavy stripping, but others suffer, and in the founder's experience tucking helps more. There is no controlled cannabis trial showing schwazzing raises yield or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md); it is an open question for [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md). Evidence: Contested. See [defoliation and lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Don't confuse with - **Lollipopping**: removes lower growth only. - **Light defoliation**: removing a few shading leaves. ## Related terms [Defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md), [Lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md), [Tucking](https://genetixbay.com/knowledge/glossary/tucking.md), [Fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md) ## Read more - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) --- # Scouting > Systematic, regular inspection of plants, traps and roots to detect pests and disease early, identify them correctly and record numbers for decisions. - Canonical: https://genetixbay.com/knowledge/glossary/scouting.html - Also written: pest scouting, crop scouting, monitoring, pest monitoring, plant inspection - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Scouting is the routine, structured inspection of a crop to find pests, disease and other problems before they spread. It includes looking at leaf [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) and undersides, [growing tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md), stems, buds, the medium surface and roots, plus reading [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md). The aim is early detection, correct identification and written counts that feed [action thresholds](https://genetixbay.com/knowledge/glossary/action-threshold.md). ## In practice A practical indoor routine: once a week, walk the whole room in the same pattern, check a set number of plants per row plus any that look off, and turn over leaves from low, mid and top canopy. Use a 10-20x hand lens for [spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) and [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) and a 40-60x scope on tips for broad and [russet mites](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md). Watch hot spots: near intakes, doors, lights and the walls. Pull a plant from its pot now and then to check roots. Record what you saw, where and how many. Flag plants with tape so you can recheck them. Scouting is cheap; missing a mite outbreak in week three of flower is not. ## Don't confuse with - **Sticky trap counts**: one part of scouting, limited to flying adults. - **Diagnosis**: working out the cause once a problem is found. ## Related terms [IPM](https://genetixbay.com/knowledge/glossary/ipm.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) ## Read more - [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) ## Sources 1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 2. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects --- # SCROG > SCROG (screen of green) trains a few plants under a horizontal net, tucking shoots so the canopy forms a flat, evenly lit layer of many tops. - Canonical: https://genetixbay.com/knowledge/glossary/scrog.html - Also written: screen of green, scrog net, scrogging, screen-of-green - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" SCROG, or screen of green, is a training method in which a horizontal net or screen is set above the pots, usually 20-30 cm (8-12 in) above the medium, and shoots are tucked under it as they grow through. The canopy spreads sideways to fill the screen, giving a flat, even layer of [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) close to the same light intensity. ## In practice A SCROG uses few plants, often one to four per square metre, and longer veg: the grower flips to flower when the screen is about 60-80% full, since the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) fills the rest. Tuck daily during late veg and the first two to three weeks of flower, then let tops grow up through the screen. Remove or tuck weak growth beneath the screen, which gets little light. SCROG pairs well with topping or mainlining and suits plant-count-limited home growers. ## Don't confuse with - **SOG**: many small plants, little or no veg, one [main cola](https://genetixbay.com/knowledge/glossary/cola.md) each. - **Trellis netting**: the same net can be used for support only, without SCROG tucking. ## Related terms [SOG](https://genetixbay.com/knowledge/glossary/sog.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Tucking](https://genetixbay.com/knowledge/glossary/tucking.md), [Trellis](https://genetixbay.com/knowledge/glossary/trellis.md), [Even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md) ## Read more - [SCROG: screen of green](https://genetixbay.com/knowledge/training/scrog.md) ## Sources 1. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 --- # Secondary nutrient > Secondary nutrients are calcium, magnesium and sulfur: macronutrients needed in substantial amounts but not included in the N-P-K numbers on a label. - Canonical: https://genetixbay.com/knowledge/glossary/secondary-nutrient.html - Also written: secondary nutrients, secondary macronutrients, secondary elements - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Secondary nutrients are calcium (Ca), magnesium (Mg) and sulfur (S). They are true macronutrients, needed in amounts comparable to phosphorus, but historically "secondary" because field soils usually supplied enough and [fertiliser labels](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md) led with [N-P-K](https://genetixbay.com/knowledge/glossary/npk-ratio.md). The term is about labelling tradition, not importance. ## In practice In [soilless growing](https://genetixbay.com/knowledge/glossary/soilless.md) they are often the first elements to run short. [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) strips the calcium and magnesium that tap water brings, coco binds calcium and magnesium on its exchange sites until buffered, and high potassium can crowd them out. A complete hydro base supplies all three: calcium from [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), magnesium and sulfur from [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md). Fertiliser labels list them under the guaranteed analysis, below N-P-K, when present. ## Don't confuse with - **Micronutrients**: needed in trace amounts only. - **Cal-Mag**: a supplement covering two of the three. - **Primary nutrients**: N, P and K. ## Related terms [Macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md), [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [Magnesium](https://genetixbay.com/knowledge/glossary/magnesium.md), [Sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md), [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) ## Read more - [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) - [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Seed bank > In cannabis slang, a seed bank is a vendor that sells seed from one or many breeders; it is not the same as a conservation genebank. - Canonical: https://genetixbay.com/knowledge/glossary/seed-bank.html - Also written: seedbank, seed banks, seed shop, seed vendor, seed company - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In cannabis culture, a seed bank is a business that sells seed, either its own lines or packs from many breeders. The term borrows from conservation science but usually means a shop. ## In practice Seed banks vary from breeder-run outlets to resellers with thousands of products. Questions worth asking any vendor: who made the seed, which batch, when, from which parents, what [germination](https://genetixbay.com/knowledge/glossary/germination.md) rate the batch tested at, and what [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md) testers reported. A vendor that cannot answer is passing on a name, not information. Buying, selling, importing or shipping [cannabis seed](https://genetixbay.com/knowledge/glossary/achene.md) is regulated differently in different countries and states. Check local rules. ## Don't confuse with - **Genebank (conservation seed bank)**: an institution that stores [accessions](https://genetixbay.com/knowledge/glossary/accession.md) long term under controlled conditions, often around -18 °C (0 °F) at low seed moisture, with passport data and periodic viability testing. - **Breeder**: makes the seed. A seed bank may or may not. - **Seed vault**: a long-term backup facility, not a shop. ## Related terms [Breeder](https://genetixbay.com/knowledge/glossary/breeder.md), [Drop](https://genetixbay.com/knowledge/glossary/drop.md), [Accession](https://genetixbay.com/knowledge/glossary/accession.md), [Germination](https://genetixbay.com/knowledge/glossary/germination.md) ## Read more - [Seed viability and storage: keeping cannabis seeds alive](https://genetixbay.com/knowledge/germination/seed-viability-storage.md) - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) --- # Seed Club > The Seed Club is GenetixBay's seed programme run through a licensed partner, offering tested seed lots with published batch records where the law allows. - Canonical: https://genetixbay.com/knowledge/glossary/seed-club.html - Also written: GenetixBay Seed Club, Bay Seed Club, the Seed Club, seed subscription - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The Seed Club is how GenetixBay members can get seed from vetted lines, including [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md). GenetixBay's core company does not handle seed: the Seed Club is a licensed partner programme, sold by the partner, and it runs only where seed sales are lawful. ## In practice Every Seed Club lot is tested, with [germination](https://genetixbay.com/knowledge/glossary/germination.md) and other results published on its [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) batch record, so members can see what they are getting before they grow it. Lines must meet the same standard as Bay Lines: a 10-plant screening grow with zero [herms](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), and a pooled [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md) from community grows that stays at or under 2% (see [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md)). Pearls are not a way to buy seed; seed is never a prize, reward or Pearl purchase. Seed laws differ widely, including on shipping, gifting and whether seed counts as cannabis. Check local rules. ## Don't confuse with - **Seed bank (vendor)**: a [seed shop](https://genetixbay.com/knowledge/glossary/seed-bank.md); the Seed Club is a curated partner programme with published batch data. - **Bay Lines**: the breeding programme; the Seed Club is a channel. ## Related terms [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md), [Herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Seed bank](https://genetixbay.com/knowledge/glossary/seed-bank.md) ## Read more - [Seed germination testing and quality control for breeders](https://genetixbay.com/knowledge/breeding/seed-germination-testing-qc.md) - [Seed viability and storage: keeping cannabis seeds alive](https://genetixbay.com/knowledge/germination/seed-viability-storage.md) --- # Seed coat > The protective outer layer of a seed; in cannabis it is fused to the fruit wall and forms the hard shell that cracks open at germination. - Canonical: https://genetixbay.com/knowledge/glossary/seed-coat.html - Also written: testa, seed shell, seed hull, shell, hull - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The seed coat (testa) is the protective layer that forms from the ovule's outer tissues and surrounds the embryo. In cannabis the testa sits tight against the pericarp (the [fruit](https://genetixbay.com/knowledge/glossary/achene.md) wall of the achene), so growers treat the two as one hard shell. It limits water uptake, guards the embryo from injury and microbes, and splits along its seam when the swelling embryo pushes the root out. ## In practice At [germination](https://genetixbay.com/knowledge/glossary/germination.md) the seed takes up water, swells, and the shell cracks along its edge; the [radicle](https://genetixbay.com/knowledge/glossary/radicle.md) emerges first, often within 24-72 hours at about 22-26 °C (72-79 °F). A [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) that comes up still wearing its shell over the [cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) is a "helmet head". Usually it falls away on its own within a day; misting it and waiting beats prying, which tears the seed leaves. Scarification (lightly sanding the shell) is sometimes used on old or very hard seed. It is rarely needed for fresh, healthy stock and can let pathogens in. ## Don't confuse with - **Achene**: the whole fruit; the seed coat is one layer of it. - **Cotyledons**: the seed leaves inside, not a covering. - **Endosperm**: stored food tissue inside the seed, not the shell. ## Related terms [Achene](https://genetixbay.com/knowledge/glossary/achene.md), [Radicle](https://genetixbay.com/knowledge/glossary/radicle.md), [Cotyledon](https://genetixbay.com/knowledge/glossary/cotyledon.md) ## Read more - [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md) ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Seed run > A seed run is a dedicated grow in which selected parents are crossed to produce a batch of seed, as opposed to growing for flower. - Canonical: https://genetixbay.com/knowledge/glossary/seed-run.html - Also written: seed runs, seed production run, making seeds, seed batch, seed lot - Glossary category: Genetics and breeding · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A seed run is a grow, or part of one, dedicated to producing seed: chosen parents are flowered together or hand-pollinated, and the plants are run until seed matures. The resulting batch is a seed lot, and every seed in it should share documented parents. ## In practice A clean seed run needs isolation (no stray pollen), labelled branches or plants, and patience: seeds generally need several weeks after pollination to mature and darken, and should be harvested from dry, intact [calyxes](https://genetixbay.com/knowledge/glossary/calyx.md). After harvest, a good breeder dries the seed, records yield and [germination](https://genetixbay.com/knowledge/glossary/germination.md) rate, and only then calls it a release candidate. The seed run is only the first half. Seed from an untested cross is a hypothesis. Tester grows show what it produces: uniformity, vigour, [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md), and [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md). GenetixBay's featured lines need a 10-plant screening grow with zero [herms](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), and only about 150 or more pooled community plants can earn "Verified under 2% herm rate" (see [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md)). ## Don't confuse with - **Pollen chucking**: making seed without selected parents, testing or records. - **Seed lot**: the batch from one seed run; a seed run can produce several lots from different crosses. - **Germination test**: a quality check on a seed lot, not the run itself. ## Related terms [Pollination](https://genetixbay.com/knowledge/glossary/pollination.md), [Cross](https://genetixbay.com/knowledge/glossary/cross.md), [Test grow](https://genetixbay.com/knowledge/glossary/test-grow.md), [Male selection](https://genetixbay.com/knowledge/glossary/male-selection.md), [Pollen](https://genetixbay.com/knowledge/glossary/pollen.md) ## Read more - [Pollination and seed production, step by step](https://genetixbay.com/knowledge/breeding/pollination-seed-production.md) - [Seed germination testing and quality control for breeders](https://genetixbay.com/knowledge/breeding/seed-germination-testing-qc.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Seed-to-sale tracking > Seed-to-sale tracking is the regulatory system that records every licensed cannabis plant and batch from propagation through harvest, processing, testing and sale. - Canonical: https://genetixbay.com/knowledge/glossary/seed-to-sale-tracking.html - Also written: seed to sale, seed-to-sale, seed-to-sale system, s2s - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Seed-to-sale tracking is the requirement, in many regulated markets, that licensed businesses record each plant or batch through its whole life: propagation, [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md), flowering, harvest, waste, drying, processing, lab [sampling](https://genetixbay.com/knowledge/glossary/homogenisation.md), packaging, transfer and retail sale. Plants or batches usually carry unique tags, often barcodes or RFID, and data is reported to a government system. ## In practice For a [licensed grower](https://genetixbay.com/knowledge/glossary/licensed-producer.md), every plant moved, every gram of waste destroyed and every package transferred has to be logged, and the inventory must reconcile. Discrepancies can trigger audits or licence action. The aim is to prevent diversion to illegal markets and to allow recalls. The concept resembles what GenetixBay does voluntarily for genetics: [GB-IDs](https://genetixbay.com/knowledge/glossary/gb-id.md) give lines, batches, plants and harvests permanent identifiers. The purposes differ. Seed-to-sale is compliance; GB-ID is provenance and preservation. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Track-and-trace**: often used as a synonym; sometimes the broader supply-chain concept. - **Batch record**: a business's internal production log. ## Related terms [Track-and-trace](https://genetixbay.com/knowledge/glossary/track-and-trace.md), [Licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md), [Compliance testing](https://genetixbay.com/knowledge/glossary/compliance-testing.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) ## Read more - [How to document lineage evidence (GB-ID evidence levels L0-L4)](https://genetixbay.com/knowledge/breeding/documenting-lineage-evidence.md) --- # Seedling > A seedling is a young cannabis plant from emergence of the cotyledons until it has several sets of true leaves, typically the first 2-3 weeks. - Canonical: https://genetixbay.com/knowledge/glossary/seedling.html - Also written: seedlings, seedling stage, sprout, baby plant - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A seedling is the young plant between emergence and the start of vigorous vegetative growth. It begins with two rounded [seed leaves](https://genetixbay.com/knowledge/glossary/cotyledon.md) (cotyledons), then produces [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) with one, then three, then five [leaflets](https://genetixbay.com/knowledge/glossary/leaflet.md). Most growers call it a seedling for roughly the first 2-3 weeks, until it has 3-4 nodes and is growing quickly. ## In practice Seedlings have small roots and little stored water, so they are easy to drown and easy to scorch. Typical targets are gentle light (about 200-400 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) PPFD), 22-26 °C (72-79 °F), fairly high humidity (about 60-70% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md)) and light watering in a small volume around the stem rather than a full soak of a big pot. Little or no feed is needed for the first week or two in most pre-fertilised mixes; in inert media a weak solution (about 0.4-0.8 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md)) is common. The classic beginner fault is [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) a seedling in a large, cold, wet pot. ## Don't confuse with - **Clone (rooted cutting)**: also small and young, but grown from a cutting, with no [taproot](https://genetixbay.com/knowledge/glossary/taproot.md) or cotyledons. - **Stretchy seedling**: a seedling with long, weak stem; usually too little light, not a separate stage. ## Related terms [Germination](https://genetixbay.com/knowledge/glossary/germination.md), [Cotyledon](https://genetixbay.com/knowledge/glossary/cotyledon.md), [Damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md), [Hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md), [Veg time](https://genetixbay.com/knowledge/glossary/veg-time.md) ## Read more - [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) --- # Segregation > Segregation is the separation of a plant's two alleles at each locus into different gametes, so offspring of a heterozygous parent vary in which allele they get. - Canonical: https://genetixbay.com/knowledge/glossary/segregation.html - Also written: Mendelian segregation, law of segregation, segregating, segregates - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Segregation is Mendel's first law: the two [alleles](https://genetixbay.com/knowledge/glossary/allele.md) a plant carries at a locus separate during meiosis, and each pollen grain or ovule receives only one of them. Offspring of a [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) parent therefore differ in which allele they inherit. ## In practice Breeders say a line "is still segregating" when its seedlings vary for a trait. That is normal in [F2](https://genetixbay.com/knowledge/glossary/f2.md) and later generations from a cross, and in [S1s](https://genetixbay.com/knowledge/glossary/s1.md) from a heterozygous clone. The F2 is where segregation is widest: traits hidden in a uniform [F1](https://genetixbay.com/knowledge/glossary/f1.md) reappear, and new combinations show up. That spread is what makes the F2 the classic generation for hunting. [Stabilising](https://genetixbay.com/knowledge/glossary/stabilisation.md) a line means selecting until segregation stops for the traits you care about: the plants become [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) there and breed true. Segregation for traits you did not select on carries on quietly. ## Don't confuse with - **Independent assortment**: about how different genes combine; segregation is about the two alleles of one gene. - **Mutation or drift**: segregation reshuffles alleles that already exist; it creates no new ones. - **Herms in a seed line**: these reflect the line's genetics and breeding history, not segregation of one simple gene. ## Related terms [Mendelian inheritance](https://genetixbay.com/knowledge/glossary/mendelian-inheritance.md), [Independent assortment](https://genetixbay.com/knowledge/glossary/independent-assortment.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md), [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md), [True breeding](https://genetixbay.com/knowledge/glossary/true-breeding.md) ## Read more - [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md) - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Selection > Selection in breeding is choosing which plants become parents, so that alleles behind the chosen traits become more common in the next generation. - Canonical: https://genetixbay.com/knowledge/glossary/selection.html - Also written: artificial selection, breeder selection, selecting, mass selection, phenotypic selection - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Selection is deciding which plants get to reproduce. In breeding it is deliberate (artificial selection): the breeder grows a population, judges it, and uses only the best plants as parents. Over generations, the [alleles](https://genetixbay.com/knowledge/glossary/allele.md) behind the chosen traits become more frequent. ## In practice Selection works on whatever the breeder measures, and only as fast as [heritability](https://genetixbay.com/knowledge/glossary/heritability.md) allows. High-heritability traits (flowering time, [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md), leaf shape) shift in a generation or two. Low-heritability traits (yield, potency percentage) need large populations, uniform conditions and repeated testing of clones or offspring. Selection also works on both sexes. Choosing the female carefully and grabbing any male wastes half the opportunity. Breeders evaluate males by structure, vigour, smell of stems and early flowers, and above all by the offspring they produce. Culling is the other half: removing every plant with [intersex](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) flowers, weak roots, poor pest resistance or off-types, whatever its other virtues. ## Units and formula Breeder's equation: R = h² × S. The response (R) equals narrow-sense heritability times the [selection differential](https://genetixbay.com/knowledge/glossary/selection-pressure.md) (S: how far the chosen parents are above the population average). ## Don't confuse with - **Natural selection**: survival in the wild or a field without a breeder choosing. - **A pheno hunt**: one round of selection among [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md). ## Related terms [Selection pressure](https://genetixbay.com/knowledge/glossary/selection-pressure.md), [Pheno hunt](https://genetixbay.com/knowledge/glossary/pheno-hunt.md), [Heritability](https://genetixbay.com/knowledge/glossary/heritability.md), [Male selection](https://genetixbay.com/knowledge/glossary/male-selection.md), [Progeny test](https://genetixbay.com/knowledge/glossary/progeny-test.md), [Stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md) ## Read more - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) - [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Selection pressure > Selection pressure is how strongly a breeder, or the environment, favours some plants over others, set by how few are kept and how demanding the criteria are. - Canonical: https://genetixbay.com/knowledge/glossary/selection-pressure.html - Also written: selective pressure, selection intensity, selection differential, breeding pressure - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Selection pressure is the strength of selection: how strongly some plants are favoured over others as parents. A breeder who keeps the top 5% of 200 plants applies heavier pressure than one who keeps the top half of 10. The environment can apply pressure too, for example a mould-prone climate culling susceptible plants. ## In practice More pressure means faster progress on the trait selected, up to a point. Keeping too few parents shrinks the [gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), raises [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) and can carry along hidden defects. Breeders balance intensity with population size, and often select for several traits at once rather than pushing one to the extreme. Pressure is also a tool. Growing a population outdoors in a wet autumn, or under pest load, shows resistance that a clean indoor room never reveals. Breeders call that "growing under pressure" to expose weaknesses. Market pressure counts. Selecting decade after decade mainly for [THC](https://genetixbay.com/knowledge/glossary/thc.md) percentage and [bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md) has pushed commercial lines towards similar profiles, a documented convergence (Smith et al. 2022). ## Units and formula Selection intensity rises as the proportion kept falls. For a normally distributed trait, keeping the top 50% gives a selection intensity of about 0.8 standard deviations; keeping the top 5% gives about 2.06, roughly two and a half times the gain per generation (Falconer and Mackay 1996). ## Don't confuse with - **Stress**: a growing condition; it becomes selection pressure only when you breed from the survivors. ## Related terms [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Heritability](https://genetixbay.com/knowledge/glossary/heritability.md), [Pheno hunt](https://genetixbay.com/knowledge/glossary/pheno-hunt.md), [Genetic bottleneck](https://genetixbay.com/knowledge/glossary/genetic-bottleneck.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md) ## Read more - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Selfing > Selfing is pollinating a plant with its own pollen, in cannabis usually by reversing part of a female to make pollen; it is the most intense form of inbreeding. - Canonical: https://genetixbay.com/knowledge/glossary/selfing.html - Also written: self-pollination, self pollination, selfed, self-fertilisation, self-fertilization, autogamy - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Selfing is fertilising a plant with its own pollen. Cannabis is dioecious, so a female does not normally make pollen; breeders induce it by treating a branch or a clone of the same female with [silver thiosulfate](https://genetixbay.com/knowledge/glossary/sts.md) ([sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md)). The seed is called [S1](https://genetixbay.com/knowledge/glossary/s1.md). ## In practice Selfing halves [heterozygosity](https://genetixbay.com/knowledge/glossary/heterozygous.md) in one generation (F = 0.5), so it brings out hidden [recessives](https://genetixbay.com/knowledge/glossary/recessive.md) quickly and can show what a clone carries. It is a fast diagnostic and a last-resort way to keep something of a clone in seed form. It is also one of the main routes to [herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) lines. Selfing a plant that has already shown [intersex](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) flowers, stacking S1 on S1, or releasing selfed seed without growing it out and culling, all spread instability. ## Don't confuse with - **S1**: the seed produced by selfing. - **Feminised seed**: any seed made with reversed female pollen; selfed seed is [feminised](https://genetixbay.com/knowledge/glossary/feminised-seed.md), but feminised seed is often a cross between two different females. - **Hermaphrodite pollination**: accidental selfing by a herm in the room, which also selects for the herm trait. ## Myth check House position: selfing is mostly frowned upon on GenetixBay. Historically it was an emergency measure to save a line, not a breeding method. Real breeding uses real, selected males, and males are encouraged and rewarded here. Only ever self a proven-stable female, then cull every intersex offspring. See [S1s and selfing](https://genetixbay.com/knowledge/breeding/s1-selfing.md). ## Related terms [S1](https://genetixbay.com/knowledge/glossary/s1.md), [Sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) ## Read more - [S1s and selfing: what happens when a plant pollinates itself](https://genetixbay.com/knowledge/breeding/s1-selfing.md) ## Sources 1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 3. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664 --- # Senescence > The programmed ageing and breakdown of leaves and other tissues, in which the plant recycles nutrients (especially nitrogen) from old leaves to developing flowers and seeds. - Canonical: https://genetixbay.com/knowledge/glossary/senescence.html - Also written: leaf senescence, fade, the fade, autumn colours, fall colors, senescing - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Senescence is the genetically controlled ageing of plant organs. In leaves, chloroplasts are dismantled and [mobile nutrients](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md) such as nitrogen, phosphorus, potassium and magnesium are moved through the phloem to growing tissue. [Chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) breaks down, unmasking yellow carotenoids and, in some cultivars, red and purple anthocyanins. Ethylene and [abscisic acid](https://genetixbay.com/knowledge/glossary/abscisic-acid.md) promote it; cytokinin delays it. ## In practice In late flower many cultivars yellow from the bottom up as the plant redirects resources to buds. That "fade" is normal in the final weeks, especially with a [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md), and growers often find it photogenic. The diagnosis question is timing and pattern: - **Normal**: gradual yellowing of older fan leaves in the last 2-3 weeks, buds still swelling. - **Too early**: lower leaves yellowing hard in mid-flower or veg, which points to nitrogen shortage, root-zone problems or [pH](https://genetixbay.com/knowledge/glossary/ph.md), not ripening. ## Don't confuse with - **Nitrogen deficiency**: same look, but at the wrong time or severity. - **Ripeness**: judged by [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md), not by leaf colour. - **Chlorosis**: yellowing from any cause. ## Myth check Plain-water pre-harvest flushing is often sold as a way to "force the fade". House position (Myth, and actively harmful): starving the plant in its most critical weeks costs yield and resin. Taper nitrogen while feeding everything else instead. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). ## Related terms [Chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md), [Anthocyanin](https://genetixbay.com/knowledge/glossary/anthocyanin.md), [Nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md), [Flowering stage](https://genetixbay.com/knowledge/glossary/flowering-stage.md), [Cytokinin](https://genetixbay.com/knowledge/glossary/cytokinin.md) ## Read more - [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) - [Mobile vs immobile nutrients: reading old vs new leaves](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. 2. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 --- # Septoria leaf spot > A fungal leaf disease caused by Septoria cannabis that produces tan to grey spots with dark margins and yellow halos, starting on lower leaves. - Canonical: https://genetixbay.com/knowledge/glossary/septoria-leaf-spot.html - Also written: septoria, Septoria cannabis, yellow leaf spot, white leaf spot, Septoria blight - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Septoria leaf spot is a fungal disease caused by *Septoria cannabis*. Spots begin small and yellow, then enlarge into tan, grey or white lesions, often angular where veins limit them, with darker edges and a yellow halo. Inside the lesions tiny black fruiting bodies (pycnidia) can be seen with a hand lens. Heavily spotted leaves yellow and drop. ## In practice Septoria is mainly an outdoor and greenhouse disease that starts on the lowest, oldest leaves and moves upward. Spores splash from infected debris and soil in rain or overhead irrigation, and leaves must stay wet for infection. Removing affected lower leaves, cleaning up fallen debris, watering at the base and mulching to stop splash slow it down. It rarely touches buds directly, but [heavy defoliation](https://genetixbay.com/knowledge/glossary/schwazzing.md) in late flower reduces yield. The fungus overwinters on plant residue, so rotate sites and remove debris at season end. Check what is registered for cannabis locally. ## Don't confuse with - **Nutrient spotting**: often symmetrical across leaves, with no pycnidia. - **Powdery mildew**: white powder on the surface, not sunken lesions. - **Spider mite stippling**: many tiny pale dots without halos. ## Related terms [Leaf spot](https://genetixbay.com/knowledge/glossary/leaf-spot.md), [Powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) ## Read more - [Septoria leaf spot (yellow leaf spot) in cannabis](https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.md) - [Rust-coloured spots on cannabis leaves: a differential](https://genetixbay.com/knowledge/diagnosis/rust-spots.md) ## Sources 1. University of Kentucky Plant Pathology. Septoria leaf spot of hemp (PPFS-AG-H-01). https://plantpathology.mgcafe.uky.edu/files/ppfs-ag-h-01.pdf 2. Utah State University Extension. Hemp leaf spot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-leaf-spot --- # Serration > The saw-toothed edge of a cannabis leaflet, with teeth pointing toward the leaflet tip. - Canonical: https://genetixbay.com/knowledge/glossary/serration.html - Also written: serrated edge, serrations, leaf teeth, toothed margin - Glossary category: Plant biology - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Serration is the toothed margin of a leaf. Cannabis leaflets are serrate: a regular row of sharp teeth along each edge, angled toward the tip. The degree of serration (fine, coarse, double) varies by genotype and is one of the visible leaf traits used in plant descriptions and variety test guidelines. ## In practice Serration is a quick identifier. The [first true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) of a seedling are serrated; the cotyledons are not. That is how growers tell them apart at a glance. Adult leaflets keep their teeth unless something distorts the leaf. Changes along the margin are diagnostic. [Burnt tips](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) that creep inward point to excess salts or high [EC](https://genetixbay.com/knowledge/glossary/ec.md); rust-coloured spotting along the edges often points to potassium or calcium issues, after [pH](https://genetixbay.com/knowledge/glossary/ph.md) and [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) are ruled out; tightly curled, twisted margins with odd serration on new growth can indicate [broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md) or herbicide drift. Some leaf-shape mutants, such as smooth-edged "duckfoot" types, lose normal leaflet separation and serration. These are genetic variants, not [deficiencies](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md). ## Don't confuse with - **Leaflet**: the blade that carries the serrated edge. - **Clawing**: leaflet tips curling down, a separate symptom. - **Trichomes**: hair-like outgrowths on the surface, not the edge. ## Related terms [Leaflet](https://genetixbay.com/knowledge/glossary/leaflet.md), [True leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md), [Fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. UPOV. 2023. Test guidelines for hemp (Cannabis sativa L.), TG/276/1. https://www.upov.int/edocs/tgdocs/en/tg276_01.pdf --- # Sesquiterpene > A sesquiterpene is a fifteen-carbon terpene made from farnesyl pyrophosphate, such as beta-caryophyllene, humulene and bisabolol; they are heavier and less volatile than monoterpenes. - Canonical: https://genetixbay.com/knowledge/glossary/sesquiterpene.html - Also written: sesquiterpenes, C15 terpene, sesquiterpenoid, sesquiterpenoids - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A sesquiterpene contains fifteen carbons, three isoprene units, built from farnesyl pyrophosphate. The common ones in cannabis are [beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md) (spicy, peppery), alpha-humulene (woody, hoppy), [alpha-bisabolol](https://genetixbay.com/knowledge/glossary/bisabolol.md) (floral, chamomile-like), nerolidol (woody, floral), guaiol (piney, woody) and valencene (citrus). The oxygenated forms are sesquiterpenoids. ## In practice Sesquiterpenes are less volatile than [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md), so in stored or dried flower their share of the [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) total tends to rise even if the absolute amount is steady. A profile that reads "caryophyllene and humulene [dominant](https://genetixbay.com/knowledge/glossary/dominant.md)" in old material may have been "[myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md) and [limonene](https://genetixbay.com/knowledge/glossary/limonene.md) dominant" when fresh. When comparing COAs, check how old the sample was and how it was stored. Beta-caryophyllene is also unusual because it binds the CB2 receptor in lab studies; no health claims follow from that. ## Don't confuse with - **Monoterpene**: C10, lighter, more volatile. - **Caryophyllene oxide**: an oxidation product of beta-caryophyllene. - **Diterpene**: C20 compounds, minor in cannabis aroma. ## Related terms [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md), [Humulene](https://genetixbay.com/knowledge/glossary/humulene.md), [Bisabolol](https://genetixbay.com/knowledge/glossary/bisabolol.md), [Nerolidol](https://genetixbay.com/knowledge/glossary/nerolidol.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # Sex ratio > The share of offspring that are female; because only females lay eggs, a female-biased ratio speeds population growth. - Canonical: https://genetixbay.com/knowledge/glossary/sex-ratio.html - Also written: female ratio, proportion of females - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sex ratio is the proportion of females among offspring, written as the female fraction or as female:male. [Spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) and [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) populations are usually female-biased in lab [life tables](https://genetixbay.com/knowledge/glossary/life-table.md), and parthenogenetic [aphids](https://genetixbay.com/knowledge/glossary/aphid.md) indoors are all female. ## In practice Only females lay eggs, so life tables include sex ratio when computing r_m and [R0](https://genetixbay.com/knowledge/glossary/net-reproductive-rate.md). A population that shifts toward males grows more slowly. Predators that eat mainly eggs and young nymphs cut future females directly. ## Don't confuse with - **Fecundity**: [eggs per female](https://genetixbay.com/knowledge/glossary/fecundity.md), before applying the sex ratio. ## Related terms [Arrhenotoky](https://genetixbay.com/knowledge/glossary/arrhenotoky.md), [Haplodiploidy](https://genetixbay.com/knowledge/glossary/haplodiploidy.md), [Life table](https://genetixbay.com/knowledge/glossary/life-table.md) ## Read more - [Temperature, humidity and pest population growth in cannabis: every major pest compared](https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.md) ## Sources 1. Birch, L.C., 1948. The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17:15-26. https://doi.org/10.2307/1605 --- # Sex reversal > Sex reversal is chemically inducing a genetically female cannabis plant to grow fertile male flowers, so its pollen can make feminised seed; silver thiosulfate is the standard agent. - Canonical: https://genetixbay.com/knowledge/glossary/sex-reversal.html - Also written: reversal, reversed female, reversed plant, colloidal silver, masculinising, masculinizing - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sex reversal is treating a genetically female (XX) plant so that it forms [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) that shed fertile pollen. Silver ions block the plant's response to [ethylene](https://genetixbay.com/knowledge/glossary/ethylene.md), a hormone involved in [female flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) development, which lets male flowers form instead (Ram and Sett 1982). [Silver thiosulfate](https://genetixbay.com/knowledge/glossary/sts.md) (STS) is the standard agent; colloidal silver works on the same principle but is less consistent. Both are generic chemical names. ## In practice Breeders reverse one female, or a branch of her, then use the pollen on other females (a [feminised](https://genetixbay.com/knowledge/glossary/feminised-seed.md) cross) or on the same plant (an [S1](https://genetixbay.com/knowledge/glossary/s1.md)). The reversed plant's own flowers are not usable bud. Silver compounds are toxic, so treated material is kept out of consumption and handled with gloves; the treatment details are in the main article. "Rodelization" is a grower term for letting a female run past ripeness in the hope she throws pollen on her own. That deliberately selects for plants that break down into [herms](https://genetixbay.com/knowledge/glossary/hermaphrodite.md), and is not good breeding. ## Don't confuse with - **Hermaphrodite**: a plant that makes both flower types on its own, from genetics or stress. Reversal is deliberate and controlled. - **Reciprocal cross**: swapping parents' roles, a different meaning of "reversed". ## Myth check Only reverse females that have stayed fully female over several runs. Reversing a plant that already herms passes that weakness on. See [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md). ## Related terms [STS](https://genetixbay.com/knowledge/glossary/sts.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md), [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md), [XY sex determination](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md) ## Read more - [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) ## Sources 1. Ram HYM, Sett R. 1982. Induction of fertile male flowers in genetically female Cannabis sativa plants by silver nitrate and silver thiosulphate anionic complex. Theoretical and Applied Genetics 62:369-375. https://doi.org/10.1007/BF00275107 2. Lubell JD, Brand MH. 2018. Foliar sprays of silver thiosulfate produce male flowers on female hemp plants. HortTechnology 28(6):743-747. https://doi.org/10.21273/HORTTECH04188-18 3. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 --- # Shake > Shake is the loose fragments of flower and sugar leaf that break off buds in handling and collect at the bottom of a bag or jar. - Canonical: https://genetixbay.com/knowledge/glossary/shake.html - Also written: shake weed, shakes, bottom of the bag, loose leaf - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Shake is the small broken pieces of bud, [sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) and loose [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) that fall off flower when it is handled, packed and moved. It gathers at the bottom of containers and is often sold cheaply. ## In practice Shake from good flower is good flower in small pieces, but it degrades faster: more surface is exposed to air, so [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) evaporate and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) oxidise sooner. Commercial "shake" can also include trim and leftovers from many batches, which is a different product. Shake is commonly used for rolling, edibles or infusions. Store shake as you would buds: airtight, cool and dark, and use it sooner. ## Don't confuse with - **Trim**: leaf cut off during trimming, before or after drying. - **Kief**: loose [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) that fall through a screen. ## Related terms [Nugs](https://genetixbay.com/knowledge/glossary/nugs.md), [Trim](https://genetixbay.com/knowledge/glossary/trim.md), [Kief](https://genetixbay.com/knowledge/glossary/kief.md), [Popcorn buds](https://genetixbay.com/knowledge/glossary/popcorn-buds.md) ## Read more - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) --- # Shatter > Shatter is a glassy, translucent solvent-based concentrate that snaps when cold, formed when an extract stays in a stable, non-crystallised state. - Canonical: https://genetixbay.com/knowledge/glossary/shatter.html - Also written: pull and snap, snap and pull, shatter BHO, amber glass - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Shatter is a [hydrocarbon extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md) with a smooth, glass-like texture that cracks cleanly like toffee. Its texture comes from the extract staying in an amorphous, non-crystalline state: [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) acids, especially [THCA](https://genetixbay.com/knowledge/glossary/thca.md), don't nucleate into [crystals](https://genetixbay.com/knowledge/glossary/trichome.md). Agitation, moisture, residual [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and time all encourage crystallisation, which turns shatter cloudy and sugary ("sugaring" or "auto-buddering"). ## In practice "Pull and snap" describes shatter that is pliable when warm and snaps when cold, typically from higher terpene content. Shatter was the [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) solvent concentrate in the early 2010s; [badder](https://genetixbay.com/knowledge/glossary/badder.md), sauce and live products have since overtaken it in many markets. Its translucence was long marketed as a sign of purity, but clarity mostly reflects the physical state, not potency or cleanliness. GenetixBay defines the product only and gives no extraction details. ## Don't confuse with - **Wax / budder**: the same chemistry agitated into an opaque, soft texture. - **Rosin**: [solventless](https://genetixbay.com/knowledge/glossary/solventless.md); can be glassy but is a different product. - **Isolate**: fully crystalline, single-compound. ## Related terms [Wax](https://genetixbay.com/knowledge/glossary/wax.md), [Badder](https://genetixbay.com/knowledge/glossary/badder.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md), [Cured resin](https://genetixbay.com/knowledge/glossary/cured-resin.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md) --- # Shore fly > Stocky dark flies of the genus Scatella (family Ephydridae) that breed in algae on wet surfaces; mostly a nuisance and contamination issue rather than a root feeder. - Canonical: https://genetixbay.com/knowledge/glossary/shore-fly.html - Also written: shore flies, Scatella, Scatella stagnalis, Ephydridae - Glossary category: Pests and diseases · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Shore flies are small flies of the family Ephydridae, mainly *Scatella* species, about 2-3 mm long. They look like stout house flies with short antennae and dark wings marked by five or so pale spots. Larvae feed on algae and microbial films on wet media, floors, benches and drip trays. ## In practice Shore flies turn up wherever algae grows: wet [rockwool cubes](https://genetixbay.com/knowledge/glossary/rockwool.md), flooded trays, hydro reservoirs open to light and puddled floors. They are not considered major root feeders, unlike [fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) larvae, but adults leave dark specks of [frass](https://genetixbay.com/knowledge/glossary/frass.md) on leaves and can carry pathogen spores between plants. Control is mostly sanitation and water management: cover cubes and reservoirs, remove standing water, and reduce algae on surfaces. [Yellow sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) show numbers. Some fungus gnat predators also take shore fly larvae, but fixing the algae solves most cases. ## Don't confuse with - **Fungus gnat**: slender, long-legged and weak fliers; larvae eat roots. - **Fruit fly**: red eyes, attracted to fermenting material. - **Whitefly**: white wings, lives on leaves. ## Related terms [Fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Biofilm](https://genetixbay.com/knowledge/glossary/biofilm.md) ## Read more - [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ## Sources 1. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf 2. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects --- # Short-day plant > A plant that flowers when the night exceeds a critical length (days are short enough); photoperiod cannabis is a short-day plant. - Canonical: https://genetixbay.com/knowledge/glossary/short-day-plant.html - Also written: short day plant, short-day plants, SDP, long-night plant, short-day flowering - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A short-day plant is one that flowers when the daily dark period is longer than a critical threshold. The name is a historical accident: experiments in the 1920s varied [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md), but it later became clear that the plant measures the uninterrupted night. "Long-night plant" is the more accurate description. Chrysanthemums, poinsettias, soybeans and photoperiod cannabis are all short-day plants. ## In practice Outdoors, photoperiod cannabis flowers in late summer as nights lengthen, earlier at higher latitudes and in cultivars from northern origins. Indoors, growers trigger it by giving a long, dark night: classically [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), and for many cultivars [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) or more light still works. The critical day length varies widely by cultivar; [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) studies found flowering triggered anywhere from about 13 to 15 hours of light depending on [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) (Zhang et al. 2021). That's why GenetixBay encourages growers to test their cultivar. A short night break (light in the middle of the dark period) can hold short-day plants vegetative. That's how mums are kept in veg commercially, and why [light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) matter. ## Don't confuse with - **Long-day plant**: flowers when nights are short (e.g. spinach). - **Day-neutral plant**: flowers by age, like [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) cannabis. - **Photoperiod**: the general day-length response, not the type. ## Related terms [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md), [Phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md), [Autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md), [Flowering stage](https://genetixbay.com/knowledge/glossary/flowering-stage.md) ## Read more - [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Sib cross > A sib cross is a cross between siblings from the same seed batch, used to advance a line (F1 × F1 gives F2) while keeping it within the family. - Canonical: https://genetixbay.com/knowledge/glossary/sib-cross.html - Also written: sibling cross, sibbing, full-sib cross, half-sib cross, sib mating - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A sib cross is a cross between siblings. Full sibs share both parents; half sibs share one. In cannabis it usually means crossing a selected female with a selected male from the same [seed batch](https://genetixbay.com/knowledge/glossary/seed-run.md), which is how [F2](https://genetixbay.com/knowledge/glossary/f2.md), [F3](https://genetixbay.com/knowledge/glossary/filial-generation.md) and later generations are made. ## In practice Sib crossing is the standard way to advance a line without bringing in outside genetics. With selection each generation, it gradually raises [homozygosity](https://genetixbay.com/knowledge/glossary/homozygous.md) and makes the line more uniform. It is slower and gentler than [selfing](https://genetixbay.com/knowledge/glossary/selfing.md). Done with tiny populations (one female, one male, every generation), sib crossing narrows the [gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md) quickly and can lead to [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md). Breeders reduce this by selecting from more plants, keeping several parallel families, and crossing families occasionally. Unlike selfing, a sib cross uses a real male. GenetixBay prefers it for exactly that reason: males are part of breeding, and a selected male carries information the female alone cannot. ## Units and formula [Inbreeding coefficient](https://genetixbay.com/knowledge/glossary/inbred-line.md) after one generation of full-sib mating from unrelated parents: F = 0.25. Half-sib: F = 0.125. ## Don't confuse with - **Selfing**: the same plant as both parents (F = 0.5 in one generation). - **Outcross**: crossing outside the family. ## Related terms [F2](https://genetixbay.com/knowledge/glossary/f2.md), [Filial generation](https://genetixbay.com/knowledge/glossary/filial-generation.md), [Inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md), [Line breeding](https://genetixbay.com/knowledge/glossary/line-breeding.md), [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md) ## Read more - [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Silica > Silica is silicon dioxide (SiO2); growers use the word loosely for any silicon supplement added to stiffen stems and improve stress tolerance. - Canonical: https://genetixbay.com/knowledge/glossary/silica.html - Also written: SiO2, silicon dioxide, silica supplement, silica additive - Glossary category: Nutrients · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Silica is silicon dioxide, the compound in quartz sand and glass, and in the glassy deposits plants form in their tissues. In growing slang, "silica" means any [silicon](https://genetixbay.com/knowledge/glossary/silicon.md) supplement, most often [potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md), sometimes [stabilised](https://genetixbay.com/knowledge/glossary/stabilisation.md) silicic acid or silica-rich amendments such as diatomaceous earth, rice [hulls](https://genetixbay.com/knowledge/glossary/seed-coat.md) or basalt dust. ## In practice Liquid silicate supplements go into plain water first, before other nutrients, then the [pH](https://genetixbay.com/knowledge/glossary/ph.md) is adjusted, because they are strongly alkaline and can gel or precipitate in a concentrated feed. Solid silica amendments release silicon slowly in soil. Cannabis does take up and deposit silicon, as Guerriero and colleagues showed, and growers report stiffer stems, though controlled cannabis yield data are limited. ## Don't confuse with - **Silicon**: the element itself. - **Silica gel**: a drying desiccant in packets, not a plant supplement. - **Diatomaceous earth for pests**: used as a physical insecticide, though it also contains silica. ## Related terms [Silicon](https://genetixbay.com/knowledge/glossary/silicon.md), [Potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md), [Beneficial element](https://genetixbay.com/knowledge/glossary/beneficial-element.md) ## Read more - [Silicon (Si) for cannabis: beneficial, not essential, and how to dose it](https://genetixbay.com/knowledge/nutrients/silicon.md) ## Sources 1. Guerriero G, Deshmukh R, Sonah H, Sergeant K, Hausman JF, Lentzen E, Valle N, Siddiqui KS, Exley C. 2019. Identification of the aquaporin gene family in Cannabis sativa and evidence for the accumulation of silicon in its tissues. Plant Science 287:110167. https://doi.org/10.1016/j.plantsci.2019.110167 2. Epstein E. 1994. The anomaly of silicon in plant biology. PNAS 91(1):11-17. https://doi.org/10.1073/pnas.91.1.11 --- # Silicon > Silicon (Si) is a beneficial element, not strictly essential, that plants absorb as silicic acid and deposit in cell walls, stiffening tissue and aiding stress tolerance. - Canonical: https://genetixbay.com/knowledge/glossary/silicon.html - Also written: Si, silicic acid, monosilicic acid, orthosilicic acid - Glossary category: Nutrients · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Silicon is classed as a [beneficial element](https://genetixbay.com/knowledge/glossary/beneficial-element.md): most plants complete their life cycle without it, but many perform better with it. Roots absorb it as uncharged monosilicic acid, and it is deposited as amorphous [silica](https://genetixbay.com/knowledge/glossary/silica.md) in cell walls and around epidermal cells. Guerriero and colleagues identified transporter [genes](https://genetixbay.com/knowledge/glossary/gene.md) and silicon accumulation in cannabis tissue. ## In practice Growers add silicon mostly as [potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md), for stiffer stems and better tolerance of heat, salt and some fungal pressure. Evidence for disease suppression is strongest in high-silicon accumulators such as grasses; cannabis is a moderate accumulator, so expect modest effects. Silicate products are strongly alkaline and must go into the water first, before other nutrients, then [pH](https://genetixbay.com/knowledge/glossary/ph.md) is adjusted. ## Don't confuse with - **Silica**: silicon dioxide, the solid form; growers often say "silica" for any silicon supplement. - **Silicone**: a synthetic polymer, unrelated to nutrition. - **Silicate**: the anion in silicate salts, which converts to silicic acid in solution. ## Myth check Silicon is not a cure for [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md). It may reduce severity a little; it does not replace environment control and sanitation (Evidence: Supported for modest effect). See [powdery mildew](https://genetixbay.com/knowledge/diseases/powdery-mildew.md). ## Related terms [Silica](https://genetixbay.com/knowledge/glossary/silica.md), [Potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md), [Beneficial element](https://genetixbay.com/knowledge/glossary/beneficial-element.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) ## Read more - [Silicon (Si) for cannabis: beneficial, not essential, and how to dose it](https://genetixbay.com/knowledge/nutrients/silicon.md) ## Sources 1. Epstein E. 1994. The anomaly of silicon in plant biology. PNAS 91(1):11-17. https://doi.org/10.1073/pnas.91.1.11 2. Guerriero G, Deshmukh R, Sonah H, Sergeant K, Hausman JF, Lentzen E, Valle N, Siddiqui KS, Exley C. 2019. Identification of the aquaporin gene family in Cannabis sativa and evidence for the accumulation of silicon in its tissues. Plant Science 287:110167. https://doi.org/10.1016/j.plantsci.2019.110167 3. Fauteux F, Remus-Borel W, Menzies JG, Belanger RR. 2005. Silicon and plant disease resistance against pathogenic fungi. FEMS Microbiology Letters 249(1):1-6. https://doi.org/10.1016/j.femsle.2005.06.034 --- # Single Convention on Narcotic Drugs, 1961 > The 1961 Single Convention on Narcotic Drugs is the UN treaty that obliges parties to control cannabis and other listed drugs, limiting them to medical and scientific use. - Canonical: https://genetixbay.com/knowledge/glossary/single-convention-1961.html - Also written: Single Convention, 1961 Single Convention, Single Convention 1961, UN drug convention - Glossary category: Legal and regulatory · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The Single Convention on Narcotic Drugs, 1961, is the main international treaty controlling cannabis. It consolidated earlier drug treaties and requires parties to limit the production, trade and use of listed substances to medical and scientific purposes, with licensing, estimates and reporting. It was amended by a 1972 Protocol. ## In practice Cannabis, cannabis resin and extracts are listed in its schedules. In December 2020 the UN Commission on Narcotic Drugs voted to remove cannabis from Schedule IV, the category for drugs considered particularly dangerous with little medical value, while keeping it in [Schedule I](https://genetixbay.com/knowledge/glossary/scheduling.md). The convention explicitly excludes cannabis grown exclusively for industrial (fibre and seed) or horticultural purposes. Countries that legalise [adult-use cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md) are, in strict treaty terms, in tension with the convention, and have argued their positions in different ways. The treaty shapes national law but does not itself set penalties. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **1971 Convention on Psychotropic Substances**: lists [THC](https://genetixbay.com/knowledge/glossary/thc.md) (dronabinol) as a substance. - **National scheduling**: each country's own drug classification. ## Related terms [Scheduling](https://genetixbay.com/knowledge/glossary/scheduling.md), [Decriminalisation vs legalisation](https://genetixbay.com/knowledge/glossary/decriminalisation.md), [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md), [Medical vs adult-use](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md) ## Sources 1. United Nations. 1961. Single Convention on Narcotic Drugs, 1961, as amended by the 1972 Protocol. https://www.unodc.org/unodc/en/treaties/single-convention.html --- # Sinsemilla > Sinsemilla (sensi) is seedless cannabis flower from unpollinated female plants; the word is Spanish for "without seed". - Canonical: https://genetixbay.com/knowledge/glossary/sinsemilla.html - Also written: sensi, sinse, sens, sin semilla - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sinsemilla (Spanish *sin semilla*, "without seed"), shortened to sensi or sinse, is flower from female plants that were never [pollinated](https://genetixbay.com/knowledge/glossary/pollination.md). Without seed to fill, the plant keeps making flowers and resin, and the dried buds have no seeds to burn or crack. ## In practice Growing sensi means removing males before they shed pollen and keeping [intersex plants](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) out of the room. Nearly all modern indoor flower is sinsemilla by default. The word was a selling point when most imported cannabis was seeded. Sinsemilla is old. Growers in many regions have produced it for centuries, and [hashish](https://genetixbay.com/knowledge/glossary/hashish.md) and [charas](https://genetixbay.com/knowledge/glossary/charas.md) traditions depend on well-grown, resinous female plants. ## Don't confuse with - **Seeded flower / brick**: cannabis grown with males present, usually compressed for export. - **Feminised seed**: a way to get all-female plants; sinsemilla is the result, however the females were obtained. ## Myth check "Old weed was weak; sensi is a modern invention." GenetixBay position (*Supported*): false. Regional growers have grown sinsemilla for generations, but the cheap seeded brick that dominated exports was what most Western users and government monitoring programmes saw. Good sensi reached the US market in volume mostly from the late 1970s and 1980s. See [old cannabis was not weak](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md). ## Related terms [Brick weed](https://genetixbay.com/knowledge/glossary/brick-weed.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md) ## Read more - [Old cannabis wasn't weak: the "so much stronger than 20 years ago" myth](https://genetixbay.com/knowledge/genetics-history/old-cannabis-was-not-weak.md) - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) ## Sources 1. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. 2. ElSohly MA, Mehmedic Z, Foster S, Gon C, Chandra S, Church JC. 2016. Changes in cannabis potency over the last 2 decades (1995-2014): analysis of current data in the United States. Biological Psychiatry 79(7):613-619. https://doi.org/10.1016/j.biopsych.2016.01.004 --- # Skunk > Skunk is a generic name for a family of early hybrid cultivars from the 1970s and 1980s, and for the pungent, musky aroma they made famous. - Canonical: https://genetixbay.com/knowledge/glossary/skunk.html - Also written: skunky, skunk weed, skunk strains, skunk family - Glossary category: Grower slang and culture · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Skunk refers to an influential family of hybrid lines developed in the 1970s and 1980s from Afghan, Mexican and Colombian material, and to the sharp, musky, skunk-like smell they carried. In UK slang "skunk" also became a general word for strong indoor herbal cannabis. ## In practice Skunk lines were among the first [stabilised](https://genetixbay.com/knowledge/glossary/stabilisation.md) [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) widely distributed as seed, and they underpin a huge part of modern indoor genetics. Original-era skunk cuts with the classic pungent aroma are now rare, many surviving only as [clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) plants in small circles. That scarcity is one reason GenetixBay pushes for open preservation of old cuts, seed and males. Research links the skunky smell to minor [volatile sulfur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) rather than to the main [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md). ## Don't confuse with - **UK "skunk"**: a media and street word for any strong indoor flower, not a lineage. - **Gas**: overlapping pungent profile, mostly from later lineages. ## Related terms [Kush](https://genetixbay.com/knowledge/glossary/kush.md), [Haze](https://genetixbay.com/knowledge/glossary/haze.md), [Elite cut](https://genetixbay.com/knowledge/glossary/elite-cut.md), [Gas](https://genetixbay.com/knowledge/glossary/gas.md) ## Read more - [How hybrid 'strains' emerged](https://genetixbay.com/knowledge/genetics-history/how-hybrid-strains-emerged.md) - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) ## Sources 1. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. --- # Slugs and snails > Molluscs such as the grey field slug (Deroceras reticulatum) that rasp ragged holes in seedlings and low leaves at night, leaving silvery slime trails. - Canonical: https://genetixbay.com/knowledge/glossary/slugs-and-snails.html - Also written: slugs, snails, slug, snail, Deroceras reticulatum, grey field slug, gray field slug - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Slugs and snails are land molluscs (class Gastropoda) that feed with a rasping tongue, the radula. The grey field slug (*Deroceras reticulatum*) is one of the most widespread plant-feeding species. They feed at night or in wet weather and hide under mulch, boards and pots by day. ## In practice Damage is ragged holes, chewed [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and shredded low leaves, plus shiny dried slime trails. They matter most for direct-sown outdoor seedlings and fresh [transplants](https://genetixbay.com/knowledge/glossary/transplanting.md); established cannabis outgrows them. A night check with a torch after rain confirms the cause. Practical controls are removing hiding places, [drip irrigation](https://genetixbay.com/knowledge/glossary/drip-irrigation.md) instead of evening overhead watering, [copper](https://genetixbay.com/knowledge/glossary/copper.md) or abrasive barriers around beds, beer traps and hand-collection. Iron [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) baits are a widely used low-toxicity active ingredient; check what is registered locally. They occasionally hitch into greenhouses on pots set on the ground. ## Don't confuse with - **Cutworms**: chew stems through at the soil line; no slime. - **Caterpillars**: leave [frass](https://genetixbay.com/knowledge/glossary/frass.md) pellets instead of slime. - **Damping-off**: rotted, pinched stems, no feeding marks. ## Related terms [Cutworm](https://genetixbay.com/knowledge/glossary/cutworm.md), [Damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md) ## Read more - [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) --- # Slurry test > A way to measure the pH and EC of a growing medium by mixing a sample with distilled water (often 1 part medium to 2 parts water), letting it stand, and measuring the liquid. - Canonical: https://genetixbay.com/knowledge/glossary/slurry-test.html - Also written: 1:2 slurry, 1:2 dilution test, slurry method, medium slurry - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A slurry test measures root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) and [EC](https://genetixbay.com/knowledge/glossary/ec.md) from a sample of the medium itself. In the common 1:2 dilution method, one volume of moist medium is mixed with two volumes of distilled water, left for about 30 minutes, and the liquid measured. Readings depend on the method, so compare like with like (Michigan State University Extension). ## In practice Use a slurry test when [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) is hard to collect, in [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), or to check a bag of medium before planting. Take samples from the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md), not the surface. The 1:2 method gives lower EC numbers than [pour-through](https://genetixbay.com/knowledge/glossary/pour-through.md), so interpret each against its own reference ranges. ## Don't confuse with - **Pour-through**: measures the liquid pushed out of the pot by added water. - **Runoff testing**: measures whatever drains after a normal watering, a rougher estimate. ## Related terms [Pour-through](https://genetixbay.com/knowledge/glossary/pour-through.md), [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md), [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) ## Read more - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) - [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ## Sources 1. Michigan State University Extension. pHix it! Getting substrate pH just right. https://www.canr.msu.edu/news/phix-it-getting-substrate-ph-just-right 2. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction --- # Smoke report > A smoke report is a grower's or consumer's write-up of how cured flower looks, smells, tastes, burns and reportedly feels, ideally linked to how it was grown. - Canonical: https://genetixbay.com/knowledge/glossary/smoke-report.html - Also written: smoke reports, smoke test, tasting notes, smoke review, smoke write-up - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A smoke report is a structured review of finished flower: appearance, aroma intact and ground, taste on the first and later draws, smoothness, ash and burn, and reported effects, plus the cure time and storage. ## In practice A good report gives context so others can learn from it: cultivar and batch, how long it dried and at what temperature and [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), cure length, jar moisture checks, and how long after harvest it was smoked. "Dried 10 days at about 15-18 °C (60-65 °F) and 58-62% RH, [cured](https://genetixbay.com/knowledge/glossary/curing.md) 6 weeks, smooth, sharp pine and lemon on the grind, grey-white ash" is useful. "Fire" is not. For comparisons, blind tasting beats open tasting: people rate what they expect. GenetixBay's [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) use blind panels for questions like hydro vs [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) taste. ## Don't confuse with - **Lab report (COA)**: measured chemistry. A smoke report is human perception; both are useful, neither replaces the other. - **Effects claims**: a smoke report records reported effects, not promised ones. ## Related terms [Grow journal](https://genetixbay.com/knowledge/glossary/grow-journal.md), [Connoisseur](https://genetixbay.com/knowledge/glossary/connoisseur.md), [Terps](https://genetixbay.com/knowledge/glossary/terps.md), [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) --- # SNP > A SNP (single nucleotide polymorphism) is a position in the DNA where plants differ by one base letter; thousands of them form the markers used in cannabis genotyping. - Canonical: https://genetixbay.com/knowledge/glossary/snp.html - Also written: single nucleotide polymorphism, SNPs, SNP marker, snip - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A SNP (pronounced "snip") is a single position in the genome where individuals differ by one DNA letter: some plants carry an A there, others a G. Each SNP is a [locus](https://genetixbay.com/knowledge/glossary/locus.md) with, usually, two [alleles](https://genetixbay.com/knowledge/glossary/allele.md). They are abundant, stable and cheap to read in bulk, which makes them the standard marker for modern [genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md). ## In practice A SNP panel reads hundreds to tens of thousands of positions at once. Comparing two cuts across a large panel gives a confident answer on whether they are the same [genotype](https://genetixbay.com/knowledge/glossary/genotype.md). Studies of North American cannabis used SNP panels to map population structure and show that commercial labels do not match genetic groups well (Henry et al. 2020). Most SNPs have no known effect on traits; they are markers, not causes. A few sit in or near [genes](https://genetixbay.com/knowledge/glossary/gene.md) that matter, such as the synthase loci, and can be used to predict a trait in [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md). ## Don't confuse with - **Mutation**: the event that originally created a SNP; a SNP is the resulting variation in the population. - **Gene**: a SNP is one letter; a gene spans thousands. - **Microsatellite (SSR)**: an older marker type based on short repeated sequences. ## Related terms [Genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md), [Marker-assisted selection](https://genetixbay.com/knowledge/glossary/marker-assisted-selection.md), [QTL](https://genetixbay.com/knowledge/glossary/qtl.md), [Locus](https://genetixbay.com/knowledge/glossary/locus.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md) ## Read more - [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md) ## Sources 1. Henry P, Khatodia S, Kapoor K, et al. 2020. A single nucleotide polymorphism assay sheds light on the extent and distribution of genetic diversity, population structure and functional basis of key traits in cultivated north American cannabis. Journal of Cannabis Research 2:26. 2. Barcaccia G, Palumbo F, Scariolo F, Vannozzi A, Borin M, Bona S. 2020. Potentials and challenges of genomics for breeding cannabis cultivars. Frontiers in Plant Science 11:573299. https://doi.org/10.3389/fpls.2020.573299 --- # Sodium > Sodium (Na) is not essential for cannabis; it enters through water, softeners and some inputs, and at high levels causes salt stress and crowds out potassium and calcium. - Canonical: https://genetixbay.com/knowledge/glossary/sodium.html - Also written: Na, Na+, sodium toxicity, salt stress - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sodium is a functional nutrient for some salt-tolerant and C4 plants but is not essential for cannabis. It is absorbed as Na+, competes with potassium at uptake sites and raises [osmotic stress](https://genetixbay.com/knowledge/glossary/osmotic-stress.md) when it accumulates. In a feed it adds [EC](https://genetixbay.com/knowledge/glossary/ec.md) without adding value. ## In practice The main sources are tap or [well water](https://genetixbay.com/knowledge/glossary/tap-water.md), water softeners (which swap calcium and magnesium for sodium), unwashed coco and some [organic amendments](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md). Yep, Gale and Zheng showed NaCl stress reduces cannabis growth, with the nutrient solution moderating the effect. Signs include leaf-margin burn, wilting despite wet media and reduced growth. Runoff that keeps climbing in EC with no rise in [feed strength](https://genetixbay.com/knowledge/glossary/input-ec.md) often points to sodium or [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) build-up. ## Don't confuse with - **Salt (in grower slang)**: any fertiliser salt, not just sodium chloride. - **Nutrient burn**: high total EC from the feed itself. - **Potassium**: needed; sodium cannot replace it in cannabis. ## Myth check Never water cannabis with softened water from an ion-exchange softener. Use the hard-water bypass, [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) or a different source. See [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md). ## Related terms [Chlorine (nutrient)](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Potassium](https://genetixbay.com/knowledge/glossary/potassium.md), [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md) ## Read more - [Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add](https://genetixbay.com/knowledge/nutrients/sodium.md) - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Sources 1. Subbarao GV, Ito O, Berry WL, Wheeler RM. 2003. Sodium: a functional plant nutrient. Critical Reviews in Plant Sciences 22(5):391-416. https://doi.org/10.1080/713610858 2. Yep B, Gale NV, Zheng Y. 2020. Aquaponic and hydroponic solutions modulate NaCl-induced stress in drug-type Cannabis sativa L. Frontiers in Plant Science 11:1169. https://doi.org/10.3389/fpls.2020.01169 --- # Sodium molybdate > Sodium molybdate dihydrate (Na2MoO4·2H2O), about 39.7% molybdenum, is the common Mo source for micronutrient mixes, used in microgram-per-litre amounts. - Canonical: https://genetixbay.com/knowledge/glossary/sodium-molybdate.html - Also written: Na2MoO4, sodium molybdate dihydrate, Na2MoO4·2H2O - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sodium molybdate is the soluble salt that supplies [molybdenum](https://genetixbay.com/knowledge/glossary/molybdenum.md) as molybdate. The dihydrate form is about 39.7% Mo and 19% Na. [Ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) molybdate is a common alternative with a higher Mo content. ## In practice Molybdenum is needed in the smallest amount of any nutrient, around 0.03-0.05 mg/L (ppm) in the final feed. At that dose the [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) it brings is negligible. It is always dosed from a concentrated [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) stock, since a single gram would supply enough for several thousand litres. It is one of the few micronutrients that becomes more available as [pH](https://genetixbay.com/knowledge/glossary/ph.md) rises. ## Units and formula 1 mg/L gives about 0.4 mg/L (ppm) Mo. To reach 0.05 ppm Mo, add about 0.13 mg/L. ## Don't confuse with - **Ammonium molybdate**: another Mo salt, with ammonium instead of sodium. - **Molybdenum disulfide**: an insoluble lubricant, not a fertiliser. ## Related terms [Molybdenum](https://genetixbay.com/knowledge/glossary/molybdenum.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Sodium](https://genetixbay.com/knowledge/glossary/sodium.md) ## Read more - [Molybdenum (Mo) in cannabis: the trace element nitrate depends on](https://genetixbay.com/knowledge/nutrients/molybdenum.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Kaiser BN, Gridley KL, Brady JN, Phillips T, Tyerman SD. 2005. The role of molybdenum in agricultural plant production. Annals of Botany 96(5):745-754. https://doi.org/10.1093/aob/mci226 2. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # SOG > SOG (sea of green) grows many small plants at high density with little or no veg time, each making one main cola, to shorten the cycle. - Canonical: https://genetixbay.com/knowledge/glossary/sog.html - Also written: sea of green, sea-of-green - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sea of green is a cultivation method that relies on plant numbers rather than plant size. Many rooted clones are flipped to flower after very short veg, often a week or two, at densities of roughly 9-20 [plants per square metre](https://genetixbay.com/knowledge/glossary/plant-density.md), so each plant grows into a single [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) [cola](https://genetixbay.com/knowledge/glossary/cola.md) and the canopy fills quickly. ## In practice SOG shortens the cycle and makes [perpetual harvests](https://genetixbay.com/knowledge/glossary/perpetual-harvest.md) practical, because the room spends little time in veg. It works best with uniform clones of a cultivar that finishes on one main cola; mixed seed plants give an uneven canopy. Lower branches are usually [lollipopped](https://genetixbay.com/knowledge/glossary/lollipopping.md), since they would only make small buds. Research on drug-type cannabis found that higher density increased yield per area but lowered the uniformity of [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) content across plants. [Plant-count rules](https://genetixbay.com/knowledge/glossary/plant-count-limit.md) in many places make SOG impractical for home growers; check local rules. ## Don't confuse with - **SCROG**: few plants, long veg, screen-trained. - **Plant density**: the measure; SOG is a method that uses high density. ## Related terms [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [Plant density](https://genetixbay.com/knowledge/glossary/plant-density.md), [Veg time](https://genetixbay.com/knowledge/glossary/veg-time.md), [Lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md), [Perpetual harvest](https://genetixbay.com/knowledge/glossary/perpetual-harvest.md) ## Read more - [SOG: sea of green](https://genetixbay.com/knowledge/training/sog.md) ## Sources 1. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 2. Vanhove W, Van Damme P, Meert N, 2011. Factors determining yield and quality of illicit indoor cannabis (Cannabis spp.) production. Forensic Science International 212(1–3):158–163. https://doi.org/10.1016/j.forsciint.2011.06.006 --- # Soil > In cannabis growing, soil means a living, organic-rich growing medium, either natural earth or a bagged mix, that supplies some nutrients and buffers pH and feeding mistakes. - Canonical: https://genetixbay.com/knowledge/glossary/soil.html - Also written: dirt, garden soil, topsoil, soil grow, native soil - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Soil, in the strict sense, is natural earth: mineral particles (sand, silt, clay) plus organic matter, water, air and living organisms. In indoor cannabis growing, "soil" is used loosely for bagged [potting mixes](https://genetixbay.com/knowledge/glossary/potting-mix.md) and composts as well, most of which are actually [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) peat- or coco-based blends with added nutrients. ## In practice Soil and soil-like mixes hold nutrients on their exchange sites and in organic matter, buffer [pH](https://genetixbay.com/knowledge/glossary/ph.md) changes, and host microbes that release nutrients over time. That makes them forgiving for beginners: missing a feed or a small pH error does less damage than in hydro. The typical target [pH range](https://genetixbay.com/knowledge/glossary/ph-scale.md) is about 6.0-7.0. Growth is generally a little slower than in well-run hydro or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), and feeding is less precise. Garden soil on its own compacts in containers and [drains](https://genetixbay.com/knowledge/glossary/runoff.md) poorly; mix it with compost and aeration ([perlite](https://genetixbay.com/knowledge/glossary/perlite.md), pumice) or use a purpose-made potting mix. ## Don't confuse with - **Soilless mix**: peat, coco or bark based, no mineral soil; often called "soil" on the bag. - **Living soil**: soil managed specifically for biology, usually reused over many cycles. ## Related terms [Potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), [Super soil](https://genetixbay.com/knowledge/glossary/super-soil.md), [Cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), [Soilless](https://genetixbay.com/knowledge/glossary/soilless.md) ## Read more - [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.md) ## Sources 1. Brady NC, Weil RR, 2017. The Nature and Properties of Soils, 15th ed. Pearson. --- # Soilless > A soilless medium contains no mineral soil, such as peat, coco, rockwool or perlite blends, and relies mostly on the grower to supply nutrients. - Canonical: https://genetixbay.com/knowledge/glossary/soilless.html - Also written: soilless mix, soilless medium, soilless growing, soil-less, inert medium - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Soilless growing uses a substrate with no mineral soil in it. Common soilless media are peat moss blends, [coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), pumice, bark and [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md), used alone or mixed. Some (peat, coco) have a [cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md) and hold nutrients; others (rockwool, perlite, clay) are nearly inert. ## In practice Soilless media are lighter, cleaner and more consistent than garden soil and are free of most soil pests. They are fed with nutrient solution, usually at every watering or nearly so, at a [pH](https://genetixbay.com/knowledge/glossary/ph.md) of about 5.5-6.5. Most "[potting soil](https://genetixbay.com/knowledge/glossary/potting-mix.md)" sold in bags is actually a soilless peat or coco mix with lime and a starter charge of fertiliser that runs out in a few weeks. [Air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), how much of the pot is air after drainage, matters more than which material is used. ## Don't confuse with - **Hydroponics**: often overlaps; soilless media fed with mineral solution are frequently called hydro. - **Soil**: contains mineral particles and, in living soil, a managed microbial population. ## Related terms [Hydroponics](https://genetixbay.com/knowledge/glossary/hydroponics.md), [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [Peat](https://genetixbay.com/knowledge/glossary/peat.md), [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [Growing medium](https://genetixbay.com/knowledge/glossary/growing-medium.md) ## Read more - [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) - [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Solvent-based extract > A solvent-based extract is a cannabis concentrate made by dissolving cannabinoids and terpenes out of plant material with a solvent such as butane, propane, ethanol or CO2. - Canonical: https://genetixbay.com/knowledge/glossary/solvent-based-extract.html - Also written: solvent extract, BHO, PHO, hydrocarbon extract, CO2 oil, CO2 extract, ethanol extract - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A solvent-based extract uses a solvent to dissolve the resin out of cannabis, after which the solvent is removed. Common solvent classes are hydrocarbons (butane, propane: BHO, PHO), alcohols (ethanol) and supercritical or subcritical [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md). The resulting crude can be sold as is or refined further into products such as shatter, wax, [badder](https://genetixbay.com/knowledge/glossary/badder.md), sauce, diamonds, [distillate](https://genetixbay.com/knowledge/glossary/distillate.md) or isolate. ## In practice These extracts dominate the commercial concentrate market. Regulated markets require residual solvent testing on them. Solvent extraction, particularly with hydrocarbons, is hazardous: amateur attempts have caused explosions, fires and serious injuries. It belongs in licensed facilities with engineered, certified equipment. GenetixBay gives definitions only and no extraction methods, solvents handling or settings. Legality varies by jurisdiction; check local rules. ## Don't confuse with - **Solventless**: [mechanical separation](https://genetixbay.com/knowledge/glossary/solventless.md) only. - **Distillate**: a refined product that usually starts from a solvent extract. - **Tincture**: an alcohol-based liquid preparation, not normally a concentrate. ## Related terms [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md), [Residual solvents](https://genetixbay.com/knowledge/glossary/residual-solvents.md), [Live resin](https://genetixbay.com/knowledge/glossary/live-resin.md), [Shatter](https://genetixbay.com/knowledge/glossary/shatter.md), [Distillate](https://genetixbay.com/knowledge/glossary/distillate.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md) --- # Solventless > Solventless describes cannabis concentrates made only by mechanical or physical separation, using screens, ice water, heat or pressure, without chemical solvents. - Canonical: https://genetixbay.com/knowledge/glossary/solventless.html - Also written: solventless concentrate, solventless extract, solvent-free, mechanical separation, non-solvent - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A solventless product is separated from the plant without dissolving it in a chemical solvent. The methods are mechanical: dry sieving ([kief](https://genetixbay.com/knowledge/glossary/kief.md), dry sift), agitation in ice water ([bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md)), hand-rubbing ([charas](https://genetixbay.com/knowledge/glossary/charas.md)), and heat-and-pressure pressing ([rosin](https://genetixbay.com/knowledge/glossary/rosin.md)). Water and ice are used in ice water hash, but water doesn't dissolve [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), so the industry counts those products as solventless. ## In practice Solventless products include kief, dry sift, ice water hash, full melt, [temple balls](https://genetixbay.com/knowledge/glossary/temple-ball.md), pressed hash, rosin and live rosin. Their appeal is simplicity and the absence of residual solvent risk, and many consumers prefer them on taste. Quality still varies widely; solventless doesn't automatically mean clean, potent or free of microbial or pesticide contamination, which come from the starting material. Russo et al. (2021) is one of few peer-reviewed studies on [fresh-frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) solventless methods. ## Don't confuse with - **Solvent-based extract**: uses butane, propane, ethanol, CO2 or similar. - **Solvent-free (marketing)**: occasionally misused for purged [solvent extracts](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md), which are not solventless. ## Related terms [Kief](https://genetixbay.com/knowledge/glossary/kief.md), [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Rosin](https://genetixbay.com/knowledge/glossary/rosin.md), [Live rosin](https://genetixbay.com/knowledge/glossary/live-rosin.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md), [Hash](https://genetixbay.com/knowledge/glossary/hash.md) ## Sources 1. Russo EB, Plumb J, Whiteley VL. 2021. Novel solventless extraction technique to preserve cannabinoid and terpenoid profiles of fresh cannabis inflorescence. Molecules 26(18):5496. https://doi.org/10.3390/molecules26185496 2. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Somaclonal variation > Somaclonal variation is genetic or epigenetic change that appears in plants regenerated from tissue culture, especially from callus, making them differ from the donor plant. - Canonical: https://genetixbay.com/knowledge/glossary/somaclonal-variation.html - Also written: somaclonal variants, somaclonal variant, tissue culture variation, in vitro variation - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Somaclonal variation is change that arises in plants grown back from [tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md). It ranges from DNA mutations and [chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md) changes to epigenetic shifts in [gene](https://genetixbay.com/knowledge/glossary/gene.md) activity. It is most common when plants are regenerated from callus (undifferentiated cell masses) and after many subculture cycles, and least common in shoot-tip and [meristem culture](https://genetixbay.com/knowledge/glossary/meristem-culture.md), which keeps organised tissue. ## In practice For preservation, somaclonal variation is a risk to manage. Labs reduce it by using meristem or shoot-tip culture instead of callus, limiting the number of subcultures, keeping growth slow, and checking regenerated plants against the original, by eye and ideally by [DNA fingerprinting](https://genetixbay.com/knowledge/glossary/genotyping.md) (Monthony et al. 2021). Some breeders in other crops use it deliberately as a source of new variation. That is not the aim when the job is to keep a clone exactly as it is. ## Don't confuse with - **Genetic drift**: a population-level process in seed lines. - **Topophysis**: [position effects](https://genetixbay.com/knowledge/glossary/topophysis.md) in cuttings, without tissue culture. - **Clone decline**: almost always pathogens or care in cuttings; somaclonal variation is specific to regenerated tissue culture plants. ## Related terms [Tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md), [Meristem culture](https://genetixbay.com/knowledge/glossary/meristem-culture.md), [Mutation](https://genetixbay.com/knowledge/glossary/mutation.md), [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md), [Polyploid](https://genetixbay.com/knowledge/glossary/polyploid.md) ## Read more - [Tissue culture basics for cannabis growers and breeders](https://genetixbay.com/knowledge/breeding/tissue-culture-basics.md) ## Sources 1. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 2. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 --- # Sooty mould > A black, soot-like fungal film that grows on the honeydew left by sap-feeding insects; it does not infect the plant but blocks light and signals an aphid, whitefly, mealybug or scale problem. - Canonical: https://genetixbay.com/knowledge/glossary/sooty-mould.html - Also written: sooty mold, black mould on leaves, black mold on leaves - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sooty mould is a group of dark fungi that live on [honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md), the sugary excretion of [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md), [mealybugs](https://genetixbay.com/knowledge/glossary/mealybug.md) and soft scales. It grows on the leaf surface without infecting the tissue, but it blocks light and makes leaves and buds unusable (UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md)). ## In practice Sooty mould is a sign, not the problem: find and control the sap-feeding insect producing the honeydew, usually directly above the blackened leaves. Once the honeydew stops, the mould dries and flakes off over time. Contaminated buds should not be used. ## Don't confuse with - **Botrytis**: grey fuzzy mould inside buds that rots the tissue. - **Frass**: [insect droppings](https://genetixbay.com/knowledge/glossary/frass.md) as pellets or specks, not a film. - **Necrosis**: dead brown tissue within the leaf, not a surface coating. ## Related terms [Honeydew](https://genetixbay.com/knowledge/glossary/honeydew.md), [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md), [Mealybug](https://genetixbay.com/knowledge/glossary/mealybug.md) ## Read more - [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) - [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) - [White or grey coating on cannabis: the master decision tree](https://genetixbay.com/knowledge/diagnosis/white-grey-coatings-decision-tree.md) ## Sources 1. UC IPM. Sooty Mold. https://ipm.ucanr.edu/home-and-landscape/sooty-mold/ --- # Spectrum > Spectrum is the mix of wavelengths a light source emits, from UV through blue, green, red and far-red; it shapes plant form, while intensity drives most yield. - Canonical: https://genetixbay.com/knowledge/glossary/spectrum.html - Also written: light spectrum, spectral distribution, SPD, spectral power distribution, light colour, light color - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A light's spectrum (spectral power distribution) is how its output is spread across wavelengths, usually shown as a graph from about 300 to 800 nm. Plants read spectrum through photoreceptors: phytochromes respond to red and [far-red](https://genetixbay.com/knowledge/glossary/far-red.md), cryptochromes and phototropins to blue and [UV-A](https://genetixbay.com/knowledge/glossary/uv-a.md), UVR8 to [UV-B](https://genetixbay.com/knowledge/glossary/uv-b.md). Spectrum steers shape, [stretch](https://genetixbay.com/knowledge/glossary/stretch.md), leaf thickness and timing; the total number of photons does most of the work on yield. ## In practice Growers talk about "veg spectrum" (more blue, compact plants) and "bloom spectrum" (more red). With modern white [LEDs](https://genetixbay.com/knowledge/glossary/led.md), the differences between fixtures are smaller than the marketing suggests. Westmoreland and colleagues (2021) found that lowering the blue fraction modestly raised cannabis yield, but that [photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) mattered more for cost. *Established*. Practical rules: a broad white spectrum with extra red is a sound default for both stages. Low [red to far-red ratio](https://genetixbay.com/knowledge/glossary/red-far-red-ratio.md) promotes stretch. Extra UV-B produced little visible change in controlled trials. ## Units and formula Bands commonly cited: UV-B 280–315 nm, UV-A 315–400 nm, blue 400–500 nm, green 500–600 nm, red 600–700 nm, far-red 700–750 nm (some definitions to 800 nm). ## Don't confuse with - **Colour temperature (K)**: a single number describing how warm or cool white light looks; two lamps with the same kelvin can have very different spectra. - **Intensity (PPFD)**: how much light, not which wavelengths. ## Related terms [Full spectrum](https://genetixbay.com/knowledge/glossary/full-spectrum.md), [Blue light](https://genetixbay.com/knowledge/glossary/blue-light.md), [Far-red](https://genetixbay.com/knowledge/glossary/far-red.md), [Red:far-red ratio](https://genetixbay.com/knowledge/glossary/red-far-red-ratio.md), [PAR](https://genetixbay.com/knowledge/glossary/par.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988 2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # Stabilisation > Stabilisation is breeding a seed line over several generations, with selection each time, until it reliably reproduces the chosen traits from seed. - Canonical: https://genetixbay.com/knowledge/glossary/stabilisation.html - Also written: stabilization, stabilising, stabilizing, stabilised, stabilized, line stabilisation - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Stabilisation is the work of taking a variable seed population and breeding it, generation by generation, until its seed reproduces the chosen traits reliably. Genetically, it means making the line [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) at the loci behind those traits while culling defects along the way. ## In practice A typical route: make an [F1](https://genetixbay.com/knowledge/glossary/f1.md), grow a large [F2](https://genetixbay.com/knowledge/glossary/f2.md), select the plants closest to the target, cross them (sib crossing), and repeat for [F3](https://genetixbay.com/knowledge/glossary/filial-generation.md), F4, F5 and beyond. [Backcrossing](https://genetixbay.com/knowledge/glossary/backcross.md) to a key parent or a few generations of careful selfing can speed it up. Each round needs enough plants to see what is still [segregating](https://genetixbay.com/knowledge/glossary/segregation.md), and strict culling for herms and weakness. A line is "stable" for the traits that were selected and measured, not for everything. Ask what was stabilised: chemotype, flowering time, structure, aroma? How many plants were grown in the last generation, and what was the [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md)? ## Don't confuse with - **A named cross**: a single F1 of two [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) is not stabilised, whatever the pack says. - **Uniformity**: a line can look uniform in one room and still segregate for traits not tested. - **Clone-only**: a single genotype, perfectly stable as cuttings but not in seed form. ## Myth check "Stable" without generation records and tester-grow data is a marketing word. See [backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md). ## Related terms [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [True breeding](https://genetixbay.com/knowledge/glossary/true-breeding.md), [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [Filial generation](https://genetixbay.com/knowledge/glossary/filial-generation.md), [Backcross](https://genetixbay.com/knowledge/glossary/backcross.md), [Uniformity](https://genetixbay.com/knowledge/glossary/uniformity.md) ## Read more - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 2. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718 --- # Staminate flower > A male flower that carries stamens (anthers on filaments) and no functional pistil; in cannabis, five drooping sepals around five pollen-shedding anthers. - Canonical: https://genetixbay.com/knowledge/glossary/staminate-flower.html - Also written: male flower, male flowers, staminate flowers, male pollen flower - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A staminate flower is a male flower: it has [stamens](https://genetixbay.com/knowledge/glossary/anther.md) and no functional [pistil](https://genetixbay.com/knowledge/glossary/pistil.md). A male cannabis flower is a small pendulous bud with five sepals (tepals) that open to expose five anthers on short filaments. The anthers split and release fine, wind-carried pollen. ## In practice On a male plant, staminate flowers appear in loose clusters (panicles), often earlier than females show. Closed male flowers look like small balls on a short stalk, with no [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md). They begin shedding pollen roughly 1-3 weeks after first appearing. Growers producing seedless flower remove males as soon as they are identified. Breeders keep the best ones. House position: males are a necessity in breeding, and GenetixBay encourages and rewards keeping and documenting good males in [the Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md). Staminate flowers or exposed anthers on a female plant mean an [intersex](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) (hermaphrodite) plant, which should be culled and not bred from. ## Don't confuse with - **Pistillate flower**: the [female flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) with stigmas. - **Anther**: the pollen-bearing part of the stamen. - **Pre-flower**: the first flower at a node, either sex. ## Related terms [Anther](https://genetixbay.com/knowledge/glossary/anther.md), [Pistillate flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md), [Dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md), [Pre-flower](https://genetixbay.com/knowledge/glossary/pre-flower.md), [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) ## Read more - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) - [Collecting and storing cannabis pollen](https://genetixbay.com/knowledge/breeding/pollen-collection-storage.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Steinernema feltiae > An entomopathogenic nematode applied as a soil drench whose infective juveniles enter fungus gnat larvae and thrips pupae and kill them with symbiotic bacteria. - Canonical: https://genetixbay.com/knowledge/glossary/steinernema-feltiae.html - Also written: beneficial nematodes, entomopathogenic nematodes, EPN, S. feltiae, nematodes - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Steinernema feltiae* is a microscopic roundworm that parasitises insects living in moist soil. Its infective juveniles enter a host through natural openings and release symbiotic bacteria (*Xenorhabdus* species) that kill it within a couple of days. New nematodes breed inside the body and leave to hunt again. It is one of several entomopathogenic nematodes sold for crops; it works at cooler soil temperatures than many others. ## In practice Growers mix the product in cool water and drench the medium, mainly against [fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) larvae and soil-pupating [thrips](https://genetixbay.com/knowledge/glossary/thrips.md). Nematodes are alive and fragile: store them refrigerated, use them before the expiry date, apply in the evening or under low light, keep the medium moist for several days afterwards, and do not mix them with high-EC solutions or disinfectants. Repeat applications every one to two weeks during heavy pressure are common. They pose no known risk to plants, people or pets. ## Don't confuse with - **Root-knot nematodes**: plant-parasitic nematodes that damage roots; a different group. - **Bti**: a bacterial toxin that must be eaten by larvae. - **Stratiolaelaps scimitus**: a [predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) for the same pests. ## Related terms [Fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md), [Bti](https://genetixbay.com/knowledge/glossary/bti.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) ## Read more - [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ## Sources 1. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ 2. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf --- # Stem snap test > A drying check: when small stems snap cleanly rather than bend, buds are usually dry enough to trim or jar for curing. - Canonical: https://genetixbay.com/knowledge/glossary/stem-snap-test.html - Also written: stem snap, snap test, snap the stem, stem bend test, small stem snap - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The stem snap test is the quickest way to judge when drying is done. Bend a small stem (a bud's stem or a thin branch tip): if it folds and stays bendy, the material is still too wet; if it snaps with a slight crack while larger stems still bend, buds are typically ready to jar. If big stems shatter like twigs, the dry has probably gone too far. ## In practice Start testing around day 5-7 of a slow dry. Test several branches from different parts of the room, especially those carrying the densest [colas](https://genetixbay.com/knowledge/glossary/cola.md), which dry last. House position: the stem snap is one of three checks, not the whole answer. Combine it with: - a calibrated hygrometer in a sealed jar, read after it has equilibrated (target about 55-65% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), i.e. about 0.55-0.65 aw); - weight loss, typically [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) at roughly 20-25% of fresh. Stems hold more water than buds, which is why a stem snap usually means the outer bud is a little drier than the core. That's also why the first days in the jar call for checking. ## Don't confuse with - **Supercropping**: deliberately crushing or bending live stems during the grow; "[stem snapping](https://genetixbay.com/knowledge/glossary/supercropping.md)" belongs there. - **Case hardening**: dry outside, wet inside; a snap test can miss it on dense buds. - **Over-drying**: stems shatter, buds crumble. ## Related terms [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md), [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), [Curing](https://genetixbay.com/knowledge/glossary/curing.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html --- # Sterile reservoir > A sterile reservoir keeps hydroponic solution as free of microbes as possible with oxidising sanitisers or UV, a valid strategy that only works if applied consistently. - Canonical: https://genetixbay.com/knowledge/glossary/sterile-reservoir.html - Also written: sterile hydro, sterilised reservoir, sterilized reservoir, clean reservoir, sanitised reservoir, oxidiser-treated reservoir - Glossary category: Systems and media · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A sterile reservoir is a hydroponic strategy that aims to keep the solution nearly free of microorganisms, both good and bad, so pathogens have no foothold. Common tools are oxidising sanitisers ([hypochlorous acid](https://genetixbay.com/knowledge/glossary/free-chlorine.md) or low-dose chlorine, chlorine dioxide, [hydrogen peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md)), UV-C sterilisers on the return line, and ozone in commercial systems, alongside clean equipment and fresh, low-organic water. ## In practice Commit fully. A half-sterile system, dosed occasionally, kills off [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md) and then lets pathogens recolonise an empty niche. Doses must be maintained to keep a residual through each change, and sanitisers break down faster in warm, organic-rich solution. Never combine a sterile programme with beneficial microbe products: they cancel each other out. Wear gloves and eye protection when handling concentrated oxidisers. ## Myth check House position: a [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) is preferred, because bacteria will turn up regardless. A sterile reservoir is valid, but you have to commit to it fully; it's a personal choice. See [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md). ## Don't confuse with - **Beneficial-microbe reservoir**: the opposite strategy. - **Clean reservoir (hygiene)**: lightproof, covered, changed on time; required in either strategy. ## Related terms [Beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md), [Hydrogen peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), [Chiller](https://genetixbay.com/knowledge/glossary/chiller.md) ## Read more - [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) - [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) ## Sources 1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ --- # Sticky > Sticky describes resin-rich flower that clings to fingers and scissors, a sign of heavy trichome cover and well-preserved resin. - Canonical: https://genetixbay.com/knowledge/glossary/sticky.html - Also written: sticky icky, stickiness, resinous, gooey - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sticky describes flower that leaves resin on [fingers](https://genetixbay.com/knowledge/glossary/leaflet.md), gloves and scissors. It comes from heavy coverage of glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) and from resin that has not been oxidised or knocked off. ## In practice [Wet trimming](https://genetixbay.com/knowledge/glossary/wet-trim.md) is famously sticky: scissors gum up within minutes and need cleaning with alcohol. Dry flower that stays sticky after a proper dry and cure is usually resin-rich and well handled. Over-dried or old flower loses stickiness as resin hardens and aroma [fades](https://genetixbay.com/knowledge/glossary/senescence.md). Excessively soft, spongy or damp-feeling buds are a different thing: that is too much moisture, and a mould risk. Check moisture by the [stem snap](https://genetixbay.com/knowledge/glossary/stem-snap-test.md) and by an equilibrated hygrometer reading in a sealed jar, not by how sticky it feels. ## Don't confuse with - **Wet or spongy**: under-dried flower, which can mould in the jar. - **Frosty**: how resin [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md); sticky is how it feels. ## Related terms [Frosty](https://genetixbay.com/knowledge/glossary/frosty.md), [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md), [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) --- # Sticky trap > A coloured card coated in non-drying glue that catches flying insects, used mainly to monitor pest trends: yellow for gnats, whiteflies and aphids, blue for thrips. - Canonical: https://genetixbay.com/knowledge/glossary/sticky-trap.html - Also written: sticky traps, sticky card, sticky cards, yellow sticky trap, blue sticky trap, glue trap - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A sticky trap is a plastic or card sheet, usually yellow or blue, coated with a non-drying adhesive. Flying insects attracted to the colour land and stick. Yellow attracts [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [shore flies](https://genetixbay.com/knowledge/glossary/shore-fly.md), whiteflies, [winged aphids](https://genetixbay.com/knowledge/glossary/alate.md), leafminers and [thrips](https://genetixbay.com/knowledge/glossary/thrips.md); blue is somewhat more attractive to thrips. They are first a monitoring tool and only secondarily a control. ## In practice Growers hang traps just above the canopy for flying [foliar](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) pests and close to the medium surface for fungus gnats, at a density such as one per few square metres. Each week they count catches by type on a marked area, write it down and replace the card. Rising counts are the early warning. Traps also catch [beneficial insects](https://genetixbay.com/knowledge/glossary/biological-control.md) such as [parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md) and Orius, so they are often removed or reduced while releasing flying beneficials. Keep traps clear of buds and hair. ## Don't confuse with - **Scouting**: looking at plants directly; traps add a record of flying adults. - **Mass trapping**: many traps to reduce numbers; rarely enough by itself. - **Pheromone trap**: uses a sex attractant for specific moths. ## Related terms [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md), [Fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Whitefly](https://genetixbay.com/knowledge/glossary/whitefly.md) ## Read more - [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Sources 1. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects 2. UC IPM. Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html --- # Stigma > The sticky, hair-like tip of the female pistil that catches pollen; each cannabis female flower has two, white when fresh and darkening with age. - Canonical: https://genetixbay.com/knowledge/glossary/stigma.html - Also written: stigmas, stigmata, white hairs, orange hairs, red hairs - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The stigma is the receptive surface of the [pistil](https://genetixbay.com/knowledge/glossary/pistil.md), where [pollen grains](https://genetixbay.com/knowledge/glossary/pollen.md) land and [germinate](https://genetixbay.com/knowledge/glossary/germination.md). In cannabis each [pistillate flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) has two long, thin stigmas, usually white or cream (sometimes pink or purple), emerging in a V from the tip of the [bract](https://genetixbay.com/knowledge/glossary/bract.md). A pollen tube grows from the grain down to the single ovule. ## In practice Receptive stigmas are fresh, white and extended. A breeder pollinates when a branch is covered in fresh stigmas, typically in the first two to four weeks of flower. Once fertilised, the stigmas of that flower wither and brown within days, which is one way to see that pollination worked. On unpollinated plants stigmas keep coming for weeks, then gradually darken and recede. Colour change also follows heat, low [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), physical handling and spraying, so stigma colour alone is a poor harvest clock. ## Don't confuse with - **Pistil**: the whole female organ; the stigma is its tip. - **Trichome**: resin gland on the bract surface, not a hair from the ovary. - **Pre-flower**: the first individual flower, identified by its stigmas. ## Related terms [Pistil](https://genetixbay.com/knowledge/glossary/pistil.md), [Bract](https://genetixbay.com/knowledge/glossary/bract.md), [Pistillate flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md), [Anther](https://genetixbay.com/knowledge/glossary/anther.md) ## Read more - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) - [Pollination and seed production, step by step](https://genetixbay.com/knowledge/breeding/pollination-seed-production.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Stippling > A pattern of many tiny pale dots on leaves where a sucking pest such as a spider mite has emptied individual cells; the first visible sign of a mite infestation. - Canonical: https://genetixbay.com/knowledge/glossary/stippling.html - Also written: stipples, leaf stippling, speckled leaves, pin-prick spots - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Stippling is the speckled look of a leaf covered in hundreds of tiny pale or white dots. Each dot is a cell, or a small group of cells, emptied by a feeding mite or insect. On cannabis it is the classic early sign of [two-spotted spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), usually seen on the upper surface while the mites feed underneath (Utah State University Extension). ## In practice When you see stippling, turn the leaf over and use a 10-30x lens: spider mites, round eggs, cast skins and fine silk confirm it. Heavy stippling merges into a bronzed, grey or dusty look and the leaf yellows. Calcium spots differ: they are fewer, larger and irregular, and no insects are present. ## Don't confuse with - **Thrips damage**: silvery, papery streaks with tiny black dots of excrement. - **Calcium spots**: rust-brown patches with no pests underneath. - **Septoria leaf spot**: larger spots with dark margins and black fruiting bodies. ## Related terms [Two-spotted spider mite](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Jeweler's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) - [Cannabis lookalike problems: how to tell them apart](https://genetixbay.com/knowledge/diagnosis/lookalikes.md) ## Sources 1. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php --- # Stock solution > A stock solution is a concentrated nutrient mix, often 100x or 200x final strength, diluted into the reservoir; calcium and sulfate/phosphate stocks must stay separate. - Canonical: https://genetixbay.com/knowledge/glossary/stock-solution.html - Also written: nutrient concentrate, stock tank, 100x stock - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A stock solution is a concentrated solution of one or more fertiliser salts, made at a fixed multiple of feeding strength, typically 100x or 200x. It is diluted into the reservoir or injected through a dosing system to give the final nutrient solution. ## In practice Stocks make home-made feeds practical: weighing salts once for 10 litres of 100x stock covers 1,000 litres of feed, and [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md) that would need milligram weighing become millilitre doses. The rule is separation. Calcium salts go in tank A; [sulfates](https://genetixbay.com/knowledge/glossary/sulfate.md) and [phosphates](https://genetixbay.com/knowledge/glossary/phosphate.md) go in tank B; [iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md) usually goes in A. Solubility limits how strong a stock can be; [potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md) is the common [bottleneck](https://genetixbay.com/knowledge/glossary/genetic-bottleneck.md). Store stocks cool and dark, label them with recipe and date, and use acid-resistant containers if acid is included. ## Units and formula For a stock at multiple M: grams of salt per litre of stock = target mg/L of element ÷ (element % × 10) × M. ## Don't confuse with - **Stock plant**: a [mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md) kept for cuttings. - **Working solution**: the diluted feed that reaches the roots. ## Related terms [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md), [ppm of an element](https://genetixbay.com/knowledge/glossary/elemental-ppm.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) ## Read more - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - [Per-element feeding tricks: what growers adjust, stage by stage](https://genetixbay.com/knowledge/nutrients/per-element-tricks.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # Stomata > Microscopic pores, mostly on the underside of leaves, each opened and closed by two guard cells to control gas exchange and water loss. - Canonical: https://genetixbay.com/knowledge/glossary/stomata.html - Also written: stoma, stomate, stomates, leaf pores, guard cells - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Stomata (singular stoma) are pores in the leaf epidermis, each flanked by two guard cells that swell to open the pore and shrink to close it. Open stomata let [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) in for [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) and let water vapour out ([transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md)). In cannabis most stomata are on the lower leaf surface. ## In practice Stomatal behaviour links the room's climate to growth: - **Light** opens them; darkness largely closes them. - **Dry air** (high [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), roughly above 1.5-1.6 kPa) makes them partly close to save water, so the plant fixes less carbon. - **Drought or root stress** triggers [abscisic acid](https://genetixbay.com/knowledge/glossary/abscisic-acid.md), which closes them. - **Elevated CO₂** (for example 800-1,200 ppm) lets plants keep stomata a bit more closed for the same carbon gain. This is why a VPD in range, typically 0.8-1.2 kPa in veg and 1.0-1.5 kPa in flower, helps growth: the plant can keep stomata open without losing water too fast. [Foliar sprays](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) work partly through stomata and cuticle, which is why spraying the leaf underside and at lights-on is common practice. ## Don't confuse with - **Trichomes**: outgrowths, not pores. - **Lenticels**: breathing pores on bark and older stems. - **Hydathodes**: water pores at leaf margins. ## Related terms [Transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md), [Photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), [Abscisic acid](https://genetixbay.com/knowledge/glossary/abscisic-acid.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) ## Read more - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) - [CO₂ enrichment: when it pays, how much, and how to stay safe](https://genetixbay.com/knowledge/environment/co2-enrichment.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. 2. Chandra S, Lata H, Khan IA, ElSohly MA. 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14:299-306. https://doi.org/10.1007/s12298-008-0027-x --- # Strain > Strain is the popular word for a named cannabis variety; it is used loosely, and studies show strain names are an unreliable guide to genetics or chemistry. - Canonical: https://genetixbay.com/knowledge/glossary/strain.html - Also written: strains, strain name, strain names, weed strain, cannabis strain - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" "Strain" is the everyday word for a named type of cannabis. It has no formal botanical meaning; in microbiology a strain is a genetic variant of a microbe. In cannabis it can mean a clone, a seed line, a cross, or just a brand name on a jar. ## In practice Use the word, but don't trust it. A name is a claim. Genetic studies of retail cannabis found that samples sold under the same name often differ genetically, and samples with different names can be near-identical (Sawler et al. 2015). Large chemical datasets show labels and names map poorly onto actual chemical profiles (Smith et al. 2022). Renaming a cut costs nothing and changes nothing in the plant. What counts as evidence is documented lineage, a DNA comparison, a lab profile and grow reports. GenetixBay prefers "cultivar" for that reason, and records each plant with an ID rather than relying on a name. ## Don't confuse with - **Cultivar**: the formal term, with defined standards of distinctness, uniformity and stability. - **Chemovar**: a type defined by its chemistry. - **Phenotype**: one plant's expression; a strain name often covers many [phenotypes](https://genetixbay.com/knowledge/glossary/phenotype.md). ## Myth check "A strain name tells you what genetics you're getting" is busted; see [why strain names are unreliable](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Cultivar](https://genetixbay.com/knowledge/glossary/cultivar.md), [Chemovar](https://genetixbay.com/knowledge/glossary/chemovar.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md), [Genotyping](https://genetixbay.com/knowledge/glossary/genotyping.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md) ## Read more - [Why strain names are unreliable: what genetic studies show](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) - [Same cut, a thousand names: renaming, relabelling and the shrinking gene pool](https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.md) ## Sources 1. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 2. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 3. Watts S, McElroy M, Migicovsky Z, Maassen H, van Velzen R, Myles S. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y --- # Stratiolaelaps scimitus > A soil-dwelling predatory mite, formerly sold as Hypoaspis miles, that hunts fungus gnat larvae, thrips pupae and other small arthropods in the growing medium. - Canonical: https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.html - Also written: Hypoaspis, Hypoaspis miles, Stratiolaelaps, soil predatory mite, S. scimitus - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" *Stratiolaelaps scimitus* is a [predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) of the family Laelapidae that lives in the top layer of soil and [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) media. It was long sold as *Hypoaspis miles*, and many growers still call it Hypoaspis. It is tan-brown, about 0.5-1 mm long, and eats [fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) larvae, [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) pupae, springtails and other small soil organisms. ## In practice Growers sprinkle it on the medium surface of mothers, clones and veg plants as a preventive layer against fungus gnats and soil-pupating thrips. It survives for weeks on organic matter and alternative prey, so one early release can persist through a run. It does best in moist but not [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) media and is less suited to bare rockwool or [deep water culture](https://genetixbay.com/knowledge/glossary/dwc.md), where it has nowhere to live. It pairs well with *[Steinernema feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md)* nematodes and with foliar predators that cover the leaf stage of thrips. Some growers report it helps against [root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md), but evidence is thin. ## Don't confuse with - **Steinernema feltiae**: a nematode that infects larvae rather than eating them. - **Dalotia coriaria**: a rove beetle used for the same soil pests. - **Springtails**: harmless soil insects often seen alongside. ## Related terms [Fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [Thrips](https://genetixbay.com/knowledge/glossary/thrips.md), [Steinernema feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md), [Root aphid](https://genetixbay.com/knowledge/glossary/root-aphid.md), [Predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) ## Read more - [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ## Sources 1. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ 2. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf --- # Stretch > The stretch is the rapid increase in height in the first two to three weeks after switching to flower, when many cultivars grow 1.5 to 3 times taller. - Canonical: https://genetixbay.com/knowledge/glossary/stretch.html - Also written: flower stretch, flowering stretch, the stretch, bloom stretch, transition stretch - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The stretch is the burst of vertical growth that follows the switch to a flowering [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md). Stems elongate and [internodes](https://genetixbay.com/knowledge/glossary/internode.md) lengthen as the plant builds the framework for its flowers. Most cultivars roughly double in height; narrow-leaflet, long-flowering types can triple, and compact types may add only 50%. ## In practice Plan for it: flip a plant when it is about half to one-third of the height the space allows below the light. Keep tucking, LST-ing and [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md) through the stretch to hold the [canopy level](https://genetixbay.com/knowledge/glossary/canopy.md). Large [day-night temperature differences](https://genetixbay.com/knowledge/glossary/dif.md) increase internode length; a cooler day than night (negative DIF) is sometimes used to reduce it. [Seedling](https://genetixbay.com/knowledge/glossary/seedling.md) stretch is a different problem: long, weak stems from too little light, not this flowering response. ## Don't confuse with - **Stretching (seedling)**: a symptom of low light in young plants; see [stretching](https://genetixbay.com/knowledge/diagnosis/stretching.md). - **Foxtailing**: spire-like bud growth late in flower. ## Related terms [Flip](https://genetixbay.com/knowledge/glossary/flip.md), [Veg time](https://genetixbay.com/knowledge/glossary/veg-time.md), [Supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md), [Internode](https://genetixbay.com/knowledge/glossary/internode.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md) ## Read more - [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) - [SCROG: screen of green](https://genetixbay.com/knowledge/training/scrog.md) --- # STS > STS (silver thiosulfate) is a silver compound sprayed on female cannabis to block ethylene action and induce fertile male flowers, the standard method for making feminised seed. - Canonical: https://genetixbay.com/knowledge/glossary/sts.html - Also written: silver thiosulfate, silver thiosulphate, silver thiosulfate solution, Ag-STS - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" STS is silver thiosulfate, a complex of silver ions with thiosulfate. Sprayed on a female cannabis plant before or at the start of flowering, it blocks [ethylene](https://genetixbay.com/knowledge/glossary/ethylene.md) action and leads the plant to form [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) with fertile pollen (Ram and Sett 1982; Lubell and Brand 2018). It is the standard agent for making [feminised](https://genetixbay.com/knowledge/glossary/feminised-seed.md) and [S1 seed](https://genetixbay.com/knowledge/glossary/s1.md). ## In practice Breeders treat one female or one branch, isolate it, and collect the pollen once the induced male flowers open, usually some weeks into flowering. The treated plant's flowers are not consumed. STS is more reliable than [colloidal silver](https://genetixbay.com/knowledge/glossary/sex-reversal.md) in published trials and in grower experience, because the thiosulfate complex moves through the plant better. Silver compounds are hazardous to people and to aquatic life. Wear gloves and eye protection, keep treated material separate, and dispose of leftovers as chemical waste according to local rules. This glossary entry is a definition; preparation and dosing details belong in the main article. ## Don't confuse with - **Colloidal silver**: a suspension of silver particles, used the same way but less consistent. - **Silver nitrate**: an ingredient used to prepare STS; not the same compound. - **Gibberellic acid (GA3)**: another hormone treatment that can induce male flowers, less used. ## Related terms [Sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md), [Pollen](https://genetixbay.com/knowledge/glossary/pollen.md) ## Read more - [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) ## Sources 1. Ram HYM, Sett R. 1982. Induction of fertile male flowers in genetically female Cannabis sativa plants by silver nitrate and silver thiosulphate anionic complex. Theoretical and Applied Genetics 62:369-375. https://doi.org/10.1007/BF00275107 2. Lubell JD, Brand MH. 2018. Foliar sprays of silver thiosulfate produce male flowers on female hemp plants. HortTechnology 28(6):743-747. https://doi.org/10.21273/HORTTECH04188-18 3. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 --- # Stud Book > The Stud Book is GenetixBay's showcase of documented male plants, with selection journals, keeper details and sire credits; males are encouraged and rewarded. - Canonical: https://genetixbay.com/knowledge/glossary/stud-book.html - Also written: the Stud Book, GenetixBay Stud Book, male showcase - Glossary category: GenetixBay terms · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The Stud Book is the male showcase on GenetixBay. Each entry is a documented male plant with its [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), selection journal, the reasons it was kept, its pollen batches, and the sire credits it earns when its offspring become lines or keepers. ## In practice Half of every seed's genetics comes from the father, yet males are routinely culled unseen, and many classic lines are now carried only by female clones. The Stud Book fixes that. A breeder or member who hunts males carefully (vigour, structure, stem rub aroma, resistance and, best of all, the quality of daughters in a [test cross](https://genetixbay.com/knowledge/glossary/test-cross.md)) can register the keeper male, and that work earns Wild Pearls and credit. Registered males make it possible to remake lines from known fathers and keep diversity alive beyond a few female gardens. ## Don't confuse with - **Elite cut**: usually a female [clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md); the Stud Book is about males. - **Pollen bank**: stored pollen; the Stud Book is the record of the males behind it. ## Myth check "Males are useless; just run [fems](https://genetixbay.com/knowledge/glossary/fems.md)." GenetixBay position: males are a necessity and are encouraged and rewarded. [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md) is mostly frowned upon. See [selection and pheno hunting](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md). ## Related terms [Keeper](https://genetixbay.com/knowledge/glossary/keeper.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Wild Pearls](https://genetixbay.com/knowledge/glossary/wild-pearls.md), [Regs](https://genetixbay.com/knowledge/glossary/regs.md) ## Read more - [Collecting and storing cannabis pollen](https://genetixbay.com/knowledge/breeding/pollen-collection-storage.md) - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) --- # Sugar leaf > A small leaf growing from within the flower cluster, often coated in trichomes, which is trimmed off and commonly kept for processing. - Canonical: https://genetixbay.com/knowledge/glossary/sugar-leaf.html - Also written: sugar leaves, trim leaves, bud leaves - Glossary category: Plant biology - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sugar leaves are the small, usually single to five-leaflet leaves that grow out from among the flowers of a bud. They take their name from the frosty, sugar-dusted look given by the glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) on their surface. They carry far more resin than [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) but less than the [bracts](https://genetixbay.com/knowledge/glossary/bract.md). ## In practice Trimming is mostly about sugar leaves. Growers trim them back to the edge of the bud for appearance and a smoother smoke, then often save the trim for processing, because the resin on it is real. The trade-off between wet and [dry trimming](https://genetixbay.com/knowledge/glossary/dry-trim.md) is largely about sugar leaves: - **Wet trim**: leaves stand out and [snip](https://genetixbay.com/knowledge/glossary/snp.md) easily, and buds dry faster. - **Dry trim**: leaves curl around the bud, protecting it as it dries. Cultivars with a "high [calyx-to-leaf ratio](https://genetixbay.com/knowledge/glossary/calyx.md)" (more swollen bracts than leaves) have fewer sugar leaves and trim much faster, a trait breeders select for. ## Don't confuse with - **Fan leaf**: large, long-stalked leaf with few trichomes. - **Bract**: the resin-laden flower sheath, part of the bud itself. - **Shake**: loose broken bud bits, not leaf. ## Related terms [Fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md), [Bract](https://genetixbay.com/knowledge/glossary/bract.md), [Wet trim](https://genetixbay.com/knowledge/glossary/wet-trim.md), [Dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md), [Capitate-sessile trichome](https://genetixbay.com/knowledge/glossary/capitate-sessile-trichome.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 --- # Sugar trim > Sugar trim is the small, resin-frosted leaves that grow from within cannabis buds, trimmed off during manicuring and prized as starting material for hash and rosin. - Canonical: https://genetixbay.com/knowledge/glossary/sugar-trim.html - Also written: sugar trim leaves, resin leaves, frosty trim, sugar-leaf trim - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" [Sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) are the small leaves that emerge from the flower clusters, so named because they are often coated with glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) that look like sugar. Sugar trim is the portion of trimmings made of these leaves, as opposed to the much less resinous [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md). It sits between flower and fan leaf in resin content. ## In practice [Hash](https://genetixbay.com/knowledge/glossary/hash.md) makers often separate sugar trim from fan leaves to make cleaner kief, [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md) or rosin. Some cultivars produce generous, frosty sugar leaves; others produce few, which affects how much hash a harvest can yield beyond the flowers. Leaving a little sugar leaf on buds is a matter of taste and market: a tight manicure looks better, while leaving it protects [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) from handling. Its yield and quality depend on the plant and how it was trimmed and stored. ## Don't confuse with - **Fan leaves**: large [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) leaves with few glandular trichomes. - **Bracts**: the small leaf-like structures enclosing each flower, part of the bud itself. - **Shake**: broken flower pieces. ## Related terms [Trim](https://genetixbay.com/knowledge/glossary/trim.md), [Kief](https://genetixbay.com/knowledge/glossary/kief.md), [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md), [Rosin](https://genetixbay.com/knowledge/glossary/rosin.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) --- # Sulfate > Sulfate (SO4 2-) is the form in which plants take up sulfur, delivered mainly by magnesium sulfate and potassium sulfate in mineral feeds. - Canonical: https://genetixbay.com/knowledge/glossary/sulfate.html - Also written: SO4, SO4 2-, sulphate, sulfate ion - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sulfate is the doubly charged anion SO4 2-, the normal source of [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) for plant roots. Plants reduce it internally to build sulfur-containing amino acids and other compounds. Many fertiliser salts carry their metal partner as a sulfate, so sulfate often enters a feed as a passenger. ## In practice [Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), [potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md) and the [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) sulfates ([manganese](https://genetixbay.com/knowledge/glossary/manganese.md), zinc, copper) all add sulfate. Calcium sulfate (gypsum) is only sparingly soluble, so concentrated calcium and sulfate stocks precipitate together. That is one of the two main reasons mineral feeds are split into [A and B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) parts. In the final dilute solution they coexist without trouble. [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) can also contribute meaningful sulfate; a water report will show it. ## Units and formula Reports may give SO4 or SO4-S. S = SO4 × 0.334. ## Don't confuse with - **Sulfite (SO3 2-)**: a preservative and reduced form, not a fertiliser. - **Sulfur**: the element; [elemental sulfur](https://genetixbay.com/knowledge/glossary/sulfur-burner.md) powder must be oxidised by microbes before plants can use it. ## Related terms [Sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md), [Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), [Potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md), [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) ## Read more - [Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources](https://genetixbay.com/knowledge/nutrients/sulfur.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Sulfur > Sulfur (S) is a secondary nutrient taken up as sulfate, used in the amino acids cysteine and methionine; deficiency yellows new growth fairly evenly. - Canonical: https://genetixbay.com/knowledge/glossary/sulfur.html - Also written: S, sulphur, sulfur deficiency, sulphur deficiency - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Sulfur is a secondary macronutrient absorbed as the [sulfate ion](https://genetixbay.com/knowledge/glossary/sulfate.md) (SO4 2-). It is built into the amino acids cysteine and methionine, into coenzymes and into many defence compounds. It is only partly mobile, so [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) tends to show on younger leaves first. ## In practice A sulfur-short plant looks like it lacks nitrogen, but the even pale yellowing starts on new or middle growth rather than the bottom leaves. True deficiency is uncommon in hydro, because [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md) and [potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md) bring plenty of S along. Feeds typically land somewhere around 50-100 mg/L (ppm) S, and plants tolerate a wide range. ## Don't confuse with - **Sulfur burner or elemental sulfur sprays**: used against mildew, not as a feed. - **Nitrogen deficiency**: starts on old leaves; sulfur deficiency starts higher up. - **Volatile sulfur compounds**: the skunky aroma molecules in cannabis contain sulfur, but feeding more S has not been shown to raise them. ## Myth check "More sulfur makes buds smell stronger" has no controlled support (Evidence: Myth until tested). The plant needs adequate S; extra sulfate mostly raises [EC](https://genetixbay.com/knowledge/glossary/ec.md). See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), [Secondary nutrient](https://genetixbay.com/knowledge/glossary/secondary-nutrient.md), [Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), [Potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md) ## Read more - [Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources](https://genetixbay.com/knowledge/nutrients/sulfur.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Sulfur burner > A heated vessel that vaporises elemental sulfur to suppress powdery mildew and mites in veg rooms; it carries fire, gas and timing risks and is never used in flower. - Canonical: https://genetixbay.com/knowledge/glossary/sulfur-burner.html - Also written: sulphur burner, sulfur vaporizer, sulphur vaporiser, sulfur evaporator, vaporised sulfur, elemental sulfur - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A sulfur burner, more accurately a [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) vaporiser, is an electric heater with a small dish that warms elemental sulfur until it sublimes and drifts through a room, settling as a fine film on leaves. That film suppresses [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) and some [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md). Elemental sulfur is a widely used, long-established fungicide and acaricide active ingredient. ## In practice Growers run vaporisers in veg and mother rooms, typically during the dark period and with nobody present. Safety and timing points: - If the sulfur overheats or ignites, it forms sulfur dioxide, a toxic, choking gas, so the unit must stay within its designed temperature and away from anything flammable. - Sulfur dust and vapour irritate eyes and lungs; keep people and pets out. - Sulfur and oil sprays near each other in time can scorch leaves. - Vaporising in flower taints aroma and leaves deposits on buds; stop well before flower. Whether sulfur use is permitted on cannabis, and on what terms, depends on product registration and local rules. Check what is registered for cannabis locally and follow the label. ## Don't confuse with - **Wettable sulfur sprays**: the same active, applied in water. - **Lime sulfur**: calcium polysulfide, a harsher product. - **Sulfur as a nutrient**: [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md) in feed, an essential plant element. ## Related terms [Powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md), [Hemp russet mite](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md), [Horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md), [Pre-harvest interval](https://genetixbay.com/knowledge/glossary/pre-harvest-interval.md), [Contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md) ## Read more - [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) ## Sources 1. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew --- # Sunrise/sunset ramp > A sunrise/sunset ramp is a programmed gradual rise and fall of fixture intensity at the start and end of the light period, adding hours of light but little DLI. - Canonical: https://genetixbay.com/knowledge/glossary/sunrise-sunset-ramp.html - Also written: sunrise sunset, light ramping, dimmer ramp, dawn dusk simulation, ramp up ramp down, sunrise mode - Glossary category: Environment and light · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A sunrise/sunset ramp is a controller setting that brings a dimmable fixture (usually [LED](https://genetixbay.com/knowledge/glossary/led.md)) up from off to full power over a set time, and back down at the end of the day. Ramps of 15–60 minutes are common. They imitate the gradual dawn and dusk plants evolved with. ## In practice Ramps soften the sudden switch from darkness to full intensity, which gives [stomata](https://genetixbay.com/knowledge/glossary/stomata.md) and [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) time to adjust and avoids a sudden spike in room heat and humidity load. They also reduce inrush on the electrical supply. They add very little light. A 30-minute linear ramp to 900 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) delivers on average 450 µmol/m²/s for half an hour, about 0.8 [mol/m²/day](https://genetixbay.com/knowledge/glossary/dli.md), so two ramps add about 1.6 mol/m²/day. This is why the founder's [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) practice amounts to roughly 12 hours of high intensity, with ramps making up the rest. Count ramp time as light time for flowering purposes: plants sense even dim light as day. If you add 1-hour ramps to a [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) schedule, your real night is now 10 hours, which some cultivars will not tolerate. ## Don't confuse with - **13/11**: a schedule; ramps are one way to fill its extra hour. - **Light leak**: unplanned light during the dark period. ## Myth check Ramps are *Grower practice*; there is little controlled cannabis evidence of a yield effect either way. Their value is in smoother transitions and control. ## Related terms [13/11](https://genetixbay.com/knowledge/glossary/13-11.md), [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), [DLI](https://genetixbay.com/knowledge/glossary/dli.md), [LED](https://genetixbay.com/knowledge/glossary/led.md) ## Read more - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) --- # Super soil > Super soil is a heavily amended organic soil mix, rich in compost and slow-release amendments, intended to feed a plant through most of its life with only water. - Canonical: https://genetixbay.com/knowledge/glossary/super-soil.html - Also written: supersoil, super-soil mix, amended soil, hot soil - Glossary category: Systems and media · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Super soil is a mix of a base soil or potting medium with large amounts of compost, worm castings and [organic amendments](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md) such as bone meal, blood meal, kelp, rock dusts and guano. It is "cooked" (left moist for several weeks) so microbes begin breaking the amendments down. The aim is "just add water" growing. ## In practice The usual setup is layered: a hot, amended layer in the lower part of the pot, topped with milder soil where [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) or clones start, so young roots reach the strong layer only when the plant is big enough. Nutrient release depends on temperature, moisture and biology, so feeding is less precise and late-flower demands can outrun it. Many growers [top-dress](https://genetixbay.com/knowledge/glossary/top-dressing.md) partway through. Super soil and [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) overlap; the difference is emphasis. Super soil is defined by a strong amendment recipe, living soil by managing biology over many cycles. ## Don't confuse with - **Hot mix burn**: seedlings planted directly into the rich layer can show [nutrient burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md). - **Potting mix**: light starter fertiliser only. ## Related terms [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), [Potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), [Top dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md), [No-till](https://genetixbay.com/knowledge/glossary/no-till.md) ## Read more - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) - [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) --- # Supercropping > Supercropping is gently crushing a stem's inner tissue between the fingers and bending it over, so the branch lowers, toughens at a knuckle and stays productive. - Canonical: https://genetixbay.com/knowledge/glossary/supercropping.html - Also written: super cropping, super-cropping, stem snapping, snapping stems, pinch and bend - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Supercropping is a [high-stress training](https://genetixbay.com/knowledge/glossary/hst.md) method: the grower squeezes a green, flexible stem between thumb and [finger](https://genetixbay.com/knowledge/glossary/leaflet.md) and rolls it until the inner pith softens, then bends the branch to 90° without tearing the skin. Within a few days the site heals into a thick knuckle and the branch carries on growing from its new, lower position. ## In practice Do it on soft, green stems in late veg or the first two weeks of flower, when the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) threatens to push [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) into the light. Pick a spot a few nodes below the tip, crush, bend, and support the branch if needed. If the skin splits, tape it; it almost always heals. Avoid woody stems, which snap clean rather than fold. ## Myth check House position: stem snapping gives better buds, and the founder does it all the time. Label: Grower practice, house-endorsed. The improved canopy and light distribution are well understood; claims that it boosts [THC](https://genetixbay.com/knowledge/glossary/thc.md) lack controlled trials, so treat that part as unproven. See [HST and supercropping](https://genetixbay.com/knowledge/training/hst-supercropping.md). ## Don't confuse with - **Topping**: removes the tip; supercropping keeps it. - **LST**: bends without crushing. ## Related terms [HST](https://genetixbay.com/knowledge/glossary/hst.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md), [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md) ## Read more - [HST and supercropping: controlled stem crushing](https://genetixbay.com/knowledge/training/hst-supercropping.md) --- # Sweat > Moisture moving from the inside of dried buds to their surface after jarring, making them feel damp again; normal early in a cure but a warning if excessive. - Canonical: https://genetixbay.com/knowledge/glossary/sweat.html - Also written: sweating, jar sweat, buds sweating, sweat in the jar, re-sweat - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" In curing, "sweat" means buds that felt dry on the rack becoming soft and damp-feeling in the jar a few hours to a day after sealing. Water still held in the bud core and stems migrates outward and raises the headspace humidity. Some sweat is expected, because the outside of a bud always dries ahead of the inside. ## In practice Read it from the equilibrated [jar RH](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md): - **About 58-65%**: normal; [burp](https://genetixbay.com/knowledge/glossary/burping.md) on schedule. - **About 65-70%**: burp longer or more often; leave the lid off for a while. - **Above about 70%, or condensation on the glass**: take the buds out and spread them on a tray or back on the rack for some hours, then re-jar. Inspect for mould and ammonia smells. Heavy sweating usually means the buds were [jarred](https://genetixbay.com/knowledge/glossary/curing-jar.md) too early or were case-hardened. Dense [colas](https://genetixbay.com/knowledge/glossary/cola.md) sweat most. Older growers sometimes used deliberate warm, tightly packed "sweats" to change colour and aroma. That's a form of microbial or oxidative curing that sits closer to fermentation and risks mould. GenetixBay doesn't recommend it. ## Don't confuse with - **Burping**: the action that releases sweat moisture. - **Mould**: a possible consequence of unchecked sweating. - **Sweat (slang)**: unrelated everyday [senses](https://genetixbay.com/knowledge/glossary/sinsemilla.md) of the word. ## Related terms [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Burping](https://genetixbay.com/knowledge/glossary/burping.md), [Case hardening](https://genetixbay.com/knowledge/glossary/case-hardening.md), [Equilibrium relative humidity](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html --- # T5 fluorescent > T5 fluorescent lights are slim 16 mm tubes giving low-intensity, low-heat light; once the standard for clones and seedlings, now largely replaced by LED. - Canonical: https://genetixbay.com/knowledge/glossary/t5-fluorescent.html - Also written: T5, T5HO, T5 HO, fluorescent, fluorescent tubes, CFL, compact fluorescent - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Fluorescent lamps make light by exciting mercury vapour to emit UV, which a phosphor coating converts to visible light. "T5" means the tube is 5/8 inch (about 16 mm) in diameter. T5HO (high output) tubes are the grow-room version, typically 54 W for a 4 ft (1.2 m) tube. CFLs (compact fluorescents) are the same technology folded into a bulb. ## In practice T5 banks were the classic clone and [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) light: gentle, even, cool enough to hang 10–20 cm (4–8 in) above plants, and cheap. A 4-tube T5HO fixture gives roughly 200–400 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) close underneath, suitable for propagation and early veg but too weak for flower. [Efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) is around 1.0–1.2 µmol/J, well below [LED](https://genetixbay.com/knowledge/glossary/led.md). Tubes lose output with age, and many growers replace them yearly. Broken tubes release mercury; clean up following local hazardous-waste guidance. Today, low-power LED bars do the same job with better efficiency and no mercury. ## Don't confuse with - **T8 and T12**: wider, older, lower-output fluorescent tubes. - **LED tubes**: LED replacements in a fluorescent form factor. - **Germicidal UV-C tubes**: look similar but emit harmful UV-C; never use them on plants or people. ## Related terms [LED](https://genetixbay.com/knowledge/glossary/led.md), [Photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md) ## Read more - [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) --- # Taco leaf > A leaf whose edges fold upward along the midrib like a taco shell or canoe, usually at the top of the canopy; a sign of heat, high VPD or excess light. - Canonical: https://genetixbay.com/knowledge/glossary/taco-leaf.html - Also written: tacoing, taco leaves, canoeing, canoe leaves, leaf tacoing - Glossary category: Plant biology · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Tacoing or canoeing is an upward fold of the [leaflet](https://genetixbay.com/knowledge/glossary/leaflet.md) along its midrib so the edges point toward the light. Plants do this to reduce the leaf area facing intense light and to cut water loss when leaves are hot or the air is dry. [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) depends on air temperature, radiation, airflow and [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) (Nelson and Bugbee 2015). ## In practice Check where it occurs. At the top of the canopy, under the fixture or in hot spots, it points to heat, high [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) or too much light: measure leaf temperature, air temperature, [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) and [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md). Across the whole plant, with spotting or distorted growth, look at roots, calcium delivery and watering. ## Don't confuse with - **Leaf clawing**: tips hook down, not edges up. - **Praying leaves**: whole leaves angled upward but flat, a sign of a happy plant. - **Broad mite damage**: twisted, glossy new growth. ## Related terms [Heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md), [Light stress](https://genetixbay.com/knowledge/glossary/light-stress.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) ## Read more - [Taco or canoeing leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/taco-canoeing-leaves.md) - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) - [Cannabis lookalike problems: how to tell them apart](https://genetixbay.com/knowledge/diagnosis/lookalikes.md) ## Sources 1. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # Tap water > Tap water is municipal or well water used for irrigation; its EC, alkalinity, hardness, sodium and disinfectant vary widely, so it should be tested before use. - Canonical: https://genetixbay.com/knowledge/glossary/tap-water.html - Also written: mains water, municipal water, city water, faucet water, well water, hard tap water - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Tap water is any drinking-quality water from a municipal supply or a private well. For growing, its relevant properties are [EC](https://genetixbay.com/knowledge/glossary/ec.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) (bicarbonate), hardness (calcium and magnesium), [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) and chloride, and the disinfectant used: [free chlorine](https://genetixbay.com/knowledge/glossary/free-chlorine.md) or chloramine. These vary by region, season and source. ## In practice Start with the facts. Municipal suppliers publish annual water-quality reports listing hardness, alkalinity, sodium and disinfectant. Well owners should get a lab test. Then measure your own EC and pH at the tap. Rough guide: tap EC below about 0.4 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) with moderate alkalinity (40–100 mg/L as CaCO3) is easy to use straight. EC above about 0.8 mS/cm, alkalinity above about 150 mg/L, or sodium above about 50 mg/L suggests acidifying, blending with [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), or switching to RO, especially in hydro and coco. Hard tap water brings useful calcium and magnesium; account for it before adding [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md). ## Don't confuse with - **RO water**: purified, near-zero EC. - **Rainwater**: low EC and alkalinity, but can carry roof contaminants. ## Myth check "Letting tap water stand for 24 hours makes it safe" is only partly true: it removes much free chlorine but **not chloramine**. Check your supplier's report. ## Related terms [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [General hardness](https://genetixbay.com/knowledge/glossary/general-hardness.md), [Chloramine](https://genetixbay.com/knowledge/glossary/chloramine.md), [Free chlorine](https://genetixbay.com/knowledge/glossary/free-chlorine.md) ## Read more - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Sources 1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality 2. Water Quality Association. 2014. Chloramine fact sheet. https://wqa.org/wp-content/uploads/2022/09/2014_Chloramine.pdf --- # Taproot > The dominant primary root that grows straight down from the radicle of a seed-grown plant, with lateral roots branching from it. - Canonical: https://genetixbay.com/knowledge/glossary/taproot.html - Also written: tap root, primary root, main root, tap-root - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A taproot is the thick primary root that grows vertically from the [radicle](https://genetixbay.com/knowledge/glossary/radicle.md) and stays [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) as lateral roots branch off it. Cannabis grown from seed forms a taproot; in open soil it can reach well over a metre deep. Clones do not have one: they grow adventitious roots from the cut stem, giving a more fibrous, spreading root system. ## In practice In containers the taproot hits the bottom within days to weeks and turns or branches, so the classic deep taproot matters less indoors. It still matters at [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md): a bent, kinked or torn taproot sets a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) back. House position (Grower practice, founder observation): [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) dislike transplanting, and much of that is about how the taproot reacts. Because an auto runs on a fixed countdown from [germination](https://genetixbay.com/knowledge/glossary/germination.md), any check costs it time it cannot get back. GenetixBay advises planting autos directly into the final container. See [photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md). ## Don't confuse with - **Radicle**: the embryonic root before it develops into the taproot. - **Adventitious roots**: roots that form on stem tissue, as in clones. - **Root hairs**: microscopic absorptive cells, not a root type. ## Related terms [Radicle](https://genetixbay.com/knowledge/glossary/radicle.md), [Root hair](https://genetixbay.com/knowledge/glossary/root-hair.md), [Rhizosphere](https://genetixbay.com/knowledge/glossary/rhizosphere.md), [Autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) ## Read more - [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) - [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Tarsonemid mite > The thread-footed mite family that includes broad mites and cyclamen mites; tiny pests of growing tips, best seen at 40x or more. - Canonical: https://genetixbay.com/knowledge/glossary/tarsonemid-mite.html - Also written: tarsonemid, tarsonemid mites, Tarsonemidae, thread-footed mite - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Tarsonemid mites (family Tarsonemidae, the thread-footed mites) are tiny, about 0.1-0.3 mm, with four pairs of legs; the hind legs of females are thread-like. The [broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md) Polyphagotarsonemus latus and [cyclamen mite](https://genetixbay.com/knowledge/glossary/cyclamen-mite.md) Phytonemus pallidus are the main plant pests. UF/IFAS describes broad mite feeding on young growth and the twisted, bronzed tissue that follows. ## In practice Tarsonemid damage [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) like a nutrient or herbicide problem: glossy, twisted, stunted new growth. Confirm at 40-60x on the youngest leaves. Males carry quiescent females to new leaves, and broad mites can ride on [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) and [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), so control of those insects also limits spread. ## Don't confuse with - **Eriophyid mites**: two pairs of legs, carrot-shaped. - **Spider mites**: larger, webbing, visible at 10x. ## Related terms [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Cyclamen mite](https://genetixbay.com/knowledge/glossary/cyclamen-mite.md), [Eriophyid mite](https://genetixbay.com/knowledge/glossary/eriophyid-mite.md) ## Read more - [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ## Sources 1. Fasulo, T.R. Broad mite, Polyphagotarsonemus latus. UF/IFAS EENY-183. https://doi.org/10.32473/edis-in340-2005 --- # TDS > TDS (total dissolved solids) is the mass of dissolved material in water; grow meters estimate it from EC with a conversion factor and display it as ppm. - Canonical: https://genetixbay.com/knowledge/glossary/tds.html - Also written: total dissolved solids, TDS meter, TDS reading, ppm reading, dissolved solids - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" TDS (total dissolved solids) is the total mass of dissolved substances in water, properly measured in a lab by evaporating a filtered sample and weighing the residue, in mg/L (ppm). Handheld "TDS meters" do not do this. They measure [EC](https://genetixbay.com/knowledge/glossary/ec.md) and multiply it by a [conversion factor](https://genetixbay.com/knowledge/glossary/conversion-factor.md) chosen by the maker, usually 0.5 or 0.7, sometimes 0.64. ## In practice Because different ions conduct differently, no single factor is accurate for every solution. A nutrient mix rich in [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) and potassium and a [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) rich in bicarbonate can have the same EC but very different true TDS. That is why two meters can read "800 ppm" and "1,120 ppm" for the same reservoir, and why ppm figures from someone else's chart are meaningless without the scale. TDS meters are still useful for checking [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) output, comparing your water to its usual baseline, and tracking reservoir changes over time with one meter. For sharing or following nutrient charts, use [EC in](https://genetixbay.com/knowledge/glossary/input-ec.md) mS/cm. ## Units and formula - TDS (ppm) ≈ EC (µS/cm) × conversion factor - [500 scale](https://genetixbay.com/knowledge/glossary/ppm500.md): × 0.5; [700 scale](https://genetixbay.com/knowledge/glossary/ppm700.md): × 0.7; some agronomy sources use 640 ppm per dS/m ## Don't confuse with - **EC**: the real measurement; TDS on a meter is derived from it. - **ppm of a single element**: e.g. 150 ppm N in a recipe; unrelated to meter TDS. ## Related terms [EC](https://genetixbay.com/knowledge/glossary/ec.md), [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md), [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md), [Conversion factor](https://genetixbay.com/knowledge/glossary/conversion-factor.md), [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) ## Read more - [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) - [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Sources 1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality 2. University of California Cooperative Extension, Ventura County. Salinity units and conversions (640 ppm = 1 dS/m). https://ucanr.edu/node/125832 --- # Temperature > In growing, temperature usually means grow-room air temperature; cannabis grows best around 24–28 °C (75–82 °F) by day and a few degrees cooler at night. - Canonical: https://genetixbay.com/knowledge/glossary/temperature.html - Also written: air temperature, room temperature, day temperature, night temperature, grow room temperature, temps - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Temperature sets the speed of nearly every process in a plant: [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), respiration, water uptake and development. For cannabis, grow-room air temperature is the number most growers track, but [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) is what the plant actually experiences, and root-zone temperature matters separately. ## In practice Common targets (air, under [LED](https://genetixbay.com/knowledge/glossary/led.md); [HPS](https://genetixbay.com/knowledge/glossary/hps.md) rooms run about 1–3 °C cooler for the same leaf temperature): | Stage | Day | Night | |---|---|---| | Clones and [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) | 24–27 °C (75–81 °F) | 21–24 °C (70–75 °F) | | Veg | 24–28 °C (75–82 °F) | 20–24 °C (68–75 °F) | | Flower | 23–28 °C (73–82 °F) | 18–22 °C (64–72 °F) | | Late flower | 20–26 °C (68–79 °F) | 17–21 °C (63–70 °F) | Chandra and colleagues (2008) found cannabis leaf photosynthesis peaked around 25–30 °C at ambient [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md). Measure at canopy height in the shade of a leaf, not near the floor or the fixture. Keep roots in hydro around 18–22 °C (64–72 °F) for good dissolved oxygen. ## Don't confuse with - **Leaf temperature**: often 1–3 °C below air under LED, and can be above air under HPS. - **DIF**: the gap between day and night temperature. - **Root-zone temperature**: medium or water temperature, a separate target. ## Related terms [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md), [DIF](https://genetixbay.com/knowledge/glossary/dif.md), [Heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) ## Read more - [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # Temple ball > A temple ball is hash worked by hand into a dense ball and cured over time, a traditional Himalayan style associated with a glossy surface and soft interior. - Canonical: https://genetixbay.com/knowledge/glossary/temple-ball.html - Also written: temple balls, Nepalese temple ball, temple-ball hash, hash ball - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A temple ball is a ball of [hash](https://genetixbay.com/knowledge/glossary/hash.md), traditionally [charas](https://genetixbay.com/knowledge/glossary/charas.md) or sieved resin, that has been worked by hand until homogeneous and then stored to age. The traditional association is with Nepal and the wider Himalayan region; the legend of temple use is popular but poorly documented. The outer surface oxidises to a dark, shiny skin, while the inside stays softer and more aromatic. ## In practice Modern makers produce temple balls from [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md) or [dry sift](https://genetixbay.com/knowledge/glossary/kief.md) to recreate the style, curing them for weeks to months. The working and curing change texture and aroma; as in any long storage, some [THC](https://genetixbay.com/knowledge/glossary/thc.md) oxidises toward [CBN](https://genetixbay.com/knowledge/glossary/cbn.md), especially at the surface. Temple balls are often prized for aged, complex aromas. GenetixBay defines the style only and doesn't give production methods. ## Don't confuse with - **Charas**: hand-rubbed resin; a temple ball is a shape and cure that may use charas. - **Pressed hash**: compressed into slabs or blocks, usually by press rather than by hand. - **Rosin**: an oil, not a worked resin ball. ## Related terms [Hashish](https://genetixbay.com/knowledge/glossary/hashish.md), [Charas](https://genetixbay.com/knowledge/glossary/charas.md), [Hash](https://genetixbay.com/knowledge/glossary/hash.md), [Pressed hash](https://genetixbay.com/knowledge/glossary/pressed-hash.md) ## Read more - [Landraces of the world: an overview](https://genetixbay.com/knowledge/genetics-history/landraces-of-the-world.md) ## Sources 1. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Tent > A tent is a fabric grow enclosure with a reflective lining, zip doors and ports for ducting and cables, the standard home indoor grow space. - Canonical: https://genetixbay.com/knowledge/glossary/tent.html - Also written: grow tent, grow tents, tents, 4x4, 2x4, 5x5 - Glossary category: Grower slang and culture - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A grow tent is a lightweight frame covered in light-proof fabric with a reflective inner lining, zip doors and sealable ports for ducting and power. Tents are sized by footprint, in feet (2x2, 2x4, 4x4, 5x5) or centimetres (60x60, 120x120). ## In practice Size the light and fan to the footprint. A 4x4 ft (1.2x1.2 m) tent in flower typically runs about 600-1,000 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) at the canopy, and an [inline fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) exchanges the tent's air roughly once a minute through a [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md). Keep [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md) (fabric slightly sucked in) so smell exits through the filter, and check for [light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) with the lights off inside the tent in a dark room, especially at zips and ports, because leaks during the dark period can stress [photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md) in flower. ## Don't confuse with - **Grow room**: a room built or converted for growing; usually larger and harder to seal. - **Grow cabinet**: a rigid box, often with built-in light and [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md). ## Related terms [Airflow](https://genetixbay.com/knowledge/glossary/airflow.md), [Light leak](https://genetixbay.com/knowledge/glossary/light-leak.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) ## Read more - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) - [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) --- # Terpene > Terpenes are volatile hydrocarbon compounds built from five-carbon isoprene units; in cannabis they are made in the trichome heads and are a major part of aroma and flavour. - Canonical: https://genetixbay.com/knowledge/glossary/terpene.html - Also written: terpenes, terpines, terpenes (cannabis) - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A terpene is a hydrocarbon assembled from isoprene (C5) units. Strictly, "terpene" means the pure hydrocarbon and "[terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md)" the oxygen-containing relatives, but growers use "terps" for both. Cannabis makes them in the same glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) as [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), using terpene synthase enzymes. More than 100 have been identified; a typical flower is dominated by a few, such as myrcene, [beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md), [limonene](https://genetixbay.com/knowledge/glossary/limonene.md), terpinolene and the pinenes. ## In practice Total terpene content in dried flower is usually somewhere around 1-3% w/w, sometimes higher in fresh material. [Monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) are the most volatile and are lost first during drying, curing and storage; Ross and ElSohly found large monoterpene losses on air-drying. Slow, cool drying and a careful cure keep more of them. Terpenes explain much of a cultivar's smell, but not all: trace [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) compounds and esters can dominate certain aromas. ## Don't confuse with - **Terpenoid**: an oxygenated terpene (linalool, bisabolol), often lumped in with terpenes. - **Cannabinoid**: a different compound class, made in the same glands. - **Volatile sulfur compounds**: tiny amounts drive the "skunk" smell, not terpenes. ## Myth check Terpenes on a label do not predict effects. House view: indica/sativa labels don't predict chemistry, and terpene-based effect claims are unproven. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Terpenoid](https://genetixbay.com/knowledge/glossary/terpenoid.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Volatile sulfur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md), [Myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. 2. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 3. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # Terpene loss > The loss of volatile aroma compounds from cannabis through evaporation, oxidation and handling, fastest for monoterpenes and worst in warm, fast drying and poor storage. - Canonical: https://genetixbay.com/knowledge/glossary/terpene-loss.html - Also written: terp loss, losing terpenes, terpene evaporation, terpene degradation, aroma loss - Glossary category: Harvest, drying and curing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Terpene loss is the decline in a plant's aromatic compounds after harvest. [Terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) are volatile. Monoterpenes such as myrcene, limonene and pinene evaporate most readily; [sesquiterpenes](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) such as β-caryophyllene are heavier and better retained. Heat, airflow across the buds, light, oxygen and handling all speed the loss. Ross & ElSohly (1996) recorded large monoterpene losses on air-drying, and drying method strongly affects terpene retention in hemp work. ## In practice Where growers lose terpenes, and what to do: - **Fast, warm dry**: dry slow and cool, about 15-21 °C (60-70 °F), 55-62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), 7-14 days. - **Fans on the buds**: move air around, not onto, them. - **Rough handling**: shaking, tumbling and warm-hand trimming break [gland heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md). - **Half-empty jars**: more air headspace means more oxidation; fill jars well. - **Storage**: warm, bright or frequently opened jars lose aroma over months. House position: [humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md) rob terpenes and are a marketing gimmick. Add a fresh bud to a jar that needs moisture instead. ## Don't confuse with - **Cannabinoid degradation**: THC to [CBN](https://genetixbay.com/knowledge/glossary/cbn.md), mainly over storage. - **Hay smell**: an off-aroma from a bad dry, not only lost terpenes. - **Terpene profile**: the mix, set by genetics, not handling. ## Related terms [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md), [60/60 rule](https://genetixbay.com/knowledge/glossary/60-60-rule.md), [Humidity pack](https://genetixbay.com/knowledge/glossary/humidity-pack.md), [Long-term storage](https://genetixbay.com/knowledge/glossary/long-term-storage.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) ## Sources 1. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. 2. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 --- # Terpene profile > A terpene profile is the measured mix of terpenes in a sample, reported as each compound's % w/w and the total, used to describe and compare cultivar aroma chemistry. - Canonical: https://genetixbay.com/knowledge/glossary/terpene-profile.html - Also written: terpene profiles, aroma profile, terpene fingerprint, terpene breakdown - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A terpene profile is the list of [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) measured in a sample, with the amount of each and usually a total. It is typically produced by [gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md) and reported in % w/w or mg/g. Profiles are often summarised by their top two or three compounds, such as "myrcene-dominant" or "caryophyllene-limonene". ## In practice A [COA](https://genetixbay.com/knowledge/glossary/coa.md) might read: [myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md) 0.62%, beta-caryophyllene 0.41%, [limonene](https://genetixbay.com/knowledge/glossary/limonene.md) 0.28%, total terpenes 1.9% w/w. Breeders use profiles to tell keepers apart and to check that a cut is what it claims to be. Hazekamp and Fischedick argued that chemical profiles, not names, are the proper way to classify cannabis. Smith et al. (2022) found that US commercial flower clusters into only a few terpene groups, evidence that commercial lines are converging. The profile changes with [harvest timing](https://genetixbay.com/knowledge/glossary/harvest-window.md), drying, curing and storage, so compare samples handled the same way. It also misses trace compounds like [VSCs](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md), which can dominate aroma. ## Don't confuse with - **Chemotype**: usually refers to the [cannabinoid ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), not terpenes. - **Strain name**: a label that frequently fails to predict the profile. ## Myth check House position: "everything tastes the same now" is backed by the clustering data; GenetixBay's answer is preservation and documentation. See [why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md). ## Related terms [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Terpene test](https://genetixbay.com/knowledge/glossary/terpene-test.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [Myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md), [Volatile sulfur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) - [Why strain names are unreliable: what genetic studies show](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Hazekamp A, Fischedick JT. 2012. Cannabis: from cultivar to chemovar. Drug Testing and Analysis 4(7-8):660-667. https://doi.org/10.1002/dta.407 --- # Terpene test > A terpene test measures the individual terpenes and total terpene content of a sample, usually by GC-FID or GC-MS, reported in % w/w or mg/g. - Canonical: https://genetixbay.com/knowledge/glossary/terpene-test.html - Also written: terpene testing, terpene analysis, terpene panel, terp test, total terpenes test - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A terpene test quantifies a lab-defined list of [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), commonly 20-40 compounds, from [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) such as myrcene, limonene and pinene to [sesquiterpenes](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) such as [beta-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md) and humulene. Most labs use [gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md), by liquid injection or headspace sampling, with FID or MS detection. Results come as each compound's % w/w plus total terpenes. ## In practice Because terpenes are volatile, sample handling dominates the result. Grinding warms the sample and releases volatiles; long shipping in warm conditions loses monoterpenes. A result of 2.1% total terpenes from fresh, carefully cured flower might read 1.4% after months of warm storage. Panels differ: one lab may include ocimene isomers, bisabolol and guaiol, another may not, so "total terpenes" isn't directly comparable between labs. Trace aroma drivers such as prenylated thiols are not on routine terpene panels. ## Don't confuse with - **Potency test**: [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), usually by HPLC. - **Residual solvents test**: also GC, but measuring solvents. - **Smell**: the nose detects compounds a terpene panel misses, and vice versa. ## Related terms [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md), [Homogenisation (sampling)](https://genetixbay.com/knowledge/glossary/homogenisation.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Ross SA, ElSohly MA. 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49-51. --- # Terpenoid > A terpenoid is a terpene-derived compound that carries extra functional groups, usually oxygen (alcohols, oxides, ketones), such as linalool, bisabolol or caryophyllene oxide. - Canonical: https://genetixbay.com/knowledge/glossary/terpenoid.html - Also written: terpenoids, isoprenoid, isoprenoids, oxygenated terpene - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A terpenoid, also called an isoprenoid, is a compound built from isoprene units like a [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) but modified, typically with oxygen. Linalool and geraniol (alcohols), eucalyptol and [caryophyllene oxide](https://genetixbay.com/knowledge/glossary/caryophyllene-oxide.md) (ethers/oxides) and [bisabolol](https://genetixbay.com/knowledge/glossary/bisabolol.md) are all terpenoids. In chemistry "terpene" is the plain hydrocarbon and "terpenoid" the modified form; in cannabis talk the two words are used interchangeably. ## In practice Lab [terpene panels](https://genetixbay.com/knowledge/glossary/terpene-test.md) list both kinds together. Oxygenated terpenoids are generally less volatile than the hydrocarbon [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md), so they tend to survive drying and storage better; some, like caryophyllene oxide, actually increase as their parent compound oxidises. [Cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) are, strictly, meroterpenoids: part terpene, part polyketide. That is the sense in which the cannabinoid and terpene pathways are related. ## Don't confuse with - **Terpene**: the hydrocarbon parent class. - **Flavonoid**: a separate class of phenolic compounds. - **Terpene profile**: the measured mix in a sample, not a chemical class. ## Related terms [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Linalool](https://genetixbay.com/knowledge/glossary/linalool.md), [Caryophyllene oxide](https://genetixbay.com/knowledge/glossary/caryophyllene-oxide.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Terpinolene > Terpinolene is a monoterpene with a fresh, herbal, piney-citrus-floral aroma that dominates a distinctive, less common cannabis chemotype. - Canonical: https://genetixbay.com/knowledge/glossary/terpinolene.html - Also written: δ-terpinene, delta-terpinene, terpinolene-dominant, terpinoline - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Terpinolene is a cyclic [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md) with a complex smell: fresh, herbal, piney, with citrus and floral notes, sometimes described as smelling like apple, lilac or cleaning products. It occurs in tea tree, lilac and conifers. In cannabis it marks one of the few clearly separate [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) [chemotypes](https://genetixbay.com/knowledge/glossary/chemotype.md) in market surveys. ## In practice Smith et al. (2022) found that commercial US flower clusters into a small number of terpene groups, and terpinolene-dominant samples formed one of the distinct, less common groups, alongside the large [myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md) and [caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md)/[limonene](https://genetixbay.com/knowledge/glossary/limonene.md) groups. Terpinolene-dominant flower often carries [ocimene](https://genetixbay.com/knowledge/glossary/ocimene.md) and myrcene too. It's volatile, so drying and storage conditions show strongly in the readings. ## Don't confuse with - **Terpinene (alpha, gamma)**: related isomers, usually minor on panels. - **Terpineol**: a terpene alcohol with a lilac smell. - **Myrcene**: frequently present in the same samples, but a different chemotype. ## Myth check Terpinolene-dominant flower is often sold as "sativa". House position: indica/sativa labels don't predict chemistry or effects. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md), [Ocimene](https://genetixbay.com/knowledge/glossary/ocimene.md), [Alpha-pinene](https://genetixbay.com/knowledge/glossary/alpha-pinene.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Terps > Terps is slang for terpenes, and loosely for a cannabis cultivar's whole aroma and flavour, even though many aroma compounds are not terpenes. - Canonical: https://genetixbay.com/knowledge/glossary/terps.html - Also written: terp, terpy, terp-heavy, terp profile, terpage - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Terps is slang for [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), the volatile compounds that give cannabis much of its smell. "Great terps" means great aroma and flavour; "terpy" flower smells strong. ## In practice The slang is broader than the chemistry. Cannabis aroma includes [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) (myrcene, limonene, pinene), [sesquiterpenes](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) (caryophyllene, humulene), and non-terpene compounds such as esters, aldehydes and [volatile sulfur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md), some of which dominate the smell at tiny concentrations. A [lab report](https://genetixbay.com/knowledge/glossary/coa.md) listing total terpenes as 2-4% w/w does not tell you how a jar smells. Terps are fragile. Heat, light, long open-air exposure and fast drying drive them off. A slow dry in a cool room and a cure that lowers moisture gradually keep them. [Two-way humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md), in GenetixBay's view, rob terpenes; if a jar is [too dry](https://genetixbay.com/knowledge/glossary/over-drying.md), a fresh bud is a better way to add moisture. ## Don't confuse with - **Terpene**: the chemical class; terps is the slang for the experience. - **Flavonoids**: colour and some flavour compounds, not terpenes. ## Myth check "Specific terpenes cause specific effects." Reported, not established for flower in real use. Effects claims based on [terpene profiles](https://genetixbay.com/knowledge/glossary/terpene-profile.md) remain largely unproven. ## Related terms [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Candy terps](https://genetixbay.com/knowledge/glossary/candy-terps.md), [Gas](https://genetixbay.com/knowledge/glossary/gas.md), [Loud](https://genetixbay.com/knowledge/glossary/loud.md), [Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) ## Sources 1. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 2. Watts S, McElroy M, Migicovsky Z, et al. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y --- # Test cross > A test cross mates a plant of unknown genotype with one that is homozygous recessive for a trait, so the offspring ratios reveal what the first plant carries. - Canonical: https://genetixbay.com/knowledge/glossary/test-cross.html - Also written: testcross, test-crossing, test crosses, progeny test cross - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A test cross is a cross used to find out a plant's [genotype](https://genetixbay.com/knowledge/glossary/genotype.md). The unknown plant is crossed with a tester that is [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) (aa) for the trait. If all offspring show the [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) trait, the unknown is probably AA. If roughly half show the recessive, it is Aa. ## In practice Breeders use test crosses to check whether a plant carries a hidden recessive before using it widely. Example: to learn whether a [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) male carries the [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) allele, cross him to an autoflowering female (homozygous recessive). Any autoflowering offspring prove he is a carrier. The term is also used more loosely for any small trial cross made to judge a parent, especially a male, by its offspring. That is closer to a [progeny test](https://genetixbay.com/knowledge/glossary/progeny-test.md). Either way, the more offspring, the firmer the answer: in a true test cross of an Aa plant, about 1 in 32 litters of 5 [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) would show no recessives purely by chance. ## Units and formula AA × aa: 100% dominant phenotype. Aa × aa: 1:1 dominant to recessive. Chance an Aa parent shows no recessive offspring in n seedlings: (1/2)^n. ## Don't confuse with - **Test grow**: growing out seed to evaluate a line, not a genetic test of one locus. - **Backcross**: crossing to a parent to recover its traits, not to diagnose a genotype. ## Related terms [Recessive](https://genetixbay.com/knowledge/glossary/recessive.md), [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md), [Progeny test](https://genetixbay.com/knowledge/glossary/progeny-test.md), [Punnett square](https://genetixbay.com/knowledge/glossary/punnett-square.md), [Male selection](https://genetixbay.com/knowledge/glossary/male-selection.md) ## Read more - [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Test grow > A test grow (tester grow) is growing out a sample of a new seed line, often by several independent growers, to measure uniformity, vigour, chemistry and herm rate before release. - Canonical: https://genetixbay.com/knowledge/glossary/test-grow.html - Also written: tester grow, tester, testers, test run, grow-out, grow out, beta test grow - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A test grow, or tester grow, is a grow-out of a new seed line before it is released or featured. Testers, ideally independent and in different environments, grow the seed and report [germination](https://genetixbay.com/knowledge/glossary/germination.md) rate, vigour, uniformity, flowering time, aroma, yield, lab results and any [intersex plants](https://genetixbay.com/knowledge/glossary/hermaphrodite.md). ## In practice Tester data is what turns a cross into a line someone can trust. It also shows [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) by environment effects: a line that behaves in one breeder's room may [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) or mould in another's. Sample size matters, especially for [herm rates](https://genetixbay.com/knowledge/glossary/herm-threshold.md). Ten clean plants cannot distinguish 0% from 20%: a line that herms 1 time in 5 shows no herms in 10 plants about 11% of the time. Demonstrating a herm rate under 2% with reasonable confidence needs about 150 plants. GenetixBay's [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md), [Seed Club](https://genetixbay.com/knowledge/glossary/seed-club.md) and featuring require a confirmed herm rate under 2% in tester grows. ## Units and formula Chance of seeing zero herms in n plants when the true rate is p: (1 - p)^n. Rule of three: zero events in n plants gives a 95% upper bound of about 3/n, so 150 clean plants supports a rate under 2%. ## Don't confuse with - **Progeny test**: testing a parent by its offspring. - **Pheno hunt**: selecting individuals from seed, not validating a line. ## Myth check "A 10-plant test grow proves a line is herm-free" is busted; see [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Seed run](https://genetixbay.com/knowledge/glossary/seed-run.md), [Progeny test](https://genetixbay.com/knowledge/glossary/progeny-test.md), [Uniformity](https://genetixbay.com/knowledge/glossary/uniformity.md), [Genotype by environment interaction](https://genetixbay.com/knowledge/glossary/genotype-by-environment.md), [Pheno hunt](https://genetixbay.com/knowledge/glossary/pheno-hunt.md) ## Read more - [Seed germination testing and quality control for breeders](https://genetixbay.com/knowledge/breeding/seed-germination-testing-qc.md) - [Selection and pheno hunting: sample sizes and scoring rubrics](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) ## Sources 1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6 --- # THC > THC (Δ9-tetrahydrocannabinol) is the neutral, decarboxylated cannabinoid mainly responsible for cannabis's reported intoxicating effects; the living plant makes it almost entirely as THCA. - Canonical: https://genetixbay.com/knowledge/glossary/thc.html - Also written: delta-9-THC, Δ9-THC, d9, delta 9, tetrahydrocannabinol, delta-9-tetrahydrocannabinol - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" THC, strictly Δ9-tetrahydrocannabinol, is the neutral [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) that acts on CB1 receptors and is associated with the reported intoxicating effects of cannabis. The plant makes very little of it directly. It makes [THCA](https://genetixbay.com/knowledge/glossary/thca.md), which loses a carboxyl group ([decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md)) with heat and time to become THC. With further oxidation, THC slowly degrades to [CBN](https://genetixbay.com/knowledge/glossary/cbn.md). ## In practice On a [COA](https://genetixbay.com/knowledge/glossary/coa.md) for dried flower, Δ9-THC itself is usually a small number, often under 1-2% w/w, while THCA might read 18-25%. The figure on a retail label is normally "total THC", which combines both. When someone says "this plant is 22% THC", they nearly always mean total THC, not the Δ9-THC line. ## Units and formula Reported as % w/w (or mg/g; 1% = 10 mg/g). [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md) = Δ9-THC + 0.877 × THCA. ## Don't confuse with - **THCA**: the acid form the plant actually makes; not intoxicating until decarboxylated. - **Delta-8 THC**: an isomer present only in traces in the plant; commercial [delta-8](https://genetixbay.com/knowledge/glossary/delta-8-thc.md) is converted from [CBD](https://genetixbay.com/knowledge/glossary/cbd.md). - **Total THC**: a calculated figure, not a single measured compound. ## Related terms [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [CBN](https://genetixbay.com/knowledge/glossary/cbn.md), [Delta-8 THC](https://genetixbay.com/knowledge/glossary/delta-8-thc.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. ElSohly MA, Slade D. 2005. Chemical constituents of marijuana: the complex mixture of natural cannabinoids. Life Sciences 78(5):539-548. 2. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. --- # THCA > THCA (tetrahydrocannabinolic acid) is the acid cannabinoid that drug-type cannabis makes in its trichomes; heat or time decarboxylates it into THC, losing about 12% of its mass. - Canonical: https://genetixbay.com/knowledge/glossary/thca.html - Also written: THC-A, THCA-A, tetrahydrocannabinolic acid, Δ9-THCA, delta-9-THCA - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" THCA, Δ9-tetrahydrocannabinolic acid, is the main cannabinoid in drug-type cannabis. The enzyme [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) builds it from [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) inside the [trichome head](https://genetixbay.com/knowledge/glossary/trichome-heads.md). THCA is not reported to be intoxicating in its own right; it becomes [THC](https://genetixbay.com/knowledge/glossary/thc.md) when its carboxyl group leaves as [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md), a reaction driven by heat (smoking, vaping, baking) and, slowly, by storage. ## In practice A good drug-type flower COA might show THCA at 20% w/w and Δ9-THC at 0.6% w/w. The plant's genetics set whether it makes mostly THCA, mostly [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md) or both, through which synthase [alleles](https://genetixbay.com/knowledge/glossary/allele.md) it carries. Growers can't turn a CBDA plant into a THCA plant with feeding or light. ## Units and formula Because the CO2 group weighs about 12.3% of the molecule, 1 g of THCA can yield at most [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) g of THC. Total THC = Δ9-THC + 0.877 × THCA. ## Don't confuse with - **THC**: the neutral, decarboxylated product. - **THCA diamonds**: a concentrate made of crystallised THCA, not a different compound. - **Total THC**: a calculated label figure combining THCA and THC. ## Related terms [THC](https://genetixbay.com/knowledge/glossary/thc.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [Acid vs neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. Sirikantaramas S, Morimoto S, Shoyama Y, et al. 2004. The gene controlling marijuana psychoactivity: molecular cloning and heterologous expression of Δ1-tetrahydrocannabinolic acid synthase from Cannabis sativa L. Journal of Biological Chemistry 279(38):39767-39774. 2. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. 3. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. --- # THCA synthase > THCA synthase is the trichome enzyme that converts CBGA into THCA; which alleles of its gene a plant carries largely decides whether it is THC-dominant. - Canonical: https://genetixbay.com/knowledge/glossary/thca-synthase.html - Also written: THCAS, THCA synthase gene, tetrahydrocannabinolic acid synthase, THC synthase - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" THCA synthase (THCAS) is an oxidocyclase enzyme that closes a ring in [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) to form [THCA](https://genetixbay.com/knowledge/glossary/thca.md). It is made in the secretory cells of glandular trichomes and works in the storage cavity under the resin head. Sirikantaramas and colleagues cloned and expressed the [gene](https://genetixbay.com/knowledge/glossary/gene.md) in 2004, confirming it as the gene behind THCA production. ## In practice Breeders treat the synthase region as the main switch for chemotype. A plant with functional THCAS [alleles](https://genetixbay.com/knowledge/glossary/allele.md) and non-functional [CBDAS](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) makes mostly THCA; one with functional CBDAS and non-functional THCAS makes mostly [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md); one with one of each tends toward a mixed profile. Genotyping tests can read these alleles in seedlings, telling a breeder the likely [THC](https://genetixbay.com/knowledge/glossary/thc.md):[CBD](https://genetixbay.com/knowledge/glossary/cbd.md) class long before flowering. They cannot predict the total percentage: that depends on many other genes, trichome density and growing conditions. ## Don't confuse with - **CBDA synthase**: the competing enzyme that makes CBDA from the same CBGA. - **THC**: the neutral product formed later by decarboxylation, not by the enzyme. - **Potency**: THCAS sets the type of cannabinoid, not how much. ## Related terms [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) - [Genotyping: what a DNA test can and can't prove](https://genetixbay.com/knowledge/breeding/genotyping-what-tests-prove.md) ## Sources 1. Sirikantaramas S, Morimoto S, Shoyama Y, et al. 2004. The gene controlling marijuana psychoactivity: molecular cloning and heterologous expression of Δ1-tetrahydrocannabinolic acid synthase from Cannabis sativa L. Journal of Biological Chemistry 279(38):39767-39774. 2. Taura F, Sirikantaramas S, Shoyama Y, et al. 2007. Cannabidiolic-acid synthase, the chemotype-determining enzyme in the fiber-type Cannabis sativa. FEBS Letters 581(16):2929-2934. 3. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004. --- # THCV > THCV (tetrahydrocannabivarin) is the propyl-chain (C3) analogue of THC, formed by decarboxylating THCVA; it is a minor cannabinoid in most cultivars but notable in some African-derived lines. - Canonical: https://genetixbay.com/knowledge/glossary/thcv.html - Also written: tetrahydrocannabivarin, Δ9-THCV, THC-V, THV - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" THCV is a varin [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md): the same ring system as [THC](https://genetixbay.com/knowledge/glossary/thc.md), but with a three-carbon (propyl) side chain instead of a five-carbon (pentyl) chain. The plant makes it as [THCVA](https://genetixbay.com/knowledge/glossary/thcva.md), which [decarboxylates](https://genetixbay.com/knowledge/glossary/decarboxylation.md) to THCV. Effects are reported to differ from THC, but human research is limited and GenetixBay makes no claims about them. ## In practice Most commercial flower shows THCV under 0.5% w/w or [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md). Some [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) and landrace-derived lines, notably from southern and eastern Africa and parts of Asia, have been reported with much higher shares of propyl cannabinoids, and breeders select for it with lab testing. Because the propyl branch starts earlier in the pathway (at the precursor), a plant high in THCV is usually low in pentyl THC, not high in both. ## Don't confuse with - **THC**: the pentyl (C5) analogue; far more common. - **THCVA**: the acid form the plant makes before decarboxylation. - **CBV / CBDV**: other varin cannabinoids, from the [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) and [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) families. ## Related terms [THCVA](https://genetixbay.com/knowledge/glossary/thcva.md), [THC](https://genetixbay.com/knowledge/glossary/thc.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. Hillig KW, Mahlberg PG. 2004. A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae). American Journal of Botany 91(6):966-975. https://doi.org/10.3732/ajb.91.6.966 2. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. --- # THCVA > THCVA (tetrahydrocannabivarinic acid) is the acid precursor of THCV, made in trichomes from CBGVA when the plant's pathway starts from divarinic acid instead of olivetolic acid. - Canonical: https://genetixbay.com/knowledge/glossary/thcva.html - Also written: THCV-A, tetrahydrocannabivarinic acid - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" THCVA is the form in which the living plant stores [THCV](https://genetixbay.com/knowledge/glossary/thcv.md). Its pathway mirrors the [THC](https://genetixbay.com/knowledge/glossary/thc.md) pathway one step earlier: instead of [olivetolic acid](https://genetixbay.com/knowledge/glossary/olivetolic-acid.md) (C5 chain), the plant uses divarinic acid (C3 chain), which combines with [geranyl pyrophosphate](https://genetixbay.com/knowledge/glossary/geranyl-pyrophosphate.md) to form CBGVA. [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) then converts CBGVA to THCVA. Heat or time decarboxylates THCVA to THCV. ## In practice On a COA, THCVA appears as its own line where the lab tests for it; many basic potency panels don't. A breeder hunting propyl-rich plants needs a lab panel that reports THCVA and THCV separately, or the trait is invisible. As with [THCA](https://genetixbay.com/knowledge/glossary/thca.md), the total is calculated: total THCV ≈ THCV + 0.867 × THCVA (the ratio is slightly lower than for THCA because the molecule is smaller). ## Don't confuse with - **THCA**: the C5 analogue, made from olivetolic acid. - **THCV**: the neutral form, after decarboxylation. - **CBDVA**: the propyl analogue of [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md), made by [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) from CBGVA. ## Related terms [THCV](https://genetixbay.com/knowledge/glossary/thcv.md), [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [Olivetolic acid](https://genetixbay.com/knowledge/glossary/olivetolic-acid.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [Acid vs neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. Gülck T, Møller BL. 2020. Phytocannabinoids: origins and biosynthesis. Trends in Plant Science 25(10):985-1004. 2. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392. --- # The Swap > The Swap is GenetixBay's pseudonymous, escrowed member-to-member exchange, reviving the Bay's 2009 peer-to-peer roots, running only in the modes local law allows. - Canonical: https://genetixbay.com/knowledge/glossary/the-swap.html - Also written: Swap, GenetixBay Swap, Bay Swap, member swap - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The Swap is the member-to-member exchange on GenetixBay. GenetixBay began as a peer-to-peer exchange around 2009, and the Swap brings that back with modern safeguards: members trade pseudonymously, value is held in escrow until the receiver confirms, and every item is tied to its [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md). ## In practice A swap moves through offer, lock (escrow), ship, deliver and confirm, with timers and a dispute process. Members can trade gear and knowledge; genetics lanes run only where the law allows and, where payment or points would be a problem, as gifts only. Receivers ship to pickup points rather than home addresses, so a sender never learns where someone lives. Value moves in Wild Pearls, never Cultured Pearls. Laws on giving, trading or shipping seeds and plants differ by country, state and province. Check local rules; the Swap enforces the most restrictive applicable mode. ## Don't confuse with - **Cut trading**: the informal tradition the Swap formalises. - **A store**: the Swap is between members; GenetixBay holds escrow, it does not sell the items. ## Related terms [Wild Pearls](https://genetixbay.com/knowledge/glossary/wild-pearls.md), [Cut trading](https://genetixbay.com/knowledge/glossary/cut-trading.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md), [Pearls](https://genetixbay.com/knowledge/glossary/pearls.md) --- # Thrips > Slender insects about 1-2 mm long, chiefly western flower thrips (Frankliniella occidentalis), that rasp leaf surfaces, leaving silvery streaks dotted with black frass. - Canonical: https://genetixbay.com/knowledge/glossary/thrips.html - Also written: thrip, western flower thrips, WFT, Frankliniella occidentalis, onion thrips, Thrips tabaci - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Thrips are tiny, slender insects of the order Thysanoptera with fringed wings. On cannabis the main indoor species is western flower thrips (*Frankliniella occidentalis*); onion thrips (*Thrips tabaci*) also occur. They scrape the leaf surface and suck the leaking contents, leaving silvery or bronze patches speckled with black droppings. The word is both singular and plural. ## In practice Thrips run a split life cycle. Eggs go inside the leaf, larvae feed on foliage, and most species drop to the growing medium to pupate. That is why good programmes hit two places: [predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md) such as *[Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md)* or *[Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md)* on the leaves, and soil predators such as *[Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md)* or nematodes in the medium. Blue or [yellow sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) at canopy height show trends; a jump from a few per card per week to dozens means act now. Western flower thrips resist many insecticide classes, so rotation by [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md) matters. Check what is registered for cannabis locally. ## Don't confuse with - **Spider mite damage**: fine pale [stippling](https://genetixbay.com/knowledge/glossary/stippling.md), no streaks or black specks. - **Leafminer trails**: winding tunnels inside the leaf, not surface scars. - **Fungus gnats on traps**: dark flies with long legs, not slim straw-coloured insects. ## Related terms [Neoseiulus cucumeris](https://genetixbay.com/knowledge/glossary/neoseiulus-cucumeris.md), [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md), [Orius](https://genetixbay.com/knowledge/glossary/orius.md), [Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md) ## Read more - [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Sources 1. UC IPM. Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html 2. UConn IPM. Biological Control of Western Flower Thrips. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-western-flower-thrips/ --- # Tincture > A tincture is a liquid cannabis preparation in which cannabinoids are dissolved in alcohol, glycerin or oil, usually taken by dropper. - Canonical: https://genetixbay.com/knowledge/glossary/tincture.html - Also written: tinctures, cannabis tincture, alcohol tincture, glycerin tincture, tincture drops - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A tincture is a traditional pharmacy form: a plant preparation dissolved in a liquid carrier. In cannabis it means a dropper-bottle liquid in which [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) are dissolved in alcohol (the original meaning), vegetable glycerin, or a carrier oil. Products labelled tinctures today are often oil-based, sometimes made by blending [distillate](https://genetixbay.com/knowledge/glossary/distillate.md) or isolate into the carrier rather than steeping the plant. ## In practice Product labels usually state cannabinoid content per millilitre and per dropper. Whether the cannabinoids are in acid or neutral form depends on whether [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md) happened in production; the label or [COA](https://genetixbay.com/knowledge/glossary/coa.md) should state it. Cannabis tinctures were common in Western pharmacopoeias in the 19th and early 20th centuries before prohibition. GenetixBay doesn't give preparation methods, dosing or health claims; effects are reported, not promised. Rules vary; check local rules. ## Don't confuse with - **Edible**: food or drink containing cannabinoids. - **Concentrate**: separated resin, not a diluted liquid. - **Extract**: a broader term; a tincture is one type of liquid preparation. ## Related terms [Edible](https://genetixbay.com/knowledge/glossary/edible.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md) --- # Tissue culture > Tissue culture is growing small pieces of a plant on sterile nutrient gel in a sealed vessel, used to multiply, clean up and store cannabis genotypes. - Canonical: https://genetixbay.com/knowledge/glossary/tissue-culture.html - Also written: plant tissue culture, micropropagation, in vitro propagation, tissue culturing - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Tissue culture is propagating plants from small pieces of tissue ([shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md), nodes or meristems) placed on sterile nutrient gel containing sugars and plant growth regulators, in sealed containers under controlled light and temperature. It can multiply a [genotype](https://genetixbay.com/knowledge/glossary/genotype.md), produce pathogen-free plantlets and store genetics in a small space (Monthony et al. 2021). ## In practice For cannabis, tissue culture is mainly a preservation and clean-stock tool. A library of jars can hold many genotypes on a shelf, needing re-culture every few weeks to months instead of a room of [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md). Combined with [meristem culture](https://genetixbay.com/knowledge/glossary/meristem-culture.md) and testing, it is the main route to cleaning a cut of [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md). It is demanding work. Sterile technique is essential, contamination from fungi and bacteria is common, and some cultivars multiply or root poorly. [Regeneration](https://genetixbay.com/knowledge/glossary/re-veg.md) from callus raises the risk of [somaclonal variation](https://genetixbay.com/knowledge/glossary/somaclonal-variation.md), so preservation labs prefer shoot-tip or node culture and verify plantlets afterwards. ## Don't confuse with - **Cloning (cuttings)**: rooting stem cuttings in a medium, non-sterile and simpler. - **Meristem culture**: a specific tissue culture technique using the tiny growing tip. - **Genetic engineering**: changing DNA; tissue culture alone does not. ## Related terms [Meristem culture](https://genetixbay.com/knowledge/glossary/meristem-culture.md), [Somaclonal variation](https://genetixbay.com/knowledge/glossary/somaclonal-variation.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md), [Germplasm](https://genetixbay.com/knowledge/glossary/germplasm.md), [Polyploid](https://genetixbay.com/knowledge/glossary/polyploid.md) ## Read more - [Tissue culture basics for cannabis growers and breeders](https://genetixbay.com/knowledge/breeding/tissue-culture-basics.md) ## Sources 1. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 --- # Tissue test > A tissue test is a lab analysis of dried leaf samples that measures the actual nutrient content of the plant, the most reliable way to confirm a deficiency or toxicity. - Canonical: https://genetixbay.com/knowledge/glossary/tissue-test.html - Also written: leaf tissue test, tissue analysis, plant tissue analysis, leaf analysis, foliar analysis - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A tissue test is a laboratory analysis of plant tissue, usually recently matured leaves, that reports the concentration of each nutrient: [macronutrients](https://genetixbay.com/knowledge/glossary/macronutrient.md) as percent of [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) and [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md) as mg/kg (ppm) of dry weight. Results are compared against sufficiency ranges for the crop. ## In practice Sample the youngest fully expanded leaves (not the newest growth, not old [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md)), from several plants of the same cultivar and stage, and send them clean and dry. Ranges depend on sampling position and stage, so follow the lab's or extension's protocol. NC State Extension publishes leaf-tissue reference ranges for floral [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) (Suchoff and colleagues), which are a useful starting point for cannabis. A tissue test shows what the plant took up; a solution or [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) test shows what was offered. Use both. ## Don't confuse with - **Runoff test**: measures [EC](https://genetixbay.com/knowledge/glossary/ec.md) and [pH](https://genetixbay.com/knowledge/glossary/ph.md) of drainage, not plant content. - **Water report**: analyses the source water. - **Soil test**: measures what is in the soil, not what the plant absorbed. ## Related terms [Nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [ppm of an element](https://genetixbay.com/knowledge/glossary/elemental-ppm.md) ## Read more - [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) ## Sources 1. Suchoff D, McGinnis M, Davis J, Whipker B, Hicks K. 2026. Hemp leaf tissue nutrient ranges: refinement of reference standards for floral hemp. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Top dressing > Top dressing is spreading dry fertiliser or amendments on the soil surface, usually under mulch, so nutrients release into the root zone as the plant is watered. - Canonical: https://genetixbay.com/knowledge/glossary/top-dressing.html - Also written: top dress, top-dress, top-dressing, topdressing, side dressing - Glossary category: Systems and media · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Top dressing means applying a solid fertiliser, compost or amendment to the surface of the medium rather than mixing it in or dissolving it in water. In organic and living-soil growing it is the main way of feeding: water and soil life carry nutrients down to the roots over days to weeks. ## In practice Typical top dressings are worm castings, compost, and blended organic dry fertilisers, scratched lightly into the top 1-2 cm (about 0.5 in) and covered with mulch to keep them moist and active. Many growers top-dress around the flip and again in early flower, timed ahead of demand because release is slow. Rates follow the product's guidance; over-application can burn and attracts [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md). Mineral slow-release granules are also top-dressed in some soil grows. ## Don't confuse with - **Mulch**: a protective surface cover; may or may not be a nutrient source. - **Compost tea**: a liquid extract; top dressing is solid. ## Related terms [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), [Super soil](https://genetixbay.com/knowledge/glossary/super-soil.md), [No-till](https://genetixbay.com/knowledge/glossary/no-till.md), [Compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) ## Read more - [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) - [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) --- # Top shelf > Top shelf is the highest price tier of flower in a shop, used as slang for any premium-looking cannabis; it reflects pricing and appearance, not verified quality. - Canonical: https://genetixbay.com/knowledge/glossary/top-shelf.html - Also written: top-shelf, top shelf flower, premium tier, tops - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Top shelf originally meant the jars on the highest shelf behind a counter, the most expensive ones. It now means premium flower in general. ## In practice Shops sort flower into tiers by appearance, demand and the potency on the label. A top-shelf jar is usually large, dense, frosty, colourful buds with strong aroma. None of that guarantees a careful dry and cure, an accurate lab number, or freedom from [irradiation](https://genetixbay.com/knowledge/glossary/irradiation.md), which is used in some regulated markets to meet microbial limits. Check the harvest or packaging date and the [lab report](https://genetixbay.com/knowledge/glossary/coa.md), and trust your nose: a [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) means a bad dry, whatever the tier. ## Don't confuse with - **Craft**: describes how it was grown (small batch, hand care), not where it sits on the price list. - **Bag appeal**: [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md), which drive the tier. ## Myth check "Top shelf tests 30%+." GenetixBay position: [label inflation](https://genetixbay.com/knowledge/glossary/label-inflation.md) is common, and most flower sold as mid-20s to 30s really tests mid-teens to low 20s (Jikomes & Zoorob 2018; Schwabe et al. 2023). Flower above about 35% [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) is not credible. See [buyer beware: label claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [Mids](https://genetixbay.com/knowledge/glossary/mids.md), [Zaza](https://genetixbay.com/knowledge/glossary/zaza.md), [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md), [Exotic](https://genetixbay.com/knowledge/glossary/exotic.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: testing reveals inflated THC potency on retail cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 --- # Topophysis > Topophysis is the tendency of cuttings to keep traits linked to the position on the mother plant they were taken from, so cuts from different parts can behave differently. - Canonical: https://genetixbay.com/knowledge/glossary/topophysis.html - Also written: position effect, cutting position effect, topophytic effect, branch position effect - Glossary category: Genetics and breeding · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Topophysis is a position effect in [vegetative propagation](https://genetixbay.com/knowledge/glossary/cloning.md): a cutting can carry on behaving like the part of the plant it came from for some time. Cuttings from lower, shaded or older branches may root, grow or flower differently from cuts taken at the top, even though they share the same [genotype](https://genetixbay.com/knowledge/glossary/genotype.md). ## In practice Cannabis growers see it as variation between clones of one mother. Cutting position measurably changes rooting in cannabis stem cuttings (Caplan et al. 2018). Growers also report differences in vigour and early growth that [fade](https://genetixbay.com/knowledge/glossary/senescence.md) after a cycle or two. House position: cuts taken from different parts of a plant can behave differently. That may or may not involve mutation. Practical advice is to take cuts from consistent locations on the mother (similar height, branch age and size) so that clones start alike, and to judge a cultivar on several clones, not one. ## Don't confuse with - **Genetic drift**: random change in [allele](https://genetixbay.com/knowledge/glossary/allele.md) frequencies in seed populations; clones do not drift. - **Somatic mutation**: a real DNA change in one branch; rare, and a mutation doesn't mean a loss. - **Pathogen decline**: a cut that gets worse every cycle is a disease or care problem, not position. ## Related terms [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md), [Somaclonal variation](https://genetixbay.com/knowledge/glossary/somaclonal-variation.md), [Mutation](https://genetixbay.com/knowledge/glossary/mutation.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md) ## Read more - [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) ## Sources 1. Caplan D, Stemeroff J, Dixon M, Zheng Y. 2018. Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science 98(5):1126-1132. https://doi.org/10.1139/cjps-2018-0038 2. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 --- # Topping > Topping is cutting off a plant's main growing tip just above a node, so the two shoots below grow into two main colas instead of one. - Canonical: https://genetixbay.com/knowledge/glossary/topping.html - Also written: top, topped, topping a plant, pinching out - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Topping removes the [apical meristem](https://genetixbay.com/knowledge/glossary/apical-meristem.md), the main growing tip, by cutting through the stem just above a node. This breaks [apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md): the two side shoots at that node become [co-dominant](https://genetixbay.com/knowledge/glossary/codominant.md) [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md). Repeating the cut on each new top doubles the count each time (2, 4, 8). ## In practice Most growers top a [photoperiod plant](https://genetixbay.com/knowledge/glossary/photoperiod.md) once it has 4-6 nodes, cutting above the 3rd to 5th node, and let it recover for about 5-7 days before the next cut. Topping lowers height, widens the plant and creates a flatter canopy, especially combined with [low-stress training](https://genetixbay.com/knowledge/glossary/lst.md). Each cut costs a few days of veg. ## Myth check House position for [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md): topping will never produce what proper LST or training does. An auto runs on a fixed countdown, so every recovery pause is lost time. If you top an auto at all, do it once, early and on a vigorous plant; LST is the better tool. See [topping](https://genetixbay.com/knowledge/training/topping.md) and [LST](https://genetixbay.com/knowledge/training/lst.md). ## Don't confuse with - **FIM**: a partial pinch of the tip that can give three or four tops; less precise. - **Top (slang)**: "top shelf", unrelated. ## Related terms [FIM](https://genetixbay.com/knowledge/glossary/fim.md), [Apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), [Mainlining](https://genetixbay.com/knowledge/glossary/mainlining.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Node](https://genetixbay.com/knowledge/glossary/node.md) ## Read more - [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md) ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ --- # Total cannabinoids > Total cannabinoids is the sum of all cannabinoids a lab measured in a sample, usually reported in % w/w, with acid forms either summed raw or decarboxylation-adjusted. - Canonical: https://genetixbay.com/knowledge/glossary/total-cannabinoids.html - Also written: total cannabinoid content, TC, sum of cannabinoids, total actives, total cannabinoid % - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Total cannabinoids is the combined amount of every [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) on a lab's panel, typically [THCA](https://genetixbay.com/knowledge/glossary/thca.md), Δ9-THC, [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [CBG](https://genetixbay.com/knowledge/glossary/cbg.md), [CBN](https://genetixbay.com/knowledge/glossary/cbn.md), [CBC](https://genetixbay.com/knowledge/glossary/cbc.md) and a few others. Labs differ on how they sum it: some add the raw acid and neutral values, others apply decarboxylation factors first. The figure depends on how many compounds the panel includes, so it is not directly comparable between labs. ## In practice A COA with total THC 19.5%, CBGA 0.9%, CBG 0.1%, CBCA 0.3% and trace CBN might report total cannabinoids around 21-22%, depending on the summing method. Always check whether the total is "raw sum" or "decarboxylated sum": the raw sum is larger by roughly 12% of the acid content. ## Units and formula Raw sum = sum of all measured cannabinoids (% w/w). Adjusted sum applies factors (0.877 for THCA, CBDA, CBCA; 0.878 for CBGA). Note the basis (dry weight or as received). ## Don't confuse with - **Total THC**: one component of the total. - **Total terpenes**: a separate measurement. ## Myth check House position: flower labelled above about 35% total cannabinoids is not credible; such numbers come from concentrates, lab shopping or inflated testing. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [Total CBD](https://genetixbay.com/knowledge/glossary/total-cbd.md), [Potency testing](https://genetixbay.com/knowledge/glossary/potency-testing.md), [Potency ceiling](https://genetixbay.com/knowledge/glossary/potency-ceiling.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 2. Jikomes N, Zoorob M. 2018. The cannabinoid content of legal cannabis in Washington State varies systematically across testing facilities and popular consumer products. Scientific Reports 8:4519. https://doi.org/10.1038/s41598-018-22755-2 --- # Total CBD > Total CBD is a calculated figure, CBD plus 0.877 × CBDA, estimating the maximum CBD a sample could yield after full decarboxylation. - Canonical: https://genetixbay.com/knowledge/glossary/total-cbd.html - Also written: total CBD calculation, CBD total, max CBD, CBDmax, total potential CBD - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Total CBD is calculated the same way as total [THC](https://genetixbay.com/knowledge/glossary/thc.md). The lab measures [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md) and [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) separately and combines them, multiplying CBDA by [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) to account for the CO2 lost on decarboxylation. [THCA](https://genetixbay.com/knowledge/glossary/thca.md) and CBDA are isomers, so the conversion factor is identical. ## In practice A hemp-type COA reports CBDA 11.5% and CBD 0.4% w/w. Total CBD = 0.4 + 0.877 × 11.5 = 0.4 + 10.1 = 10.5%. Breeders use total CBD alongside total THC to place a plant in its chemotype class: the same plant's total THC might read 0.4%, giving a [CBD:THC ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md) of about 26:1, a type III plant. For anyone working under a hemp THC limit, the important number is usually total THC, not total CBD. A high-CBD plant still makes some THCA, because [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) isn't perfectly specific. ## Units and formula Total CBD (% w/w) = CBD + 0.877 × CBDA. Factor = 314.5 / 358.5 (molecular weights of CBD and CBDA). ## Don't confuse with - **CBDA**: one input to the calculation, not the total. - **Total cannabinoids**: the sum of all measured [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). - **CBD content on a product label**: may be per serving or per container, not % w/w. ## Related terms [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md), [CBD](https://genetixbay.com/knowledge/glossary/cbd.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [Chemotype ratio](https://genetixbay.com/knowledge/glossary/chemotype-ratio.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md) ## Read more - [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) ## Sources 1. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. --- # Total THC > Total THC is a calculated figure, Δ9-THC plus 0.877 × THCA, estimating the maximum THC a sample could yield after full decarboxylation. - Canonical: https://genetixbay.com/knowledge/glossary/total-thc.html - Also written: total THC calculation, THC total, max THC, THCmax, total potential THC, 0.877 - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Total THC is not measured directly. The lab measures [THCA](https://genetixbay.com/knowledge/glossary/thca.md) and [Δ9-THC](https://genetixbay.com/knowledge/glossary/thc.md) separately, usually by [HPLC](https://genetixbay.com/knowledge/glossary/hplc.md), then combines them, applying 0.877 to the THCA because [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md) removes [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) and about 12.3% of the molecule's mass. It is the figure most labels and legal limits use. ## In practice A [COA](https://genetixbay.com/knowledge/glossary/coa.md) shows THCA 22.0% and Δ9-THC 0.8% w/w. Total THC = 0.8 + 0.877 × 22.0 = 0.8 + 19.3 = 20.1%. Adding the two lines without the factor (22.8%) inflates the figure by about 2.7 points, a common error or trick. Real-world conversion during smoking or cooking is lower than the theoretical total because of losses. ## Units and formula Total THC (% w/w) = Δ9-THC + 0.877 × THCA. The factor is the molecular weight ratio, 314.5 / 358.5. Some rules define it differently (for example, also counting other THC isomers); check the definition the lab applied. ## Don't confuse with - **THCA**: one input to the calculation. - **Total cannabinoids**: all measured [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), not only THC. ## Myth check House position: most flower people believe tests in the mid-20s to 30s really tests mid-teens to low 20s. See [buyer beware](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [THCA](https://genetixbay.com/knowledge/glossary/thca.md), [THC](https://genetixbay.com/knowledge/glossary/thc.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [Total CBD](https://genetixbay.com/knowledge/glossary/total-cbd.md), [Total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md), [COA](https://genetixbay.com/knowledge/glossary/coa.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. 2. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 --- # Track-and-trace > Track-and-trace is the ability to follow a regulated product through the supply chain and back to its source, the basis of cannabis tracking and recalls. - Canonical: https://genetixbay.com/knowledge/glossary/track-and-trace.html - Also written: track and trace, traceability, cannabis tracking system, product traceability - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Track-and-trace is the general regulatory and supply-chain idea that each unit of a product can be tracked forward (where did this batch go?) and traced back (where did this package come from?). In cannabis it is usually delivered through a [seed-to-sale system](https://genetixbay.com/knowledge/glossary/seed-to-sale-tracking.md). ## In practice If a lab finds a contaminant in a retail package, track-and-trace lets the regulator identify the batch, the harvest, the cultivation room and every other package from that batch, and order a recall. Lot numbers on labels connect the consumer product to that record. For genetics, a similar idea applies voluntarily: recording which [seed batch](https://genetixbay.com/knowledge/glossary/seed-run.md), mother and father a plant came from lets problems such as [herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) batches or [viroid](https://genetixbay.com/knowledge/glossary/viroid.md) infections be traced to their source. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Seed-to-sale tracking**: the specific cannabis implementation, often used interchangeably. - **Chain of custody**: the documented handling of one sample, such as a lab sample. ## Related terms [Seed-to-sale tracking](https://genetixbay.com/knowledge/glossary/seed-to-sale-tracking.md), [Licensed producer](https://genetixbay.com/knowledge/glossary/licensed-producer.md), [Labelling requirements](https://genetixbay.com/knowledge/glossary/labelling-requirements.md), [GB-ID](https://genetixbay.com/knowledge/glossary/gb-id.md) --- # Transpiration > The evaporation of water from a plant, mainly through open stomata, which pulls water and dissolved nutrients up from the roots. - Canonical: https://genetixbay.com/knowledge/glossary/transpiration.html - Also written: transpire, transpiring, evapotranspiration, leaf water loss - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Transpiration is water loss from plant surfaces as vapour, almost all through [stomata](https://genetixbay.com/knowledge/glossary/stomata.md). As water evaporates inside the leaf, tension pulls a continuous water column up the [xylem](https://genetixbay.com/knowledge/glossary/xylem.md) from the roots. That flow also carries calcium and other ions that move with water, and it cools the leaf. ## In practice The main driver is [vapour pressure deficit](https://genetixbay.com/knowledge/glossary/vpd.md) (VPD): how much drier the air is than the inside of the leaf. Higher light, warmer leaves and drier air raise transpiration; still, humid air lowers it. What that means in the grow: - **Too low** (humid, still air, VPD below about 0.4-0.5 kPa): slow water and calcium movement, guttation, and conditions for mould. - **Too high** (hot, dry air, VPD above about 1.6 kPa): stomata close, leaves taco or droop, and growth slows. - **Calcium-related tip problems** on fast new growth often reflect low transpiration, not low calcium in the feed. A large plant in flower can transpire litres per day. That is why rooms gain humidity with canopy size. ## Don't confuse with - **Evaporation from the medium**: water lost from the pot surface, not through the plant. - **Guttation**: liquid droplets pushed out at leaf edges by root pressure. - **Relative humidity**: one input to VPD, not the plant's water loss. ## Related terms [Stomata](https://genetixbay.com/knowledge/glossary/stomata.md), [Xylem](https://genetixbay.com/knowledge/glossary/xylem.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) ## Read more - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) - [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Transplanting > Transplanting moves a plant and its root ball into a new container or the ground; done gently it causes little shock, but GenetixBay advises against it for autoflowers. - Canonical: https://genetixbay.com/knowledge/glossary/transplanting.html - Also written: transplant, transplanted, transplant shock, moving to a bigger pot - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Transplanting is moving a plant, with its root ball, from one container or site to another. The aim is more root room without breaking roots. Transplant shock is the pause in growth that follows when roots are damaged, dried out or exposed to a sudden change of medium, temperature or light. ## In practice Water the plant a few hours beforehand so the root ball holds together, pre-moisten the new medium, set the plant at the same depth (or slightly deeper for leggy [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md)), and keep light a little gentler for a day or two. Transplant when roots reach the walls but before they circle. For [photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md), a careful transplant costs very little. For [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) it is a different story. ## Don't confuse with - **Up-potting**: one specific kind of transplant, into a larger pot of the same medium. - **Hardening off**: [acclimatising](https://genetixbay.com/knowledge/glossary/hardening-off.md) a plant to outdoor conditions; often done before an outdoor transplant, but a different step. ## Myth check House position (grower practice): for autoflowers, transplanting is almost a no-no. Autos run on a fixed countdown from [germination](https://genetixbay.com/knowledge/glossary/germination.md), so any setback costs time they cannot make up, and in the founder's experience their [taproot](https://genetixbay.com/knowledge/glossary/taproot.md) reacts worse to disturbance than a photoperiod's. Sow autos straight into the final pot. See [transplanting](https://genetixbay.com/knowledge/germination/transplanting.md) and [photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md). ## Related terms [Up-potting](https://genetixbay.com/knowledge/glossary/up-potting.md), [Root-bound](https://genetixbay.com/knowledge/glossary/root-bound.md), [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md), [Autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md), [Hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) ## Read more - [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) ## Sources 1. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # Trellis > A trellis is a net, mesh or frame that supports plants and spreads their branches, either as a SCROG screen or as support for heavy colas in flower. - Canonical: https://genetixbay.com/knowledge/glossary/trellis.html - Also written: trellis net, trellis netting, plant netting, support net, scrog screen, yo-yos - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A trellis is a support structure, most often a flexible net with square cells of about 10-15 cm (4-6 in), stretched horizontally over the plants. Indoors it does two jobs: a training screen ([SCROG](https://genetixbay.com/knowledge/glossary/scrog.md)) that spreads [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) into a [flat canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md), and a support layer that stops heavy [colas](https://genetixbay.com/knowledge/glossary/cola.md) falling over in late flower. ## In practice Many growers run two layers: the first 20-30 cm (8-12 in) above the medium for training, the second 30-40 cm (12-16 in) higher for support during the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). The net must be anchored tightly to a frame or tent poles; a sagging net does neither job. Outdoors, vertical nets, cages or stakes do the same work against wind and rain. Hanging retractable supports ("yo-yos") are used for single heavy branches. ## Don't confuse with - **SCROG**: the training method; a trellis is the equipment. - **Stakes and ties**: individual supports rather than a whole-canopy net. ## Related terms [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [Plant ties](https://genetixbay.com/knowledge/glossary/plant-ties.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md), [Tucking](https://genetixbay.com/knowledge/glossary/tucking.md) ## Read more - [SCROG: screen of green](https://genetixbay.com/knowledge/training/scrog.md) --- # Trichome > A hair-like outgrowth of the plant's skin; in cannabis the glandular types make and store the resin holding cannabinoids and terpenes. - Canonical: https://genetixbay.com/knowledge/glossary/trichome.html - Also written: trichomes, resin glands, resin heads, crystals, glandular hairs - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A trichome is any hair or outgrowth from the epidermis of a plant. Cannabis has two broad groups. [Non-glandular trichomes](https://genetixbay.com/knowledge/glossary/cystolith-trichome.md) are simple pointed [hairs](https://genetixbay.com/knowledge/glossary/pistil.md) that protect the surface. Glandular trichomes are secretory: a disc of cells makes resin rich in cannabinoid acids (such as [THCA](https://genetixbay.com/knowledge/glossary/thca.md) and CBDA) and terpenes and stores it in a cavity under a waxy cuticle at the gland head. ## In practice The three glandular types are bulbous (tiny), capitate-sessile (on leaves and early flowers) and [capitate-stalked](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md) (the mushroom-shaped glands on bracts that hold most of the resin). When growers say "frost", "crystals" or "trichomes", they almost always mean capitate-stalked heads. With a 60-100x loupe or microscope, head colour shows maturity: clear, then cloudy (milky), then amber. GenetixBay's harvest guidance is a matter of taste, ideally a mix of a few clear, mostly cloudy and some amber heads. [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) are fragile. Rough handling, warm temperatures and agitation knock them off, which matters for trimming and storage. ## Don't confuse with - **Pistil (stigma)**: the white or orange hairs of the flower, not resin glands. - **Kief**: loose detached trichome heads, a processing term. - **Powdery mildew**: a fungal coating that sits flat on leaf surfaces, not on stalks. ## Myth check Frost is not potency. Visible trichome density did not reliably predict [THC](https://genetixbay.com/knowledge/glossary/thc.md) in field work, and [bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md) is not quality (Supported). See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Capitate-stalked trichome](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md), [Capitate-sessile trichome](https://genetixbay.com/knowledge/glossary/capitate-sessile-trichome.md), [Bulbous trichome](https://genetixbay.com/knowledge/glossary/bulbous-trichome.md), [Cystolith trichome](https://genetixbay.com/knowledge/glossary/cystolith-trichome.md), [Trichome ripeness](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md) ## Read more - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) ## Sources 1. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 2. Punja ZK, Sutton DB, Kim T. 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 --- # Trichome heads > Trichome heads are the bulbous resin-filled tops of capitate glandular trichomes, where cannabis makes and stores nearly all its cannabinoids and terpenes; they are the raw material of hash. - Canonical: https://genetixbay.com/knowledge/glossary/trichome-heads.html - Also written: gland heads, trichome head, capitate heads, trichome gland heads - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A trichome head is the glandular top of a [capitate stalked trichome](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md): a disc of secretory cells under a cuticle that swells into a storage cavity filled with resin. Livingston et al. (2020) showed that these stalked glands, which dominate mature flowers, are the main sites of [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) production. Head diameter on mature stalked trichomes is commonly in the range of roughly 50-120 µm, which is why hash makers grade them with [micron screens](https://genetixbay.com/knowledge/glossary/micron-bags.md). ## In practice Everything solventless processing does is about separating heads from plant tissue. The cleaner the separation, the higher the cannabinoid content: pure heads are far richer than flower, because flower is mostly bract, leaf and stem by mass. That gap is also the logic behind the GenetixBay [potency ceiling](https://genetixbay.com/knowledge/glossary/potency-ceiling.md): dried flower can't approach the cannabinoid content of its isolated heads. Heads are fragile; warmth, handling and agitation break them and smear resin onto plant matter. ## Don't confuse with - **Trichome (whole)**: includes the stalk; growers often mean the head. - **Non-glandular trichomes**: [hairs](https://genetixbay.com/knowledge/glossary/pistil.md) with no resin. - **Pistils**: the visible "hairs" of the flower, not [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md). ## Myth check Frost shows how many heads you can see, not how full they are. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Kief](https://genetixbay.com/knowledge/glossary/kief.md), [Hash](https://genetixbay.com/knowledge/glossary/hash.md), [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Full melt](https://genetixbay.com/knowledge/glossary/full-melt.md), [Potency ceiling](https://genetixbay.com/knowledge/glossary/potency-ceiling.md), [Solventless](https://genetixbay.com/knowledge/glossary/solventless.md) ## Read more - [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) ## Sources 1. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 2. Clarke RC. 1998. Hashish! Red Eye Press, Los Angeles (updated edition 2010). --- # Trichome ripeness > The maturity of glandular trichome heads, read by colour under magnification: clear (immature), cloudy or milky (mature), then amber (ageing). - Canonical: https://genetixbay.com/knowledge/glossary/trichome-ripeness.html - Also written: trichome colour, trichome color, clear cloudy amber, milky trichomes, amber trichomes, cloudy trichomes, clear trichomes - Glossary category: Harvest, drying and curing · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Trichome ripeness is the standard way growers judge harvest. [Capitate-stalked](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md) [gland heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) start clear and glassy, turn cloudy (milky, opaque white) as they fill and mature, and some go amber or brown as they age and their contents oxidise. Research confirms that gland heads change in colour, size and metabolite content as flowers mature, and that timing varies with [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) (Livingston et al. 2020; Punja et al. 2023). ## In practice How to read it: - **Clear**: still developing. Too early. - **Cloudy**: mature heads. The core of the [harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md). - **Amber**: ageing heads. A share of amber shows you are late in the window. GenetixBay house position: cloudy versus amber is a matter of preference. Ideally take a nice mix: a few clear, mostly cloudy, some amber. Look at bract [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) on several buds over several days, because sugar-leaf glands ripen and amber earlier. Use a 60-100x loupe or a pocket digital microscope; 30x is borderline. ## Don't confuse with - **Pistil colour**: a weaker, more stress-affected indicator. - **Bag appeal (frost)**: how many heads, not how ripe. - **Cystolith hairs**: clear non-glandular [hairs](https://genetixbay.com/knowledge/glossary/pistil.md) with no head. ## Myth check "Amber trichomes give a couch-lock high from [CBN](https://genetixbay.com/knowledge/glossary/cbn.md)" is unsupported. CBN forms mainly by oxidation after harvest, and amber marks ageing glands, not a different effect (house position, agreed). See [trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md). ## Related terms [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md), [Capitate-stalked trichome](https://genetixbay.com/knowledge/glossary/capitate-stalked-trichome.md), [Harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md), [Jeweler's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) ## Read more - [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) ## Sources 1. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 2. Punja ZK, Sutton DB, Kim T. 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 3. Sutton DB, Punja ZK, Hamarneh G. 2023. Characterization of trichome phenotypes to assess maturation and flower development in Cannabis sativa L. by automatic trichome gland analysis. Smart Agricultural Technology. --- # Trim > Trim is the leaf material cut away from buds after harvest, especially the small resin-coated sugar leaves, often saved for making kief, hash or other concentrates. - Canonical: https://genetixbay.com/knowledge/glossary/trim.html - Also written: trimmings, trim material, shake and trim, leaf trim, fan trim - Glossary category: Processing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Trim is the by-product of manicuring buds: [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md), the small [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) that grow out of the flower clusters, and bits of stem. Fan leaves carry few glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md); sugar leaves can be heavily coated. Growers usually separate the two and keep the resinous trim for processing into [kief](https://genetixbay.com/knowledge/glossary/kief.md), [ice water hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), rosin or edible infusions. ## In practice Trim from a well-grown, resinous cultivar can be valuable starting material; trim from low-resin plants is often discarded or composted. [Wet trim](https://genetixbay.com/knowledge/glossary/wet-trim.md) (cut before drying) and [dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md) (cut after drying) produce different trim: dry-trim material tends to lose more heads to handling, which collect as kief. House position: wet versus dry trimming is grower preference. The founder prefers brushing dry buds to scissoring wet ones, even at the cost of a little trichome loss, since it all gets used anyway. Store trim like flower, cool, dark and dry, or freeze it for live processing. ## Don't confuse with - **Shake**: loose bits of flower broken off in handling, more potent than leaf trim. - **Sugar trim**: the resin-rich subset of trim. - **Trimming**: the act, rather than the material. ## Related terms [Sugar trim](https://genetixbay.com/knowledge/glossary/sugar-trim.md), [Kief](https://genetixbay.com/knowledge/glossary/kief.md), [Bubble hash](https://genetixbay.com/knowledge/glossary/bubble-hash.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md), [Fresh frozen](https://genetixbay.com/knowledge/glossary/fresh-frozen.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) --- # True breeding > A true-breeding line produces offspring that consistently look like the parents for a given trait, because the plants are homozygous for the alleles behind it. - Canonical: https://genetixbay.com/knowledge/glossary/true-breeding.html - Also written: breeds true, breeding true, true-to-type, true to type, pure-breeding - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A [line breeds](https://genetixbay.com/knowledge/glossary/line-breeding.md) true for a trait when its offspring reliably show that trait, generation after generation. Genetically, every plant is [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) for the relevant [alleles](https://genetixbay.com/knowledge/glossary/allele.md), so there is nothing left to segregate. Mendel's pea lines were true-breeding before he crossed them. ## In practice True breeding is trait by trait. An inbred cannabis line may breed true for [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) and flowering time and still vary for aroma or yield. A balanced 1:1 THC:CBD plant can never breed true from seed because its chemotype comes from being [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md); crossing two of them gives the 1:2:1 split. Breeders test it with a grow-out of enough seed. If every plant in 30 or more matches the target for the trait, the line is very likely true-breeding for it. Clones are always true to type for every trait, because they are copies, not offspring. ## Don't confuse with - **True to type (clone)**: a cutting matches its mother. In seed, "true to type" means the line breeds true. - **Uniformity**: often a sign of true breeding, but an [F1](https://genetixbay.com/knowledge/glossary/f1.md) of two [inbred lines](https://genetixbay.com/knowledge/glossary/inbred-line.md) is uniform and still does not breed true in the next generation. - **Stable sex**: a separate quality. True breeding for aroma says nothing about [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md). ## Related terms [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md), [Uniformity](https://genetixbay.com/knowledge/glossary/uniformity.md), [Open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md) ## Read more - [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md) ## Sources 1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/ 2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # True leaves > The first leaves produced by the shoot tip after the cotyledons, with the plant's characteristic serrated leaflets. - Canonical: https://genetixbay.com/knowledge/glossary/true-leaves.html - Also written: first true leaves, true leaf, first set of leaves, first serrated leaves - Glossary category: Plant biology - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" True leaves are leaves produced by the [shoot apical meristem](https://genetixbay.com/knowledge/glossary/apical-meristem.md), as opposed to the [cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) formed in the embryo. In cannabis the first pair has a single serrated [leaflet](https://genetixbay.com/knowledge/glossary/leaflet.md) each; later pairs carry three, then five, and more leaflets as the plant matures, up to seven to eleven or more on large [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md). ## In practice Growers count true-leaf nodes to time things. Common landmarks: start light feeding at roughly the second or third set of true leaves; topping is often done at the third to fifth node; seedlings are usually ready to [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) from a small cell once they have a few sets of true leaves and roots reach the cell edge. Early leaves arise in opposite pairs. As the plant moves toward flowering, phyllotaxy usually switches to alternate (one leaf per node). That switch is a maturity marker, not a sex indicator. Slow, cupped or pale first true leaves usually point to light intensity, [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) or medium [pH](https://genetixbay.com/knowledge/glossary/ph.md) before nutrients. ## Don't confuse with - **Cotyledons**: the smooth, rounded seed leaves that come first. - **Leaflet**: one blade of a compound true leaf. - **Sugar leaves**: small resinous leaves within the flower clusters. ## Related terms [Cotyledon](https://genetixbay.com/knowledge/glossary/cotyledon.md), [Leaflet](https://genetixbay.com/knowledge/glossary/leaflet.md), [Serration](https://genetixbay.com/knowledge/glossary/serration.md), [Node](https://genetixbay.com/knowledge/glossary/node.md), [Fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md) ## Read more - [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) ## Sources 1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Tucking > Tucking is moving fan leaves and shoots behind or under others, or beneath a screen, so bud sites get light without removing any leaf area. - Canonical: https://genetixbay.com/knowledge/glossary/tucking.html - Also written: tuck, leaf tucking, tucking leaves, tuck don't pluck - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Tucking is a training method in which a leaf that is shading a bud site is folded behind a stem, slid under a neighbouring leaf, or pushed beneath a [trellis net](https://genetixbay.com/knowledge/glossary/trellis.md), instead of being cut off. In [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), tucking also means pulling [growing tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) back under the screen so they spread sideways. ## In practice Tuck daily while plants are in late veg and the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md); leaves are pliable and stay where they are put once they reorient to the light. Large [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) can be tucked under the stem of the leaf next to them. The leaf keeps photosynthesising, the bud underneath gets light, and nothing needs to heal. ## Myth check House position: "tuck, don't pluck" is GenetixBay's standard advice. Maximise leaf surface area, like a solar farm for the buds, and prefer tucking and training over stripping. Whether [heavy defoliation](https://genetixbay.com/knowledge/glossary/schwazzing.md) helps or hurts is an open question for [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md); tucking gives the light benefit without the gamble. Evidence: Grower practice, house-endorsed. See [defoliation and lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md). ## Don't confuse with - **Defoliation**: removes leaves; tucking only moves them. - **LST**: bends stems; tucking usually refers to leaves and tips. ## Related terms [Defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md), [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md), [Fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md) ## Read more - [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) - [SCROG: screen of green](https://genetixbay.com/knowledge/training/scrog.md) --- # Two-point calibration > Two-point calibration sets a pH meter with two buffers, usually pH 7.00 then 4.01, fixing both its offset and its slope for accurate readings. - Canonical: https://genetixbay.com/knowledge/glossary/two-point-calibration.html - Also written: 2-point calibration, two point cal, dual-point calibration, slope calibration, multi-point calibration - Glossary category: pH, EC and water · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Two-point calibration adjusts a [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) using two reference buffers. The first, almost always [pH](https://genetixbay.com/knowledge/glossary/ph.md) 7.00, sets the offset (the zero point, where an ideal electrode outputs 0 mV). The second, usually pH 4.01 for acidic work, sets the slope, the millivolts per pH unit. An ideal electrode gives about 59.16 mV per pH unit at 25 °C. One-point calibration fixes only the offset and can mislead on worn probes. ## In practice For grow solutions in the 5–7 range, calibrate at 7.00 then 4.01. Steps: rinse with distilled water, place in pH 7, let the reading settle, confirm; rinse; place in pH 4, settle, confirm. Many meters then report slope as a percentage. A slope of roughly 95–105% means the electrode is healthy; below about 90% suggests cleaning or replacing it. Calibrate weekly for regular hydro use, and always after storage, cleaning, or a reading that [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) wrong. A three-point calibration (adding pH 10) helps only if you measure alkaline samples. ## Units and formula Nernst slope ≈ 59.16 mV per pH unit at 25 °C; slope % = measured slope ÷ theoretical slope × 100. ## Don't confuse with - **EC calibration**: usually one-point, with a standard such as 1.413 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md). - **Temperature compensation**: corrects for temperature, not for electrode ageing. ## Related terms [Calibration solution](https://genetixbay.com/knowledge/glossary/calibration-solution.md), [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md), [ATC](https://genetixbay.com/knowledge/glossary/atc.md) ## Read more - [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) --- # Two-spotted spider mite > Tetranychus urticae, the commonest cannabis mite indoors: a 0.5 mm sap-feeder that stipples leaves pale and spins webbing, breeding fastest in hot, dry rooms. - Canonical: https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.html - Also written: spider mite, spider mites, twospotted spider mite, TSSM, red spider mite, Tetranychus urticae, mites - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The two-spotted spider mite (*Tetranychus urticae*) is a plant-feeding mite, not an insect, that pierces leaf cells and empties them. Each emptied cell shows as a pale dot, called [stippling](https://genetixbay.com/knowledge/glossary/stippling.md). Adults are about 0.5 mm long, pale yellow-green with two dark blotches on the body. Heavy populations spin silk that can cover [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md). ## In practice Growers find them with a 10-20x hand lens on leaf undersides: mites, round clear eggs and cast skins. Speed is the problem. At about 24 °C (75 °F) a generation can finish in under a week, so a few stippled leaves become a webbed canopy within a month. Control rests on early scouting, cooler and more humid air where the stage allows, and [predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md) such as *[Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md)* released while numbers are low. Contact sprays belong in veg, not on flowers. Check what is registered for cannabis locally before using any product. ## Don't confuse with - **Broad mite and hemp russet mite**: far smaller, invisible without 40x or more, and they cause twisting or russeting rather than stippling. - **Thrips damage**: silvery streaks with black specks of [frass](https://genetixbay.com/knowledge/glossary/frass.md), not fine dots. - **Nutrient spotting**: no mites, eggs or webbing under the leaf. ## Related terms [Broad mite](https://genetixbay.com/knowledge/glossary/broad-mite.md), [Phytoseiulus persimilis](https://genetixbay.com/knowledge/glossary/phytoseiulus-persimilis.md), [Neoseiulus californicus](https://genetixbay.com/knowledge/glossary/neoseiulus-californicus.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Pesticide resistance](https://genetixbay.com/knowledge/glossary/pesticide-resistance.md) ## Read more - [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ## Sources 1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 2. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php 3. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf --- # Underwatering > Underwatering is letting the medium dry too far between waterings, so the plant loses turgor and wilts, with limp, papery leaves and crisping edges if repeated. - Canonical: https://genetixbay.com/knowledge/glossary/underwatering.html - Also written: under-watering, underwatered, too little water, dry wilt - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Underwatering means the plant runs short of water before the next irrigation. Leaves lose turgor and hang limp and thin, the pot feels very light, and the medium may shrink away from the pot wall. Repeated cycles cause crispy leaf edges, nutrient problems (calcium moves with water), and stunting. ## In practice The fix is to water thoroughly and evenly; very dry [peat](https://genetixbay.com/knowledge/glossary/peat.md) and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) can repel water at first, so water slowly in stages or bottom-water until they rewet. Plants usually recover within hours. Long term, increase watering frequency, use larger pots, mulch the surface, or move to automated irrigation. A mild, controlled dry-down is not the same as underwatering. Research found controlled drought late in flower increased [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) concentration, and GenetixBay endorses a mild late drought for cultivars that respond to it, but every cultivar responds differently. ## Don't confuse with - **Overwatering**: firm, swollen, droopy leaves from wet roots; the pot feels heavy. - **Heat stress**: can also cause wilting; check the medium first. ## Related terms [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), [Wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md), [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md), [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) ## Read more - [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ## Sources 1. Caplan D, Dixon M, Zheng Y, 2019. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience 54(5):964–969. https://doi.org/10.21273/HORTSCI13510-18 --- # Uniformity > Uniformity is how alike the plants of one seed batch are for traits such as height, timing and chemistry; F1s of inbred parents and IBLs are most uniform. - Canonical: https://genetixbay.com/knowledge/glossary/uniformity.html - Also written: uniform, consistency, line uniformity, batch uniformity - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Uniformity describes how similar the plants from one [seed batch](https://genetixbay.com/knowledge/glossary/seed-run.md) are: in height, structure, flowering time, aroma and cannabinoid profile. It is measured by growing many plants under the same conditions and looking at the spread. ## In practice Uniform seed is worth a lot to growers running a [sea of green](https://genetixbay.com/knowledge/glossary/sog.md) or a commercial room: plants finish together, fill the canopy evenly and test alike. Two routes give it. An [F1](https://genetixbay.com/knowledge/glossary/f1.md) between two different [inbred lines](https://genetixbay.com/knowledge/glossary/inbred-line.md) is uniform because every seed gets the same pair of genotypes. An IBL is uniform because its plants are highly [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md). Most [cannabis seed](https://genetixbay.com/knowledge/glossary/achene.md) is neither, so variation is normal. Breeders describing uniformity should quantify it from tester grows: "flowering time 56 to 63 days across 40 plants" says more than "very uniform". Uniformity is not quality, and not always a goal. Preservation seed lines and [landraces](https://genetixbay.com/knowledge/glossary/landrace.md) keep variation on purpose, because diversity is what lets a population adapt and gives later breeders something to select from. ## Don't confuse with - **True breeding**: offspring match parents over generations; an F1 can be uniform without [breeding true](https://genetixbay.com/knowledge/glossary/true-breeding.md). - **Stability of sex**: a uniform line can still carry a herm problem. ## Related terms [True breeding](https://genetixbay.com/knowledge/glossary/true-breeding.md), [F1](https://genetixbay.com/knowledge/glossary/f1.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md), [Test grow](https://genetixbay.com/knowledge/glossary/test-grow.md) ## Read more - [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md) ## Sources 1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0 --- # Up-potting > Up-potting moves a plant into progressively larger containers as its roots fill each one, instead of starting in the final pot. - Canonical: https://genetixbay.com/knowledge/glossary/up-potting.html - Also written: uppotting, potting up, pot up, step-up potting - Glossary category: Cultivation and training · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Up-potting is the practice of moving a plant through a series of larger containers, for example a 0.5 L cup, then a 3-4 L pot, then a 15-25 L final pot, as roots fill each one. The idea is that a small root system in a small volume of medium wets and dries quickly, which keeps roots oxygenated and reduces the [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) risk of a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) in a huge, cold, wet pot. ## In practice Up-pot when white roots reach the wall and the root ball lifts out intact, but before roots circle densely. Each move should go to roughly two to four times the volume. Many growers skip the middle step and go cup to final. The alternative is planting straight into the final pot and watering only a small circle around the stem at first; that works well and avoids handling. For [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) GenetixBay recommends the final pot from day one. ## Don't confuse with - **Transplanting**: the general term; up-potting is a [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) into a bigger pot. - **Root pruning**: deliberately cutting roots to keep a plant (often a mother) in the same pot. ## Related terms [Transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md), [Root-bound](https://genetixbay.com/knowledge/glossary/root-bound.md), [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) ## Read more - [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) ## Sources 1. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # UPOV > UPOV is the International Union for the Protection of New Varieties of Plants and its convention, the treaty framework most national plant breeders' rights laws follow. - Canonical: https://genetixbay.com/knowledge/glossary/upov.html - Also written: UPOV Convention, International Union for the Protection of New Varieties of Plants, UPOV 1991, UPOV 91 - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" UPOV is an intergovernmental organisation based in Geneva, set up by the International Convention for the Protection of New Varieties of Plants of 1961. The convention was revised in 1972, 1978 and 1991. Member states write national [plant breeders' rights](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md) laws in line with one of these Acts. ## In practice The 1991 Act sets the main rules: protectable varieties must be new, distinct, uniform and stable; protection lasts at least 20 years (25 for trees and vines); a breeder's exemption allows protected varieties to be used for further breeding; and saving farm seed is an optional exception member states may allow within limits. It also introduced "essentially derived varieties", so minor modifications of a protected variety cannot escape the original rights. UPOV is debated: supporters say it rewards breeding investment; critics argue it restricts farmers' seed saving and favours commercial breeders over traditional ones. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Nagoya Protocol**: about access to [genetic resources](https://genetixbay.com/knowledge/glossary/germplasm.md) and [benefit-sharing](https://genetixbay.com/knowledge/glossary/benefit-sharing.md), not breeders' rights. - **WIPO**: the UN agency for intellectual property in general. ## Related terms [Plant variety protection](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md), [Plant patent](https://genetixbay.com/knowledge/glossary/plant-patent.md), [Nagoya Protocol](https://genetixbay.com/knowledge/glossary/nagoya-protocol.md), [Open-source seed](https://genetixbay.com/knowledge/glossary/open-source-seed.md) ## Read more - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) ## Sources 1. UPOV. 1991. International Convention for the Protection of New Varieties of Plants (1991 Act). https://www.upov.int/upovlex/en/conventions/1991/content.html --- # Urea > Urea is a 46% nitrogen organic compound that soil enzymes convert to ammonium; it is cheap in field fertilisers but a poor choice for hydroponic cannabis. - Canonical: https://genetixbay.com/knowledge/glossary/urea.html - Also written: CO(NH2)2, carbamide, 46-0-0, urea nitrogen - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Urea is a small organic molecule, CO(NH2)2, containing 46% nitrogen. It is the world's most used nitrogen fertiliser. Plants can absorb some urea directly, but most is first converted to [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) by urease, a nickel-dependent enzyme produced by microbes and plants. ## In practice In soil, urea behaves like a slow ammonium source and acidifies over time; it can lose nitrogen as ammonia gas if left on the surface. In hydro and [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) systems it is a poor fit: it is not counted by [EC](https://genetixbay.com/knowledge/glossary/ec.md) meters as an ion until converted, its conversion depends on microbial activity, and the ammonium it releases can upset the NH4/[NO3](https://genetixbay.com/knowledge/glossary/nitrate.md) balance. Some liquid bottle nutrients and [foliar](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) products include it. On labels, urea-N is often listed separately from nitrate-N and ammoniacal-N. ## Don't confuse with - **Ammonium**: urea becomes ammonium; they are not the same compound. - **Urine**: contains urea, but also salts and [sodium](https://genetixbay.com/knowledge/glossary/sodium.md); not a measured feed. - **Uric acid**: a different nitrogen compound found in bird and bat manures. ## Related terms [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), [Nickel](https://genetixbay.com/knowledge/glossary/nickel.md), [Foliar feeding](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) ## Read more - [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) - [Nickel (Ni) in cannabis: essential, needed in traces, almost never worth adding](https://genetixbay.com/knowledge/nutrients/nickel.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Brown PH, Welch RM, Cary EE. 1987. Nickel: a micronutrient essential for higher plants. Plant Physiology 85(3):801-803. https://doi.org/10.1104/pp.85.3.801 --- # Utility patent > A utility patent protects a new, useful and non-obvious invention; for plants it can cover varieties, seeds, specific traits or breeding and processing methods. - Canonical: https://genetixbay.com/knowledge/glossary/utility-patent.html - Also written: utility patents, plant utility patent, trait patent, method patent - Glossary category: Legal and regulatory - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A utility patent is the standard patent for inventions. In the US, plants, seeds, plant parts, genetic traits and methods of breeding or processing can all be claimed in utility patents if the claimed invention is new, useful and not obvious. Protection generally lasts 20 years from filing. ## In practice Utility patents can be broader than [plant patents](https://genetixbay.com/knowledge/glossary/plant-patent.md): a claim might cover any plant with a defined trait or chemical profile, not just one clone. Cannabis utility patents exist and are public records. Their scope is often tested only if challenged, and prior art, meaning earlier public disclosure, is one way claims are limited. This is why GenetixBay's documentation matters: dated, public records of lines, traits and chemistry can serve as prior art. Present patent records factually; do not speculate about any holder's motives. Rules differ by country, state, province and city, and change often. This is a general definition, not legal advice: check local rules. ## Don't confuse with - **Plant patent**: limited to one asexually reproduced variety. - **Plant variety protection**: [breeders' rights](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md) with a breeder's exemption for research. ## Related terms [Plant patent](https://genetixbay.com/knowledge/glossary/plant-patent.md), [Plant variety protection](https://genetixbay.com/knowledge/glossary/plant-variety-protection.md), [Defensive publication](https://genetixbay.com/knowledge/glossary/defensive-publication.md), [Open-source seed](https://genetixbay.com/knowledge/glossary/open-source-seed.md) ## Read more - [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md) ## Sources 1. United States Code, Title 35, sections 161-164 (Plant Patents). --- # UV-A > UV-A is ultraviolet light from 315 to 400 nm; plants sense it much like deep blue, and adding it gives no proven gain in yield or potency. - Canonical: https://genetixbay.com/knowledge/glossary/uv-a.html - Also written: UVA, UV-A light, ultraviolet A, near-UV, 385 nm, 395 nm - Glossary category: Environment and light · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" UV-A is the longest-wavelength ultraviolet band, 315–400 nm. It is mostly sensed by the same blue-light receptors (cryptochromes and phototropins) that respond to 400–500 nm, so plants treat it much like extra-deep blue. It is the safest UV band, but still harmful to eyes and skin with long exposure. Many fixtures marketed with "UV" actually emit 385–405 nm, at or just inside the edge of this band. ## In practice Growers add UV-A hoping for more resin or [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md). Controlled cannabis trials have not shown consistent gains. Llewellyn and colleagues (2022) found UV treatments did not affect yield or [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) content, and Westmoreland and colleagues (2023) found elevated UV photon fluxes changed cannabinoid concentration only minimally. Small amounts of UV-A are harmless and may help compactness slightly. They are not a substitute for intensity. Wear UV-rated eye protection when working under any fixture with UV channels, and switch them off during maintenance. ## Don't confuse with - **UV-B**: shorter (280–315 nm), more biologically active and more damaging. - **UV-C**: 100–280 nm, germicidal; never use on living plants or people. - **Violet (400–420 nm)**: visible light; often sold as "UV". ## Myth check "UV-A boosts [THC](https://genetixbay.com/knowledge/glossary/thc.md)" is not supported by controlled trials. *Myth* as a reliable potency claim. ## Related terms [UV-B](https://genetixbay.com/knowledge/glossary/uv-b.md), [Blue light](https://genetixbay.com/knowledge/glossary/blue-light.md), [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md), [Full spectrum](https://genetixbay.com/knowledge/glossary/full-spectrum.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 2. Westmoreland FM, Kusuma P, Bugbee B, 2023. Elevated UV photon fluxes minimally affected cannabinoid concentration in a high-CBD cultivar. Frontiers in Plant Science 14:1220585. https://doi.org/10.3389/fpls.2023.1220585 --- # UV-B > UV-B is ultraviolet light from 280 to 315 nm; added to grow rooms in hopes of more resin, it gives little or no visible difference in controlled trials. - Canonical: https://genetixbay.com/knowledge/glossary/uv-b.html - Also written: UVB, UV-B light, ultraviolet B, UVB supplementation, UV-B lamps - Glossary category: Environment and light · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" UV-B is ultraviolet light from 280 to 315 nm. Plants sense it through the UVR8 photoreceptor and respond with protective pigments, thicker leaves and, at high doses, tissue damage. Sunlight at ground level contains a small amount; most indoor fixtures contain none unless UV-B lamps or diodes are added. ## In practice The popular theory is that cannabis makes resin to shield itself from UV-B, so adding UV-B should raise [THC](https://genetixbay.com/knowledge/glossary/thc.md). Controlled trials do not bear this out. Rodriguez-Morrison, Llewellyn and Zheng (2021) found UV-B did not increase inflorescence yield or [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) concentration and reduced yield at higher doses. Llewellyn and colleagues (2022) and Westmoreland and colleagues (2023) reached similar conclusions for UV generally. UV-B is also a real hazard: it burns skin and damages eyes (photokeratitis) quickly. Never look at UV-B sources and switch them off before working in the room. ## Don't confuse with - **UV-A**: longer wavelength, gentler, acts more like deep blue. - **UV-C**: germicidal; used for surface or air sterilisation, never on plants. ## Myth check GenetixBay house position: UV-B produces **little or no visible difference** in the finished crop. That matches the controlled trials. *Supported*. Members who want to test their own cultivars can run a side-by-side trial; see [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [UV-A](https://genetixbay.com/knowledge/glossary/uv-a.md), [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md), [Light stress](https://genetixbay.com/knowledge/glossary/light-stress.md), [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis inflorescence yield and cannabinoid concentration are not increased with exposure to short-wavelength ultraviolet-B radiation. Frontiers in Plant Science 12:725078. https://doi.org/10.3389/fpls.2021.725078 2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 3. Westmoreland FM, Kusuma P, Bugbee B, 2023. Elevated UV photon fluxes minimally affected cannabinoid concentration in a high-CBD cultivar. Frontiers in Plant Science 14:1220585. https://doi.org/10.3389/fpls.2023.1220585 --- # Valencene > Valencene is a sweet, citrus, orange-peel sesquiterpene named after Valencia oranges and found as a minor terpene in some cannabis cultivars. - Canonical: https://genetixbay.com/knowledge/glossary/valencene.html - Also written: (+)-valencene, valencine, valancene - Glossary category: Cannabinoids and terpenes · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Valencene is a bicyclic [sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) first isolated from Valencia orange oil. It smells sweet, citrus and woody, a softer, longer-lasting orange note than [limonene](https://genetixbay.com/knowledge/glossary/limonene.md). Because it is a C15 compound, it is far less volatile than the C10 citrus [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), which is why the flavour industry values it as a lasting orange note. ## In practice In cannabis, valencene is usually minor, from [not detected](https://genetixbay.com/knowledge/glossary/non-detect.md) to around 0.1% w/w. Cultivars described as "orange" or "tangerine" may carry it, but citrus aroma in cannabis often comes from limonene, [terpinolene](https://genetixbay.com/knowledge/glossary/terpinolene.md) or non-terpene compounds as well. Only a [terpene test](https://genetixbay.com/knowledge/glossary/terpene-test.md) that includes valencene will show it; many basic panels don't. ## Don't confuse with - **Limonene**: the main citrus [monoterpene](https://genetixbay.com/knowledge/glossary/monoterpene.md), more volatile. - **Nootkatone**: grapefruit ketone made by oxidising valencene; rarely reported in cannabis. - **Valerian**: a plant, not a terpene. ## Related terms [Sesquiterpene](https://genetixbay.com/knowledge/glossary/sesquiterpene.md), [Limonene](https://genetixbay.com/knowledge/glossary/limonene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md) ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. --- # Veg time > Veg time is how long a photoperiod plant is kept in vegetative growth under long days before being flipped to flower, which largely sets its final size. - Canonical: https://genetixbay.com/knowledge/glossary/veg-time.html - Also written: vegetative period, veg period, vegging, veg phase, length of veg, vegetative stage - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Veg time is the length of the vegetative phase, from [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) or rooted clone until the flowering [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) begins. Under long days (18 h or more of light) a photoperiod plant stays vegetative indefinitely, so the grower chooses how long it grows before flowering. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) have no controllable veg time; they flower by age. ## In practice Common ranges: [SOG](https://genetixbay.com/knowledge/glossary/sog.md) clones get 1-2 weeks; most tent grows with a few trained plants get 3-6 weeks; [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md) and mainlined plants often get 6-8 weeks or more until the screen is mostly full. Because plants [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) after the flip, veg time is usually decided by height and canopy fill rather than calendar. GenetixBay endorses [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) lighting in veg: cannabis does not need a dark period during vegetative growth. ## Don't confuse with - **Days from seed**: autoflowers are timed from [germination](https://genetixbay.com/knowledge/glossary/germination.md), not by veg time. - **Flowering time**: the weeks from flip to harvest, set mainly by genetics. ## Related terms [Flip](https://genetixbay.com/knowledge/glossary/flip.md), [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md), [Mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md), [SOG](https://genetixbay.com/knowledge/glossary/sog.md), [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md) ## Read more - [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) --- # Vermiculite > Vermiculite is expanded mica-like mineral flakes that hold water and nutrients in a mix, used to increase moisture retention rather than drainage. - Canonical: https://genetixbay.com/knowledge/glossary/vermiculite.html - Also written: exfoliated vermiculite, vermiculite mix - Glossary category: Systems and media · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Vermiculite is a hydrated silicate mineral that, when heated, expands into light, accordion-like flakes. Unlike [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), it soaks up water and has a high [cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), so it holds potassium, calcium, magnesium and [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) on its surfaces. It is used in seed-starting mixes and in soils where more water holding is wanted. ## In practice Growers add 10-20% vermiculite to sandy or very open mixes, or use it in seed starting and [cloning](https://genetixbay.com/knowledge/glossary/cloning.md) mixes. Too much in a [container mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) reduces [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) and can make the medium stay wet for long periods. Some older vermiculite from specific mines was contaminated with asbestos; modern horticultural grades are tested, but avoid breathing dust from any dry mineral product. ## Don't confuse with - **Perlite**: adds air and [drainage](https://genetixbay.com/knowledge/glossary/runoff.md); vermiculite adds water and nutrient holding. - **Mica**: the related mineral family; not used directly as a medium. ## Related terms [Perlite](https://genetixbay.com/knowledge/glossary/perlite.md), [Cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), [Potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), [Field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md) ## Read more - [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Viroid > The smallest known plant pathogen: a short circular RNA, usually 246-401 nucleotides, with no protein coat and no protein-coding genes, copied by the host's own enzymes. - Canonical: https://genetixbay.com/knowledge/glossary/viroid.html - Also written: viroids, Pospiviroidae, infectious RNA - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A viroid is an infectious, single-stranded circular RNA molecule, usually about 246-401 nucleotides long, that causes disease in plants. Unlike a [virus](https://genetixbay.com/knowledge/glossary/plant-virus.md) it has no protein coat and does not code for any proteins. It relies entirely on host enzymes to copy itself, and disrupts the plant's [gene](https://genetixbay.com/knowledge/glossary/gene.md) regulation as it does. The best-known example in cannabis is [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md) (HLVd). ## In practice Viroids are very stable and spread mainly mechanically: on cutting tools, hands, grafts and propagation material, and in some cases via seed or pollen. Common alcohol wipes are not reliable against them; growers use disinfectants with documented [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), such as diluted [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) [hypochlorite](https://genetixbay.com/knowledge/glossary/free-chlorine.md) (bleach) solutions, between plants. Viroids cannot be treated with any spray. Testing by RT-PCR and discarding infected stock are the only reliable controls, with [tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md) to recover clean lines. ## Don't confuse with - **Plant virus**: has a protein coat and genes; often spread by insects. - **Prion**: a misfolded protein in animals, nothing to do with plants. - **Bacteria**: living cells that can be cultured; viroids cannot. ## Related terms [Hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), [Plant virus](https://genetixbay.com/knowledge/glossary/plant-virus.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) ## Read more - [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ## Sources 1. Adkar-Purushothama CR, Sano T, Perreault J-P, 2023. Hop latent viroid: a hidden threat to the cannabis industry. Viruses 15(3):681. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10053334/ 2. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Viroid Diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases --- # Volatile sulfur compounds > Volatile sulfur compounds (VSCs) are trace sulfur-containing aroma molecules, especially prenylated thiols, that give cannabis its skunky, gassy smell at concentrations far below terpenes. - Canonical: https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.html - Also written: VSCs, VSC, VSCs (cannabis), sulfur volatiles, sulphur volatiles, volatile sulphur compounds, skunk compounds, thiols - Glossary category: Cannabinoids and terpenes · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Volatile sulfur compounds are small aroma molecules containing [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md), such as thiols, sulfides and thioesters. Oswald et al. (2021, *ACS Omega*) used two-dimensional [gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md) with sulfur detection to identify a family of prenylated VSCs in cannabis. The most important, [3-methyl-2-butene-1-thiol](https://genetixbay.com/knowledge/glossary/prenylthiol.md) (prenylthiol), was the main driver of the "[skunk](https://genetixbay.com/knowledge/glossary/skunk.md)" aroma. ## In practice VSCs occur at trace concentrations, far below the 1-3% w/w total of the [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), but human odour thresholds for thiols are extremely low, so tiny amounts dominate the smell. That explains why two flowers with near-identical [terpene panels](https://genetixbay.com/knowledge/glossary/terpene-test.md) can smell very different. The same group reported VSC levels rising late in flowering and into curing and falling during storage. A follow-up (Oswald et al. 2023) found that minor non-terpenoid compounds drive many distinctive "exotic" aromas. ## Don't confuse with - **Terpenes**: the bulk aroma class, but not the source of skunk. - **Sulfur nutrition**: feeding more sulfur has no demonstrated effect on VSC levels. ## Myth check "Extra sulfur feeding makes buds skunkier" has no controlled evidence. See [sulfur](https://genetixbay.com/knowledge/nutrients/sulfur.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md). ## Related terms [Prenylthiol](https://genetixbay.com/knowledge/glossary/prenylthiol.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md) ## Read more - [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) - [Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources](https://genetixbay.com/knowledge/nutrients/sulfur.md) ## Sources 1. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196 2. Oswald IWH, Paryani TR, Sosa ME, et al. 2023. Minor, nonterpenoid volatile compounds drive the aroma differences of exotic cannabis. ACS Omega 8(42):39203-39216. https://doi.org/10.1021/acsomega.3c04496 --- # VPD > Vapour pressure deficit: how much more water vapour the air could hold at its temperature, in kPa; it is the main environmental driver of transpiration. - Canonical: https://genetixbay.com/knowledge/glossary/vpd.html - Also written: vapor pressure deficit, vapour pressure deficit, vapor-pressure deficit, VPD chart, air VPD - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Vapour pressure deficit (VPD) is the difference between the saturation vapour pressure of air at a given temperature and the actual vapour pressure, in kilopascals (kPa). It measures the drying power of the air. High VPD pulls water from leaves quickly; low VPD slows [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md), nutrient flow and drying of surfaces. It combines temperature and humidity into one number that tracks plant water use far better than [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) alone. ## In practice Common targets (leaf VPD): | Stage | kPa | |---|---| | Clones | 0.4–0.8 | | Veg | 0.8–1.2 | | Flower | 1.0–1.5 | | Late flower | 1.2–1.6 | Too low (below about 0.4 kPa in flower) invites mould and soft growth. Too high (above about 1.6–1.8 kPa) can cause [stomata](https://genetixbay.com/knowledge/glossary/stomata.md) to close, stalling [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), and leaves to curl. ## Units and formula Saturation vapour pressure (Tetens, kPa): es = 0.6108 × exp(17.27 × T ÷ (T + 237.3)), T in °C. - Air VPD = es(air) × (1 − RH ÷ 100) - [Leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md) = es(leaf) − es(air) × RH ÷ 100 Example: 26 °C air at 60% RH gives an air VPD of about 1.35 kPa. If the leaf is 24 °C, leaf VPD is about 1.0 kPa. ## Don't confuse with - **Leaf VPD**: uses [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md); what the plant actually experiences. - **Relative humidity**: a percentage that means different things at different temperatures. ## Related terms [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md), [Leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md), [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md), [Dew point](https://genetixbay.com/knowledge/glossary/dew-point.md), [Transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) ## Read more - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) - [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Sources 1. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # Water activity > A 0-1 measure of how freely available the water in a material is; for dried cannabis flower the accepted range is about 0.55-0.65 aw. - Canonical: https://genetixbay.com/knowledge/glossary/water-activity.html - Also written: aw, a_w, a w, water activity (aw) - Glossary category: Harvest, drying and curing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Water activity (aw) is the ratio of the vapour pressure of water in a material to that of pure water at the same temperature. It runs from 0 ([bone dry](https://genetixbay.com/knowledge/glossary/over-drying.md)) to 1.0 (pure water). Unlike [moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md), it measures how available the water is to microbes and chemical reactions, which is what decides mould risk and shelf stability. ## In practice ASTM D8197 specifies 0.55-0.65 aw as the acceptable range for dried cannabis flower: below it buds get brittle and harsh, above it mould risk rises. Many moulds can't grow below about 0.70 aw. House position: what matters during the cure is the bud's moisture content and water activity, not the [jar RH](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md) as such. Ways to check: - a calibrated hygrometer in a sealed jar, read only after it has equilibrated (several hours or overnight); then aw ≈ [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) / 100; - a bench water-activity meter, the lab method (ASTM D8196); - the [stem snap](https://genetixbay.com/knowledge/glossary/stem-snap-test.md) and weight loss as cross-checks. ## Units and formula aw = p / p₀ (vapour pressure over sample / over pure water, same temperature). At equilibrium, aw = ERH / 100. So 0.62 aw ≈ 62% equilibrated jar RH. ## Don't confuse with - **Moisture content**: how much water there is, in % by weight. - **Jar RH**: only equals aw × 100 once equilibrated. - **Relative humidity of the room**: air, not bud. ## Related terms [Equilibrium relative humidity](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md), [Moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md), [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Stem snap test](https://genetixbay.com/knowledge/glossary/stem-snap-test.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (D8196 water activity measurement; D8197 range). https://sn.astm.org/node/2445/printable/print --- # Water activity test > A water activity test measures how much of a sample's water is free to support microbial growth, reported as aw from 0 to 1, with cured flower targeted around 0.55-0.65. - Canonical: https://genetixbay.com/knowledge/glossary/water-activity-test.html - Also written: aw test, water activity testing, aw measurement, water activity meter, a_w test - Glossary category: Lab testing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A water activity test seals a small sample in a chamber and measures the [equilibrium relative humidity](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md) of the air above it, with a chilled-mirror [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) or capacitance sensor. [Water activity (aw)](https://genetixbay.com/knowledge/glossary/water-activity.md) is that equilibrium RH divided by 100. It tells you how freely water is available to microbes and chemical reactions, which total moisture alone does not. ## In practice Regulated markets often set an upper limit around 0.65 aw for flower; check local rules. A [COA](https://genetixbay.com/knowledge/glossary/coa.md) might read aw 0.58 with moisture 10.8%: well-cured and stable. Readings above about 0.65-0.70 raise the risk of mould growth during storage. Home growers approximate the test by sealing buds in a jar with an accurate hygrometer and waiting for it to equilibrate; the jar RH then roughly equals aw × 100. Jar readings before equilibrium are only a proxy. ## Units and formula aw = equilibrium RH (%) / 100. Dimensionless, 0-1. Pure water = 1.0. ## Don't confuse with - **Moisture content**: the mass of water (% w/w); two samples with equal moisture can have different aw. - **Jar RH before equilibrium**: tells you about the air, not yet the bud. ## Myth check House position: [humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md) rob [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and are a marketing gimmick; curing is a slow moisture decline, not holding it constant. See [curing](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md). ## Related terms [Water activity](https://genetixbay.com/knowledge/glossary/water-activity.md), [Moisture correction](https://genetixbay.com/knowledge/glossary/moisture-correction.md), [Dry-weight basis](https://genetixbay.com/knowledge/glossary/dry-weight-basis.md), [Microbial testing](https://genetixbay.com/knowledge/glossary/microbial-testing.md), [Mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - [Long-term storage: keeping cured flower potent and aromatic](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) --- # Water curing > Submerging harvested buds in water, changed daily for about a week, to leach out water-soluble compounds before drying; GenetixBay labels it Contested and does not recommend it. - Canonical: https://genetixbay.com/knowledge/glossary/water-curing.html - Also written: water cure, water-cured, water curing cannabis, soak curing - Glossary category: Harvest, drying and curing · Evidence: Contested - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Water curing is a niche method: freshly harvested buds are kept fully submerged in clean water, which is changed every day for roughly 5-10 days, then dried. Advocates say it [leaches](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) out water-soluble compounds such as [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) breakdown products, sugars and salts, giving a smoother smoke and a faster route to finished flower. The [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) are not water-soluble and largely stay in the resin. ## In practice What is generally reported: smoother smoke, and a noticeable loss of aroma and [bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md), since many [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and the bud's structure suffer; reduced weight; and a dull, flattened look. GenetixBay house position (Contested): not proven, and the founder isn't sold on it. We don't recommend it. A proper slow dry and cure gives smooth smoke without sacrificing aroma. Some growers use water curing to salvage poor material; that's a salvage step, not a quality method. If you want to test it, split a harvest and compare blind against a conventional dry and cure, a good small-scale [Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md). ## Don't confuse with - **Curing**: slow moisture decline in sealed jars. - **Flushing**: a pre-harvest root practice (Myth). - **Water-based processing**: [hash](https://genetixbay.com/knowledge/glossary/hash.md) making uses ice water, a separate topic. ## Myth check Contested, not recommended. See [curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md). ## Related terms [Curing](https://genetixbay.com/knowledge/glossary/curing.md), [Terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md), [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md) ## Read more - [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) --- # Watering to runoff > Watering to runoff means applying enough water or solution that some drains from the bottom of the container, typically 10-20% of the volume applied. - Canonical: https://genetixbay.com/knowledge/glossary/watering-to-runoff.html - Also written: water to runoff, watering till runoff, drain-through, 10-20% runoff, leachate - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Watering to runoff is irrigating until a portion of the applied water [drains](https://genetixbay.com/knowledge/glossary/runoff.md) out of the pot. Runoff confirms the whole medium has been wetted, and it carries away excess salts that would otherwise accumulate. In [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md) coco and rockwool, a set runoff fraction, often 10-20% of the volume applied, is a standard control target. ## In practice Apply slowly and evenly across the surface until drainage starts, then measure: if 2 L goes in and 0.3 L comes out, runoff is 15%. Testing runoff [pH](https://genetixbay.com/knowledge/glossary/ph.md) and [EC](https://genetixbay.com/knowledge/glossary/ec.md) compared with the input tells you whether salts are building up in the medium. In [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), many growers avoid heavy runoff to keep nutrients and microbes in the bed and water to near [field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md) instead. ## Don't confuse with - **Flushing**: deliberately pushing large volumes through to strip the medium. A [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) to remove [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) is valid at any stage; a pre-harvest "flush" of the plant is a myth that harms yield, per GenetixBay. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md). - **Leaching fraction**: the agronomy name for the same runoff percentage. ## Related terms [Drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md), [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), [Wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md), [Salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md) ## Read more - [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) - [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 --- # Wax > Wax is an opaque, soft-to-crumbly solvent-based concentrate whose texture comes from cannabinoids partly crystallising; budder and crumble are its creamy and dry variants. - Canonical: https://genetixbay.com/knowledge/glossary/wax.html - Also written: budder, crumble, honeycomb, cannabis wax, wax concentrate - Glossary category: Processing · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Wax is a catch-all for opaque extracts with a waxy, cake-like or crumbly texture. The texture comes from partial crystallisation of the [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) acids in the extract, often encouraged deliberately by agitation during processing, and from the extract's moisture and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) content. "Budder" (or "butter") is the smooth, creamy, frosting-like form. "Crumble" and "honeycomb" are drier, more brittle forms. ## In practice Consumers choose wax-type textures mainly for handling, since they're easier to portion than sticky oils or brittle shatter. Texture alone says little about potency or purity: chemically similar extracts can end up as shatter, budder or crumble depending on how they were finished and stored. The word also gets used loosely for any non-glassy extract. GenetixBay defines the product only. ## Don't confuse with - **Badder**: a looser, wetter batter-like texture, often whipped. - **Shatter**: the glassy, non-crystalline form. - **Plant waxes**: the lipids that refining removes; not the product name. ## Related terms [Shatter](https://genetixbay.com/knowledge/glossary/shatter.md), [Badder](https://genetixbay.com/knowledge/glossary/badder.md), [Solvent-based extract](https://genetixbay.com/knowledge/glossary/solvent-based-extract.md), [Concentrate](https://genetixbay.com/knowledge/glossary/concentrate.md), [Cured resin](https://genetixbay.com/knowledge/glossary/cured-resin.md) --- # Wet trim > Trimming sugar leaves from buds immediately after harvest, while the plant is still fresh, before drying. - Canonical: https://genetixbay.com/knowledge/glossary/wet-trim.html - Also written: wet trimming, trimming wet, fresh trim, green trim, wet-trimmed - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Wet trimming means removing fan and [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) from buds right after the plant is cut, while everything is still turgid and full of water. Buds are then dried on racks or hung by trimmed branches. ## In practice GenetixBay presents wet versus [dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md) as grower preference. Both work when done well. Reasons growers wet trim: - leaves stand out from the bud and are easy to [snip](https://genetixbay.com/knowledge/glossary/snp.md); - less mass to dry, which helps in humid rooms or with limited [drying space](https://genetixbay.com/knowledge/glossary/drying-room.md); - faster overall dry, sometimes useful when mould risk is high; - tidy, sculpted appearance. The costs: - sticky, slow work, with resin gumming scissors; - buds can dry too fast, especially in a warm, dry room; - more handling of fragile fresh [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md). If you wet trim, slow the dry down to compensate: aim for roughly 15-21 °C (60-70 °F) and 55-62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), with gentle indirect airflow, so the dry still takes around 7-14 days. ## Don't confuse with - **Dry trim**: trimming after the buds have dried. - **Bucking**: removing buds from branches, a separate step. - **Defoliation**: leaf removal during the grow, not at harvest. ## Myth check Neither method is "superior" in GenetixBay's view (house ruling). The founder, who has trimmed hundreds of pounds, prefers brushing dry buds over scissoring wet ones. See [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md). ## Related terms [Dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md), [Sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md), [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) ## Sources 1. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 --- # Wet weight > The weight of cannabis freshly cut, before drying; buds typically lose about 70-80% of it, so dry weight is roughly a quarter of wet. - Canonical: https://genetixbay.com/knowledge/glossary/wet-weight.html - Also written: fresh weight, wet weight at harvest, green weight, fresh mass, wet yield - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Wet weight is the mass of harvested plant material straight after the chop, while it still holds most of its water. Fresh cannabis flower is around 75-80% water, so wet weight says more about water than about the finished crop. ## In practice Growers weigh wet for two reasons: - **Tracking the dry**: weigh a marked branch or a set of buds at chop and again every day or two. When it has lost about 70-75% of its fresh weight, it's usually close to jar-ready. Confirm with the [stem snap](https://genetixbay.com/knowledge/glossary/stem-snap-test.md) and an equilibrated jar reading. - **Rough yield estimates**: a common rule of thumb puts dry bud at about 20-25% of trimmed wet bud weight, lower for airy material and higher for very dense buds. Whole-plant wet weight, with stems and [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md), is a much poorer guide. Always say which wet weight you mean: whole plant, branches, or trimmed buds. Comparisons between grows only make sense with the same basis. ## Units and formula Expected dry ≈ trimmed wet × 0.20-0.25. Water lost (%) = (wet - dry) / wet × 100. ## Don't confuse with - **Dry weight**: the weight after drying and trimming. - **Dry-weight basis**: a lab reporting convention for [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) percentages. - **Yield**: usually means final dry trimmed weight. ## Related terms [Dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md), [Moisture content](https://genetixbay.com/knowledge/glossary/moisture-content.md), [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md), [Yield](https://genetixbay.com/knowledge/glossary/yield.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) --- # Wet-dry cycle > The wet-dry cycle is the alternation between watering a container and letting it dry back, which refreshes oxygen in the root zone between irrigations. - Canonical: https://genetixbay.com/knowledge/glossary/wet-dry-cycle.html - Also written: wet/dry cycle, wet dry cycle, wet-dry cycling, letting it dry out, watering cycle - Glossary category: Cultivation and training · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" The wet-dry cycle describes how a container moves from saturation after watering, through [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) and plant uptake, to drier conditions before the next watering. As [water leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) the pores, air replaces it, and roots get fresh oxygen. Roots also grow towards moisture, so moderate drying encourages them to explore the pot. ## In practice In soil, the classic advice is to [water to runoff](https://genetixbay.com/knowledge/glossary/watering-to-runoff.md), then wait until the pot is light (often when the top 2-3 cm, about 1 in, is dry) before watering again. Lift the pot to learn its wet and [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md). In coco and rockwool, the cycle is shorter and measured as [dryback](https://genetixbay.com/knowledge/glossary/dryback.md), the percentage of [water content](https://genetixbay.com/knowledge/glossary/moisture-content.md) lost between irrigations; crop steering uses the size of that dryback deliberately. Too wet too often suffocates roots; [too dry](https://genetixbay.com/knowledge/glossary/over-drying.md) wilts the plant. The ideal size of the cycle depends on medium, [pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) and stage. ## Don't confuse with - **Dryback**: the measured drop in substrate water content in a single cycle; a quantified wet-dry cycle. - **Drought stress**: deliberate or accidental extended drying. ## Related terms [Dryback](https://genetixbay.com/knowledge/glossary/dryback.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), [Underwatering](https://genetixbay.com/knowledge/glossary/underwatering.md), [Field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md), [Crop steering](https://genetixbay.com/knowledge/glossary/crop-steering.md) ## Read more - [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - [Drain-to-waste drip and crop steering (generative vs vegetative dryback)](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 2. Stemeroff J, 2018. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 --- # White mould > A fungal disease caused by Sclerotinia sclerotiorum that girdles stems with cottony white growth and hard black sclerotia, killing branches above the lesion. - Canonical: https://genetixbay.com/knowledge/glossary/white-mould.html - Also written: white mold, Sclerotinia, Sclerotinia sclerotiorum, hemp canker, stem canker, sclerotinia stem rot - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" White mould is a disease caused by the fungus *Sclerotinia sclerotiorum*, which attacks hundreds of crops including [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), sunflower, beans and canola. On cannabis it causes stem cankers: water-soaked, bleached lesions on the main stem or branches that become covered in cottony white mycelium. Hard, black, seed-like resting bodies called sclerotia form on and inside the stem. ## In practice Branches above a canker wilt and die because the stem is girdled. Splitting the stem often shows sclerotia inside the hollow pith. The fungus survives in soil as sclerotia for several years and releases spores in cool, wet conditions, so it is an outdoor and greenhouse disease, worst in dense plantings after rain. Management relies on spacing for airflow, avoiding fields with a history of sclerotinia in susceptible crops, removing infected plants with their sclerotia, and long rotations. Check what is registered for cannabis locally. ## Don't confuse with - **Botrytis**: grey fuzzy spores, usually in buds rather than stem cankers. - **Powdery mildew**: thin white powder on leaf surfaces. - **Fusarium wilt**: brown streaks in the vascular tissue, no cottony growth or sclerotia. ## Related terms [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md), [Mold](https://genetixbay.com/knowledge/glossary/mold.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) ## Read more - [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Sources 1. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 2. BC Ministry of Agriculture. Diseases of cannabis in British Columbia (factsheet). https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/agriculture-and-seafood/animal-and-crops/plant-health/disease-factsheets/specialty-crops/diseases_of_cannabis_in_british_columbia.pdf --- # Whitefly > Small white-winged sap-sucking insects of the family Aleyrodidae, mainly Trialeurodes vaporariorum and Bemisia tabaci, that fly up when disturbed and coat leaves in honeydew. - Canonical: https://genetixbay.com/knowledge/glossary/whitefly.html - Also written: whiteflies, white fly, greenhouse whitefly, Trialeurodes vaporariorum, silverleaf whitefly, sweetpotato whitefly, Bemisia tabaci - Glossary category: Pests and diseases · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Whiteflies are sap-feeding insects of the family Aleyrodidae, about 1-2 mm long, with powdery white wings held over the body. The two that matter on cannabis are the greenhouse whitefly (*Trialeurodes vaporariorum*) and the silverleaf or sweetpotato whitefly (*Bemisia tabaci*). Adults fly up in a cloud when a plant is shaken. Nymphs are flat, oval and fixed to leaf undersides like tiny scales. ## In practice Feeding yellows leaves and deposits honeydew, which grows black [sooty mould](https://genetixbay.com/knowledge/glossary/sooty-mould.md). *Bemisia* is also a virus vector; whitefly-transmitted lettuce chlorosis virus has been reported on cannabis. [Yellow sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) catch adults and show population trends. [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md) uses *[Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md)* against eggs and young nymphs, [parasitic wasps](https://genetixbay.com/knowledge/glossary/aphidius.md) (*Encarsia* and *Eretmocerus* species) and [entomopathogenic fungi](https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.md). *Bemisia* populations resist many insecticide groups, so [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) and biocontrol carry more weight than sprays. Check what is registered for cannabis locally. ## Don't confuse with - **Aphids**: no wings in most colony members; they walk rather than fly up. - **Fungus gnats**: dark grey flies that hover near the medium. - **Mealybugs**: waxy and crawling, never flying. ## Related terms [Aphid](https://genetixbay.com/knowledge/glossary/aphid.md), [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md), [Sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md), [Beauveria bassiana](https://genetixbay.com/knowledge/glossary/beauveria-bassiana.md), [Plant virus](https://genetixbay.com/knowledge/glossary/plant-virus.md) ## Read more - [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) ## Sources 1. UC IPM. Pest Notes: Whiteflies (Publication 7401). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7401.html 2. UConn IPM. Biological Control of Whiteflies. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-whiteflies 3. UMass Extension. Whiteflies on greenhouse crops. https://www.umass.edu/agriculture-food-environment/greenhouse-floriculture/fact-sheets/whiteflies-on-greenhouse-crops --- # Whole-plant hang > Drying an entire harvested plant upside down, uncut except at the base, so the large stem mass slows the dry. - Canonical: https://genetixbay.com/knowledge/glossary/whole-plant-hang.html - Also written: whole plant hang, whole plant drying, hang the whole plant, full plant hang, whole-plant dry - Glossary category: Harvest, drying and curing · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A whole-plant hang means cutting the plant at the base and hanging it upside down intact, with branches, often [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md), and [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) left on. The main stalk and branches hold a large reserve of water that bleeds slowly into the buds, slowing and evening out the dry. ## In practice Whole-plant hangs are popular with dry-trim growers and in dry climates or rooms that struggle to hold humidity. In a room at about 15-21 °C (60-70 °F) and 55-62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), a whole plant typically takes 10-14 days or more. Points to watch: - **Space**: large plants need a lot of hanging height and room. - **Mould**: in a humid room the slow dry can turn into mould. Dense [colas](https://genetixbay.com/knowledge/glossary/cola.md) deep inside the plant dry last; part them and check. - **Uneven ripeness**: lower buds still dry with the plant even if they were less ripe. Some growers remove fan leaves first to prevent a "leafy" smell and improve airflow, while leaving sugar leaves on. ## Don't confuse with - **Hang dry**: hanging branches, the general method. - **Bucking**: taking buds off the stems before drying. - **Wet trim**: removing leaves before drying, the opposite approach. ## Related terms [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), [Dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md), [Drying room](https://genetixbay.com/knowledge/glossary/drying-room.md), [Case hardening](https://genetixbay.com/knowledge/glossary/case-hardening.md) ## Read more - [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) --- # Wick system > A wick system is a passive watering method in which an absorbent cord draws water or nutrient solution up from a reservoir into the medium by capillary action. - Canonical: https://genetixbay.com/knowledge/glossary/wick-system.html - Also written: wick watering, wick hydroponics, wicking, wick-fed, self-watering pot - Glossary category: Systems and media · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" A wick system is the simplest passive hydroponic or self-watering arrangement: a cotton, nylon or felt cord runs from a reservoir up into the growing medium, and capillary action moves solution to the roots as they dry the medium out. Self-watering pots with a reservoir in the base work on the same idea. ## In practice Wicks suit small plants, [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md), herbs and light-drinking setups, and they need a light, airy medium such as a peat-perlite or coco-perlite mix. Large cannabis plants in peak flower can use several litres per day, more than most wicks deliver, so plants may wilt in hot weather. Salts accumulate at the surface because water moves only upward; [flush the medium](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) from the top occasionally. Use synthetic wicks; cotton can rot. ## Don't confuse with - **Bottom watering**: water is placed in a tray and soaks up through the pot base; no wick. - **Ceramic sensor watering**: a valve that opens on demand from a gravity-fed line. ## Related terms [Bottom watering](https://genetixbay.com/knowledge/glossary/bottom-watering.md), [Ceramic sensor watering](https://genetixbay.com/knowledge/glossary/ceramic-sensor-watering.md), [Kratky method](https://genetixbay.com/knowledge/glossary/kratky.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md) ## Read more - [Bottom-watering, soak trays and wick (self-watering) systems](https://genetixbay.com/knowledge/systems/bottom-watering-wick.md) --- # Wild Pearls > Wild Pearls are GenetixBay points earned by contributing, such as journals, males, preservation and trials; they can move between members but have no cash value. - Canonical: https://genetixbay.com/knowledge/glossary/wild-pearls.html - Also written: Wild Pearl, earned Pearls, Wild Pearl balance - Glossary category: GenetixBay terms - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Wild Pearls are the earned kind of Pearl. Members get them for contributions that build the archive and the community: documented grows, keepers nominated and picked as [Bay Lines](https://genetixbay.com/knowledge/glossary/bay-lines.md) parents, males in [the Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md), preservation work, open trial participation and honest reviews. ## In practice Only Wild Pearls can move between members, for sends, tips and escrow in the Swap, and only inside the platform. They carry no cash value and cannot be bought, so value from money never reaches the member-to-member layer. In some regions, rules about whether points count as "consideration" for genetics mean certain lanes run as gifts only; the platform follows whatever mode the local law allows. Example: a member whose keeper is picked as a Bay Lines parent receives a Wild Pearl award and a credit on the line's record. ## Don't confuse with - **Cultured Pearls**: purchased, store-only, never transferable. - **Pearls**: the umbrella term for both kinds. ## Related terms [Pearls](https://genetixbay.com/knowledge/glossary/pearls.md), [Cultured Pearls](https://genetixbay.com/knowledge/glossary/cultured-pearls.md), [The Swap](https://genetixbay.com/knowledge/glossary/the-swap.md), [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md), [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) --- # Wind burn > Leaf damage from a fan blowing directly and constantly on the same leaves: curled, clawed or crispy leaves on the side facing the fan, sometimes with brown, dried patches. - Canonical: https://genetixbay.com/knowledge/glossary/wind-burn.html - Also written: windburn, fan burn, wind damage - Glossary category: Environment and light · Evidence: Grower practice - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Wind burn is local damage on leaves that sit in a constant direct airflow. The leaves lose water faster than the roots can supply it, so they curl, claw, rattle or turn crispy, typically only on the side of the plant facing the fan. Airflow changes [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) and [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) (Nelson and Bugbee 2015); the term itself is *Grower practice*. ## In practice The giveaway is position: damage on one side, matching the fan, while the rest of the plant is fine. Angle fans to move air across and above the canopy so leaves flutter gently, use [oscillating fans](https://genetixbay.com/knowledge/glossary/oscillating-fan.md), and keep them off the [colas](https://genetixbay.com/knowledge/glossary/cola.md). ## Don't confuse with - **Heat stress**: [tacoing](https://genetixbay.com/knowledge/glossary/taco-leaf.md) across the top of the canopy wherever it is hottest. - **Leaf clawing**: tips hooked down across the plant, linked to nitrogen or water. - **Underwatering**: the whole plant goes limp. ## Related terms [Airflow](https://genetixbay.com/knowledge/glossary/airflow.md), [Oscillating fan](https://genetixbay.com/knowledge/glossary/oscillating-fan.md), [VPD](https://genetixbay.com/knowledge/glossary/vpd.md), [Transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) ## Read more - [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) - [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Sources 1. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # XY sex determination > Cannabis uses an XY sex determination system: females carry two X chromosomes (XX) and males an X and a Y (XY), so regular seed is roughly half male. - Canonical: https://genetixbay.com/knowledge/glossary/xy-sex-determination.html - Also written: XY system, sex chromosomes, X and Y chromosomes, XX female, XY male - Glossary category: Genetics and breeding · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Cannabis has an XY sex determination system. Females are XX; males are XY. The Y [chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md) is the larger of the pair, and its region that does not recombine with the X carries the male-determining genes (Divashuk et al. 2014; Prentout et al. 2020). ## In practice Regular seed comes from a female (XX) pollinated by a male (XY). Each seed gets an X from the mother and either X or Y from the father, so regular [seed runs](https://genetixbay.com/knowledge/glossary/seed-run.md) close to 50:50 female to male. Males can be identified early with a DNA sex test on a leaf sample (Toth et al. 2020), saving months of veg space. [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md) works because of this system. A female reversed with [silver thiosulfate](https://genetixbay.com/knowledge/glossary/sts.md) makes pollen that carries only X chromosomes. Every seed from that pollen is XX. Sex expression can still be disturbed in genetically weak lines, which is why stable feminised seed depends on reversing only proven-stable [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md). ## Don't confuse with - **Hermaphrodite**: a plant that shows both flower types. It is a sex-expression failure, not a third chromosome type. - **Monoecious hemp**: bred deliberately to carry both flowers on one plant; drug-type cannabis is [dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md). ## Myth check Cannabis has been recorded as dioecious throughout history. [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) lines are mainly breeder error, not the plant's nature; see [male, female and hermaphrodite](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md). ## Related terms [Chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md), [Regular seed](https://genetixbay.com/knowledge/glossary/regular-seed.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [Sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md), [Male selection](https://genetixbay.com/knowledge/glossary/male-selection.md) ## Read more - [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) - [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) ## Sources 1. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 2. Prentout D, Razumova O, Rhone B, et al. 2020. An efficient RNA-seq-based segregation analysis identifies the sex chromosomes of Cannabis sativa. Genome Research 30(2):164-172. https://doi.org/10.1101/gr.251207.119 3. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 --- # Xylem > The plant's water-conducting tissue, which carries water and dissolved mineral ions upward from roots to leaves, driven mainly by transpiration. - Canonical: https://genetixbay.com/knowledge/glossary/xylem.html - Also written: xylem vessels, xylem tissue, water-conducting tissue, tracheids - Glossary category: Plant biology · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Xylem is vascular tissue made of hollow, dead, lignified cells (vessels and tracheids) that form continuous pipes from roots to leaves. Water moves up under tension created by [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) at the leaves, carrying [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), calcium, potassium and other ions taken up by the roots. Xylem also gives stems much of their strength; wood is mostly xylem. ## In practice Xylem explains several growing problems: - **Calcium and [boron](https://genetixbay.com/knowledge/glossary/boron.md)** travel almost only in the xylem, so they go where water goes. Fast new growth in humid, still air (low transpiration) can show calcium-type symptoms even with plenty in the feed. - **Wilting** in hot, [dry rooms](https://genetixbay.com/knowledge/glossary/drying-room.md) happens when water loss beats what the roots and xylem can supply. - **Clones**: cutting stems underwater or quickly into the rooting medium avoids air entering the xylem (embolism), which can block water flow. - **Wilt pathogens** such as *[Fusarium oxysporum](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md)* block xylem, causing wilting even in moist media. ## Don't confuse with - **Phloem**: carries sugars and [mobile nutrients](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md), both up and down. - **Pith**: soft central tissue of the stem. - **Cambium**: the layer that makes new xylem and [phloem](https://genetixbay.com/knowledge/glossary/phloem.md). ## Related terms [Phloem](https://genetixbay.com/knowledge/glossary/phloem.md), [Transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md), [Stomata](https://genetixbay.com/knowledge/glossary/stomata.md), [Root hair](https://genetixbay.com/knowledge/glossary/root-hair.md) ## Read more - [Mobile vs immobile nutrients: reading old vs new leaves](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) - [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ## Sources 1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates. --- # Yield > Yield is the dry weight of usable flower harvested, usually expressed per plant, per square metre of canopy (g/m²) or per watt of light (g/W). - Canonical: https://genetixbay.com/knowledge/glossary/yield.html - Also written: harvest weight, dry yield, yields, g/m², grams per square metre, grams per square meter - Glossary category: Cultivation and training · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Yield is the amount of harvestable product, by convention the [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) of trimmed flower. It is reported per plant (g/plant), per area of canopy (g/m² or g/ft²) or per unit of electrical light (g/W). For comparison between grows, per-area figures are the most meaningful, because per-plant numbers depend heavily on spacing. ## In practice Indoor yields are driven mostly by light: across trials, flower yield rose roughly linearly with [photosynthetic photon flux](https://genetixbay.com/knowledge/glossary/ppf.md) up to very high intensities. Genetics, [plant density](https://genetixbay.com/knowledge/glossary/plant-density.md), [veg time](https://genetixbay.com/knowledge/glossary/veg-time.md), root-zone management and climate set the rest. A meta-analysis of cannabis yield studies identified light intensity, plant density and nutrient supply among the strongest factors. Indicative ranges: [home grows](https://genetixbay.com/knowledge/glossary/home-grow.md) commonly report 300-600 g/m²; dialled-in high-light rooms report more. [Wet weight](https://genetixbay.com/knowledge/glossary/wet-weight.md) is roughly four to five times dry weight. ## Units and formula - g/m² = total dry grams / [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md) in m² (1 m² = 10.76 ft²; 1 oz = 28.35 g). - g/W = total dry grams / light wattage drawn at the wall. ## Don't confuse with - **Potency**: [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) percentage; high yield and high potency are separate traits. - **Wet weight**: weight before drying. ## Related terms [Grams per watt](https://genetixbay.com/knowledge/glossary/grams-per-watt.md), [Plant density](https://genetixbay.com/knowledge/glossary/plant-density.md), [Canopy](https://genetixbay.com/knowledge/glossary/canopy.md), [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) ## Read more - [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) ## Sources 1. Backer R, Schwinghamer T, Rosenbaum P, et al., 2019. Closing the yield gap for cannabis: a meta-analysis of factors determining cannabis yield. Frontiers in Plant Science 10:495. https://doi.org/10.3389/fpls.2019.00495 2. Westmoreland FM, Kusuma P, Bugbee B., 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLOS ONE 16(3):e0248988. https://doi.org/10.1371/journal.pone.0248988 3. Vanhove W, Van Damme P, Meert N, 2011. Factors determining yield and quality of illicit indoor cannabis (Cannabis spp.) production. Forensic Science International 212(1–3):158–163. https://doi.org/10.1016/j.forsciint.2011.06.006 --- # YPFD > Yield photon flux density: PPFD weighted by how efficiently each wavelength drives photosynthesis (the McCree curve), so red photons count more than blue. - Canonical: https://genetixbay.com/knowledge/glossary/ypfd.html - Also written: yield photon flux density, YPF, yield photon flux - Glossary category: Environment and light · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" YPFD (yield photon flux density) is a photon flux in which each wavelength is weighted by its relative quantum efficiency for [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), based on McCree's measurements on crop leaves in 1972. Red photons around 600–650 nm get the highest weight; blue and green photons count for less. It is reported in [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) like PPFD, but the value is always lower than the unweighted PPFD for the same light. ## In practice Few hobby meters report YPFD; spectroradiometers do. It is useful for comparing spectra on paper: two fixtures with identical PPFD can differ by several percent in YPFD because one has more blue. For daily growing, PPFD remains the working number, and the difference between spectra is small compared with the difference between too little and enough light. The McCree curve was measured on single leaves under short exposures. It ignores [far-red](https://genetixbay.com/knowledge/glossary/far-red.md) (above 700 nm), which contributes to whole-canopy photosynthesis when mixed with other light, and it does not capture the shape and leaf-thickness effects of [blue light](https://genetixbay.com/knowledge/glossary/blue-light.md). Treat YPFD as a refinement, not a replacement for PPFD. ## Don't confuse with - **PPFD**: every photon from 400 to 700 nm counts equally. - **ePAR**: extends the counted band to 750 nm but does not weight wavelengths. ## Related terms [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [PAR](https://genetixbay.com/knowledge/glossary/par.md), [Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md), [Far-red](https://genetixbay.com/knowledge/glossary/far-red.md) ## Read more - [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) ## Sources 1. McCree KJ, 1972. The action spectrum, absorptance and quantum yield of photosynthesis in crop plants. Agricultural Meteorology 9:191–216. 2. Zhen S, Bugbee B, 2020. Far-red photons have equivalent efficiency to traditional photosynthetic photons: implications for redefining photosynthetically active radiation. Plant, Cell & Environment 43(5):1259–1272. https://doi.org/10.1111/pce.13730 --- # Zaza > Zaza is slang for flower marketed as premium or exotic, usually with loud aroma and bright bag appeal; the word signals price and fashion, not tested quality. - Canonical: https://genetixbay.com/knowledge/glossary/zaza.html - Also written: za, exotic za, zaza weed, the za - Glossary category: Grower slang and culture · Evidence: Supported - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Zaza (or "za") is slang for flower sold as premium, exotic or top-tier, usually with strong aroma, dense frosty buds and fashionable colours. The word spread through music and social media and now works more as a price signal than a description. ## In practice "Zaza" on a jar or a menu tells you almost nothing about genetics, potency or how it was grown. Judge the actual flower: aroma when broken, a clean white or grey ash and smooth smoke (signs of a good dry and cure rather than of "[flushing](https://genetixbay.com/knowledge/glossary/flushing.md)"), no hay or musty smell, no mould, and a harvest date. Packaging and a trendy name are not evidence. ## Don't confuse with - **Top shelf**: a dispensary price tier, which zaza often claims. - **Exotic**: very close in meaning; exotic is the older retail word. - **Craft**: small-batch, carefully grown flower, which may or may not be marketed as zaza. ## Myth check "Zaza is stronger than regular weed." Label potency is often inflated, and premium marketing does not change what flower can produce (Schwabe et al. 2023). See [buyer beware: label claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md). ## Related terms [Exotic](https://genetixbay.com/knowledge/glossary/exotic.md), [Top shelf](https://genetixbay.com/knowledge/glossary/top-shelf.md), [Bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md), [Hype strain](https://genetixbay.com/knowledge/glossary/hype-strain.md), [Gas](https://genetixbay.com/knowledge/glossary/gas.md) ## Read more - [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) ## Sources 1. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: testing reveals inflated THC potency on retail cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 --- # Zinc > Zinc (Zn) is a micronutrient needed for auxin production and many enzymes; deficiency gives small, twisted new leaves and shortened internodes. - Canonical: https://genetixbay.com/knowledge/glossary/zinc.html - Also written: Zn, Zn2+, zinc deficiency - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Zinc is a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) absorbed as Zn2+. It is a cofactor for many enzymes and is needed for making the growth hormone auxin, which is why shortage shows as stunted, compressed growth. It is only moderately mobile in the plant. ## In practice [Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) produces small, narrow, twisted or wrinkled new leaves, [interveinal chlorosis](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) near the tips and very [short internodes](https://genetixbay.com/knowledge/glossary/node-stacking.md) ("rosetting"). High phosphorus and high [pH](https://genetixbay.com/knowledge/glossary/ph.md) both reduce zinc availability, so a heavy bloom-booster regime is a classic trigger. Hydro feeds usually carry somewhere around 0.1-0.5 mg/L (ppm) Zn. [Zinc sulfate](https://genetixbay.com/knowledge/glossary/zinc-sulfate.md) or a [chelate](https://genetixbay.com/knowledge/glossary/chelate.md) supplies it; galvanised pipes and fittings can leach extra zinc. ## Don't confuse with - **Heat or light stress**: can also curl new growth, but without the short internodes. - **Broad or russet mites**: twisted, glossy new growth with no nutrient pattern; check with a loupe. - **Manganese deficiency**: mottling without the leaf distortion. ## Myth check Zinc problems in flower are often caused rather than cured by high-P additives. See [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) and [nutrient antagonism](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md). ## Related terms [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Zinc sulfate](https://genetixbay.com/knowledge/glossary/zinc-sulfate.md), [Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md) ## Read more - [Zinc (Zn) in cannabis: small leaves, margin burn and the phosphorus link](https://genetixbay.com/knowledge/nutrients/zinc.md) ## Sources 1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # Zinc sulfate > Zinc sulfate (ZnSO4) is the standard soluble zinc salt for micronutrient mixes, about 22.7% Zn as the heptahydrate and 35.5% as the monohydrate. - Canonical: https://genetixbay.com/knowledge/glossary/zinc-sulfate.html - Also written: ZnSO4, zinc sulphate, ZnSO4·7H2O, zinc sulfate monohydrate - Glossary category: Nutrients · Evidence: Established - Status: Draft: awaiting expert review · Updated: 2026-10-31 - Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary" Zinc sulfate is the salt of [zinc](https://genetixbay.com/knowledge/glossary/zinc.md) and [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md). The two common forms are the heptahydrate (ZnSO4·7H2O, about 22.7% Zn) and the monohydrate (ZnSO4·H2O, about 35.5% Zn). Which one is in the bag changes the dose by more than half again, so read the label. ## In practice It supplies zinc in DIY [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) stocks. Plants need only a fraction of a mg/L (ppm) in solution, so the salt is weighed in milligrams or made into a concentrated stock. Like other unchelated metals, it becomes less available as [pH](https://genetixbay.com/knowledge/glossary/ph.md) rises and is tied up by high phosphorus. Overdosing is easy with a kitchen scale; a 0.01 g scale or a [stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md) is the safe route. ## Units and formula 1 mg/L of the heptahydrate gives about 0.23 mg/L (ppm) Zn; 1 mg/L of the monohydrate gives about 0.36 mg/L Zn. ## Don't confuse with - **Zinc oxide**: insoluble, used in soil blends and sunscreen, not hydro. - **Zinc chelate (Zn-EDTA)**: stays soluble at higher pH. ## Related terms [Zinc](https://genetixbay.com/knowledge/glossary/zinc.md), [Sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md) ## Read more - [Zinc (Zn) in cannabis: small leaves, margin burn and the phosphorus link](https://genetixbay.com/knowledge/nutrients/zinc.md) - [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # GenetixBay quick answers: every answer > 164 answers. Index: https://genetixbay.com/knowledge/answers/ --- # Can I flower a photoperiod plant 12/12 from seed? > Yes, a photoperiod plant can be grown 12/12 from seed, but it won't flower straight away: it first has to mature, forming its first single flowers at around the 7th node, typically after 3–5 weeks. The result is a short plant with one main cola, ready in roughly 3 months. It suits low headroom or many small plants, but per plant it yields less than a vegged plant. - Canonical: https://genetixbay.com/knowledge/answers/12-12-from-seed.html - Topic: Basics · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Also asked as: 12/12 from seed | Flowering from seed | Can I skip veg? | Running photoperiods on 12/12 from day one - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. A [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) on [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) grows normally until it matures, then flowers straight away, giving a short plant with one [main cola](https://genetixbay.com/knowledge/glossary/cola.md) in roughly three months. It costs yield per plant, and suits low headroom or many small plants. *Supported* for the maturity step; outcomes are *Grower practice*. ## Why Seedlings must grow up first. Cannabis seedlings pass from a juvenile to an adult, flower-ready stage on their own, whatever the day length; in one cultivar the first single flowers formed at the 7th node [1]. Before that, long nights have little to work on. Once mature, long nights take over. Short days make the [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) branch into compact inflorescences [2]. With no veg, there's little frame to build on, so the plant makes one [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) cola and a few small side buds. Light hours cost growth. At the same intensity, 12 h gives two-thirds of the daily light of 18 h, and yield follows light [4]. Small plants also leave canopy gaps unless packed densely; higher density raises yield per area but lowers it per plant [3]. ## The numbers | | 12/12 from seed | Vegged photo (4 weeks) | |---|---|---| | [Veg time](https://genetixbay.com/knowledge/glossary/veg-time.md) | ~3–5 weeks while it matures | 4+ weeks at [18/6](https://genetixbay.com/knowledge/glossary/18-6.md), then flip | | Shape | One main cola | Multi-top, trainable | | Final height (typical) | Short | 1.5–3× height at flip | | Seed to harvest | ~3 months | ~3.5–5 months | | Yield per plant | Low | Higher | | Best use | Low headroom, testing, many small plants | Filling a canopy with few plants | ## What to do 1. Use a compact cultivar and a 7–11 L (2–3 gal) pot. 2. Run 12/12 (or [13/11](https://genetixbay.com/knowledge/glossary/13-11.md)) from [sprouting](https://genetixbay.com/knowledge/glossary/germination.md), at seedling intensity first. 3. Keep the dark period truly dark from day one. 4. Grow several [plants per square metre](https://genetixbay.com/knowledge/glossary/plant-density.md) to fill the canopy, within legal limits. 5. Harvest by [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md), not the calendar. ## Common mistakes - Expecting flowers in week 1. - Using a stretchy, long-flowering cultivar. - Leaving one tiny plant alone under a big light. - [Light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md), which push the plant back towards veg. ## Related - Full article: [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Answers: [autos and photos in one tent](https://genetixbay.com/knowledge/answers/autos-and-photos-in-one-tent.md) · [when to flip](https://genetixbay.com/knowledge/answers/when-to-flip-to-flower.md) · [why flowering needs long nights](https://genetixbay.com/knowledge/answers/why-flowering-needs-darkness.md) - Article: [Sea of green](https://genetixbay.com/knowledge/training/sog.md) - Terms: [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) · [veg time](https://genetixbay.com/knowledge/glossary/veg-time.md) ## Follow-up questions **Why doesn't a seedling flower immediately on 12/12?** A cannabis seedling doesn't flower immediately on 12/12 because it must pass from a juvenile to an adult stage first. Research found this change happens on its own, with the first pair of single flowers forming around the 7th node in one cultivar, whatever the day length. Until then long nights have little to act on, so the seedling grows leaves and nodes. **Is 12/12 from seed better than autoflowers?** 12/12 from seed and autoflowers both give small, fast plants, but they suit different goals. Autos run 18–20 hours of light from seed, giving about 1.5–1.7 times the daily light of 12 hours at the same intensity, so they usually grow more per day. 12/12 from seed suits a photoperiod cultivar you want to sex, test or grow small without vegging. **Does 12/12 from seed help sex plants early?** Running seedlings on 12/12 can show sex a little sooner, because the plants flower as soon as they mature, but preflowers appear with age under long days too, usually at about 4–6 weeks. A cheaper way to sex without stunting the plant is to root a labelled cutting and flower it on 12/12, which answers in roughly 1–2 weeks. ## Sources 1. Spitzer-Rimon B, Shafran-Tomer H, Gottlieb GH, et al. 2022. Non-photoperiodic transition of female cannabis seedlings from juvenile to adult reproductive stage. Plant Reproduction 35(4):265-277. https://doi.org/10.1007/s00497-022-00449-0 2. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 3. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 4. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # How do I stop algae in my reservoir or on my medium? > Algae in a cannabis reservoir or on the medium means light is reaching wet, nutrient-rich surfaces. Stop it by keeping light out: opaque reservoirs and lids, no gaps around net pots, covered tubing, and a dry or covered top layer on coco and rockwool. Keep the solution at 18–22 °C (64–72 °F). Scrub and disinfect between runs. Algicides and routine peroxide are not the fix. - Canonical: https://genetixbay.com/knowledge/answers/algae-in-reservoir.html - Topic: Diseases · Type: Troubleshooting - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) - Also asked as: Green algae in my reservoir | Algae growing on top of my coco | Is algae caused by a light leak into the res? | How to get rid of algae in hydro - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Algae in a reservoir or on the medium means light is reaching wet surfaces that have nutrients on them. Keep the light out and the algae stop. Use opaque reservoirs and lids, close the gaps around [net pots](https://genetixbay.com/knowledge/glossary/net-pot.md), cover tubing, and keep the top of the medium dry or covered. Keep the solution at 18–22 °C (64–72 °F). *Established*. ## Why Algae need three things: water, nutrients and light. A hydroponic system supplies the first two on purpose, so light is the only one you can take away. Oregon State's [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) guidance is to cover the water surface with opaque material and size the rafts so there are no gaps, because algae thrive wherever wet, light-exposed surfaces have nutrients [1]. Warm water adds to the problem. Warm, poorly aerated solution holds less oxygen and favours [Pythium root rot](https://genetixbay.com/knowledge/glossary/pythium.md) [2][3]. A reservoir that has gone green is often warm as well. Cleaning between runs removes the biofilm that algae and microbes leave behind. Organic matter neutralises chlorine, so always scrub before you disinfect [4]. ## The numbers | Item | Target | |---|---| | Reservoir and lid | Opaque; no light visible inside with the room lights on | | Solution temperature | 18–22 °C (64–72 °F); alarm above 24 °C (75 °F) [2] | | Dissolved oxygen | ≥ 6 mg/L [3] | | Gaps around net pots or rafts | None [1] | | Cleaning bleach (between runs) | 10% household bleach, 10 min, then rinse [4] | ## What to do 1. With the lights on, look inside the reservoir with the lid closed. Any glow is a leak. 2. Wrap or paint clear reservoirs, tubing and channels. Use black-and-white film or tape. 3. Fill gaps around net pots with collars or neoprene inserts. 4. On [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) or [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), cover the top with a mat or dry [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), and stop [drippers](https://genetixbay.com/knowledge/glossary/drip-irrigation.md) from pooling. 5. Cool the reservoir if it runs above 22 °C. 6. Between runs, scrub, disinfect, rinse and dry. Wear gloves and eye protection, ventilate, and never mix bleach with acids. ## Common mistakes - Clear or translucent reservoirs and lines. - Dosing algicide or [peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) instead of fixing the [light leak](https://genetixbay.com/knowledge/glossary/light-leak.md). - Disinfecting without scrubbing first. - Ignoring algae until it clogs the pump. ## Related - Full article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) - Answers: [top off with water or nutrients?](https://genetixbay.com/knowledge/answers/top-off-reservoir-water-or-nutrients.md) - Articles: [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) · [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) - Terms: [biofilm](https://genetixbay.com/knowledge/glossary/biofilm.md) · [shore fly](https://genetixbay.com/knowledge/glossary/shore-fly.md) · [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) ## Follow-up questions **Is algae harmful to cannabis roots?** Algae is not a root disease in itself, but it is a problem for cannabis. It grows into a biofilm on roots and in lines, stains roots, clogs drippers and pumps, uses up nutrients, breeds shore flies and makes pH harder to hold. Above all it shows that light is reaching the solution, which should never happen. **Should I add hydrogen peroxide to kill algae?** Do not add hydrogen peroxide routinely to kill algae in a cannabis reservoir. It only kills what it touches, the algae return as long as light gets in, and it also kills the beneficial microbes GenetixBay prefers in a living reservoir. Lightproof the system, then clean it properly between runs. Wear gloves and eye protection when handling concentrated peroxide. **Why is my coco turning green on top?** Coco turns green on top when light and nutrient solution meet on a surface that stays wet, usually from frequent fertigation. It is surface algae, harmless to the roots below but a breeding ground for shore flies and fungus gnats. Cover the top with a coco mat or dry perlite, or use slab wraps, and keep the drippers from pooling. ## Sources 1. Nelson M, Langellotto G, Nackley L, 2025. Hydro hints: Deep water culture (EM 9455). Oregon State University Extension Service. https://extension.oregonstate.edu/catalog/pub/em9455 2. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems (68–72 °F). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 3. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic production (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf 4. Oregon State University Extension. Hop latent viroid in hemp (EM 9570). https://extension.oregonstate.edu/catalog/em-9570-hop-latent-viroid-hemp --- # Why do my curing jars smell like ammonia? > An ammonia or musty smell in a curing jar means the buds went in too wet and microbes are starting to break them down, a step before visible mould. Act at once: tip the buds out, check the cores for rot, and spread them on a screen to dry until a sealed sample reads a stable 58–65% RH. Burping more often alone won't fix it. - Canonical: https://genetixbay.com/knowledge/answers/ammonia-smell-in-jars.html - Topic: Harvest and cure · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Also asked as: Why does my weed smell like ammonia? | My jar smells like pee | Sour or musty smell during the cure | Ammonia smell when burping jars - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer An ammonia or musty smell in a [curing jar](https://genetixbay.com/knowledge/glossary/curing-jar.md) means the buds went in too wet and microbes have started working on them. It is the step before visible mould. Tip the buds out now, check the cores, and dry them until a sealed sample reads a stable 58–65% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). [Burping](https://genetixbay.com/knowledge/glossary/burping.md) more often won't fix it. *Grower practice*. ## Why Wet buds feed microbes. Above [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.65, dried flower is outside the ASTM range that guards against mould, and above 0.68 it needs further drying [1][2]. A sealed jar holds that moisture against the buds. The smell is a warning. Growers report ammonia, sour or musty notes in over-wet jars before any fuzz appears, which fits microbes breaking down plant tissue. There is no cannabis study of the chemistry, so read the smell as a moisture alarm. The safety risk is mould. Mouldy flower can carry spores and mycotoxin-producing fungi, which is why regulated markets test for yeast and mould [3]. ## The numbers | Sign | Meaning | Action | |---|---|---| | Faint ammonia or sour smell | Too wet | Tip the buds out and dry them | | Equilibrated jar above 65–68% RH | Too wet [2] | Dry the buds further | | 75%+ RH overnight | Jarred far too wet | Dry them now | | Fuzz, grey dust, brown core | Mould | Throw it away | | Stable 58–65% RH, clean smell | Ready | Re-jar and cure | ## What to do 1. Empty the jar onto a clean screen or tray. Break open the biggest buds. 2. Throw out any bud with fuzz, dust, a brown core or a strong musty smell. 3. Dry the rest in the dark at 15–21 °C (60–70 °F) and 55–62% RH, usually 12–48 hours. 4. When the stems snap, re-jar loosely to about ¾ full in a clean jar. 5. Leave it sealed 12–24 hours, then read the hygrometer. Re-dry if it is above 65%. 6. Burp once or twice a day for the first week and sniff every time. ## Common mistakes - Burping more often instead of drying the buds. - Jarring by feel without a sealed hygrometer test. - Packing jars tight. - Over-correcting into crispy, hay-smelling buds. ## Related - Full article: [Curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Answers: [mould in jars](https://genetixbay.com/knowledge/answers/mould-in-curing-jars.md) · [how full to fill jars](https://genetixbay.com/knowledge/answers/how-full-to-fill-curing-jars.md) · [how soon can I smoke?](https://genetixbay.com/knowledge/answers/how-soon-after-harvest-can-i-smoke.md) - Article: [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Terms: [burping](https://genetixbay.com/knowledge/glossary/burping.md) · [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) ## Follow-up questions **Is ammonia-smelling weed safe to smoke?** Ammonia-smelling cannabis is a warning sign, not proof of mould, but treat it with suspicion. Break open the buds: any fuzz, grey dust, brown core or lasting musty smell means discard them. Buds that dry out clean and lose the smell are usually usable, though some aroma may be lost. When in doubt, throw it out, especially for anyone with a weak immune system. **Will the ammonia smell go away?** A mild ammonia smell usually fades once over-wet cannabis buds are dried back to water activity 0.55–0.65 and cured properly, according to grower practice. A strong, lasting sour or musty smell, or a hay smell after an over-correction, rarely clears fully. Act on the first whiff: tip the jar out and dry the buds, rather than just burping more often. **How do I stop jars smelling of ammonia next time?** Stop curing jars smelling of ammonia by jarring only properly dried buds: small stems snap and a sample sealed for 12–24 hours reads a stable 58–65% RH. Fill jars loosely to about three-quarters, burp once or twice a day in the first week and sniff each time. A jar that jumps to 75% RH or more overnight needs emptying and drying. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (salt-based humidity control sachets for aw below 0.68). https://sn.astm.org/node/2445/printable/print 3. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full --- # Can I grow autoflowers outdoors? > Yes: autoflowers grow well outdoors because they flower by age, not day length, finishing about 9–14 weeks from seed. Sow straight into the final container or bed once nights stay above about 10 °C (50 °F). At mid-latitudes a late-spring sowing finishes in mid to late summer, and a second sowing by early summer can finish before autumn rain. Any setback costs yield: no transplanting, LST instead of topping. - Canonical: https://genetixbay.com/knowledge/answers/autoflowers-outdoors.html - Topic: Outdoor growing · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Also asked as: Growing autos outdoors | When to plant autoflowers outside | Can I get two autoflower harvests in one summer? | Autoflower outdoor season | Are autoflowers good for a short outdoor season? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) flower by age, usually 3–5 weeks from [sprouting](https://genetixbay.com/knowledge/glossary/germination.md), and finish about 9–14 weeks from seed whatever the [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md), so they suit outdoor gardens, short seasons and second crops. House position: any setback costs an auto yield, so sow straight into the final container or bed, and use [LST](https://genetixbay.com/knowledge/glossary/lst.md), not topping. *Grower practice*, house-endorsed. ## Why Autos ignore the calendar. Autoflowering is controlled by a [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) [locus](https://genetixbay.com/knowledge/glossary/locus.md), *Autoflower1*, so the plant flowers on its own clock rather than waiting for long nights [1]. Sun is a bonus. Yield rose in a straight line with light in a controlled trial [2], and long summer days give an auto far more daily light than it would get indoors. Root setbacks cost time. Any [transplant shock](https://genetixbay.com/knowledge/glossary/transplanting.md) eats into a fixed countdown, and the founder finds the auto [taproot](https://genetixbay.com/knowledge/glossary/taproot.md) reacts badly to being moved. Bigger containers give bigger plants within reason [3], so choose the final size at sowing. Timing dodges the weather. A summer finish avoids the cool, wet autumn that drives gray mould on dense buds [4]. ## The numbers | Item | Northern Hemisphere (mid-latitudes) | Southern Hemisphere | |---|---|---| | First sowing | After last frost, late May | Late November | | First harvest | Mid–late August | Mid–late February | | Latest second sowing | Early July | Early January | | Second harvest | Late September–early October | Late March–early April | | Seed to harvest | ~9–14 weeks | ~9–14 weeks | | Container | 11–25 L (3–7 US gal), final from day one | Same | ## What to do 1. Check local rules on outdoor growing first. 2. Sow after the last frost, once nights stay above about 10 °C (50 °F). 3. Sow directly in the final container or prepared bed; no transplanting. 4. Protect [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) from slugs and wind for the first two weeks. 5. Tie the main stem down in weeks 2–4 for LST; never top. 6. Water and feed without gaps; a hungry or dry week costs yield. 7. For a second crop, sow by early July (early January in the south). ## Common mistakes - Starting autos in cups and transplanting them outside. - Topping an outdoor auto. - Sowing the second crop too late, into autumn rain. - Treating autos as easy: they punish stress. ## Related - Full article: [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Answers: [How long autoflowers take](https://genetixbay.com/knowledge/answers/how-long-do-autoflowers-take.md) · [Plant straight into the final pot](https://genetixbay.com/knowledge/answers/plant-straight-into-final-pot.md) · [Short northern seasons](https://genetixbay.com/knowledge/answers/outdoor-short-season.md) - Article: [Low-stress training](https://genetixbay.com/knowledge/training/lst.md) - Terms: [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) ## Follow-up questions **Can I get two autoflower harvests outdoors in one season?** Yes, two outdoor autoflower harvests in one season are possible at mid-latitudes. Sow the first round after the last frost, in late May in the Northern Hemisphere or late November in the Southern, for a harvest about 9–14 weeks later. Sow the second round by early July (early January in the south) so it finishes before autumn rain and cold. This is grower practice. **Should I top outdoor autoflowers?** No, don't top outdoor autoflowers. GenetixBay's house position is that topping never produces what proper low-stress training does on an auto, because the plant runs on a strict countdown and cannot pause to recover. Bend and tie the main stem down early in veg instead to open the canopy to the sun. The same rule applies indoors and out. **What size container for outdoor autoflowers?** Outdoor autoflowers do well in about 11–25 litre (3–7 US gallon) containers, or sown direct in a prepared bed, and the container should be the final one from day one. Bigger pots give bigger plants within reason but dry more slowly, so match the pot to how often you can water. In hot sun, small pots can dry within a day, so check them daily. ## Sources 1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 3. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 4. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker --- # Can I grow autoflowers and photoperiods in the same tent? > You can grow autoflowers and photoperiods in the same tent, but one schedule must lose. On 18/6 to 20/4 the autos thrive and the photos stay in veg; on 12/12 the photos flower and the autos lose about a third of their daily light, and yield with it. The best plan is to veg photos alongside autos, then flip after the autos are harvested, or use two spaces. - Canonical: https://genetixbay.com/knowledge/answers/autos-and-photos-in-one-tent.html - Topic: Basics · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Also asked as: Mixing autos and photos | Auto and photo together in one tent | Autos in a 12/12 tent | Can I grow autos on 12/12? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes, but only one of them gets its ideal schedule. On [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) or 20/4, [autos](https://genetixbay.com/knowledge/glossary/autoflower.md) thrive and [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md) stay in veg. On [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), photos flower and autos lose about a third of their daily light. The usual fix: grow them together under long days and flip the photos once the autos are harvested. *Grower practice*. ## Why Autos ignore the clock. Plants with two copies of the [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) auto [allele](https://genetixbay.com/knowledge/glossary/allele.md) flower by age, even under long days [1]. They don't need 12/12. Photos read the night. Photoperiod cannabis stays vegetative until the uninterrupted night passes its critical length, and even dim stray light can delay flowering [3]. Light hours are yield for an auto. At the same intensity, 18–20 h of light gives 1.5–1.7 times the daily light of 12 h, and yield rose with light in a controlled trial [2]. An auto on 12/12 flowers on schedule, but smaller. ## The numbers | Schedule | Autos | Photos | [DLI](https://genetixbay.com/knowledge/glossary/dli.md) at 600 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) | |---|---|---|---| | 20/4 | Ideal | Stay in veg | 43.2 mol/m²/day | | 18/6 | Ideal | Stay in veg | 38.9 mol/m²/day | | [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) | Lose light | Flower (endorsed) | 28.1 mol/m²/day | | 12/12 | Lose ~a third of light | Flower | 25.9 mol/m²/day | DLI = PPFD × hours × 0.0036. ## What to do 1. Start autos and photos together on 18/6 or 20/4. 2. Train the photos low ([LST](https://genetixbay.com/knowledge/glossary/lst.md)) while the autos run their course. 3. Harvest the autos at 9–14 weeks. 4. Flip the photos to 12/12 or 13/11 at about half the height you can fit. 5. If you must flower both at once, run 12/12 or 13/11 and accept smaller autos. 6. With two spaces, give each its own schedule. ## Common mistakes - Putting a new auto into a flowering tent and expecting a full-size plant. - Running 18/6 and wondering why the photos never flower. - Opening the tent during the dark period to tend autos. - Hanging one light for two very different canopy heights. ## Related - Full article: [Photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Answers: [12/12 from seed](https://genetixbay.com/knowledge/answers/12-12-from-seed.md) · [when to flip](https://genetixbay.com/knowledge/answers/when-to-flip-to-flower.md) · [opening the tent at night](https://genetixbay.com/knowledge/answers/opening-tent-during-dark-period.md) - Article: [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Terms: [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) · [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) ## Follow-up questions **Can I grow autos on 12/12?** Yes, autoflowers will still flower on 12/12, because they flower by age rather than night length. But it wastes their potential: on 12/12 an auto gets much less daily light than on 18–20 hours, which give about 1.5–1.7 times the light at the same intensity. With a fixed countdown, the auto can't make up the lost growth later. **What is the best way to mix autos and photos?** The best way to mix autos and photos in one tent is to start them together on 18/6 or 20/4. The autos flower and finish on their own clock while the photoperiods veg and get trained. Once the autos are harvested at about 9–14 weeks, flip the photos to 12/12. Plan headroom: the photos will be big by then. **Will an autoflower mess up my photoperiods?** An autoflower won't change your photoperiods' flowering, because light schedule, not neighbouring plants, sets when photos flower. The real risks are a mismatched schedule, uneven canopy heights under one light, and pollen if either plant is male or hermaphrodite. Opening the tent in the dark period to tend autos would be a light leak for flowering photos. ## Sources 1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 3. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 --- # What is the best medium for rooting clones? > There's no single best medium for rooting cannabis clones; the best is the one that stays moist while holding plenty of air. Studies disagree: rockwool rooted best (up to 80%) in one hemp trial, but worst (0% at 9 days) when kept at full water capacity in another, where a 50:50 peat-perlite mix won. Rockwool, peat or coco plugs and aeroponic cloners all work if not waterlogged. - Canonical: https://genetixbay.com/knowledge/answers/best-medium-for-rooting-clones.html - Topic: Cloning and mother plants · Type: Comparison - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: Rockwool vs plugs for clones | Can I root clones in soil? | Aero cloner vs cubes | Best cloning medium - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer The best medium for rooting cannabis clones is one that stays moist but airy. In trials, [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) won in one study and lost badly in another, where a 50:50 peat-perlite mix rooted most. Rockwool, [peat](https://genetixbay.com/knowledge/glossary/peat.md) or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) plugs and [aeroponic](https://genetixbay.com/knowledge/glossary/aeroponics.md) cloners all work when not [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md). *Supported*, with conflicting trials. ## Why Medium had the biggest effect on rooting in a [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) trial, with success ranging from 13% to 80% across four media; rockwool came out best [1]. A cannabis trial reversed it. After 9 days, peat-perlite rooted 41% of cuttings, coir 29%, peat 16% and rockwool 0%, with all media held at full water capacity; the authors credited peat-perlite's better [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) and [EC](https://genetixbay.com/knowledge/glossary/ec.md) [2]. Read together, the lesson is water management. In the hemp trial, media were rewetted by hand only when cuttings began to wilt [1]; in the cannabis trial, everything stayed saturated [2], and rockwool, with less air space than the peat-perlite mix, failed. Aeroponic cloners and water both supply oxygen differently, but warm, wet [root zones](https://genetixbay.com/knowledge/glossary/root-zone.md) invite [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) and [Fusarium](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md) [3]. ## The numbers | Medium | Trial result | Strength | Weakness | |---|---|---|---| | Rockwool cube | Best of 4 in [1]; 0% at 9 days when saturated [2] | Clean, uniform | Easy to drown; start at [pH](https://genetixbay.com/knowledge/glossary/ph.md) ~5.5 | | Peat-perlite 50:50 | 41% at 9 days, best in [2] | Airy, cheap | Messier; mix your own | | Coir plug | 29% at 9 days [2] | Airy, reusable stock | Can hold salts; rinse/buffer | | Peat plug | 16% at 9 days [2] | Cheap, easy | Can stay wet | | Aeroponic cloner | Not tested in [1][2] | Lots of oxygen | Reservoir hygiene; bare roots | | Plain water | Not tested | Free | Low oxygen, brittle roots | **Verdict:** pick the airy option you can keep moist without saturating; the setup and hygiene matter more than the brand of cube. ## What to do 1. Pre-moisten the medium, then squeeze or [drain](https://genetixbay.com/knowledge/glossary/runoff.md) the excess. 2. Lift trays and water only when they lighten. 3. Keep medium at 22–26 °C (72–79 °F). 4. Clean cloner reservoirs between batches. ## Common mistakes - Sitting cubes in a puddle of water. - Rich [potting soil](https://genetixbay.com/knowledge/glossary/potting-mix.md) for unrooted cuttings. - Unbuffered coir with high salts. - Never cleaning the cloner. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Rockwool](https://genetixbay.com/knowledge/systems/rockwool.md) · [Can I root clones in water?](https://genetixbay.com/knowledge/answers/rooting-clones-in-water.md) - [Do clones need nutrients?](https://genetixbay.com/knowledge/answers/do-clones-need-nutrients.md) - Terms: [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) · [aeroponics](https://genetixbay.com/knowledge/glossary/aeroponics.md) ## Follow-up questions **Is rockwool good for clones?** Rockwool works well for cannabis clones if you manage its water. In one hemp trial it gave the highest rooting success of four media, but in another cannabis trial, rockwool kept at full water capacity rooted no cuttings within 9 days. Pre-soak it at pH about 5.5, squeeze out excess water, and let it lighten between waterings. **Can I root clones directly in soil?** Yes. Cannabis clones can root directly in a light, airy mix, such as seedling mix or peat with 30–50% perlite. In one trial a 50:50 peat-perlite mix rooted the most cuttings, ahead of coir, peat and rockwool. Heavy, rich potting soil holds too much water and salts for a rootless cutting. Keep it moist, not wet, and use a dome. **Is an aeroponic cloner better than plugs?** An aeroponic cloner roots cannabis cuttings in humid air sprayed with water, so oxygen at the stem is excellent and many growers find it fast and even. Its weak points are hygiene and transplanting: warm reservoirs breed Pythium, and bare roots need careful potting. Plugs are slower to set up wrong. Both work; pick the one you will keep clean. ## Sources 1. Campbell SM, Anderson SL, Brym ZT, Pearson BJ, 2021. Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.). PLOS ONE 16(7): e0249160. https://doi.org/10.1371/journal.pone.0249160 2. Hwang SJ, Collado CE, Hwang HS, Yun JH, Hernandez R, 2026. Impacts of commercial and custom substrates on rooting and morphology of Cannabis sativa 'Suver Haze' stem. HortTechnology 36(3):429–434. https://doi.org/10.21273/HORTTECH05810-26 3. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 --- # What pot size is best for autoflowers? > For autoflowers, an 11–15 L (3–4 gal) pot is the usual final pot, and up to 19 L (5 gal) is forgiving for a first grow. Sow the seed straight into it and don't transplant. Bigger pots give bigger plants within reason, but pot size trades against feeding frequency: small pots can still grow big autos if you water and feed often. - Canonical: https://genetixbay.com/knowledge/answers/best-pot-size-for-autoflowers.html - Topic: Basics · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) - Also asked as: Best pot for autos | 3 gallon or 5 gallon for an autoflower? | Autoflower container size | Can I grow an auto in a small pot? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Use an 11–15 L (3–4 gal) final pot for most [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md), or 19 L (5 gal) if you want more margin for missed waterings. Sow the seed directly into it: don't [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) an auto. *Grower practice* and a GenetixBay house position. ## Why Roots set the ceiling, within reason. Across 65 studies, doubling [rooting volume](https://genetixbay.com/knowledge/glossary/pot-size.md) raised plant biomass by about 43% on average [1]. GenetixBay's position: bigger pots give bigger [yields](https://genetixbay.com/knowledge/glossary/yield.md) within reason. But pot size trades against feeding frequency. A small pot holds less water and nutrient, so it needs refilling more often. The founder has grown a QP+ (4 oz+, about 115 g+) from a 16 oz (about 0.5 L) cup by pushing water and feed hard with [high-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md). Big things come in small packages if you can irrigate that often. Moving an auto costs time it doesn't have. Transplant shock is a normal setback for any [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) [3]; an auto flowers by age and can't absorb it, and the founder finds the auto [taproot](https://genetixbay.com/knowledge/glossary/taproot.md) reacts badly to moving. A big pot around a tiny root ball stays wet and short of air [2]. Water only a small ring at first. ## The numbers | Pot | Volume | Fits | Watering once the plant is big | |---|---|---|---| | 2 gal | ~7.5 L | Very small tents, skilled growers | Daily or more | | 3 gal | ~11 L | 60 x 60 cm (2 x 2 ft) tent | Every 1–2 days | | 4 gal | ~15 L | Most auto grows | Every 1–3 days | | 5 gal | ~19 L | Forgiving first grow | Every 2–3 days | | 16 oz cup | ~0.5 L | High-frequency fertigation only | Several times a day | Watering frequency is a rough guide; lift the pot and water by weight. ## What to do 1. Choose 11–19 L (3–5 gal) for a first auto. 2. Fill it, water it to about 10% [runoff](https://genetixbay.com/knowledge/glossary/runoff.md), and let it drain for a day. 3. Plant the seed 0.5–1 cm (¼–½ in) deep in the centre. 4. Water a 50–100 mL ring around the stem for the first 10–14 days, then widen it. 5. Below about 11 L, plan to water and feed very often. ## Common mistakes - Starting in a cup and transplanting "to be safe". - Soaking the whole big pot around a seedling. - A tiny pot with once-a-week watering. ## Related - Full article: [Transplanting](https://genetixbay.com/knowledge/germination/transplanting.md) - Answers: [planting straight into the final pot](https://genetixbay.com/knowledge/answers/plant-straight-into-final-pot.md) · [why my auto is small](https://genetixbay.com/knowledge/answers/why-is-my-autoflower-small.md) · [fabric vs plastic pots](https://genetixbay.com/knowledge/answers/fabric-pots-vs-plastic-pots.md) - Guide: [Autoflower first grow, week by week](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md) - Terms: [pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) · [high-frequency fertigation](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md) ## Follow-up questions **Is 3 gallons or 5 gallons better for an autoflower?** Both work for an autoflower. A 3 gal (11 L) pot dries faster, suits a small tent and needs watering every day or two once the plant is big. A 5 gal (19 L) pot holds more water and forgives a missed day, but a seedling in it needs careful ring watering for the first two weeks. Pick the size that matches how often you can water. **Can I start an autoflower in a solo cup?** You can, but GenetixBay advises against it. Transplanting an autoflower is almost a no-no: any setback costs it time on its fixed clock, and the founder finds the auto taproot reacts badly to being moved. Sow straight into the final pot and water only a small ring around the stem for the first 10–14 days instead. **Do bigger pots mean bigger yields?** Bigger pots give bigger cannabis yields within reason. Across 65 studies on many crops, doubling pot size raised plant biomass by about 43% on average. But root volume isn't the whole story: the GenetixBay founder has grown over 4 oz (about 115 g) from a 16 oz cup using high-frequency fertigation. Small pots work if you water and feed often. ## Sources 1. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container size and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 3. University of Minnesota Extension. Starting seeds indoors (transplanting seedlings, hardening). https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors --- # What soil should I use for growing cannabis? > The best soil for growing cannabis indoors is a quality bagged potting mix, peat- or coco-based with compost and a light starter fertiliser, opened up with 20–35% perlite or pumice. Never use garden soil in pots. The starter charge feeds for 2–4 weeks; after that, feed at EC 0.8–1.6 mS/cm with water at pH 6.2–6.8. - Canonical: https://genetixbay.com/knowledge/answers/best-soil-for-cannabis.html - Topic: Systems · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - Also asked as: What is the best soil mix for cannabis? | Can I use normal potting soil for weed? | Do I need perlite in soil? | Can I use hydro nutrients in soil? | Can I use garden soil in pots? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Use a quality bagged [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), peat- or coco-based with compost and a light starter fertiliser, and add 20–35% [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) or pumice. Don't use garden soil in pots. The starter charge feeds a plant for about 2–4 weeks; then feed at [EC](https://genetixbay.com/knowledge/glossary/ec.md) 0.8–1.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) with water at [pH](https://genetixbay.com/knowledge/glossary/ph.md) 6.2–6.8. *Supported* for the container physics; brand choice matters far less than [drainage](https://genetixbay.com/knowledge/glossary/runoff.md). ## Why Indoor "soil" is really potting mix. It has three jobs: hold water, hold air and hold nutrients on its exchange sites. Compost and [peat](https://genetixbay.com/knowledge/glossary/peat.md) buffer pH, which is why soil forgives small mistakes. Air matters as much as water. A dense mix stays saturated, roots run short of oxygen and the plant wilts in wet soil [1]. Perlite or pumice adds large pores that drain and refill with air. Garden soil compacts in a container and can carry [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) and root-rot organisms [2]. Organic or mineral feeding both work. Cannabis grew well in organic, coir-based media once nitrogen supply was high enough [3]; the plant mostly doesn't care where its ions come from. ## The numbers | Item | Target | |---|---| | Base | Peat- or coco-based potting mix with compost | | Perlite or pumice | 20–35% of volume, mixed through | | Starter charge lasts | About 2–4 weeks | | Irrigation pH | 6.2–6.8 (soil range 6.0–7.0) | | Feed EC, once charge runs out | 0.8–1.6 mS/cm (400–800 [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md) / 560–1,120 [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md)) | | [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md), [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) | 11–25 L (3–7 US gal) | | Pot size, [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) | 11–15 L (3–4 US gal), planted directly | ## What to do 1. Buy a mix labelled for containers; avoid "moisture control" mixes with wetting gels. 2. Add 20–35% perlite or pumice and mix it through evenly. 3. Water with plain, pH-adjusted water while the starter charge lasts. 4. Start feeding at half the label rate when lower leaves begin to pale. 5. Check runoff EC and pH monthly; if runoff EC climbs well above input, do a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) with 2–3× the pot volume. ## Common mistakes - Garden soil or topsoil in pots. - A hot, heavily fertilised mix for [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md), which burns them. - Hydro-strength feed on top of a fertilised mix. - A gravel layer at the bottom instead of perlite through the mix. ## Related - Full article: [Growing in soil](https://genetixbay.com/knowledge/systems/soil.md) - Answers: [when soil runs out of nutrients](https://genetixbay.com/knowledge/answers/when-does-soil-run-out-of-nutrients.md) · [mixing soil and coco](https://genetixbay.com/knowledge/answers/can-i-mix-soil-and-coco.md) · [super soil](https://genetixbay.com/knowledge/answers/what-is-super-soil.md) · [reusing soil](https://genetixbay.com/knowledge/answers/can-i-reuse-soil.md) - Terms: [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) · [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) ## Follow-up questions **Do I need to add perlite to potting soil?** Yes, add perlite or pumice to potting soil for cannabis, at about 20–35% of the volume. Most bagged mixes are made for small houseplants and hold too much water for a big, thirsty plant in a deep pot. Extra perlite raises air space so roots get oxygen between waterings. Mix it evenly through the whole pot, never as a bottom layer. **Can I use hydro nutrients in soil?** You can use hydro mineral nutrients in soil, but only at soil strength. Wait until the mix's starter charge runs out, usually 2–4 weeks, then start at half the label rate and feed at EC 0.8–1.6 mS/cm every second or third watering. Check runoff EC monthly, because a rising reading means salts are building up in the pot. **Can I use garden soil for cannabis in pots?** No, don't use garden soil in pots. Garden soil compacts in a container, drains poorly and starves roots of air, and it can carry pathogens that cause damping-off and root rot. Outdoors in the ground, native soil can work well once amended. Indoors, use a bagged potting mix with added perlite or pumice. ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 2. University of Minnesota Extension. How to prevent seedling damping off (sanitation; avoid garden soil in containers). https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 3. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17 --- # Are purple (blurple) LEDs as good as white LEDs? > Purple (blurple) LEDs grow cannabis about as well as white LEDs at the same PPFD, because photon quantity and efficacy matter far more than colour. White LEDs win in practice: green light reaches lower leaves, you can see deficiencies and pests, and good white fixtures exceed 2.5–3 µmol/J. Judge any LED by its measured PPFD and µmol/J, not its colour. - Canonical: https://genetixbay.com/knowledge/answers/blurple-vs-white-led.html - Topic: Environment · Type: Comparison - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) - Also asked as: Blurple vs full-spectrum white LED | Are red and blue LEDs good for cannabis? | White LED vs purple LED for growing | Is green light wasted on plants? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer At the same [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), purple (red-and-blue) [LEDs](https://genetixbay.com/knowledge/glossary/led.md) grow cannabis about as well as white LEDs: photon quantity and [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) matter far more than colour [1]. White LEDs win in practice: they light lower leaves better, let you **see the plant**, and good white fixtures exceed **2.5–3 µmol/J** [2]. *Supported*. ## Why Plants use photons across 400–700 nm. Across three cannabis studies, changing the [blue fraction](https://genetixbay.com/knowledge/glossary/blue-light.md) from 4 % to 20 % moved yield only about 12 %, and the authors concluded efficacy was more important for cost [1]. Different LED spectra do change plant shape and chemistry. In one trial two LED spectra gave more compact plants and higher [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) concentrations than [HPS](https://genetixbay.com/knowledge/glossary/hps.md), with equal total cannabinoid yield [3]. Spectrum is a tuning knob, not a yield switch. Green light is not wasted. Leaves absorb less of it, so it travels deeper into the canopy and drives [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) in lower leaves. Pink-purple light hides [deficiencies](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) and pests. That alone is a reason to prefer white. Older blurple fixtures were often sold on "equivalent watts" with low efficacy. Modern red-and-blue diodes can be efficient; check the numbers. ## The numbers | | White [full-spectrum LED](https://genetixbay.com/knowledge/glossary/full-spectrum.md) | Blurple (red + blue) LED | |---|---|---| | Yield at equal PPFD | similar | similar | | Typical efficacy | 2.5–3+ µmol/J (good fixtures) [2] | varies widely; check the datasheet | | Lower-canopy light | better (green penetrates) | less | | Seeing problems | easy | hard | | Blue fraction | ~5–15 % | often higher | | Plant shape | normal | more blue = more compact [1] | **Verdict:** a white LED is the better buy for almost every home grower; a blurple light with a good measured PPFD and µmol/J still grows good plants. ## What to do 1. Compare fixtures by µmol/J and PPFD map, whatever the colour. 2. If you already own a blurple light, keep it and set it by measured PPFD. 3. Inspect plants under white light every few days. 4. Wear rated glasses; bright blue diodes strain eyes. ## Common mistakes - Choosing by colour story or "full spectrum" marketing. - Diagnosing leaf colour under purple light. - Believing a red-heavy "[bloom](https://genetixbay.com/knowledge/glossary/flowering-stage.md)" spectrum is required (*Myth*). - Running a dim "veg spectrum": low light, not missing blue, causes [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). ## Related - Full article: [Light spectrum](https://genetixbay.com/knowledge/environment/light-spectrum.md) - [LED or HPS: which is better?](https://genetixbay.com/knowledge/answers/led-vs-hps.md) - [What should I look for when buying a grow light?](https://genetixbay.com/knowledge/answers/what-to-look-for-in-a-grow-light.md) - Terms: [full spectrum](https://genetixbay.com/knowledge/glossary/full-spectrum.md) · [spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md) ## Follow-up questions **Is green light wasted on cannabis?** No, green light is not wasted on cannabis; that is a myth. Leaves absorb less green than red or blue, but green penetrates deeper into the canopy and drives photosynthesis in shaded lower leaves. Broad white LED spectra, which include plenty of green, grow cannabis as well as red and blue fixtures at the same PPFD and make the plants easier to inspect. **Why do purple grow lights make it hard to see problems?** Purple grow lights make it hard to see cannabis problems because red and blue light without green distorts leaf colour. Yellowing, pale new growth, rust spots and pests such as mites all look different or disappear under pink-purple light. Growers using blurple fixtures should inspect plants under white light, a headlamp or with the grow light off, every few days. **Do I need more red light for flowering?** No, cannabis does not need a red-heavy spectrum to flower; that is a myth. Broad white LED spectra with roughly 5–15 % blue flower fine, and HPS at about 4 % blue also works. Research shows yield fell about 12 % as blue rose from 4 % to 20 %, a modest effect, while fixture efficacy in µmol/J matters much more. ## Sources 1. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://pmc.ncbi.nlm.nih.gov/articles/PMC7987162/ 2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 3. Magagnini G, Grassi G, Kotiranta S, 2018. The effect of light spectrum on the morphology and cannabinoid content of Cannabis sativa L. Medical Cannabis and Cannabinoids 1(1):19–27. https://doi.org/10.1159/000489030 --- # Why did my buds lose their smell? > Buds lose their smell mostly because volatile terpenes escaped during a fast, warm or over-dry dry, and then during storage in warmth, light or air. Humidity packs and frequent jar opening make it worse. The aroma doesn't come back: a cure never fixes a bad dry. Next time, dry for 7–14 days at 15–21 °C and 55–62% RH and keep buds at water activity 0.55–0.65. - Canonical: https://genetixbay.com/knowledge/answers/buds-lost-their-smell.html - Topic: Harvest and cure · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Also asked as: Why don't my buds smell? | No smell after the cure | My terpenes faded | Buds smelled great on the plant but not now - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Buds lose their smell mainly because volatile [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) escaped during a dry that was too fast, too warm or [too dry](https://genetixbay.com/knowledge/glossary/over-drying.md), and then in storage with warmth, light or air. That aroma doesn't come back: *a cure never fixes a bad dry* (*House position*). [Terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md) on drying and storage is *Supported*. ## Why The brightest aromas are the most volatile. Air-dried buds lose [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md), and [sesquiterpenes](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) become a larger share of the oil [1]. Some loss is normal. A fast, warm dry multiplies it. The dry matters more than storage for aroma. In [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), terpenes depended more on drying method than on storage, while [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) depended more on storage [2]. Over-drying strips aroma too. Below [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55 flower turns brittle [3] and smells faint or like hay. The house position is that a [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) means bacteria, over-drying or drying too fast, and it never truly comes out. Storage conditions finish the job. Light and air break down cannabinoids in storage [4], and warmth, frequent opening and half-empty jars give terpenes more chance to escape. [Humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md) rob terpenes, in the house view. Genetics sets the ceiling. Some cultivars are simply quiet, however well they are dried. ## The numbers | Factor | Target | |---|---| | Drying | 7–14 days, 15–21 °C (60–70 °F), 55–62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), dark | | Bud water activity | 0.55–0.65 [3]; never below 0.55 | | Curing | aw from 0.62–0.65 falling slowly to 0.55–0.58 | | Storage | Airtight glass, dark, cool | | Humidity packs | None (house position) | ## What to do 1. Check a jar: seal it for 12–24 hours and read it. Below 55% means over-dried. 2. If it is dry, add a fresh bud for a day to bring it up. Expect the feel to improve, not the smell. 3. Move jars somewhere cool and dark. Open them only when you need to after the cure. 4. Take out any humidity packs. 5. Next harvest, dry slower and cooler, with no fan on the buds, and jar as soon as the stems snap. 6. Note the cultivar. If it was quiet on the plant too, that is the genetics. ## Common mistakes - Drying in a warm room with a fan on the buds. - Leaving jars in a sunny or warm spot. - Grinding or handling buds long before use. - Storing in plastic bags. ## Related - Full article: [Curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Answers: [rehydrating over-dried buds](https://genetixbay.com/knowledge/answers/rehydrate-over-dried-buds.md) · [why is my weed harsh?](https://genetixbay.com/knowledge/answers/why-is-my-weed-harsh.md) · [what are terpenes?](https://genetixbay.com/knowledge/answers/what-are-terpenes.md) - Article: [long-term storage](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) - Terms: [terpene loss](https://genetixbay.com/knowledge/glossary/terpene-loss.md) · [humidity pack](https://genetixbay.com/knowledge/glossary/humidity-pack.md) · [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) ## Follow-up questions **Can I bring the smell back to my buds?** You cannot bring lost aroma back to cannabis buds. Evaporated monoterpenes are gone, and a cure only limits further loss and lets the remaining aroma settle. Bringing over-dried buds back to water activity 0.55–0.62 with a fresh bud in the jar can make them seem slightly livelier, but the lost terpenes do not return. **Do humidity packs make buds lose smell?** In GenetixBay's view, humidity packs rob terpenes and are a marketing gimmick. The only data claiming a terpene benefit comes from a pack maker's own test, and no independent study exists either way. Cure by the bud's water activity instead, letting it fall slowly from about 0.62–0.65 towards 0.55–0.58, and add a fresh bud if a jar goes too dry. **Why did my buds smell strong on the plant but weak after drying?** Cannabis buds often smell stronger on the plant because the freshest monoterpenes are the most volatile, and air-drying shifts the oil towards heavier sesquiterpenes. Some loss is normal. A big drop, or a hay or grassy smell, points to a dry that was too fast, warm or over-dry. Slow the next dry and keep the room dark. ## Sources 1. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa (monoterpene loss on drying and storage). Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 2. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp (terpenes affected by drying, cannabinoids by storage). https://openscholar.uga.edu/record/27813 3. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. https://store.astm.org/d8197-22.html 4. Fairbairn JW, Liebmann JA, Rowan MG, 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1–7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x --- # How do I check if my hygrometer is accurate? > Check a hygrometer with a salt test: seal it for 12–24 hours in a bag or jar with a damp slurry of table salt, which holds air at about 75 % RH at room temperature. Note how far it reads off and correct for that. For a second point, magnesium chloride gives about 33 %. Cheap sensors drift 3–5 % RH, enough to mislead VPD and bud-rot decisions. - Canonical: https://genetixbay.com/knowledge/answers/calibrate-a-hygrometer.html - Topic: Environment · Type: How-to - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - Also asked as: How do I do a salt test on a hygrometer? | Hygrometer calibration for a grow tent | My humidity reading seems wrong | Why do my two hygrometers disagree? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Do a **salt test**: seal the hygrometer for **12–24 hours** with a damp slurry of table salt, which holds the air at about **75 % [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md)** at room temperature [1]. The difference from 75 is your offset. For a second point, **magnesium [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md)** gives about **33 %** [1]. *Established* physics. ## Why A saturated salt solution in a sealed space settles at a fixed relative humidity set by the salt and the temperature. These "humidity fixed points" are a standard reference for calibrating humidity sensors [1]. [Sodium](https://genetixbay.com/knowledge/glossary/sodium.md) chloride sits near 75 % across normal room temperatures, which makes table salt a cheap, reliable check. Cheap RH sensors drift 3–5 % RH. Every [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) calculation uses RH [2], so a sensor reading 5 % low can have you running a late-flower room far more humid than you think. That matters because humidity is an established driver of cannabis [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) [3]. A wrong number is worse than no number if you trust it. ## The numbers | Reference | RH at about 25 °C (77 °F) | |---|---| | Saturated sodium chloride (table salt) | ~75 % [1] | | Saturated magnesium chloride | ~33 % [1] | | Typical cheap sensor drift | 3–5 % RH | | Acceptable offset to just correct for | within about ±3 % | | Replace if | off by more than ~5 % or changing between tests | ## What to do 1. Put a quarter cup of plain salt in a cap or dish; add water until it's a damp slurry, with undissolved salt visible. 2. Seal it and the hygrometer in a zip bag or jar. Keep the slurry off the sensor. 3. Leave it 12–24 hours at a steady room temperature, out of sun. 4. Read it. Note the offset (for example, reads 71 % = 4 % low). 5. Adjust the meter if it allows; otherwise add the offset mentally and label it. 6. Optional: repeat with magnesium chloride for a low point. 7. Retest every few months, and after any humid spell. ## Common mistakes - A wet salt solution with no undissolved [crystals](https://genetixbay.com/knowledge/glossary/trichome.md). - Reading after an hour instead of 12–24. - Testing in a room with big temperature swings. - Trusting a sensor near the light or in still air. - Correcting a drifting sensor forever instead of replacing it. ## Related - Full article: [Humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - [VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md) - [How do I lower the humidity in my grow tent?](https://genetixbay.com/knowledge/answers/how-to-lower-humidity-in-a-grow-tent.md) - [What meters do I actually need?](https://genetixbay.com/knowledge/answers/meters-you-need-for-growing.md) - Terms: [relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) · [two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md) ## Follow-up questions **How do I do a hygrometer salt test?** To do a hygrometer salt test, mix about a quarter cup of table salt with just enough water to make a damp slurry, not a solution, in a jar cap or small dish. Seal it with the hygrometer in a zip bag or jar, out of sunlight at a steady room temperature, for 12–24 hours. The air settles near 75 % RH; the difference from 75 is your offset. **How accurate are cheap hygrometers?** Cheap digital hygrometers are typically within a few percent RH when new and often drift 3–5 % RH over time, more at the high end of the scale and after exposure to very humid air. That is enough to move a calculated VPD by 0.1–0.2 kPa or hide a lights-off humidity spike. Check them with a salt test every few months and replace one that keeps drifting. **Why do my two hygrometers show different readings?** Two hygrometers in the same grow tent often disagree because of sensor drift, different placement and temperature: a probe nearer the light or in still air reads a different microclimate. Put both together in a salt test to find each one's offset. Then place the trusted one at canopy height, shaded from the light and in moving air, as your reference. ## Sources 1. Greenspan L, 1977. Humidity fixed points of binary saturated aqueous solutions. Journal of Research of the National Bureau of Standards 81A(1):89–96. https://doi.org/10.6028/jres.081A.011 2. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm 3. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Can I take clones from a flowering plant? > Yes. You can clone a flowering cannabis plant (monster cropping), but expect slower rooting, often 2–4 weeks, and a further 2–6 weeks of odd, single-bladed regrowth while the cutting re-vegs under 18–24 hours of light. Success is best from the first 2–3 weeks of flower, using lower branches with little bud. It's a rescue method; cloning before the flip is far easier. - Canonical: https://genetixbay.com/knowledge/answers/can-i-clone-a-flowering-plant.html - Topic: Cloning and mother plants · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: Can I clone a plant in flower? | Re-veg clone from a flowering plant | Will a flowering cutting root? | What is monster cropping? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. Cuttings from a flowering cannabis plant can root and [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) ([monster cropping](https://genetixbay.com/knowledge/glossary/monster-cropping.md)), but rooting often takes 2–4 weeks and the regrowth is odd and slow for another 2–6 weeks. Best results come from the first 2–3 weeks of flower. *Grower practice*. ## Why [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis flowers in response to long nights and stays vegetative under long days [1]. Put a flowering cutting on 18–24 hours of light and it gradually switches back. The switch takes time. The cutting first finishes the flowers it started, then throws rounded, smooth-edged or single-bladed leaves before normal leaves return. Cuttings carry over the state of the shoot they came from, a known effect in propagation [2]. A shoot committed to flowering roots more slowly than a vegetative one. Leaves still matter. In vegetative cannabis cuttings, three full, uncut leaves gave better root quality than two [3]. Flowering branches often carry fewer, smaller leaves, so keep every one you can. ## The numbers | Item | Vegetative cutting | Flowering cutting | |---|---|---| | Time to roots | 7–14 days | Often 2–4 weeks | | Re-veg time | None | 2–6 weeks of odd growth | | Best source | Mid-to-late veg | Weeks 1–3 of flower, lower branches | | Light | 50–150 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), 18–24 h | Same, 18–24 h | | Success | High | Variable by cultivar | ## What to do 1. Choose lower, leafy branches with the least bud. 2. Take extra cuttings: expect losses. 3. Pick off flowers and [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) clusters; keep every leaf you can. 4. Use [rooting hormone](https://genetixbay.com/knowledge/glossary/rooting-hormone.md), a dome at 75–90% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) and 18–24 h of light. 5. Once rooted, keep on long days and feed lightly until normal leaves return. ## Common mistakes - Waiting until week 7 of flower to try. - Stripping the few leaves the cutting has. - Putting re-vegging cuttings back on [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) too soon. - Relying on this instead of [cloning](https://genetixbay.com/knowledge/glossary/cloning.md) before the flip. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [How do I reveg a plant?](https://genetixbay.com/knowledge/answers/how-to-reveg-a-plant.md) · [Single-finger leaves](https://genetixbay.com/knowledge/answers/single-finger-leaves-reveg.md) - Terms: [monster cropping](https://genetixbay.com/knowledge/glossary/monster-cropping.md) · [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) ## Follow-up questions **What is monster cropping?** Monster cropping is taking cuttings from a cannabis plant in flower, usually in its first few weeks, and rooting them under long days so they revert to vegetative growth. The re-vegging cuttings often grow bushy with many shoots after a slow start of small, rounded or single-bladed leaves. Evidence is anecdotal; treat the bushy growth as a side effect, not a guaranteed yield gain. **How late in flower can I take a cutting?** Cannabis cuttings root most reliably from the first 2–3 weeks after the flip, before buds have bulked. Cuttings from mid or late flower can still root, but slower and with more losses, because the shoot is committed to flowering. Choose lower, leafy branches with the least bud, keep any remaining leaves, and pick off the flowers before sticking. **Why does my flowering clone have single-finger leaves?** A cannabis clone taken from a flowering plant grows single-finger or smooth, rounded leaves while it reverts from flowering to vegetative growth under long days. It's a normal stage of re-veg and usually lasts 2–6 weeks before normal serrated, multi-fingered leaves return. Keep it on 18–24 hours of light, feed lightly and be patient. ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Olesen PO. 1978. On cyclophysis and topophysis. Silvae Genetica 27(5):173-178. https://www.thuenen.de/media/institute/fg/PDF/Silvae_Genetica/1978/Vol._27_Heft_5/27_5_173.pdf 3. Caplan D, Stemeroff J, Dixon M, Zheng Y. 2018. Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science 98(5):1126-1132. https://doi.org/10.1139/cjps-2018-0038 --- # Can I defoliate autoflowers? > You can defoliate autoflowers, but only lightly, and GenetixBay advises tucking instead. An autoflower runs on a fixed countdown of about 9–14 weeks from germination, so any setback costs yield it can't recover. Tuck fan leaves away from bud sites, remove only damaged, dying or soil-touching leaves, take no more than a few at a time, and never schwazz an auto. - Canonical: https://genetixbay.com/knowledge/answers/can-i-defoliate-autoflowers.html - Topic: Training · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) - Also asked as: Should I defoliate my autos? | Can I strip autoflower leaves? | Is lollipopping autoflowers a good idea? | Can I schwazz an autoflower? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer You can, but only lightly, and GenetixBay advises tucking instead. An [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) runs on a fixed countdown of about 9–14 weeks from [germination](https://genetixbay.com/knowledge/glossary/germination.md), so any setback costs yield it can't recover. Tuck [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) away from [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md) and remove only damaged, dying or soil-touching leaves. *Grower practice* and house position; no controlled trial has tested [defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md) on autos. ## Why Autoflowers are day-neutral. The trait is [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) and genetically mapped [2], and it means an auto flowers at a fixed age whatever the light schedule. A [photoperiod plant](https://genetixbay.com/knowledge/glossary/photoperiod.md) can be vegged longer to recover from stress; an auto can't. Leaves are the solar farm that feeds the buds. On an auto with a short veg, every fan leaf lost early is growing capacity that never comes back. Defoliation didn't raise yield even on large photoperiod plants: stripping within reason left flower yield per plant unchanged [1]. If there's no gain on a forgiving plant, there's only risk on an unforgiving one. There is one good reason to remove leaves: airflow. Dense, humid interiors favour [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) [3]. On a small auto, tucking and spreading branches usually fixes that without cutting. ## The numbers | Action | On an autoflower | Evidence | |---|---|---| | Tuck fan leaves | Yes, any time | House position | | Remove damaged, dying or soil-touching leaves | Yes | Grower practice | | Light [lollipop](https://genetixbay.com/knowledge/glossary/lollipopping.md), tiny lower shoots | Once, flower weeks 1–2 | Grower practice | | Remove healthy fan leaves | A few at most, per session | Grower practice | | Heavy strip or [schwazz](https://genetixbay.com/knowledge/glossary/schwazzing.md) | No | House position | | Topping | No; use [LST](https://genetixbay.com/knowledge/glossary/lst.md) | House position | | [Transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md) | Avoid; plant in the final pot | House position | ## What to do 1. Plant straight into the final pot, 11–15 L (3–4 US gal) in soil. 2. Start LST at 3–5 nodes and spread the branches flat. 3. Tuck fan leaves under or behind bud sites instead of cutting them. 4. Remove only leaves that are damaged, dying or touching the medium. 5. If the interior is dense and humid, spread branches and raise airflow first. ## Common mistakes - Copying a photoperiod schwazz schedule onto an auto. - Stripping leaves during the short veg. - Topping and defoliating the same auto. - Removing healthy leaves when the real problem is weak light. ## Related - Full article: [Defoliation and lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) - Answers: [what is schwazzing](https://genetixbay.com/knowledge/answers/what-is-schwazzing.md) · [why is my autoflower small](https://genetixbay.com/knowledge/answers/why-is-my-autoflower-small.md) · [how long autos take](https://genetixbay.com/knowledge/answers/how-long-do-autoflowers-take.md) - Training: [LST](https://genetixbay.com/knowledge/training/lst.md) - Terms: [tucking](https://genetixbay.com/knowledge/glossary/tucking.md) · [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) ## Follow-up questions **Should I lollipop autoflowers?** A light lollipop is acceptable on an autoflower, done in one gentle pass in the first week or two of flowering, removing only tiny shoots in the lowest, darkest part of the plant. Don't strip the lower third the way you might on a big photoperiod plant. Autos are small, so most of their branches can still reach good light with low-stress training. **Why are autoflowers more sensitive to defoliation?** Autoflowers are more sensitive to defoliation because they are day-neutral and flower at a fixed age, usually 3–5 weeks from sprouting, whatever the light schedule. A photoperiod plant can be vegged longer to recover from stress; an auto can't. Leaf area lost in its short veg is growing capacity it never gets back, so removing leaves costs more on an auto. **What training is best for autoflowers?** Low-stress training is the best training for autoflowers. Bending and tying branches outward builds several tops in the brightest light with near-zero recovery time, which suits an auto's fixed countdown. GenetixBay's house position is that topping never produces what proper LST does on an auto. Plant straight into the final pot, start LST at 3–5 nodes, and tuck leaves rather than pluck. ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 2. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 3. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Can I dry my buds in my grow tent? > Yes, a grow tent makes a good drying space once the plants are out and the light is off. Keep it dark, at 15–21 °C (60–70 °F) and 55–62% RH, with the exhaust on low and a fan moving room air, not blowing on the buds. Never dry in a tent with the grow light or heat running, or alongside live plants. Expect 7–14 days. - Canonical: https://genetixbay.com/knowledge/answers/can-i-dry-in-my-grow-tent.html - Topic: Harvest and cure · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Also asked as: Can I dry weed in my grow tent? | How to set up a tent for drying | Drying in the grow room after harvest | Should I turn the light off to dry in the tent? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. An empty grow tent with the light off makes a good [drying space](https://genetixbay.com/knowledge/glossary/drying-room.md). Keep it dark at 15–21 °C (60–70 °F) and 55–62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), run the [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) low and keep air moving without blowing on the buds. Expect 7–14 days. Never dry with the grow light or heat on, or next to growing plants. *Grower practice*. ## Why A tent is a small room you can control. It is dark once the light is off, it already has an exhaust and [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md), and it is easy to keep at drying targets. A grower survey averaged about 65 °F (18 °C) and 53% RH in drying rooms [2]. [Light damages](https://genetixbay.com/knowledge/glossary/light-stress.md) the crop. Light exposure is a major cause of [THC](https://genetixbay.com/knowledge/glossary/thc.md) loss in stored cannabis [3]. A grow light left running also heats the buds and dries them far too fast. Humidity has to leave. Fresh flower is mostly water, and in a closed tent that water raises the RH quickly. Still, wet air lets [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) keep growing in the buds [4], so a low, steady exhaust matters. The end point is in the bud. Dried flower should settle at [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55–0.65 [1], which you check with a sealed sample jar, not with the tent's hygrometer. ## The numbers | Setting | Target | |---|---| | Grow light | Off, and the tent closed so it stays dark | | Temperature | 15–21 °C (60–70 °F) | | RH | 55–62% | | Exhaust | Lowest speed that holds RH in range | | Air | Gentle circulation, not aimed at buds | | Duration | 7–14 days | | End point | Stems snap; sealed jar reads a stable 58–65% RH | ## What to do 1. Harvest, then clean the tent: take out the pots and spilled media, and wipe the floor. 2. Hang branches from the tent bars or a drying net, with no buds touching. 3. Put a calibrated hygrometer at bud height. 4. Set the exhaust low on a speed controller. Point the [clip fan](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) at the tent wall, not the buds. 5. Check twice a day for the first 3 days. If RH climbs above 65%, raise the exhaust a little. 6. From day 5, test stems. When they snap, run the sealed-jar test. ## Common mistakes - Leaving the light on a timer. - Drying next to live plants. - Running the exhaust flat out. - Packing the tent wall to wall with branches. ## Related - Full article: [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Answers: [whole plant or branches?](https://genetixbay.com/knowledge/answers/hang-whole-plant-or-branches.md) · [quick-drying methods](https://genetixbay.com/knowledge/answers/quick-drying-methods.md) · [lower tent humidity](https://genetixbay.com/knowledge/answers/how-to-lower-humidity-in-a-grow-tent.md) · [raise tent humidity](https://genetixbay.com/knowledge/answers/how-to-raise-humidity-in-a-grow-tent.md) - Terms: [drying room](https://genetixbay.com/knowledge/glossary/drying-room.md) · [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) ## Follow-up questions **Should the exhaust fan run while drying in a tent?** Run the tent's exhaust fan on its lowest setting while drying, enough to remove the moisture coming off the buds and keep RH at 55–62%. Full speed dries buds too fast and strips terpenes, and no exhaust lets humidity build and mould grow. Use a speed controller and check a hygrometer at bud height twice a day for the first few days. **Can I dry in the tent while other plants are growing?** Do not dry buds in a tent where plants are still growing under lights. The light, heat and plant transpiration push temperature and humidity outside drying targets, and light degrades cannabinoids. Move live plants out, or dry in a separate tent, cupboard or room that you can keep dark at 15–21 °C and 55–62% RH. **What if my tent's humidity is too low for drying?** If a drying tent runs below about 50% RH, slow the dry: turn the exhaust down, hang whole plants or larger branches instead of trimmed buds, or leave the sugar leaves on and dry trim later. A humidifier in the room outside the tent helps. Over-dried buds below water activity 0.55 turn brittle and lose aroma. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. Cannabis Business Times. Special report: cannabis post-harvest benchmarks (grower survey; average drying ~53 % RH, ~65 °F). https://www.cannabisbusinesstimes.com/business-issues-benchmarks/cannabis-post-harvest-operations/article/15689633/post-harvest-benchmarks-with-room-to-experiment 3. Fairbairn JW, Liebmann JA, Rowan MG, 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1–7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x 4. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Can I grow seeds I found in my weed? > You can grow seeds found in your weed, but bag seed is a gamble. Seed in sinsemilla bud often comes from a plant that hermed and pollinated itself, so it tends to be nearly all female and to pass the herm tendency on. Its parents, sex and flowering time are unknown. It is fine for practice; for a real grow, buy documented seed. Check local seed rules first. - Canonical: https://genetixbay.com/knowledge/answers/can-i-grow-bag-seed.html - Topic: Basics · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Regular, feminised, autoflower or clone: choosing your starting material](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md) - Also asked as: Is bag seed worth growing? | Growing bagseed | Seeds found in bud | Will seeds from my weed be female? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes, [bag seed](https://genetixbay.com/knowledge/glossary/bagseed.md) will often [sprout](https://genetixbay.com/knowledge/glossary/seedling.md) and grow, but it's a gamble. Seed in seedless-style bud usually means a plant hermed and [pollinated](https://genetixbay.com/knowledge/glossary/pollination.md) itself, so the seed tends to be nearly all female and to carry the [herm tendency](https://genetixbay.com/knowledge/glossary/herm-prone.md). Grow it for practice, not for a crop you care about. *Grower practice*, with the GenetixBay breeder position on [herms](https://genetixbay.com/knowledge/glossary/hermaphrodite.md). **Legal first.** Rules on seed possession and [home growing](https://genetixbay.com/knowledge/glossary/home-grow.md) vary; check your local rules. ## Why Self-pollinated seed is female but herm-prone. Pollen from a hermaphrodite's own [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) carries only X [chromosomes](https://genetixbay.com/knowledge/glossary/chromosome.md); in a controlled study, that seed produced only female plants, while cross-fertilised seed gave about 1:1 [1]. [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md) works the same way, but a good breeder uses a female proven stable before reversing it [2]. A herm in someone's flower room had no such test. The parents are unknown. The strain name on the bag tells you little; same-named retail samples often turned out to be different [genotypes](https://genetixbay.com/knowledge/glossary/genotype.md) [3]. Bag seed is a cross of something with something. Seed can also come from a stray male. Then expect roughly half males. ## The numbers | | Bag seed | Documented seed | |---|---|---| | Parents | Unknown | Recorded | | Females | Often nearly all (if from a herm); ~50% if from a male | Nearly all (feminised) or ~50% (regular) | | Herm risk | Higher | Grow-out data should show it | | Flowering time | Unknown | Stated, and checkable in journals | | Cost | Free | Paid | ## What to do 1. Check that growing is legal where you live. 2. [Germinate](https://genetixbay.com/knowledge/glossary/germination.md) a few seeds; immature pale ones rarely sprout. 3. Grow them as [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md) unless they flower by week 5 on [18/6](https://genetixbay.com/knowledge/glossary/18-6.md). 4. In flower, check every week for [pollen sacs](https://genetixbay.com/knowledge/glossary/anther.md) and [bananas](https://genetixbay.com/knowledge/glossary/nanners.md) with a [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md). 5. Remove any plant that makes pollen sacs. Don't keep it as a mother or save its seed. 6. For a crop you care about, buy seed with grow-out records. ## Common mistakes - Growing bag seed beside a good plant and getting the good plant seeded. - Saving seed from the bag-seed plant that hermed. - Trusting the strain name on the bag. ## Related - Full article: [Regular, feminised, autoflower or clone](https://genetixbay.com/knowledge/basics/seed-types-regular-feminised-auto-clone.md) - Answers: [why there are seeds in my buds](https://genetixbay.com/knowledge/answers/why-are-there-seeds-in-my-buds.md) · [preventing hermaphrodites](https://genetixbay.com/knowledge/answers/how-to-prevent-hermaphrodites.md) - Articles: [male, female and hermaphrodite](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) · [reading a seed listing](https://genetixbay.com/knowledge/guides/reading-a-seed-listing.md) - Terms: [bagseed](https://genetixbay.com/knowledge/glossary/bagseed.md) · [hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) ## Follow-up questions **Will bag seed be female?** Bag seed is often mostly female, but not for a good reason. Seed found in sinsemilla bud frequently comes from a hermaphrodite's own pollen, which carries only X chromosomes, so its seed is nearly all female. A controlled study confirmed seed from hermaphroditic flowers gave only female plants. Those plants are likely to inherit the herm tendency, so watch them closely in flower. **Is bag seed good for a first grow?** Bag seed is fine for a practice first grow, because it costs nothing and teaches the basics. Expect surprises: unknown parents, unknown flowering time, possible males and a higher risk of hermaphrodites. Keep it away from other plants, check for pollen sacs weekly in flower, and never keep a bag-seed plant that herms as a mother or breed from it. **Are seeds from a hermie plant worth keeping?** No. Seeds from a hermaphrodite cannabis plant aren't worth keeping. They are nearly all female, but they carry the same readiness to herm, so the problem passes straight on. GenetixBay's breeder position is that herm-prone lines come mainly from bad breeding, and that the answer is to cull them, not to grow out or share their seed. ## Sources 1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092 3. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 --- # Can I grow cannabis in a closet or cupboard? > Yes, you can grow cannabis in a closet or cupboard if it can be made light-tight, ventilated and safely powered. A space about 60 x 60 cm (2 x 2 ft) and 140–180 cm tall suits one or two plants under a 100–150 W efficient LED, with an extractor fan changing the air about once a minute through a carbon filter. Check local rules first. - Canonical: https://genetixbay.com/knowledge/answers/can-i-grow-in-a-closet.html - Topic: Basics · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.md) - Also asked as: Closet grow setup | Cabinet grow | Small space grow setup | Can I grow weed in a wardrobe? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. A closet or cupboard works if you can make it dark, move air through it and power it safely. About 60 x 60 cm (2 x 2 ft) and 140–180 cm tall holds one or two plants under a 100–150 W efficient [LED](https://genetixbay.com/knowledge/glossary/led.md). *Grower practice*. **Legal first.** [Home growing](https://genetixbay.com/knowledge/glossary/home-grow.md), [plant limits](https://genetixbay.com/knowledge/glossary/plant-count-limit.md) and rules on visibility vary; check your local rules. ## Why Light per area is what matters, not room size. Yield rose with canopy light in controlled trials [1], so a small, well-lit closet beats a big, dim room. Efficient LEDs (2.5–3 [µmol/J](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) and up) [2] give enough light from 100–150 W in 0.36 m² without much heat. Air is the hard part. A sealed cupboard heats up and fills with humid air in hours. An [extractor fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) pulling about one closet-volume a minute, through a [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md), removes heat, humidity and smell, and keeps the space under slight [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md). Darkness matters in flower. Stray light as dim as about 2 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) has delayed flowering in sensitive cultivars [3]. Door gaps are the usual leak. Power must be safe. Small spaces trap heat around plugs and drivers; overloaded outlets and extension cords are a recognised fire cause [4]. ## The numbers | Item | 60 x 60 cm (2 x 2 ft) closet | |---|---| | Plants | 1–2, in 11 L (3 gal) pots | | LED (efficient) | 100–150 W | | Flower PPFD target | 600–900 µmol/m²/s | | Extractor fan | 100 mm (4 in), 50–100 [CFM](https://genetixbay.com/knowledge/glossary/cfm.md) real airflow | | Temperature | 22–28 °C (72–82 °F) lights on | | Usable plant height | Closet height − pot − 30–45 cm light gap − fixture | ## What to do 1. Measure the space and the nearest outlet; check your legal limit. 2. Seal light gaps, or put a small tent inside the closet. 3. Fit an extractor fan and carbon filter at the top, with a low intake gap. 4. Run the light and fan empty for 48 h and log temperature and [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). 5. Use an RCD/GFCI outlet, no daisy-chained power strips, and a smoke alarm nearby. 6. Grow [autos](https://genetixbay.com/knowledge/glossary/autoflower.md) or trained [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md); flip photos at half the usable height. ## Common mistakes - No exhaust, so the closet hits 35 °C (95 °F) in a day. - [Light leaking](https://genetixbay.com/knowledge/glossary/light-leak.md) in round the door during flower. - Plants too tall for the space after the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). ## Related - Full article: [Choosing your growing system](https://genetixbay.com/knowledge/systems/choosing-a-system.md) - Guide: [Choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md) - Answers: [what size tent](https://genetixbay.com/knowledge/answers/what-size-grow-tent.md) · [controlling smell](https://genetixbay.com/knowledge/answers/how-to-control-grow-smell.md) · [electrical safety](https://genetixbay.com/knowledge/answers/grow-room-electrical-safety.md) - Terms: [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) · [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md) ## Follow-up questions **Is a grow tent better than a closet?** A grow tent is usually better than a bare closet, because it is light-tight, reflective, waterproof at the base and has ports for ducting. Many growers put a small tent inside the closet to get both: the closet hides it and the tent controls light, spills and airflow. A bare closet works too, once gaps are sealed and the walls are white or reflective. **How do I ventilate a closet grow?** Ventilate a closet grow with an inline extractor fan that replaces the air about once a minute, plus 25% for a carbon filter. Work out the volume in cubic feet and use that as the airflow in CFM. Exhaust to a room or window with good air, and give the closet a low intake gap so fresh air can get in. **What plants suit a small closet?** Autoflowers and trained photoperiods suit a small closet. Autoflowers stay short and need no light change; photoperiods can be kept low with low-stress training and flipped at about half the height you can fit, since most grow 50–100% taller after the flip. Grow one or two plants in 11 L (3 gal) pots in a 2 x 2 ft space. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 3. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 4. US Fire Administration. Electrical fire safety (overloaded outlets, extension cords, smoke alarms). https://www.usfa.fema.gov/prevention/home-fires/prevent-fires/electrical/ --- # Can I grow cannabis with household LED or CFL bulbs? > You can keep seedlings and clones alive under household LED or CFL bulbs, but you can't grow good flower with them. Seedlings need about 150–300 µmol/m²/s; flower wants 600–1,200 µmol/m²/s over the whole canopy, which takes roughly 25–40 W of efficient horticultural LED per square foot. A handful of household bulbs delivers a fraction of that, so yields are small and buds airy. - Canonical: https://genetixbay.com/knowledge/answers/can-i-grow-with-household-bulbs.html - Topic: Environment · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: Can I grow weed with regular light bulbs? | Growing cannabis with CFLs | Can I use a normal LED bulb for plants? | Cheapest light to grow one plant - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Household [LED](https://genetixbay.com/knowledge/glossary/led.md) or [CFL](https://genetixbay.com/knowledge/glossary/t5-fluorescent.md) bulbs will raise **[seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and clones** (150–300 and 50–150 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md)), but they can't grow good flower. Flower wants **600–1,200 µmol/m²/s** across the canopy, which takes roughly **25–40 W of efficient horticultural LED per square foot**. A few household bulbs give a fraction of that. *Supported*. ## Why Cannabis yield follows light. In a controlled trial, dry flower yield rose linearly from 116 [g/m²](https://genetixbay.com/knowledge/glossary/yield.md) at 120 µmol/m²/s to 519 g/m² at 1,800 [1]. Starve the plant of light and you get proportionally less, plus airy, stretched buds. Household bulbs are designed to light a room for human eyes. They throw light in every direction, so most misses the plant, and intensity falls quickly with distance. Their total output is small: a 10–15 W bulb against a 100–150 W grow light for even a 2 × 2 ft space. [Efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) matters too. Good horticultural LEDs exceed 2.5–3 µmol/J [2]; household bulbs aren't rated for [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) photons at all, so you can't plan with them. Cuttings need little light: about 100–150 µmol/m²/s at most while rooting, by horticultural guidance [3]. That's why household bulbs work for propagation. ## The numbers | Stage | PPFD needed | Household bulbs? | |---|---|---| | Unrooted clones | 50–150 µmol/m²/s | yes, close to the plants | | Seedlings | 150–300 µmol/m²/s | yes, for the first 2–3 weeks | | Veg | 300–700 µmol/m²/s | marginal, leggy growth | | Flower | 600–1,200 µmol/m²/s | no: small, airy yield | | 2 × 2 ft (0.36 m²) flower light | 100–150 W efficient LED | — | ## What to do 1. Use daylight-white household bulbs for seedlings or clones only, 18 h a day. 2. Keep them close, and check leaves aren't heating up. 3. Move plants to a horticultural LED by veg. 4. On a tight budget, buy one small dimmable LED for a 2 × 2 ft space rather than many bulbs. 5. Check every bulb socket and cord is rated and dry. ## Common mistakes - Flowering under a few CFLs and blaming the strain for airy buds. - Judging bulbs by lumens. - Daisy-chaining clamp lamps and extension cords. - Hanging bulbs so close they scorch leaves. ## Related - Full article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [Why don't lumens matter for grow lights?](https://genetixbay.com/knowledge/answers/lumens-vs-ppfd.md) - [What wattage LED do I need for my tent?](https://genetixbay.com/knowledge/answers/what-wattage-light-for-my-tent.md) - [Why are my buds airy?](https://genetixbay.com/knowledge/answers/why-are-my-buds-airy.md) - Terms: [T5 fluorescent](https://genetixbay.com/knowledge/glossary/t5-fluorescent.md) · [light intensity](https://genetixbay.com/knowledge/glossary/light-intensity.md) ## Follow-up questions **Can I flower cannabis under CFLs?** You can flower cannabis under CFLs, but the yield will be small and the buds airy. Flower wants roughly 600–1,200 µmol/m²/s at the canopy, and compact fluorescents spread a modest amount of light in all directions, so it falls off fast with distance. Research shows cannabis yield rises in step with light, so a weak light means proportionally fewer grams per square metre. **Are household bulbs fine for seedlings and clones?** Yes, household LED or fluorescent bulbs are fine for cannabis seedlings and clones, which need only about 150–300 µmol/m²/s for seedlings and 50–150 µmol/m²/s for unrooted cuttings. Use daylight-white bulbs, keep them close but not touching, and run 18 hours a day. Move plants to a proper grow light once they have three or four sets of true leaves. **What is the cheapest light that actually works for one plant?** The cheapest light that properly flowers one cannabis plant is a small dimmable horticultural LED of about 100–150 W from a fixture rated around 2.5 µmol/J or better, sized for a 60 × 60 cm (2 × 2 ft) space. It delivers roughly 600–900 µmol/m²/s over that area, which a cluster of household bulbs cannot, and costs less to run per gram. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 3. Michigan State University. Lighting of cuttings (rooting-phase PPFD). https://www.canr.msu.edu/uploads/resources/pdfs/lighting-of-cuttings.pdf --- # Can I mix soil and coco? > Yes, you can mix soil and coco: adding buffered coco to potting mix lightens it, holds water well and stays airy. Decide which system the blend behaves like. Mostly soil (coco 50% or less): water at pH 6.2–6.8 and feed at soil strength. Mostly coco: run pH 5.8–6.2 and feed every watering. Use washed, buffered coco or it will grab calcium and magnesium. - Canonical: https://genetixbay.com/knowledge/answers/can-i-mix-soil-and-coco.html - Topic: Systems · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) - Also asked as: Can I mix coco into potting soil? | Is a 50/50 coco soil mix good? | Soil and coco mix for cannabis | Do I feed a coco soil mix like soil or coco? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes, you can mix soil and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md). Buffered coco lightens a heavy [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) and holds water and air at the same time. Decide which system the blend behaves like: mostly soil, water at [pH](https://genetixbay.com/knowledge/glossary/ph.md) 6.2–6.8 and feed at soil strength; mostly coco, run pH 5.8–6.2 and feed every watering. *Grower practice*; the coir chemistry behind it is established. ## Why Coir pith is a [peat](https://genetixbay.com/knowledge/glossary/peat.md) substitute with good water holding and [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), and it has been used in commercial potting mixes for decades [1]. Raw coir carries potassium and [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) from the husk and has modest [exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md) [1]. Feed it calcium and it swaps calcium onto its sites and releases potassium, so unbuffered coco shows early calcium and magnesium shortages. Washed, buffered coco avoids this [2]. The two media feed differently. Potting mix brings compost and a starter charge and buffers pH. Coco brings no nutrients and buffers pH weakly. A blend sits between the two, and the larger share sets the rules. Organic feeding works in coir blends too, once nitrogen supply is adequate [3]. ## The numbers | Blend (coco share) | Behaves like | Irrigation pH | Feeding | |---|---|---|---| | 10–30% | Soil | 6.2–6.8 | Starter charge, then soil strength, [EC](https://genetixbay.com/knowledge/glossary/ec.md) 0.8–1.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) | | 40–50% | Mostly soil | 6.2–6.5 | Starter charge, then feed every second watering | | 60% and up | Coco | 5.8–6.2 | Full mineral feed every watering, EC 1.2–2.4, 10–20% [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) | Add 20–30% [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) through any blend that will be hand-watered. ## What to do 1. Use washed, buffered coco, or rinse to runoff EC below about 0.5 mS/cm and buffer it. 2. Pick your blend and decide up front whether you'll run it as soil or as coco. 3. Mix evenly and add perlite through the whole pot. 4. Check runoff pH and EC a few times in the first three weeks. 5. Adjust: if lower leaves pale early, the starter charge was diluted, so start feeding sooner. ## Common mistakes - Raw, unbuffered coco, then blaming the lights for calcium spots (that's a *Myth*; coco, [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) and the cultivar drive it). - Running a mostly-coco blend like soil, with plain-water days. - Assuming the blend still has a full starter charge after diluting the soil by half. ## Related - Full article: [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) - Answers: [coco to perlite ratio](https://genetixbay.com/knowledge/answers/coco-perlite-ratio.md) · [best soil for cannabis](https://genetixbay.com/knowledge/answers/best-soil-for-cannabis.md) - Systems: [growing in soil](https://genetixbay.com/knowledge/systems/soil.md) - Terms: [coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md) · [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) ## Follow-up questions **Should I pH a coco soil mix like soil or coco?** Run a coco soil mix at the pH of whichever part dominates. A blend that is half or more potting mix keeps soil's buffering and does well at pH 6.2–6.8. A blend that is mostly coco behaves like hydroponics in a pot and wants pH 5.8–6.2. Check runoff pH a few times in the first weeks to see what the root zone is doing. **Does coco in soil cause calcium deficiency?** Coco mixed into soil can cause calcium and magnesium shortages if the coco is raw and unbuffered. Raw coir is loaded with potassium and sodium and pulls calcium and magnesium from the feed onto its exchange sites. Use coco sold as washed and buffered, or rinse and buffer it yourself, and the compost in the soil part supplies some extra calcium. **Is coco better than perlite for lightening soil?** Coco and perlite do different jobs in soil. Coco lightens heavy mixes and holds water and air at once, but it decomposes slowly and has some exchange capacity. Perlite adds air only and holds little water. Many growers use both: buffered coco to replace part of the peat, and 20–30% perlite through the whole mix for drainage. ## Sources 1. Abad M, Noguera P, Puchades R, Maquieira A, Noguera V, 2002. Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology 82(3):241–245. https://doi.org/10.1016/S0960-8524(01)00189-4 2. Greenhouse Grower, 2023. Washed, low-EC, or buffered? How to specify coco substrate for your crop. https://www.greenhousegrower.com/?p=180860 3. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17 --- # Can I reuse soil from my last grow? > Yes, you can reuse soil from your last grow if the plants were healthy. Break up the root ball, add fresh compost or worm castings, slow-release organic amendments and perlite, then keep it moist for 2–4 weeks before planting. Don't reuse soil from plants with root rot, wilt or root pests. Coco can be rinsed and re-buffered; living soil is reused in place, no-till. - Canonical: https://genetixbay.com/knowledge/answers/can-i-reuse-soil.html - Topic: Systems · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - Also asked as: Can I reuse potting soil for cannabis? | How do I recycle old grow soil? | How do I amend old soil for the next run? | Can I reuse coco coir? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes, reuse soil from a healthy grow. Break up the root ball, mix in fresh compost or worm castings, slow-release [organic amendments](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md) and [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), and keep it moist for 2–4 weeks before planting. Don't reuse soil from plants with [root disease](https://genetixbay.com/knowledge/glossary/root-rot.md) or root pests. *Grower practice*, consistent with established soil-health principles. ## Why A finished run leaves the mix depleted, not ruined. The plant used up the starter charge, and the [peat](https://genetixbay.com/knowledge/glossary/peat.md) or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) has broken down a little, so the mix holds more water and less air [4]. Old roots are food. Left in the mix, they decompose and feed soil life, and keeping soil covered and biologically active is a core soil-health principle [1]. The danger is disease. [Fusarium](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md), [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) and similar pathogens survive in old roots and media [2][3]. Soil from a sick crop carries them into the next one. [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) goes further: it isn't emptied at all. Stems are cut at the surface, roots stay, and the bed is top-dressed and replanted ([no-till](https://genetixbay.com/knowledge/glossary/no-till.md)) [1]. ## The numbers | Step | Amount or time | |---|---| | Fresh compost or worm castings | About 20–30% of volume | | Extra perlite or pumice | 10–20% to restore [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) | | Slow-release organic amendment | Label rate for the volume | | Rest, moist and warm | 2–4 weeks before planting | | Coco: rinse | To [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md) below about 0.5 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), then re-buffer | | Pot disinfection | 10–15% household bleach solution [2] | ## What to do 1. Check the last crop. Any root rot, wilt or [root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md): bag and discard the soil. 2. Dry the old mix slightly, crumble it and pull out the large root masses. 3. Mix in compost or castings, perlite and a slow-release amendment. 4. Rehydrate, cover and leave it warm and moist for 2–4 weeks. 5. Plant, water with plain water, and feed only when lower leaves begin to pale. 6. Wash pots and trays. Wear gloves and eye protection with bleach, and never mix it with acids or ammonia. ## Common mistakes - Reusing soil from a crop that wilted or had brown roots. - Planting [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) straight into freshly amended "hot" soil. - Reusing the same mix for many runs without restoring air space. - Sterilising healthy soil and killing its biology. ## Related - Full article: [Growing in soil](https://genetixbay.com/knowledge/systems/soil.md) - Answers: [what is super soil](https://genetixbay.com/knowledge/answers/what-is-super-soil.md) · [best soil for cannabis](https://genetixbay.com/knowledge/answers/best-soil-for-cannabis.md) · [when soil runs out of nutrients](https://genetixbay.com/knowledge/answers/when-does-soil-run-out-of-nutrients.md) - Systems: [living soil](https://genetixbay.com/knowledge/systems/living-soil.md) - Terms: [top-dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md) · [no-till](https://genetixbay.com/knowledge/glossary/no-till.md) ## Follow-up questions **Do I need to sterilise old soil before reusing it?** No, you don't need to sterilise old soil from a healthy grow, and doing so kills the beneficial organisms you want. Sterilising or pasteurising only makes sense if the last crop had root disease, and then discarding the soil is usually simpler. Instead, re-amend it with compost and nutrients, rehydrate it and let it rest moist and warm for 2–4 weeks. **Can I reuse soil from plants with root rot or pests?** Don't reuse soil from plants that had root rot, Fusarium wilt, root aphids or a heavy fungus gnat infestation. These organisms survive in old roots and media and will attack the next crop. Bag the soil and dispose of it away from the grow, then wash pots and trays and disinfect them with a 10–15% household bleach solution before reuse. **Can I reuse coco coir?** Yes, coco coir can be reused after a healthy run. Remove as much root mass as you can, rinse until runoff EC is below about 0.5 mS/cm, and re-buffer it with a calcium-magnesium solution before replanting. Root debris raises water holding and disease risk, so add some fresh coco and perlite, and don't reuse coco more than a couple of times. ## Sources 1. USDA Natural Resources Conservation Service. Soil health principles (minimise disturbance, keep soil covered, maintain living roots, maximise biodiversity). https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soil/soil-health 2. Utah State University Extension. Fusarium Wilt (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-fusarium-wilt 3. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 4. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (organic substrates and compost chapters). https://doi.org/10.1016/C2015-0-01807-5 --- # Can I use distilled water or rainwater for cannabis? > Yes. Distilled, RO and clean rainwater work well for cannabis because they start near EC 0 with no sodium, chloride or alkalinity, but they also carry no calcium or magnesium and no pH buffer. Add a complete feed that includes Ca and Mg, or a Cal-Mag supplement, to reach about 150-200 mg/L Ca and 40-70 mg/L Mg, and expect pH to swing easily. Rain is naturally about pH 5.6. - Canonical: https://genetixbay.com/knowledge/answers/can-i-use-distilled-water.html - Topic: pH and EC · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - Also asked as: Is distilled water good for plants? | Can I use rainwater for weed? | Can I use bottled water for plants? | Is RO water better than tap water? | Do I need Cal-Mag with distilled water? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. Distilled, [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) and clean rainwater are excellent starting water: near [EC](https://genetixbay.com/knowledge/glossary/ec.md) 0, with no [sodium](https://genetixbay.com/knowledge/glossary/sodium.md), [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) or [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md). The trade-off is that they carry no calcium or magnesium and no [pH](https://genetixbay.com/knowledge/glossary/ph.md) buffer. Feed a complete nutrient that supplies Ca and Mg, or add [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md), and expect pH to move easily. *Supported.* ## Why Pure water gives you control. [Hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) can bring sodium, chloride, [boron](https://genetixbay.com/knowledge/glossary/boron.md) and bicarbonate, and its alkalinity pushes root-zone pH up over weeks [1][2]. Distilled, RO and rain bring none of that. It also brings no calcium or magnesium, so a base nutrient written for tap water will run short. How much Cal-Mag you need depends heavily on cultivar: leaf calcium varied widely among [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md) grown side by side [4]. [Coco](https://genetixbay.com/knowledge/glossary/coco-coir.md)'s [cation exchange](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md) adds to the demand. [LEDs](https://genetixbay.com/knowledge/glossary/led.md) do not; the "Cal-Mag under LED" claim is a *Myth*. No alkalinity means no buffer. A few drops of acid or base move pH a long way, so adjust in small steps. Natural rain is slightly acidic, about pH 5.6, from dissolved [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) [3]. ## The numbers | Water | EC ([mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md)) | Ca, Mg | Alkalinity | Notes | |---|---|---|---|---| | Distilled | ~0 | None | None | Costly in volume | | RO | <0.05 | ~0 | ~0 | Carbon prefilter; reject water | | Rain, clean roof | ~0–0.1 | Very low | Very low | ~pH 5.6 [3] | | Good tap | 0.2–0.8 | Some | Low–high | Get a report | | Softened tap | Variable | Swapped for sodium | High | Avoid | Feed targets with pure water: Ca ~150–200 mg/L, Mg ~40–70 mg/L. ## What to do 1. Measure the water's EC to confirm it's near zero. 2. Use a base nutrient made for soft or RO water, or add Cal-Mag. 3. Add nutrients, then adjust pH in small doses. 4. Collect rain from a clean roof; divert the first [flush](https://genetixbay.com/knowledge/glossary/flushing.md); store it covered and dark. 5. Watch new growth for calcium symptoms, especially in coco. ## Common mistakes - Using a hard-water base nutrient with RO water. - Overshooting pH because there's no buffer. - Storing rainwater in clear, open containers. - Using softened water. ## Related - Full article: [Water quality: RO vs tap](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - Articles: [Cal-Mag, and when you need it](https://genetixbay.com/knowledge/nutrients/cal-mag.md) - Answers: [do I need to pH?](https://genetixbay.com/knowledge/answers/do-i-need-to-ph-my-water.md) · [how to adjust pH](https://genetixbay.com/knowledge/answers/how-to-adjust-ph.md) - Terms: [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) · [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) ## Follow-up questions **Do I need Cal-Mag with RO or distilled water?** Usually yes. RO and distilled water supply essentially no calcium or magnesium, and many base nutrients assume some comes from the tap. Add only the gap between your base feed and targets of about 150-200 mg/L calcium and 40-70 mg/L magnesium. Need also varies by cultivar and medium, especially unbuffered coco; LEDs do not create a Cal-Mag need. **Is rainwater safe for cannabis?** Rainwater is usually good for cannabis: it is low in salts and alkalinity and naturally slightly acidic, about pH 5.6. Collect it from a clean roof and gutter, discard the first runoff of each storm, store it covered and dark so algae and mosquitoes stay out, and treat it like RO water by feeding calcium and magnesium. **Can I use bottled spring or mineral water?** You can, but bottled spring or mineral water is expensive and varies by brand: some are very low in minerals, others carry high bicarbonate or sodium. Read the label's mineral analysis as you would a water report. For most growers, RO, filtered tap or rainwater is cheaper and more predictable. ## Sources 1. NC State Extension. Producing conventional tobacco transplants in greenhouses: water quality. https://content.ces.ncsu.edu/producing-conventional-tobacco-transplants-in-greenhouses-water-quality 2. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 3. US Geological Survey. pH and water. Water Science School. https://www.usgs.gov/special-topic/water-science-school/science/ph-and-water 4. Kalinowski J, et al., 2020. Augmenting nutrient acquisition ranges of greenhouse grown CBD (cannabidiol) hemp (Cannabis sativa) cultivars. Horticulturae 6(4):98. https://doi.org/10.3390/horticulturae6040098 --- # Can you clone an autoflower? > You can root a cutting from an autoflower, but it is impractical. The clone keeps flowering on its parent's age-based clock, so it starts flowering while it is still rooting and finishes tiny, often only a few grams. An autoflower also can't be kept as a mother. To repeat a good auto, grow its seed again, or breed from it. - Canonical: https://genetixbay.com/knowledge/answers/can-you-clone-autoflowers.html - Topic: Basics · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Also asked as: Cloning autos | Do autoflower clones work? | Can I take cuttings from an autoflower? | Can you keep an autoflower mother? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes, an [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) cutting will root, but it's rarely worth it. The clone carries on flowering on its parent's clock, so it flowers while it's still rooting and finishes as one small bud. You can't keep an auto as a mother either. *Grower practice*: almost nobody does it twice. ## Why An auto flowers by age, not by night length. Autoflowering is a [recessive trait](https://genetixbay.com/knowledge/glossary/recessive.md) at a mapped [locus](https://genetixbay.com/knowledge/glossary/locus.md), *Autoflower1*: plants with two copies flower even under [continuous light](https://genetixbay.com/knowledge/glossary/24-0.md) [1]. [Gene](https://genetixbay.com/knowledge/glossary/gene.md) dosage at that locus changes flowering time [3], but no light schedule switches it off. A cutting is as old as its donor. Cannabis passes from a juvenile to an adult, flower-ready stage on its own [2]. A cutting from a 4-week-old auto is already adult, so it starts flowering as soon as it can, with no veg to build a frame. [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) clones work differently. Under [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) a photoperiod cutting stays in veg as long as you like, which is why [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md) and [clone-only cuts](https://genetixbay.com/knowledge/glossary/clone-only.md) exist at all. ## The numbers | | Autoflower cutting | Photoperiod cutting | |---|---|---| | Rooting time | ~7–14 days | ~7–14 days | | [Veg time](https://genetixbay.com/knowledge/glossary/veg-time.md) you control | None | As long as you like | | Can be kept as a mother | No | Yes, for years | | Typical result | One small bud | A full plant | ## What to do 1. To repeat a great auto, grow more seed of the same line. 2. To keep its genetics, [pollinate](https://genetixbay.com/knowledge/glossary/pollination.md) it with a good auto male and grow the seed out. 3. To make a photoperiod version, cross to a photo and select from the [F2](https://genetixbay.com/knowledge/glossary/f2.md) (about 1 in 4 autos reappear). 4. If you clone one out of curiosity, take it early, from a healthy plant, and expect a novelty, not a harvest. ## Common mistakes - [Taking cuttings](https://genetixbay.com/knowledge/glossary/cloning.md) in flower and expecting a full plant. - Putting an auto under [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) or 24/0 to "hold" it as a mother. - Crossing an auto to a photo and expecting auto seed in the [F1](https://genetixbay.com/knowledge/glossary/f1.md). ## Related - Full article: [Photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Answers: [how to clone cannabis](https://genetixbay.com/knowledge/answers/how-to-clone-cannabis.md) · [is a clone the same as its mother?](https://genetixbay.com/knowledge/answers/is-a-clone-the-same-as-its-mother.md) - Articles: [breeding autoflowers](https://genetixbay.com/knowledge/breeding/breeding-autoflowers.md) · [clone-only preservation](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Terms: [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) · [mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md) ## Follow-up questions **Why don't autoflower clones get big?** Autoflower clones stay small because an auto flowers by age, and a cutting is as old as the plant it came from. By the time it has rooted, in about 7–14 days, it is already flowering, with almost no veg time to build roots and branches. The result is a single small bud, which rarely justifies the space and light. **Can I keep an autoflower as a mother plant?** No, you can't keep an autoflower as a mother plant. An auto ignores the light schedule, so long days won't hold it in veg: it flowers at its set age, finishes and dies like any annual. To keep a genotype you like, collect its seed, cross it with another auto, or make a photoperiod version through a breeding project. **How do I keep a great autoflower going?** To keep a great autoflower going, breed it. Pollinate it with a good auto male, or another auto, and the seed will be autos too, because the trait is recessive and two autos give 100% autos. Crossing to a photoperiod gives all-photoperiod F1 seed, and autos reappear in about a quarter of the F2. ## Sources 1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 2. Spitzer-Rimon B, Shafran-Tomer H, Gottlieb GH, et al. 2022. Non-photoperiodic transition of female cannabis seedlings from juvenile to adult reproductive stage. Plant Reproduction 35(4):265-277. https://doi.org/10.1007/s00497-022-00449-0 3. Kurtz LE, Brand MH, Lubell-Brand JD. 2023. Gene dosage at the autoflowering locus effects flowering timing and plant height in triploid cannabis. Journal of the American Society for Horticultural Science 148(2):83-88. https://doi.org/10.21273/JASHS05293-23 --- # Can you smoke buds from a hermaphrodite plant? > Yes, buds from a hermaphrodite plant can be used if they are free of mould. The herm doesn't make them unsafe, but if they were pollinated, seed formation lowers quality and seeds need picking out. Finish or harvest the plant, pick out the seeds, check the buds for rot, and never keep the plant as a mother or grow its seeds. A herm is a genetic defect to cull. - Canonical: https://genetixbay.com/knowledge/answers/can-you-smoke-a-hermie.html - Topic: Diagnosis · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - Also asked as: Can I smoke a hermie? | Is hermie weed OK to use? | Does a herm ruin bud quality? | Are seeded buds safe? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. Buds from a [hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) plant can be used if they are free of mould. Hermaphroditism doesn't make flower unsafe. Pollination lowers its quality, though, because seeds take resources from the flowers and have to be picked out. Use the buds, but cull the plant: never clone it, keep it as a mother or grow its seeds (*House position*). The quality effect is *Supported*. ## Why A herm is still a female plant. Cannabis is [dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md) [3], and an intersex plant is a female that also makes [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md). The [resin glands](https://genetixbay.com/knowledge/glossary/trichome.md) on its buds are the same kind as on any other female. Pollination is what costs you. In a controlled study, herm [anthers](https://genetixbay.com/knowledge/glossary/anther.md) made working pollen, seeded inflorescences held 22–48 seeds, and seed formation reduced quality [1]. A late herm that never opened its anthers may leave the buds almost untouched. Mould is the real safety question. Seeded, dense or over-ripe buds are a fine place for rot, and mouldy flower carries spores and possible [mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md) whatever the plant's sex [2]. Its seeds are the problem to avoid. Herm pollen gives almost all female seed carrying the same tendency [1]. ## The numbers | Situation | What to do | |---|---| | A few closed [bananas](https://genetixbay.com/knowledge/glossary/nanners.md), last days | Pluck with tweezers, finish in isolation | | Many anthers or pollen shedding | Bag the plant, remove it, harvest early if near maturity | | Seeds per seeded inflorescence | 22–48 [1]: pick them out | | Grey core or fuzz in any bud | Bin it | ## What to do 1. Isolate the plant. Bag it before you move it so pollen doesn't spread. 2. Decide whether to finish it or harvest now. Shedding pollen means harvest. 3. Dry and cure it as normal: 15–21 °C (60–70 °F), 55–62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), 7–14 days. 4. Pick the seeds out before use. Burning seeds gives harsh, popping smoke. 5. Break open the big buds and check the cores for rot. 6. Throw the seeds away, take no cuts, and record the event for the breeder. ## Common mistakes - Planting the seeds as free [feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md). - Keeping the plant as a mother because it smoked well. - Leaving an open herm among the other plants. - Smoking seeded buds without checking them for mould. ## Related - Full article: [Hermaphrodite cannabis (bananas and nanners)](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - Answers: [seeds in my buds](https://genetixbay.com/knowledge/answers/why-are-there-seeds-in-my-buds.md) · [preventing herms](https://genetixbay.com/knowledge/answers/how-to-prevent-hermaphrodites.md) · [mould in jars](https://genetixbay.com/knowledge/answers/mould-in-curing-jars.md) - Article: [male, female and hermaphrodite plants](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) - Terms: [hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) · [nanners](https://genetixbay.com/knowledge/glossary/nanners.md) ## Follow-up questions **Are seeded buds weaker?** Seeded cannabis buds are generally lower in quality, because the plant diverts resources into filling seeds instead of flowers. Research on hermaphrodite cannabis found seeded inflorescences held 22–48 seeds each. Pick seeds out before use, since burning them is harsh, and expect lighter bag appeal. Unseeded buds from a plant that hermed late are much closer to normal. **Should I harvest a hermie early?** Harvest a hermaphrodite cannabis plant early if it is shedding pollen and near maturity, because it is seeding itself and every plant around it. If it has only a few closed bananas in the last days, pluck them with tweezers and finish it in isolation. Either way, take no cuttings and make no seed from it. **Do herm buds give a different effect?** There is no evidence that buds from a hermaphrodite cannabis plant give a different effect in themselves. Effects depend on chemistry, dose and the person, and any differences are reported, not promised. Heavily seeded buds have less flower mass and may test lower, and a plant harvested early to stop pollen will be less ripe than planned. ## Sources 1. Punja ZK, Holmes JE., 2020. Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences: Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Punja ZK, et al., 2019. Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://doi.org/10.3389/fpls.2019.01120 3. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 --- # What coco to perlite ratio should I use? > The usual coco to perlite ratio is 70:30 for hand-watered pots. Coco takes 0–30% perlite: hand watering once a day or less suits 20–30% perlite for extra air and margin, while automated high-frequency drip can run 0–20% or plain coco. More perlite means more air, faster drying and more irrigations; less perlite holds more water. - Canonical: https://genetixbay.com/knowledge/answers/coco-perlite-ratio.html - Topic: Systems · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) - Also asked as: What coco perlite mix should I use? | Is 70/30 coco perlite right? | Do I need perlite in coco? | How much perlite to add to coco coir? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Use 70:30 [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) to [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) for hand-watered pots. Coco takes anywhere from 0% to 30% perlite: hand watering once a day or less suits 20–30%, while automated high-frequency drip can run 0–20% or straight coco. *Grower practice*: the ranges are well established among growers, but no cannabis trial has compared ratios. ## Why Coir pith already holds a lot of water while staying airy [1]. That is why coco works on its own when it is watered little and often. Perlite is inert, does not hold water inside its particles and adds large pores. Adding it raises [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) and lowers water-holding capacity [2]. More air helps roots in a pot that stays wet for long periods. The trade-off is drying speed. A pot with more perlite reaches its watering point sooner, so it needs more irrigations a day. Coco should never dry out fully, because dry coir turns hydrophobic and plants can crash. Coco quality varies more than perlite does. Fibre content, particle size and washing change how much water a coir product holds [3], so the right ratio shifts with the bag you buy. ## The numbers | Watering style | Perlite share | Coco share | Notes | |---|---|---|---| | Automated drip, 2–6 shots a day | 0–20% | 80–100% | Evenly moist; less perlite needed | | Hand watering, daily | 20–30% | 70–80% | The common 70:30 | | Large pot, small plant | 30% | 70% | Extra air while roots fill the pot | | [Seedlings](https://genetixbay.com/knowledge/glossary/seedling.md), clones | 0–30% | 70–100% | Keep moist, not soaked | Water to 10–20% [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) every irrigation at [pH](https://genetixbay.com/knowledge/glossary/ph.md) 5.8–6.2, whatever the ratio. ## What to do 1. Start at 70:30 if you hand-water; drop to 80:20 or less with automated drip. 2. Hydrate and rinse the coco first, and buffer it if it isn't pre-buffered. 3. Dampen and rinse the perlite. Wear a dust mask when handling it dry. 4. Mix evenly through the whole pot; don't layer it. 5. Watch drying speed: if pots dry in hours, use less perlite next run; if they stay heavy for days, use more. ## Common mistakes - Pouring perlite in a layer at the bottom instead of mixing it through. - Using 50% or more perlite, then letting coco dry out between waterings. - Skipping buffering and blaming the perlite for calcium spots. ## Related - Full article: [Growing in coco coir](https://genetixbay.com/knowledge/systems/coco.md) - Answers: [mixing soil and coco](https://genetixbay.com/knowledge/answers/can-i-mix-soil-and-coco.md) · [how often to water](https://genetixbay.com/knowledge/answers/how-often-to-water.md) - Terms: [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) · [coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md) · [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) ## Follow-up questions **Can I use coco without perlite?** Yes, you can use coco without perlite if you irrigate often, because good coir is already airy. Plain coco suits automated drip with several small shots a day, which keeps it evenly moist. For hand watering, adding 20–30% perlite gives more air and more margin against overwatering, especially in large pots with small plants that drink slowly. **Is 50/50 coco perlite too much?** A 50/50 coco perlite mix is more perlite than the 0–30% range most coco growers use. It drains and dries very fast, so plants need more irrigations a day to stay evenly moist, and coco should never dry out completely. It can suit a grower who habitually overwaters, but most hand-watered pots do well at 70:30. **Should I rinse perlite before mixing it with coco?** Rinse perlite before mixing it into coco to wash off fine dust, which can clog pores and lower air space at the bottom of the pot. Dampen it first to keep the dust down, and wear a dust mask when handling dry perlite. Mix it evenly through the coco rather than layering it, so water moves the same way through the whole pot. ## Sources 1. Abad M, Noguera P, Puchades R, Maquieira A, Noguera V, 2002. Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology 82(3):241–245. https://doi.org/10.1016/S0960-8524(01)00189-4 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5 3. Greenhouse Grower, 2023. Washed, low-EC, or buffered? How to specify coco substrate for your crop. https://www.greenhousegrower.com/?p=180860 --- # Do clones need nutrients before they root? > No. Unrooted cannabis clones don't need nutrients: they live on reserves in their stem and leaves, and plain water or a very weak solution (EC up to about 0.4 mS/cm, 200 ppm500) is enough. Strong feed can burn the cut stem. Once roots show, feed rooted clones and seedlings at a quarter to half strength, EC 0.4–0.8 mS/cm (200–400 ppm500). - Canonical: https://genetixbay.com/knowledge/answers/do-clones-need-nutrients.html - Topic: Cloning and mother plants · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: Should I feed my clones? | Nutrients for cuttings | What EC for clones? | What EC for seedlings and clones? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer No. Unrooted cannabis clones live on their own reserves, so plain water or a very weak solution ([EC](https://genetixbay.com/knowledge/glossary/ec.md) up to about 0.4 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), 200 [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md)) is enough. Start feeding at EC 0.4–0.8 mS/cm once roots appear. *Grower practice*. ## Why A cutting has no roots to take up much feed. Its job is to make roots from the sugars and nutrients already in its stem and leaves. Research cuttings root on almost nothing. In one cannabis substrate trial, cuttings were kept on water at an EC of just 0.20 mS/cm and still rooted within 9 days in the best medium [1]. The leaves are the cutting's pantry. Cuttings with three leaves made better roots than those with two [2], which is why stripping leaves hurts more than skipping feed. Salt at a fresh wound is a stressor. A strong solution around the stem base draws water out rather than in. Feeding has its moment. Extension [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) guidance waits until [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) form before adding fertiliser [3]; for clones the equivalent is visible roots. ## The numbers | Stage | EC (mS/cm) | ppm500 | [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md) | |---|---|---|---| | Unrooted cutting | 0–0.4 | 0–200 | 0–280 | | Rooted clone / seedling, 2–3 true-leaf sets | 0.4–0.8 | 200–400 | 280–560 | | Plug [pH](https://genetixbay.com/knowledge/glossary/ph.md), [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) | 5.5–6.0 | | | | Plug pH, [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) or [peat](https://genetixbay.com/knowledge/glossary/peat.md) | 5.8–6.2 | | | ## What to do 1. Soak plugs in pH-adjusted plain water, or EC ≤ 0.4. 2. Keep plugs moist, not dripping. 3. Mist with plain water only, if at all. 4. When roots show, give a quarter-strength feed (EC ~0.4). 5. Step up to half strength (EC ~0.8) after [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) as new growth starts. ## Common mistakes - Soaking plugs in full-strength veg feed. - [Foliar](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) spraying nutrients under a sealed dome. - Treating normal lower-leaf yellowing on day 7–10 as a [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md). - Never feeding rooted clones sitting in inert plugs. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Why are my seedling's leaves yellow?](https://genetixbay.com/knowledge/answers/seedling-leaves-yellow.md) · [Best medium for rooting clones](https://genetixbay.com/knowledge/answers/best-medium-for-rooting-clones.md) - Terms: [EC](https://genetixbay.com/knowledge/glossary/ec.md) · [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md) ## Follow-up questions **What EC for seedlings and clones?** Feed rooted cannabis clones and seedlings with 2–3 sets of true leaves at about EC 0.4–0.8 mS/cm (200–400 ppm500, 280–560 ppm700), a quarter to half strength. Unrooted cuttings need little or nothing: plain water or EC up to about 0.4 mS/cm. Seedlings and clones in inert media such as coco, rockwool or hydro need feed sooner than those in amended soil. **Should I foliar feed clones?** Foliar feeding unrooted cannabis clones is not needed and often backfires. Cuttings live on stored reserves while they root, and nutrient sprays leave salts on leaves under a humid dome, which can scorch tissue and feed mould. If you want to mist, use plain water to keep humidity up. Start feeding through the medium once roots have formed. **What pH for clone plugs?** Soak cannabis clone plugs in water at about pH 5.5–6.0 for rockwool, 5.8–6.2 for coco or peat plugs. Rockwool starts alkaline and benefits from a pre-soak at about 5.5. Keep the water at room temperature and the plugs moist but not dripping; squeeze out excess before sticking cuttings. ## Sources 1. Hwang SJ, Collado CE, Hwang HS, Yun JH, Hernandez R, 2026. Impacts of commercial and custom substrates on rooting and morphology of Cannabis sativa 'Suver Haze' stem. HortTechnology 36(3):429–434. https://doi.org/10.21273/HORTTECH05810-26 2. Caplan D, Stemeroff J, Dixon M, Zheng Y. 2018. Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science 98(5):1126-1132. https://doi.org/10.1139/cjps-2018-0038 3. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping --- # Will damaged leaves recover after I fix the problem? > Mostly no. Brown, burnt or dead leaf tissue never recovers, and badly yellowed leaves rarely regreen; only mildly pale leaves may partly recover once the nutrient is back. Judge your fix on new growth, which should look healthy within about 5-10 days. Leave damaged leaves that are still mostly green, because they still photosynthesise. Remove only leaves that are mostly dead, diseased, or shading nothing useful. - Canonical: https://genetixbay.com/knowledge/answers/do-damaged-leaves-recover.html - Topic: Nutrients · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Mobile vs immobile nutrients: reading old vs new leaves](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) - Also asked as: Do yellow leaves turn green again? | Do burnt leaves recover? | Should I remove damaged leaves? | How many leaves can I remove? | How do I know my fix worked? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Mostly no. Brown, crispy or [dead tissue](https://genetixbay.com/knowledge/glossary/necrosis.md) is gone for good, and strongly yellowed leaves rarely regreen; only mildly pale leaves may partly recover. Judge the fix on new growth, which should look normal within about 5–10 days. Keep damaged leaves that are still mostly green: they still feed the plant. *Grower practice.* ## Why Necrosis is dead cells. Nothing brings them back. Yellowing from a [mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md) is the plant stripping an old leaf to feed new growth. Nitrogen, phosphorus, potassium and magnesium move out through the [phloem](https://genetixbay.com/knowledge/glossary/phloem.md), and the old leaf is sacrificed [1]. Once broken down that far, a leaf seldom rebuilds its [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md). [Immobile nutrients](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md) work the other way. Calcium, [boron](https://genetixbay.com/knowledge/glossary/boron.md), iron, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md), [copper](https://genetixbay.com/knowledge/glossary/copper.md) and [zinc](https://genetixbay.com/knowledge/glossary/zinc.md) stay where they were laid down, so leaves that formed short stay marked, and the cure shows only in leaves formed afterwards [1]. Cannabis follows these textbook patterns for most elements [2][3], so the youngest leaves are the honest test of whether a fix worked. Leaf area is yield. GenetixBay's house position is "tuck, don't pluck": keep as much working leaf as possible. ## The numbers | Leaf state | Recovers? | Keep it? | |---|---|---| | Slightly pale, mobile nutrient | Sometimes, partly | Yes | | [Interveinal yellowing](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md), new growth | Rarely; new leaves will be fine | Yes | | [Burnt tips](https://genetixbay.com/knowledge/glossary/nutrient-burn.md), <10% of leaf | No, but stops spreading | Yes | | Spots or necrosis on >50% of leaf | No | Remove | | Diseased or rotting | No | Remove and bin | New growth should look normal 5–10 days after the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) is corrected. ## What to do 1. Fix the cause: [pH](https://genetixbay.com/knowledge/glossary/ph.md), [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md), roots, feed. 2. Tag the youngest damaged leaf. 3. Watch growth above the tag for 5–10 days. 4. Leave mostly green leaves on; tuck rather than strip. 5. Remove only dead, diseased or fully shaded leaves. ## Common mistakes - Waiting for old leaves to turn green as proof. - Stripping every spotted leaf and slowing the plant. - Changing the feed again before new growth has shown the result. - Ignoring disease that spreads from dead leaves. ## Related - Full article: [Mobile vs immobile nutrients](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) - Answers: [fixing lockout](https://genetixbay.com/knowledge/answers/how-to-fix-nutrient-lockout.md) · [late-flower deficiency](https://genetixbay.com/knowledge/answers/fix-deficiency-in-late-flower.md) - Articles: [how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md) · [defoliation](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) - Terms: [mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md) · [defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md) ## Follow-up questions **Should I remove damaged leaves?** Remove damaged cannabis leaves only when they are more than about half dead, diseased, or rotting. A leaf with burnt tips or some spots is still mostly working tissue feeding the plant. The GenetixBay position is tuck, don't pluck: keep as much healthy leaf area as possible and move leaves out of the way rather than stripping them. **How many leaves can I remove?** Remove as few as you can. Leaves are the plant's solar panels, and the GenetixBay house position is tuck, don't pluck: tuck leaves aside to open bud sites rather than stripping them. Responses vary by cultivar; some tolerate heavy defoliation, others suffer. If you must remove, take only dead, diseased or fully shaded leaves, a few at a time. **How do I know my fix worked?** Your fix worked if the newest leaves come in with normal colour and shape within about 5-10 days and the symptom stops spreading to fresh leaves. Old damage will not disappear, so mark the youngest affected leaf with a twist tie and watch above it. If new growth still shows symptoms, recheck pH, runoff EC and the roots. ## Sources 1. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Cockson P, Landis H, Smith T, Hicks K, Whipker BE, 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 3. Llewellyn D, Golem S, Jones AMP, Zheng Y, 2023. Foliar symptomology, nutrient content, yield, and secondary metabolite variability of cannabis grown hydroponically with different single-element nutrient deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 --- # Do seeds that float mean they are duds? > No. A cannabis seed that floats is not necessarily a dud; the float test is unreliable because it mostly measures air trapped in or on the shell, and many floaters sink within a few hours and germinate normally. The only reliable check is a germination test: 10 seeds on a damp towel at 22–26 °C (72–79 °F) in the dark for 7 days. - Canonical: https://genetixbay.com/knowledge/answers/do-floating-seeds-mean-duds.html - Topic: Germination · Type: Myth check - Evidence: Myth · Status: Draft: awaiting expert review - Full article: [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md) - Also asked as: Does the float test work for seeds? | My seeds are floating, are they dead? | Sink or float: which seeds are good? | Should I throw away seeds that float? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer No. A floating [cannabis seed](https://genetixbay.com/knowledge/glossary/achene.md) is not necessarily dead; the float test mostly measures trapped air, and many floaters sink within hours and [sprout](https://genetixbay.com/knowledge/glossary/seedling.md) normally. Judge seeds with a 7-day [germination](https://genetixbay.com/knowledge/glossary/germination.md) test instead. *Myth*. ## Why A dry seed carries air in and around its [shell](https://genetixbay.com/knowledge/glossary/seed-coat.md). Until water gets in, that air can keep a perfectly viable seed on the surface. Hydration, not viability, decides when it sinks. Seeds take up water over several hours, which is why a 12–24 hour soak is used to speed germination [3]. A floater on hour one often sinks by hour six. Viability is measured by germinating seeds. Seed laboratories test [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) by putting seeds in a germinator for 7–14 days and counting sprouts [4]; the simple home version is 10 seeds on a damp towel. What really kills seeds is storage. Warm, moist storage costs germination capacity, while cold, dry storage at about 5 °C (41 °F) kept it for around six years [2]. Old, slow seed may still be pushed with a 1% [hydrogen peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) protocol [1]. ## The numbers | Check | Reliable? | Notes | |---|---|---| | Float test | No | Mostly measures trapped air | | Colour and hardness | Rough guide | Varies by genetics | | 10-seed towel test | Yes | 22–26 °C (72–79 °F), dark, 7 days | | Lab germination test | Yes | 7–14 days in a germinator | | Soak length | ≤ 24 h | Longer risks oxygen starvation | ## What to do 1. Ignore floating; plant or towel the seed anyway. 2. If a seed floats after 12 hours, tap it under gently, then move on at 24 hours. 3. For a big or old batch, run a 10-seed test first. 4. Store the rest cold, dry and airtight. ## Common mistakes - Binning floaters from a precious pack. - Soaking for days waiting for a seed to sink. - Squeezing seeds to "test" them and cracking good ones. ## Related - Full article: [Germination methods compared](https://genetixbay.com/knowledge/germination/germination-methods.md) - [Seed viability and storage](https://genetixbay.com/knowledge/germination/seed-viability-storage.md) · [Seed germination testing](https://genetixbay.com/knowledge/breeding/seed-germination-testing-qc.md) - [Why won't my seeds germinate?](https://genetixbay.com/knowledge/answers/why-wont-my-seeds-germinate.md) - Terms: [seed coat](https://genetixbay.com/knowledge/glossary/seed-coat.md) · [germination](https://genetixbay.com/knowledge/glossary/germination.md) ## Follow-up questions **How do I test if my seeds are viable?** Test cannabis seed viability with a germination test, not a float test. Place 10 seeds on a damp paper towel in a closed dish at 22–26 °C (72–79 °F) in the dark, check daily for 7 days, then count the seeds with a taproot. Eight sprouts means 80% germination. Old stock can take up to 10 days, so give it a little longer. **Should I soak seeds before planting?** Soaking cannabis seeds before planting is optional. A 12–24 hour soak in room-temperature water speeds water uptake, and one study found soaking improved germination, but soaks longer than 24–36 hours risk starving the seed of oxygen. Never soak for days. Floating during a soak means nothing on its own: plant the seed once it has soaked or cracked. **Do dark seeds germinate better than pale ones?** Darker cannabis seeds are usually mature and harder, but colour varies with genetics, so a pale seed is not necessarily a dud and a dark one is no guarantee. Treat colour as a rough sign of maturity only. Very pale, soft or crushed seeds are poor bets; anything firm deserves a fair germination test before you judge it. ## Sources 1. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 2. Small E, Brookes B, 2012. Temperature and moisture content for storage maintenance of germination capacity of seeds of industrial hemp, marijuana, and ditchweed forms of Cannabis sativa. Journal of Natural Fibers 9(4):240–255. https://doi.org/10.1080/15440478.2012.737179 3. Physical and chemical pretreatments on germination efficiency and seedling growth of Cannabis sativa. Nativa (UFMT). https://periodicoscientificos.ufmt.br/ojs/index.php/nativa/article/view/20226 4. Oregon State University Seed Laboratory. Industrial hemp seed testing. https://seedlab.oregonstate.edu/seed-testing/industrial-hemp --- # Do I need an intake fan or is passive intake enough? > Passive intake is enough for most grow tents: an exhaust fan pulls air out and low, open intake ports let fresh air in, keeping the tent under slight negative pressure so smell can't escape. Make the open intake area about 2–3 times the exhaust duct area. Add an intake fan only for big rooms or long intake runs, and keep it weaker than the exhaust. - Canonical: https://genetixbay.com/knowledge/answers/do-i-need-an-intake-fan.html - Topic: Environment · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) - Also asked as: Is passive intake enough for a grow tent? | How do I get negative pressure in a tent? | Do I need an intake fan? | Tent walls sucking in too much - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Passive intake is enough for most grow tents. The [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) pulls air out through the [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md), and low open ports let fresh air in. Give the intake about **2–3 times the open area of the exhaust duct**. Add an intake fan only for large rooms or long intake runs, and always keep it **weaker than the exhaust**. *Grower practice*. ## Why The exhaust's job is to remove heat and humidity, typically one full tent volume every 1–3 minutes in a lit tent. Stagnant, hot, humid air raises [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) [1] and invites mould [2]. Air has to come in as fast as it leaves. With passive intake the fan creates slight [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md), which draws air through the ports. That same pressure keeps smell inside: every leak flows inwards. An intake fan stronger than the exhaust flips this. The tent goes positive, walls bulge, and unfiltered air escapes through zips and seams. Intake ports too small make the fan work against a vacuum, so real airflow drops and the tent runs hot. ## The numbers | Item | Target | |---|---| | Exhaust, lit tent (no CO₂) | 1 full volume every 1–3 minutes | | Filter and ducting allowance | +25–50 % fan capacity | | Passive intake open area | ≈ 2–3 × exhaust duct area | | Intake position | low, opposite side from the exhaust | | Intake fan, if used | lower airflow than the exhaust | | Walls | bowing gently inwards | ## What to do 1. Put the exhaust and filter high; open intake ports low on the far side. 2. Start with intake area about 2–3 times the exhaust duct area. 3. Watch the walls: gentle inward bow is right. 4. Walls sucking in hard? Open another port. 5. Tent still hot with the fan at full speed? Check the room temperature before buying an intake fan. 6. If you add an intake fan, run it slower than the exhaust and screen it against pests. ## Common mistakes - An intake fan stronger than the exhaust, pushing smell out. - Intake ports high, next to the exhaust, so fresh air short-circuits out. - Too little intake, starving the fan. - Unscreened intakes in summer, pulling in pests. ## Related - Full article: [Airflow](https://genetixbay.com/knowledge/environment/airflow.md) - Guide: [Smell control basics](https://genetixbay.com/knowledge/guides/smell-control-basics.md) - [How do I stop my grow tent from smelling?](https://genetixbay.com/knowledge/answers/how-to-control-grow-smell.md) - [Should my exhaust fan run 24/7?](https://genetixbay.com/knowledge/answers/run-exhaust-fan-24-7.md) - Terms: [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md) · [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) ## Follow-up questions **How big should passive intake be?** Passive intake for a grow tent should have about 2–3 times the open area of the exhaust duct, placed low on the opposite side from the exhaust. With a 150 mm (6 in) exhaust, that means two or three open ports of similar size. Too little intake makes the walls suck in hard and starves the fan; too much, and the walls stop drawing in at all. **Should my tent walls bow in?** Yes, a grow tent's walls should bow gently inwards with the exhaust running. That shows negative pressure: the fan removes air faster than it leaks in, so gaps and zips leak clean room air in rather than smelly air out. If the walls suck in hard and flap, open another low intake; if they are flat or bulge, raise the fan speed or seal leaks. **When do I need an intake fan?** You need an intake fan when passive ports can't supply enough air: large rooms, intake air ducted from another room or outdoors, or long duct runs with bends. Run the intake fan at a lower airflow than the exhaust so the space stays under negative pressure. Screen or filter the intake, because it can pull in pests and dust. ## Sources 1. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 2. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Do I need rooting hormone for clones? > You don't strictly need rooting hormone for cannabis clones, but it clearly helps. In a controlled study, an IBA gel gave 2.1 times the rooting success of a willow-extract gel, and in hemp, hormone-treated cuttings rooted far better than untreated ones. Use an IBA gel or powder (commonly 1,000–3,000 ppm), dip once from a decanted portion, and expect roots in 7–14 days. - Canonical: https://genetixbay.com/knowledge/answers/do-i-need-rooting-hormone.html - Topic: Cloning and mother plants · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: Do I need rooting gel? | Rooting powder or gel for clones? | Can I clone without rooting hormone? | Does willow water work for clones? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Not strictly, but use it. An [IBA](https://genetixbay.com/knowledge/glossary/auxin.md) [rooting gel](https://genetixbay.com/knowledge/glossary/rooting-hormone.md) gave 2.1 times the rooting success of a willow-extract gel in cannabis, and hormone-treated [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) cuttings rooted far better than untreated ones. Expect roots in 7–14 days with hormone. *Supported*. ## Why Rooting hormones are synthetic auxins, mostly indole-3-butyric acid (IBA). Auxin at a fresh wound triggers adventitious roots, so cuttings root sooner and more evenly. The cannabis evidence is direct. IBA gel beat a willow-extract gel 2.1 times on rooting success and 1.6 times on root quality [1]. The hemp evidence agrees. Across eight cultivars, hormone treatments raised rooting success well above untreated controls, but strength and form (1,000 or 3,000 ppm IBA powder, an IBA/NAA dip) made no significant difference [2]. Cannabis is not a hard-to-root plant, so some cuttings root without help. Hormone mainly buys reliability: more of the tray rooted, sooner. ## The numbers | Option | Evidence | Result | |---|---|---| | IBA gel | Cannabis trial [1] | 2.1× rooting success vs willow gel | | IBA powder 1,000–3,000 ppm | Hemp trial [2] | Similar to other hormones; better than none | | IBA/NAA liquid dip | Hemp trial [2] | Similar to other hormones | | Willow extract | Cannabis trial [1] | Weaker rooting and root quality | | No hormone | Hemp trial [2] | Lowest rooting | ## What to do 1. Buy an IBA gel or powder labelled for softwood cuttings. 2. Pour a small amount into a clean cap; discard leftovers. 3. Dip the fresh cut 1–2 cm deep, tap off excess, and stick it straight into the plug. 4. Keep the rest of the setup right: 22–26 °C medium, high humidity, gentle light. ## Common mistakes - Dipping straight into the stock pot and spreading pathogens. - Soaking stems in strong liquid for minutes "to be sure". - Expecting hormone to rescue a cold, soggy plug. - Using old, stale hormone. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [How do I clone a cannabis plant?](https://genetixbay.com/knowledge/answers/how-to-clone-cannabis.md) · [Can I root clones in water?](https://genetixbay.com/knowledge/answers/rooting-clones-in-water.md) - Terms: [rooting hormone](https://genetixbay.com/knowledge/glossary/rooting-hormone.md) · [auxin](https://genetixbay.com/knowledge/glossary/auxin.md) ## Follow-up questions **Is gel or powder better for clones?** Neither is clearly better for cannabis clones. A hemp study compared IBA powders at 1,000 and 3,000 ppm and a liquid IBA/NAA dip and found no significant differences between hormone types or concentrations, while all beat no hormone. Gels stay on the stem and seal the cut, which many growers like. Whatever you use, pour a small portion out and never dip back into the stock. **Does willow water or honey work as rooting hormone?** Not as well. In a controlled cannabis study, a willow-extract gel gave less than half the rooting success of an IBA gel, at 2.1 times lower, and had poorer root quality. Honey has no good evidence in cannabis. If you want reliable, even rooting across a tray of clones, use a product containing indole-3-butyric acid (IBA). **Can too much rooting hormone hurt clones?** Yes. Very strong auxin doses or long soaks can burn the stem base, cause swollen callus with few roots, or yellow the cutting. Stick to the label rate, typically a quick dip for liquids and a light coat for gels or powders at 1,000–3,000 ppm IBA, and tap off the excess. More hormone is not more roots. ## Sources 1. Caplan D, Stemeroff J, Dixon M, Zheng Y. 2018. Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science 98(5):1126-1132. https://doi.org/10.1139/cjps-2018-0038 2. Campbell SM, Anderson SL, Brym ZT, Pearson BJ, 2021. Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.). PLOS ONE 16(7): e0249160. https://doi.org/10.1371/journal.pone.0249160 --- # Do I really need to pH my water? > In coco, rockwool and hydro, yes: adjust every batch to about pH 5.5-6.2 in hydro or 5.8-6.3 in coco, because these media barely buffer pH. In bagged soil, adjusting to pH 6.2-6.8 is good practice but the mix buffers small errors, and your water's alkalinity matters more than its pH. In living soil, generally no. The accepted ranges are soil 6.0-7.0 and soilless 5.5-6.5. - Canonical: https://genetixbay.com/knowledge/answers/do-i-need-to-ph-my-water.html - Topic: pH and EC · Type: How-to - Evidence: Established · Status: Draft: awaiting expert review - Full article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) - Also asked as: Do I need to pH my water? | What happens if I don't pH my water? | Is pH necessary in soil? | Do I need to pH water for living soil? | Can I skip pH in coco? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer In [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) and hydro, yes, every batch: about [pH](https://genetixbay.com/knowledge/glossary/ph.md) 5.5–6.2 in hydro and 5.8–6.3 in coco. In [bagged soil](https://genetixbay.com/knowledge/glossary/potting-mix.md) it's good practice (pH 6.2–6.8), but the mix forgives small errors and your water's [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) matters more than its pH. In [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), generally no. The ranges, soil 6.0–7.0 and [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) 5.5–6.5, are broadly agreed accepted practice. *Established.* ## Why pH sets how soluble each nutrient is. Above about 6.5 in soilless media, iron, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md), zinc and [boron](https://genetixbay.com/knowledge/glossary/boron.md) drop out and phosphorus precipitates with calcium [1][3]. Below about 5.3, iron and manganese can reach toxic levels while calcium and magnesium fall [3]. Soilless media have little buffer. Hydro has none. Whatever pH you pour is close to what the roots get, so it must be right each time [2]. Soil buffers. Peat, compost and lime absorb small pH errors for weeks. The slow threat is alkalinity: bicarbonate in [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md) acts like adding lime at every watering and pushes root-zone pH up over a grow, whatever the water's pH reads [1]. Drift within the range is normal. Aim for a band, not one perfect number. ## The numbers | Medium | Adjust water? | Target | |---|---|---| | [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [NFT](https://genetixbay.com/knowledge/glossary/nft.md) | Every batch | 5.5–6.2 | | Coco, rockwool | Every batch | Feed 5.8–6.3, [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) 5.8–6.5 | | Bagged soil, bottled feed | Recommended | 6.2–6.8 | | Living soil | Generally no | [Root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) ~6.3–7.0 | | Any medium, water alkalinity | Treat if high | Act above 100–150 mg/L as CaCO₃ | ## What to do 1. Calibrate your [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) with pH 7 and pH 4 buffers. 2. Hydro and coco: add nutrients, then adjust pH, every batch. 3. Soil: adjust to 6.2–6.8 and check runoff monthly. 4. Get a water report; acidify if alkalinity is high. 5. Living soil: dechlorinate and leave pH alone. *Safety:* pH down is a concentrated acid. Gloves and eye protection; add acid to water. ## Common mistakes - Skipping pH in coco "because soil doesn't need it". - Chasing exactly 5.8 several times a day. - pH-ing plain water before adding nutrients. - Ignoring alkalinity. ## Related - Full article: [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) - Answers: [how to adjust pH](https://genetixbay.com/knowledge/answers/how-to-adjust-ph.md) · [pH before or after nutrients](https://genetixbay.com/knowledge/answers/ph-before-or-after-nutrients.md) · [fix soil pH](https://genetixbay.com/knowledge/answers/fix-soil-ph.md) - Articles: [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - Terms: [pH](https://genetixbay.com/knowledge/glossary/ph.md) · [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) ## Follow-up questions **What happens if I don't pH my water in hydro?** If you don't pH-adjust in hydro, the solution usually sits well above 6.5 after nutrients go in with alkaline tap water and climbs further as plants take up nitrate. Above about 6.5 in soilless systems, iron, manganese, zinc and boron become less available and new growth yellows between the veins. Hydro has no buffer, so pH every batch. **Do I need to pH water for soil?** In bagged potting soil, pH-adjusting water to about 6.2-6.8 is cheap insurance but not critical every time, because peat, compost and lime in the mix buffer small errors for weeks. What matters more is alkalinity: hard, bicarbonate-rich tap water pushes soil pH up over a grow. Check runoff or pour-through pH monthly to see the trend. **Do I need to pH water for living soil?** You generally do not need to pH-adjust water for living soil. Its organic matter and carbonates buffer the root zone near neutral, about pH 6.3-7.0, and microbes work best when left alone. Use dechlorinated water as it comes unless it is very alkaline. Adjusting to pH 6.0 out of habit is a common mistake. ## Sources 1. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 2. Michigan State University Extension. pH and EC issues still a problem in some greenhouses. https://www.canr.msu.edu/news/ph_and_ec_issues_still_a_problem_in_some_greenhouses 3. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Do mycorrhizae help cannabis? > Mycorrhizae can help cannabis a little, mainly with phosphorus uptake in low-phosphorus soil, but commercial inoculants often don't deliver. In a seedling trial the highest dose raised root length 34% and phosphorus content 24%. A global test of 28 commercial products found most failed to colonise roots. In fully fed hydro or coco, phosphorus is plentiful and colonisation is suppressed, so inoculants are mostly wasted money. - Canonical: https://genetixbay.com/knowledge/answers/do-mycorrhizae-help.html - Topic: Nutrients · Type: How-to - Evidence: Contested · Status: Draft: awaiting expert review - Full article: [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) - Also asked as: Do mycorrhizal fungi help weed? | Is a root inoculant worth it? | Do myco products work? | Should I add mycorrhizae in hydro or coco? | Mycorrhizae for transplanting - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A little, sometimes. [Mycorrhizal fungi](https://genetixbay.com/knowledge/glossary/mycorrhizae.md) colonise cannabis roots and can improve phosphorus uptake, mostly in low-phosphorus soil. In fully fed hydro and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) they add little, and many commercial inoculants fail to colonise at all. *Contested*: small cannabis studies, no yield trials in finished plants. ## Why Arbuscular mycorrhizal fungi extend the root system with fine hyphae and trade phosphorus and some [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md) for plant sugars. The benefit is largest when soil phosphorus is scarce; high soluble phosphorus suppresses colonisation [3]. The cannabis evidence is thin. In a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) float-system trial, the highest spore dose raised root length 34%, stem [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) 21% and phosphorus content 24%, while root mass and nitrogen were unchanged [1]. That is seedlings, not [harvest weight](https://genetixbay.com/knowledge/glossary/yield.md). Product quality is the bigger problem. In a global evaluation of 28 commercial inoculants, most failed to colonise host roots [2]. [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) is where fungi can earn their keep: no tilling, living roots and minimal disturbance keep soil networks intact [4]. ## The numbers | Situation | Likely benefit | Why | |---|---|---| | Living soil, low soluble P | Small, plausible | Native fungi often present already | | [Bagged soil](https://genetixbay.com/knowledge/glossary/potting-mix.md) with bottled feed | Little | P supplied by feed | | Coco or [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), fed every irrigation | Very little | High P suppresses colonisation | | [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [NFT](https://genetixbay.com/knowledge/glossary/nft.md) | None to negligible | Constant P, often sanitised | | Seedlings (one trial) | +34% root length, +24% P content | Highest dose only [1] | ## What to do 1. Decide by system: worth trying only in soil, especially living soil. 2. Buy fresh, dated product; store it cool. 3. Put it in contact with roots at planting or [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md). 4. Keep soluble phosphorus moderate; skip [bloom boosters](https://genetixbay.com/knowledge/glossary/bloom-booster.md). 5. Don't pair it with [peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) or other root-zone sanitisers. ## Common mistakes - Paying for inoculants in a high-P hydro feed. - Sprinkling powder on the surface instead of at the roots. - Expecting bigger buds rather than, at best, slightly better roots. - Killing the fungi with chlorinated or peroxide water. ## Related - Full article: [Living soil](https://genetixbay.com/knowledge/systems/living-soil.md) - Answers: [compost tea](https://genetixbay.com/knowledge/answers/does-compost-tea-work.md) · [super soil](https://genetixbay.com/knowledge/answers/what-is-super-soil.md) - Articles: [organic vs mineral](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) - Terms: [mycorrhizae](https://genetixbay.com/knowledge/glossary/mycorrhizae.md) · [rhizosphere](https://genetixbay.com/knowledge/glossary/rhizosphere.md) ## Follow-up questions **Do mycorrhizae work in hydro or coco?** Mycorrhizae mostly do not pay their way in hydro or coco. These systems feed phosphorus and other nutrients directly at every irrigation, and high phosphorus supply suppresses mycorrhizal colonisation, so the fungi have little to offer. Root-zone sanitisers such as peroxide kill them as well. Save the money for a calibrated meter. **Are mycorrhizal inoculants alive when I buy them?** Often not. A global evaluation of 28 commercial arbuscular mycorrhizal products under greenhouse and field conditions found that most failed to colonise host roots. Spores lose viability with storage time and heat. If you buy one, choose a fresh, dated product, keep it cool, and put it in contact with roots at planting rather than on the surface. **Do mycorrhizae help living soil?** Living soil is the best case for mycorrhizae, because it runs low soluble phosphorus, no sanitisers and no tilling, which lets fungal networks persist between runs. A good compost-rich soil usually already carries native fungi, though, so an inoculant is optional insurance rather than a requirement. There are no controlled cannabis yield trials of inoculated versus uninoculated living soil. ## Sources 1. Kakabouki I, Mavroeidis A, Tataridas A, et al., 2021. Effect of Rhizophagus irregularis on growth and quality of Cannabis sativa seedlings. Plants 10(7):1333. https://doi.org/10.3390/plants10071333 2. Salomon MJ, Demarmels R, Watts-Williams SJ, McLaughlin MJ, Kafle A, Ketelsen C, Soupir A, Bücking H, Cavagnaro TR, van der Heijden MGA, 2022. Global evaluation of commercial arbuscular mycorrhizal inoculants under greenhouse and field conditions. Applied Soil Ecology 169:104225. https://doi.org/10.1016/j.apsoil.2021.104225 3. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 4. USDA Natural Resources Conservation Service. Soil health principles. https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soil/soil-health --- # Do cannabis seedlings need a humidity dome? > Cannabis seedlings don't strictly need a humidity dome, but one helps in dry rooms for the first 3–7 days by holding 65–75% RH around them. Vent it daily, and remove it gradually once the first true leaves are growing well. A dome left closed for days breeds mould and damping-off. If your room already sits at 60–70% RH, skip the dome. - Canonical: https://genetixbay.com/knowledge/answers/do-seedlings-need-a-dome.html - Topic: Germination · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - Also asked as: Should I use a humidity dome for seedlings? | Humidity dome for seedlings, yes or no? | When do I remove the dome from seedlings? | Do seedlings need high humidity? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Cannabis [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) don't strictly need a dome, but one helps for the first 3–7 days in a [dry room](https://genetixbay.com/knowledge/glossary/drying-room.md) by holding 65–75% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). Vent it daily and remove it gradually once [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) are growing. *Grower practice*. ## Why A seedling has a tiny root and thin leaves. In dry air it loses water faster than the root can replace it, so it droops. Humid air lowers that pull. The pull is the [vapour pressure deficit](https://genetixbay.com/knowledge/glossary/vpd.md). At 25 °C, air at 70% RH has a much smaller deficit than air at 40% RH, which follows directly from how vapour pressure rises with temperature [3]. The same still, saturated air suits [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) pathogens. Extension guidance warns against keeping seedlings wet under covers with poor air movement [1][2]. So the dome is a short bridge, not a home. Once the root system grows, the seedling handles normal room humidity. ## The numbers | Stage | RH | Air temperature | Dome | |---|---|---|---| | Days 0–5 (emerging) | 65–75% | 23–27 °C (73–81 °F) | On, vented daily | | Days 5–10 (true leaves) | 65–75% | 23–27 °C | Vents open, lid propped | | Days 10–21 | 60–70% | 23–27 °C | Off | | [Leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md) target | 0.4–0.8 kPa | | | ## What to do 1. Measure room RH first. If it's already 60–70%, skip the dome. 2. If it's dry, dome the seedlings and open the lid for a few minutes each day. 3. Wipe away condensation; it means the air is saturated. 4. Open vents as true leaves form, then prop the lid for a day or two. 5. Remove it fully by about day 10, and keep gentle air moving. ## Common mistakes - Sealing the dome for a week and finding fuzz on the mix. - Removing it in one go in a dry, hot room. - Using a dome to fix [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) (it makes it worse). - Setting a domed tray right under a hot lamp. ## Related - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - [Damping-off](https://genetixbay.com/knowledge/germination/damping-off.md) · [Humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - [Humidity and light for clones](https://genetixbay.com/knowledge/answers/humidity-and-light-for-clones.md) - Terms: [cloning dome](https://genetixbay.com/knowledge/glossary/cloning-dome.md) · [hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) ## Follow-up questions **When should I take the dome off seedlings?** Take the dome off cannabis seedlings gradually once the first set of true leaves is growing, usually around days 5–10. Open the vents first, then prop the lid for a day or two, then remove it. Taking it off in one go in a dry room can make them droop for a day. Condensation running down the lid means it is overdue for venting. **What humidity do seedlings need?** Cannabis seedlings do best at about 65–75% relative humidity with air at 23–27 °C (73–81 °F), a leaf VPD of roughly 0.4–0.8 kPa. Their small roots can't replace water quickly, so very dry air makes them wilt. Much wetter than that, with no airflow, favours damping-off and soft stems. These targets are grower practice rather than cannabis-specific research. **Can a humidity dome cause damping-off?** Yes. A humidity dome left sealed over cannabis seedlings, combined with a wet surface and still air, creates the conditions that damping-off organisms such as Pythium favour. The dome itself isn't the problem; neglect is. Vent it at least once a day, wipe heavy condensation, keep the mix just moist rather than wet, and remove the lid once true leaves are growing. ## Sources 1. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 2. NC State Extension. Damping-off in flower and vegetable seedlings. https://content.ces.ncsu.edu/damping-off-in-flower-and-vegetable-seedlings 3. Allen RG et al., 1998. FAO-56 Chapter 3 (vapour pressure). https://www.fao.org/4/x0490e/x0490e07.htm --- # Do cannabis seeds need light to germinate? > No. Cannabis seeds do not need light to germinate; they need warmth (22–27 °C / 72–81 °F), moisture and air, and germinate well in the dark. Light becomes essential the moment the seedling breaks the surface: start at about 100–200 µmol/m²/s for 18 hours, rising to 150–300. A seedling left in the dark after emerging stretches and weakens within a day or two. - Canonical: https://genetixbay.com/knowledge/answers/do-seeds-need-light-to-germinate.html - Topic: Germination · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md) - Also asked as: Should seeds germinate in the dark or the light? | Do cannabis seeds need light? | Should seeds be kept in the dark? | How much light does cannabis need? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer No. [Cannabis seeds](https://genetixbay.com/knowledge/glossary/achene.md) [germinate](https://genetixbay.com/knowledge/glossary/germination.md) in the dark; they need warmth (22–27 °C / 72–81 °F), moisture and air. Light matters from the moment the [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) breaks the surface, starting at about 100–200 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) for 18 hours. *Supported*. ## Why A germinating [seed runs](https://genetixbay.com/knowledge/glossary/seed-run.md) on its own stored reserves, not [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md). A standard cannabis protocol germinates seeds in closed tubes in the dark and only moves them under light once sprouted [1]. Temperature, not light, sets the pace. [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md) germinates fastest in roughly the 19–30 °C band and slows sharply in the cold [2]. Once the shoot emerges, the reserves run out fast. Young plants given enough daily light produce better roots and more mass; below a [DLI](https://genetixbay.com/knowledge/glossary/dli.md) of about 8 mol/m²/day plugs of other crops were inferior [3]. Later on, light is the biggest yield lever indoors: flower yield rose linearly with light from 120 to 1,800 µmol/m²/s in one trial [4]. ## The numbers | Stage | PPFD (µmol/m²/s) | Hours | DLI (mol/m²/day) | |---|---|---|---| | Germinating seed | None needed | Dark is fine | 0 | | Emerging seedling | 100–200 | 18 | 6–13 | | Seedling, [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) | 150–300 | 18 | 10–19 | | Veg | 300–700 (up to ~900) | 18–24 | 19–58 | | Flower | 800–1,200 | 12–13 | 35–56 | ## What to do 1. Germinate in a warm, dark place: a cupboard, or a tub on a gentle heat mat. 2. Check daily for a [taproot](https://genetixbay.com/knowledge/glossary/taproot.md); plant at 0.5–2 cm. 3. Put the planted seed under the light straight away, or within hours of emergence. 4. Start at 100–200 µmol/m²/s, and raise intensity as true leaves appear. ## Common mistakes - Germinating on a sunny windowsill that cooks or dries the towel. - Leaving emerged seedlings in a dark cupboard "one more day". - Blasting new seedlings with full flowering intensity. ## Related - Full article: [Germination methods compared](https://genetixbay.com/knowledge/germination/germination-methods.md) - [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [What light schedule for seedlings?](https://genetixbay.com/knowledge/answers/light-schedule-for-seedlings.md) - Terms: [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) · [germination](https://genetixbay.com/knowledge/glossary/germination.md) ## Follow-up questions **How much light does cannabis need?** Cannabis needs about 100–300 µmol/m²/s as a seedling, 50–150 as an unrooted clone, 300–700 (up to about 900) in veg and 800–1,200 in flower, more with added CO2. In a controlled indoor trial, flower yield rose in a straight line from 120 to 1,800 µmol/m²/s with no change in potency. Measure PPFD at the canopy; wattage and lumens don't tell you. **When do seedlings need light?** A cannabis seedling needs light as soon as its hook or cotyledons break the surface, usually 1–3 days after planting a sprouted seed. Before that, light does nothing for it. Start gentle, around 100–200 µmol/m²/s on 18 hours, and raise it to 150–300 as the first true leaves open. Leaving an emerged seedling in the dark makes it stretch thin and pale. **Does light hurt germinating seeds?** Light itself doesn't hurt a germinating cannabis seed, but what comes with it can. A lamp or windowsill can heat and dry a paper towel or plug, killing a fresh taproot. That's why towels and tubs are kept in a warm, dark place. Once planted under a light, keep the surface just moist and check the medium temperature stays near 22–27 °C. ## Sources 1. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 2. Geneve RL, et al., 2022. Temperature limits for seed germination in industrial hemp (Cannabis sativa L.). Crops 2(4):415–427. https://doi.org/10.3390/crops2040029 3. Runkle E. The benefits of lighted plugs. Michigan State University Extension. https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs 4. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # Do sticky traps work? > Sticky traps work as a monitoring tool, not a cure. Yellow cards catch fungus gnats, whiteflies, winged aphids and leafminers; blue cards are somewhat more attractive to thrips. They catch only flying adults, so they never fix larvae in the medium or spider mites. Count catches weekly and replace the card: a rising count is your early warning, and a falling count shows the real treatment is working. - Canonical: https://genetixbay.com/knowledge/answers/do-sticky-traps-work.html - Topic: Pests · Type: How-to - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) - Also asked as: Do yellow sticky traps work? | Blue sticky traps for thrips | Will sticky traps get rid of fungus gnats? | Where should I put sticky traps in my tent? | Yellow or blue sticky cards? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) work well for what they are: a counter of flying adult pests. Yellow cards catch [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md), [winged aphids](https://genetixbay.com/knowledge/glossary/alate.md) and [leafminers](https://genetixbay.com/knowledge/glossary/leafminer.md); blue cards pull somewhat more [thrips](https://genetixbay.com/knowledge/glossary/thrips.md). Counted weekly they give early warning, but they rarely control a pest by themselves. *Established* as a monitoring method. ## Why Insects fly to the colour. Many small flying pests are drawn to yellow, and thrips are drawn to blue and yellow [1][2]. Only adults are caught. Fungus gnat larvae live and feed in the top few centimetres of wet medium, so cards do nothing about the stage that chews roots [3]. Control comes from drier media plus Bti, [nematodes](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md) or [soil predatory mites](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md) [4]. Wingless pests are invisible to cards. [Spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) are found with a lens on leaf undersides, not on cards [5]. Trends beat totals. A count that climbs week on week is the signal to act; a count that falls over 2–3 weeks confirms a treatment is working [3]. ## The numbers | Pest | Card colour | Placement | |---|---|---| | Fungus gnats | Yellow | Flat on or just above the medium | | Whiteflies, winged aphids, leafminers | Yellow | Just above the canopy, several per room | | Thrips | Blue or yellow | Just above the canopy | | Spider, broad and [russet mites](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md) | Not caught | Use a 10–20x lens | | Counting | Weekly | Count by type, record, replace | ## What to do 1. Hang one or two cards per small tent, more in rooms, from day one. 2. Put gnat cards low and foliar-pest cards just above the canopy. 3. Count weekly by pest type and write it down. 4. When counts rise, identify the pest and treat the cause: watering for gnats, predators for thrips. 5. Remove or reduce cards while releasing flying [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md), which they also catch. ## Common mistakes - Expecting cards to clear an infestation. - Leaving the same card up for months, so nobody knows what is new. - Looking for spider mites on cards. - Letting cards touch buds or hair. ## Related - Full article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) - Answers: [Preventing pests indoors](https://genetixbay.com/knowledge/answers/how-to-prevent-pests-indoors.md) · [Small white bugs in soil](https://genetixbay.com/knowledge/answers/small-white-bugs-in-soil.md) - Articles: [Thrips](https://genetixbay.com/knowledge/pests/thrips.md) · [Whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md) - Terms: [sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md) · [Bti](https://genetixbay.com/knowledge/glossary/bti.md) ## Follow-up questions **Will sticky traps get rid of fungus gnats?** Sticky traps will not get rid of fungus gnats on their own, because they catch only flying adults while the larvae keep feeding in the wet medium. Fix the watering first by letting the top 2–5 cm (1–2 in) of soil dry, then use Bti, Steinernema feltiae nematodes or soil predatory mites against larvae. Use yellow cards to count adults weekly and confirm numbers are falling. **Do sticky traps catch spider mites?** Sticky traps do not catch spider mites usefully, because spider mites are wingless and walk or drift between plants rather than fly to coloured cards. Find them with a 10–20x lens on leaf undersides, looking for oval mites about 0.5 mm long, round clear eggs and pale stippling on the upper leaf surface. A branch tapped over white paper also shows moving specks. **Where should I put sticky traps?** Place sticky traps for fungus gnats flat on or just above the surface of the medium, and traps for thrips, whiteflies and winged aphids just above the canopy, away from buds and hair. Use several in a room, because whiteflies do not fly far. Mark a counting area, count catches by type every week, write the number down and replace the card. ## Sources 1. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects 2. UC IPM. Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html 3. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf 4. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ 5. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # Does compost tea work for cannabis? > Compost tea is not a meaningful fertiliser for cannabis, and its disease-control effects are inconsistent. Reviews found some teas suppressed some diseases in some trials, with no reliable recipe, and there are no controlled cannabis trials. Adding molasses, kelp or fish to brew grew E. coli and Salmonella 10- to 10,000-fold in one study. If you use it, apply it to living soil, not flowers, within hours of brewing. - Canonical: https://genetixbay.com/knowledge/answers/does-compost-tea-work.html - Topic: Nutrients · Type: How-to - Evidence: Contested · Status: Draft: awaiting expert review - Full article: [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) - Also asked as: Does aerated compost tea work? | Is ACT good for weed plants? | What are the benefits of compost tea? | Does compost tea feed the plant? | Should I add molasses to compost tea? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Not reliably. [Compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) carries too little nutrition to feed cannabis, and its disease-suppression effects vary from trial to trial with no dependable recipe [1]. No controlled cannabis trials exist. It is harmless on [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) if brewed cleanly and used fresh, but it is not a substitute for amendments. *Contested.* ## Why Compost tea is a water extract of compost, brewed with or without aeration. It is dilute: whatever nutrients it carries are a small fraction of a flowering plant's demand. The disease claims are mixed. A major review found that some teas suppressed some plant diseases, but results depended on compost, brewing method, crop and pathogen, and no single recipe worked across systems [1]. Food safety matters. When commercial nutrient supplements were added to brewing tea, E. coli O157:H7, Salmonella and faecal coliforms grew by 1–4 log units (10- to 10,000-fold) [2]. That is a strong reason never to spray tea on flowers. The microbes are fragile. [Chloramine](https://genetixbay.com/knowledge/glossary/chloramine.md) in [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) doesn't gas off on standing; long-contact carbon or ascorbic acid removes it [3]. The house position on sugar applies: [molasses](https://genetixbay.com/knowledge/glossary/molasses.md) feeds microbes, not the plant. ## The numbers | Factor | Grower practice | |---|---| | Brew time, aerated | 24–36 h | | Water | Dechlorinated, chloramine removed | | Use within | ~4 h of brewing | | Where | Soil surface or drench only | | Flowers | Never | ## What to do 1. Build the soil first: compost, castings and [top-dresses](https://genetixbay.com/knowledge/glossary/top-dressing.md) do the feeding. 2. If you brew, use clean equipment and dechlorinated water. 3. Skip or minimise sugary and protein-rich supplements. 4. Apply as a soil drench soon after brewing. 5. Judge it on your own side-by-side plants, not on promises. ## Common mistakes - Treating tea as the plant's feed. - Spraying tea on buds in flower. - Brewing with chloraminated tap water. - Leaving tea standing for days, then using it. ## Related - Full article: [Living soil](https://genetixbay.com/knowledge/systems/living-soil.md) - Answers: [mycorrhizae](https://genetixbay.com/knowledge/answers/do-mycorrhizae-help.md) · [super soil](https://genetixbay.com/knowledge/answers/what-is-super-soil.md) - Articles: [water quality and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - Terms: [compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) · [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) ## Follow-up questions **Does compost tea add nutrients?** Compost tea adds very little nutrition. It is a dilute water extract of compost, so it carries small amounts of soluble nitrogen, potassium and other ions, far below what a flowering cannabis plant needs. Its value, if any, is biological. Feed living soil with top-dressed amendments and compost itself, and treat tea as optional. **Is it safe to spray compost tea on buds?** No, do not spray compost tea on cannabis buds. Teas can carry and grow human pathogens: in one study, nutrient supplements added to brewing compost tea made E. coli and Salmonella multiply by 1 to 4 log units. Wet flowers also invite bud rot. Keep teas to the soil, and never to flowers people will smoke or eat. **Should I add molasses to compost tea?** Molasses in compost tea feeds the microbes in the brew, not the plant, which makes its own sugars by photosynthesis. It speeds microbial growth, including unwanted bacteria, and drains dissolved oxygen faster. If you brew tea, keep any sugar small, aerate well, use dechlorinated water and apply the tea within a few hours. ## Sources 1. Scheuerell S, Mahaffee W, 2002. Compost tea: principles and prospects for plant disease control. Compost Science & Utilization 10(4):313-338. https://doi.org/10.1080/1065657X.2002.10702095 2. Ingram DT, Millner PD, 2007. Factors affecting compost tea as a potential source of Escherichia coli and Salmonella on fresh produce. Journal of Food Protection 70(4):828-834. https://doi.org/10.4315/0362-028X-70.4.828 3. Water Quality Association, 2014. Chloramine fact sheet. https://wqa.org/wp-content/uploads/2022/09/2014_Chloramine.pdf --- # Does foliar feeding work on cannabis? > Foliar feeding works on cannabis as a quick, small top-up, not as a feed. Leaves absorb little and unevenly, so a spray can green new growth within days for magnesium, iron or zinc in veg, but it cannot supply nitrogen, potassium or calcium in useful amounts. Use it in veg only, at low light or lights-off, and never spray flowers. Fix the root zone at the same time. - Canonical: https://genetixbay.com/knowledge/answers/does-foliar-feeding-work.html - Topic: Nutrients · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Also asked as: Do foliar nutrient sprays work? | Can I spray leaves with Cal-Mag? | Is it OK to foliar feed in flower? | How much Epsom salt for a foliar spray? | Can foliar feeding replace root feeding? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer As a quick top-up, yes; as a feed, no. A [foliar spray](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) can green new cannabis leaves within days for magnesium, iron or [zinc](https://genetixbay.com/knowledge/glossary/zinc.md) in veg, but leaves absorb too little to supply nitrogen, potassium or calcium. Spray in veg only, at low light or lights-off, and never on flowers. *Supported* for [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) fixes; the specific rates are *Grower practice*. ## Why Leaves are built to keep water in, not let solutes through. The cuticle limits uptake, and how much enters depends on the nutrient, the formulation, humidity and the leaf itself, which makes results uncertain [1]. Small doses work for nutrients needed in small amounts. A few mg/L of iron or a few grams of [Epsom salt](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md) per litre can correct a micronutrient or magnesium shortfall on the sprayed leaves. Large doses can't. A flowering plant takes up hundreds of mg of nitrogen and potassium per litre of water it drinks; no spray competes with that. Mobility decides reach. Calcium and boron barely move in the phloem, so sprayed calcium stays where it lands [2]. Iron, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md) and zinc [deficiencies](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) show on new growth first, which is where a spray should be aimed [3]. ## The numbers | Spray | Rate (grower practice) | Use for | |---|---|---| | Epsom salt | 2–5 g/L + wetting agent | Magnesium, veg | | [Iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md) ([DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md) or [EDTA](https://genetixbay.com/knowledge/glossary/edta.md)) | ~50–100 mg/L Fe | Iron [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md), veg | | [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md) or [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) | ~0.5–1 g/L | Sprayed new leaves only | | [Zinc sulfate](https://genetixbay.com/knowledge/glossary/zinc-sulfate.md) | 0.1–0.5 g/L of product | Zinc, veg | | Any spray on buds | None | Never | ## What to do 1. Diagnose first: check root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md). 2. Fix the root-zone cause; the spray only buys time. 3. Spray at lights-off or low light, with a wetting agent. 4. Test one branch and wait 24 h for burn. 5. Stop once buds form. ## Common mistakes - Using foliar feeds instead of fixing pH. - Spraying under full light and scorching leaves. - Spraying flowers. - Expecting foliar calcium to protect new growth. ## Related - Full article: [Building a cannabis feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Answers: [deficiency in late flower](https://genetixbay.com/knowledge/answers/fix-deficiency-in-late-flower.md) · [macro vs micronutrients](https://genetixbay.com/knowledge/answers/macro-vs-micronutrients.md) - Articles: [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md) · [bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) - Terms: [foliar feeding](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) · [immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md) ## Follow-up questions **How much Epsom salt for a foliar spray?** Grower practice for a cannabis magnesium foliar spray is about 2-5 g/L of Epsom salt (magnesium sulfate heptahydrate) with a wetting agent, applied in veg at lights-off or low light. Test on one branch first and wait a day for burn. New leaves green within days, but fix the root-zone cause, usually pH, potassium excess or a low-magnesium feed. **Can I foliar feed in flower?** No, do not foliar feed cannabis in flower once buds are forming. Water and residues sit in the flowers, which invites bud rot, and anything sprayed may end up in what is smoked. Correct flower-stage deficiencies through the root zone instead: check pH and runoff EC first, then adjust the feed itself. **Can I foliar feed Cal-Mag for calcium deficiency?** Foliar calcium helps only the leaves it lands on. Calcium barely moves in the phloem, so a spray of calcium nitrate or calcium chloride at about 0.5-1 g/L can help sprayed new leaves in veg but cannot reach new growth that forms later. Most calcium problems are delivery problems: fix VPD, roots and root-zone pH. ## Sources 1. Fernández V, Brown PH, 2013. From plant surface to plant metabolism: the uncertain fate of foliar-applied nutrients. Frontiers in Plant Science 4:289. https://doi.org/10.3389/fpls.2013.00289 2. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 3. Cockson P, Landis H, Smith T, Hicks K, Whipker BE, 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # How much electricity does a home grow use? > A home grow uses about 300 kWh per photoperiod run in a 2 x 2 ft tent (150 W LED plus fans) and about 850 kWh in a 4 x 4 ft tent (500 W LED plus fans), with 4 weeks of veg at 18/6 and 10 weeks of flower at 12/12. At 0.15 per kWh that is roughly 45 and 130 in local currency. Dehumidifiers and heaters add more. - Canonical: https://genetixbay.com/knowledge/answers/electricity-cost-of-growing.html - Topic: Basics · Type: Numbers - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Also asked as: Electric bill for growing weed | Cost to run a grow light | How much does it cost to grow at home? | How many kWh does a grow tent use? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A small [home grow](https://genetixbay.com/knowledge/glossary/home-grow.md) uses about 300 kWh per [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) run in a 2 x 2 ft tent and about 850 kWh in a 4 x 4 ft tent, with 4 weeks of veg at [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) and 10 weeks of flower at [12/12](https://genetixbay.com/knowledge/glossary/12-12.md). The light is most of it. *Established*: it's arithmetic, kWh = watts × hours ÷ 1,000. ## Why Indoor growing is energy-hungry at scale. One estimate put indoor cannabis at about 1% of US electricity use [1]. At home the same physics applies, just smaller. The light dominates, and [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) sets its cost. Good [LEDs](https://genetixbay.com/knowledge/glossary/led.md) exceed 2.5–3 µmol/J [3]. In one trial, the best LED fixture gave about 27% more flower per dollar of electricity than a [double-ended HPS](https://genetixbay.com/knowledge/glossary/hps.md), at about 1.1–1.3 cents per mole of light against 1.6 cents at 0.10 per kWh [2]. Hours matter as much as watts. 18/6 veg uses 50% more lighting energy per day than 12/12 flower, and [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) uses double. Climate gear is the hidden bill: a [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) or heater can rival the light. ## The numbers | Setup | Daily use | Run total | At 0.15/kWh | |---|---|---|---| | 2 x 2 ft: 150 W LED + 40 W [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md), veg 18/6 | 3.7 kWh | 28 days ≈ 100 kWh | | | Same, flower 12/12 | 2.8 kWh | 70 days ≈ 195 kWh | | | **2 x 2 ft photo run** | | **≈ 300 kWh** | **≈ 45** | | 4 x 4 ft: 500 W LED + 80 W fans, veg 18/6 | 10.9 kWh | 28 days ≈ 305 kWh | | | Same, flower 12/12 | 7.9 kWh | 70 days ≈ 555 kWh | | | **4 x 4 ft photo run** | | **≈ 860 kWh** | **≈ 130** | | 2 x 2 ft [auto](https://genetixbay.com/knowledge/glossary/autoflower.md), 20/4 for 11 weeks | 4.0 kWh | ≈ 305 kWh | ≈ 46 | | Add: 300 W dehumidifier, half the time | 3.6 kWh | +350 kWh per 14 weeks | +53 | Use your own tariff. ## What to do 1. Use the light's real wall wattage, ideally read from a plug-in energy meter. 2. Add every device and its daily hours. 3. Buy fixture efficacy (µmol/J); it pays back every day. 4. Keep the tent in a room that is already near target temperature and [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). 5. Keep continuous load under 80% of the circuit rating [4]. ## Common mistakes - Using a fixture's "equivalent" wattage. - Forgetting fans run 24 hours. - Ignoring the dehumidifier or heater. ## Related - Full article: [Your first grow](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Guide: [Electrical and water safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md) - Answers: [fire risk](https://genetixbay.com/knowledge/answers/grow-room-electrical-safety.md) · [what wattage for my tent](https://genetixbay.com/knowledge/answers/what-wattage-light-for-my-tent.md) · [LED vs HPS](https://genetixbay.com/knowledge/answers/led-vs-hps.md) - Terms: [photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) · [LED](https://genetixbay.com/knowledge/glossary/led.md) ## Follow-up questions **How do I calculate my grow's electricity use?** To calculate a grow's electricity use, multiply each device's real wattage by the hours it runs per day and divide by 1,000 to get kWh per day. Add up the light, fans, dehumidifier and heater, multiply by the days in each stage, then by your price per kWh. A plug-in energy meter gives the real numbers instead of label figures. **Do autoflowers use more electricity?** Autoflowers use more lighting power per day than flowering photoperiods, because they run 18–20 hours of light rather than 12, but they finish in about 9–14 weeks with no separate veg. A 150 W auto run at 20/4 for 11 weeks uses about 300 kWh with fans, close to a photoperiod run with 4 weeks of veg in the same tent. **Are LEDs cheaper to run than HPS?** Efficient LEDs are cheaper to run than HPS for the same light at the plants. In one trial, the best LED fixture made about 2.5 µmol of light per joule against 1.7 for a double-ended HPS, and produced about 27% more flower per dollar of electricity. Whether LED or HPS grows better buds is a separate, open question GenetixBay is testing in a Bay Trial. ## Sources 1. Mills E, 2012. The carbon footprint of indoor Cannabis production. Energy Policy 46:58-67. https://doi.org/10.1016/j.enpol.2012.03.023 2. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988 3. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 4. National Fire Protection Association. NFPA 70, National Electrical Code (continuous loads at 80 % of branch-circuit rating; GFCI requirements). https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70 --- # Are fabric pots better than plastic pots? > Fabric pots are better than plastic pots for hand-watered soil, mainly because they dry faster and run cooler. Water evaporates through the walls, which cuts overwatering risk and kept substrate about 6 °C (11 °F) cooler than black plastic in one nursery study. The cost is more frequent watering. Plastic suits automated drip, coco and growers who water rarely. - Canonical: https://genetixbay.com/knowledge/answers/fabric-pots-vs-plastic-pots.html - Topic: Systems · Type: Comparison - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - Also asked as: Fabric pots vs plastic pots for cannabis | Are fabric grow bags worth it? | Air pots vs fabric pots | Do fabric pots stop root circling? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Fabric pots](https://genetixbay.com/knowledge/glossary/fabric-pot.md) are better than plastic for hand-watered soil, because they dry faster and run cooler, which makes [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) harder. In one nursery study fabric containers ran about 6 °C (11 °F) cooler than black plastic in summer [1]. The cost is more frequent watering. Plastic is fine, and sometimes better, for drip-fed [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and growers who water rarely. *Supported* for temperature and water loss; yield effects in cannabis are untested. ## Why Water evaporates through fabric walls. That sidewall loss cooled the substrate and raised total water use in nursery trials [1]. Faster drying matters because roots need air. A container that [drains](https://genetixbay.com/knowledge/glossary/runoff.md) and dries back pulls fresh air into the mix; one that stays saturated starves roots of oxygen [2]. Roots that reach a fabric wall meet dry air and stop, so they branch inside the pot rather than circling the wall (*Grower practice*, widely observed). [Pot volume](https://genetixbay.com/knowledge/glossary/pot-size.md) matters more than pot material. Bigger rooting volume generally means bigger plants across crops [3], and the GenetixBay position is that bigger pots yield more within reason, traded against how often you can water. ## The numbers | | Fabric pot | Plastic pot | |---|---|---| | Drying speed | Fast (walls breathe) | Slow (top and holes only) | | Substrate temperature | About 6 °C (11 °F) cooler in hot conditions [1] | Warmest, especially black | | Overwatering risk | Lower | Higher with dense mixes | | Watering frequency | Higher | Lower | | Root circling | Less (air-pruned at wall) | More | | Mess and spills | Wicks onto floors, needs a tray | Clean | | Reuse | Wash; wears out in a few runs | Lasts years, easy to disinfect | **Verdict:** pick fabric for hand-watered soil and warm rooms; pick plastic for automated coco or when you can't water often, and give it an airy mix either way. ## What to do 1. Choose fabric if you hand-water soil, especially if you tend to overwater. 2. Choose plastic, or larger fabric, if you can't check pots daily in flower. 3. Use a free-draining mix with 20–35% [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) in either. 4. Stand fabric pots on a raised tray so the base breathes and runoff drains away. 5. Water by pot weight, not by schedule. ## Common mistakes - Switching to fabric and keeping the same watering schedule, then [underwatering](https://genetixbay.com/knowledge/glossary/underwatering.md) in flower. - Standing fabric pots in a saucer of runoff. - Buying a small pot to save water when the real limit is root volume. ## Related - Full article: [Growing in soil](https://genetixbay.com/knowledge/systems/soil.md) - Answers: [gravel in the bottom of pots](https://genetixbay.com/knowledge/answers/gravel-in-bottom-of-pots.md) · [how often to water](https://genetixbay.com/knowledge/answers/how-often-to-water.md) - Terms: [fabric pot](https://genetixbay.com/knowledge/glossary/fabric-pot.md) · [air pot](https://genetixbay.com/knowledge/glossary/air-pot.md) · [pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) ## Follow-up questions **Do fabric pots need more water?** Yes, fabric pots need more frequent watering than plastic, because water evaporates through the side walls as well as being used by the plant. Nursery research found fabric containers had the highest sidewall water loss of the containers tested. In hot rooms and small fabric pots in late flower, that can mean watering daily. Lift the pot rather than assuming. **Do fabric pots prevent root rot?** Fabric pots lower the risk of root rot from overwatering because the walls breathe and the mix dries back faster, pulling air into the root zone. They don't prevent it outright. A dense, peaty mix watered daily still drowns roots in a fabric pot, so use a free-draining mix with 20–35% perlite and water when the pot is light. **What about air pots?** Air pots are rigid plastic pots with holes or cones in the walls, aiming for the same effect as fabric: air at the edge, drier walls and fewer circling roots. They dry quickly, much like fabric, and need frequent watering. They spill water and mix more easily when hand-watered, so they suit growers watering slowly or on drip. ## Sources 1. Nambuthiri S, Geneve RL, Sun Y, Wang X, Fernandez RT, Niu G, Bi G, Fulcher A. 2015. Substrate temperature in plastic and alternative nursery containers. HortTechnology 25(1):50–56. https://doi.org/10.21273/HORTTECH.25.1.50 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 3. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # What is the difference between fan leaves and sugar leaves? > Fan leaves are the big palmate leaves, usually 5–9 serrated leaflets on long stalks, that do most of a cannabis plant's photosynthesis and carry few trichomes. Sugar leaves are the small, resin-coated leaves growing out of the buds, trimmed at harvest and often kept for processing. GenetixBay's house rule is 'tuck, don't pluck': keep fan leaves working and move them aside instead of stripping them. - Canonical: https://genetixbay.com/knowledge/answers/fan-leaves-vs-sugar-leaves.html - Topic: Basics · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - Also asked as: Fan leaves vs sugar leaves | What are sugar leaves? | Big leaves vs small leaves on buds | Should I remove fan leaves? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) are the large palmate leaves with usually 5–9 long [leaflets](https://genetixbay.com/knowledge/glossary/leaflet.md) that power the plant. [Sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) are the small leaves growing out of the buds, frosted with [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md), trimmed at harvest. Keep fan leaves working: "tuck, don't pluck". *Established* botany; the tucking rule is a GenetixBay house position. ## Why Fan leaves are the solar panels. They are the plant's main [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) surface and store [mobile nutrients](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md) the plant draws on late in flower [3]. They carry few glandular trichomes. Sugar leaves sit inside the flower cluster. As the [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) switch to flowering, new leaves shrink and come with fewer leaflets, ending as small leaves among the [bracts](https://genetixbay.com/knowledge/glossary/bract.md) [1]. Glandular trichomes there make [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), so sugar leaves are resinous [2], though less so than the bracts. That's why they're treated differently. Fan leaves feed the buds while the plant grows; sugar leaves are trimmed for [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) and a smoother smoke, and the trim is often kept. ## The numbers | | Fan leaf | Sugar leaf | |---|---|---| | Leaflets | Usually 5–9 (up to 11) | 1–5, small | | Where | Main stem and branches, on long stalks | Growing out of the buds | | Trichomes | Few | Many | | Job | Photosynthesis, nutrient store | Part of the flower cluster | | At harvest | Removed first, discarded | Trimmed to the bud outline, often kept | ## What to do 1. In veg and flower, tuck fan leaves aside so light reaches [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md). 2. Remove only dead, diseased or fully yellow leaves. 3. Let lower fans [fade](https://genetixbay.com/knowledge/glossary/senescence.md) slowly in the last 2–3 weeks; that's normal. 4. At harvest, take fan leaves off first, then trim sugar leaves wet or dry, as you prefer. 5. Save [sugar-leaf trim](https://genetixbay.com/knowledge/glossary/sugar-trim.md), dry and cool, for processing. ## Common mistakes - Stripping healthy fans early "to send energy to the buds". - Throwing away resinous sugar-leaf trim. - Judging [deficiencies](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) on sugar leaves instead of fan leaves. ## Related - Full article: [Cannabis plant biology](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - Answers: [how to trim buds](https://genetixbay.com/knowledge/answers/how-to-trim-buds.md) · [what schwazzing is](https://genetixbay.com/knowledge/answers/what-is-schwazzing.md) · [defoliating autos](https://genetixbay.com/knowledge/answers/can-i-defoliate-autoflowers.md) - Article: [Defoliation and lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) - Terms: [fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md) · [sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) ## Follow-up questions **Should I remove fan leaves?** GenetixBay's house rule is 'tuck, don't pluck': maximise leaf area, like a solar farm for the buds, and tuck fan leaves out of the way of bud sites rather than stripping them. Responses vary by cultivar: some clones lost most of their fans with no effect, others suffered. Stripping within reason doesn't seem to hurt yield, but tucking helps more in the founder's experience. **What do I do with sugar leaf trim?** Sugar leaf trim carries real resin, so many growers keep it rather than throwing it away. Trim sugar leaves back to the outline of the bud, then store the trim cool and dry for processing such as kief or solventless hash. Fan leaves carry far fewer trichomes and are usually discarded or composted. **Why are my fan leaves yellowing in late flower?** Fan leaves yellowing slowly from the bottom in the last two to three weeks of flower is normal: the plant moves mobile nutrients such as nitrogen from old leaves into the buds. Fast yellowing earlier in flower, or yellowing that climbs quickly, points to hunger, a pH problem or root trouble. Check pH and runoff before adding nutrients. ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 3. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # Should I feed every time I water? > Whether to feed every watering depends on the medium. In coco, rockwool and hydro, yes: every irrigation carries nutrient solution at stage strength, about EC 1.2-1.8 mS/cm in veg and 1.6-2.2 in flower. In bagged soil, feed every second or third watering at EC 0.8-1.6 once the starter charge runs out. In living soil, water only and top-dress. Runoff EC tells you if the rhythm is right. - Canonical: https://genetixbay.com/knowledge/answers/feed-every-watering.html - Topic: Nutrients · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Also asked as: Should I do feed, water, feed? | Do I add nutrients every watering? | Feed then plain water: is that right? | How often should I give nutrients in soil? | Do I feed every watering in coco? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer It depends on the medium. In [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) and hydro, feed every irrigation at stage strength. In [bagged soil](https://genetixbay.com/knowledge/glossary/potting-mix.md), feed every second or third watering at [EC](https://genetixbay.com/knowledge/glossary/ec.md) 0.8–1.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) once the mix's own charge runs out. In [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md), water only and feed the soil by [top-dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md). *Grower practice*, built on how each medium holds nutrients. ## Why Inert media hold almost no plant food, so the solution you pour in is the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md)'s entire supply [1]. Plain-water irrigations in coco or rockwool dilute it, then the next feed spikes it again. Potting soil is different. Peat, compost and the starter fertiliser hold nutrients on exchange sites and buffer what you add, so a feed every second or third watering keeps up without stacking salts. More is not better. In deep-flow hydro, doubling [feed strength](https://genetixbay.com/knowledge/glossary/input-ec.md) from 2 to 4 mS/cm raised solution nutrients but not yield or quality [2]. The aim is steady supply, not maximum strength. [Runoff](https://genetixbay.com/knowledge/glossary/runoff.md) or [pour-through](https://genetixbay.com/knowledge/glossary/pour-through.md) EC is the check: it shows whether salts are building up or running short [3]. ## The numbers | Medium | Feed how often | Feed EC (mS/cm) | |---|---|---| | Coco, rockwool, drip | Every irrigation | 1.2–1.8 veg, 1.6–2.2 flower | | [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [NFT](https://genetixbay.com/knowledge/glossary/nft.md) | Constant (reservoir) | Same ranges | | Bagged soil | Every 2nd–3rd watering, after weeks 2–4 | 0.8–1.6 | | Living soil | Never; water only | n/a (top-dress) | ## What to do 1. Identify your medium and pick the rhythm above. 2. Measure feed EC including your water. 3. Check runoff EC weekly in coco and monthly in soil. 4. Runoff more than ~0.8–1.0 mS/cm above input and rising: feed weaker or less often. 5. Runoff well below input: the plant wants more; raise strength slightly. ## Common mistakes - Plain-water irrigations in coco. - Hydro-strength feeds every watering in fertilised soil. - Feeding a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) in fresh potting mix that already holds 2–4 weeks of food. - Never measuring runoff, so [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) goes unseen. ## Related - Full article: [Building a cannabis feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Answers: [full-strength feeding chart?](https://genetixbay.com/knowledge/answers/full-strength-feeding-chart.md) · [when soil runs out](https://genetixbay.com/knowledge/answers/when-does-soil-run-out-of-nutrients.md) · [how often to water](https://genetixbay.com/knowledge/answers/how-often-to-water.md) - Articles: [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) · [coco](https://genetixbay.com/knowledge/systems/coco.md) · [soil](https://genetixbay.com/knowledge/systems/soil.md) - Terms: [runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md) · [feed chart](https://genetixbay.com/knowledge/glossary/feed-chart.md) ## Follow-up questions **Should I feed every watering in coco?** Yes, feed every watering in coco. Coco holds little usable nutrition, so plain-water irrigations starve the plant and swing root-zone EC and pH. Feed at stage strength, about EC 1.2-1.8 mS/cm in veg and 1.6-2.2 in flower, to 10-30% runoff each time. If runoff EC climbs well above input, lower feed EC slightly rather than skipping feeds. **Is feed, water, feed right for soil?** Feed, water, feed is a sound soil rhythm once the potting mix's starter charge has run out, usually after 2-4 weeks. Feed at about EC 0.8-1.6 mS/cm every second or third watering and give plain pH-adjusted water in between. Check runoff EC monthly: if it keeps rising, feed less often or at lower strength. **Can I just use a weaker feed every watering in soil?** Yes, a weaker feed every watering in soil works as well as feed, water, feed, as long as the total delivered is similar. Many growers run about half their normal soil strength each time. The rule is the same either way: watch runoff EC, and back off if it climbs more than about 0.8-1.0 mS/cm above what you pour in. ## Sources 1. Sonneveld C, Voogt W, 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Hershkowitz JA, Westmoreland FM, Bugbee B, 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 3. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download --- # How should I feed autoflowers? > Feed autoflowers lighter than photoperiods but don't starve them: plain water or about EC 0.4–0.6 mS/cm for the first two weeks, 0.8–1.2 in weeks 3–4 and 1.2–1.8 in flower, starting at a quarter to half the label rate. Quality bagged soil often needs water only for 2–3 weeks. Feed through to harvest; don't flush. Hunger in week 3 costs yield an auto can't recover. - Canonical: https://genetixbay.com/knowledge/answers/feeding-autoflowers.html - Topic: Basics · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Also asked as: Do autoflowers need less nutrients? | Autoflower feeding schedule | How much nutrients for autos? | What EC should I feed my autoflower? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Feed an [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) lightly early and steadily later: about [EC](https://genetixbay.com/knowledge/glossary/ec.md) 0.4–0.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) for the first two weeks (or water only in good soil), 0.8–1.2 in weeks 3–4, and 1.2–1.8 in flower. Start at a quarter to half the label rate and feed right through to harvest. *Grower practice*, house-endorsed. ## Why An auto can't catch up. It flowers by age, so a hungry or burnt plant in week 3 builds a smaller frame and flowers on it anyway. Both [overfeeding](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) and underfeeding cost yield. Nutrient rate matters in veg. In coir-based media, cannabis grew best at a moderate fertiliser rate, with poorer growth above and below it [1]. Nitrogen is the one to taper, not everything. Lower nitrogen late can raise [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) percentage while lowering total yield [2]. The GenetixBay approach is to cut nitrogen back near the finish while keeping P, K, Ca, Mg, S and the [micros](https://genetixbay.com/knowledge/glossary/micronutrient.md) fed. [Flushing](https://genetixbay.com/knowledge/glossary/flushing.md) doesn't help. In controlled work, withholding fertiliser before harvest tended to lower dry mass and cannabinoid yield [3]. It starves the plant during its heaviest weeks. ## The numbers | Week from [sprouting](https://genetixbay.com/knowledge/glossary/germination.md) | Feed EC (mS/cm, [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md)) | [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md) | [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md) | |---|---|---|---| | 1 | 0–0.4 | 0–200 | 0–280 | | 2 | 0.4–0.6 | 200–300 | 280–420 | | 3 | 0.6–1.0 | 300–500 | 420–700 | | 4 | 0.8–1.2 | 400–600 | 560–840 | | 5 | 1.0–1.4 | 500–700 | 700–980 | | 6–7 | 1.2–1.6 | 600–800 | 840–1,120 | | 8–harvest | 1.4–1.8 | 700–900 | 980–1,260 | Soil: often water only until week 3, then feed at about half label rate. [pH](https://genetixbay.com/knowledge/glossary/ph.md) 6.2–6.8 in soil, 5.8–6.2 in coco. ## What to do 1. Start at a quarter to half label strength; raise it as the plant grows. 2. Check [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) EC weekly; if it climbs well above your input, cut back. 3. Read the leaf tips: slight [burnt tips](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) mean back off, pale lower leaves mean feed more. 4. Keep feeding at stage strength to the chop. Taper only nitrogen, if you mix single salts. ## Common mistakes - Full-strength chart doses from week one. - Starving the plant "because autos are small". - Flushing for the last two weeks. - Blaming nutrients before checking pH and [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md). ## Related - Full article: [Photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Answers: [when to stop feeding](https://genetixbay.com/knowledge/answers/when-to-stop-feeding-before-harvest.md) · [full-strength feeding charts](https://genetixbay.com/knowledge/answers/full-strength-feeding-chart.md) · [feed every watering?](https://genetixbay.com/knowledge/answers/feed-every-watering.md) - Articles: [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) · [feeding basics](https://genetixbay.com/knowledge/guides/feeding-basics.md) - Terms: [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) · [EC](https://genetixbay.com/knowledge/glossary/ec.md) ## Follow-up questions **Do autoflowers need less nutrients than photoperiods?** Autoflowers usually need less nutrient in total than photoperiods because they are smaller and live only 9–14 weeks, so start at a quarter to half of the label rate. They do not need weaker feed in flower: by then most run EC 1.2–1.8 mS/cm in coco. Underfeeding is as costly as overfeeding, because an auto can't extend its veg to catch up. **Should I flush my autoflower before harvest?** No, don't flush an autoflower before harvest. Pre-harvest flushing is a myth, and harmful: plain water in the last one to two weeks starves the plant while it packs on most of its final weight and resin, and controlled work found it tended to lower yield. Keep feeding at stage strength. If you mix single salts, taper only nitrogen in the final weeks. **When should I start feeding an autoflower?** Start feeding an autoflower at about week 2–3 from sprouting. In coco, feed lightly at every watering from the first true leaves, at EC 0.4–0.6 mS/cm. In quality bagged soil, water only until about week 3, when the seedling has used the starter charge. Raise strength gradually and judge by leaf tips: slight burnt tips mean back off. ## Sources 1. Caplan D, Dixon M, Zheng Y. 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307-1312. https://doi.org/10.21273/HORTSCI12401-17 2. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 3. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 --- # Is it worth fixing a deficiency in late flower? > It depends what you're seeing. Lower fan leaves yellowing in the last 2-3 weeks is normal remobilisation, not a deficiency, so leave it. A real problem that spreads to sugar leaves and new growth with 3 or more weeks to go is worth fixing, usually by correcting root-zone pH or runoff EC and keeping the feed at stage strength. Never flush, and never foliar spray buds. - Canonical: https://genetixbay.com/knowledge/answers/fix-deficiency-in-late-flower.html - Topic: Nutrients · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Mobile vs immobile nutrients: reading old vs new leaves](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) - Also asked as: Deficiency in week 7 of flower: what do I do? | How do I fix a late flower deficiency? | Is it too late to fix my plant? | Yellow leaves in the last weeks of flower | Should I feed more at the end? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Only if it's real and you have time. Lower [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) fading in the last 2–3 weeks is normal and needs no fix. A problem spreading to [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) and fresh growth with 3 or more weeks left is worth correcting, usually through root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md), with the feed held at stage strength. *Grower practice.* ## Why Late flower is when the plant remobilises. Nitrogen, phosphorus, potassium and magnesium are mobile, so the plant strips them from old leaves to fill the flowers [4]. Lower-leaf [fade](https://genetixbay.com/knowledge/glossary/senescence.md) near harvest is the design, not a fault. Real shortages still cost you. In a hydroponic trial, withholding single elements through flowering changed cannabis yield and secondary metabolites depending on the element [1]. A spreading [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) in week 5 of an 8–9 week flower has time to do damage. Nitrogen is the exception. Lower nitrogen late in flower raised [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) concentration while trimming yield [2], which is why GenetixBay tapers nitrogen and nothing else. Starving the plant to "clean" it doesn't help. Longer nutrient withdrawal cut dried bud weight in [flushing](https://genetixbay.com/knowledge/glossary/flushing.md) trials [3]. ## The numbers | What you see | Weeks to harvest | Action | |---|---|---| | Lower fans yellowing, top green | ≤3 | Normal; keep feeding | | Yellowing climbing fast, sugar leaves affected | ≥3 | Check pH and EC; correct | | [Interveinal yellowing](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) on new growth | Any | Check root-zone pH first | | [Burnt tips](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) spreading, high runoff EC | Any | [Root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md), then feed | | Whole plant pale in week 2–4 of flower | 5+ | Raise feed to stage strength | ## What to do 1. Calibrate the meter; measure input and runoff pH and EC. 2. Decide: normal fade or spreading problem? 3. Correct pH or [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) first. 4. Keep feeding at late-flower strength; taper only nitrogen. 5. Watch new sugar leaves for 5–10 days. ## Common mistakes - Feeding harder to green up fading fans. - Flushing to "fix" a deficiency. - [Foliar](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) spraying buds. - Panicking over normal end-of-season colour. ## Related - Full article: [Mobile vs immobile nutrients](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) - Articles: [per-element tricks](https://genetixbay.com/knowledge/nutrients/per-element-tricks.md) · [yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) - Answers: [stop feeding before harvest?](https://genetixbay.com/knowledge/answers/when-to-stop-feeding-before-harvest.md) · [damaged leaves](https://genetixbay.com/knowledge/answers/do-damaged-leaves-recover.md) - Terms: [mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md) · [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) ## Follow-up questions **Is yellowing at the end of flower normal?** Yes, yellowing of the lower and middle fan leaves in the last 2-3 weeks of flower is normal. The plant moves nitrogen, phosphorus, potassium and magnesium out of old leaves into the flowers, so the leaves fade from the bottom up. Keep feeding at stage strength, taper only nitrogen, and judge harvest by trichomes, not leaf colour. **Can I foliar spray a deficiency in flower?** No, do not foliar spray cannabis once buds have formed. Spray residue and moisture sit in the flowers, which invites bud rot and leaves material in what you will smoke. Fix a flowering-stage deficiency through the roots: check pH and runoff EC, then adjust the feed itself. Leaves that are already damaged will not recover. **Should I raise my feed strength late in flower?** No, do not raise feed strength late in flower to fix fading leaves. Most late fading is normal remobilisation, and higher EC adds salt build-up risk without raising yield. Keep phosphorus, potassium, calcium, magnesium, sulfur and micros at normal late-flower strength and taper only nitrogen. Raise a single element only for a confirmed, spreading shortage. ## Sources 1. Llewellyn D, Golem S, Jones AMP, Zheng Y, 2023. Foliar symptomology, nutrient content, yield, and secondary metabolite variability of cannabis grown hydroponically with different single-element nutrient deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 2. Saloner A, Bernstein N, 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 3. Alden MJ, Faust JE, 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 4. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # How do I fix soil pH that is too high or too low? > Raise soil pH with agricultural or dolomitic lime and lower it with elemental sulfur; both take weeks, so build them into the mix before planting. In a pot mid-grow, correct slowly through the water instead: pH-adjust each watering and treat hard water's alkalinity. Aim for a root zone of pH 6.0-7.0, ideally 6.2-6.8, and act if runoff stays below about 5.8 or above 7.3. - Canonical: https://genetixbay.com/knowledge/answers/fix-soil-ph.html - Topic: pH and EC · Type: How-to - Evidence: Established · Status: Draft: awaiting expert review - Full article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) - Also asked as: How do I raise soil pH? | How do I lower soil pH? | Should I use lime to fix soil pH? | My runoff pH is 7.5: what do I do? | How do I test soil pH in a pot? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Raise it with agricultural or dolomitic lime; lower it with [elemental sulfur](https://genetixbay.com/knowledge/glossary/sulfur-burner.md). Both take weeks, so they belong in the mix before planting. Mid-grow, correct slowly through the water: pH-adjust each watering and neutralise [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md)'s [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md). Target a [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) of [pH](https://genetixbay.com/knowledge/glossary/ph.md) 6.0–7.0, ideally 6.2–6.8. *Established.* ## Why Soil pH is buffered. [Peat](https://genetixbay.com/knowledge/glossary/peat.md), compost, clay and lime resist change, which is why one watering at the "wrong" pH barely matters and why fixing a real drift takes time [1][2]. Lime is a base that dissolves slowly and raises pH; dolomitic lime also supplies magnesium. Elemental sulfur lowers pH only after soil bacteria oxidise it to sulfuric acid, which needs warmth, moisture and weeks [4]. The usual cause of high soil pH in pots is the water, not the soil. Bicarbonate alkalinity acts like adding lime at every watering [1]. Treat the water and the drift stops. Out-of-range pH starves the plant even when the feed is complete: high pH cuts iron, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md), [zinc](https://genetixbay.com/knowledge/glossary/zinc.md) and phosphorus; low pH cuts calcium, magnesium and [molybdenum](https://genetixbay.com/knowledge/glossary/molybdenum.md) [4]. Measure the root zone with a [pour-through](https://genetixbay.com/knowledge/glossary/pour-through.md), not the water you pour in [3]. ## The numbers | Root-zone pH (soil) | Meaning | Action | |---|---|---| | Below ~5.8 | Too low | Water at 6.8–7.0; lime in next mix | | 6.0–7.0 | Accepted range | Leave it; drift is normal | | 6.2–6.8 | Sweet spot | n/a | | Above ~7.3 | Too high | Acidify water; water at 6.0–6.2 | | Water alkalinity above 100–150 mg/L CaCO₃ | Will push pH up | Neutralise with acid | ## What to do 1. Calibrate the meter and do a pour-through. 2. Confirm the trend over two or three readings. 3. Too high: acidify the water and water at 6.0–6.2. 4. Too low: water at 6.8–7.0; skip ammonium-heavy feeds. 5. Next run: build lime or [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) into the mix weeks before planting. *Safety:* acids and lime are irritants. Gloves, eye protection and a dust mask for powders. ## Common mistakes - Dumping lime or sulfur on a flowering plant and expecting a quick fix. - Swinging water pH hard in both directions. - Testing the water instead of the root zone. - Ignoring water alkalinity. ## Related - Full article: [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) - Articles: [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) · [water quality](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - Answers: [do I need to pH?](https://genetixbay.com/knowledge/answers/do-i-need-to-ph-my-water.md) · [how to adjust pH](https://genetixbay.com/knowledge/answers/how-to-adjust-ph.md) - Terms: [pH buffer](https://genetixbay.com/knowledge/glossary/ph-buffer.md) · [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) ## Follow-up questions **How do I lower soil pH in a pot quickly?** To lower pot soil pH during a grow, water at the low end of the soil range, about pH 6.0-6.2, and neutralise most of your water's alkalinity with a mineral acid. Ammonium-containing feeds also acidify slightly. Elemental sulfur is too slow to help this run. Recheck runoff or pour-through pH weekly and stop once it is back in range. **How do I raise soil pH in a pot quickly?** To raise pot soil pH during a grow, water at the top of the soil range, about pH 6.8-7.0, and avoid ammonium-heavy feeds. Fine dolomitic or agricultural lime top-dressed and watered in works slowly; liquid lime products act faster but still take days. Check runoff weekly and stop once it is back above about 6.0. **How do I test soil pH in a pot?** Test pot soil pH with a pour-through: water normally, wait 30 minutes to 2 hours, pour about 0.3-0.5 L of pH-adjusted water on top, catch the first 50 mL that drains and measure it with a calibrated meter. A slurry of one part soil to two parts distilled water is another option. Track the trend, not single readings. ## Sources 1. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 2. Michigan State University Extension. pHix it! Getting substrate pH just right. https://www.canr.msu.edu/news/phix-it-getting-substrate-ph-just-right 3. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download 4. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # Should I use full-strength nutrients from the feeding chart? > Usually not at first. Feeding charts are written as upper limits, often for hard water and vigorous plants. Start at about half to three-quarters of the chart and steer by EC instead: about 0.6-1.0 mS/cm for seedlings, 1.2-1.8 in veg and 1.6-2.2 in flower for coco and hydro, and 0.8-1.6 in soil. Raise strength only if runoff EC and leaves say the plant wants more. - Canonical: https://genetixbay.com/knowledge/answers/full-strength-feeding-chart.html - Topic: Nutrients · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Also asked as: Should I use half-strength nutrients? | Is the feeding chart too strong? | Should I start at quarter strength? | Why are my tips burning on the recommended dose? | Do I follow the bottle's feed schedule? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Not to start with. Treat a bottle's chart as a ceiling, begin at about half to three-quarters of it, and steer by [EC](https://genetixbay.com/knowledge/glossary/ec.md): roughly 0.6–1.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) for [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md), 1.2–1.8 in veg and 1.6–2.2 in flower in [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and hydro, and 0.8–1.6 in soil. Raise strength only when [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) and new growth ask for it. *Supported.* ## Why Charts are generic. They don't know your water, which may already carry 0.2–0.8 mS/cm, your medium or your cultivar. Full chart strength on top of [hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) or fertilised soil is a common route to [tip burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md). The research backs a moderate feed. In deep-flow hydro, doubling input from 2 to 4 mS/cm raised solution nutrients but not yield or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) [1]. Elevated phosphorus raised [leachate](https://genetixbay.com/knowledge/glossary/watering-to-runoff.md) P without improving yield or quality [2]. Charts quoting ppm are ambiguous: the same 1.0 mS/cm reads 500 ppm on one meter and 700 on another [3]. A 700-scale chart followed on a 500-scale meter overfeeds by about 40%. ## The numbers | Stage | Coco / hydro EC (mS/cm) | Soil EC (mS/cm) | [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md) (coco/hydro) | |---|---|---|---| | Seedling, clone | 0.6–1.0 | Water only, weeks 1–4 | 300–500 | | Veg | 1.2–1.8 | 0.8–1.6 | 600–900 | | Flower | 1.6–2.2 | 0.8–1.6 | 800–1,100 | | Late flower | 1.2–1.8 | 0.8–1.6 | 600–900 | All values are total solution EC, including the water. ## What to do 1. Measure your water's EC. 2. Mix at half to three-quarters of the chart and read the EC. 3. Adjust to the stage target above, not the chart's number. 4. Check runoff EC; more than ~0.8–1.0 mS/cm above input means back off. 5. Step up 0.1–0.2 mS/cm at a time if lower leaves pale early. ## Common mistakes - Running full chart plus every additive in the range. - Following a ppm chart without knowing its scale. - Ignoring the EC your tap water already brings. - Reading dark green, [clawed leaves](https://genetixbay.com/knowledge/glossary/leaf-clawing.md) as "healthy and hungry". ## Related - Full article: [Building a cannabis feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Answers: [feed every watering?](https://genetixbay.com/knowledge/answers/feed-every-watering.md) · [TDS vs EC meter](https://genetixbay.com/knowledge/answers/tds-meter-vs-ec-meter.md) - Articles: [EC vs ppm scales](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) · [brown, burnt tips](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) - Terms: [nutrient burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) · [feed chart](https://genetixbay.com/knowledge/glossary/feed-chart.md) ## Follow-up questions **What strength should I feed seedlings?** Feed cannabis seedlings and fresh clones at about EC 0.6-1.0 mS/cm in coco or hydro, which is often a quarter to half of a bottle's veg rate. In fresh potting soil, feed nothing for the first 2-4 weeks because the mix's starter charge already covers them. Raise strength gradually towards the veg range of 1.2-1.8 mS/cm as roots establish. **How do I know if I'm feeding too strong?** You are feeding too strong when leaf tips burn and the burn creeps inward, leaves turn very dark and clawed, and runoff EC climbs more than about 0.8-1.0 mS/cm above what you pour in. Cut feed EC by 10-20%, check root-zone pH, and judge on new growth. Burnt tips never heal, so watch fresh leaves. **Does feeding stronger give bigger yields?** No, feeding stronger does not give bigger cannabis yields beyond a moderate EC. In deep-flow hydro, doubling feed from 2 to 4 mS/cm raised solution nutrients but not yield or cannabinoids, and phosphorus above about 30-60 mg/L gave no gain in several trials. Extra strength mainly raises cost, salt build-up and the risk of tip burn. ## Sources 1. Hershkowitz JA, Westmoreland FM, Bugbee B, 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 2. Westmoreland FM, Bugbee B, 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 3. Prasad L, Meehan M, 2025. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923. https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test --- # How much yield should I expect per watt or per square foot? > Expect roughly 100–500 g of dry flower per square metre (about 10–50 g, or 0.3–1.6 oz, per square foot) indoors, rising with light; well-run research rooms at 750–900 µmol/m²/s measured 500–750 g/m². Worked back from those trials, that is roughly 0.7–2 g per watt of efficient LED. A 4 x 4 ft tent therefore gives about 150–700 g, set mainly by canopy light. - Canonical: https://genetixbay.com/knowledge/answers/grams-per-watt.html - Topic: Basics · Type: Numbers - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: Grams per watt | Yield per square foot | How much will a 4x4 yield? | What is a good g/W? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Indoors, expect roughly 100–500 g of dry flower per m² (about 10–50 g, 0.3–1.6 oz, per ft²), rising with canopy light. Well-run research rooms reached 500–750 [g/m²](https://genetixbay.com/knowledge/glossary/yield.md). Worked back from the trials, that's about 0.7–2 g per watt of efficient [LED](https://genetixbay.com/knowledge/glossary/led.md). *Supported* for the light response; the g/W range is our arithmetic. ## Why Yield follows light. Dry flower rose linearly from 116 g/m² at 120 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) to 519 g/m² at 1,800 µmol/m²/s [1], and a second trial found the same proportional response [3]. Another group measured 500–750 g/m² at 750–900 µmol/m²/s and 0.22–0.36 g per mole of photons [2]. Watts become photons through [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md). Good LEDs exceed 2.5–3 µmol/J [4]. At 2.5 µmol/J, an average 900 µmol/m²/s needs about 360 W per m² of fixture, if the light lands on the canopy. So g/W is a ratio of two numbers you can estimate. At about 300 g/m² under 450 W/m² (a less efficient fixture), you get ~0.7 g/W. At 720 g/m² under 360 W/m², ~2 g/W. Tent walls and edges waste some light, so home tents sit lower. ## The numbers | Canopy light (µmol/m²/s) | Dry yield, g/m² | g/ft² | 2 x 2 ft tent | 4 x 4 ft tent | |---|---|---|---|---| | ~120 (weak) | ~115 | ~11 | ~40 g | ~165 g | | ~600 | ~230 | ~21 | ~80 g | ~330 g | | ~900 | ~300 | ~28 | ~110 g | ~430 g | | 750–900, dialled in [2] | 500–750 | 46–70 | 180–270 g | 720–1,080 g | | ~1,800 (very high) | ~520 | ~48 | ~185 g | ~750 g | Rows 1–3 and 5 interpolate the linear response in [1]; cultivars differ. ## What to do 1. Use g/m² to compare grows; quote g/W only with the fixture's wall watts. 2. Measure average PPFD across the canopy, not the centre point. 3. Raise light gradually towards 800–1,200 µmol/m²/s in flower. 4. Buy efficacy (µmol/J), not "equivalent watts". ## Common mistakes - Using a fixture's marketed "equivalent" wattage. - Comparing g/W across different run lengths. - Chasing g/W with light the plants can't use without CO₂. - Expecting more light to raise [THC](https://genetixbay.com/knowledge/glossary/thc.md): it raises grams, not potency [1]. ## Related - Full article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Answers: [yield per plant](https://genetixbay.com/knowledge/answers/how-much-does-one-plant-yield.md) · [what wattage for my tent](https://genetixbay.com/knowledge/answers/what-wattage-light-for-my-tent.md) · [increasing yield](https://genetixbay.com/knowledge/answers/how-to-increase-yield-indoors.md) - Terms: [grams per watt](https://genetixbay.com/knowledge/glossary/grams-per-watt.md) · [photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) · [yield](https://genetixbay.com/knowledge/glossary/yield.md) ## Follow-up questions **Is grams per watt a good measure?** Grams per watt is a rough measure. It mixes the light fixture's efficiency with the grower's skill and the run length, so a long-flowering cultivar or an efficient LED inflates it. Grams per square metre is better for comparing grows, and grams per mole of photons is the most physical: one trial measured 0.22–0.36 g of dry flower per mole. **How much will a 4x4 tent yield?** A 4 x 4 ft (1.44 m²) tent yields roughly 150–700 g of dry flower, depending mostly on canopy light. At about 300 g/m², a reasonable target for moderate light, that's around 430 g (15 oz). Research rooms at 750–900 µmol/m²/s reached 500–750 g/m², about 720–1,080 g in a 4 x 4, but a first grow should plan on the low end. **Does more light always mean more yield?** More light meant more yield in the best indoor trial: dry flower rose in a straight line from 116 to 519 g/m² as canopy light rose from 120 to 1,800 µmol/m²/s at ambient CO2, with no change in potency. In practice, above about 1,200 µmol/m²/s without added CO2 plants often show stress, and each extra gram costs more electricity. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988 3. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 4. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # Should I put gravel or rocks in the bottom of my pots? > No, you don't need gravel or rocks in the bottom of a pot, and the idea that a drainage layer is necessary to stop waterlogging is a myth. Its effect on drainage is small and disputed, and it takes away root volume. A free-draining mix with 20–35% perlite or pumice, open drainage holes and an empty saucer do the job better. - Canonical: https://genetixbay.com/knowledge/answers/gravel-in-bottom-of-pots.html - Topic: Systems · Type: Myth check - Evidence: Myth · Status: Draft: awaiting expert review - Full article: [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - Also asked as: Should I put rocks in my pots for drainage? | Does a gravel layer help drainage? | Do pots need a drainage layer? | Clay pebbles in the bottom of the pot - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer No. A gravel or rock layer isn't needed, and the belief that a pot must have one to avoid waterlogging is a *Myth*. Its effect on [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) is small and disputed, and it costs [root volume](https://genetixbay.com/knowledge/glossary/pot-size.md). Mix 20–35% [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) or pumice through the whole pot, keep the holes open and empty the saucer. ## Why Every container has a saturated zone at the bottom, the perched water table, because gravity can't pull water out of fine pores against their capillary grip [3]. The classic extension argument is that gravel makes this worse. Water doesn't cross easily from fine mix into coarse gravel, so the saturated zone shifts up into the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) [2]. Measured pots tell a more modest story. A 2025 study found drainage layers mostly reduced total water held in the container slightly, and almost never increased it; 60 mm of coarse sand worked best, and the study didn't measure plant growth [1]. So the effect is small in either direction. What isn't disputed is the cost: every centimetre of gravel is a centimetre roots can't use, and bigger root volume generally means bigger plants. [Air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) comes from the mix. Perlite or pumice mixed through raises air-filled porosity in every layer, not just the bottom [3]. ## The numbers | Option | Effect on drainage | Cost | |---|---|---| | Gravel layer, 3–6 cm | Small; slight drop in water held [1] | Lost root volume, heavier pot | | Coarse sand layer, 6 cm | Most consistent drop in water held [1] | Lost root volume | | 20–35% perlite or pumice mixed through | Air space throughout | None | | [Fabric pot](https://genetixbay.com/knowledge/glossary/fabric-pot.md) | Fast drying through walls | More frequent watering | | Raised tray or pot feet | Free drainage from holes | None | ## What to do 1. Fill the pot with one uniform mix, top to bottom. 2. Mix in 20–35% perlite or pumice. 3. Check the drainage holes are clear; cover large ones with mesh. 4. Stand the pot on feet or a raised tray. 5. Empty the saucer within 30 minutes of watering. ## Common mistakes - Using gravel to rescue a dense, peaty mix. - Pots without drainage holes, "made safe" with rocks. - Pots standing in their own runoff. - Shrinking root volume in an already small pot. ## Related - Full article: [Growing in soil](https://genetixbay.com/knowledge/systems/soil.md) - Answers: [water runs through or pools](https://genetixbay.com/knowledge/answers/water-runs-through-or-pools.md) · [fabric vs plastic pots](https://genetixbay.com/knowledge/answers/fabric-pots-vs-plastic-pots.md) · [best soil for cannabis](https://genetixbay.com/knowledge/answers/best-soil-for-cannabis.md) - Terms: [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) · [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) ## Follow-up questions **Does gravel in the bottom of a pot cause a perched water table?** For decades extension advice held that a gravel layer raises the perched water table, the saturated zone at the bottom of a container, because water doesn't move easily from fine mix into coarse gravel. A 2025 study measuring real pots found drainage layers mostly reduced total water held, slightly. Either way the effect is small, and the gravel still costs root volume. **What should I put in the bottom of my pot instead?** Put nothing in the bottom of the pot except the same mix that fills the rest. Mix 20–35% perlite or pumice evenly through the whole volume, make sure the drainage holes are open, and stand the pot on a raised tray or feet so water can escape. A piece of mesh over large holes keeps mix in without blocking drainage. **Can I use clay pebbles at the bottom of a soil pot?** You can, but there's no good reason to. A layer of clay pebbles takes up root space and adds little drainage compared with mixing perlite or pumice through the soil. If a pot has very large holes, a single layer of pebbles or a mesh disc stops mix washing out. Save the clay pebbles for hydroponic systems, where they belong. ## Sources 1. Rowe A, 2025. Effect of drainage layers on water retention of potting media in containers. PLOS ONE 20(2):e0318716. https://doi.org/10.1371/journal.pone.0318716 2. Trinklein D, 2023. Gardening advice: fact or fiction. Missouri Environment and Garden, University of Missouri IPM. https://ipm.missouri.edu/meg/2023/1/gardeningMyths-DT 3. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 --- # Is an indoor grow a fire risk? > An indoor grow is a real fire risk only when it's set up badly: overloaded circuits, daisy-chained power strips, damaged cords, heaters and water near plugs. Keep continuous load under 80 % of the circuit (about 1,440 W on a 15 A, 120 V circuit; about 2,900 W on 16 A, 230 V), use RCD/GFCI protection, give cables drip loops and fit a working smoke alarm. - Canonical: https://genetixbay.com/knowledge/answers/grow-room-electrical-safety.html - Topic: Equipment · Type: How-to - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Also asked as: Can a grow tent catch fire? | Electrical safety for a home grow | Is it safe to run a grow light from a power strip? | How many watts can I run on one circuit? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer An indoor grow is a fire risk when it's improvised: **overloaded circuits, daisy-chained power strips, damaged cords, heaters, and water near plugs**. Keep continuous load **under 80 %** of the circuit (about **1,440 W on 15 A, 120 V**; about **2,900 W on 16 A, 230 V**) [2], use **RCD/GFCI protection**, give every cable a **drip loop** and fit a **working smoke alarm**. *Established*. ## Why Most home electrical fires start at overloaded outlets, damaged cords and misused extension leads [1]. A grow runs lights, [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) and often a heater or [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) for hours on end, which is exactly the load that heats a weak connection. Continuous loads, those running 3 hours or more, should stay under 80 % of the breaker rating under the North American electrical code [2]; it's good practice everywhere. Water and mains in one small box add shock risk. An RCD or GFCI cuts power within a fraction of a second if current leaks to ground [3][4]. ## The numbers | Circuit | Full capacity | 80 % continuous limit | |---|---|---| | 120 V, 15 A | 1,800 W | **1,440 W** (12 A) | | 120 V, 20 A | 2,400 W | **1,920 W** (16 A) | | 230 V, 13 A plug (UK) | ~3,000 W | **~2,400 W** | | 230 V, 16 A | 3,680 W | **~2,900 W** | | RCD/GFCI trip | | 30 mA or less | **Example:** a 320 W [LED](https://genetixbay.com/knowledge/glossary/led.md), fans, a 300 W dehumidifier and a pump draw about 680 W. Add a 1,500 W heater on the same 15 A, 120 V circuit and you're at ~2,180 W: over the limit. ## What to do 1. List everything on the circuit; keep the total under 80 %. 2. Use an RCD/GFCI outlet or adapter; test it monthly. 3. One overload-protected strip, straight into the wall, mounted high. 4. Drip-loop every cable; plugs above the highest water level. 5. Rated hangers for lights; drivers ventilated. 6. A tested smoke alarm, and an extinguisher rated for electrical fires. 7. Feel plugs after hours at full load: warm is a warning, hot is a fault. **Safety:** unplug before reaching into a reservoir; new circuits are a job for a licensed electrician. ## Common mistakes - Daisy-chained strips and thin extension cords. - A space heater on the lighting circuit. - Plugs on the floor beside saucers. ## Related - Full article: [Your first grow](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Guide: [Electrical and water safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md) - [How much electricity does a home grow use?](https://genetixbay.com/knowledge/answers/electricity-cost-of-growing.md) - [How do I keep my grow tent warm in winter?](https://genetixbay.com/knowledge/answers/how-to-keep-a-grow-tent-warm.md) ## Follow-up questions **How many watts can I run on one circuit?** On a 120 V circuit, a 15 A breaker supplies 1,800 W and a 20 A breaker 2,400 W, but continuous loads such as grow lights should stay under 80 %: about 1,440 W and 1,920 W. On a 230 V, 16 A circuit that is about 2,900 W continuous. Divide watts by volts to get amps, and count everything else on that circuit, not just the grow. **Is it safe to use a power strip for grow lights?** A single quality power strip with its own overload protection, rated for the load and mounted off the floor, is acceptable for grow lights and fans. Never plug strips or extension cords into each other, never run a heater or dehumidifier through a thin extension cord, and replace any strip or plug that feels warm, smells hot or shows discolouration. Heat at a plug is a fire warning. **Do I need a GFCI or RCD for my grow?** Yes. Any grow with water, pumps or wet floors should run from an outlet protected by a GFCI (North America) or RCD (UK, Europe, Australia) that trips at 30 mA or less. It cuts power within a fraction of a second if current leaks to ground through water or a person. Test it with its button monthly; a plug-in adapter works where outlets lack one. ## Sources 1. US Fire Administration. Electrical fire safety (overloaded outlets, extension cords, smoke alarms). https://www.usfa.fema.gov/prevention/home-fires/prevent-fires/electrical/ 2. National Fire Protection Association. NFPA 70, National Electrical Code (continuous loads at 80 % of branch-circuit rating; GFCI requirements). https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70 3. US Occupational Safety and Health Administration. Electrical safety: hazards and controls. https://www.osha.gov/electrical 4. UK Health and Safety Executive. Electrical safety and you: RCDs, overloading and inspection. https://www.hse.gov.uk/electricity/ --- # Should I hang the whole plant or cut branches to dry? > Hang the whole plant if your dry room runs on the dry side or you want the slowest dry, because the stem and leaves slow water loss. Cut branches if space is tight or the room is humid, since smaller pieces dry faster and evenly. Wet-trimmed buds go on a rack and dry fastest. Whatever the method, aim for 7–14 days at 15–21 °C (60–70 °F) and 55–62% RH. - Canonical: https://genetixbay.com/knowledge/answers/hang-whole-plant-or-branches.html - Topic: Harvest and cure · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Also asked as: Should I hang the whole plant to dry? | Hang branches or whole plant? | Can I dry buds on a rack? | Whole-plant hang vs drying rack - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Hang the whole plant](https://genetixbay.com/knowledge/glossary/whole-plant-hang.md) when your [dry room](https://genetixbay.com/knowledge/glossary/drying-room.md) runs dry or you want the slowest possible dry. Cut it into branches when space is tight or the room is humid. [Wet-trimmed](https://genetixbay.com/knowledge/glossary/wet-trim.md) buds go on a rack. Every method aims for the same end: 7–14 days at 15–21 °C (60–70 °F) and 55–62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). *Grower practice*. ## Why The aim is a slow, even dry. Air-drying shifts the oil away from volatile [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) [2], and drying fast and warm loses more of them. A whole plant, with its stem and leaves, gives up water slowly. Too slow is also a risk. Wet, still air and crowded branches let [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) and other moulds keep growing during the dry [4]. In a humid room, smaller pieces with gaps between them are safer. The finish line is the same either way. Flower should reach [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55–0.65, the ASTM range that guards against mould without making buds brittle [1]. A grower survey averaged about 65 °F (18 °C) and 53% RH for drying rooms [3]. ## The numbers | Method | Drying speed | Best for | |---|---|---| | Whole plant | Slowest | Dry rooms, terpene-focused growers, [dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md) | | Branches | Medium | Most rooms, limited space | | Wet-trimmed buds on a rack | Fastest | Humid rooms, high mould risk | | All methods | 7–14 days, 15–21 °C, 55–62% RH | End at aw 0.55–0.65 [1] | ## What to do 1. Look at your room's RH log. Mostly under 50%: hang whole plants. Over 62%: cut branches or dehumidify. 2. Take off the big [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) either way. 3. Hang with gaps so no buds touch. Use a line, hangers or a net. 4. Keep air moving in the room, but not blowing on the buds. Keep it dark. 5. Tag and weigh one branch, and watch for a slow, steady loss. 6. From day 5, test small stems. When they snap, seal a sample jar for 12–24 hours and read it. ## Common mistakes - Hanging whole wet plants in a crowded, humid room. - Fans blowing straight onto the buds. - Packing a drying rack in layers. - Judging dryness by the outside of the bud alone. ## Related - Full article: [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Answers: [drying in the grow tent](https://genetixbay.com/knowledge/answers/can-i-dry-in-my-grow-tent.md) · [how to trim](https://genetixbay.com/knowledge/answers/how-to-trim-buds.md) · [how soon can I smoke?](https://genetixbay.com/knowledge/answers/how-soon-after-harvest-can-i-smoke.md) - Article: [curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Terms: [whole-plant hang](https://genetixbay.com/knowledge/glossary/whole-plant-hang.md) · [hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md) ## Follow-up questions **Does hanging the whole plant make a better dry?** Hanging the whole cannabis plant slows the dry, because the main stem and leaves hold water and release it gradually, which helps keep terpenes in rooms that run dry. It is not proven better in itself; it is grower practice. In a humid room, whole plants can dry too slowly and invite mould, so cut them into branches there. **Can I dry buds on a drying rack?** Yes, cannabis buds can be dried on a mesh drying rack, usually after a wet trim. Spread them in one layer without touching, keep air moving in the room but not on the buds, and turn them once a day so they don't flatten. Racked buds dry faster than hanging branches, so start checking them for a stem snap around day 4–5. **How far apart should drying branches hang?** Hang drying cannabis branches so the buds don't touch each other, usually a few centimetres apart, with air able to move between every branch. Crowded branches create wet pockets where botrytis can keep growing during the dry. If space runs out, cut smaller branches or dry in two batches rather than packing a line tight. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 3. Cannabis Business Times. Special report: cannabis post-harvest benchmarks (grower survey; average drying ~53 % RH, ~65 °F). https://www.cannabisbusinesstimes.com/business-issues-benchmarks/cannabis-post-harvest-operations/article/15689633/post-harvest-benchmarks-with-room-to-experiment 4. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # Should I harvest the whole plant at once or in stages? > Harvest a cannabis plant in stages when the top colas are ready and the lower buds clearly aren't, often a difference of several days. Cut the tops at mostly cloudy with some amber, then give the lower buds roughly 5–10 more days, feeding normally. If the whole plant reads within a few percent, or bud rot or pollen threatens, harvest everything at once. Never flush or darken before either cut. - Canonical: https://genetixbay.com/knowledge/answers/harvest-in-stages.html - Topic: Harvest and cure · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Also asked as: Should I harvest the top colas first? | How do I do a staggered harvest? | My bottom buds aren't ready yet | Is it worth harvesting in two stages? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Harvest in stages when the [top colas](https://genetixbay.com/knowledge/glossary/cola.md) are ready and the lower buds clearly aren't. Cut the [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) at mostly cloudy with some amber, then give the lower buds roughly 5–10 more days, fed and lit as normal. If the plant reads the same top to bottom, or rot or pollen is a risk, harvest everything at once. *Grower practice*. ## Why Buds on one plant ripen unevenly. [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md) maturation varies with [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) and plant age, and heads on the same [bract](https://genetixbay.com/knowledge/glossary/bract.md) sit at mixed stages [1]. Top colas in full light often run days ahead of shaded lower buds. The chemistry peaks and plateaus. [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) content changes through flowering, and peak times differ between plants and [chemotypes](https://genetixbay.com/knowledge/glossary/chemotype.md) [2]. A short wait for the lower buds lets them reach their own plateau. Waiting costs something too. [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) risk rises as flowers age, and dense colas left in a humid room are the usual victims [3]. A [staggered harvest](https://genetixbay.com/knowledge/glossary/perpetual-harvest.md) only works when the room stays dry. ## The numbers | Item | Typical | |---|---| | Top vs lower ripeness gap | Several days on untrained, tall plants | | Extra time for lower buds | About 5–10 days (grower practice) | | [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) while lower buds finish | 40–50% | | Harvest-mix target | Mostly cloudy, about 5–20% amber | | Feed in the final days | Stage strength, with nitrogen tapered; no [flush](https://genetixbay.com/knowledge/glossary/flushing.md) | ## What to do 1. Score trichomes at the top, middle and bottom of the plant. 2. If the tops are ready and the lower buds are mostly clear, cut the tops cleanly with sanitised pruners. 3. Keep the light schedule, feeding and airflow as they were. Don't flush and don't give a dark period: both are *Myths* that cost resin. 4. Re-check the lower buds every 2–3 days, and pry open dense ones for rot. 5. Harvest the rest when it reaches your mix, and dry each batch separately. 6. Next run, train for an [even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md) so everything ripens together. ## Common mistakes - Waiting weeks for larf that will never fill out. - Letting room humidity climb while the lower buds finish. - Flushing the plant between the two cuts. - Mixing wet and part-dried batches in one dry space. ## Related - Full article: [Trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Answers: [how to check trichomes](https://genetixbay.com/knowledge/answers/how-to-check-trichomes.md) · [too early or too late](https://genetixbay.com/knowledge/answers/harvesting-too-early-or-late.md) · [when to stop feeding](https://genetixbay.com/knowledge/answers/when-to-stop-feeding-before-harvest.md) - Article: [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Terms: [harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md) · [larf](https://genetixbay.com/knowledge/glossary/larf.md) ## Follow-up questions **Do lower buds get bigger after the top is harvested?** Lower cannabis buds often fill out somewhat after the top colas are harvested, because they get more light and are less shaded, according to grower practice. There is no controlled study measuring the gain. Expect a modest improvement over 5–10 days, not top-cola buds. Keep feeding normally and keep humidity at 40–50% while they finish. **Is a staggered harvest worth the effort?** A staggered cannabis harvest is worth the effort when the top colas are clearly riper than the lower buds, typically on tall plants or plants without much canopy training. It costs an extra drying session and more handling. For an even, trained canopy such as a SCROG, where trichomes read the same top to bottom, harvesting once is simpler. **Does cutting the top stress the rest of the plant?** Cutting the top colas does stress a cannabis plant a little, but in the last days of flower that rarely matters. Use clean, sharp pruners, cut cleanly, and keep feeding, watering and the light schedule unchanged. Watch the open cuts and the dense lower buds for rot, and keep air moving under the canopy. ## Sources 1. Punja ZK, Sutton DB, Kim T, 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 2. Aizpurua-Olaizola O, Soydaner U, Öztürk E, et al., 2016. Evolution of the cannabinoid and terpene content during the growth of Cannabis sativa plants from different chemotypes. Journal of Natural Products 79(2):324–331. https://pubmed.ncbi.nlm.nih.gov/26836472/ 3. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker --- # What happens if I harvest too early or too late? > Harvest too early and you lose weight and resin: buds are still filling, and cannabinoid concentration hasn't reached its plateau. Harvest too late and the plant senesces, cannabinoid concentration starts falling, and bud-rot risk climbs. The window between is fairly wide. Most growers cut at mostly cloudy with about 5–20% amber, a matter of preference. Amber doesn't mean CBN or couch-lock. - Canonical: https://genetixbay.com/knowledge/answers/harvesting-too-early-or-late.html - Topic: Harvest and cure · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Also asked as: What happens if I harvest cannabis early? | I think I harvested too late | Effects of an early chop | Does harvesting late make it stronger? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Harvest too early and you give up weight and resin, because the buds are still filling. Harvest too late and the plant senesces, [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) concentration falls and bud-rot risk rises. Cannabinoids peaking and then declining is *Supported*. Within the window, cloudy versus amber is preference (*House position*): most growers cut at mostly cloudy with about 5–20% amber. ## Why Cannabinoids rise, plateau and fall. Across [chemotypes](https://genetixbay.com/knowledge/glossary/chemotype.md), cannabinoid and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) content changes through flowering, with peaks at different times [1]. In [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) peaked about 6–7 weeks after flowering began and then declined as plants senesced, with plateau length varying by variety [2]. [Trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) age as well. Heads brown, senesce and can detach late in maturation [3]. Amber marks that ageing, not a switch to a different high. [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) mostly forms after harvest. [THC](https://genetixbay.com/knowledge/glossary/thc.md) oxidises to CBN in air during storage, and light destroys THC without forming CBN [4]. That is why "leave it for amber to get CBN" doesn't hold up. Late flower is also rot season. [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) risk rises as flowers age, especially in dense [colas](https://genetixbay.com/knowledge/glossary/cola.md) and cool, humid nights [5]. ## The numbers | Harvest | Trichomes ([calyx](https://genetixbay.com/knowledge/glossary/calyx.md)) | Trade-off | |---|---|---| | Early | Many clear | Lower weight and resin | | Typical window | A few clear, mostly cloudy, about 5–20% amber | Preference | | Late | Heavy amber, browning heads | Falling concentration, rot risk | | Plateau in hemp | Peak about 6–7 weeks after flowering began [2] | Varies by variety | ## What to do 1. Plan from the flip: the breeder's flowering time plus the 10–14 day transition. 2. Score calyx trichomes at 60–100× every 2–3 days. 3. Keep feeding through to harvest, [tapering nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md). A [pre-harvest flush](https://genetixbay.com/knowledge/glossary/flushing.md) is a *Myth*: it starves the plant while it is packing on its final weight and resin. 4. Don't give a dark period before the chop. That is a *Myth* too. 5. If rot or pollen forces an early cut, harvest, dry and cure as normal. 6. Record the score, date and result, and adjust next run. ## Common mistakes - Chopping at the breeder's week count without checking trichomes. - Waiting for heavy amber to "get CBN". - Judging by [pistils](https://genetixbay.com/knowledge/glossary/pistil.md) alone. - Flushing or darkening the plant at the end. ## Related - Full article: [Trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Answers: [how to check trichomes](https://genetixbay.com/knowledge/answers/how-to-check-trichomes.md) · [harvest in stages](https://genetixbay.com/knowledge/answers/harvest-in-stages.md) · [outdoor harvest](https://genetixbay.com/knowledge/answers/when-to-harvest-outdoors.md) - Article: [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) - Terms: [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) · [senescence](https://genetixbay.com/knowledge/glossary/senescence.md) · [darkness before harvest](https://genetixbay.com/knowledge/glossary/darkness-before-harvest.md) ## Follow-up questions **Is it bad to harvest when trichomes are mostly clear?** Harvesting cannabis when trichomes are mostly clear is early. The buds are still adding weight and resin, so you give up yield and cannabinoid content that the last weeks would have added. If you must cut early, for example because of bud rot or pollen, dry and cure as normal; the flower is usable, just not finished. **Does harvesting late make cannabis more sedating?** Harvesting cannabis late is not proven to make it more sedating. The idea that amber trichomes mean CBN and couch-lock is a myth: CBN forms mainly when THC oxidises after harvest and in storage, and effects depend on dose, chemistry and the person. Late harvests are reported to feel heavier, but that is anecdote, not evidence. **How long is the harvest window?** The cannabis harvest window is usually about one to two weeks wide for a given cultivar, according to grower practice, from mostly cloudy with few amber heads to mostly cloudy with about 20% amber. Studies show cannabinoid levels rise to a plateau before declining, and in hemp the peak came around 6–7 weeks after flowering began, with plateau length varying by variety. ## Sources 1. Aizpurua-Olaizola O, Soydaner U, Öztürk E, et al., 2016. Evolution of the cannabinoid and terpene content during the growth of Cannabis sativa plants from different chemotypes. Journal of Natural Products 79(2):324–331. https://pubmed.ncbi.nlm.nih.gov/26836472/ 2. Yang R, Berthold EC, McCurdy CR, et al., 2020. Development of cannabinoids in flowers of industrial hemp (Cannabis sativa L.): a pilot study. Journal of Agricultural and Food Chemistry. https://pubmed.ncbi.nlm.nih.gov/32392412/ 3. Punja ZK, Sutton DB, Kim T, 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 4. Fairbairn JW, Liebmann JA, Rowan MG, 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1–7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x 5. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker --- # What is the difference between hemp and marijuana? > Hemp and marijuana are the same species, Cannabis sativa. The difference is chemistry, breeding and law: hemp is cannabis grown for fibre, seed or low-THC flower, defined in many laws as no more than 0.3% THC by dry weight, while marijuana is drug-type cannabis bred for high THC. The two groups are genetically distinct populations, and many fibre hemps are bred monoecious. - Canonical: https://genetixbay.com/knowledge/answers/hemp-vs-marijuana.html - Topic: Basics · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - Also asked as: Hemp vs weed | Is hemp the same plant as cannabis? | Hemp vs cannabis difference | Is hemp just low-THC cannabis? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md) and marijuana are the same species, *[Cannabis sativa](https://genetixbay.com/knowledge/glossary/cannabis-sativa.md)*. Hemp is cannabis bred and grown for fibre, seed or low-THC flower, and many laws define it as no more than 0.3% [THC](https://genetixbay.com/knowledge/glossary/thc.md) by [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md). Marijuana is drug-type cannabis bred for high THC. *Established* botany; the legal line varies by place. ## Why One species, two uses. Most botanists treat all cultivated cannabis as *Cannabis sativa*, with fibre, seed and drug types shaped by thousands of years of human selection [3]. The 0.3% line is a convention. Small and Cronquist proposed 0.3% THC in dry flowering [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) as a practical boundary between the groups in 1976 [1]. Many laws later adopted it, with differences in which THC is counted (THC only, or total THC including [THCA](https://genetixbay.com/knowledge/glossary/thca.md)) and how samples are taken. The groups are genetically distinct. Genome-wide markers separated hemp from marijuana as different populations [2]. Chemistry differs too: drug types are mostly THC-dominant, many hemps CBD-dominant or low in all [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) [4]. Breeding goals differ. Fibre hemp is bred tall, dense-sown and often [monoecious](https://genetixbay.com/knowledge/glossary/monoecious.md), with both sexes on one plant. Drug-type cannabis is grown as seedless ([sinsemilla](https://genetixbay.com/knowledge/glossary/sinsemilla.md)) females for resin. ## The numbers | | Hemp | Drug-type cannabis | |---|---|---| | Species | *Cannabis sativa* | *Cannabis sativa* | | Legal THC limit (many places) | ≤ 0.3% by dry weight | None, or licensed | | Bred for | Fibre, grain, oil, [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) | THC-rich resin | | Typical [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) | CBD-dominant or low | THC-dominant | | Sex system | Often monoecious (fibre types) | [Dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md); females grown | ## What to do 1. Treat "hemp" as a legal and use category, not a separate plant. 2. Growing hemp? Rules, licences and testing vary; check your local rules. 3. Growing CBD flower? Test before harvest; CBD-dominant plants still make some THC. 4. Keep hemp pollen away from a sinsemilla grow. ## Common mistakes - Thinking hemp and marijuana are different species. - Assuming "hemp" seed will always test under the limit. - Assuming the 0.3% rule means the same thing everywhere. ## Related - Full article: [Cannabis plant biology](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - Answers: [THC vs CBD plants](https://genetixbay.com/knowledge/answers/thc-vs-cbd-plants.md) · [strain vs cultivar](https://genetixbay.com/knowledge/answers/strain-vs-cultivar.md) - Article: [Indica, sativa and ruderalis](https://genetixbay.com/knowledge/genetics-history/indica-sativa-ruderalis.md) - Terms: [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) · [marijuana](https://genetixbay.com/knowledge/glossary/marijuana.md) · [monoecious](https://genetixbay.com/knowledge/glossary/monoecious.md) ## Follow-up questions **Where does the 0.3% THC hemp limit come from?** The 0.3% THC line between hemp and drug-type cannabis traces to a 1976 taxonomy by Small and Cronquist, who used 0.3% THC in dry flowering tops as a practical boundary between the two groups. Laws in the US, Canada and the EU later adopted 0.3%, though they differ on which THC counts and how samples are taken. Check your local rules. **Can hemp get you high?** Most fibre and grain hemp has too little THC to produce the effects reported for drug-type cannabis, because it is bred to stay under about 0.3% THC. Some 'hemp' flower is bred high in CBD and close to the legal THC limit, and THC-rich plants can appear in mixed seed. Effects are reported, not promised; legal status depends on testing, not on the name. **Is CBD flower hemp?** CBD flower is usually legally hemp: drug-type-looking buds from CBD-dominant plants kept under the hemp THC limit, often 0.3%. Botanically it is the same species as THC-dominant cannabis, with a different synthase gene. CBD-dominant plants still make a little THC, so a crop can test over the limit, and rules on selling smokable hemp flower vary by place. ## Sources 1. Small E, Cronquist A. 1976. A practical and natural taxonomy for Cannabis. Taxon 25(4):405-435. https://doi.org/10.2307/1220524 2. Sawler J, Stout JM, Gardner KM, et al. 2015. The genetic structure of marijuana and hemp. PLoS ONE 10(8):e0133292. https://doi.org/10.1371/journal.pone.0133292 3. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 4. Hillig KW, Mahlberg PG. 2004. A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae). American Journal of Botany 91(6):966-975. https://doi.org/10.3732/ajb.91.6.966 --- # What is eating holes in my leaves? > Holes in cannabis leaves are usually chewing pests, and the clue left behind names them. Dark frass pellets mean caterpillars; silvery slime trails mean slugs or snails; ragged margins on outdoor edge plants mean grasshoppers; a seedling cut through at the soil line means cutworms. Indoors, chewers are rare: holes there are more often dead, dried tissue from nutrient or burn spots falling out. Check at night with a torch. - Canonical: https://genetixbay.com/knowledge/answers/holes-in-leaves.html - Topic: Pests · Type: Troubleshooting - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) - Also asked as: Why are there holes in my cannabis leaves? | Something is chewing my leaves | Leaf damage from bugs outdoors | Ragged holes in leaves overnight | Holes in leaves indoors but no bugs - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Holes in cannabis leaves mean a chewer, and the evidence it leaves tells you which: [frass](https://genetixbay.com/knowledge/glossary/frass.md) for caterpillars, slime for slugs, ragged edges for [grasshoppers](https://genetixbay.com/knowledge/glossary/grasshopper.md), cut stems for [cutworms](https://genetixbay.com/knowledge/glossary/cutworm.md). Indoors, holes without frass are usually dead spots dropping out, not pests. *Established*. ## Why Caterpillars leave droppings. Young larvae chew small holes in leaves; older [corn earworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md) larvae, up to about 25 mm (1 in), bore into buds, and their frass lets [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md) in [1][3]. Outdoor chewers come from the surroundings. Grasshoppers move in from field edges in dry summers, and cutworms hide in soil by day and cut young stems at night; both are listed among [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) pests [2]. Slugs and snails feed at night and in wet weather, leaving ragged holes and slime on [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and low leaves. [Leafminers](https://genetixbay.com/knowledge/glossary/leafminer.md) make tunnels, not holes: pale winding trails inside the leaf [4]. Indoors, chewing pests are uncommon and usually arrive through open intakes or doors [1]. ## The numbers | Clue | Likely cause | Where | |---|---|---| | Holes plus dark frass pellets | Caterpillars | Outdoors mostly; buds in flower | | Ragged holes plus slime trails | Slugs, snails | Seedlings, low leaves, after rain | | Missing leaf margins, edge plants first | Grasshoppers | Outdoors, dry summers | | Seedling cut at soil line | Cutworm | Fresh outdoor [transplants](https://genetixbay.com/knowledge/glossary/transplanting.md) | | Pale winding trails | Leafminer | [Fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) | | Brown-edged holes, no frass | Dead spots falling out | Indoors | ## What to do 1. Look on and under leaves at dusk and after dark with a torch. 2. Search for frass, slime, larvae and cut stems. 3. Hand-pick caterpillars, slugs and cutworms; bag damaged bud sections. 4. Use stem collars on transplants and fine netting where practical. 5. From early flower, scout upper [colas](https://genetixbay.com/knowledge/glossary/cola.md) twice weekly for eggs and frass. 6. Indoors with no frass, check nutrients, [pH](https://genetixbay.com/knowledge/glossary/ph.md) and spray or [light burn](https://genetixbay.com/knowledge/glossary/light-stress.md). ## Common mistakes - Spraying before identifying the culprit. - Ignoring leaf holes in late summer until buds rot. - Using Bt on large larvae already inside buds. - Blaming insects for nutrient spots indoors. ## Related - Full article: [Caterpillars and budworms on cannabis](https://genetixbay.com/knowledge/pests/caterpillars.md) - Answer: [What can I spray in flower?](https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.md) - Article: [Rust or brown spots on leaves](https://genetixbay.com/knowledge/diagnosis/rust-spots.md) - Terms: [slugs and snails](https://genetixbay.com/knowledge/glossary/slugs-and-snails.md) · [cutworm](https://genetixbay.com/knowledge/glossary/cutworm.md) · [grasshopper](https://genetixbay.com/knowledge/glossary/grasshopper.md) · [leafminer](https://genetixbay.com/knowledge/glossary/leafminer.md) ## Follow-up questions **What is eating my cannabis leaves at night?** Leaves of cannabis eaten overnight point to night feeders: slugs and snails, which leave ragged holes and silvery slime trails, caterpillars, which leave dark frass pellets, and cutworms, which chew young stems through at the soil line. Go out an hour or two after dark with a torch, especially after rain, and look on and under the leaves and around the stem base. **Why are there holes in my leaves indoors with no bugs?** Holes in indoor cannabis leaves with no bugs and no frass are usually dead tissue falling out, not feeding. Brown or rust spots from nutrient problems, spray burn or light burn dry out and crack away, leaving holes with brown edges. Chewing pests are uncommon indoors and usually arrive through open intakes or doors. Check leaf undersides with a lens before blaming insects. **Do I need to treat for caterpillars if I see holes?** A few caterpillar holes in fan leaves cost little, but they warn you that moths are laying eggs, and in flower the larvae bore into buds and start bud rot. Hand-pick larvae at dusk or dawn, scout upper colas for eggs and frass from early flower, and use fine netting where practical. Bt works only on small larvae, under about 12 mm (0.5 in). ## Sources 1. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 2. Cranshaw, W. Hemp pests (CSU, 2020). https://webdoc.agsci.colostate.edu/bspm/InsectInformation/Talks2020/HempPests.pdf 3. Utah State University Extension. Corn Earworm (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-corn-earworm 4. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects --- # Do milk or baking soda sprays work for powdery mildew? > Milk and bicarbonate sprays suppress powdery mildew on leaves; they do not cure it. Trials on squash and pumpkin found milk above about 10% and 0.5% bicarbonate plus oil cut disease, but there are no cannabis trials. Use them only in veg, with full coverage every 7–10 days, alongside airflow and stable humidity. Never spray them on buds after the first 2–3 weeks of flower. - Canonical: https://genetixbay.com/knowledge/answers/home-remedies-for-powdery-mildew.html - Topic: Diseases · Type: Myth check - Evidence: Myth · Status: Draft: awaiting expert review - Full article: [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) - Also asked as: Does milk spray cure powdery mildew? | Baking soda spray for powdery mildew on cannabis | Is potassium bicarbonate good for PM? | Home remedy for white powder on leaves - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Milk and bicarbonate sprays can slow [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) on leaves, but the idea that they cure it is a *Myth*. They work by contact, need full coverage every 7–10 days, and belong in veg only. Suppression is *Supported* in other crops; there are no cannabis trials. ## Why Potassium bicarbonate is a recognised contact option for [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) powdery mildew. It raises the [pH](https://genetixbay.com/knowledge/glossary/ph.md) on the leaf surface and dries the colonies, and it has to be repeated every 7–10 days [1]. Milk has some evidence behind it, on squash. In a greenhouse trial, sprays of more than 10% cow's milk cut zucchini powdery mildew about as well as the fungicides it was compared with [2]. That is a different fungus on a different crop. Bicarbonate works better with oil. On pumpkin, 0.5% [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) or potassium bicarbonate mixed with 0.5% spray oil beat either one alone, and worked best when applied before infection. Potassium bicarbonate above 0.5% burned infected leaves [3]. None of these sprays reaches the spores already waiting on nearby leaves. The mildew comes back unless you fix still air and humidity spikes, and wet buds invite [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) [1][4]. ## The numbers | Spray | Rate tested | Crop | Result | |---|---|---|---| | Cow's milk | > 10% | Zucchini | Severity cut, close to fungicide [2] | | Na/K bicarbonate + oil | 0.5% + 0.5% | Pumpkin | Better than either alone [3] | | Potassium bicarbonate | > 0.5% | Pumpkin | Leaf injury [3] | | Any spray | Every 7–10 days | Hemp | Contact only [1] | ## What to do 1. Check it is mildew: rub it with a damp [finger](https://genetixbay.com/knowledge/glossary/leaflet.md) and see whether it grows back in the same spot. 2. Fix the room first: [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) above and below the canopy, thin the inner growth, and keep humidity steady at lights-off. 3. Bag infected leaves and remove them from the room. 4. In veg, spray potassium bicarbonate at label rate. Cover leaf [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) and undersides, and repeat every 7–10 days. 5. Check the label and your local rules on what may be used on cannabis. ## Common mistakes - Spraying buds in mid or late flower. - Spraying once and calling it [cured](https://genetixbay.com/knowledge/glossary/curing.md). - Using strong mixes that burn leaves. - Spraying only the spots you can see. ## Related - Full article: [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) - Answers: [what can I spray in flower?](https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.md) · [should I wash my buds?](https://genetixbay.com/knowledge/answers/should-i-wash-my-buds.md) - Terms: [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) · [horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md) ## Follow-up questions **Is potassium bicarbonate better than baking soda for powdery mildew?** Potassium bicarbonate is the usual choice over baking soda (sodium bicarbonate) because it leaves potassium rather than sodium on the plant, and it is the bicarbonate the PNW Handbook lists for hemp powdery mildew. Both work by contact only. In a pumpkin trial, potassium bicarbonate above 0.5% damaged infected leaves, so stay at or below label rate and test a few leaves first. **Can I spray milk on cannabis in flower?** Do not spray milk on cannabis buds in flower. Milk, like any wet spray, raises moisture inside dense flowers and invites botrytis bud rot, and it leaves residue and smell on the product. GenetixBay's rule is no sprays on buds after the first 2–3 weeks of flower. Remove the worst branches and fix airflow and humidity instead. **Why does powdery mildew come back after I spray?** Powdery mildew comes back after spraying because contact sprays only kill the colonies they touch. Airborne spores are already on neighbouring leaves and plants, and a fresh crop of spores appears in roughly a week when the room is humid and still. Repeat full coverage every 7–10 days in veg, and fix night-time humidity spikes and dead air pockets. ## Sources 1. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew 2. Bettiol W, 1999. Effectiveness of cow's milk against zucchini squash powdery mildew (Sphaerotheca fuliginea) in greenhouse conditions. Crop Protection 18(8):489–492. https://doi.org/10.1016/S0261-2194(99)00046-0 3. Ziv O, Zitter TA, 1992. Effects of bicarbonates and film-forming polymers on cucurbit foliar diseases. Plant Disease 76:513–517. https://www.apsnet.org/publications/plantdisease/backissues/Documents/1992Abstracts/PD_76_513.htm 4. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full --- # How cold is too cold for cannabis? > Cannabis gets too cold when air at the canopy stays below about 15 °C (59 °F): growth, water use and ripening slow sharply, and humid cold nights invite bud rot. Lights-on air below about 20 °C (68 °F) already costs growth. Late-flower nights of 16–20 °C (61–68 °F) are fine. Keep the root zone at 18–22 °C (64–72 °F); cold roots stall a plant even when the air is warm. - Canonical: https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.html - Topic: Environment · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - Also asked as: What is the minimum temperature for cannabis? | My grow room is cold: is that a problem? | Is 60 °F (15 °C) too cold for cannabis? | How cold can cannabis plants get at night? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Cannabis is too cold when canopy air stays below about **15 °C (59 °F)**. Lights-on air below about **20 °C (68 °F)** already costs growth, and the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) should not fall below **18 °C (64 °F)**. Late-flower nights of 16–20 °C (61–68 °F) are normal. *Supported* for the [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) response; the limits are *Grower practice*. ## Why Photosynthesis in cannabis peaks around 25–30 °C (77–86 °F) [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) under strong light and falls steadily as leaves cool [1]. A cold day wastes the light you are paying for. Cold roots take up water and nutrients slowly, so a plant in a cold pot or reservoir sulks even when the air is warm. Extension guidance puts hydroponic root zones at 18–22 °C [2]. Young plants are least tolerant. [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md) seed [germination](https://genetixbay.com/knowledge/glossary/germination.md) slows sharply at the cool end of its range [3], and [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and clones stall in cold rooms. In flower, [cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) push [relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) up and surfaces towards the [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md). Wet, cool buds are where *[Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md)* starts [4]. ## The numbers | Situation | Fine | Too cold | |---|---|---| | Veg, lights on | 24–28 °C (75–82 °F) | below 20 °C (68 °F) | | Flower, lights on | 22–26 °C (72–79 °F) | below 20 °C (68 °F) | | Late-flower night | 16–20 °C (61–68 °F) | below 15 °C (59 °F) | | Seedlings and clones | 23–27 °C (73–81 °F) | below 20 °C (68 °F) | | Root zone / reservoir | 18–22 °C (64–72 °F) | below 18 °C (64 °F) | | Any stage | | frost, 0 °C (32 °F), kills soft tissue | ## What to do 1. Measure at canopy height and in the pot, not on the floor or ceiling. 2. Log 48 hours; the coldest point is usually the end of the dark period. 3. Lift pots off cold floors onto insulation. 4. Keep the lights-off drop to 3–6 °C (5–10 °F). 5. Add a thermostat-controlled heater if the room still runs cold (see [keeping a tent warm](https://genetixbay.com/knowledge/answers/how-to-keep-a-grow-tent-warm.md)). ## Common mistakes - Reading the room thermostat instead of the canopy. - Ignoring cold pots on a concrete floor. - Chilling nights hard to "boost [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md)": colour only, in cultivars that carry it. - Cold nights in late flower with no [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) running. ## Related - Full article: [Temperature by stage](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - [How do I keep my grow tent warm in winter?](https://genetixbay.com/knowledge/answers/how-to-keep-a-grow-tent-warm.md) - [How do I lower the humidity in my grow tent?](https://genetixbay.com/knowledge/answers/how-to-lower-humidity-in-a-grow-tent.md) - Terms: [cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) · [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) ## Follow-up questions **Is 60 °F (15.5 °C) too cold for cannabis?** 60 °F (15.5 °C) is at the cold limit for cannabis. As a night temperature in late flower it is survivable but slows ripening and pushes humidity up towards the dew point, which invites bud rot. As a daytime temperature it is too cold: photosynthesis is far below its best, which sits around 25–30 °C leaf temperature. Aim for nights of 16–20 °C (61–68 °F) in late flower. **Will a cold night kill my plant?** A single cold night rarely kills an established cannabis plant unless it freezes. Above 0 °C (32 °F) the usual damage is slowed growth, purple or droopy leaves in sensitive cultivars and, in flower, condensation that starts bud rot. Seedlings and clones are far less tolerant. Frost kills soft tissue outright, so protect outdoor plants below about 2–4 °C (36–39 °F). **Do cold nights make buds purple?** Cold nights can bring out purple colour in cannabis, but only in cultivars that carry the genes for anthocyanin pigments; colour is mostly genetic. Cold does not add terpenes, flavour or resin, which is a myth unless peer-reviewed data shows otherwise. Big cold nights also slow ripening and raise bud-rot risk, so treat purple as a trade-off, not a technique. ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 2. e-GRO / Colorado State University Extension, Root disease problems and management in hydroponic systems (root-zone 68–72 °F). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 3. Geneve RL et al., 2022. Temperature limits for seed germination in industrial hemp (Cannabis sativa L.). Crops 2(4):415–427. https://doi.org/10.3390/crops2040029 4. Utah State University Extension. Hemp bud rot (IPM fact sheet). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot.php --- # How did pests get into my sealed tent? > Pests don't appear from nowhere in a sealed cannabis tent; something carried them in. The usual routes, most likely first, are new clones, your own clothes and hands after the garden, pets and houseplants, unfinished compost or open media bags (fungus gnats), and the intake air for tiny fliers like thrips and whiteflies. Low populations hide for weeks, so the source often predates the symptoms. - Canonical: https://genetixbay.com/knowledge/answers/how-did-pests-get-in-my-tent.html - Topic: Pests · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - Also asked as: Where do bugs come from in an indoor grow? | Spider mites appeared out of nowhere | How do pests get into a closed grow room? | How did I get thrips in my tent? | Can pests come in through the fan? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Something carried them in. A tent is sealed against light, not insects: pests ride in on clones, clothes, pets, houseplants, potting media and intake air. The most common single source is new plant material. *Supported*; the ranking of routes is *Grower practice*. ## Why Clones and [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md) are the main vehicle. Pests and pathogens move between facilities on cuttings, which is why quarantine is the first rule [1]. People and pets carry [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md). Spider mites walk between plants and drift on air currents [2], and growers commonly carry them in on clothing after time in the garden (*Grower practice*). Media breeds gnats. Incompletely composted organic matter in [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) often carries [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) in, and open bags attract egg-laying adults [3]. Air brings small fliers. Moths and other fliers arrive through open intakes or doors [4]; [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) and [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) are small enough to pass unscreened gaps. Infestations hide. [Root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md) live on roots out of sight and arrive on incoming plants [5]; reused media can carry them into the next cycle. By the time leaves show damage, the population may be weeks old. ## The numbers | Route | Typical pests | Fix | |---|---|---| | New clones | Mites, thrips, [aphids](https://genetixbay.com/knowledge/glossary/aphid.md), root aphids, mildew | 2–3 week quarantine | | Clothes, hands, pets | Spider mites, thrips | Grow before the garden; change clothes | | Houseplants, cut flowers | Mites, aphids, whiteflies | Keep them out of the grow space | | Unfinished compost, open bags | Fungus gnats | Pasteurised media, closed storage | | Unscreened intake | Thrips, whiteflies, moths | Fine screen or filter | | Reused media, debris | Root aphids, gnats | Clean-out and fallow between cycles | ## What to do 1. List what entered the tent in the last month: plants, media, people, pets. 2. Check the most recent clone source first. 3. Screen the intake and seal gaps around ducts and zips. 4. Keep houseplants and pets away from the grow. 5. Change clothes and wash hands after outdoor gardening, before the tent. 6. Between cycles, remove all plant material and media and leave the space empty and dry for several days. ## Common mistakes - Believing pests "spawned" from the soil or the seed. - Visiting the tent straight from the vegetable patch. - Reusing medium from an infested run. - Fixing the outbreak but not the route. ## Related - Full article: [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - Guide: [Pest prevention for beginners](https://genetixbay.com/knowledge/guides/pest-prevention-for-beginners.md) - Answers: [Preventing pests indoors](https://genetixbay.com/knowledge/answers/how-to-prevent-pests-indoors.md) · [Do sticky traps work?](https://genetixbay.com/knowledge/answers/do-sticky-traps-work.md) - Terms: [quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) · [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) ## Follow-up questions **Can spider mites come in on seeds?** Spider mites do not come in on seeds; seeds are the cleanest way to start a cannabis grow, which is why sanitation guidance prefers seeds or tested clean stock over untested cuttings. Mites arrive on clones, houseplants, clothes and pets, then walk between plants and drift on air currents. If mites appear in a seed-only grow, look at people, pets and nearby plants. **Can pests get in through my intake fan?** Yes, small flying pests can get into a cannabis tent through an unscreened intake, especially thrips and whiteflies, and caterpillar moths through open intakes or doors. Spider mites also drift on air currents. Fit fine insect screening or a filter on passive and active intakes, check it after each cycle, and keep the grow away from windows, doors and houseplants. **Why do pests come back every grow?** Pests that return every cannabis cycle usually survive between cycles or keep being reintroduced. Root aphids and gnats can persist in reused medium, mites and thrips hide in debris, and the same mother or clone source reinfects each run. Remove all plant material and media, clean then disinfect surfaces, leave the room plant-free and dry for several days, and quarantine incoming plants. ## Sources 1. Punja ZK et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 3. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf 4. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 5. Cranshaw, W. and Wainwright-Evans, S., 2020. Cannabis sativa as a host of rice root aphid (Hemiptera: Aphididae) in North America. Journal of Integrated Pest Management 11(1):15. Summary: https://entomologytoday.org/2020/07/24/rice-root-aphid-indoor-grown-cannabis-integrated-pest-management/ --- # How full should I fill my curing jars? > Fill curing jars about three-quarters full, loosely, so the buds don't crush and air can move around them when you burp. A packed jar holds wet pockets and flattens buds. A jar that is mostly empty holds a lot of air and swings humidity. Once the cure is done, after 2–8 weeks, fill storage jars fuller to cut the air in contact with the buds. - Canonical: https://genetixbay.com/knowledge/answers/how-full-to-fill-curing-jars.html - Topic: Harvest and cure · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Also asked as: How full should curing jars be? | Should jars be three-quarters full? | Can I pack my jars tight? | Jar fill level for curing - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Fill [curing jars](https://genetixbay.com/knowledge/glossary/curing-jar.md) about ¾ full, loosely, so the buds aren't crushed and the air can move when you [burp](https://genetixbay.com/knowledge/glossary/burping.md). Too full traps wet pockets. Too empty gives a big [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) that swings the humidity. After the cure, fill storage jars fuller. *Grower practice*. ## Why A cure is a slow decline in moisture. The bud's [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) should start around 0.62–0.65 and fall towards 0.55–0.58 over the weeks, inside the ASTM range of 0.55–0.65 [1]. Loose buds at about ¾ full give up their excess water evenly when you burp. Packed jars stay wet in the middle. Moisture in a crushed mass of buds can't reach the air, and above water activity 0.68 flower needs more drying [2]. That is where mould and ammonia smells start. The hygrometer needs room to read. Once a sealed jar has equilibrated, its [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) divided by 100 equals the bud's water activity [1]. With a sensible fill it reflects the buds, not one wet corner. Storage is different. After curing, the job is to slow oxidation: air turns [THC](https://genetixbay.com/knowledge/glossary/thc.md) into [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) in storage, and light destroys THC [3]. A fuller, airtight jar kept in the dark limits both. ## The numbers | Stage | Fill level | Why | |---|---|---| | Curing (weeks 1–8) | About ¾, loose | Air to burp, buds uncrushed | | Storage after the cure | Fuller, still not crushed | Less air, less oxidation [3] | | Practical jar size | 0.5–1 L glass | Equalises overnight, limits losses | | Equilibrated [jar RH](https://genetixbay.com/knowledge/glossary/equilibrium-relative-humidity.md) | 55–65% | aw 0.55–0.65 [1] | ## What to do 1. Jar buds only when the stems snap and a sealed sample reads a stable 58–65% RH. 2. Drop buds in loosely to about ¾ full. Don't press them down. 3. Add a calibrated mini hygrometer, seal the jar, and label it with cultivar and date. 4. Burp for 10–15 minutes once or twice a day in week 1, every 2–3 days in week 2, then weekly. 5. Shake each jar gently when you burp so the buds turn. 6. After the cure, combine jars into fuller ones and store them cool and dark. ## Common mistakes - Pressing buds down to fit one more in. - One giant jar for the whole harvest. - Reading the hygrometer straight after opening. - Storing jars in sunlight. ## Related - Full article: [Curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Answers: [mould in jars](https://genetixbay.com/knowledge/answers/mould-in-curing-jars.md) · [ammonia smell](https://genetixbay.com/knowledge/answers/ammonia-smell-in-jars.md) · [buds lost their smell](https://genetixbay.com/knowledge/answers/buds-lost-their-smell.md) - Article: [long-term storage](https://genetixbay.com/knowledge/harvest-cure/long-term-storage.md) - Terms: [curing jar](https://genetixbay.com/knowledge/glossary/curing-jar.md) · [burping](https://genetixbay.com/knowledge/glossary/burping.md) ## Follow-up questions **What happens if I pack curing jars too tight?** Packing cannabis curing jars too tight crushes the buds and damages trichomes, and it leaves wet pockets where moisture can't escape, so a tight jar is more likely to grow mould. It also makes the hygrometer read the air around the edge rather than the bulk of the bud. Fill about three-quarters full, loosely, and shake the jar gently when you burp. **Does jar size matter for curing?** Jar size matters less than fill level, but mid-sized airtight glass jars of about 0.5–1 litre are easiest for home cures. Each one holds a manageable amount, reaches equilibrium overnight and loses less if one jar goes wrong. Very large jars crush the bottom buds and take longer to equalise. Label each jar with cultivar and date. **Should storage jars be full after curing?** Yes, once curing is finished, storage jars should be fuller than curing jars. After 2–8 weeks the buds no longer need burping, and less air in the jar means less oxidation of THC to CBN over months. Keep buds at water activity 0.55–0.65 in airtight, opaque or dark-stored glass, cool and out of light. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (salt-based humidity control sachets for aw below 0.68). https://sn.astm.org/node/2445/printable/print 3. Fairbairn JW, Liebmann JA, Rowan MG, 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1–7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x --- # How long can mixed nutrient solution be stored? > Mixed mineral nutrient solution keeps about a week if it is covered, dark and cool, roughly the same 7-14 days a DWC reservoir runs between changes; an open, warm, lit jug is best used within 1-3 days. Light breaks down chelated iron, warmth grows microbes, and organic or sugary additives spoil within a day or two. Recheck pH and EC before use. - Canonical: https://genetixbay.com/knowledge/answers/how-long-can-mixed-nutrients-sit.html - Topic: Nutrients · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - Also asked as: Can I mix nutrients in advance? | How long does premixed nutrient water last? | Is old nutrient solution still good? | Can I store leftover feed for next week? | How long do nutrient concentrates last once opened? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A covered, dark, cool container of mixed mineral feed stays usable for about a week, in line with the 7–14 days a [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) reservoir runs between changes. An open, warm or lit jug is best used within 1–3 days. Feeds with organic, amino or sugary additives spoil within a day or two. *Grower practice*, backed by the chemistry below. ## Why Light destroys [iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md). Irradiated Fe-DTPA nutrient solutions lost both [chelate](https://genetixbay.com/knowledge/glossary/chelate.md) and soluble iron, which dropped out as a precipitate [1]. A clear jug on a sunny bench is the worst case. Concentrates are another matter. Calcium meets [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md) and [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) and precipitates when [A and B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) are combined strong; at [feed strength](https://genetixbay.com/knowledge/glossary/input-ec.md) they stay dissolved [2]. Never mix the two concentrates together "to save time". Warm, still water grows microbes. [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) is the classic root pathogen of hydroponic cannabis [3], and warm, stagnant solution suits it. Organic supplements make it worse: kelp, fish and similar additives drove fast bacterial growth in [compost teas](https://genetixbay.com/knowledge/glossary/compost-tea.md) [4]. [pH](https://genetixbay.com/knowledge/glossary/ph.md) also drifts in storage as dissolved [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) exchanges with the air. ## The numbers | Storage | Usable for | Notes | |---|---|---| | Mineral mix, sealed, dark, 15–20 °C (59–68 °F) | ~5–7 days | Recheck pH and [EC](https://genetixbay.com/knowledge/glossary/ec.md) | | Mineral mix, aerated reservoir, light-proof | 7–14 days | Normal DWC refresh | | Mineral mix, open or lit, >25 °C (77 °F) | 1–3 days | Iron loss, algae | | With organics, amino acids or sugars | Same day to 2 days | Ferments, smells | | Separate A and B concentrates, sealed | Months | Watch for [crystals](https://genetixbay.com/knowledge/glossary/trichome.md) | ## What to do 1. Mix what you'll use in a few days. 2. Store in an opaque, lidded container, out of light. 3. Keep it cool, ideally 15–20 °C. 4. Add organic or microbial products on the day you feed. 5. Stir, then recheck pH and EC before each use. 6. Discard anything cloudy, slimy or smelly. ## Common mistakes - Storing feed in a clear jug in a lit tent. - Mixing A and B concentrates together. - Leaving [molasses](https://genetixbay.com/knowledge/glossary/molasses.md) or amino mixes overnight. - Using stored mix without rechecking pH. ## Related - Full article: [Hydroponic salts explained](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - Answers: [mixing order](https://genetixbay.com/knowledge/answers/order-to-mix-nutrients.md) · [topping off the reservoir](https://genetixbay.com/knowledge/answers/top-off-reservoir-water-or-nutrients.md) - Articles: [DWC](https://genetixbay.com/knowledge/systems/dwc.md) - Terms: [stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md) · [A-B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) · [iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md) ## Follow-up questions **Why does stored nutrient solution go bad?** Stored nutrient solution goes bad in three ways. Light breaks down iron chelates such as Fe-DTPA, dropping soluble iron out as a precipitate. Warm water grows bacteria, fungi and algae, especially when organic, amino or sugary additives are present. And pH drifts as carbon dioxide exchanges with the air. A dark, cool, covered container slows all three. **Can I mix part A and part B in advance?** You can mix part A and part B in advance only at feed strength, diluted in the full volume of water, never as a combined concentrate. Concentrated together, calcium from part A reacts with sulfate and phosphate from part B and precipitates as gypsum and calcium phosphate, which takes those nutrients out of the feed for good. **How long do nutrient concentrates last?** Mineral nutrient concentrates kept sealed, separate, dark and cool usually last many months; check the label's date. Watch for crystals, sludge or colour change, which mean something has precipitated or degraded. Organic liquids, amino acids and microbial products have much shorter lives and can ferment or swell, so buy them in amounts you will use within a season. ## Sources 1. Albano JP, Miller WB, 2001. Photodegradation of FeDTPA in nutrient solutions. I. Effects of irradiance, wavelength, and temperature. HortScience 36(2):313-316. https://doi.org/10.21273/HORTSCI.36.2.313 2. Sonneveld C, Voogt W, 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 3. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 4. Ingram DT, Millner PD, 2007. Factors affecting compost tea as a potential source of Escherichia coli and Salmonella on fresh produce. Journal of Food Protection 70(4):828-834. https://doi.org/10.4315/0362-028X-70.4.828 --- # How long do autoflowers take from seed to harvest? > Autoflowers usually take about 9–14 weeks from sprouting to harvest, with fast lines near week 9–10 and long lines near week 13–14. They start flowering at about 3–5 weeks old whatever the light schedule. Add 1–2 weeks of drying before the buds are smokeable. Any setback, such as overwatering, transplanting or hunger, costs time the plant can't recover. - Canonical: https://genetixbay.com/knowledge/answers/how-long-do-autoflowers-take.html - Topic: Basics · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Also asked as: How long do autos take? | Autoflower total time from seed | When are autos ready? | How many weeks is an autoflower? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) take about 9–14 weeks from [sprouting](https://genetixbay.com/knowledge/glossary/germination.md) to harvest. Fast lines finish near week 9–10, long lines near week 13–14, and the light schedule doesn't change that. Add 7–14 days of drying. *Grower practice* for the durations; the age-based flowering behind them is *Supported* genetics. ## Why An autoflower is day-neutral. It carries two copies of a [recessive allele](https://genetixbay.com/knowledge/glossary/recessive.md) at a mapped [locus](https://genetixbay.com/knowledge/glossary/locus.md), *Autoflower1*, so it flowers by age rather than by night length [1]. [Gene](https://genetixbay.com/knowledge/glossary/gene.md) dosage at that locus shifts flowering time and height, which is part of why lines differ by weeks [2]. The clock starts at germination and doesn't stop. A [photoperiod plant](https://genetixbay.com/knowledge/glossary/photoperiod.md) can stay in veg until it recovers from a mistake. An auto flowers on schedule whether it has recovered or not, so a setback costs size, and often a few days on the finish, never a longer [harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md) you can use. That's the GenetixBay house position: any setback costs an auto. More light means more growth in the same time, not an earlier finish. Yield rose with light in a controlled trial [3]; autos on 18–20 h get 1.5–1.7× the daily light of 12 h at the same intensity. ## The numbers | Week from sprouting | What's happening | |---|---| | 1–2 | Seedling, [first true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) | | 3–4 | Fast veg; [preflowers](https://genetixbay.com/knowledge/glossary/pre-flower.md) appear | | 3–5 | [Pistils](https://genetixbay.com/knowledge/glossary/pistil.md) at the main tip: flowering starts | | 5–7 | [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md), early flower | | 8–10 | Bulking | | 9–14 | Ripening and harvest, by [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) | | +1–2 | Drying | ## What to do 1. Plan the space for 14 weeks, and be pleased if it's 10. 2. Sow straight into the final pot; don't [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md). 3. Run one schedule throughout: [18/6](https://genetixbay.com/knowledge/glossary/18-6.md), 20/4 or 24/0. 4. From about week 8, check trichomes every 2–3 days. 5. Harvest at a few clear, mostly cloudy, some amber heads. ## Common mistakes - Harvesting on the breeder's week count instead of the trichomes. - Switching an auto to [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) "to speed it up". It doesn't; it only cuts light. - Starting in a cup and transplanting, which stalls the plant while the clock runs. - Assuming every seed in an auto pack is a true auto. Poorly [stabilised lines](https://genetixbay.com/knowledge/glossary/ibl.md) throw photoperiods. ## Related - Full article: [Photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Guide: [Autoflower first grow, week by week](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md) - Answers: [when autos start flowering](https://genetixbay.com/knowledge/answers/when-do-autoflowers-start-flowering.md) · [why my auto is small](https://genetixbay.com/knowledge/answers/why-is-my-autoflower-small.md) · [checking trichomes](https://genetixbay.com/knowledge/answers/how-to-check-trichomes.md) - Terms: [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) ## Follow-up questions **Do autoflowers finish faster on 24 hours of light?** No, autoflowers do not finish faster on more hours of light. They flower by age, so 18/6, 20/4 or 24/0 give roughly the same 9–14 week timeline. Longer days add daily light: at the same intensity, 18–20 hours gives about 1.5–1.7 times the light of 12 hours, which means more growth in the same number of days, not an earlier harvest. **Why is my auto taking longer than the breeder says?** An autoflower usually runs past the breeder's stated time because of genetics, setbacks or optimistic marketing. Stress early in the grow slows growth without stopping the flowering clock, and some 'autos' are poorly stabilised lines. Breeder times are claims, so plan for 9–14 weeks and decide the harvest day by trichomes, not the calendar. **How long does it take to grow an autoflower start to finish?** An autoflower takes about 9–14 weeks from seed to harvest, then roughly 7–14 days of drying and at least two weeks of curing for good flavour. Allow about 3–4 months from planting to a cured jar. A photoperiod plant grown indoors from seed usually takes about 3–5 months before drying. ## Sources 1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 2. Kurtz LE, Brand MH, Lubell-Brand JD. 2023. Gene dosage at the autoflowering locus effects flowering timing and plant height in triploid cannabis. Journal of the American Society for Horticultural Science 148(2):83-88. https://doi.org/10.21273/JASHS05293-23 3. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # How long do clones take to root? > Most cannabis clones root in 7–14 days, with the first roots showing around days 7–12 at a medium temperature of 22–26 °C (72–79 °F), high humidity and gentle light. Cuttings in a cold medium, from flowering plants or without rooting hormone can take 2–4 weeks or fail. If nothing after 3 weeks, check medium temperature, wetness and the cutting's source. - Canonical: https://genetixbay.com/knowledge/answers/how-long-do-clones-take-to-root.html - Topic: Cloning and mother plants · Type: Numbers - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: Clone root time | How many days do cuttings take to root? | My clones are not rooting | Why is my cannabis clone not growing after rooting? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Most cannabis clones root in 7–14 days at a medium temperature of 22–26 °C (72–79 °F) with high humidity and gentle light. Slow or flowering cuttings can take 2–4 weeks. *Supported* by propagation trials. ## Why Trials show the timescale. [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md) cuttings at about 25 °C under 24-hour light were ready 12 days after sticking, once more than half showed roots [1]. Drug-type cuttings in a growth chamber were assessed after 9 days, with the best medium rooting 41% by then [2]. Medium choice changes the result. Rooting success ranged from 13% to 80% across media in one trial [1], and from 0% to 41% in another [2]. Hormone speeds it. [IBA](https://genetixbay.com/knowledge/glossary/auxin.md) gel gave 2.1 times the rooting success of a willow-extract gel [3]. Warm roots grow faster. A cold plug slows callus and root formation more than cool air does. ## The numbers | Situation | Typical time to roots | |---|---| | Vegetative cutting, IBA, 22–26 °C medium | 7–14 days | | No hormone | Slower, fewer rooted | | Medium below ~20 °C (68 °F) | 2–3 weeks | | Cutting from a flowering plant | 2–4 weeks, then [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) | | Ready to [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) | Several white roots 2–5 cm (1–2 in) out of the plug | ## What to do 1. Put a thermometer probe in a plug; aim for 22–26 °C. 2. Keep plugs moist but not wet. 3. Use IBA gel or powder on every cut. 4. Check from day 7 for root tips at the plug's sides or base; don't tug. 5. After 21 days with no roots and no callus, re-cut fresh. ## Common mistakes - Pulling clones up to look. - Cold floors or windowsills. - Soggy plugs that rot the stem. - Cutting from plants already in flower. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [How do I clone a cannabis plant?](https://genetixbay.com/knowledge/answers/how-to-clone-cannabis.md) · [When are clones ready to transplant?](https://genetixbay.com/knowledge/answers/when-to-transplant-clones.md) · [Why are my clones wilting?](https://genetixbay.com/knowledge/answers/why-are-my-clones-wilting.md) - Terms: [cloning](https://genetixbay.com/knowledge/glossary/cloning.md) · [rooting hormone](https://genetixbay.com/knowledge/glossary/rooting-hormone.md) ## Follow-up questions **Why is my cannabis clone not growing after rooting?** A newly rooted cannabis clone often sits still for a week or so while it builds roots and adjusts to lower humidity. If it stalls longer, the usual causes are too few roots when it left the dome, a soggy medium, low light, or no feed in an inert medium. Give it 150–300 µmol/m²/s and a light feed once roots show. **Why are my clones not rooting?** Cannabis clones usually fail to root because the medium is too cold or too wet, the cutting came from a flowering or stressed plant, or no rooting hormone was used. Aim for a medium temperature of 22–26 °C (72–79 °F), plugs moist but not soggy, and an IBA gel. Some cultivars simply root slower; give them three weeks before discarding. **Does a heat mat speed up rooting?** A heat mat can speed up cannabis rooting in a cool room by warming the medium toward 22–26 °C (72–79 °F), which matters more than air temperature. In a warm room it adds little and can dry the plugs or push the medium too hot. Put a thermometer probe in a plug and use a thermostat rather than running the mat flat out. ## Sources 1. Campbell SM, Anderson SL, Brym ZT, Pearson BJ, 2021. Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.). PLOS ONE 16(7): e0249160. https://doi.org/10.1371/journal.pone.0249160 2. Hwang SJ, Collado CE, Hwang HS, Yun JH, Hernandez R, 2026. Impacts of commercial and custom substrates on rooting and morphology of Cannabis sativa 'Suver Haze' stem. HortTechnology 36(3):429–434. https://doi.org/10.21273/HORTTECH05810-26 3. Caplan D, Stemeroff J, Dixon M, Zheng Y. 2018. Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science 98(5):1126-1132. https://doi.org/10.1139/cjps-2018-0038 --- # How long does a carbon filter last? > A grow-tent carbon filter usually lasts about 12–18 months of continuous use, less in humid rooms or with very pungent cultivars, longer if it only runs in flower. Replace it when you can smell flowering plants at the exhaust outlet. A washable pre-filter sleeve cleaned monthly, and RH kept below about 60 %, are what stretch filter life. - Canonical: https://genetixbay.com/knowledge/answers/how-long-does-a-carbon-filter-last.html - Topic: Environment · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) - Also asked as: When should I replace my carbon filter? | Carbon filter lifespan for a grow tent | My carbon filter stopped working | Can you recharge a carbon filter? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A grow-tent [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) usually lasts about **12–18 months of continuous use**: less in humid rooms or with very pungent cultivars, longer if it only runs in flower. The real test is your nose: replace it when you can smell flowering plants at the **[exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) outlet**. *Grower practice*; no controlled data exist for grow filters. ## Why Activated carbon holds odour molecules on a huge internal surface. Once those sites are full, smell passes straight through. How fast they fill depends on how much odour and how much water vapour the air carries. Flowering cannabis makes potent [volatile sulphur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) that the nose detects at tiny concentrations [1], so a nearly full filter can still leak a noticeable smell. Water vapour competes for the same sites. Above about 60–70 % [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), filters saturate sooner. Dust coats the carbon and cuts airflow. A pre-filter sleeve catches it. There is no safe chemical shortcut. Ozone generators sold as air cleaners can harm lungs without removing odour well [2]. ## The numbers | Condition | Typical life | |---|---| | Continuous use, RH in range | 12–18 months | | Humid room (RH often above 60–70 %) | noticeably shorter | | Run only in flower | longer, often two or more runs | | Pre-filter sleeve | wash monthly | | Filter rating | at or above the fan's [CFM](https://genetixbay.com/knowledge/glossary/cfm.md) | ## What to do 1. Sniff-test the exhaust outlet weekly in flower. 2. If it smells, check seals, closed top ports and fan direction (pulling through the filter) first. 3. Confirm the filter is rated at or above the fan's airflow. 4. Wash the pre-filter monthly with plain water and dry it before refitting. 5. Keep RH at stage targets, 40–50 % in late flower. 6. Replace or refill the carbon when the outlet still smells. 7. Write the install date on the filter and in your journal. ## Common mistakes - Blaming the plants when the filter is two years old. - Never washing the pre-filter. - Running a humid tent and wondering why the carbon died early. - Baking a filter and expecting it to come back. - Masking smell with sprays instead of replacing the carbon. ## Related - Full article: [Airflow](https://genetixbay.com/knowledge/environment/airflow.md) - Guide: [Smell control basics](https://genetixbay.com/knowledge/guides/smell-control-basics.md) - [How do I stop my grow tent from smelling?](https://genetixbay.com/knowledge/answers/how-to-control-grow-smell.md) - [Should my exhaust fan run 24/7?](https://genetixbay.com/knowledge/answers/run-exhaust-fan-24-7.md) - Terms: [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) · [CFM](https://genetixbay.com/knowledge/glossary/cfm.md) ## Follow-up questions **How do I know my carbon filter is finished?** A carbon filter is finished when you can smell flowering plants at the exhaust outlet with the fan at its normal speed and every joint sealed. Rule out the cheaper causes first: open top ports, leaky duct joints, the fan pushing rather than pulling, or a filter rated below the fan's airflow. If those are fine and the outlet still smells, replace the carbon. **Does humidity shorten carbon filter life?** Yes, high humidity shortens carbon filter life. Above about 60–70 % RH, water vapour competes with odour molecules for space on the activated carbon, so the filter saturates sooner. Keeping the grow at its stage RH target, 40–50 % in late flower, protects both the filter and the buds. This is grower practice consistent with how carbon adsorption works. **Can I recharge or bake a carbon filter?** Recharging a home grow carbon filter by baking it or leaving it in the sun is not reliable. Industrial activated carbon is regenerated at very high temperatures in controlled furnaces, far beyond a domestic oven or sunlight. Some filters let you refill the carbon bed, which is fine. Otherwise replace the filter, and extend its life with a clean pre-filter and sensible RH. ## Sources 1. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196 2. US Environmental Protection Agency. Ozone generators that are sold as air cleaners. https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners --- # How long does the flowering stage take? > Most photoperiod cannabis flowers for about 7–10 weeks, counted from the first pistil clusters, but harvest comes about 9–12 weeks after the flip, because the flip isn't day 1 of flower: a 10–14 day transition comes first. A breeder's '8 weeks' usually means harvest about 9.5–10 weeks after switching to 12/12. Long-flowering equatorial types can take 11–16 weeks or more. - Canonical: https://genetixbay.com/knowledge/answers/how-long-does-flowering-take.html - Topic: Environment · Type: Numbers - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [The flip isn't day 1 of flower: the 10–14 day transition and how to count it](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - Also asked as: How many weeks does cannabis take to flower? | How long from the flip to harvest? | Indoor flowering time for photoperiod plants | Why is my plant taking longer than the breeder said? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Most [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis flowers for about **7–10 weeks** counted from the first [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) clusters, so harvest lands about **9–12 weeks after the flip**. **House position: the flip isn't day 1 of flower.** A transition of about **10–14 days** comes first, so a breeder's "8 weeks" usually means harvest **9.5–10 weeks** after switching to [12/12](https://genetixbay.com/knowledge/glossary/12-12.md). *Supported*. ## Why Switching to long nights starts floral induction, not flowering. The [shoot tip](https://genetixbay.com/knowledge/glossary/apical-meristem.md) spends the next week or two rebuilding itself. In controlled studies, the first proper pistil clusters at the top of the main shoot appeared about 8–14 days after short days began [1][2]. Across 27 [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md) the average was 13–14 days, and slow ones took three weeks [2]. Many breeders count flowering time from that point ("flower set"), not from the flip. That's why most runs seem to go about two weeks long. Flower length itself is genetic. Indoor medical [genotypes](https://genetixbay.com/knowledge/glossary/genotype.md) typically run 7–14 weeks of flowering [4]; equatorial types run longer. A [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) schedule barely changes the clock: about 1.5 days later onset in one cultivar, none in another, with more yield [3]. ## The numbers | Plant type | Weeks of flower | Weeks from flip to harvest | |---|---|---| | Fast indica-leaning hybrid | 7–8 | ~9–10 | | Typical hybrid | 8–10 | ~10–12 | | Long equatorial type | 11–16+ | ~13–18+ | | Transition (flip to first pistil clusters) | — | 10–14 days typical; up to 3 weeks | | Breeder's "8 weeks" | 56 days | 66–70 days | ## What to do 1. Log two dates: the flip, and the first 3+ pairs of pistils at the top of the main shoot. 2. Add 10–14 days to any breeder's stated time. 3. Plan the room on the longer figure. 4. Start [trichome](https://genetixbay.com/knowledge/glossary/trichome.md) checks about two weeks before the expected finish. 5. Harvest on trichomes, mostly cloudy with some amber to taste, not the calendar. ## Common mistakes - Counting the flip as day 1 and harvesting two weeks early. - Calling veg [preflowers](https://genetixbay.com/knowledge/glossary/pre-flower.md) "flowering". - [Light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) in the first two weeks, stalling induction. - Judging ripeness by pistil colour alone. ## Related - Full article: [The flip isn't day 1 of flower](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - [When should I flip my plants to flower?](https://genetixbay.com/knowledge/answers/when-to-flip-to-flower.md) - [In which weeks of flower do buds grow the most?](https://genetixbay.com/knowledge/answers/when-do-buds-grow-the-most.md) - [How do I check trichomes?](https://genetixbay.com/knowledge/answers/how-to-check-trichomes.md) - Terms: [flowering stage](https://genetixbay.com/knowledge/glossary/flowering-stage.md) · [flip](https://genetixbay.com/knowledge/glossary/flip.md) ## Follow-up questions **How long after the flip to harvest?** Most photoperiod cannabis is ready about 9–12 weeks after the flip to 12/12: a transition of roughly 10–14 days before the first pistil clusters, then 7–10 weeks of flower for typical hybrids. Long-flowering equatorial cultivars can need 13–18 weeks from the flip. Decide the actual day by trichomes, mostly cloudy with some amber to taste, not by the calendar. **Why does my strain take longer than the breeder says?** A cannabis strain usually takes longer than the breeder's stated flowering time because many breeders count from flower set, the first visible pistil clusters, not from the flip. The 10–14 day transition gets added on top, so a stated 8 weeks typically means harvest about 9.5–10 weeks after switching to 12/12. Count both clocks in your journal. **Does 13/11 make flowering take longer?** A 13/11 photoperiod adds very little to cannabis flowering time: in one study of two THC-dominant cultivars, 13 hours delayed flowering onset by about 1.5 days in one and not at all in the other, while yield rose 1.35× and 1.5×. GenetixBay endorses 13/11. Sensitive cultivars may need a day or two more, so test your own. **How long do autoflowers take?** Autoflowers don't follow the flip-to-harvest clock, because the photoperiod doesn't trigger their flowering. Most run about 9–14 weeks from germination to harvest on 18/6 to 20/4 light, starting to flower on their own after a few weeks of growth. Any setback costs an autoflower time it can't win back, so plant it straight in its final pot. ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 3. Ahrens A, Llewellyn D, Zheng Y. 2024. Longer photoperiod substantially increases indoor-grown cannabis' yield and quality. Plants 13(3):433. https://doi.org/10.3390/plants13030433 4. Crispim Massuela D, Hartung J, Munz S, Erpenbach F, Graeff-Hönninger S, 2022. Impact of harvest time and pruning technique on total CBD concentration and yield of medicinal cannabis. Plants 11(1):140. https://doi.org/10.3390/plants11010140 --- # How long is the seedling stage? > The cannabis seedling stage lasts about 2–3 weeks from emergence. It ends when the plant has 3–4 nodes of true leaves with full-sized, multi-fingered leaflets and roots filling a small pot; then it's in veg. At 150–300 µmol/m²/s, 18 hours a day and 23–27 °C (73–81 °F) it moves fastest. Cold, low light or overwatering can stretch it to 4 weeks or more. - Canonical: https://genetixbay.com/knowledge/answers/how-long-is-the-seedling-stage.html - Topic: Germination · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - Also asked as: How long are cannabis plants seedlings? | When does the seedling stage end? | When does a seedling become veg? | Why is my cannabis seedling so stretched? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer The cannabis [seedling stage](https://genetixbay.com/knowledge/glossary/seedling.md) lasts about 2–3 weeks from emergence, ending at 3–4 nodes of [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) with multi-fingered [leaflets](https://genetixbay.com/knowledge/glossary/leaflet.md). Good light (150–300 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), 18 h) and warmth (23–27 °C / 73–81 °F) keep it short. *Grower practice*. ## Why A seedling is limited by its tiny root and few leaves. Growth accelerates once true leaves are photosynthesising and roots have filled a small container. Light sets the pace. Young plants given a [DLI](https://genetixbay.com/knowledge/glossary/dli.md) of about 10–14 mol/m²/day root and grow better than dimly lit ones in other crops [1], and cannabis responds to higher light in veg with compact, robust growth [2]. [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md) is the sign of too little light. The stem elongates looking for it, giving a tall, weak seedling that can flop. The end of the seedling stage is practical, not botanical: when roots fill the plug or cup it's time to [pot up](https://genetixbay.com/knowledge/glossary/up-potting.md) [3] and treat the plant as veg. ## The numbers | Days from emergence | What you see | Light (µmol/m²/s) | |---|---|---| | 0–5 | [Cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) open | 100–200 | | 5–10 | First true leaves (1–3 fingers) | 150–250 | | 10–21 | Nodes 2–4, leaves with more fingers | 200–300+ | | ~14–21 | Roots fill plug or cup; enter veg | 300+ as veg begins | | Condition | Target | |---|---| | [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) | [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) ([24/0](https://genetixbay.com/knowledge/glossary/24-0.md) also fine) | | Air | 23–27 °C (73–81 °F), 65–75% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) | | First feed | [EC](https://genetixbay.com/knowledge/glossary/ec.md) 0.4–0.8 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) at 2–3 true-leaf sets | ## What to do 1. Count nodes, not days. 2. Measure PPFD; raise it if the stem stretches. 3. Keep the medium just moist, never soggy. 4. Start a light feed at 2–3 sets of true leaves. 5. Pot up photoperiods when roots reach the edges; leave [autos](https://genetixbay.com/knowledge/glossary/autoflower.md) in their final pot. ## Common mistakes - A weak light 1 m away, then wondering why it stretched. - Calling it "veg" by the calendar while it still has two nodes. - Holding a seedling in a tiny cup until it is [root-bound](https://genetixbay.com/knowledge/glossary/root-bound.md). ## Related - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - [Stretching](https://genetixbay.com/knowledge/diagnosis/stretching.md) · [Life cycle](https://genetixbay.com/knowledge/basics/life-cycle.md) - [Light schedule for seedlings](https://genetixbay.com/knowledge/answers/light-schedule-for-seedlings.md) - Terms: [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) · [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) ## Follow-up questions **Why is my cannabis seedling so stretched?** A cannabis seedling that grows a long, thin, pale stem is usually getting too little light, or the light is too far away. Raise intensity gradually toward 150–300 µmol/m²/s for 18 hours, and add gentle air movement to firm the stem. At transplant, bury the stretched stem deeper in soil or coco. A pinched, brown stem base is damping-off instead. **When do seedlings get their first true leaves?** Cannabis seedlings usually show their first true leaves, often single-bladed or three-fingered, about 5–10 days after emerging. Each new node then brings leaves with more fingers, typically 5 by the third or fourth node. Seedlings that take much longer are usually cold, under-lit or overwatered rather than slow genetics. **When should I transplant a seedling?** Transplant a cannabis seedling when roots reach the sides and bottom of its plug or cup but before they circle, typically 2–3 weeks from sprouting at about 2–4 true-leaf nodes. Water lightly the day before so the root ball holds together. Autoflowers are the exception: sow them straight into the final pot and don't transplant. ## Sources 1. Runkle E. The benefits of lighted plugs. Michigan State University Extension. https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs 2. Moher M, Llewellyn D, Jones M, Zheng Y, 2021. High light intensities can be used to grow healthy and robust cannabis plants during the vegetative stage of indoor production. Preprints (not peer reviewed). https://doi.org/10.20944/preprints202104.0417.v1 3. University of Minnesota Extension. Starting seeds indoors (transplanting seedlings, hardening). https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors --- # How many plants can I fit in my grow tent? > A grow tent fits about one or two trained plants in 60 x 60 cm (2 x 2 ft), two in 2 x 4 ft and two to four in 4 x 4 ft: roughly 1–4 plants per square metre. A sea of green packs 9–25 small plants per square metre. More plants raise yield per area only up to a point, and legal plant limits usually decide first. - Canonical: https://genetixbay.com/knowledge/answers/how-many-plants-per-tent.html - Topic: Basics · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [SOG: sea of green](https://genetixbay.com/knowledge/training/sog.md) - Also asked as: How many plants in a 2x4 tent? | How many plants in a 4x4 tent? | Plants per square metre | How many plants per square metre for SOG? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer For trained plants in 11–19 L (3–5 gal) pots, fit one or two in a 2 x 2 ft tent, two in a 2 x 4, two or three in a 3 x 3 and two to four in a 4 x 4: about 1–4 [plants per m²](https://genetixbay.com/knowledge/glossary/plant-density.md). A [sea of green](https://genetixbay.com/knowledge/glossary/sog.md) packs 9–25 small plants per m². *Grower practice*; your legal [plant limit](https://genetixbay.com/knowledge/glossary/plant-count-limit.md) comes first. **Legal first.** Many places cap the number of plants per home. Check your local rules before you plan. ## Why The canopy is the limit, not the plant count. Higher planting density raised yield per area in controlled work on drug-type cannabis, but lowered yield per plant and made [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) content less uniform [1]. Density is among the strongest yield drivers in the cannabis literature [2], yet past full canopy cover, more plants mostly add crowding. Fewer plants need longer veg. Two trained plants can fill a 4 x 4; sixteen small ones fill it with almost no veg. Belgian yield trials used 12–20 plants per m² [3]. Crowding blocks airflow at the base and lets disease spread between plants. ## The numbers | Tent | Area | Trained plants (11–19 L) | [Autos](https://genetixbay.com/knowledge/glossary/autoflower.md) (11–15 L) | Sea of green (1–4 L) | |---|---|---|---|---| | 2 x 2 ft (60 x 60 cm) | 0.36 m² | 1–2 | 1–2 | 3–9 | | 3 x 3 ft (90 x 90 cm) | 0.81 m² | 2–3 | 2–4 | 7–20 | | 2 x 4 ft (60 x 120 cm) | 0.72 m² | 2 | 2–3 | 6–18 | | 4 x 4 ft (120 x 120 cm) | 1.44 m² | 2–4 | 4–6 | 13–36 | | 5 x 5 ft (150 x 150 cm) | 2.25 m² | 4–6 | 6–9 | 20–56 | SOG column = 9–25 plants/m² × area. ## What to do 1. Check your legal plant limit. 2. Decide how long you can veg: long veg means fewer plants. 3. Pick a pot that fits the footprint with a few centimetres to spare. 4. Train each plant with [LST](https://genetixbay.com/knowledge/glossary/lst.md) or a net so the canopy fills edge to edge. 5. Leave room to reach every plant and keep air moving under the canopy. ## Common mistakes - Cramming in plants instead of training fewer. - Running a sea of green from mixed seed, which [stretches](https://genetixbay.com/knowledge/glossary/stretch.md) unevenly. - Ignoring the plant limit because "it's only a tent". ## Related - Full article: [Sea of green](https://genetixbay.com/knowledge/training/sog.md) - Answers: [yield per plant](https://genetixbay.com/knowledge/answers/how-much-does-one-plant-yield.md) · [what size tent](https://genetixbay.com/knowledge/answers/what-size-grow-tent.md) - Articles: [SCROG](https://genetixbay.com/knowledge/training/scrog.md) · [choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md) - Terms: [plant density](https://genetixbay.com/knowledge/glossary/plant-density.md) · [plant-count limit](https://genetixbay.com/knowledge/glossary/plant-count-limit.md) ## Follow-up questions **How many plants for a sea of green?** A sea of green typically runs 9–25 small cannabis plants per square metre, about 1–2.3 per square foot, usually rooted clones of one cultivar in 1–4 L pots, flowered after 0–14 days of veg. Belgian yield trials used 12–20 plants per square metre. Check plant-count rules first: many places make SOG illegal for home growers. **Is one big plant or several small ones better?** Several small plants and one big plant can fill the same canopy and yield about the same per square metre. Fewer plants need longer veg and more training; more plants finish sooner but need more seed or clones and crowd the air at the base. Higher density raised yield per area in research but lowered yield per plant and cannabinoid uniformity. **How many autoflowers fit in a 4x4 tent?** About four to six autoflowers fit in a 4 x 4 ft (1.2 x 1.2 m) tent in 11–15 L (3–4 gal) pots, because autos stay smaller and can't be vegged longer to fill space. Use LST to spread each plant. Fewer, larger photoperiods would fill the same tent, but autos finish in 9–14 weeks with no light change. ## Sources 1. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 2. Backer R, Schwinghamer T, Rosenbaum P, et al., 2019. Closing the yield gap for cannabis: a meta-analysis of factors determining cannabis yield. Frontiers in Plant Science 10:495. https://doi.org/10.3389/fpls.2019.00495 3. BELSPO MARCANT project summary (plant densities 12–20 plants/m² in yield trials). https://www.belspo.be/Belspo/fedra/DR/DR92_MARCANT_summ_en.pdf --- # How much weed does one plant produce? > One indoor cannabis plant produces whatever its share of the canopy yields: roughly 100–500 g of dry flower per square metre of canopy in controlled trials, depending mostly on light. A single plant filling a 60 x 60 cm (2 x 2 ft) tent at moderate light gives about 40–180 g (1.5–6 oz). Per plant is a poor measure: yield follows canopy area and light, not plant count. - Canonical: https://genetixbay.com/knowledge/answers/how-much-does-one-plant-yield.html - Topic: Basics · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Also asked as: Yield per plant indoors | How many ounces per plant? | Average yield for a first grow | How many grams does one plant give? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer One indoor plant [yields](https://genetixbay.com/knowledge/glossary/yield.md) its share of the canopy. Controlled trials measured roughly 116–519 g of dry flower per square metre as light rose from low to very high, and 500–750 g/m² in well-run rooms at 750–900 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md). One plant filling a 2 x 2 ft (0.36 m²) tent typically gives about 40–180 g (1.5–6 oz). *Grower practice* arithmetic on *Supported* trial data. ## Why Light drives yield. In one trial, dry flower rose in a straight line from 116 g/m² at 120 µmol/m²/s to 519 g/m² at 1,800 µmol/m²/s [1]. Another group measured 500–750 g/m² at 750–900 µmol/m²/s [2]. Cultivars and growers differ, so treat these as research-room numbers, not a promise. [Plant count](https://genetixbay.com/knowledge/glossary/plant-count-limit.md) splits the canopy, it doesn't add to it. Higher density raised yield per area but lowered yield per plant [3]. One big plant and four small ones can fill the same tent. [Root volume](https://genetixbay.com/knowledge/glossary/pot-size.md) and feeding set how fast a plant fills its space. Doubling pot size raised biomass by about 43% on average across many crops [4], though frequent feeding lets small pots punch above their size. ## The numbers Yield per plant ≈ [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md) the plant fills × g/m². | Canopy per plant | At ~120 g/m² (weak light) | At ~300 g/m² (moderate) | At ~500 g/m² (strong, dialled in) | |---|---|---|---| | 0.36 m² (2 x 2 ft) | ~45 g (1.5 oz) | ~110 g (4 oz) | ~180 g (6 oz) | | 0.72 m² (2 x 4 ft) | ~85 g (3 oz) | ~215 g (7.5 oz) | ~360 g (12.5 oz) | | 1.44 m² (4 x 4 ft) | ~175 g (6 oz) | ~430 g (15 oz) | ~720 g (25 oz) | 1 oz = 28.35 g. Figures are dry, trimmed flower. ## What to do 1. Measure your canopy area, not your plant count. 2. Measure light at the canopy; it is the biggest lever. 3. Train plants to fill the space evenly ("tuck, don't pluck"). 4. Plan a first grow on the weak-to-moderate column, and log the real number. ## Common mistakes - Quoting yield per plant without the canopy area or light. - Adding plants instead of filling the canopy with fewer, trained ones. - Weighing wet buds; [wet weight](https://genetixbay.com/knowledge/glossary/wet-weight.md) is roughly four to five times dry. ## Related - Full article: [Your first grow](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Answers: [grams per watt and per square foot](https://genetixbay.com/knowledge/answers/grams-per-watt.md) · [plants per tent](https://genetixbay.com/knowledge/answers/how-many-plants-per-tent.md) · [increasing yield](https://genetixbay.com/knowledge/answers/how-to-increase-yield-indoors.md) - Article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Terms: [yield](https://genetixbay.com/knowledge/glossary/yield.md) · [ounce](https://genetixbay.com/knowledge/glossary/ounce.md) ## Follow-up questions **How much does an autoflower yield?** An autoflower usually yields less per plant than a photoperiod, because it has no extra veg time, but it can match photos per square metre per year. A small auto in a 2 x 2 ft tent might give 30–100 g. The GenetixBay founder's best elite auto gave about 340 g (3/4 lb) in under 80 days, a ceiling when everything goes right, not a typical result. **Do more plants mean more yield?** More plants raise yield per square metre only up to a point. Controlled research on drug-type cannabis found higher planting density increased yield per area but lowered yield per plant and made cannabinoid content less uniform. Two to four well-trained plants usually fill a 4 x 4 ft tent as well as many small ones, and stay inside legal plant limits. **Does a bigger pot give more yield per plant?** A bigger pot gives a bigger plant within reason: across many crops, doubling pot size raised biomass by about 43% on average. But root volume isn't everything. The GenetixBay founder has grown over 4 oz (about 115 g) from a 16 oz cup using high-frequency fertigation. Feeding frequency trades against pot size. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988 3. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 4. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # How much sun does outdoor cannabis need? > Outdoor cannabis needs at least 6–8 hours of direct sun a day, and more is better: full summer sun reaches 1,500–2,000 µmol/m²/s at midday and a daily light integral of roughly 40–60 mol/m²/day on clear days. Yield rises roughly in proportion to light, so a part-shaded spot yields less, not nothing. Under about 4 hours of direct sun, expect thin, airy buds. - Canonical: https://genetixbay.com/knowledge/answers/how-much-sun-outdoors.html - Topic: Outdoor growing · Type: Numbers - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: How many hours of direct sun does cannabis need? | Can cannabis grow in partial shade? | Sunlight needs for outdoor plants | Is 4 hours of sun enough? | Morning sun or afternoon sun for cannabis? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Give outdoor cannabis at least 6–8 hours of direct sun a day, and as much more as the site allows. Clear summer days deliver roughly 40–60 [mol/m²/day](https://genetixbay.com/knowledge/glossary/dli.md) of light, above most indoor flower rooms, and yield rises with every extra hour of direct sun. *Supported* for the light–yield link; the hour count is *Grower practice*. ## Why More light, more grams. In two controlled trials, flower yield rose in proportion to canopy light from 120 to 1,800 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), with no change in potency per gram [1][2]. Outdoor light is generous but variable. Daily light integral changes with month, latitude and cloud; monthly maps show midsummer values far above winter ones across the United States [3]. Shade costs twice. Shaded plants make less and airier flower, and leaves and buds stay wet longer after dew or rain, which favours mildew and rot [4]. Light, not heat, is the goal. Midday summer sun reaches about 1,500–2,000 µmol/m²/s; the risk in hot climates is root and leaf heat, not the light itself. ## The numbers | Direct sun per day | What to expect | |---|---| | 8 h or more | Full-size plants, dense buds | | 6–8 h | Good results, somewhat smaller | | 4–6 h | Smaller plants, airier buds | | Under 4 h | Thin, airy buds; consider another site | | Measure | Typical value | |---|---| | Midday summer sun | ~1,500–2,000 µmol/m²/s | | Clear midsummer DLI | ~40–60 mol/m²/day | | Indoor flower target (for comparison) | 35–56 mol/m²/day at 800–1,200 µmol/m²/s | ## What to do 1. Watch your site through a full sunny day in early summer and count direct-sun hours. 2. Prefer sites open to the south and east (north and east in the Southern Hemisphere). 3. Use containers if you need to move plants to follow the sun. 4. Prune overhanging branches before planting. 5. Harden indoor-raised plants off over 7–14 days. 6. In very hot climates, give roots shade and mulch, not the leaves. ## Common mistakes - Judging a site in spring, before trees leaf out. - Planting in a damp, shaded corner where buds never dry. - Moving plants from a tent straight into midday sun. ## Related - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Answers: [Bigger, denser buds](https://genetixbay.com/knowledge/answers/how-to-get-bigger-denser-buds.md) · [Why buds are airy](https://genetixbay.com/knowledge/answers/why-are-my-buds-airy.md) · [Start indoors, move outside](https://genetixbay.com/knowledge/answers/start-indoors-move-outside.md) - Terms: [DLI](https://genetixbay.com/knowledge/glossary/dli.md) · [outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md) ## Follow-up questions **Can cannabis grow in partial shade?** Cannabis grows in partial shade but yields less, because flower yield rose roughly in proportion to light across 120–1,800 µmol/m²/s in controlled trials. A spot with 4–6 hours of direct sun gives smaller, airier buds than one with 8 or more. Shade also slows drying of dew and rain on buds, which raises bud-rot risk. Prune overhanging branches where you can. **Is morning or afternoon sun better for cannabis?** Morning sun is usually more useful for outdoor cannabis than late-afternoon sun. Early light dries dew from leaves and buds sooner, cutting the hours of wetness that powdery mildew and bud rot need, while hot afternoon sun in warm climates adds heat stress. Given the choice, pick a site open to the east and south (north in the Southern Hemisphere). This is grower practice. **Can outdoor cannabis get too much sun?** Outdoor cannabis rarely gets too much sun once hardened off, since yield kept rising up to 1,800 µmol/m²/s at canopy level in trials and midday summer sun reaches about 1,500–2,000. Trouble comes from heat and dryness rather than light: in very hot climates, afternoon shade, mulch and light-coloured containers protect roots. Indoor-raised plants need 7–14 days of hardening off to avoid bleaching. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 3. Faust JE, Logan J, 2018. Daily light integral: a research review and high-resolution maps of the United States. HortScience 53(9):1250-1257. https://doi.org/10.21273/HORTSCI13144-18 4. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew --- # How much water does a cannabis plant use per day? > A cannabis plant uses roughly 50–250 mL of water a day as a seedling, 0.5–1.5 L in veg and about 1.5–2 L a day as a large flowering plant indoors. Plan the room at up to about 10 L per m² of flowering canopy per day (1 L per ft²) under strong light and heat. Nearly all of it is transpired, so light, temperature and VPD drive use. - Canonical: https://genetixbay.com/knowledge/answers/how-much-water-per-day.html - Topic: Systems · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Also asked as: How many litres does a cannabis plant drink per day? | How much water do plants drink in flower? | Daily water use per plant indoors | How much water does a grow tent use? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer An indoor cannabis plant uses roughly 50–250 mL a day as a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md), 0.5–1.5 L in veg and about 1.5–2 L a day as a large flowering plant. For planning, allow up to about 10 L per m² of flowering canopy per day (1 L per ft²) under strong light and heat [1]. *Grower practice*: cannabis water use hasn't been measured in many controlled trials, and plants vary widely. ## Why Almost all the water a plant takes up leaves through its leaves as [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md); one estimate puts it at about 95% [1]. Very little stays in the plant. Transpiration follows the climate. More light, higher temperature, lower humidity (higher [VPD](https://genetixbay.com/knowledge/glossary/vpd.md)) and more airflow all raise it. A cooler, dimmer, humid room can use half the water of a hot, bright one. Leaf area, and with it water use, climbs fast from mid veg to mid flower. Water use is also a health signal. Roots that are rotting or short of oxygen take up less. A sudden fall in daily use with no climate change is worth investigating. Deliberately giving less is a separate tool: a controlled, mild drought in late flower raised [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) in one study [2], but that is steering, not rationing. ## The numbers | Stage | Typical water use per plant per day | |---|---| | Seedling | 50–250 mL (given every 1–2 days) | | Early veg, 1–4 L pot | 0.2–0.5 L | | Late veg, 11–19 L pot | 0.5–1.5 L | | Large plant, mid flower | 1.5–2 L | | Room planning maximum | Up to 10 L/m²/day canopy (1 L/ft²) [1] | Add 10–30% on top for [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) in [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md). ## What to do 1. Weigh the pot after a full watering and again when it's due; the difference is what the plant used. 2. Log it for a week. You'll see use climb as the plant grows. 3. Size your reservoir or watering jug for the planning maximum, not the average. 4. Water by weight, not by a fixed daily amount [3]. 5. If daily use drops suddenly, check the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) and climate before anything else. ## Common mistakes - Giving the same volume every day from seedling to harvest. - Assuming a thirsty-looking plant needs water without lifting the pot. - Ignoring a sudden fall in water use. ## Related - Full article: [Drooping: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Answers: [how often to water](https://genetixbay.com/knowledge/answers/how-often-to-water.md) · [water at lights-on or lights-off](https://genetixbay.com/knowledge/answers/water-at-lights-on-or-off.md) - Terms: [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) · [dryback](https://genetixbay.com/knowledge/glossary/dryback.md) · [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) ## Follow-up questions **How much water does a grow tent use per day?** A grow tent in full flower uses up to about 10 litres of water per square metre of canopy per day, or about 1 litre per square foot, as a planning maximum. A 1.2 × 1.2 m (4 × 4 ft) tent can therefore need up to about 14–16 litres a day under strong light and heat, while cooler, dimmer rooms use far less. Add 10–30% for runoff. **Why does my plant drink more some days?** A cannabis plant drinks more on days with more light, higher temperature, lower humidity and stronger airflow, because almost all the water it takes up is transpired through the leaves. Water use also rises steeply as the plant grows from mid veg to mid flower. A sudden drop in water use with no change in climate is a warning sign: check the roots. **Should I give the same amount every day?** No. Give water by pot weight, not a fixed daily volume. Daily use changes with plant size, light and climate, so a fixed amount overwaters small plants and starves big ones. Weigh the pot after a full watering and again when dry, water at roughly the halfway point, and give enough for a little runoff in soil or 10–20% in coco. ## Sources 1. Douglas R, 2022. Ways to calculate water use and transpiration rates for indoor cannabis cultivation. Greenhouse Grower. https://www.greenhousegrower.com/?p=157955 2. Caplan D, Dixon M, Zheng Y, 2019. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience 54(5):964–969. https://doi.org/10.21273/HORTSCI13510-18 3. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 --- # How often should I water my cannabis plants? > Water by weight, not by calendar. In soil, water when the pot feels about 40–50% lighter than just after watering, usually every 2–4 days for established plants. Coco and rockwool want watering once to several times a day with 10–30% runoff. Seedlings in big pots need small amounts around the stem. The pot's weight and the plant's size set the schedule, not the day of the week. - Canonical: https://genetixbay.com/knowledge/answers/how-often-to-water.html - Topic: Systems · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Also asked as: How often do you water weed plants? | How often should I water in soil? | How many times a day do I water coco? | Watering schedule for autoflowers | Am I watering too much? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Water cannabis by pot weight, not by the calendar. In soil, water when the pot is about 40–50% lighter than just after watering, usually every 2–4 days for an established plant. In [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), water once to several times a day with 10–30% [runoff](https://genetixbay.com/knowledge/glossary/runoff.md). *Grower practice*, backed by basic root physiology. ## Why Roots need air as much as water. A saturated pot fills the pore spaces with water, roots run short of oxygen and the plant droops even though it is wet. Constantly wet media also favour [Pythium root rot](https://genetixbay.com/knowledge/glossary/pythium.md) [1] and [fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) larvae [2]. Letting the pot [dry back](https://genetixbay.com/knowledge/glossary/dryback.md) between waterings pulls fresh air into the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). A mild, controlled dry-down in late flower has even raised yield and [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) content in one trial [3], but that is deliberate steering, not neglect. ## The numbers | Medium | When to water | How much | |---|---|---| | Soil, established plant | Pot 40–50% lighter, top 3–5 cm dry | To light runoff, ~10–20% of [pot volume](https://genetixbay.com/knowledge/glossary/pot-size.md) | | Coco coir | 1–6 times a day as the plant grows | 10–30% runoff every time | | Rockwool | Several times a day in flower | 10–30% runoff, steer by dryback | | [Seedling](https://genetixbay.com/knowledge/glossary/seedling.md) in a large pot | Every 1–3 days | A small circle around the stem only | ## What to do 1. Weigh or lift the pot right after a full watering, and again when it is dry. Learn both. 2. Water when the pot is roughly halfway between the two. 3. Water slowly, in two passes, until a little runs out of the bottom. 4. Empty the saucer so the pot doesn't sit in runoff. 5. As the plant grows and drinks faster, shorten the interval rather than drenching harder. ## Common mistakes - Watering on a fixed schedule ("every Tuesday") without lifting the pot. - Putting a seedling in a huge pot and soaking the whole thing. - Daily small sips in coco with no runoff, which builds salts. - Treating every droop as thirst: an [overwatered](https://genetixbay.com/knowledge/glossary/overwatering.md) plant droops too. ## Related - Full article: [Drooping: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Media: [growing in soil](https://genetixbay.com/knowledge/systems/soil.md) · [growing in coco](https://genetixbay.com/knowledge/systems/coco.md) - Terms: [field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md) · [dryback](https://genetixbay.com/knowledge/glossary/dryback.md) · [watering to runoff](https://genetixbay.com/knowledge/glossary/watering-to-runoff.md) ## Follow-up questions **Should I water every day?** Water every day only in coco, rockwool or small containers where the plant drinks the pot dry within a day. In soil, daily drenching keeps roots short of oxygen and is the most common cause of drooping, slow growth and fungus gnats. Lift the pot first: if it is still heavy, wait. **How much water should I give per watering?** In soil, give enough to wet the whole pot with a little runoff, roughly 10–20% of the pot's volume for an established plant. In coco and rockwool, water to 10–30% runoff each time so salts don't build up. Seedlings need far less: wet a small circle around the stem. **How do I know when my plant needs water?** Your plant needs water when the pot is clearly lighter than just after watering, the top few centimetres are dry and leaves are just starting to soften. Learn the weight of a freshly watered pot and of a dry one, then water at roughly the halfway point. A moisture probe 5 cm down helps in big pots. ## Sources 1. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 2. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ 3. Caplan D, Dixon M, Zheng Y, 2019. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience 54(5):964–969. https://doi.org/10.21273/HORTSCI13510-18 --- # How soon after harvest can I smoke my buds? > Cannabis can be smoked once it is properly dried, usually 7–14 days after harvest, when small stems snap and a sealed sample jar reads a stable 58–65% RH. It is noticeably better after at least 2 weeks of curing, and most growers cure for 4–8 weeks. Fresh or fast-dried samples smoke harsh and grassy and don't represent how the finished crop will taste. - Canonical: https://genetixbay.com/knowledge/answers/how-soon-after-harvest-can-i-smoke.html - Topic: Harvest and cure · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Also asked as: Can I smoke buds right after drying? | Can I smoke before the cure? | How long until my weed is smokable? | How many days after harvest can I try it? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer You can smoke cannabis once it is properly dried, usually 7–14 days after harvest, when small stems snap and a sealed sample jar reads a stable 58–65% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). It gets noticeably better after at least 2 weeks of curing, and most growers cure for 4–8 weeks. *Grower practice*: the timings are well established in practice, not optimised by research. ## Why Dryness sets the earliest date. Dried flower should sit at [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55–0.65 [1]. Wetter buds burn badly, go out and risk mould in the jar. Drying and curing shape the aroma. Air-drying shifts the oil away from volatile [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) [2], and in [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) were more affected by drying method than by storage [4]. A slow dry keeps more of them, and the cure lets the aroma settle. Potency doesn't climb with time. In storage [THC](https://genetixbay.com/knowledge/glossary/thc.md) slowly declines, oxidising to [CBN](https://genetixbay.com/knowledge/glossary/cbn.md) with air and breaking down with light [3]. Curing changes smoothness and aroma, not strength. ## The numbers | Stage | Days from harvest | Result | |---|---|---| | Fresh or fast-dried sample | 1–5 | Harsh, grassy; not representative | | Dried (stems snap) | 7–14 | Smokable | | Short cure | +2 weeks | Noticeably smoother (reported) | | Typical full cure | +4–8 weeks | Settled aroma (reported) | | Jar check | 12–24 h sealed | Stable 58–65% RH to start the cure | ## What to do 1. Dry for 7–14 days in the dark at 15–21 °C (60–70 °F) and 55–62% RH. 2. From day 5, bend small stems. When they snap, seal a sample in a jar for 12–24 hours. 3. If the jar reads a stable 58–65%, jar the crop about ¾ full and start curing. 4. Try a little after the first week of curing if you like, but judge the crop after 2–4 weeks or more. 5. [Burp the jars](https://genetixbay.com/knowledge/glossary/burping.md) daily in week 1, every 2–3 days in week 2, then weekly. ## Common mistakes - Microwaving a bud to try it on harvest day. - [Jarring](https://genetixbay.com/knowledge/glossary/curing-jar.md) before the stems snap. - Judging a whole crop on a sample that was dried fast. - Leaving jars in sunlight. ## Related - Full article: [Drying cannabis](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Answers: [why is my weed harsh?](https://genetixbay.com/knowledge/answers/why-is-my-weed-harsh.md) · [quick-drying methods](https://genetixbay.com/knowledge/answers/quick-drying-methods.md) · [whole plant or branches?](https://genetixbay.com/knowledge/answers/hang-whole-plant-or-branches.md) - Article: [curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Terms: [curing](https://genetixbay.com/knowledge/glossary/curing.md) · [stem snap test](https://genetixbay.com/knowledge/glossary/stem-snap-test.md) ## Follow-up questions **Can I quick-dry a sample bud to try early?** You can dry a small sample bud early, but it will smoke harsh and taste grassy, so it says little about the finished crop. Fast drying, with heat or a microwave, also drives off volatile terpenes and can partly decarboxylate cannabinoids. If you must sample, air-dry one small bud for a few days in a dark, dry spot and judge the real crop after the cure. **How long should I cure before smoking?** Cure cannabis for at least 2 weeks before judging it, and 4–8 weeks is common, according to grower practice. Over that time the bud's water activity should fall slowly from about 0.62–0.65 towards 0.55–0.58. Smoother smoke and rounder aroma are widely reported with longer cures, within reason, though curing chemistry is not well studied. **Does weed get stronger as it cures?** There is no good evidence that cannabis gets stronger as it cures. Cannabinoids in stored flower slowly decline, and THC oxidises to CBN with air and light, so potency at best holds steady. What curing changes is the experience reported by smokers: smoother smoke and settled aroma as moisture evens out. Store cured buds cool and dark. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 2. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 3. Fairbairn JW, Liebmann JA, Rowan MG, 1976. The stability of cannabis and its preparations on storage. Journal of Pharmacy and Pharmacology 28(1):1–7. https://doi.org/10.1111/j.2042-7158.1976.tb04014.x 4. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 --- # How tall do cannabis plants get indoors? > Indoor cannabis usually finishes about 60–150 cm (2–5 ft) tall, because the grower sets the height: a photoperiod plant grows 50–100% taller after the flip, stretchy cultivars up to 3×, so a plant flipped at 40–60 cm ends near 60–150 cm. Autoflowers usually fit a 140–160 cm tent. Outdoors, unrestricted plants reach about 1–5 m (3–16 ft). - Canonical: https://genetixbay.com/knowledge/answers/how-tall-do-plants-get-indoors.html - Topic: Basics · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) - Also asked as: How big do weed plants get? | Plant height indoors | Final height of a cannabis plant | How tall will my plant be after the flip? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Indoor cannabis usually finishes about 60–150 cm (2–5 ft) tall, because you decide. A [photoperiod plant](https://genetixbay.com/knowledge/glossary/photoperiod.md) grows 50–100% taller after the flip, and stretchy cultivars up to 3×, so final height ≈ height at the flip × 1.5–3. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) usually fit a 140–160 cm (4.6–5.3 ft) tent. *Grower practice*, anchored to [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) research. ## Why Veg height is your choice. A photoperiod plant stays vegetative under long days until you flip it, so [veg time](https://genetixbay.com/knowledge/glossary/veg-time.md) sets the starting height. The stretch adds the rest. Under short days, stems and [internodes](https://genetixbay.com/knowledge/glossary/internode.md) lengthened fastest from about day 5 to day 10 [1]. A plant-patent description puts the gain at 50–100% over the first two to three weeks after induction [2]; growers report 1.5× to 3×. Light shapes the plant. Higher light in veg gave shorter internodes and more compact plants [3]. A dim or distant light makes plants stretch and gap. Outdoors, there's no ceiling. Unrestricted plants commonly reach 1–5 m (3–16 ft), depending on [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) and season [4]. ## The numbers | Height at flip | Final, 1.5× | Final, 2× | Final, 3× | |---|---|---|---| | 30 cm (1 ft) | 45 cm | 60 cm | 90 cm | | 45 cm (1.5 ft) | 70 cm | 90 cm | 135 cm | | 60 cm (2 ft) | 90 cm | 120 cm | 180 cm | | Tent height | Usable plant height (about) | |---|---| | 140–160 cm | 55–90 cm | | 180–200 cm | 95–130 cm | Usable height = tent − pot (~30 cm) − 30–45 cm light gap − fixture and hangers (~10–15 cm). ## What to do 1. Work out your usable height before you plant. 2. Flip photoperiods at about half of it; a third for very stretchy cultivars. 3. Train flat with [LST](https://genetixbay.com/knowledge/glossary/lst.md) from early veg. 4. Keep light strong enough to hold internodes short. 5. Keep a little headroom for the light to be raised in week 3. ## Common mistakes - Vegging by the calendar and running out of room in week 3. - Assuming the breeder's "medium height" fits your tent. - Raising a weak light higher, which makes stretch worse. ## Related - Full article: [The cannabis life cycle](https://genetixbay.com/knowledge/basics/life-cycle.md) - Answers: [when to flip](https://genetixbay.com/knowledge/answers/when-to-flip-to-flower.md) · [plant too tall for the tent](https://genetixbay.com/knowledge/answers/plant-too-tall-for-tent.md) · [what size tent](https://genetixbay.com/knowledge/answers/what-size-grow-tent.md) - Article: [Stretchy, leggy cannabis](https://genetixbay.com/knowledge/diagnosis/stretching.md) - Terms: [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) · [internode](https://genetixbay.com/knowledge/glossary/internode.md) ## Follow-up questions **How much do plants stretch after the flip?** Cannabis plants usually stretch 50–100% in the first two to three weeks after the flip to 12/12, and grower reports range from about 1.5× to 3× the height at the flip. Stems and internodes lengthen fastest from about day 5 to day 10 of short days. Plan for it by flipping at about half the height you can fit. **How do I keep my plants short indoors?** Keep cannabis plants short indoors by flipping early, at about half your usable height, and training them flat. Low-stress training bends the main stem sideways; topping and a net (SCROG) spread the canopy. Strong light close to the canopy also keeps internodes short, while a weak or distant light makes plants stretch and grow gappy. **How tall should my grow tent be?** A grow tent for photoperiods should be about 180–200 cm (6–6.6 ft) tall, because plants commonly double in height after the flip. Autoflowers and short, trained plants fit a 140–160 cm (4.6–5.3 ft) tent. Allow for the pot, a 30–45 cm (12–18 in) gap to the light and the fixture itself when working out the plant's usable height. ## Sources 1. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 2. US Plant Patent PP30,434 (cannabis plant 'LW-BB1'), botanical description of post-induction stretch. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/PP30434 3. Moher M, Llewellyn D, Jones M, Zheng Y, 2021. High light intensities can be used to grow healthy and robust cannabis plants during the vegetative stage of indoor production. Preprints 2021040417 (not peer reviewed). https://doi.org/10.20944/preprints202104.0417.v1 4. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # How do I raise or lower the pH of my water? > Lower pH with a mineral acid pH down (phosphoric, nitric or sulfuric) and raise it with potassium hydroxide or potassium silicate, after the nutrients are in. Add a few drops per 10 litres, stir, wait, re-read. In hydro, recheck after 15-30 minutes of circulation. A steady rise of 0.1-0.4 pH per day in a healthy reservoir is normal, from nitrate uptake and aeration stripping CO2. - Canonical: https://genetixbay.com/knowledge/answers/how-to-adjust-ph.html - Topic: pH and EC · Type: How-to - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - Also asked as: How much pH down should I use? | How do I lower pH? | How do I raise pH? | Why does my hydro pH keep going up? | Does an air stone raise pH? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Lower [pH](https://genetixbay.com/knowledge/glossary/ph.md) with a mineral-acid pH down (phosphoric, nitric or sulfuric acid); raise it with potassium hydroxide or [potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md). Adjust after the nutrients are in, a few drops per 10 litres at a time, stirring and re-reading between doses. In hydro, recheck after 15–30 minutes of circulation. *Established.* ## Why Every acid and base is also a nutrient. [Phosphoric acid](https://genetixbay.com/knowledge/glossary/phosphoric-acid.md) adds phosphorus, nitric adds nitrogen, sulfuric adds [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md), and potassium hydroxide adds potassium [2]. Small doses don't matter; daily heavy dosing does, so count them. [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) is what fights you. Bicarbonate in [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md) neutralises acid, so the same dose of pH down moves soft water a long way and hard water barely at all [1]. One meq/L of acid neutralises one meq/L of alkalinity [1][2]. Hydro pH rises on its own. Plants take up [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), an anion, and release hydroxide or bicarbonate to stay balanced, so a nitrate-fed reservoir drifts upward as plants grow [3][4]. Aeration strips dissolved [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) and pushes pH up in the first hours after mixing. ## The numbers | Goal | Use | Adds | |---|---|---| | Lower pH, veg | Nitric or phosphoric acid | N or P | | Lower pH, flower / [N taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) | Phosphoric or sulfuric acid | P or S | | Raise pH | Potassium hydroxide | K | | Raise pH, with [silica](https://genetixbay.com/knowledge/glossary/silica.md) | Potassium silicate | K, Si | | Normal hydro drift | 0.1–0.4 pH/day upward | n/a | | Treat water alkalinity above | 100–150 mg/L as CaCO₃ (2–3 meq/L) | n/a | ## What to do 1. Calibrate the meter. 2. Mix all nutrients first; in hydro, aerate 30–60 minutes. 3. Add adjuster a few drops per 10 L, stir, wait 1–2 minutes, re-read. 4. Hydro: recheck after 15–30 minutes of circulation. 5. Let pH ride within the band (5.5–6.2 hydro, 5.8–6.3 [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md)); reset only when it leaves. 6. If pH won't hold, get a water report and treat alkalinity. *Safety:* concentrated acids and hydroxides burn skin and eyes. Gloves and goggles, good ventilation, and always add acid to water, never water to acid. ## Common mistakes - Overshooting, then correcting back and forth. - Adjusting before nutrients go in. - Chasing normal upward drift several times a day. - Using [nitric acid](https://genetixbay.com/knowledge/glossary/nitric-acid.md) during a nitrogen taper. ## Related - Full article: [Water quality: alkalinity and acids](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - Articles: [pH drift in hydro](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) - Answers: [pH before or after nutrients](https://genetixbay.com/knowledge/answers/ph-before-or-after-nutrients.md) · [vinegar or lemon?](https://genetixbay.com/knowledge/answers/vinegar-or-lemon-to-lower-ph.md) - Terms: [pH down](https://genetixbay.com/knowledge/glossary/ph-down.md) · [pH up](https://genetixbay.com/knowledge/glossary/ph-up.md) · [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md) ## Follow-up questions **Why does my hydro pH keep going up?** Hydro reservoir pH keeps going up mainly because cannabis absorbs nitrate faster than cations and releases hydroxide or bicarbonate to stay electrically balanced. Aeration stripping carbon dioxide, alkaline top-up water and algae in a lit reservoir add to it. A steady climb of about 0.1-0.4 pH per day with falling EC is normal; reset it when it leaves 5.5-6.2. **Does an air stone raise pH?** Yes, an air stone can raise reservoir pH, because strong aeration strips dissolved carbon dioxide, which otherwise forms carbonic acid. The effect is largest in the first hours after mixing, especially with carbonated groundwater, and depends on the water's alkalinity. Aerate a fresh mix for 30-60 minutes before the final pH adjustment so the reading settles. **Why does my pH bounce back after I add pH down?** pH bounces back after pH down when the water is high in alkalinity: bicarbonate buffers the acid, and as carbon dioxide leaves the solution the pH climbs again. Get a water report; above about 100-150 mg/L alkalinity as calcium carbonate, neutralise most of it with acid, leaving roughly 0.5-1 meq/L as a buffer in hydro. ## Sources 1. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 2. NC State Extension. Producing conventional tobacco transplants in greenhouses: water quality. https://content.ces.ncsu.edu/producing-conventional-tobacco-transplants-in-greenhouses-water-quality 3. Bugbee B, 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 4. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # How do I check trichomes? > Check cannabis trichomes with a 60–100× loupe or clip-on phone microscope, looking at the heads on the calyxes, not the sugar leaves. Sample a top cola, a mid-canopy bud and a lower bud, and score the share of clear, cloudy and amber heads. Start checking at the early end of the cultivar's window, counted from the flip plus the 10–14 day transition, and repeat every 2–3 days. - Canonical: https://genetixbay.com/knowledge/answers/how-to-check-trichomes.html - Topic: Harvest and cure · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Also asked as: How do I use a jeweller's loupe on trichomes? | What magnifier do I need for trichomes? | Can I check trichomes with a phone microscope? | Where on the bud should I look at trichomes? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Check [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) with a 60–100× [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) or clip-on phone microscope, on the [calyxes](https://genetixbay.com/knowledge/glossary/calyx.md) rather than the [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md). Sample the top, middle and bottom of the plant and score the share of clear, cloudy and amber heads. Most growers harvest at mostly cloudy with roughly 5–20% amber, and the exact mix is a matter of preference (*House position*). The method is *Grower practice*. ## Why [Trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) change as flowers mature. Research confirms that heads go from clear to cloudy to amber or brown, and that browning marks the gland ageing and dying back [1][3]. One bud is never uniform. Heads on the same [bract](https://genetixbay.com/knowledge/glossary/bract.md) mature at different rates, and those rates vary with [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) and plant age [1]. That is why you sample several buds and score a percentage instead of looking for one colour. Colour is a proxy, not a lab test. Automated trichome analysis was developed precisely because the clear/cloudy/brown scale is so widely used yet so little studied [2]. Your own records, run after run, are the calibration. ## The numbers | Item | Target | |---|---| | Magnification | 60–100× | | Where to look | Calyx heads, not sugar leaves | | Sites | [Top cola](https://genetixbay.com/knowledge/glossary/cola.md), mid canopy, lower bud | | Typical harvest mix | A few clear, mostly cloudy, about 5–20% amber | | Check frequency | Every 2–3 days, daily near the end | | Window | Count from the flip plus a 10–14 day transition | ## What to do 1. Check the date first: the breeder's flowering time plus 10–14 days from the flip. 2. Use bright, white light. Hold the bud steady, or cut a small sample. 3. Focus on the mushroom-shaped heads on the swollen calyxes. 4. Roughly score clear, cloudy and amber, for example 10/80/10. 5. Photograph the same buds each time. 6. Combine this with other signs: swollen calyxes, receded [pistils](https://genetixbay.com/knowledge/glossary/pistil.md), slowing water use. 7. Write down the score and harvest date in your journal for next time. ## Common mistakes - Reading the sugar leaves. - Checking only the top cola. - Using 30× and guessing. - Leaving plants for more amber until rot or [senescence](https://genetixbay.com/knowledge/glossary/senescence.md) sets in. - Putting plants in darkness before the chop. It's a *Myth*. ## Related - Full article: [Trichome ripeness: clear, cloudy, amber](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Answers: [harvest too early or late](https://genetixbay.com/knowledge/answers/harvesting-too-early-or-late.md) · [harvest in stages](https://genetixbay.com/knowledge/answers/harvest-in-stages.md) · [pistils browning early](https://genetixbay.com/knowledge/answers/pistils-turning-brown-early.md) - Article: [the flip-to-flower transition](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - Terms: [jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) · [trichome ripeness](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md) ## Follow-up questions **What magnification do I need to see trichomes?** You need about 60–100× magnification to read cannabis trichome heads properly. A 30× loupe shows the trichomes but makes clear, cloudy and amber heads hard to tell apart. A clip-on phone microscope or a pocket digital microscope in that range also lets you take photos, so you can compare the same bud over several days. **Why shouldn't I check trichomes on sugar leaves?** Do not judge cannabis ripeness from sugar-leaf trichomes, because they turn amber earlier than those on the calyxes. Reading them makes a plant look riper than it is and pushes growers to harvest too early. Look at the heads on the swollen calyxes in the body of the bud, at the top, middle and bottom of the plant. **How often should I check trichomes?** Check cannabis trichomes every 2–3 days once the plant reaches the early end of its flowering window, and daily as it gets close. Use the same buds each time and photograph them. Remember that a breeder's stated time often counts from first pistils, so add the 10–14 day transition after the flip when you plan. ## Sources 1. Punja ZK, Sutton DB, Kim T, 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 2. Sutton DB, Punja ZK, Hamarneh G, 2023. Characterization of trichome phenotypes to assess maturation and flower development in Cannabis sativa L. by automatic trichome gland analysis. Smart Agricultural Technology. https://www.limswiki.org/index.php/Journal:Characterization_of_trichome_phenotypes_to_assess_maturation_and_flower_development_in_Cannabis_sativa_L._by_automatic_trichome_gland_analysis 3. Livingston SJ, Quilichini TD, Booth JK, et al., 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37–56. https://doi.org/10.1111/tpj.14516 --- # How do I clone a cannabis plant? > To clone cannabis, cut an 8–15 cm (3–6 in) shoot tip with 2–3 nodes from a healthy vegetative plant, cut below a node with a clean blade, dip it in IBA rooting gel and set it in a moist plug. Keep it at 22–26 °C (72–79 °F), 75–90% RH under gentle light of 50–150 µmol/m²/s. Most cuttings root in 7–14 days. - Canonical: https://genetixbay.com/knowledge/answers/how-to-clone-cannabis.html - Topic: Cloning and mother plants · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: How do I take clones? | Cloning steps for beginners | How to take cuttings from a cannabis plant | Should I clone before flowering? | Is it OK to rename a clone? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Cut an 8–15 cm [shoot tip](https://genetixbay.com/knowledge/glossary/apical-meristem.md) with 2–3 nodes from a healthy vegetative plant, dip it in [IBA](https://genetixbay.com/knowledge/glossary/auxin.md) [rooting gel](https://genetixbay.com/knowledge/glossary/rooting-hormone.md), set it in a moist plug, and hold it at 22–26 °C (72–79 °F), 75–90% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) and 50–150 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md). Most cannabis cuttings root in 7–14 days. *Supported*. ## Why Auxin speeds rooting. An IBA gel gave 2.1 times the rooting success of a willow-extract gel and better root quality [1]. In [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), hormone-treated cuttings rooted far better than untreated ones [2]. Leaves feed the cutting. Three full leaves gave better roots than two, and trimming leaf tips cut rooting success from 71% to 53% [1]. Medium matters a great deal: in one trial rooting ranged from 13% to 80% across four media, with [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) best [2]. Clean cutting, clean clone. [Hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md) spreads through infected cuttings and tools [3]. Where you cut also matters: cuttings can carry over the character of the branch they came from [4], so take them from consistent spots. ## The numbers | Item | Target | |---|---| | Cutting | 8–15 cm (3–6 in), 2–3 nodes, ≥ 3 full leaves | | Medium temperature | 22–26 °C (72–79 °F) | | Humidity | 75–90% RH under a vented dome | | Light | 50–150 µmol/m²/s, 18–24 h | | Time to roots | 7–14 days | ## What to do 1. Water the mother the day before. Sterilise the blade. 2. Cut 45° just below a node on a firm upper-to-mid shoot. 3. Drop the cut straight into water so air doesn't enter the stem. 4. Remove only the lowest leaves; keep at least three full leaves. 5. Dip in rooting gel from a small decanted portion, then stick in a pre-moistened plug. 6. Dome, vent daily, and keep gentle light on. ## Common mistakes - Cuttings from a stressed, flowering or pest-ridden plant. - Double-dipping into the hormone stock. - Trimming every leaf in half. - Soggy plugs. - No labels: unnamed cuts get lost or renamed. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [How long do clones take to root?](https://genetixbay.com/knowledge/answers/how-long-do-clones-take-to-root.md) · [Do I need rooting hormone?](https://genetixbay.com/knowledge/answers/do-i-need-rooting-hormone.md) · [Best medium for rooting clones](https://genetixbay.com/knowledge/answers/best-medium-for-rooting-clones.md) - Terms: [cloning](https://genetixbay.com/knowledge/glossary/cloning.md) · [cutting](https://genetixbay.com/knowledge/glossary/cutting.md) · [mother plant](https://genetixbay.com/knowledge/glossary/mother-plant.md) ## Follow-up questions **Should I clone before flowering?** Yes. Take cannabis clones before you flip a plant to flower, ideally from a healthy plant in mid-to-late veg. Vegetative cuttings root in about 7–14 days, while cuttings from flowering plants root slower, often 2–4 weeks, and must re-veg. Cloning every candidate before flowering is the simple way to keep a keeper you only identify after harvest. **Is it OK to rename a clone?** No. A clone is the same genotype as its source, so it should keep its original name and a written history of who it came from and when. Renaming known cuts is a big part of why one cut circulates under many names and why buyers can't tell what they have. If you don't know the name, say so, and record what you do know. **Do I need to trim the leaves on a cutting?** Usually not. In a controlled cannabis study, cutting off leaf tips reduced rooting success from 71% to 53%, and cuttings with three leaves had better roots than those with two. Keep at least three fully expanded, uncut leaves, remove only the lowest ones that would sit in the medium, and control water loss with humidity instead. ## Sources 1. Caplan D, Stemeroff J, Dixon M, Zheng Y. 2018. Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science 98(5):1126-1132. https://doi.org/10.1139/cjps-2018-0038 2. Campbell SM, Anderson SL, Brym ZT, Pearson BJ, 2021. Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.). PLOS ONE 16(7): e0249160. https://doi.org/10.1371/journal.pone.0249160 3. Adkar-Purushothama CR, Sano T, Perreault JP. 2023. Hop latent viroid: a hidden threat to the cannabis industry. Viruses 15(3):681. https://doi.org/10.3390/v15030681 4. Olesen PO. 1978. On cyclophysis and topophysis. Silvae Genetica 27(5):173-178. https://www.thuenen.de/media/institute/fg/PDF/Silvae_Genetica/1978/Vol._27_Heft_5/27_5_173.pdf --- # How do I stop my grow tent from smelling? > Stop a grow tent smelling by keeping it under negative pressure and sending all exhaust air through an activated-carbon filter rated at or above the fan's airflow. Size the fan for about one tent air exchange per minute plus 25–50 % for filter and duct losses, seal unused ports, and keep RH below about 60 %. Never use an ozone generator in an occupied home. - Canonical: https://genetixbay.com/knowledge/answers/how-to-control-grow-smell.html - Topic: Environment · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) - Also asked as: How do I control weed smell from a grow? | Odour control for an indoor grow | Carbon filter but still smells | How do I hide grow smell at harvest? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Stop a grow tent smelling by keeping it under **[negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md)** and pulling every bit of [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) through an **activated-carbon filter rated at or above the fan's airflow**. Size the fan for about **one tent air exchange per minute, plus 25–50 %** for filter and duct losses. *Grower practice*. Rules on odour vary: some places require [home grows](https://genetixbay.com/knowledge/glossary/home-grow.md) to be undetectable from outside, so check your local rules. ## Why Flowering cannabis is loud on purpose. Besides [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), it makes [volatile sulphur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) the nose picks up at tiny concentrations [2]. Activated carbon traps odour molecules only while air is in contact with it. A filter rated above the fan, with the fan turned down, gives the air more contact time. Negative pressure means the fan removes air faster than it leaks in, so the walls bow slightly inwards. Every gap then leaks room air in, not smell out, and the filter becomes the only exit. Harvest and drying release the most smell, because cut plants lose water and volatiles fast [3]. Ozone generators are not the answer: they can reach harmful indoor levels without removing odour well [1]. ## The numbers | Tent | Volume | Fan, with filter | |---|---|---| | 60 × 60 × 160 cm (2 × 2 ft) | 0.58 m³ (20 ft³) | 100 mm (4 in), ~100 [CFM](https://genetixbay.com/knowledge/glossary/cfm.md) | | 90 × 90 × 180 cm (3 × 3 ft) | 1.5 m³ (52 ft³) | 100–125 mm (4–5 in), 100–200 CFM | | 120 × 120 × 200 cm (4 × 4 ft) | 2.9 m³ (102 ft³) | 150 mm (6 in), 150–250 CFM | | Filter rating | | at or above the fan's CFM | ## What to do 1. Hang the filter high, where warm, smelly air collects. 2. Connect filter → duct → fan → outlet so the fan **pulls** through the filter. 3. Seal joints; close every port except the low intakes. 4. Check the walls bow gently inwards. 5. Keep [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) below about 60 %; water vapour shortens carbon life. 6. Sniff the outlet weekly in flower; replace the carbon when it smells. 7. Dry, trim and [burp](https://genetixbay.com/knowledge/glossary/burping.md) jars inside the filtered space. ## Common mistakes - Fan before the filter, pushing smell out of every joint. - A filter smaller than the fan, run flat out. - Top ports left open. - Masking sprays or ozone instead of fixing airflow. - Drying in an open room. ## Related - Full article: [Airflow](https://genetixbay.com/knowledge/environment/airflow.md) - Guide: [Smell control basics](https://genetixbay.com/knowledge/guides/smell-control-basics.md) - [How long does a carbon filter last?](https://genetixbay.com/knowledge/answers/how-long-does-a-carbon-filter-last.md) - [Do I need an intake fan?](https://genetixbay.com/knowledge/answers/do-i-need-an-intake-fan.md) - Terms: [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) · [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md) ## Follow-up questions **Why does my tent still smell with a carbon filter?** A grow tent still smells with a carbon filter when air escapes around it: top ports or zips left open, a fan pushing through the filter instead of pulling, leaky duct joints, or a filter smaller than the fan, so air moves too fast to be cleaned. A saturated filter is the other cause; if you can smell plants at the exhaust outlet, replace the carbon. **Are ozone generators safe for grow smell?** No, ozone generators are not safe for controlling grow smell in a home. Ozone is a lung irritant, and public health guidance warns that generators sold as air cleaners can reach harmful indoor levels without removing odour well. They also damage plants, rubber and plastics. Use an activated-carbon filter on the exhaust instead, and never run ozone where people or pets breathe. **When does a grow smell the most?** A cannabis grow smells most from about week 2–3 of flower to harvest, and peaks during harvest, trimming and drying, when cut plants release volatiles fast. Strong cannabis aroma comes partly from volatile sulphur compounds the nose detects at tiny concentrations. Dry and trim inside the filtered tent with the fan running, and jar buds promptly once dry. ## Sources 1. US Environmental Protection Agency. Ozone generators that are sold as air cleaners. https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners 2. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196 3. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf --- # How do I lower the temperature in my grow tent? > Lower grow-tent temperature by removing the light's heat faster: more exhaust from a cooler room, drivers or ballasts outside the tent, lights dimmed 10–20 %, and lights run in the coolest hours. Aim for 24–28 °C (75–82 °F) in veg and 22–26 °C (72–79 °F) in flower. Above about 30 °C (86 °F) without added CO₂, photosynthesis falls. - Canonical: https://genetixbay.com/knowledge/answers/how-to-cool-a-grow-tent.html - Topic: Environment · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - Also asked as: My grow tent is too hot | How do I cool down a grow room? | Heat problems in my tent | Is 30 °C too hot for cannabis? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Lower grow-tent temperature by moving the light's heat out faster than it builds: more [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) from a cooler room, drivers outside the tent, lights dimmed **10–20 %**, and lights on during the coolest hours. Target **24–28 °C (75–82 °F) in veg** and **22–26 °C (72–79 °F) in flower**; above about **30 °C (86 °F)** without CO₂, [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) falls [1]. *Supported*. ## Why Nearly every watt the light draws ends up as heat in the tent. The exhaust fan can only replace hot air with room air, so the room temperature sets your floor. In cannabis, net photosynthesis and water-use efficiency drop above about 30 °C [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) unless light and CO₂ are both high [1]. CO₂ enrichment shifts the optimum warmer [2], which is why commercial enriched rooms run hotter than a tent should. Leaf temperature is what counts. Under [LED](https://genetixbay.com/knowledge/glossary/led.md), well-watered leaves usually run a little below air; under [HPS](https://genetixbay.com/knowledge/glossary/hps.md) they run warmer [3]. Hot rooms also warm the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). Above 24 °C (75 °F) in [DWC](https://genetixbay.com/knowledge/glossary/dwc.md), root-rot risk rises sharply [4]. ## The numbers | Item | Target | |---|---| | Veg, lights on | 24–28 °C (75–82 °F) | | Flower, lights on | 22–26 °C (72–79 °F) | | Late flower | 20–24 °C (68–75 °F) | | Hard limit, no CO₂ | 30–32 °C (86–90 °F) sustained | | Exhaust, lit tent | 1 full volume every 1–3 minutes, +25–50 % for filter and ducting | | Reservoir | 18–22 °C (64–72 °F) | ## What to do 1. Measure at canopy height with a shaded probe, plus leaf temperature with an [IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md). 2. Move LED drivers or ballasts outside the tent. 3. Raise exhaust speed; pull intake air from the coolest place you can. 4. Run the lights at night in summer. 5. Dim or raise the light 10–20 % if leaves read above about 28 °C (82 °F). 6. If the room itself is hot, cool the room (air conditioning) or run less light. ## Common mistakes - Copying a 28–30 °C CO₂-room setpoint into a tent without CO₂. - A bigger fan pulling 30 °C air from a hot attic. - Ignoring the reservoir in summer. - Plugging an air conditioner into the circuit already carrying the lights. ## Related - Full article: [Temperature by stage](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - [Should I run my room warmer with LEDs than with HPS?](https://genetixbay.com/knowledge/answers/led-grow-room-temperature.md) - [Do I need an intake fan?](https://genetixbay.com/knowledge/answers/do-i-need-an-intake-fan.md) - [Heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md) · [Airflow](https://genetixbay.com/knowledge/environment/airflow.md) - Terms: [heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md) ## Follow-up questions **Is 30 °C (86 °F) too hot for a grow tent?** 30 °C (86 °F) is the upper edge for cannabis in a tent without added CO₂. Research shows net photosynthesis and water-use efficiency fall above about 30 °C leaf temperature unless light and CO₂ are high. Sustained air above 30–32 °C (86–90 °F) is a hard limit. CO₂-enriched rooms run 28–30 °C, but copying that into an un-enriched tent is a mistake. **Should I run my lights at night to keep the tent cool?** Yes, running grow lights during the coolest part of the day, usually night-time, is a cheap way to keep a tent cool in summer. The heat load then lands when the intake air is coolest. Keep the dark period truly dark, and make sure the room stays quiet and light-tight during the daytime dark period. **Does a bigger exhaust fan always cool a tent?** A bigger exhaust fan cools a grow tent only if the air it pulls in is cooler than the tent. A lit tent usually needs one full air exchange every 1–3 minutes plus 25–50 % extra for a carbon filter and ducting. If the room itself runs at 30 °C, more airflow can't get the tent below 30 °C; then you need air conditioning or less light. ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 2. Chandra S, Lata H, Khan IA, ElSohly MA, 2011. Photosynthetic response of Cannabis sativa L., an important medicinal plant, to elevated levels of CO2. Physiology and Molecular Biology of Plants 17:291–295. https://doi.org/10.1007/s12298-011-0066-6 3. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 4. e-GRO / Colorado State University Extension, Root disease problems and management in hydroponic systems (root-zone 68–72 °F). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ --- # How do I fix nutrient lockout? > Fix nutrient lockout by finding its cause first: most lockout is root-zone pH out of range, salt build-up or damaged roots, not true antagonism. Calibrate your meter, check runoff pH and EC, and look at the roots. If runoff EC is about 0.8-1.0 mS/cm or more above input, flush the root zone with 2-3 times the pot volume, then resume normal feeding. Correct pH gradually and stop stacking boosters. - Canonical: https://genetixbay.com/knowledge/answers/how-to-fix-nutrient-lockout.html - Topic: Nutrients · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md) - Also asked as: How do I fix lockout? | My plant is not taking up nutrients | Should I flush for lockout? | Deficiency even though I'm feeding | What causes nutrient lockout? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Find the cause before you treat it. Most "[lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md)" is root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) out of range, [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) or failing roots, not a nutrient fight. If [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md) sits about 0.8–1.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) or more above what you feed, [flush](https://genetixbay.com/knowledge/glossary/flushing.md) the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) with 2–3 times the [pot volume](https://genetixbay.com/knowledge/glossary/pot-size.md), then go straight back to normal feeding. *Supported.* ## Why pH controls solubility. At high pH iron, manganese and zinc drop out of solution; at low pH calcium and magnesium uptake falls [3][4]. Alkaline water pushes the root zone up week by week even if you pH every feed [3]. Real [antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md) exists but is narrower than charts suggest. A review of 117 interactions found synergy far more often than antagonism; the ones that matter are among the cations [1]. In cannabis, high potassium supply lowered calcium and magnesium uptake [2], which is what stacked PK boosters do. Salt build-up raises root-zone EC until roots struggle to take up water and ions. That is the one case where a flush helps, because it treats the medium. ## The numbers | Check | Normal | Act if | |---|---|---| | Runoff pH, [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) or rockwool | 5.8–6.5 | Outside, or >0.5 from input and rising | | Runoff pH, soil | 6.0–7.0 | Below 5.8 or above 7.3 | | [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md) vs input | Equal to +0.5 mS/cm | +0.8–1.0 mS/cm or more | | Roots | White to cream, firm | Brown, slimy, smelly | ## What to do 1. Calibrate the [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) in fresh pH 7 and [pH 4 buffer](https://genetixbay.com/knowledge/glossary/calibration-solution.md). 2. Measure input and runoff pH and EC. 3. Check roots and watering: soggy pots and rot mimic lockout. 4. Salty root zone: flush 2–3× pot volume, slowly, then feed normally. 5. pH off: correct the input gradually; acidify alkaline water. 6. Stop stacking boosters and [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) on a complete base. ## Common mistakes - Flushing with plain water for every [leaf spot](https://genetixbay.com/knowledge/glossary/leaf-spot.md). - Adding more of the "missing" nutrient, which raises EC further. - Trusting an uncalibrated pen. - Expecting damaged leaves to turn green again. ## Related - Full article: [Nutrient antagonism and Mulder's chart](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md) - Articles: [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) · [pH and availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) - Answers: [do I need to pH?](https://genetixbay.com/knowledge/answers/do-i-need-to-ph-my-water.md) · [do damaged leaves recover?](https://genetixbay.com/knowledge/answers/do-damaged-leaves-recover.md) - Terms: [nutrient lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md) · [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) ## Follow-up questions **What is nutrient lockout?** Nutrient lockout is when a plant shows deficiencies although the feed contains the nutrient, because the roots cannot take it up. The usual causes are root-zone pH out of range, salt build-up in the medium, damaged or rotting roots, and occasionally a real antagonism such as excess potassium suppressing calcium and magnesium. Measure before guessing. **How do I flush for lockout?** To flush for lockout, record input and runoff pH and EC, then run about 2-3 times the container volume through slowly in several passes: pH-adjusted water at about 6.3-6.8 for soil, or a light solution at EC 0.4-0.8 mS/cm with calcium and magnesium at pH 5.8-6.0 for coco. Stop when runoff EC is within 0.3-0.5 of input, then feed normally. **How long does it take a plant to recover from lockout?** Once the root zone is back in range, new growth usually looks normal within about a week, which is grower experience rather than a tested figure. Damaged leaves stay damaged, so judge recovery on the newest growth only. If new leaves still show symptoms after 7-10 days, recheck pH, EC and the roots before adding anything. ## Sources 1. Rietra RPJJ, Heinen M, Dimkpa CO, Bindraban PS, 2017. Effects of nutrient antagonism and synergism on yield and fertilizer use efficiency. Communications in Soil Science and Plant Analysis 48(16):1895-1920. https://hub.ifdc.org/handle/20.500.14297/2410 2. Saloner A, Sacks MM, Bernstein N, 2019. Response of medical cannabis (Cannabis sativa L.) genotypes to K supply under long photoperiod. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 3. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 4. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # How do I get bigger, denser buds? > Bigger, denser buds come mainly from more light at every bud site: 800–1,200 µmol/m²/s at canopy in flower at ambient CO₂, on an even canopy. Then keep flower days at 22–26 °C (72–79 °F), feed a complete, balanced flower diet through to harvest, and harvest ripe. Bloom boosters, pre-harvest flushing and 48-hour darkness don't help. - Canonical: https://genetixbay.com/knowledge/answers/how-to-get-bigger-denser-buds.html - Topic: Training · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: How do I get dense buds? | Tips for bigger buds | How do I fatten up buds in late flower? | What makes buds rock hard? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Bigger, denser buds come mainly from more light at each bud site: 800–1,200 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) at canopy in flower at ambient CO₂, on an [even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md). Then keep flower days at 22–26 °C (72–79 °F), feed a balanced diet through to harvest and harvest ripe. *Supported* for light; the rest is established practice. ## Why Light is the biggest lever. Dry flower yield rose linearly from 116 to 519 g/m² as canopy light went from 120 to 1,800 µmol/m²/s, with no change in potency per gram [1]. Light has to reach the buds. Lower, shaded buds are smaller and carry fewer [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) [2], so training for an even canopy matters as much as the lamp. Tuck, don't pluck: leaves are the solar farm feeding the buds. Heat loosens buds: [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) falls above about 30 °C (86 °F) [3], and hot tops [foxtail](https://genetixbay.com/knowledge/glossary/foxtailing.md). Feed enough, not extra. Yield plateaued at about 25–60 mg/L phosphorus; more P added nothing [4]. Don't starve the finish. Pre-harvest [flushing](https://genetixbay.com/knowledge/glossary/flushing.md) is a *Myth* and harmful: buds pack on most of their final weight and resin late. [Taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) instead, keeping P, K, Ca, Mg and [micros](https://genetixbay.com/knowledge/glossary/micronutrient.md) fed. A mild, controlled dry-down in late flower raised [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) and cannabinoids in one study [5], and the founder uses it; cultivars differ. ## The numbers | Lever | Target | |---|---| | Flower PPFD, ambient CO₂ | 800–1,200 µmol/m²/s (35–56 mol/m²/day) | | Flower PPFD, 900–1,200 ppm CO₂ | 1,000–1,500 µmol/m²/s | | Canopy evenness | Tops within 10–15 cm (4–6 in) | | Day temperature, mid flower | 22–26 °C (72–79 °F) | | Phosphorus | About 40–60 mg/L; no gain above | | Harvest | Mostly [cloudy trichomes](https://genetixbay.com/knowledge/glossary/trichome-ripeness.md), some amber | ## What to do 1. Measure PPFD at canopy with a quantum sensor; raise it 10–15% every 3–5 days toward 800–1,200. 2. Level the canopy with [LST](https://genetixbay.com/knowledge/glossary/lst.md), [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md) or supercropping; lollipop the lower third. 3. Hold [canopy temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) at 22–26 °C. 4. Feed a complete flower diet; taper nitrogen in the last weeks. 5. Count from the flip plus the 10–14 day transition, and harvest on the [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md). ## Common mistakes - Pre-harvest flushing or [48 hours of darkness](https://genetixbay.com/knowledge/glossary/darkness-before-harvest.md). Both are *Myths*. - Stacking [bloom boosters](https://genetixbay.com/knowledge/glossary/bloom-booster.md) on a full feed. - Harvesting early because the calendar says "week 8". ## Related - Full article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Answers: [airy buds](https://genetixbay.com/knowledge/answers/why-are-my-buds-airy.md) · [increasing yield](https://genetixbay.com/knowledge/answers/how-to-increase-yield-indoors.md) · [when buds grow most](https://genetixbay.com/knowledge/answers/when-do-buds-grow-the-most.md) - Nutrients: [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) · [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) ## Follow-up questions **Do bloom boosters make buds denser?** No. Bloom boosters, mostly concentrated phosphorus and potassium, don't make cannabis buds bigger or denser once the base feed is complete. Controlled trials found flower yield plateaued at around 25–60 mg/L phosphorus, and more did nothing but raise runoff. Spend the money on light and canopy evenness instead, which reliably raise yield. **Does darkness before harvest make buds denser?** No. Putting plants in 24–72 hours of darkness before harvest is a myth, and GenetixBay calls it nonsense: it cuts photosynthesis in the final days, when the plant is still finishing. The founder has run a standing 20-year challenge for a sound peer-reviewed study showing a benefit, with a seed prize, and nobody has claimed it. Harvest on the trichomes instead. **Does supercropping make better buds?** GenetixBay endorses supercropping for better buds: the founder snaps stems all the time and finds the buds improve. That is grower practice, house-endorsed; no controlled study has measured it yet. The supported benefit is canopy levelling, which puts more tops in strong light. Supercrop green stems in late veg or the first two weeks of flower, gently, without splitting the skin. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 3. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 4. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323 5. Caplan D, Dixon M, Zheng Y, 2019. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience 54(5):964–969. https://doi.org/10.21273/HORTSCI13510-18 --- # How can I increase my yield indoors? > Increase indoor yield with more usable light first: dry flower yield rose linearly from 116 to 519 g/m² as canopy PPFD went from 120 to 1,800 µmol/m²/s. Then fill the space with an even canopy, through training or more plants per m², give roots enough volume and water, and feed through to harvest. Defoliation doesn't raise yield; pre-harvest flushing costs it. - Canonical: https://genetixbay.com/knowledge/answers/how-to-increase-yield-indoors.html - Topic: Training · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: How do I increase my cannabis yield? | Tips for more yield indoors | How do I maximise my harvest? | Does defoliation increase yield? | Does higher planting density increase yield? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Add usable light first. Dry flower yield rose linearly from 116 to 519 [g/m²](https://genetixbay.com/knowledge/glossary/yield.md) as canopy [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) went from 120 to 1,800 µmol/m²/s at ambient CO₂ [1]. Then fill the floor with an [even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md), give roots enough volume and water, and feed through to harvest. *Supported* by controlled cannabis trials. ## Why Light is the biggest lever, and the response didn't saturate in the best trial [1]. Practical flower targets are 800–1,200 µmol/m²/s, higher with CO₂. Light only counts if the canopy catches it. Bare floor wastes photons. Higher [planting density](https://genetixbay.com/knowledge/glossary/plant-density.md) raised yield per m² in controlled work [2], and density is among the strongest yield drivers in the cannabis literature [4]. Training a few plants flat ([SCROG](https://genetixbay.com/knowledge/glossary/scrog.md), [LST](https://genetixbay.com/knowledge/glossary/lst.md)) fills space the same way. [Defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md) doesn't add yield. Removing leaves three weeks before harvest, or the lower third at the flip, left yield per plant unchanged [3]. The house position is tuck, don't pluck. Roots set a ceiling. Doubling [rooting volume](https://genetixbay.com/knowledge/glossary/pot-size.md) raised biomass by about 43% across crops [5]; bigger pots yield more within reason, traded against how often you can water and feed. The finish counts. Pre-harvest [flushing](https://genetixbay.com/knowledge/glossary/flushing.md) is a *Myth* that starves the plant while it packs on final weight; [taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) instead. ## The numbers | Lever | Target | Evidence | |---|---|---| | Flower PPFD, ambient CO₂ | 800–1,200 µmol/m²/s | Supported [1] | | Canopy cover at flip | 70–80% of floor, filled by [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) | Grower practice | | Density, [sea of green](https://genetixbay.com/knowledge/glossary/sog.md) | 9–25 plants/m² (1–2.3 per ft²) | Supported [2] | | Pot, [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) in soil | 11–25 L (3–7 US gal) | Supported [5] | | Flower day temperature | 22–26 °C (72–79 °F) | Grower practice | | Defoliation | Neutral for yield | Supported [3] | ## What to do 1. Measure PPFD with a quantum sensor grid; fix dark corners first. 2. Fill the floor: more plants, or train fewer plants flat before the flip. 3. Use the biggest pot you can water properly. 4. Keep the climate steady and feed a complete diet through to harvest. 5. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md): plant in the final pot and use LST, not topping; any setback costs yield. 6. Check local [plant-count rules](https://genetixbay.com/knowledge/glossary/plant-count-limit.md) before adding plants. ## Common mistakes - Buying additives before measuring light. - Bare floor at the flip. - Stripping leaves for yield. - Flushing or darkening plants before harvest. ## Related - Full article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Answers: [bigger, denser buds](https://genetixbay.com/knowledge/answers/how-to-get-bigger-denser-buds.md) · [yield per watt](https://genetixbay.com/knowledge/answers/grams-per-watt.md) · [plants per tent](https://genetixbay.com/knowledge/answers/how-many-plants-per-tent.md) - Training: [defoliation](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) · [SOG](https://genetixbay.com/knowledge/training/sog.md) - Terms: [plant density](https://genetixbay.com/knowledge/glossary/plant-density.md) ## Follow-up questions **Does defoliation increase yield?** No. In the best controlled data, defoliation three weeks before harvest and lower-third removal at the flip didn't change flower or cannabinoid yield per plant, and at commercial density yield per square metre matched the control. Stripping within reason doesn't hurt, but GenetixBay's house position is tuck, don't pluck: the founder finds tucking leaves away from buds helps more. **Does higher planting density increase yield?** Yes, higher planting density increases cannabis yield per square metre, according to controlled research on drug-type cannabis, and density is one of the strongest yield drivers in a meta-analysis of the literature. The trade-off is less uniform cannabinoids between plants, harder airflow at the base and faster disease spread. Plant-count limits apply in many places; check your local rules. **Do bigger pots increase yield?** Bigger pots increase yield within reason: across many crops, doubling rooting volume raised plant biomass by about 43% on average. Pot size is a trade-off with feeding frequency, though. GenetixBay's founder has grown over 4 ounces from a 16-ounce cup by watering and feeding very often. Small pots need frequent care; big pots forgive more but dry slower. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 3. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 4. Backer R, Schwinghamer T, Rosenbaum P, et al., 2019. Closing the yield gap for cannabis: a meta-analysis of factors determining cannabis yield. Frontiers in Plant Science 10:495. https://doi.org/10.3389/fpls.2019.00495 5. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 --- # How do I keep my grow tent warm in winter? > Keep a grow tent warm in winter by keeping the light's own heat in: slow the exhaust on a thermostat, insulate the tent and floor, run the lights during the coldest hours, and only then add a thermostat-controlled heater. Hold 24–28 °C (75–82 °F) by day in veg, 22–26 °C (72–79 °F) in flower, nights 3–6 °C (5–10 °F) cooler, and the root zone at 18–22 °C (64–72 °F). - Canonical: https://genetixbay.com/knowledge/answers/how-to-keep-a-grow-tent-warm.html - Topic: Environment · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - Also asked as: My grow tent is too cold | How do I heat a grow tent? | Growing in a cold garage or basement | Grow tent temperature drops at night - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Keep a grow tent warm in winter by keeping the light's heat in before buying any: slow the [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) on a thermostat, insulate, run the lights in the coldest hours, then add a **thermostat-controlled heater**. Hold **24–28 °C (75–82 °F)** by day in veg, **22–26 °C (72–79 °F)** in flower, nights **3–6 °C (5–10 °F)** cooler. *Grower practice*. ## Why Cold leaves photosynthesise slowly; the cannabis optimum is around 25–30 °C [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) under strong light [1]. A cold tent wastes the light. Cold roots take up water and nutrients slowly. Hydroponic [root zones](https://genetixbay.com/knowledge/glossary/root-zone.md) belong at 18–22 °C (64–72 °F) [2], and pots on a winter floor can sit far below air temperature. Big lights-off drops push humidity up. Cold, damp nights in flower are when [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md) starts [4]. Heaters are the biggest single electrical load in many [home grows](https://genetixbay.com/knowledge/glossary/home-grow.md), and overloaded outlets and cords are a leading cause of home electrical fires [3]. ## The numbers | Item | Target | |---|---| | Veg, lights on | 24–28 °C (75–82 °F) | | Flower, lights on | 22–26 °C (72–79 °F) | | Night drop | 3–6 °C (5–10 °F) | | Root zone / reservoir | 18–22 °C (64–72 °F) | | Too cold | canopy below 15 °C (59 °F) | | Heater on a 15 A, 120 V circuit | keep the whole circuit under 1,440 W continuous | ## What to do 1. Put the exhaust on a thermostat or speed controller so it slows when the tent is cool. 2. Run the lights through the coldest hours, usually overnight. 3. Lift pots onto foam board or a pallet; insulate under a reservoir. 4. Wrap the tent in a blanket or foam panels, keeping intakes clear. 5. Add an enclosed, thermostat-controlled electric heater with tip-over and overheat cut-offs, outside or low in the tent. 6. Plug the heater straight into a wall outlet and add up the circuit's load. **Safety:** never run open-element or combustion heaters near the tent, never through a thin extension cord, and keep a working smoke alarm nearby [3]. ## Common mistakes - Heating the tent while the exhaust runs flat out. - A heater with no thermostat. - Heater and lights on the same overloaded circuit. - Warm air, cold pots on concrete. - Daylight leaking into a garage during the dark period. ## Related - Full article: [Temperature by stage](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.md) - [Is an indoor grow a fire risk?](https://genetixbay.com/knowledge/answers/grow-room-electrical-safety.md) - Guide: [Electrical and water safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md) - Terms: [temperature](https://genetixbay.com/knowledge/glossary/temperature.md) ## Follow-up questions **What heater is safe for a grow tent?** The safest grow-tent heater is an enclosed, thermostat-controlled electric unit such as an oil-filled radiator or a ceramic heater with tip-over and overheat cut-offs, placed outside or low in the tent away from water and fabric. Never use an open-element heater near plastic or water, never use a combustion heater inside, and plug it straight into the wall, not a shared power strip. **Should my lights be on at night in winter?** Yes, in a cold room run the grow lights during the coldest hours, usually overnight, so their heat lands when the tent most needs it. The dark period then falls in the warmer daytime. Keep the dark period truly dark: a garage or basement with daylight leaks will interrupt flowering in photoperiod plants. **How do I keep the roots warm in a cold grow room?** Keep roots warm in a cold grow room by lifting pots off concrete onto foam board or a wooden pallet, and by watering with water at about 20 °C (68 °F). In hydro, use an aquarium heater in the reservoir set to 18–20 °C (64–68 °F). Cold roots slow water and nutrient uptake even when the air is warm, and the target is 18–22 °C. ## Sources 1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 2. e-GRO / Colorado State University Extension, Root disease problems and management in hydroponic systems (root-zone 68–72 °F). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ 3. US Fire Administration. Electrical fire safety (overloaded outlets, extension cords, smoke alarms). https://www.usfa.fema.gov/prevention/home-fires/prevent-fires/electrical/ 4. Utah State University Extension. Hemp bud rot (IPM fact sheet). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot.php --- # How do I lower the humidity in my grow tent? > Lower grow-tent humidity by removing the water the plants transpire: more exhaust if the room air is drier, then a dehumidifier sized to roughly the litres you irrigate per day, running through lights-off. Targets are 55–70 % RH in veg, 50–60 % in early flower and 40–50 % in late flower. Ramp temperature down slowly at lights-off and remove standing water. - Canonical: https://genetixbay.com/knowledge/answers/how-to-lower-humidity-in-a-grow-tent.html - Topic: Environment · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - Also asked as: Humidity too high in my grow tent | How do I reduce RH in a grow room? | How can I lower humidity without a dehumidifier? | Why does humidity spike when the lights go off? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Lower grow-tent humidity by removing the water your plants breathe out: [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) more air if the room is drier, and if it isn't, run a [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) sized to roughly the litres you irrigate per day. Aim for **40–50 % [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) in late flower** and keep it at or below **55 % at lights-off**. *Supported* for the disease risk; sizing is *Grower practice*. ## Why Almost all irrigation [water leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) the plant as vapour. Four big plants in a 1.2 × 1.2 m (4 × 4 ft) tent can add 6–8 L a day. That water has to go somewhere. High humidity in flower is how [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) start [2][3]. In a 2025 cannabis study, roughly 78–98 % RH delayed flowering and lowered biomass and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) compared with 37–58 % RH [1]. When the lights go off, air cools and relative humidity rises even though no water was added. Surfaces near the [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) get wet [4]. ## The numbers | Stage | RH target | Air temperature | |---|---|---| | Veg | 55–70 % | 24–28 °C (75–82 °F) | | Flower weeks 1–4 | 50–60 % | 23–27 °C (73–81 °F) | | Flower week 5 to harvest | 40–50 % | 20–25 °C (68–77 °F) | | Lights-off in flower | ≤ 55 %, surfaces ≥ 3 °C (5 °F) above dew point | | | Dehumidifier capacity | ≈ litres irrigated per day, at real conditions | | ## What to do 1. Check the hygrometer first (salt test) and read it at canopy height. 2. Raise exhaust speed if the room air is drier than the tent. 3. Empty saucers and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) trays; lid any reservoir. 4. Thin dense interior leaves so air reaches the middle of the canopy ("tuck, don't pluck" first). 5. Add a dehumidifier on a humidistat, inside or beside the tent, and keep it on through lights-off. 6. Ramp temperature down over 30–60 minutes at lights-off. ## Common mistakes - Buying a dehumidifier on its 30 °C / 80 % RH rating; it removes far less at 24 °C / 50 %. - Watching the daytime average and missing the lights-off spike. - Turning fans off at night. - Pulling "dry" air from a room that is just as humid as the tent. ## Related - Full article: [Humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - [How do I raise the humidity in my grow tent?](https://genetixbay.com/knowledge/answers/how-to-raise-humidity-in-a-grow-tent.md) - [How do I check if my hygrometer is accurate?](https://genetixbay.com/knowledge/answers/calibrate-a-hygrometer.md) - [VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md) - Terms: [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) · [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) ## Follow-up questions **How can I lower humidity without a dehumidifier?** Without a dehumidifier, lower grow-tent humidity by exhausting more air, as long as the room you pull from is drier than the tent; that is the cheapest fix. Then remove standing water and runoff trays, water early in the light period, thin dense interior leaves and keep the tent slightly warmer at lights-off. If the room itself sits above about 60 % RH, only a dehumidifier will work. **What size dehumidifier for a grow tent?** As a first estimate, a grow-tent dehumidifier should remove about as many litres per day as the plants are irrigated, because most irrigation water is transpired into the air. Four large plants in a 1.2 × 1.2 m (4 × 4 ft) tent can add 6–8 L of vapour daily. Check the rating conditions: units rated at 30 °C and 80 % RH remove far less at 24 °C and 50 %. **Why does humidity spike at lights-off?** Humidity spikes at lights-off because the air cools: the same water vapour in cooler air means higher relative humidity, and surfaces near the dew point collect condensation, where bud rot starts. Ramp the temperature down over 30–60 minutes instead of a sudden drop, keep the dehumidifier and circulation fans running in the dark, or add a little heat during the dark period. ## Sources 1. Corredor-Perilla IC, Kwon H, Park J, 2025. High relative humidity effects in cannabis. Frontiers in Plant Science 16:1678142. https://doi.org/10.3389/fpls.2025.1678142 2. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 3. Utah State University Extension. Hemp bud rot (IPM fact sheet). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot.php 4. Allen RG et al., 1998. FAO-56 Chapter 3 (vapour pressure). https://www.fao.org/4/x0490e/x0490e07.htm --- # How do I stop my plants from turning hermaphrodite? > Prevent hermaphrodites by starting with well-bred genetics first, then removing the stresses that reveal weak plants. Choose lines with a published herm rate and plant count, keep the 12-hour dark period fully light-tight, hold canopy temperature under about 30 °C (86 °F), and avoid heavy pruning or drought in flower. A herm is mainly a breeding fault: cull any plant that herms and never breed from it. - Canonical: https://genetixbay.com/knowledge/answers/how-to-prevent-hermaphrodites.html - Topic: Diagnosis · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - Also asked as: How do I prevent herms? | How to avoid nanners in flower | Stop my plants hermying | What causes cannabis to herm? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Start with sound genetics, then take away the stresses that reveal weak plants. Buy lines that publish a [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md) with a [plant count](https://genetixbay.com/knowledge/glossary/plant-count-limit.md), keep the 12-hour dark period fully light-tight, and keep the canopy under about 30 °C (86 °F). *House position*: [herms](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) are mainly breeder error, so cull any plant that herms and never breed from it. The stress triggers are *Supported*. ## Why Genetics comes first. In [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), sex expression has a genetic basis and responds to selection [2], and genome-wide work has mapped [loci](https://genetixbay.com/knowledge/glossary/locus.md) tied to it [3]. A line built on repeated [selfing](https://genetixbay.com/knowledge/glossary/selfing.md), careless feminising or untested crosses carries the tendency into every pack. Stress is the trigger. Research links interrupted darkness, altered [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md), low temperatures and certain chemicals to [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) on female plants [1]. Heat at the [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) stresses the plant as well [4]. A stable plant next to the same leak stays female, which is why GenetixBay reads stress as a test the plant either passes or fails. Herms spread their own weakness. Pollen from a herm gives almost all female seed carrying the same tendency [1]. ## The numbers | Control | Target | |---|---| | Dark period in flower | 12 h (or 11 h on [13/11](https://genetixbay.com/knowledge/glossary/13-11.md)), uninterrupted, light-tight | | Leak test | Nothing visible after 5–10 minutes with eyes adjusted | | [Canopy temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) | Under about 30 °C (86 °F) | | Herm onset to watch for | Week 4 of flower onwards [1] | | Line standard | Published herm rate; under 2% needs about 150 plants to verify | ## What to do 1. Buy from breeders who publish tester herm rates with plant counts. Avoid lines of untested crosses of famous cuts. 2. Seal the leaks: zipper ends, duct ports, equipment [LEDs](https://genetixbay.com/knowledge/glossary/led.md). Use a timer you trust. 3. Don't open the tent in the dark period. 4. Keep leaf temperature down at the tops, and keep watering and feeding steady through flower. 5. Do heavy pruning in veg, not mid-flower. 6. Inspect bud interiors and nodes weekly from week 3–4 with a hand lens. 7. If a plant herms, bag it, remove it, record it and tell the breeder. ## Common mistakes - Buying "free" or untested seed and blaming the tent. - Keeping a herm clone because it smokes well. - Running far past the [harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md). - Calling late [bananas](https://genetixbay.com/knowledge/glossary/nanners.md) normal. ## Related - Full article: [Hermaphrodite cannabis (bananas and nanners)](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - Answers: [seeds in my buds](https://genetixbay.com/knowledge/answers/why-are-there-seeds-in-my-buds.md) · [can you smoke a hermie?](https://genetixbay.com/knowledge/answers/can-you-smoke-a-hermie.md) · [opening the tent at night](https://genetixbay.com/knowledge/answers/opening-tent-during-dark-period.md) - Articles: [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) · [feminised seed and sex reversal](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md) - Terms: [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md) · [herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) ## Follow-up questions **Can I stop a herm-prone strain from herming?** You can reduce, but not reliably stop, herming in a herm-prone cannabis line. A perfect environment removes the triggers, such as light leaks, heat and drought, but the tendency is in the genetics and can still show late in flower. GenetixBay's position is that herm-prone lines are mainly breeder error: grow them out once if you must, cull any herm, and replace the line. **Do feminised seeds herm more than regular seeds?** Feminised seeds herm more only when they come from careless feminising, such as reversing an unproven female or using pollen from a stress herm. Well-made feminised seed from a female proven stable over several runs can be very stable. Ask for the herm rate and plant count from tester grows; GenetixBay disqualifies lines above 2% in tester grows. **Does stress cause hermaphrodites?** Stress triggers hermaphrodite flowers in cannabis plants that are already susceptible; it does not make a well-bred female herm. Research links interrupted darkness, altered photoperiods, low temperatures and chemicals to male flowers on females, yet the same light leak leaves a stable clone beside it untouched. Fix the stress to protect the room, and cull the plant that failed the test. ## Sources 1. Punja ZK, Holmes JE., 2020. Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences: Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Faux AM, Berhin A, Dauguet N, Bertin P. 2014. Sex chromosomes and quantitative sex expression in monoecious hemp (Cannabis sativa L.). Euphytica 196(2):183-197. https://doi.org/10.1007/s10681-013-1023-y 3. Petit J, Salentijn EMJ, Paulo MJ, Denneboom C, Trindade LM. 2020. Genetic architecture of flowering time and sex determination in hemp (Cannabis sativa L.): a genome-wide association study. Frontiers in Plant Science 11:569958. https://doi.org/10.3389/fpls.2020.569958 4. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x --- # How do I prevent pests in an indoor grow? > To prevent pests in an indoor grow, stop them coming in and catch the rest early. Quarantine every new clone for 2–3 weeks, start from seed where you can, keep outdoor clothes, pets and houseplants out, and work clean rooms first. Scout leaf undersides weekly with a 10–20x lens, count sticky cards weekly, release preventive predators in veg, and clean the room between cycles. - Canonical: https://genetixbay.com/knowledge/answers/how-to-prevent-pests-indoors.html - Topic: Pests · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - Also asked as: IPM for an indoor grow | How do I prevent pests in a grow tent? | How do I keep bugs out of my grow room? | Pest prevention routine indoors | How do I stop spider mites and thrips getting in? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Prevent indoor pests in two layers: keep them out, then find the ones that get in while they are few. Quarantine every incoming plant for 2–3 weeks, scout weekly with a 10–20x lens and [sticky cards](https://genetixbay.com/knowledge/glossary/sticky-trap.md), and set up predators in veg. *Supported*; the quarantine length is *Grower practice*. ## Why Most problems arrive on plants, people and media rather than appearing from nowhere: clones and [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md) carry [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md), [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) and mildew into rooms [1]. Early numbers are small and fixable. A spider mite generation can finish in under a week when it is warm, so a colony missed for a fortnight becomes a room problem [2]. Cards and lenses see different pests. Sticky cards catch flying adults such as gnats, thrips and [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md) [3]; mites need a lens on leaf undersides [2]. Predators work best before the outbreak. Releasing when pests are first seen, at low numbers, is the standard advice [4]. Wet media breeds gnats. Constantly wet, organic-rich media and unfinished compost feed [fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) larvae [5]. ## The numbers | Task | How often | Detail | |---|---|---| | Quarantine new plants | Every arrival | 2–3 weeks, separate space | | Leaf-underside scouting | Weekly | 10–20x lens, about 12 leaves across the canopy | | Sticky cards | Count and replace weekly | Yellow near media and canopy; blue for thrips | | Preventive predators | In veg | Species that persist on low prey | | Room clean-out | Between cycles | Plant-free and dry for several days | ## What to do 1. Start from seed or tested clean stock where you can. 2. Quarantine and inspect every clone before it joins the room. 3. Visit the grow before the garden, never after it in the same clothes. Keep pets and houseplants out. 4. Screen or filter the intake. 5. Let soil surfaces dry between waterings; store media bags closed. 6. Scout and count weekly, and write it down. 7. Release preventive predators in veg; avoid residual pesticides. 8. Clean and empty the room between cycles. ## Common mistakes - Skipping quarantine "because it's from a friend". - Waiting for webbing before looking. - Hanging sticky cards and never counting them. - Spraying on a calendar instead of scouting. ## Related - Full article: [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - Guide: [Pest prevention for beginners](https://genetixbay.com/knowledge/guides/pest-prevention-for-beginners.md) - Answers: [How pests get into a sealed tent](https://genetixbay.com/knowledge/answers/how-did-pests-get-in-my-tent.md) · [Do sticky traps work?](https://genetixbay.com/knowledge/answers/do-sticky-traps-work.md) - Terms: [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) · [quarantine](https://genetixbay.com/knowledge/glossary/quarantine.md) · [predatory mite](https://genetixbay.com/knowledge/glossary/predatory-mite.md) ## Follow-up questions **How long should I quarantine new clones?** Quarantine new cannabis clones in a separate space for at least 2–3 weeks, which grower practice treats as long enough for a pest generation and latent powdery mildew to show. Inspect leaf undersides with a 30–60x loupe for mites, thrips, whitefly eggs and mildew. Test mothers for hop latent viroid too, because no inspection will show a viroid. **Should I release predatory mites before I see pests?** Yes, preventive predator releases suit indoor cannabis, as long as you choose species that survive on few prey. Neoseiulus californicus tolerates warmer, drier rooms and persists at low prey numbers, so it fits preventive use against spider mites, and soil predatory mites help against gnats and thrips pupae. Release in veg and avoid residual pesticides, which kill them. **What should I check every week for pests?** Every week, check the undersides of about a dozen leaves across the canopy with a 10–20x lens, tap a few branches over white paper, and count and replace sticky cards. Note hot spots near lights and walls, and write the counts down. Rising card counts or the first stippled leaves are your early warning, while numbers are still small enough to fix in veg. ## Sources 1. Punja ZK et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 2. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 3. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects 4. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf 5. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf --- # How do I raise the humidity in my grow tent? > Raise grow-tent humidity by keeping the water your plants transpire: slow the exhaust first, then add a humidifier on a humidistat. Targets are 65–75 % RH for seedlings, 55–70 % in veg and 50–60 % in early flower. Low RH matters most for seedlings and clones; in late flower, 40–50 % is the goal, so dry air is rarely a problem then. - Canonical: https://genetixbay.com/knowledge/answers/how-to-raise-humidity-in-a-grow-tent.html - Topic: Environment · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - Also asked as: Humidity too low in my grow tent | How do I increase RH in a grow room? | Low humidity in my grow tent: what can I do? | How do I raise humidity for seedlings? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Raise grow-tent humidity by holding on to the water your plants [transpire](https://genetixbay.com/knowledge/glossary/transpiration.md): turn the [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) down first, then add a [humidifier](https://genetixbay.com/knowledge/glossary/humidifier.md) on a humidistat. Aim for **65–75 % [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) for [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md)**, **55–70 % in veg** and **50–60 % in early flower**. *Grower practice*, built on [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) physics. ## Why Relative humidity sets how hard the air pulls water from the leaf, the vapour pressure deficit [1]. Dry air at normal temperatures means a high VPD: [stomata](https://genetixbay.com/knowledge/glossary/stomata.md) partly close, CO₂ uptake drops and leaf edges crisp. Seedlings and fresh clones have few roots. In dry air they lose water faster than they can replace it, which is why young plants get the highest RH. Under [LEDs](https://genetixbay.com/knowledge/glossary/led.md), leaves often sit 1–3 °C (2–5 °F) below air temperature [2], so the leaf feels less dry than an air reading suggests. Read [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) before chasing a number. Don't overshoot. Damp air and wet surfaces in flower invite *[Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md)* and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) [3]. ## The numbers | Stage | RH target | Air temperature | |---|---|---| | Unrooted clones (dome) | 75–90 % | 23–26 °C (73–79 °F) | | Seedlings | 65–75 % | 23–26 °C (73–79 °F) | | Veg | 55–70 % | 24–28 °C (75–82 °F) | | Flower weeks 1–4 | 50–60 % | 23–27 °C (73–81 °F) | | Flower week 5 to harvest | 40–50 % | 20–25 °C (68–77 °F) | ## What to do 1. Check the hygrometer is accurate and sits at canopy height. 2. Slow the exhaust fan, keeping temperature in range. 3. Cool the room a degree or two if it runs hot; warm air reads drier. 4. For seedlings, use a vented dome or group the pots. 5. Add a humidifier with a humidistat, low in the tent, away from lights and plugs. 6. Use [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) or distilled water in it if your [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) is hard. ## Common mistakes - Misting plants instead of humidifying the air. - Running the exhaust flat out in a dry winter room. - A humidifier with no controller, soaking the tent overnight. - Raising RH in late flower, when 40–50 % is the goal. ## Related - Full article: [Humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - [How do I lower the humidity in my grow tent?](https://genetixbay.com/knowledge/answers/how-to-lower-humidity-in-a-grow-tent.md) - [Should I mist my plants?](https://genetixbay.com/knowledge/answers/should-i-mist-my-plants.md) - [VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md) - Terms: [humidifier](https://genetixbay.com/knowledge/glossary/humidifier.md) · [leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md) ## Follow-up questions **How can I raise humidity without a humidifier?** Without a humidifier, raise grow-tent humidity by slowing the exhaust fan so the air the plants transpire stays in, as long as temperature stays in range. Group plants together, add more plants or a larger canopy, and lay a damp towel in a tray below the canopy for seedlings. Avoid spraying buds, and don't leave standing water near electrics. **Is 30 % humidity too low for cannabis?** 30 % relative humidity is too low for most of a cannabis grow. Seedlings and clones want about 65–75 %, veg 55–70 % and early flower 50–60 %. At 30 % and normal room temperatures, leaf VPD runs well above 1.6 kPa, stomata partly close and leaf edges crisp. Late flower tolerates 40–50 %; going lower to 'boost trichomes' has no controlled evidence. **Where should I put a humidifier in a grow tent?** Put a grow-tent humidifier low in the tent or at the intake side, away from the light, plugs and buds, with a humidistat set to the stage target. Mist from it should evaporate before it reaches leaves or walls. Fill it with RO or distilled water if your tap water is hard, or it will leave white mineral dust on leaves and the tent. ## Sources 1. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, high pressure sodium and light emitting diodes. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 3. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # How do I reveg a plant after harvest? > To reveg a photoperiod cannabis plant after harvest, leave the lower branches with some leaves and small buds, put it back on 18/6 or 24/0, feed lightly and wait. Expect 2–6 weeks of rounded, single-bladed leaves before normal growth returns. Success varies: stripped, very late or autoflower plants usually fail. Clone the new shoots as soon as they look normal. - Canonical: https://genetixbay.com/knowledge/answers/how-to-reveg-a-plant.html - Topic: Cloning and mother plants · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Also asked as: How do I reveg a cannabis plant? | Revegging after harvest | How do I put a plant back into veg? | How long does reveg take? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Harvest the top, leave the lower branches with leaves and small buds, put the plant back on [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) or [24/0](https://genetixbay.com/knowledge/glossary/24-0.md), feed lightly and wait 2–6 weeks for normal leaves to return. [Photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md) only; success varies by cultivar and condition. *Grower practice*. ## Why Photoperiod cannabis flowers when nights are long and stays vegetative when they are short [1]. Remove the long night and the plant's flowering signal goes with it. Even brief light in the night keeps cannabis vegetative; commercial growers use a night break to hold [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md) in veg [2]. Continuous or long days do the same job more firmly. The plant needs something to regrow from. New shoots come from remaining buds and nodes, and leaves supply the energy. A plant stripped bare has little left to work with. Reversion is slow and messy. The first leaves are rounded or single-bladed, a typical sign of [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md), before normal leaves return. ## The numbers | Item | Target | |---|---| | Light | 18/6 or 24/0 (24/0 endorsed for veg) | | Intensity | Low end of veg, around 300 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) | | Leave on plant | Lower branches, some leaves, small buds | | Time to normal leaves | 2–6 weeks | | Feed | Light veg feed, about half strength | | Night darkness | Not needed; avoid long nights | ## What to do 1. At harvest, leave a few lower branches with green leaves and some small buds. 2. Move the plant to 18/6 or 24/0 straight away. 3. Water and feed lightly; refresh the medium or pot down if roots are tired. 4. Wait for new shoots with normal, serrated leaves. 5. Take cuttings from that new growth and root them; they are easier to keep than the old plant. ## Common mistakes - Stripping every leaf at harvest. - Leaving it in a dim corner on [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) "to rest". - Over-feeding a plant with few leaves. - Trying to reveg an [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md). ## Related - Full article: [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - [Can I clone a flowering plant?](https://genetixbay.com/knowledge/answers/can-i-clone-a-flowering-plant.md) · [Single-finger leaves](https://genetixbay.com/knowledge/answers/single-finger-leaves-reveg.md) - [Selection and pheno hunting](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) - Terms: [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) · [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) ## Follow-up questions **How long does it take to reveg a plant?** Revegging a harvested photoperiod cannabis plant usually takes 2–6 weeks under 18/6 or 24/0. The first new growth is odd: small, rounded, smooth-edged or single-bladed leaves, often in clusters. Normal serrated, multi-fingered leaves return gradually. Plants harvested very late, stripped of all leaves or kept in a stressed root zone can take longer or never recover. **Can you reveg an autoflower?** Not reliably. Autoflowers are day-neutral, so long days don't switch them back to vegetative growth the way they do a photoperiod plant. A harvested auto has usually finished its life cycle and declines. If you want to keep an autoflower's genetics, the realistic route is seed: pollinate it or make crosses, rather than trying to reveg it. **Is it better to reveg or keep a clone?** Keeping a clone is far better than revegging. Take one or two cuttings from every candidate plant before the flip and hold them on long days; once you've harvested and judged the plants, keep the clones of the keepers and bin the rest. Revegging is a rescue for when you forgot, and it is slower, less reliable and harder on the plant. ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Examining the night break method in Cannabis sativa horticulture: vegetative daily light integral affects yield of extractable biomass, 2025. Plants 14(19):3095. https://pmc.ncbi.nlm.nih.gov/articles/PMC12525983/ --- # How do I set up a grow tent? > Set up a grow tent in this order: check the circuit, build the frame, hang the carbon filter high with the exhaust fan pulling through it, open low intakes on the far side, hang the light level over the canopy, add a clip fan, mount power off the floor, then run the empty tent for 48 hours, logging temperature and RH, before any plant goes in. - Canonical: https://genetixbay.com/knowledge/answers/how-to-set-up-a-grow-tent.html - Topic: Equipment · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Also asked as: Grow tent setup step by step | In what order do I assemble a grow tent? | Where do I hang the fan and carbon filter? | How should I lay out a grow tent? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Set up a grow tent in this order: **power, frame, air, light, circulation, test**. Hang the [carbon filter](https://genetixbay.com/knowledge/glossary/carbon-filter.md) high with the [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) **pulling** through it, open **low intakes** on the far side, hang the light level over the canopy, mount power off the floor, then **run the empty tent for 48 hours** before any plant goes in. *Grower practice*. Check that [home growing](https://genetixbay.com/knowledge/glossary/home-grow.md) is legal where you live first. ## Why Most first-grow problems are climate problems that existed before the seed: hot tents, humid nights, leaks. A 48-hour empty run finds them while nothing can die. Air goes in before the light because the light is the heat source. Exhaust high (hot air rises) with intake low on the opposite side sweeps the whole tent. Pulling through the filter keeps [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md), so smell can't escape. The light should match the canopy footprint: yield rises with canopy [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) [1], and corners starve if the fixture is off-centre. Stray night light can delay flowering [2], so seal zips and ports. Still, humid air is where mould starts [3]; a [clip fan](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) fixes that. Overloaded circuits and cords cause most home electrical fires [4]. ## The numbers | Item | Target | |---|---| | Exhaust | ~1 tent volume per minute, +25–50 % for filter and ducting | | Passive intake | ≈ 2–3 × exhaust duct area, low, opposite side | | Light start height | 45–60 cm (18–24 in) over [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md), dimmed 25–40 % | | Leaf-level air speed | 0.3–1.0 m/s (60–200 ft/min) | | Circuit load | under 80 % of rating | | Empty test | 48 h, lights-on and lights-off logged | ## What to do 1. Check the circuit and plan an RCD/GFCI-protected outlet. 2. Build the frame on a level floor; add a tray or mat. 3. Hang the carbon filter high; connect filter → duct → fan → outlet; seal joints. 4. Open low intakes on the far side; close every other port. 5. Hang the light level and centred on rated hangers. 6. Clip a fan above the canopy, blowing across, not down. 7. Mount the power strip and controllers high; drip-loop every cable. 8. Place a thermo-hygrometer at canopy height, shaded. 9. Run 48 hours on the real timer; check walls, leaks, plugs. ## Common mistakes - Plants in before the empty test. - Fan pushing into the filter. - Power strip on the floor. - No headroom for the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). ## Related - Full article: [Your first grow](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Guide: [Choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md) - [What size grow tent should I get?](https://genetixbay.com/knowledge/answers/what-size-grow-tent.md) - [Do I need an intake fan?](https://genetixbay.com/knowledge/answers/do-i-need-an-intake-fan.md) - [Is an indoor grow a fire risk?](https://genetixbay.com/knowledge/answers/grow-room-electrical-safety.md) - Terms: [tent](https://genetixbay.com/knowledge/glossary/tent.md) ## Follow-up questions **Where should the carbon filter and fan go in a tent?** The carbon filter goes high in the grow tent, where warm, smelly air collects, with the inline exhaust fan after it so the fan pulls air through the filter: filter, duct, fan, outlet. That keeps the tent under negative pressure. Open the passive intakes low on the opposite side, with about 2–3 times the exhaust duct's area, and close all other ports. **How high should I hang the light when setting up?** When setting up a grow tent, hang the LED level over the centre of the canopy area on rated adjustable hangers, starting at about 45–60 cm (18–24 in) above seedlings and dimmed to 25–40 %. Then set height and dimming by the fixture's PPFD map or a quantum meter, not by a fixed distance, and leave room above the plants for the post-flip stretch. **Why run an empty grow tent for 48 hours?** Running an empty grow tent for 48 hours with lights and fans on their timers shows its real climate before plants are at risk. Log temperature and RH at lights-on and lights-off, check the walls bow inwards, look for light leaks in the dark, and feel every plug for heat. Fix the room first; plants won't fix it for you. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 3. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 4. US Fire Administration. Electrical fire safety (overloaded outlets, extension cords, smoke alarms). https://www.usfa.fema.gov/prevention/home-fires/prevent-fires/electrical/ --- # How do I trim buds? > Trim cannabis by removing the big fan leaves at harvest, then snipping or brushing the sugar leaves back to the bud, either wet on harvest day or dry once small stems snap after 7–14 days. Wet versus dry trim is grower preference. Use sharp, small scissors, gloves and a tray to catch trichomes, and keep the trim for hash or edibles. Handle buds by the stem. - Canonical: https://genetixbay.com/knowledge/answers/how-to-trim-buds.html - Topic: Harvest and cure · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Also asked as: How do I manicure buds? | Trimming tips for beginners | Scissors or a trim machine? | Should I wet trim or dry trim? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Take off the big [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) at harvest. Then cut or brush the [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) back to the outline of the bud, either wet on harvest day or dry once the small stems snap after 7–14 days. Wet versus dry is preference (*House position*). Use small, sharp scissors, gloves and a tray, and keep the trim. *Grower practice*: no independent study compares the two methods. ## Why Trimming changes how the bud dries. Sugar leaves left on act as a jacket and slow the dry, which helps in a [dry room](https://genetixbay.com/knowledge/glossary/drying-room.md), where a fast dry costs volatile [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) [1]. [Trimming wet](https://genetixbay.com/knowledge/glossary/wet-trim.md) speeds drying, which helps in a humid room where mould is the bigger risk. Both have to reach [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55–0.65 by the end [2]. Resin gets in the way. Wet buds are sticky and gum up scissors. Dry sugar leaves are crisp and brush off easily, at the cost of a few more [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md) knocked loose. The founder, who has trimmed hundreds of pounds by hand, prefers [dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md) for that reason. Timing and conditions vary. Commercial growers report a range of drying and trimming set-ups [3], and there is no single right answer. Choose the method that suits your room and your hands. ## The numbers | | Wet trim | Dry trim | |---|---|---| | When | Harvest day | After 7–14 days, once stems snap | | Drying speed | Faster | Slower | | Best room | Humid, high mould risk | Dry, buds crisp easily | | Hands | Sticky, slower | Easier at volume | | [Trichome](https://genetixbay.com/knowledge/glossary/trichome.md) loss | Slightly less | Slightly more (collects in the trim) | **Verdict:** pick the method that suits your room's humidity. Both make excellent flower. ## What to do 1. Remove the large fan leaves at the chop. 2. Wet trim: cut the sugar leaves back while the buds are fresh, then dry them on a rack or hanging. 3. Dry trim: hang the branches untrimmed, then trim once the stems snap and before [jarring](https://genetixbay.com/knowledge/glossary/curing-jar.md). 4. Hold buds by the stem and turn them as you cut. Don't squeeze the bud. 5. Work over a fine screen or tray to catch the trichomes. Clean the scissors with alcohol. 6. Bag the trim and keep it cold for [hash](https://genetixbay.com/knowledge/glossary/hash.md) or edibles. ## Common mistakes - Blunt scissors that tear the bud. - Squeezing buds to steady them. - Trimming in a warm, bright room. - Throwing the trim away. ## Related - Full article: [Drying cannabis](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Answers: [whole plant or branches?](https://genetixbay.com/knowledge/answers/hang-whole-plant-or-branches.md) · [fan leaves vs sugar leaves](https://genetixbay.com/knowledge/answers/fan-leaves-vs-sugar-leaves.md) · [drying in the tent](https://genetixbay.com/knowledge/answers/can-i-dry-in-my-grow-tent.md) - Terms: [dry trim](https://genetixbay.com/knowledge/glossary/dry-trim.md) · [wet trim](https://genetixbay.com/knowledge/glossary/wet-trim.md) · [sugar trim](https://genetixbay.com/knowledge/glossary/sugar-trim.md) ## Follow-up questions **Is wet trim or dry trim better?** Wet or dry trimming is grower preference, and both make excellent cannabis. Wet trim dries faster and suits humid rooms with high mould risk. Dry trim slows the dry, because sugar leaves act as a jacket, and is far easier on the hands at volume. GenetixBay's founder prefers dry trim, accepting slight trichome loss because the trim gets used anyway. **How much sugar leaf should I leave on?** Leave cannabis sugar leaves trimmed back to roughly the outline of the bud, with any resin-coated tips that sit flush left on. Remove the parts that stick out and show mostly green leaf. A tighter trim looks neater and smokes cleaner; a looser trim keeps more weight. Either way, the trim is resin-rich and worth saving for hash or edibles. **Should I use a trim machine?** A trim machine is faster than hand trimming for large harvests, but it handles buds harder, can knock off trichome heads and gives a less precise finish. For a home grow of a few plants, sharp scissors and an hour or two per plant give a better result. If you use a machine, dry trim with a light touch and save the collected resin. ## Sources 1. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 2. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 3. Cannabis Business Times. Special report: cannabis post-harvest benchmarks (grower survey; average drying ~53 % RH, ~65 °F). https://www.cannabisbusinesstimes.com/business-issues-benchmarks/cannabis-post-harvest-operations/article/15689633/post-harvest-benchmarks-with-room-to-experiment --- # What humidity and light do clones need? > Unrooted cannabis clones do best at 75–90% RH (a leaf VPD of about 0.2–0.5 kPa), a medium temperature of 22–26 °C (72–79 °F), and gentle light of 50–150 µmol/m²/s on 18–24 hours, a DLI of about 3–10 mol/m²/day. Once roots show, lower humidity over 3–5 days toward 65–75% and raise light toward 150–300 µmol/m²/s. - Canonical: https://genetixbay.com/knowledge/answers/humidity-and-light-for-clones.html - Topic: Cloning and mother plants · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: What humidity for clones in a dome? | How much light do clones need? | What RH for cuttings? | Light schedule for clones - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Unrooted cannabis clones need 75–90% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), a medium at 22–26 °C (72–79 °F), and gentle light of 50–150 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) for 18–24 hours. After roots appear, step humidity down toward 65–75% and light up toward 150–300 µmol/m²/s. *Grower practice*, consistent with propagation research. ## Why A rootless cutting can't replace much water. High humidity shrinks the [vapour pressure deficit](https://genetixbay.com/knowledge/glossary/vpd.md), the pull on its leaves; at 25 °C the gap between 85% and 60% RH is large [3]. Light is needed, but only a little. Horticultural guidance keeps cuttings at roughly 100–150 µmol/m²/s at sticking [1]. [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md) cuttings rooted in 12 days at about 54 µmol/m²/s on 24-hour light [2]. Too-dry air shows up fast. That same hemp trial, at about 64% RH, had to resaturate media and remove leaves to stop cuttings losing turgor [2]. Roots change the rules. Once they can supply water, lower humidity and more light build a sturdier plant. ## The numbers | Phase | RH | [Leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md) | PPFD (µmol/m²/s) | Hours | [DLI](https://genetixbay.com/knowledge/glossary/dli.md) (mol/m²/day) | |---|---|---|---|---|---| | Days 0–7, unrooted | 80–90% | 0.2–0.4 kPa | 50–100 | 18–24 | 3–8 | | Days 7–14, rooting | 75–85% | 0.3–0.5 kPa | 100–150 | 18–24 | 6–10 | | Rooted, [hardening](https://genetixbay.com/knowledge/glossary/hardening-off.md) | 65–75% | 0.4–0.8 kPa | 150–300 | 18 | 10–19 | Temperature: medium 22–26 °C (72–79 °F); air 23–26 °C (73–79 °F). ## What to do 1. Mist the dome inside and set the tray on a thermostatted heat mat if the room is cool. 2. Measure PPFD at the leaves; dim or raise the light to 50–150. 3. Vent the dome once a day and wipe heavy condensation. 4. When roots show, open vents, then prop the lid, over 3–5 days. 5. Raise light gradually as the clones harden. ## Common mistakes - Running clones under the veg light at full power. - Sealed domes with standing water and no venting. - Reading air temperature and ignoring a cold plug. - Hardening off before roots are visible. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) · [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [Why are my clones wilting?](https://genetixbay.com/knowledge/answers/why-are-my-clones-wilting.md) - Terms: [cloning dome](https://genetixbay.com/knowledge/glossary/cloning-dome.md) · [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) ## Follow-up questions **Do clones need light to root?** Yes, but not much. Unrooted cannabis clones need gentle light, about 50–150 µmol/m²/s on 18–24 hours, so the leaves can make sugars for new roots without drying out. A hemp trial rooted cuttings in 12 days at just 54 µmol/m²/s on 24-hour light. Full veg intensity on rootless cuttings makes them wilt and burn. **Should clones get 24/0 light?** Clones can run on 24/0 or 18/6; both work. Long days are common in propagation because a low-intensity light kept on longer gives a steady, gentle daily dose. A hemp trial rooted cuttings on 24-hour light at about 54 µmol/m²/s. The house position is that cannabis needs no sleep period in veg, so pick the schedule your mothers or nursery already run. **What temperature do clones need?** Cannabis clones root best with the medium at about 22–26 °C (72–79 °F) and the air at 23–26 °C (73–79 °F). The medium temperature matters most: a cold plug slows rooting badly. A heat mat with a thermostat solves a cold room, but measure inside a plug, because mats can easily push the medium above 28 °C (82 °F) and dry it out. ## Sources 1. Michigan State University. Lighting of cuttings (rooting-phase PPFD). https://www.canr.msu.edu/uploads/resources/pdfs/lighting-of-cuttings.pdf 2. Campbell SM, Anderson SL, Brym ZT, Pearson BJ, 2021. Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.). PLOS ONE 16(7): e0249160. https://doi.org/10.1371/journal.pone.0249160 3. Allen RG et al., 1998. FAO-56 Chapter 3 (vapour pressure). https://www.fao.org/4/x0490e/x0490e07.htm --- # Is a clone the same sex and age as its mother? > A cannabis clone is genetically the same as its mother, including her sex: every clone of a female is female. It is also physiologically mature, not a new seedling, so it can flower as soon as it gets 12/12. Apart from rare somatic mutations and carried-over pathogens such as hop latent viroid, it is the same genotype; there is zero genetic drift. - Canonical: https://genetixbay.com/knowledge/answers/is-a-clone-the-same-as-its-mother.html - Topic: Cloning and mother plants · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: Is a clone the same as the mother plant? | How old is a clone? | Is a clone the same sex as its mother? | Why do clones from the same mother grow differently? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A cannabis clone is the same [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) as its mother, so it is the same sex: clones of a female are female. It is also mature tissue, the "age" of the mother rather than a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md), and can flower as soon as it gets [12/12](https://genetixbay.com/knowledge/glossary/12-12.md). *Established*. ## Why [Cloning](https://genetixbay.com/knowledge/glossary/cloning.md) is vegetative propagation: a rooted cutting carries the donor's full genome, including the [sex chromosomes](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md) [1]. Mutations are rare and not a loss. Sequencing finds a few somatic mutations accumulating in different parts of a plant and its clones [2]. House position: zero [genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md) in a well-kept cut apart from pathogens. Cuttings keep their physiological age. Propagation science calls this cyclophysis and [topophysis](https://genetixbay.com/knowledge/glossary/topophysis.md): a cutting carries the maturity and character of the shoot it came from [3]. That's why a clone can flower small and why cuts from different branches can behave differently for a while. Pathogens travel too. [Hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md) passes through infected cuttings and reduces flower mass and quality, often without obvious symptoms [4]. ## The numbers | Trait | Same as mother? | |---|---| | Genotype | Yes, apart from rare somatic mutations | | Sex | Yes | | Ability to flower | Immediately on long nights ([photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md)) | | [Chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) potential | Yes, environment permitting | | Pathogens (HLVd, [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md)) | Yes, if present | | Early growth habit | Can differ by cutting position | ## What to do 1. Take cuts from consistent locations: vigorous upper-to-mid shoots. 2. Label every clone with its source and date. 3. Test valuable [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md) for HLVd and quarantine new cuts. 4. Expect a clone to flower small; give it enough veg for the canopy you want. 5. Compare clones side by side before blaming "genetics". ## Common mistakes - Expecting a clone to need weeks of "growing up" before it can flower. - Assuming a clone of a [herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) plant will be stable. - Blaming age for a weak cut without testing for HLVd. - Taking cuts from random spots, then calling them different [phenotypes](https://genetixbay.com/knowledge/glossary/phenotype.md). ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Sex: male, female, hermaphrodite](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) · [Hop latent viroid](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) - [Can you clone an autoflower?](https://genetixbay.com/knowledge/answers/can-you-clone-autoflowers.md) - Terms: [topophysis](https://genetixbay.com/knowledge/glossary/topophysis.md) · [cloning](https://genetixbay.com/knowledge/glossary/cloning.md) ## Follow-up questions **Why do clones from the same mother grow differently?** Clones from the same cannabis mother can grow differently because of position effects, called topophysis: a cutting can 'remember' whether it came from a vigorous leader or a shaded lower branch. This is a physiological carry-over and may or may not involve mutation. Pathogens such as HLVd, and differences in how cuts are rooted and grown, also cause differences. **Can a clone flower straight away?** Yes. A rooted cannabis clone from a photoperiod mother is mature tissue, so it can flower as soon as it gets long nights, even at 15 cm (6 in) tall. That is how sea-of-green growers flower small clones after a short veg. A clone from an autoflower is a different case: it keeps the mother's countdown and usually flowers small. **Do clones get weaker with every generation?** No. GenetixBay's position is that a well-kept cannabis cut shows zero genetic drift apart from pathogens such as hop latent viroid. Sequencing does find rare somatic mutations, but no study links them to the decline growers describe, and the founder keeps cuts over 40 years old with no decline. If a cut 'got weak', test it for HLVd first. ## Sources 1. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571 2. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169 3. Olesen PO. 1978. On cyclophysis and topophysis. Silvae Genetica 27(5):173-178. https://www.thuenen.de/media/institute/fg/PDF/Silvae_Genetica/1978/Vol._27_Heft_5/27_5_173.pdf 4. Adkar-Purushothama CR, Sano T, Perreault JP. 2023. Hop latent viroid: a hidden threat to the cannabis industry. Viruses 15(3):681. https://doi.org/10.3390/v15030681 --- # Do banana peels, coffee grounds or eggshells feed cannabis? > No, not in any useful way: feeding cannabis with kitchen scraps is a Myth. Banana peels hold some potassium but release it only as they rot; peel water is a trace dose. Raw coffee grounds reduced plant growth in a controlled study. Eggshells are calcium carbonate that dissolves very slowly and acts more like lime than feed. Compost the scraps first, and feed the plant properly. - Canonical: https://genetixbay.com/knowledge/answers/kitchen-scraps-as-fertiliser.html - Topic: Nutrients · Type: Myth check - Evidence: Myth · Status: Draft: awaiting expert review - Full article: [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) - Also asked as: Does banana peel water work for plants? | Are coffee grounds good for weed? | Do eggshells add calcium? | Can I use kitchen scraps as fertiliser? | Homemade fertiliser for cannabis - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Not usefully. The idea that kitchen scraps make a cannabis fertiliser is a *Myth*. Peel water is a trace dose, raw coffee grounds can stunt plants, and eggshells dissolve too slowly to feed anything this season. Compost the scraps, then use the compost; feed the plant with a complete fertiliser. ## Why Roots take up dissolved ions, not food waste [2]. Organic material has to be broken down by microbes first, and that takes weeks to months. Even purpose-made organic liquid feeds need higher nominal nitrogen to match mineral ones, around 389 mg/L N in one cannabis veg trial [3]. A [banana](https://genetixbay.com/knowledge/glossary/nanners.md) peel soaked overnight is nowhere near that. Coffee grounds are worse than useless raw. Applied directly to soil, spent grounds greatly reduced growth of the plants tested, regardless of soil type or added fertiliser, with evidence of [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) being immobilised [1]. Composting changes them. Eggshells are calcium carbonate. Coarse [shell](https://genetixbay.com/knowledge/glossary/seed-coat.md) dissolves very slowly in soil and acts more like a liming agent, raising [pH](https://genetixbay.com/knowledge/glossary/ph.md) a little, than a calcium feed [2]. Plants mostly don't care where ions come from. They do care whether the ions are there, now, in the right amounts. ## The numbers | Scrap | Main element | Available this grow? | Better use | |---|---|---|---| | Banana peel / peel water | K | Trace | Compost | | Raw coffee grounds | N (locked up at first) | No; growth fell in trials [1] | Compost (small share) | | Eggshell, coarse | Ca (as carbonate) | Barely | Compost or skip | | Eggshell, finely ground | Ca | Slowly, liming effect | Pre-mix months ahead | | Complete fertiliser | All | Yes | Feed the plant | ## What to do 1. Put scraps in a compost heap or worm bin, not the pot. 2. Use finished compost or castings as part of a soil mix or [top-dress](https://genetixbay.com/knowledge/glossary/top-dressing.md). 3. Feed the plant from a complete fertiliser at stage strength. 4. Fix calcium problems through pH, watering and the feed. ## Common mistakes - Pouring peel water into a hydro reservoir. - Top-dressing raw coffee grounds on a pot. - Crushing eggshells into a pot to cure calcium spotting. - Assuming "natural" means "available". ## Related - Full article: [Organic vs mineral nutrition](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) - Answers: [garden fertiliser on cannabis](https://genetixbay.com/knowledge/answers/use-regular-plant-fertiliser.md) · [super soil](https://genetixbay.com/knowledge/answers/what-is-super-soil.md) - Articles: [living soil](https://genetixbay.com/knowledge/systems/living-soil.md) - Terms: [organic fertiliser](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md) · [top-dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md) ## Follow-up questions **Does banana peel water add potassium?** Banana peel water adds only a trace of potassium, far below what a flowering cannabis plant takes up, and soaking peels mostly grows microbes and smells. Peels release their potassium as they decompose, which takes weeks. If you want to use them, compost them. For potassium in flower, a complete feed or potassium sulfate does the job reliably. **Are coffee grounds good for cannabis?** Raw coffee grounds are not good for cannabis as a fertiliser. In a controlled study, spent coffee grounds applied directly to soil greatly reduced plant growth across several species, regardless of soil type or fertiliser, with signs of nitrogen being locked up. Composted grounds behave differently and are a reasonable compost ingredient. **Do eggshells add calcium to soil?** Eggshells are mostly calcium carbonate, so they can add calcium in the long run, but whole or coarse shells dissolve extremely slowly and behave more like a liming material that nudges pH up than a feed. Finely ground shells work faster. They cannot fix a calcium deficiency in an active grow; fix root-zone pH, watering and the feed instead. ## Sources 1. Hardgrove SJ, Livesley SJ, 2016. Applying spent coffee grounds directly to urban agriculture soils greatly reduces plant growth. Urban Forestry & Urban Greening 18:1-8. https://doi.org/10.1016/j.ufug.2016.02.015 2. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 3. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307-1312. https://doi.org/10.21273/HORTSCI11903-17 --- # Is it normal for leaves to droop at night? > Yes, cannabis leaves commonly droop or lower during the dark period and lift again within an hour or two of lights-on. Daily leaf movement is normal in many plants. Worry only if the leaves are still drooping 2 hours after lights-on, or droop during the day: then lift the pot to check for over- or underwatering, and check the roots if the pot is a normal weight. - Canonical: https://genetixbay.com/knowledge/answers/leaves-droop-at-night.html - Topic: Diagnosis · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Also asked as: Why do my leaves droop when the lights go off? | Leaves drooping in the dark period | Night droop: normal or not? | Plant looks sad at lights-off - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. Cannabis leaves commonly droop or lower in the dark period and lift again within an hour or two of lights-on. Worry only if they are still drooping 2 hours after lights-on, or droop in the day. Then lift the pot and check the watering and roots. *Grower practice*. ## Why Plants move their leaves on a daily rhythm. Many species lower or fold their leaves at night and raise them by day [1], and cannabis leaves often settle in the dark and rise after lights-on. The reasons are still debated [1]. In practice it is harmless. A plant that droops by day is different. [Overwatered](https://genetixbay.com/knowledge/glossary/overwatering.md) roots run short of oxygen and the leaves droop thick and firm. [Underwatered](https://genetixbay.com/knowledge/glossary/underwatering.md) plants go limp and papery. Some daytime wilting points to the roots. A plant that wilts in a moist pot of normal weight, especially one plant at a time, fits [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) or [Fusarium root rot](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md) [2] or Fusarium wilt [3]. ## The numbers | Observation | Meaning | |---|---| | Leaves lower after lights-off, up by lights-on + 1–2 h | Normal | | Still drooping 2 h after lights-on, heavy pot | Overwatered | | Still drooping, very light pot | Underwatered; recovers 30–120 min after watering | | Wilting in a normal-weight pot | Check the roots for rot [2] | | Brown streaks inside a cut stem | Possible Fusarium wilt [3] | ## What to do 1. Look again 1–2 hours after lights-on. If the leaves have lifted, you're done. 2. If not, lift the pot and compare it with one freshly watered. 3. Heavy: let it [dry back](https://genetixbay.com/knowledge/glossary/dryback.md) until it is about 40–50% lighter before watering. 4. Light: water slowly in two passes to light [runoff](https://genetixbay.com/knowledge/glossary/runoff.md). 5. Normal weight but still wilting: slide the plant out or pull the [net pot](https://genetixbay.com/knowledge/glossary/net-pot.md) and check that the roots are white and firm. 6. In hydro, check the air pump and keep the solution at 18–22 °C (64–72 °F). ## Common mistakes - Watering at lights-off because the plant "[looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) thirsty". - Opening the tent in the dark period to check on it. - Treating every droop as thirst. - Ignoring daytime drooping because "it does that at night". ## Related - Full article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Answers: [praying leaves](https://genetixbay.com/knowledge/answers/praying-leaves.md) · [water at lights-on or off?](https://genetixbay.com/knowledge/answers/water-at-lights-on-or-off.md) · [how often to water](https://genetixbay.com/knowledge/answers/how-often-to-water.md) - Article: [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) - Terms: [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) · [underwatering](https://genetixbay.com/knowledge/glossary/underwatering.md) ## Follow-up questions **Why does my plant droop right after lights-off?** A cannabis plant lowering its leaves right after lights-off is usually normal daily leaf movement, as photosynthesis and transpiration slow in the dark. It is common across many plant species. If the plant also droops by day, or the leaves look limp and papery or thick and swollen, check pot weight and roots instead of assuming it is the night rhythm. **How long after lights-on should leaves perk up?** Cannabis leaves that lowered overnight should lift within roughly 1–2 hours of lights-on, according to grower practice. If they are still drooping after 2 hours, lift the pot: a heavy pot points to overwatering, a very light one to thirst. A normal-weight pot with a still-wilting plant points to root problems such as rot. **Should I water if my plant droops at night?** Do not water a cannabis plant just because it droops at night. Night drooping is usually normal leaf movement, and watering at lights-off keeps the pot wet through the dark when the plant uses little water, raising humidity and root-rot risk. Check the pot weight the next morning and water then if it is genuinely light. ## Sources 1. Minorsky PV, 2019. The functions of foliar nyctinasty: a review and hypothesis. Biological Reviews 94(1):216–229. https://doi.org/10.1111/brv.12444 2. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 3. Utah State University Extension. Fusarium Wilt (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-fusarium-wilt --- # Should I run my room warmer with LEDs than with HPS? > Yes, run an LED room about 1–3 °C (2–5 °F) warmer than an HPS room. Under LEDs, well-watered leaves usually sit 1–3 °C below air temperature; under HPS they sit near or above it, because HPS radiates more heat onto the leaf. For a target leaf temperature of about 24–27 °C (75–81 °F), that means roughly 26–28 °C (79–82 °F) air under LED. Measure leaves with an IR thermometer. - Canonical: https://genetixbay.com/knowledge/answers/led-grow-room-temperature.html - Topic: Environment · Type: Numbers - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - Also asked as: What temperature should an LED grow room be? | Should I run warmer under LED? | Leaf temperature under LED vs HPS | Why are my leaves cold under LED? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. Run an [LED](https://genetixbay.com/knowledge/glossary/led.md) room about **1–3 °C (2–5 °F) warmer** than you would with [HPS](https://genetixbay.com/knowledge/glossary/hps.md). Under LED, healthy leaves usually sit **1–3 °C below air**; under HPS they sit **near or above it** [1]. For a leaf at about 24–27 °C (75–81 °F), that means roughly **26–28 °C (79–82 °F) air under LED**. *Supported*. ## Why HPS lamps emit a lot of infrared and radiant heat that lands directly on the leaf. LEDs put far less radiant heat on the canopy for the same [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), so a [transpiring](https://genetixbay.com/knowledge/glossary/transpiration.md) leaf cools below the air around it [1]. The plant responds to [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md), not air temperature. Cannabis [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) peaks around 25–30 °C leaf temperature under strong light [2]. A leaf that's 3 °C colder than you think is working below its best. Leaf temperature also sets leaf [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) [3]. Cool leaves under LED mean a lower real VPD than an air-based reading suggests, so LED rooms run at HPS settings often end up effectively too humid. That, not the light, is the real story behind the Cal-Mag-under-LED *Myth*. ## The numbers | | LED | HPS | |---|---|---| | Leaf vs air (well-watered, moving air) | −1 to −3 °C (−2 to −5 °F) | 0 to +2 °C (0 to +4 °F) | | Veg air for a good leaf temperature | 26–28 °C (79–82 °F) | 24–27 °C (75–81 °F) | | Mid-flower air | 24–27 °C (75–81 °F) | 22–26 °C (72–79 °F) | | Late-flower air | 21–25 °C (70–77 °F) | 20–24 °C (68–75 °F) | | Upper air limit without CO₂ | ~30 °C (86 °F) | ~30 °C (86 °F) | ## What to do 1. Measure leaf temperature with an [IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md) (emissivity ~0.95) on lit top leaves. 2. Compare with air at canopy height. 3. Raise air temperature until leaves read about 24–27 °C in veg and early flower. 4. Recalculate leaf VPD and adjust [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) to hit the stage band. 5. Re-check after any change in light intensity or fan setup. ## Common mistakes - Keeping HPS setpoints after switching to LED. - Using air VPD from an app with LEDs. - Adding [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) instead of fixing leaf temperature and VPD. - Measuring leaf temperature in shade or from too far away. ## Related - Full article: [Temperature by stage](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) - [LED or HPS: which is better?](https://genetixbay.com/knowledge/answers/led-vs-hps.md) - [VPD explained](https://genetixbay.com/knowledge/environment/vpd-explained.md) - [How do I lower the temperature in my grow tent?](https://genetixbay.com/knowledge/answers/how-to-cool-a-grow-tent.md) - Terms: [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) · [IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md) ## Follow-up questions **How do I measure leaf temperature?** Measure cannabis leaf temperature with an infrared thermometer set to emissivity about 0.95, aimed at a fully lit top leaf from 10–20 cm away so the spot covers only leaf. Take several readings across the canopy and compare with air temperature at the same height. Under LED a healthy, transpiring leaf usually reads 1–3 °C below air; above air suggests water stress or still air. **Does leaf temperature change VPD under LED?** Yes, cooler leaves under LED lower the real leaf VPD. At 26 °C air and 60 % RH, an app using air temperature shows about 1.34 kPa, but a leaf at 24 °C is only at about 0.97 kPa. Growers who ignore this run LED rooms too humid. Raising air temperature 1–3 °C, or lowering RH, brings leaf VPD back into the 1.0–1.5 kPa flower band. **Is 28 °C too hot under LED?** 28 °C (82 °F) air is fine for cannabis under LED in veg and early flower, because leaves usually sit 1–3 °C cooler, near the 25–30 °C leaf optimum. Without added CO₂, keep air below about 30 °C (86 °F). In late flower, 20–24 °C (68–75 °F) air is the usual target. Check leaf temperature and leaf VPD rather than air alone. ## Sources 1. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 2. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 3. Allen RG, Pereira LS, Raes D, Smith M, 1998. Crop evapotranspiration: guidelines for computing crop water requirements (FAO Irrigation and Drainage Paper 56), Chapter 3. FAO. https://www.fao.org/4/x0490e/x0490e07.htm --- # LED or HPS: which is better for cannabis? > LED versus HPS for cannabis quality and yield per photon is an open question at GenetixBay: perhaps. At equal PPFD, research shows similar yields, while LED wins clearly on running cost, about 2.5–3 µmol/J against roughly 1.7 µmol/J for HPS, and on leaf heat load. One small trial found more flower mass under HPS but higher cannabinoid concentration under LED. A Bay Trial will test it. - Canonical: https://genetixbay.com/knowledge/answers/led-vs-hps.html - Topic: Environment · Type: Comparison - Evidence: Contested · Status: Draft: awaiting expert review - Full article: [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md) - Also asked as: LED vs HPS yield | Is LED better than HPS for cannabis? | HPS vs LED bud quality | Does HPS give denser buds than LED? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer On running cost, [LED](https://genetixbay.com/knowledge/glossary/led.md) wins: about **2.5–3 [µmol/J](https://genetixbay.com/knowledge/glossary/photon-efficacy.md)** against roughly **1.7 µmol/J** for [HPS](https://genetixbay.com/knowledge/glossary/hps.md) [2]. On yield and quality per photon, the GenetixBay answer is **"perhaps"**: at equal [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) the research shows broadly similar results, the trials are few, and the question is down for a controlled [Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md). *Contested* (house position: open question). ## Why Photon quantity drives cannabis yield far more than colour. Across three studies, a lower [blue fraction](https://genetixbay.com/knowledge/glossary/blue-light.md) (HPS is about 4 % blue) slightly raised yield, but the authors concluded fixture efficacy mattered more for cost [1]. In a 2018 trial at about 450 µmol/m²/s, plants under HPS were taller and made more flower [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) than under two LED spectra, while the LED plants had higher [THC](https://genetixbay.com/knowledge/glossary/thc.md) and [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) concentrations; total [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) yield didn't differ [3]. It was small and funded by an LED maker, so treat it as one data point. HPS puts more radiant heat on the leaf; LED leaves usually run cooler than the air [4]. That changes the climate you need, not just the bill. ## The numbers | | White LED | HPS | |---|---|---| | Efficacy | 2.5–3+ µmol/J [2] | ~1.7 µmol/J [2] | | Electricity for the same PPFD | ~35–45 % less | baseline | | [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) vs air | usually 1–3 °C (2–5 °F) cooler | near air or warmer [4] | | Blue fraction | ~5–15 % typical | ~4 % [1] | | Yield at equal PPFD | similar in most work | similar; more mass in one small trial [3] | | Cannabinoid concentration | higher in one trial [3] | lower in that trial | | Lamp replacement | none for years | bulbs lose output | **Verdict:** pick LED for cost, heat and control; whether HPS buds are better per photon is unproven either way, so GenetixBay is testing it in a Bay Trial. ## What to do 1. Compare fixtures by µmol/J and PPFD map, not lamp type alone. 2. Switching to LED? Raise air temperature 1–3 °C and re-check leaf [VPD](https://genetixbay.com/knowledge/glossary/vpd.md). 3. Running HPS? Keep it; just measure leaf temperature and cool accordingly. 4. Want to know for your cultivar? Run a side-by-side at the same PPFD and log grams and lab results. ## Common mistakes - Comparing an LED at 600 µmol/m²/s with HPS at 1,000. - Keeping HPS room settings after switching to LED. - Treating one manufacturer-funded trial as settled. - Adding [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) "because it's LED" (*Myth*). ## Related - Full article: [Light spectrum](https://genetixbay.com/knowledge/environment/light-spectrum.md) - [Are purple (blurple) LEDs as good as white LEDs?](https://genetixbay.com/knowledge/answers/blurple-vs-white-led.md) - [Should I run my room warmer with LEDs?](https://genetixbay.com/knowledge/answers/led-grow-room-temperature.md) - [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Terms: [LED vs HPS](https://genetixbay.com/knowledge/glossary/led-vs-hps.md) · [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) ## Follow-up questions **Does HPS give better buds than LED?** Whether HPS gives better cannabis buds than LED is an open question; the GenetixBay answer is 'perhaps', and it is slated for a controlled Bay Trial. One 2018 trial at about 450 µmol/m²/s found more flower dry weight under HPS but higher THC and CBD concentration under the LEDs, with equal total cannabinoid yield. Other work finds similar yield at equal PPFD. Evidence is thin. **Is LED cheaper to run than HPS?** Yes, LED is cheaper to run than HPS for the same light on the canopy. Good current LED fixtures exceed 2.5–3 µmol of photosynthetic photons per joule, against about 1.7 µmol/J for HPS, so an LED needs roughly 35–45 % less electricity for the same PPFD. Less wasted heat also means smaller cooling bills. This part of the comparison is established. **Do I need to change my grow room settings when switching from HPS to LED?** Yes, switching from HPS to LED changes leaf temperature. HPS radiates heat that warms leaves to around air temperature or above, while LED leaves usually run 1–3 °C cooler than the air. Many growers raise air temperature by 1–3 °C under LED to keep leaf temperature and VPD where they were. Measure leaf temperature with an IR thermometer rather than guessing. ## Sources 1. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://pmc.ncbi.nlm.nih.gov/articles/PMC7987162/ 2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 3. Magagnini G, Grassi G, Kotiranta S, 2018. The effect of light spectrum on the morphology and cannabinoid content of Cannabis sativa L. Medical Cannabis and Cannabinoids 1(1):19–27. https://doi.org/10.1159/000489030 4. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ --- # What light schedule should seedlings get? > Photoperiod and autoflower seedlings both do well on 18/6: 18 hours of light at about 150–300 µmol/m²/s, a DLI of 10–19 mol/m²/day. 24/0 is fine too, because cannabis needs no sleep period in veg; it just costs more power, so drop the intensity to keep the same DLI. Never put photoperiod seedlings on 12/12 unless you want them to flower small. - Canonical: https://genetixbay.com/knowledge/answers/light-schedule-for-seedlings.html - Topic: Germination · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - Also asked as: 18/6 or 24/0 for seedlings? | How many hours of light do seedlings need? | Seedling light cycle | What light schedule for autoflower seedlings? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Give cannabis [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) at about 150–300 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), a [DLI](https://genetixbay.com/knowledge/glossary/dli.md) of 10–19 mol/m²/day. [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) also works (house position: no sleep period needed in veg), as long as you lower intensity to keep the same daily dose. *Grower practice*. ## Why What the seedling actually counts is the total daily light, the DLI. Young plants of other crops grown below about 8 mol/m²/day were inferior, while 10–14 gave better roots and mass [1]. 18 hours is a proven default. A cannabis [germination](https://genetixbay.com/knowledge/glossary/germination.md) protocol grew its seedlings on at 24 °C under 18/6 and 200 µmol/m²/s [2]. [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis is a [short-day plant](https://genetixbay.com/knowledge/glossary/short-day-plant.md): long days keep it vegetative and long nights trigger flowering [3]. A seedling on [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) can flower while tiny. 24/0 simply removes the night, which keeps it firmly in veg. Hours and intensity trade off. A longer day at lower PPFD delivers the same DLI with less heat and stress at the canopy. ## The numbers | Schedule | PPFD for seedlings (µmol/m²/s) | DLI (mol/m²/day) | Notes | |---|---|---|---| | 18/6 | 150–300 | 10–19 | Default | | 20/4 | 140–260 | 10–19 | Common for [autos](https://genetixbay.com/knowledge/glossary/autoflower.md) | | 24/0 | 115–220 | 10–19 | House-endorsed; highest power use | | 12/12 | Not for photoperiod seedlings | — | Triggers early flowering | DLI = PPFD × hours × 0.0036. ## What to do 1. Pick 18/6 unless you have a reason not to. 2. Start at 100–200 µmol/m²/s as the [cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) open. 3. Raise towards 300 as [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) form, watching for [bleaching](https://genetixbay.com/knowledge/glossary/light-stress.md) or hard praying. 4. On 24/0, dim the light to keep DLI inside 10–19. ## Common mistakes - Running 24/0 at full veg intensity on new seedlings. - Starting photoperiods on 12/12 to "save time". - Choosing the schedule and ignoring the PPFD. - [Light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) or timer drift on a mother or nursery shelf near a flower room. ## Related - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - [How long is the seedling stage?](https://genetixbay.com/knowledge/answers/how-long-is-the-seedling-stage.md) - Terms: [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) · [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) · [DLI](https://genetixbay.com/knowledge/glossary/dli.md) ## Follow-up questions **Is 24/0 bad for seedlings?** No. 24/0 is fine for cannabis seedlings; GenetixBay endorses it, because cannabis does not need a sleep period in vegetative growth. The plant only measures night length to decide when to flower. The catch is cost and dose: 24 hours at 300 µmol/m²/s is a DLI of about 26 mol/m²/day, so run around 150–220 µmol/m²/s to stay in the seedling band. **How do I convert hours and PPFD to DLI?** Daily light integral (DLI) in mol/m²/day equals PPFD in µmol/m²/s times hours of light times 0.0036. For cannabis seedlings, 200 µmol/m²/s for 18 hours gives about 13 mol/m²/day, inside the 10–19 target. The same 200 µmol/m²/s for 24 hours gives about 17. Longer days let you use a dimmer light for the same total dose. **Do autoflower seedlings need a different schedule?** No. Autoflower seedlings use the same schedule as photoperiod seedlings, usually 18/6 or 20/4, and many growers run them that way to harvest. Autoflowers are day-neutral, so the light schedule doesn't trigger their flowering, but any setback costs them time they can't recover. Keep intensity gentle at 150–300 µmol/m²/s while they are seedlings. ## Sources 1. Runkle E. The benefits of lighted plugs. Michigan State University Extension. https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs 2. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 3. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 --- # What happens if my lights accidentally stay on during flower? > One accidental 24-hour light period in flower usually costs a photoperiod plant a day or two, not the crop. Fix the timer and return to your normal 12/12 or 13/11 straight away; no long 'make-up' darkness is needed. It matters most in the first two weeks after the flip, when induction can stall. Watch for pollen sacs for 2–3 weeks: a plant that herms from one night is herm-prone. - Canonical: https://genetixbay.com/knowledge/answers/lights-stayed-on-during-flower.html - Topic: Environment · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Also asked as: My timer failed in flower: what now? | Lights were on for 24 hours by mistake | I missed a dark period in flower | Will one night of light cause hermies? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer One missed dark period in flower usually costs a [photoperiod plant](https://genetixbay.com/knowledge/glossary/photoperiod.md) **a day or two**, not the crop. Fix the timer and go straight back to your normal **[12/12](https://genetixbay.com/knowledge/glossary/12-12.md) or [13/11](https://genetixbay.com/knowledge/glossary/13-11.md)**; no long make-up darkness is needed. The risk is highest in the **first two weeks after the flip**. *Grower practice*; the biology behind it is *Supported*. ## Why Cannabis flowers in response to long, uninterrupted nights. Inflorescence development needed at least three consecutive short days in one study, and moving plants back to long days raised [gibberellin](https://genetixbay.com/knowledge/glossary/gibberellin.md) and [auxin](https://genetixbay.com/knowledge/glossary/auxin.md) at the [shoot tip](https://genetixbay.com/knowledge/glossary/apical-meristem.md) and pulled the forming inflorescence apart [1]. That's [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) in slow motion. One long day doesn't undo weeks of induction in an established flower, but it does stall it. Several days can start reversion. Even dim stray light delays flowering in sensitive cultivars [2][3], so a full day of light is a bigger signal. **House position:** [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md) reveals [herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) genetics; it doesn't make a stable plant [hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md). A plant that throws [pollen sacs](https://genetixbay.com/knowledge/glossary/anther.md) after one bad night is the problem, not the timer. Extra "reset" darkness is a cousin of the darkness-before-harvest *Myth*: no evidence, and a day of lost [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md). ## The numbers | What happened | Likely effect | Action | |---|---|---| | One 24 h light period, mid or late flower | delay of about a day or two | resume schedule | | One 24 h light period, first 2 weeks after the flip | induction stalls, more [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) | resume; count from the restart | | Several days of light | possible re-veg, single-finger leaves | resume; expect 1–2 weeks added | | Watch window for pollen sacs | 2–3 weeks | inspect every few days | ## What to do 1. Reset or replace the timer and return to normal at the next lights-off. 2. Note the date in your journal and adjust your harvest estimate. 3. Inspect plants every few days for 2–3 weeks for pollen sacs. 4. Remove isolated sacs; cull a plant that keeps producing them, and never breed from it. 5. Fit a timer you trust, and check it after every power cut. ## Common mistakes - Giving 24–48 h of darkness "to reset". - Panic-harvesting early. - Excusing [late-flower bananas](https://genetixbay.com/knowledge/glossary/nanners.md) as normal. - Not checking the timer after a power cut. ## Related - Full article: [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - [Can I open my tent during the dark period?](https://genetixbay.com/knowledge/answers/opening-tent-during-dark-period.md) - [Why is my plant growing single-finger leaves?](https://genetixbay.com/knowledge/answers/single-finger-leaves-reveg.md) - [Hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - Terms: [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) · [nanners](https://genetixbay.com/knowledge/glossary/nanners.md) ## Follow-up questions **Should I give extra darkness after the lights stayed on?** No, you don't need to give extra darkness after a light schedule failure in flower. Return to your normal 12/12 or 13/11 at the next scheduled lights-off. A long 'reset' dark period has no evidence behind it and cuts a day of photosynthesis. The plant measures each uninterrupted night, so normal long nights get flowering back on track. **Will one night of light cause hermaphrodites?** One night of light can trigger pollen sacs on herm-prone plants, but in GenetixBay's breeder position the stress reveals unstable genetics rather than creating them: stable plants beside them stay female. Check the plants every few days for 2–3 weeks. Remove any pollen sacs, and cull and don't breed from a plant that herms. Late-flower bananas are not normal. **What if my lights stayed on for several days in flower?** Several days of continuous light in flower can stall a photoperiod plant or start it reverting, with new single-finger leaves on the buds, because induction needs consecutive long nights. Return to 12/12 or 13/11 immediately; most plants resume flowering within about a week or two, adding that time to harvest. Plants early in flower are affected most. ## Sources 1. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 3. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis --- # Why don't lumens matter for grow lights? > Lumens don't matter for grow lights because lumens, lux and foot-candles measure light as the human eye sees it, weighted heavily to green-yellow, while plants use photons from 400–700 nm about equally. The plant-relevant numbers are PPF (µmol/s from the fixture), PPFD (µmol/m²/s at the canopy), DLI (mol/m²/day) and efficacy (µmol/J). Lux converts to PPFD only roughly, and only for a known spectrum. - Canonical: https://genetixbay.com/knowledge/answers/lumens-vs-ppfd.html - Topic: Environment · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: Lumens vs PAR for grow lights | How much lux do plants need? | How many lumens per square foot for cannabis? | Is lux the same as PPFD? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Lumens, lux and [foot-candles](https://genetixbay.com/knowledge/glossary/foot-candle.md) measure light **as the human eye sees it**, weighted heavily to green-yellow. Plants use photons from **400–700 nm** about equally. So the numbers that matter are **[PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md)** (µmol/m²/s at the canopy), **[DLI](https://genetixbay.com/knowledge/glossary/dli.md)** (mol/m²/day) and fixture **[efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md)** (µmol/J). *Established*. ## Why Photometric units (lumens, lux) and quantum units (µmol) describe different things. Converting between them needs a factor that depends on the light source's spectrum; published factors differ from lamp to lamp [1]. A red-heavy grow light [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) dim to us and scores low lumens, yet delivers plenty of [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) photons. A cool white household lamp can score high lumens and deliver fewer photons per watt than a horticultural fixture. Lumens rank these lights in the wrong order. Grow lights are therefore rated in [PPF](https://genetixbay.com/knowledge/glossary/ppf.md) (µmol/s) and efficacy (µmol/J). Good horticultural [LEDs](https://genetixbay.com/knowledge/glossary/led.md) exceed 2.5–3 µmol/J [2]. PPFD at the canopy is the number that predicts yield: dry flower yield rose linearly from 120 to 1,800 µmol/m²/s in one controlled cannabis trial [3]. ## The numbers | Unit | Measures | Use for plants? | |---|---|---| | Lumen (lm) | total visible light, eye-weighted | no | | Lux (lm/m²) | eye-weighted light per m² | rough only, known spectrum | | Foot-candle | lux per ft² (1 fc ≈ 10.76 lux) | rough only | | PPF (µmol/s) | fixture's 400–700 nm photon output | yes | | PPFD (µmol/m²/s) | photons reaching the canopy | yes: the setpoint | | DLI (mol/m²/day) | PPFD × hours × 0.0036 | yes | | Efficacy (µmol/J) | PPF ÷ watts | yes: running cost | **Rough sunlight conversion:** about 54 lux per µmol/m²/s [1]. Other spectra differ. ## What to do 1. Ignore lumen and "equivalent watt" claims on grow lights. 2. Ask for PPF, µmol/J and a PPFD map at stated heights. 3. Set the light by PPFD: 150–300 [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md), 300–700 veg, 800–1,200 flower. 4. Use [lux meters](https://genetixbay.com/knowledge/glossary/lux.md) only to compare spots under the same light. ## Common mistakes - Choosing a grow light by lumens per square foot. - Applying the sunlight lux factor to LEDs. - Assuming a brighter-looking light grows better. ## Related - Full article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [How can I measure PPFD without a PAR meter?](https://genetixbay.com/knowledge/answers/measure-ppfd-without-a-par-meter.md) - [Can I grow with household LED or CFL bulbs?](https://genetixbay.com/knowledge/answers/can-i-grow-with-household-bulbs.md) - Terms: [lux](https://genetixbay.com/knowledge/glossary/lux.md) · [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) · [DLI](https://genetixbay.com/knowledge/glossary/dli.md) · [foot-candle](https://genetixbay.com/knowledge/glossary/foot-candle.md) ## Follow-up questions **What is the difference between lux and PPFD?** Lux measures how bright light looks to a human per square metre, weighted to the eye's peak sensitivity in green-yellow. PPFD counts the photosynthetic photons between 400 and 700 nm landing on a square metre each second, in µmol/m²/s, which is what drives photosynthesis. A red-heavy lamp can have low lux but high PPFD; the two don't convert without knowing the spectrum. **How many lumens does cannabis need?** Cannabis needs are not set in lumens: lumens measure brightness to the human eye, not plant-usable light. Use PPFD instead: about 150–300 µmol/m²/s for seedlings, 300–700 in veg and 800–1,200 in flower at ambient CO₂. As a rough sunlight-only guide, 1,000 µmol/m²/s is about 54,000 lux, but lamps with other spectra convert differently. **What do PPF, PPFD and DLI mean?** PPF (photosynthetic photon flux) is a fixture's total output of 400–700 nm photons, in µmol/s. PPFD (photosynthetic photon flux density) is how many of those land on a square metre of canopy each second, in µmol/m²/s. DLI (daily light integral) is the day's total, in mol/m²/day: PPFD × hours × 0.0036. Efficacy, in µmol/J, is PPF divided by watts. ## Sources 1. Thimijan RW, Heins RD, 1983. Photometric, radiometric, and quantum light units of measure: a review of procedures for interconversion. HortScience 18(6):818–822. https://doi.org/10.21273/HORTSCI.18.6.818 2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 3. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # What are macronutrients and micronutrients? > Macronutrients are the elements cannabis needs in large amounts: nitrogen, phosphorus and potassium (primary) plus calcium, magnesium and sulfur (secondary), fed at roughly 30-250 mg/L each. Micronutrients are needed in traces, under about 3 mg/L: iron, manganese, zinc, copper, boron, molybdenum, plus chloride and nickel. Carbon, hydrogen and oxygen come from air and water. Silicon is beneficial, not essential. - Canonical: https://genetixbay.com/knowledge/answers/macro-vs-micronutrients.html - Topic: Nutrients · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Mobile vs immobile nutrients: reading old vs new leaves](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) - Also asked as: What are macro and micro nutrients? | Which nutrients does cannabis need? | What are the essential elements for plants? | What are secondary nutrients? | Is silica a nutrient? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Macronutrients](https://genetixbay.com/knowledge/glossary/macronutrient.md) are the elements cannabis uses in large amounts: nitrogen, phosphorus and potassium (the primaries) and calcium, magnesium and [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) (the secondaries), fed at roughly 30–250 mg/L each. [Micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md) are just as essential but needed in traces, under about 3 mg/L: iron, [manganese](https://genetixbay.com/knowledge/glossary/manganese.md), [zinc](https://genetixbay.com/knowledge/glossary/zinc.md), [copper](https://genetixbay.com/knowledge/glossary/copper.md), boron, [molybdenum](https://genetixbay.com/knowledge/glossary/molybdenum.md), [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) and nickel. *Established.* ## Why An element is essential when the plant cannot complete its life cycle without it and nothing else can replace it [1]. That gives 17 for higher plants: carbon, hydrogen and oxygen from air and water, plus 14 mineral elements from the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) [1]. Macro and micro describe quantity, not importance. Macronutrients build bulk: nitrogen in proteins and [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md), calcium in cell walls, potassium as the main cell solute [1]. Micronutrients mostly run enzymes, so a little goes a long way and too much is toxic. Cannabis shows a distinct, recognisable [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) for each element when it is withheld [3], which is why diagnosis starts with knowing the list. [Beneficial elements](https://genetixbay.com/knowledge/glossary/beneficial-element.md) such as silicon and [sodium](https://genetixbay.com/knowledge/glossary/sodium.md) can help some crops but are not essential [1]. ## The numbers | Group | Elements | Typical cannabis feed (mg/L) [2] | |---|---|---| | Primary macro | N, P, K | N 150–200, P 30–60, K 175–250 | | Secondary macro | Ca, Mg, S | Ca 150–200, Mg 40–70, S 60–120 | | Micro | Fe, Mn, Zn, Cu, B, Mo | Fe 1.5–3, Mn 0.3–0.8, Zn 0.1–0.5, B 0.2–0.5, Cu 0.03–0.1, Mo 0.01–0.05 | | Micro (rarely added) | Cl, Ni | Supplied by water and impurities | | Beneficial | Si, Na | Si 20–50 if used; Na as low as possible | ## What to do 1. Use a complete base feed that lists both macros and micros. 2. Check that calcium and magnesium are covered, especially with [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) or soft water. 3. Never add single micronutrients by guesswork. 4. Diagnose by where symptoms start: old leaves (mobile) or new growth (immobile). ## Common mistakes - Thinking [NPK](https://genetixbay.com/knowledge/glossary/npk-ratio.md) is the whole feed. - Adding iron or zinc "just in case" and causing [toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md). - Calling silica essential. - Ignoring what the water already supplies. ## Related - Full article: [Mobile vs immobile nutrients](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) - Articles: [feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Answers: [what NPK means](https://genetixbay.com/knowledge/answers/what-does-npk-mean.md) - Terms: [macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md) · [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) · [secondary nutrient](https://genetixbay.com/knowledge/glossary/secondary-nutrient.md) ## Follow-up questions **Which nutrients are mobile and immobile?** In cannabis, the mobile nutrients are nitrogen, phosphorus, potassium and magnesium, plus chloride, nickel and, moderately, molybdenum; their shortages show on old, lower leaves first. The immobile or low-mobility nutrients are calcium, boron, iron, manganese, copper and zinc; their shortages show on new growth. Sulfur is intermediate, often showing mid-canopy and on newer leaves. **Are micronutrients less important than macronutrients?** No. Micronutrients are needed in tiny amounts but are just as essential: a plant short of iron or boron fails as surely as one short of nitrogen. The difference is dose. A cannabis feed carries iron at about 1.5-3 mg/L and molybdenum at 0.01-0.05 mg/L, against nitrogen at 150-200 mg/L. Overdosing micronutrients is toxic, so never guess. **Is silica an essential nutrient for cannabis?** Silicon is not an essential nutrient for cannabis; plants complete their life cycle without it, so it is classed as a beneficial element. In many crops it strengthens cell walls and reduces some stresses, and cannabis does take it up, but cannabis-specific evidence for yield or quality gains is thin. Growers commonly add 20-50 mg/L silicon. ## Sources 1. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Sonneveld C, Voogt W, 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 3. Cockson P, Landis H, Smith T, Hicks K, Whipker BE, 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 --- # How can I measure PPFD without a PAR meter? > Without a PAR meter, estimate PPFD from the fixture's published PPFD map at your hanging height, cross-check with watts × µmol/J ÷ canopy area, and use a phone or lux meter only for comparisons. Lux-to-PPFD conversion depends on spectrum (about 54 lux per µmol/m²/s in sunlight) and phone apps are often off by 20 % or more. Watch the top leaves to confirm. - Canonical: https://genetixbay.com/knowledge/answers/measure-ppfd-without-a-par-meter.html - Topic: Environment · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: Can I use a phone light meter app for PPFD? | How do I convert lux to PPFD? | Do I need a PAR meter? | How do I know how much light my plants get? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Without a [PAR](https://genetixbay.com/knowledge/glossary/par.md) meter, take [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) from the fixture's **published PPFD map** at your hanging height, cross-check with **watts × [µmol/J](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) ÷ [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md)**, and use a phone or [lux meter](https://genetixbay.com/knowledge/glossary/lux.md) only to **compare spots**. Lux-to-PPFD conversion depends on the spectrum (about **54 lux per µmol/m²/s in sunlight**) [1], and phone apps are often off by **20 % or more**. *Supported*. ## Why Lux meters and phone cameras are weighted to the human eye, which sees green best. Plants use photons from 400–700 nm about equally well. So the same lux reading means different PPFD under different lights; published [conversion factors](https://genetixbay.com/knowledge/glossary/conversion-factor.md) differ by light source [1]. A fixture's total photon output is its wattage times its efficacy in µmol/J [2]. Divide by the canopy area and you get the best-case average PPFD. Real canopies get somewhat less, especially at the edges. PPFD matters because yield indoors rises with it: linearly from 120 to 1,800 µmol/m²/s in one controlled trial [3]. Guessing low costs grams; guessing high costs leaves. ## The numbers | Method | Accuracy | Use for | |---|---|---| | Quantum (PAR) sensor | best | setpoints | | Fixture PPFD map at your height | fair, if measured honestly | first setup | | Watts × µmol/J ÷ area | best-case average | sanity check | | Lux meter + conversion | depends on spectrum | rough estimate | | Phone app | ±20 % or worse | hot and dim spots, trends | **Worked example:** 300 W × 2.7 µmol/J = 810 µmol/s over 0.81 m² (3 × 3 ft) = **1,000 µmol/m²/s best case**; expect perhaps 800–900 on the canopy, less in corners. ## What to do 1. Read the fixture's PPFD map at 30, 45 and 60 cm (12, 18, 24 in). 2. Do the watts × µmol/J ÷ area check. 3. Use a phone app in a grid (centre, corners, halfway) to find weak spots. 4. Dim by the map, then raise in 10 % steps every few days. 5. Watch the [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md): [bleaching](https://genetixbay.com/knowledge/glossary/light-stress.md), upward cupping or [tacoing](https://genetixbay.com/knowledge/glossary/taco-leaf.md) means back off 10–20 %. 6. Borrow or rent a quantum meter once to calibrate your eye. ## Common mistakes - Trusting a phone number as an absolute setpoint. - Using the centre-point PPFD at 30 cm as "my PPFD". - Converting lux with the sunlight factor under red-heavy [LEDs](https://genetixbay.com/knowledge/glossary/led.md). - Never measuring the corners. ## Related - Full article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [Why don't lumens matter for grow lights?](https://genetixbay.com/knowledge/answers/lumens-vs-ppfd.md) - [What wattage LED do I need for my tent?](https://genetixbay.com/knowledge/answers/what-wattage-light-for-my-tent.md) - Guide: [Lights for beginners](https://genetixbay.com/knowledge/guides/lights-for-beginners.md) - Terms: [lux](https://genetixbay.com/knowledge/glossary/lux.md) · [PAR](https://genetixbay.com/knowledge/glossary/par.md) ## Follow-up questions **How accurate are phone PPFD apps?** Phone PPFD apps are rough: phone sensors measure light weighted for human vision, and converting to PPFD depends on the light's spectrum, so readings are often off by 20 % or more and can be worse with red-heavy fixtures. They are fine for finding hot and dim spots and for checking that today matches last week, not for setting an absolute target like 900 µmol/m²/s. **How do I convert lux to PPFD?** To convert lux to PPFD, divide lux by a factor that depends on the light source's spectrum. For sunlight the factor is about 54 lux per µmol/m²/s, so 54,000 lux is roughly 1,000 µmol/m²/s. Other lamps need different factors, and white LEDs vary with colour temperature, so a lux-based PPFD is an estimate. A quantum sensor measures PPFD directly. **Is a PAR meter worth buying?** A quantum (PAR) meter is worth buying once you grow regularly or run lights above about 800 µmol/m²/s, because it lets you set intensity by measurement, map the corners and check dimmer settings. For a first small grow, a fixture with a published PPFD map, a dimmer and careful attention to the top leaves is enough. Rent or borrow one if you can. ## Sources 1. Thimijan RW, Heins RD, 1983. Photometric, radiometric, and quantum light units of measure: a review of procedures for interconversion. HortScience 18(6):818–822. https://doi.org/10.21273/HORTSCI.18.6.818 2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 3. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # What meters do I actually need for growing? > For a first grow you need three meters: a pH meter calibrated with pH 7 and pH 4 buffers, an EC meter checked against a 1.413 mS/cm standard, and a thermo-hygrometer with min/max memory, salt-tested for accuracy. An IR thermometer is a cheap fourth. A PAR meter is worth it once you grow regularly. A meter you don't calibrate is worse than none. - Canonical: https://genetixbay.com/knowledge/answers/meters-you-need-for-growing.html - Topic: Equipment · Type: How-to - Evidence: Established · Status: Draft: awaiting expert review - Full article: [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) - Also asked as: What are the essential grow meters? | Do I need a pH pen, EC meter and hygrometer? | Do I need a PAR meter? | Which meters are worth buying for a first grow? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer You need three: a **[pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md)** (calibrated with [pH](https://genetixbay.com/knowledge/glossary/ph.md) 7 and pH 4 buffers), an **[EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md)** (checked against **1.413 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md)**) and a **thermo-hygrometer** with min/max memory (salt-tested). An **[IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md)** is a cheap fourth; a **[PAR](https://genetixbay.com/knowledge/glossary/par.md) meter** pays off once you grow regularly. *Established* for calibration practice. ## Why pH controls which nutrients roots can take up. A pH meter is only as good as its last calibration: two fresh buffers that bracket your readings, at least weekly [1]. [EC](https://genetixbay.com/knowledge/glossary/ec.md) tells you how strong the feed and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) are. EC meters drift less than pH probes, but still need checking against a standard and after drops or battery changes [2]. [TDS](https://genetixbay.com/knowledge/glossary/tds.md) meters show the same reading converted to ppm by a factor that varies. Temperature and humidity drive [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) and disease risk. Min/max memory catches the lights-off humidity spike you never see. A salt test shows whether the [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) reading is honest [3]. Light is the biggest yield lever indoors [4]. A quantum meter turns guessing into setting. ## The numbers | Meter | Must-have? | Check against | How often | |---|---|---|---| | pH meter | yes ([coco](https://genetixbay.com/knowledge/glossary/coco-coir.md)/hydro); strongly advised (soil) | pH 7.00 + 4.01 buffers | weekly, before decisions | | EC meter | yes | 1.413 mS/cm standard | monthly, after drops | | Thermo-hygrometer, min/max | yes | salt test, ~75 % RH | every few months | | IR thermometer | useful | emissivity ~0.95 | — | | Quantum (PAR) meter | later | — | — | | [Jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md), 60× | yes, at harvest | — | — | | pH probe life | | | ~1–2 years stored wet | ## What to do 1. Buy pH, EC and thermo-hygrometer first; buffers and [EC standard](https://genetixbay.com/knowledge/glossary/calibration-solution.md) with them. 2. Calibrate pH with pH 7, then pH 4; re-read pH 7 (within ±0.05). 3. Store the pH probe wet in storage solution, never in [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md). 4. Salt-test the hygrometer before trusting it. 5. Log readings in your journal every time. 6. Add an IR thermometer, then a PAR meter as you scale up. ## Common mistakes - Never calibrating the pH pen. - Storing the probe dry. - Reading ppm off a TDS meter without knowing its scale. - One hygrometer on the floor, far from the canopy. ## Related - Full article: [pH and EC meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) - [How do I check if my hygrometer is accurate?](https://genetixbay.com/knowledge/answers/calibrate-a-hygrometer.md) - [How can I measure PPFD without a PAR meter?](https://genetixbay.com/knowledge/answers/measure-ppfd-without-a-par-meter.md) - [Is a TDS meter the same as an EC meter?](https://genetixbay.com/knowledge/answers/tds-meter-vs-ec-meter.md) - Terms: [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) · [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) · [jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) ## Follow-up questions **Do I need a pH meter for soil?** For quality living or amended soil, a pH meter is useful but less critical, because soil buffers pH and runs at 6.2–6.8. For coco and hydro, where pH should be 5.5–6.5 and drifts quickly, a calibrated pH meter is essential. Either way, calibrate with fresh pH 7 and pH 4 buffers at least weekly and store the glass probe wet, never dry. **Is a TDS meter good enough instead of an EC meter?** A TDS meter measures the same thing as an EC meter, electrical conductivity, then multiplies it by a conversion factor to show ppm. The factor varies, commonly 500 or 700, so two TDS meters can show different ppm for the same solution. Read or convert to EC in mS/cm, which is unambiguous, and check the meter against a 1.413 mS/cm standard. **How long does a pH probe last?** A glass pH probe typically lasts about one to two years when stored wet in storage solution or pH 4 or 7 buffer. Storing it dry or in RO water shortens its life. Replace the probe when it can no longer be adjusted to match buffer, or when its slope stays below about 90–95 % after cleaning. ## Sources 1. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download 2. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test 3. Greenspan L, 1977. Humidity fixed points of binary saturated aqueous solutions. Journal of Research of the National Bureau of Standards 81A(1):89–96. https://doi.org/10.6028/jres.081A.011 4. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # My buds got mouldy in the jar: what now? > Mouldy buds in a curing jar must be thrown away, not trimmed and smoked. Mouldy flower carries spores and possible mycotoxins. Bin every bud with fuzz, grey dust or brown inner tissue, then open every other jar and check it. Spread the rest out to dry until a sealed sample reads a stable 55–65% RH (water activity 0.55–0.65). Jar mould usually means buds went in too wet. - Canonical: https://genetixbay.com/knowledge/answers/mould-in-curing-jars.html - Topic: Diseases · Type: Troubleshooting - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) - Also asked as: Mould in my curing jars | Moldy buds after cure: can I save them? | Fuzzy buds in the jar | White fuzz on buds in jar - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer If buds in a [curing jar](https://genetixbay.com/knowledge/glossary/curing-jar.md) have gone mouldy, throw them away. Don't trim around the mould and don't smoke them. Then check every other jar, and dry the clean buds until a sealed sample reads a stable 55–65% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) ([water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55–0.65). *Established*: mouldy flower isn't safe to smoke, vape or extract. ## Why Mouldy cannabis can carry spores and mycotoxin-producing fungi, which is why regulated markets test flower for yeast and mould [1]. Mould grows when the bud's water activity is too high. ASTM sets 0.55–0.65 aw as the safe range for dried flower, and says flower above 0.68 needs more drying [2][3]. A jar holds in whatever moisture is still in the bud cores. [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) can also come in from the plant. It rots dense [colas](https://genetixbay.com/knowledge/glossary/cola.md) from the inside, often before anything shows, when late-flower humidity is high or water condenses at lights-off [4]. Buds infected that way can rot in the jar even when the dry looked right. ## The numbers | Reading | Meaning | Action | |---|---|---| | Sealed jar, stable 55–65% RH | aw 0.55–0.65, safe [2] | Keep curing | | 65–68% RH | Borderline | Take the buds out and dry them more | | > 68% RH, or 75%+ overnight | Too wet [3] | Dry them now and watch for mould | | Fuzz, grey dust, brown core | Mould | Throw it away | ## What to do 1. Wear a mask and gloves. Bag the mouldy buds where they sit so the spores don't spread. 2. Throw out every bud with fuzz, dust, a brown core or a musty smell, and every bud that touched one. 3. Open every jar. Break open the largest buds and check the cores. 4. Spread the clean buds on a screen at 15–21 °C (60–70 °F) and 55–62% RH until the small stems snap. 5. Re-jar them in clean jars, about ¾ full. Read the hygrometer only after 12–24 hours sealed. 6. Wash the old jars with hot soapy water and dry them fully. ## Common mistakes - Trimming off the fuzzy bit and keeping the bud. - Jarring buds by feel, without a sealed hygrometer test. - Packing jars tight. - Leaving a jar unopened for weeks early in the cure. ## Related - Full article: [Botrytis (bud rot / grey mould)](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) - Answers: [ammonia smell in jars](https://genetixbay.com/knowledge/answers/ammonia-smell-in-jars.md) · [how full to fill jars](https://genetixbay.com/knowledge/answers/how-full-to-fill-curing-jars.md) - Articles: [curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) · [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Terms: [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) · [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) · [mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md) ## Follow-up questions **Can I cut the mould off and keep the rest of the bud?** You cannot safely cut mould off a bud and keep the rest. Bud rot works from the inside, so the visible fuzz is the end of the infection, not its edge, and the spores spread through the jar. Discard the whole bud and any bud that touched it. Break open the biggest remaining buds and check for a clean core. **Why did my buds go mouldy in the jar?** Buds go mouldy in a jar because they were jarred too wet or packed too tight. A sealed jar traps the moisture still in the bud cores, and above water activity 0.65 mould can grow. A jar that spikes to 75% RH or more overnight went in too wet. Wet, dense colas from a humid late flower can also carry botrytis in already. **Are the other buds in the jar safe?** The other buds in a mouldy jar are only safe if they show no fuzz, no grey dust, no brown core and no musty smell when broken open. Spores will have spread in the jar air, so dry those buds out on a screen, re-check them, and put them in clean jars. When in doubt, throw it out, especially for anyone with a weak immune system. ## Sources 1. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 2. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 3. ASTM International, Standardization News. Two cannabis standards you should know about (D8196 water activity measurement; D8197 range). https://sn.astm.org/node/2445/printable/print 4. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker --- # Can I use neem oil in flower? > No: neem oil does not belong on cannabis in flower. 'Natural, so it's safe on buds' is a myth. Neem leaves an oily, bitter residue on resin, wet buds invite bud rot, and azadirachtin (crude neem's active) is one of 96 actives Canada tests licensed cannabis for. Use neem only in veg, and stop all oil sprays before flowers form, roughly by the end of the 10–14 day transition. - Canonical: https://genetixbay.com/knowledge/answers/neem-oil-in-flower.html - Topic: Pests · Type: Myth check - Evidence: Myth · Status: Draft: awaiting expert review - Full article: [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) - Also asked as: Is neem oil safe on buds? | Can I spray neem during flowering? | Neem oil in late flower | Is neem oil safe because it's natural? | When should I stop using neem oil? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer No. [Neem oil](https://genetixbay.com/knowledge/glossary/neem-oil.md) belongs in veg only; stop all oil sprays before flowers form, roughly by the end of the 10–14 day transition after the flip. The idea that neem is "natural, so safe on buds" is a *Myth*: natural origin says nothing about residue, taste or [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md). ## Why Neem is a contact oil. It works by coating soft-bodied pests and has to reach leaf undersides to do anything [1]. On a flower, that same coating sits on the [resin glands](https://genetixbay.com/knowledge/glossary/trichome.md) you intend to smoke. Residue is measurable. Azadirachtin, the insect-active compound in crude neem, is on Canada's mandatory test list for licensed cannabis, at a [limit of quantification](https://genetixbay.com/knowledge/glossary/loq.md) of 1 ppm [2]. In regulated markets only products registered for cannabis may be used, on label terms [4]. Wet buds rot. Botrytis needs free moisture on flower tissue, and dense [colas](https://genetixbay.com/knowledge/glossary/cola.md) dry slowly [3]. Spraying anything onto buds in late flower is a bud-rot invitation. ## The numbers | Stage | Neem or other oils | Notes | |---|---|---| | Veg | Acceptable where registered | Full coverage of leaf undersides; not under hot lights | | Transition (days 0–14 after flip) | Last chance, early in the window | Before [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) clusters form (*Grower practice*) | | Flower (pistils showing) | No | Residue, taste, botrytis risk | | Late flower, heavy pests | No spray | Remove leaves, harvest early if needed | ## What to do 1. Scout weekly in veg with a 10–20x lens so pests are dealt with before the flip. 2. If you use neem, use it in veg, at dawn or lights-off, never under hot lights or near [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md). 3. Do a final clean-up treatment before flowers form. 4. In flower, switch to [predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md), leaf removal and tolerance. 5. Check what is registered for cannabis where you live; rules vary. ## Common mistakes - Spraying "just once more" in week 4 of flower because it is organic. - Assuming clarified neem is residue-free. - Spraying buds at lights-off, leaving them wet all night. - Treating the pest in flower instead of preventing it in veg. ## Related - Full article: [Spider mites on cannabis: ID, lifecycle and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) - Answers: [What can I spray in flower?](https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.md) · [Preventing pests indoors](https://genetixbay.com/knowledge/answers/how-to-prevent-pests-indoors.md) - Terms: [neem oil](https://genetixbay.com/knowledge/glossary/neem-oil.md) · [horticultural oil](https://genetixbay.com/knowledge/glossary/horticultural-oil.md) · [contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md) ## Follow-up questions **When is the last time I can spray neem oil?** Spray neem oil on cannabis only in veg, and make the last application before flowers form, roughly by the end of the 10–14 day transition after the flip. That timing is grower practice, not a label rule. Once pistil clusters appear, any oil lands on the tissue you will smoke. Labels and local registration rules come first, so check what is permitted where you live. **Is clarified neem oil safer in flower than crude neem?** Clarified hydrophobic neem oil has most of the azadirachtin removed, so it acts mainly as a horticultural oil that smothers soft-bodied pests on contact. That does not make it safe on buds. Any oil coats resin glands, changes smell and taste, and leaves buds wet, which favours botrytis. In flower the answer is the same for every neem product: keep it off. **What can I use instead of neem in flower?** Instead of neem in flower, use predatory mites and other beneficials, remove infested leaves, and accept some damage. For spider mites, Neoseiulus californicus or Phytoseiulus persimilis released early work best. If a late-flower infestation is severe, harvest early rather than spray. The real fix is upstream: scout and treat in veg so pest numbers are low before buds form. ## Sources 1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html 2. Health Canada, 2019 (updated 2026). Mandatory cannabis testing for pesticide active ingredients: list and limits. Government of Canada. https://www.canada.ca/en/public-health/services/publications/drugs-health-products/cannabis-testing-pesticide-list-limits.html 3. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker 4. Health Canada. Pest control products for use on cannabis. Government of Canada. https://www.canada.ca/en/health-canada/services/cannabis-regulations-licensed-producers/pest-control-products.html --- # Can I open my tent during the dark period? > You can open a flowering tent during the dark period only if the room outside is dark too, and briefly. Light in the dark period, even very dim, can delay or weaken flowering: delays have been reported from about 2 µmol/m²/s in hemp and 0.01 µmol/m²/s in sensitive cannabis. If you must work, use a dim green headlamp for a few minutes. In veg, it doesn't matter. - Canonical: https://genetixbay.com/knowledge/answers/opening-tent-during-dark-period.html - Topic: Environment · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Also asked as: Can I use a green light during the dark period? | Can I check my plants at night in flower? | Does opening the tent interrupt the dark cycle? | How dark does a flowering tent need to be? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer In flower, open the tent during the dark period only if the room around it is **dark too**, and only briefly. Stray light as dim as **2 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md)** delayed flowering in [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) [1], and a conference report saw delays in sensitive cannabis at **0.01 µmol/m²/s** [2]. If you must work, use a **dim green headlamp** for a few minutes. In veg it doesn't matter. *Supported*. ## Why [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis measures the length of the **uninterrupted** night. [Phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md) in the leaf tracks red and [far-red light](https://genetixbay.com/knowledge/glossary/far-red.md); a pulse of light mid-night resets the count. Commercial growers use exactly this "night break" on purpose to keep [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md) vegetative [3]. Induction is most fragile in the first two weeks after the flip. It needs consecutive short days, and returning plants to long-day conditions pulled the forming inflorescence apart in one study [4]. Green light is less active on phytochrome than red, but not inactive. Dim and brief is the rule (*Grower practice*). ## The numbers | Situation | Risk | |---|---| | Veg ([18/6](https://genetixbay.com/knowledge/glossary/18-6.md), 20/4, [24/0](https://genetixbay.com/knowledge/glossary/24-0.md)) | none: open freely | | Flower, dark room, tent opened | low | | Flower, dim green headlamp, a few minutes | low (*Grower practice*) | | Flower, room lights on, tent opened | can delay flowering in sensitive cultivars | | Stray light that delayed flowering | ~2 µmol/m²/s (hemp) [1]; 0.01 µmol/m²/s (sensitive cannabis) [2] | | Most sensitive window | first ~2 weeks after the flip [4] | ## What to do 1. Do your daily check during lights-on. 2. Turn off room lights before unzipping at night. 3. Use a dim green headlamp, aimed low, for minutes, not an hour. 4. Fix the cause of night visits: put pumps, timers and sensors where you can reach them without opening the tent. 5. After the flip, sit in the dark tent for five minutes once; anything you can see is a leak. ## Common mistakes - "One minute won't matter", every night. - A bright green work light left on. - Opening the tent with the room lights on. - Phone screens and controller [LEDs](https://genetixbay.com/knowledge/glossary/led.md) inside the tent. ## Related - Full article: [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - [What happens if my lights accidentally stay on during flower?](https://genetixbay.com/knowledge/answers/lights-stayed-on-during-flower.md) - [Why do photoperiod plants need long nights to flower?](https://genetixbay.com/knowledge/answers/why-flowering-needs-darkness.md) - [The flip isn't day 1 of flower](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - Terms: [light leak](https://genetixbay.com/knowledge/glossary/light-leak.md) · [phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md) ## Follow-up questions **Is green light safe during the dark period?** Green light is less active on the phytochrome that times cannabis flowering than red light, but it is not inactive. A dim green headlamp used for a few minutes during the dark period is grower practice and generally tolerated. A bright green work light, or one left on, can still delay flowering in sensitive cultivars. Keep it dim, brief and pointed away from the tops. **Will one minute of light ruin flowering?** One brief flash of light during the dark period rarely ruins cannabis flowering, but it can matter for sensitive cultivars, especially in the first two weeks after the flip while induction is still being set up. A pulse of light in mid-night resets the plant's night measurement, which is how commercial night-break lighting keeps mothers vegetative. Don't make it a habit. **Does opening the tent at night cause hermaphrodites?** Light during the dark period is a commonly reported trigger for hermaphrodite flowers, but in GenetixBay's breeder position a light interruption reveals herm-prone genetics rather than creating them: a stable plant beside the same leak stays female. Controlled evidence is limited. Avoid night light anyway, and cull any plant that throws pollen sacs rather than breeding from it. ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis 3. Examining the night break method in Cannabis sativa horticulture: vegetative daily light integral affects yield of extractable biomass, 2025. Plants 14(19):3095. https://pmc.ncbi.nlm.nih.gov/articles/PMC12525983/ 4. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 --- # In what order should I mix nutrients? > Mix nutrients into the full volume of water in this order: silica first, then Cal-Mag or part A, then part B, then any additives, stirring between each, and adjust pH last. Silica first because it is strongly alkaline (pH about 11-12). Calcium and the sulfates and phosphates in part B must meet only once diluted, or they precipitate. Then check EC against your target. - Canonical: https://genetixbay.com/knowledge/answers/order-to-mix-nutrients.html - Topic: Nutrients · Type: How-to - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - Also asked as: What is the right nutrient mixing order? | Does silica go in first? | Part A or part B first? | Why do I add silica first when mixing nutrients? | When do I add Cal-Mag? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Into the full volume of water: [silica](https://genetixbay.com/knowledge/glossary/silica.md) first, then [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) or part A, then part B, then additives, stirring between each, and [pH](https://genetixbay.com/knowledge/glossary/ph.md) last. Then check [EC](https://genetixbay.com/knowledge/glossary/ec.md). The order stops calcium meeting [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md) and [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) at high concentration, and keeps alkaline silica from shocking a mixed feed. *Established* chemistry. ## Why Calcium forms insoluble calcium sulfate (gypsum) and calcium phosphate when it meets sulfate or phosphate concentrated. At [feed strength](https://genetixbay.com/knowledge/glossary/input-ec.md) they stay dissolved; at concentrate strength they don't [1]. That is why feeds come as [A and B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md), and why each goes into the water separately. Classic nutrient solutions have always been made this way: separate [stock solutions](https://genetixbay.com/knowledge/glossary/stock-solution.md), each diluted into the tank in turn [2]. [Silicon](https://genetixbay.com/knowledge/glossary/silicon.md) is a [beneficial element](https://genetixbay.com/knowledge/glossary/beneficial-element.md), not an essential one [3]. [Potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md) stock is strongly alkaline, around pH 11–12. Added first to plain water it disperses before it can spike pH around calcium and iron. pH comes last because every salt, and silica most of all, shifts it. Adjust before the salts and you adjust twice. ## The numbers | Step | What | Wait | |---|---|---| | 0 | Water, measure its EC; 18–22 °C (64–72 °F) | n/a | | 1 | Silica (potassium silicate), 20–50 mg/L Si if used | Stir, 2–5 min | | 2 | Cal-Mag, if needed | Stir | | 3 | Part A (calcium, iron) | Stir | | 4 | Part B (phosphate, sulfate, [micros](https://genetixbay.com/knowledge/glossary/micronutrient.md)) | Stir | | 5 | Additives | Stir | | 6 | pH adjust (hydro: aerate 30–60 min first) | Re-read | | 7 | Check EC | n/a | ## What to do 1. Fill with the full volume of water first. 2. Add each product separately, stirring between. 3. Use a separate syringe or cup for each bottle. 4. Adjust pH in small doses once everything is in. 5. Confirm EC against your stage target. *Safety:* pH adjusters and silicate are caustic or acidic. Gloves and eye protection. ## Common mistakes - A and B in the same measuring cup. - Silica added last, into an acidic mix. - pH adjusted before the nutrients. - Mixing into a little water, then topping up. ## Related - Full article: [Hydroponic salts explained](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md) - Articles: [silicon](https://genetixbay.com/knowledge/nutrients/silicon.md) - Answers: [pH before or after nutrients](https://genetixbay.com/knowledge/answers/ph-before-or-after-nutrients.md) · [storing mixed feed](https://genetixbay.com/knowledge/answers/how-long-can-mixed-nutrients-sit.md) - Terms: [A-B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) · [stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md) ## Follow-up questions **Why do I add silica first when mixing nutrients?** Silica goes in first, into plain water, because potassium silicate is strongly alkaline, around pH 11-12. Added to a mixed, acidic nutrient solution it creates local pH spikes that can precipitate calcium and iron, while silicic acid polymerises at low pH. Stir it in, wait a few minutes, add the A and B nutrients, then adjust pH last. **Does part A or part B go in first?** Add part A first, stir, then part B, each into the full volume of water. Part A carries calcium and iron; part B carries the sulfates and phosphates. At feed strength they stay dissolved, but if they meet concentrated, calcium sulfate and calcium phosphate precipitate. Never pour A and B into the same measuring cup. **When should I add pH down?** Add pH down or pH up last, after every nutrient and additive is in and stirred, because the salts themselves change pH. In hydro, aerate a fresh mix for 30-60 minutes before the final adjustment, since carbon dioxide loss raises pH in the first hours. Add adjuster in small doses and re-read after mixing. ## Sources 1. Sonneveld C, Voogt W, 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Hoagland DR, Arnon DI, 1950. The water-culture method for growing plants without soil. California Agricultural Experiment Station Circular 347. https://archive.org/details/watercultureme3450hoag/ 3. Epstein E, 1994. The anomaly of silicon in plant biology. PNAS 91(1):11-17. https://doi.org/10.1073/pnas.91.1.11 --- # How do I grow outdoors in a short northern season? > To grow outdoors in a short northern season (roughly 50° latitude and above, with frost by late September or October), pick plants that finish by late September: autoflowers, or early-finishing photoperiod lines. Start indoors 3–6 weeks before last frost, harden off, plant out in early June, and use a greenhouse, hoop cover or light deprivation to dodge autumn rain. Check local rules first. - Canonical: https://genetixbay.com/knowledge/answers/outdoor-short-season.html - Topic: Outdoor growing · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) - Also asked as: Short-season outdoor growing | Growing cannabis outdoors in a cold climate | Outdoor grow in Canada or northern Europe | What finishes before frost up north? | Outdoor growing at 50 degrees latitude - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Grow plants that finish by late September: [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md), or [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) lines bred to flower early. Start indoors, plant out after the last frost (usually early June at 50° and above), and keep rain off the buds in autumn. *Grower practice*. [Home growing](https://genetixbay.com/knowledge/glossary/home-grow.md) outdoors is legal only in some places, so check local rules first. ## Why Long northern days delay flowering. Cannabis flowers when nights pass a cultivar's threshold, often near 14 h of day [1]. At 50° latitude days stay above 14 h until about 23 August, against 9 August at 40° (calculated, sunrise to sunset). Add the 10–14 day transition and an 8–10 week flower, and a typical cultivar finishes in late October. Genetics can move the date. Breeding work has mapped *Autoflower1* and an early-flowering [locus](https://genetixbay.com/knowledge/glossary/locus.md), *Early1* [2]. Autos ignore day length; early photoperiod lines simply start and finish sooner. A head start indoors buys weeks. [Seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) started indoors and hardened off go out at a useful size the day frost risk passes [3]. Autumn wet is the real threat. Gray mould thrives in cool, wet weather on dense buds [4], and northern Septembers deliver both. ## The numbers | Approach | Plant out (N / S) | Harvest (N / S) | |---|---|---| | Autoflower, sown direct | Early June / early December | Mid-August–early September / mid-February–early March | | Early photoperiod line | Early June / early December | Mid–late September / mid–late March | | Typical photoperiod | Early June / early December | Late October or later / late April or later | | [Light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md) (~12 h dark from early July) | Early June / early December | Late August–September / late February–March | ## What to do 1. Choose autos or proven early-finishing photoperiods; avoid late tropical lines. 2. Start photoperiods indoors 3–6 weeks before last frost on long days. 3. [Harden off](https://genetixbay.com/knowledge/glossary/hardening-off.md) for 7–14 days. 4. Plant out after the last frost, in the sunniest, best-drained spot. 5. Use containers, a greenhouse or a hoop cover to warm roots and keep rain off. 6. Consider light deprivation for photoperiods. 7. Watch forecasts from September and harvest ripe plants ahead of long rain or a hard freeze. ## Common mistakes - Growing a 12-week cultivar where frost arrives in early October. - Planting out too early and losing plants to a late frost. - Closing a greenhouse up tight and breeding mould. - Skipping the local-rules check. ## Related - Full article: [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) - Answers: [Autoflowers outdoors](https://genetixbay.com/knowledge/answers/autoflowers-outdoors.md) · [When outdoor plants flower](https://genetixbay.com/knowledge/answers/when-do-outdoor-plants-flower.md) · [When to harvest outdoors](https://genetixbay.com/knowledge/answers/when-to-harvest-outdoors.md) - Terms: [light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md) · [greenhouse growing](https://genetixbay.com/knowledge/glossary/greenhouse-growing.md) ## Follow-up questions **Why do outdoor plants finish late up north?** Outdoor photoperiod cannabis finishes late at high latitude because long summer days delay flowering. At 50° latitude, days stay above 14 hours until about late August, against early August at 40°, so a cultivar needing 8–10 weeks plus a 10–14 day transition finishes in late October, after frost in many northern areas. Early-flowering genetics or light deprivation fix it. **Are autoflowers best for short northern seasons?** Autoflowers are often the safest choice for short northern seasons, because they flower by age and finish about 9–14 weeks from seed whatever the day length. Sown in early June, after the last frost, they finish from mid-August to early September, ahead of autumn rain and frost. Sow straight into the final container and use LST rather than topping, because any setback costs yield. **Does a greenhouse help in a short season?** A greenhouse or plastic hoop cover helps a short-season cannabis grow by keeping rain off buds, holding warmth on cold nights and letting you plant out a few weeks earlier. Ventilate it well, because heat and humidity build fast inside. Add light-deprivation covers to force photoperiods to flower in midsummer and harvest before autumn weather. Check local rules on greenhouse growing too. ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 3. University of Minnesota Extension. Starting seeds indoors (transplanting seedlings, hardening). https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors 4. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker --- # How should I prepare soil or pots for outdoor plants? > For outdoor cannabis in the ground, dig a hole about 60–90 cm (2–3 ft) wide and 45–60 cm (18–24 in) deep, mix in compost and perlite or pumice, and aim for soil pH 6.0–7.0 with good drainage. In containers, use potting mix, not garden soil: about 75–380 L (20–100 US gal) for full-season photoperiods and 11–25 L (3–7 US gal) for autoflowers. Bigger holds more water. - Canonical: https://genetixbay.com/knowledge/answers/outdoor-soil-and-pot-size.html - Topic: Outdoor growing · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - Also asked as: How big a hole for an outdoor cannabis plant? | Should I grow in the ground or in pots outdoors? | What size container for outdoor cannabis? | How do I amend clay soil for cannabis? | Can I use garden soil in pots? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer In the ground, dig wide (about 60–90 cm, 2–3 ft) rather than just deep, blend in compost and coarse aeration, and aim for [pH](https://genetixbay.com/knowledge/glossary/ph.md) 6.0–7.0 and good [drainage](https://genetixbay.com/knowledge/glossary/runoff.md). In containers, use [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), and go big: about 75–380 L (20–100 US gal) for full-season [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md), 11–25 L (3–7 US gal) for [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md). *Grower practice*, consistent with container physics. ## Why [Root volume](https://genetixbay.com/knowledge/glossary/pot-size.md) sets the ceiling. Across many crops, bigger rooting volume generally means bigger plants [1]. House position: bigger pots give bigger [yields](https://genetixbay.com/knowledge/glossary/yield.md) within reason, but pot size is a trade-off against how often you can water and feed. Air matters as much as water. A saturated medium has little [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) and roots suffocate; coarse material keeps pores open [2]. Clay that holds water after a day will do the same to roots in the ground. Garden soil fails in pots. Confined in a container it compacts and can carry pathogens; potting mix is built for the job [3]. Outdoor sun dries pots fast. Small and fabric containers can dry within a day in summer, and dark pots heat the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) above the 18–24 °C (64–75 °F) roots prefer. ## The numbers | Setup | Size | Notes | |---|---|---| | In-ground hole | ~60–90 cm (2–3 ft) wide, 45–60 cm (18–24 in) deep | Loosen the surrounding soil too | | Raised bed or mound (clay) | 30–45 cm (12–18 in) high | Avoids a [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) "bucket" hole | | Container, full-season photoperiod | ~75–380 L (20–100 US gal) | Bigger dries slower | | Container, autoflower | 11–25 L (3–7 US gal) | Final pot from day one | | Container mix | Potting mix + 20–35% [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) or pumice | No garden soil | | Soil pH | 6.0–7.0 | Test before planting | ## What to do 1. Check local rules on outdoor growing first. 2. Test drainage: water poured into the hole should be gone within a day. 3. Test soil pH and correct it slowly if needed. 4. On good soil, dig wide and blend in compost. 5. On clay or rock, build a raised bed or use large containers. 6. Mulch to keep roots cool; use light-coloured pots in hot climates. ## Common mistakes - A deep hole in clay backfilled with rich mix: a bathtub for roots. - Garden soil in pots. - Small pots in full summer sun. ## Related - Full article: [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - Answers: [Best soil for cannabis](https://genetixbay.com/knowledge/answers/best-soil-for-cannabis.md) · [Fabric vs plastic pots](https://genetixbay.com/knowledge/answers/fabric-pots-vs-plastic-pots.md) · [Fix soil pH](https://genetixbay.com/knowledge/answers/fix-soil-ph.md) - Terms: [soil](https://genetixbay.com/knowledge/glossary/soil.md) · [outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md) ## Follow-up questions **Is it better to grow cannabis in the ground or in pots outdoors?** Growing cannabis in the ground gives the biggest outdoor plants, because roots are unlimited and the soil buffers water for days. Pots let you move plants, control the mix and grow where the native soil is poor, but they dry fast in summer sun and cap plant size. Choose the ground if your soil drains well; pots or raised beds if it doesn't. **How do I grow cannabis in clay soil?** To grow cannabis in heavy clay, don't dig a deep hole and backfill it with rich mix, because the hole can fill with water like a bucket. Build a raised bed or mound 30–45 cm (12–18 in) high instead, or dig wide and shallow and blend compost plus coarse material into a large area. Test drainage first: water should not still be standing after a day. **Can I use garden soil in containers?** Don't use garden soil in containers for cannabis. Dug soil compacts in a pot, drains poorly, starves roots of air and can carry soil-borne pathogens. Use a bagged potting mix with about 20–35% perlite or pumice instead. Garden soil is fine for in-ground planting where it drains well, improved with compost, but it behaves very differently once confined in a pot. ## Sources 1. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 3. University of Minnesota Extension. How to prevent seedling damping off (sanitation; avoid garden soil in containers). https://extension.umn.edu/solve-problem/how-prevent-seedling-damping --- # Should I pH my water before or after adding nutrients? > Adjust pH after adding nutrients. Fertiliser salts, and silica most of all, change the solution's pH, so adjusting plain water first means adjusting twice. Mix everything, stir, then bring the feed to about pH 5.5-6.2 for hydro, 5.8-6.3 for coco or 6.2-6.8 for soil. In hydro, aerate a fresh mix 30-60 minutes before the final reading. Calibrate the meter first. - Canonical: https://genetixbay.com/knowledge/answers/ph-before-or-after-nutrients.html - Topic: pH and EC · Type: How-to - Evidence: Established · Status: Draft: awaiting expert review - Full article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) - Also asked as: Do I pH after adding nutrients? | When should I pH my water? | Should I pH first, then add nutes? | Why does my pH meter drift? | When should I replace my pH probe? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer After. Nutrient salts change the [pH](https://genetixbay.com/knowledge/glossary/ph.md) of the water, so adjust once everything is mixed: about pH 5.5–6.2 for hydro, 5.8–6.3 for [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and 6.2–6.8 for soil. In hydro, aerate a fresh mix for 30–60 minutes before the final adjustment. *Established.* ## Why Fertiliser salts are acids and bases in their own right. Most nitrate-based feeds pull pH down when added to alkaline [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md); [potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md) pushes it sharply up. Adjusting before mixing means adjusting twice and wasting acid. Water pH matters less than you think. [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), the water's bicarbonate buffer, is what moves the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) over time [1]. Measure the finished solution and the [runoff](https://genetixbay.com/knowledge/glossary/runoff.md), not the tap. In [recirculating hydro](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) exchange and [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) uptake keep moving pH after mixing [4], so a reading taken straight after stirring is provisional. A reading is only as good as the meter. Calibrate with at least two fresh buffers, pH 7 then pH 4, and store the probe wet [2][3]. ## The numbers | Item | Target | |---|---| | Hydro feed | pH 5.5–6.2 | | Coco feed | pH 5.8–6.3 (runoff 5.8–6.5) | | Soil feed | pH 6.2–6.8 | | Hydro settle time | 30–60 min aeration, then final adjust | | Calibration | Two buffers (7 and 4), at least weekly | | Probe slope, healthy | 95–102%; replace if stuck below ~90–95% | | Probe life | ~1–2 years, stored wet | ## What to do 1. Calibrate the meter if it's been a week or readings seem odd. 2. Fill with water, add nutrients in order, stir. 3. Hydro: aerate 30–60 minutes. 4. Adjust pH in small doses, re-reading between. 5. Store the probe in storage solution or [pH 4 buffer](https://genetixbay.com/knowledge/glossary/calibration-solution.md). *Safety:* gloves and eye protection when handling pH adjusters. ## Common mistakes - Adjusting plain water, then adding nutrients. - Trusting a pen that hasn't seen buffer in months. - Storing the probe dry or in [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md). - Reading pH in a cold sample with no [temperature compensation](https://genetixbay.com/knowledge/glossary/atc.md). ## Related - Full article: [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) - Articles: [meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) - Answers: [how to adjust pH](https://genetixbay.com/knowledge/answers/how-to-adjust-ph.md) · [mixing order](https://genetixbay.com/knowledge/answers/order-to-mix-nutrients.md) · [drops vs meter](https://genetixbay.com/knowledge/answers/ph-drops-vs-ph-meter.md) - Terms: [two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md) · [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) ## Follow-up questions **Why does my pH meter drift?** A pH meter drifts mainly because the glass membrane and reference junction age, and drying out, storage in pure water, biofilm and salt crusts speed that up. Slow readings that take over 30-60 seconds to settle point to a dirty junction or old probe. A two-point calibration with fresh pH 7 and pH 4 buffer corrects drift until the probe can't be adjusted. **When should I replace my pH probe?** Replace a pH probe when it can no longer be adjusted to match fresh buffer, or when its slope stays below about 90-95% after cleaning; an offset beyond about 30 mV at pH 7 is another warning sign. Glass pH electrodes typically last about one to two years when stored wet in storage solution or buffer, never dry or in RO water. **Should I measure pH of plain water at all?** Measuring plain water pH tells you little on its own, because tap water pH has much less effect on the root zone than its alkalinity. It is useful as a quick check that your meter reads sensibly, and RO or distilled water often reads unstable on cheap pens. Make decisions on the pH of the finished nutrient solution and the runoff. ## Sources 1. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 2. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download 3. Mettler-Toledo. pH measurement and USP <791> (white paper). https://www.mt.com/my/en/home/library/white-papers/lab-analytical-instruments/pH-measurement-USP-791.html 4. Bugbee B, 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12 --- # Are pH test drops accurate enough? > pH test drops and strips are accurate enough for soil and rough water checks, but not for hydro or coco. Colour kits read in steps of roughly 0.5 pH unit and are hard to judge in coloured nutrient solution, while hydro's working band, 5.5-6.2, is only 0.7 wide. A calibrated digital meter reads to 0.1 or better. Use drops as a backup that catches a failing meter. - Canonical: https://genetixbay.com/knowledge/answers/ph-drops-vs-ph-meter.html - Topic: pH and EC · Type: Comparison - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) - Also asked as: pH drops vs a pH pen: which is better? | Is a liquid pH test kit good enough? | Are pH strips accurate? | Do I need a digital pH meter? | Why don't my drops match my meter? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer For soil and rough checks of [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md), yes. For hydro and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), no. Colour kits read in steps of about half a [pH](https://genetixbay.com/knowledge/glossary/ph.md) unit and are hard to judge in coloured nutrient solution, while a hydro target band of 5.5–6.2 is only 0.7 wide. A calibrated digital meter reading to 0.1 or better is the tool for [soilless growing](https://genetixbay.com/knowledge/glossary/soilless.md). *Grower practice.* ## Why Drops and strips are dyes that change colour across a [pH range](https://genetixbay.com/knowledge/glossary/ph-scale.md). You match the colour to a chart by eye, so resolution is limited by the steps on the chart and by your lighting. Tinted nutrients and organic feeds muddy the match. A glass-electrode meter measures a voltage that changes about 59 mV per pH unit at 25 °C and converts it to a number [2]. Properly calibrated, that resolves tenths and hundredths. The catch is maintenance. A meter is only accurate after a [two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md) with fresh buffers that bracket your readings, and when its probe is stored wet [1][3]. An uncalibrated pen can be wrong by more than a colour kit. That makes drops a useful backup: if the meter and the drops disagree badly, calibrate the meter. ## The numbers | | Drops or strips | Calibrated digital meter | |---|---|---| | Typical resolution | ~0.5 pH unit | 0.01–0.1 pH | | Coloured nutrient solution | Hard to read | Unaffected | | Upkeep | None; reagent expires | Buffers, storage solution, weekly calibration | | Lifespan | Until reagent runs out | Probe ~1–2 years | | Good enough for soil | Yes | Yes | | Good enough for hydro, coco | No | Yes | **Verdict:** soil growers can start with drops; hydro and coco growers need a calibrated meter, with drops kept as a cross-check. ## What to do 1. Soil: drops are fine for checking water and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) trends. 2. Hydro or coco: buy a meter with [temperature compensation](https://genetixbay.com/knowledge/glossary/atc.md). 3. Calibrate with pH 7 then [pH 4 buffer](https://genetixbay.com/knowledge/glossary/calibration-solution.md), at least weekly. 4. Store the probe wet in storage solution or pH 4 buffer. 5. Cross-check the meter against drops monthly. ## Common mistakes - Reading drops under a purple [LED](https://genetixbay.com/knowledge/glossary/led.md). - Trusting an uncalibrated pen over a fresh test kit. - Storing the meter dry. - Using expired reagent. ## Related - Full article: [pH and EC meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) - Answers: [pH before or after nutrients](https://genetixbay.com/knowledge/answers/ph-before-or-after-nutrients.md) · [meters you need](https://genetixbay.com/knowledge/answers/meters-you-need-for-growing.md) · [TDS vs EC meter](https://genetixbay.com/knowledge/answers/tds-meter-vs-ec-meter.md) - Terms: [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) · [calibration solution](https://genetixbay.com/knowledge/glossary/calibration-solution.md) ## Follow-up questions **Are pH strips accurate for nutrient solution?** Most pH strips are not accurate enough for cannabis nutrient solution. Wide-range strips step in whole or half pH units, and the dyes in some nutrients and the tint of organic feeds make colours hard to match. For soil watering they give a usable ballpark. For hydro and coco, where a few tenths matter, use a calibrated meter. **Why don't my pH drops match my meter?** pH drops and a meter disagree for two common reasons: the meter has drifted and needs calibrating, or the drops are being read against a coloured solution in poor light. Calibrate the meter with fresh pH 7 and pH 4 buffer and re-test. If the meter now reads both buffers correctly, trust it over the drops. **What kind of pH meter should I buy?** Buy a pH meter with automatic temperature compensation, two-point calibration, a replaceable or well-supported glass probe, and a resolution of 0.01-0.1 pH. Budget for fresh pH 7 and pH 4 buffer and storage solution, because a cheap meter calibrated weekly beats an expensive one never calibrated. Expect to replace the probe every one to two years. ## Sources 1. NC State University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download 2. Mettler-Toledo. pH measurement and USP <791> (white paper). https://www.mt.com/my/en/home/library/white-papers/lab-analytical-instruments/pH-measurement-USP-791.html 3. US Geological Survey. National Field Manual for the Collection of Water-Quality Data, Chapter A6.4: pH. https://www.usgs.gov/mission-areas/water-resources/science/national-field-manual-collection-water-quality-data-nfm --- # Why are my pistils turning brown early? > Pistils that brown early, before about week 6 of flower, have usually been pollinated, heat- or light-stressed near the lamp, handled, or are the cultivar's normal colour. They are not a harvest signal by themselves. Check the buds nearest the light (leaf temperature under about 30 °C / 86 °F), look for seeds and anthers, and judge ripeness by calyx trichomes under 60–100× magnification. - Canonical: https://genetixbay.com/knowledge/answers/pistils-turning-brown-early.html - Topic: Diagnosis · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Also asked as: Why are my hairs turning orange early? | Pistils brown in week 4 of flower | Early pistil browning | Are brown pistils a sign of harvest? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer When [pistils](https://genetixbay.com/knowledge/glossary/pistil.md) brown early, before about week 6 of flower, the usual causes are pollination, heat or [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md) at the [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md), handling, or the cultivar's normal colour. Early-brown pistils don't mean the plant is ready. Check for seeds, [anthers](https://genetixbay.com/knowledge/glossary/anther.md) and heat at the tops, then judge ripeness by [calyx](https://genetixbay.com/knowledge/glossary/calyx.md) [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md). *Grower practice*: pistil colour is a weak signal. ## Why Pistils are the receptive part of the [female flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md). Once one has been fertilised it has done its job and withers. [Hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) anthers can appear from about week 4 of flower, and their pollen can seed buds [2], so a sudden mid-flower browning is worth checking for seeds. Heat and intense light stress the tops nearest the lamp. Cannabis [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) falls off at high [leaf temperatures](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) [3], and the [colas](https://genetixbay.com/knowledge/glossary/cola.md) closest to the light are usually the first to bleach and brown. Colour is not ripeness. Trichomes on the same plant mature at different rates that vary by [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) and plant age [1], and pistil colour varies with stress and genetics. Calyx trichomes are the better guide. Rot can look like ripening. Early [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) browns a small cluster of pistils or a [sugar leaf](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) on one cola while the rest stays green [4]. ## The numbers | Pattern | Likely cause | |---|---| | Whole clusters brown, calyxes swelling | Pollination: look for seeds and anthers [2] | | Top buds nearest the lamp only | Heat or light stress; keep leaves under about 30 °C (86 °F) | | One spot on a cola, pulls out easily | Bud rot [4] | | Even browning in the last 2–3 weeks | Normal ripening | | Brown from the start, plant healthy | Cultivar trait | ## What to do 1. Check the date: count from the flip and add the 10–14 day transition. 2. Measure leaf temperature and [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) at the tops. Dim or raise the light if the tops are hot. 3. Open a few calyxes and look for seeds. Inspect the plant for [bananas](https://genetixbay.com/knowledge/glossary/nanners.md) and pollen sacs. 4. Pry open any cola with a dead-looking patch. 5. Keep feeding normally, and read calyx trichomes at 60–100× before deciding to harvest. ## Common mistakes - Harvesting by pistil colour alone. - Ignoring hot spots under the lamp. - Missing a herm because the bananas are hidden inside the buds. - Flushing because the plant "looks done". ## Related - Full article: [Trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Answers: [how to check trichomes](https://genetixbay.com/knowledge/answers/how-to-check-trichomes.md) · [seeds in my buds](https://genetixbay.com/knowledge/answers/why-are-there-seeds-in-my-buds.md) · [what are pistils?](https://genetixbay.com/knowledge/answers/what-are-pistils.md) - Articles: [heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md) · [botrytis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) - Term: [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) ## Follow-up questions **Do brown pistils mean my plant was pollinated?** Brown pistils can mean a cannabis plant was pollinated, because a fertilised pistil withers within days while the calyx starts to swell around a seed. If whole clusters brown at once mid-flower, check for seeds in swelling calyxes and for anthers or pollen sacs on the plant or its neighbours. Unpollinated pistils stay white longer as the plant keeps pushing new ones. **Can I harvest when most pistils are brown?** Do not harvest just because most pistils are brown. Pistil colour is affected by stress and genetics, so it is a supporting sign, not the main one. Check calyx trichomes under 60–100× magnification and harvest when they are mostly cloudy with some amber, within the cultivar's flowering window counted from the flip plus the 10–14 day transition. **Can bud rot make pistils turn brown?** Yes, bud rot can make pistils turn brown. Early botrytis shows as one sugar leaf or a small cluster of pistils on a cola going dull, then brown and dry while the rest stays green, and it pulls out easily. Pry the bud open: a brown, mushy or grey core is bud rot. Cut it out with a 5–10 cm margin. ## Sources 1. Punja ZK, Sutton DB, Kim T, 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 2. Punja ZK, Holmes JE., 2020. Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences: Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 3. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 4. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker --- # Can I plant seeds straight into the final pot? > Yes. You can plant cannabis seeds straight into the final pot, and for autoflowers it's the GenetixBay house position: sow into an 11–15 L final pot, because any setback costs an auto time. Photoperiods can be sown direct too. The catch is watering: wet only a small circle around the seedling for the first 2–3 weeks, or the big unrooted volume stays soggy. - Canonical: https://genetixbay.com/knowledge/answers/plant-straight-into-final-pot.html - Topic: Germination · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) - Also asked as: Can I direct sow into the final pot? | Can I skip transplanting? | Is it OK to start a seedling in a big pot? | Should autoflowers go straight in the final pot? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. Sowing cannabis straight into the final pot works, and for [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) it is the house position: sow into an 11–15 L final pot and never [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md). [Photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md) can go direct too, if you water only around the [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) for the first 2–3 weeks. *Grower practice*, house position for autos. ## Why Autoflowers can't afford a setback. They flower on a fixed clock from [germination](https://genetixbay.com/knowledge/glossary/germination.md), so a transplant stall is lost time; the founder also finds the auto [taproot](https://genetixbay.com/knowledge/glossary/taproot.md) reacts badly to being moved (house position). The danger in a big pot is water, not size. A large volume with no roots in it dries slowly and stays wet [2], and wet, airless media favour [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) [3]. Bigger pots give bigger plants, within reason: a meta-analysis across crops found growth rises with [rooting volume](https://genetixbay.com/knowledge/glossary/pot-size.md) [1]. The house view treats this as a trade-off against feeding frequency, since small pots fed often can still yield heavily. [Potting up](https://genetixbay.com/knowledge/glossary/up-potting.md) exists to match the [wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md) to root size [2]. Direct sowing just means you do that matching with the watering can instead. ## The numbers | Plant | Final pot | Approach | |---|---|---| | Autoflower | 11–15 L (3–4 US gal) | Sow direct; never transplant | | Photoperiod, direct | 11–25 L | Sow direct; ring-water 2–3 weeks | | Photoperiod, potted up | Plug → 1–3 L → final | Each step ~2–4× volume | | Seedling watering in big pot | ~250 mL around the stem | Widen as roots spread | ## What to do 1. Fill the final pot and pre-moisten it evenly to "wrung sponge". 2. Sow 0.5–1.5 cm deep in the centre. 3. Water only a small circle around the seedling. 4. Let the pot lighten between waterings; lift it to check. 5. From about week 3, water the whole pot to light [runoff](https://genetixbay.com/knowledge/glossary/runoff.md). ## Common mistakes - Drenching a 15 L pot for a two-day-old seedling. - Transplanting autoflowers "just once". - Using a heavy, unamended mix that never dries. - Sowing too deep in a big pot. ## Related - Full article: [Transplanting](https://genetixbay.com/knowledge/germination/transplanting.md) - [Photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - [Best pot size for autoflowers](https://genetixbay.com/knowledge/answers/best-pot-size-for-autoflowers.md) · [Why is my seedling drooping?](https://genetixbay.com/knowledge/answers/why-is-my-seedling-drooping.md) - Terms: [transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md) · [up-potting](https://genetixbay.com/knowledge/glossary/up-potting.md) ## Follow-up questions **Should autoflowers be sown in the final pot?** Yes. Autoflowers should go straight into an 11–15 L final pot; this is GenetixBay's house position. An auto runs on a fixed clock from germination, so transplant shock or any other setback costs it time it can't recover. The founder also finds the autoflower taproot reacts badly to being moved compared with photoperiods. Save the potting-up for photoperiods. **How do I water a seedling in a big pot?** Water a cannabis seedling in a big pot in a small ring around the stem, roughly a cup at a time, and leave the rest of the pot alone. Pre-moisten the whole pot before sowing so it starts evenly damp, then let the outer volume dry slowly. Widen the watering circle as roots spread, and give full pot waterings from about week three. **Does pot size limit yield?** Pot size can limit cannabis yield, but it is a trade-off rather than a fixed rule. Across many crops, bigger rooting volume generally means bigger plants, and bigger pots yield more within reason. Yet the GenetixBay founder has grown over 4 oz (about 115 g) from a 16 oz cup using high-frequency fertigation. Small pots simply need more frequent watering and feeding. ## Sources 1. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 2. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container size and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 3. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping --- # My plant is too tall for my tent: what can I do? > If your plant is too tall for the tent, bend it rather than cut it. In veg or the first two weeks of flower, supercrop or tie the tallest tops down and outward; later, bend and tie woody tops sideways. Raise or dim the light so tops get no more than about 1,200 µmol/m²/s, drop the pot off any riser, and next time flip at half the final height. - Canonical: https://genetixbay.com/knowledge/answers/plant-too-tall-for-tent.html - Topic: Training · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [LST: low-stress training](https://genetixbay.com/knowledge/training/lst.md) - Also asked as: My plant is hitting the light | My plant is too tall in flower | I'm running out of height in my tent | How do I lower a tall cannabis plant? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Bend it; don't cut it. In veg or the first two weeks of flower, supercrop or tie the tallest [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) down and outward. Later, tie woody tops sideways. Raise or dim the light so the tops get no more than about 1,200 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), lower the pot, and next run flip at half the final height. *Grower practice*. ## Why Most height arrives after the flip. Stems and [internodes](https://genetixbay.com/knowledge/glossary/internode.md) elongate fastest around days 5–10 of short days [1], and many cultivars finish 1.5–3 times their flip height (*Grower practice*). Tops too close to the [light burn](https://genetixbay.com/knowledge/glossary/light-stress.md). Yield rises with light [2], but at ambient CO₂ the practical ceiling for [top colas](https://genetixbay.com/knowledge/glossary/cola.md) is about 1,200 µmol/m²/s, and [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) falls above about 30 °C (86 °F) [3]. Heat and light stress shows as bleached tops and [foxtails](https://genetixbay.com/knowledge/glossary/foxtailing.md). Bending keeps the cola. A supercropped stem forms a knuckle in 3–7 days and keeps growing; a cut top is gone, and topping in flower costs recovery time the plant doesn't have. The house endorses [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md): the founder snaps stems all the time. ## The numbers | Stage | Best fix | Notes | |---|---|---| | Veg | [LST](https://genetixbay.com/knowledge/glossary/lst.md), topping, supercropping | Plenty of time to recover | | Flower weeks 1–2 | Supercrop, tie down, tuck under a net | Stems still green | | Flower week 3+ | Tie tops sideways; stakes | Woody stems crease | | Any time | Raise or dim light; remove pot risers | Measure PPFD at tops | | Top-cola PPFD limit, ambient CO₂ | About 1,200 µmol/m²/s | Measure, don't guess | | [Canopy temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) | Under 30 °C (86 °F) | 22–26 °C ideal in flower | | Flip height | About half the usable height | [Stretch](https://genetixbay.com/knowledge/glossary/stretch.md) 1.5–3× | ## What to do 1. Measure PPFD and temperature at the tallest top. 2. Raise the light to the ceiling or dim it until the tops are under about 1,200 µmol/m²/s. 3. Take the pot off any riser or saucer stack. 4. Supercrop green tops 5–15 cm below the tip, or tie woody tops sideways to the pot rim. 5. Next run, flip at half the final height and train during veg. ## Common mistakes - Cutting the main cola in flower. - Leaving tops touching or almost touching the fixture. - Bending woody stems sharply in late flower. - Flipping a plant already two-thirds of the tent height. ## Related - Full article: [LST: low-stress training](https://genetixbay.com/knowledge/training/lst.md) - Answers: [when to stop training](https://genetixbay.com/knowledge/answers/when-to-stop-training.md) · [how tall plants get indoors](https://genetixbay.com/knowledge/answers/how-tall-do-plants-get-indoors.md) - Training: [supercropping](https://genetixbay.com/knowledge/training/hst-supercropping.md) · [SCROG](https://genetixbay.com/knowledge/training/scrog.md) - Terms: [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) · [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md) ## Follow-up questions **How close can buds be to an LED?** Keep buds far enough from an LED that the top colas receive no more than about 1,200 µmol/m²/s at ambient CO₂, and keep canopy temperature under about 30 °C (86 °F). The safe distance depends on the fixture, so measure PPFD at the tallest tops rather than relying on a fixed distance. Bleached, yellow-white top bracts mean the light is too close. **Can I cut the top off a plant in flower?** Don't cut the top off a plant in flower. Topping needs 3–7 days to recover, which comes straight out of bud time, and in flower you lose the main cola outright. Bend it instead: supercrop green stems in the first two weeks, or tie woody tops sideways later. Cutting is a last resort only if a cola is already burning. **How much will my plant stretch after the flip?** A cannabis plant commonly stretches about 1.5 to 3 times its height in the first two to three weeks after switching to 12/12, with elongation fastest around days 5–10. The amount depends heavily on cultivar. Plan for it by flipping at about half the final height your space allows, minus the room the light and its safe distance need. ## Sources 1. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 3. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x --- # Are praying leaves a good sign? > Praying leaves, with fan leaves angled upwards and the blades flat, usually mean a cannabis plant is well watered and getting good light. It is a good sign, but not proof of perfect health. If the leaf edges curl up into a taco near the lamp, that is heat or light stress: keep leaf temperature under about 30 °C (86 °F). Leaves often lower again at night, which is normal. - Canonical: https://genetixbay.com/knowledge/answers/praying-leaves.html - Topic: Diagnosis · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Also asked as: Why are my leaves pointing up? | What do praying leaves mean? | Leaves raised towards the light | Praying or heat stress? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. Praying leaves, with the [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) angled upwards and the blades held flat, usually mean the plant is well watered and getting good light. It is a reassuring sign, not proof of perfect health. Leaves whose edges curl up near the lamp are a different thing: that is heat or [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md). *Grower practice*. ## Why Leaf angle depends on water pressure. A well-watered plant keeps its cells and [petioles](https://genetixbay.com/knowledge/glossary/petiole.md) firm (full turgor), so the leaves can lift. A thirsty or root-starved plant can't hold them up. Daily leaf movement is common in plants. Many species raise and lower their leaves on a day-night rhythm [1], and cannabis leaves often rise after lights-on and settle at night. Upward edge curl is a stress response. Leaves near the lamp heat up, and [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) can run well above air temperature when air movement and water are short [2]. Cannabis [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) falls at high leaf temperatures [3], and tacoed [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) are the visible sign. The difference is in the shape: praying leaves tilt from the stalk with flat blades, while tacoed leaves fold along the midrib. ## The numbers | Posture | What it means | Action | |---|---|---| | Leaves angled up, blades flat | Good water and light | None | | Edges curled up, top leaves only | Heat or light stress | Leaf temperature under about 30 °C (86 °F); dim or raise the light | | Lowered at night, up by lights-on + 1 h | Normal daily movement | None | | Drooping 2 h after lights-on | Water or roots | Lift the pot, check the roots | ## What to do 1. Look at the shape of the leaf: tilted with flat blades is praying, folded along the midrib is [tacoing](https://genetixbay.com/knowledge/glossary/taco-leaf.md). 2. If the tops are tacoing, measure the leaf temperature with an [IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md) and the [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) at the canopy. 3. Keep air moving over the canopy so the leaves can shed heat. 4. Keep checking leaf colour, new growth and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [pH](https://genetixbay.com/knowledge/glossary/ph.md) and [EC](https://genetixbay.com/knowledge/glossary/ec.md). Praying doesn't replace those checks. ## Common mistakes - Treating praying as a perfect health score. - Confusing tacoing with praying and pushing the light harder. - Panicking when the leaves lower at night. - Chasing praying with extra feed. ## Related - Full article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Answers: [leaves droop at night](https://genetixbay.com/knowledge/answers/leaves-droop-at-night.md) - Articles: [taco and canoeing leaves](https://genetixbay.com/knowledge/diagnosis/taco-canoeing-leaves.md) · [heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md) - Terms: [heat stress](https://genetixbay.com/knowledge/glossary/heat-stress.md) · [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) ## Follow-up questions **What is the difference between praying and tacoing?** Praying cannabis leaves tilt upwards from the petiole with the blades flat, and they settle back down at night. Tacoing leaves fold their edges upwards along the midrib like a taco shell, usually on the top leaves nearest the light, as heat or light stress. Praying is a healthy posture; tacoing means measure leaf temperature and PPFD and back the light off. **Why do my leaves pray in the morning and drop at night?** Cannabis leaves often rise after lights-on and lower in the dark, a daily leaf movement that many plant species show. A plant with a healthy root zone praying by day and resting by night is behaving normally. Leaves still drooping two hours after lights-on point to a watering or root problem, so lift the pot. **Do praying leaves mean my plant is happy?** Praying leaves suggest a cannabis plant has full turgor and good light, which is a good sign, but they are not a full health check. Look at leaf colour, new growth, roots, pH and runoff EC as well. A plant can pray while carrying a nutrient problem, so use praying as a reassuring signal, not a diagnosis. ## Sources 1. Minorsky PV, 2019. The functions of foliar nyctinasty: a review and hypothesis. Biological Reviews 94(1):216–229. https://doi.org/10.1111/brv.12444 2. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/ 3. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x --- # Can I quick-dry buds in an oven, microwave or paper bag? > Quick-drying cannabis in an oven or microwave makes harsh, grassy flower and drives off the volatile terpenes a slow dry keeps; the idea that it is a harmless shortcut is a Myth. Paper bags are a slow method, not a fast one, and work for small amounts in a dry room if turned daily. For good flower, dry in the dark for 7–14 days at 15–21 °C and 55–62% RH. - Canonical: https://genetixbay.com/knowledge/answers/quick-drying-methods.html - Topic: Harvest and cure · Type: Myth check - Evidence: Myth · Status: Draft: awaiting expert review - Full article: [Drying cannabis: the 60/60 method and water activity](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Also asked as: How do I quick-dry weed? | Can I microwave buds to dry them? | Does paper bag drying work? | Fastest way to dry buds - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer You can, but oven and microwave drying make harsh, grassy flower and drive off the [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md). Calling them a harmless shortcut is a *Myth*. A paper bag is a slow method, not a fast one, and works for small amounts in a [dry room](https://genetixbay.com/knowledge/glossary/drying-room.md). For good flower, dry in the dark for 7–14 days at 15–21 °C (60–70 °F) and 55–62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). *A cure never fixes a bad dry* (*House position*). ## Why Terpenes leave with the water. Air-drying measurably shifts cannabis oil away from volatile [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) [1], and heat speeds that loss. In [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), terpene content depended more on drying method than on storage [2]. Heat dries unevenly. An oven or microwave crisps the outside and can leave a wet core, and the [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) that a slow dry lets [fade](https://genetixbay.com/knowledge/glossary/senescence.md) stays in the bud as a green, hay-like note. Heat also starts converting [acid cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md) to their neutral forms, which is [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md). Slow has its own limit. A paper bag holds moisture in. Packed tight, or in a humid room, it gives wet, still air, the conditions moulds need [4]. Whatever the method, buds should end up at [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55–0.65 [3]. ## The numbers | Method | Time | Quality | |---|---|---| | Microwave or oven | Minutes to hours | Harsh, grassy, terpenes lost | | Fan on the buds, warm room | 2–4 days | Harsh; hay-smell risk | | Paper bag, loose, turned daily | About 5–10 days | Fine for small amounts in a dry room | | [Hang dry](https://genetixbay.com/knowledge/glossary/hang-dry.md), 15–21 °C, 55–62% RH | 7–14 days | The standard | | [Freeze drying](https://genetixbay.com/knowledge/glossary/freeze-drying.md) | Hours to days | *Contested*; not recommended | ## What to do 1. For an early sample, air-dry one small bud for a few days somewhere dark and dry. Treat it as a preview. 2. Dry the main crop slowly: hang it in the dark with gentle room air and no fan on the buds. 3. For a few loose buds, use a paper bag filled loosely in one layer. Turn the buds daily and check the cores. 4. Jar when the stems snap and a sealed sample reads 58–65% RH after 12–24 hours. ## Common mistakes - Microwaving buds "just to try it". - Packing a paper bag full of wet buds. - Blasting a fan at the drying line to finish sooner. - Expecting the cure to fix a fast dry. ## Related - Full article: [Drying cannabis](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Answers: [how soon can I smoke?](https://genetixbay.com/knowledge/answers/how-soon-after-harvest-can-i-smoke.md) · [why is my weed harsh?](https://genetixbay.com/knowledge/answers/why-is-my-weed-harsh.md) · [drying in the tent](https://genetixbay.com/knowledge/answers/can-i-dry-in-my-grow-tent.md) - Terms: [freeze drying](https://genetixbay.com/knowledge/glossary/freeze-drying.md) · [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md) · [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) ## Follow-up questions **Does microwaving weed ruin it?** Microwaving cannabis to dry it ruins the quality of that flower. It heats the bud unevenly from the inside, drives off volatile monoterpenes, can partly decarboxylate cannabinoids and leaves harsh, hay-like smoke. A cure will never fix a bad dry. If you want an early sample, air-dry one small bud for a few days instead and judge the crop after curing. **Is paper bag drying good for cannabis?** Paper bag drying can work for small amounts of cannabis, such as a few trimmed buds or popcorn, in a room that runs dry. The bag slows the dry and keeps light out. Fill it loosely in one layer, fold the top, and shake or turn the buds daily. Packed bags or humid rooms grow mould, so check the cores before jarring. **Is freeze drying a good way to dry cannabis fast?** Freeze drying is not proven better for cannabis, and GenetixBay rates it contested and does not recommend it. It is fast and keeps the bud's shape, but a slow hang dry followed by a jar cure remains the standard. The main goal of any drying method is keeping volatile monoterpenes, so a slow, cool, dark dry matters more than the equipment. ## Sources 1. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 2. University of Georgia (thesis). Effects of drying method and storage on cannabinoids and terpenes in hemp. https://openscholar.uga.edu/record/27813 3. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html 4. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # How long does a plant take to recover after topping? > A healthy cannabis plant takes about 3–7 days after topping before the two new shoots show visible regrowth, and roughly a week until they grow at equal speed. Allow 5–10 days of recovery before flipping, and do the last top at least 7–10 days before 12/12. Stressed, root-bound or very young plants recover more slowly. - Canonical: https://genetixbay.com/knowledge/answers/recovery-after-topping.html - Topic: Training · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md) - Also asked as: How long is topping recovery time? | Is my plant stressed after topping? | How long after topping does it start growing again? | When can I flip after topping? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A healthy cannabis plant shows visible regrowth about 3–7 days after topping, and the two new [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) are growing at equal speed within roughly a week. Allow 5–10 days of recovery before flipping, and do the last top at least 7–10 days before [12/12](https://genetixbay.com/knowledge/glossary/12-12.md). *Grower practice*; recovery times haven't been measured in controlled trials. ## Why The main tip makes [auxin](https://genetixbay.com/knowledge/glossary/auxin.md) that suppresses the side buds below it. Cut it off and the suppression lifts, but the side shoots need a few days to switch on and start growing. During those days the plant isn't idle. It is redirecting growth into the side shoots and the lower branches, which is how topping makes a flatter plant with more tops. Recovery speed depends on vigour. A well-rooted plant with 4–6 nodes under good light bounces back fast; a stressed, [root-bound](https://genetixbay.com/knowledge/glossary/root-bound.md) or very young plant stalls longer. The payoff is canopy shape. In a controlled trial on large greenhouse plants, pruning twice was the only architecture treatment that raised flower yield per plant [1]. Density and architecture interact, so small indoor plants may respond differently [2], but more tops in even light is the aim, because yield follows light [3]. ## The numbers | Item | Typical | |---|---| | First top | 4–6 nodes, about 3–4 weeks from seed | | Visible regrowth | 3–7 days | | New tops at equal speed | About 7 days | | Before topping again | 2–3 new nodes on each shoot | | Last top before the flip | At least 7–10 days | | [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) | Don't top; use [LST](https://genetixbay.com/knowledge/glossary/lst.md) | ## What to do 1. Top only healthy, vigorous plants with 4–6 nodes. 2. Cut 3–5 mm above the node with clean scissors wiped in 70% alcohol. 3. Keep conditions steady for a week: no [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md), no feed changes. 4. Start gentle LST on the new shoots once they're growing. 5. If nothing happens after 10 days, check roots, light and temperature. ## Common mistakes - Topping a stressed or root-bound plant, then waiting two weeks. - Topping and transplanting on the same day. - Topping again before the last top recovered. - Topping autoflowers, which run on a fixed clock and can't spare the days. ## Related - Full article: [Topping](https://genetixbay.com/knowledge/training/topping.md) - Answers: [when to stop training](https://genetixbay.com/knowledge/answers/when-to-stop-training.md) · [defoliating autoflowers](https://genetixbay.com/knowledge/answers/can-i-defoliate-autoflowers.md) - Training: [LST](https://genetixbay.com/knowledge/training/lst.md) - Terms: [topping](https://genetixbay.com/knowledge/glossary/topping.md) · [apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md) ## Follow-up questions **Why has my plant stopped growing after topping?** A topped cannabis plant often seems to stall for 3–7 days while it redirects growth from the removed tip to the side shoots and roots. That is normal recovery. If there is no visible new growth after about 10 days, look for another problem: a root-bound or overwatered pot, low light, cold, or a plant that was too young or stressed when topped. **Can I top again before the plant recovers?** Wait until the new shoots have grown 2–3 nodes before topping them again. Topping a plant that hasn't recovered stacks stress on stress and stretches veg time without adding many more tops. Each round of topping costs 3–7 days, so plan multiple tops into a longer veg, and finish the last one at least 7–10 days before the flip. **How long should I wait after topping to flip to flower?** Wait at least 7–10 days after the last topping before flipping to 12/12, so the new tops are established and growing at equal speed. Flipping a plant that hasn't recovered can leave uneven tops and fewer strong bud sites. Training with LST during that week helps spread the new tops apart into an even canopy. ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 2. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 3. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # How do I rehydrate over-dried buds? > To rehydrate over-dried buds, seal them in a jar with a fresh, slightly moister bud for about a day, then check that the equilibrated jar reads 55–62% RH (water activity 0.55–0.62). This restores the feel, not the lost aroma: a cure never fixes a bad dry. GenetixBay doesn't recommend humidity packs, which rob terpenes, or fruit peel and lettuce, which add mould risk and off-flavours. - Canonical: https://genetixbay.com/knowledge/answers/rehydrate-over-dried-buds.html - Topic: Harvest and cure · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Also asked as: My buds are too dry: what can I do? | How to rehydrate weed | Over-dried, crispy buds | Can I use a humidity pack to rehydrate? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Seal over-dried buds in a jar with a fresh, slightly moister bud for about a day. Then leave the jar sealed for 12–24 hours and check it reads a stable 55–62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) ([water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55–0.62). That brings back the feel, not the lost aroma: *a cure never fixes a bad dry* (*House position*). No [humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md). The method is *Grower practice*. ## Why Buds trade water with the air in a sealed jar. Once the jar has equilibrated, its RH divided by 100 equals the bud's water activity [1]. A moister bud gives some of its water to the dry ones until they meet in the middle. The safe range is narrow. ASTM sets 0.55–0.65 aw for dried flower: below 0.55 it crumbles, and above 0.65 mould becomes a risk [1]. Bringing buds up slowly and checking them keeps them inside it. Lost aroma stays lost. Volatile [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) escape during drying and storage [3], and adding water doesn't put them back. The standard does mention sachets. ASTM lists salt-based sachets as one way to bring under-range flower back up [2]. That is a storage convenience, not evidence that packs improve flower, and the house position is that they cost [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md). ## The numbers | Jar reading after 12–24 h sealed | Meaning | Action | |---|---|---| | Below 55% RH | Over-dried | Add a fresh bud for about a day | | 55–62% RH | Target | Remove the added bud and cure on | | Above 65% RH | Too wet [1] | Open the jar and air the buds | ## What to do 1. Put the dry buds in a jar about ¾ full with a calibrated hygrometer. 2. Add one fresh, slightly moister bud from the same harvest, or one from a jar reading higher. 3. Seal it for about 24 hours, then take the added bud out. 4. Leave the jar sealed another 12–24 hours and read it. 5. Repeat if it is still under 55%. Go slowly. 6. Next harvest, dry for 7–14 days at 55–62% RH and jar sooner. ## Common mistakes - Humidity packs left in for weeks. - [Fruit](https://genetixbay.com/knowledge/glossary/achene.md) peel, lettuce or a damp paper towel left in the jar. - Reading the hygrometer straight after opening the jar. - Expecting the [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) to cure out. ## Related - Full article: [Curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Answers: [why is my weed harsh?](https://genetixbay.com/knowledge/answers/why-is-my-weed-harsh.md) · [buds lost their smell](https://genetixbay.com/knowledge/answers/buds-lost-their-smell.md) · [how full to fill jars](https://genetixbay.com/knowledge/answers/how-full-to-fill-curing-jars.md) - Article: [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Terms: [humidity pack](https://genetixbay.com/knowledge/glossary/humidity-pack.md) · [over-drying](https://genetixbay.com/knowledge/glossary/over-drying.md) · [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) ## Follow-up questions **Do humidity packs fix over-dried buds?** GenetixBay does not recommend humidity packs for over-dried buds. In the house view they are a marketing gimmick that robs terpenes, and the only data claiming a benefit comes from a pack maker's own test. Put a fresh, slightly moister bud in the jar for a day instead, then check the jar's RH after it has sat sealed for 12–24 hours. **Does orange peel or lettuce rehydrate buds?** Orange peel or lettuce will add moisture to dry buds, but GenetixBay does not recommend them. They release water unevenly, can push the jar above water activity 0.65 where mould grows, and can taint the aroma. A fresh, slightly moister bud from the same harvest adds moisture with no foreign smell. Remove whatever you add after about a day. **Can over-dried buds be saved?** Over-dried cannabis buds can be made pleasant to handle again, but their lost terpenes do not come back. Bring them up slowly to water activity 0.55–0.62 with a fresh bud in the jar, then cure as normal. Below aw 0.55 buds turn brittle and smell faint or like hay, and that hay note never truly comes out. ## Sources 1. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. https://store.astm.org/d8197-22.html 2. ASTM International, Standardization News. Two cannabis standards you should know about (salt-based humidity control sachets for aw below 0.68). https://sn.astm.org/node/2445/printable/print 3. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa (monoterpene loss on drying and storage). Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf --- # Can I root clones in plain water? > Yes. Cannabis cuttings can root in plain water, usually in 10–21 days, but results are less even than in a plug or aeroponic cloner. Keep the water dark, at 20–24 °C (68–75 °F), change it every 2–3 days, and add an air stone if you can. Move them to medium when roots are 2–5 cm (1–2 in) long; long water roots transplant badly. - Canonical: https://genetixbay.com/knowledge/answers/rooting-clones-in-water.html - Topic: Cloning and mother plants · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: Can I clone in a glass of water? | Water cloning cannabis | Cuttings in a cup of water | Do water roots survive in soil? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. Cannabis cuttings root in plain water, usually in 10–21 days, though less evenly than in plugs or an [aeroponic](https://genetixbay.com/knowledge/glossary/aeroponics.md) cloner. Keep the water dark, 20–24 °C (68–75 °F), changed every 2–3 days, and [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) at 2–5 cm of root. *Grower practice*. ## Why Cannabis roots readily, so a cut stem in water will often form roots without any medium. Oxygen is the limit. Still water holds little oxygen and loses more as it warms; oxygen management is central to keeping [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) out of hydroponic roots [3]. Warm, stagnant water breeds rot. Pythium and [Fusarium](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md) both infect cannabis roots in hydroponic systems [1], and a brown, slimy stem base in a glass is the same problem. Air in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) helps rooting in any medium. In one cannabis trial, cuttings in an airy peat-perlite mix rooted best, while [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) held at full water capacity, with less [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), rooted worst [2]. Water roots are a different shape. They are thick and brittle and must regrow fine roots once moved to soil or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md). ## The numbers | Item | Target | |---|---| | Water temperature | 20–24 °C (68–75 °F) | | Water change | Every 2–3 days | | Depth | Bottom 3–5 cm (1–2 in) of stem only | | Light | 50–150 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), 18–24 h | | Time to roots | ~10–21 days | | Transplant at | 2–5 cm (1–2 in) roots | ## What to do 1. Use a dark or foil-wrapped glass so algae don't grow. 2. Fill with clean, room-temperature water; add an [air stone](https://genetixbay.com/knowledge/glossary/air-stone.md) if you have one. 3. Stand the fresh-cut stem 3–5 cm deep; keep leaves dry. 4. Change the water every 2–3 days. 5. Pot into a light, moist mix at 2–5 cm of root, then keep humidity high for 3–5 days. ## Common mistakes - Clear glass in a sunny window. - Never changing the water. - Leaving roots to grow 15 cm long before potting. - Submerging leaves. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Best medium for rooting clones](https://genetixbay.com/knowledge/answers/best-medium-for-rooting-clones.md) · [When to transplant clones](https://genetixbay.com/knowledge/answers/when-to-transplant-clones.md) - [Root rot (Pythium)](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) - Terms: [aeroponics](https://genetixbay.com/knowledge/glossary/aeroponics.md) · [dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md) ## Follow-up questions **Why do water-rooted clones struggle after transplanting?** Cannabis roots grown in water are adapted to it: thick, brittle and short of the fine root hairs that work in soil or coco. Moved into a medium, they need time to grow new roots, so the clone stalls or wilts for a few days. Transplant early, when roots are 2–5 cm (1–2 in) long, into a light, moist mix, and keep humidity high for 3–5 days. **How often should I change the water for clones?** Change the water for cannabis cuttings every 2–3 days, or sooner if it goes cloudy or smells. Still, warm water loses oxygen and grows bacteria and root-rot organisms such as Pythium, which turn stems brown and slimy. Use clean, room-temperature water, keep the container dark, and an aquarium air stone makes a real difference. **Is an aeroponic cloner better than a glass of water?** Usually, yes. An aeroponic cloner sprays the stems with fine water so they sit in humid air rather than standing water, giving roots far more oxygen. Many growers find it roots cannabis cuttings faster and more evenly than a glass. The catch is hygiene: clean the reservoir between batches, keep it below about 24 °C (75 °F), and watch for slimy stems. ## Sources 1. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 2. Hwang SJ, Collado CE, Hwang HS, Yun JH, Hernandez R, 2026. Impacts of commercial and custom substrates on rooting and morphology of Cannabis sativa 'Suver Haze' stem. HortTechnology 36(3):429–434. https://doi.org/10.21273/HORTTECH05810-26 3. University of Kentucky Cooperative Extension, E706 (hydroponic Pythium and oxygen management). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf --- # Should my exhaust fan run 24/7? > Yes, in most vented tents the exhaust fan should run 24/7, slowed by a temperature and humidity controller rather than switched off. Lights-off is when humidity spikes and, in flower, when smell builds, so an off fan invites bud rot and odour. Circulation fans should always run 24 hours. The exception is a sealed CO₂ room, where exhaust stays off during lights-on. - Canonical: https://genetixbay.com/knowledge/answers/run-exhaust-fan-24-7.html - Topic: Environment · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) - Also asked as: Should the exhaust fan run all the time? | Should I turn my fans off when the lights are off? | Can I put my inline fan on a timer? | Exhaust fan at night in flower - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. In a vented tent, run the [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) **24/7** and let a temperature and humidity controller **slow it**, not switch it off. [Circulation fans](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) always run 24 hours. The one exception is a **sealed CO₂ room**, where the exhaust stays off during lights-on and air conditioning plus a [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) do the work. *Grower practice*. ## Why At lights-off the air cools, so the same water vapour gives a higher [relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md) and surfaces approach the [dew point](https://genetixbay.com/knowledge/glossary/dew-point.md) [3]. An exhaust that stops at that moment traps the moisture. Humid, still air in dense [colas](https://genetixbay.com/knowledge/glossary/cola.md) is how *[Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md)* bud rot and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) start [1][2]. Night is when it happens. In flower, a stopped fan also lets the tent go neutral or positive, and smell escapes through every zip. In veg there is more leeway: smell is low and the exhaust can follow the light, as long as night-time RH stays in range. ## The numbers | Situation | Exhaust | Circulation fans | |---|---|---| | Veg, vented tent | 24 h on a controller, or follow the light if RH stays in range | 24 h | | Flower from about week 2, vented tent | 24 h, slowed at lights-off | 24 h | | Drying in the tent | 24 h, low speed, filter on | indirect only, never on buds | | Sealed CO₂ room, lights on | off except emergencies | 24 h | | Lights-off RH in flower | ≤ 55 % | | | Leaf-level air speed | | 0.3–1.0 m/s (60–200 ft/min) | ## What to do 1. Fit a speed controller tied to temperature and RH. 2. Set a lower night speed rather than off. 3. Log RH through the lights-off transition for 48 hours. 4. If nights run cold, slow the fan further and add a small thermostat-controlled heater. 5. Keep circulation fans on day and night. ## Common mistakes - [Fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) off at night "to let the plants rest". - Cutting the exhaust to keep a cold tent warm. - A timer that switches the exhaust fully off. - Running exhaust flat out in a sealed CO₂ room. ## Related - Full article: [Airflow](https://genetixbay.com/knowledge/environment/airflow.md) - [Humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - [How do I lower the humidity in my grow tent?](https://genetixbay.com/knowledge/answers/how-to-lower-humidity-in-a-grow-tent.md) - [How do I stop my grow tent from smelling?](https://genetixbay.com/knowledge/answers/how-to-control-grow-smell.md) - Terms: [exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) · [oscillating fan](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) ## Follow-up questions **Can I turn the exhaust fan off at night to keep the tent warm?** Turning the exhaust fan fully off at night to keep a grow tent warm is a common mistake. Humidity spikes at lights-off, and still, damp air in dense colas is where bud rot starts; in flower, smell also builds and escapes. Instead, slow the fan with a thermostat or speed controller, and add a small thermostat-controlled heater if the tent still runs cold. **Should circulation fans run at night?** Yes, circulation fans in a cannabis grow should run 24 hours a day, including lights-off. Humidity rises when the lights go off, and moving air dries the microclimates inside dense colas where Botrytis and powdery mildew start. Keep leaf-level air speed around 0.3–1.0 m/s (60–200 ft/min): leaves should flutter gently, never whip. **Is a fan speed controller better than a timer?** Yes, a speed controller tied to temperature and humidity is better than an on/off timer for a grow-tent exhaust fan. It keeps the tent under steady negative pressure and holds climate within range, ramping up when lights are on and slowing at lights-off. A timer that cuts the fan entirely lets humidity, heat and smell swing, which is harder on plants and neighbours. ## Sources 1. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 2. Utah State University Extension. Hemp bud rot (IPM fact sheet). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot.php 3. Allen RG et al., 1998. FAO-56 Chapter 3 (vapour pressure). https://www.fao.org/4/x0490e/x0490e07.htm --- # What do I do if the seed shell is stuck on my seedling? > A seed shell stuck on a cannabis seedling (helmet head) usually comes off by itself within a day or two. Mist it, keep the air humid at 65–75% RH, wait 24–48 hours, then ease it off gently only if it is still trapping the leaves. Pulling a dry shell can snap the cotyledons or stem. It is most often caused by planting too shallow or a surface that dried out. - Canonical: https://genetixbay.com/knowledge/answers/seed-shell-stuck-on-seedling.html - Topic: Germination · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - Also asked as: Helmet head seedling, what do I do? | Seed husk stuck on the leaves | How do I remove the shell from a seedling? | Seedling can't open its leaves - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Mist the stuck [shell](https://genetixbay.com/knowledge/glossary/seed-coat.md), keep the air humid (65–75% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md)), and wait 24–48 hours; most cannabis [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) shed it themselves. Only ease it off gently once it is soft and still trapping the leaves. Never pull a dry shell. *Grower practice*. ## Why The shell (seed coat) dries hard once it is above the surface and grips the [cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md). Water softens it and lets it slide off. Soil normally holds the shell back as the shoot pulls through. Shallow planting or a dry, crusted surface lets the shell ride up with the leaves. The cotyledons feed the seedling until [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) take over, so tearing one off is a real setback. Losing a day or two waiting costs less. Don't overcorrect by flooding the pot. A soggy surface and a sealed, unvented dome invite [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) [2]. Once the leaves open, give the seedling proper light: young plants lit well root and grow better than dim ones [1]. ## The numbers | Item | Target | |---|---| | Wait before intervening | 24–48 h | | Air humidity | 65–75% RH | | Air temperature | 23–27 °C (73–81 °F) | | Planting depth to prevent it | 0.5–1.5 cm (¼–½ in) | ## What to do 1. Mist the shell with room-temperature water two or three times a day. 2. Put a vented dome or clear cup over the seedling to keep humidity up. 3. After 24 hours, mist again, wait five minutes, then try a gentle wiggle. 4. If a thin inner membrane binds the leaves, tease it open with a clean needle tip. 5. If it won't budge, stop and try again the next day. ## Common mistakes - Pulling a dry shell and snapping the stem. - Squeezing the cotyledons rather than the shell's edges. - Burying the seedling deeper to "push" the shell off. - [Drowning](https://genetixbay.com/knowledge/glossary/overwatering.md) the pot instead of misting the shell. ## Related - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - [Which way up do I plant a seed?](https://genetixbay.com/knowledge/answers/which-way-up-to-plant-a-seed.md) · [Do seedlings need a dome?](https://genetixbay.com/knowledge/answers/do-seedlings-need-a-dome.md) - Terms: [seed coat](https://genetixbay.com/knowledge/glossary/seed-coat.md) · [cotyledon](https://genetixbay.com/knowledge/glossary/cotyledon.md) ## Follow-up questions **Should I pull the seed shell off my seedling?** Not straight away. A dry cannabis seed shell clings tightly, and pulling it can tear the cotyledons or snap the stem just below them. Mist the shell, wait a few minutes until it softens, and try a gentle wiggle with clean fingers or tweezers. If it resists, leave it and try again after 24 hours. Many shells drop off on their own. **Why does the seed shell get stuck?** A cannabis seed shell gets stuck when the seed was planted too shallow or the surface dried out. Normally the soil holds the shell while the shoot pulls its leaves free. With too little cover or a dry, crusted surface, the shell rides up on the cotyledons and hardens. Plant 0.5–1.5 cm (¼–½ in) deep and keep the surface just moist. **Will a seedling die if the shell stays on?** A cannabis seedling with a stuck shell usually survives. Most shed it within a day or two once it softens, and the true leaves can still grow out from between trapped cotyledons. The risk is a shell that stays clamped for several days, which can stunt or kill the seedling if it stops the leaves opening. Damaging the stem while removing it is the bigger danger. ## Sources 1. Runkle E. The benefits of lighted plugs. Michigan State University Extension. https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs 2. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping --- # Why are my seedling's leaves yellow or pale? > Yellow or pale cannabis seedling leaves usually mean overwatering, too little light, or hunger in an inert medium. Cotyledons yellowing around days 10–14 is often normal as true leaves take over. Check the pot weight and PPFD (150–300 µmol/m²/s) first; in coco, rockwool or hydro, start a light feed at EC 0.4–0.8 mS/cm (200–400 ppm500). Soil seedlings rarely need feed before 2–3 weeks. - Canonical: https://genetixbay.com/knowledge/answers/seedling-leaves-yellow.html - Topic: Germination · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - Also asked as: Why is my seedling yellow? | Pale seedling leaves | Seedling cotyledons turning yellow | Yellow seedling in coco - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yellow or pale cannabis [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) are usually [overwatered](https://genetixbay.com/knowledge/glossary/overwatering.md), under-lit, or hungry in an [inert medium](https://genetixbay.com/knowledge/glossary/soilless.md). [Cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) yellowing at days 10–14 is often normal. Check pot weight and light (150–300 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md)) before reaching for nutrients. *Supported*. ## Why Wet roots can't breathe. A soggy plug starves roots of oxygen, so uptake stops and leaves pale even in a rich mix. Constantly wet media also favour [Pythium root rot](https://genetixbay.com/knowledge/glossary/pythium.md) [3] and [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) [1]. Weak light makes pale, stretched seedlings. Young plants below about 8 [mol/m²/day](https://genetixbay.com/knowledge/glossary/dli.md) of light grow inferior roots and mass in other crops [2]. Inert media carry no food. [Coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) and hydro seedlings run out once the cotyledons' reserves are spent, so they yellow from the bottom up. Cotyledons are temporary. As [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) take over, the seed leaves often yellow and drop, which is not a problem by itself. Over-feeding causes damage of its own. Extension advice is to hold fertiliser until true leaves appear [1]. ## The numbers | Symptom | Likely cause | Check | |---|---|---| | Whole seedling pale, wet mix, droop | Overwatering | Pot still heavy days later | | Pale and stretched | Low light | PPFD under 150 µmol/m²/s | | Cotyledons yellow, day 10–14, true leaves green | Normal | Nothing to fix | | Lower leaves yellowing in coco/rockwool | Hunger | No feed yet; start [EC](https://genetixbay.com/knowledge/glossary/ec.md) 0.4–0.8 | | Bleached top, crisp edges | Too much light or heat | Over 300 µmol/m²/s or hot lamp | ## What to do 1. Lift the pot. If it's heavy, stop watering until it lightens. 2. Measure PPFD at the leaves and adjust to 150–300 µmol/m²/s. 3. In coco, rockwool or hydro, feed at EC 0.4–0.8 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md) 5.8–6.2. 4. In soil, wait for 2–3 sets of true leaves before feeding. 5. Check the stem base: pinched and brown means damping-off. ## Common mistakes - Feeding full strength to "green it up". - Calling normal cotyledon yellowing a [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md). - Plain water only in coco for three weeks. - Watering daily on a schedule. ## Related - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - [Why is my seedling drooping?](https://genetixbay.com/knowledge/answers/why-is-my-seedling-drooping.md) · [Yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) - Terms: [cotyledon](https://genetixbay.com/knowledge/glossary/cotyledon.md) · [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) · [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) ## Follow-up questions **Is it normal for cotyledons to turn yellow?** Yes, often. A cannabis seedling's cotyledons, the two round first leaves, feed it until the true leaves take over, and yellowing around days 10–14 is commonly normal. Worry if the true leaves yellow too, if it happens before day 7, or if growth stalls. In coco, rockwool or hydro, early cotyledon yellowing usually means the seedling needs a light feed. **Can overwatering make seedlings yellow?** Yes. Overwatering is one of the commonest causes of pale or yellow cannabis seedlings. A soggy plug or a big pot soaked for a tiny root leaves the roots short of oxygen, so they can't take up nutrients even when they are present. The seedling also droops. Let the pot lighten noticeably before the next small watering around the stem. **Should I feed a yellow seedling?** Feed a yellow cannabis seedling only if the medium has no starter charge, such as coco, rockwool or hydro, or once it has 2–3 sets of true leaves. Use a quarter to half strength feed, EC 0.4–0.8 mS/cm (200–400 ppm500). In amended soil, yellowing at this age is far more often water or light, and extra feed can burn tender roots. ## Sources 1. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 2. Runkle E. The benefits of lighted plugs. Michigan State University Extension. https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs 3. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 --- # Should I mist my plants? > Don't mist established cannabis plants, and never mist buds in flower. A spray of water raises humidity for minutes, not hours, and wet leaves and buds invite powdery mildew and bud rot. Misting is useful only for unrooted clones under a dome, at 75–90 % RH. To raise humidity for growing plants, use a humidifier on a humidistat or slow the exhaust. - Canonical: https://genetixbay.com/knowledge/answers/should-i-mist-my-plants.html - Topic: Environment · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - Also asked as: Should I spray my cannabis leaves with water? | Is misting cannabis good? | Does a water spray on leaves raise humidity? | Should I mist seedlings or clones? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Don't mist established cannabis plants, and **never mist buds in flower**. A spray of water lifts humidity for minutes, then leaves wet surfaces that invite **[powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) and [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md)** [1][2]. The exception: **unrooted clones** under a dome at **75–90 % [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md)**. *Grower practice*, backed by disease evidence. ## Why A tent's [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) and warm air remove sprayed water within minutes. What stays behind is water sitting on leaves and in buds, not humid air. Wet surfaces are where fungal disease starts. *Botrytis* bud rot begins inside dense, damp [colas](https://genetixbay.com/knowledge/glossary/cola.md), and humidity is an established driver of both bud rot and powdery mildew in cannabis [1][2]. Very humid conditions also hurt flowering itself: in a 2025 study, roughly 78–98 % RH delayed flowering and lowered biomass and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) compared with 37–58 % [3]. Unrooted clones are different. They have no roots, so cutting water loss from the leaves keeps them alive until roots form. A dome holds humidity; misting [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) it up. Misting in [high-pressure aeroponics](https://genetixbay.com/knowledge/glossary/hpa.md) is a different thing: that's root-zone irrigation inside a chamber, not leaf spraying (see [HPA aeroponics](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md)). ## The numbers | Plant | Mist? | Humidity target | |---|---|---| | Unrooted clones (dome) | yes, lightly, 1–2 times a day | 75–90 % RH | | [Seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) | rarely; use a vented dome instead | 65–75 % RH | | Veg | no; use a [humidifier](https://genetixbay.com/knowledge/glossary/humidifier.md) | 55–70 % RH | | Flower | never on buds | 50–60 %, then 40–50 % RH | ## What to do 1. Check the hygrometer before deciding the air is dry. 2. For clones, mist lightly under a dome and vent daily. 3. For growing plants, slow the exhaust or add a humidifier on a humidistat. 4. If a [foliar spray](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) is truly needed in veg, apply early in the light period so leaves dry within an hour or two. 5. Never spray in flower. ## Common mistakes - Misting to "fix" low humidity, then getting mildew. - Spraying flowers to "cool" them. - Misting right before lights-off. - Spraying near hot lamps or electrics. ## Related - Full article: [Humidity by stage](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) - [How do I raise the humidity in my grow tent?](https://genetixbay.com/knowledge/answers/how-to-raise-humidity-in-a-grow-tent.md) - [What humidity and light do clones need?](https://genetixbay.com/knowledge/answers/humidity-and-light-for-clones.md) - [Botrytis bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) - Terms: [humidifier](https://genetixbay.com/knowledge/glossary/humidifier.md) · [foliar feeding](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) ## Follow-up questions **Does misting raise humidity in a grow tent?** Misting raises grow-tent humidity only for a few minutes, because the exhaust and warm air remove the water almost at once, leaving wet leaves behind. To hold humidity at 65–75 % for seedlings or 55–70 % in veg, use a humidifier on a humidistat or slow the exhaust fan. Misting is the least effective and riskiest way to add humidity. **Should I mist clones?** Yes, light misting helps unrooted cannabis clones, which have no roots to replace water lost through their leaves. Keep them under a dome at about 75–90 % RH and 23–26 °C (73–79 °F), mist the dome walls or leaves lightly once or twice a day, and vent daily to avoid mould. Stop misting and lower humidity gradually once roots appear. **Can I spray buds with water in flower?** No, don't spray cannabis buds with water in flower. Dense, wet buds are where Botrytis bud rot and powdery mildew start, and water trapped inside a cola can stay wet for hours. Late-flower humidity should sit at 40–50 % RH. If plants look dry, check root-zone moisture and leaf VPD rather than wetting the flowers. ## Sources 1. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ 2. Utah State University Extension. Hemp bud rot (IPM fact sheet). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot.php 3. Corredor-Perilla IC, Kwon H, Park J, 2025. High relative humidity effects in cannabis. Frontiers in Plant Science 16:1678142. https://doi.org/10.3389/fpls.2025.1678142 --- # Should I wash my buds after harvest? > Wash buds only if they are dirty, such as outdoor plants covered in dust, ash, pollen or insects. Washing doesn't rescue buds with powdery mildew or bud rot, and no study shows it removes mould. If you do wash, shake the water off at once and hang the buds in moving air so the extra water doesn't start mould. Indoor plants from a clean room don't need washing. - Canonical: https://genetixbay.com/knowledge/answers/should-i-wash-my-buds.html - Topic: Diseases · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) - Also asked as: Should I do a bud wash? | Washing buds with hydrogen peroxide | Rinse buds after harvest | Can washing remove powdery mildew from buds? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Wash buds only when they are visibly dirty, such as outdoor plants carrying dust, ash or insects. A bud wash won't rescue flower with [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) or [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md). If you wash, get the water off fast and dry the buds in moving air at 15–21 °C (60–70 °F) and 55–62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). *Grower practice*: there is no published research on bud washing. ## Why Mouldy flower is a safety problem, not a dirt problem. Spores and possible [mycotoxins](https://genetixbay.com/knowledge/glossary/mycotoxins.md) are why regulated markets test for yeast and mould [1]. No study shows that rinsing brings infected buds back into a safe range. Powdery mildew lives on the surface of leaves and [bracts](https://genetixbay.com/knowledge/glossary/bract.md) and sporulates there [2]. In dense flowers a rinse removes some of the powder at best. Removing infected material is the standard advice. The water you add matters. Botrytis needs free water or very high humidity [3], and wet [colas](https://genetixbay.com/knowledge/glossary/cola.md) hung close together in a still room are an easy target. Drying has to bring buds down to [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55–0.65 [4], and washing adds water you then have to remove. ## The numbers | Situation | Wash? | |---|---| | Clean indoor room | No | | Outdoor dust, ash, pollen, insects | Optional, gentle | | Powdery mildew on buds | No: remove or bin | | Bud rot | No: bin | | After washing | Dry at 15–21 °C, 55–62% RH, air moving in the room | ## What to do 1. Inspect first. Break open the biggest colas and bin anything brown, grey or fuzzy. 2. If the buds are only dusty, dip whole branches in a tub of clean, cool water and swish gently. Repeat in a second tub. 3. Shake off the excess at once and hang the branches with space between them. 4. Keep the room air moving, but don't point a fan at the buds. 5. If you add [peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md), keep it dilute and rinse afterwards. Wear gloves and eye protection when handling the concentrate. ## Common mistakes - Washing PM-coated buds and calling them clean. - Hanging soaked branches in a crowded, humid room. - Scrubbing or squeezing the buds. - Washing clean indoor buds out of habit. ## Related - Full article: [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) - Answers: [milk and baking soda sprays](https://genetixbay.com/knowledge/answers/home-remedies-for-powdery-mildew.md) · [mould in curing jars](https://genetixbay.com/knowledge/answers/mould-in-curing-jars.md) - Article: [drying](https://genetixbay.com/knowledge/harvest-cure/drying.md) - Terms: [hydrogen peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) · [microbial testing](https://genetixbay.com/knowledge/glossary/microbial-testing.md) ## Follow-up questions **Does washing buds remove powdery mildew?** Washing buds does not reliably remove powdery mildew, and no study shows it makes infected flower clean. Mildew mycelium and spores sit among the trichomes and bracts, and rinsing removes some surface powder at best. Remove or discard PM-coated buds instead. Prevent the problem next run with airflow, stable humidity and clean clones. **Is a hydrogen peroxide bud wash safe?** A dilute hydrogen peroxide bud wash is a common grower practice, but there is no cannabis research showing it improves safety or quality, and it does not make mouldy buds safe. If you use one, keep it dilute, rinse in clean water afterwards and dry fast. Concentrated peroxide burns skin and eyes, so wear gloves and eye protection. **Will washing buds wash off trichomes or terpenes?** Gentle washing knocks off some trichome heads and can carry away some aroma, so handle buds as little as possible and never scrub them. The bigger risk is the water: wet buds hung in a crowded, humid room can grow mould. Wash only when buds are visibly dirty, and dry them in moving air at 55–62% RH. ## Sources 1. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 2. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa) - Powdery Mildew. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-powdery-mildew 3. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold (Botrytis Bud Blight and Stem Canker). https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker 4. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html --- # Why is my plant growing single-finger leaves? > Single-finger, rounded leaves on a cannabis plant usually mean it is revegging: switching from flowering back to vegetative growth because its nights became too short or were broken by light. Common causes are light leaks in flower, timer faults, outdoor plants put out under short spring days, and clones cut from flowering plants. Keep the dark period truly dark, below about 0.01–2 µmol/m²/s. - Canonical: https://genetixbay.com/knowledge/answers/single-finger-leaves-reveg.html - Topic: Diagnosis · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Also asked as: Is my plant revegging? | Round, single-blade leaves on my plant | Revegging plant in flower | Smooth leaves with no serrations - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Single-finger, rounded leaves usually mean a cannabis plant is [revegging](https://genetixbay.com/knowledge/glossary/re-veg.md): going from flower back to vegetative growth because its nights got too short or were broken by light. The common causes are [light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) or timer faults in flower, outdoor plants set out under short spring days, and clones cut from flowering plants. *Supported*. ## Why [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis reads the night. Flowering starts once the uninterrupted dark is long enough, and it stalls or reverses when nights shorten or are broken [1]. Very little light can break a night. A [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) study reported flowering delays from stray light at about 2 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) [1], and a 2024 conference report saw delays in the most sensitive cannabis cultivars at 0.01 µmol/m²/s [2]. A mid-night pulse of light is used on purpose. Growers keep [mother plants](https://genetixbay.com/knowledge/glossary/mother-plant.md) vegetative on [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) with a 1-hour night break [3], which shows how well a short interruption works. An accidental leak does the same thing to a flowering plant. Revegging leaves look distinctive. New growth comes in as single blades or 3-finger leaves with smooth or rounded edges, sometimes poking out of the buds. ## The numbers | Situation | Threshold | |---|---| | Dark-period stray light | As near 0 as you can measure; below 0.01–2 µmol/m²/s [1][2] | | Eye test | Nothing visible after 5 minutes with eyes adjusted | | Flower schedule | 12/12 or [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) (house-endorsed), uninterrupted dark | | Reveg recovery | About 2–4 weeks before normal leaves return (grower practice) | ## What to do 1. Sit in the dark room for 5 minutes. Tape over indicator [LEDs](https://genetixbay.com/knowledge/glossary/led.md), zipper ends and duct ports. 2. Check that the timer and controller logs match the schedule, especially after a power cut. 3. Make sure no light reaches the room from a veg area or a door gap. 4. Outdoors, plant out photoperiod cultivars once the days are long, or add light in early spring. 5. Take clones from vegetative mothers, not flowering plants. 6. Once you've fixed the cause, give the plant time. Don't add stress on top. ## Common mistakes - Opening the tent during the dark period. - Trusting a mechanical timer that drifts. - Putting photoperiod plants outside in early spring. - Mistaking a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md)'s first single-blade leaves for reveg. ## Related - Full article: [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Answers: [how to reveg a plant](https://genetixbay.com/knowledge/answers/how-to-reveg-a-plant.md) · [lights stayed on in flower](https://genetixbay.com/knowledge/answers/lights-stayed-on-during-flower.md) · [opening the tent at night](https://genetixbay.com/knowledge/answers/opening-tent-during-dark-period.md) · [when to plant outdoors](https://genetixbay.com/knowledge/answers/when-to-plant-outdoors.md) - Terms: [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) · [light leak](https://genetixbay.com/knowledge/glossary/light-leak.md) ## Follow-up questions **How long does revegging take?** Revegging a cannabis plant usually takes about 2–4 weeks before normal multi-finger leaves return, according to grower practice, and it can be slower on a plant cut from late flower. Expect odd single-blade and smooth-edged leaves first. Keep it on 18/6 or longer days in veg conditions, and leave plenty of green growth and bud sites when harvesting a plant you plan to reveg. **Why are my outdoor plants growing single-blade leaves?** Outdoor cannabis planted early in spring often grows single-blade leaves because short spring days start flowering, and then lengthening days push it back into veg, a reveg. Plant photoperiod cultivars out after days are long enough to keep them vegetative, or give them extra light indoors first. Expect a 2–4 week stall while they recover. **Are single-finger leaves normal on clones?** Single-finger leaves are normal on clones cut from a flowering or recently flowering mother, because the cutting has to reveg before it grows normally. On clones from a vegetative mother on 18/6 or longer, they shouldn't appear. Take cuttings from vegetative mothers for faster rooting and growth, and expect a slow start from flowering cuts. ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis 3. Examining the night break method in Cannabis sativa horticulture: vegetative daily light integral affects yield of extractable biomass, 2025. Plants 14(19):3095. https://pmc.ncbi.nlm.nih.gov/articles/PMC12525983/ --- # What are the small white bugs in my soil? > Small white bugs in cannabis soil that jump when disturbed are almost always springtails: about 1.5 mm (1/16 in), harmless scavengers of wet, organic media. Slow, round specks are soil mites, often harmless or predatory. The ones that matter are worm-like larvae with a shiny black head (fungus gnats) and pale aphids clustered on roots (root aphids). Tip the plant out and look at the roots. - Canonical: https://genetixbay.com/knowledge/answers/small-white-bugs-in-soil.html - Topic: Pests · Type: Troubleshooting - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) - Also asked as: Are these springtails? | Tiny white bugs jumping in my soil | Small white mites in my soil | White bugs crawling when I water | Are white soil bugs harmful to cannabis? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Tiny white bugs that jump when you water or poke the soil are almost certainly springtails, about 1.5 mm (1/16 in) long and harmless to established plants. Worry instead about black-headed larvae ([fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md)) or pale [aphids](https://genetixbay.com/knowledge/glossary/aphid.md) on the roots ([root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md)). *Established*. ## Why Springtails are scavengers. They live in moist, compost-rich soil and [potting mixes](https://genetixbay.com/knowledge/glossary/potting-mix.md), feed on fungi and decay, and jump using a folded tail. Mature plants are not significantly injured, and sprays are generally not recommended [1]. Fungus gnat larvae do chew roots. They are translucent white, up to about 6 mm, with a shiny black head, and they hurt [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) and clones most [2]. Root aphids feed on roots, out of sight. Pale to olive colonies on the rootball cause slow growth, wilting and yellowing that look like a nutrient problem [3]. Soil [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) are usually neutral or helpful. The predatory soil mite sold for gnat control eats gnat larvae, [thrips](https://genetixbay.com/knowledge/glossary/thrips.md) pupae and springtails [4]. ## The numbers | Bug | Size and look | Behaviour | Harmful? | |---|---|---|---| | Springtail | ~1.5 mm, white to grey | Jumps when disturbed | No, except very young seedlings | | Soil mite | About 0.5–1 mm, round, tan or white | Crawls slowly | Usually no | | Fungus gnat larva | Up to ~6 mm, worm-like, black head | In top few cm of wet media | Yes, for seedlings and clones | | Root aphid | Small, pale to olive, pear-shaped | Clusters on roots, doesn't jump | Yes | ## What to do 1. Watch a few seconds: jumping means springtails. 2. Lay a raw potato slice on the medium for 2–4 days; larvae underneath mean gnats. 3. If the plant is stalling, tip it out and inspect the roots with a 10x lens. 4. Let the top 2–5 cm (1–2 in) dry between waterings and empty saucers. 5. Treat only what is harmful: Bti or [nematodes](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md) for gnats; see the root aphid article for those. ## Common mistakes - Drenching insecticide for harmless springtails. - Missing root aphids because "it's just springtails". - Keeping the medium soaked, which feeds every bug on this list. ## Related - Full article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) - Article: [Root aphids](https://genetixbay.com/knowledge/pests/root-aphids.md) - Answers: [Do sticky traps work?](https://genetixbay.com/knowledge/answers/do-sticky-traps-work.md) · [White fuzz on soil](https://genetixbay.com/knowledge/answers/white-fuzz-on-soil.md) - Terms: [root aphid](https://genetixbay.com/knowledge/glossary/root-aphid.md) · [Bti](https://genetixbay.com/knowledge/glossary/bti.md) · [Stratiolaelaps scimitus](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md) ## Follow-up questions **Are springtails bad for cannabis?** Springtails are not bad for established cannabis. They are tiny, wingless scavengers about 1.5 mm (1/16 in) long that feed on fungi and decaying matter in moist soil, especially compost-rich mixes. Some species may chew very young seedlings, but mature plants are not significantly injured and control is rarely warranted. Large numbers mainly tell you the medium stays very wet. **How do I tell springtails from root aphids?** Tell springtails from root aphids by behaviour and location. Springtails jump when disturbed, using a spring-like tail, and run over the soil surface or saucer water. Root aphids do not jump; they are pale to olive, pear-shaped insects clustered on roots, often near the edge of the rootball, and the plant slowly stalls and yellows. Tip the plant out to check. **How do I get rid of springtails?** Get rid of springtails by drying things out, not by spraying. Let the top of the soil dry slightly between waterings, empty saucers so drainage water does not stand, and avoid piling excess organic mulch on the pot surface. Insecticide sprays are generally not recommended for springtails. If numbers stay high in a dry-surfaced pot, check that you are not dealing with fungus gnats. ## Sources 1. UC IPM. Pest Notes: Springtails (Publication 74136). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn74136.html 2. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf 3. Utah State University Extension. Rice Root Aphids (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-rice-root-aphid 4. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/ --- # Can I start plants indoors and move them outside? > Yes: starting photoperiod cannabis indoors 3–6 weeks before your last frost and moving it outside is standard practice, if you harden it off over 7–14 days. Keep it on long days indoors (18 h or more), and move it out only once natural days are about 14.5 hours or longer, or it may flower and re-veg. Autoflowers should start in the final container, which you carry outside. - Canonical: https://genetixbay.com/knowledge/answers/start-indoors-move-outside.html - Topic: Outdoor growing · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) - Also asked as: Can I start inside and move outside? | How do I harden off cannabis plants? | Transplanting cannabis outdoors | Will my indoor plant flower when I put it outside? | How long to harden off seedlings? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes. Start [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md) indoors 3–6 weeks before your last frost, keep them on 18 h or longer days, harden them off over 7–14 days, and plant out once natural days pass about 14.5 hours. *Grower practice*. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) go in their final container from day one. ## Why Indoor leaves are soft. Plants raised under weak light and still air need gradual exposure to sun, wind and cool nights, the standard hardening-off step for any [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) [1]. Raising indoor light towards 500–900 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) late in veg also builds tougher, more compact plants [4]. Day length can trigger flowering. Cannabis flowers when nights pass its threshold; some [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md) responded at 13 h 45 min to 14 h of day [2]. A plant moved from 18 h indoors into a 13.5 h April day can start flowering, then [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md). Root balls should move intact. Moving a plant in a pot sized for its roots, into pre-moistened soil, avoids [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) unrooted medium and stalls [3]. ## The numbers | Step | Target | Notes | |---|---|---| | Start indoors | 3–6 weeks before last frost | Photoperiods only, [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) to [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) | | [Hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) | 7–14 days | Shade first, then more sun daily | | Night temperature to plant out | Reliably above ~10 °C (50 °F) | Bring in on [cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) until then | | Safe outdoor day length | ~14.5 h or more | From early May at 45° N; early November at 45° S (calculated) | | Midday full sun | 1,500–2,000+ µmol/m²/s | Several times indoor light | ## What to do 1. Sow photoperiods 3–6 weeks before last frost; sow autos in their final container. 2. Run 18 h or longer days indoors so plants stay vegetative. 3. Ten days before planting out, start hardening: 1–2 h shade, then more sun each day. 4. Plant out on an overcast day or in the evening. 5. Set the root ball intact into pre-moistened soil and water in. 6. Protect from wind and slugs for the first week. ## Common mistakes - Moving straight from a tent into full midday sun. - Planting out in April and triggering early flowers. - Transplanting autoflowers instead of carrying out their pot. - Leaving [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) out on a frosty night. ## Related - Full article: [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) - Answers: [When to plant outdoors](https://genetixbay.com/knowledge/answers/when-to-plant-outdoors.md) · [Plant straight into the final pot](https://genetixbay.com/knowledge/answers/plant-straight-into-final-pot.md) · [Autoflowers outdoors](https://genetixbay.com/knowledge/answers/autoflowers-outdoors.md) - Terms: [hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) · [transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md) ## Follow-up questions **How do I harden off cannabis seedlings?** Harden off cannabis seedlings over 7–14 days. Start with an hour or two outdoors in shade or gentle morning sun, sheltered from wind, then add time and direct sun each day. Bring plants in on cold nights until nights stay above about 10 °C (50 °F). Full midday sun can exceed 1,500–2,000 µmol/m²/s, several times typical indoor light, so rushing bleaches leaves. **Will my plant flower when I move it outside?** A photoperiod plant moved from 18 hours of indoor light to shorter natural days can start flowering if outdoor days are below its threshold, often around 14 hours. At 45° latitude days pass 14.5 hours in early May, so moving out from late May is usually safe at mid-latitudes. Plants moved too early often flower briefly, then re-veg as days lengthen, which costs weeks. **Can I start autoflowers indoors and move them outside?** Yes, but sow the autoflower in its final container indoors and carry the whole pot outside, rather than transplanting it. An auto runs on a strict countdown from germination, so transplant shock costs time it cannot recover, and the GenetixBay founder finds the auto taproot reacts badly to being moved. Harden the container plant off over a week, as with any seedling. ## Sources 1. University of Minnesota Extension. Starting seeds indoors (transplanting seedlings, hardening). https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors 2. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 3. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container size and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 4. Moher M, Llewellyn D, Jones M, Zheng Y, 2021. High light intensities can be used to grow healthy and robust cannabis plants during the vegetative stage of indoor production. Preprints 2021040417 (not peer reviewed). https://doi.org/10.20944/preprints202104.0417.v1 --- # What is the difference between a strain and a cultivar? > A cultivar is a formal botanical term: a cultivated plant group that is distinct, uniform and stable when propagated, by seed or cuttings. A strain is the popular cannabis word, used loosely for anything from one clone to a brand name. A chemovar is a cultivar defined by its chemistry. Genetic studies show many strain names don't reliably mean one genotype. - Canonical: https://genetixbay.com/knowledge/answers/strain-vs-cultivar.html - Topic: Basics · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Why strain names are unreliable: what genetic studies show](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) - Also asked as: Strain vs cultivar | What is a cultivar? | Chemovar vs strain | Why do people say cultivar instead of strain? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A cultivar is the botanical term for a cultivated plant group that is distinct, uniform and stable when propagated. "Strain" is the popular cannabis word, used for anything from a single clone to a marketing name. A [chemovar](https://genetixbay.com/knowledge/glossary/chemovar.md) is a cultivar defined by its chemistry. *Established* terminology. ## Why "Cultivar" has rules. The International Code of Nomenclature for Cultivated Plants sets how cultivars are defined and named [1]. A clonal cultivar is one [genotype](https://genetixbay.com/knowledge/glossary/genotype.md); a seed cultivar must come true from seed. "Strain" has none. It's borrowed from microbiology and applied loosely. [Genetic testing](https://genetixbay.com/knowledge/glossary/genotyping.md) of retail cannabis found genetic outliers within most same-named strains [3], so a strain name is a claim, not an identity. "Chemovar" describes what's in the jar. Researchers argued that [medicinal cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md) should be classified by its chemical profile, because names don't predict chemistry [2]. Large lab datasets confirm that commercial labels align poorly with [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md), though some names are consistent [4]. ## The numbers | Term | Defined by | Example of correct use | |---|---|---| | Cultivar | Distinct, uniform, stable traits (ICNCP) [1] | A [clone-only cut](https://genetixbay.com/knowledge/glossary/clone-only.md); a true-breeding seed line | | Strain | Popular usage, no rules | Any named cannabis on a menu | | Chemovar | [Cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) [2] | "THC-dominant, [caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md)–[limonene](https://genetixbay.com/knowledge/glossary/limonene.md)" | | [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md) | One plant's observed traits | The keeper from a [pheno](https://genetixbay.com/knowledge/glossary/pheno.md) hunt | ## What to do 1. Treat a strain name as a claim; ask for the source and grow-out records. 2. For a clone, ask for chain of custody. 3. Choose by chemistry: read the cannabinoid and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) sections of the [certificate of analysis](https://genetixbay.com/knowledge/glossary/coa.md). 4. Call a one-off hybrid cross a cross, not a cultivar, until it [breeds true](https://genetixbay.com/knowledge/glossary/true-breeding.md). ## Common mistakes - Assuming two plants with the same name are the same genotype. - Calling every seed pack a stable cultivar. - Treating "indica" or "sativa" on a label as a chemovar. ## Related - Full article: [Why strain names are unreliable](https://genetixbay.com/knowledge/genetics-history/why-strain-names-are-unreliable.md) - Answers: [what terpenes are](https://genetixbay.com/knowledge/answers/what-are-terpenes.md) · [hemp vs marijuana](https://genetixbay.com/knowledge/answers/hemp-vs-marijuana.md) - Article: [Same cut, a thousand names](https://genetixbay.com/knowledge/genetics-history/same-cut-a-thousand-names.md) - Terms: [cultivar](https://genetixbay.com/knowledge/glossary/cultivar.md) · [strain](https://genetixbay.com/knowledge/glossary/strain.md) · [chemovar](https://genetixbay.com/knowledge/glossary/chemovar.md) ## Follow-up questions **What is a chemovar?** A chemovar is a chemical variety: a cannabis cultivar or group defined by its chemical profile, mainly its cannabinoids and dominant terpenes, rather than by name or shape. Researchers proposed classifying medicinal cannabis this way because names and 'indica' or 'sativa' labels don't predict chemistry. On a certificate of analysis, the chemovar is what the numbers show. **Is a clone-only a cultivar?** Yes, a clone-only is a clonal cultivar: one genotype kept alive by cuttings, so every plant of it is genetically identical apart from rare mutations and pathogens. Its name only means that genotype if the chain of custody is sound. Cuts get renamed and mixed up, so the same name from two sources can be two different plants. **Is a seed strain a cultivar?** A seed strain is a cultivar only if it breeds true for its key traits: distinct, uniform and stable from seed. Many seed releases are one-off crosses of two hybrids, whose seedlings vary widely, so strictly they are not yet cultivars. An inbred line (IBL) or a well-stabilised seed line can qualify. ## Sources 1. Brickell CD, et al. (eds). 2016. International Code of Nomenclature for Cultivated Plants, 9th edition. Scripta Horticulturae 18. ISHS. https://www.ishs.org/scripta-horticulturae/international-code-nomenclature-cultivated-plants-ninth-edition 2. Hazekamp A, Fischedick JT. 2012. Cannabis: from cultivar to chemovar. Drug Testing and Analysis 4(7-8):660-667. https://doi.org/10.1002/dta.407 3. Schwabe AL, McGlaughlin ME. 2019. Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry. Journal of Cannabis Research 1:3. https://doi.org/10.1186/s42238-019-0001-1 4. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLoS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 --- # Is a TDS meter the same as an EC meter? > Yes, essentially. A TDS or ppm meter measures electrical conductivity (EC) and multiplies it by an assumed factor: 0.5 on the 500 scale, 0.7 on the 700 scale, sometimes 0.64. So 1.0 mS/cm reads 500 ppm on one meter and 700 on another. The ppm figure is an estimate, not your nutrients' real concentration. Read and talk in EC, or always state the scale. - Canonical: https://genetixbay.com/knowledge/answers/tds-meter-vs-ec-meter.html - Topic: pH and EC · Type: Comparison - Evidence: Established · Status: Draft: awaiting expert review - Full article: [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) - Also asked as: TDS vs EC: what's the difference? | Are ppm meters accurate? | What does a TDS meter actually measure? | Is my meter 500 or 700 scale? | Should I use ppm or EC? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Essentially, yes. A [TDS](https://genetixbay.com/knowledge/glossary/tds.md) or "ppm" meter measures [electrical conductivity](https://genetixbay.com/knowledge/glossary/ec.md) and multiplies it by an assumed factor: 0.5 on the [500 scale](https://genetixbay.com/knowledge/glossary/ppm500.md), 0.7 on the [700 scale](https://genetixbay.com/knowledge/glossary/ppm700.md), sometimes 0.64 [1]. The same 1.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) solution reads 500 ppm on one meter and 700 on another. Work in EC (mS/cm), or always state the scale. *Established.* ## Why Dissolved salts carry current; more ions, more conductivity. That is what the probe measures, corrected to 25 °C [1]. Converting conductivity to dissolved solids needs a factor, and no single factor is right. Different salts conduct differently per gram, and for natural waters the true factor rises from about 0.65 at 1,000 [µS/cm](https://genetixbay.com/knowledge/glossary/us-cm.md) to about 0.82 at 10,000 µS/cm [1]. Meter makers just pick one. EC also says nothing about which ions are present [2]. [Sodium](https://genetixbay.com/knowledge/glossary/sodium.md) [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md) has EC too, so a reading tells you strength, not balance. ## The numbers | | [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) | TDS / ppm meter | |---|---|---| | What the probe measures | Conductivity | Conductivity | | Displays | mS/cm or µS/cm | EC × 0.5, 0.64 or 0.7 | | 1.0 mS/cm reads | 1.0 | 500, 640 or 700 ppm | | 1.413 mS/cm standard reads | 1.413 | ~707 (500) or ~990 (700) | | Comparable across meters | Yes | Only on the same scale | | Tells you which nutrients | No | No | **Verdict:** same sensor, different label; choose a meter that can show EC and use that. ## What to do 1. Check your meter's scale in the manual or settings. 2. Switch the display to EC if it allows. 3. Calibrate against a 1.413 mS/cm standard. 4. Convert any ppm [feed chart](https://genetixbay.com/knowledge/glossary/feed-chart.md) to EC using its stated scale. 5. Measure your water first; feed charts usually mean total EC. ## Common mistakes - Following a 700-scale chart with a 500-scale meter and [overfeeding](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) by 40%. - Comparing ppm numbers between growers on different meters. - Reading TDS ppm as ppm of nitrogen. - Using a meter with no [temperature compensation](https://genetixbay.com/knowledge/glossary/atc.md). ## Related - Full article: [EC vs PPM: the 500 and 700 scales](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md) - Articles: [meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) - Answers: [full-strength feeding chart?](https://genetixbay.com/knowledge/answers/full-strength-feeding-chart.md) · [meters you need](https://genetixbay.com/knowledge/answers/meters-you-need-for-growing.md) - Terms: [TDS](https://genetixbay.com/knowledge/glossary/tds.md) · [EC](https://genetixbay.com/knowledge/glossary/ec.md) · [ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md) · [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md) ## Follow-up questions **Is my meter 500 or 700 scale?** To tell whether your meter is 500 or 700 scale, check the manual or settings menu, or test it in a 1.413 mS/cm calibration standard: a 500-scale meter reads about 707 ppm and a 700-scale meter about 990 ppm. If the meter can display EC directly, switch it to EC and stop using ppm altogether. **How do I convert ppm to EC?** To convert ppm to EC, divide by your meter's factor: ppm divided by 500 on the 500 scale, or by 700 on the 700 scale, gives EC in mS/cm. So 800 ppm500 is 1.6 mS/cm, while 800 ppm700 is about 1.14 mS/cm. To switch scales, multiply 500-scale ppm by 1.4 to get 700-scale ppm. **Is TDS ppm the same as ppm of nitrogen on a recipe?** No. A TDS meter's ppm is an estimate of all dissolved salts from conductivity, while a recipe's ppm of nitrogen or calcium is the actual mass of that element per litre, also written mg/L. They are different numbers. A feed with 180 mg/L nitrogen might read anywhere from about 800 to 1,300 on a TDS meter, depending on scale and recipe. ## Sources 1. Prasad L, Meehan M, 2025. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923. https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test 2. Sonneveld C, Voogt W, 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 --- # What is the difference between THC and CBD plants? > THC and CBD plants are the same species; the difference is which enzyme turns the shared precursor CBGA into cannabinoid acids. THC-dominant plants carry working THCA synthase, CBD-dominant plants CBDA synthase, and mixed 1:1 plants one of each. The trait is inherited as one near-codominant block, so THC x CBD gives mixed F1s and a 1:2:1 split in the F2. - Canonical: https://genetixbay.com/knowledge/answers/thc-vs-cbd-plants.html - Topic: Basics · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) - Also asked as: THC vs CBD plant | CBD strain vs THC strain | Hemp CBD vs THC cannabis | How is the THC to CBD ratio inherited? | Can a 1:1 THC:CBD plant breed true? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [THC](https://genetixbay.com/knowledge/glossary/thc.md) and [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) plants are the same species with a different enzyme at one fork in the pathway. A THC-dominant plant turns the precursor [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) into [THCA](https://genetixbay.com/knowledge/glossary/thca.md); a CBD-dominant plant turns it into [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md); a mixed plant does both. The trait inherits as one near-codominant block. *Established* genetics. ## Why One precursor, competing enzymes. CBGA sits at a fork, and [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) and [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) compete for it. Crossing pure THC and pure CBD plants gave uniformly mixed [F1s](https://genetixbay.com/knowledge/glossary/f1.md) and a 1:2:1 split in the [F2](https://genetixbay.com/knowledge/glossary/f2.md), explained by one locus with [codominant](https://genetixbay.com/knowledge/glossary/codominant.md) [alleles](https://genetixbay.com/knowledge/glossary/allele.md) [1]. The "locus" is really a [gene](https://genetixbay.com/knowledge/glossary/gene.md) block. The two synthase genes sit in large, repeat-rich, low-recombination regions, so they pass on together [2]. CBD in drug-type lines often traces to [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) bred into marijuana backgrounds [3]. [Seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) can be screened. Validated DNA markers identify [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) from young plants [4], weeks before flower. How much cannabinoid a plant makes is a separate, many-gene trait. Chemotype sets the ratio, not the potency. ## The numbers | Chemotype | Ratio | Synthase alleles | Breeds true? | |---|---|---|---| | I, THC-dominant | THC:CBD > ~10:1 | THC / THC | Yes | | II, mixed | ~0.5:1 to 3:1 | THC / CBD | No: 1:2:1 | | III, CBD-dominant | CBD:THC > ~10:1 (hemp often 20–30:1) | CBD / CBD | Yes | | IV, CBG-dominant | High [CBG](https://genetixbay.com/knowledge/glossary/cbg.md) | Non-functional, both copies | Yes, once homozygous | | Cross | Offspring | |---|---| | I x III | 100% II | | II x II | 25% I : 50% II : 25% III | | II x III | 50% II : 50% III | ## What to do 1. Want a 1:1 plant? Keep it as a clone; its seed won't hold the ratio. 2. Breeding CBD into a THC line? Cross, then select type III in the F2 or backcross. 3. Screen seedlings with a chemotype test, then confirm with flower tests. 4. Growing CBD as hemp? Test before harvest; rules vary, so check local limits. ## Common mistakes - Expecting a 1:1 cultivar to breed true. - Assuming CBD plants contain no THC. - Confusing chemotype (the ratio) with potency (the amount). ## Related - Full article: [Chemotype inheritance](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md) - Answers: [what THCA is](https://genetixbay.com/knowledge/answers/what-is-thca.md) · [hemp vs marijuana](https://genetixbay.com/knowledge/answers/hemp-vs-marijuana.md) - Article: [Mendelian genetics for growers](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md) - Terms: [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) · [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) · [CBDA synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) ## Follow-up questions **How is the THC to CBD ratio inherited?** The THC to CBD ratio in cannabis is inherited as one block, close to codominant. The THCA synthase and CBDA synthase genes are separate but tightly linked in low-recombination regions, so they pass on together like a single locus with two alleles. Two copies of either give a pure type; one of each gives a mixed type II plant. **Can a 1:1 THC:CBD plant breed true?** No, a 1:1 THC:CBD cannabis plant cannot breed true. Mixed chemotype II plants carry one THC synthase and one CBD synthase allele, so their seed segregates about 25% THC-dominant, 50% mixed and 25% CBD-dominant. Keep a 1:1 cultivar as a clone, or remake it each time by crossing a pure THC parent with a pure CBD parent. **Do CBD plants contain any THC?** Yes, CBD-dominant cannabis plants still contain some THC. Even good CBD hemp lines typically show THC:CBD ratios around 1:20 to 1:30, so a plant at 15% CBD can carry about 0.5–0.75% THC. That is why CBD crops grown as hemp can test over a 0.3% legal limit. Test before harvest and check your local rules. ## Sources 1. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335 2. Laverty KU, Stout JM, Sullivan MJ, et al. 2019. A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci. Genome Research 29(1):146-156. https://doi.org/10.1101/gr.242594.118 3. Grassa CJ, Weiblen GD, Wenger JP, et al. 2021. A new Cannabis genome assembly associates elevated cannabidiol (CBD) with hemp introgressed into marijuana. New Phytologist 230(4):1665-1679. https://doi.org/10.1111/nph.17243 4. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 --- # Should I top off my reservoir with plain water or nutrient solution? > Let the reservoir's EC decide what you top off a hydro reservoir with. If EC has risen since the last check, top off with plain, pH-adjusted water; if it holds steady, top off with solution at the reservoir's current EC; if it falls, the plants are hungry, so use solution at full target strength. Without a meter, plain or quarter-strength water is the safe default. Refresh fully every 7–14 days. - Canonical: https://genetixbay.com/knowledge/answers/top-off-reservoir-water-or-nutrients.html - Topic: Systems · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) - Also asked as: Should I top off with plain water? | How do I top up my DWC reservoir? | What EC should my reservoir top-off be? | Top off with nutrients or just water? | Why does my reservoir EC go up when the water level drops? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Top off a hydro reservoir according to what its [EC](https://genetixbay.com/knowledge/glossary/ec.md) did since the last check. EC up: plain, pH-adjusted water. EC steady: solution at the reservoir's current EC. EC down: solution at full target strength. With no meter, plain or quarter-strength water is the safe default, and a full refresh every 7–14 days resets everything. *Grower practice*, built on basic uptake chemistry. ## Why Plants absorb water and nutrient ions at different ratios, and the ratio changes with stage, light and humidity [1]. When they drink more water than salts, the solution concentrates and EC rises. When they take more salts than water, EC falls. A fixed-strength top-off ignores which is happening: full strength on a rising EC builds salts; plain water on a falling EC starves the plant. EC is a total, not a recipe. Each element is taken up at its own rate, so the ion balance drifts even when EC reads correctly. That is why [closed systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md) still need periodic full changes [2]. Fresh top-off water should be at reservoir temperature, 18–22 °C (64–72 °F). Warm top-ups raise root-rot risk [3]. ## The numbers | EC change since last check | Top off with | [pH](https://genetixbay.com/knowledge/glossary/ph.md) | |---|---|---| | Rising (+0.2 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) or more) | Plain water | 5.6–6.0 | | Steady (±0.1 mS/cm) | Solution at current [reservoir EC](https://genetixbay.com/knowledge/glossary/input-ec.md) | 5.6–6.0 | | Falling (−0.2 mS/cm or more) | Solution at full target EC | 5.6–6.0 | | No meter | Plain or quarter-strength | 5.6–6.0 | | Full change | Every 7–14 days | 5.6–6.0 | [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) EC targets: 0.6–1.0 mS/cm [seedling](https://genetixbay.com/knowledge/glossary/seedling.md), 1.0–1.6 veg, 1.4–2.0 flower ([ppm500](https://genetixbay.com/knowledge/glossary/ppm500.md) = EC × 500; [ppm700](https://genetixbay.com/knowledge/glossary/ppm700.md) = EC × 700). ## What to do 1. Mark the full line and log EC and pH daily. 2. Before topping off, compare EC with yesterday's reading. 3. Mix the top-off to match the table, at reservoir temperature. 4. Re-check pH after topping off; adjust within 5.6–6.0. Wear gloves and eye protection with pH-down acid. 5. Change the whole reservoir every 7–14 days. ## Common mistakes - Topping off with full-strength nutrients every time, so EC climbs all week. - Top-off water much colder or warmer than the reservoir. - Skipping full changes because the EC "[looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) fine". ## Related - Full article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) - Answers: [algae in the reservoir](https://genetixbay.com/knowledge/answers/algae-in-reservoir.md) · [how long mixed nutrients keep](https://genetixbay.com/knowledge/answers/how-long-can-mixed-nutrients-sit.md) - Systems: [RDWC](https://genetixbay.com/knowledge/systems/rdwc.md) · [recirculating drip](https://genetixbay.com/knowledge/systems/recirculating-drip.md) - Terms: [reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md) · [EC](https://genetixbay.com/knowledge/glossary/ec.md) ## Follow-up questions **Why does my reservoir EC rise as the water drops?** Reservoir EC rises as the level drops because the plants are drinking water faster than they take up nutrient ions, so the salts left behind become more concentrated. This is common in warm, dry rooms with high transpiration. Top off with plain, pH-adjusted water to bring EC back down, and consider lowering the strength of your next fresh batch a little. **Why does my reservoir EC keep dropping?** Reservoir EC drops when the plants take up nutrients faster than water, which usually means they are hungry and the solution is weaker than they want. It is common in mid flower and in cool, humid rooms. Top off with solution at your full target EC, and raise the strength of the next fresh batch by about 0.1–0.2 mS/cm if it keeps happening. **How often should I change the reservoir if I top it off?** Change a hydro reservoir completely every 7–14 days even if you top it off between changes. Topping off corrects volume and EC, but the plants take up each element at a different rate, so the balance of ions drifts away from the recipe over time even when the EC reading looks right. A common rule is to change sooner once you have topped off about one reservoir's worth. ## Sources 1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 2. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press (closed vs open systems). https://doi.org/10.1201/9781003133254 3. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems (68–72 °F). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/ --- # Can I use regular garden fertiliser on cannabis? > Yes, regular garden fertiliser works on cannabis in soil, because roots take up the same ions whatever the label says. Pick a complete feed with calcium, magnesium and micronutrients, and dose by element: aim for roughly 150-200 mg/L nitrogen in veg and 30-60 mg/L phosphorus. All-purpose feeds suit veg, tomato feeds suit flower. Avoid lawn feeds with herbicides, and use fully soluble salts in hydro. - Canonical: https://genetixbay.com/knowledge/answers/use-regular-plant-fertiliser.html - Topic: Nutrients · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Also asked as: Can I use tomato fertiliser for weed? | Is all-purpose plant food OK for cannabis? | Can I use slow-release fertiliser on cannabis? | Do I need special cannabis nutrients? | Can I use lawn fertiliser? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Yes, in soil. Cannabis roots take up [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md), potassium and the rest exactly as any crop does, so a complete garden fertiliser works if you dose it by element. All-purpose feeds suit veg, potassium-rich tomato feeds suit flower. Avoid weed-and-feed lawn products, and use fully soluble, complete salts in hydro. *Supported.* ## Why Plants absorb ions, not brands [1]. A "cannabis" bottle is a blend of the same salts sold for tomatoes and houseplants. What matters is the analysis. [NPK](https://genetixbay.com/knowledge/glossary/npk-ratio.md) percentages convert to dose: 1 g/L gives the element percentage × 10 in mg/L, after converting P2O5 × 0.44 and K2O × 0.83 [2]. Nitrogen is the main lever in veg. In a controlled cannabis trial, vegetative growth peaked at about 160 mg/L nitrogen [3]. Phosphorus has a ceiling: elevated root-zone phosphorus did not improve yield or quality [4], so a high-P "[bloom](https://genetixbay.com/knowledge/glossary/flowering-stage.md)" garden feed adds nothing. Garden feeds often skip calcium, magnesium or [micros](https://genetixbay.com/knowledge/glossary/micronutrient.md). Soft water or [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) then leaves a gap. ## The numbers | Product type | Typical use | Watch for | |---|---|---| | Complete soluble all-purpose (e.g. 20-20-20 + micros) | Veg in soil | High P relative to need | | Tomato feed (K-rich) | Flower in soil | Low N for veg; check Mg | | Controlled-release pellets | Soil, outdoor pots | Can't taper or adjust | | Lawn feed | Avoid | Herbicides, very high N | | Agricultural-grade granular salts | Soil only | Insoluble fillers in hydro | Targets: N ~150–200 mg/L in veg, P 30–60 mg/L, soil [feed EC](https://genetixbay.com/knowledge/glossary/input-ec.md) 0.8–1.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md). ## What to do 1. Read the label for Ca, Mg and micronutrients, not just NPK. 2. Convert to mg/L and compare with stage targets. 3. Start at half the label rate in soil and check [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md). 4. Switch from an all-purpose to a K-rich feed in flower. 5. In hydro and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), use complete fully soluble feeds only. ## Common mistakes - Using weed-and-feed lawn fertiliser. - Assuming a cannabis label means better chemistry. - Doubling up a garden feed on fertilised [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md). - Granular field fertiliser in a hydro reservoir. ## Related - Full article: [Building a cannabis feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Answers: [what NPK means](https://genetixbay.com/knowledge/answers/what-does-npk-mean.md) · [which nutrients to buy](https://genetixbay.com/knowledge/answers/which-nutrients-to-buy.md) · [kitchen scraps](https://genetixbay.com/knowledge/answers/kitchen-scraps-as-fertiliser.md) - Articles: [organic vs mineral](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md) - Terms: [mineral fertiliser](https://genetixbay.com/knowledge/glossary/mineral-fertiliser.md) · [NPK ratio](https://genetixbay.com/knowledge/glossary/npk-ratio.md) ## Follow-up questions **Is tomato feed good for cannabis in flower?** Tomato feed is a reasonable flowering feed for cannabis in soil. It is usually potassium-rich with moderate nitrogen, which suits flower. Check the label for magnesium and micronutrients, dose to about EC 0.8-1.6 mS/cm in soil, and add a calcium source if your water is soft. It is too low in nitrogen for veg. **Can I use slow-release fertiliser pellets on cannabis?** Controlled-release fertiliser pellets work for cannabis in soil and outdoor containers, mixed into the potting mix at planting at the label rate for container plants. They release nutrients with temperature and moisture, so you can't taper or adjust them quickly. Avoid them in coco, rockwool and hydro, where you need precise, adjustable feeding at every irrigation. **Why shouldn't I use lawn fertiliser on cannabis?** Avoid lawn fertiliser on cannabis because many products are weed-and-feed mixes containing broadleaf herbicides, which cannabis is very sensitive to. Plain lawn feeds are also very high in nitrogen, often with little phosphorus, magnesium or micronutrients, and some use urea or ammonium heavily. A complete general-purpose or tomato feed is safer. ## Sources 1. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 2. Waltz C, 2003. Know the numbers on a fertilizer bag. University of Georgia CAES Field Report. https://fieldreport.caes.uga.edu/?p=19743 3. Saloner A, Bernstein N, 2020. Response of medical cannabis (Cannabis sativa L.) to nitrogen supply under long photoperiod. Frontiers in Plant Science 11:572293. https://doi.org/10.3389/fpls.2020.572293 4. Westmoreland FM, Bugbee B, 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 --- # Can I use vinegar or lemon juice to lower pH? > You can, but you shouldn't: the idea that vinegar or lemon juice is a fine pH down is a Myth. In a hydroponic trial, vinegar cut yields of lettuce, basil and Swiss chard, and lime juice cut basil and chard yields, while a mineral pH down held pH most steadily with the least product. Kitchen acids are weak and rebound. Use phosphoric, nitric or sulfuric acid. - Canonical: https://genetixbay.com/knowledge/answers/vinegar-or-lemon-to-lower-ph.html - Topic: pH and EC · Type: Myth check - Evidence: Myth · Status: Draft: awaiting expert review - Full article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - Also asked as: Can I use vinegar as pH down? | Does lemon juice lower pH for plants? | Is citric acid a good pH down? | Natural pH down for cannabis | Homemade pH down - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer You can, but it's a poor choice, and the claim that it's a fine substitute for [pH](https://genetixbay.com/knowledge/glossary/ph.md) down is a *Myth*. In a hydroponic trial, vinegar reduced [yields](https://genetixbay.com/knowledge/glossary/yield.md) of all three crops tested and lime juice reduced two of three, while mineral pH down held pH most stably with the least product [1]. Use phosphoric, nitric or sulfuric acid. ## Why The only controlled comparison we know of grew lettuce, basil and Swiss chard in [ebb-and-flow](https://genetixbay.com/knowledge/glossary/ebb-and-flow.md) hydro at pH 5.5–6.5. Vinegar cut yields of all three; lime juice cut basil and chard but not lettuce; the phosphoric-acid pH down was the most stable and needed the least product [1]. No cannabis trial exists, but nothing suggests cannabis would react better. Organic acids are weak and short-lived. The water's bicarbonate neutralises acid as it goes [2], and microbes in the reservoir or medium eat citric and acetic acid, so pH rebounds (grower observation). What's left feeds biofilm. [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) is the real enemy. If pH keeps climbing, the fix is neutralising bicarbonate with a mineral acid, sized to the water report [2][3]. ## The numbers | Adjuster | pH stability | Plant effect (trial [1]) | Adds | |---|---|---|---| | Mineral [pH down (phosphoric)](https://genetixbay.com/knowledge/glossary/phosphoric-acid.md) | Best | No yield loss | P | | Lime or lemon juice (citric) | Short-lived | Lower yield in 2 of 3 crops | Carbon for microbes | | White vinegar (acetic) | Short-lived | Lower yield in 3 of 3 crops | Carbon for microbes | | Nitric or sulfuric acid | Good | Standard practice | N or S | **Verdict:** buy a mineral-acid pH down; kitchen acids cost yield and come back to bite. ## What to do 1. Buy horticultural pH down (phosphoric, nitric or sulfuric). 2. Add it after nutrients, a few drops per 10 L. 3. If pH won't hold, get a water report and treat alkalinity. 4. In an emergency, a small dose of citric acid once is tolerable in soil; replace it at the next feed. *Safety:* mineral acids burn. Gloves, goggles, and always add acid to water. ## Common mistakes - Dosing vinegar into a [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) reservoir and growing slime. - Treating pH rebound with more lemon juice. - Ignoring the alkalinity that caused the problem. - Forgetting that acids add nutrients. ## Related - Full article: [Water quality: alkalinity and acids](https://genetixbay.com/knowledge/ph-ec/water-quality.md) - Answers: [how to adjust pH](https://genetixbay.com/knowledge/answers/how-to-adjust-ph.md) · [do I need to pH?](https://genetixbay.com/knowledge/answers/do-i-need-to-ph-my-water.md) - Articles: [pH drift in hydro](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md) - Terms: [pH down](https://genetixbay.com/knowledge/glossary/ph-down.md) · [phosphoric acid](https://genetixbay.com/knowledge/glossary/phosphoric-acid.md) ## Follow-up questions **Why does pH go back up after adding lemon juice?** pH climbs back after lemon juice or vinegar because citric and acetic acids are weak organic acids that microbes in the reservoir or medium consume, and because the water's bicarbonate keeps buffering them. Once the acid is used up, pH rebounds and the sugars and organic matter left behind feed biofilm. Mineral acids are not consumed that way. **Is citric acid OK in soil?** A little citric acid in soil is unlikely to cause harm, because soil buffers pH and its microbes break citric acid down quickly. That is also why it does little good: the pH effect is short-lived. If hard water is pushing soil pH up, treat the water's alkalinity with a mineral acid or let the mix's buffer handle it. **What is the best pH down for cannabis?** The best pH down for cannabis is a dilute mineral acid matched to the stage: nitric or phosphoric acid in veg, phosphoric or sulfuric acid in flower and during a nitrogen taper. Each adds a nutrient (nitrogen, phosphorus or sulfur), so count it. Buy it diluted for horticulture, and wear gloves and eye protection. ## Sources 1. Singh H, Dunn B, Payton M, 2019. Hydroponic pH modifiers affect plant growth and nutrient content in leafy greens. Journal of Horticultural Research 27(1):31-36. https://doi.org/10.2478/johr-2019-0004 2. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf 3. NC State Extension. Producing conventional tobacco transplants in greenhouses: water quality. https://content.ces.ncsu.edu/producing-conventional-tobacco-transplants-in-greenhouses-water-quality --- # Should I water when the lights come on or before they go off? > Water cannabis soon after the lights come on, ideally within the first 1–3 hours. Plants transpire mostly in the light, so a morning watering is used during the day and the pot dries back overnight. Watering just before lights-off leaves a wet, cool pot in the dark, which slows dryback, raises humidity and favours fungus gnats and root rot. Drip-fed coco stops irrigating 2–6 hours before lights-off. - Canonical: https://genetixbay.com/knowledge/answers/water-at-lights-on-or-off.html - Topic: Systems · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Also asked as: What is the best time to water cannabis? | Can I water at night? | Is it bad to water at lights-off? | Water in the morning or evening indoors? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Water soon after the lights come on, ideally in the first 1–3 hours. The plant uses most of that water while the lights are on, and the pot dries back overnight. Watering right before lights-off leaves a wet, cool pot in the dark. *Grower practice*, based on how [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) works. ## Why Plants move water mainly by transpiration, and nearly all the water they take up leaves through the leaves [1]. Transpiration runs with light, when [stomata](https://genetixbay.com/knowledge/glossary/stomata.md) are open, and almost stops in the dark. A morning watering matches supply to demand. The plant draws the pot down through the day, and by lights-off the mix is already drying and pulling air back into the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). An evening watering does the opposite. The pot sits saturated through a cooler night when the plant barely drinks, and the extra evaporation raises tent humidity in the dark period. Constantly wet media favour [fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) larvae [2] and [Pythium root rot](https://genetixbay.com/knowledge/glossary/pythium.md) [3]. Night-time humidity adds bud-rot risk in flower. Drip-fed [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) follows the same logic with more precision: growers stop irrigating hours before lights-off so the substrate dries back overnight [4]. ## The numbers | System | When to water | Notes | |---|---|---| | Soil, hand-watered | First 1–3 h after lights-on | Lift the pot first | | Coco, hand-watered | First 1–3 h; second watering by midday if needed | Never let it dry fully | | Coco or [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), drip (vegetative steer) | First shot 0.5–1.5 h after lights-on; last 2–3 h before lights-off | Grower practice [4] | | Coco or rockwool, drip (generative steer) | First shot 2–3 h after lights-on; last 4–6 h before lights-off | Grower practice [4] | | Emergency wilt | Any time | Small amount, then normal routine | ## What to do 1. Check pots at the same time every day, just after lights-on. 2. Water the ones that are light; leave the heavy ones. 3. Bring water to room temperature, 18–22 °C (64–72 °F). 4. If you only get home in the evening, shift the light schedule so lights-on matches when you're there. 5. On drip, set the last shot well before lights-off. ## Common mistakes - Watering at lights-off because that's when you remember. - Leaving pots in saucers of [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) overnight. - Mistaking normal night-time leaf droop for thirst. ## Related - Full article: [Drooping: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Answers: [how often to water](https://genetixbay.com/knowledge/answers/how-often-to-water.md) · [how much water per day](https://genetixbay.com/knowledge/answers/how-much-water-per-day.md) · [leaves droop at night](https://genetixbay.com/knowledge/answers/leaves-droop-at-night.md) - Systems: [crop steering](https://genetixbay.com/knowledge/systems/drain-to-waste-crop-steering.md) - Terms: [dryback](https://genetixbay.com/knowledge/glossary/dryback.md) ## Follow-up questions **Is it bad to water just before lights-off?** Watering just before lights-off isn't an emergency, but it is the worst routine time. Plants close their stomata in the dark and use little water, so the pot stays saturated through the cool night period, roots get less air and humidity in the tent rises. Over many weeks that favours fungus gnats, root rot and bud rot. Move the watering to the first hours after lights-on. **Can I water during the dark period if my plant is wilting?** Yes. If a plant is badly wilted from a dry pot, water it now, whatever the light schedule, using a small amount slowly and topping up at lights-on. Use a dim green light or open the tent briefly; a short look won't harm flowering. Then move your routine so the pot is checked and watered in the first hours of the light period. **When should the last irrigation be in coco?** In drip-fed coco or rockwool, the last irrigation of the day usually comes 2–3 hours before lights-off for vegetative steering and 4–6 hours before for generative steering, so the substrate dries back overnight. These timings are grower practice adapted from greenhouse crop steering. Hand-watered coco should simply be watered early in the light period. ## Sources 1. Douglas R, 2022. Ways to calculate water use and transpiration rates for indoor cannabis cultivation. Greenhouse Grower. https://www.greenhousegrower.com/?p=157955 2. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ 3. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 4. Greenhouse Grower. The details behind crop steering in cannabis production. https://www.greenhousegrower.com/production/the-details-behind-crop-steering-in-cannabis-production/ --- # Why does water run straight through or pool on top of my pot? > Water runs straight through a pot when the mix has dried out, shrunk from the wall and turned water-repellent, so water channels down the sides and out the bottom while the root ball stays dry. Water pools on top when the surface is crusted or compacted, the mix is too fine, or drainage holes are blocked. Fix both by watering slowly in 2–3 passes or bottom-soaking for 20–30 minutes. - Canonical: https://genetixbay.com/knowledge/answers/water-runs-through-or-pools.html - Topic: Systems · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Also asked as: Why is water not soaking into my soil? | Is my soil hydrophobic? | Why is water pooling on top of my soil? | Water runs out the bottom straight away - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Water runs straight through when the mix has dried out, shrunk from the pot wall and turned water-repellent: water channels down the gap and out of the holes while the root ball stays dry. Water pools on top when the surface is crusted or compacted, the mix is too fine, or the [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) holes are blocked. Water slowly in 2–3 passes, or bottom-soak for 20–30 minutes. *Grower practice*, grounded in container physics. ## Why [Peat](https://genetixbay.com/knowledge/glossary/peat.md) and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) are easy to wet when moist and hard to wet when [bone dry](https://genetixbay.com/knowledge/glossary/over-drying.md). Once dry, they shrink away from the wall and leave a channel [1]. Water takes the easy path down the channel and out, so you see runoff while the middle stays dry. Pooling is the opposite problem: water can't get in. Fine, compacted mixes with too little [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) drain slowly and stay saturated for days [1]. A pot that stays [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) starves roots of oxygen and favours [Pythium root rot](https://genetixbay.com/knowledge/glossary/pythium.md) [2] and [fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) larvae [3]. So persistent pooling is worth fixing, not just waiting out. ## The numbers | Sign | Likely cause | Fix | |---|---|---| | Instant runoff, pot still light | Mix dried and shrunk from wall | Slow passes, or bottom-soak 20–30 min | | Gap visible at the pot edge | Shrinkage | Press the edge down; water slowly | | Water sits on top for minutes | Crust or compaction | Loosen top 1 cm; water slower | | Pooling every time, heavy pot for days | Mix too dense | 20–35% [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) next run | | Runoff never appears | Blocked holes or standing saucer | Clear holes; empty saucer within 30 min | ## What to do 1. Lift the pot after watering. Light means the water didn't stay; heavy means it did. 2. For a dry pot, water a little over the whole surface, wait five minutes, and repeat 2–3 times. 3. If that fails, stand the pot in 3–5 cm of pH-adjusted water for 20–30 minutes, then drain. 4. For pooling, loosen the surface gently with a fork and clear the drainage holes. 5. Next run, mix 20–35% perlite through the mix and don't let peat or coco dry out completely. ## Common mistakes - Reading runoff as proof the pot is wet. - Letting coco dry out fully "to make roots search". - Adding a gravel layer to fix pooling, instead of a better mix. ## Related - Full article: [Drooping: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Answers: [how often to water](https://genetixbay.com/knowledge/answers/how-often-to-water.md) · [gravel in the bottom of pots](https://genetixbay.com/knowledge/answers/gravel-in-bottom-of-pots.md) · [fabric vs plastic pots](https://genetixbay.com/knowledge/answers/fabric-pots-vs-plastic-pots.md) - Terms: [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) · [field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md) ## Follow-up questions **How do I rewet bone-dry soil or coco?** Rewet bone-dry soil or coco slowly. Pour a small amount over the whole surface, wait five minutes, and repeat two or three times until the mix darkens and swells back against the pot wall. For a badly dried pot, stand it in a tray of pH-adjusted water 3–5 cm deep for 20–30 minutes, then drain fully. Lift the pot to confirm it is heavy again. **Why does water pool on my soil?** Water pools on soil when the surface has crusted or compacted, the mix is too fine and short of perlite, or the drainage holes are blocked by roots or a saucer full of runoff. Gently loosen the top centimetre with a fork, clear the holes, and water more slowly. If pooling persists every watering, the mix itself is too dense: add more perlite next time. **Is it a problem if water runs straight out the bottom?** Yes. Water running straight out the bottom means the root zone isn't getting wet, so the plant can be underwatered while runoff makes it look well watered. It also means runoff readings are unreliable, because the water hasn't passed through the mix. Lift the pot after watering: if it is still light, the mix didn't take the water. ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container media physics and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 2. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 3. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ --- # Why are my stems weak and floppy? > Weak, floppy cannabis stems usually come from too little light, which makes plants stretch, and too little air movement, because stems thicken in response to being moved. Give seedlings and veg plants enough light, run a fan so leaves flutter gently at about 0.3–1.0 m/s, and support heavy flowering branches with a trellis or stakes. If the whole plant wilts, check the watering first. - Canonical: https://genetixbay.com/knowledge/answers/weak-floppy-stems.html - Topic: Diagnosis · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) - Also asked as: Why are my cannabis stems so weak? | My plant keeps falling over | Thin, stretchy stems on seedlings | Branches can't hold the buds up - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Weak, floppy cannabis stems usually mean the plant has too little light and too little air movement. Low light makes plants [stretch](https://genetixbay.com/knowledge/glossary/stretch.md), and still air gives them no reason to thicken their stems. Run a fan so the leaves flutter gently, at about 0.3–1.0 m/s, give the plant enough light, and support heavy branches in flower. *Supported*. ## Why Plants build stronger stems when they are moved. Repeated bending and shaking triggers thigmomorphogenesis, a well-described response that gives shorter, thicker stems [1]. A plant grown in still air never gets that signal. Moving air helps in other ways too. It thins the still layer of air around each leaf, and in research on other crops, raising air speed over the canopy from 0.1 to 1.0 m/s roughly doubled canopy [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) [2]. It also dries the pockets where moulds start [3]. Low light causes stretch: long [internodes](https://genetixbay.com/knowledge/glossary/internode.md) and thin stems as the plant reaches for the lamp. In flower, even a well-grown stem can bend under heavy [colas](https://genetixbay.com/knowledge/glossary/cola.md), which is normal and needs support rather than a fix. ## The numbers | Item | Target | |---|---| | Leaf-level air speed | 0.3–1.0 m/s (60–200 ft/min); leaves flutter, never whip | | [Circulation fans](https://genetixbay.com/knowledge/glossary/oscillating-fan.md) | Running 24 h, including lights-off | | [Fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) in flower | One above and one below the canopy | | Support in flower | [Trellis](https://genetixbay.com/knowledge/glossary/trellis.md) or stakes set by week 3–4 of flower | ## What to do 1. Rule out wilting first. If the leaves droop too, lift the pot and check the watering. 2. Add an oscillating fan blowing across the plants, not straight down onto them. 3. Check the light. Stretched [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) need the lamp closer or brighter, within seedling levels. 4. Bury stretched [seedling stems](https://genetixbay.com/knowledge/glossary/hypocotyl.md) deeper at [transplant](https://genetixbay.com/knowledge/glossary/transplanting.md). 5. In veg, gentle daily bending or [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md) toughens the stems. 6. Before buds get heavy, set a trellis net or stakes with [soft ties](https://genetixbay.com/knowledge/glossary/plant-ties.md). ## Common mistakes - No fan at all in a small tent. - One strong fan blasting the plants from one side. - Keeping seedlings under a dome in still air for too long. - Adding support only after the branches have snapped. ## Related - Full article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) - Answers: [bigger, denser buds](https://genetixbay.com/knowledge/answers/how-to-get-bigger-denser-buds.md) · [why is my seedling drooping?](https://genetixbay.com/knowledge/answers/why-is-my-seedling-drooping.md) - Articles: [stretching](https://genetixbay.com/knowledge/diagnosis/stretching.md) · [drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) - Terms: [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md) · [trellis](https://genetixbay.com/knowledge/glossary/trellis.md) ## Follow-up questions **Does a fan make cannabis stems stronger?** Yes, a fan helps make cannabis stems stronger. Plants respond to being bent and shaken (thigmomorphogenesis) by growing shorter, thicker stems, a response documented across plant species. Gentle circulation of about 0.3–1.0 m/s at leaf level, enough to make leaves flutter, also dries the canopy. Avoid a strong fan blasting one side, which causes windburn rather than strength. **Why are my seedlings tall and floppy?** Cannabis seedlings go tall and floppy when light is too weak or too far away, so they stretch towards it, often in still, humid air under a dome. Bring the light closer or raise its intensity within seedling levels, add a gentle fan, and bury the stretched stem deeper at transplant. Cannabis stems can be buried up to the first leaves. **How do I hold up heavy buds?** Hold up heavy cannabis buds with a trellis net over the canopy, bamboo stakes with soft ties, or yo-yo hangers, set before the buds get heavy in mid flower. Supported colas also keep air moving between them, which lowers bud-rot risk. Supercropping stems in veg or early flower, a house-endorsed grower practice, leaves a thick knuckle that carries weight well. ## Sources 1. Chehab EW, Eich E, Braam J, 2009. Thigmomorphogenesis: a complex plant response to mechano-stimulation. Journal of Experimental Botany 60(1):43–56. https://doi.org/10.1093/jxb/ern315 2. Kitaya Y, Tsuruyama J, Shibuya T, Yoshida M, Kiyota M, 2003. Effects of air current speed on gas exchange in plant leaves and plant canopies. Advances in Space Research 31(1):177–182. https://www.science.gov/topicpages/a/air+current+speed 3. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # What are pistils? > Pistils are the female reproductive organs of cannabis flowers. The white or coloured 'hairs' growers call pistils are strictly the stigmas: each female flower has two, sticking out of its bract to catch pollen. They appear first at the nodes as preflowers, then by the hundred in buds, and darken through orange or brown with age, heat or pollination. Judge harvest by trichomes, not pistil colour. - Canonical: https://genetixbay.com/knowledge/answers/what-are-pistils.html - Topic: Basics · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - Also asked as: Pistils meaning | White hairs on buds | Stigmas on cannabis | Why are my pistils turning orange? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) is the female part of a flower: ovary, style and [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md). On cannabis, the white or coloured "hairs" growers call pistils are the stigmas, two per flower, reaching out of the [bract](https://genetixbay.com/knowledge/glossary/bract.md) to catch pollen. They darken with age. *Established* botany. ## Why Each [female flower](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) is simple. One ovary sits inside a small leafy bract (the "[calyx](https://genetixbay.com/knowledge/glossary/calyx.md)" to growers), topped by two long stigmas [2]. A [pollinated](https://genetixbay.com/knowledge/glossary/pollination.md) flower makes a single seed. Pistils show sex first. Single flowers form at the nodes once the plant matures; in one cultivar the first pair appeared at the 7th node, whatever the [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md) [3]. Paired white hairs at a node mean female. Clusters of pistils mark real flowering. On photoperiod plants, at least three pairs of pistils at the top of the main shoot is the research definition of flowering onset, usually 8–14 days after short days begin [1]. The resin isn't on the hairs. Glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md), densest on the bracts, make the [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) and [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) [4]. That's why trichome maturity, not stigma colour, is the better harvest clock. ## The numbers | Stage | What pistils look like | |---|---| | [Preflower](https://genetixbay.com/knowledge/glossary/pre-flower.md) (~4–6 weeks from seed) | One pair of white hairs at a node | | Onset of flower (~10–14 days after flip) | 3+ pairs clustered at the top | | Mid flower | Masses of fresh white stigmas | | Late flower | Most curled, orange, red or brown | | Pollinated flower | Withers and browns within days | ## What to do 1. Use paired white hairs at the nodes to identify females. 2. Log the day pistils cluster at the top as day 1 of flower. 3. Treat sudden, early browning as a stress clue: check heat and [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md). 4. Decide harvest with a 60x [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) on the [trichome heads](https://genetixbay.com/knowledge/glossary/trichome-heads.md). ## Common mistakes - Harvesting by pistil colour alone. - Calling the bract and stigmas "the pistil" and expecting resin there. - Confusing stipules at the nodes with preflowers. ## Related - Full article: [Cannabis plant biology](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - Answers: [pistils browning early](https://genetixbay.com/knowledge/answers/pistils-turning-brown-early.md) · [checking trichomes](https://genetixbay.com/knowledge/answers/how-to-check-trichomes.md) · [when plants show sex](https://genetixbay.com/knowledge/answers/when-do-plants-show-sex.md) - Article: [Trichome ripeness](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Terms: [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) · [stigma](https://genetixbay.com/knowledge/glossary/stigma.md) · [bract](https://genetixbay.com/knowledge/glossary/bract.md) ## Follow-up questions **When do pistils first appear?** Pistils first appear as single preflowers at the nodes once a cannabis plant matures, usually about 4–6 weeks from seed under long days, and around the 7th node in one study. On a photoperiod plant, clusters of pistils at the top of the main shoot appear about 10–14 days after the switch to 12/12, marking the real start of flower. **Why are my pistils turning brown?** Cannabis pistils turn brown or orange as the flowers age, which is normal in the last weeks of flower. They also darken early from heat, low humidity, handling, sprays or pollination, which withers the stigmas of fertilised flowers within days. Browning on its own is a weak harvest guide; check trichome heads with a 60x loupe instead. **Should I harvest when 70% of pistils are brown?** 'Harvest when 70–90% of pistils are brown' is a rough rule, not a reliable one, because pistil colour also changes with heat, handling, humidity and cultivar. GenetixBay judges harvest by trichome heads: a few clear, mostly cloudy and some amber is a good mix, with the exact balance a matter of preference. ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 3. Spitzer-Rimon B, Shafran-Tomer H, Gottlieb GH, et al. 2022. Non-photoperiodic transition of female cannabis seedlings from juvenile to adult reproductive stage. Plant Reproduction 35(4):265-277. https://doi.org/10.1007/s00497-022-00449-0 4. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 --- # What are terpenes in cannabis? > Terpenes are the volatile aroma compounds cannabis makes in its glandular trichomes, alongside cannabinoids; myrcene, limonene, caryophyllene, pinene and terpinolene are common. Total terpenes average about 2% of flower weight. In nearly 90,000 US lab results, THC-dominant flower fell into three terpene groups. The 'gas' smell comes mostly from trace sulfur compounds, not terpenes. Terpenes evaporate, so drying and storage matter. - Canonical: https://genetixbay.com/knowledge/answers/what-are-terpenes.html - Topic: Basics · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) - Also asked as: What do terpenes do? | Terpenes meaning | Why does weed smell? | What are the main terpene profiles in cannabis? | Does irradiation destroy terpenes? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) are the volatile compounds that give cannabis most of its smell and taste: [myrcene](https://genetixbay.com/knowledge/glossary/myrcene.md), [limonene](https://genetixbay.com/knowledge/glossary/limonene.md), [β-caryophyllene](https://genetixbay.com/knowledge/glossary/beta-caryophyllene.md), [pinene](https://genetixbay.com/knowledge/glossary/alpha-pinene.md), [terpinolene](https://genetixbay.com/knowledge/glossary/terpinolene.md) and many more. The plant makes them in its glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md), alongside [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). Total terpenes average about 2% of flower weight. *Established* chemistry. ## Why Terpenes are made in the resin glands. Terpene synthase enzymes in the trichomes build [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) (10 carbons, lighter and more volatile) and [sesquiterpenes](https://genetixbay.com/knowledge/glossary/sesquiterpene.md) (15 carbons, heavier) from shared precursors [1]. Which synthase genes a plant carries largely sets its profile [1][5]. Commercial flower clusters into a few profiles. In 89,923 US lab results, THC-dominant flower fell into three terpene groups: caryophyllene–limonene, myrcene–pinene and terpinolene–myrcene, with the first two holding 87.4% of samples [2]. Not every smell is a terpene. The fuel-like "gas" note comes mostly from trace prenylated [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) compounds, detected at tiny levels [3]. Terpenes are fragile. Monoterpenes evaporate and oxidise with heat, air and time. [Gamma irradiation](https://genetixbay.com/knowledge/glossary/irradiation.md) cut some volatile monoterpenes by 10–20%, up to 38% for one compound [4]; slow drying and cool, dark, airtight storage keep more. Labels track terpenes loosely. "Indica" and "sativa" tags associate with a few terpenes, not with genome-wide ancestry [5]. ## The numbers | Terpene | Class | Common aroma | |---|---|---| | Myrcene | Monoterpene | Earthy, musky | | Limonene | Monoterpene | Citrus | | α- and β-pinene | Monoterpene | Pine | | Terpinolene | Monoterpene | Fresh, herbal, "haze" | | β-caryophyllene | Sesquiterpene | Pepper, spice | | Humulene | Sesquiterpene | Woody, hoppy | | Total terpenes | — | ~2% of flower weight on average | ## What to do 1. Read the terpene section of a [certificate of analysis](https://genetixbay.com/knowledge/glossary/coa.md), not just [THC](https://genetixbay.com/knowledge/glossary/thc.md). 2. Dry slowly, about 18–21 °C (64–70 °F) and 55–62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) for 7–14 days. 3. Cure and store in full, airtight, dark jars; skip [humidity packs](https://genetixbay.com/knowledge/glossary/humidity-pack.md), which rob terpenes. 4. Pheno-hunt by nose and keep unusual profiles. ## Common mistakes - Assuming a terpene predicts an effect. Effects are reported, not promised. - Fast, warm drying that drives off monoterpenes. - Believing very high total-terpene claims without a lab name and date. ## Related - Full article: [Why everything tastes the same](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md) - Answers: [why buds lose their smell](https://genetixbay.com/knowledge/answers/buds-lost-their-smell.md) · [strain vs cultivar](https://genetixbay.com/knowledge/answers/strain-vs-cultivar.md) - Article: [Irradiated cannabis](https://genetixbay.com/knowledge/harvest-cure/irradiated-cannabis.md) - Terms: [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) · [terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md) · [volatile sulfur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) ## Follow-up questions **What are the main terpene profiles in cannabis?** The main terpene profiles in commercial THC-dominant cannabis are three groups found in a 2022 study of US lab data: caryophyllene–limonene, myrcene–pinene and terpinolene–myrcene. The first two held 87.4% of samples, and terpinolene-led flower was the smallest group. Rarer dominants include ocimene and the sesquiterpene alcohols guaiol and eudesmols. **Does irradiation destroy terpenes?** Irradiation does not destroy terpenes, but it can reduce them. Some studies found no significant terpene change, while others measured 10–20% losses of volatile monoterpenes such as myrcene, ocimene and terpinolene, up to 38% for one compound, with sesquiterpenes barely changing. In one study, months of normal storage cost more terpenes than the treatment did. **Do terpenes change the effects of cannabis?** Whether terpenes change the effects of cannabis is not settled. Aroma is linked with reported subjective effects in some consumer studies, and 'indica' and 'sativa' labels track only a few terpenes, not effects. No controlled evidence shows a given terpene reliably produces a given effect, so treat terpene-based effect claims as reported experience, not a promise. ## Sources 1. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa – From plant genome to humans. Plant Science 284:67-72. https://doi.org/10.1016/j.plantsci.2019.03.022 2. Smith CJ, Vergara D, Keegan B, Jikomes N. 2022. The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE 17(5):e0267498. https://doi.org/10.1371/journal.pone.0267498 3. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196 4. Hazekamp A. 2016. Evaluating the effects of gamma-irradiation for decontamination of medicinal cannabis. Frontiers in Pharmacology 7:108. https://doi.org/10.3389/fphar.2016.00108 5. Watts S, McElroy M, Migicovsky Z, et al. 2021. Cannabis labelling is associated with genetic variation in terpene synthase genes. Nature Plants 7:1330-1334. https://doi.org/10.1038/s41477-021-01003-y --- # What can I safely spray on plants in flower? > On cannabis in flower, the safe default is to spray nothing on buds. Stop oils, soaps, sulfur and bicarbonates by the first 2–3 weeks of flower; after that, wet buds invite botrytis and residues stay in the product. Outdoors, Bt for small caterpillars is one of the few options, only where registered for cannabis. Otherwise rely on beneficials, removal and climate, and harvest early if needed. - Canonical: https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.html - Topic: Pests · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - Also asked as: What can I spray during flowering? | Is it safe to spray buds? | What is the last day to spray in flower? | Can I foliar spray in flower? | Spray for pests in late flower - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Once buds are forming, the safe default is to spray nothing on them. Finish oils, soaps, [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) and bicarbonates by the first 2–3 weeks of flower. After that, control pests with [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md), removal and climate, and harvest early if a problem is severe. *Supported* for the bud-rot risk; the cut-off week is *Grower practice*. ## Why Wet buds rot. [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md) grows where free water sits on flower tissue, and a dense [cola](https://genetixbay.com/knowledge/glossary/cola.md) can stay wet for hours [1]. Residues stay in the product. Contact sprays work only by coating the target [4], so on flowers they coat the resin. Regulated producers may use only products registered for cannabis, within residue limits and on label terms [3]. Some biologicals are the exception, outdoors. Bt must be eaten by young caterpillars and breaks down in sunlight in under a week, which is why it is used in flower against [budworm](https://genetixbay.com/knowledge/glossary/corn-earworm.md) where permitted [2]. Disinfectants never go on plants. They are for tools, surfaces and water. ## The numbers | Spray | Veg | Flower weeks 1–3 | Flower week 4 onward | |---|---|---|---| | Oils, [neem](https://genetixbay.com/knowledge/glossary/neem-oil.md), soaps | Yes, if registered | Early only | No | | Sulfur, bicarbonates | Yes, if registered | Early only | No | | Bt (caterpillars, outdoors) | Yes, if registered | Where registered | Only where label and law allow | | Plain water, home remedies | Veg only | No | No | | Disinfectants (bleach, [peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md)) | Never on plants | Never | Never | ## What to do 1. Do your spraying in veg, so pest numbers are low at the flip. 2. Make the last oil or sulfur pass by flower week 2–3. 3. In flower, release predators, cut out infested leaves and bud sections, and bag them. 4. Outdoors, if you use Bt, spray early morning so buds dry by evening. 5. If late-flower damage is severe, harvest early rather than spray. 6. Check local registration and follow the label; rules vary. ## Common mistakes - Spraying at lights-off and leaving buds wet all night. - Assuming "organic" means residue-free. - Washing buds on the plant with water or peroxide. - Raising humidity in late flower to slow [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md). ## Related - Full article: [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - Answers: [Neem oil in flower](https://genetixbay.com/knowledge/answers/neem-oil-in-flower.md) · [Milk or baking soda for mildew](https://genetixbay.com/knowledge/answers/home-remedies-for-powdery-mildew.md) - Articles: [Botrytis bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) · [Caterpillars](https://genetixbay.com/knowledge/pests/caterpillars.md) - Terms: [contact vs systemic](https://genetixbay.com/knowledge/glossary/contact-vs-systemic.md) · [Bt](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md) ## Follow-up questions **When is the last day I can spray in flower?** The last day to spray cannabis with oils, soaps, sulfur or bicarbonates is around the end of the first 2–3 weeks of flower, which is grower consensus rather than a universal rule. After that, residues land on the buds you will consume. Product labels set their own pre-harvest intervals and registration varies by jurisdiction, so the label and local rules always win. **Can I spray Bt on buds for caterpillars?** Bt (Bacillus thuringiensis subsp. kurstaki or aizawai) is one of the few biological options listed for hemp in some US states, and it works on caterpillars only when they eat it. It breaks down in sunlight in under a week. Whether it is allowed on cannabis in flower depends on where you live. Spray early in the day so buds dry before night. **Can I spray plain water on buds?** Avoid spraying plain water on cannabis buds in flower. Free water sitting in dense colas is exactly what botrytis needs, and raising humidity in late flower costs more than any benefit. To clean dust or pests off flowering plants, remove affected leaves or branches instead. Mist only in veg, if at all, and keep flowering-room humidity at 40–50% in mid to late flower. ## Sources 1. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker 2. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp 3. Health Canada. Pest control products for use on cannabis. Government of Canada. https://www.canada.ca/en/health-canada/services/cannabis-regulations-licensed-producers/pest-control-products.html 4. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html --- # What does N-P-K mean on a fertiliser label? > N-P-K on a fertiliser label is the guaranteed percentage by weight of nitrogen (N), phosphate (P2O5) and potash (K2O). Only the N figure is the actual element. Multiply the middle number by 0.44 for elemental phosphorus and the last by 0.83 for potassium, so a 10-10-10 holds 10% N, about 4.4% P and 8.3% K. Cannabis feed targets and research use elements in mg/L, not oxides. - Canonical: https://genetixbay.com/knowledge/answers/what-does-npk-mean.html - Topic: Nutrients · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Also asked as: What do the NPK numbers mean? | What is a 10-10-10 fertiliser? | P2O5 vs P: what's the difference? | How do I convert NPK to ppm? | Is the middle number on the bottle phosphorus? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [N-P-K](https://genetixbay.com/knowledge/glossary/npk-ratio.md) is the guaranteed percentage by weight of nitrogen, [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) (P2O5) and potash (K2O) in the product. Only nitrogen is reported as the element. Multiply the middle number by 0.44 to get phosphorus and the last by 0.83 to get potassium [1]: a 10-10-10 is 10% N, about 4.4% P and 8.3% K. *Established.* ## Why Labels report phosphorus and potassium as oxides by convention and, in many places, by law [1]. That inflates the last two numbers. Plants take up ions, not oxides, and nutrient science works in elements [2]. A fertiliser's percentage tells you dose directly: 1 g/L of any product supplies (percentage × 10) mg/L of each element [2]. That is how you compare a bottle with the element targets in a [feed chart](https://genetixbay.com/knowledge/glossary/feed-chart.md). NPK also says nothing about calcium, magnesium, [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) or [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md), which a complete cannabis feed needs. And the middle number has a ceiling: cannabis trials found a flower phosphorus optimum near 59 mg/L, with no gain from more [3]. ## The numbers | Label | Elemental N % | Elemental P % | Elemental K % | At 1 g/L (mg/L N / P / K) | |---|---|---|---|---| | 10-10-10 | 10 | 4.4 | 8.3 | 100 / 44 / 83 | | 20-20-20 | 20 | 8.7 | 16.6 | 200 / 87 / 166 | | [0-52-34](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) (MKP) | 0 | 22.8 | 28.7 | 0 / 228 / 287 | | [13-0-46](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md) (potassium nitrate) | 13 | 0 | 38 | 130 / 0 / 380 | ## What to do 1. Read the [guaranteed analysis](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md), not the marketing name. 2. Convert P2O5 × 0.44 and K2O × 0.83. 3. Multiply each element percentage by 10 for mg/L per 1 g/L (or per 1 mL/L for liquids, adjusted for density). 4. Compare with the stage targets in the feed article. 5. Check the label for Ca, Mg, S and micros as well. ## Common mistakes - Reading the middle number as elemental phosphorus. - Choosing a [bloom](https://genetixbay.com/knowledge/glossary/flowering-stage.md) product by the biggest middle number. - Ignoring calcium and magnesium because they aren't in the three numbers. - Forgetting that liquid percentages are by weight, not volume. ## Related - Full article: [Building a cannabis feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Answers: [macro vs micronutrients](https://genetixbay.com/knowledge/answers/macro-vs-micronutrients.md) · [garden fertiliser on cannabis](https://genetixbay.com/knowledge/answers/use-regular-plant-fertiliser.md) - Terms: [NPK ratio](https://genetixbay.com/knowledge/glossary/npk-ratio.md) · [elemental ppm](https://genetixbay.com/knowledge/glossary/elemental-ppm.md) ## Follow-up questions **How do I convert an NPK label to ppm?** To convert an NPK label to ppm, first turn the oxides into elements: phosphorus = P2O5 x 0.44 and potassium = K2O x 0.83; nitrogen needs no conversion. Then 1 g of product per litre gives the element's percentage x 10 in mg/L. A 20-20-20 powder at 1 g/L supplies about 200 mg/L N, 87 mg/L P and 166 mg/L K. **What is a good NPK ratio for flowering cannabis?** Rather than an NPK ratio, aim for element targets: in mid flower about 140-190 mg/L nitrogen, 40-60 mg/L phosphorus and 200-280 mg/L potassium. Controlled cannabis trials found no yield gain above about 60 mg/L phosphorus, so high-middle-number bloom formulas add little. Calcium, magnesium and sulfur, which NPK numbers ignore, matter as much. **Why do labels use P2O5 and K2O instead of P and K?** Fertiliser labels use P2O5 and K2O because early fertiliser chemists reported phosphorus and potassium as oxides, and fertiliser laws in many places still require it. It makes the middle and last numbers look larger than the real element content: P2O5 is only about 44% phosphorus and K2O about 83% potassium. ## Sources 1. Waltz C, 2003. Know the numbers on a fertilizer bag. University of Georgia CAES Field Report. https://fieldreport.caes.uga.edu/?p=19743 2. Sonneveld C, Voogt W, 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6 3. Bevan L, Jones M, Zheng Y, 2021. Optimisation of nitrogen, phosphorus, and potassium for soilless production of Cannabis sativa in the flowering stage using response surface analysis. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 --- # What is a node on a cannabis plant? > A node on a cannabis plant is the point on a stem where a leaf and its axillary bud attach; branches, flowers, preflowers and clone roots all start there. The stem between two nodes is the internode. Count nodes upward from the cotyledons, which are not counted. Topping is usually done above the 3rd to 5th node, and preflowers often appear around the 4th to 7th. - Canonical: https://genetixbay.com/knowledge/answers/what-is-a-node.html - Topic: Basics · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Cannabis plant biology: the parts and what they do](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - Also asked as: What is a node? | Nodes and internodes | How to count nodes | Where are the nodes on a weed plant? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A node is the point on a cannabis stem where a leaf attaches, with an [axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md) tucked in the angle between [leaf stalk](https://genetixbay.com/knowledge/glossary/petiole.md) and stem. Branches, flowers and clone roots all start at nodes. The stem between two nodes is the [internode](https://genetixbay.com/knowledge/glossary/internode.md). *Established* botany. ## Why Each node is a growth point. A cannabis node carries a leaf on its petiole, an axillary bud that can become a branch, and a pair of small stipules [1][3]. Remove the tip and the buds at the nodes below take over, which is how topping works. Nodes are where the first flowers appear. Single flowers form at the nodes once the plant matures; in one cultivar the first pair appeared at the 7th node, whatever the [day length](https://genetixbay.com/knowledge/glossary/photoperiod.md) [2]. In flower, every node on a productive branch becomes a [bud site](https://genetixbay.com/knowledge/glossary/bud-site.md) [1]. Node pattern shows maturity. Young plants grow opposite nodes; mature and flowering shoots shift towards alternate nodes [1]. Internode length shows growing conditions. [Short internodes](https://genetixbay.com/knowledge/glossary/node-stacking.md) mean compact plants and stacked buds; long ones mean weak light or the post-flip [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). ## The numbers | Item | Typical value | |---|---| | Counting start | [First true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) = node 1 ([cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) not counted) | | Topping height | Above the 3rd–5th node | | First [preflowers](https://genetixbay.com/knowledge/glossary/pre-flower.md) | ~4th–7th node | | Internode, compact plant | ~2–5 cm (1–2 in) | | Internode, stretchy plant | 10 cm (4 in) or more | | Clone cutting | 2–3 nodes, one buried or just above the cut | ## What to do 1. Find node 1 at the first true leaves and count up the main stem. 2. Top or start [LST](https://genetixbay.com/knowledge/glossary/lst.md) once there are 4–6 nodes. 3. Check the upper nodes with a [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) for preflowers from about week 4. 4. Take clone cuts with 2–3 nodes; roots form best near a node. 5. If internodes are long and gappy, check light intensity first. ## Common mistakes - Counting the cotyledons as node 1. - Mistaking stipules at a node for preflowers. - Blaming genetics for long internodes under a weak light. ## Related - Full article: [Cannabis plant biology](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - Answers: [recovery after topping](https://genetixbay.com/knowledge/answers/recovery-after-topping.md) · [fan leaves vs sugar leaves](https://genetixbay.com/knowledge/answers/fan-leaves-vs-sugar-leaves.md) - Article: [Topping](https://genetixbay.com/knowledge/training/topping.md) - Terms: [node](https://genetixbay.com/knowledge/glossary/node.md) · [internode](https://genetixbay.com/knowledge/glossary/internode.md) · [axillary bud](https://genetixbay.com/knowledge/glossary/axillary-bud.md) ## Follow-up questions **How do I count nodes on a cannabis plant?** Count cannabis nodes from the bottom up, starting with the first pair of true leaves as node 1. The round seed leaves, the cotyledons, aren't usually counted. Each place where a pair of leaves, or later a single leaf, joins the stem is the next node. Count only the main stem when someone says 'top above the 5th node'. **What is an internode?** An internode is the length of stem between two adjacent nodes. Short internodes, about 2–5 cm on compact plants, mean tight bud stacking; long ones, 10 cm or more, mean stretch. Low light, a high far-red share and warmer days than nights lengthen them; stronger light and training keep them short. Most cultivars' internodes lengthen in the first weeks after the flip. **Why do nodes switch from opposite to alternate?** Young cannabis grows opposite nodes, with two leaves facing each other at each node. As the plant matures, new nodes switch to alternate, one leaf per node in a staggered pattern. The switch is a sign the plant has reached its adult stage, when preflowers appear and it can respond to long nights by flowering. ## Sources 1. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 2. Spitzer-Rimon B, Shafran-Tomer H, Gottlieb GH, et al. 2022. Non-photoperiodic transition of female cannabis seedlings from juvenile to adult reproductive stage. Plant Reproduction 35(4):265-277. https://doi.org/10.1007/s00497-022-00449-0 3. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 --- # What is schwazzing? > Schwazzing is an aggressive defoliation schedule that strips almost every fan leaf at the start of flower and again around day 21. Proponents say it pushes light into bud sites; no controlled cannabis trial shows it raises yield or cannabinoids. GenetixBay's position is tuck, don't pluck: strip within reason if you must, never on stressed plants or autoflowers. - Canonical: https://genetixbay.com/knowledge/answers/what-is-schwazzing.html - Topic: Training · Type: Definition - Evidence: Contested · Status: Draft: awaiting expert review - Full article: [Defoliation and lollipopping: what to remove, when, and the evidence](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) - Also asked as: What is schwazzing defoliation? | Should I strip all the leaves twice in flower? | Does schwazzing increase yield? | Day 1 and day 21 defoliation - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Schwazzing](https://genetixbay.com/knowledge/glossary/schwazzing.md) is a heavy defoliation schedule: strip almost every [fan leaf](https://genetixbay.com/knowledge/glossary/fan-leaf.md) at the start of flower, let the plant regrow for three weeks, and strip it again around day 21. No controlled cannabis trial shows it raises yield or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). *Contested*. GenetixBay's position is tuck, don't pluck. ## Why The idea is that bare plants push light and energy into [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md) and get better airflow. The counter-argument is that leaves are the solar farm feeding the buds, and stripping them removes [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) capacity. The nearest controlled data are for ordinary [defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md), not schwazzing. On large greenhouse plants, defoliation three weeks before harvest left flower and cannabinoid yield per plant unchanged and made cannabinoids more uniform [1]. At commercial density, yield per m² matched the control [2]. A [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) study found early-flower defoliation raised total cannabinoid concentration while other timings didn't [3], but it simulated hail damage and may not transfer to indoor drug-type cannabis. Airflow is a real benefit. Dense, humid interiors favour [bud rot](https://genetixbay.com/knowledge/glossary/botrytis.md) and [powdery mildew](https://genetixbay.com/knowledge/glossary/powdery-mildew.md) [4], though tucking and spreading branches often achieves the same. Cultivars differ a lot. Some clones lose most of their leaves with no effect, or even grow faster; others suffer. Tuck vs strip is an open GenetixBay [Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md) question. ## The numbers | | Schwazzing | Tuck-first (house) | |---|---|---| | Leaves removed | Nearly all fan leaves, twice | Only those that can't be tucked | | Timing | Flower day 1 and about day 21 | Any time; light thinning around day 21 | | Per session | Most of the leaf area | About 20–30% at most | | Yield evidence | None for schwazzing | Defoliation neutral for yield [1][2] | | Suits | Vigorous, healthy [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md) only | Every cultivar | | [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) | No | Yes | ## What to do 1. Tuck fan leaves under or behind bud sites first. 2. [Lollipop](https://genetixbay.com/knowledge/glossary/lollipopping.md) the lower third at the flip. 3. Remove only leaves you can't tuck that crowd a humid interior. 4. If you want to test schwazzing, run it on one plant beside a matched tucked clone and weigh the [dry yield](https://genetixbay.com/knowledge/glossary/yield.md). ## Common mistakes - Schwazzing stressed, hungry or slow plants. - Schwazzing autoflowers. - Trying it first on an untested cultivar across the whole room. - Stripping when the real problem is weak light. ## Related - Full article: [Defoliation and lollipopping](https://genetixbay.com/knowledge/training/defoliation-lollipopping.md) - Answers: [defoliating autoflowers](https://genetixbay.com/knowledge/answers/can-i-defoliate-autoflowers.md) · [increasing yield](https://genetixbay.com/knowledge/answers/how-to-increase-yield-indoors.md) - Terms: [schwazzing](https://genetixbay.com/knowledge/glossary/schwazzing.md) · [defoliation](https://genetixbay.com/knowledge/glossary/defoliation.md) · [tucking](https://genetixbay.com/knowledge/glossary/tucking.md) · [lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md) ## Follow-up questions **Does schwazzing increase yield?** No controlled cannabis trial shows that schwazzing increases yield. The best data, on large greenhouse plants, found that ordinary defoliation three weeks before harvest left flower and cannabinoid yield per plant unchanged. Schwazzing goes much further, stripping almost all leaves twice. Some cultivars shrug it off and others suffer, so GenetixBay treats it as contested and prefers tucking leaves. **Should I schwazz an autoflower?** No, don't schwazz an autoflower. Autoflowers run on a fixed countdown from germination and can't be vegged longer to regrow lost leaves, so stripping almost all their foliage twice costs yield they never recover. Tuck fan leaves away from bud sites and spread branches with low-stress training instead, removing only leaves that are damaged, dying or touching the medium. **How is schwazzing different from lollipopping?** Schwazzing and lollipopping remove different parts of the plant. Lollipopping removes small shoots and leaves from the shaded lower third, growth that would only make airy larf, at or soon after the flip. Schwazzing strips nearly every fan leaf from the whole plant twice, on day 1 and around day 21 of flower. Lollipopping is mainstream practice; schwazzing is contested. ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 2. Danziger N, Bernstein N, 2022. Too dense or not too dense: higher planting density reduces cannabinoid uniformity but increases yield/area in drug-type medical cannabis. Frontiers in Plant Science 13:713481. https://doi.org/10.3389/fpls.2022.713481 3. Sandoval SM et al., 2024. Defoliation timing effects on phytocannabinoids in hemp (simulated hail). Industrial Crops and Products; MSc thesis version, Colorado State University. https://mountainscholar.org/bitstreams/a8421af5-2146-4d67-8751-397a58816f1b/download 4. Punja ZK, 2021. Emerging diseases of Cannabis sativa and sustainable management. Pest Management Science 77:3857–3870. https://pmc.ncbi.nlm.nih.gov/articles/PMC8451794/ --- # What is super soil? > Super soil is a heavily amended organic soil, rich in compost, worm castings and slow-release amendments, cooked moist for weeks and meant to feed a cannabis plant through most of its life with plain water. It is usually layered: a strong layer low in the pot, milder soil on top for young roots. Many growers still top-dress in mid flower. - Canonical: https://genetixbay.com/knowledge/answers/what-is-super-soil.html - Topic: Systems · Type: Definition - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Living soil (no-till, water-only organic growing)](https://genetixbay.com/knowledge/systems/living-soil.md) - Also asked as: What is a super soil recipe? | Super soil vs living soil | Is super soil just add water? | Can seedlings go in super soil? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Super soil](https://genetixbay.com/knowledge/glossary/super-soil.md) is a heavily amended organic soil, rich in compost, worm castings and slow-release amendments, cooked moist for a few weeks and intended to feed a cannabis plant through most of its life with plain water. It is usually layered, with a strong layer low in the pot and milder soil on top. *Grower practice*: popular and workable, but no controlled cannabis trial has compared it with other systems. ## Why [Organic amendments](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md) don't feed the plant directly. Soil organisms break them down and release plant-available nutrients, and that release depends on moisture, temperature and biology [1][3]. Cooking the mix starts that breakdown before planting. A freshly amended mix can be "hot", releasing [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) and salts fast enough to burn [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md). Layering solves the seedling problem. Young roots grow in mild soil and reach the strong layer only when the plant can use it. The weakness is precision. Release is slow and hard to adjust, and late-flower demand can outrun it. Organic feeding can still give high [yields](https://genetixbay.com/knowledge/glossary/yield.md) when nitrogen supply is high enough [2], which is why many growers [top-dress](https://genetixbay.com/knowledge/glossary/top-dressing.md) in mid flower. The plant mostly doesn't care where its ions come from. Claims that super soil makes better-tasting buds are *Grower practice*, untested in controlled trials. ## The numbers | Item | Typical | |---|---| | Container | 25–100 L (7–25 US gal) | | Strong layer | Lower half to two-thirds of the pot | | Mild top layer | Top third, plain [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) | | Cook time | 2–4 weeks, moist and warm | | Water [pH](https://genetixbay.com/knowledge/glossary/ph.md) | As-is unless very alkaline ([root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) about 6.3–7.0) | | Soil temperature | 18–24 °C (64–75 °F); biology slows below about 15 °C | | Top-dress | Mid veg and early-to-mid flower if plants pale | ## What to do 1. Mix base soil with compost, castings, [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) and a balanced organic amendment package. 2. Moisten, cover and cook for 2–4 weeks. 3. Fill the pot with the strong layer, then top with mild potting mix. 4. Plant, water with dechlorinated water and mulch the surface. 5. Watch lower leaves from mid flower; top-dress if they pale early. ## Common mistakes - Planting seedlings straight into the hot layer. - Small pots of super soil that run out by week 4 of flower. - [Flushing before harvest](https://genetixbay.com/knowledge/glossary/flushing.md). That's a *Myth* that costs yield; keep watering normally. ## Related - Full article: [Living soil](https://genetixbay.com/knowledge/systems/living-soil.md) - Answers: [reusing soil](https://genetixbay.com/knowledge/answers/can-i-reuse-soil.md) · [do mycorrhizae help](https://genetixbay.com/knowledge/answers/do-mycorrhizae-help.md) · [kitchen scraps as fertiliser](https://genetixbay.com/knowledge/answers/kitchen-scraps-as-fertiliser.md) - Terms: [super soil](https://genetixbay.com/knowledge/glossary/super-soil.md) · [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) · [top-dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md) ## Follow-up questions **What is the difference between super soil and living soil?** Super soil and living soil overlap, but the emphasis differs. Super soil is defined by a strong amendment recipe built to feed one plant for one run with water only. Living soil is defined by managing soil biology over many runs: a large container or bed, no-till, mulch and top-dressing between crops. A super soil reused and mulched gradually becomes a living soil. **Can I plant seedlings directly in super soil?** Don't plant seedlings directly into the rich layer of super soil, because the high nutrient load can burn them. Fill the top third or so of the pot with milder potting mix, or start seedlings in a small pot of plain mix and move them once roots are established. By the time roots reach the strong layer, the plant is big enough to use it. **Do I need to pH water for super soil?** You generally don't need to pH-adjust water for super soil. Compost and organic matter buffer the root zone, and plants and soil biology work around a near-neutral pH of roughly 6.3–7.0. Use dechlorinated water as it is unless it is very alkaline. Adjusting water to pH 6.0 out of habit, as for hydro, is a common mistake in organic soils. ## Sources 1. USDA Natural Resources Conservation Service. Soil health principles (minimise disturbance, keep soil covered, maintain living roots, maximise biodiversity). https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soil/soil-health 2. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17 3. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (organic substrates and compost chapters). https://doi.org/10.1016/C2015-0-01807-5 --- # What is THCA? > THCA (tetrahydrocannabinolic acid) is the acid form of THC that the living cannabis plant actually makes and stores in its trichome heads. Fresh and dried flower is mostly THCA, not THC. Heat (smoking, vaping, baking) removes a CO2 molecule and turns THCA into THC. Labels report total THC = THC + 0.877 × THCA, so 30% THCA means about 26% total THC. - Canonical: https://genetixbay.com/knowledge/answers/what-is-thca.html - Topic: Basics · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) - Also asked as: THCA vs THC | Is THCA the same as THC? | Does raw weed have THC? | What does total THC mean on a label? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [THCA](https://genetixbay.com/knowledge/glossary/thca.md) (tetrahydrocannabinolic acid) is the form of [THC](https://genetixbay.com/knowledge/glossary/thc.md) the cannabis plant actually makes. Fresh and dried buds are mostly THCA; heat turns it into THC. Labels give total THC = THC + [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) × THCA, so 30% THCA is about 26% total THC. *Established* chemistry. ## Why The plant makes acids. Secretory cells in the glandular [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) make [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) acids, THCA among them, and store them in the gland head [2]. They become neutral THC mainly by heat, not on the living plant [3]. Heat knocks off a [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md). That reaction, [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), was measured at 80–145 °C: THCA converted to THC following first-order kinetics, faster at higher temperatures, and faster than [CBDA](https://genetixbay.com/knowledge/glossary/cbda.md) or [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) [1]. Smoking, vaping and baking all do it. The 0.877 factor is just molecular weight. THC weighs about 314.5 g/mol and THCA about 358.5 g/mol, so 1 g of THCA can become at most 0.877 g of THC. Real conversion is usually less than complete. Labels can run high. A retest of retail flower found many products below their labelled THC [4]. GenetixBay's position: flower labelled above about 35% [total cannabinoids](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) isn't credible. ## The numbers | Measure | Meaning | Example | |---|---|---| | THCA % | Acid form in the bud | 25% | | THC % (delta-9) | Already neutral; usually small in fresh flower | 1% | | Total THC | THC + 0.877 × THCA | 1 + 21.9 ≈ 22.9% | | 0.877 | 314.5 ÷ 358.5 g/mol | — | | Ceiling for flower | Total cannabinoids above ~35% not credible | — | ## What to do 1. Read a [certificate of analysis](https://genetixbay.com/knowledge/glossary/coa.md) for both THCA and THC, and the total. 2. Treat "THCA flower" as ordinary cannabis: heat converts it. 3. Store buds cool, dark and airtight to slow conversion and oxidation. 4. Check local rules: some places regulate by total THC, others by delta-9 only. ## Common mistakes - Thinking high-THCA flower is "not THC". - Adding THCA and THC without the 0.877 factor. - Trusting a 40%+ flower label. ## Related - Full article: [Buyer beware: label claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md) - Answers: [THC vs CBD plants](https://genetixbay.com/knowledge/answers/thc-vs-cbd-plants.md) · [checking trichomes](https://genetixbay.com/knowledge/answers/how-to-check-trichomes.md) - Article: [Cannabis plant biology](https://genetixbay.com/knowledge/basics/cannabis-plant-biology.md) - Terms: [THCA](https://genetixbay.com/knowledge/glossary/thca.md) · [decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md) · [total THC](https://genetixbay.com/knowledge/glossary/total-thc.md) ## Follow-up questions **How is total THC calculated?** Total THC on a cannabis label is calculated as THC + 0.877 × THCA. The 0.877 factor is the mass ratio of THC to THCA, about 314.5 / 358.5 g/mol: heating removes a carbon dioxide molecule from each THCA molecule, so 1 g of THCA becomes at most 0.877 g of THC. A bud with 30% THCA therefore has about 26% total THC. **Does raw cannabis contain THC?** Raw cannabis contains mostly THCA and only a little neutral THC. The plant makes cannabinoids as acids in its glandular trichomes, and they convert to neutral THC mainly when heated, not on the living plant. Some THCA converts slowly during drying, curing and storage, and much faster above about 100 °C. Effects are reported, not promised. **Can flower really test 35% THCA?** Flower labelled above about 35% total cannabinoids is not credible, in GenetixBay's position. Cannabinoids are made only in trichome heads, and most of a bud's dry weight is bract, stem and leaf. A 42% total THC label would need about 48% THCA in the dry bud, which only a lump of resin, not flower, could reach. ## Sources 1. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271. https://doi.org/10.1089/can.2016.0020 2. Livingston SJ, Quilichini TD, Booth JK, et al. 2020. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal 101(1):37-56. https://doi.org/10.1111/tpj.14516 3. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3 4. Schwabe AL, Johnson V, Harrelson J, McGlaughlin ME. 2023. Uncomfortably high: Testing reveals inflated THC potency on retail Cannabis labels. PLOS ONE 18(4):e0282396. https://doi.org/10.1371/journal.pone.0282396 --- # What size grow tent should I get? > For a first grow, a 60 × 60 cm (2 × 2 ft) to 90 × 90 cm (3 × 3 ft) tent, 160–180 cm (5.3–6 ft) tall, is the forgiving choice: one to three plants and a 100–320 W LED. A 120 × 120 cm (4 × 4 ft) tent suits two to four plants and 400–650 W. Check your legal plant limit and ceiling first. - Canonical: https://genetixbay.com/knowledge/answers/what-size-grow-tent.html - Topic: Equipment · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Also asked as: Should I get a 2x4 or 4x4 tent? | What is the best grow tent size for a beginner? | What size grow tent for 2 plants? | How tall should my grow tent be? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer For a first grow, a **60 × 60 cm (2 × 2 ft) to 90 × 90 cm (3 × 3 ft)** tent, **160–180 cm (5.3–6 ft)** tall, is the forgiving choice: one to three plants, a 100–320 W [LED](https://genetixbay.com/knowledge/glossary/led.md) and a small fan. A **120 × 120 cm (4 × 4 ft)** tent [yields](https://genetixbay.com/knowledge/glossary/yield.md) more but costs more to light, cool and run. *Grower practice*. Plant-count limits vary by place, so check your local rules first: they decide the tent. ## Why Yield indoors scales with lit [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md) and light intensity [1]; light and [planting density](https://genetixbay.com/knowledge/glossary/plant-density.md) were among the main yield factors in a cannabis meta-analysis [2]. A bigger tent only pays if you can light it properly. Light cost scales with area. A 4 × 4 ft tent has four times the floor of a 2 × 2 and needs roughly four times the light, a bigger fan and more cooling. [Efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) sets what that costs to run [4]. Bigger pots give bigger plants within reason [3], traded against feeding frequency; 11–19 L (3–5 gal) is the forgiving middle. Height catches people out. [Photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md) commonly [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) 50–150 % after the flip. ## The numbers | Tent | Plants (pot) | Efficient LED (flower) | [Exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) | |---|---|---|---| | 60 × 60 cm (2 × 2 ft) | 1–2 (11 L / 3 gal) | 100–150 W | 100 mm (4 in) | | 90 × 90 cm (3 × 3 ft) | 2–3 (11–19 L / 3–5 gal) | 225–320 W | 100–125 mm (4–5 in) | | 60 × 120 cm (2 × 4 ft) | 2 (19 L / 5 gal) | 200–300 W | 100–125 mm (4–5 in) | | 120 × 120 cm (4 × 4 ft) | 2–4 (19 L / 5 gal) | 400–650 W | 150 mm (6 in) | | 150 × 150 cm (5 × 5 ft) | 4–6 (19–25 L / 5–7 gal) | 650–1,000 W | 150–200 mm (6–8 in) | ## What to do 1. Check your legal [plant limit](https://genetixbay.com/knowledge/glossary/plant-count-limit.md). 2. Measure floor, ceiling and the nearest outlet; leave 30 cm (12 in) around the tent. 3. Pick the footprint; when unsure, go one size smaller. 4. Pick height: 140–160 cm for [autos](https://genetixbay.com/knowledge/glossary/autoflower.md), 180–200 cm for photoperiods. 5. Size light and fan to the footprint. ## Common mistakes - Buying the biggest tent that fits. - Too many plants, too little airflow. - No headroom for the stretch. - A big tent with a small light. ## Related - Full article: [Your first grow](https://genetixbay.com/knowledge/basics/first-grow-guide.md) - Guide: [Choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md) - [How many plants can I fit in my grow tent?](https://genetixbay.com/knowledge/answers/how-many-plants-per-tent.md) - [What wattage LED do I need?](https://genetixbay.com/knowledge/answers/what-wattage-light-for-my-tent.md) - Terms: [tent](https://genetixbay.com/knowledge/glossary/tent.md) · [plant-count limit](https://genetixbay.com/knowledge/glossary/plant-count-limit.md) ## Follow-up questions **Is a 2x4 or a 4x4 tent better?** A 2 × 4 ft (60 × 120 cm) tent suits two plants in 19 L (5 gal) pots and a 200–300 W LED, and fits narrow spaces. A 4 × 4 ft (120 × 120 cm) tent suits two to four plants and 400–650 W, with roughly twice the canopy and running cost. Choose 4 × 4 if you have the space, power and cooling; 2 × 4 if you don't. **How tall should a grow tent be?** A grow tent should be tall enough for pot height plus the plant plus a 30–45 cm (12–18 in) light gap plus the fixture and hangers. That is usually 140–160 cm (4.6–5.3 ft) for autoflowers and trained plants and 180–200 cm (6–6.6 ft) for photoperiods, which commonly stretch 50–150 % after the flip. Flip at about half the final height you can fit. **What size tent for two plants?** Two cannabis plants fit well in a 60 × 120 cm (2 × 4 ft) or 90 × 90 cm (3 × 3 ft) tent in 11–19 L (3–5 gal) pots, with a 200–320 W efficient LED. Two well-trained plants fill a 3 × 3 ft canopy as well as six cramped ones, with better airflow and less mould risk. Check your local plant-count limit before buying. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Backer R, Schwinghamer T, Rosenbaum P, et al., 2019. Closing the yield gap for cannabis: a meta-analysis of factors determining cannabis yield. Frontiers in Plant Science 10:495. https://doi.org/10.3389/fpls.2019.00495 3. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 4. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # What should I do with a male plant? > A male cannabis plant must leave the flowering room before its pollen sacs open, usually within 1–2 weeks of showing, or it will seed every female. That doesn't mean binning it. Males carry half of every seed's genes, and GenetixBay encourages and rewards them. Either isolate a good male, collect and store its pollen and record it in the Stud Book, or remove it if you're not breeding. - Canonical: https://genetixbay.com/knowledge/answers/what-to-do-with-a-male-plant.html - Topic: Breeding · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Breeders vs pollen chuckers: what real cannabis breeding looks like](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) - Also asked as: Should I kill my male plants? | Is it worth keeping a male plant? | How do I use a male for pollen? | I found a male: what now? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Get the male out of the flowering room before his [pollen sacs](https://genetixbay.com/knowledge/glossary/anther.md) open, usually within 1–2 weeks of the first sacs showing. Then decide: keep a good male in isolation and collect his pollen, or remove him if you're not breeding. *House position*: males are a necessity, and they are encouraged and rewarded on GenetixBay. The breeding arithmetic is *Established*. ## Why Half of every seed's [genes](https://genetixbay.com/knowledge/glossary/gene.md) come from the father. Under the breeder's equation, the gain from selection depends on how far both parents sit above average, so using an unselected male halves your progress every generation [1]. You judge a male by his offspring. A male's resin and flavour can't be seen directly, so breeders progeny-test candidates: cross, grow out the seed, and keep the male whose daughters are good and uniform [3]. Pollen doesn't keep long. It lasts about a week in a fridge, and only pollen dried with a carrier and properly frozen has kept for months [2]. ## The numbers | Item | Value | |---|---| | Pollen, open air | Hours to about 1–2 days | | Pollen, sealed and dry, fridge 2–6 °C | Days to about 1 week [2] | | Pollen + baked flour 1:10, frozen | Weeks to months; test it [2] | | Gain with an unselected male | Half that of a selected male [1] | ## What to do 1. Confirm the sex. Male [pre-flowers](https://genetixbay.com/knowledge/glossary/pre-flower.md) are round sacs on short stalks at the nodes, with no [white hairs](https://genetixbay.com/knowledge/glossary/stigma.md). 2. Move the male to a separate space with no flowering females, or close the room's air off from his. 3. Judge him on vigour, structure, stem-rub aroma and sex stability, and take a cutting to keep him. 4. Collect pollen on clean paper once the first sacs open, sieve it, dry it briefly, then use it or freeze it with flour. 5. Record him: parents, traits and [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md). On GenetixBay, register him in [the Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md). 6. If you're not breeding, remove him before the sacs open. [Plant-count rules](https://genetixbay.com/knowledge/glossary/plant-count-limit.md) can include males, so check your local rules. ## Common mistakes - Leaving a male in the room "just a few more days". - Binning every male without looking at him. - Collecting pollen near flowering females or with [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md) running. - [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md) a female to avoid needing a male. ## Related - Full article: [Breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) - Articles: [collecting and storing pollen](https://genetixbay.com/knowledge/breeding/pollen-collection-storage.md) · [selection and pheno hunting](https://genetixbay.com/knowledge/breeding/selection-pheno-hunting.md) - Answers: [when plants show sex](https://genetixbay.com/knowledge/answers/when-do-plants-show-sex.md) - Terms: [male selection](https://genetixbay.com/knowledge/glossary/male-selection.md) · [Stud Book](https://genetixbay.com/knowledge/glossary/stud-book.md) · [pollen](https://genetixbay.com/knowledge/glossary/pollen.md) ## Follow-up questions **How do I know if a male is worth keeping?** A cannabis male is worth keeping if it is vigorous, well structured, sex-stable, smells strong when you rub the stem, and above all gives good daughters. You cannot see a male's resin or flavour directly, so breeders progeny-test: they cross it to a known female, grow out the seed and keep the male whose offspring are good and uniform. **How long can I store cannabis pollen?** Cannabis pollen lasts hours to about 1–2 days in open air and about a week sealed and dry in a fridge at 2–6 °C. For longer storage, mix it 1:10 by weight with oven-dried flour, seal small portions with silica gel and freeze them, never refreezing a portion. Home-freezer survival over months is grower practice, so test pollen before relying on it. **Why does GenetixBay value males?** GenetixBay values male cannabis plants because half of every seed's genes come from the father. Under the breeder's equation, using an unselected male halves the response to selection each generation. Males are encouraged and rewarded on GenetixBay, documented in the Stud Book, and selfing females to avoid needing a male is mostly frowned upon. ## Sources 1. Suza W, Lamkey K (eds). 2023. Quantitative Genetics for Plant Breeding. Iowa State University Digital Press. https://iastate.pressbooks.pub/quantitativegenetics/ 2. Gaudet D, Yadav NS, Sorokin A, Bilichak A, Kovalchuk I. 2020. Development and optimization of a germination assay and long-term storage for Cannabis sativa pollen. Plants 9(5):665. https://doi.org/10.3390/plants9050665 3. Fehr WR, Suza WP. 2025. Principles of Cultivar Development (open edition of Fehr WR 1987/1991, Vol. 1: Theory and Technique). Iowa State University Digital Press. https://doi.org/10.31274/isudp.2025.200 --- # What should I look for when buying a grow light? > When buying a grow light, look first for efficacy above about 2.5 µmol/J, a measured PPFD map over your tent's footprint showing 600–900 µmol/m²/s average with edges at least 70–80 % of the centre, and a real wattage at the wall. Then a dimmer, a broad white spectrum, a driver you can mount outside the tent and an electrical safety certification. Ignore lumens and 'equivalent watts'. - Canonical: https://genetixbay.com/knowledge/answers/what-to-look-for-in-a-grow-light.html - Topic: Environment · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: What grow light specs matter? | What does µmol/J mean on a grow light? | How do I choose an LED grow light? | Which grow light specs are marketing? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Buy on three numbers: **[efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) above about 2.5 µmol/J**, a **measured [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) map** over your footprint (about **600–900 µmol/m²/s average**, edges at least **70–80 %** of the average), and the **real wall wattage**. Then a dimmer, a broad white spectrum and a remote driver. *Supported*. ## Why Efficacy sets running cost and heat. Good current [LEDs](https://genetixbay.com/knowledge/glossary/led.md) exceed 2.5–3 µmol/J; [HPS](https://genetixbay.com/knowledge/glossary/hps.md) is about 1.7 [1]. In cannabis lighting research, efficacy mattered more for cost-effective production than spectrum [2]. The PPFD map tells you what the canopy gets. Yield rose linearly with canopy PPFD in controlled trials [3], so a light that's bright in the middle and dim at the edges grows big centre [colas](https://genetixbay.com/knowledge/glossary/cola.md) and larf in the corners. Spectrum matters less than marketing suggests. A broad white spectrum works for veg and flower [2]. UV gave no useful rise in yield or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) [4]. ## The numbers | Spec | Look for | Red flag | |---|---|---| | Efficacy | ≥ 2.5 µmol/J, measured | not stated, or only "lumens" | | [PPF](https://genetixbay.com/knowledge/glossary/ppf.md) | stated in µmol/s | missing | | Wall wattage | real draw, e.g. 320 W | "equivalent 1,000 W" | | PPFD map | your footprint, stated height, average shown | centre point only, tiny area | | Uniformity | edges ≥ 70–80 % of average | corners at half | | Dimming | 0–100 % or close | none | | Spectrum | broad white, ~5–15 % blue | colour story as the main selling point | | Driver | detachable, can sit outside the tent | sealed in, hot | | Safety | recognised electrical certification for your country | none | ## What to do 1. Measure your canopy footprint. 2. Shortlist fixtures with a PPFD map for that footprint. 3. Compare µmol/J and actual watts; size with 25–40 W/ft² for flower. 4. Prefer dimmable fixtures with a remote driver. 5. Check the certification mark and warranty. 6. Confirm the circuit can carry the load under 80 % of its rating. ## Common mistakes - Buying on "equivalent watts" or lumens. - Trusting a centre-point PPFD at 30 cm. - Paying extra for UV to "boost [THC](https://genetixbay.com/knowledge/glossary/thc.md)" (*Myth*). - Oversizing for a small tent with no dimmer. - Skipping certification to save money. ## Related - Full article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [What wattage LED do I need for my tent?](https://genetixbay.com/knowledge/answers/what-wattage-light-for-my-tent.md) - [Why don't lumens matter?](https://genetixbay.com/knowledge/answers/lumens-vs-ppfd.md) - [LED or HPS?](https://genetixbay.com/knowledge/answers/led-vs-hps.md) · [Light spectrum](https://genetixbay.com/knowledge/environment/light-spectrum.md) - Terms: [photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) · [full spectrum](https://genetixbay.com/knowledge/glossary/full-spectrum.md) ## Follow-up questions **What is a good µmol/J for a grow light?** A good current LED grow light delivers about 2.5–3 µmol/J or more of photosynthetic photons per joule of electricity; HPS is about 1.7 µmol/J. Higher efficacy means less electricity and less heat for the same light on the canopy. Look for a figure measured in an integrating sphere and stated with PPF in µmol/s and the actual wall wattage. **What is a PPFD map and how do I read it?** A PPFD map shows measured light intensity in µmol/m²/s at points across a stated footprint and hanging height. Check that it matches your tent size, read the average rather than the centre, and compare the corners with the centre: edges should be at least about 70–80 % of the average. A map measured at 30 cm over a smaller area than advertised flatters the fixture. **Do I need UV or far-red in a grow light?** No, you don't need UV or far-red in a cannabis grow light. Controlled trials found UV gave no commercially useful rise in yield or cannabinoids and high doses cut yield. Far-red is contested: it stretches plants, and its effect on yield seems to trade off against cannabinoid concentration. Buy a broad white spectrum with good efficacy; add extras only for a side-by-side trial. ## Sources 1. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 2. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://pmc.ncbi.nlm.nih.gov/articles/PMC7987162/ 3. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 4. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis inflorescence yield and cannabinoid concentration are not increased with exposure to short-wavelength ultraviolet-B radiation. Frontiers in Plant Science 12:725078. https://doi.org/10.3389/fpls.2021.725078 --- # What wattage LED do I need for my tent? > For flower, plan on roughly 25–40 W of efficient LED (2.5–3.0 µmol/J) per square foot, about 270–430 W/m², which gives an average of about 600–900 µmol/m²/s. That's 100–150 W for a 2 × 2 ft tent, 225–320 W for 3 × 3, 200–300 W for 2 × 4 and 400–650 W for 4 × 4. Experienced growers pushing 1,000–1,200 µmol/m²/s need about 35–50 W/ft². - Canonical: https://genetixbay.com/knowledge/answers/what-wattage-light-for-my-tent.html - Topic: Environment · Type: Numbers - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: How many watts for a 4x4 tent? | What LED for a 2x4 tent? | How many watts per square foot for cannabis? | What light size for a 3x3 tent? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer For flower, plan on roughly **25–40 W of efficient [LED](https://genetixbay.com/knowledge/glossary/led.md) per square foot** (about 270–430 W/m²) at **2.5–3.0 [µmol/J](https://genetixbay.com/knowledge/glossary/photon-efficacy.md)**, which delivers an average of about **600–900 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md)**. That's **100–150 W** for a 2 × 2 ft tent, **225–320 W** for 3 × 3 and **400–650 W** for 4 × 4. *Supported* for the light–yield link; the watt rules are *Grower practice*. ## Why Yield indoors tracks light. In controlled trials, dry flower yield rose linearly from 120 to 1,800 µmol/m²/s at ambient CO₂ [1][2]. More light buys more grams, up to what the plant, the climate and your power bill can handle. Watts are only half the picture. A fixture's output is watts × efficacy (µmol/J). Good current LEDs exceed 2.5–3 µmol/J, [HPS](https://genetixbay.com/knowledge/glossary/hps.md) about 1.7 [3]. The same wattage can deliver very different light. Rough check: average PPFD ≈ watts × µmol/J ÷ [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md), a little less in practice, and less in the corners. ## The numbers | Tent | Area | LED for 600–900 µmol/m²/s | LED for 1,000–1,200 (CO₂ or experience) | |---|---|---|---| | 2 × 2 ft (60 × 60 cm) | 0.36 m² (4 ft²) | 100–150 W | 150–200 W | | 3 × 3 ft (90 × 90 cm) | 0.81 m² (9 ft²) | 225–320 W | 320–450 W | | 2 × 4 ft (60 × 120 cm) | 0.72 m² (8 ft²) | 200–300 W | 300–400 W | | 4 × 4 ft (120 × 120 cm) | 1.44 m² (16 ft²) | 400–650 W | 550–800 W | | 5 × 5 ft (150 × 150 cm) | 2.25 m² (25 ft²) | 650–1,000 W | 900–1,250 W | Figures assume 2.5–3.0 µmol/J. At 2.0 µmol/J, add about a third. ## What to do 1. Measure the footprint you'll actually fill with canopy. 2. Pick a fixture whose published PPFD map covers that footprint at 600–900 µmol/m²/s average. 3. Check its µmol/J; compute watts × µmol/J ÷ area as a sanity check. 4. Buy a dimmable light and set it by measured canopy PPFD. 5. Check the circuit: lights plus everything else under 80 % of the rating. ## Common mistakes - Buying by "equivalent watts". - Pushing above about 1,200 µmol/m²/s without CO₂ and healthy roots. - Ignoring corners: edges can get half the centre's light. ## Related - Full article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - [What should I look for when buying a grow light?](https://genetixbay.com/knowledge/answers/what-to-look-for-in-a-grow-light.md) - [What size grow tent should I get?](https://genetixbay.com/knowledge/answers/what-size-grow-tent.md) - Guide: [Lights for beginners](https://genetixbay.com/knowledge/guides/lights-for-beginners.md) - Terms: [photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) · [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) ## Follow-up questions **How many watts do I need for a 4x4 tent?** A 4 × 4 ft (120 × 120 cm) tent needs about 400–650 W of efficient LED at 2.5–3.0 µmol/J for flower, which gives an average of roughly 600–900 µmol/m²/s across the canopy. Experienced growers aiming for 1,000–1,200 µmol/m²/s need about 550–800 W. Judge the fixture by its measured PPFD map over a 4 × 4 footprint, not by 'equivalent' watts. **Can I use a bigger light dimmed down?** Yes, a bigger LED dimmed down works well in a smaller tent and often runs more efficiently than a small light at full power. Set the dimmer by measured PPFD at the canopy, not by percentage. The catch is footprint: a fixture designed for 4 × 4 ft hung in a 2 × 2 tent wastes light on the walls and may be too hot for the space. **Do watts matter or only µmol/J?** Watts tell you what a grow light costs to run; µmol/J tells you how much plant-usable light each watt makes. Multiply them to get the light's output: a 300 W fixture at 2.7 µmol/J makes about 810 µmol/s of photons. Two 300 W lights at 1.7 and 2.8 µmol/J differ by about 65 % in light delivered. Always compare both numbers. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 3. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7 --- # When do autoflowers start flowering? > Autoflowers usually start flowering about 3–5 weeks after sprouting, with white pistils at the main tip around day 21–35, whatever the light schedule. Preflowers at the nodes often appear a few days earlier, in week 4. Photoperiod plants are different: they flower only after long nights begin, with pistil clusters about 10–14 days after the switch to 12/12. - Canonical: https://genetixbay.com/knowledge/answers/when-do-autoflowers-start-flowering.html - Topic: Basics · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Also asked as: When do autos show pistils? | Autoflower preflower week | How many weeks until autos flower? | When does cannabis start flowering? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) start flowering about 3–5 weeks after [sprouting](https://genetixbay.com/knowledge/glossary/germination.md), with [pistils](https://genetixbay.com/knowledge/glossary/pistil.md) at the main tip around day 21–35, on any light schedule. [Preflowers](https://genetixbay.com/knowledge/glossary/pre-flower.md) at the nodes often show in week 4. [Photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md) wait for long nights instead: pistil clusters appear about 10–14 days after the [flip to 12/12](https://genetixbay.com/knowledge/glossary/12-12.md). *Grower practice* for auto timing; *Supported* for photoperiods. ## Why An auto's switch runs on age. Plants with two copies of the [recessive allele](https://genetixbay.com/knowledge/glossary/recessive.md) at the *Autoflower1* [locus](https://genetixbay.com/knowledge/glossary/locus.md) flowered even under long days in mapped populations [1]. Lines differ by a week or two, which is why the window is wide. All cannabis makes preflowers with age. Single flowers at the nodes form through an internal juvenile-to-adult change, not the light schedule; in one cultivar the first pair appeared at the 7th node [2]. On a photoperiod plant under [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) that's as far as it goes. On an auto, clustered flowers at the tips follow. Photoperiod plants measure the night. After the switch to short days, visible pistil clusters at the top took about 8–14 days in controlled studies [3], around 13–14 days on average across many [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md) and three weeks in slow ones [4]. ## The numbers | Plant type | First preflowers | Flowering starts | Trigger | |---|---|---|---| | Autoflower | ~week 3–4 | ~day 21–35 from sprouting | Age | | Photoperiod, 18/6 | ~week 4–6 from seed | Not until nights lengthen | — | | Photoperiod, after flip | Already present | ~10–14 days after 12/12 | Long nights | ## What to do 1. Note the [sprout](https://genetixbay.com/knowledge/glossary/seedling.md) date; it's day 1 for an auto. 2. From week 3, check the main tip with a [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) every few days. 3. Log the day pistils cluster at the tip as "day 1 of flower". 4. Finish main [LST](https://genetixbay.com/knowledge/glossary/lst.md) bends by about day 35; stems stiffen in the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md). 5. No pistils by week 7 under 18/6? Treat it as a photoperiod and flip it. ## Common mistakes - Calling a single pair of preflowers "flowering". - Switching autos to 12/12 to "make them flower". They don't need it. - Training hard after day 40, when stems have stiffened. - Counting a photoperiod's flip as day 1 of flower. ## Related - Full article: [Photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Answers: [how long autos take](https://genetixbay.com/knowledge/answers/how-long-do-autoflowers-take.md) · [when plants show sex](https://genetixbay.com/knowledge/answers/when-do-plants-show-sex.md) · [when to flip](https://genetixbay.com/knowledge/answers/when-to-flip-to-flower.md) - Article: [the flip isn't day 1 of flower](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - Terms: [pre-flower](https://genetixbay.com/knowledge/glossary/pre-flower.md) · [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) ## Follow-up questions **Why hasn't my autoflower started flowering?** An autoflower that shows no pistils by week 5–6 is usually either a slow line or a photoperiod plant in disguise. Autoflowering is recessive, so a seed needs two copies of the auto allele, and poorly stabilised lines throw photoperiods. If it is still vegging at week 7 under 18/6, treat it as a photoperiod and flip it to 12/12. **When does a photoperiod plant start flowering?** A photoperiod cannabis plant starts flowering about 10–14 days after the switch to 12/12, when three or more pairs of pistils cluster at the top of the main shoot. Controlled studies found onset roughly 8–14 days after short days began, around 13–14 days on average in many hemp cultivars, and up to three weeks in slow ones. Preflowers in veg don't count. **Are preflowers the start of flowering on an auto?** Preflowers on an autoflower are the first sign, not the start of real flowering. Single flowers at the nodes form with age in all cannabis, and research found the first pair around the 7th node. Flowering proper begins when pistils cluster at the main tip and branch tips; on an auto that usually follows within days, around weeks 3–5. ## Sources 1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 2. Spitzer-Rimon B, Shafran-Tomer H, Gottlieb GH, et al. 2022. Non-photoperiodic transition of female cannabis seedlings from juvenile to adult reproductive stage. Plant Reproduction 35(4):265-277. https://doi.org/10.1007/s00497-022-00449-0 3. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 4. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 --- # In which weeks of flower do buds grow the most? > Cannabis buds put on most of their mass from roughly week 3 to week 7 of flower, counted from the first pistil clusters, and keep gaining weight and resin right through the final weeks. In one controlled trial, inflorescence dry weight kept increasing at every harvest from week 5 to week 11. That is why the last weeks need full light and feed: taper nitrogen, don't flush. - Canonical: https://genetixbay.com/knowledge/answers/when-do-buds-grow-the-most.html - Topic: Environment · Type: Numbers - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [The flip isn't day 1 of flower: the 10–14 day transition and how to count it](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - Also asked as: When is the bulking phase in flower? | When do buds fatten up? | Which week do buds grow the most? | Do buds keep growing in the last weeks? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Cannabis buds put on most of their mass from about **week 3 to week 7 of flower** (counted from the first [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) clusters), and they **keep gaining weight and resin to the end**. In a controlled trial, inflorescence [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) rose at every harvest from **week 5 to week 11** [1]. *Supported* that growth continues late; the week-by-week split is *Grower practice*. ## Why The first two to three weeks after the flip belong to the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md): stem elongation peaks around days 5–10 of short days, then the [shoot tip](https://genetixbay.com/knowledge/glossary/apical-meristem.md) condenses into a [cola](https://genetixbay.com/knowledge/glossary/cola.md) [3]. Little bud mass is built yet. Once [internodes](https://genetixbay.com/knowledge/glossary/internode.md) stop lengthening, the plant puts its effort into [bracts](https://genetixbay.com/knowledge/glossary/bract.md) and flowers. That's the bulking phase most growers see from about week 3. It doesn't stop when the calendar says "ripening". Dry weight kept climbing through 11 weeks in one indoor [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) [1], and [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) keep developing as flowers age [2]. **House position:** the final weeks are when the plant packs on much of its final weight and resin. Pre-harvest [flushing](https://genetixbay.com/knowledge/glossary/flushing.md) and darkness are *Myths* that starve it at exactly the wrong time. More light means more bulk: yield rose linearly with canopy [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) [4]. ## The numbers | Weeks of flower (typical 8–10 week cultivar) | What's happening | |---|---| | Flip to ~day 14 | transition and stretch; pistil clusters appear | | Weeks 1–3 | stretch slows, colas form | | Weeks 3–7 | fastest visible bulking | | Final 2–3 weeks | bracts swell, resin ripens, weight still rising [1][2] | ## What to do 1. Count from the first pistil clusters, and log the flip date too. 2. Keep light at full intensity to harvest. 3. Feed normally; [taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) over the last few weeks while keeping P, K, Ca, Mg and [micros](https://genetixbay.com/knowledge/glossary/micronutrient.md). 4. Hold late-flower [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) at 40–50 % and keep air moving through dense colas. 5. Check the largest buds for rot from week 6 on. ## Common mistakes - Flushing for the last 1–2 weeks and losing bulk. - Harvesting by the calendar while buds are still filling. - Dimming lights for "ripening". - Ignoring humidity as buds densify. ## Related - Full article: [The flip isn't day 1 of flower](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - [How long does the flowering stage take?](https://genetixbay.com/knowledge/answers/how-long-does-flowering-take.md) - [How do I get bigger, denser buds?](https://genetixbay.com/knowledge/answers/how-to-get-bigger-denser-buds.md) - [The flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) - Terms: [flowering stage](https://genetixbay.com/knowledge/glossary/flowering-stage.md) · [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) ## Follow-up questions **Do buds still grow in the last two weeks?** Yes, cannabis buds still gain weight and resin in the last two weeks of flower. In a controlled indoor trial, inflorescence dry weight kept increasing across harvests from week 5 to week 11, and trichome development continues as flowers age. This is why GenetixBay calls pre-harvest flushing and darkness myths: both starve the plant while it is still packing on weight. Taper nitrogen instead. **When does the stretch stop and bulking start?** The cannabis stretch mostly happens in the first two to three weeks after the flip, with stem elongation fastest from about day 5 to day 10 of short days. Once new internodes stay short and pistil clusters stack at the tops, the plant switches its effort to building flowers. Bulking then runs roughly from weeks 3 to 7 of flower in a typical 8–10 week cultivar. **How do I get buds to bulk up more?** To get cannabis buds to bulk up more, give them more light within reason, a healthy root zone and steady feeding through the final weeks. Yield rose linearly with canopy light up to 1,800 µmol/m²/s in a controlled trial. Keep late-flower RH at 40–50 % so dense buds don't rot, keep the dark period truly dark, and taper nitrogen rather than flushing. ## Sources 1. Crispim Massuela D, Hartung J, Munz S, Erpenbach F, Graeff-Hönninger S, 2022. Impact of harvest time and pruning technique on total CBD concentration and yield of medicinal cannabis. Plants 11(1):140. https://doi.org/10.3390/plants11010140 2. Punja ZK, Sutton DB, Kim T, 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 3. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 4. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # When do outdoor plants start flowering? > Outdoor photoperiod cannabis starts flowering when days shorten past its cultivar's threshold, often around 14–14.5 hours of daylight. At 35–50° latitude that is usually late July to mid-August in the Northern Hemisphere and late January to mid-February in the Southern. Plants show pistils over the next 10–14 days. Higher latitudes cross the threshold later; near the tropics plants can flower almost any time. - Canonical: https://genetixbay.com/knowledge/answers/when-do-outdoor-plants-flower.html - Topic: Outdoor growing · Type: Numbers - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Also asked as: Outdoor flowering time | When do outdoor plants start to bud? | Do outdoor plants flower in August? | When does outdoor cannabis flower in the southern hemisphere? | Why is my outdoor plant flowering in June? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Outdoor [photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md) start flowering as days shorten past their threshold, often around 14–14.5 h of daylight. At 35–50° latitude that is usually late July to mid-August in the Northern Hemisphere, late January to mid-February in the Southern, with [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) clusters showing 10–14 days later. *Supported*; exact dates vary by cultivar. ## Why Cannabis measures night length. Once the night passes a cultivar-specific threshold, [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) switch from leaves to flower clusters [3]. Thresholds differ. Some [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md) had a critical day length of 13 h 45 min to 14 h, and very dim twilight counted as light [1]. Many drug-type cultivars flower at 14 h days, and some at 14–15 h [4]. Latitude shifts the date. Days are longest at high latitude, so they fall through 14 h later: about 9 August at 40°, 23 August at 50° (sunrise to sunset, calculated). Flowering is not instant. A transition of roughly 10–14 days follows before pistil clusters show at the [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md). Night light interferes. Stray light of about 2 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) delayed flowering in hemp [1], and as little as 0.01 µmol/m²/s in sensitive cannabis cultivars [2]. ## The numbers | Latitude | Day falls below 14.5 h | Day falls below 14 h | Typical flower onset (N / S) | |---|---|---|---| | 30° | Never above it | ~7 July | Early–mid July / early–mid January | | 40° | ~25 July | ~9 August | Late July–mid August / late January–mid February | | 45° | ~6 August | ~17 August | Early–late August / early–late February | | 50° | ~15 August | ~23 August | Mid–late August / mid–late February | | 55° | ~22 August | ~28 August | Late August / late February | Southern dates: add six months. Sunrise-to-sunset values; twilight adds a little. ## What to do 1. Note when your days drop below 14.5 h and 14 h; expect flowers from then. 2. Count flowering weeks from first pistils, plus the 10–14 day transition. 3. Keep plants away from streetlights and security lights. 4. In short seasons, choose early cultivars or [light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md). ## Common mistakes - Expecting outdoor plants to flower "on [12/12](https://genetixbay.com/knowledge/glossary/12-12.md)" in September. - Planting under a security light. - Assuming a breeder's 8 weeks starts the day you see the first pistil. ## Related - Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Answers: [When to plant outdoors](https://genetixbay.com/knowledge/answers/when-to-plant-outdoors.md) · [When to harvest outdoors](https://genetixbay.com/knowledge/answers/when-to-harvest-outdoors.md) · [Why flowering needs long nights](https://genetixbay.com/knowledge/answers/why-flowering-needs-darkness.md) - Article: [The flip isn't day 1 of flower](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - Terms: [light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md) · [outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md) ## Follow-up questions **Why is my outdoor plant flowering in June?** An outdoor photoperiod cannabis plant flowering in June was usually planted out while days were still short, started from a clone taken off a flowering plant, or is an autoflower. Early-spring days at mid-latitudes are under the 13 h 45 min to 14 h threshold measured in some cultivars. Most such plants re-veg as days lengthen, losing weeks. Plant photoperiods out from late May. **Do streetlights stop outdoor plants flowering?** Streetlights and security lights can delay or disrupt flowering in outdoor cannabis, because the plant measures uninterrupted darkness. A hemp study reported delays from stray light of about 2 µmol/m²/s, and conference work saw delays in sensitive cultivars at 0.01 µmol/m²/s. Plant away from night lighting, or shield the plant, and expect uneven flowering on the lit side. **Can I make outdoor plants flower earlier?** Yes, you can make outdoor cannabis flower earlier with light deprivation: pull a truly lightproof cover over the plants each evening and remove it each morning to give about 12 hours of uninterrupted darkness. Photoperiod plants then flower even in midsummer, which lets growers harvest before autumn rain and mould. Covers must go on at the same time daily, and heat builds underneath. ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ, 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis 3. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 4. Peterswald TJ, Mieog JC, Azman Halimi R, et al., 2023. Moving away from 12:12; the effect of different photoperiods on biomass yield and cannabinoids in medicinal cannabis. Plants 12(5):1061. https://doi.org/10.3390/plants12051061 --- # When do cannabis plants show their sex? > Cannabis plants usually show their sex about 4–6 weeks from seed under long days, when single preflowers form at the nodes; research found the first pair around the 7th node. You need a 30–60x loupe. Males often show first. For an earlier answer, flower a cutting on 12/12 (about 1–2 weeks) or use a DNA sex test from the first true leaves. - Canonical: https://genetixbay.com/knowledge/answers/when-do-plants-show-sex.html - Topic: Basics · Type: Numbers - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) - Also asked as: When can you tell if a plant is male? | How long until preflowers show? | When do preflowers appear? | How to sex cannabis plants early - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Cannabis plants usually show their sex about 4–6 weeks from seed under long days, as single [preflowers](https://genetixbay.com/knowledge/glossary/pre-flower.md) at the nodes. Look with a 30–60x [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md). Males often show a little earlier. *Supported* by research on preflower timing; the week range is *Grower practice*. ## Why Preflowers come with age. Cannabis [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) pass from a juvenile to an adult stage on their own, then form single flowers at the nodes whatever the light schedule; in one cultivar the first pair formed at the 7th node [1]. Solitary flowers are age-dependent and not induced by [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) [2]. Sex is genetic. Cannabis is [dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md) with an [XY system](https://genetixbay.com/knowledge/glossary/xy-sex-determination.md): females XX, males XY [4]. A preflower simply shows which one the plant is. DNA tests read the [chromosomes](https://genetixbay.com/knowledge/glossary/chromosome.md) directly. Validated Y-linked markers identify males from seedling leaves [3], weeks before any flower shows. ## The numbers | Method | When you get an answer | Cost | |---|---|---| | Watch preflowers | ~4–6 weeks from seed (from ~7th node) | Free, plus a loupe | | Flower a labelled cutting on [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) | ~1–2 weeks after the cut goes into long nights | Space and time | | PCR or PACE [DNA test](https://genetixbay.com/knowledge/glossary/genotyping.md) | From the [first true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) | Lab fee | | [Autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) | ~week 3–5, as it starts flowering | Free | | Sign | Female | Male | |---|---|---| | Shape | Teardrop [bract](https://genetixbay.com/knowledge/glossary/bract.md) | Round ball on a short stalk | | [Hairs](https://genetixbay.com/knowledge/glossary/pistil.md) | Two [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md) | None | ## What to do 1. From week 4, check the upper nodes every 2–3 days with a loupe. 2. Look where the [leaf stalk](https://genetixbay.com/knowledge/glossary/petiole.md) meets the stem, behind the stipule. 3. Wait for hairs before calling a female; a ball on a stalk with no hairs is male. 4. Label every plant and keep the record in your journal. 5. Not making seed? Remove males before the sacs open, which often happens within 1–3 weeks of flowering. ## Common mistakes - Mistaking stipules for preflowers. - Calling sex too early from one ambiguous node. - Flipping the whole room just to sex plants, when a cutting would do. - Keeping a male "to see" in the same room as females. ## Related - Full article: [Male, female and hermaphrodite cannabis](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md) - Guide: [Telling sex and spotting herms](https://genetixbay.com/knowledge/guides/telling-sex-and-spotting-herms.md) - Answers: [what to do with a male plant](https://genetixbay.com/knowledge/answers/what-to-do-with-a-male-plant.md) · [when autos start flowering](https://genetixbay.com/knowledge/answers/when-do-autoflowers-start-flowering.md) - Terms: [pre-flower](https://genetixbay.com/knowledge/glossary/pre-flower.md) · [node](https://genetixbay.com/knowledge/glossary/node.md) · [stigma](https://genetixbay.com/knowledge/glossary/stigma.md) ## Follow-up questions **What does a female preflower look like?** A female cannabis preflower is a small teardrop-shaped bract at a node, with two white or coloured stigmas, the 'hairs', poking out of its tip. A male preflower is a small round ball on a short stalk with no hairs, which later opens into pollen sacs. Use a 30–60x loupe, and don't mistake stipules, the small leafy spurs at each node, for preflowers. **Do I need to flip to 12/12 to see sex?** No, you don't need to flip to 12/12 to see a cannabis plant's sex. Preflowers form with age, not with the light schedule, so they appear under 18/6 or 24/0 too, usually about 4–6 weeks from seed. Flipping a cutting rather than the whole plant gives a clear answer in about 1–2 weeks without stopping the mother's veg. **Can a DNA test tell sex from a seedling?** Yes, a PCR or PACE DNA test can identify a male cannabis plant from the first true leaves, using validated Y-linked markers, with high accuracy. It tells you the plant is genetically male or female. It cannot tell you whether a genetic female will later turn hermaphrodite; only growing her out shows that. ## Sources 1. Spitzer-Rimon B, Shafran-Tomer H, Gottlieb GH, et al. 2022. Non-photoperiodic transition of female cannabis seedlings from juvenile to adult reproductive stage. Plant Reproduction 35(4):265-277. https://doi.org/10.1007/s00497-022-00449-0 2. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 3. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667 4. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 --- # When does pre-fertilised soil run out of nutrients? > A typical pre-fertilised bagged potting mix feeds cannabis for about 2-4 weeks, then runs short, usually in mid-veg. Heavily amended or super-soil-style mixes and big pots last longer. The sign is the oldest, lowest leaves turning pale yellow from the tip inward and climbing, which is nitrogen running out. Then start feeding at half the label rate, around EC 0.8-1.6 mS/cm, every second or third watering. - Canonical: https://genetixbay.com/knowledge/answers/when-does-soil-run-out-of-nutrients.html - Topic: Nutrients · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md) - Also asked as: When should I start feeding in soil? | How long does potting soil feed a plant? | How long do soil nutrients last? | My lower leaves are yellowing in new soil | Do I need nutrients with pre-fertilised soil? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A typical pre-fertilised bagged [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) feeds cannabis for about 2–4 weeks, so most plants run short in mid-veg. Richly amended or super-soil-style mixes and bigger pots last longer. When the lowest leaves start to pale and the fading climbs, begin feeding at half the label rate. *Grower practice.* ## Why Bagged mixes carry a modest starter charge of fertiliser. A [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) barely touches it; a plant in fast veg strips it quickly, and each watering [leaches](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) a little more. Nitrogen usually runs out first. It is mobile, so the plant moves it from old leaves to new growth, and the oldest, lowest leaves yellow first while the top stays green [4]. Cannabis trials show exactly that pattern: [nitrogen deficiency](https://genetixbay.com/knowledge/glossary/nitrogen.md) starts on lower leaves and climbs [1][2]. Organic mixes release nutrients through microbes, so their supply depends on warmth, moisture and how much was mixed in. Organic feeds need more nominal nitrogen to match mineral ones, around 389 mg/L N in one vegetative [coir](https://genetixbay.com/knowledge/glossary/coco-coir.md) trial [3], which is why lightly amended mixes [fade](https://genetixbay.com/knowledge/glossary/senescence.md) early. ## The numbers | Mix | Typical feeding time before you add more | |---|---| | Light starter mix (seedling or general potting) | 1–3 weeks | | Standard pre-fertilised potting mix | 2–4 weeks | | Heavily amended organic / super-soil style | 4–8+ weeks, often longer | | [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) with [top-dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md) | Topped up by top-dress, not bottles | When you start: half label rate, [EC](https://genetixbay.com/knowledge/glossary/ec.md) ~0.8–1.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), every second or third watering. ## What to do 1. Water seedlings with plain, pH-adjusted water ([pH](https://genetixbay.com/knowledge/glossary/ph.md) 6.2–6.8). 2. Check the lowest leaves every few days from week 2. 3. When they pale evenly, check [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) pH to rule out [lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md). 4. Start feeding at half the label rate. 5. Check runoff EC monthly; back off if it climbs. ## Common mistakes - Feeding from day one on top of a fertilised mix. - Waiting until half the plant is yellow. - Reading normal late-flower leaf fade as hunger. - Treating a pH problem as a feed problem. ## Related - Full article: [Growing in soil](https://genetixbay.com/knowledge/systems/soil.md) - Answers: [feed every watering?](https://genetixbay.com/knowledge/answers/feed-every-watering.md) · [super soil](https://genetixbay.com/knowledge/answers/what-is-super-soil.md) - Articles: [mobile vs immobile nutrients](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) · [yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) - Terms: [top-dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md) · [nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) ## Follow-up questions **How do I know when my soil is running out of nutrients?** Soil is running out of nutrients when the oldest, lowest leaves of a growing plant turn evenly pale, then yellow, and the fading climbs up the plant while new growth stays green. That is nitrogen, a mobile nutrient, being moved to new leaves. Check runoff pH first; if it is in range, begin feeding at half the label rate. **Should I feed seedlings in fertilised soil?** No, do not feed seedlings planted in fertilised potting mix. The mix's starter charge usually covers the first 2-4 weeks, and seedlings need very little. Extra feed on top risks burnt tips and stalled roots. Water with plain, pH-adjusted water until the lower leaves start to pale, then start feeding gently. **Do bigger pots hold nutrients longer?** Yes, bigger pots of the same mix hold more total fertiliser, so a plant in a larger pot of fertilised mix usually runs longer before needing feed. The concentration is the same, though, so a seedling isn't overfed by a big pot. Watering habits matter more there: big pots of wet mix stay soggy and slow a young plant. ## Sources 1. Cockson P, Landis H, Smith T, Hicks K, Whipker BE, 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y, 2023. Foliar symptomology, nutrient content, yield, and secondary metabolite variability of cannabis grown hydroponically with different single-element nutrient deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307-1312. https://doi.org/10.21273/HORTSCI11903-17 4. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9 --- # When should I flip my plants to flower? > Flip a photoperiod plant to 12/12 (or 13/11) when it is about half the final height your space allows, because most plants grow 50–100% taller, sometimes up to 3×, in the first two to three weeks after the flip. The plant must also be mature, showing preflowers at the nodes. The flip is not day 1 of flower: real flowering starts about 10–14 days later. - Canonical: https://genetixbay.com/knowledge/answers/when-to-flip-to-flower.html - Topic: Basics · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [The flip isn't day 1 of flower: the 10–14 day transition and how to count it](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - Also asked as: When should I switch to 12/12? | When should I flip? | How big should my plant be before flowering? | When to flip photoperiod plants | How tall should plants be at the flip? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Flip a [photoperiod plant](https://genetixbay.com/knowledge/glossary/photoperiod.md) to [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) when it is about half the final height you can fit under the light, and once it shows [preflowers](https://genetixbay.com/knowledge/glossary/pre-flower.md). Most cannabis grows 50–100% taller after the flip, and stretchy cultivars up to 3×. Then count on 10–14 days of transition before flowering really starts. *Supported* for the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) timing; the half-height rule is *Grower practice*. ## Why The stretch belongs to the flip. Under short days, stems and [internodes](https://genetixbay.com/knowledge/glossary/internode.md) lengthened fastest from about day 5 to day 10, before the compact flower cluster took over [1]. A plant-patent description puts the height gain at 50–100% over the first two to three weeks [2]. The flip starts induction, not flowering. Visible [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) clusters at the top of the plant appeared about 8–14 days after short days began in controlled studies [3][4]. That gap is why runs go "long" against breeder times. A plant has to be mature to respond. Preflowers at the nodes form with age, not with the light schedule [3], so they are a good sign the plant is ready. You don't have to run exactly 12/12. At 13 hours, onset moved by about 1.5 days or not at all, with more yield [5]. ## The numbers | Space for the plant (top of pot to lowest safe light height) | Flip at about | |---|---| | 60 cm (2 ft) | 30 cm (12 in) | | 90 cm (3 ft) | 45 cm (18 in) | | 120 cm (4 ft) | 60 cm (24 in) | | Very stretchy cultivar (up to 3×) | One third of the space | ## What to do 1. Measure from the top of the pot to the lowest height your light can safely sit above the canopy. 2. Flip when the plant reaches half of that, or a third for a known stretchy cultivar. 3. Check for preflowers with a [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md) before flipping. 4. Make the dark period truly dark from the first night. 5. Log "days since flip" and, when 3+ pairs of pistils cluster at the top, "day 1 of flower". ## Common mistakes - Flipping by the calendar ("four weeks of veg") instead of by height. - Forgetting the stretch and running out of headroom in week 3. - Counting the flip as day 1 of flower and harvesting two weeks early. - [Light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) in the first two weeks, while induction is still being set up. ## Related - Full article: [The flip isn't day 1 of flower](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - Answers: [how long flowering takes](https://genetixbay.com/knowledge/answers/how-long-does-flowering-take.md) · [how tall plants get indoors](https://genetixbay.com/knowledge/answers/how-tall-do-plants-get-indoors.md) · [plant too tall for the tent](https://genetixbay.com/knowledge/answers/plant-too-tall-for-tent.md) - Terms: [the flip](https://genetixbay.com/knowledge/glossary/flip.md) · [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) · [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) ## Follow-up questions **Is the flip day 1 of flower?** No, the flip to 12/12 is not day 1 of flower. Switching to long nights starts floral induction, and the shoot tip spends roughly 10–14 days rebuilding itself before the first pistil clusters show at the top of the main shoot. Breeder flowering times often count from that point, so a stated 8 weeks usually means harvest about 9.5–10 weeks after the flip. **Should I wait for preflowers before flipping?** Waiting for preflowers before flipping is sensible. Preflowers are single flowers at the nodes that appear with age, not with the light schedule, and they show the plant is mature enough to flower and what sex it is. In research they first formed around the 7th node. A plant flipped before then still flowers, but only after it reaches maturity. **Can I flip on 13/11 instead of 12/12?** Yes, you can flip on 13/11; GenetixBay endorses it. In one study of two THC-dominant cultivars, 13 hours of light delayed flowering by about 1.5 days in one and not at all in the other, while yield rose 1.35× and 1.5×. Sensitive cultivars may take a day or two longer to set flower, so test your own cultivar. ## Sources 1. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 2. US Plant Patent PP30,434 (cannabis plant 'LW-BB1'), botanical description of post-induction stretch. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/PP30434 3. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 4. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 5. Ahrens A, Llewellyn D, Zheng Y. 2024. Longer photoperiod substantially increases indoor-grown cannabis' yield and quality. Plants 13(3):433. https://doi.org/10.3390/plants13030433 --- # When is outdoor cannabis ready to harvest? > Outdoor cannabis is ready when its trichomes are mostly cloudy with some amber (roughly 5–20%), which at 35–50° latitude usually falls between mid-September and late October in the Northern Hemisphere and between March and April in the Southern. Early cultivars finish first; late tropical lines run into November or May. Weather can overrule the trichomes: harvest ahead of long rain spells or a hard freeze. - Canonical: https://genetixbay.com/knowledge/answers/when-to-harvest-outdoors.html - Topic: Outdoor growing · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Also asked as: Outdoor harvest time | Is October harvest normal for outdoor cannabis? | Outdoor finish date | When to harvest outdoor plants in the southern hemisphere | Should I harvest early because of rain or frost? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Outdoor cannabis is ready when [calyx](https://genetixbay.com/knowledge/glossary/calyx.md) [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) are mostly cloudy with some amber, roughly 5–20%. At 35–50° latitude that is usually mid-September to late October in the Northern Hemisphere and March to April in the Southern. Cloudy versus amber is a matter of preference (house position). *Grower practice*, and the weather can overrule it. ## Why Plants ripen at their own pace. Trichome maturation differs by [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) and plant age, and heads on one [bract](https://genetixbay.com/knowledge/glossary/bract.md) mature unevenly [1]. [Cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) plateau, then fall. In [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), totals peaked about 6–7 weeks after flowering began, then declined with [senescence](https://genetixbay.com/knowledge/glossary/senescence.md) [2]. Leaving plants "for more amber" past the plateau costs quality. Autumn weather is the outdoor grower's real deadline. Gray mould ([botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md)) thrives in cool, wet weather and dense flowers [3], and bud rot is the main late-season outdoor loss [4]. The calendar follows the flowering date. Plants that set flower in mid-August and carry an 8–10 week cultivar, plus the 10–14 day transition, finish in mid to late October. ## The numbers | Cultivar type | Northern Hemisphere (35–50°) | Southern Hemisphere (35–50°) | |---|---|---| | Early outdoor lines, [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) | Late August–late September | Late February–late March | | Typical drug-type [photoperiods](https://genetixbay.com/knowledge/glossary/photoperiod.md) | Late September–late October | Late March–late April | | Late, tropical-leaning lines | November or later | May or later | | Trichome target | Mostly cloudy, ~5–20% amber, a few clear | Same | ## What to do 1. Note when [pistils](https://genetixbay.com/knowledge/glossary/pistil.md) first showed; count the cultivar's weeks from then. 2. From two weeks before the expected date, check calyx trichomes at the top, middle and bottom with a 60–100x [loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md). 3. Keep feeding; [taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) in the final weeks rather than [flushing](https://genetixbay.com/knowledge/glossary/flushing.md). 4. Watch the 10-day forecast. Harvest near-ripe plants before long rain or a hard freeze. 5. After rain, shake [colas](https://genetixbay.com/knowledge/glossary/cola.md) dry and open the biggest ones to check for grey mould. 6. Harvest the ripest [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) first if lower buds lag. ## Common mistakes - Leaving plants through a week of rain for a few more amber heads. - Reading sugar-leaf trichomes, which amber early. - Pre-harvest flushing, a *Myth* that starves the plant at its most important stage. - Choosing a 12-week cultivar where first frost comes in early October. ## Related - Full article: [Trichome ripeness: clear, cloudy, amber, and what the evidence says](https://genetixbay.com/knowledge/harvest-cure/trichome-ripeness.md) - Answers: [How to check trichomes](https://genetixbay.com/knowledge/answers/how-to-check-trichomes.md) · [When outdoor plants flower](https://genetixbay.com/knowledge/answers/when-do-outdoor-plants-flower.md) · [Harvesting too early or late](https://genetixbay.com/knowledge/answers/harvesting-too-early-or-late.md) - Articles: [Botrytis bud rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) · [The flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) - Terms: [outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md) ## Follow-up questions **Should I harvest early because of rain?** Harvest outdoor cannabis early ahead of a long spell of cool, wet weather if the buds are close to ripe, because rain soaking dense colas drives bud rot and can lose more than the last few days of ripening would gain. A short shower followed by sun and wind is usually survivable. Shake water off after rain and inspect the inside of the biggest colas for grey mould. **Will frost kill my outdoor plants before harvest?** A light frost often damages only exposed leaves on mature outdoor cannabis, but a hard freeze kills the plant and ends ripening, and frozen, thawed buds rot fast. If a hard freeze is forecast and the buds are near ready, harvest beforehand. Covering plants overnight with frost cloth can buy a few nights. Choose cultivars that finish before your usual first frost. **Should I flush or put outdoor plants in darkness before harvest?** No. Pre-harvest flushing is a myth that starves the plant while it is still packing on weight and resin, so keep feeding at stage strength, tapering nitrogen in the final weeks. Darkness before harvest is a myth too, and impossible outdoors anyway. Judge ripeness by calyx trichomes, swollen calyxes and receded pistils, and let the weather set the final day. ## Sources 1. Punja ZK, Sutton DB, Kim T, 2023. Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences. Journal of Cannabis Research 5:12. https://doi.org/10.1186/s42238-023-00178-9 2. Yang R, Berthold EC, McCurdy CR, et al., 2020. Development of cannabinoids in flowers of industrial hemp (Cannabis sativa L.): a pilot study. Journal of Agricultural and Food Chemistry. https://pubmed.ncbi.nlm.nih.gov/32392412/ 3. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker 4. Utah State University Extension. Hemp bud rot (IPM Notes). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-bud-rot --- # When should I plant cannabis outdoors? > Plant cannabis outdoors after your last frost, once nights stay above about 10 °C (50 °F). At mid-latitudes (35–50°) that is usually mid-May to mid-June in the Northern Hemisphere and mid-November to mid-December in the Southern. Planting photoperiods much earlier, while days are under about 14 hours, risks early flowering and re-veg. Autoflowers can go out any time with 9–14 warm weeks left. - Canonical: https://genetixbay.com/knowledge/answers/when-to-plant-outdoors.html - Topic: Outdoor growing · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) - Also asked as: Outdoor planting date for cannabis | When can I put my plants outside? | Should I plant after the last frost? | When to plant cannabis outdoors in the southern hemisphere | Is April too early to plant outside? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Plant outdoors after your last frost, once nights stay above about 10 °C (50 °F). At 35–50° latitude that usually means mid-May to mid-June in the Northern Hemisphere and mid-November to mid-December in the Southern. *Grower practice*. [Home growing](https://genetixbay.com/knowledge/glossary/home-grow.md) outdoors is legal only in some places: check local rules first. ## Why Cold sets plants back. Frost-tender [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) need settled weather, and anything raised indoors needs [hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) before it goes out [2]. [Day length](https://genetixbay.com/knowledge/glossary/photoperiod.md) decides what a photoperiod plant does. Cannabis measures the night; once nights pass a cultivar's threshold, [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) switch to flowers [3]. Some [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md) had a critical day length of 13 h 45 min to 14 h [1]. Early spring days are short. At 45° latitude mid-April gives only about 13.4 h from sunrise to sunset (calculated), so a plant set out then may start flowering, then [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) as days lengthen. [Autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md) ignore day length. They flower by age, under a separate genetic pathway [4], so only temperature and season length limit them. ## The numbers | Latitude | Northern Hemisphere | Southern Hemisphere | Longest day (sunrise–sunset, calculated) | |---|---|---|---| | 25–30° | Late April–May (frost rarely limits) | Late October–November | ~13.7–14.1 h | | 35–40° | Mid-May–early June | Mid-November–early December | ~14.5–15.0 h | | 45–50° | Late May–mid-June | Late November–mid-December | ~15.6–16.4 h | | 55° | Early–mid-June | Early–mid-December | ~17.4 h | Your local last-frost date overrides this table. ## What to do 1. Find your average last-frost date and add a safety week. 2. Wait for nights reliably above about 10 °C (50 °F). 3. Start photoperiods indoors 3–6 weeks before, under long days. 4. Harden off for 7–14 days. 5. Plant out on a cloudy day or evening, and water in. 6. For autos, sow straight into the final container or bed when nights are warm. ## Common mistakes - Planting photoperiods in April for a "head start", then losing weeks to re-veg. - Skipping hardening off and [bleaching](https://genetixbay.com/knowledge/glossary/light-stress.md) the leaves. - Planting late at high latitude, so flowering runs into autumn rain. - Ignoring local rules on outdoor growing. ## Related - Full article: [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md) - Answers: [Start indoors, move outside](https://genetixbay.com/knowledge/answers/start-indoors-move-outside.md) · [When outdoor plants flower](https://genetixbay.com/knowledge/answers/when-do-outdoor-plants-flower.md) · [Short northern seasons](https://genetixbay.com/knowledge/answers/outdoor-short-season.md) - Terms: [outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md) · [hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) · [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) ## Follow-up questions **Why do plants flower if I put them out too early?** Photoperiod cannabis put outdoors too early in spring can start flowering because days are still short: at 45° latitude, mid-April gives about 13.4 hours from sunrise to sunset, below the 13 h 45 min to 14 h critical day length measured in some hemp cultivars. As days lengthen the plant may revert to leafy growth (re-veg), losing weeks. Waiting until late May avoids it. **When should I plant outdoors in the southern hemisphere?** In the Southern Hemisphere the outdoor cannabis calendar runs six months offset from the north. At mid-latitudes, plant photoperiods out from mid-November to mid-December, after the last frost and once nights stay above about 10 °C (50 °F). Plants flower as days shorten from late January or February and are harvested from about March to May, depending on cultivar. **When should I plant outdoors near the tropics?** Near the tropics, below about 25–30° latitude, the longest day is only about 13.5–14 hours, so many photoperiod cultivars flower soon after planting at any time of year. Plant just before the longest days to get the most vegetative growth, expect smaller plants, or use autoflowers. Frost is rarely the limit there; heat, rain and pests are. Check local rules first. ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. University of Minnesota Extension. Starting seeds indoors (transplanting seedlings, hardening). https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors 3. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350 4. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 --- # When should I stop feeding before harvest? > Don't stop feeding before harvest. Stopping nutrients or flushing with plain water in the last 1-3 weeks is a harmful Myth: the plant is still packing on weight and resin. Feed through to the chop at stage strength. The GenetixBay approach is to taper only nitrogen over the last 3-4 weeks, down to 0-20 mg/L in the final days, while keeping P, K, Ca, Mg, S and micros fed. - Canonical: https://genetixbay.com/knowledge/answers/when-to-stop-feeding-before-harvest.html - Topic: Nutrients · Type: How-to - Evidence: Myth · Status: Draft: awaiting expert review - Full article: [Per-element feeding tricks: what growers adjust, stage by stage](https://genetixbay.com/knowledge/nutrients/per-element-tricks.md) - Also asked as: When do I stop nutrients before harvest? | When is the last feed before the chop? | Should I feed right up until harvest? | How many weeks should I flush before harvest? | Do I need to stop nutrients to get white ash? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Don't. Feed cannabis through to harvest at stage strength. Stopping nutrients or [flushing](https://genetixbay.com/knowledge/glossary/flushing.md) with plain water in the final 1–3 weeks is a *Myth*, and it does harm: it starves the plant while it is still adding most of its final weight, [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) and resin. Taper only nitrogen over the last 3–4 weeks, to 0–20 mg/L at the finish. ## Why Cannabis stores what it takes up. Nutrients are built into proteins, [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) and cell walls, so plain water at the end does not rinse them out of the flower. In Utah State work, leaf nitrogen fell during a flush but flower nitrogen did not change [3]. Controlled flushing trials found no gain in quality, minerals or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md). Short flushes of 2 weeks or less showed no consistent yield change; flushes of 3 weeks or more cut dried bud weight [2][4]. Nitrogen is the one element worth trimming. Lower nitrogen raised cannabinoid and [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) concentration while yield rose with N up to about 160 mg/L [1]. That is a deliberate trade-off, made by cutting N alone, not everything. ## The numbers | Weeks before harvest | Nitrogen | Everything else | |---|---|---| | 4 | 100–150 mg/L (normal late flower) | Normal late-flower strength | | 3 | ~75% of that | Unchanged | | 2 | ~50% | Unchanged | | 1 | ~25% | Unchanged | | Final days | 0–20 mg/L | Unchanged | ## What to do 1. Keep feeding at your late-flower [EC](https://genetixbay.com/knowledge/glossary/ec.md); don't switch to plain water. 2. If you use single salts or [per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md), step nitrogen down as above. 3. With a bottled two-part, keep feeding normally rather than diluting everything. 4. Watch [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) EC; flush the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) only if salts have built up. 5. Judge harvest by trichomes, and put your effort into a slow dry and cure. ## Common mistakes - Flushing for two weeks "for taste" and losing weight and resin. - Blaming dark ash on nutrients instead of drying and curing. - "Tapering" by diluting a two-part, which cuts calcium and potassium too. - Panicking over lower [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) fading in the last 2–3 weeks; that's normal. ## Related - Full article: [Per-element feeding tricks](https://genetixbay.com/knowledge/nutrients/per-element-tricks.md) - Main article: [Pre-harvest flushing: a myth](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) · [Nitrogen](https://genetixbay.com/knowledge/nutrients/nitrogen.md) - Answers: [fixing lockout](https://genetixbay.com/knowledge/answers/how-to-fix-nutrient-lockout.md) · [deficiency in late flower](https://genetixbay.com/knowledge/answers/fix-deficiency-in-late-flower.md) - Terms: [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) · [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) ## Follow-up questions **Does flushing before harvest improve taste?** No. Flushing before harvest does not improve taste or ash colour; that is a Myth. Controlled studies found no gain in flower quality, minerals or cannabinoids, and in one taste trial tasters preferred unflushed flower. Harsh smoke and dark ash come from fast drying, rushed curing and how the material burns, not from nutrients left in the plant. **How do I taper nitrogen before harvest?** Taper nitrogen in steps from about 4 weeks before harvest: around 75% of your late-flower nitrogen at 3 weeks out, 50% at 2 weeks, 25% in the last week and 0-20 mg/L in the final days. Keep phosphorus, potassium, calcium, magnesium, sulfur and micros at normal strength. A diluted two-part bottle cannot do this; single salts or per-element dosing can. **Is there ever a good reason to flush?** Yes, one. A root-zone flush washes accumulated salts out of the medium when runoff EC sits roughly 1.0 mS/cm or more above input, or you see salt crust, spreading burnt tips or lockout. It treats the medium, not the plant, can be done at any stage, and is followed by normal feeding. It is not a pre-harvest ritual. ## Sources 1. Saloner A, Bernstein N, 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516 2. Alden MJ, Faust JE, 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 3. Hershkowitz JA, 2024. Nutrient management of cannabis in controlled environments. MS thesis, Utah State University. https://digitalcommons.usu.edu/etd2023/178 4. Stemeroff J, 2017. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 --- # When should I stop training my plants? > Stop training cannabis by technique. Do the last topping at least 7–10 days before the flip to 12/12. Finish hard LST bending and supercropping by flower week 2–3, when stems lignify at the end of the stretch. Keep tucking under a net for about the first 2 weeks of stretch. After that, only gentle guiding and support. - Canonical: https://genetixbay.com/knowledge/answers/when-to-stop-training.html - Topic: Training · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [LST: low-stress training](https://genetixbay.com/knowledge/training/lst.md) - Also asked as: When should I stop LST in flower? | Can I train during the stretch? | What is the last day to top before flowering? | Can I LST in flower? | When to stop supercropping - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Stop each kind of training at its own point. Top for the last time at least 7–10 days before the flip. Finish hard [LST](https://genetixbay.com/knowledge/glossary/lst.md) bending and [supercropping](https://genetixbay.com/knowledge/glossary/supercropping.md) by flower week 2–3, when the [stretch](https://genetixbay.com/knowledge/glossary/stretch.md) ends and stems stiffen. Keep tucking under a net for about the first 2 weeks of stretch, then only gentle guiding. *Grower practice*. ## Why Training builds an [even canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md), and an even canopy puts more [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md) in good light. Yield follows light [2], and shaded lower buds carry lower, less uniform [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) [1]. Topping is the slowest to recover from: 3–7 days before visible regrowth. Done in flower, that recovery comes out of bud-building time. The stretch is the last chance to shape the plant. Stems and [internodes](https://genetixbay.com/knowledge/glossary/internode.md) elongate fastest roughly 5–10 days into short days [3], so most height gain happens in the first 2–3 weeks after the flip. Remember the flip isn't day 1 of flower. The first 10–14 days after [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) are a transition, and that's exactly the window when bending and tucking still work. By week 3 stems have lignified. Woody stems crease or snap when bent, and the plant is now spending its energy on flowers, not on regrowing. ## The numbers | Technique | Last done | Notes | |---|---|---| | Topping, [FIM](https://genetixbay.com/knowledge/glossary/fim.md) | 7–10+ days before the flip | Never in flower | | Hard LST bending | Flower week 2–3 | Gentle guiding after | | Supercropping | First 2 weeks of flower | Green stems only | | [SCROG](https://genetixbay.com/knowledge/glossary/scrog.md) tucking | About the first 10–14 days of stretch | Then let [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) grow up | | [Lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md) | Flip to about day 21 | Lower third only | | Leaf tucking | Any time | Tuck, don't pluck | | Support (stakes, [trellis](https://genetixbay.com/knowledge/glossary/trellis.md)) | Any time | Heavy [colas](https://genetixbay.com/knowledge/glossary/cola.md) need it in late flower | ## What to do 1. Plan back from the flip date: last top 7–10 days earlier. 2. Keep LST ties moving every 2–4 days through veg and early stretch. 3. Tuck shoots under the net for the first 2 weeks after the flip. 4. Supercrop any runaway tops before week 3. 5. From week 3, only support, tuck leaves and adjust gently. ## Common mistakes - Topping after the flip. - Starting hard bends in week 4 and snapping woody branches. - Forgetting ties as stems thicken in flower. - Stripping leaves instead of tucking them. ## Related - Full article: [LST: low-stress training](https://genetixbay.com/knowledge/training/lst.md) - Answers: [recovery after topping](https://genetixbay.com/knowledge/answers/recovery-after-topping.md) · [plant too tall for the tent](https://genetixbay.com/knowledge/answers/plant-too-tall-for-tent.md) · [when to flip](https://genetixbay.com/knowledge/answers/when-to-flip-to-flower.md) - Training: [topping](https://genetixbay.com/knowledge/training/topping.md) · [supercropping](https://genetixbay.com/knowledge/training/hst-supercropping.md) - Terms: [tucking](https://genetixbay.com/knowledge/glossary/tucking.md) ## Follow-up questions **Can I LST in flower?** Yes, you can keep LST going into early flower, but stop hard bending by mid-stretch, around flower week 2–3, when stems turn woody. During the stretch, tuck tops under a net or steer them gently instead of forcing sharp bends. Later, bending woody stems risks creasing or snapping; if one creases, tape it and it usually heals. **Can I top in flower?** Don't top in flower. The plant needs 3–7 days before visible regrowth after topping, and in flower that recovery comes straight out of bud-building time. Do the last top at least 7–10 days before switching to 12/12 so the new tops are growing strongly at the flip. If a plant is too tall in flower, supercrop or bend it instead. **Can I supercrop during the stretch?** Yes, supercropping works well in the first two weeks of flower, while stems are still green and the stretch is pushing tall tops toward the light. Pick a pliable section 5–15 cm below the tip, soften it gently and bend it over. After about week 3, stems are woody and more likely to snap, so switch to support stakes or a trellis. ## Sources 1. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 3. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 --- # When are rooted clones ready to transplant? > Rooted cannabis clones are ready to transplant when several white roots, about 2–5 cm (1–2 in) long, are poking out of the sides or base of the plug, usually 10–14 days after cutting. Harden them off from the dome over 3–5 days first. Move them into a 0.5–3 L pot of pre-moistened medium at the same pH and keep light gentle for a few days. - Canonical: https://genetixbay.com/knowledge/answers/when-to-transplant-clones.html - Topic: Cloning and mother plants · Type: Numbers - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: When do I transplant clones? | How long should clone roots be before transplanting? | When can I up-pot clones? | How can I back up a clone? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Transplant](https://genetixbay.com/knowledge/glossary/transplanting.md) rooted cannabis clones when several white roots, 2–5 cm (1–2 in) long, show at the sides or base of the plug, usually 10–14 days after cutting. Harden them off over 3–5 days, then pot into 0.5–3 L of pre-moistened medium. *Grower practice*. ## Why Roots have to supply the leaves once the dome comes off. One stub of root can't; a handful can. Timing in trials matches. [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md) cuttings were judged ready 12 days after sticking, once more than half showed visible roots [2]. Moving too late costs too. Roots that circle a plug for weeks become a tangle that is slow to grow out into new medium. [Pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) should match the root ball. A small container wets and dries in step with a small root system, while a huge pot stays wet where there are no roots [1]. Rooted clones are also your backup. Holding a few as a slow line, alongside [tissue culture](https://genetixbay.com/knowledge/glossary/tissue-culture.md) banking, protects a [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) against loss [3]. ## The numbers | Sign | Ready? | |---|---| | No roots visible after 7 days | No, wait | | One short root | Not yet | | Several white roots 2–5 cm out of plug | Yes | | Roots brown, matted, circling | Overdue | | Step | Target | |---|---| | [Hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) | 3–5 days, vents then lid off | | First pot | 0.5–3 L, ~2–4× plug volume | | Medium [pH](https://genetixbay.com/knowledge/glossary/ph.md) | Soil 6.2–6.8; [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) 5.8–6.2 | | Light after move | 150–300 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), rising | ## What to do 1. Check plug sides and bottoms from day 7; don't pull. 2. Open dome vents once roots show, then prop and remove the lid over 3–5 days. 3. Pre-moisten the new medium to "wrung sponge" and pH it. 4. Set the plug in whole, firm gently, water in lightly. 5. Keep light gentle for 2–3 days, then raise it. ## Common mistakes - Transplanting the day the [first root](https://genetixbay.com/knowledge/glossary/radicle.md) tip appears. - Moving clones and removing the dome on the same day. - Plug straight into a 20 L pot. - Tearing roots by pulling the plug apart. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Transplanting](https://genetixbay.com/knowledge/germination/transplanting.md) - [How long do clones take to root?](https://genetixbay.com/knowledge/answers/how-long-do-clones-take-to-root.md) · [Why are my clones wilting?](https://genetixbay.com/knowledge/answers/why-are-my-clones-wilting.md) - Terms: [transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md) · [hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) ## Follow-up questions **How can I back up a clone?** Back up a cannabis clone by keeping two clean mothers in two locations, holding a slow-growing clone line as a living spare at about 18–22 °C under 100–200 µmol/m²/s, and banking the genotype in tissue culture, where meristem culture also helps clean infected stock. As extra insurance, make honestly labelled S1s or crosses, which preserve the clone's genes if the plant is lost. **Can I transplant a clone with only one root?** You can, but it's risky. A cannabis clone with a single short root can't yet supply its leaves, so it often wilts once it leaves the dome and stalls in the new pot. Wait a few more days until several white roots show at the plug's edge. If you must move it, keep it under the dome at high humidity for another 3–5 days. **What size pot should rooted clones go into?** Put rooted cannabis clones into a 0.5–3 L pot first, roughly 2–4 times the plug volume, then into the final pot later. A small pot wets and dries in step with a small root ball. Going straight from a plug into a 20 L pot leaves most of the medium rootless and wet, which slows growth and invites root disease. ## Sources 1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (container size and air-filled porosity). https://doi.org/10.1016/C2015-0-01807-5 2. Campbell SM, Anderson SL, Brym ZT, Pearson BJ, 2021. Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.). PLOS ONE 16(7): e0249160. https://doi.org/10.1371/journal.pone.0249160 3. Monthony AS, Page SR, Hesami M, Jones AMP. 2021. The past, present and future of Cannabis sativa tissue culture. Plants 10(1):185. https://doi.org/10.3390/plants10010185 --- # Which nutrients do I actually need for a first grow? > For a first grow you need one complete base nutrient made for your medium (soil, or a two-part A and B for coco and hydro), Cal-Mag only if you use RO or soft water or coco, a pH down, and a pH and EC meter. Boosters, sugars and most additives are optional: cannabis trials found no yield gain above about 30-60 mg/L phosphorus or from doubling feed strength. - Canonical: https://genetixbay.com/knowledge/answers/which-nutrients-to-buy.html - Topic: Nutrients · Type: How-to - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Also asked as: What is a basic nutrient line for beginners? | What nutrients should I buy? | Do I need all the additives? | Do I need bloom boosters? | Minimum nutrients for growing cannabis - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer One complete base nutrient made for your medium, [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) only if your water or medium calls for it, a [pH](https://genetixbay.com/knowledge/glossary/ph.md) down, and meters for pH and [EC](https://genetixbay.com/knowledge/glossary/ec.md). [Bloom boosters](https://genetixbay.com/knowledge/glossary/bloom-booster.md), sugars and most additives are optional at best. Controlled cannabis trials found no gain above about 30–60 mg/L phosphorus or from doubling overall strength [1][2][3]. *Supported.* ## Why A complete base feed supplies all the essential elements. That is all the plant can use. Phosphorus has a plateau. Several independent trials agree that once the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) carries roughly 30–60 mg/L P, more does not raise yield or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) [1][3]. Extra phosphorus raised leachate P instead [1]. Strength has a plateau too. Doubling feed from 2 to 4 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) in deep-flow hydro raised solution nutrients but not yield or cannabinoids [2]. Stacking products can backfire. Higher potassium supply lowered calcium and magnesium uptake in cannabis [4], which is what a PK booster on top of a complete base does. House positions apply here: Cal-Mag need is driven by cultivar, [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), not by [LEDs](https://genetixbay.com/knowledge/glossary/led.md), and [molasses](https://genetixbay.com/knowledge/glossary/molasses.md) feeds microbes, not the plant. ## The numbers | Item | Need it? | Notes | |---|---|---| | Complete base (soil one-part, or [A and B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) for coco and hydro) | Yes | Matched to medium | | pH down | Yes, for coco and hydro | Mineral acid | | [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) + buffers | Yes, for coco and hydro | Calibrate weekly | | [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) | Yes | Read in mS/cm | | Cal-Mag | Only with RO, soft water or coco | Fill the gap to Ca 150–200, Mg 40–70 mg/L | | Silica | Optional | Thin cannabis evidence | | [Bloom](https://genetixbay.com/knowledge/glossary/flowering-stage.md) / PK booster | No | P plateau at ~30–60 mg/L | | Molasses, sugars | No | Feeds microbes, not the plant | ## What to do 1. Pick your medium first. 2. Buy one complete base made for it. 3. Get a water report or measure your water's EC. 4. Add Cal-Mag only if the numbers say so. 5. Spend the rest on a good pH meter and fresh buffers. ## Common mistakes - Buying the whole ten-bottle line. - Stacking boosters on a complete base. - Running Cal-Mag with [hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md). - Skipping the meters to buy additives. ## Related - Full article: [Building a cannabis feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) - Articles: [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) · [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md) - Answers: [meters you need](https://genetixbay.com/knowledge/answers/meters-you-need-for-growing.md) · [full-strength chart?](https://genetixbay.com/knowledge/answers/full-strength-feeding-chart.md) - Terms: [A-B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) · [cal-mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) ## Follow-up questions **Do I need bloom boosters?** No, you do not need bloom boosters. Controlled cannabis trials found no yield or cannabinoid gain once the feed supplies about 30-60 mg/L phosphorus; extra phosphorus mostly ended up in the runoff. A complete base feed already covers flower. Stacking a PK booster on top can push potassium high enough to suppress calcium and magnesium. **Do I need Cal-Mag?** You need Cal-Mag only when your water and base nutrient together supply too little calcium and magnesium: RO or very soft water, new or unbuffered coco, or a base made for hard water. Need also varies by cultivar. LED lighting does not create a Cal-Mag need; that claim is a myth. Check your water report before buying. **Do I need molasses or sugar additives?** No. Molasses and sugars feed soil microbes, not the plant, which makes its own sugars by photosynthesis and does not take up meaningful sucrose through its roots. In soil they are harmless at small doses; in hydro they feed biofilm, strip oxygen and raise root rot risk. Taste comes from plant health, drying and curing. ## Sources 1. Westmoreland FM, Bugbee B, 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652 2. Hershkowitz JA, Westmoreland FM, Bugbee B, 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985 3. Shiponi S, Bernstein N, 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323 4. Saloner A, Sacks MM, Bernstein N, 2019. Response of medical cannabis (Cannabis sativa L.) genotypes to K supply under long photoperiod. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369 --- # Which way up do I plant a germinated seed? > Plant a germinated cannabis seed taproot (radicle) pointing down, 0.5–1.5 cm (¼–½ in) deep, in moist, light mix. Move it once the taproot is about 0.5–2 cm long, before it gets long and brittle. If you get it wrong, don't dig it up: the root turns down by itself. Handling and breaking the taproot does more harm than planting it sideways. - Canonical: https://genetixbay.com/knowledge/answers/which-way-up-to-plant-a-seed.html - Topic: Germination · Type: How-to - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md) - Also asked as: Taproot down or up? | I planted my seed upside down, is it ruined? | How do I plant a sprouted seed? | How deep do I plant a germinated seed? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Plant a germinated [cannabis seed](https://genetixbay.com/knowledge/glossary/achene.md) [taproot](https://genetixbay.com/knowledge/glossary/taproot.md) down, 0.5–1.5 cm (¼–½ in) deep, ideally when the taproot is 0.5–2 cm long. If it went in sideways or upside down, leave it: the root turns down on its own. *Grower practice*. ## Why The taproot ([radicle](https://genetixbay.com/knowledge/glossary/radicle.md)) responds to gravity and grows down; the shoot grows up. A seed set the wrong way spends a little energy turning round, then carries on. The real risk is handling. A long taproot is brittle and easily snapped when lifted from a towel, which is why lab protocols [germinate](https://genetixbay.com/knowledge/glossary/germination.md) seeds in a tube and transfer them early [1]. Depth matters more than orientation. Too deep and the [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) spends its reserves climbing; too shallow and it dries out or emerges with the [shell](https://genetixbay.com/knowledge/glossary/seed-coat.md) stuck on. Warmth gets it up fast. Keep the medium around 22–27 °C (72–81 °F); [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) germination slows sharply in the cold [2]. ## The numbers | Item | Target | |---|---| | Orientation | Taproot down; sideways is fine | | Planting depth | 0.5–1.5 cm (¼–½ in) | | Taproot length at planting | 0.5–2 cm (¼–¾ in) | | Medium temperature | 22–27 °C (72–81 °F) | | Time to surface | Usually 1–3 days after planting | ## What to do 1. Pre-moisten a light seedling mix or plug so it holds together but doesn't drip. 2. Make a hole 0.5–1.5 cm deep with a pencil. 3. Lift the seed by the shell, not the root, with clean tweezers. 4. Drop it in taproot down, cover loosely, firm very lightly. 5. Keep it warm and just moist; don't flood it [3]. ## Common mistakes - Digging the seed up to check on it. - Leaving the taproot in the towel until it is 5 cm long. - Planting 3 cm deep "to be safe". - Watering a fresh plant so hard the seed washes out. ## Related - Full article: [Germination methods compared](https://genetixbay.com/knowledge/germination/germination-methods.md) - [What if the seed shell is stuck?](https://genetixbay.com/knowledge/answers/seed-shell-stuck-on-seedling.md) · [Why won't my seeds germinate?](https://genetixbay.com/knowledge/answers/why-wont-my-seeds-germinate.md) - Terms: [taproot](https://genetixbay.com/knowledge/glossary/taproot.md) · [radicle](https://genetixbay.com/knowledge/glossary/radicle.md) ## Follow-up questions **What if I planted my seed upside down?** Leave it. A cannabis seed planted upside down or sideways usually corrects itself, because the taproot grows downward with gravity and the shoot grows up. It may surface a day or so later and with a slight bend in the stem. Digging it up to turn it risks snapping the fragile taproot, which does far more damage than the wrong orientation. **How long should the taproot be before planting?** Plant a cannabis seed from a paper towel once the taproot is about 0.5–2 cm (¼–¾ in) long. Shorter is fine; longer taproots are brittle, may grow root hairs into the towel and break when you lift them. If one has grown long, lay it in a pre-made hole with the root pointing down and cover it gently rather than forcing it straight. **Should the seed be covered completely?** Yes. Cover a germinated cannabis seed completely with 0.5–1.5 cm (¼–½ in) of light, moist mix, and firm it very lightly. A seed left on the surface can dry out, and a shallow seed often comes up with its shell still stuck on the leaves. Planting much deeper than about 1.5 cm wastes the seed's reserves on a long climb to the light. ## Sources 1. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 2. Geneve RL, et al., 2022. Temperature limits for seed germination in industrial hemp (Cannabis sativa L.). Crops 2(4):415–427. https://doi.org/10.3390/crops2040029 3. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping --- # What is the white fuzz on top of my soil? > White fuzz on top of cannabis soil is usually harmless fungal growth (mycelium) feeding on organic matter in a surface that stays wet. It rarely harms the plant, but it means you water too often or the air is too still, and wet surfaces breed fungus gnats. Let the top 3–5 cm dry between waterings and move air over the pots. A hard, crunchy white crust is salt, not fungus. - Canonical: https://genetixbay.com/knowledge/answers/white-fuzz-on-soil.html - Topic: Diseases · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Sanitation and disease prevention for cannabis grows](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - Also asked as: White mould on top of my soil | Fungus growing on the soil surface | Is mycelium in my pot bad? | White crust on top of the pot - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer White fuzz on top of cannabis soil is usually saprophytic fungus: mycelium living on organic matter in a surface that never dries. It rarely hurts the plant directly. It does mean the top of the pot stays wet, so water less often and move air over the pots. *Grower practice*. ## Why Potting media are full of fungi. Unpasteurised [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), for example, carries fungal communities of its own [2]. Most of them break down organic matter, and they only grow a visible white mat when the surface stays damp and the air is still. The wet surface is the real problem. [Fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) lay their eggs in moist, fungus-rich media, and their larvae feed on fungi and on roots [1]. A pot that never dries back also keeps the roots short of oxygen. Constantly wet roots favour [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) and [Fusarium root rot](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md), which cause wilting and yellowing [3]. ## The numbers | What you see | Likely cause | Action | |---|---|---| | Soft white fluff, grows back on wet spots | Decomposer fungi | Dry the surface, add airflow | | Hard, crunchy white or tan crust | [Salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) | Check [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md); [flush](https://genetixbay.com/knowledge/glossary/flushing.md) the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) | | Fuzz plus a drooping plant, heavy pot | [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), possible [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) | Check the roots | | Fuzz plus small black flies | Fungus gnats | Dry the top 3–5 cm, use [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) | ## What to do 1. Lift the pot. If it is still heavy, wait until it is about 40–50% lighter before watering. 2. Scrape off the fuzz and the top centimetre or so of mix. Bag it and take it out of the room. 3. Let the top 3–5 cm dry between waterings, and water so the pot drains freely. 4. Run a fan low across the pots so the surface dries. 5. Topping the pot with a thin layer of dry, coarse material such as [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) keeps the surface drier. 6. If the plant is wilting or yellowing as well, slide it out and check that the roots are white. ## Common mistakes - Spraying fungicide or [peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) on the soil without fixing how you water. - Mistaking salt crust for mould. - Watering a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) in a huge pot every day. - Leaving runoff sitting in the saucer. ## Related - Full article: [Sanitation and disease prevention](https://genetixbay.com/knowledge/diseases/sanitation-and-prevention.md) - Answers: [small white bugs in soil](https://genetixbay.com/knowledge/answers/small-white-bugs-in-soil.md) · [how often to water](https://genetixbay.com/knowledge/answers/how-often-to-water.md) - Articles: [drooping: over- vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) · [fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md) - Terms: [fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) · [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) ## Follow-up questions **Is white mould on soil harmful to cannabis?** White mould on cannabis soil is usually not harmful in itself. It is mostly fungi breaking down organic matter on a wet surface. The risk is what it tells you: the pot stays wet, which starves roots of oxygen and favours fungus gnats and root rot. If the plant is drooping or yellowing as well, check the roots. **How do I tell fungus from salt crust on my pot?** Fungus on cannabis soil is soft, fluffy or web-like and grows back within days on wet spots. Salt crust is hard, crystalline and crunchy, white or tan, and forms where water evaporates, often at the pot rim, on fabric pots or on rockwool. Salt points to high runoff EC and calls for a root-zone flush rather than less watering. **Is white fuzz in living soil a good sign?** White fuzz in living soil or a thick mulch layer is often normal decomposer fungi and part of a healthy soil food web, not a disease. Treat it differently in bagged soilless mixes and seedling pots, where it usually just means the surface never dries. In either case, keep air moving and avoid daily surface drenching. ## Sources 1. UConn IPM. Managing Fungus Gnats in the Greenhouse. https://ipm.cahnr.uconn.edu/managing-fungus-gnats-in-the-greenhouse/ 2. Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. https://www.frontiersin.org/articles/10.3389/fpls.2019.01120/full 3. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 --- # Why is my whole plant pale or light green? > A cannabis plant that is pale all over is usually short of nitrogen, or has roots that can't take nitrogen up because they are overwatered, cold or at the wrong pH. Check the root zone first: pH 6.0–7.0 in soil, 5.5–6.5 in coco and hydro, and roots at about 20 °C (68 °F). Then raise nitrogen modestly, by 10–20%. Some cultivars are naturally lime green. - Canonical: https://genetixbay.com/knowledge/answers/whole-plant-pale-green.html - Topic: Diagnosis · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) - Also asked as: Why is my cannabis plant pale? | Light green leaves all over the plant | Plant losing its colour | Whole plant lime green, not yellow - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A cannabis plant that is pale all over is most often short of nitrogen. More often still, the roots can't take nitrogen up because they are [overwatered](https://genetixbay.com/knowledge/glossary/overwatering.md), cold or at the wrong [pH](https://genetixbay.com/knowledge/glossary/ph.md). Check the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) before you feed more, and if nitrogen really is low, raise it by about 10–20%. *Supported*. ## Why Nitrogen goes into [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md). In controlled cannabis trials, nitrogen-short plants paled evenly, with the yellowing climbing from the lower leaves. Healthy recent leaves held about 3.3–4.8% nitrogen by [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md), against 1.6% in deficient plants [1][2]. Roots have to be able to absorb. Waterlogged, cold or [rotting roots](https://genetixbay.com/knowledge/glossary/root-rot.md) take up less, and in hydro, root rot gives yellowing and stunting with a full reservoir [4]. [Feed strength](https://genetixbay.com/knowledge/glossary/input-ec.md) matters within limits. In one [soilless](https://genetixbay.com/knowledge/glossary/soilless.md) flowering trial, the predicted yield optimum was about 194 mg/L of mineral nitrogen [3]. Doubling the feed won't help roots that can't absorb. [Light bleaching](https://genetixbay.com/knowledge/glossary/light-stress.md) [looks](https://genetixbay.com/knowledge/glossary/bag-appeal.md) different. It pales the tops nearest the lamp first, while the lower leaves stay green [5]. ## The numbers | Check | Target | |---|---| | pH, soil | 6.0–7.0 | | pH, [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and hydro | 5.5–6.5 (hydro 5.5–6.0) | | Root-zone temperature | About 20 °C (68 °F); hydro 18–22 °C | | Leaf N, healthy | 3.3–4.8% of dry weight [1] | | Mineral N, flower (one trial) | About 194 mg/L predicted optimum [3] | | Feed increase if N is low | 10–20% of the current rate | ## What to do 1. Lift the pot. If it is heavy and wet, let it [dry back](https://genetixbay.com/knowledge/glossary/dryback.md) before doing anything else. 2. Measure the pH and [EC](https://genetixbay.com/knowledge/glossary/ec.md) of the [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) or reservoir with a calibrated meter. 3. Check the roots: white and firm is healthy, brown and slimy is not. Warm a cold root zone. 4. Look at the pattern. Even paleness that climbs from the bottom points to nitrogen. Pale tops only point to light, or to sulfur or iron (see yellow new growth). 5. If nitrogen is low, raise it by 10–20%. Organic growers can [top-dress](https://genetixbay.com/knowledge/glossary/top-dressing.md) and allow 1–2 weeks. 6. Know your cultivar: some are lime green when healthy. Late-flower fading is normal. ## Common mistakes - Feeding more to an overwatered plant. - Chasing paleness with extra [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md). - Pushing nitrogen into ripening buds late in flower. - Blaming the light unmeasured. ## Related - Full article: [Yellowing lower leaves: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) - Answers: [seedling leaves yellow](https://genetixbay.com/knowledge/answers/seedling-leaves-yellow.md) · [fix nutrient lockout](https://genetixbay.com/knowledge/answers/how-to-fix-nutrient-lockout.md) · [do I need to pH?](https://genetixbay.com/knowledge/answers/do-i-need-to-ph-my-water.md) - Article: [yellow new growth](https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.md) - Terms: [nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md) · [nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) ## Follow-up questions **Is a pale cannabis plant a nitrogen deficiency?** A pale cannabis plant often has a nitrogen deficiency, but only when the roots can absorb. Controlled trials show nitrogen shortage as even pale-to-lemon yellowing that climbs from the lower leaves. Healthy recent leaves hold about 3.3–4.8% nitrogen by dry weight. Rule out overwatering, a cold root zone and pH first, because those block uptake from a perfectly good feed. **Why is my plant pale after transplanting?** A cannabis plant often goes pale for a few days after transplanting because damaged or settling roots take up less nitrogen, and a big pot of wet mix stays cold and airless. Water lightly around the root ball, keep the root zone near 20 °C (68 °F) and wait for new growth. If paleness lasts more than a week, check pH and feed. **Can too much light make a plant pale?** Too much light bleaches cannabis from the top down, turning the leaves nearest the lamp pale, yellow or white while lower leaves stay green. Even paleness over the whole plant is more likely nitrogen or the root zone. Measure canopy PPFD and leaf temperature, keeping leaves under about 30 °C (86 °F), before blaming the light. ## Sources 1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432 2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422 3. Bevan L, Jones M, Zheng Y., 2021. Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103 4. Punja ZK, Rodriguez G., 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466 5. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 --- # Why are my buds airy or larfy? > Airy, larfy buds are usually buds that got too little light: lower and inner sites often receive a fraction of the canopy-top PPFD, well below the 800–1,200 µmol/m²/s flower target. Other causes are heat above about 30 °C (86 °F), harvesting too early, root-zone or feeding problems, and cultivars that naturally make loose flowers. Check light at the bud, not the top. - Canonical: https://genetixbay.com/knowledge/answers/why-are-my-buds-airy.html - Topic: Training · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Also asked as: Why are my buds airy? | Why are my buds fluffy and not dense? | How do I stop larf? | Why do I get popcorn buds at the bottom? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Airy, larfy buds usually got too little light. Lower and inner [bud sites](https://genetixbay.com/knowledge/glossary/bud-site.md) often receive a fraction of the canopy-top [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), well below the 800–1,200 µmol/m²/s flower target. Other causes: heat above about 30 °C (86 °F), harvesting early, root-zone or feeding trouble, and cultivars that make loose flowers. *Supported* for light; the rest is diagnosis. ## Why Yield follows light almost linearly in flower. Two indoor trials found dry flower yield rose in proportion to canopy PPFD [1][4]. A bud sitting at 200 µmol/m²/s builds a fraction of the mass of one at 1,000. Light falls off fast with depth. Lower buds in cannabis carry fewer [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), tracking that poor light penetration [2]. Those sites become larf. Heat loosens [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md). Cannabis [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) falls above about 30 °C [3], and hot, over-lit [colas](https://genetixbay.com/knowledge/glossary/cola.md) [foxtail](https://genetixbay.com/knowledge/glossary/foxtailing.md) into airy spears. Time matters. Buds bulk in the second half of flower, so a harvest timed from the flip as day 1 of flower comes up to two weeks early. The first 10–14 days after [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) are transition. Genetics sets the ceiling. Some cultivars make open flowers in perfect conditions, and indica or sativa labels don't predict it. ## The numbers | Clue | Likely cause | First check | |---|---|---| | Lower buds only | Low light at the site | PPFD at the bud; [lollipop](https://genetixbay.com/knowledge/glossary/lollipopping.md) | | Top buds spiky and loose | Heat or [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md) | [Canopy temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md); PPFD at tops | | Whole plant loose | Low light overall, early harvest, or cultivar | Room average PPFD; [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) | | Loose with pale leaves | Underfeeding or root-zone trouble | [Runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [pH](https://genetixbay.com/knowledge/glossary/ph.md) and [EC](https://genetixbay.com/knowledge/glossary/ec.md); roots | | Target PPFD in flower | 800–1,200 µmol/m²/s | Ambient CO₂ | | Target day temperature | 22–26 °C (72–79 °F) | Canopy height | ## What to do 1. Measure PPFD at the buds that went airy, not only at the top. 2. Measure canopy temperature at the top colas. 3. Check trichomes before harvest: mostly cloudy, some amber. 4. Next run, lollipop the lower third at the flip and train a [flat canopy](https://genetixbay.com/knowledge/glossary/even-canopy.md); tuck leaves rather than strip them. 5. Check runoff pH and EC if leaves are pale too. ## Common mistakes - Judging light by the lamp's wattage or a centre-point reading. - Leaving lower branches that will never reach good light. - Harvesting by calendar. - Blaming the cultivar before measuring light and heat. ## Related - Full article: [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md) - Answers: [bigger, denser buds](https://genetixbay.com/knowledge/answers/how-to-get-bigger-denser-buds.md) · [harvesting early or late](https://genetixbay.com/knowledge/answers/harvesting-too-early-or-late.md) - Diagnosis: [foxtails](https://genetixbay.com/knowledge/diagnosis/foxtails.md) - Terms: [larf](https://genetixbay.com/knowledge/glossary/larf.md) · [popcorn buds](https://genetixbay.com/knowledge/glossary/popcorn-buds.md) · [lollipopping](https://genetixbay.com/knowledge/glossary/lollipopping.md) ## Follow-up questions **Why are only my lower buds airy?** Only the lower buds are airy because light falls off fast below the top of the canopy, so lower sites get a fraction of the PPFD the tops get. Research found lower-plant cannabinoids track that poor light penetration. Lollipop the lower third at the flip or by about day 21, and train the canopy flat so more sites share the top light. **Why are my top buds airy and spiky?** Airy, spiky top buds are often foxtailing from heat or too much light: the tops are too close to the lamp or the canopy runs above about 30 °C (86 °F). Measure canopy temperature and PPFD at the top colas. Raise the light or dim it, improve airflow, and keep flower days at 22–26 °C (72–79 °F). Some cultivars foxtail naturally as they ripen. **Do indica strains make denser buds than sativas?** Bud density is a cultivar trait, but indica and sativa labels don't reliably predict it, because nearly all modern cannabis is hybrid and labels often don't match the genetics. Some cultivars make loose, open flowers even under perfect conditions. Judge density by the cultivar's own record, ideally from grow journals of the same cut, not by the label. ## Sources 1. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 2. Danziger N, Bernstein N, 2021. Shape matters: plant architecture affects chemical uniformity in large-size medical cannabis plants. Plants 10(9):1834. https://pmc.ncbi.nlm.nih.gov/articles/PMC8468686/ 3. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in PPFD, temperature and CO2. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x 4. Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y, 2022. Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content. Frontiers in Plant Science 13:974018. https://doi.org/10.3389/fpls.2022.974018 --- # Why are my clones wilting? > Cannabis clones wilt because they have no roots to replace the water their leaves lose. Some droop on day 1–2 is normal; lasting wilt means humidity is too low (aim 75–90% RH), light or heat too strong (keep 50–150 µmol/m²/s), or the stem rotting in a soggy plug. Yellowing after a week is usually the cutting using its stored reserves, not a disaster. - Canonical: https://genetixbay.com/knowledge/answers/why-are-my-clones-wilting.html - Topic: Cloning and mother plants · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - Also asked as: Clones drooping | My cuttings are dying | Clones turning yellow | Clones wilted after I removed the dome - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Cannabis clones wilt because they have no roots to replace water lost through their leaves. A little droop on days 1–2 is normal. Lasting wilt means humidity too low (aim 75–90% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md)), light or heat too strong, or a rotting stem in a soggy plug. *Grower practice*. ## Why An unrooted cutting can only drink through its cut stem. Every leaf keeps [transpiring](https://genetixbay.com/knowledge/glossary/transpiration.md), so dry air pulls it flat. Light adds to the load. Horticultural guidance keeps cuttings at a low maximum, around 100–150 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), at sticking [1]. Strong light on rootless leaves dries them faster than they can drink. Humidity is the brake. In a [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) trial run at only about 64% RH, flats wilted at times, so the researchers resaturated the media and removed lower leaves to keep cuttings turgid [2]. Under a dome at 75–90% RH, that pressure mostly disappears. Waterlogging kills from below. A soggy plug suffocates the stem base and invites [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) and [Fusarium](https://genetixbay.com/knowledge/glossary/fusarium-wilt.md), which also infect cannabis roots [3]. ## The numbers | Symptom | Likely cause | Fix | |---|---|---| | Flat on day 1–2, recovers | Normal | Nothing | | Flat past day 3, dry air | RH too low | Dome, 75–90% RH | | Crisp edges, wilts at midday | Light or heat too high | 50–150 µmol/m²/s, 22–26 °C | | Soft brown stem base | Rot in a soggy plug | Drier plugs; re-cut healthy [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md) | | Lower leaves yellow after a week | Using reserves | Normal; feed once rooted | | Wilts after dome removal | [Hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) too fast | Lid back on; slow down | ## What to do 1. Check the dome: RH 75–90%, vented once a day. 2. Lower or dim the light to 50–150 µmol/m²/s. 3. Squeeze a plug. If water runs out, stop watering. 4. Check medium temperature: 22–26 °C (72–79 °F). 5. Remove only cuttings with rotten stems. ## Common mistakes - Clones under a full-power veg light. - No dome in a [dry room](https://genetixbay.com/knowledge/glossary/drying-room.md). - Watering plugs daily "because they're wilting". - Pulling the dome off in one go. ## Related - Full article: [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md) - [Humidity and light for clones](https://genetixbay.com/knowledge/answers/humidity-and-light-for-clones.md) · [How long do clones take to root?](https://genetixbay.com/knowledge/answers/how-long-do-clones-take-to-root.md) - Terms: [cloning dome](https://genetixbay.com/knowledge/glossary/cloning-dome.md) · [hardening off](https://genetixbay.com/knowledge/glossary/hardening-off.md) ## Follow-up questions **Is it normal for clones to droop the first day?** Yes. Fresh cannabis cuttings often droop for the first 24–48 hours while the cut end seals and the cutting adjusts. Under a dome at 75–90% RH and gentle light of 50–150 µmol/m²/s, they should stand back up within a day or two. If they're still flat on day 3, lower the light, raise humidity and check the plugs aren't waterlogged. **Why are my clones turning yellow?** Cannabis clones commonly yellow after about a week because an unrooted cutting can barely take up nutrients and draws on its own leaves. Lower leaves yellowing while the tip stays green is normal and often a sign that roots are close. Whole-cutting yellowing with a soft, brown stem base means rot from a soggy plug. Once roots show, a light feed greens them up. **Why did my clones wilt when I took the dome off?** Cannabis clones wilt when the dome comes off too fast because their new roots can't yet supply what the leaves lose in drier air. Harden them off over 3–5 days: open the vents, then prop the lid, then remove it, only once several roots are visible. If they droop, put the lid back for a day and slow down. ## Sources 1. Michigan State University. Lighting of cuttings (rooting-phase PPFD). https://www.canr.msu.edu/uploads/resources/pdfs/lighting-of-cuttings.pdf 2. Campbell SM, Anderson SL, Brym ZT, Pearson BJ, 2021. Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.). PLOS ONE 16(7): e0249160. https://doi.org/10.1371/journal.pone.0249160 3. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 --- # Why are there seeds in my buds? > Seeds in cannabis buds mean the flowers were pollinated, usually weeks before harvest. With no male in the room, the usual source is a hermaphrodite: a female growing anthers, often hidden inside the buds. Herm-prone plants are mainly the result of poor breeding, and stress reveals them. Find the source, cull the herm, and don't grow the seeds: they carry the same tendency. - Canonical: https://genetixbay.com/knowledge/answers/why-are-there-seeds-in-my-buds.html - Topic: Diagnosis · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - Also asked as: Why did I find seeds in my bud? | Seeds in buds but I had no male | Why are my buds seeded? | Can a female make seeds on her own? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Seeds in your buds mean the flowers were [pollinated](https://genetixbay.com/knowledge/glossary/pollination.md), usually weeks before harvest. If there was no male in the room, the pollen almost always came from a [hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md): a female growing [anthers](https://genetixbay.com/knowledge/glossary/anther.md), often hidden inside the buds. [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) plants are mainly the product of poor breeding, and stress reveals them (*House position*). The biology here is *Supported*. ## Why Cannabis is [dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md). Females are XX and males XY, and a well-bred female stays female [2]. A seed needs pollen, so seeds point to [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) somewhere. Hermaphrodite anthers make working pollen. In a controlled study, anthers formed in clusters next to the [stigmas](https://genetixbay.com/knowledge/glossary/stigma.md) from about week 4 of flower, their pollen germinated 10–30% in vitro, and seeded inflorescences held 22–48 seeds [1]. Sex expression is [heritable](https://genetixbay.com/knowledge/glossary/heritability.md). In [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), how much male and female flowering a plant shows has a genetic basis [3]. Stress such as [light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) or heat triggers intersex flowers in susceptible plants. GenetixBay's position is that this reveals weak genetics rather than creating them. Seed from herm pollen is almost all female [1], so the seeds you found are untested [feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md) carrying the same tendency. ## The numbers | Fact | Value | |---|---| | Herm anthers appear | From about week 4 of flower [1] | | Herm pollen [germination](https://genetixbay.com/knowledge/glossary/germination.md) | 10–30% in vitro [1] | | Seeds per seeded inflorescence | 22–48 [1] | | GenetixBay [herm threshold](https://genetixbay.com/knowledge/glossary/herm-threshold.md) | Above 2% in tester grows disqualifies a line | ## What to do 1. Look for the source. Check bud interiors, nodes and the leaves below for [bananas](https://genetixbay.com/knowledge/glossary/nanners.md), pollen sacs and [pollen dust](https://genetixbay.com/knowledge/glossary/pollen.md). 2. Bag any plant with anthers before moving it, then take it out of the room. 3. Check the dark period for leaks, and check the timer logs and canopy heat. Fix whatever triggered it. 4. Pick seeds out before use. Don't plant them or pass them on. 5. Record the event and tell the breeder of the line. 6. Next run, buy seed from breeders who publish herm rates with [plant counts](https://genetixbay.com/knowledge/glossary/plant-count-limit.md). ## Common mistakes - Blaming only the light leak and keeping the clone. - Saving the seeds as "free feminised seed". - Calling late bananas normal. They aren't. - Missing anthers hidden inside dense buds. ## Related - Full article: [Hermaphrodite cannabis (bananas and nanners)](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) - Answers: [how to prevent herms](https://genetixbay.com/knowledge/answers/how-to-prevent-hermaphrodites.md) · [can you smoke a hermie?](https://genetixbay.com/knowledge/answers/can-you-smoke-a-hermie.md) · [growing bag seed](https://genetixbay.com/knowledge/answers/can-i-grow-bag-seed.md) - Article: [breeders vs pollen chuckers](https://genetixbay.com/knowledge/breeding/breeders-vs-pollen-chuckers.md) - Terms: [hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) · [sinsemilla](https://genetixbay.com/knowledge/glossary/sinsemilla.md) · [nanners](https://genetixbay.com/knowledge/glossary/nanners.md) ## Follow-up questions **Can a female plant make seeds without a male?** A female cannabis plant only makes seeds if pollen reaches it. With no male present, the pollen almost always came from a hermaphrodite, a female growing male anthers, either the seeded plant itself or a neighbour. Pollen can also come in on clothes or from outdoor plants. Look inside buds and at nodes for yellow bananas and pollen sacs. **Should I plant seeds I found in my buds?** Do not plant seeds found in buds from a hermaphrodite plant. Research shows seed from hermaphrodite pollen gives almost all female plants that carry the same herm tendency, so you would be growing unstable, untested feminised seed. GenetixBay's breeder standard is to cull herm-prone plants and never breed from them. Buy seed from breeders who publish herm rates with plant counts. **How many seeds does a pollinated bud make?** A pollinated cannabis bud can hold dozens of seeds. In a controlled study of hermaphroditism in commercial indoor cannabis, seeded inflorescences held 22–48 seeds, and seed formation diverted resources and lowered quality. One open herm can seed many buds on many plants, which is why the source plant must be bagged and removed as soon as you find it. ## Sources 1. Punja ZK, Holmes JE., 2020. Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences: Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718 2. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118 3. Faux AM, Berhin A, Dauguet N, Bertin P. 2014. Sex chromosomes and quantitative sex expression in monoecious hemp (Cannabis sativa L.). Euphytica 196(2):183-197. https://doi.org/10.1007/s10681-013-1023-y --- # Why do photoperiod plants need long nights to flower? > Photoperiod cannabis is a short-day plant: it measures the uninterrupted night with phytochrome, a light-sensing pigment, and flowers once the night passes a cultivar-specific critical length, around 10–11 hours of darkness in drug-type cultivars tested. 12/12 works for essentially all cultivars; 13/11 also works for many. Light during the night, even very dim, resets the count and can delay flowering in sensitive cultivars. - Canonical: https://genetixbay.com/knowledge/answers/why-flowering-needs-darkness.html - Topic: Basics · Type: Definition - Evidence: Established · Status: Draft: awaiting expert review - Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Also asked as: Why 12/12? | Phytochrome and flowering | Night length and flowering | Does cannabis measure day or night? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis is a [short-day plant](https://genetixbay.com/knowledge/glossary/short-day-plant.md), which really means a long-night plant: it flowers once the uninterrupted dark passes a cultivar-specific length, around 10–11 hours in the drug-type cultivars tested. [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) triggers essentially all cultivars; [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) works for many and is house-endorsed. *Established* plant physiology. ## Why The plant times the night, not the day. [Phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md) in the leaf flips between active and inactive forms under red and [far-red light](https://genetixbay.com/knowledge/glossary/far-red.md). Through a long night the active form decays, and past the critical night length, flowering signals switch on at the [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md). The threshold varies by cultivar. One drug-type [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) needed at least about 10.8 h of uninterrupted dark [2]. In [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), some essential-oil cultivars had a critical day length between 13 h 45 min and 14 h [1]. At 13 h, two THC-dominant cultivars flowered within about 1.5 days of their 12 h timing [5]. The nights must keep coming. Inflorescence onset needed at least three consecutive short days, and returning plants to long days pulled the forming inflorescence apart [3]. Night light resets the count. Stray light as dim as about 2 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) delayed flowering in hemp [1], and a conference report saw delays in the most sensitive cannabis cultivars at 0.01 µmol/m²/s [4]. ## The numbers | Schedule | Night | Effect on photoperiod cannabis | |---|---|---| | [24/0](https://genetixbay.com/knowledge/glossary/24-0.md), 20/4, [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) | 0–6 h | Stays vegetative | | 14/10 | 10 h | Flowered in all three lines in one study; test yours | | 13/11 | 11 h | Flowers; endorsed | | 12/12 | 12 h | Flowers in essentially all cultivars | | Stray night light | — | Delays seen from 0.01–2 µmol/m²/s | Sunrise and sunset ramps count as day; the plant measures the dark after them. ## What to do 1. Give flowering plants an uninterrupted night of at least 11–12 hours. 2. Sit in the dark tent for 5 minutes; any light you can see is a leak. 3. Tape over device [LEDs](https://genetixbay.com/knowledge/glossary/led.md) and seal zip ends and duct ports. 4. Use a timer you trust and check it after power cuts. 5. Trying 13/11 or 14/10? Test one cultivar first. ## Common mistakes - Thinking plants need "rest" in veg. - Opening the tent during the dark period. - Assuming a minute of light can't matter. ## Related - Full article: [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) - Answers: [12/12 from seed](https://genetixbay.com/knowledge/answers/12-12-from-seed.md) · [lights stayed on in flower](https://genetixbay.com/knowledge/answers/lights-stayed-on-during-flower.md) · [when outdoor plants flower](https://genetixbay.com/knowledge/answers/when-do-outdoor-plants-flower.md) - Article: [The flip isn't day 1 of flower](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) - Terms: [phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md) · [short-day plant](https://genetixbay.com/knowledge/glossary/short-day-plant.md) ## Follow-up questions **How does phytochrome control flowering?** Phytochrome is a pigment in the leaf that switches between an active and inactive form under red and far-red light. During a long night the active form decays; once the night is longer than the cultivar's critical length, flowering genes switch on at the shoot tips. A pulse of light in the night resets this clock, which is why a light leak can stall flowering. **Does cannabis need a dark period in veg?** No, cannabis doesn't need a dark period in veg; GenetixBay endorses 24/0. Photoperiod cannabis measures night length only to decide when to flower, so continuous light simply keeps it vegetative. Short nights, or none, are what stop flowering. The trade-off of 24/0 is more electricity per day than 18/6, not a measured yield penalty. **Why do outdoor plants flower in late summer?** Outdoor photoperiod cannabis flowers in late summer because nights lengthen after the June solstice in the northern hemisphere and eventually pass the plant's critical night length. The exact date depends on latitude and cultivar: some hemp cultivars responded to days as long as 13 h 45 min to 14 h, while others need shorter days. ## Sources 1. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153 2. Moher M, Jones M, Zheng Y. 2021. Photoperiodic response of in vitro Cannabis sativa plants. HortScience 56(1):108-113. https://doi.org/10.21273/HORTSCI15452-20 3. Alter H, Sade Y, Sood A, et al. 2024. Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin. Horticulture Research 11(11):uhae245. https://doi.org/10.1093/hr/uhae245 4. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis 5. Ahrens A, Llewellyn D, Zheng Y. 2024. Longer photoperiod substantially increases indoor-grown cannabis' yield and quality. Plants 13(3):433. https://doi.org/10.3390/plants13030433 --- # Why is my autoflower so small? > An autoflower ends up small when something slows it in the first 3–5 weeks, before it starts flowering by age. The usual causes are overwatering a seedling in a big wet pot, transplant shock, a small pot, topping, weak light under about 300–600 µmol/m²/s, or hunger and pH problems. The auto keeps its countdown regardless, so the lost growth never comes back. - Canonical: https://genetixbay.com/knowledge/answers/why-is-my-autoflower-small.html - Topic: Basics · Type: Troubleshooting - Evidence: Grower practice · Status: Draft: awaiting expert review - Full article: [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Also asked as: Stunted autoflower | My auto finished tiny | Autoflower not growing big | Why did my auto stop growing? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer An [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) finishes small when something slowed it in its first 3–5 weeks. [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), [transplanting](https://genetixbay.com/knowledge/glossary/transplanting.md), a small pot, topping, weak light and hunger are the usual suspects. It flowers by age regardless, so lost growth stays lost. *Grower practice*, and the GenetixBay house position: any setback costs an auto. ## Why The clock doesn't wait. Autoflowering is genetic: plants carrying two copies of the [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) auto [allele](https://genetixbay.com/knowledge/glossary/allele.md) flower by age, even under long days [4]. Veg ends on schedule, recovered or not. Roots set the size of the frame. Across many crops, doubling [pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) raised plant biomass by about 43% on average [1]. A [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) drowned in a big wet pot, or one stalled by a move, builds fewer roots in exactly the weeks that matter. Waterlogged media also favour [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) [3]. Light sets the growth rate. Yield rose roughly in a straight line with light in a controlled trial [2]. An auto under a weak light, or a light hung too high, flowers on time but small. ## The numbers | Cause | Typical sign | Fix for next time | |---|---|---| | Overwatered seedling | Droopy, slow first 2 weeks | Water a 50–100 mL ring around the stem | | Transplanted | 4–7 days with no new growth | Sow in the final pot | | Pot under ~11 L (3 gal) | Dries daily, plant stalls | 11–19 L (3–5 gal), or [feed and water](https://genetixbay.com/knowledge/glossary/fertigation.md) very often | | Topped | Stall after the cut | [LST](https://genetixbay.com/knowledge/glossary/lst.md) from day 14–21 | | Weak light | Stretched, pale, gappy | 300–600 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) in veg, 600–900 in flower | | Hungry or [pH](https://genetixbay.com/knowledge/glossary/ph.md) off | Pale lower leaves in week 3–4 | Feed lightly from week 2–3; soil pH 6.2–6.8, [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) 5.8–6.2 | | Short line | Healthy but small | Read the line's grow journals | ## What to do 1. Check your journal for a 4–7 day stall and what happened just before it. 2. Measure PPFD at the canopy; a phone app is fine for trends. 3. Check pH of input and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) before blaming nutrients. 4. Keep this plant steady to harvest; don't add new stress trying to "fix" size. 5. Next run: final pot from day one, ring watering, LST, no topping. ## Common mistakes - Starting in a cup and transplanting. - Topping an auto. - Soaking the whole pot around a seedling. - Assuming it's genetics before ruling out the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). ## Related - Full article: [Photoperiod vs autoflower](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md) - Answers: [best pot size for autos](https://genetixbay.com/knowledge/answers/best-pot-size-for-autoflowers.md) · [planting straight into the final pot](https://genetixbay.com/knowledge/answers/plant-straight-into-final-pot.md) · [feeding autoflowers](https://genetixbay.com/knowledge/answers/feeding-autoflowers.md) - Articles: [transplanting](https://genetixbay.com/knowledge/germination/transplanting.md) · [LST](https://genetixbay.com/knowledge/training/lst.md) - Terms: [pot size](https://genetixbay.com/knowledge/glossary/pot-size.md) · [LST](https://genetixbay.com/knowledge/glossary/lst.md) ## Follow-up questions **Can a stunted autoflower recover?** A stunted autoflower can recover its health but not its lost size. It flowers at a set age, so days spent stalled in weeks 1–5 come straight out of the frame it flowers on. Fix the cause at once, keep light and feeding steady, and expect a smaller harvest from that plant. Apply the lesson to the next seed. **Does topping make autoflowers smaller?** Topping often makes an autoflower smaller. Removing the main tip costs the plant several days of regrowth while its flowering clock keeps running, and an auto has no spare veg time. GenetixBay's house position is that topping never produces what proper low-stress training does on an auto: bend and tie the main stem from about day 14–21 instead. **How big should an autoflower get?** Autoflower size varies by line, but a healthy auto in an 11–19 L (3–5 gal) pot under good light usually fits comfortably in a 140–160 cm (4.6–5.3 ft) tall tent. One that stays tiny, with a few nodes and a single small bud, has usually had a setback in its first weeks or is a very short line. ## Sources 1. Poorter H, Bühler J, van Dusschoten D, Climent J, Postma JA. 2012. Pot size matters: a meta-analysis of the effects of rooting volume on plant growth. Functional Plant Biology 39(11):839-850. https://doi.org/10.1071/FP12049 2. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020 3. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 4. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680 --- # Why is my seedling drooping? > A drooping cannabis seedling is most often overwatered: a big pot or soggy plug leaves its tiny roots short of oxygen. Less often it is dry, hot or under a light that is too strong. If the stem is pinched and brown at the soil line, it is damping-off and can't be saved. Water small amounts around the stem only when the pot lightens, at 23–27 °C (73–81 °F). - Canonical: https://genetixbay.com/knowledge/answers/why-is-my-seedling-drooping.html - Topic: Germination · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - Also asked as: Droopy seedling | Seedling leaves drooping down | Why is my seedling wilting? | Seedling fell over at the base - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer A drooping cannabis [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) is usually [overwatered](https://genetixbay.com/knowledge/glossary/overwatering.md). Less often it's dry, hot or under too much light. A stem pinched and brown at the soil line means [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md). Lift the pot before you water again. *Supported*. ## Why Roots need air. A tiny root in a soggy plug, or a big pot soaked for a seedling, sits in water with little oxygen, so the plant can't move water and droops even though it is wet. Wet, cool media favour root pathogens. [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) infects cannabis roots in wet conditions [3], and the same organisms cause damping-off in seedlings [1][2]. Damping-off is different from droop. The stem rots and collapses at the soil line, often with green leaves still on it, and the seedling can't recover [2]. Dry air and heat cause a quick, midday wilt. Small roots can't keep up with a strong pull from hot, dry air or an intense lamp. ## The numbers | Clue | Overwatered | [Underwatered](https://genetixbay.com/knowledge/glossary/underwatering.md) | Damping-off | |---|---|---|---| | Pot weight | Heavy | Light | Usually heavy | | Leaves | Curl down, firm | Limp, thin | Often still green | | Stem base | Normal | Normal | Pinched, brown, wet | | Recovers | In 1–3 days if left to dry | Within an hour of water | No | Targets: 23–27 °C (73–81 °F) air, 65–75% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), 150–300 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), medium at 21–25 °C (70–77 °F). ## What to do 1. Lift the pot. Heavy: wait. Light: water a small ring around the stem. 2. Check the stem at the soil line for pinching. 3. Use room-temperature water, never cold [1]. 4. Check air temperature and light distance. 5. Next time, start seedlings in a small cup or plug, or water only near the stem in a big pot. ## Common mistakes - Watering a droopy seedling that is already wet. - Soaking a 15 L pot for a seedling with a 2 cm root. - Cold [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) straight onto the stem. - Sealing it under a dome to "help" an overwatered plant. ## Related - Full article: [Seedling care: the first three weeks](https://genetixbay.com/knowledge/germination/seedling-care.md) - [Drooping: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) · [Damping-off](https://genetixbay.com/knowledge/germination/damping-off.md) - [Why are my seedling's leaves yellow?](https://genetixbay.com/knowledge/answers/seedling-leaves-yellow.md) - Terms: [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) · [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md) ## Follow-up questions **How do I tell overwatering from underwatering in seedlings?** Lift the pot. An overwatered cannabis seedling droops with firm, heavy, dark-looking mix and leaves that curl down but feel full. An underwatered one droops with a light pot, a dry surface and limp, thin leaves that perk up within an hour of watering. Overwatering is far more common at this stage, especially in big pots. **Why did my seedling fall over at the base?** A cannabis seedling that topples with a thin, water-soaked or brown stem right at the soil line almost always has damping-off, caused by soil-borne pathogens such as Pythium and Rhizoctonia. It can't be saved. Remove it and the mix around it, then sow again in fresh, clean mix with lighter watering. An evenly thin, pale stem points instead to low-light stretch. **Can too much light make a seedling droop?** Yes, but it looks different. Cannabis seedlings under too much light or heat tend to hold their leaves stiffly up and folded ('praying') and bleach at the tips, and may wilt at midday if the air is hot and dry. Keep seedlings at 150–300 µmol/m²/s and 23–27 °C (73–81 °F). Long, floppy, pale stems mean too little light instead. ## Sources 1. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping 2. NC State Extension. Damping-off in flower and vegetable seedlings. https://content.ces.ncsu.edu/damping-off-in-flower-and-vegetable-seedlings 3. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466 --- # Why is my homegrown weed harsh? > Homegrown cannabis is usually harsh because it was dried too fast, over-dried, or smoked before a proper cure, not because it wasn't flushed. Flushing is a Myth that costs yield and resin. Dry slowly for 7–14 days at 15–21 °C (60–70 °F) and 55–62% RH, then cure for at least 2 weeks, with water activity falling slowly from about 0.62–0.65 towards 0.55–0.58. - Canonical: https://genetixbay.com/knowledge/answers/why-is-my-weed-harsh.html - Topic: Harvest and cure · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Curing and burping: jars, humidity and how long](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Also asked as: Why is my homegrown smoke so harsh? | Homegrown makes me cough | Harsh buds: did I not flush? | How do I make my bud smoother? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer Homegrown cannabis is usually harsh because it was dried too fast, over-dried, or smoked before a proper cure. It isn't harsh because you didn't [flush](https://genetixbay.com/knowledge/glossary/flushing.md). Pre-harvest flushing is a *Myth*, and a harmful one (*House position*). Dry slowly for 7–14 days, then cure for at least 2 weeks. *Supported*. ## Why Flushing doesn't change the smoke. Controlled studies found no improvement in flower quality from withdrawing nutrients before harvest, and longer withdrawal tended to cut yield [1][2]. Cannabis stores what it takes up in its tissue. Starving it in the last weeks takes food away just as it is packing on its final weight and resin. The dry decides most of it. Air-drying shifts the oil away from volatile [monoterpenes](https://genetixbay.com/knowledge/glossary/monoterpene.md) [3], and a fast, warm dry crisps the outside while the core stays wet. The result is harsh, grassy or hay-like smoke. *A cure never fixes a bad dry* (*House position*). Moisture has to be right. ASTM sets [water activity](https://genetixbay.com/knowledge/glossary/water-activity.md) 0.55–0.65 for dried flower [4]. Too wet and the bud burns badly and risks mould. [Too dry](https://genetixbay.com/knowledge/glossary/over-drying.md) and it burns hot and fast. ## The numbers | Stage | Target | |---|---| | Dry | 7–14 days, 15–21 °C (60–70 °F), 55–62% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), dark | | Ready to jar | Stems snap; sealed jar reads a stable 58–65% RH after 12–24 h | | Cure | Water activity from 0.62–0.65 falling slowly to 0.55–0.58 | | Cure length | 2 weeks minimum; 4–8 weeks common | | Late-flower feeding | [Taper nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md); keep P, K, Ca, Mg and [micros](https://genetixbay.com/knowledge/glossary/micronutrient.md) fed | ## What to do 1. Check a jar: seal it for 12–24 hours and read the hygrometer. 2. If it reads above 65%, dry the buds further. If it reads below 55%, add a fresh bud for a day. 3. Cure for at least 2 more weeks, [burping](https://genetixbay.com/knowledge/glossary/burping.md) as needed, and let the reading drift down. 4. Next run, dry slower: cooler, darker, and with no fan blowing on the buds. 5. Keep feeding to the end, tapering nitrogen rather than flushing. 6. Rule out pests or mould on the buds as well. ## Common mistakes - Blaming nutrients and flushing next time. - Drying in 3 days in summer heat. - Smoking straight off the [drying line](https://genetixbay.com/knowledge/glossary/hang-dry.md). - Expecting a [long cure](https://genetixbay.com/knowledge/glossary/curing.md) to rescue a [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md). ## Related - Full article: [Curing and burping](https://genetixbay.com/knowledge/harvest-cure/curing-burping.md) - Answers: [when to stop feeding](https://genetixbay.com/knowledge/answers/when-to-stop-feeding-before-harvest.md) · [rehydrating over-dried buds](https://genetixbay.com/knowledge/answers/rehydrate-over-dried-buds.md) · [how soon can I smoke?](https://genetixbay.com/knowledge/answers/how-soon-after-harvest-can-i-smoke.md) - Article: [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md) - Terms: [hay smell](https://genetixbay.com/knowledge/glossary/hay-smell.md) · [curing](https://genetixbay.com/knowledge/glossary/curing.md) · [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) ## Follow-up questions **Will flushing make my weed smoother?** Flushing will not make your weed smoother. Controlled studies found no gain in flower quality, minerals or cannabinoids from a pre-harvest flush, and longer nutrient withdrawal tended to cut yield. Cannabis stores what it takes up, and plain water at the end does not wash it out. Smoothness comes from plant health, a slow dry and a proper cure. Taper nitrogen instead. **Does a longer cure make smoke smoother?** A longer cure is widely reported to make cannabis smoke smoother, within reason, as moisture evens out through the bud and aroma settles. At least 2 weeks is the minimum and 4–8 weeks is common, but the chemistry is not well studied. A cure cannot rescue a 3-day hot dry: that harshness and any hay smell stay with the flower. **Can wet buds be harsh?** Yes, buds that are still too wet burn unevenly, go out, and give a heavy, harsh smoke, and they risk mould in the jar. Check that small stems snap and that a sealed sample jar reads a stable 58–65% RH after 12–24 hours. If a jar climbs above about 65–68%, take the buds out and dry them further. ## Sources 1. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25 2. Stemeroff J. 2017. Irrigation management strategies for medical cannabis in controlled environments. MSc thesis, University of Guelph. http://hdl.handle.net/10214/12125 3. Ross SA, ElSohly MA, 1996. The volatile oil composition of fresh and air-dried buds of Cannabis sativa. Journal of Natural Products 59(1):49–51. https://diverdi.colostate.edu/C442/references/analysis/GC/j_nat_prod_1996_v59_p49.pdf 4. ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. ASTM International. https://store.astm.org/d8197-22.html --- # Why won't my seeds germinate? > Cannabis seeds usually fail to germinate because they are too cold, too wet, too dry or old. Fresh seed shows a taproot in 1–5 days at 22–27 °C (72–81 °F); old seed can take up to 10 days. Below about 18 °C (64 °F) germination slows sharply, and soaking longer than 24 hours or a sopping towel can drown the seed. Old seed may still sprout in 1% hydrogen peroxide. - Canonical: https://genetixbay.com/knowledge/answers/why-wont-my-seeds-germinate.html - Topic: Germination · Type: Troubleshooting - Evidence: Supported · Status: Draft: awaiting expert review - Full article: [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md) - Also asked as: Why are my seeds not germinating? | Seeds not sprouting after a week | No taproot after 5 days | My seed didn't pop, what went wrong? | Why won't my cannabis seeds crack? - Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)" ## Short answer [Cannabis seeds](https://genetixbay.com/knowledge/glossary/achene.md) that won't [germinate](https://genetixbay.com/knowledge/glossary/germination.md) are usually too cold, too wet, [too dry](https://genetixbay.com/knowledge/glossary/over-drying.md) or too old. Fresh seed shows a [taproot](https://genetixbay.com/knowledge/glossary/taproot.md) in 1–5 days at 22–27 °C (72–81 °F); old seed can take up to 10 days. Fix the temperature and moisture before blaming the seed. *Supported*. ## Why Germination speed is set by temperature. [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md) seed germinates across roughly 19–30 °C, with an optimum near 29.6 °C, and slows sharply on a cold windowsill [1]. A seed needs oxygen as well as water. Long soaks and [waterlogged](https://genetixbay.com/knowledge/glossary/overwatering.md) towels or plugs suffocate the embryo and favour the rot organisms that cause [damping-off](https://genetixbay.com/knowledge/glossary/damping-off.md) [4]. Seed age and storage matter. Seeds kept cold and dry at about 5 °C (41 °F) held their germination capacity for around six years; warm, humid storage costs viability far sooner [3]. Old, slow seed can sometimes be pushed. Germinating in 1% [hydrogen peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) in the dark gave faster, higher germination than water, including for very old seed [2]. ## The numbers | Factor | Good | Problem | |---|---|---| | Temperature | 22–27 °C (72–81 °F) | Below ~18 °C (64 °F): slow or stalled | | Soak | ≤ 24 h | Over 24–36 h: oxygen starvation | | Time to taproot | 1–5 days fresh seed | Nothing after 10 days | | Storage | ~5 °C (41 °F), dry, airtight | Warm, humid, bright | ## What to do 1. Measure the temperature where the seeds sit, not the room. Aim for 22–27 °C. 2. Keep towels damp, not dripping; plugs moist, not wet. 3. Wait 10 days before giving up on older seed. 4. For old stock, try 1% hydrogen peroxide in a closed tube in the dark [2]. Gloves and eye protection when diluting stronger peroxide. 5. Run a 10-seed test on a batch before planting the lot. ## Common mistakes - Germinating on a cold windowsill or floor. - Soaking for days "until it cracks". - Letting a paper towel dry out once the [shell](https://genetixbay.com/knowledge/glossary/seed-coat.md) has split. - Storing seed in a warm drawer for years, then blaming the breeder. ## Related - Full article: [Germination methods compared](https://genetixbay.com/knowledge/germination/germination-methods.md) - [Seed viability and storage](https://genetixbay.com/knowledge/germination/seed-viability-storage.md) - [Do floating seeds mean duds?](https://genetixbay.com/knowledge/answers/do-floating-seeds-mean-duds.md) · [Do seeds need light to germinate?](https://genetixbay.com/knowledge/answers/do-seeds-need-light-to-germinate.md) - Terms: [germination](https://genetixbay.com/knowledge/glossary/germination.md) · [radicle](https://genetixbay.com/knowledge/glossary/radicle.md) ## Follow-up questions **How long should I wait before giving up on a seed?** Wait about 10 days before giving up on a cannabis seed. Fresh seed normally shows a taproot within 1–5 days at 22–27 °C (72–81 °F), but old or hard seed can take up to 10. If nothing has happened by then and the seed is soft, mouldy or smells sour, it has rotted. Check the temperature first, because a cold room is the most common cause of a slow start. **Can a seed rot from too much water?** Yes. A cannabis seed needs air as well as water to germinate. Soaking it for more than 24–36 hours, or leaving it in a sopping paper towel or waterlogged plug, starves the embryo of oxygen and invites mould and damping-off organisms. Use a towel that is damp but not dripping, a medium that holds together when squeezed but does not drip, and never soak for days. **Can I rescue old seeds that won't sprout?** Old cannabis seeds can sometimes be rescued. In a lab protocol, germinating seeds in 1% hydrogen peroxide in the dark gave faster, higher germination than plain water and helped very old, low-viability seed. Seeds stored cold and dry at about 5 °C (41 °F) keep their germination capacity for around six years, so warm storage is a common hidden cause. Wear gloves when diluting stronger peroxide. ## Sources 1. Geneve RL, et al., 2022. Temperature limits for seed germination in industrial hemp (Cannabis sativa L.). Crops 2(4):415–427. https://doi.org/10.3390/crops2040029 2. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875 3. Small E, Brookes B, 2012. Temperature and moisture content for storage maintenance of germination capacity of seeds of industrial hemp, marijuana, and ditchweed forms of Cannabis sativa. Journal of Natural Fibers 9(4):240–255. https://doi.org/10.1080/15440478.2012.737179 4. University of Minnesota Extension. How to prevent seedling damping off. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping --- # GenetixBay symptom checker: every symptom > 142 symptoms. Interactive checker: https://genetixbay.com/knowledge/diagnose/ --- # Lower (older) leaves turning evenly yellow: likely causes and fixes > Lower (older) leaves turning evenly yellow on cannabis is most often Nitrogen deficiency, Normal late-flower fade (senescence) or Overwatering (roots short of air). How to tell them apart, the fix for each and what recovery looks like. Also called: bottom leaves yellow, old leaves yellowing, yellowing from the bottom up, fan leaves going yellow at the bottom, lower leaves lemon yellow. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=yellow-lower-leaves ## Likely causes, most likely first ### Nitrogen deficiency (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Fix roots, watering and pH first. If N is genuinely short, raise feed N by about 10-20% (not double): mineral feeds around 150-200 mg/L N in veg and early flower; one DWC flowering trial predicted a yield optimum near 194 mg/L. Coco/hydro: raise base feed EC by ~0.2 mS/cm. Soil: liquid feed at label rate. Living soil: top-dress a fast organic N source and allow 1-2 weeks. Late flower: a gradual fade is the planned N taper, not a fault. - Recovery: Yellowing stops climbing within 5-7 days and new leaves emerge mid-green; already-yellow leaves do not recover. Runoff EC climbs back toward input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Normal late-flower fade (senescence) (Less likely) - Kind: Normal ageing; urgency: Low urgency - Fix: Nothing to fix in the last 2-3 weeks of flower. Keep feeding at stage strength with N tapered; don't 'flush' (pre-harvest flushing starves the plant while it packs on final weight and resin, and controlled studies show no quality gain). Fade before week 5-6 of flower suggests N was cut too early. - Recovery: Buds keep swelling and ripening normally while fan leaves fade. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) ### Overwatering (roots short of air) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Shaded lower leaves dying back (normal) (Less likely) - Kind: Normal ageing; urgency: Low urgency - Fix: A few yellowing leaves deep in a dense canopy are normal; the plant recycles them. Tuck and train to open the canopy rather than stripping (house: tuck, don't pluck). - Recovery: Only shaded leaves affected; upper canopy healthy. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) ### General underfeeding (whole feed too weak) (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Raise the whole feed in steps of about 0.2-0.3 mS/cm toward the stage target (veg 1.2-1.8, flower 1.6-2.2 mS/cm in coco and hydro). Stop any 'flush': plain water for weeks starves the plant, and pre-harvest flushing is a myth that costs yield. - Recovery: Colour deepens and growth speeds up within a week; runoff EC tracks input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ### Root rot (Pythium) (Less likely) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ### Twospotted spider mites (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Act now: they breed fastest hot and dry. Remove the worst leaves into a sealed bag, cool the room and raise RH a little (in veg), release predatory mites (Phytoseiulus persimilis for hot spots, Neoseiulus californicus as a preventive) before numbers explode. Soaps or horticultural oils only in veg, never on buds. Quarantine new clones. - Recovery: No new stippling on new leaves and no live mites at 10-20x after 7-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Article: [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ### Fusarium wilt or crown rot (Less likely) - Kind: Disease; urgency: Act within a day or two - Fix: No cure once infected: remove the plant with its medium in a bag, sanitise pots, trays and water lines, and use clean clones and new media. Reduce root stress (overwatering, heat, salts) on the rest. - Recovery: No further wilting plants over the next 2-3 weeks. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Fusarium in cannabis: wilt, crown rot and bud rot](https://genetixbay.com/knowledge/diseases/fusarium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Whole plant pale or lime green: likely causes and fixes > Whole plant pale or lime green on cannabis is most often General underfeeding (whole feed too weak), Nitrogen deficiency or Overwatering (roots short of air). How to tell them apart, the fix for each and what recovery looks like. Also called: plant looks washed out, light green all over, pale green plant, lime green leaves, plant lost its colour. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=whole-plant-pale ## Likely causes, most likely first ### General underfeeding (whole feed too weak) (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Raise the whole feed in steps of about 0.2-0.3 mS/cm toward the stage target (veg 1.2-1.8, flower 1.6-2.2 mS/cm in coco and hydro). Stop any 'flush': plain water for weeks starves the plant, and pre-harvest flushing is a myth that costs yield. - Recovery: Colour deepens and growth speeds up within a week; runoff EC tracks input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ### Nitrogen deficiency (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Fix roots, watering and pH first. If N is genuinely short, raise feed N by about 10-20% (not double): mineral feeds around 150-200 mg/L N in veg and early flower; one DWC flowering trial predicted a yield optimum near 194 mg/L. Coco/hydro: raise base feed EC by ~0.2 mS/cm. Soil: liquid feed at label rate. Living soil: top-dress a fast organic N source and allow 1-2 weeks. Late flower: a gradual fade is the planned N taper, not a fault. - Recovery: Yellowing stops climbing within 5-7 days and new leaves emerge mid-green; already-yellow leaves do not recover. Runoff EC climbs back toward input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Overwatering (roots short of air) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Twospotted spider mites (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Act now: they breed fastest hot and dry. Remove the worst leaves into a sealed bag, cool the room and raise RH a little (in veg), release predatory mites (Phytoseiulus persimilis for hot spots, Neoseiulus californicus as a preventive) before numbers explode. Soaps or horticultural oils only in veg, never on buds. Quarantine new clones. - Recovery: No new stippling on new leaves and no live mites at 10-20x after 7-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Article: [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ### Cold root zone (below about 16 °C / 61 °F) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Raise root-zone temperature to 18-22 °C (64-72 °F): lift pots off cold floors onto insulation, warm the room at night, use an aquarium heater in reservoirs (with a thermostat), water with room-temperature solution. - Recovery: Growth resumes and new leaves green within a week. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) ### Not enough light (Less likely) - Kind: Light; urgency: Low urgency - Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat. - Recovery: New internodes shorten within a week; denser buds on the following weeks of growth. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ### Root-bound in a pot too small (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Up-pot photoperiods into a container about 2-3x larger, loosening circling roots gently. Autoflowers: don't transplant; increase watering and feeding frequency instead. Small pots can still grow big plants with high-frequency fertigation (several feeds a day). - Recovery: New white roots in the fresh medium within 5-7 days; daily wilting stops. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Cannabis root problems: the master decision tree](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md) ### Sulfur deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Rare unless a feed is built only from nitrates and chlorides. Supply about 50-120 mg/L S as sulfate, e.g. via magnesium sulfate or potassium sulfate at normal rates. - Recovery: New leaves emerge green within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources](https://genetixbay.com/knowledge/nutrients/sulfur.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Yellow between the veins on older leaves, veins stay green: likely causes and fixes > Yellow between the veins on older leaves, veins stay green on cannabis is most often Magnesium deficiency, Low root-zone pH starving calcium and magnesium or Unbuffered or new coco pulling calcium and magnesium. How to tell them apart, the fix for each and what recovery looks like. Also called: green veins yellow leaves bottom, interveinal chlorosis lower leaves, tiger striping on old leaves, bottom leaves yellow with green veins. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=interveinal-yellow-old ## Likely causes, most likely first ### Magnesium deficiency (Possible) - Kind: Nutrient; urgency: Low urgency - Fix: Check root-zone pH (Mg uptake falls at low pH) and whether heavy K or Ca is crowding it out. If short, bring Mg to about 40-70 mg/L with magnesium sulfate (roughly 0.4-0.5 g/L of the heptahydrate adds ~40-50 mg/L Mg) or magnesium nitrate. A 1-2 g/L magnesium sulfate foliar spray greens veg leaves faster; never spray buds. - Recovery: Interveinal yellowing stops climbing in 5-7 days; leaves above the damage stay green. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Magnesium (Mg) in cannabis: interveinal yellowing, targets and the K-Ca competition](https://genetixbay.com/knowledge/nutrients/magnesium.md) ### Low root-zone pH starving calcium and magnesium (Possible) - Kind: pH; urgency: Deal with it this week - Fix: Raise root-zone pH to range: coco 5.8-6.2, hydro 5.6-6.0, soil 6.2-6.8. Use pH up (potassium hydroxide or carbonate) in small steps; in coco, feed at 6.0-6.2 for a few waterings with Ca and Mg on board. A fast fall in hydro points to dying roots or microbes; check them. - Recovery: pH holds in range for a week; new leaves spot-free within 7-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Unbuffered or new coco pulling calcium and magnesium (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Feed with Ca and Mg on board: calcium nitrate and magnesium sulfate, or a Cal-Mag, bringing the feed to about 150-200 mg/L Ca and 40-60 mg/L Mg, at pH 5.8-6.2. For the next batch, rinse and buffer coco by soaking it in a calcium (and magnesium) nitrate solution before planting. - Recovery: New leaves clean within 7-10 days; runoff Ca/Mg symptoms stop spreading. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Buffering coco coir: why it matters and how to do it](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md) ### Cal-Mag overuse (excess calcium and nitrogen) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: On hard tap water with a complete base feed, stop the Cal-Mag supplement; it adds N and pushes K and Mg out of balance. Use it only for RO or soft water and unbuffered coco. LEDs do not create a Cal-Mag need. - Recovery: K and Mg symptoms stop spreading within 7-10 days. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) ### Excess potassium crowding out magnesium and calcium (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Stop K boosters and keep K near 175-250 mg/L; cation antagonism (K vs Mg and Ca) is the interaction that reliably matters in practice. - Recovery: Interveinal yellowing stops climbing in 7 days. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md) ### Sulfur deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Rare unless a feed is built only from nitrates and chlorides. Supply about 50-120 mg/L S as sulfate, e.g. via magnesium sulfate or potassium sulfate at normal rates. - Recovery: New leaves emerge green within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources](https://genetixbay.com/knowledge/nutrients/sulfur.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Yellow edges and leaf teeth on older leaves: likely causes and fixes > Yellow edges and leaf teeth on older leaves on cannabis is most often Potassium deficiency, Manganese toxicity (usually low pH) or Salt build-up in the root zone. How to tell them apart, the fix for each and what recovery looks like. Also called: edges of bottom leaves yellow, yellow serrations, leaf edges turning yellow then brown, yellow rim on old leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=yellow-margins-old ## Likely causes, most likely first ### Potassium deficiency (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Check runoff EC first: salt burn looks the same. If K is genuinely short, feed about 175-250 mg/L K (potassium sulfate, potassium nitrate or MKP) at a normal EC. A flowering DWC trial saw no yield response anywhere from 60 to 340 mg/L, so more is not better. Cut heavy Cal-Mag or sodium-rich water that competes with K. - Recovery: Margin scorch stops advancing up the plant within 7 days; new leaves open with clean margins. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md) ### Manganese toxicity (usually low pH) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Raise root-zone pH into range (soilless 5.8-6.2, soil 6.2-6.8); check that the micro mix is not over-dosed. Tissue tests may not flag it: in one trial, symptomatic plants had normal leaf Mn. - Recovery: Margin yellowing stops climbing within 7 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) ### Salt build-up in the root zone (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth. - Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like. - Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ### Boron toxicity (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Test the water (some wells carry B) and stop extra boron products; supply only 0.2-0.5 mg/L B in total. Cannabis tolerated about 10x for weeks, but symptoms appeared after 7 weeks at ~4.9 mg/L. - Recovery: No new margin scorch on leaves that mature after the change. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) ### Cal-Mag overuse (excess calcium and nitrogen) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: On hard tap water with a complete base feed, stop the Cal-Mag supplement; it adds N and pushes K and Mg out of balance. Use it only for RO or soft water and unbuffered coco. LEDs do not create a Cal-Mag need. - Recovery: K and Mg symptoms stop spreading within 7-10 days. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) ### Unbuffered or new coco pulling calcium and magnesium (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Feed with Ca and Mg on board: calcium nitrate and magnesium sulfate, or a Cal-Mag, bringing the feed to about 150-200 mg/L Ca and 40-60 mg/L Mg, at pH 5.8-6.2. For the next batch, rinse and buffer coco by soaking it in a calcium (and magnesium) nitrate solution before planting. - Recovery: New leaves clean within 7-10 days; runoff Ca/Mg symptoms stop spreading. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Buffering coco coir: why it matters and how to do it](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # New growth evenly pale or yellow: likely causes and fixes > New growth evenly pale or yellow on cannabis is most often High root-zone pH locking out iron, manganese, zinc, boron and copper, Aphids or Sulfur deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: top leaves yellow, new leaves coming in yellow, yellow tops, pale new growth, new growth lime. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=yellow-new-growth ## Likely causes, most likely first ### High root-zone pH locking out iron, manganese, zinc, boron and copper (Likely) - Kind: pH; urgency: Deal with it this week - Fix: Bring root-zone pH into range: soil 6.2-6.8, coco and rockwool 5.8-6.2, hydro 5.5-6.2. Lower input pH by 0.2-0.3 units at a time rather than crashing it; neutralise alkaline water with a mineral acid (phosphoric, nitric or sulfuric; wear gloves and eye protection, add acid to water). Use an iron chelate stable at your pH (DTPA or EDDHA above 6.5). - Recovery: Runoff or reservoir pH back in range at two consecutive checks; new leaves open green within 5-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Aphids (Less likely) - Kind: Pest; urgency: Deal with it this week - Fix: Squash or rinse small colonies; release parasitoid wasps (Aphidius), predatory midges or lacewings; insecticidal soap or oil only before flower. Control ants that farm them. - Recovery: Colonies shrink and mummified (parasitised) aphids appear within 1-2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ### Sulfur deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Rare unless a feed is built only from nitrates and chlorides. Supply about 50-120 mg/L S as sulfate, e.g. via magnesium sulfate or potassium sulfate at normal rates. - Recovery: New leaves emerge green within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources](https://genetixbay.com/knowledge/nutrients/sulfur.md) ### Iron deficiency (usually high pH) (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Bring root-zone pH into range first: soilless 5.5-6.2, soil 6.0-6.8. Neutralise alkaline water with acid. Supply 1.5-3 mg/L Fe as a chelate matched to pH: EDTA to about pH 6.5, DTPA to about 7.5, EDDHA to about 9. A foliar iron chelate spray (veg only) greens leaves in days. - Recovery: The next new leaves open green within 5-10 days; the whitened leaves re-green partly or not at all. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) ### Plant virus (e.g. beet curly top, lettuce chlorosis virus) (Less likely) - Kind: Disease; urgency: Deal with it this week - Fix: No cure: remove the plant. Control insect vectors (leafhoppers outdoors for curly top; whiteflies for some others) and test clone sources. - Recovery: No new symptomatic plants over the next 2-4 weeks. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Yellow between the veins on the newest leaves, veins green: likely causes and fixes > Yellow between the veins on the newest leaves, veins green on cannabis is most often High root-zone pH locking out iron, manganese, zinc, boron and copper, Hard, alkaline water pushing pH up over weeks or Uncalibrated or failing pH or EC meter. How to tell them apart, the fix for each and what recov Also called: new growth yellow with green veins, interveinal chlorosis top, yellow new leaves green veins, iron chlorosis look. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=interveinal-yellow-new ## Likely causes, most likely first ### High root-zone pH locking out iron, manganese, zinc, boron and copper (Likely) - Kind: pH; urgency: Deal with it this week - Fix: Bring root-zone pH into range: soil 6.2-6.8, coco and rockwool 5.8-6.2, hydro 5.5-6.2. Lower input pH by 0.2-0.3 units at a time rather than crashing it; neutralise alkaline water with a mineral acid (phosphoric, nitric or sulfuric; wear gloves and eye protection, add acid to water). Use an iron chelate stable at your pH (DTPA or EDDHA above 6.5). - Recovery: Runoff or reservoir pH back in range at two consecutive checks; new leaves open green within 5-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Hard, alkaline water pushing pH up over weeks (Less likely) - Kind: Root zone; urgency: Low urgency - Fix: Alkalinity, not water pH, drives the climb. Above about 100-150 mg/L as CaCO3 (2-3 meq/L), neutralise most of it with acid to an input pH of 5.8-6.2, or blend with RO water. Track runoff pH weekly. - Recovery: Runoff pH stops climbing over 2-3 weeks. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ### Uncalibrated or failing pH or EC meter (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Calibrate the pH meter with fresh pH 7 then pH 4 buffer before decisions and at least weekly; store the probe wet in storage solution, never in RO water. Check EC against 1.413 mS/cm. Replace probes that won't calibrate (typical life 1-2 years). Drops and strips are too coarse to diagnose with. - Recovery: Readings match the buffers within 0.1 pH; the 'problem' pH disappears or is confirmed. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Article: [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) ### Iron deficiency (usually high pH) (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Bring root-zone pH into range first: soilless 5.5-6.2, soil 6.0-6.8. Neutralise alkaline water with acid. Supply 1.5-3 mg/L Fe as a chelate matched to pH: EDTA to about pH 6.5, DTPA to about 7.5, EDDHA to about 9. A foliar iron chelate spray (veg only) greens leaves in days. - Recovery: The next new leaves open green within 5-10 days; the whitened leaves re-green partly or not at all. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) ### Excess phosphorus (bloom boosters) inducing Zn, Fe and Ca shortages (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Drop the booster. Keep P at about 30-60 mg/L; four controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, and excess P just leaves in the runoff. - Recovery: New growth greens within 10 days of returning to a balanced feed. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: ["Bloom boosters" for cannabis: what's real and what's marketing](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) ### Manganese deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Correct high pH and alkalinity first. Supply about 0.3-0.8 mg/L Mn (manganese sulfate or chelate); avoid large iron chelate doses that compete with Mn. - Recovery: New upper leaves lose the netted pattern within 7-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) ### Copper toxicity (copper sprays, ionisers, pipework) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Stop copper fungicides and ionisers, replace copper pipework contact; change the reservoir. Keep Cu at about 0.03-0.1 mg/L. - Recovery: New white root tips within a week. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md) ### Zinc toxicity (galvanised fittings, over-dosed micros) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Remove galvanised fittings from recirculating water; cap Zn near 0.1-0.5 mg/L. Excess Zn induces iron deficiency. - Recovery: New leaves green within 10-14 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Zinc (Zn) in cannabis: small leaves, margin burn and the phosphorus link](https://genetixbay.com/knowledge/nutrients/zinc.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Netted yellowing on upper and middle leaves with small tan specks: likely causes and fixes > Netted yellowing on upper and middle leaves with small tan specks on cannabis is most often High root-zone pH locking out iron, manganese, zinc, boron and copper or Manganese deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: mottled yellow upper leaves, yellow mesh pattern with spots, netted chlorosis, yellow between veins with brown dots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=netted-yellow-upper-spots ## Likely causes, most likely first ### High root-zone pH locking out iron, manganese, zinc, boron and copper (Likely) - Kind: pH; urgency: Deal with it this week - Fix: Bring root-zone pH into range: soil 6.2-6.8, coco and rockwool 5.8-6.2, hydro 5.5-6.2. Lower input pH by 0.2-0.3 units at a time rather than crashing it; neutralise alkaline water with a mineral acid (phosphoric, nitric or sulfuric; wear gloves and eye protection, add acid to water). Use an iron chelate stable at your pH (DTPA or EDDHA above 6.5). - Recovery: Runoff or reservoir pH back in range at two consecutive checks; new leaves open green within 5-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Manganese deficiency (Possible) - Kind: Nutrient; urgency: Low urgency - Fix: Correct high pH and alkalinity first. Supply about 0.3-0.8 mg/L Mn (manganese sulfate or chelate); avoid large iron chelate doses that compete with Mn. - Recovery: New upper leaves lose the netted pattern within 7-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # New leaves almost white: likely causes and fixes > New leaves almost white on cannabis is most often Light bleaching at the canopy top, High root-zone pH locking out iron, manganese, zinc, boron and copper or Iron deficiency (usually high pH). How to tell them apart, the fix for each and what recovery looks like. Also called: white new growth, albino tops, new leaves bleached white, ghost leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=white-new-growth ## Likely causes, most likely first ### Light bleaching at the canopy top (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Raise or dim the light by 10-20% so top-canopy PPFD sits around 800-1,100 µmol/m²/s at ambient CO2 (up to ~1,500 with CO2 and good climate). Keep the canopy even so one cola doesn't sit in a hotspot. Bleached tissue won't re-green. - Recovery: No new bleaching within 3-5 days; new bracts and leaves at the top stay green. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### High root-zone pH locking out iron, manganese, zinc, boron and copper (Possible) - Kind: pH; urgency: Deal with it this week - Fix: Bring root-zone pH into range: soil 6.2-6.8, coco and rockwool 5.8-6.2, hydro 5.5-6.2. Lower input pH by 0.2-0.3 units at a time rather than crashing it; neutralise alkaline water with a mineral acid (phosphoric, nitric or sulfuric; wear gloves and eye protection, add acid to water). Use an iron chelate stable at your pH (DTPA or EDDHA above 6.5). - Recovery: Runoff or reservoir pH back in range at two consecutive checks; new leaves open green within 5-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Iron deficiency (usually high pH) (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Bring root-zone pH into range first: soilless 5.5-6.2, soil 6.0-6.8. Neutralise alkaline water with acid. Supply 1.5-3 mg/L Fe as a chelate matched to pH: EDTA to about pH 6.5, DTPA to about 7.5, EDDHA to about 9. A foliar iron chelate spray (veg only) greens leaves in days. - Recovery: The next new leaves open green within 5-10 days; the whitened leaves re-green partly or not at all. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Yellow then tan edges on new leaves: likely causes and fixes > Yellow then tan edges on new leaves on cannabis is most often High root-zone pH locking out iron, manganese, zinc, boron and copper, Calcium deficiency (often a delivery problem) or Zinc deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: new leaves brown edges, yellow margins on top leaves, edges of new growth dying. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=yellow-new-margins ## Likely causes, most likely first ### High root-zone pH locking out iron, manganese, zinc, boron and copper (Possible) - Kind: pH; urgency: Deal with it this week - Fix: Bring root-zone pH into range: soil 6.2-6.8, coco and rockwool 5.8-6.2, hydro 5.5-6.2. Lower input pH by 0.2-0.3 units at a time rather than crashing it; neutralise alkaline water with a mineral acid (phosphoric, nitric or sulfuric; wear gloves and eye protection, add acid to water). Use an iron chelate stable at your pH (DTPA or EDDHA above 6.5). - Recovery: Runoff or reservoir pH back in range at two consecutive checks; new leaves open green within 5-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Calcium deficiency (often a delivery problem) (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out mites with a 30-60x lens first. Then fix delivery: leaf VPD 0.8-1.5 kPa (lights-on RH not stuck high), airflow under the canopy, root-zone pH not below ~5.8 in coco. If supply is short (RO water, unbuffered coco), bring Ca to about 150-200 mg/L with calcium nitrate or a Cal-Mag at label rate. LEDs do not create a Cal-Mag need; that is a myth. - Recovery: Leaves that open 7-10 days after the fix are flat and spot-free; old spots stay. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) ### Zinc deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Lower high pH, stop excess phosphorus 'boosters' (high P ties up Zn), then supply about 0.1-0.5 mg/L Zn as zinc sulfate or chelate. - Recovery: New leaves reach normal size with clean margins in 7-14 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Zinc (Zn) in cannabis: small leaves, margin burn and the phosphorus link](https://genetixbay.com/knowledge/nutrients/zinc.md) ### Excess phosphorus (bloom boosters) inducing Zn, Fe and Ca shortages (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Drop the booster. Keep P at about 30-60 mg/L; four controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, and excess P just leaves in the runoff. - Recovery: New growth greens within 10 days of returning to a balanced feed. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: ["Bloom boosters" for cannabis: what's real and what's marketing](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) ### Nickel deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: No published cannabis case. Only conceivable on very pure RO systems fed urea; do not add nickel otherwise (excess is toxic and cannabis accumulates metals). - Recovery: Not applicable in practice; look for another cause. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nickel (Ni) in cannabis: essential, needed in traces, almost never worth adding](https://genetixbay.com/knowledge/nutrients/nickel.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Top leaves or bracts bleached white or yellow nearest the light: likely causes and fixes > Top leaves or bracts bleached white or yellow nearest the light on cannabis is most often Light bleaching at the canopy top, Heat or light stress foxtailing on the top colas or Light burn: too much light for the plant's climate and CO2. How to tell them apart, the fix for each and what recovery look Also called: light bleaching, bleached tops, white tops, top colas turning white, sun bleached leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=bleached-top-leaves ## Likely causes, most likely first ### Light bleaching at the canopy top (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Raise or dim the light by 10-20% so top-canopy PPFD sits around 800-1,100 µmol/m²/s at ambient CO2 (up to ~1,500 with CO2 and good climate). Keep the canopy even so one cola doesn't sit in a hotspot. Bleached tissue won't re-green. - Recovery: No new bleaching within 3-5 days; new bracts and leaves at the top stay green. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Heat or light stress foxtailing on the top colas (Possible) - Kind: Light; urgency: Low urgency - Fix: Lower top-cola PPFD and leaf temperature (leaf under ~28-30 °C / 82-86 °F); even out the canopy. Evidence is mostly grower observation. - Recovery: No new spires on top colas over the next week. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Foxtailing buds on cannabis: genetics or stress?](https://genetixbay.com/knowledge/diagnosis/foxtails.md) ### Light burn: too much light for the plant's climate and CO2 (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Dim or raise the light 10-20%; ramp intensity over 7-10 days after a light change. Seedlings and clones need only 100-300 µmol/m²/s. High PPFD works only with leaf temperature, VPD, roots and feed all in range. - Recovery: Top leaves flatten within 1-3 days. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Middle leaves yellowing first: likely causes and fixes > Middle leaves yellowing first on cannabis is most often Sulfur deficiency, Molybdenum deficiency or Very low pH limiting molybdenum. How to tell them apart, the fix for each and what recovery looks like. Also called: middle of plant yellow, mid-canopy yellowing, yellowing in the middle leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=yellow-middle-leaves ## Likely causes, most likely first ### Sulfur deficiency (Possible) - Kind: Nutrient; urgency: Low urgency - Fix: Rare unless a feed is built only from nitrates and chlorides. Supply about 50-120 mg/L S as sulfate, e.g. via magnesium sulfate or potassium sulfate at normal rates. - Recovery: New leaves emerge green within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources](https://genetixbay.com/knowledge/nutrients/sulfur.md) ### Molybdenum deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Almost never the answer: cannabis grown 9 weeks without Mo showed no visible symptoms. Correct low pH (Mo availability falls as pH drops); supply about 0.01-0.05 mg/L Mo via a complete micro mix. - Recovery: Pale middle leaves stop spreading after pH correction. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Molybdenum (Mo) in cannabis: the trace element nitrate depends on](https://genetixbay.com/knowledge/nutrients/molybdenum.md) ### Very low pH limiting molybdenum (Less likely) - Kind: pH; urgency: Low urgency - Fix: Raise pH into range; Mo becomes more available as pH rises, unlike the other micros. Cannabis showed no visible Mo symptoms in a 9-week trial, so look harder for other causes. - Recovery: Pale middle leaves stop spreading. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Molybdenum (Mo) in cannabis: the trace element nitrate depends on](https://genetixbay.com/knowledge/nutrients/molybdenum.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Mottled mosaic or yellow streaks, distorted leaves: likely causes and fixes > Mottled mosaic or yellow streaks, distorted leaves on cannabis is most often Plant virus (e.g. beet curly top, lettuce chlorosis virus), Hop latent viroid (dudding) or Herbicide drift or residue. How to tell them apart, the fix for each and what recovery looks like. Also called: mosaic pattern on leaves, yellow streaks, mottled leaves, blotchy yellow pattern, virus looking leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=mosaic-mottle ## Likely causes, most likely first ### Plant virus (e.g. beet curly top, lettuce chlorosis virus) (Possible) - Kind: Disease; urgency: Deal with it this week - Fix: No cure: remove the plant. Control insect vectors (leafhoppers outdoors for curly top; whiteflies for some others) and test clone sources. - Recovery: No new symptomatic plants over the next 2-4 weeks. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ### Hop latent viroid (dudding) (Less likely) - Kind: Disease; urgency: Act within a day or two - Fix: No cure in a plant. Test mothers (roots and leaves) by RT-PCR or RT-qPCR, discard positives, disinfect tools with 10% bleach or heat (alcohol and peroxide don't inactivate it), and use meristem tissue culture to rescue valuable genetics. Don't take cuttings from stunted plants. - Recovery: Negative tests on new mothers; no more duds in the next cycle. - Confirm: Lab test for hop latent viroid (RT-PCR or RT-qPCR): Send root and leaf samples (roots detect HLVd earlier in young plants) to a lab offering HLVd RT-PCR or RT-qPCR. Test mother plants and any stunted plant among healthy siblings. A positive plant cannot be cured; tissue culture of meristem tips can rescue genetics. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ### Herbicide drift or residue (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Outdoors or with contaminated compost, manure or straw (persistent herbicide residues). Remove the source, repot into clean media; new growth may normalise slowly. Cannabis-specific symptom descriptions are scarce. - Recovery: New growth normalises over 2-4 weeks after the source is removed. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Why are my cannabis leaves curling? The master curling and clawing decision tree](https://genetixbay.com/knowledge/diagnosis/curling-clawing-decision-tree.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Fan leaves yellowing late in flower while buds keep ripening: likely causes and fixes > Fan leaves yellowing late in flower while buds keep ripening on cannabis is most often Normal late-flower fade (senescence). How to tell them apart, the fix for each and what recovery looks like. Also called: fade, autumn colours, leaves yellowing near harvest, fan leaves dying week 7, senescence. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=late-flower-fade ## Likely causes, most likely first ### Normal late-flower fade (senescence) (Likely) - Kind: Normal ageing; urgency: Low urgency - Fix: Nothing to fix in the last 2-3 weeks of flower. Keep feeding at stage strength with N tapered; don't 'flush' (pre-harvest flushing starves the plant while it packs on final weight and resin, and controlled studies show no quality gain). Fade before week 5-6 of flower suggests N was cut too early. - Recovery: Buds keep swelling and ripening normally while fan leaves fade. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Sudden yellowing across the plant within days: likely causes and fixes > Sudden yellowing across the plant within days on cannabis is most often Root rot (Pythium) or Low dissolved oxygen in the root zone. How to tell them apart, the fix for each and what recovery looks like. Also called: plant yellowed overnight, yellowing fast, whole plant turned yellow quickly, rapid yellowing. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=sudden-yellowing ## Likely causes, most likely first ### Root rot (Pythium) (Possible) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ### Low dissolved oxygen in the root zone (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Restore oxygen: clean or replace air stones, size the air pump for at least ~1 L/min per 4 L, keep a 2-5 cm air gap under net pots once roots reach the water, cool the solution to 18-22 °C (64-72 °F). Aim for 6-8+ mg/L DO. - Recovery: Fresh white root tips within 3-5 days; wilting stops. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Seedling leaves (cotyledons) yellowing: likely causes and fixes > Seedling leaves (cotyledons) yellowing on cannabis is most often Seed leaves yellowing as true leaves take over (normal), Overwatering (roots short of air) or Nitrogen deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: seed leaves yellow, round leaves turning yellow, cotyledons dying, seedling first leaves yellow. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=yellow-cotyledons ## Likely causes, most likely first ### Seed leaves yellowing as true leaves take over (normal) (Likely) - Kind: Normal ageing; urgency: Low urgency - Fix: Normal after 2-4 weeks once several true-leaf sets are growing. Early yellowing with wet medium is overwatering; with hot soil it may be over-strong soil. - Recovery: True leaves keep growing green. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Why are my seedling's leaves yellow or pale?](https://genetixbay.com/knowledge/answers/seedling-leaves-yellow.md) ### Overwatering (roots short of air) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Nitrogen deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Fix roots, watering and pH first. If N is genuinely short, raise feed N by about 10-20% (not double): mineral feeds around 150-200 mg/L N in veg and early flower; one DWC flowering trial predicted a yield optimum near 194 mg/L. Coco/hydro: raise base feed EC by ~0.2 mS/cm. Soil: liquid feed at label rate. Living soil: top-dress a fast organic N source and allow 1-2 weeks. Late flower: a gradual fade is the planned N taper, not a fault. - Recovery: Yellowing stops climbing within 5-7 days and new leaves emerge mid-green; already-yellow leaves do not recover. Runoff EC climbs back toward input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Damage only on one side of the plant or one area of the room: likely causes and fixes > Damage only on one side of the plant or one area of the room on cannabis is most often Wind burn from a fan blowing directly on leaves, Physical damage (kinks, splits, broken branches) or Fusarium wilt or crown rot. How to tell them apart, the fix for each and what recovery looks like. Also called: only one side affected, damage near the fan, one corner of the tent, problem only by the light edge. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=damage-one-side ## Likely causes, most likely first ### Wind burn from a fan blowing directly on leaves (Likely) - Kind: Environment; urgency: Low urgency - Fix: Aim fans across and under the canopy, not straight at leaves: leaves should rustle, not thrash (roughly 0.3-1.0 m/s at leaf level). Damaged leaves stay damaged. Cannabis-specific evidence is grower observation. - Recovery: No new damage on the fan side within a week. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) ### Physical damage (kinks, splits, broken branches) (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Splint and tape a split stem within hours (tape, plant tie or a straw splint); a supercropped knuckle heals stronger in 3-7 days. Remove fully broken branches with a clean cut. Support heavy colas with a trellis. - Recovery: Leaves above the wound regain turgor within 1-2 days; a callus forms within a week. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Article: [HST and supercropping: controlled stem crushing](https://genetixbay.com/knowledge/training/hst-supercropping.md) ### Fusarium wilt or crown rot (Less likely) - Kind: Disease; urgency: Act within a day or two - Fix: No cure once infected: remove the plant with its medium in a bag, sanitise pots, trays and water lines, and use clean clones and new media. Reduce root stress (overwatering, heat, salts) on the rest. - Recovery: No further wilting plants over the next 2-3 weeks. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Fusarium in cannabis: wilt, crown rot and bud rot](https://genetixbay.com/knowledge/diseases/fusarium.md) ### Herbicide drift or residue (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Outdoors or with contaminated compost, manure or straw (persistent herbicide residues). Remove the source, repot into clean media; new growth may normalise slowly. Cannabis-specific symptom descriptions are scarce. - Recovery: New growth normalises over 2-4 weeks after the source is removed. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Why are my cannabis leaves curling? The master curling and clawing decision tree](https://genetixbay.com/knowledge/diagnosis/curling-clawing-decision-tree.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Rust-brown spots on newer and middle leaves: likely causes and fixes > Rust-brown spots on newer and middle leaves on cannabis is most often Calcium deficiency (often a delivery problem), Low root-zone pH starving calcium and magnesium or Unbuffered or new coco pulling calcium and magnesium. How to tell them apart, the fix for each and what recovery looks like. Also called: brown spots on leaves, rust spots, calcium spots, brown speckles on new growth, rusty dots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=rust-spots-new ## Likely causes, most likely first ### Calcium deficiency (often a delivery problem) (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out mites with a 30-60x lens first. Then fix delivery: leaf VPD 0.8-1.5 kPa (lights-on RH not stuck high), airflow under the canopy, root-zone pH not below ~5.8 in coco. If supply is short (RO water, unbuffered coco), bring Ca to about 150-200 mg/L with calcium nitrate or a Cal-Mag at label rate. LEDs do not create a Cal-Mag need; that is a myth. - Recovery: Leaves that open 7-10 days after the fix are flat and spot-free; old spots stay. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) ### Low root-zone pH starving calcium and magnesium (Possible) - Kind: pH; urgency: Deal with it this week - Fix: Raise root-zone pH to range: coco 5.8-6.2, hydro 5.6-6.0, soil 6.2-6.8. Use pH up (potassium hydroxide or carbonate) in small steps; in coco, feed at 6.0-6.2 for a few waterings with Ca and Mg on board. A fast fall in hydro points to dying roots or microbes; check them. - Recovery: pH holds in range for a week; new leaves spot-free within 7-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Unbuffered or new coco pulling calcium and magnesium (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Feed with Ca and Mg on board: calcium nitrate and magnesium sulfate, or a Cal-Mag, bringing the feed to about 150-200 mg/L Ca and 40-60 mg/L Mg, at pH 5.8-6.2. For the next batch, rinse and buffer coco by soaking it in a calcium (and magnesium) nitrate solution before planting. - Recovery: New leaves clean within 7-10 days; runoff Ca/Mg symptoms stop spreading. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Buffering coco coir: why it matters and how to do it](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md) ### Uncalibrated or failing pH or EC meter (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Calibrate the pH meter with fresh pH 7 then pH 4 buffer before decisions and at least weekly; store the probe wet in storage solution, never in RO water. Check EC against 1.413 mS/cm. Replace probes that won't calibrate (typical life 1-2 years). Drops and strips are too coarse to diagnose with. - Recovery: Readings match the buffers within 0.1 pH; the 'problem' pH disappears or is confirmed. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Article: [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) ### Twospotted spider mites (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Act now: they breed fastest hot and dry. Remove the worst leaves into a sealed bag, cool the room and raise RH a little (in veg), release predatory mites (Phytoseiulus persimilis for hot spots, Neoseiulus californicus as a preventive) before numbers explode. Soaps or horticultural oils only in veg, never on buds. Quarantine new clones. - Recovery: No new stippling on new leaves and no live mites at 10-20x after 7-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Article: [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ### Humidity too high / VPD too low (Less likely) - Kind: Environment; urgency: Act within a day or two - Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids. - Recovery: RH holds in band through lights-off for 3+ days; no new mould signs. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ### Spray or foliar burn (pesticide, oil, soap, foliar feed) (Less likely) - Kind: Physical damage; urgency: Low urgency - Fix: Stop spraying; rinse residue off with plain water at lights-off if damage is fresh. In future spray only at lights-off or with lights raised, test one leaf 24-48 h first, never mix sulfur with oils, and never spray buds. - Recovery: No new damage on leaves that grow after the spray. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers. - Article: [What can I safely spray on plants in flower?](https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.md) ### Ammonium toxicity (too much NH4 in the feed) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Keep ammonium at or below about 10-30% of total N (cannabis trials showed toxicity and lost yield above ~30%); switch to a mostly nitrate feed and correct root-zone pH. - Recovery: pH stops falling and new leaves lose the dark claw within a week. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Dark olive or brown sunken spots on older leaves: likely causes and fixes > Dark olive or brown sunken spots on older leaves on cannabis is most often Phosphorus deficiency or High pH reducing phosphorus availability. How to tell them apart, the fix for each and what recovery looks like. Also called: dark spots on bottom leaves, bronze blotches lower leaves, phosphorus spots, olive green blotches. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=olive-spots-old ## Likely causes, most likely first ### Phosphorus deficiency (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Warm the root zone to 18-22 °C (64-72 °F) and nights above ~15 °C (59 °F) first; cold blocks P uptake. Correct pH (soilless 5.5-6.5, soil 6.0-7.0). If genuinely short, supply about 30-60 mg/L P; controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, so skip 'bloom boosters'. Soil: a balanced liquid feed; living soil: a slow P amendment acts in weeks. - Recovery: No new olive spots on leaves that open after the fix, within 7-10 days; growth rate picks up. Spotted leaves stay damaged. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) ### High pH reducing phosphorus availability (Possible) - Kind: pH; urgency: Deal with it this week - Fix: Bring soil pH to 6.2-6.8 (soilless 5.8-6.2) and neutralise alkaline water; above about pH 7, phosphate precipitates with calcium. Do not add more P to compensate. - Recovery: No new olive spots on leaves that open after pH correction. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Round brown spots with yellow halos on lower leaves: likely causes and fixes > Round brown spots with yellow halos on lower leaves on cannabis is most often Septoria leaf spot. How to tell them apart, the fix for each and what recovery looks like. Also called: leaf spot, brown spots yellow ring, target spots, septoria, yellow leaf spot. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=spots-yellow-halo ## Likely causes, most likely first ### Septoria leaf spot (Possible) - Kind: Disease; urgency: Deal with it this week - Fix: Mainly outdoor and greenhouse. Strip infected lower leaves into a bag, keep foliage dry (water at the base), mulch to stop splash, open the lower canopy, clear debris; protectants only where registered. - Recovery: Spots stop climbing within 1-2 weeks. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Septoria leaf spot (yellow leaf spot) in cannabis](https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Tan, crispy scorched edges on older leaves: likely causes and fixes > Tan, crispy scorched edges on older leaves on cannabis is most often Potassium deficiency, Nutrient burn (feed too strong) or Ammonium toxicity (too much NH4 in the feed). How to tell them apart, the fix for each and what recovery looks like. Also called: burnt edges on bottom leaves, leaf edges crispy, brown leaf margins old leaves, scorched leaf edges. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=scorched-margins-old ## Likely causes, most likely first ### Potassium deficiency (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Check runoff EC first: salt burn looks the same. If K is genuinely short, feed about 175-250 mg/L K (potassium sulfate, potassium nitrate or MKP) at a normal EC. A flowering DWC trial saw no yield response anywhere from 60 to 340 mg/L, so more is not better. Cut heavy Cal-Mag or sodium-rich water that competes with K. - Recovery: Margin scorch stops advancing up the plant within 7 days; new leaves open with clean margins. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md) ### Nutrient burn (feed too strong) (Possible) - Kind: Too much of something; urgency: Low urgency - Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up). - Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ### Ammonium toxicity (too much NH4 in the feed) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Keep ammonium at or below about 10-30% of total N (cannabis trials showed toxicity and lost yield above ~30%); switch to a mostly nitrate feed and correct root-zone pH. - Recovery: pH stops falling and new leaves lose the dark claw within a week. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Manganese toxicity (usually low pH) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Raise root-zone pH into range (soilless 5.8-6.2, soil 6.2-6.8); check that the micro mix is not over-dosed. Tissue tests may not flag it: in one trial, symptomatic plants had normal leaf Mn. - Recovery: Margin yellowing stops climbing within 7 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) ### Sodium build-up (softened water, coco, recirculation) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Never use ion-exchange softened water. Keep feed sodium below about 50 mg/L (more than ~5 mM NaCl, 115 mg/L Na, may cut hydro yield and cannabinoids fall as NaCl rises). Dump and refill recirculating reservoirs more often; rinse coco before planting. - Recovery: Tip burn stops advancing on new leaves within a week. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add](https://genetixbay.com/knowledge/nutrients/sodium.md) ### Boron toxicity (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Test the water (some wells carry B) and stop extra boron products; supply only 0.2-0.5 mg/L B in total. Cannabis tolerated about 10x for weeks, but symptoms appeared after 7 weeks at ~4.9 mg/L. - Recovery: No new margin scorch on leaves that mature after the change. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) ### Chloride excess (salinity) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Keep chloride below about 50-70 mg/L in the feed; switch potassium chloride for potassium sulfate; blend high-chloride water with RO. - Recovery: No new tip burn after the change. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add](https://genetixbay.com/knowledge/nutrients/chlorine.md) ### Molybdenum deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Almost never the answer: cannabis grown 9 weeks without Mo showed no visible symptoms. Correct low pH (Mo availability falls as pH drops); supply about 0.01-0.05 mg/L Mo via a complete micro mix. - Recovery: Pale middle leaves stop spreading after pH correction. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Molybdenum (Mo) in cannabis: the trace element nitrate depends on](https://genetixbay.com/knowledge/nutrients/molybdenum.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Brown, burnt leaf tips: likely causes and fixes > Brown, burnt leaf tips on cannabis is most often Nutrient burn (feed too strong), Salt build-up in the root zone or Sodium build-up (softened water, coco, recirculation). How to tell them apart, the fix for each and what recovery looks like. Also called: nute burn, burnt tips, crispy tips, tip burn, brown tips on leaves, nutrient burn. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=burnt-tips ## Likely causes, most likely first ### Nutrient burn (feed too strong) (Likely) - Kind: Too much of something; urgency: Low urgency - Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up). - Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ### Salt build-up in the root zone (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth. - Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like. - Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ### Sodium build-up (softened water, coco, recirculation) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Never use ion-exchange softened water. Keep feed sodium below about 50 mg/L (more than ~5 mM NaCl, 115 mg/L Na, may cut hydro yield and cannabinoids fall as NaCl rises). Dump and refill recirculating reservoirs more often; rinse coco before planting. - Recovery: Tip burn stops advancing on new leaves within a week. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add](https://genetixbay.com/knowledge/nutrients/sodium.md) ### Air too dry / VPD too high (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Raise RH or lower temperature to bring leaf VPD to 0.4-0.8 kPa (clones, seedlings), 0.8-1.2 (veg), 1.0-1.5 (flower). Humidifier, less exhaust when cool, fewer dry hot air inputs. Dry air also speeds spider mites. - Recovery: Leaves flatten within a day. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ### Spray or foliar burn (pesticide, oil, soap, foliar feed) (Less likely) - Kind: Physical damage; urgency: Low urgency - Fix: Stop spraying; rinse residue off with plain water at lights-off if damage is fresh. In future spray only at lights-off or with lights raised, test one leaf 24-48 h first, never mix sulfur with oils, and never spray buds. - Recovery: No new damage on leaves that grow after the spray. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers. - Article: [What can I safely spray on plants in flower?](https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.md) ### Too much nitrogen (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Cut feed N by 20-30% (or the whole feed EC by ~0.3-0.5 mS/cm); for a heavy overdose in containers, run a root-zone flush with pH-adjusted, quarter-strength feed to 20-30% runoff. In flower, taper N while keeping P, K, Ca, Mg, S and micros fed. - Recovery: New leaves come in lighter green and flat within 5-7 days; clawed leaves relax partly. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Wind burn from a fan blowing directly on leaves (Less likely) - Kind: Environment; urgency: Low urgency - Fix: Aim fans across and under the canopy, not straight at leaves: leaves should rustle, not thrash (roughly 0.3-1.0 m/s at leaf level). Damaged leaves stay damaged. Cannabis-specific evidence is grower observation. - Recovery: No new damage on the fan side within a week. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) ### Excess potassium crowding out magnesium and calcium (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Stop K boosters and keep K near 175-250 mg/L; cation antagonism (K vs Mg and Ca) is the interaction that reliably matters in practice. - Recovery: Interveinal yellowing stops climbing in 7 days. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Small tan dead specks between veins on upper leaves: likely causes and fixes > Small tan dead specks between veins on upper leaves on cannabis is most often Manganese deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: tiny brown dots upper leaves, pinpoint necrosis, speckled top leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=tan-specks-upper ## Likely causes, most likely first ### Manganese deficiency (Possible) - Kind: Nutrient; urgency: Low urgency - Fix: Correct high pH and alkalinity first. Supply about 0.3-0.8 mg/L Mn (manganese sulfate or chelate); avoid large iron chelate doses that compete with Mn. - Recovery: New upper leaves lose the netted pattern within 7-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Brown or dark speckling and bronzing on older leaves: likely causes and fixes > Brown or dark speckling and bronzing on older leaves on cannabis is most often Manganese toxicity (usually low pH), Low root-zone pH starving calcium and magnesium or Iron and manganese excess at very low pH. How to tell them apart, the fix for each and what recovery looks like. Also called: dark speckles on old leaves, brown freckles, bronze speckled lower leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=brown-speckles-old ## Likely causes, most likely first ### Manganese toxicity (usually low pH) (Possible) - Kind: Too much of something; urgency: Low urgency - Fix: Raise root-zone pH into range (soilless 5.8-6.2, soil 6.2-6.8); check that the micro mix is not over-dosed. Tissue tests may not flag it: in one trial, symptomatic plants had normal leaf Mn. - Recovery: Margin yellowing stops climbing within 7 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) ### Low root-zone pH starving calcium and magnesium (Less likely) - Kind: pH; urgency: Deal with it this week - Fix: Raise root-zone pH to range: coco 5.8-6.2, hydro 5.6-6.0, soil 6.2-6.8. Use pH up (potassium hydroxide or carbonate) in small steps; in coco, feed at 6.0-6.2 for a few waterings with Ca and Mg on board. A fast fall in hydro points to dying roots or microbes; check them. - Recovery: pH holds in range for a week; new leaves spot-free within 7-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Iron and manganese excess at very low pH (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Raise root-zone pH above ~5.5 (soilless) or 6.0 (soil); below about 5.3, Fe and Mn become very soluble. Cannabis Fe toxicity itself is not characterised. - Recovery: No new speckling on leaves that develop after pH correction. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Irregular dead or bleached patches after spraying: likely causes and fixes > Irregular dead or bleached patches after spraying on cannabis is most often Spray or foliar burn (pesticide, oil, soap, foliar feed). How to tell them apart, the fix for each and what recovery looks like. Also called: spray burn, leaves burnt after spraying, foliar burn, droplet burn spots, neem burn, white patches after spray. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=random-dead-patches ## Likely causes, most likely first ### Spray or foliar burn (pesticide, oil, soap, foliar feed) (Likely) - Kind: Physical damage; urgency: Low urgency - Fix: Stop spraying; rinse residue off with plain water at lights-off if damage is fresh. In future spray only at lights-off or with lights raised, test one leaf 24-48 h first, never mix sulfur with oils, and never spray buds. - Recovery: No new damage on leaves that grow after the spray. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers. - Article: [What can I safely spray on plants in flower?](https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Crispy, papery or scorched top leaves: likely causes and fixes > Crispy, papery or scorched top leaves on cannabis is most often Heat stress, Light burn: too much light for the plant's climate and CO2 or Air too dry / VPD too high. How to tell them apart, the fix for each and what recovery looks like. Also called: leaves fried at the top, light burn, heat burn, crispy upper leaves, top leaves crunchy. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=crispy-top-leaves ## Likely causes, most likely first ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Light burn: too much light for the plant's climate and CO2 (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Dim or raise the light 10-20%; ramp intensity over 7-10 days after a light change. Seedlings and clones need only 100-300 µmol/m²/s. High PPFD works only with leaf temperature, VPD, roots and feed all in range. - Recovery: Top leaves flatten within 1-3 days. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Air too dry / VPD too high (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Raise RH or lower temperature to bring leaf VPD to 0.4-0.8 kPa (clones, seedlings), 0.8-1.2 (veg), 1.0-1.5 (flower). Humidifier, less exhaust when cool, fewer dry hot air inputs. Dry air also speeds spider mites. - Recovery: Leaves flatten within a day. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ### Underwatering (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Water slowly in 2-3 passes until 10-20% runoff, so the whole root ball wets. Water when the pot is clearly lighter, before the plant droops. Mild late-flower dry-back is a house-endorsed practice for some cultivars (Caplan 2019), but wilting is not. - Recovery: Turgor returns within 1-6 hours of watering. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Dry, torn or curled leaves facing a fan: likely causes and fixes > Dry, torn or curled leaves facing a fan on cannabis is most often Wind burn from a fan blowing directly on leaves. How to tell them apart, the fix for each and what recovery looks like. Also called: wind burn, fan burn, leaves shredded by fan, leaves clawing near the fan, windburn. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=wind-burn ## Likely causes, most likely first ### Wind burn from a fan blowing directly on leaves (Likely) - Kind: Environment; urgency: Low urgency - Fix: Aim fans across and under the canopy, not straight at leaves: leaves should rustle, not thrash (roughly 0.3-1.0 m/s at leaf level). Damaged leaves stay damaged. Cannabis-specific evidence is grower observation. - Recovery: No new damage on the fan side within a week. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Lower leaves dying and dropping quickly: likely causes and fixes > Lower leaves dying and dropping quickly on cannabis is most often Nitrogen deficiency, Shaded lower leaves dying back (normal) or Septoria leaf spot. How to tell them apart, the fix for each and what recovery looks like. Also called: bottom leaves falling off, leaves dropping, losing lower leaves fast, leaves crisping and falling. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=lower-leaves-dying-fast ## Likely causes, most likely first ### Nitrogen deficiency (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Fix roots, watering and pH first. If N is genuinely short, raise feed N by about 10-20% (not double): mineral feeds around 150-200 mg/L N in veg and early flower; one DWC flowering trial predicted a yield optimum near 194 mg/L. Coco/hydro: raise base feed EC by ~0.2 mS/cm. Soil: liquid feed at label rate. Living soil: top-dress a fast organic N source and allow 1-2 weeks. Late flower: a gradual fade is the planned N taper, not a fault. - Recovery: Yellowing stops climbing within 5-7 days and new leaves emerge mid-green; already-yellow leaves do not recover. Runoff EC climbs back toward input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Shaded lower leaves dying back (normal) (Less likely) - Kind: Normal ageing; urgency: Low urgency - Fix: A few yellowing leaves deep in a dense canopy are normal; the plant recycles them. Tuck and train to open the canopy rather than stripping (house: tuck, don't pluck). - Recovery: Only shaded leaves affected; upper canopy healthy. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) ### Septoria leaf spot (Less likely) - Kind: Disease; urgency: Deal with it this week - Fix: Mainly outdoor and greenhouse. Strip infected lower leaves into a bag, keep foliage dry (water at the base), mulch to stop splash, open the lower canopy, clear debris; protectants only where registered. - Recovery: Spots stop climbing within 1-2 weeks. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Septoria leaf spot (yellow leaf spot) in cannabis](https://genetixbay.com/knowledge/diseases/septoria-leaf-spot.md) ### Magnesium deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Check root-zone pH (Mg uptake falls at low pH) and whether heavy K or Ca is crowding it out. If short, bring Mg to about 40-70 mg/L with magnesium sulfate (roughly 0.4-0.5 g/L of the heptahydrate adds ~40-50 mg/L Mg) or magnesium nitrate. A 1-2 g/L magnesium sulfate foliar spray greens veg leaves faster; never spray buds. - Recovery: Interveinal yellowing stops climbing in 5-7 days; leaves above the damage stay green. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Magnesium (Mg) in cannabis: interveinal yellowing, targets and the K-Ca competition](https://genetixbay.com/knowledge/nutrients/magnesium.md) ### Root-bound in a pot too small (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Up-pot photoperiods into a container about 2-3x larger, loosening circling roots gently. Autoflowers: don't transplant; increase watering and feeding frequency instead. Small pots can still grow big plants with high-frequency fertigation (several feeds a day). - Recovery: New white roots in the fresh medium within 5-7 days; daily wilting stops. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Cannabis root problems: the master decision tree](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md) ### Underwatering (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Water slowly in 2-3 passes until 10-20% runoff, so the whole root ball wets. Water when the pot is clearly lighter, before the plant droops. Mild late-flower dry-back is a house-endorsed practice for some cultivars (Caplan 2019), but wilting is not. - Recovery: Turgor returns within 1-6 hours of watering. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Manganese toxicity (usually low pH) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Raise root-zone pH into range (soilless 5.8-6.2, soil 6.2-6.8); check that the micro mix is not over-dosed. Tissue tests may not flag it: in one trial, symptomatic plants had normal leaf Mn. - Recovery: Margin yellowing stops climbing within 7 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.md) ### Phosphorus deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Warm the root zone to 18-22 °C (64-72 °F) and nights above ~15 °C (59 °F) first; cold blocks P uptake. Correct pH (soilless 5.5-6.5, soil 6.0-7.0). If genuinely short, supply about 30-60 mg/L P; controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, so skip 'bloom boosters'. Soil: a balanced liquid feed; living soil: a slow P amendment acts in weeks. - Recovery: No new olive spots on leaves that open after the fix, within 7-10 days; growth rate picks up. Spotted leaves stay damaged. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Dark, water-soaked lesions on leaves or stems: likely causes and fixes > Dark, water-soaked lesions on leaves or stems on cannabis is most often Botrytis bud rot (grey mould) or Humidity too high / VPD too low. How to tell them apart, the fix for each and what recovery looks like. Also called: wet looking spots, greasy spots, dark soggy patches, water soaked leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=water-soaked-lesions ## Likely causes, most likely first ### Botrytis bud rot (grey mould) (Possible) - Kind: Disease; urgency: Act now - Fix: Act now. Bag infected buds before cutting them out, 3-5 cm (1-2 in) past visible rot, and clean tools; never shake them. Drop RH to about 40-50% in late flower, control the lights-off dew point, move air through dense colas. There is no cure in flower; consider harvesting early if it keeps spreading. - Recovery: No new rot on weekly cola checks for 2 weeks. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ### Humidity too high / VPD too low (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids. - Recovery: RH holds in band through lights-off for 3+ days; no new mould signs. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Small raised blisters or corky bumps on leaf undersides: likely causes and fixes > Small raised blisters or corky bumps on leaf undersides on cannabis is most often Humidity too high / VPD too low, Overwatering (roots short of air) or Oedema (water uptake outrunning transpiration). How to tell them apart, the fix for each and what recovery looks like. Also called: oedema, edema, blisters under leaves, bumps on leaves, corky spots underside. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=oedema-bumps ## Likely causes, most likely first ### Humidity too high / VPD too low (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids. - Recovery: RH holds in band through lights-off for 3+ days; no new mould signs. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ### Overwatering (roots short of air) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Oedema (water uptake outrunning transpiration) (Less likely) - Kind: Environment; urgency: Low urgency - Fix: Lower RH and keep air moving, water in the morning or at lights-on, and avoid watering cold, wet pots. Documented in many greenhouse crops; cannabis reports are anecdotal. - Recovery: No new blisters on new leaves within a week. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Spots, brown patches and dead edges on cannabis leaves: the master decision tree](https://genetixbay.com/knowledge/diagnosis/spots-necrosis-decision-tree.md) ### Cold stress (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Keep days at 22-28 °C (72-82 °F) and nights no more than 3-6 °C (5-10 °F) cooler and above ~15 °C (59 °F); warm the root zone. Cold-for-colour is real in purple cultivars, but claims of more terpenes or resin are unsupported. - Recovery: Growth resumes within a week; new leaves come in green. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Dark brown lesions on sugar leaves in flower: likely causes and fixes > Dark brown lesions on sugar leaves in flower on cannabis is most often Potassium deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: sugar leaves turning brown, brown spots on bud leaves, dark sugar leaf tips. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=dark-lesions-sugar-leaves ## Likely causes, most likely first ### Potassium deficiency (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Check runoff EC first: salt burn looks the same. If K is genuinely short, feed about 175-250 mg/L K (potassium sulfate, potassium nitrate or MKP) at a normal EC. A flowering DWC trial saw no yield response anywhere from 60 to 340 mg/L, so more is not better. Cut heavy Cal-Mag or sodium-rich water that competes with K. - Recovery: Margin scorch stops advancing up the plant within 7 days; new leaves open with clean margins. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Holes chewed in leaves or ragged edges: likely causes and fixes > Holes chewed in leaves or ragged edges on cannabis is most often Caterpillars and budworms. How to tell them apart, the fix for each and what recovery looks like. Also called: holes in leaves, something eating my leaves, chewed leaves, bite marks, ragged leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=holes-in-leaves ## Likely causes, most likely first ### Caterpillars and budworms (Possible) - Kind: Pest; urgency: Act within a day or two - Fix: Hand-pick; exclude moths with netting; use Bt (kurstaki or aizawai) while larvae are small, since it must be eaten and breaks down in sunlight in days. Remove bored buds: frass starts bud rot. - Recovery: No fresh frass or holes after 1 week. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Article: [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Dark green, glossy leaves with tips hooking down (the claw): likely causes and fixes > Dark green, glossy leaves with tips hooking down (the claw) on cannabis is most often Nutrient burn (feed too strong), Too much nitrogen or Overwatering (roots short of air). How to tell them apart, the fix for each and what recovery looks like. Also called: the claw, nitrogen claw, eagle claw leaves, leaves curling down at tips, dark green clawing. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=clawing-dark ## Likely causes, most likely first ### Nutrient burn (feed too strong) (Possible) - Kind: Too much of something; urgency: Low urgency - Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up). - Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ### Too much nitrogen (Possible) - Kind: Too much of something; urgency: Low urgency - Fix: Cut feed N by 20-30% (or the whole feed EC by ~0.3-0.5 mS/cm); for a heavy overdose in containers, run a root-zone flush with pH-adjusted, quarter-strength feed to 20-30% runoff. In flower, taper N while keeping P, K, Ca, Mg, S and micros fed. - Recovery: New leaves come in lighter green and flat within 5-7 days; clawed leaves relax partly. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Overwatering (roots short of air) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Ammonium toxicity (too much NH4 in the feed) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Keep ammonium at or below about 10-30% of total N (cannabis trials showed toxicity and lost yield above ~30%); switch to a mostly nitrate feed and correct root-zone pH. - Recovery: pH stops falling and new leaves lose the dark claw within a week. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Wind burn from a fan blowing directly on leaves (Less likely) - Kind: Environment; urgency: Low urgency - Fix: Aim fans across and under the canopy, not straight at leaves: leaves should rustle, not thrash (roughly 0.3-1.0 m/s at leaf level). Damaged leaves stay damaged. Cannabis-specific evidence is grower observation. - Recovery: No new damage on the fan side within a week. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Leaves curling down and limp while the pot is wet: likely causes and fixes > Leaves curling down and limp while the pot is wet on cannabis is most often Overwatering (roots short of air), Humidity too high / VPD too low or Oedema (water uptake outrunning transpiration). How to tell them apart, the fix for each and what recovery looks like. Also called: droopy curled leaves, leaves curling down overwatered, whole leaf curls under, puffy droopy leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=curl-down-wet ## Likely causes, most likely first ### Overwatering (roots short of air) (Likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Humidity too high / VPD too low (Less likely) - Kind: Environment; urgency: Act within a day or two - Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids. - Recovery: RH holds in band through lights-off for 3+ days; no new mould signs. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ### Oedema (water uptake outrunning transpiration) (Less likely) - Kind: Environment; urgency: Low urgency - Fix: Lower RH and keep air moving, water in the morning or at lights-on, and avoid watering cold, wet pots. Documented in many greenhouse crops; cannabis reports are anecdotal. - Recovery: No new blisters on new leaves within a week. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Spots, brown patches and dead edges on cannabis leaves: the master decision tree](https://genetixbay.com/knowledge/diagnosis/spots-necrosis-decision-tree.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Leaves folding up along the midrib (taco): likely causes and fixes > Leaves folding up along the midrib (taco) on cannabis is most often Heat stress, Light burn: too much light for the plant's climate and CO2 or Air too dry / VPD too high. How to tell them apart, the fix for each and what recovery looks like. Also called: taco leaves, leaves folding up, leaves cupping up, tacoing, folded leaves at the top. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=taco-leaves ## Likely causes, most likely first ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Light burn: too much light for the plant's climate and CO2 (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Dim or raise the light 10-20%; ramp intensity over 7-10 days after a light change. Seedlings and clones need only 100-300 µmol/m²/s. High PPFD works only with leaf temperature, VPD, roots and feed all in range. - Recovery: Top leaves flatten within 1-3 days. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Air too dry / VPD too high (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Raise RH or lower temperature to bring leaf VPD to 0.4-0.8 kPa (clones, seedlings), 0.8-1.2 (veg), 1.0-1.5 (flower). Humidifier, less exhaust when cool, fewer dry hot air inputs. Dry air also speeds spider mites. - Recovery: Leaves flatten within a day. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ### Light bleaching at the canopy top (Less likely) - Kind: Light; urgency: Deal with it this week - Fix: Raise or dim the light by 10-20% so top-canopy PPFD sits around 800-1,100 µmol/m²/s at ambient CO2 (up to ~1,500 with CO2 and good climate). Keep the canopy even so one cola doesn't sit in a hotspot. Bleached tissue won't re-green. - Recovery: No new bleaching within 3-5 days; new bracts and leaves at the top stay green. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Spray or foliar burn (pesticide, oil, soap, foliar feed) (Less likely) - Kind: Physical damage; urgency: Low urgency - Fix: Stop spraying; rinse residue off with plain water at lights-off if damage is fresh. In future spray only at lights-off or with lights raised, test one leaf 24-48 h first, never mix sulfur with oils, and never spray buds. - Recovery: No new damage on leaves that grow after the spray. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers. - Article: [What can I safely spray on plants in flower?](https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Leaf edges curling up (canoeing): likely causes and fixes > Leaf edges curling up (canoeing) on cannabis is most often Heat stress, Air too dry / VPD too high or Light burn: too much light for the plant's climate and CO2. How to tell them apart, the fix for each and what recovery looks like. Also called: canoeing, edges rolling up, leaf margins curling up, leaves turning up at the sides. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=canoe-edges-up ## Likely causes, most likely first ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Air too dry / VPD too high (Possible) - Kind: Environment; urgency: Deal with it this week - Fix: Raise RH or lower temperature to bring leaf VPD to 0.4-0.8 kPa (clones, seedlings), 0.8-1.2 (veg), 1.0-1.5 (flower). Humidifier, less exhaust when cool, fewer dry hot air inputs. Dry air also speeds spider mites. - Recovery: Leaves flatten within a day. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ### Light burn: too much light for the plant's climate and CO2 (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Dim or raise the light 10-20%; ramp intensity over 7-10 days after a light change. Seedlings and clones need only 100-300 µmol/m²/s. High PPFD works only with leaf temperature, VPD, roots and feed all in range. - Recovery: Top leaves flatten within 1-3 days. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Hemp russet mites (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm at 30-60x (they look like moving dust). Remove badly infested plants; release predatory mites preventively; quarantine clones; leave a plant-free gap between cycles. - Recovery: Bronzing stops climbing and no live mites at 30-60x in 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ### Calcium deficiency (often a delivery problem) (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out mites with a 30-60x lens first. Then fix delivery: leaf VPD 0.8-1.5 kPa (lights-on RH not stuck high), airflow under the canopy, root-zone pH not below ~5.8 in coco. If supply is short (RO water, unbuffered coco), bring Ca to about 150-200 mg/L with calcium nitrate or a Cal-Mag at label rate. LEDs do not create a Cal-Mag need; that is a myth. - Recovery: Leaves that open 7-10 days after the fix are flat and spot-free; old spots stay. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) ### Wind burn from a fan blowing directly on leaves (Less likely) - Kind: Environment; urgency: Low urgency - Fix: Aim fans across and under the canopy, not straight at leaves: leaves should rustle, not thrash (roughly 0.3-1.0 m/s at leaf level). Damaged leaves stay damaged. Cannabis-specific evidence is grower observation. - Recovery: No new damage on the fan side within a week. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md) ### Phosphorus deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Warm the root zone to 18-22 °C (64-72 °F) and nights above ~15 °C (59 °F) first; cold blocks P uptake. Correct pH (soilless 5.5-6.5, soil 6.0-7.0). If genuinely short, supply about 30-60 mg/L P; controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, so skip 'bloom boosters'. Soil: a balanced liquid feed; living soil: a slow P amendment acts in weeks. - Recovery: No new olive spots on leaves that open after the fix, within 7-10 days; growth rate picks up. Spotted leaves stay damaged. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Leaves held upward, praying, healthy colour: likely causes and fixes > Leaves held upward, praying, healthy colour on cannabis is most often Normal leaf movement (praying by day, drooping at night). How to tell them apart, the fix for each and what recovery looks like. Also called: praying leaves, leaves pointing up, leaves reaching to the light. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=praying-leaves ## Likely causes, most likely first ### Normal leaf movement (praying by day, drooping at night) (Likely) - Kind: Normal ageing; urgency: Low urgency - Fix: Nothing to fix. Healthy cannabis angles leaves toward strong light and relaxes them at night. - Recovery: Leaves follow the light cycle with no damage. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Are praying leaves a good sign?](https://genetixbay.com/knowledge/answers/praying-leaves.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Twisted, distorted or crinkled new growth: likely causes and fixes > Twisted, distorted or crinkled new growth on cannabis is most often Calcium deficiency (often a delivery problem), Broad mites or Aphids. How to tell them apart, the fix for each and what recovery looks like. Also called: deformed new growth, twisted leaves, mutated new leaves, crinkled top leaves, new growth growing weird. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=twisted-new-growth ## Likely causes, most likely first ### Calcium deficiency (often a delivery problem) (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out mites with a 30-60x lens first. Then fix delivery: leaf VPD 0.8-1.5 kPa (lights-on RH not stuck high), airflow under the canopy, root-zone pH not below ~5.8 in coco. If supply is short (RO water, unbuffered coco), bring Ca to about 150-200 mg/L with calcium nitrate or a Cal-Mag at label rate. LEDs do not create a Cal-Mag need; that is a myth. - Recovery: Leaves that open 7-10 days after the fix are flat and spot-free; old spots stay. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) ### Broad mites (Possible) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm at 30-60x. Remove and bag heavily infested plants; mothers and clones are the usual source. Release predatory mites (e.g. Neoseiulus californicus or Amblyseius swirskii) on the rest, keep tools and clothes clean, quarantine new stock. In flower, removal is usually the only clean option. - Recovery: New growth expands normally (not glossy or twisted) within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ### Aphids (Less likely) - Kind: Pest; urgency: Deal with it this week - Fix: Squash or rinse small colonies; release parasitoid wasps (Aphidius), predatory midges or lacewings; insecticidal soap or oil only before flower. Control ants that farm them. - Recovery: Colonies shrink and mummified (parasitised) aphids appear within 1-2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ### Low root-zone pH starving calcium and magnesium (Less likely) - Kind: pH; urgency: Deal with it this week - Fix: Raise root-zone pH to range: coco 5.8-6.2, hydro 5.6-6.0, soil 6.2-6.8. Use pH up (potassium hydroxide or carbonate) in small steps; in coco, feed at 6.0-6.2 for a few waterings with Ca and Mg on board. A fast fall in hydro points to dying roots or microbes; check them. - Recovery: pH holds in range for a week; new leaves spot-free within 7-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Thrips (Less likely) - Kind: Pest; urgency: Deal with it this week - Fix: Two levels: predatory mites (Neoseiulus cucumeris, Amblyseius swirskii) or Orius on the foliage, plus soil predators (Stratiolaelaps scimitus) or Steinernema nematodes in the medium where they pupate. Blue or yellow cards to monitor. Sprays only in veg. - Recovery: Card counts fall and no new silvering on new leaves within 2-3 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ### Unbuffered or new coco pulling calcium and magnesium (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Feed with Ca and Mg on board: calcium nitrate and magnesium sulfate, or a Cal-Mag, bringing the feed to about 150-200 mg/L Ca and 40-60 mg/L Mg, at pH 5.8-6.2. For the next batch, rinse and buffer coco by soaking it in a calcium (and magnesium) nitrate solution before planting. - Recovery: New leaves clean within 7-10 days; runoff Ca/Mg symptoms stop spreading. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Buffering coco coir: why it matters and how to do it](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md) ### Boron deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out broad mites first. Supply about 0.2-0.5 mg/L B (boric acid ~1.1-2.9 mg/L, or a complete micro mix). The gap between enough and too much is narrow: never add B 'just in case' on top of a complete feed. - Recovery: New shoots grow normally from the tip or from side buds within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) ### Herbicide drift or residue (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Outdoors or with contaminated compost, manure or straw (persistent herbicide residues). Remove the source, repot into clean media; new growth may normalise slowly. Cannabis-specific symptom descriptions are scarce. - Recovery: New growth normalises over 2-4 weeks after the source is removed. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Why are my cannabis leaves curling? The master curling and clawing decision tree](https://genetixbay.com/knowledge/diagnosis/curling-clawing-decision-tree.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Glossy, stiff, curled growing tips that stop growing: likely causes and fixes > Glossy, stiff, curled growing tips that stop growing on cannabis is most often Broad mites. How to tell them apart, the fix for each and what recovery looks like. Also called: shiny new growth, glassy leaves at top, tips look wet and shiny, new growth stiff and curled, broad mite damage. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=glossy-hardened-tips ## Likely causes, most likely first ### Broad mites (Possible) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm at 30-60x. Remove and bag heavily infested plants; mothers and clones are the usual source. Release predatory mites (e.g. Neoseiulus californicus or Amblyseius swirskii) on the rest, keep tools and clothes clean, quarantine new stock. In flower, removal is usually the only clean option. - Recovery: New growth expands normally (not glossy or twisted) within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Growing tips dying or aborting: likely causes and fixes > Growing tips dying or aborting on cannabis is most often Calcium deficiency (often a delivery problem), Boron deficiency or Broad mites. How to tell them apart, the fix for each and what recovery looks like. Also called: top died, growing tip turned brown, new growth dying, shoot tip dead, dead tops. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=dying-growing-tips ## Likely causes, most likely first ### Calcium deficiency (often a delivery problem) (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out mites with a 30-60x lens first. Then fix delivery: leaf VPD 0.8-1.5 kPa (lights-on RH not stuck high), airflow under the canopy, root-zone pH not below ~5.8 in coco. If supply is short (RO water, unbuffered coco), bring Ca to about 150-200 mg/L with calcium nitrate or a Cal-Mag at label rate. LEDs do not create a Cal-Mag need; that is a myth. - Recovery: Leaves that open 7-10 days after the fix are flat and spot-free; old spots stay. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) ### Boron deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out broad mites first. Supply about 0.2-0.5 mg/L B (boric acid ~1.1-2.9 mg/L, or a complete micro mix). The gap between enough and too much is narrow: never add B 'just in case' on top of a complete feed. - Recovery: New shoots grow normally from the tip or from side buds within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) ### Broad mites (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm at 30-60x. Remove and bag heavily infested plants; mothers and clones are the usual source. Release predatory mites (e.g. Neoseiulus californicus or Amblyseius swirskii) on the rest, keep tools and clothes clean, quarantine new stock. In flower, removal is usually the only clean option. - Recovery: New growth expands normally (not glossy or twisted) within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Small, narrow or cupped new leaves: likely causes and fixes > Small, narrow or cupped new leaves on cannabis is most often Calcium deficiency (often a delivery problem), High root-zone pH locking out iron, manganese, zinc, boron and copper or Broad mites. How to tell them apart, the fix for each and what recovery looks like. Also called: tiny new leaves, narrow leaflets, leaves getting smaller, cupped new leaves, skinny new leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=small-narrow-new-leaves ## Likely causes, most likely first ### Calcium deficiency (often a delivery problem) (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out mites with a 30-60x lens first. Then fix delivery: leaf VPD 0.8-1.5 kPa (lights-on RH not stuck high), airflow under the canopy, root-zone pH not below ~5.8 in coco. If supply is short (RO water, unbuffered coco), bring Ca to about 150-200 mg/L with calcium nitrate or a Cal-Mag at label rate. LEDs do not create a Cal-Mag need; that is a myth. - Recovery: Leaves that open 7-10 days after the fix are flat and spot-free; old spots stay. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) ### High root-zone pH locking out iron, manganese, zinc, boron and copper (Possible) - Kind: pH; urgency: Deal with it this week - Fix: Bring root-zone pH into range: soil 6.2-6.8, coco and rockwool 5.8-6.2, hydro 5.5-6.2. Lower input pH by 0.2-0.3 units at a time rather than crashing it; neutralise alkaline water with a mineral acid (phosphoric, nitric or sulfuric; wear gloves and eye protection, add acid to water). Use an iron chelate stable at your pH (DTPA or EDDHA above 6.5). - Recovery: Runoff or reservoir pH back in range at two consecutive checks; new leaves open green within 5-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Broad mites (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm at 30-60x. Remove and bag heavily infested plants; mothers and clones are the usual source. Release predatory mites (e.g. Neoseiulus californicus or Amblyseius swirskii) on the rest, keep tools and clothes clean, quarantine new stock. In flower, removal is usually the only clean option. - Recovery: New growth expands normally (not glossy or twisted) within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ### Boron deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out broad mites first. Supply about 0.2-0.5 mg/L B (boric acid ~1.1-2.9 mg/L, or a complete micro mix). The gap between enough and too much is narrow: never add B 'just in case' on top of a complete feed. - Recovery: New shoots grow normally from the tip or from side buds within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) ### Copper deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Very rare with a complete micro mix. Supply about 0.03-0.1 mg/L Cu; do not overshoot (excess Cu damages roots). - Recovery: New leaves regain size and turgor in 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md) ### Herbicide drift or residue (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Outdoors or with contaminated compost, manure or straw (persistent herbicide residues). Remove the source, repot into clean media; new growth may normalise slowly. Cannabis-specific symptom descriptions are scarce. - Recovery: New growth normalises over 2-4 weeks after the source is removed. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Why are my cannabis leaves curling? The master curling and clawing decision tree](https://genetixbay.com/knowledge/diagnosis/curling-clawing-decision-tree.md) ### Zinc deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Lower high pH, stop excess phosphorus 'boosters' (high P ties up Zn), then supply about 0.1-0.5 mg/L Zn as zinc sulfate or chelate. - Recovery: New leaves reach normal size with clean margins in 7-14 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Zinc (Zn) in cannabis: small leaves, margin burn and the phosphorus link](https://genetixbay.com/knowledge/nutrients/zinc.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Single-bladed, round or smooth-edged new leaves: likely causes and fixes > Single-bladed, round or smooth-edged new leaves on cannabis is most often Light leak or interrupted dark period or Re-vegetation from too-long days in flower. How to tell them apart, the fix for each and what recovery looks like. Also called: single finger leaves, round leaves, reveg leaves, mutant leaves, leaves with no serrations. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=single-blade-leaves ## Likely causes, most likely first ### Light leak or interrupted dark period (Possible) - Kind: Light; urgency: Act within a day or two - Fix: Seal the dark period: pinholes, zips, vents and equipment LEDs (tape them), and check the timer. Even dim night light can delay flowering in sensitive cultivars and reveal herm-prone genetics. Use a green headlamp only for brief checks. - Recovery: Flowering resumes within 1-2 weeks; no new single-blade leaves. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ### Re-vegetation from too-long days in flower (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Restore an uninterrupted 12-13 h dark period (13/11 is fine; some cultivars flower at 14-15 h days with ramps). Outdoors, early-season plants under long days re-veg; plant later or use light deprivation. - Recovery: No new single-blade growth within 2 weeks. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [How do I reveg a plant after harvest?](https://genetixbay.com/knowledge/answers/how-to-reveg-a-plant.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Leaf edges rolling under, leaves curling downward without darkening: likely causes and fixes > Leaf edges rolling under, leaves curling downward without darkening on cannabis is most often Heat stress, Calcium deficiency (often a delivery problem) or CO2 set far too high. How to tell them apart, the fix for each and what recovery looks like. Also called: edges curling down, leaves rolling under, leaf margins curl under. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=margins-roll-under ## Likely causes, most likely first ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Calcium deficiency (often a delivery problem) (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out mites with a 30-60x lens first. Then fix delivery: leaf VPD 0.8-1.5 kPa (lights-on RH not stuck high), airflow under the canopy, root-zone pH not below ~5.8 in coco. If supply is short (RO water, unbuffered coco), bring Ca to about 150-200 mg/L with calcium nitrate or a Cal-Mag at label rate. LEDs do not create a Cal-Mag need; that is a myth. - Recovery: Leaves that open 7-10 days after the fix are flat and spot-free; old spots stay. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md) ### CO2 set far too high (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Hold 800-1,200 ppm; above that there is little further gain in cannabis. Leaf rolling and chlorosis at very high CO2 are documented in tomato and other greenhouse crops. People: keep occupied rooms under the 5,000 ppm 8-hour limit and never enter a room above 30,000 ppm. - Recovery: Symptoms stop on new growth after CO2 is lowered. - Confirm: Measure CO2 during the light period: Read a CO2 monitor at canopy height through the light period. A sealed room without enrichment can fall below 300-350 ppm and stall growth; enriched rooms should hold 800-1,200 ppm. Keep occupied spaces below the 5,000 ppm workplace limit. - Article: [CO₂ enrichment: when it pays, how much, and how to stay safe](https://genetixbay.com/knowledge/environment/co2-enrichment.md) ### Copper deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Very rare with a complete micro mix. Supply about 0.03-0.1 mg/L Cu; do not overshoot (excess Cu damages roots). - Recovery: New leaves regain size and turgor in 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Drooping while the pot is heavy and wet: likely causes and fixes > Drooping while the pot is heavy and wet on cannabis is most often Overwatering (roots short of air). How to tell them apart, the fix for each and what recovery looks like. Also called: overwatered, droopy and wet soil, drooping after watering, plant sad and soil wet, limp leaves wet soil. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=droop-wet-pot ## Likely causes, most likely first ### Overwatering (roots short of air) (Likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Wilting with a light, dry pot: likely causes and fixes > Wilting with a light, dry pot on cannabis is most often Underwatering or Dry, water-repellent medium (water runs straight through). How to tell them apart, the fix for each and what recovery looks like. Also called: underwatered, thirsty plant, dry soil drooping, plant wilted dry, leaves hanging limp dry pot. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=wilt-dry-pot ## Likely causes, most likely first ### Underwatering (Likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Water slowly in 2-3 passes until 10-20% runoff, so the whole root ball wets. Water when the pot is clearly lighter, before the plant droops. Mild late-flower dry-back is a house-endorsed practice for some cultivars (Caplan 2019), but wilting is not. - Recovery: Turgor returns within 1-6 hours of watering. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Dry, water-repellent medium (water runs straight through) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Rewet slowly: small amounts every 10-15 minutes, or bottom-soak the pot for 20-30 minutes; a drop of plant-safe wetting agent helps peat. Don't let peat mixes go bone dry again. - Recovery: Pot gains its normal wet weight and holds it for a day or more. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Why does water run straight through or pool on top of my pot?](https://genetixbay.com/knowledge/answers/water-runs-through-or-pools.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Wilting even though the root zone is moist, not recovering overnight: likely causes and fixes > Wilting even though the root zone is moist, not recovering overnight on cannabis is most often Root rot (Pythium), Low dissolved oxygen in the root zone or Reservoir or root zone too warm. How to tell them apart, the fix for each and what recovery looks like. Also called: wilting but soil is wet, drooping won't recover, plant wilting in hydro, wilting with wet roots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=wilt-moist-not-recovering ## Likely causes, most likely first ### Root rot (Pythium) (Possible) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ### Low dissolved oxygen in the root zone (Possible) - Kind: Root zone; urgency: Act within a day or two - Fix: Restore oxygen: clean or replace air stones, size the air pump for at least ~1 L/min per 4 L, keep a 2-5 cm air gap under net pots once roots reach the water, cool the solution to 18-22 °C (64-72 °F). Aim for 6-8+ mg/L DO. - Recovery: Fresh white root tips within 3-5 days; wilting stops. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ### Reservoir or root zone too warm (Possible) - Kind: Root zone; urgency: Act within a day or two - Fix: Keep solution at 18-22 °C (64-72 °F): insulate and shade the reservoir, move it off the warm floor or away from the light, use a chiller or frozen water bottles in an emergency, avoid submersible pumps that add heat, cool the room. - Recovery: Solution holds below 22 °C through the light period; new white roots in 3-5 days. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Article: [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ### Fusarium wilt or crown rot (Less likely) - Kind: Disease; urgency: Act within a day or two - Fix: No cure once infected: remove the plant with its medium in a bag, sanitise pots, trays and water lines, and use clean clones and new media. Reduce root stress (overwatering, heat, salts) on the rest. - Recovery: No further wilting plants over the next 2-3 weeks. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Fusarium in cannabis: wilt, crown rot and bud rot](https://genetixbay.com/knowledge/diseases/fusarium.md) ### Pump, timer, air or emitter failure in a hydro, aero or drip system (Less likely) - Kind: Root zone; urgency: Act now - Fix: Restore flow or air immediately: check power, timer, float switches, filters and nozzles. Mist exposed roots by hand or lower plants into solution while you fix it. In HPA and NFT, fit an alarm and a backup pump; roots die fast when misting or flow stops. - Recovery: Plants regain turgor within hours if roots were not dead; brown, collapsed roots mean rot risk next. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [High-pressure aeroponics (HPA)](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) ### Root aphids (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm on the roots. Apply soil-dwelling biologicals (Beauveria bassiana drenches, Stratiolaelaps scimitus, Steinernema or Heterorhabditis nematodes), sanitise, and leave a plant-free gap between cycles; dispose of infested media. - Recovery: No live aphids on root checks after 2-3 weeks; growth resumes. - Confirm: Root-ball and drainage-hole insect check: Tip the plant out and inspect the outer roots, pot bottom and drainage holes with a 10x loupe. Root aphids are small, pear-shaped and wingless, often with white waxy flecks; check several plants, and the drain trays, since colonies hide at the pot edge. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Root aphids (rice root aphid) on indoor cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/root-aphids.md) ### Boron deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out broad mites first. Supply about 0.2-0.5 mg/L B (boric acid ~1.1-2.9 mg/L, or a complete micro mix). The gap between enough and too much is narrow: never add B 'just in case' on top of a complete feed. - Recovery: New shoots grow normally from the tip or from side buds within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Sudden collapse of a hydro or aero plant within hours: likely causes and fixes > Sudden collapse of a hydro or aero plant within hours on cannabis is most often Pump, timer, air or emitter failure in a hydro, aero or drip system. How to tell them apart, the fix for each and what recovery looks like. Also called: plant crashed overnight, whole plant wilted in DWC, aero plants collapsed, pump failed plants wilted. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=sudden-collapse-hydro ## Likely causes, most likely first ### Pump, timer, air or emitter failure in a hydro, aero or drip system (Possible) - Kind: Root zone; urgency: Act now - Fix: Restore flow or air immediately: check power, timer, float switches, filters and nozzles. Mist exposed roots by hand or lower plants into solution while you fix it. In HPA and NFT, fit an alarm and a backup pump; roots die fast when misting or flow stops. - Recovery: Plants regain turgor within hours if roots were not dead; brown, collapsed roots mean rot risk next. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [High-pressure aeroponics (HPA)](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Wilting under the lights that recovers at lights-off: likely causes and fixes > Wilting under the lights that recovers at lights-off on cannabis is most often Heat stress, Air too dry / VPD too high or Low dissolved oxygen in the root zone. How to tell them apart, the fix for each and what recovery looks like. Also called: droops in the afternoon, wilts midday, fine in the morning droopy at noon, midday droop. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=midday-wilt ## Likely causes, most likely first ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Air too dry / VPD too high (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Raise RH or lower temperature to bring leaf VPD to 0.4-0.8 kPa (clones, seedlings), 0.8-1.2 (veg), 1.0-1.5 (flower). Humidifier, less exhaust when cool, fewer dry hot air inputs. Dry air also speeds spider mites. - Recovery: Leaves flatten within a day. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ### Low dissolved oxygen in the root zone (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Restore oxygen: clean or replace air stones, size the air pump for at least ~1 L/min per 4 L, keep a 2-5 cm air gap under net pots once roots reach the water, cool the solution to 18-22 °C (64-72 °F). Aim for 6-8+ mg/L DO. - Recovery: Fresh white root tips within 3-5 days; wilting stops. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ### Reservoir or root zone too warm (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Keep solution at 18-22 °C (64-72 °F): insulate and shade the reservoir, move it off the warm floor or away from the light, use a chiller or frozen water bottles in an emergency, avoid submersible pumps that add heat, cool the room. - Recovery: Solution holds below 22 °C through the light period; new white roots in 3-5 days. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Article: [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ### Root-bound in a pot too small (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Up-pot photoperiods into a container about 2-3x larger, loosening circling roots gently. Autoflowers: don't transplant; increase watering and feeding frequency instead. Small pots can still grow big plants with high-frequency fertigation (several feeds a day). - Recovery: New white roots in the fresh medium within 5-7 days; daily wilting stops. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Cannabis root problems: the master decision tree](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md) ### Underwatering (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Water slowly in 2-3 passes until 10-20% runoff, so the whole root ball wets. Water when the pot is clearly lighter, before the plant droops. Mild late-flower dry-back is a house-endorsed practice for some cultivars (Caplan 2019), but wilting is not. - Recovery: Turgor returns within 1-6 hours of watering. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Salt build-up in the root zone (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth. - Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like. - Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ### Dry, water-repellent medium (water runs straight through) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Rewet slowly: small amounts every 10-15 minutes, or bottom-soak the pot for 20-30 minutes; a drop of plant-safe wetting agent helps peat. Don't let peat mixes go bone dry again. - Recovery: Pot gains its normal wet weight and holds it for a day or more. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Why does water run straight through or pool on top of my pot?](https://genetixbay.com/knowledge/answers/water-runs-through-or-pools.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # A single branch wilting or dying: likely causes and fixes > A single branch wilting or dying on cannabis is most often Physical damage (kinks, splits, broken branches) or Fusarium wilt or crown rot. How to tell them apart, the fix for each and what recovery looks like. Also called: one branch drooping, one stem dying, half the plant wilted, branch collapsed. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=branch-wilt ## Likely causes, most likely first ### Physical damage (kinks, splits, broken branches) (Possible) - Kind: Physical damage; urgency: Deal with it this week - Fix: Splint and tape a split stem within hours (tape, plant tie or a straw splint); a supercropped knuckle heals stronger in 3-7 days. Remove fully broken branches with a clean cut. Support heavy colas with a trellis. - Recovery: Leaves above the wound regain turgor within 1-2 days; a callus forms within a week. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Article: [HST and supercropping: controlled stem crushing](https://genetixbay.com/knowledge/training/hst-supercropping.md) ### Fusarium wilt or crown rot (Possible) - Kind: Disease; urgency: Act within a day or two - Fix: No cure once infected: remove the plant with its medium in a bag, sanitise pots, trays and water lines, and use clean clones and new media. Reduce root stress (overwatering, heat, salts) on the rest. - Recovery: No further wilting plants over the next 2-3 weeks. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Fusarium in cannabis: wilt, crown rot and bud rot](https://genetixbay.com/knowledge/diseases/fusarium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Seedling stem pinched and collapsing at the soil line: likely causes and fixes > Seedling stem pinched and collapsing at the soil line on cannabis is most often Damping-off, Fungus gnats or Root rot (Pythium). How to tell them apart, the fix for each and what recovery looks like. Also called: damping off, seedling fell over, seedling stem rotted, seedling stem thin at the base, seedling died suddenly. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=damping-off ## Likely causes, most likely first ### Damping-off (Possible) - Kind: Disease; urgency: Act within a day or two - Fix: A collapsed seedling can't be saved. For the rest: clean containers, fresh mix, warm medium (22-26 °C / 72-79 °F), water lightly, good light and airflow. - Recovery: No further collapses. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Damping-off: why seedlings collapse at the soil line](https://genetixbay.com/knowledge/germination/damping-off.md) ### Fungus gnats (Possible) - Kind: Pest; urgency: Low urgency - Fix: Fix the watering first: let the top 2-3 cm dry. Then Bti drenches (larvicide), Steinernema feltiae nematodes or Stratiolaelaps mites; yellow cards for adults. Larvae chew seedling and clone roots and can open the door to Pythium. - Recovery: Card catches fall within 2-3 weeks; no larvae under potato slices. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Confirm: Potato slice test for larvae in the medium: Press 2-3 raw potato slices (1 cm thick) cut side down onto the medium surface. Lift after 2-4 days and look underneath: translucent larvae with shiny black heads are fungus gnat larvae. - Article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ### Root rot (Pythium) (Less likely) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Cuttings wilting: likely causes and fixes > Cuttings wilting on cannabis is most often Cuttings losing water faster than they can root, Air too dry / VPD too high or Fungus gnats. How to tell them apart, the fix for each and what recovery looks like. Also called: clones wilting, clones drooping, cuttings flopped, clones not rooting and wilting. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=clone-wilting ## Likely causes, most likely first ### Cuttings losing water faster than they can root (Possible) - Kind: Environment; urgency: Deal with it this week - Fix: Keep clones at about 75-90% RH (VPD ~0.4-0.8 kPa), 22-26 °C (72-79 °F), PPFD 100-200 µmol/m²/s; trim large fan leaves by half; vent the dome gradually only once roots show. - Recovery: Cuttings stand up within 24 h; roots in 7-14 days. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Why are my clones wilting?](https://genetixbay.com/knowledge/answers/why-are-my-clones-wilting.md) ### Air too dry / VPD too high (Possible) - Kind: Environment; urgency: Deal with it this week - Fix: Raise RH or lower temperature to bring leaf VPD to 0.4-0.8 kPa (clones, seedlings), 0.8-1.2 (veg), 1.0-1.5 (flower). Humidifier, less exhaust when cool, fewer dry hot air inputs. Dry air also speeds spider mites. - Recovery: Leaves flatten within a day. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [VPD explained: vapour pressure deficit for cannabis growers](https://genetixbay.com/knowledge/environment/vpd-explained.md) ### Fungus gnats (Possible) - Kind: Pest; urgency: Low urgency - Fix: Fix the watering first: let the top 2-3 cm dry. Then Bti drenches (larvicide), Steinernema feltiae nematodes or Stratiolaelaps mites; yellow cards for adults. Larvae chew seedling and clone roots and can open the door to Pythium. - Recovery: Card catches fall within 2-3 weeks; no larvae under potato slices. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Confirm: Potato slice test for larvae in the medium: Press 2-3 raw potato slices (1 cm thick) cut side down onto the medium surface. Lift after 2-4 days and look underneath: translucent larvae with shiny black heads are fungus gnat larvae. - Article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ### Chlorine or chloramine in tap water harming roots and soil life (Less likely) - Kind: Root zone; urgency: Low urgency - Fix: Usual tap levels rarely hurt the plant directly; the concern is living soil, beneficial microbes and young roots. Chlorine gasses off in 24 h of aeration; chloramine does not. Remove chloramine with long-contact or catalytic carbon, or about 1 g of ascorbic acid per 100-400 L, or use RO. - Recovery: Biology recovers over weeks; seedlings resume growth within a week. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Drooping or stall right after transplanting: likely causes and fixes > Drooping or stall right after transplanting on cannabis is most often Transplant shock or Recovery stall after topping, supercropping or heavy defoliation. How to tell them apart, the fix for each and what recovery looks like. Also called: transplant shock, droopy after repotting, stalled after up-potting, sad after transplant. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=droop-after-transplant ## Likely causes, most likely first ### Transplant shock (Likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Move the root ball intact into pre-moistened medium of the same type and pH, water in with a mild solution, lower light 10-20% and keep RH slightly higher for 2-3 days. Mild droop for 2-5 days is normal; longer means root damage, waterlogging or a pH mismatch. Autos: sow in the final pot instead. - Recovery: Turgor back in 1-3 days; new growth within a week. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) ### Recovery stall after topping, supercropping or heavy defoliation (Less likely) - Kind: Physical damage; urgency: Low urgency - Fix: Give 3-7 days for photoperiods to recover from topping or HST before the next session; don't stack stresses. Prefer tucking to stripping leaves. On autos use LST only. - Recovery: New growth resumes within a week. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [How long does a plant take to recover after topping?](https://genetixbay.com/knowledge/answers/recovery-after-topping.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Leaves droop at lights-off and lift in the morning: likely causes and fixes > Leaves droop at lights-off and lift in the morning on cannabis is most often Normal leaf movement (praying by day, drooping at night). How to tell them apart, the fix for each and what recovery looks like. Also called: leaves droop at night, drooping in the dark, sleeping leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=night-droop ## Likely causes, most likely first ### Normal leaf movement (praying by day, drooping at night) (Likely) - Kind: Normal ageing; urgency: Low urgency - Fix: Nothing to fix. Healthy cannabis angles leaves toward strong light and relaxes them at night. - Recovery: Leaves follow the light cycle with no damage. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Are praying leaves a good sign?](https://genetixbay.com/knowledge/answers/praying-leaves.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Weak, floppy stems that can't hold the plant up: likely causes and fixes > Weak, floppy stems that can't hold the plant up on cannabis is most often Not enough light, General underfeeding (whole feed too weak) or Too much nitrogen. How to tell them apart, the fix for each and what recovery looks like. Also called: floppy stems, stems falling over, weak stalk, stem too thin, plant leaning. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=weak-stems ## Likely causes, most likely first ### Not enough light (Possible) - Kind: Light; urgency: Low urgency - Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat. - Recovery: New internodes shorten within a week; denser buds on the following weeks of growth. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ### General underfeeding (whole feed too weak) (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Raise the whole feed in steps of about 0.2-0.3 mS/cm toward the stage target (veg 1.2-1.8, flower 1.6-2.2 mS/cm in coco and hydro). Stop any 'flush': plain water for weeks starves the plant, and pre-harvest flushing is a myth that costs yield. - Recovery: Colour deepens and growth speeds up within a week; runoff EC tracks input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ### Too much nitrogen (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Cut feed N by 20-30% (or the whole feed EC by ~0.3-0.5 mS/cm); for a heavy overdose in containers, run a root-zone flush with pH-adjusted, quarter-strength feed to 20-30% runoff. In flower, taper N while keeping P, K, Ca, Mg, S and micros fed. - Recovery: New leaves come in lighter green and flat within 5-7 days; clawed leaves relax partly. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Potassium deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Check runoff EC first: salt burn looks the same. If K is genuinely short, feed about 175-250 mg/L K (potassium sulfate, potassium nitrate or MKP) at a normal EC. A flowering DWC trial saw no yield response anywhere from 60 to 340 mg/L, so more is not better. Cut heavy Cal-Mag or sodium-rich water that competes with K. - Recovery: Margin scorch stops advancing up the plant within 7 days; new leaves open with clean margins. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Kinked, split or snapped stem: likely causes and fixes > Kinked, split or snapped stem on cannabis is most often Physical damage (kinks, splits, broken branches). How to tell them apart, the fix for each and what recovery looks like. Also called: broken branch, stem split, snapped stem, cracked stem, kinked stem. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=stem-damage ## Likely causes, most likely first ### Physical damage (kinks, splits, broken branches) (Likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Splint and tape a split stem within hours (tape, plant tie or a straw splint); a supercropped knuckle heals stronger in 3-7 days. Remove fully broken branches with a clean cut. Support heavy colas with a trellis. - Recovery: Leaves above the wound regain turgor within 1-2 days; a callus forms within a week. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Article: [HST and supercropping: controlled stem crushing](https://genetixbay.com/knowledge/training/hst-supercropping.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Brown, soft or sunken stem base or crown: likely causes and fixes > Brown, soft or sunken stem base or crown on cannabis is most often Fusarium wilt or crown rot or Root rot (Pythium). How to tell them apart, the fix for each and what recovery looks like. Also called: stem rotting at the base, crown rot, brown stem at soil, soft stem near roots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=stem-base-rot ## Likely causes, most likely first ### Fusarium wilt or crown rot (Possible) - Kind: Disease; urgency: Act within a day or two - Fix: No cure once infected: remove the plant with its medium in a bag, sanitise pots, trays and water lines, and use clean clones and new media. Reduce root stress (overwatering, heat, salts) on the rest. - Recovery: No further wilting plants over the next 2-3 weeks. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Fusarium in cannabis: wilt, crown rot and bud rot](https://genetixbay.com/knowledge/diseases/fusarium.md) ### Root rot (Pythium) (Less likely) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Brown streaks inside the stem when cut: likely causes and fixes > Brown streaks inside the stem when cut on cannabis is most often Fusarium wilt or crown rot. How to tell them apart, the fix for each and what recovery looks like. Also called: vascular browning, brown inside the stem, stem discoloured inside. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=stem-internal-browning ## Likely causes, most likely first ### Fusarium wilt or crown rot (Possible) - Kind: Disease; urgency: Act within a day or two - Fix: No cure once infected: remove the plant with its medium in a bag, sanitise pots, trays and water lines, and use clean clones and new media. Reduce root stress (overwatering, heat, salts) on the rest. - Recovery: No further wilting plants over the next 2-3 weeks. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Fusarium in cannabis: wilt, crown rot and bud rot](https://genetixbay.com/knowledge/diseases/fusarium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Lesions or grey mould on stems: likely causes and fixes > Lesions or grey mould on stems on cannabis is most often Botrytis bud rot (grey mould). How to tell them apart, the fix for each and what recovery looks like. Also called: stem canker, mould on stem, stem lesion, grey patch on branch. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=stem-cankers ## Likely causes, most likely first ### Botrytis bud rot (grey mould) (Possible) - Kind: Disease; urgency: Act now - Fix: Act now. Bag infected buds before cutting them out, 3-5 cm (1-2 in) past visible rot, and clean tools; never shake them. Drop RH to about 40-50% in late flower, control the lights-off dew point, move air through dense colas. There is no cure in flower; consider harvesting early if it keeps spreading. - Recovery: No new rot on weekly cola checks for 2 weeks. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Brittle stems that snap easily: likely causes and fixes > Brittle stems that snap easily on cannabis is most often Hop latent viroid (dudding) or Hemp russet mites. How to tell them apart, the fix for each and what recovery looks like. Also called: stems break easily, brittle branches, snapping stems, stem brittle. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=brittle-stems ## Likely causes, most likely first ### Hop latent viroid (dudding) (Possible) - Kind: Disease; urgency: Act within a day or two - Fix: No cure in a plant. Test mothers (roots and leaves) by RT-PCR or RT-qPCR, discard positives, disinfect tools with 10% bleach or heat (alcohol and peroxide don't inactivate it), and use meristem tissue culture to rescue valuable genetics. Don't take cuttings from stunted plants. - Recovery: Negative tests on new mothers; no more duds in the next cycle. - Confirm: Lab test for hop latent viroid (RT-PCR or RT-qPCR): Send root and leaf samples (roots detect HLVd earlier in young plants) to a lab offering HLVd RT-PCR or RT-qPCR. Test mother plants and any stunted plant among healthy siblings. A positive plant cannot be cured; tissue culture of meristem tips can rescue genetics. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ### Hemp russet mites (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm at 30-60x (they look like moving dust). Remove badly infested plants; release predatory mites preventively; quarantine clones; leave a plant-free gap between cycles. - Recovery: Bronzing stops climbing and no live mites at 30-60x in 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Purple or red stems and petioles: likely causes and fixes > Purple or red stems and petioles on cannabis is most often Genetic purple colour (anthocyanin), Cold stress or Cold root zone (below about 16 °C / 61 °F). How to tell them apart, the fix for each and what recovery looks like. Also called: purple stems, red stems, red petioles, stems turning purple, purple leaf stems. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=purple-stems ## Likely causes, most likely first ### Genetic purple colour (anthocyanin) (Likely) - Kind: Genetics; urgency: Low urgency - Fix: Nothing to fix: purple stems, petioles and bracts are mostly genetic and harmless, brought out by cool nights 5-10 °C (9-18 °F) below day. Purple is bag appeal, not potency. - Recovery: Leaves stay healthy and green apart from the colour; no spotting. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) ### Cold stress (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Keep days at 22-28 °C (72-82 °F) and nights no more than 3-6 °C (5-10 °F) cooler and above ~15 °C (59 °F); warm the root zone. Cold-for-colour is real in purple cultivars, but claims of more terpenes or resin are unsupported. - Recovery: Growth resumes within a week; new leaves come in green. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.md) ### Cold root zone (below about 16 °C / 61 °F) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Raise root-zone temperature to 18-22 °C (64-72 °F): lift pots off cold floors onto insulation, warm the room at night, use an aquarium heater in reservoirs (with a thermostat), water with room-temperature solution. - Recovery: Growth resumes and new leaves green within a week. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) ### Phosphorus deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Warm the root zone to 18-22 °C (64-72 °F) and nights above ~15 °C (59 °F) first; cold blocks P uptake. Correct pH (soilless 5.5-6.5, soil 6.0-7.0). If genuinely short, supply about 30-60 mg/L P; controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, so skip 'bloom boosters'. Soil: a balanced liquid feed; living soil: a slow P amendment acts in weeks. - Recovery: No new olive spots on leaves that open after the fix, within 7-10 days; growth rate picks up. Spotted leaves stay damaged. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Red-purple petioles with yellowing lower leaves: likely causes and fixes > Red-purple petioles with yellowing lower leaves on cannabis is most often Nitrogen deficiency or Normal late-flower fade (senescence). How to tell them apart, the fix for each and what recovery looks like. Also called: red stems and yellow leaves, purple petioles lower leaves yellow. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=red-petioles-yellow-lower ## Likely causes, most likely first ### Nitrogen deficiency (Likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Fix roots, watering and pH first. If N is genuinely short, raise feed N by about 10-20% (not double): mineral feeds around 150-200 mg/L N in veg and early flower; one DWC flowering trial predicted a yield optimum near 194 mg/L. Coco/hydro: raise base feed EC by ~0.2 mS/cm. Soil: liquid feed at label rate. Living soil: top-dress a fast organic N source and allow 1-2 weeks. Late flower: a gradual fade is the planned N taper, not a fault. - Recovery: Yellowing stops climbing within 5-7 days and new leaves emerge mid-green; already-yellow leaves do not recover. Runoff EC climbs back toward input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Normal late-flower fade (senescence) (Possible) - Kind: Normal ageing; urgency: Low urgency - Fix: Nothing to fix in the last 2-3 weeks of flower. Keep feeding at stage strength with N tapered; don't 'flush' (pre-harvest flushing starves the plant while it packs on final weight and resin, and controlled studies show no quality gain). Fade before week 5-6 of flower suggests N was cut too early. - Recovery: Buds keep swelling and ripening normally while fan leaves fade. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Purple leaves, bracts or sugar leaves: likely causes and fixes > Purple leaves, bracts or sugar leaves on cannabis is most often Genetic purple colour (anthocyanin), Normal late-flower fade (senescence) or Cold stress. How to tell them apart, the fix for each and what recovery looks like. Also called: purple leaves, leaves turning purple, purple buds, purpling, purple sugar leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=purple-leaves ## Likely causes, most likely first ### Genetic purple colour (anthocyanin) (Possible) - Kind: Genetics; urgency: Low urgency - Fix: Nothing to fix: purple stems, petioles and bracts are mostly genetic and harmless, brought out by cool nights 5-10 °C (9-18 °F) below day. Purple is bag appeal, not potency. - Recovery: Leaves stay healthy and green apart from the colour; no spotting. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) ### Normal late-flower fade (senescence) (Possible) - Kind: Normal ageing; urgency: Low urgency - Fix: Nothing to fix in the last 2-3 weeks of flower. Keep feeding at stage strength with N tapered; don't 'flush' (pre-harvest flushing starves the plant while it packs on final weight and resin, and controlled studies show no quality gain). Fade before week 5-6 of flower suggests N was cut too early. - Recovery: Buds keep swelling and ripening normally while fan leaves fade. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md) ### Cold stress (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Keep days at 22-28 °C (72-82 °F) and nights no more than 3-6 °C (5-10 °F) cooler and above ~15 °C (59 °F); warm the root zone. Cold-for-colour is real in purple cultivars, but claims of more terpenes or resin are unsupported. - Recovery: Growth resumes within a week; new leaves come in green. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Very dark green, glossy leaves: likely causes and fixes > Very dark green, glossy leaves on cannabis is most often Nutrient burn (feed too strong), Too much nitrogen or Cal-Mag overuse (excess calcium and nitrogen). How to tell them apart, the fix for each and what recovery looks like. Also called: leaves too dark, deep green leaves, dark shiny leaves, blue green leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=dark-green-leaves ## Likely causes, most likely first ### Nutrient burn (feed too strong) (Possible) - Kind: Too much of something; urgency: Low urgency - Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up). - Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ### Too much nitrogen (Possible) - Kind: Too much of something; urgency: Low urgency - Fix: Cut feed N by 20-30% (or the whole feed EC by ~0.3-0.5 mS/cm); for a heavy overdose in containers, run a root-zone flush with pH-adjusted, quarter-strength feed to 20-30% runoff. In flower, taper N while keeping P, K, Ca, Mg, S and micros fed. - Recovery: New leaves come in lighter green and flat within 5-7 days; clawed leaves relax partly. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Cal-Mag overuse (excess calcium and nitrogen) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: On hard tap water with a complete base feed, stop the Cal-Mag supplement; it adds N and pushes K and Mg out of balance. Use it only for RO or soft water and unbuffered coco. LEDs do not create a Cal-Mag need. - Recovery: K and Mg symptoms stop spreading within 7-10 days. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Dark, dull blue-green leaves with purple or bronze blotches: likely causes and fixes > Dark, dull blue-green leaves with purple or bronze blotches on cannabis is most often Cold stress, High pH reducing phosphorus availability or Phosphorus deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: dull dark leaves, blue green with purple, leaves dark and dull, purple blotches on leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=dark-dull-purple-blotch ## Likely causes, most likely first ### Cold stress (Possible) - Kind: Environment; urgency: Deal with it this week - Fix: Keep days at 22-28 °C (72-82 °F) and nights no more than 3-6 °C (5-10 °F) cooler and above ~15 °C (59 °F); warm the root zone. Cold-for-colour is real in purple cultivars, but claims of more terpenes or resin are unsupported. - Recovery: Growth resumes within a week; new leaves come in green. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.md) ### High pH reducing phosphorus availability (Less likely) - Kind: pH; urgency: Deal with it this week - Fix: Bring soil pH to 6.2-6.8 (soilless 5.8-6.2) and neutralise alkaline water; above about pH 7, phosphate precipitates with calcium. Do not add more P to compensate. - Recovery: No new olive spots on leaves that open after pH correction. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Phosphorus deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Warm the root zone to 18-22 °C (64-72 °F) and nights above ~15 °C (59 °F) first; cold blocks P uptake. Correct pH (soilless 5.5-6.5, soil 6.0-7.0). If genuinely short, supply about 30-60 mg/L P; controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, so skip 'bloom boosters'. Soil: a balanced liquid feed; living soil: a slow P amendment acts in weeks. - Recovery: No new olive spots on leaves that open after the fix, within 7-10 days; growth rate picks up. Spotted leaves stay damaged. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) ### Cold root zone (below about 16 °C / 61 °F) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Raise root-zone temperature to 18-22 °C (64-72 °F): lift pots off cold floors onto insulation, warm the room at night, use an aquarium heater in reservoirs (with a thermostat), water with room-temperature solution. - Recovery: Growth resumes and new leaves green within a week. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Bronzed, rusty-looking leaf surfaces: likely causes and fixes > Bronzed, rusty-looking leaf surfaces on cannabis is most often Hemp russet mites, Twospotted spider mites or Broad mites. How to tell them apart, the fix for each and what recovery looks like. Also called: bronzing, leaves look bronze, rusty leaves, leaves turning copper, russet leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=bronze-leaves ## Likely causes, most likely first ### Hemp russet mites (Possible) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm at 30-60x (they look like moving dust). Remove badly infested plants; release predatory mites preventively; quarantine clones; leave a plant-free gap between cycles. - Recovery: Bronzing stops climbing and no live mites at 30-60x in 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ### Twospotted spider mites (Possible) - Kind: Pest; urgency: Act within a day or two - Fix: Act now: they breed fastest hot and dry. Remove the worst leaves into a sealed bag, cool the room and raise RH a little (in veg), release predatory mites (Phytoseiulus persimilis for hot spots, Neoseiulus californicus as a preventive) before numbers explode. Soaps or horticultural oils only in veg, never on buds. Quarantine new clones. - Recovery: No new stippling on new leaves and no live mites at 10-20x after 7-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Article: [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ### Broad mites (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm at 30-60x. Remove and bag heavily infested plants; mothers and clones are the usual source. Release predatory mites (e.g. Neoseiulus californicus or Amblyseius swirskii) on the rest, keep tools and clothes clean, quarantine new stock. In flower, removal is usually the only clean option. - Recovery: New growth expands normally (not glossy or twisted) within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Broad mites on cannabis: life table, spread and control (plus russet mite summary)](https://genetixbay.com/knowledge/pests/broad-russet-mites.md) ### Iron and manganese excess at very low pH (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Raise root-zone pH above ~5.5 (soilless) or 6.0 (soil); below about 5.3, Fe and Mn become very soluble. Cannabis Fe toxicity itself is not characterised. - Recovery: No new speckling on leaves that develop after pH correction. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Dull, grey-green, leathery leaves: likely causes and fixes > Dull, grey-green, leathery leaves on cannabis is most often Sodium build-up (softened water, coco, recirculation), Salt build-up in the root zone or Chloride excess (salinity). How to tell them apart, the fix for each and what recovery looks like. Also called: leaves look grey, dull leaves, leaves lost their shine, leathery leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=dull-grey-leaves ## Likely causes, most likely first ### Sodium build-up (softened water, coco, recirculation) (Possible) - Kind: Too much of something; urgency: Deal with it this week - Fix: Never use ion-exchange softened water. Keep feed sodium below about 50 mg/L (more than ~5 mM NaCl, 115 mg/L Na, may cut hydro yield and cannabinoids fall as NaCl rises). Dump and refill recirculating reservoirs more often; rinse coco before planting. - Recovery: Tip burn stops advancing on new leaves within a week. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add](https://genetixbay.com/knowledge/nutrients/sodium.md) ### Salt build-up in the root zone (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth. - Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like. - Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ### Chloride excess (salinity) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Keep chloride below about 50-70 mg/L in the feed; switch potassium chloride for potassium sulfate; blend high-chloride water with RO. - Recovery: No new tip burn after the change. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add](https://genetixbay.com/knowledge/nutrients/chlorine.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Purple or dark buds in late flower: likely causes and fixes > Purple or dark buds in late flower on cannabis is most often Genetic purple colour (anthocyanin). How to tell them apart, the fix for each and what recovery looks like. Also called: purple buds, dark buds, black buds, buds turning purple. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=purple-buds ## Likely causes, most likely first ### Genetic purple colour (anthocyanin) (Likely) - Kind: Genetics; urgency: Low urgency - Fix: Nothing to fix: purple stems, petioles and bracts are mostly genetic and harmless, brought out by cool nights 5-10 °C (9-18 °F) below day. Purple is bag appeal, not potency. - Recovery: Leaves stay healthy and green apart from the colour; no spotting. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White powdery spots that wipe off and come back: likely causes and fixes > White powdery spots that wipe off and come back on cannabis is most often Powdery mildew or Humidity too high / VPD too low. How to tell them apart, the fix for each and what recovery looks like. Also called: powdery mildew, white powder on leaves, PM, flour on leaves, white fuzzy spots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=white-powder ## Likely causes, most likely first ### Powdery mildew (Likely) - Kind: Disease; urgency: Act within a day or two - Fix: Treat early in veg: remove the worst leaves into a bag, improve airflow and stable humidity (avoid big day-night RH swings), and use least-toxic contact options (e.g. potassium bicarbonate, sulfur, or biological products, in veg only; never sulfur near oils or in flower). Once it reaches flowers there is no clean fix. Choose resistant genetics and clean clones. - Recovery: No new colonies on treated or new leaves within 7-10 days. - Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) ### Humidity too high / VPD too low (Less likely) - Kind: Environment; urgency: Act within a day or two - Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids. - Recovery: RH holds in band through lights-off for 3+ days; no new mould signs. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Grey, fuzzy mould: likely causes and fixes > Grey, fuzzy mould on cannabis is most often Botrytis bud rot (grey mould) or Humidity too high / VPD too low. How to tell them apart, the fix for each and what recovery looks like. Also called: grey mould, gray mold, fuzzy grey stuff, botrytis, mouldy leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=grey-fuzz ## Likely causes, most likely first ### Botrytis bud rot (grey mould) (Likely) - Kind: Disease; urgency: Act now - Fix: Act now. Bag infected buds before cutting them out, 3-5 cm (1-2 in) past visible rot, and clean tools; never shake them. Drop RH to about 40-50% in late flower, control the lights-off dew point, move air through dense colas. There is no cure in flower; consider harvesting early if it keeps spreading. - Recovery: No new rot on weekly cola checks for 2 weeks. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ### Humidity too high / VPD too low (Less likely) - Kind: Environment; urgency: Act within a day or two - Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids. - Recovery: RH holds in band through lights-off for 3+ days; no new mould signs. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White crust or residue that wipes off and stays gone: likely causes and fixes > White crust or residue that wipes off and stays gone on cannabis is most often Hard-water or spray residue, Spray or foliar burn (pesticide, oil, soap, foliar feed) or Hard, alkaline water pushing pH up over weeks. How to tell them apart, the fix for each and what recovery looks like. Also called: white spots after spraying, hard water spots, mineral residue, white film on leaves, dried spray residue. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=white-residue ## Likely causes, most likely first ### Hard-water or spray residue (Possible) - Kind: Physical damage; urgency: Low urgency - Fix: Harmless in itself; stop misting with hard water (use RO for foliar sprays) and wipe off heavy residue that blocks light. - Recovery: Doesn't come back after wiping. - Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers. - Article: [White powder or white spots on cannabis leaves: a differential](https://genetixbay.com/knowledge/diagnosis/white-powder-on-leaves.md) ### Spray or foliar burn (pesticide, oil, soap, foliar feed) (Possible) - Kind: Physical damage; urgency: Low urgency - Fix: Stop spraying; rinse residue off with plain water at lights-off if damage is fresh. In future spray only at lights-off or with lights raised, test one leaf 24-48 h first, never mix sulfur with oils, and never spray buds. - Recovery: No new damage on leaves that grow after the spray. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers. - Article: [What can I safely spray on plants in flower?](https://genetixbay.com/knowledge/answers/what-can-i-spray-in-flower.md) ### Hard, alkaline water pushing pH up over weeks (Less likely) - Kind: Root zone; urgency: Low urgency - Fix: Alkalinity, not water pH, drives the climb. Above about 100-150 mg/L as CaCO3 (2-3 meq/L), neutralise most of it with acid to an input pH of 5.8-6.2, or blend with RO water. Track runoff pH weekly. - Recovery: Runoff pH stops climbing over 2-3 weeks. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Sticky, shiny leaves (honeydew): likely causes and fixes > Sticky, shiny leaves (honeydew) on cannabis is most often Aphids, Whiteflies or Mealybugs. How to tell them apart, the fix for each and what recovery looks like. Also called: sticky leaves, shiny sticky residue, leaves feel tacky, honeydew, sticky floor under plants. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=sticky-honeydew ## Likely causes, most likely first ### Aphids (Possible) - Kind: Pest; urgency: Deal with it this week - Fix: Squash or rinse small colonies; release parasitoid wasps (Aphidius), predatory midges or lacewings; insecticidal soap or oil only before flower. Control ants that farm them. - Recovery: Colonies shrink and mummified (parasitised) aphids appear within 1-2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ### Whiteflies (Less likely) - Kind: Pest; urgency: Deal with it this week - Fix: Yellow cards; identify the species; release Encarsia formosa (greenhouse whitefly) or Eretmocerus (warmer rooms, silverleaf whitefly) plus predatory mites; keep sprays out of flower. - Recovery: Card counts fall within 3-4 weeks; parasitised black nymphs appear. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) ### Mealybugs (Less likely) - Kind: Pest; urgency: Deal with it this week - Fix: Remove colonies with a cotton bud dipped in 70% isopropyl alcohol (veg only, test a leaf first); release mealybug predators (e.g. Cryptolaemus beetles) or parasitoids; quarantine new stock; discard heavily infested plants. - Recovery: No new cottony clusters after 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Mealybugs and root mealybugs on cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/mealybugs.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Black sooty coating on leaves: likely causes and fixes > Black sooty coating on leaves on cannabis is most often Whiteflies, Aphids or Mealybugs. How to tell them apart, the fix for each and what recovery looks like. Also called: black mould on leaves, sooty mould, black film, soot on leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=sooty-mould ## Likely causes, most likely first ### Whiteflies (Possible) - Kind: Pest; urgency: Deal with it this week - Fix: Yellow cards; identify the species; release Encarsia formosa (greenhouse whitefly) or Eretmocerus (warmer rooms, silverleaf whitefly) plus predatory mites; keep sprays out of flower. - Recovery: Card counts fall within 3-4 weeks; parasitised black nymphs appear. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) ### Aphids (Possible) - Kind: Pest; urgency: Deal with it this week - Fix: Squash or rinse small colonies; release parasitoid wasps (Aphidius), predatory midges or lacewings; insecticidal soap or oil only before flower. Control ants that farm them. - Recovery: Colonies shrink and mummified (parasitised) aphids appear within 1-2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ### Mealybugs (Less likely) - Kind: Pest; urgency: Deal with it this week - Fix: Remove colonies with a cotton bud dipped in 70% isopropyl alcohol (veg only, test a leaf first); release mealybug predators (e.g. Cryptolaemus beetles) or parasitoids; quarantine new stock; discard heavily infested plants. - Recovery: No new cottony clusters after 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Mealybugs and root mealybugs on cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/mealybugs.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White cottony or waxy clumps in leaf axils and stems: likely causes and fixes > White cottony or waxy clumps in leaf axils and stems on cannabis is most often Mealybugs. How to tell them apart, the fix for each and what recovery looks like. Also called: white fluff on stems, cotton balls on plant, white waxy bugs, mealybugs. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=white-cottony-clumps ## Likely causes, most likely first ### Mealybugs (Possible) - Kind: Pest; urgency: Deal with it this week - Fix: Remove colonies with a cotton bud dipped in 70% isopropyl alcohol (veg only, test a leaf first); release mealybug predators (e.g. Cryptolaemus beetles) or parasitoids; quarantine new stock; discard heavily infested plants. - Recovery: No new cottony clusters after 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Mealybugs and root mealybugs on cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/mealybugs.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White fuzz or threads on the medium surface: likely causes and fixes > White fuzz or threads on the medium surface on cannabis is most often Harmless white fungus (mycelium) on organic medium. How to tell them apart, the fix for each and what recovery looks like. Also called: white fuzz on soil, mould on soil, white web on top of soil, white mycelium in pot. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=white-fuzz-medium ## Likely causes, most likely first ### Harmless white fungus (mycelium) on organic medium (Likely) - Kind: Root zone; urgency: Low urgency - Fix: Usually beneficial or harmless decomposers on mulch and organic matter. Let the surface dry more between waterings and improve airflow; scrape it off if it bothers you. - Recovery: Plant stays healthy; fuzz recedes as the surface dries. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [What is the white fuzz on top of my soil?](https://genetixbay.com/knowledge/answers/white-fuzz-on-soil.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White crust on the medium surface or pot edges: likely causes and fixes > White crust on the medium surface or pot edges on cannabis is most often Salt build-up in the root zone or Hard, alkaline water pushing pH up over weeks. How to tell them apart, the fix for each and what recovery looks like. Also called: white crust on soil, salt build up on pot, crystals on coco, white ring on pot. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=salt-crust-medium ## Likely causes, most likely first ### Salt build-up in the root zone (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth. - Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like. - Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ### Hard, alkaline water pushing pH up over weeks (Less likely) - Kind: Root zone; urgency: Low urgency - Fix: Alkalinity, not water pH, drives the climb. Above about 100-150 mg/L as CaCO3 (2-3 meq/L), neutralise most of it with acid to an input pH of 5.8-6.2, or blend with RO water. Track runoff pH weekly. - Recovery: Runoff pH stops climbing over 2-3 weeks. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Green slime or algae on the medium, roots or in the reservoir: likely causes and fixes > Green slime or algae on the medium, roots or in the reservoir on cannabis is most often Algae from light reaching wet surfaces or the reservoir. How to tell them apart, the fix for each and what recovery looks like. Also called: algae, green stuff on soil, green reservoir, slime in res, green film on rockwool. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=green-slime ## Likely causes, most likely first ### Algae from light reaching wet surfaces or the reservoir (Likely) - Kind: Root zone; urgency: Low urgency - Fix: Block all light from reservoirs, tubing and the medium surface (opaque lids, covers on rockwool). Clean surfaces between runs. Algae competes for oxygen and feeds gnats and shore flies. - Recovery: No new green growth within 1-2 weeks of light-proofing. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [How do I stop algae in my reservoir or on my medium?](https://genetixbay.com/knowledge/answers/algae-in-reservoir.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Yellow patches on top of leaves with grey-purple fuzz underneath: likely causes and fixes > Yellow patches on top of leaves with grey-purple fuzz underneath on cannabis is most often Downy mildew. How to tell them apart, the fix for each and what recovery looks like. Also called: downy mildew, fuzz under leaves, yellow patches with mould underneath. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=fuzzy-underside-yellow-top ## Likely causes, most likely first ### Downy mildew (Possible) - Kind: Disease; urgency: Deal with it this week - Fix: Rarely reported on cannabis. Remove infected leaves, drop RH and avoid cool wet nights; confirm with a lab before treating. - Recovery: No new patches within 2 weeks. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [White or grey coating on cannabis: the master decision tree](https://genetixbay.com/knowledge/diagnosis/white-grey-coatings-decision-tree.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White crystals or sparkles on leaves and buds that don't wipe off: likely causes and fixes > White crystals or sparkles on leaves and buds that don't wipe off on cannabis is most often Trichomes or harmless features mistaken for a problem or Thrips. How to tell them apart, the fix for each and what recovery looks like. Also called: white crystals, white dots on leaves, frosty leaves, glitter on leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=white-sparkle-trichomes ## Likely causes, most likely first ### Trichomes or harmless features mistaken for a problem (Likely) - Kind: Normal ageing; urgency: Low urgency - Fix: Nothing to fix: under a lens, trichomes are stalked glands with round heads, not powder. - Recovery: They don't wipe off and increase with ripeness. - Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [White powder or white spots on cannabis leaves: a differential](https://genetixbay.com/knowledge/diagnosis/white-powder-on-leaves.md) ### Thrips (Less likely) - Kind: Pest; urgency: Deal with it this week - Fix: Two levels: predatory mites (Neoseiulus cucumeris, Amblyseius swirskii) or Orius on the foliage, plus soil predators (Stratiolaelaps scimitus) or Steinernema nematodes in the medium where they pupate. Blue or yellow cards to monitor. Sprays only in veg. - Recovery: Card counts fall and no new silvering on new leaves within 2-3 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Single yellow or brown sugar leaf on an otherwise green cola: likely causes and fixes > Single yellow or brown sugar leaf on an otherwise green cola on cannabis is most often Botrytis bud rot (grey mould). How to tell them apart, the fix for each and what recovery looks like. Also called: one dead leaf in bud, brown leaf in my bud, bud rot sign, dead sugar leaf pulls out easily. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=bud-rot-dead-leaf ## Likely causes, most likely first ### Botrytis bud rot (grey mould) (Likely) - Kind: Disease; urgency: Act now - Fix: Act now. Bag infected buds before cutting them out, 3-5 cm (1-2 in) past visible rot, and clean tools; never shake them. Drop RH to about 40-50% in late flower, control the lights-off dew point, move air through dense colas. There is no cure in flower; consider harvesting early if it keeps spreading. - Recovery: No new rot on weekly cola checks for 2 weeks. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Brown, mushy or grey tissue inside buds: likely causes and fixes > Brown, mushy or grey tissue inside buds on cannabis is most often Botrytis bud rot (grey mould) or Caterpillars and budworms. How to tell them apart, the fix for each and what recovery looks like. Also called: bud rot, rotten buds, mushy bud, grey inside bud, brown inside the cola. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=bud-brown-inside ## Likely causes, most likely first ### Botrytis bud rot (grey mould) (Possible) - Kind: Disease; urgency: Act now - Fix: Act now. Bag infected buds before cutting them out, 3-5 cm (1-2 in) past visible rot, and clean tools; never shake them. Drop RH to about 40-50% in late flower, control the lights-off dew point, move air through dense colas. There is no cure in flower; consider harvesting early if it keeps spreading. - Recovery: No new rot on weekly cola checks for 2 weeks. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ### Caterpillars and budworms (Possible) - Kind: Pest; urgency: Act within a day or two - Fix: Hand-pick; exclude moths with netting; use Bt (kurstaki or aizawai) while larvae are small, since it must be eaten and breaks down in sunlight in days. Remove bored buds: frass starts bud rot. - Recovery: No fresh frass or holes after 1 week. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Article: [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White powder on buds and sugar leaves: likely causes and fixes > White powder on buds and sugar leaves on cannabis is most often Powdery mildew. How to tell them apart, the fix for each and what recovery looks like. Also called: powdery mildew on buds, PM on buds, white powder buds. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=powder-on-buds ## Likely causes, most likely first ### Powdery mildew (Likely) - Kind: Disease; urgency: Act within a day or two - Fix: Treat early in veg: remove the worst leaves into a bag, improve airflow and stable humidity (avoid big day-night RH swings), and use least-toxic contact options (e.g. potassium bicarbonate, sulfur, or biological products, in veg only; never sulfur near oils or in flower). Once it reaches flowers there is no clean fix. Choose resistant genetics and clean clones. - Recovery: No new colonies on treated or new leaves within 7-10 days. - Confirm: Wipe test for white coatings: Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Powdery mildew in cannabis](https://genetixbay.com/knowledge/diseases/powdery-mildew.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Foxtails: new calyx spires growing out of mature buds: likely causes and fixes > Foxtails: new calyx spires growing out of mature buds on cannabis is most often Heat or light stress foxtailing on the top colas, Heat stress or Cultivar foxtailing (genetic). How to tell them apart, the fix for each and what recovery looks like. Also called: foxtailing, buds growing towers, fox tails, spiky buds, new calyxes on top of buds. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=foxtails ## Likely causes, most likely first ### Heat or light stress foxtailing on the top colas (Possible) - Kind: Light; urgency: Low urgency - Fix: Lower top-cola PPFD and leaf temperature (leaf under ~28-30 °C / 82-86 °F); even out the canopy. Evidence is mostly grower observation. - Recovery: No new spires on top colas over the next week. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Foxtailing buds on cannabis: genetics or stress?](https://genetixbay.com/knowledge/diagnosis/foxtails.md) ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Cultivar foxtailing (genetic) (Less likely) - Kind: Genetics; urgency: Low urgency - Fix: Nothing to fix if it appears evenly through the canopy, including shaded buds, in a cultivar known for it. Record it on the cultivar's GB-ID journal. - Recovery: Same pattern in siblings or the same cut in other grows. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Foxtailing buds on cannabis: genetics or stress?](https://genetixbay.com/knowledge/diagnosis/foxtails.md) ### Light bleaching at the canopy top (Less likely) - Kind: Light; urgency: Deal with it this week - Fix: Raise or dim the light by 10-20% so top-canopy PPFD sits around 800-1,100 µmol/m²/s at ambient CO2 (up to ~1,500 with CO2 and good climate). Keep the canopy even so one cola doesn't sit in a hotspot. Bleached tissue won't re-green. - Recovery: No new bleaching within 3-5 days; new bracts and leaves at the top stay green. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Light leak or interrupted dark period (Less likely) - Kind: Light; urgency: Act within a day or two - Fix: Seal the dark period: pinholes, zips, vents and equipment LEDs (tape them), and check the timer. Even dim night light can delay flowering in sensitive cultivars and reveal herm-prone genetics. Use a green headlamp only for brief checks. - Recovery: Flowering resumes within 1-2 weeks; no new single-blade leaves. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Yellow banana-shaped anthers in the buds: likely causes and fixes > Yellow banana-shaped anthers in the buds on cannabis is most often Hermaphrodite (herm-prone genetics revealed by stress), Light leak or interrupted dark period or Heat stress. How to tell them apart, the fix for each and what recovery looks like. Also called: nanners, bananas, herm, yellow bananas in buds, male parts in flower. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=nanners ## Likely causes, most likely first ### Hermaphrodite (herm-prone genetics revealed by stress) (Possible) - Kind: Genetics; urgency: Act within a day or two - Fix: Fix light leaks and stress, but treat the plant as defective genetics: remove it if it sheds pollen, never keep it as a mother and never breed from it. Late-flower bananas are not normal. A few early anthers can be picked off to save the crop, then check twice a week. - Recovery: No new anthers on twice-weekly checks; unaffected plants stay seed-free. - Confirm: Inspect buds and nodes for anthers and pollen sacs: From week 2 of flower, check nodes and buds with a 10x loupe twice a week. Look for pollen sacs on stalks at nodes and pale-yellow banana-shaped anthers among the pistils. Mark and photograph what you find; check the whole plant, not one bud. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) ### Light leak or interrupted dark period (Possible) - Kind: Light; urgency: Act within a day or two - Fix: Seal the dark period: pinholes, zips, vents and equipment LEDs (tape them), and check the timer. Even dim night light can delay flowering in sensitive cultivars and reveal herm-prone genetics. Use a green headlamp only for brief checks. - Recovery: Flowering resumes within 1-2 weeks; no new single-blade leaves. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ### Heat stress (Less likely) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Pollen sacs (balls) at nodes of a female plant: likely causes and fixes > Pollen sacs (balls) at nodes of a female plant on cannabis is most often Hermaphrodite (herm-prone genetics revealed by stress) or Light leak or interrupted dark period. How to tell them apart, the fix for each and what recovery looks like. Also called: balls on my female, pollen sacs, male flowers on female, hermie balls. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=pollen-sacs ## Likely causes, most likely first ### Hermaphrodite (herm-prone genetics revealed by stress) (Possible) - Kind: Genetics; urgency: Act within a day or two - Fix: Fix light leaks and stress, but treat the plant as defective genetics: remove it if it sheds pollen, never keep it as a mother and never breed from it. Late-flower bananas are not normal. A few early anthers can be picked off to save the crop, then check twice a week. - Recovery: No new anthers on twice-weekly checks; unaffected plants stay seed-free. - Confirm: Inspect buds and nodes for anthers and pollen sacs: From week 2 of flower, check nodes and buds with a 10x loupe twice a week. Look for pollen sacs on stalks at nodes and pale-yellow banana-shaped anthers among the pistils. Mark and photograph what you find; check the whole plant, not one bud. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) ### Light leak or interrupted dark period (Possible) - Kind: Light; urgency: Act within a day or two - Fix: Seal the dark period: pinholes, zips, vents and equipment LEDs (tape them), and check the timer. Even dim night light can delay flowering in sensitive cultivars and reveal herm-prone genetics. Use a green headlamp only for brief checks. - Recovery: Flowering resumes within 1-2 weeks; no new single-blade leaves. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Seeds in the buds: likely causes and fixes > Seeds in the buds on cannabis is most often Hermaphrodite (herm-prone genetics revealed by stress). How to tell them apart, the fix for each and what recovery looks like. Also called: seeds in my buds, seedy buds, found seeds, pollinated buds. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=seeds-in-buds ## Likely causes, most likely first ### Hermaphrodite (herm-prone genetics revealed by stress) (Possible) - Kind: Genetics; urgency: Act within a day or two - Fix: Fix light leaks and stress, but treat the plant as defective genetics: remove it if it sheds pollen, never keep it as a mother and never breed from it. Late-flower bananas are not normal. A few early anthers can be picked off to save the crop, then check twice a week. - Recovery: No new anthers on twice-weekly checks; unaffected plants stay seed-free. - Confirm: Inspect buds and nodes for anthers and pollen sacs: From week 2 of flower, check nodes and buds with a 10x loupe twice a week. Look for pollen sacs on stalks at nodes and pale-yellow banana-shaped anthers among the pistils. Mark and photograph what you find; check the whole plant, not one bud. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [Hermaphrodite cannabis (bananas and nanners): what to do](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Airy, loose, larfy buds: likely causes and fixes > Airy, loose, larfy buds on cannabis is most often Hop latent viroid (dudding), Not enough light or Heat stress. How to tell them apart, the fix for each and what recovery looks like. Also called: larf, airy buds, fluffy buds, buds not dense, popcorn buds. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=airy-buds ## Likely causes, most likely first ### Hop latent viroid (dudding) (Possible) - Kind: Disease; urgency: Act within a day or two - Fix: No cure in a plant. Test mothers (roots and leaves) by RT-PCR or RT-qPCR, discard positives, disinfect tools with 10% bleach or heat (alcohol and peroxide don't inactivate it), and use meristem tissue culture to rescue valuable genetics. Don't take cuttings from stunted plants. - Recovery: Negative tests on new mothers; no more duds in the next cycle. - Confirm: Lab test for hop latent viroid (RT-PCR or RT-qPCR): Send root and leaf samples (roots detect HLVd earlier in young plants) to a lab offering HLVd RT-PCR or RT-qPCR. Test mother plants and any stunted plant among healthy siblings. A positive plant cannot be cured; tissue culture of meristem tips can rescue genetics. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ### Not enough light (Possible) - Kind: Light; urgency: Low urgency - Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat. - Recovery: New internodes shorten within a week; denser buds on the following weeks of growth. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### General underfeeding (whole feed too weak) (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Raise the whole feed in steps of about 0.2-0.3 mS/cm toward the stage target (veg 1.2-1.8, flower 1.6-2.2 mS/cm in coco and hydro). Stop any 'flush': plain water for weeks starves the plant, and pre-harvest flushing is a myth that costs yield. - Recovery: Colour deepens and growth speeds up within a week; runoff EC tracks input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ### Too much nitrogen (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Cut feed N by 20-30% (or the whole feed EC by ~0.3-0.5 mS/cm); for a heavy overdose in containers, run a root-zone flush with pH-adjusted, quarter-strength feed to 20-30% runoff. In flower, taper N while keeping P, K, Ca, Mg, S and micros fed. - Recovery: New leaves come in lighter green and flat within 5-7 days; clawed leaves relax partly. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### CO2 depleted in a sealed room without enrichment (Less likely) - Kind: Environment; urgency: Low urgency - Fix: Exchange air (exhaust with passive or active intake) or enrich to 800-1,200 ppm during lights-on when PPFD is above ~900 µmol/m²/s and the room is sealed. - Recovery: Lights-on CO2 holds above ~400 ppm; growth rate returns. - Confirm: Measure CO2 during the light period: Read a CO2 monitor at canopy height through the light period. A sealed room without enrichment can fall below 300-350 ppm and stall growth; enriched rooms should hold 800-1,200 ppm. Keep occupied spaces below the 5,000 ppm workplace limit. - Article: [CO₂ enrichment: when it pays, how much, and how to stay safe](https://genetixbay.com/knowledge/environment/co2-enrichment.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Pistils browning early in flower: likely causes and fixes > Pistils browning early in flower on cannabis is most often Heat stress, Heat or light stress foxtailing on the top colas or Light bleaching at the canopy top. How to tell them apart, the fix for each and what recovery looks like. Also called: hairs turning brown early, pistils browning, red hairs early, orange hairs week 3. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=pistils-brown-early ## Likely causes, most likely first ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Heat or light stress foxtailing on the top colas (Less likely) - Kind: Light; urgency: Low urgency - Fix: Lower top-cola PPFD and leaf temperature (leaf under ~28-30 °C / 82-86 °F); even out the canopy. Evidence is mostly grower observation. - Recovery: No new spires on top colas over the next week. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Foxtailing buds on cannabis: genetics or stress?](https://genetixbay.com/knowledge/diagnosis/foxtails.md) ### Light bleaching at the canopy top (Less likely) - Kind: Light; urgency: Deal with it this week - Fix: Raise or dim the light by 10-20% so top-canopy PPFD sits around 800-1,100 µmol/m²/s at ambient CO2 (up to ~1,500 with CO2 and good climate). Keep the canopy even so one cola doesn't sit in a hotspot. Bleached tissue won't re-green. - Recovery: No new bleaching within 3-5 days; new bracts and leaves at the top stay green. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Light burn: too much light for the plant's climate and CO2 (Less likely) - Kind: Light; urgency: Deal with it this week - Fix: Dim or raise the light 10-20%; ramp intensity over 7-10 days after a light change. Seedlings and clones need only 100-300 µmol/m²/s. High PPFD works only with leaf temperature, VPD, roots and feed all in range. - Recovery: Top leaves flatten within 1-3 days. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Droppings (frass), webbing or holes in buds: likely causes and fixes > Droppings (frass), webbing or holes in buds on cannabis is most often Caterpillars and budworms. How to tell them apart, the fix for each and what recovery looks like. Also called: poop in buds, frass, caterpillar in bud, black pellets in buds, bud eaten from inside. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=frass-in-buds ## Likely causes, most likely first ### Caterpillars and budworms (Likely) - Kind: Pest; urgency: Act within a day or two - Fix: Hand-pick; exclude moths with netting; use Bt (kurstaki or aizawai) while larvae are small, since it must be eaten and breaks down in sunlight in days. Remove bored buds: frass starts bud rot. - Recovery: No fresh frass or holes after 1 week. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Article: [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Flowering not starting or very slow after the flip: likely causes and fixes > Flowering not starting or very slow after the flip on cannabis is most often Light leak or interrupted dark period or Long-flowering or light-sensitive cultivar. How to tell them apart, the fix for each and what recovery looks like. Also called: not flowering, still vegging after flip, no pistils after 3 weeks, won't flower. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=flowering-delayed ## Likely causes, most likely first ### Light leak or interrupted dark period (Likely) - Kind: Light; urgency: Act within a day or two - Fix: Seal the dark period: pinholes, zips, vents and equipment LEDs (tape them), and check the timer. Even dim night light can delay flowering in sensitive cultivars and reveal herm-prone genetics. Use a green headlamp only for brief checks. - Recovery: Flowering resumes within 1-2 weeks; no new single-blade leaves. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ### Long-flowering or light-sensitive cultivar (Less likely) - Kind: Genetics; urgency: Low urgency - Fix: After the flip there is a 10-14 day transition before flowering really starts (up to 3 weeks in slow cultivars). Count from the flip and add the transition; flip earlier or train flatter for big-stretch cultivars. - Recovery: Pistils at the top of the main stem by about 3 weeks after the flip. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [The flip isn't day 1 of flower: the 10–14 day transition and how to count it](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Bud swell stalls in mid-late flower: likely causes and fixes > Bud swell stalls in mid-late flower on cannabis is most often Nitrogen deficiency, Re-vegetation from too-long days in flower or Potassium deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: buds stopped growing, buds not fattening, flowers stalled, buds not getting bigger. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=buds-stall ## Likely causes, most likely first ### Nitrogen deficiency (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Fix roots, watering and pH first. If N is genuinely short, raise feed N by about 10-20% (not double): mineral feeds around 150-200 mg/L N in veg and early flower; one DWC flowering trial predicted a yield optimum near 194 mg/L. Coco/hydro: raise base feed EC by ~0.2 mS/cm. Soil: liquid feed at label rate. Living soil: top-dress a fast organic N source and allow 1-2 weeks. Late flower: a gradual fade is the planned N taper, not a fault. - Recovery: Yellowing stops climbing within 5-7 days and new leaves emerge mid-green; already-yellow leaves do not recover. Runoff EC climbs back toward input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Re-vegetation from too-long days in flower (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Restore an uninterrupted 12-13 h dark period (13/11 is fine; some cultivars flower at 14-15 h days with ramps). Outdoors, early-season plants under long days re-veg; plant later or use light deprivation. - Recovery: No new single-blade growth within 2 weeks. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [How do I reveg a plant after harvest?](https://genetixbay.com/knowledge/answers/how-to-reveg-a-plant.md) ### Potassium deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Check runoff EC first: salt burn looks the same. If K is genuinely short, feed about 175-250 mg/L K (potassium sulfate, potassium nitrate or MKP) at a normal EC. A flowering DWC trial saw no yield response anywhere from 60 to 340 mg/L, so more is not better. Cut heavy Cal-Mag or sodium-rich water that competes with K. - Recovery: Margin scorch stops advancing up the plant within 7 days; new leaves open with clean margins. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Musty, mouldy smell in the canopy: likely causes and fixes > Musty, mouldy smell in the canopy on cannabis is most often Botrytis bud rot (grey mould) or Humidity too high / VPD too low. How to tell them apart, the fix for each and what recovery looks like. Also called: smells like mould, musty smell, damp smell in tent, mildew smell. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=musty-smell ## Likely causes, most likely first ### Botrytis bud rot (grey mould) (Possible) - Kind: Disease; urgency: Act now - Fix: Act now. Bag infected buds before cutting them out, 3-5 cm (1-2 in) past visible rot, and clean tools; never shake them. Drop RH to about 40-50% in late flower, control the lights-off dew point, move air through dense colas. There is no cure in flower; consider harvesting early if it keeps spreading. - Recovery: No new rot on weekly cola checks for 2 weeks. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ### Humidity too high / VPD too low (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids. - Recovery: RH holds in band through lights-off for 3+ days; no new mould signs. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Brown, slimy roots; outer layer slides off: likely causes and fixes > Brown, slimy roots; outer layer slides off on cannabis is most often Root rot (Pythium), Reservoir or root zone too warm or Low dissolved oxygen in the root zone. How to tell them apart, the fix for each and what recovery looks like. Also called: root rot, brown roots, slimy roots, pythium, snotty roots, roots look like wet noodles. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=roots-brown-slimy ## Likely causes, most likely first ### Root rot (Pythium) (Possible) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ### Reservoir or root zone too warm (Possible) - Kind: Root zone; urgency: Act within a day or two - Fix: Keep solution at 18-22 °C (64-72 °F): insulate and shade the reservoir, move it off the warm floor or away from the light, use a chiller or frozen water bottles in an emergency, avoid submersible pumps that add heat, cool the room. - Recovery: Solution holds below 22 °C through the light period; new white roots in 3-5 days. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Article: [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ### Low dissolved oxygen in the root zone (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Restore oxygen: clean or replace air stones, size the air pump for at least ~1 L/min per 4 L, keep a 2-5 cm air gap under net pots once roots reach the water, cool the solution to 18-22 °C (64-72 °F). Aim for 6-8+ mg/L DO. - Recovery: Fresh white root tips within 3-5 days; wilting stops. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Tan or tea-stained roots that are still firm: likely causes and fixes > Tan or tea-stained roots that are still firm on cannabis is most often Harmless root staining (nutrients, tannins, additives) or Ammonium toxicity (too much NH4 in the feed). How to tell them apart, the fix for each and what recovery looks like. Also called: roots turning tan, stained roots, orange roots, roots not white but firm. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=roots-stained-firm ## Likely causes, most likely first ### Harmless root staining (nutrients, tannins, additives) (Likely) - Kind: Root zone; urgency: Low urgency - Fix: Nothing to fix if roots are firm, odourless and still growing white tips. Organic additives, humic products and some nutrient colours stain roots tan. - Recovery: New tips keep appearing white; plant grows normally. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ### Ammonium toxicity (too much NH4 in the feed) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Keep ammonium at or below about 10-30% of total N (cannabis trials showed toxicity and lost yield above ~30%); switch to a mostly nitrate feed and correct root-zone pH. - Recovery: pH stops falling and new leaves lose the dark claw within a week. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Rotten, sour or sewer smell from roots, medium or reservoir: likely causes and fixes > Rotten, sour or sewer smell from roots, medium or reservoir on cannabis is most often Low dissolved oxygen in the root zone, Reservoir or root zone too warm or Root rot (Pythium). How to tell them apart, the fix for each and what recovery looks like. Also called: reservoir smells, roots smell bad, sour soil, rotten egg smell, smells like sewage, swampy smell. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=root-zone-smell ## Likely causes, most likely first ### Low dissolved oxygen in the root zone (Possible) - Kind: Root zone; urgency: Act within a day or two - Fix: Restore oxygen: clean or replace air stones, size the air pump for at least ~1 L/min per 4 L, keep a 2-5 cm air gap under net pots once roots reach the water, cool the solution to 18-22 °C (64-72 °F). Aim for 6-8+ mg/L DO. - Recovery: Fresh white root tips within 3-5 days; wilting stops. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ### Reservoir or root zone too warm (Possible) - Kind: Root zone; urgency: Act within a day or two - Fix: Keep solution at 18-22 °C (64-72 °F): insulate and shade the reservoir, move it off the warm floor or away from the light, use a chiller or frozen water bottles in an emergency, avoid submersible pumps that add heat, cool the room. - Recovery: Solution holds below 22 °C through the light period; new white roots in 3-5 days. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Article: [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ### Root rot (Pythium) (Possible) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ### Overwatering (roots short of air) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Thick mat of circling roots at the pot wall: likely causes and fixes > Thick mat of circling roots at the pot wall on cannabis is most often Root-bound in a pot too small. How to tell them apart, the fix for each and what recovery looks like. Also called: root bound, rootbound, roots circling, roots out the bottom, pot full of roots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=roots-circling ## Likely causes, most likely first ### Root-bound in a pot too small (Likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Up-pot photoperiods into a container about 2-3x larger, loosening circling roots gently. Autoflowers: don't transplant; increase watering and feeding frequency instead. Small pots can still grow big plants with high-frequency fertigation (several feeds a day). - Recovery: New white roots in the fresh medium within 5-7 days; daily wilting stops. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Cannabis root problems: the master decision tree](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # No fresh white root tips: likely causes and fixes > No fresh white root tips on cannabis is most often Low dissolved oxygen in the root zone, Chlorine or chloramine in tap water harming roots and soil life or Pump, timer, air or emitter failure in a hydro, aero or drip system. How to tell them apart, the fix for each and what recovery looks like. Also called: roots not growing, no new roots, roots stopped growing, roots look old. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=no-new-root-tips ## Likely causes, most likely first ### Low dissolved oxygen in the root zone (Possible) - Kind: Root zone; urgency: Act within a day or two - Fix: Restore oxygen: clean or replace air stones, size the air pump for at least ~1 L/min per 4 L, keep a 2-5 cm air gap under net pots once roots reach the water, cool the solution to 18-22 °C (64-72 °F). Aim for 6-8+ mg/L DO. - Recovery: Fresh white root tips within 3-5 days; wilting stops. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ### Chlorine or chloramine in tap water harming roots and soil life (Less likely) - Kind: Root zone; urgency: Low urgency - Fix: Usual tap levels rarely hurt the plant directly; the concern is living soil, beneficial microbes and young roots. Chlorine gasses off in 24 h of aeration; chloramine does not. Remove chloramine with long-contact or catalytic carbon, or about 1 g of ascorbic acid per 100-400 L, or use RO. - Recovery: Biology recovers over weeks; seedlings resume growth within a week. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ### Pump, timer, air or emitter failure in a hydro, aero or drip system (Less likely) - Kind: Root zone; urgency: Act now - Fix: Restore flow or air immediately: check power, timer, float switches, filters and nozzles. Mist exposed roots by hand or lower plants into solution while you fix it. In HPA and NFT, fit an alarm and a backup pump; roots die fast when misting or flow stops. - Recovery: Plants regain turgor within hours if roots were not dead; brown, collapsed roots mean rot risk next. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [High-pressure aeroponics (HPA)](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Short, stubby, brown root tips: likely causes and fixes > Short, stubby, brown root tips on cannabis is most often Nutrient burn (feed too strong), Salt build-up in the root zone or Copper toxicity (copper sprays, ionisers, pipework). How to tell them apart, the fix for each and what recovery looks like. Also called: roots burnt, short roots, root tips brown and dead, stunted roots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=stubby-root-tips ## Likely causes, most likely first ### Nutrient burn (feed too strong) (Possible) - Kind: Too much of something; urgency: Low urgency - Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up). - Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ### Salt build-up in the root zone (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth. - Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like. - Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ### Copper toxicity (copper sprays, ionisers, pipework) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Stop copper fungicides and ionisers, replace copper pipework contact; change the reservoir. Keep Cu at about 0.03-0.1 mg/L. - Recovery: New white root tips within a week. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md) ### Ammonium toxicity (too much NH4 in the feed) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Keep ammonium at or below about 10-30% of total N (cannabis trials showed toxicity and lost yield above ~30%); switch to a mostly nitrate feed and correct root-zone pH. - Recovery: pH stops falling and new leaves lose the dark claw within a week. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Boron deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out broad mites first. Supply about 0.2-0.5 mg/L B (boric acid ~1.1-2.9 mg/L, or a complete micro mix). The gap between enough and too much is narrow: never add B 'just in case' on top of a complete feed. - Recovery: New shoots grow normally from the tip or from side buds within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White waxy residue and tiny insects on roots: likely causes and fixes > White waxy residue and tiny insects on roots on cannabis is most often Root aphids or Mealybugs. How to tell them apart, the fix for each and what recovery looks like. Also called: root aphids, white powder on roots, bugs on roots, tiny bugs at the pot bottom, white waxy roots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=root-aphids ## Likely causes, most likely first ### Root aphids (Possible) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm on the roots. Apply soil-dwelling biologicals (Beauveria bassiana drenches, Stratiolaelaps scimitus, Steinernema or Heterorhabditis nematodes), sanitise, and leave a plant-free gap between cycles; dispose of infested media. - Recovery: No live aphids on root checks after 2-3 weeks; growth resumes. - Confirm: Root-ball and drainage-hole insect check: Tip the plant out and inspect the outer roots, pot bottom and drainage holes with a 10x loupe. Root aphids are small, pear-shaped and wingless, often with white waxy flecks; check several plants, and the drain trays, since colonies hide at the pot edge. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Root aphids (rice root aphid) on indoor cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/root-aphids.md) ### Mealybugs (Less likely) - Kind: Pest; urgency: Deal with it this week - Fix: Remove colonies with a cotton bud dipped in 70% isopropyl alcohol (veg only, test a leaf first); release mealybug predators (e.g. Cryptolaemus beetles) or parasitoids; quarantine new stock; discard heavily infested plants. - Recovery: No new cottony clusters after 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Mealybugs and root mealybugs on cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/mealybugs.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Tiny clear larvae with black heads in the medium: likely causes and fixes > Tiny clear larvae with black heads in the medium on cannabis is most often Fungus gnats or Overwatering (roots short of air). How to tell them apart, the fix for each and what recovery looks like. Also called: worms in soil, larvae in coco, maggots in pot, small white worms with black heads. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=larvae-in-medium ## Likely causes, most likely first ### Fungus gnats (Likely) - Kind: Pest; urgency: Low urgency - Fix: Fix the watering first: let the top 2-3 cm dry. Then Bti drenches (larvicide), Steinernema feltiae nematodes or Stratiolaelaps mites; yellow cards for adults. Larvae chew seedling and clone roots and can open the door to Pythium. - Recovery: Card catches fall within 2-3 weeks; no larvae under potato slices. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Confirm: Potato slice test for larvae in the medium: Press 2-3 raw potato slices (1 cm thick) cut side down onto the medium surface. Lift after 2-4 days and look underneath: translucent larvae with shiny black heads are fungus gnat larvae. - Article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ### Overwatering (roots short of air) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Small black flies around the medium: likely causes and fixes > Small black flies around the medium on cannabis is most often Fungus gnats, Overwatering (roots short of air) or Algae from light reaching wet surfaces or the reservoir. How to tell them apart, the fix for each and what recovery looks like. Also called: fungus gnats, gnats, little flies in my tent, black flies around soil. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=gnats-flying ## Likely causes, most likely first ### Fungus gnats (Likely) - Kind: Pest; urgency: Low urgency - Fix: Fix the watering first: let the top 2-3 cm dry. Then Bti drenches (larvicide), Steinernema feltiae nematodes or Stratiolaelaps mites; yellow cards for adults. Larvae chew seedling and clone roots and can open the door to Pythium. - Recovery: Card catches fall within 2-3 weeks; no larvae under potato slices. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Confirm: Potato slice test for larvae in the medium: Press 2-3 raw potato slices (1 cm thick) cut side down onto the medium surface. Lift after 2-4 days and look underneath: translucent larvae with shiny black heads are fungus gnat larvae. - Article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ### Overwatering (roots short of air) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Algae from light reaching wet surfaces or the reservoir (Less likely) - Kind: Root zone; urgency: Low urgency - Fix: Block all light from reservoirs, tubing and the medium surface (opaque lids, covers on rockwool). Clean surfaces between runs. Algae competes for oxygen and feeds gnats and shore flies. - Recovery: No new green growth within 1-2 weeks of light-proofing. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [How do I stop algae in my reservoir or on my medium?](https://genetixbay.com/knowledge/answers/algae-in-reservoir.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Reservoir or root zone water warm (above 23 °C / 73 °F): likely causes and fixes > Reservoir or root zone water warm (above 23 °C / 73 °F) on cannabis is most often Reservoir or root zone too warm or Pump, timer, air or emitter failure in a hydro, aero or drip system. How to tell them apart, the fix for each and what recovery looks like. Also called: res too hot, warm reservoir, water temperature high, reservoir temp 26. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=reservoir-warm ## Likely causes, most likely first ### Reservoir or root zone too warm (Likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Keep solution at 18-22 °C (64-72 °F): insulate and shade the reservoir, move it off the warm floor or away from the light, use a chiller or frozen water bottles in an emergency, avoid submersible pumps that add heat, cool the room. - Recovery: Solution holds below 22 °C through the light period; new white roots in 3-5 days. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Article: [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ### Pump, timer, air or emitter failure in a hydro, aero or drip system (Less likely) - Kind: Root zone; urgency: Act now - Fix: Restore flow or air immediately: check power, timer, float switches, filters and nozzles. Mist exposed roots by hand or lower plants into solution while you fix it. In HPA and NFT, fit an alarm and a backup pump; roots die fast when misting or flow stops. - Recovery: Plants regain turgor within hours if roots were not dead; brown, collapsed roots mean rot risk next. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [High-pressure aeroponics (HPA)](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Cloudy, foamy or slimy reservoir: likely causes and fixes > Cloudy, foamy or slimy reservoir on cannabis is most often Algae from light reaching wet surfaces or the reservoir, Reservoir or root zone too warm or Root rot (Pythium). How to tell them apart, the fix for each and what recovery looks like. Also called: cloudy res, foam in reservoir, biofilm, slimy tubes, milky water. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=reservoir-cloudy ## Likely causes, most likely first ### Algae from light reaching wet surfaces or the reservoir (Possible) - Kind: Root zone; urgency: Low urgency - Fix: Block all light from reservoirs, tubing and the medium surface (opaque lids, covers on rockwool). Clean surfaces between runs. Algae competes for oxygen and feeds gnats and shore flies. - Recovery: No new green growth within 1-2 weeks of light-proofing. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [How do I stop algae in my reservoir or on my medium?](https://genetixbay.com/knowledge/answers/algae-in-reservoir.md) ### Reservoir or root zone too warm (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Keep solution at 18-22 °C (64-72 °F): insulate and shade the reservoir, move it off the warm floor or away from the light, use a chiller or frozen water bottles in an emergency, avoid submersible pumps that add heat, cool the room. - Recovery: Solution holds below 22 °C through the light period; new white roots in 3-5 days. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Article: [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md) ### Root rot (Pythium) (Less likely) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Root-zone or reservoir pH climbing steadily: likely causes and fixes > Root-zone or reservoir pH climbing steadily on cannabis is most often Hard, alkaline water pushing pH up over weeks, High root-zone pH locking out iron, manganese, zinc, boron and copper or Algae from light reaching wet surfaces or the reservoir. How to tell them apart, the fix for each and what rec Also called: pH keeps rising, pH creeping up, runoff pH high, res pH going up. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=ph-rising ## Likely causes, most likely first ### Hard, alkaline water pushing pH up over weeks (Possible) - Kind: Root zone; urgency: Low urgency - Fix: Alkalinity, not water pH, drives the climb. Above about 100-150 mg/L as CaCO3 (2-3 meq/L), neutralise most of it with acid to an input pH of 5.8-6.2, or blend with RO water. Track runoff pH weekly. - Recovery: Runoff pH stops climbing over 2-3 weeks. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ### High root-zone pH locking out iron, manganese, zinc, boron and copper (Possible) - Kind: pH; urgency: Deal with it this week - Fix: Bring root-zone pH into range: soil 6.2-6.8, coco and rockwool 5.8-6.2, hydro 5.5-6.2. Lower input pH by 0.2-0.3 units at a time rather than crashing it; neutralise alkaline water with a mineral acid (phosphoric, nitric or sulfuric; wear gloves and eye protection, add acid to water). Use an iron chelate stable at your pH (DTPA or EDDHA above 6.5). - Recovery: Runoff or reservoir pH back in range at two consecutive checks; new leaves open green within 5-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Algae from light reaching wet surfaces or the reservoir (Less likely) - Kind: Root zone; urgency: Low urgency - Fix: Block all light from reservoirs, tubing and the medium surface (opaque lids, covers on rockwool). Clean surfaces between runs. Algae competes for oxygen and feeds gnats and shore flies. - Recovery: No new green growth within 1-2 weeks of light-proofing. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [How do I stop algae in my reservoir or on my medium?](https://genetixbay.com/knowledge/answers/algae-in-reservoir.md) ### Uncalibrated or failing pH or EC meter (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Calibrate the pH meter with fresh pH 7 then pH 4 buffer before decisions and at least weekly; store the probe wet in storage solution, never in RO water. Check EC against 1.413 mS/cm. Replace probes that won't calibrate (typical life 1-2 years). Drops and strips are too coarse to diagnose with. - Recovery: Readings match the buffers within 0.1 pH; the 'problem' pH disappears or is confirmed. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Article: [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Reservoir pH falling fast without explanation: likely causes and fixes > Reservoir pH falling fast without explanation on cannabis is most often Low root-zone pH starving calcium and magnesium, Ammonium toxicity (too much NH4 in the feed) or Root rot (Pythium). How to tell them apart, the fix for each and what recovery looks like. Also called: pH dropping, pH crashing, pH keeps going down, runoff pH low. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=ph-falling ## Likely causes, most likely first ### Low root-zone pH starving calcium and magnesium (Possible) - Kind: pH; urgency: Deal with it this week - Fix: Raise root-zone pH to range: coco 5.8-6.2, hydro 5.6-6.0, soil 6.2-6.8. Use pH up (potassium hydroxide or carbonate) in small steps; in coco, feed at 6.0-6.2 for a few waterings with Ca and Mg on board. A fast fall in hydro points to dying roots or microbes; check them. - Recovery: pH holds in range for a week; new leaves spot-free within 7-10 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) ### Ammonium toxicity (too much NH4 in the feed) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Keep ammonium at or below about 10-30% of total N (cannabis trials showed toxicity and lost yield above ~30%); switch to a mostly nitrate feed and correct root-zone pH. - Recovery: pH stops falling and new leaves lose the dark claw within a week. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Root rot (Pythium) (Less likely) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ### Uncalibrated or failing pH or EC meter (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Calibrate the pH meter with fresh pH 7 then pH 4 buffer before decisions and at least weekly; store the probe wet in storage solution, never in RO water. Check EC against 1.413 mS/cm. Replace probes that won't calibrate (typical life 1-2 years). Drops and strips are too coarse to diagnose with. - Recovery: Readings match the buffers within 0.1 pH; the 'problem' pH disappears or is confirmed. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Article: [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Reservoir EC rising as the water level drops: likely causes and fixes > Reservoir EC rising as the water level drops on cannabis is most often Nutrient burn (feed too strong). How to tell them apart, the fix for each and what recovery looks like. Also called: ppm going up, EC climbing in res, TDS rising. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=ec-rising ## Likely causes, most likely first ### Nutrient burn (feed too strong) (Likely) - Kind: Too much of something; urgency: Low urgency - Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up). - Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Runoff EC well above input EC: likely causes and fixes > Runoff EC well above input EC on cannabis is most often Nutrient burn (feed too strong), Salt build-up in the root zone or Sodium build-up (softened water, coco, recirculation). How to tell them apart, the fix for each and what recovery looks like. Also called: high runoff ppm, runoff EC high, salt build up, runoff higher than input. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=runoff-ec-high ## Likely causes, most likely first ### Nutrient burn (feed too strong) (Possible) - Kind: Too much of something; urgency: Low urgency - Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up). - Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md) ### Salt build-up in the root zone (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth. - Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like. - Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) ### Sodium build-up (softened water, coco, recirculation) (Less likely) - Kind: Too much of something; urgency: Deal with it this week - Fix: Never use ion-exchange softened water. Keep feed sodium below about 50 mg/L (more than ~5 mM NaCl, 115 mg/L Na, may cut hydro yield and cannabinoids fall as NaCl rises). Dump and refill recirculating reservoirs more often; rinse coco before planting. - Recovery: Tip burn stops advancing on new leaves within a week. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Sodium (Na) and cannabis: a salt to keep low, not a nutrient to add](https://genetixbay.com/knowledge/nutrients/sodium.md) ### Uncalibrated or failing pH or EC meter (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Calibrate the pH meter with fresh pH 7 then pH 4 buffer before decisions and at least weekly; store the probe wet in storage solution, never in RO water. Check EC against 1.413 mS/cm. Replace probes that won't calibrate (typical life 1-2 years). Drops and strips are too coarse to diagnose with. - Recovery: Readings match the buffers within 0.1 pH; the 'problem' pH disappears or is confirmed. - Confirm: Check the meters against fresh standards: Put the pH probe in fresh pH 7.0 and 4.0 buffer and the EC probe in a 1.413 mS/cm standard. If pH reads more than 0.1-0.2 off, recalibrate; if it can't be calibrated or the slope is below ~90-95%, replace the probe. Many 'lockouts' are a drifting meter. - Article: [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md) ### Cal-Mag overuse (excess calcium and nitrogen) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: On hard tap water with a complete base feed, stop the Cal-Mag supplement; it adds N and pushes K and Mg out of balance. Use it only for RO or soft water and unbuffered coco. LEDs do not create a Cal-Mag need. - Recovery: K and Mg symptoms stop spreading within 7-10 days. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) ### Excess phosphorus (bloom boosters) inducing Zn, Fe and Ca shortages (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: Drop the booster. Keep P at about 30-60 mg/L; four controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, and excess P just leaves in the runoff. - Recovery: New growth greens within 10 days of returning to a balanced feed. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: ["Bloom boosters" for cannabis: what's real and what's marketing](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Runoff EC much lower than input, or reservoir EC dropping fast: likely causes and fixes > Runoff EC much lower than input, or reservoir EC dropping fast on cannabis is most often General underfeeding (whole feed too weak) or Nitrogen deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: runoff ppm low, plant eating everything, EC dropping in res. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=runoff-ec-low ## Likely causes, most likely first ### General underfeeding (whole feed too weak) (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Raise the whole feed in steps of about 0.2-0.3 mS/cm toward the stage target (veg 1.2-1.8, flower 1.6-2.2 mS/cm in coco and hydro). Stop any 'flush': plain water for weeks starves the plant, and pre-harvest flushing is a myth that costs yield. - Recovery: Colour deepens and growth speeds up within a week; runoff EC tracks input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ### Nitrogen deficiency (Possible) - Kind: Nutrient; urgency: Deal with it this week - Fix: Fix roots, watering and pH first. If N is genuinely short, raise feed N by about 10-20% (not double): mineral feeds around 150-200 mg/L N in veg and early flower; one DWC flowering trial predicted a yield optimum near 194 mg/L. Coco/hydro: raise base feed EC by ~0.2 mS/cm. Soil: liquid feed at label rate. Living soil: top-dress a fast organic N source and allow 1-2 weeks. Late flower: a gradual fade is the planned N taper, not a fault. - Recovery: Yellowing stops climbing within 5-7 days and new leaves emerge mid-green; already-yellow leaves do not recover. Runoff EC climbs back toward input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Medium stays wet for 4+ days after watering: likely causes and fixes > Medium stays wet for 4+ days after watering on cannabis is most often Overwatering (roots short of air), Humidity too high / VPD too low or Cold root zone (below about 16 °C / 61 °F). How to tell them apart, the fix for each and what recovery looks like. Also called: soil never dries, pot always wet, soil stays soggy, coco not drying. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=medium-stays-wet ## Likely causes, most likely first ### Overwatering (roots short of air) (Likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Humidity too high / VPD too low (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids. - Recovery: RH holds in band through lights-off for 3+ days; no new mould signs. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ### Cold root zone (below about 16 °C / 61 °F) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Raise root-zone temperature to 18-22 °C (64-72 °F): lift pots off cold floors onto insulation, warm the room at night, use an aquarium heater in reservoirs (with a thermostat), water with room-temperature solution. - Recovery: Growth resumes and new leaves green within a week. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Medium dries out within a day; water runs straight through or down the sides: likely causes and fixes > Medium dries out within a day; water runs straight through or down the sides on cannabis is most often Root-bound in a pot too small, Underwatering or Dry, water-repellent medium (water runs straight through). How to tell them apart, the fix for each and what recovery looks like. Also called: water runs right through, soil hydrophobic, dry pockets in pot, soil pulled away from pot. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=medium-dries-fast ## Likely causes, most likely first ### Root-bound in a pot too small (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Up-pot photoperiods into a container about 2-3x larger, loosening circling roots gently. Autoflowers: don't transplant; increase watering and feeding frequency instead. Small pots can still grow big plants with high-frequency fertigation (several feeds a day). - Recovery: New white roots in the fresh medium within 5-7 days; daily wilting stops. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Cannabis root problems: the master decision tree](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md) ### Underwatering (Possible) - Kind: Root zone; urgency: Act within a day or two - Fix: Water slowly in 2-3 passes until 10-20% runoff, so the whole root ball wets. Water when the pot is clearly lighter, before the plant droops. Mild late-flower dry-back is a house-endorsed practice for some cultivars (Caplan 2019), but wilting is not. - Recovery: Turgor returns within 1-6 hours of watering. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Dry, water-repellent medium (water runs straight through) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Rewet slowly: small amounts every 10-15 minutes, or bottom-soak the pot for 20-30 minutes; a drop of plant-safe wetting agent helps peat. Don't let peat mixes go bone dry again. - Recovery: Pot gains its normal wet weight and holds it for a day or more. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Why does water run straight through or pool on top of my pot?](https://genetixbay.com/knowledge/answers/water-runs-through-or-pools.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White scale on pots, pumps, drippers or the meter: likely causes and fixes > White scale on pots, pumps, drippers or the meter on cannabis is most often Hard, alkaline water pushing pH up over weeks or Cal-Mag overuse (excess calcium and nitrogen). How to tell them apart, the fix for each and what recovery looks like. Also called: limescale, white deposits on equipment, clogged drippers, scale in reservoir. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=white-scale-equipment ## Likely causes, most likely first ### Hard, alkaline water pushing pH up over weeks (Possible) - Kind: Root zone; urgency: Low urgency - Fix: Alkalinity, not water pH, drives the climb. Above about 100-150 mg/L as CaCO3 (2-3 meq/L), neutralise most of it with acid to an input pH of 5.8-6.2, or blend with RO water. Track runoff pH weekly. - Recovery: Runoff pH stops climbing over 2-3 weeks. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable. - Article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ### Cal-Mag overuse (excess calcium and nitrogen) (Less likely) - Kind: Too much of something; urgency: Low urgency - Fix: On hard tap water with a complete base feed, stop the Cal-Mag supplement; it adds N and pushes K and Mg out of balance. Use it only for RO or soft water and unbuffered coco. LEDs do not create a Cal-Mag need. - Recovery: K and Mg symptoms stop spreading within 7-10 days. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Article: [Cal-Mag: what it is, when you need it and when you don't](https://genetixbay.com/knowledge/nutrients/cal-mag.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Stretched, thin plant with long gaps between nodes: likely causes and fixes > Stretched, thin plant with long gaps between nodes on cannabis is most often Normal stretch after the flip or Not enough light. How to tell them apart, the fix for each and what recovery looks like. Also called: leggy, stretching, too tall and thin, long internodes, reaching for the light. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=stretchy ## Likely causes, most likely first ### Normal stretch after the flip (Possible) - Kind: Normal ageing; urgency: Low urgency - Fix: Most cultivars grow 1.5-3x in the first 2-3 weeks after the flip. Plan height before the flip; supercrop or LST through it. - Recovery: Stretch stops by about weeks 3-4 of flower. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ### Not enough light (Possible) - Kind: Light; urgency: Low urgency - Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat. - Recovery: New internodes shorten within a week; denser buds on the following weeks of growth. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Excessive stretch after the flip (more than about 3x): likely causes and fixes > Excessive stretch after the flip (more than about 3x) on cannabis is most often Long-flowering or light-sensitive cultivar, Normal stretch after the flip or Not enough light. How to tell them apart, the fix for each and what recovery looks like. Also called: stretched too much in flower, plant doubled after flip, flower stretch out of control. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=excess-flower-stretch ## Likely causes, most likely first ### Long-flowering or light-sensitive cultivar (Possible) - Kind: Genetics; urgency: Low urgency - Fix: After the flip there is a 10-14 day transition before flowering really starts (up to 3 weeks in slow cultivars). Count from the flip and add the transition; flip earlier or train flatter for big-stretch cultivars. - Recovery: Pistils at the top of the main stem by about 3 weeks after the flip. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [The flip isn't day 1 of flower: the 10–14 day transition and how to count it](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md) ### Normal stretch after the flip (Possible) - Kind: Normal ageing; urgency: Low urgency - Fix: Most cultivars grow 1.5-3x in the first 2-3 weeks after the flip. Plan height before the flip; supercrop or LST through it. - Recovery: Stretch stops by about weeks 3-4 of flower. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ### Not enough light (Less likely) - Kind: Light; urgency: Low urgency - Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat. - Recovery: New internodes shorten within a week; denser buds on the following weeks of growth. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Leggy seedling with a long, thin stem: likely causes and fixes > Leggy seedling with a long, thin stem on cannabis is most often Not enough light. How to tell them apart, the fix for each and what recovery looks like. Also called: stretched seedling, seedling too tall, seedling falling over thin stem. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=leggy-seedling ## Likely causes, most likely first ### Not enough light (Likely) - Kind: Light; urgency: Low urgency - Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat. - Recovery: New internodes shorten within a week; denser buds on the following weeks of growth. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Stunted, slow growth across the plant: likely causes and fixes > Stunted, slow growth across the plant on cannabis is most often Overwatering (roots short of air), Autoflower stunted by early stress or General underfeeding (whole feed too weak). How to tell them apart, the fix for each and what recovery looks like. Also called: plant not growing, slow growth, stunted, plant stalled, barely growing. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=stunted ## Likely causes, most likely first ### Overwatering (roots short of air) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Autoflower stunted by early stress (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Autos run on a countdown from germination, so lost growth never returns. Next run: sow straight into the final 11-19 L (3-5 gal) pot, never transplant, water seedlings in small rings, give 300-600+ µmol/m²/s early, train with LST only (topping never matches proper LST). This run: keep conditions steady and feed well; don't add more stress. - Recovery: Steady weekly growth from here on; size gap to siblings stops widening. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Why is my autoflower so small?](https://genetixbay.com/knowledge/answers/why-is-my-autoflower-small.md) ### General underfeeding (whole feed too weak) (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Raise the whole feed in steps of about 0.2-0.3 mS/cm toward the stage target (veg 1.2-1.8, flower 1.6-2.2 mS/cm in coco and hydro). Stop any 'flush': plain water for weeks starves the plant, and pre-harvest flushing is a myth that costs yield. - Recovery: Colour deepens and growth speeds up within a week; runoff EC tracks input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md) ### Hop latent viroid (dudding) (Less likely) - Kind: Disease; urgency: Act within a day or two - Fix: No cure in a plant. Test mothers (roots and leaves) by RT-PCR or RT-qPCR, discard positives, disinfect tools with 10% bleach or heat (alcohol and peroxide don't inactivate it), and use meristem tissue culture to rescue valuable genetics. Don't take cuttings from stunted plants. - Recovery: Negative tests on new mothers; no more duds in the next cycle. - Confirm: Lab test for hop latent viroid (RT-PCR or RT-qPCR): Send root and leaf samples (roots detect HLVd earlier in young plants) to a lab offering HLVd RT-PCR or RT-qPCR. Test mother plants and any stunted plant among healthy siblings. A positive plant cannot be cured; tissue culture of meristem tips can rescue genetics. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ### Low dissolved oxygen in the root zone (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Restore oxygen: clean or replace air stones, size the air pump for at least ~1 L/min per 4 L, keep a 2-5 cm air gap under net pots once roots reach the water, cool the solution to 18-22 °C (64-72 °F). Aim for 6-8+ mg/L DO. - Recovery: Fresh white root tips within 3-5 days; wilting stops. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ### Not enough light (Less likely) - Kind: Light; urgency: Low urgency - Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat. - Recovery: New internodes shorten within a week; denser buds on the following weeks of growth. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md) ### Recovery stall after topping, supercropping or heavy defoliation (Less likely) - Kind: Physical damage; urgency: Low urgency - Fix: Give 3-7 days for photoperiods to recover from topping or HST before the next session; don't stack stresses. Prefer tucking to stripping leaves. On autos use LST only. - Recovery: New growth resumes within a week. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [How long does a plant take to recover after topping?](https://genetixbay.com/knowledge/answers/recovery-after-topping.md) ### Root rot (Pythium) (Less likely) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # One plant much smaller than identical siblings: likely causes and fixes > One plant much smaller than identical siblings on cannabis is most often Hop latent viroid (dudding), Weak or slow individual phenotype or Root aphids. How to tell them apart, the fix for each and what recovery looks like. Also called: runt, one plant behind, one clone not growing, dud plant. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=one-plant-stunted ## Likely causes, most likely first ### Hop latent viroid (dudding) (Possible) - Kind: Disease; urgency: Act within a day or two - Fix: No cure in a plant. Test mothers (roots and leaves) by RT-PCR or RT-qPCR, discard positives, disinfect tools with 10% bleach or heat (alcohol and peroxide don't inactivate it), and use meristem tissue culture to rescue valuable genetics. Don't take cuttings from stunted plants. - Recovery: Negative tests on new mothers; no more duds in the next cycle. - Confirm: Lab test for hop latent viroid (RT-PCR or RT-qPCR): Send root and leaf samples (roots detect HLVd earlier in young plants) to a lab offering HLVd RT-PCR or RT-qPCR. Test mother plants and any stunted plant among healthy siblings. A positive plant cannot be cured; tissue culture of meristem tips can rescue genetics. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ### Weak or slow individual phenotype (Possible) - Kind: Genetics; urgency: Low urgency - Fix: Seed-grown siblings vary; a consistently slow plant with healthy roots and a negative HLVd test is a phenotype, not a fault. Don't select it as a keeper or mother. - Recovery: Healthy roots, negative HLVd test, otherwise normal colour. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Confirm: Lab test for hop latent viroid (RT-PCR or RT-qPCR): Send root and leaf samples (roots detect HLVd earlier in young plants) to a lab offering HLVd RT-PCR or RT-qPCR. Test mother plants and any stunted plant among healthy siblings. A positive plant cannot be cured; tissue culture of meristem tips can rescue genetics. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Slow or stunted cannabis growth: a differential](https://genetixbay.com/knowledge/diagnosis/slow-growth.md) ### Root aphids (Less likely) - Kind: Pest; urgency: Act within a day or two - Fix: Confirm on the roots. Apply soil-dwelling biologicals (Beauveria bassiana drenches, Stratiolaelaps scimitus, Steinernema or Heterorhabditis nematodes), sanitise, and leave a plant-free gap between cycles; dispose of infested media. - Recovery: No live aphids on root checks after 2-3 weeks; growth resumes. - Confirm: Root-ball and drainage-hole insect check: Tip the plant out and inspect the outer roots, pot bottom and drainage holes with a 10x loupe. Root aphids are small, pear-shaped and wingless, often with white waxy flecks; check several plants, and the drain trays, since colonies hide at the pot edge. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Root aphids (rice root aphid) on indoor cannabis: ID, life cycle in numbers and IPM](https://genetixbay.com/knowledge/pests/root-aphids.md) ### Plant virus (e.g. beet curly top, lettuce chlorosis virus) (Less likely) - Kind: Disease; urgency: Deal with it this week - Fix: No cure: remove the plant. Control insect vectors (leafhoppers outdoors for curly top; whiteflies for some others) and test clone sources. - Recovery: No new symptomatic plants over the next 2-4 weeks. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Short internodes, compact growth and small leaves: likely causes and fixes > Short internodes, compact growth and small leaves on cannabis is most often Hop latent viroid (dudding), Light burn: too much light for the plant's climate and CO2 or Cold stress. How to tell them apart, the fix for each and what recovery looks like. Also called: plant stays tiny, rosetting, bunched leaves, small leaves short nodes. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=compact-small-leaves ## Likely causes, most likely first ### Hop latent viroid (dudding) (Possible) - Kind: Disease; urgency: Act within a day or two - Fix: No cure in a plant. Test mothers (roots and leaves) by RT-PCR or RT-qPCR, discard positives, disinfect tools with 10% bleach or heat (alcohol and peroxide don't inactivate it), and use meristem tissue culture to rescue valuable genetics. Don't take cuttings from stunted plants. - Recovery: Negative tests on new mothers; no more duds in the next cycle. - Confirm: Lab test for hop latent viroid (RT-PCR or RT-qPCR): Send root and leaf samples (roots detect HLVd earlier in young plants) to a lab offering HLVd RT-PCR or RT-qPCR. Test mother plants and any stunted plant among healthy siblings. A positive plant cannot be cured; tissue culture of meristem tips can rescue genetics. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) ### Light burn: too much light for the plant's climate and CO2 (Less likely) - Kind: Light; urgency: Deal with it this week - Fix: Dim or raise the light 10-20%; ramp intensity over 7-10 days after a light change. Seedlings and clones need only 100-300 µmol/m²/s. High PPFD works only with leaf temperature, VPD, roots and feed all in range. - Recovery: Top leaves flatten within 1-3 days. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Cold stress (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Keep days at 22-28 °C (72-82 °F) and nights no more than 3-6 °C (5-10 °F) cooler and above ~15 °C (59 °F); warm the root zone. Cold-for-colour is real in purple cultivars, but claims of more terpenes or resin are unsupported. - Recovery: Growth resumes within a week; new leaves come in green. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.md) ### Zinc deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Lower high pH, stop excess phosphorus 'boosters' (high P ties up Zn), then supply about 0.1-0.5 mg/L Zn as zinc sulfate or chelate. - Recovery: New leaves reach normal size with clean margins in 7-14 days. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Zinc (Zn) in cannabis: small leaves, margin burn and the phosphorus link](https://genetixbay.com/knowledge/nutrients/zinc.md) ### CO2 set far too high (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Hold 800-1,200 ppm; above that there is little further gain in cannabis. Leaf rolling and chlorosis at very high CO2 are documented in tomato and other greenhouse crops. People: keep occupied rooms under the 5,000 ppm 8-hour limit and never enter a room above 30,000 ppm. - Recovery: Symptoms stop on new growth after CO2 is lowered. - Confirm: Measure CO2 during the light period: Read a CO2 monitor at canopy height through the light period. A sealed room without enrichment can fall below 300-350 ppm and stall growth; enriched rooms should hold 800-1,200 ppm. Keep occupied spaces below the 5,000 ppm workplace limit. - Article: [CO₂ enrichment: when it pays, how much, and how to stay safe](https://genetixbay.com/knowledge/environment/co2-enrichment.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Seedling stalled for over a week: likely causes and fixes > Seedling stalled for over a week on cannabis is most often Overwatering (roots short of air), Autoflower stunted by early stress or Fungus gnats. How to tell them apart, the fix for each and what recovery looks like. Also called: seedling not growing, seedling stuck, seedling not making new leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=seedling-stalled ## Likely causes, most likely first ### Overwatering (roots short of air) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Autoflower stunted by early stress (Possible) - Kind: Environment; urgency: Deal with it this week - Fix: Autos run on a countdown from germination, so lost growth never returns. Next run: sow straight into the final 11-19 L (3-5 gal) pot, never transplant, water seedlings in small rings, give 300-600+ µmol/m²/s early, train with LST only (topping never matches proper LST). This run: keep conditions steady and feed well; don't add more stress. - Recovery: Steady weekly growth from here on; size gap to siblings stops widening. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Why is my autoflower so small?](https://genetixbay.com/knowledge/answers/why-is-my-autoflower-small.md) ### Fungus gnats (Less likely) - Kind: Pest; urgency: Low urgency - Fix: Fix the watering first: let the top 2-3 cm dry. Then Bti drenches (larvicide), Steinernema feltiae nematodes or Stratiolaelaps mites; yellow cards for adults. Larvae chew seedling and clone roots and can open the door to Pythium. - Recovery: Card catches fall within 2-3 weeks; no larvae under potato slices. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Confirm: Potato slice test for larvae in the medium: Press 2-3 raw potato slices (1 cm thick) cut side down onto the medium surface. Lift after 2-4 days and look underneath: translucent larvae with shiny black heads are fungus gnat larvae. - Article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md) ### Chlorine or chloramine in tap water harming roots and soil life (Less likely) - Kind: Root zone; urgency: Low urgency - Fix: Usual tap levels rarely hurt the plant directly; the concern is living soil, beneficial microbes and young roots. Chlorine gasses off in 24 h of aeration; chloramine does not. Remove chloramine with long-contact or catalytic carbon, or about 1 g of ascorbic acid per 100-400 L, or use RO. - Recovery: Biology recovers over weeks; seedlings resume growth within a week. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md) ### Damping-off (Less likely) - Kind: Disease; urgency: Act within a day or two - Fix: A collapsed seedling can't be saved. For the rest: clean containers, fresh mix, warm medium (22-26 °C / 72-79 °F), water lightly, good light and airflow. - Recovery: No further collapses. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Damping-off: why seedlings collapse at the soil line](https://genetixbay.com/knowledge/germination/damping-off.md) ### Seed coat stuck on the cotyledons (helmet head) (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Mist the shell to soften it and raise RH around the seedling (dome) for a few hours; if it is still stuck, ease it off gently with clean tweezers. Plant seeds about 0.5-1.5 cm (1/4-1/2 in) deep so the medium scrapes the coat off on the way up. - Recovery: Cotyledons open within a day. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [What do I do if the seed shell is stuck on my seedling?](https://genetixbay.com/knowledge/answers/seed-shell-stuck-on-seedling.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Autoflower started flowering while still small: likely causes and fixes > Autoflower started flowering while still small on cannabis is most often Autoflower stunted by early stress, Overwatering (roots short of air) or Recovery stall after topping, supercropping or heavy defoliation. How to tell them apart, the fix for each and what recovery looks like. Also called: auto stayed tiny, autoflower small, auto flowering early and small, stunted auto. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=auto-small ## Likely causes, most likely first ### Autoflower stunted by early stress (Possible) - Kind: Environment; urgency: Deal with it this week - Fix: Autos run on a countdown from germination, so lost growth never returns. Next run: sow straight into the final 11-19 L (3-5 gal) pot, never transplant, water seedlings in small rings, give 300-600+ µmol/m²/s early, train with LST only (topping never matches proper LST). This run: keep conditions steady and feed well; don't add more stress. - Recovery: Steady weekly growth from here on; size gap to siblings stops widening. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Article: [Why is my autoflower so small?](https://genetixbay.com/knowledge/answers/why-is-my-autoflower-small.md) ### Overwatering (roots short of air) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Recovery stall after topping, supercropping or heavy defoliation (Less likely) - Kind: Physical damage; urgency: Low urgency - Fix: Give 3-7 days for photoperiods to recover from topping or HST before the next session; don't stack stresses. Prefer tucking to stripping leaves. On autos use LST only. - Recovery: New growth resumes within a week. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [How long does a plant take to recover after topping?](https://genetixbay.com/knowledge/answers/recovery-after-topping.md) ### Transplant shock (Less likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Move the root ball intact into pre-moistened medium of the same type and pH, water in with a mild solution, lower light 10-20% and keep RH slightly higher for 2-3 days. Mild droop for 2-5 days is normal; longer means root damage, waterlogging or a pH mismatch. Autos: sow in the final pot instead. - Recovery: Turgor back in 1-3 days; new growth within a week. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Article: [Transplanting: when, into what, and avoiding transplant shock](https://genetixbay.com/knowledge/germination/transplanting.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Flowering plant pushing new leafy growth instead of buds: likely causes and fixes > Flowering plant pushing new leafy growth instead of buds on cannabis is most often Light leak or interrupted dark period or Re-vegetation from too-long days in flower. How to tell them apart, the fix for each and what recovery looks like. Also called: reveg, reverting to veg, leaves growing out of buds, plant went back to veg. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=reveg-in-flower ## Likely causes, most likely first ### Light leak or interrupted dark period (Possible) - Kind: Light; urgency: Act within a day or two - Fix: Seal the dark period: pinholes, zips, vents and equipment LEDs (tape them), and check the timer. Even dim night light can delay flowering in sensitive cultivars and reveal herm-prone genetics. Use a green headlamp only for brief checks. - Recovery: Flowering resumes within 1-2 weeks; no new single-blade leaves. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md) ### Re-vegetation from too-long days in flower (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Restore an uninterrupted 12-13 h dark period (13/11 is fine; some cultivars flower at 14-15 h days with ramps). Outdoors, early-season plants under long days re-veg; plant later or use light deprivation. - Recovery: No new single-blade growth within 2 weeks. - Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off. - Article: [How do I reveg a plant after harvest?](https://genetixbay.com/knowledge/answers/how-to-reveg-a-plant.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Sudden leaf drop over a day or two: likely causes and fixes > Sudden leaf drop over a day or two on cannabis is most often Cold stress. How to tell them apart, the fix for each and what recovery looks like. Also called: leaves falling off suddenly, plant dropping leaves, leaves shed overnight. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=leaf-drop-sudden ## Likely causes, most likely first ### Cold stress (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Keep days at 22-28 °C (72-82 °F) and nights no more than 3-6 °C (5-10 °F) cooler and above ~15 °C (59 °F); warm the root zone. Cold-for-colour is real in purple cultivars, but claims of more terpenes or resin are unsupported. - Recovery: Growth resumes within a week; new leaves come in green. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Fine pale stippling (tiny white or yellow dots) on leaf tops: likely causes and fixes > Fine pale stippling (tiny white or yellow dots) on leaf tops on cannabis is most often Twospotted spider mites, Thrips or Whiteflies. How to tell them apart, the fix for each and what recovery looks like. Also called: tiny white dots on leaves, speckled leaves, stippling, pinprick dots, leaves look dusty with dots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=stippling ## Likely causes, most likely first ### Twospotted spider mites (Likely) - Kind: Pest; urgency: Act within a day or two - Fix: Act now: they breed fastest hot and dry. Remove the worst leaves into a sealed bag, cool the room and raise RH a little (in veg), release predatory mites (Phytoseiulus persimilis for hot spots, Neoseiulus californicus as a preventive) before numbers explode. Soaps or horticultural oils only in veg, never on buds. Quarantine new clones. - Recovery: No new stippling on new leaves and no live mites at 10-20x after 7-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Article: [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ### Thrips (Possible) - Kind: Pest; urgency: Deal with it this week - Fix: Two levels: predatory mites (Neoseiulus cucumeris, Amblyseius swirskii) or Orius on the foliage, plus soil predators (Stratiolaelaps scimitus) or Steinernema nematodes in the medium where they pupate. Blue or yellow cards to monitor. Sprays only in veg. - Recovery: Card counts fall and no new silvering on new leaves within 2-3 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ### Whiteflies (Less likely) - Kind: Pest; urgency: Deal with it this week - Fix: Yellow cards; identify the species; release Encarsia formosa (greenhouse whitefly) or Eretmocerus (warmer rooms, silverleaf whitefly) plus predatory mites; keep sprays out of flower. - Recovery: Card counts fall within 3-4 weeks; parasitised black nymphs appear. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Fine silk webbing on leaves, buds or tips: likely causes and fixes > Fine silk webbing on leaves, buds or tips on cannabis is most often Twospotted spider mites. How to tell them apart, the fix for each and what recovery looks like. Also called: webs on my plant, spider webs on buds, webbing, silk on leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=webbing ## Likely causes, most likely first ### Twospotted spider mites (Likely) - Kind: Pest; urgency: Act within a day or two - Fix: Act now: they breed fastest hot and dry. Remove the worst leaves into a sealed bag, cool the room and raise RH a little (in veg), release predatory mites (Phytoseiulus persimilis for hot spots, Neoseiulus californicus as a preventive) before numbers explode. Soaps or horticultural oils only in veg, never on buds. Quarantine new clones. - Recovery: No new stippling on new leaves and no live mites at 10-20x after 7-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Article: [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Tiny moving dots under the leaves: likely causes and fixes > Tiny moving dots under the leaves on cannabis is most often Twospotted spider mites. How to tell them apart, the fix for each and what recovery looks like. Also called: tiny bugs under leaves, moving specks, mites under leaves, little red dots moving. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=moving-dots-underside ## Likely causes, most likely first ### Twospotted spider mites (Likely) - Kind: Pest; urgency: Act within a day or two - Fix: Act now: they breed fastest hot and dry. Remove the worst leaves into a sealed bag, cool the room and raise RH a little (in veg), release predatory mites (Phytoseiulus persimilis for hot spots, Neoseiulus californicus as a preventive) before numbers explode. Soaps or horticultural oils only in veg, never on buds. Quarantine new clones. - Recovery: No new stippling on new leaves and no live mites at 10-20x after 7-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Article: [Spider mites on cannabis: life tables, ID and IPM](https://genetixbay.com/knowledge/pests/spider-mites.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Silvery streaks or patches dotted with black specks: likely causes and fixes > Silvery streaks or patches dotted with black specks on cannabis is most often Thrips. How to tell them apart, the fix for each and what recovery looks like. Also called: silver leaves, silvery scars, thrips damage, shiny streaks with black dots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=silvering ## Likely causes, most likely first ### Thrips (Likely) - Kind: Pest; urgency: Deal with it this week - Fix: Two levels: predatory mites (Neoseiulus cucumeris, Amblyseius swirskii) or Orius on the foliage, plus soil predators (Stratiolaelaps scimitus) or Steinernema nematodes in the medium where they pupate. Blue or yellow cards to monitor. Sprays only in veg. - Recovery: Card counts fall and no new silvering on new leaves within 2-3 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Clusters of soft, pear-shaped insects on stems or leaf undersides: likely causes and fixes > Clusters of soft, pear-shaped insects on stems or leaf undersides on cannabis is most often Aphids. How to tell them apart, the fix for each and what recovery looks like. Also called: aphids, green bugs on plant, little bugs on stems, clusters of insects under leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=aphid-clusters ## Likely causes, most likely first ### Aphids (Likely) - Kind: Pest; urgency: Deal with it this week - Fix: Squash or rinse small colonies; release parasitoid wasps (Aphidius), predatory midges or lacewings; insecticidal soap or oil only before flower. Control ants that farm them. - Recovery: Colonies shrink and mummified (parasitised) aphids appear within 1-2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # White flakes (shed insect skins) on leaves: likely causes and fixes > White flakes (shed insect skins) on leaves on cannabis is most often Aphids. How to tell them apart, the fix for each and what recovery looks like. Also called: white flakes on leaves, dandruff on leaves, shed skins. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=white-cast-skins ## Likely causes, most likely first ### Aphids (Likely) - Kind: Pest; urgency: Deal with it this week - Fix: Squash or rinse small colonies; release parasitoid wasps (Aphidius), predatory midges or lacewings; insecticidal soap or oil only before flower. Control ants that farm them. - Recovery: Colonies shrink and mummified (parasitised) aphids appear within 1-2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Tiny white flies that rise when the plant is shaken: likely causes and fixes > Tiny white flies that rise when the plant is shaken on cannabis is most often Whiteflies. How to tell them apart, the fix for each and what recovery looks like. Also called: whiteflies, white flies, little white moths, white bugs flying. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=whiteflies ## Likely causes, most likely first ### Whiteflies (Possible) - Kind: Pest; urgency: Deal with it this week - Fix: Yellow cards; identify the species; release Encarsia formosa (greenhouse whitefly) or Eretmocerus (warmer rooms, silverleaf whitefly) plus predatory mites; keep sprays out of flower. - Recovery: Card counts fall within 3-4 weeks; parasitised black nymphs appear. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Whiteflies on cannabis: life table, temperature, parasitoids and IPM](https://genetixbay.com/knowledge/pests/whiteflies.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Caterpillars on leaves or buds: likely causes and fixes > Caterpillars on leaves or buds on cannabis is most often Caterpillars and budworms. How to tell them apart, the fix for each and what recovery looks like. Also called: caterpillars, worms on my plant, green worm, budworms. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=caterpillars-visible ## Likely causes, most likely first ### Caterpillars and budworms (Likely) - Kind: Pest; urgency: Act within a day or two - Fix: Hand-pick; exclude moths with netting; use Bt (kurstaki or aizawai) while larvae are small, since it must be eaten and breaks down in sunlight in days. Remove bored buds: frass starts bud rot. - Recovery: No fresh frass or holes after 1 week. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Article: [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Ants on the plant: likely causes and fixes > Ants on the plant on cannabis is most often Aphids. How to tell them apart, the fix for each and what recovery looks like. Also called: ants on my plant, ants on stems, ants in the pot. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=ants ## Likely causes, most likely first ### Aphids (Possible) - Kind: Pest; urgency: Deal with it this week - Fix: Squash or rinse small colonies; release parasitoid wasps (Aphidius), predatory midges or lacewings; insecticidal soap or oil only before flower. Control ants that farm them. - Recovery: Colonies shrink and mummified (parasitised) aphids appear within 1-2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Aphids on cannabis: species, life tables, population growth and IPM](https://genetixbay.com/knowledge/pests/aphids.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Winding pale trails in leaves: likely causes and fixes > Winding pale trails in leaves on cannabis is most often Leafminers. How to tell them apart, the fix for each and what recovery looks like. Also called: leaf miner trails, squiggly lines on leaves, tunnels in leaves, snake trails on leaves. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=leaf-trails ## Likely causes, most likely first ### Leafminers (Possible) - Kind: Pest; urgency: Low urgency - Fix: Pinch mined leaflets and the larva inside; yellow cards for adults; parasitoid wasps (e.g. Diglyphus) in greenhouses. Cosmetic in light infestations. - Recovery: No new mines after 2 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Article: [Spots, brown patches and dead edges on cannabis leaves: the master decision tree](https://genetixbay.com/knowledge/diagnosis/spots-necrosis-decision-tree.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Purple or red veins, mostly on leaf undersides: likely causes and fixes > Purple or red veins, mostly on leaf undersides on cannabis is most often Genetic purple colour (anthocyanin), Cold stress or Phosphorus deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: purple veins, red veins under leaves, veins turning purple, purple leaf veins. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=purple-veins ## Likely causes, most likely first ### Genetic purple colour (anthocyanin) (Likely) - Kind: Genetics; urgency: Low urgency - Fix: Nothing to fix: purple stems, petioles and bracts are mostly genetic and harmless, brought out by cool nights 5-10 °C (9-18 °F) below day. Purple is bag appeal, not potency. - Recovery: Leaves stay healthy and green apart from the colour; no spotting. - Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed. - Article: [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md) ### Cold stress (Less likely) - Kind: Environment; urgency: Deal with it this week - Fix: Keep days at 22-28 °C (72-82 °F) and nights no more than 3-6 °C (5-10 °F) cooler and above ~15 °C (59 °F); warm the root zone. Cold-for-colour is real in purple cultivars, but claims of more terpenes or resin are unsupported. - Recovery: Growth resumes within a week; new leaves come in green. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.md) ### Phosphorus deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Warm the root zone to 18-22 °C (64-72 °F) and nights above ~15 °C (59 °F) first; cold blocks P uptake. Correct pH (soilless 5.5-6.5, soil 6.0-7.0). If genuinely short, supply about 30-60 mg/L P; controlled cannabis trials found no yield or cannabinoid gain above roughly 25-60 mg/L, so skip 'bloom boosters'. Soil: a balanced liquid feed; living soil: a slow P amendment acts in weeks. - Recovery: No new olive spots on leaves that open after the fix, within 7-10 days; growth rate picks up. Spotted leaves stay damaged. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Phosphorus (P) in cannabis: what it does, deficiency, excess and how much is enough](https://genetixbay.com/knowledge/nutrients/phosphorus.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Pinkish-white mould inside buds: likely causes and fixes > Pinkish-white mould inside buds on cannabis is most often Fusarium wilt or crown rot. How to tell them apart, the fix for each and what recovery looks like. Also called: pink mould in buds, pink fuzz in bud, salmon coloured rot, white pink mold. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=pink-bud-rot ## Likely causes, most likely first ### Fusarium wilt or crown rot (Possible) - Kind: Disease; urgency: Act within a day or two - Fix: No cure once infected: remove the plant with its medium in a bag, sanitise pots, trays and water lines, and use clean clones and new media. Reduce root stress (overwatering, heat, salts) on the rest. - Recovery: No further wilting plants over the next 2-3 weeks. - Confirm: Cut a wilting stem lengthwise: On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Article: [Fusarium in cannabis: wilt, crown rot and bud rot](https://genetixbay.com/knowledge/diseases/fusarium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Brown, crispy bracts or bud tips on the top colas: likely causes and fixes > Brown, crispy bracts or bud tips on the top colas on cannabis is most often Heat stress or Light bleaching at the canopy top. How to tell them apart, the fix for each and what recovery looks like. Also called: burnt bud tips, crispy buds at the top, top buds fried, brown bracts under the light. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=bud-tips-burnt ## Likely causes, most likely first ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Light bleaching at the canopy top (Possible) - Kind: Light; urgency: Deal with it this week - Fix: Raise or dim the light by 10-20% so top-canopy PPFD sits around 800-1,100 µmol/m²/s at ambient CO2 (up to ~1,500 with CO2 and good climate). Keep the canopy even so one cola doesn't sit in a hotspot. Bleached tissue won't re-green. - Recovery: No new bleaching within 3-5 days; new bracts and leaves at the top stay green. - Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Tiny black specks on leaf surfaces: likely causes and fixes > Tiny black specks on leaf surfaces on cannabis is most often Thrips. How to tell them apart, the fix for each and what recovery looks like. Also called: black dots on leaves, tiny black specks, black flecks on leaves, pepper spots. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=thrips-frass ## Likely causes, most likely first ### Thrips (Likely) - Kind: Pest; urgency: Deal with it this week - Fix: Two levels: predatory mites (Neoseiulus cucumeris, Amblyseius swirskii) or Orius on the foliage, plus soil predators (Stratiolaelaps scimitus) or Steinernema nematodes in the medium where they pupate. Blue or yellow cards to monitor. Sprays only in veg. - Recovery: Card counts fall and no new silvering on new leaves within 2-3 weeks. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Tap a branch over white paper: Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier. - Confirm: Sticky cards for 1-2 weeks: Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby. - Article: [Thrips on cannabis: life table, temperature, scouting and biological control](https://genetixbay.com/knowledge/pests/thrips.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Plant stopped drinking; pot or reservoir level barely drops: likely causes and fixes > Plant stopped drinking; pot or reservoir level barely drops on cannabis is most often Overwatering (roots short of air), Root rot (Pythium) or Cold root zone (below about 16 °C / 61 °F). How to tell them apart, the fix for each and what recovery looks like. Also called: plant not drinking, not using water, pot still heavy days later, reservoir level not dropping. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=plant-not-drinking ## Likely causes, most likely first ### Overwatering (roots short of air) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Root rot (Pythium) (Possible) - Kind: Disease; urgency: Act now - Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems. - Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks. - Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) ### Cold root zone (below about 16 °C / 61 °F) (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Raise root-zone temperature to 18-22 °C (64-72 °F): lift pots off cold floors onto insulation, warm the room at night, use an aquarium heater in reservoirs (with a thermostat), water with room-temperature solution. - Recovery: Growth resumes and new leaves green within a week. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) ### Low dissolved oxygen in the root zone (Less likely) - Kind: Root zone; urgency: Act within a day or two - Fix: Restore oxygen: clean or replace air stones, size the air pump for at least ~1 L/min per 4 L, keep a 2-5 cm air gap under net pots once roots reach the water, cool the solution to 18-22 °C (64-72 °F). Aim for 6-8+ mg/L DO. - Recovery: Fresh white root tips within 3-5 days; wilting stops. - Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [Deep water culture (DWC)](https://genetixbay.com/knowledge/systems/dwc.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Condensation or wet leaves at lights-off: likely causes and fixes > Condensation or wet leaves at lights-off on cannabis is most often Humidity too high / VPD too low or Botrytis bud rot (grey mould). How to tell them apart, the fix for each and what recovery looks like. Also called: water droplets on leaves at night, condensation in tent, tent walls wet, dew on plants. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=whole&s=condensation ## Likely causes, most likely first ### Humidity too high / VPD too low (Likely) - Kind: Environment; urgency: Act within a day or two - Fix: Target about 55-70% RH in veg, 50-60% early flower, 40-50% late flower (leaf VPD 1.0-1.5 kPa in flower). Dehumidify, raise exhaust, keep air moving under the canopy and watch the lights-off spike (dew point). High RH in flower raised bud-rot risk and in one study delayed flowering and lowered cannabinoids. - Recovery: RH holds in band through lights-off for 3+ days; no new mould signs. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Humidity by stage: RH targets from clone to cure](https://genetixbay.com/knowledge/environment/humidity-by-stage.md) ### Botrytis bud rot (grey mould) (Less likely) - Kind: Disease; urgency: Act now - Fix: Act now. Bag infected buds before cutting them out, 3-5 cm (1-2 in) past visible rot, and clean tools; never shake them. Drop RH to about 40-50% in late flower, control the lights-off dew point, move air through dense colas. There is no cure in flower; consider harvesting early if it keeps spreading. - Recovery: No new rot on weekly cola checks for 2 weeks. - Confirm: Open the densest colas: In flower, gently spread the largest, densest colas at the base and look for brown, mushy or grey tissue around the stem, a single wilted sugar leaf that pulls out easily, frass or caterpillars. Check 5-10 colas per plant each week from mid-flower, more when RH is high. Bag any rot before removing it. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Botrytis (bud rot / grey mould) in cannabis](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Some pots dry while others on the same line stay wet: likely causes and fixes > Some pots dry while others on the same line stay wet on cannabis is most often Pump, timer, air or emitter failure in a hydro, aero or drip system. How to tell them apart, the fix for each and what recovery looks like. Also called: drippers clogged, uneven watering on drip, one pot not getting water, emitter blocked. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=uneven-drip-wetting ## Likely causes, most likely first ### Pump, timer, air or emitter failure in a hydro, aero or drip system (Possible) - Kind: Root zone; urgency: Act now - Fix: Restore flow or air immediately: check power, timer, float switches, filters and nozzles. Mist exposed roots by hand or lower plants into solution while you fix it. In HPA and NFT, fit an alarm and a backup pump; roots die fast when misting or flow stops. - Recovery: Plants regain turgor within hours if roots were not dead; brown, collapsed roots mean rot risk next. - Confirm: Check pumps, timers, nozzles and drippers: Watch one full cycle: the pump starts on time, every nozzle mists or every dripper delivers, NFT channels have flow end to end, air stones bubble. Clear clogged emitters and filters. In HPA, a failed pump or blocked nozzle can kill exposed roots fast, so check this first when plants on one system wilt together. - Article: [High-pressure aeroponics (HPA)](https://genetixbay.com/knowledge/systems/hpa-aeroponics.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Reservoir or root zone cold (below 16 °C / 61 °F): likely causes and fixes > Reservoir or root zone cold (below 16 °C / 61 °F) on cannabis is most often Cold root zone (below about 16 °C / 61 °F). How to tell them apart, the fix for each and what recovery looks like. Also called: res too cold, cold water in reservoir, cold floor pots, water temperature low. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=reservoir-cold ## Likely causes, most likely first ### Cold root zone (below about 16 °C / 61 °F) (Possible) - Kind: Root zone; urgency: Deal with it this week - Fix: Raise root-zone temperature to 18-22 °C (64-72 °F): lift pots off cold floors onto insulation, warm the room at night, use an aquarium heater in reservoirs (with a thermostat), water with room-temperature solution. - Recovery: Growth resumes and new leaves green within a week. - Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Temperature by stage: day, night and root-zone targets](https://genetixbay.com/knowledge/environment/temperature-by-stage.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Seed shell stuck on the seedling's first leaves: likely causes and fixes > Seed shell stuck on the seedling's first leaves on cannabis is most often Seed coat stuck on the cotyledons (helmet head). How to tell them apart, the fix for each and what recovery looks like. Also called: helmet head, seed shell stuck, cotyledons trapped in seed coat, seedling can't shed its shell. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=seed-shell-stuck ## Likely causes, most likely first ### Seed coat stuck on the cotyledons (helmet head) (Likely) - Kind: Physical damage; urgency: Deal with it this week - Fix: Mist the shell to soften it and raise RH around the seedling (dome) for a few hours; if it is still stuck, ease it off gently with clean tweezers. Plant seeds about 0.5-1.5 cm (1/4-1/2 in) deep so the medium scrapes the coat off on the way up. - Recovery: Cotyledons open within a day. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [What do I do if the seed shell is stuck on my seedling?](https://genetixbay.com/knowledge/answers/seed-shell-stuck-on-seedling.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Yellow tips on lower fan leaves moving down the leaflet: likely causes and fixes > Yellow tips on lower fan leaves moving down the leaflet on cannabis is most often Nitrogen deficiency or Potassium deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: lower leaf tips yellow, yellow tips on bottom leaves, tips of old leaves yellowing. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=yellow-tips-lower ## Likely causes, most likely first ### Nitrogen deficiency (Likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Fix roots, watering and pH first. If N is genuinely short, raise feed N by about 10-20% (not double): mineral feeds around 150-200 mg/L N in veg and early flower; one DWC flowering trial predicted a yield optimum near 194 mg/L. Coco/hydro: raise base feed EC by ~0.2 mS/cm. Soil: liquid feed at label rate. Living soil: top-dress a fast organic N source and allow 1-2 weeks. Late flower: a gradual fade is the planned N taper, not a fault. - Recovery: Yellowing stops climbing within 5-7 days and new leaves emerge mid-green; already-yellow leaves do not recover. Runoff EC climbs back toward input. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md) ### Potassium deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Check runoff EC first: salt burn looks the same. If K is genuinely short, feed about 175-250 mg/L K (potassium sulfate, potassium nitrate or MKP) at a normal EC. A flowering DWC trial saw no yield response anywhere from 60 to 340 mg/L, so more is not better. Cut heavy Cal-Mag or sodium-rich water that competes with K. - Recovery: Margin scorch stops advancing up the plant within 7 days; new leaves open with clean margins. - Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed. - Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days. - Article: [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Newest leaves limp while older leaves stay firm: likely causes and fixes > Newest leaves limp while older leaves stay firm on cannabis is most often Heat stress, Copper deficiency or Boron deficiency. How to tell them apart, the fix for each and what recovery looks like. Also called: top leaves floppy, new growth wilting, new leaves droopy, limp tops. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=new-growth-limp ## Likely causes, most likely first ### Heat stress (Possible) - Kind: Environment; urgency: Act within a day or two - Fix: Bring canopy leaf temperature under about 30 °C (86 °F): more exhaust (one tent air exchange every 1-3 minutes), raise or dim the light, add canopy airflow (0.3-1.0 m/s), keep RH so VPD stays 1.0-1.5 kPa, water well. Above ~30 °C photosynthesis falls unless CO2 and light are high. - Recovery: Leaves flatten within a day; no new foxtails or crisping. - Confirm: IR leaf temperature at the canopy top: Point an IR thermometer at the top leaves under the light (5-10 cm away, emissivity 0.95) and at shaded leaves. Leaf temperature above about 30 °C (86 °F) at the top only points to heat or radiant load; leaf VPD can be calculated from leaf temperature and RH. - Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point. - Article: [Heat and light stress: taco leaves, bleaching and foxtails](https://genetixbay.com/knowledge/environment/heat-light-stress.md) ### Copper deficiency (Less likely) - Kind: Nutrient; urgency: Low urgency - Fix: Very rare with a complete micro mix. Supply about 0.03-0.1 mg/L Cu; do not overshoot (excess Cu damages roots). - Recovery: New leaves regain size and turgor in 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md) ### Boron deficiency (Less likely) - Kind: Nutrient; urgency: Deal with it this week - Fix: Rule out broad mites first. Supply about 0.2-0.5 mg/L B (boric acid ~1.1-2.9 mg/L, or a complete micro mix). The gap between enough and too much is narrow: never add B 'just in case' on top of a complete feed. - Recovery: New shoots grow normally from the tip or from side buds within 10-14 days. - Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency. - Article: [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Water pools on the surface and drains slowly: likely causes and fixes > Water pools on the surface and drains slowly on cannabis is most often Overwatering (roots short of air) or Root-bound in a pot too small. How to tell them apart, the fix for each and what recovery looks like. Also called: water sits on top, soil compacted, slow draining pot, puddles on soil. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=water-pools-slow-drain ## Likely causes, most likely first ### Overwatering (roots short of air) (Likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering. - Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case. - Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) ### Root-bound in a pot too small (Less likely) - Kind: Root zone; urgency: Deal with it this week - Fix: Up-pot photoperiods into a container about 2-3x larger, loosening circling roots gently. Autoflowers: don't transplant; increase watering and feeding frequency instead. Small pots can still grow big plants with high-frequency fertigation (several feeds a day). - Recovery: New white roots in the fresh medium within 5-7 days; daily wilting stops. - Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining. - Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst. - Article: [Cannabis root problems: the master decision tree](https://genetixbay.com/knowledge/diagnosis/root-problems-decision-tree.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth. --- # Tiny white insects jumping on the medium surface: likely causes and fixes > Tiny white insects jumping on the medium surface on cannabis is most often Springtails (harmless soil insects). How to tell them apart, the fix for each and what recovery looks like. Also called: small white bugs in soil, white jumping bugs, springtails, tiny white bugs in water tray. Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=tiny-white-jumpers-soil ## Likely causes, most likely first ### Springtails (harmless soil insects) (Likely) - Kind: Pest; urgency: Low urgency - Fix: Nothing to fix: springtails eat decaying organic matter and fungi. Let the surface dry more between waterings if numbers bother you. Check the roots to rule out root aphids, which are pear-shaped, slow and sit on the roots. - Recovery: Plant healthy; roots clean. - Confirm: Root-ball and drainage-hole insect check: Tip the plant out and inspect the outer roots, pot bottom and drainage holes with a 10x loupe. Root aphids are small, pear-shaped and wingless, often with white waxy flecks; check several plants, and the drain trays, since colonies hide at the pot edge. - Article: [What are the small white bugs in my soil?](https://genetixbay.com/knowledge/answers/small-white-bugs-in-soil.md) ## Note Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.